Patent Application
20150057165
The sequence listing is filed with the application in electronic format only and is incorporated by reference herein. The sequence listing text file “WO_ASFILED_SequenceListing.txt” was created on Dec. 3, 2010, and is 262,254 bytes in size.
Naive B cells migrate through the circulation to lymphoid organs where they undergo the T cell-dependent germinal center reaction. Adaptive immunity is acquired as specific antigen-reactive germinal center B cells differentiate into the major effector B cells of the adaptive immune system: memory cells and plasma cells. See, e.g.,
Many malignancies derived from mature B cells are known and are believed to constitute the majority of leukemias and lymphomas. Such malignancies appear to reflect defined stages of normal B cell differentiation. Diagnosis of leukemias and lymphomas can be particularly difficult because of their shared lineage. These cancers frequently display overlapping morphologies, genetic abnormalities, and expression of surface markers, which can complicate the diagnosis. However, the distinction of these tumors is clinically important because there are important differences in the treatments and expected response to treatment. Thus methods that improve the accuracy of their diagnosis should provide to improved outcomes for these patients.
MicroRNAs are commonly 18-22 nucleotide-long RNA molecules that regulate expression of genes. There is an increasing recognition of the role of microRNAs in oncogenesis, lineage-selection, and immune cell function, including early B cell differentiation. See Cahn et al. N Engl J Med. 2005; 353:1793-1801; O'Donnell et al. Nature. 2005; 435:839-843; Chen et al. Science. 2004; 303:83-86; Lim et al. Nature. 2005; 433:769-773; Li et al. Cell. 2007; 129:147-161; Xiao et al., Nat Immunol. 2008; 9:405-414; Baltimore et al. Nat Immunol. 2008; 9:839-845; and Ventura et al. Cell. 2008; 132:875-886. However, the full extent and function of microRNA expression during mature B cell differentiation and in B cell malignancies are not known.
Correct diagnosis of B cell malignancies is important from both a clinical standpoint and from the standpoint of setting appropriate patient expectations. A misdiagnosed B cell malignancy may lead to an inappropriate therapy, which can unnecessarily endanger the patient's life and/or be an ineffective treatment for the B cell malignancy. As an example, the diagnostic distinction of Burkitt lymphoma (BL) from diffuse large B cell lymphomas (DLBCLs) can be difficult because of overlapping morphology, immunophenotype and cytogenetics. Burkitt lymphoma tumors are molecularly distinct from DLBCL, however. The difficulty and importance of obtaining the correct diagnosis in BL was highlighted by the experience of a multicenter clinical trial, CALGB trial#925119, in which nearly half of the 100 patients with an assigned diagnosis of BL were found to have another diagnosis upon further pathology review.
If diagnosed and treated appropriately, nearly 80% of patients with BL can be cured with intensive (high dose) chemotherapy regimens. Thus, a misclassification of BL as DLBCL can result in a missed opportunity to cure the malignancy. On the other hand, misclassification of DLBCL as BL leads to unnecessarily morbidity from intensive chemotherapy regimens. Thus, methods that improve the diagnosis of BL, and other B cell malignancies, can provide better outcomes in patients.
DLBCLs can also be subclassified into two different B cell malignancies, activated B-cell (ABC) DLBCL and germinal center B cell like (GCB) DLBCL. There are at least two important clinical applications for the molecular sub-grouping of DLBCL patients. First, the prognostic information could inform the choices and expectations of patients and their physicians. Second, the important molecular differences in these subgroups form the basis of testing different targeted therapies in these patients. The possibility of a differential response to therapy among ABC and GCB DLBCLs is supported by data that suggest that the benefit of receiving a proteosome inhibitor, bortozemib, is predominantly limited to those patients who have ABC DLBCL. However, the clinical distinction of the subgroups of DLBCL using immunohistochemistry is difficult with current methods distinguishing GCB DLBCL from non-GCB DLBCL with limited success.
Mature B cell differentiation is important for the development of adaptive immunity. The process is also of interest because B cell malignancies are common and retain a number of features derived from their normal counterpart B cell subsets. Unlike other maturation pathways in the hematopoietic and other cell lineages, successive stages of mature B cells do not simply signify progressive differentiation away from the stem cell stage. Rather, each stage represents a specialized state with specific functions. Thus, germinal center (GC) cells interact with CD4 T cells and dendritic cells and undergo somatic hypermutation and Ig-heavy chain class-switching. On the other hand, plasma cells secrete immunoglobulin, while memory cells are primed to proliferate and differentiate into plasma cells upon repeat contact with antigen. The specialized functions demand a finely tuned program of gene regulation.
MicroRNAs represent a novel class of biomarkers that provide new opportunities for clinical translation. First, intact microRNAs can be isolated from tissues preserved using standard methods, such as formalin fixed, paraffin embedded (FFPE) tissue. Thus, microRNA-based biomarkers could be easy to translate to clinical use. Second, microRNAs can be readily assayed using real-time PCR and other methods available in conventional pathology.
In an aspect the disclosure provides an isolated nucleic acid molecule having at least 80% sequence identity to any one of SEQ ID NOs: 763-1350 or 1565 or a complementary sequence thereof. Embodiments provide for sequence identity of at least 90% or 95%.
In an aspect the disclosure provides an isolated nucleic acid molecule comprises any one of SEQ ID NOs: 763-1350 or 1565 or a complementary sequence thereof. Embodiments provide for isolated nucleic acid molecules comprising a primary miRNA, a precursor miRNA, a mature miRNA, or a DNA molecule coding therefore. Embodiments further provide for a cDNA molecule comprising sequence that corresponds to a miRNA sequence of any one of SEQ ID NOs: 763-1350 or 1565.
Aspects of the disclosure provide compositions, pharmaceutical compositions, vectors, host cells, and DNA libraries comprising at least one nucleic acid molecule described herein.
In an aspect the disclosure provides a method of determining the B cell stage of a B cell malignancy in a subject comprising determining the level of expression of at least one microRNA in a sample comprising a B cell taken from the subject relative the level of expression of the at least one microRNA in a control sample, wherein the at least one microRNA is selected from the microRNAs listed in Table 4.
In an aspect the disclosure provides a method of identifying a B cell malignancy in a subject comprising determining the level of expression of at least one microRNA in a sample comprising a B cell taken from the subject relative the level of expression of the at least one microRNA in a control sample, wherein the at least one microRNA is selected from the microRNAs listed in Table 4.
In an aspect the disclosure provides a method of diagnosing a B cell malignancy in a subject comprising determining the level of expression of at least one microRNA in a sample comprising a B cell taken from the subject relative the level of expression of the at least one microRNA in a control sample, wherein the at least one microRNA is selected from the microRNAs listed in Table 4.
In an aspect the disclosure provides a method of identifying a B cell malignancy in a subject comprising determining the level of expression of at least one microRNA in a sample comprising a B cell taken from the subject relative the level of expression of the at least one microRNA in a control sample, wherein the at least one microRNA is selected from the microRNAs listed in any one of Tables 7 to 35.
In an aspect the disclosure provides a method of diagnosing a B cell malignancy in a subject comprising determining the level of expression of at least one microRNA in a sample comprising a B cell taken from the subject relative to the level of expression of the at least one microRNA in a control sample, wherein the at least one microRNA is selected from the microRNAs listed in any one of Tables 7 to 35.
Embodiments of these aspects provide for identification or diagnosis of a B cell malignancy selected from chronic lymphocytic leukemia, follicular lymphoma, Hodgkin's lymphoma, activated B-cell diffuse large B cell lymphoma (DLBCL), germinal center-like DLBCL, and Burkitt lymphoma.
In an aspect the disclosure provides a method of determining whether a B cell malignancy in a sample is Burkitt lymphoma, activated B cell-like diffuse large B cell lymphoma (DLBCL), or germinal center-like DLBCL, comprising determining the level of expression of at least one microRNA in the sample relative to the level of expression of the at least one microRNA in a control sample, wherein the at least one microRNA is selected from the microRNAs listed in Table 10, column “BL miRNA list”; Table 14, column “BL High”; Table 11; Table 14, column “ABC High”; Table 10, column “GCB miRNA list”; Table 14, column “GCB High”; Table 32, or Table 35.
In an aspect the disclosure provides a method of determining whether a B cell malignancy in a sample is Burkitt lymphoma, activated B cell-like diffuse large B cell lymphoma (DLBCL), or germinal center-like DLBCL, comprising determining the level of expression of at least one microRNA in the sample relative to the level of expression of the at least one microRNA in a control sample, wherein the at least one microRNA is selected from the microRNAs listed in at least one column labeled “GCBvsBL” or “GCBvsABC” in Table 7 or “ABCvsBL” in Table 8.
In an aspect the disclosure provides a method of determining whether a B cell malignancy in a sample is activated B cell-like diffuse large B cell lymphoma (DLBCL), or germinal center-like DLBCL, comprising determining the level of expression of at least one microRNA in the sample relative to the level of expression of the at least one microRNA in a control sample, wherein the at least one microRNA is selected from the microRNAs listed in Table 35.
In an aspect the disclosure provides a microarray comprising miRNA-specific probe oligonucleotides wherein at least one miRNA-specific probe oligonucleotide is specific for a sequence of SEQ ID NOs: 763-1350 or 1565, or any combination thereof.
In an aspect the disclosure provides a kit comprising at least one primer sequence that can detect any one of SEQ ID NOs: 763-1350 or 1565, or a combination thereof.
In an aspect the disclosure provides a kit comprising at least one isolated nucleic acid molecule having a sequence of any one of SEQ ID NOs: 1351-1564.
In an aspect, the disclosure provides a method of identifying a B cell malignancy comprising determining the level of expression of at least one microRNA selected from the microRNAs listed in Table 4. In certain embodiments, a method comprises determining the level of expression of at least one microRNA selected from the microRNAs listed in Tables 7-35.
Other aspects and embodiments will be apparent to one of skill in the art in light of the following detailed description.
All patent and non-patent literature references that are cited herein are incorporated herein by reference in their entirety.
In a general sense, the disclosure relates to nucleic acid sequences, such as microRNAs (miRNA), as well as to the identification and analysis of microRNA expression levels and/or patterns in B cells. Through concomitant microRNA and mRNA profiling, the inventors have identified regulatory roles for microRNAs at each stage in mature B cell differentiation. This provides methods identifying microRNA-mediated regulation of oncogenes and key transcription factors in B cell differentiation. This work establishes the landscape of normal microRNA expression in mature B cells and its role in regulating normal B cell differentiation. Further, our work demonstrates that in contrast to the described down-regulation in other malignancies, stage-specific microRNAs are retained in B cell malignancies. The lineage of common B cell malignancies can be predicted based upon miRNA profiles of normal B cells, pointing to a role for microRNAs in the maintenance of mature B cell phenotypes in normal and malignant B cells.
In an aspect, the disclosure relates to an isolated nucleic acid molecule comprising: (a) a nucleotide sequence as shown in Table 32; (b) a nucleotide sequence which is the complement of (a), (c) a nucleotide sequence comprising a sequence identity of at least 80%, (e.g., 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or at least 99%), to a sequence of (a) or (b) and/or (d) a nucleotide sequence which hybridizes under stringent conditions to a sequence of (a), (b) and/or (c). In some embodiments, the identity of sequence (c) to a sequence of (a) or (b) is at least 90%. In other embodiments, the identity of sequence (c) to a sequence of (a) or (b) at least 95%. The percent identity can be calculated by any routine method used by one of skill in the art such as, for example, the methods described herein.
In embodiments, the isolated nucleic acid molecule relates to a miRNA molecule and analogs thereof, a miRNA precursor molecule, or a primary miRNA molecule, as well as to DNA molecules encoding miRNA, miRNA precursor, or primary miRNA molecules. Accordingly, in such embodiments, the isolated nucleic acid molecule can function as a miRNA molecule under suitable conditions. Suitable conditions include, but are not limited to, various buffer systems that approximate physiologically relevant ionic concentrations and pHs, as well as physiological conditions.
In some embodiments, the nucleic acid molecule comprises a sequence that hybridizes to a nucleotide sequence as shown in Table 32, a complementary sequence thereof or a nucleic acid molecule having at least 80% sequence identity under stringent hybridization conditions. The basic parameters affecting the choice of hybridization conditions and guidance for devising suitable conditions are set forth by Sambrook, et al. (See, 1989, Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.; and Current Protocols in Molecular Biology, 1995, Ausubel et al., eds., John Wiley & Sons, Inc.), and can be readily determined by those of ordinary skill in the art based on, for example, the length and/or base composition of the DNA. Generally, stringent salt concentration will ordinarily be less than about 750 mM NaCl and 75 mM trisodium citrate, or less than about 500 mM NaCl and 50 mM trisodium citrate, or even less than about 250 mM NaCl and 25 mM trisodium citrate. High stringency hybridization conditions can be obtained by adding an amount of organic solvent (e.g., at least about 35% to about 50% formamide). Stringent temperature conditions will ordinarily include temperatures of at least about 30° C., (e.g., at least about 37° C., 42° C., 45° C., 50° C., or 55° C.). Varying additional parameters, such as hybridization time, the concentration of detergent (e.g., 0.1-1.0% sodium dodecyl sulfate (SDS)), and the inclusion or exclusion of carrier DNA (e.g., about 100-200 μg/ml denatured salmon sperm DNA (ssDNA)), are well known to those skilled in the art. Stringent hybridization conditions are known in the art and include non-limiting examples such as, washing for 1 hr in 300 mM NaCl, 30 mM trisodium citrate and 0.1% SDS at 45-50° C.; washing for 1 h in 300 mM NaCl, 30 mM trisodium citrate and 0.1% SDS at 45-50° C.; in 500 mM NaCl, 50 mM trisodium citrate, 1% SDS, 35% formamide, and 100 μg/ml denatured salmon sperm DNA (ssDNA) at 37° C.; or in 250 mM NaCl, 25 mM trisodium citrate, 1% SDS, 50% formamide, and 200 μg/ml ssDNA at 42° C. Useful variations on these conditions will be readily apparent to those skilled in the art.
The isolated nucleic acid molecules provided herein suitably have a length of from about 18 to about 100 nucleotides. In embodiments wherein the isolated nucleic acid molecules are miRNAs, the lengths of the miRNAs are suitably in an expected range for the particular type of miRNA molecule. For example, mature miRNAs are typically from about 15 to about 28 nucleotides in length, and suitably have a length of about 19 to about 24 nucleotides (e.g., 19, 20, 21, 22, 23, or 24 nucleotides). Precursor miRNAs typically comprise the mature miRNA sequence and contain a stem-loop structure, suitably of length of about 50 to about 90 nucleotides (e.g., 50, 55, 60, 65, 70, 75, 80, 85, or 90 nucleotides). Primary miRNAs (e.g., a primary transcript comprising a precursor miRNA) can suitably have a length of greater than 100 nucleotides.
The nucleic acid molecules can be provided in either a single-stranded or double-stranded form. Typically, a miRNA as such is identified as a single-stranded molecule, while the precursor miRNA is typically at least partially self-complementary and capable of forming double-stranded portions, e.g. stem- and loop-structures. DNA molecules encoding the miRNA and miRNA precursor molecules (e.g., expression vectors, cloning vectors, and the like) are typically double-stranded. The individual nucleic acids that comprise the isolated nucleic acid molecules can be selected from RNA, DNA, or nucleic acid analog molecules, such as chemically modified sugar (e.g., 2′-modified (2′-F, 2′-OMe, etc.) or backbone (e.g., phosphorothioates), or cap (e.g., 5′- and/or 3′-abasic groups) moieties of ribonucleotides or deoxyribonucleotides. Other nucleic acid analogs, such as peptide nucleic acids (PNA) or locked nucleic acids (LNA), are also suitable in various embodiments described herein. In some embodiments the nucleic acid molecules can comprise any combination of nucleic acid analog(s).
While many of the nucleic acid molecules in the Tables are identified as RNA sequences, e.g., miRNAs, the disclosure of those sequences should be understood to encompass the corresponding DNA (e.g., cDNA) sequences, wherein the uracil (U) nucleotides of the disclosed RNAs are substituted by thymidine (T) nucleotides in the corresponding DNA. One of skill in the art is able to generate such DNA sequences (e.g., cDNA) through routine microbiological techniques known in the art such as, for example, reverse transcription using methods that incorporate the reverse transcriptase enzyme.
In another aspect, the disclosure provides a recombinant expression vector comprising a recombinant nucleic acid sequence operatively linked to an expression control sequence, wherein expression of the recombinant nucleic acid sequence provides a miRNA sequence, a precursor miRNA sequence, or a primary miRNA sequence as described herein. The resulting sequence (e.g., primary or precursor miRNAs) can optionally be further processed to provide the miRNA sequence. In embodiments, the recombinant expression vector comprises at least one sequence in Table 32. Any suitable expression vector can be used such as, for example, a DNA vector (e.g., viral vector, plasmid, etc.). In some embodiments the expression vector is selected for expression in a eukaryotic cell such as, for example, a mammalian cell. One of skill in the art will be able to select an appropriate vector based on the particular application and/or expression system to be employed.
Thus, embodiments provide nucleic acid constructs in the form of plasmids, vectors, transcription or expression cassettes which comprise at least one nucleotide sequence encoding a miRNA described herein, or fragments thereof, and a suitable promoter region. Suitable vectors can be chosen or constructed, which contain appropriate regulatory sequences, such as promoter sequences, terminator sequences, polyadenylation sequences, enhancer sequences, marker genes and other sequences as desired. Vectors can be plasmids, phage (e.g. phage, or phagemid) or viral (e.g. lentivirus, adenovirus, AAV) or any other appropriate vector. For further details see, for example, Molecular Cloning: a Laboratory Manual: 2nd edition, Sambrook et al., 1989, Cold Spring Harbor Laboratory Press.
Relatedness of Nucleic Acid Molecules/Sequences
The term “identity” refers to a relationship between the sequences of two or more two or more nucleic acid molecules, as determined by comparing the sequences. In the art, “identity” also means the degree of sequence relatedness between amino acid or nucleic acid molecule sequences, as the case may be, as determined by the match between strings of nucleotide or amino acid sequences. “Identity” measures the percent of identical matches between two or more sequences with gap alignments addressed by a particular mathematical model or computer programs (i.e., “algorithms”).
Identity of related nucleic acid molecules can be readily calculated by known methods, including but not limited to those described in Computational Molecular Biology, Lesk, A. M., ed., Oxford University Press, New York, 1988; Biocomputing: Informatics and Genome Projects, Smith, D. W., ed., Academic Press, New York, 19933; Computer Analysis of Sequence Data, Part 1, Griffin, A. M., and Griffin, H. G., eds., Humana Press, New Jersey, 1994; Sequence Analysis in Molecular Biology, von Heinje, G., Academic Press, 1987; and Sequence Analysis Primer, Gribskov, M. and Devereux, J., eds., M. Stockton Press, New York, 1991; and Carillo, H., and Lipman, D., SIAM J. Applied Math., 48:1073 (1988).
Non-limiting methods for determining identity are designed to give the largest match between the sequences tested. Methods to determine identity are codified in publicly available computer programs. Preferred computer program methods to determine identity between two sequences include, but are not limited to, the GCG program package, including GAP (Devereux, et al., Nucleic Acids Research 12:387 [1984]; Genetics Computer Group, University of Wisconsin, Madison, Wis.), BLASTN, and FASTA (Atschul et al., J. Molec. Biol. 215:403-410 [1990]). The BLAST X program is publicly available from the National Center for Biotechnology Information (NCBI) and other sources (BLAST Manual, Altschul] et al., NCB NLM NIH Bethesda, Md. 20894; Altschul et al., J. Mol. Biol. 215:403-410 [1990]). The well known Smith Waterman algorithm may also be used to determine identity.
Exemplary parameters for nucleic acid molecule sequence comparison include the following:
Algorithm: Needleman and Wunsch, J. Mol Biol. 48:443-453 (1970)
Comparison matrix: matches=+10, mismatch=0
Gap Penalty: 50
Gap Length Penalty: 3
The GAP program is also useful with the above parameters. The aforementioned parameters are the default parameters for nucleic acid molecule comparisons.
Other exemplary algorithms, gap opening penalties, gap extension penalties, comparison matrices, thresholds of similarity, etc. can be used by those of skill in the art, including those set forth in the Program Manual, Wisconsin Package, Version 9, September 1997. The particular choices to be made will depend on the specific comparison to be made, such as DNA to DNA or RNA to DNA; and additionally, whether the comparison is between given pairs of sequences (in which case GAP or BestFit are generally preferred) or between one sequence and a large database of sequences (in which case FASTA or BLASTA are preferred).
In an aspect, the disclosure provides a vector comprising the isolated polynucleotide as described herein such as, for example one or more of SEQ ID NOs 773-1046 or 1450-1542. In embodiments, the vector can be any type of vector that finds use as a vehicle to transfer foreign genetic material into a cell. Non-limiting examples of vectors include plasmids, viral vectors (e.g., derived from lentivirus, adenovirus, adeno-associated virus (AAV), retrovirus, etc.), bacteriophage, cosmids, and artificial chromosomes. In embodiments, the vector can be an expression (or expression constructs) for driving expression of the polynucleotide in a target cell. Vectors and methods for inserting them into a target cell are known in the art [See, e.g., Sambrook et al., 1989].
In an aspect, the disclosure provides recombinant cells that comprise the vectors and/or polynucleotides described herein. The cells can be any cell suitable as a host for recombinant nucleic acid molecules, and selected based on well known techniques. Techniques for generating and maintaining recombinant cells are known in the art, such as those described in Sambrook et al., 1989.
The term “B cell malignancy,” as used herein, refers to a malignancy derived from any stage of B cell, including, but not limited to, naïve cells, germinal center cells, memory B cells, and plasma cells. Examples of B cell malignancies include, but are not limited to, mantle cell lymphoma, follicular lymphoma, Hodgkin's lymphoma, Burkitt lymphoma, germinal center B-cell like diffuse large B cell lymphoma (DLBCL), chronic lymphocytic leukemia, small lymphocytic lymphoma, lymphoplasmacytic lymphoma, multiple myeloma, and activated B-cell like DLBCL.
In an aspect, the disclosure provides a method of distinguishing B cell malignancies on the basis of the B-cell origin. In certain embodiments, methods of diagnosing B cell malignancies on the basis of the B-cell origin are provided. In certain such embodiments, a B cell malignancy is determined to be derived from a particular B-cell stage. The B-cell origin of a B cell malignancy may be determined, in certain embodiments, by detecting one or more microRNAs that can be used to distinguish B-cell stages. Certain exemplary B-cell stages include, but are not limited to, naïve cells, germinal center cells, memory B cells, and plasma cells. Certain exemplary microRNAs that can be used to distinguish B-cell stages are shown in Table 4. In various embodiments, the method comprises detecting at least one, at least two, at least five, at least 10, at least 20, at least 30, at least 50, at least 75, or at least 100 microRNAs.
In certain embodiments, a panel of microRNAs is selected that will allow determination of the B cell stage from which a B cell malignancy is derived. For example, in certain embodiments, two or more microRNAs from Table 4 are selected such that detection of the levels of those microRNAs in a B cell malignancy will indicate whether the B cell malignancy is derived from naïve, germinal center, plasma, or memory B cells. In various embodiments, the panel of microRNAs comprises at least one, at least two, at least five, at least 10, at least 20, at least 30, at least 50, at least 75, or at least 100 microRNAs from Table 4. One skilled in the art can select a suitable panel of microRNAs, including one or more microRNAs from Table 4, according to the intended use of the panel.
As described throughout the disclosure, the methods herein can include detecting one or a plurality of miRNAs. When the term “at least” is used in association with a number (e.g., “at least 20”) that term will be understood to include 20 as well as optionally any integer after 20 and up to and including the total number of microRNAs disclosed herein.
In some embodiments, a B cell malignancy derived from naïve cells is mantle cell lymphoma. In other embodiments, a B cell malignancy derived from germinal center cells includes, but is not limited to, follicular lymphoma, Hodgkin's lymphoma, Burkitt lymphoma, or germinal center B-cell like diffuse large B cell lymphoma (DLBCL). In other embodiments, a B cell malignancy derived from memory B cells includes, but is not limited to, chronic lymphocytic leukemia or small lymphocytic lymphoma. In some embodiments, a B cell malignancy derived from plasma cells includes, but is not limited to, multiple myeloma or activated B-cell DLBCL.
Certain B cell malignancies can be difficult to distinguish using current methodologies. In extreme cases, almost any B cell malignancy can be confused with another. As illustrative examples, Burkitt lymphoma and DLBCLs are often confused. Similarly, mantle cell lymphoma and small lymphocytic lymphoma can also be confused. Burkitt lymphoma and germinal center DLBCL are both derived from germinal center cells, while activated B-cell DLBCL is derived from plasma cells. Thus, if a B cell malignancy appears to be Burkitt lymphoma or a DLBCL, in certain embodiments, microRNA analysis can be used to narrow down the B cell malignancy to either a germinal center cell-derived B cell malignancy or a plasma cell-derived B cell malignancy. If the B cell malignancy is plasma-cell derived, then it may be activated B-cell DLBCL.
Thus, in certain embodiments, when the identity of a particular B cell malignancy has been narrowed down to two or more possible B cell malignancies, and at least two of those B cell malignancies are derived from different B cell stages, microRNAs that distinguish certain B cell stages can be used to further narrow down the identity of the B cell malignancy. In certain embodiments, microRNAs that distinguish certain B cell stages can be used to identify the B cell malignancy. One or more such microRNAs can be selected, in certain embodiments, from the microRNAs in Table 4. One skilled in the art can select a suitable set of microRNAs, including at least one microRNA from Table 4, for distinguishing particular B cell stages.
In an aspect, the disclosure provides a method of identifying a B cell malignancy comprising detecting one or a plurality of microRNAs. In certain embodiments, the method can provide a diagnosis of a B cell malignancy. In certain embodiments, one or more microRNAs that are characteristic of a particular B cell malignancy are used to identify the B cell malignancy. In certain embodiments, the identity of the B cell malignancy is first narrowed down to a list of two or more particular B cell malignancies using, for example, tumor morphology and/or immunohistochemistry and/or microRNA detection, e.g., to determine the B cell stage from which the tumor is derived. Certain exemplary microRNAs that can be used to identify B cell malignancies are shown in the Tables (e.g., Tables 7-35).
In certain embodiments, methods of identifying B cell malignancies comprise detecting one or more microRNAs from one or more of Tables 7 to 15, and Appendix B, Tables 16 to 30. That is, in certain embodiments, a panel of microRNAs is selected that will identify a B cell malignancy as being one of a particular selection of B cell malignancies. As a non-limiting example, a panel of microRNAs can be designed to identify a B cell malignancy as one of Burkitt lymphoma, ABC DLBCL, or GCB DLBCL. In certain such embodiments, the panel of microRNAs comprises at least one microRNA from Table 10, column “BL miRNA list” and/or Table 14, column “BL High”; at least one microRNA from Table 11 and/or Table 14, column “ABC High”; and at least one microRNA from Table 10, column “GCB miRNA list” and/or Table 14, column “GCB High”.
When other methods indicate a particular identity for a B cell malignancy, in certain embodiments, microRNAs can be used to confirm that identification. Thus, for example, if a B cell malignancy is believed to be a Burkitt lymphoma, that identification can be confirmed by determining the expression level of one or more microRNAs listed in Table 10, column “BL miRNA list” and/or Table 14, column “BL High”. Similarly, if a B cell malignancy is believed to be ABC DLBCL, that identification can be confirmed by determining the expression level of one or more microRNAs listed in Table 11 and/or Table 14, column “ABC High”. If a B cell malignancy is believed to be GCB DLBCL, that identification can be confirmed by determining the expression level of one or more microRNAs listed in Table 10, column “GCB miRNA list” and/or Table 14, column “GCB High”. If a B cell malignancy is believed to be chronic lymphocytic leukemia, that identification can be confirmed by determining the expression level of one or more microRNAs listed in Table 12 and/or Table 15, column “CLL High”. If a B cell malignancy is believed to be Hodgkin's lymphoma, that identification can be confirmed by determining the expression level of one or more microRNAs listed in Table 13 and/or Table 15, column “HL High”. If a B cell malignancy is believed to be follicular lymphoma, that identification can be confirmed by determining the expression level of one or more microRNAs listed in Table 10, column “FL miRNA list” and/or Table 15, column “FL High”.
In certain embodiments, when the identity of a B cell malignancy has been narrowed down to two B cell malignancies selected from Burkitt lymphoma, GCB DLBCL, ABC DLBCL, chronic lymphocytic leukemia, follicular lymphoma, and Hodgkin's lymphoma, the identity of the B cell malignancy can be determined by detecting one or more microRNAs from Tables 16 to 30.
As discussed in the Examples, the miRNAs described herein as differentially expressed in a B cell malignancy have been identified with high confidence, and thus, identification of one miRNA is adequate to perform the methods of identification and diagnosis disclosed herein. Accordingly, in various embodiments, the methods can comprise detecting at least one, at least two, at least five, at least 10, at least 20, at least 30, or at least 50 microRNAs in order to narrow down the identity of, or identify, a B cell malignancy.
As noted above, the treatment regimens and prognoses for the various B cell malignancies can differ significantly. Thus, determining the correct identity and/or origin of a B cell malignancy can be important for selecting an effective therapy and/or setting appropriate patient expectations. B cell malignancy samples may be obtained and prepared using methods known in the art. One skilled in the art can select an appropriate method of obtaining a B cell malignancy sample according to various parameters, such as the age, size, medical history, and/or identity of the patient. One skilled in the art can select an appropriate method of preparing a B cell malignancy sample for analysis according to the B cell malignancy sample source, size, quality, and/or intended use. For example, in certain embodiments, a B cell malignancy sample is prepared in a manner that preserves microRNAs in the sample as much as practicable under the circumstances.
MicroRNAs can be detected using any method known in the art. Exemplary methods of detecting microRNAs include, but are not limited to, hybridization-based methods and amplification-based methods. Certain exemplary detection methods include, but are not limited to, arrays (including microarrays and bead-based arrays), in situ hybridization, Northern blotting, TaqMan probes, RT-PCR, real-time PCR, and direct sequencing. One skilled in the art can select a suitable detection method according to the sample source, size, quality, and/or particular application.
In certain embodiments, real-time PCR is employed to determine the expression level of a microRNA. In some embodiments a miRNA is considered present in a subpopulation if the cycling time (CT) is less than 36 in all three biological replicates, and a CT greater than 36 is undetected.
In certain embodiments, the expression level of a microRNA in a sample is determined relative to a control sample. A control sample may be selected, in various embodiments, because it is expected to have either high or low expression of the microRNA.
In certain embodiments, the expression level of a microRNA may be normalized to the expression level of a polynucleotide that is expected to be expressed at similar levels in several different cell types and/or at constant levels in the cell type being analyzed.
In certain embodiments, an identified miRNA from Tables 7-35 is used to distinguish one of the six exemplified B cell malignancies from the other malignanicies. A “high” and a “low” in Tables 10 to 13 refer to at least a 2-fold difference in the expression of the identified miRNA when one lymphoma is compared to other lymphomas and benign lymph nodes.
In embodiments, mRNA levels can be profiled by using a microarray. In some embodiments, array elements with median signal intensities of less than 7 log 2 units across samples are removed from analysis. In embodiments, a gene is considered for further analysis if it is on-average 2-fold or higher differentially expressed in a binary comparison of B cell subsets and expressed in at least one of the two B cell subsets being compared.
In an embodiment, the level of at least one miRNA is measured by reverse transcribing RNA from a test sample obtained from a subject to provide a set of target oligodeoxynucleotides, hybridizing the target oligodeoxynucleotides to one or more miRNA-specific probe oligonucleotides (e.g., a microarray that comprises miRNA-specific probe oligonucleotides) to provide a hybridization profile for the test sample, and comparing the test sample hybridization profile to a hybridization profile generated from a control sample. An alteration in the signal of at least one miRNA in the test sample relative to the control sample is indicative of the subject either having, or being at risk for developing, a B-cell malignancy. In an embodiment, the signal of at least one miRNA is upregulated, relative to the signal generated from the control sample. In another embodiment, the signal of at least one miRNA is down-regulated, relative to the signal generated from the control sample. In some embodiments, the microarray comprises miRNA-specific probe oligonucleotides for a substantial portion of all known human miRNAs. In a further embodiment, the microarray comprises miRNA-specific probe oligonucleotides for one or more miRNAs selected from the group consisting of SEQ ID NOs: 763-1350, or 1565 and any combination thereof.
The microarray can be prepared from gene-specific oligonucleotide probes generated from known miRNA sequences. The array may contain two different oligonucleotide probes for each miRNA, one containing the active, mature sequence and the other being specific for the precursor of the miRNA. The array may also contain controls, such as one or more mouse sequences differing from human orthologs by only a few bases, which can serve as controls for hybridization stringency conditions. tRNAs and other RNAs (e.g., rRNAs, mRNAs) from both species may also be printed on the microchip, providing an internal, relatively stable, positive control for specific hybridization. One or more appropriate controls for non-specific hybridization may also be included on the microchip. For this purpose, sequences are selected based upon the absence of any homology with any known miRNAs.
The microarray may be fabricated using techniques known in the art. For example, probe oligonucleotides of an appropriate length, e.g., 40 nucleotides, are 5′-amine modified at position C6 and printed using commercially available microarray systems. Labeled cDNA corresponding to the target RNA sequence(s) is prepared by reverse transcribing the target RNA with labeled primer. Following first strand synthesis, the RNA/DNA hybrids are denatured to degrade the RNA templates. The labeled target cDNAs thus prepared are then hybridized to the microarray chip under typical hybridizing conditions. At positions on the array where the immobilized probe DNA recognizes a complementary target cDNA in the sample, hybridization occurs. The labeled target cDNA marks the exact position on the array where binding occurs, allowing automatic detection and quantification. The output consists of a list of hybridization events, indicating the relative abundance of specific cDNA sequences, and therefore the relative abundance of the corresponding complementary miRNAs, in the patient sample.
In an aspect, the disclosure relates to kits. Such kits can be used in methods of identifying a miRNA or mRNA described herein; an expression level or expression pattern of one or more miRNA(s) or mRNA(s) described herein; and/or identifying a B-cell malignancy. In some embodiments the kit can provide a diagnosis of a B-cell type and or a B-cell malignancy. In some embodiments the kit can differentiate one B-cell malignancy from other B-cell malignancies (e.g., ABC-DLBCL from GBC-DLBCL), and can provide information useful to a medical professional regarding a preferred course of therapeutic treatment. Suitably, a kit can comprise an isolated nucleic acid molecule or a plurality of isolated nucleic acid molecules as described herein (e.g., a sequence complementary to any of the miRNAs disclosed in the Tables). In embodiments, the isolated nucleic acid molecule can comprise a sequence of one or more RT-PCR target sequences, primers directed thereto, or a sequence complementary thereto. The kit can also include adapter nucleic acid molecules (e.g., universal adapter molecules for attachment to expressed miRNAs/mRNAs for reverse transcription and amplification); appropriate buffer systems and reagents, detectable labels, an energy source (e.g., ATP), and other agents and components that can be used in performing analysis of miRNA expression (e.g., in RT-PCR, deep sequencing, or microarray-based methods). Kits also include instructions for use.
It will be understood that any numerical value recited herein includes all values from the lower value to the upper value. For example, if a concentration range is stated as 1% to 50%, it is intended that values such as 2% to 40%, 10% to 30%, or 1% to 3%, etc., are expressly enumerated in this specification. These are only examples of what is specifically intended, and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application.
In an aspect, the disclosure provides a DNA library comprising one or more miRNA sequences from Tables 4-5, or 6-33. In a related aspect, the disclosure provides a method for generating such a DNA library. In an embodiment the library comprises a cDNA library that includes sequences derived from a sample of the miRNAs or, in addition or alternatively, the mRNA purified from a particular source such as, for example, a collection of cells, a particular tissue, or an entire organism. In embodiments, the source of the cDNA library is a B cell, such as a B cell in any stage (e.g., naïve, germinal center, memory, activated, or plasma, etc.) or a B cell malignancy (e.g., mantle cell lymphoma, follicular lymphoma, Hodgkin's lymphoma, Burkitt lymphoma, germinal center B-cell like diffuse large B cell lymphoma (DLBCL), chronic lymphocytic leukemia, small lymphocytic lymphoma, lymphoplasmacytic lymphoma, multiple myeloma, and activated B-cell like DLBCL). Typically, the isolated miRNA (or mRNA) is converted to a DNA template by reverse transcription, and comprises the cDNA version of the expressed RNA (e.g., miRNA or mRNA). Thus, a library can represent the cDNA version of the active “transcriptome” in a particular source under the physiological, developmental, or environmental conditions that existed when the miRNA/mRNA was purified.
In an embodiment, the library comprises a miRNA sequence described in Tables 4-5; 7-33. In embodiments, the library comprises at least one of SEQ ID NOs 763-1350 or 1565, and any combination thereof. In an embodiment, the library comprises a collection of miRNA sequences comprising SEQ ID NOs 763-1350 or 1565. In embodiments the library can be used to identify and/or differentiate a B-cell malignancy from other B-cell malignancies. In such embodiments, the library comprises at least one miRNA sequence selected from those listed in any of Tables 4 or 7-35.
As used herein, a “library” is a collection of DNA sequences that is stored and propagated in a population of microorganisms through standard molecular cloning processes. A DNA library can be of any type such as, for example, a cDNA library (formed from reverse-transcribed RNA) or a genomic library (formed from genomic DNA). The DNA library can be used in any routine application or technique known in the art (e.g., gene discovery; cloning of full-length cDNAs to identify/study gene function; miRNA/mRNA expression in different cells or tissues; splice variants in different cells or tissues) and, in some embodiments, can depend on the source of the original DNA fragments. In embodiments, the library can be used to isolate, characterize, and/or quantify the actively expressed miRNA is a population of cells such as, for example, B-cells or B-cell malignancies. In some embodiments, the library can be used to study miRNA-protein interactions or miRNA-based regulation of protein expression or activity.
Any known method of library preparation can be used to make the library described herein, including the methods described in the detailed description and non-limiting Examples. Further general techniques can be based on the methods and techniques known in the art, (see, e.g., RNA Methodologies: A Laboratory Guide for Isolation and Characterization (R. E. Farrell, Academic Press, 1998); cDNA Library Protocols (Cowell & Austin, eds., Humana Press; Functional Genomics (Hunt & Livesey, eds., 2000); and the Annual Review of Genomics and Human Genetics (E. Lander, ed., yearly publications by Annual Reviews). Suitably, the nucleotide sequences of interest in a library are preserved as inserts in a plasmid or the genome of a bacteriophage that has been used to infect bacterial cells. There are differences in the cloning vectors and techniques used in library preparation, but in general each DNA fragment is uniquely inserted into a cloning vector and the pool of recombinant DNA molecules is then transferred into a population of bacteria or yeast such that each organism contains on average one construct (vector+insert). The DNA molecules are copied and propagated along with the population of organisms in culture (thus, effectively, “cloned”). Accordingly, in some embodiments, the term “library” can refer to a population of organisms, each of which carries a DNA molecule inserted into a cloning vector, or alternatively to the collection of all of the cloned vector molecules.
An “increased level” of expression, as used herein, refers to a level of expression that is at least 2-fold greater than the level of expression in a control cell type or tissue. In various embodiments, the level of expression is at least 2.5-fold, at least 3-fold, at least 5-fold, or at least 10-fold, greater than the level of expression in a control cell. Exemplary control cells and tissues include, but are not limited to, normal cells, benign lymph nodes, and other B cell malignancies. In certain embodiments, benign lymph nodes are used as a control tissue. Such benign lymph node tissue contains a variety of cell types.
A “decreased level” of expression, as used herein, refers to a level of expression that is less than 50% of the level of expression in a control cell.
The term “differentially expressed” or “differential expression” relates to a difference in the observed or detected level of expression of a biomolecule such as, for example, nucleic acids (e.g., a polynucleotide, mRNA, miRNA, etc.) or amino acid sequence (e.g., protein, polypeptide, etc.) in a test sample relative to the observed or detected level of expression of the same biomolecule in a control sample or other reference (e.g., a previously established reference level). The difference in expression can be either an increase or a decrease in the expression of the biomolecule in the test sample relative to the control sample.
The Examples that follow provide further illustration of certain aspects and embodiments described in the foregoing description. These illustrative Examples should not be interpreted as limiting the scope of the appended claims.
Patient Sample Processing
B cell populations were obtained from young patients undergoing routine tonsillectomy using a protocol approved by the Clinical Center at the National Institutes of Health. Patient tonsils were disaggregated and separated by Ficoll. The mononuclear cell layer was harvested, washed in PBS, and resuspended in ACK lysing buffer to remove small numbers of red blood cells. After a wash and resuspension with 10 ml of PBS with 10% Bovine Serum Albumin, cells were counted and 200 million were stained with fluorochrome-tagged monoclonal antibodies to CDI9, IgD, CD38 and CD27. The specific monoclonal antibodies employed were anti-CDI9-PE-Cy5.5, anti-IgD-FITC, anti-CD27-PE, and anti-CD38-APC, all from BD Biosciences and BD Pharmingen (San Jose Calif.). Cells were sorted using the MoFIo Cell sorter (Dako Cytomation, Colorado Springs, Colo.) into naive B cells (CDI9+IgD+CD2TCD38+), germinal center B cells (CDI9+IgD-CD38++), memory B cells (CDI9+IgD-CD27+CD38dim) and plasma cells (CDI9dimIgD-CD27++CD38+++). Three replicates of each B cell subset were obtained from separate patients. The sample purity was verified by FACS and found to be over 90% in all cases.
Tumor specimens were obtained from patients who were examined under a protocol approved by the Duke University Medical Center Institutional Review Board. The pathologic diagnosis of the samples was verified prior to analysis. Samples from patients with diffuse large B cell lymphoma were further subclassified as described previously. See Hans et al. (2004) Blood 103: 275-282. Chronic lymphocytic leukemia samples were processed and purified as described previously. See Volkheimer et al. (2007) Blood 109: 1559-1567. Total RNA was extracted using the phenol-chloroform method to preserve miRNAs, using Ambion reagents.
microRNA Profiling Using Multiplexed Real-Time PCR
MiRNA expression profiling was conducted using the Applied Biosystems 384-well multiplexed real-time PCR assay using 400 ng of total RNA. Eight reactions, each containing 50 ng of RNA and a multiplex looped primer pool with endogenous small nucleolar (sno)-RNA controls, were used to reverse-transcribe the miRNAs in parallel fashion. Each completed reaction was loaded onto the 384-well plate per manufacturer's instructions, and real-time PCR was run on the ABI 7900HT Prism. For each 384-well plate, we used the automatically determined cycle-threshold (CT) using the SDS 2.2.1 software (Applied Biosystems). Consistent with manufacturer recommendations, we considered CT greater than 36 as undetected. A miRNA was considered to be present in a subpopulation if the CT was less than 36 in all three biological replicates. The probes deemed to be present were normalized to the average expression of a sno-RNA control. The expression values were calculated as 2−ΔCT, then median centered to 500 and log 2-transformed.
Gene Expression (mRNA) Profiling Using Microarrays
Gene expression profiling and normalization were performed using methods identical to those we have described previously. See Dave et al. (2004) N. Engl. J. Med. 351: 2159-2169. Array elements with median signal intensities of less than 7 log 2 units across the samples were removed from analysis, in order to exclude poorly measured genes and genes not appreciably expressed in the samples. Genes that were on-average 2-fold or higher differentially expressed in a binary comparison of B cell subsets, and appreciably expressed in at least one of the 2 B cell subsets being compared, were selected for further analysis as described below. The data have been deposited in the publicly available Gene Expression Omnibus database (GSE12366).
MiRNA Profiling Using Microarray
MiRNA expression profiling from human B cell malignancies was conducted using up to 1 μg of total RNA from sample and reference (normal lymph node), which were labeled with Cy3 or Cy5 fluorescent dyes, using the miRNA/LNA labeling kit (Exiqon, Denmark). The fluorescently labeled samples were combined and hybridized to a miRNA microarray (v. 10.0, Exiqon, Denmark), in a nitrogen atmosphere. The micro array slides were scanned with GenePix 4100 Scanner. The quantified signals were normalized using the global Lowess algorithm, using Genespring (Agilent) software. The intensity values for multiple spots were averaged and the normalized values were log 2-transformed. Missing values were replaced with the lowest value for analysis.
MiRNA Target Prediction
Annotated genes on the U133plus 2.0 array were matched to the miRNA target list downloaded from TargetScan (www.targetscan.org). For the purpose of this study, a target gene was defined by the presence of a seed sequence match (nucleotides 2-8) and conservation of the seed sequence and 3′UTR in humans, dog, rat, mouse and chicken. Additional conservation was examined in miRNA target genes selected for experimental validation. The distribution of the mRNA expression for these genes was plotted as a density plot using the Splus statistical software (Insightful Corporation). The difference in distribution between the B cell subsets was calculated using a two-sample, 1-sided Kolmogorov-Smirnov test to examine the hypothesis that being a miRNA target conferred repression in the appropriate population (consistent with the known biology of miRNA effects).
The 3′UTRs of LM02, MYBL1 and PRDM1 were aligned using Blastz alignment of Human, Chimp, Mouse, Rat, Dog, Chicken, Frog (Xenopus) and Zebrafish, and were displayed using the UCSC genome browser. The conservation of miR-223 seed sequence and the 3′UTRs of LM02 and MYBL1, as well as that of the miR-30 family and miR-9 on PRDM1, were thus verified.
Western Blot
RIPA Lysis buffer (1× phosphate-buffered saline [PBS], 1% Nonidet P-40, 0.5% sodium deoxycholate, 0.1% SDS, 10 mM phenylmethylsulfonyl fluoride, 1 μg/mL aprotinin, and 100 mM sodium orthovanadate) was added to 750,000 cells and incubated on ice for 30 minutes. The mixture was spun down and the supernatant was transferred to a new tube as the whole cell extract. A total of 20 μg of cell lysate was separated on a 4-18% Tris-Bis NuPAGE gel (Invitrogen) and transferred using the iBlot transfer device (Invitrogen) program 3 for 7 minutes (LM02 detection) or program 2 for 6 minutes (PRDM1). The blots were probed using 1:200 mouse-anti-LM02 (Santa Cruz Biotechnologies SC-65736), 1:750 mouse-anti-Blimp-1 (Santa Cruz Biotechnologies SC-66015) or 1:5000 goat-anti-B-actin (Santa Cruz Biotechnologies SC-47778) for 1 hour at room temperature. The antibodies were detected using 1:10,000 goat-anti-mouse horseradish peroxidase conjugated antibodies (Santa Cruz Biotechnologies). Western Blotting Luminol Reagent (Santa Cruz Biotechnologies) was used to visualize the bands corresponding to each antibody.
Single miRNA/mRNA Expression Using Real-Time Polymerase Chain Reaction (RT-PCR)
With 10 ng of RNA per reaction, miRNAs of interest were reverse-transcribed with ABI individual stem-loop primers designed to detect only mature miRNA, and measured by Taqman real-time PCR normalized to the small nucleolar RNA, RNU48. In order to assess mRNA expression using RT-PCR, 1 μg of RNA was reverse-transcribed with the ABI High Capacity cDNA Reverse Transcription kit. Gene expression was measured with exon-spanning Taqman probes, and normalized to beta-2 micro globulin expression.
Cell Culture
BJAB and H929 were cultured in RPMI (Gibco) supplemented with 10% fetal bovine serum, and U266 was cultured in RPMI supplemented with 15% fetal bovine serum. 293T cells were grown in DMEM media (Gibco) with 10% FBS. All cell lines were grown in 37° C. humidified cell culture incubators with CO2 maintained at 5%.
MiRNA Functional Analysis
MicroRNA Transfection
miRNAs of interest were over-expressed in cell lines of interest by transfecting the appropriate miRNA precursors (Ambion) at 100 nanomoles using Amaxa's Nucleofector system. In particular, BJAB was transfected with Nucleofector solution T, program T-016, U266 with Nucleofector C, program X-005, and H929 with Nucleofector V, program T-001. 1.5 million cells were used per transfection and mixed with appropriate miRNA precursors (Ambion) for a concentration of 100 nM.
Statistical Analysis
Identifying Differentially Expressed miRNA and mRNA
MiRNAs were considered to be differentially expressed if the mean signal was changed at least 2-fold and a false discovery rate (q) was less than 5% using Significance Analysis of Microarrays (SAM) with 1000 permutations. See Tusher et al. Proc Natl Acad Sci USA. 2001; 98:5116-5121.
Differentially expressed genes (mRNA) in Naive versus Germinal Center, Germinal Center versus Plasma Cells, and Germinal Center versus Memory Cells comparisons were identified using SAM. Genes that were 2-fold differentially expressed at a false discovery rate (q) less than 1% with 1000 permutations were identified as significantly differentially expressed.
Transcription Factors and miRNA Target Genes
Transcription factors were identified based on the gene ontology (GO search term “transcription factor”) and matched to the probes of the Affymetrix U133plus 2.0 microarray. Of the total of 938 transcription factor genes thus identified, we selected 364 genes that were differentially expressed in at least one of the B cell stage transitions. We evaluated the breakdown of the differentially expressed transcription factors among miRNA targets versus non targets. The p-values were computed using a chi-square test separately in each B cell stage-transition.
B Cell Malignancy Sample Classification
The top 50 most differentially expressed miRNAs (P<0.01) in each pair-wise B cell malignancy type comparison were chosen as the initial predictor. Singular value decomposition was applied to reduce the list to 20 most informative miRNAs in each pair-wise comparison. See West et al. Proc Natl Acad Sci USA. 2001; 98:11462-11467. A Bayesian logistic regression was performed in Matlab (Mathworks) using the 20-predictor miRNAs for each pair-wise comparison. Each sample was tested using the microRNA-based predictor in a leave-one-out fashion to determine the accuracy of each prediction. For a sample to be classified as a particular B cell malignancy (or normal) type, it had to be predicted as such in every pair-wise comparison.
Normal B Cell Stage Classification of B Cell Malignancies
We constructed a Bayesian predictor to distinguish normal naive from germinal center B cells based on the 32 miRNAs depicted in
Western Blot Quantitative Analysis
Western blot scans were quantified using NIH ImageJ software. For each experiment, the ratios of protein of interest (LM02, PRDM1) to Actin were determined and mean centered to 100 across the experiment. The average and standard deviation of these values across the three experiments were calculated and displayed relative to the scrambled control expression.
Luciferase Indicator Assay Quantitative Analysis
Firefly luciferase reporter constructs were created in the pL/SV40/GL3 vector for the LM02 3′UTR and the LM02 3′UTR with the predicted miR-223 binding site mutated, as described below. Mature microRNA expression of a pL/CMV/eGFP vector coding for pri-miR-223 from the 3′UTR of EGFP of the vector was confirmed by Taqman-real time PCR in transfected 293T cells. gl3 activity was normalized in dual luciferase assays to pL/SV40/RLuc, with which it was cotransfected. The PRDMI 3′UTR was also cloned into the pL/SV40/GL3 vector. microRNA expression vectors and their respective seed sequence mutants were created for miR-9-2, miR-30b, and miR-30d.
LM02
The LM02 3′UTR was PCR-amplified from BJAB cDNA using primers 1 and 2 (SEQ ID NOs: 1 and 2, respectively) and ligated into the XhoI and XbaI sites of the previously described lentiviral vector pL/SV40/GL3, which expresses firefly luciferase. See Tusher et al. Proc Natl Acad Sci USA. 2001; 98:5116-5121. As a control, an LM02 3′UTR mutant was created using mutant PCR primers 3 and 4 and then outer primers 1 and 2. The resulting fragment was also placed into the XhoI and XbaI sites of pL/SV40/GL3. In this LM02 3′UTR mutant, the seed match predicted to bind to nucleotides 2-8 of miR-223 is converted from 5′AACUGAC 3′ to 5′AACAGUC 3′. To create a miR-223 expression vector, a ˜350 nucleotide-long fragment of pri-miR-223, encompassing the pre-miRNA stem loop in its middle, was PCR-amplified from genomic BJAB DNA with primers 6 and 7 (SEQ ID NOs. 6 and 7) and ligated into the XhoI and XbaI sites of the pL/CMV/eGFP vector. This pL/CMV/eGFP vector was generated by ligating a fragment containing the CMV promoter and the EGFP ORF into the BamHI and XhoI sites of the previously described lentiviral backbone pL. See Tusher et al. Proc Natl Acad Sci USA. 2001; 98:5116-5121. The expression of miR-223 from the 3′UTR of EGFP in the resulting vector was confirmed by Taqman real time PCR in transfected 293T cells.
For luciferase indicator assays, 293T cells plated in 24 well plates were transfected using FUGENE6 as follows:
Reporter expression was evaluated by dual luciferase assays (Promega) 48 hours post-transfection. Firefly Luciferase (GL3) to internal control Renilla Luciferase (RLuc) ratios from 293T cells transfected with pL/CMV/eGFP/miR-223 were divided by those obtained from 293T transfected with the pL/CMV/eGFP vector control. The average and standard deviation were taken across five experiments for the pL/SV40/gl3 empty, LM02, and LM02 mutant vectors.
Firefly Luciferase (GL3) activity readings of the PRDM1 3′UTR construct were divided by internal control Renilla Luciferase (RLuc) activity readings. The average and standard deviation of these ratios across three experiments were calculated and scaled relative to the empty vector (pL/CMV/eGFP) transfection.
PRDM1
The PRDM1 3′UTR was PCR-amplified from BJAB genomic DNA in two reactions using primer pairs 7 and 8 in one reaction, and 9 and 10 in another (SEQ ID NOs: 7 to 10, respectively). The two fragments were then ligated together into the XhoI and NotI sites of pL/SV40/GL3 to generate the entire PRDM1 3′UTR. microRNA expression vectors were created as described above for mir-9-2, mir-30b, and mir-30d with the primers listed below. Again, over-expression from the 3′UTR of EGFP in the resulting vector was confirmed by Taqman real-time PCR in transfected 293T cells. For the PRDM1 luciferase assays, we used the sequences listed below to PCR-mutate the seed sequence of the microRNA expression vectors rather than the PRDM1 3′UTR, which had numerous seed sequence binding sites.
CTTATCTAGCTGTATGAGT
TAGATAACAACTCGCTTCC
GATCCCCGACTGGAAGCTG
AACAACAACAGACTTTCTG
Luciferase assays were carried out in a manner similar to those described for LM02.
IgVH Mutation Status of Chronic Lymphocytic Leukemia Samples
IgVH mutation status was determined as described in Volkheimer et al. (Blood. 2007; 109:1559-1567) using genomic DNA. In brief, genomic DNA was isolated from purified CLL cells and isolated using the GenElute Mammalian DNA extraction Kit from Sigma (St. Louis, Mo.) according to the manufacturer's instructions. DNA was amplified using nested PCR primers. PCR products were electrophoresed, purified, and sequenced using an automated DNA sequencer (Applied Biosystems, Foster City, Calif.) with the BigDye Terminator kit (Perkin Elmer, Boston, Mass.). Forward and reverse sequences were aligned into a single resolved sequence using Sequencher 4.1 software (Gene Codes Corporation, Ann Arbor, Mich.), and then aligned with germline sequences derived from DNA Plot on the V BASE directory website (http://vbase.mrc-cpe.cam.ac.uk/). The percent sequence identity was calculated by dividing the number of mutations from FR1 to FR3 by the total number of nucleotides in this region. Samples were considered somatically mutated if they had greater than 2% mutations in this region.
Mature B cell subsets can be defined by the expression of surface CD19, IgD, CD38, and CD27, and were obtained by fluorescence activated cell sorting of tonsils from young individuals undergoing routine tonsillectomy. See
To determine whether mature B cell subsets had unique patterns of microRNA (miRNA) expression, we used a 384-well multiplexed real time polymerase chain reaction (RT-PCR) assay (Applied Biosystems) that allowed measurement of all 365 miRNAs in miRBase 9.2. See Chen et al. Nucleic Acids Res. 2005; 33:e179; and He et al. Nature. 2007; 447:1130-1134. We detected a total of 113 unique miRNAs in the B cell populations. See Table 4. This detection frequency compares favorably to the identification of 71 unique miRNAs (45 miRNAs with more than one clone) through the examination of 3101 sequences cloned from unselected CD19-positive mature B cells. See Landgraf et al. Cell. 2007; 129:1401-1414. We identified differentially expressed miRNAs in mature B cell subsets using a false discovery rate of less than 5%. See
In Table 4, normalized expression values for B-cell subsets are shown, along with significance analysis of microarrays q values. Empty microRNA expression cells indicate below-threshold values, defined as RT-QPCR Ct values greater than 36 or undetected. SAM q values greater than 5 were considered non-significant and not displayed.
The B cell subsets were profiled for gene expression at the whole genome level, as described previously. See Dave et al. N Engl J Med. 2004; 351:2159-2169. At each stage, we identified differentially expressed genes as those genes with a mean two-fold difference in expression and a false-discovery rate of less than 1%. See
In the naïve→germinal center (GC) B cell transition, we identified 32 miRNAs that were differentially expressed. Interestingly, all but 4 miRNAs were found to be expressed more highly in GC cells than in naive B cells. See
The expression pattern of all the miRNAs that were measurable in at least one of the B cell subsets is summarized in
Separately, we examined the expression of predicted target genes of differentially expressed microRNAs. We also found that predicted mRNA target genes of microRNAs expressed highly in GC cells were expressed at lower levels in GC cells compared to other stages. See
In the naïve to germinal center transition (see
A similar analysis was carried out for the transitions from germinal center to plasma cell (
Finally, we found that a higher proportion of differentially expressed transcription factors are predicted microRNA targets. See
MiR-223 has previously been described as being important in the commitment to myeloid lineage. See Chen et al. Science. 2004; 303:83-86; Johnnidis et al. Nature. 2008; 451:1125-1129. We found miR-223 to be expressed at nearly 8-fold higher levels in both naive and memory cells compared to GC cells. This miRNA has a highly conserved sequence complementarity to the 3′UTR of 2 transcription factors that are expressed highly during GC cell differentiation: LM02 (
We evaluated the effects of miR-223 expression on its predicted target gene, LM02, by transfecting precursors of miR-223 into a cell line derived from GC cell lymphoma cells (BlAB). Over-expression of miR-223 resulted in a consistent down-regulation of LM02 at the transcript level compared to a transfection with a scrambled control with no sequence complementarity to the human genome. See
As additional validation, we investigated whether the miR-223 had a direct effect on LM02 by cloning the 3′UTR sequence of LM02 3′ to the firefly luciferase ORF (Flue). See Gottwein et al. Nature. 2007; 450:1096-1099. The resulting constructs and the unmodified vector were co-transfected into 293T cells along with a Renilla luciferase internal control and pL-CMV-eGFP constructs expressing either no miRNA or miR-223. Flue expression from constructs bearing LM02 3′ UTR sequences were differentially down-regulated by miR-223 compared to those with mutated seed sequences; the seed sequence mutant construct had consistently diminished miR-223 repression compared to the wild-type construct in 5 separate experiments. See
Activation of LM02 has been associated with the development of leukemia in patients undergoing gene therapy. Hacein-Bey-Abina et al. Science. 2003; 302:415-419. On the other hand, higher expression of PRDM1 alone is sufficient to induce plasma cell-differentiation. Turner et al. Cell. 1994; 77:297-306. Inappropriate expression of such genes must be effectively turned off for a cell to maintain its state. This mode of regulation is reflected in the effects of miR-223, miR-9 and miR-30, which turn off the inappropriate expression of LM02 and PRDMI and might promote state maintenance and inhibition of lymphomagenesis.
On the other hand, our data also identify a number of instances in which miRNAs are co-expressed with their predicted targets. It is possible that such interactions within the cell help to stabilize a defined expression level by dampening fluctuations. For example, in GC cells, we found that miR-181b was strongly co-expressed with its predicted target, BCL6. Such interactions could also be important in B cell stage maintenance and curbing the oncogenic potential of genes involved in B cell differentiation. See Cattoretti et al. Cancer Cell. 2005; 7:445-455; Dorsett et al. Immunity. 2008; 28:630-638.
In the GC→plasma cell transition, we observed that several members of the miR-30 family were expressed at 2-fold or higher levels in GC cells. See
The 3′UTR of PRDM1 contains 3 highly conserved binding sites complementary to the seed sequence of members of the miR-30 family, as well as 3 binding sites for the seed sequence of miR-9, 2 of which are highly conserved across multiple species. See
To evaluate the effects of the miR-30 family and miR-9 on PRDM1 expression in plasma cells, we introduced precursors of miR-9, miR-30b and miR-30d into the U266 multiple myeloma (plasma cell) cell line. Overexpression of miR-30 family members miR-30b and miR-30d, as well as miR-9, had no effect on PRDM1 at the mRNA level. See
Additionally, luciferase reporter activity of the PRDM1 3′UTR construct was decreased by overexpression of miR-9, miR-30b, and miR-30d, but not their respective seed sequence mutants. See
The combined effect of 5 different microRNA species (miR-30a, miR-30b, miR-30c, miR-30d and miR-9) is likely to be more potent than that of a single microRNA. The role of mutual repression of BCL6 and PRDMI in the germinal center to plasma cell differentiation as been described previously. See Martins et al. Immunol. 2008; 26:133-169. Our data suggest that microRNAs may bolster the effects of BCL6 in the inhibition of PRDM1.
Our data show that members of the miR-17˜92 family are consistently expressed in GC cells and may play a role in mature B cell differentiation. Interestingly, the miR-17˜92 family has been implicated in early B cell differentiation and mice lacking the loci that encode these miRNAs have arrested early B cell development. See Ventura et al. Cell. 2008; 132:875-886. The expression patterns of the miR-17˜92 family suggest that the regulatory motifs embedded in the interaction of this miRNA family and its targets might have an additional function in regulating mature B cell differentiation.
A striking observation in this study is the high degree of asymmetry observed in relative expression of miRNAs in GC cells compared to naive and plasma cells. At least 2 hypotheses could account for these findings. First, miRNA expression may promote a highly regulated state that enables GC cells to interact with T cells and antigen presenting cells, and to leave the GC cells poised for differentiation into memory or plasma cells. Second, miRNAs expressed highly in naive and plasma cells may be underrepresented in current miRNA libraries. Such libraries are often constructed from lymph nodes, which are typically enriched in GC cells. High throughput sequencing of sorted populations of B cells could reveal novel miRNAs that are highly expressed in those populations. Interestingly, a larger number of miRNAs were highly expressed in memory cells compared to GC cells. This observation might stem from the fact that memory cells are known to be heterogeneous (Sanz et al. Semin Immunol. 2008; 20:67-82) and standard methods used to select memory cells may capture a diverse group of memory subpopulations.
To examine the expression of B cell stage-specific microRNAs in B cell malignancies, we undertook miRNA profiling of 75 tissue samples derived from normal lymph nodes (N=5) as well as patients with B cell malignancies including the molecular subsets of diffuse large B cell lymphoma (DLBCL; see Rosenwald et al. N Engl J Med. 2002; 346:1937-1947), germinal center B cell-like (GCB) DLBCL (N=20) and activated B cell-like (ABC) DLBCL (N=20), as well as cases of IgV mutated and unmutated chronic lymphocytic leukemia (N=20) and Burkitt lymphoma (N=10).
We constructed a Bayesian predictor from miRNAs that distinguished normal memory B cells from GC cells. See
An interesting aspect regarding the role of miRNAs in malignancies is their reported down-regulation in a number of malignancies compared to normal cells from the same lineage. See Lu et al. Nature. 2005; 435:834-838. To further examine this effect in B cell malignancies, we examined the expression of 113 miRNAs that we had identified in normal B cells. See Table 4, above. Of the 113 miRNAs, 103 were detected using the microarrays that we used to profile B cell malignancies and normal lymph nodes. We applied a 2-sided student's t-test to evaluate the relative expression of those 103 miRNAs in B cell malignancies (N=60) and normal lymph nodes (N=5). 34 miRNAs were differentially expressed (P<0.05) at higher levels in malignant cells and 9 miRNAs were expressed more highly in normal cells. 60 miRNAs were not differentially expressed. See
As additional validation, we examined miRNA cloning frequencies for sequences cloned from normal and malignant B cells. See Landgraf et al. Cell. 2007; 129:1401-1414. MiRNAs for which a sequence was identified in at least 2 of the 3 available normal B cell samples were used in the analysis. We applied a 2-sided student's t-test (P<0.05) to compare the differential cloning frequency of the miRNAs between normal B cells (N=3) and a variety of mature B cell malignancy patient samples and cell lines (N=42). In all, we found 56 miRNAs that were consistently expressed in normal B cells. We found 13 of those 56 miRNAs were differentially expressed (P<0.05) between normal and malignant B cells, of which 12 miRNAs were expressed more highly in malignant cells and 1 miRNA was expressed more highly in normal cells. See
These results demonstrate that miRNAs are not down-regulated in B cell malignancies compared to normal B cells and that normal B cell stage-specific miRNAs are maintained in B cell malignancies.
MicroRNA profiling also revealed that each B cell malignancy type had a distinctive pattern of miRNA expression. See
We tested the performance of the predictor using leave-one-out cross-validation applied to the predictors for Burkitt lymphoma, chronic lymphocytic leukemia, activated B-cell diffuse large B-cell lymphoma, and germinal center B-cell DLBCL. For a sample prediction to be correct, it had to be classified correctly in each pair-wise comparison with all remaining entities. We found it to be over 90% accurate in the identification of each entity. See
We next expanded the analysis to include follicular lymphoma and Hodgkin's lymphoma. We included the samples from the earlier study and we undertook miRNA profiling of the following additional samples: normal lymph nodes (N=5) and patients with germinal center B cell-like (GCB) DLBCL (N=10), activated B cell-like (ABC) DLBCL (N=10), chronic lymphocytic leukemia (N=10), Burkitt lymphoma (N=10), follicular lymphoma (N=10), and Hodgkin's lymphoma (N=9). As before, microRNA profiling revealed that each B cell malignancy type had a distinctive pattern of miRNA expression. See
From that data, we identified microRNAs that can be used to distinguish each of the six B cell malignancies analyzed from the other five. Lists of those microRNAs, and whether they are expressed in high levels or low levels relative to the other 5 B cell malignancies, are shown in Tables 10 through 13. In certain embodiments, each of those microRNAs could be used to distinguish one of the six B cell malignancies from the other five. High and low in the table refer to at least a 2 fold difference when compared to other lymphomas and benign lymph nodes.
From the data in Tables 10 through 13, we identified subsets of microRNAs that are sufficient to distinguish each of the six B cell malignancies from the other five. We selected only microRNAs that are expressed more highly in the selected B cell malignancy. Those microRNAs are listed in Tables 14 and 15. In certain embodiments, each of the microRNAs listed in Tables 14 and 15 can be used to distinguish one B cell malignancy from the other five.
Finally, we identified sets of microRNAs that can distinguish between each pair of B cell malignancies in the study. Lists of those microRNAs are shown in Appendix B, Tables 16 to 30. In certain embodiments, each of the listed microRNAs is sufficient to distinguish between the two B cell malignancies listed in the table description.
The consistent expression of a number of miRNAs in a diverse set of B cell malignances suggests a role for miRNAs in the maintenance of tumor phenotype. Assays for stage-specific B cell markers such as BCL6, a marker for GC cells, are essential in the clinical diagnosis of B cell malignancies. Our data suggest that stage-specific biology in B cell malignancies is retained at the miRNA level. Recent work has demonstrated the utility of gene expression profiling in reliably distinguishing closely related B cell malignancies. See Hummel et al. N Engl J Med. 2006; 354:2419-2430; Dave et al. N Engl J Med. 2006; 354:2431-2442. However, clinical translation of gene expression profiling has proved to be difficult because of the need for freshly frozen tissue. Since intact miRNAs can be isolated from tissues preserved using standard methods (see, e.g., Doleshal et al. J Mol Diagn. 2008; 10:203-211; Xi et al. Rna. 2007; 13:1668-1674), diagnostic methods based upon miRNA profiles could be fairly easy to translate to clinical use.
Interestingly, in contrast to a previous study (Lu et al. Nature 2005; 435:834-838), we did not note a decrease in the expression of the total number or overall expression levels of miRNAs in B cell malignancies compared to normal lymph nodes. Although B cell malignancies maintain the expression of a number of stage-specific miRNAs, their miRNA expression patterns are clearly deranged compared to normal lymph nodes. The consequences of altered miRNA expression in B cell tumors would be important to explore in future studies.
In conclusion, our study demonstrates that mature B cell subsets have distinct patterns of microRNA expression, suggesting a role for miRNAs in B cell differentiation. We provide experimental evidence that transcription factors such as LM02 and PRDMI are direct targets of differentially expressed miRNAs. B cell malignancies demonstrate a distinct pattern of miRNA expression that could be useful in distinguishing morphologically identical subtypes of these tumors. The conserved expression of stage-specific microRNAs in normal and malignant B cells suggests a role for microRNAs in the maintenance of the mature B cell phenotype.
As discussed above, microRNAs have shown promise as biomarkers in a number of malignancies. Diffuse large B cell lymphoma (DLBCL) is the most common form of lymphoma and is known to comprise at least 2 molecularly distinct subgroups with different responses to standard therapy. These two distinct subgroups are typically identified as ABC DLBCL and GC (or GCB) DLBCL.
However, the current methods used to distinguish GCB from non GCB DLBCL are limited fashion and can yield inconsistent results. While gene expression profiling remains the gold standard for distinguishing these 2 molecular subgroups it is not routinely performed in clinical laboratories. In an effort to expand and improve the existing analytical options we sought to develop microRNA-based assays. We created RNA libraries from 31 different samples and performed deep sequencing analysis to identify the present miRNAs.
Small RNA Library Creation and Deep Sequencing
Total RNA was extracted from the 31 samples using the phenol-chloroform method to preserve microRNAs, using Ambion reagents. Total RNA (typically 5 μg) from each sample was run on denaturing polyacrylamide-urea gels. The ˜17-25 nucleotide RNAs were excised from the gel, ligated to sequencing adaptors on both ends and reverse transcribed. The resulting cDNA library was PCR-amplified for 15 cycles and gel purified on 6% acrylamide gel. The gel-purified amplicon quality and quantity were analyzed on a 6% acrylamide gel relative to oligonucleotides of known concentration and size. 120 μl of 1-4 pM library were loaded on to the Illumina cluster station, where DNA molecules were attached to high-density universal adaptors in the flow cells and amplified. The DNA clusters generated via this process were sequenced with sequencing-by-synthesis technology, where successive high-resolution images of the four-color fluorescence excitation dependent on the base incorporated during each cycle were captured. Sequencing reads were generated for each of the 31 samples and base calls were rendered using Illumina software. All the primary sequencing data and gene expression data is publicly available through the GEO archive through accession GSE22898.
The small RNA libraries from the 31 samples which were subjected to massively parallel, high-throughput sequencing using the Illumina platform generated a total of 328 million separate reads. Our approach to analyzing the sequences and discovering microRNAs broadly follows a previously described method (see, Zheng, Q., et al. GOEAST: a web-based software toolkit for Gene Ontology enrichment analysis, Nucleic acids Res. 2008; 36 (Web Server issue: W358-363). All bioinformatics analyses were performed using a cluster of 1024 Linux computer nodes. Preprocessing was carried out using locally written Shell and Perl scripts.
From the raw sequences generated by high-throughput sequencing, the 3′- and 5′-adaptor sequences were trimmed. Low quality sequences were identified as those sequencing reads that contained stretches of consecutive identical bases or uncalled nucleotides (N) in the first 12 bases and sequencing reads shorter than 17 nucleotides. To minimize redundancy, reads were initially curtailed to the first 22 nucleotides and identical sequences were represented with a single fasta entry for analysis. Each unique sequence was mapped to the reference genome (Ensembl, build 50) and reads were filtered such that only perfect alignments (full length, 100% identity) were retained. Reads that aligned to more than five positions in the genome and reads that overlapped with the UCSC RNA genes were identified and excluded from microRNA analysis.
Identification and Analysis of the Captured miRNA Sequences
Sequences that occurred 20 or more times in at least one sample were consolidated and annotated for the 31 samples. Genomic loci that overlapped with microRNAs described in miRBase (version 13) were identified as known microRNAs (see Table 31). The remaining genomic loci were identified as encoding candidate novel microRNAs (see Table 32).
The vast majority (96%) of the candidate novel microRNAs were found in more than one sample, with only a small minority of microRNAs were expressed exclusively in a specific B cell subset or malignancy. Many of the microRNAs that we identified in normal and malignant B cells were expressed at ten-fold or higher levels in these non B cell cases. These findings suggest that the microRNAs we have identified are broadly expressed and may have roles in a number of diverse tissue types.
miRNA Profiling Using Real-Time PCR
miRNA expression profiling was conducted using the Applied Biosystems 384-well multiplexed real-time PCR assay using 400 ng of total RNA. Eight reactions, each containing 50 ng of RNA and a multiplex looped primer pool with endogenous small nucleolar (sno)-RNA controls, were used to reverse-transcribe the miRNAs in parallel fashion (see Tables 33 and 34 for primers). The completed reactions were loaded onto the 384-well plate per manufacturer's instructions, and real-time PCR was run on the ABI 7900HT Prism instrument. For each 384-well plate, we used the automatically determined cycle-threshold (CT) using the SDS 2.2.1 software (Applied Biosystems). Consistent with manufacturer recommendations, a CT greater than 35 was treated as undetected. The probes deemed to be present were normalized to the average expression of a sno-RNA control. The expression values were calculated as 2−ΔCT, then median centered to 500 and log 2-transformed.
For further validation of the deep sequencing results, we selected candidate novel microRNAs (see Table 34) that were detectably measured in at the sequencing data from least one of four diffuse large B cell lymphoma (DLBCL) cases. Using stem-loop reverse transcription (Ashburner, M., et al., Nat Genet. (2000); 25(1):25-29) for quantitative PCR, we tested the expression of the candidate microRNAs in 101 primary tumors from patients with DLBCL and found that about 92% were detectably measured by real-time PCR in at least 10% of these cases, suggesting that real-time PCR reproducibly identifies microRNAs that are expressed in lymphomas. We also used real-time PCR to measure the expression of known microRNAs (see Table 33) in the same 101 samples and found that over 90% of these were also detected in at least 10% of the cases using real-time PCR. We found that six of the seven RT-PCR constructs that targeted RNA hairpins that had low probability of being a microRNA resulted in no detectable signal. These results suggest that our assays have high specificity for microRNAs and that the computational predictions based on our sequencing data correctly identified microRNAs.
Differentiating ABC DLBCL Vs. GCB DLBCL Malignancies
Gene expression profiling of patients with DLBCL has demonstrated that the tumors comprise at least two distinct diseases with different response rates to standard chemotherapy regimens (Chen, C., et al., Nucleic Acids Res. (2005); 33(20):e179). We hypothesized that microRNAs might be used to make this clinically important distinction for which gene expression profiling remains the gold standard. We performed gene expression profiling on 101 DLBCL cases and further subdivided these cases into the molecular subgroups.
Tumor samples from 101 patients with diffuse large B cell lymphoma were obtained at the time of diagnosis and freshly frozen. These cases were profiled using Affymetrix Gene 1.0 ST arrays. The molecular subgroups were distinguished using a Bayesian approach described previously (Ambros, V., et al., RNA (2003);9(3):277-279).
We found that 25 microRNAs with the highest t-statistic were equally efficacious as the gene expression profiling in differentiating the two groups of DLBCL with over 95% overlap between the classifications rendered by the two methods, using leave out one cross-validation (see Table 35). Interestingly, a subset of these 25 predictor microRNAs was candidate novel microRNAs, suggesting a biological and clinical relevance for these candidate novel microRNAs in DLBCL tumors.
Our work provides an exhaustive identification of the microRNAs in normal and malignant B cells; that is a prerequisite to the delineation of their role. Further, we have developed a comprehensive framework that spans the identification of microRNAs from deep sequencing data to measuring their expression using real-time PCR and validating their expression in primary human tumors.
It is also conceivable that some of the low-abundance microRNAs that we have identified in our study may be expressed at higher levels in other development stages or in other cell types. This notion is confirmed by our examination of the novel microRNAs in non B cell data. For instance, a number of the microRNAs that we discovered were also present at 10-fold or higher levels in cell lines derived from breast cancer and cervical cancer, suggesting that the microRNAs that we have discovered in B cells have broad biological significance.
Deep Sequencing Reveals a Novel miRNA Cluster that Regulates the TGF-β Pathway
Although microRNAs appear to be distributed throughout the genome, a number of microRNAs have been found in clusters such as miR-17-92 that are transcribed from a single primary transcript and cleaved into the individual microRNAs by the enzyme DROSHA. We found 2 separate clusters of candidate novel microRNAs on chromosome 9 and chromosome 14 (within the IgH locus), respectively. The first cluster was previously annotated as a hypothetical gene LOC100130622, and subsequently discarded from Refseq when no associated protein was identified. Our data demonstrate that this cluster (miR-2355), conserved only in primates, encodes 6 separate microRNAs: has-miR-2355a-1, has-miR-2356-1, has-miR-2355a-2, has-miR-2356-2, hsa-miR2355a—3, and hsa-miR-2355b (see Table 32 for sequence).
In order to evaluate whether the microRNAs encoded in these clusters originate from the same primary transcript, we took KMS12 multiple myeloma cells which express these microRNAs and used siRNA to knock-down the expression of the microRNA processing enzyme Drosha. This enzyme acts at the first step of microRNA processing by cleaving microRNA precursors from the primary transcript. We found that decreased Drosha expression was associated with increased accumulation of primary transcripts of both the miR-17-92 cluster as well as the novel miR-2355 cluster. MicroRNAs from miR-2355 cluster were found to be expressed more highly in normal germinal center (GC) B cells compared to memory cells.
The microRNAs of this cluster all share the same seed sequence, suggesting that they target the same genes. Among the computationally predicted targets of this microRNA cluster, we identified SMAD2 and SMAD3 which are well known mediators of the TGF-beta signaling pathway. We noted that gene expression of both SMAD2 and SMAD3 in our set of 101 DLBCLs were inversely correlated with this cluster (P<0.001, correlation test). Gene set enrichment analysis revealed that expression of the TGF-beta pathway in DLBCL samples varied inversely with the expression of the microRNA cluster, with a higher expression of the microRNA associated with a lower expression of the pathway (P<10−6), which has been noted as a factor in the biology of these tumors.
This application is related to and claims the benefit of priority of U.S. Provisional Application Ser. No. 61/266,733, filed Dec. 4, 2009, which is incorporated herein by reference.
This invention was made with United States government support from the National Institutes of Health grant no. K12-CA-100639. The United States government has certain rights in this invention.
| Number | Date | Country | |
|---|---|---|---|
| 61266733 | Dec 2009 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13513757 | Aug 2012 | US |
| Child | 14317879 | US |
