Patent Application
20140121128
The invention relates to a prognostic method for breast tumours based on the expression of the prolyl isomerase enzyme Pin1 combined with detection of the presence of missense mutations in the TP53 gene and on the use of a molecular signature produced by the characteristic 10-gene expression associated with the Pin1/mutant p53 axis.
Several evidences have shed light on how point mutations within the TP53 gene represent crucial preconditions for tumour onset and transformation, and the formation of metastases. Mutations of the tumour suppressor gene TP53 are among the most frequently genetic changes of human tumours (Soussi T. and Wiman K., 2007). Besides being responsible for sporadic cancers, in humans hereditary mutations in TP53 cause the Li-Fraumeni syndrome, a disorder characterised by the early-onset of a wide range of cancers (Malkin D. et al., 1990). This type of mutation causes p53 to lose its ability to bind wild-type protein responsive elements present on DNA, and in this way mutant p53 loses the capacity to perform its tumour-suppressor functions and may exert a dominant-negative effect on the wild-type protein. Furthermore, many mutant p53 proteins acquire de novo a series of functional activities which significantly contribute to the manifestation of various aspects of cancer progression. In particular, strong evidence has shed light on the ability of the mutated protein to promote cell migration and metastasis formation (Adorno M. et al., 2009; Caulin C. et al., 2007; Muller P. et al., 2009; Terzian T. et al., 2008).
For the gain of new functions, it is essential that mutant p53 forms aberrant protein complexes perturbing the activity of the interacting protein partners. One example of how mutant p53 contributes to the occurrence of the cancer phenotype by influencing characteristics such as cell migration and invasion, or genomic instability, is the interaction of mutant p53 with the anti-metastatic factor p63 or with Mre11, and the consequent inactivation thereof (Adorno et al., 2009; Song H. et al., 2007).
Many in vivo studies have demonstrated that, in cancer cells, the efficient gain of new functions by mutant p53 is associated with the presence of high levels of the same protein (Song H. et al., 2007; Soussi T. and Beroud C., 2001; Terzian T. et al., 2008). This evidence supports the hypothesis according to which stress signals may activate mutant p53 via mechanisms similar to those necessary for stimulating the action of wild-type p53 (Song H. et al., 2007; Terzian T. et al., 2008). The mechanisms by which oncogenic signals trigger the activity of mutant p53 are, however, still little understood.
Among the factors potentially capable of representing a link between specific cell signals of tumoral transformation and the functions performed by mutant p53, a candidate particularly interesting is the prolyl isomerase enzyme, Pin1. This is an enzyme which converts the phosphorylation signals present on its substrates in conformational changes involving modulation of their functions (Lu K. P. and Zhou X. Z., 2007; Yeh E. and Means A. R., 2007). This enzyme has been recognised as a critical regulator of the activities exerted by the wild-type protein p53 in cells exposed to genotoxic stress (Mantovani F. et al., 2007; Zacchi P. et al., 2002; Zheng H. et al., 2002). Despite Pin1 is essential for the development of wild-type p53 functions, Pin1−/− mice do not develop tumours (Atchinson F.W. et al., 2003). In human tumours, on the other hand, Pin1 is frequently overexpressed (Bao L. et al, 2004), and in mammary cells it has been shown to be capable of promoting tumoral transformation events which depend on the proteins Her2/Neu/Ras or Notch1 (Rustighi A. et al., 2009; Wulf G. et al., 2004).
However, it is not known how, during tumoral transformation, the role played by Pin1 in the physiological surveillance systems of the cell is altered, rendering it a crucial amplifier of the oncogenic functions of mutant p53.
TP53 mutations represent, in particular, one of changes, which frequently characterise breast cancers (Langerød A. et al., 2007).
In general, breast carcinoma in women represents not only the most frequently diagnosed type of cancer, but also the principal cause of death (Jemal A et al., 2011), and the basal-like sub-type is the type thereof with the highest risk of recurrence. It is estimated that, worldwide, the number of women to whom it is diagnosed exceeds one million (Coughlin S. et al., 2009).
Indeed, breast cancer is a disease characterised by strong heterogeneity from various viewpoints, ranging from the histological to that of the response to the therapeutic treatments or the mode of metastatic spread into different regions of the body (Prat A. et al., 2011).
Over the years, progress in the field of diagnosis and in prevention programmes and the development of new therapeutic strategies have led to a reduction in mortality due to this type of cancer (Jemal A. et al., 2009). Nevertheless, it has been estimated that, in the United States and Europe, more than 120,000 women die of this disease each year (Jemal A. et al., 2009; La Vecchia C. et al., 2010). This is partly explained by the fact that the intrinsic complexity of this cancer is not associated to a complete knowledge of its biology, and even less to the availability of markers for use in clinical practice which fully reflect its heterogeneity, and which allow an accurate prognosis to be made in each case and enable the likelihood of success of the treatments to be determined. These factors are essential for guiding the choice of treatment, and, when necessary, the development of new intervention strategies.
In current clinical practice, the diagnosis of breast carcinoma is made by means of histopathological tissue investigation. The prognosis and the choice of treatment depend on this type of investigation, on evaluation of clinical parameters, such as the dimensions of the tumour, its stage, the age of the patient, and invasion of the lymph nodes by cancer cells, and on the molecular characterisation of the tumour based on expression of hormone receptors, HER2, and of a number of proliferation markers. Although these represent standard prognostic methods, they are not always effective in predicting the progression of the disease. Nevertheless, the possibility of more and more accurate evaluation of risk factors and formulating more precise predictions of the clinical course and of the outcome of the disease could have a considerable impact in respect of the treatment of breast tumours, because it would improve patient stratification. This need has given rise to the idea of linking the tests normally carried out with more in-depth molecular characterisation of the tumour. A prognostic test for breast tumours, the MammaPrint®, based on analysis of the expression of more than 70 genes using cDNA MicroArray technology, has therefore been developed (and approved by the FDA), the value of which for prognostic purposes has been demonstrated by means of studies conducted by van't Veer et al. (van't Veer L. et al., 2002).
This is the context into which the present invention fits, offering the advantage of an analysis of high predictive value, from the prognostic viewpoint, but based on determination of a reduced number of parameters and on the use of simpler technologies, which can therefore be used immediately and with greater ease.
The present invention is based on experimental evidence proving that Pin1 promotes tumoral transformation in a mouse model of Li-Fraumeni syndrome and amplifies the oncogenic functions of mutant p53, whilst in human breast cancer the overexpression of Pin1 combined with the presence of missense mutations in TP53 correlates with an unfavourable outcome of the disease.
In human cell lines derived from breast carcinoma, the inventors have found that the two proteins together promote a transcriptional programme which favours tumour aggressiveness and that 10 genes (forming a molecular signature associated with the Pin1/mutant p53 axis), of which 7 proved to be adequate for the prognostic evaluation, are involved in this programme.
In a first aspect, therefore, the invention relates to a prognostic method for breast cancer, comprising the detection in biopsy samples of expression levels of Pin1 combined with the assessment of the presence of mutations in the TP53 gene and/or with the determination of levels of the p53 protein, given the correlation existing in tumoral samples between the presence of elevated levels of the protein p53 and the presence of “missense” mutations therein.
In another aspect, the invention relates to a prognostic method for breast cancer, which comprises the detection of expression levels of a molecular signature associated with Pin1/mutant p53 by determination of the expression of the genes DEPDC1 (Gene ID No 55635, isoform 1: RefSeq NM—001114120.1, NP—001107592.1; isoform 2: RefSeq NM—017779.4, NP—060249.2), CPSF6 (Gene ID No 11052, RefSeq NM—007007.2, NP—008938.2), C21orf45 (Gene ID No 54069, RefSeq NM—018944.2, NP—061817.1), CENPA (Gene ID No 1058, isoform 1: RefSeq NM—001809.3, NP—001800.1; isoform 2: RefSeq NM—001042426.1, NP—001035891.1), FAM64A (Gene ID No 54478, RefSeq NM—019013.2, NP—061886.2), CCNE2 (Gene ID No 9134, RefSeq NM—057749.2, NP—477097.1), BUB1 (Gene ID No 699, RefSeq NM—004336.3, NP—004327.1), EPB41L4B (Gene ID No 54566, isoform 1: RefSeq NM—018424.2, NP—060894.2; isoform 2: RefSeq NM—019114.3, NP—061987.3), NCAPH (Gene ID No 23397, RefSeq NM—015341.3, NP—056156.2), WDR67 (Gene ID No 93594, isoform 1: RefSeq NM—145647.3, NP—663622.2; isoform 2: RefSeq NM—001145088.1, NP—001138560.1). Of these 10 genes, also the determination of the expression levels of the 7 genes DEPDC1, CPSF6, C21orf45, FAM64A, EPB41L4B, NCAPH, WDR6 has been demonstrated sufficient for prognostic purposes, these genes can, therefore, be considered a minimum molecular signature. The use of this molecular signature in particular also offers the advantage of stratifying patients with ER+ (oestrogen-positive) tumours. Indeed, by means of the method proposed by the inventors, it is possible to identify within this group of cases—which is typically considered homogenous—two different subgroups, which show significant differences in respect of the prognosis. The stratification permitted by this method could lead to a choice of treatment different from that currently operated in these cases, enabling identification of those patients within the group of ER+ cases who could or may not benefit from the combination of hormone treatment and chemotherapy.
In a further aspect, the invention relates to kits for carrying out the prognostic method for tumours on the basis of determination of the levels of Pin1 combined with detection of the presence of mutations in the TP53 gene and/or determination of the levels of the p53 protein, and/or determination of the expression levels of the genes of the molecular signature associated with the expression of Pin1/mutant p53.
(A) Desmedt dataset (X2=25.7, P=4.1×10−7, n=198, log-rank test);
(B) Miller dataset (X2=9.7, P=0.002, n=251, log-rank test);
(C) Pawitan dataset (X2=7.7, P=0.00557, n=187, log-rank test);
(D) Sotiriou dataset (X2=11.6, P=0.00065, n=189, log-rank test).
(E) and (F): Kaplan-Meier analysis of the survival of patients with a breast tumour positive for the oestrogen receptor (ER+). Dotted line: cases with elevated levels of expression of the 10 genes. Solid line: cases with low levels of expression of the 10 genes:
(E) Desmedt dataset (X2=14.3, P=0.00016, n=134, log-rank test);
(F) Miller dataset (X2=8.6, P=0.00334, n=211, log-rank test).
Gene TP53 is used to mean the gene (Gene ID No 7157, RefSeq NM—000546.4, NP—000537.3) coding for the native (or wild-type) human protein p53 (GenBank accession No ABB80262).
The prolyl isomerase enzyme Pin1 is the protein (GenBank accession No AAC50492.1) coded by the gene Pin1 (Gene ID No 5300, RefSeq NM—006221.2, NP—006212.1).
Minimum molecular signature associated with the Pin1/mutant p53 axis is used to mean the group consisting of the following seven genes:
DEPDC1 (DEP domain containing 1) identified by the Gene ID No 55635, Homo sapiens (isoform 1: RefSeq NM—001114120.1, NP—001107592.1; isoform 2: RefSeq NM—017779.4, NP—060249.2);
CPSF6 (cleavage and polyadenylation specific factor 6, 68 kDa) identified by the Gene ID No 11052, Homo sapiens RefSeq NM—007007.2, NP—008938.2;
C21orf45 (chromosome 21 open reading frame 45), identified by the Gene ID No 54069, Homo sapiens RefSeq NM—018944.2, NP—061817.1;
FAM64A (family with sequence similarity 64, member A) identified by the Gene ID No 54478, Homo sapiens RefSeq NM—019013.2, NP—061886.2;
EPB41L4B (erythrocyte membrane protein band 4.1 like 4B) identified by the Gene ID No 54566, Homo sapiens (isoform 1: RefSeq NM—018424.2, NP—060894.2; isoform 2: RefSeq NM—019114.3, NP—061987.3);
NCAPH (non-SMC condensin I complex, subunit H) identified by the Gene ID No 23397, Homo sapiens RefSeq NM—015341.3, NP—056156.2;
WDR67 (WD repeat domain 67), identified by the Gene ID No 93594, Homo sapiens (isoform 1: RefSeq NM—145647.3, NP—663622.2; isoform 2: RefSeq NM—001145088.1, NP—001138560.1).
Molecular signature associated with the Pin1/mutant p53 axis is used to mean the whole of the minimum molecular signature mentioned previously, and the following three genes:
CENPA (centromere protein A) identified by the Gene ID No 1058, Homo sapiens (isoform 1: RefSeq NM—001809.3, NP—001800.1; isoform 2: RefSeq NM—001042426.1, NP—001035891.1);
CCNE2 (cyclin E2) identified by the Gene ID No 9134, Homo sapiens RefSeq NM—057749.2, NP—477097.1;
BUB1 (budding uninhibited by benzimidazoles 1 homologue (yeast)) identified by the Gene ID No 699, Homo sapiens RefSeq NM—004336.3, NP—004327.1.
“Score of the molecular signature” is used to mean the score associated with each sample, calculated using the value of expression of the genes of the molecular signature and the value of expression of three further genes used as a reference threshold and defined as “reference genes”.
“Reference genes” is used to mean genes whose expression is comparable in intensity to the genes of the molecular signature, and the presence of which is constant in biopsy samples, such as for example:
ERCC6 (excision repair cross-complementing rodent repair deficiency, complementation, group 6), identified by the Gene ID No 2074 Homo sapiens RefSeq. NM—000124.2, NP—000115.1;
ADCY3 (adenylate cyclase 3) identified by the Gene ID No 109, Homo sapiens RefSeq. NM—004036.3, NP—004027.2;
TUBGCP2 (tubulin, gamma complex associated protein 2) identified by the Gene ID No 10844, Homo sapiens RefSeq. NM—006659.2, NP—006650.1;
SOX15 (sex determining region Y-box 15) identified by the Gene ID No 6665 Homo sapiens RefSeq. NM—006942.1, NP—008873.1;
RPL10 (ribosomal protein L10) identified by the Gene ID No 6134 Homo sapiens RefSeq. NM—006013.3, NP—006004.2;
DGCR14 (DiGeorge syndrome critical region gene 14) identified by the Gene ID No 8220 Homo sapiens RefSeq. NM—022719.2, NP—073210.1;
KIAA0586 identified by the Gene ID No 9786 Homo sapiens RefSeq. NM—014749.3, NP—055564.3;
ZBTB17 (zinc finger and BTB domain containing 17) identified by the Gene ID No 7709 Homo sapiens RefSeq. NM—003443.2, NP—003434.2;
TFIP11 (tuftelin interacting protein 11) identified by the Gene ID 24144 Homo sapiens RefSeq. NM—001008697.1, NP—001008697.1;
ZNF672 (zinc finger protein 672) identified by the Gene ID No 79894 Homo sapiens RefSeq. NM—024836.1, NP—079112.1;
TXN2 (thioredoxin 2) identified by the Gene ID No 25828 Homo sapiens RefSeq. NM—012473.3, NP—036605.2.
The preferred reference genes are: ERCC6, ADCY3, TUBGCP2.
The “molecular signature” score is graded into three levels: low score, medium score and high score. The procedure and application of the molecular signature score are described in detail in what follows in the Description.
Many studies performed using a mouse model knockin for mutant p53 have shown how, in order to be functionally active, mutant p53 requires the presence of an oncogenic context. With the scientific evidence underlying the present invention, one of the linking elements, which act as a bridge between the oncogenic signals and acquisition of the aggressive phenotype, is provided by demonstrating how, within the cancer cells, the enzyme Pin1 and mutant p53 are integrated into a molecular axis activated following phosphorylation of mutant p53 in dependence on specific phosphorylation sites.
This conclusion is confirmed by the results of research conducted and reported in detail below.
In particular, the following observations support the importance of this isomerase in the events leading to the transduction of oncogenic signals, and the onset of mutant p53 activity:
On the basis of the results reported in detail below, it can be deduced that Pin1 is important in these model systems as a crucial linking element between the presence of oncogenic signals and the full activation of mutant p53, which translates as an increase in genomic instability and in the development of metastases.
It has also been observed that, in breast carcinoma cells, the presence of aberrant signals leads to the phosphorylation of the S/T-P sites of the mutant p53 protein, favouring recognition of the protein by Pin1. This event is necessary to trigger the effect of mutant p53 for promoting cell migration and invasion.
The effects of the Pin1/mutant p53 axis have significant clinical relevance, as demonstrated by series of studies conducted on a cohort of patients with breast carcinoma. From the analyses it is, in fact, emerged that the prognostic value of the presence of mutation in p53 is strengthened if combined with quantification of the levels of Pin1. The multivariate statistical analysis demonstrated that the simultaneous presence of elevated levels of Pin1 expression (quantification of the nuclear signal greater than 5, evaluated immunohistochemically using the “Quick score” method (Detre S. et al., 1995) and of missense mutations in TP53 represents already by itself an independent and strong prognostic factor of the clinical outcome of the disease. The TP53 status in tumours which overexpress Pin1 has in fact enabled better stratification of patients into groups characterised by a longer or shorter survival time. This effect has also been observed for a sample of patients receiving anthracycline-based adjuvant chemotherapy.
The data, therefore, indicate that the use of the prognostic method proposed by the inventors, based on quantification of the levels of Pin1 and on detection of the mutational status of TP53, could offer significant advantages in disease characterisation stages. Combined analysis of these two parameters, by contrast with what occurs by considering only the presence of mutations of the TP53 gene, allows better patient stratification. Indeed, a critical aspect at the time of classification of the disease is typically the identification of the cases at elevated risk of recurrence and the ability to predict (by means of specific biomarkers) the response of patients to the treatments. This is an essential prerequisite for being able to implement the treatment strategies and guide future therapeutic choices. From this point of view, in particular, the method based on quantification of the levels of Pin1, and on the mutational status of TP53, allows differentiation among the various cases of breast carcinoma of the subgroup of patients who: i) have a lower likelihood of survival; ii) respond inadequately to the therapeutic interventions (and in particular to the anthracycline-based adjuvant chemotherapy).
As well as by quantification of the levels of the protein Pin1 and identification of the mutational status of TP53, the prognostic value of the Pin1/mutant p53 axis can also be evaluated by combining quantification of the levels of the proteins Pin1 and p53, elevated levels of which correlate with the presence of missense mutations in its gene (Goh A. M. et al., 2011), thus obtaining just as precise a prognostic method, but based on a unique investigative system, that is immunohistochemical analysis of both proteins.
Such investigations may be performed on fresh or frozen biopsy samples, or biopsy samples that have been fixed and embedded in paraffin, by identifying a signal using the known methods of immunochemistry and/or molecular biology, based on determination of nucleic acids, such as the Polymerase Chain Reaction (PCR) and analysis with the use of specific kits already in use for the protein p53 (for example the AmpliChip P53 test) and/or sequencing or other methods known to the person skilled in the art. The prognosis is therefore evaluated on the basis of a score derived by quantification of the signal identified for expression of the proteins Pin1 and p53.
Entering into the specific details of the assay, in the case wherein the parameters to be measured are the levels of expression of the Pin1 protein and of the mutational status of the TP53 gene, the immunohistochemical analysis for Pin1 on biopsy samples in paraffin and sequencing of the TP53 gene can preferably be performed on RNA extracted from the fresh or frozen biopsy sample.
The detection of the immunohistochemical labelling and the detection of a gene mutation constitute the signals to be acquired and measured in order to determine the expression levels of Pin1 and of the TP53 gene mutational status.
For the immunohistochemical-type evaluation, the reagents for determination of the expression of Pin1 are specifically polyclonal and monoclonal anti-Pin1 antibodies advantageously labelled for identification purposes.
To identify the mutational status of the TP53 gene specific oligonucleotides are necessary, consisting of DNA sequences (5′-3′ forward and reverse primer) for the amplification reaction, such as the for example, the known oligonucleotides indicated below in Table 1:
Rather than by sequencing, the mutational status of TP53 could alternatively and preferably be inferred by evaluating the protein levels of p53 (quantification of the nuclear signal greater than 5, using the “Quick score” method (Detre S. et al., 1995) by immunohistochemical means with polyclonal and monoclonal anti-p53 antibodies on the same biopsy samples of breast cancer on which the Pin1 expression evaluation is performed. Such assessment of the p53 protein is, then, to be preferred as can be carried out in combination with the determination of the expression of Pin1 protein.
The method for breast cancer prognosis based on the Pin1 expression in combination with the detection of the TP53 gene mutational status or p53 protein expression comprises essentially the following steps of:
The immunohistochemical labelling is carried out as known to an expert in the field and comprises at least the following steps of:
In case the option to measure the expression levels of p53 is chosen, the sections are subjected to double labelling by treating the samples with a primary antibody consisting in a poly- or monoclonal anti-p53 antibody.
The detection of TP53 gene mutational status can be performed by PCR.
For signal measurement and assignment of a score according to the Quick score method; are essential the following steps of:
On the basis of the proposed method, it is possible to subdivide patients with breast cancers into two categories having a better (80% without metastases at 10 years), or worse prognosis (40% without metastases at 10 years). The cases in the latter group are those in which the tumour presents overexpressed Pin1 and p53 (for both, the immunohistochemical score must be greater than 5) or those in which the tumour overexpresses Pin1 (immunohistochemical score greater than 5) and presents mutations in TP53 (identified by sequencing).
In a second aspect, this method of prognosis can be perfected by integrating the detection of the levels of Pin1 and of the mutational status of TP53 and/or of the levels of the p53 protein with the analysis of the molecular signature associated with the Pin1/mutant p53 axis. This evaluation, which is based on detection of the expression levels of the genes of the molecular signature, not only enables the prognosis of the disease to be obtained, even without knowing the status of Pin1 and p53, but also allows stratification of patients with breast tumours positive for oestrogen receptors.
The levels of expression of the genes of this molecular signature can be monitored on fresh or biopsy samples or on nucleic acids extracted therefrom, by determination of their levels of mRNA by PCR. Consideration should also be given to the convenience of more rapid analysis by detection of the levels of the proteins expressed by these genes, to be performed by immunohistochemistry on biological samples fixed and embedded in paraffin. In this case, also, the prognostic evaluation can be performed on the basis of the score derived by quantification of the signal ascertained for expression of the genes and/or of the proteins expressed by these genes.
The data obtained by the inventors, in fact, also show that the combined action of Pin1 and mutant p53 favours an aggressive tumoral phenotype via introduction of a specific transcriptional programme. Among the targets of the overexpressed Pin1 and mutant p53 axis, 10 genes, which constitute a molecular signature associated therewith: DEPDC1 (Gene ID No 55635), CPSF6 (Gene ID No 11052), C21orf45 (Gene ID No 54069), CENPA (Gene ID No 1058), FAM64A (Gene ID No 54478), CCNE2 (Gene ID No 9134), BUB1 (Gene ID No 699), EPB41L4B (Gene ID No 54566), NCAPH (Gene ID No 23397), WDR67 (Gene ID No 93594), have been identified.
This molecular signature has been found to significantly correlate with the clinical outcome of the disease, as shown by analysis of four independent datasets relating to different breast cancers cases on which a Kaplan-Meier analysis was performed:
To arrive at a definition of this molecular signature, therefore, the inventors moved from analysis of global gene expression under conditions of silencing both Pin1 and mutant p53, to a human cell model of triple-negative breast carcinoma. They then verified the importance of the transcriptional programme induced by Pin1 and by mutant p53 in primary tumours via investigation of four independent series of data relative to more than 800 cases of breast cancer. From this analysis, it has been found that overexpression of the genes most regulated under conditions of silencing both Pin1 and mutant p53 (31 genes) was encountered in tumours of patients having a less favourable prognosis. Starting from this group of 31 genes, a molecular signature was obtained on the basis of the score of correlation of the expression of each gene with the clinical data, using a Cox proportional hazards model. See Table 2 for the classification of the genes thus obtained.
From the gene classification based on association with the clinical data, genes having a score greater than 3 were selected, thus obtaining a molecular signature associated with the Pin1/mutant p53 axis, consisting of 10 genes DEPDC1, CPSF6, C21orf45, CENPA, FAM64A, CCNE2, BUB1, EPB41L4B, NCAPH, WDR67.
The expression of these genes correlates significantly with the clinical outcome of the disease: in patients who expressed these genes at higher levels relative to the mean value for all patients, the time interval between diagnosis of the primary tumour and that of metastases in other body regions (Time to Distant Metastasis, TDM) was shorter (2-3 years depending on the dataset) and survival was reduced (Overall Survival, OS, 2-3 years depending on the dataset). Expression of these 10 genes also has prognostic value when considering exclusively the patients with breast tumours positive for the oestrogen receptor. Similar results were obtained by analysing the expression of a group of seven genes consisting of: C21orf45, CPSF6, DEPDC1, EPB41L4B, FAM64A, NCAPH e WDR67.
The expression of the molecular signature associated with Pin1/mutant p53 can be determined by measuring, using PCR, the expression of the mRNA of the 7 or 10 genes of the molecular signature associated with Pin1/mutant p53 on fresh or frozen biopsy samples and of reference genes whose expression is of comparable intensity to genes of the molecular signature, and the presence of which is constant in biopsy samples. These genes may be selected from ERCC6, ADCY3, TUBGCP2, SOX15, RPL10, DGCR14, KIAA0586, ZBTB17, TFIP11, ZNF672, TXN2. The reference genes are preferably the three genes ERCC6, ACCY3, TUBGCP2. The reagents may be the primers necessary for amplification of the mRNA extracted from the test sample, which primers are presented below in Table 3:
Therefore, the signal to be measured and acquired for the detection of the gene set forming the molecular signature is the expression of the gene sequence detected by amplification with the PCR on samples consisting of fresh biopsies of breast cancer or a nucleic acid extracted from the same according to methods known in the state of the art.
By quantification of the expression of these 7 or 10 genes, it is possible to subdivide the patients with breast tumours into three categories, having a good, moderately good or poor prognosis.
Such a stratification is possible on the basis of a molecular signature score obtained by calculating the relative genes scores by evaluating, for each of the genes, the relative expression with respect to one of the reference genes, as shown in Table 4 below:
In particular, the gene score of the molecular signature is calculated on the basis of the following formula:
where:
a) if a gene i of the molecular signature has an expression value Expi of less than −0.5 on the base 2 logarithmic scale by comparison with the corresponding expression value Expr of its reference gene r (equivalent to saying that there exists a difference of 0.5 RT-PCR cycles), this gene is attributed a gene score of zero.
b) if a gene i of the molecular signature has an expression value Expi of higher than 0.5 on the base 2 logarithmic scale by comparison with the corresponding expression value Expr of its reference gene r (equivalent to saying that there exists a difference of 0.5 RT-PCR cycles), this gene is attributed a gene score of two.
c) if a gene i of the molecular signature has an expression value Expi intermediate to the two values of cases a) and b) by comparison with the corresponding expression value Expr of its reference gene r, this gene is attributed a gene score of one.
The sum of the gene scores (Sg) thus obtained determines the value of the score for the molecular signature of the 10 genes (signature score Sf):
Sf=ΣSg
and
Alternatively, expression of the molecular signature associated with Pin1/mutant p53 could be determined in biopsy samples fixed and embedded in paraffin by measuring the levels of the protein products of the 7 genes of the minimum molecular signature, and preferably of all 10 genes of the molecular signature associated with Pin1/mutant p53 by means of immunohistochemical analysis. In this case, the reagents are suitably labelled polyclonal and monoclonal antibodies against the proteins produced by the gene. In this case, also, the nuclear signal can be quantified using the “Quick score” method (Detre S. et al., 1995). The same procedures of evaluation previously described for determination of the levels of Pin1 and/or p53 are applied.
Therefore, the method for breast cancer prognosis based on the detection in a biopsy sample of a molecular signature consisting of the expression of a panel of genes comprises at least the steps of:
Sf=ΣSg
The kit for performing the prognostic method that is the object of the invention, based on determination of the levels of Pin1 and detection of the mutational status of TP53 and/or levels of p53, comprises at least:
The kit for performing the prognostic method that is the object of the invention, based on determination of the expression levels of the genes of the molecular signature, and/or of the proteins expressed thereby comprises at least:
Molecular characterisation of the tumour by detecting the levels of Pin1 in association with the present/absence of mutant p53 and/or via the molecular signature of 10 genes represents a reliable, sensitive and low-cost system, enabling prediction of the outcome of the disease, the risk of recurrence and the response of patients to the treatment (especially to the anthracycline-based adjuvant chemotherapy), especially in basal-like cases. To date, these represent a challenge in terms of treatment because they constitute a subgroup of breast tumours comprising predominantly triple-negative cases, defined as such because they do not express the hormonal receptors and do not overexpress HER2, have five-year survival rates very low, and are characterised by a high incidence of recurrences, which occur in spite of the adjuvant chemotherapy.
MDA-MB-231 (p53R280K) and MDA-MB-468 (p53R273H) are human cells derived from breast carcinomas of the triple-negative type. SK-BR-3 (p53R175H) are human cells derived from breast tumours which overexpress HER2. All the cell lines were kept in culture in Dulbecco's modified Eagles Medium (DMEM) to which 10% FBS, penicillin (100 IU/ml) and streptomycin (1001U/ml) had been added. The MEF cells were generated by crossing mice of the appropriate genotype and recovering the cells from the embryos at 13.5 dpc, as described (Zacchi et al., 2002). pLPC and pLPC-H-RasV12 were kindly provided by M. Serrano (Efeyan et al. 2009); pGEX-Pin1 for the expression of GST-Pin1 and pGEX used as a control have already been described (Zacchi et al., 2002). pcDNA3-p53K280 and pcDNA3-p53K280-4M were created by site-specific mutagenesis, starting from the described constructs pcDNA3-p53 and pcDNA3-Mp53 (Zacchi et al., 2002). pMSCV-HAPin1 was generated by sub-cloning the specific coding sequence for Pin1 from the construct pcDNA3-HAPin1 (Mantovani et al., 2007) in the vector pMSCV. pMSCV-HAPin1r and pMSCV-HAPin1r S67E were generated by introducing, for site-specific mutagenesis of the constructs pcDNA3-HAPin1 and pcDNA3-HAPin1 S67E (Rustighi et al., 2009), silent mutations (G300A, G303A and T309C, relative to the sequence NM—006221.2) within the target region of the siRNA (A) specific to Pin1 and by then subcloning the mutagenically altered regions in the vector pMSCV. pLPC-p53K280 and pLPC-p53K280-4M have been created by subcloning the specific coding regions for p53K280 and p53K280-4M respectively, in the vector pLPC containing a HA tag.
The construct pSRshPin1 was created by cloning the double-stranded siRNA (A) specific to Pin1 (see below) in the vector pSuper Retro (Rustighi et al., 2009). The plasmid pSRshp53 was kindly provided by R. Agami (Drost J et al., 2010). The vector pSRshLAcZ has been described in Rustighi et al., 2009.
The lentiviral vector coding for the reporter gene of firefly luciferase used in assays to study the development of metastases in vivo, was described in Adorno et al., 2009.
Where not specified, the base vectors (commercially available) employed to create the various constructs were used as control vectors in the various experiments.
The siRNA are given in Table 5.
H. sapiens
H. sapiens
H. sapiens
H. sapiens
E. coli
The mouse cohorts used in this study originated from crossing p53M/+ or p53+/− mice with Pin1+/− mice, all having a genetic background of the type C57BL/6. The animals' genotype was characterised by analysing the polymerase chain reactions (PCR), as previously described (Atchinson F. W. et al., 2003; Lang G. A. et al., 2004). Animal showing signs of disease or the clear presence of tumours during the observations were sacrificed. The organs removed from them were kept for 24 hours in a solution of PBS, with 10% formalin for fixing. The tissues were embedded in paraffin and cut into slices 5 μm thick. Before being subjected to pathological analysis, they were treated to eliminate the paraffin residues and stained with haematoxylin and eosin. The procedures involving animals were performed in accordance with the institutional guidelines, which had been drawn up with regard for the legislation and the relevant international policies (UKCCCR, 1989).
For the assays, murine embryo fibroblasts (MEF) from the mice of the strains p53M/M Pin1+/+, p53M/M p53−/− Pin1+/+ and p53−/− Pin1−/−, which had undergone a low number of passages in culture, were used. The cells infected with the vector pLPC H-RasV12 or with its empty vector were resuspended in DMEM, to which had been added 10% foetal bovine serum, penicillin (100 Um′) and streptomycin (IU/ml), and containing 0.3% agarose. The cells were plated at a density of 1×106 per plate 60 mm in diameter, on the surface of the layer of medium, presenting the same characteristics as the previous one, with the exception that it contains 1% agarose. After culturing for 14 days, the number of colonies reaching at least 100 μm in diameter were counted. All the experiments were conducted in triplicate using at least two different clones for genotype. To verify the tumorigenesis capacity of the MEFs, infected with the construct expressing H-RasV12, 1×106 cells were injected subcutaneously, and bilaterally in NOD SCID mice. After two weeks, the tumour volume was measured using a calliper, as described previously (Rustighi A. et al., 2009).
For the cicatrisation assays, the MDA-MB-231 transfected cells were seeded in 35 mm in diameter plates and cultured until 90% confluence was achieved. The cells were scraped from the surface using a 200-μl needle tip. Closure of the lesion was monitored for 36 hours. For the transwell migration assays, PET inserts of 24 wells (pore dimension 8.0 μm, Falcon) were used. The assays of invasiveness were conducted in PET inserts of 24 wells (pore dimension 8.0 μm, Falcon), using Matrigel®-coated filters.
For the assays of pulmonary colonisation, cells of human MDA-MB-231 cell lines derived from breast tumours were co-transduced with a lentiviral vector coding for the reporter gene of firefly luciferase and with pSR shLacZ or pSR shPin1 (six animals in each group). 106 cells were resuspended in 100 μl of PBS and inoculated into the caudal vein of SCID mice. For in vivo visualisation, at different times from the cell inoculation bioluminescence images were acquired using a “cooled charge-coupled” acquisition device mounted above the camera obscura used for lodging the sample (IVIS Lumina II Imaging System; Caliper Life Sciences, Alameda, Calif.). 10 minutes prior to acquisition of the images, a solution containing 150 mg/kg of D-luciferin (Caliper Life Sciences) in PBS was administered i.p. to the anaesthetised animals. The histological analyses on samples of pulmonary tissue embedded in paraffin and stained with haematoxylin and eosin were conducted one month after injection of the MDA-MB-231. For the computerised analysis of the pulmonary tissue, the area covered by the metastatic foci, detectable in the pulmonary lobe sections, was measured. The parameter was calculated using a Leica DM200 microscope, fitted with a Leica DFC295 digital colour camera and Leica Application Suite (LAS) V3 software. The values for the total area and for the sum of the areas were, finally, compared with the value for the area of the whole pulmonary lobe. The expression of Pin1 was analysed by immunohistochemistry (IHC) using a monoclonal antibody (G-8, sc-46660, Santa Cruz) against this enzyme.
The total RNA was extracted using Trizol (Invitrogen) and then subjected to treatment with DNasi-I (Ambion). For the microarray experiments, the mRNAs of three different biological samples for each group (siPin1 or sip53) were used for hybridisation of the Affymetrix GeneChip Human Genome U133A 2.0 array. In the experiments of quantitative RT-PCR, the mRNA was transcribed using the Superscript III (Invitrogen) system. The Real Time PCR was performed using a SYBR Green PCR master mix and an Applied Biosystems StepOne Plus thermal cycler. The sequences of the primers (sense 5′-3′) for analysis of gene expression using qRT-PCR for the 10 genes of the molecular signature, and for the three control genes are presented in the previous Table 3, and correspond to the sequences: BUB 1 for SEQIDNO:6; BUB1 rev SEQIDNO:7; C210RF45 for SEQIDNO:8; C210RF45 rev SEQIDNO:9; CCNE2 for SEQIDNO:10; CCNE2 rev SEQIDNO:11; CENPA for SEQIDNO:12; CENPA rev SEQIDNO:13; CPSF6 for SEQIDNO:14; CPSF6 rev SEQIDNO:15; DEPDC1 for SEQIDNO:16; DEPDC1 rev SEQIDNO:17; EPB41L4B for SEQIDNO:18; EPB41L4B rev SEQIDNO:19; FAM64A for SEQIDNO:20; FAM64A rev SEQIDNO:21; NCAPH for SEQIDNO:22; NCAPH rev SEQIDNO:23; WDR67 for SEQIDNO:24; WDR67 rev SEQIDNO:25; ERCC6 for SEQIDNO:26; ERCC6 rev SEQIDNO:27; ADCY3 for SEQIDNO:28; ADCY3 rev SEQIDNO:29; TUBGCP2 rev SEQIDNO:30; TUBGCP2 for SEQIDNO:31.
Annotations relating to gene expression and pre-processing: the intensity of the rough signals of gene expression was normalised at the level of the probe using the RMA algorithm, as previously described (Irizarry R. A. et al., 2003). The analysis at a low level of the microarray data was performed in an R/Bioconductor environment using, in particular, the limma and affy packages for microarray (http://www.R-project.org). The datasets publicly accessible used (GSE7390, GSE2990, GSE3494, GSE1456) were downloaded from the Gene Expression Omnibus web site (GSE7390, GSE2990, GSE3494) or from the web site of the authors of the study who produced them (GSE1456, http://www.mebki.se/˜yudpaw/). The gene annotations relating to all the platforms considered were obtained from R-Bioconductor metadata packages (Gentleman R. C. et al., 2004). The analysis of differential expression of the genes of all the data sets considered in this study was conducted using functions and methods implemented in R/Bioconductor (Gentleman R. C. et al., 2004; Smyth G. K., 2004). In short, a fixed-effect linear model was individually applied to each gene to estimate the differences in expression between the groups of samples to be compared. To moderate the standard errors of the values of M, an empirical Bayes approach was used (Smyth, 2004). Finally, for each gene analysed, the moderated t-statistics, the log-odd ratio of differential expression (B-statistics), and the raw and adjusted P values were obtained (FDR control by means of the method of Benjamini and Hochberg).
To verify the presence or otherwise of an association between expression of the 31 genes shown above in Table 2, concurrently more repressed under the two different experimental conditions analysed, and the survival time of patients with breast carcinoma (Desmedt et al., 2007), the Cox proportional hazards model was used. In particular, this model (Wald statistics) was applied to the expression of each gene to test its association with the survival data, so as to produce a coefficient or score of association with the clinical data. From classification of the genes based on association with the clinical data, those genes having a score of more than 3 were selected, thus obtaining a molecular signature consisting of 10 genes. To verify the correlation existing between the 10-gene molecular signature and the clinical data in cases of breast carcinoma, a Mantel Haenszel test was performed on the other normalised datasets used (GSE2990, GSE3494, GSE1456) (survival R package).
From the expression matrix for each dataset, the expression values for the genes forming the 10-gene signature were extracted by the use of the identifying univocal probe-set, thus obtaining a sub-matrix of expression. This matrix is composed of m rows/genes per n columns/samples, with m ranging from one to ten and n, ranging from 1 to the number of samples present in the study. To assign the same weight to each gene, the genes were normalised using the following procedure:
therefore for each row/gene j, yielding:
SVj{SXj,1,SXj,2, . . . ,SXj,n}
SVj=standardised vector of gene expression, representing the values of gene expression standardised for a specific gene/row j for all the samples of the dataset (n);
Vj=vector of gene expression, representing the values of gene expression for a specific gene/row j for all the samples of the data set (n). Vj={Xj,1, Xj,2, . . . , Xj,n};
Vj=estimated mean for a specific expression vector Vj for a specific gene/row j. mad(Vj)=median deviation for a specific expression vector Vj for a specific gene/row j.
To measure the contribution of each gene to the 10-gene signature, a virtual gene (VG) vector is calculated by taking the average of each contribution of each gene starting from the standardised gene expression vector for all genes/rows m.
Finally, a sample k was defined as a “high-level 10-gene signature” if the value VGk was greater than the median value of the vector for the virtual gene VG, whereas a sample k was defined as a “low-level 10-gene signature” if the value VGk was less than the median value of the vector for the virtual gene VG:
High level: VGk>median VG,
Low level: VGk<median VG.
The survival curves were constructed using the Kaplan-Meier method (survival package). Thus with the log-rank test, the differences in expression of the 10 genes of the molecular signature were analysed (as described above) relative to the duration of the time interval between first appearance of the primary tumour, and that of metastases in other regions of the body (if the data was available), or relative to survival.
Chromatin was immunoprecipitated using the p53 DOI antibody (Santa Cruz) or a polyclonal antibody against Pin1 (Zacchi P. et al., 2002). The negative controls used were purified IgGs from rabbit or mouse serum. The co-immunoprecipitated DNA was analysed through Real Time PCR using a StepOne Plus thermal cycler (Applied Biosystems) and a SYBR Green Universal PCR master mix (Applied Biosystems). The presence of the factor on chromatin of the promoters analysed was calculated as a percentage of the immunoprecipitated quantity of chromatin used as the input, using the 2−ΔCt method. The primer sequences are presented below in Table 6:
The tissue microarrays (TMAs) used in this study to ascertain the levels of Pin1 in samples of tumour tissue derive from a historic series of breast carcinoma samples, taken from 212 primary tumours previously untreated and not selected in any other way. The TMAs were created using a specific manual arrayer (Beecher Instruments Inc), with on average six circular sections with a diameter of 0.6 mm per sample. A pathologist expert in the study of the mammary gland (L.J.) labelled for each sample the representative areas of tumour on glass slides stained with haematoxylin and eosin before taking the sections.
The sections (4 microns in thickness) cut from the TMA blocks were spread out on Superfrost® slides (VWR International Ltd) and dried for 1 hour at 60° C. before the paraffin was removed in Histoclear (National Diagnostics). The sections were then rehydrated by immersion in a series of solutions of gradually decreasing alcohol percentage. The sections were incubated in a buffer solution containing 10 mM citric acid at pH 6.0. They were then heated in a microwave oven for 15 min before being immunolabelled using the Dako Autostainer processing system and the Vectastain® ABC kit (Vector Labs), in accordance with the protocol supplied by the manufacturer. Briefly, the sections were blocked for 20 min using normal goat serum, added with 10% (v/v) with a stock solution of avidine (Vector Labs) and then incubated for 1 hour in a solution containing the primary antibody (monoclonal antibody against Pin1 (G-8, sc-46660), dilution 1:250) and added with 10% (v/v) with a stock solution of biotin (Vector Labs), so as to reduce the non-specific end labelling. The sections were then incubated for 30 minutes in the presence of a biotinylated universal secondary antibody (Vectastain® ABC kit, Vector Labs), and then for another 30 minutes in the presence of the reagent Vectastain® Elite ABC. Liquid diaminobenzidine (DAB) (DAKO) was used as the chromogen, incubating the sections for 5 min. These were then counterstained with a solution of Mayers haematoxylin. During the immunolabelling, between each passage and the next, the slides were washed briefly in Tris-based saline buffer (TBS) at pH 7.6. Each experiment included samples, which could certainly be labelled positively, and negative controls, prepared using TBS buffer in place of the solution containing primary antibody.
The immunolabelled TMA slides were examined (Scancope XT, Aperio Technologies) using a 40× magnifying objective, and catalogued in the Aperio Spectrum Plus+TMA database (version 9.0.748.1521). The TMAs relating to the cases of breast carcinoma were analysed under blind conditions. The classification of the samples was checked by the same pathologist who conducted the first evaluations, by means of standard analysis by optical microscopy, using a Nikon Eclipse E600 and microscope. Only the circular sections containing tumoral tissue were analysed; criteria excluding sectors from the analysis were: dimensions less than 20% of expectations, the overlapping of the sections, the prevalence of adipose tissue, stroma, or of normal epithelial breast tissue. Thus, 212 tumour samples were sufficient for the evaluation. Only invasive malignant tumours were considered, while tumours in situ, the surrounding epithelial and stroma were ignored. The positivity to labelling with the antibodies was evaluated in each section having adequate characteristics and a score using the “Quick Score” method (Detre S. et al., 1995) was assigned. In brief, the percentage of positive cells was calculated and on this basis a score was assigned on the scale from 1 to 6: 0-4%=1; 5-19%=2; 20-39%=3; 40-59%=4; 60-79%=5 and 80-100%=6. The mean intensity of the signals coming from labelling of positive cells was evaluated, and the thereto a score from 0 to 3 was assigned: no signal=0, signal from weak labelling=1, intermediate signal=2 and strong signal=3. The Quick Score was then obtained by multiplying the score relating to the percentage of labelled cells by the score relating to the intensity of the labelling, with a maximum achievable value of 18. Given that, for the majority of the samples, several sections were available for the evaluation, a total Quick Score was obtained that was unique to each tumour, and therefore to each patient. Also the localization type, cytoplasmic or nuclear, of the immunolabelling signal was annotated, and thus each cellular compartment, was separately considered, so obtaining two Quick Score for each patient.
The TP53 status was analysed by sequencing, using as the starting material the total RNA extracted from samples of frozen breast tumour tissue. The total RNA was extracted using the QIAGEN RNA assay kit. The quality of the nucleic acid recovered was evaluated via the Agilent-bioanalyzer microfluid platform. Samples which, upon analysis, yielded a ratio between the absorbances at 280 nm and 260 nm of less than 1.2 were discarded.
The retrotranscription reaction was conducted starting with 500 ng of total RNA using primers specific to p53 so as to amplify all its isoforms.
Primers for Analysing the Mutational Status of TP53 by Sequencing
Methods for Determining the Presence of the Molecular Signature Via qRT-PCR
From the expression matrix for the dataset of Desmedt et al., 2007 (GSE7390), the expression values were extracted for the genes showing the lowest variation (standard deviation less than 0.4) between the samples; among these genes, three were identified, having absolute expression values included within the absolute variation of expression of the 10 genes. A score for the molecular signature was then constructed, adding the relative gene score evaluating for each of the genes the relative expression with respect to one of the reference genes, as in the table below:
In particular, the gene score of the molecular signature is calculated on the basis of the following formula:
where:
a) if a gene i of the molecular signature has an expression value Expi less than 0.5 on the base 2 logarithmic scale by comparison with the corresponding expression value Expr of its reference gene r (equivalent to saying that there exists a difference of 0.5 RT-PCR cycles), this gene is attributed a gene score of zero.
b) if a gene i of the molecular signature has an expression value Expi higher than 0.5 on the base 2 logarithmic scale by comparison with the corresponding expression value Expr of its reference gene r (equivalent to saying that there exists a difference of 0.5 RT-PCR cycles), this gene is attributed a gene score of two.
c) if a gene i of the molecular signature has an expression value Expi intermediate to the two values of cases a) and b) by comparison with the corresponding expression value Expr of its reference gene r, this gene is attributed a gene score of one.
The sum of the genes scores (Sg) determines the value of the score for the molecular signature of the 10 genes (Sf):
Sf=ΣSg
According to the value of Sf, it is possible to evaluate the prognosis of the patient on the basis of the following criteria:
The survival of the patient was calculated using as time range the time from the date on which treatment was started to the date of death, or, if the patient was still alive, the date on which the assessment was carried out. The survival curves were constructed using the Kaplan-Meier method. The differences between the various tumour characteristics are estimated by means of the log-rank test. The chemotherapeutic treatment was carried out according to a classical protocol based on anthracycline.
To calculate the death risk in the 212 tumour cases included in the TMAs, an analysis using the Cox proportional hazards regression model was conducted. Parameters examined were the relationship existing between patient survival, the presence of missense in TP53 and the levels of Pin1 and the status of a series of other predictive parameters commonly used in clinical practice, including the tumour size, the presence or absence of receptors for oestrogen (ER status) or progesterone (PGR status), the lymph node status, the expression levels of HER2, the existence of lymph-node infiltration, and the tumour grade. The Cox proportional hazards regression model was applied in the first instance to the clinical variables available. The variables related to the presence of missense mutations in TP53, and to the level of Pin1 were then added. The clinical parameters were considered in the following manner:
In order to understand the type of influence exerted by Pin1 on mutant p53 during tumorigenesis, mice “knockin” for mutant p53—bearing a “knockin” allele coding for the protein p53R172H (p53M/+)—(Lang G. A. et al., 2004) were crossed with Pin1+/− mice (Atchinson F. W. et al., 2003). Two cohorts of mice derived from these crosses, composed of animals with the wild-type or knock-out genotype for Pin1 and bearing one or two alleles knockin for mutant p53 (p53M/+ Pin1+/+, p53M/+ Pin1−/− and p53M/M Pin1+/+, p53M/M Pin1−/−) were generated and analysed. The survival data relating to the p53M/M Pin1+/+ and p53M/+ Pin1+/+ were consistent with previously published studies (Lang G. A. et al., 2004). In both cohorts to which the mice lacking Pin1 belonged, the median survival in the absence of tumours was higher (
With regard to the cohort of p53M/+ Pin1−/− mice as compared to p53M+ Pin1+/+ mice, however, a markedly reduction in the frequency of tumours, a reduced number of lymphomas, and the complete absence of carcinomas were observed (
Mice of the genotypes p53+/− Pin1+/+ and p53+/− Pin1−/− were also taken into consideration, for which were recorded no differences in tumour-free survival, in the frequency or spectrum of the tumours (
In mice, therefore, the absence of Pin1 is associated with the reduction in tumorigenesis phenomena only in one context in which mutant p53 is expressed.
From these data, it can therefore be deduced that Pin1 and mutant p53 co-operate during the events which lead to tumoral transformation.
Regarding the mechanisms underlying this genetic interaction between Pin1 and mutant p53 it has emerged that, in samples of tumour tissue from p53M/+ Pin1+/+ mice, Pin1 co-immunoprecipitated with p53. Given that the enzyme specifically recognises the phosphorylated S/T-P motifs on its own substrates, these observations lead one to suppose that Pin1 may bind mutant p53, regulating its function in response to the phosphorylation signals produced by oncogenic stress.
The effect of Pin1 on the ability of mutant p53 to favour in primary cells the tumoral transformation induced by Ras (Lang G. A. et al., 2004) was evaluated on embryo fibroblasts (MEF) obtained from p53M/M Pin1+/+, p53M/M p53−/−, Pin1+/+ and p53−/− Pin1−/− mice. The effect was analysed in assays directed at ascertaining their growth capacity independently of anchorage to the substrates and their tumorigenesis potential in vivo following introduction of the H-RasV12 cells by means of retroviral vectors. The p53M/M Pin1+/+ cells proved capable of giving rise to two-fold more the number of colonies in soft agar (
In MEF p53M/M Pin1+/+ cells transduced with H-RasV12, in agreement with the results obtained in previous studies, it was observed that overexpression of the protein H-RasV12 caused an increase in the levels of mutant p53 and of Pin1 (Ryo A. et al., 2002). Moreover, the immunoblotting experiments, in which specific antibodies were used, which recognise phosphorylated S/T-P amino acid residues, have demonstrated that the overexpression of H-RasV12 lead to an increase in the levels of mutant p53 phosphorylation, at the level of the amino acid residues constituting the motifs for recognition and binding by Pin1 (
Overall, these results suggest that Pin1 is necessary for the ability of mutant p53 to promote cell transformation and tumoral progression, reveal for the enzyme, a crucial role as an oncogenic signalling transducer, which leads to activation of mutant p53 gain of function.
Also in human tumour cells of the lines MDA-MB-231 and SK-BR-3, derived from breast tumours, it has been observed that the enzyme binds the protein endogenous mutant p53. To establish whether Pin1 is able, in this context, to promote the oncogenic functions of mutant p53, the role of Pin1 in the induction of cell migration and invasion was evaluated, these being the critical aspects of the metastatic phenotype, which is manifested following the action of mutant p53 (Adorno M. et al., 2009; Muller P. et al., 2009). Knocking down by means of RNAi the expression levels of either mutant p53 or Pin1, a significant reduction in the ability of MDA-MB-231 to migrate and to be invasive, has been obtained (
The next step was therefore to investigate whether Pin1 is capable of producing the observed effects epistatically, by modulating the mutant p53 functions. As shown in
Overall, these results indicate that the binding of Pin1 to mutant p53 triggers the action of mutant p53 in favour of cell migration.
the Pin1/Mutant p53 Axis Activates a Specific Transcription Programme, which Favours the Aggressive Tumour Phenotype
In the attempt to understand how Pin1 and mutant p53 are able globally to alter gene expression, the transcriptional profile of MDA-MB-231 cells was analysed after depletion of either Pin1 or mutant p53. In both cases, an effect on the transcription of genes belonging to the same functional categories was observed, suggesting that Pin1 and mutant p53 are involved in the regulation of similar cellular processes, including proliferation, motility, dynamic organisation of the cytoskeleton, metabolism and signalling transduction. In particular, 386 genes were identified which, following depletion of either Pin1 or mutant p53 levels, are up-regulated, and 303 which, on the other hand, are down-regulated under the same conditions. On the basis of this result, it may be suppose that one group of genes is regulated by the concerted action of these two proteins (
The effect caused by depletion of either Pin1 or mutant p53 on the expression of the selected genes has been confirmed by qRT-PCR (
The transcription programme induced by the combined action of mutant p53 and Pin1 includes genes which play a relevant role in determining tumour aggressiveness, and may therefore influence breast cancer prognosis. To test this hypothesis, an analysis was conducted on primary tumours in the search for a correlation between the expression of genes induced by Pin1 and mutant p53 (that is, those genes down-regulated in the transcriptional profiling experiments), and the disease prognosis, by using four independent data sets relating to a total of 800 cases of breast cancer (Desmedt C. et al., 2007; Miller L. D. et al., 2005; Pawitan Y. et al., 2005; Sotiriou C. et al., 2006). From among the 303 down-regulated genes, those selected for the analysis were the subgroup (consisting of 31 genes) of genes most repressed under both silencing conditions. The Desmedt dataset (Desmedt C. et al., 2007) was used as a “training set” for construction of a system of gene classification based on a correlation with the clinical data (see Table 2).
From the classification of genes based on the association with clinical data, the genes having a score of more than 3 were selected, thus obtaining a molecular signature associated with Pin1/mutant p53, consisting of the 10 genes listed in Table 2 mentioned above.
The expression of these genes correlate significantly with the clinical outcome of the disease: in patients who expressed these genes at high levels, the time interval between diagnosis of the primary tumour and that of metastases in other regions of the body (Time to Distant Metastasis, TDM) was shorter and survival was reduced (Overall Survival, OS) (
The subsequent step was to test whether these 10 genes were regulated by the concerted action of Pin1 and mutant p53. As shown in
To analyse in detail the mechanism underlying the transcriptional activation mediated by the concerted action of Pin1 and mutant p53, chromatin immunoprecipitation (ChIP) experiments were conducted in MDA-MB-231 cells. As shown in
Overall, the data indicate that these genes are direct targets for the action of transcriptional induction exerted by the Pin1/mutant p53 axis, and that Pin1 could be required for the proper interaction of mutant p53 with various functional sites present on chromatin. In this regard, a more in-depth analysis of these promoter regions has revealed the presence of sites of recognition and binding for many transcription factors known for their ability to interact with mutant p53. These include Ets-1, NF-Y, Sp1 and VDR (Brosh R. and Rotter V., 2009) (data not shown).
The majority of these genes proved to be regulated by Pin1 and mutant p53 even in MDA-MB-468 cells which, as the endogenous mutant form, express the protein p53H273 (
To attempt. to understand the functional role of these 10 genes as mediators of Pin1/mutant p53-dependent cell migration, we analysed what happens to the MDA-MB-231 cells following their silencing, and identified six genes, whose silencing had the effect of reducing the migration ability of these cells. Depletion of the levels of DEPDC1 caused the more marked effect, with an impact also on the invasiveness of these cells.
Overall, these results indicate that Pin1 acts in concert with mutant p53 in re-programming gene expression of cancer cells, by activating a specific transcriptional programme in which a number of genes, that are important for the cell migration and invasion, takes part. These genes had not been identified up to now as direct targets of the transcriptional action of mutant p53.
Overexpression of Pin1 and the Presence of Mutations in p53, Influence the Clinical Outcome of Breast Tumours
The next step in the analysis was to evaluate in breast tumour, the type of association existing between the expression of Pin1 and the mutational status of p53, and the clinical outcome of the disease. Quantitative immunohistochemical assays were conducted for the purpose of evaluating the expression of Pin1 and of p53 in primary mammary carcinoma. The p53 status was analysed by means of direct sequencing, and only those tumours proving to bear the wild-type or missense mutations alleles were included in this study, for a total of 212 samples. Pin1 was shown to be over expressed in 144 out of 212 cases (68%), whereas in 46 out of 212 (22%), missense mutations in TP53 were found (Table 9).
No association emerged between the survival probability and the overexpression of Pin1 (
Evidence of the fact that the prognostic value of the presence of mutation in p53 depends on the Pin1 expression levels is further reinforced by the observation that the correlation between the presence of mutation in p53 and the decrease in the survival probability is present only in cases in which expression of Pin1 is high (
Overall, therefore, the data produced by the inventors indicate that, in cancer cells, the combined action of Pin1 and mutant p53 has a deep impact on the programme of gene expression by directly activating a transcriptional programme, which promotes the aggressive tumoral phenotype (
Brosh, R. and Rotter, V. (2009). When mutants gain new powers: news from the mutant p53 field. Nat. Rev. Cancer 9, 701-713.
| Number | Date | Country | Kind |
|---|---|---|---|
| PD2011A000201 | Jun 2011 | IT | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB2012/053021 | 6/15/2012 | WO | 00 | 12/13/2013 |
