BRCA1 gene mutation and loss of heterozygosity on chromosome 17q21 in primary prostate cancer

Detection of hypermethylation BRCA1/2 gene promoter in breast tumours among Moroccan women

BACKGROUND

The promoter region is a key element of gene expression regulation. In mammals, most of the genes present, at the level of their promoter, a large number of islands CpG. Age also is seen as another factor for developing breast cell cancer reaching the tumour stage.

AIM

This study aimed to explore the hypermethylation of the BRCA1/2 promoter gene in women breast cancer and correlation with age and tumour stage.

MATERIALS AND METHODS

Fifty biopsies were derived from Moroccan women treated for breast carcinoma, the DNA extracted was treated by bisulphite and the targeted BRCA1/2 Amplicons were amplified by specific methylation primers (MSP).

RESULTS

The result shows that 62% of the samples were BRCA1 methylated in addition and negative result for BRCA2, these positive epigenetic factor were remarkable in women over 47 years and at the stage of malignant tumour.

CONCLUSION

These results show that half of the methylated samples are positive with a majority of over 47 years old, and confirms that age might be an additional factor for breast cancer development.

A systematic review of the prevalence of DNA damage response gene mutations in prostate cancer

Several ongoing international prostate cancer (PC) clinical trials are exploring therapies that target the DNA damage response (DDR) pathway. This systematic review summarizes the prevalence of DDR mutation carriers in the unselected (general) PC and familial PC populations. A total of 11 electronic databases, 10 conference proceedings, and grey literature sources were searched from their inception to December 2017. Studies reporting the prevalence of somatic and/or germline DDR mutations were summarized. Metastatic PC (mPC), castration‑resistant PC (CRPC) and metastatic CRPC (mCRPC) subgroups were included. A total of 11,648 records were retrieved, and 80 studies (103 records) across all PC populations were included; 59 records were of unselected PC and 13 records of familial PC. Most data were available for DDR panels (n=12 studies), ataxia telangiectasia mutated (ATM; n=13), breast cancer susceptibility gene (BRCA)1 (n=14) and BRCA2 (n=20). ATM, BRCA2 and partner and localizer of BRCA2 (PALB2) had the highest mutation rates (≥4%). Median prevalence rates for DDR germline mutations were 18.6% in PC (range, 17.2‑19%; three studies, n=1,712), 11.6% in mPC (range, 11.4‑11.8%; two studies, n=1,261) and 8.3% in mCRPC (range, 7.5‑9.1%; two studies, n=738). Median prevalence rates for DDR somatic mutations were 10.7% in PC (range, 4.9‑22%; three studies, n=680), 13.2% in mPC (range, 10‑16.4%; two studies, n=105) and not reported (NR) in mCRPC. The prevalence of DDR germline and/or somatic mutations was 27% in PC (one study, n=221), 22.67% in mCRPC (one study, n=150) and NR in mPC. In familial PC, median mutation prevalence was 12.1% (range, 7.3‑16.9%) for germline DDR (two studies, n=315) and 3.7% (range, 1.3‑7.9%) for BRCA2 (six studies, n=945). In total, 88% of studies were at a high risk of bias. The prevalence of DDR gene mutations in PC varied widely within somatic subgroups depending on study size, genetic screening techniques, DDR mutation definition and PC diagnosis; somatic and/or germline DDR mutation prevalence was in the range of 23‑27% in PC. These findings support DDR mutation testing for all patients with PC (including those with mCRPC). With the advent of the latest clinical practice PC guidelines highlighting the importance of DDR mutation screening, and ongoing mCRPC clinical trials evaluating DDR mutation‑targeted drugs, future larger epidemiological studies are warranted to further quantify the international burden of DDR mutations in PC.

Loss of heterozygosity for chromosomal regions 15q14-21.1, 17q21.31, and 13q12.3-13.1 and its relevance for prostate cancer

Although prostate cancer is one of the most common cancers in men, the genetic defects underlying its pathogenesis remain poorly understood. DNA damage repair mechanisms have been implicated in human cancer. Accumulating evidence indicates that the fidelity of the response to DNA double-strand breaks is critical for maintaining genome integrity. RAD51 is a central player in double-strand break repair via homologous recombination, and its alterations may confer and increase the risk of cancer. RAD51 functioning depends on the indirect or direct interactions with BRCA1 and BRCA2. To evaluate the contribution of RAD51 to sporadic prostate cancer, loss of heterozygosity (LOH) for chromosomal region 15q14-21.1 (RAD51locus) was determined and compared to LOH in 17q21.31 (BRCA1 locus) and 13q12.3-13.1 (BRCA2 region). DNA was isolated from prostate biopsies and matched peripheral blood of 50 patients. The regions 15q14-21.1, 17q21.31, and 13q12.3-13.1 were examined using microsatellite markers on chromosome 15 (D15S118, D15S214, D15S1006), chromosome 17 (D17S855, D17S1323), and chromosome 13 (D13S260, D13S290), respectively. The LOH in tumors was analyzed by PCR with fluorescently labeled primers and an ABI PRISM 377 DNA Sequencer. Allele sizing was determined by GeneScan version 3.1.2 and Genotyper version 2.5 software (Applied Biosystems, USA). LOH was identified in 57.5, 23, and 40 % for chromosomal regions 15q14-21.1, 17q21.31, and 13q12.3-13.1, respectively. Twenty-six percent of studied cases manifested LOH for at least one marker in 15q14-21.1 exclusively. A significant correlation was found between LOH for studied region and PSAD (prostate-specific antigen density). The findings suggest that RAD51 may be considered as a prostate cancer susceptibility gene.

Fine-mapping the HOXB region detects common variants tagging a rare coding allele: evidence for synthetic association in prostate cancer

The HOXB13 gene has been implicated in prostate cancer (PrCa) susceptibility. We performed a high resolution fine-mapping analysis to comprehensively evaluate the association between common genetic variation across the HOXB genetic locus at 17q21 and PrCa risk. This involved genotyping 700 SNPs using a custom Illumina iSelect array (iCOGS) followed by imputation of 3195 SNPs in 20,440 PrCa cases and 21,469 controls in The PRACTICAL consortium. We identified a cluster of highly correlated common variants situated within or closely upstream of HOXB13 that were significantly associated with PrCa risk, described by rs117576373 (OR 1.30, P = 2.62×10(-14)). Additional genotyping, conditional regression and haplotype analyses indicated that the newly identified common variants tag a rare, partially correlated coding variant in the HOXB13 gene (G84E, rs138213197), which has been identified recently as a moderate penetrance PrCa susceptibility allele. The potential for GWAS associations detected through common SNPs to be driven by rare causal variants with higher relative risks has long been proposed; however, to our knowledge this is the first experimental evidence for this phenomenon of synthetic association contributing to cancer susceptibility.

Aberrant expression of the PRAC gene in prostate cancer

Identification of aberrant expression patterns of genes in prostate cancer (PCa) is a key step towards the development of effective therapies. Prostate-specific antigen (PSA) levels are commonly measured for the early detection of PCa, but which itself is still not an ideal biomarker. We analysed the expression patterns of prostate cancer susceptibility candidate (PRAC) in prostate cancer. The PRAC gene is known to be commonly expressed in prostate tissue, rectum and colon. To provide clear insights into the expression patterns of PRAC in PCa, we examined the gene expression by quantitative real-time PCR (qRT-PCR), western blot analysis and immunohistochemistry (IHC). The results showed that PRAC expression levels in androgen‑insensitive cells (DU145 and PC3) are lower than those in androgen-sensitive cell lines (LNCaP, LNCaP-R and CW22R). However, treatment of the LNCaP cell line with androgen and anti-androgen demonstrated that PRAC is expressed in an androgen-independent manner. Further, PRAC expression was restored upon treatment of DU145 and PC3 cells with the methyltransferase inhibitor, 5-aza-2'-deoxycytidine (5-aza-CdR), which indicates the effect of methylation in the control of PRAC expression. In addition, IHC analysis revealed a significantly decreased immunoreactivity of PRAC protein in PCa tissues compared to benign prostatic hyperplasia (BPH) (p<0.0001). Thus, our findings suggest that the pathogenesis of PCa may be due to the expression levels of PRAC protein, and this protein can serve as a potential biomarker for the management of PCa.

Androgen receptor signaling and mutations in prostate cancer

Normal and neoplastic growth of the prostate gland are dependent on androgen receptor (AR) expression and function. Androgenic activation of the AR, in association with its coregulatory factors, is the classical pathway that leads to transcriptional activity of AR target genes. Alternatively, cytoplasmic signaling crosstalk of AR by growth factors, neurotrophic peptides, cytokines or nonandrogenic hormones may have important roles in prostate carcinogenesis and in metastatic or androgen-independent (AI) progression of the disease. In addition, cross-modulation by various nuclear transcription factors acting through basal transcriptional machinery could positively or negatively affect the AR or AR target genes expression and activity. Androgen ablation leads to an initial favorable response in a significant number of patients; however, almost invariably patients relapse with an aggressive form of the disease known as castration-resistant or hormone-refractory prostate cancer (PCa). Understanding critical molecular events that lead PCa cells to resist androgen-deprivation therapy is essential in developing successful treatments for hormone-refractory disease. In a significant number of hormone-refractory patients, the AR is overexpressed, mutated or genomically amplified. These genetic alterations maintain an active presence for a highly sensitive AR, which is responsive to androgens, antiandrogens or nonandrogenic hormones and collectively confer a selective growth advantage to PCa cells. This review provides a brief synopsis of the AR structure, AR coregulators, posttranslational modifications of AR, duality of AR function in prostate epithelial and stromal cells, AR-dependent signaling, genetic changes in the form of somatic and germline mutations and their known functional significance in PCa cells and tissues.

BRCA1 loss preexisting in small subpopulations of prostate cancer is associated with advanced disease and metastatic spread to lymph nodes and peripheral blood

PURPOSE

A preliminary study performed on a small cohort of multifocal prostate cancer (PCa) detected BRCA1 allelic imbalances among circulating tumor cells (CTC). The present analysis was aimed to elucidate the biological and clinical roles of BRCA1 losses in metastatic spread and tumor progression in PCa patients.

EXPERIMENTAL DESIGN

To map molecular progression in PCa outgrowth, we used fluorescence in situ hybridization analysis of primary tumors and lymph node sections, and CTCs from peripheral blood.

RESULTS

We found that 14% of 133 tested patients carried monoallelic BRCA1 loss in at least one tumor focus. Extended molecular analysis of chr17q revealed that this aberration was often a part of larger cytogenetic rearrangement involving chr17q21 accompanied by allelic imbalance of the tumor suppressor gene PTEN and lack of BRCA1 promoter methylation. The BRCA1 losses correlated with advanced T stage (P < 0.05), invasion to pelvic lymph nodes (P < 0.05), as well as biochemical recurrence (P < 0.01). Their prevalence was twice as high within 62 lymph node metastases (LNM) as in primary tumors (27%, P < 0.01). The analysis of 11 matched primary PCa-LNM pairs confirmed the suspected transmission of genetic abnormalities between these two sites. In four of seven patients with metastatic disease, BRCA1 losses appeared in a minute fraction of cytokeratin- and vimentin-positive CTCs.

CONCLUSIONS

Small subpopulations of PCa cells bearing BRCA1 losses might be one confounding factor initiating tumor dissemination and might provide an early indicator of shortened disease-free survival.

Identification of a novel germline missense mutation of the androgen receptor in African American men with familial prostate cancer

Race, family history and age are the unequivocally accepted risk factors for prostate cancer (PCa). Androgen receptor (AR)-dependent signaling is an important element in prostate carcinogenesis and its progression to metastatic disease. We examined the possibility of genomic changes in the AR in association with familial PCa in African Americans who have a higher incidence and mortality rate and a clinically more aggressive disease presentation than Caucasians. Genomic DNAs of 60 patients from 30 high-risk African American and Caucasian families participating in the Louisiana State University Health Sciences Center genetic linkage study of PCa were studied. Exon-specific polymerase-chain reaction, bi-directional automated sequencing and restriction enzyme genotyping were used to analyze for mutations in the coding region of the AR gene. We identified a germline AR (A1675T) (T559S) substitution mutation in the DNA-binding domain in three PCa-affected members of an African-American family with a history of early-onset disease. The present study describes the first AR germline mutation in an African-American family with a history of familial PCa. The AR (T559S) mutation may contribute to the disease by altering AR DNA-binding affinity and/or its response to androgens, non-androgenic steroids or anti-androgens. Additional studies will be required to define the frequency and contribution of the AR (A1675T) allele to early-onset and/or familial PCa in African Americans.

Tumor suppressor BRCA1 is expressed in prostate cancer and controls insulin-like growth factor I receptor (IGF-IR) gene transcription in an androgen receptor-dependent manner

PURPOSE

The insulin-like growth factor (IGF) system plays an important role in prostate cancer. The BRCA1 gene encodes a transcription factor with tumor suppressor activity. The involvement of BRCA1 in prostate cancer, however, has not yet been elucidated. The purpose of the present study was to examine the functional correlations between BRCA1 and the IGF system in prostate cancer.

EXPERIMENTAL DESIGN

An immunohistochemical analysis of BRCA1 was done on tissue microarrays comprising 203 primary prostate cancer specimens. In addition, BRCA1 levels were measured in prostate cancer xenografts and in cell lines representing early stages (P69 cells) and advanced stages (M12 cells) of the disease. The ability of BRCA1 to regulate IGF-I receptor (IGF-IR) expression was studied by coexpression experiments using a BRCA1 expression vector along with an IGF-IR promoter-luciferase reporter.

RESULTS

We found significantly elevated BRCA1 levels in prostate cancer in comparison with histologically normal prostate tissue (P<0.001). In addition, an inverse correlation between BRCA1 and IGF-IR levels was observed in the androgen receptor (AR)-negative prostate cancer-derived P69 and M12 cell lines. Coexpression experiments in M12 cells revealed that BRCA1 was able to suppress IGF-IR promoter activity and endogenous IGF-IR levels. On the other hand, BRCA1 enhanced IGF-IR levels in LNCaP C4-2 cells expressing an endogenous AR.

CONCLUSIONS

We provide evidence that BRCA1 differentially regulates IGF-IR expression in AR-positive and AR-negative prostate cancer cells. The mechanism of action of BRCA1 involves modulation of IGF-IR gene transcription. In addition, immunohistochemical data are consistent with a potential survival role of BRCA1 in prostate cancer.

Molecular biology of prostate cancer

Development of any cancer reflects a progressive accumulation of alterations in various genes. Oncogenes, tumour suppressor genes, DNA repair genes and metastasis suppressor genes have been investigated in prostate cancer. Here, we review current understanding of the molecular biology of prostate cancer. Detailed understanding of the molecular basis of prostate cancer will provide insights into the aetiology and prognosis of the disease, and suggest avenues for therapeutic intervention in the future.

Evaluation of familial clustering of breast and prostate cancer in the Minnesota Breast Cancer Family Study

Few studies examining familial clustering of breast and prostate cancer (PC) have focused on a clearly defined high-risk population with epidemiologic risk factors. We conducted a cohort study of prostate cancer among a subset of 426 families ascertained through female breast cancer probands. Three groups of males were included: 804 relatives in 60 families with four or more breast or ovarian cancers, 536 marry-ins in these high-risk families, and 484 relatives in 81 families where only the proband had breast cancer. A total of 118 prostate cancers were reported. The rate of prostate cancer among blood relatives in high-risk families was significantly lower than among marry-ins (RR = 0.6, 95% C.I.: 0.4-0.9). The rate of prostate cancer among blood relatives in low-risk families was not significantly different from the rate among marry-ins (RR = 0.8, 95% C.I.: 0.5-1.2). These results provide little evidence that male relatives in high-risk breast cancer families are at increased risk of prostate cancer.

PRAC2: a new gene expressed in human prostate and prostate cancer

BACKGROUND

The database of human Expressed Sequence Tags was previously used to identify PRAC (Prostate 47:125-131, 2001), a novel gene specifically expressed in human prostate, prostate cancer, rectum, and distal colon. In this report, we have identified PRAC2, another gene with a similar expression pattern that is located adjacent to the original PRAC gene on chromosome 17q21.3.

METHODS

Using a computer-based analysis, a cluster of sequence homologous ESTs was identified that is mainly derived from human prostate cDNA libraries. The tissue specificity was examined by multiple tissue RNA dot blots and RT-PCR. The PRAC2 transcript and protein were identified using Northern blot analysis, RACE-PCR, primer extension, and Western blots.

RESULTS

PRAC2 encodes a 564 nucleotide RNA found in prostate, rectum, distal colon, and testis. Weak expression was also found in placenta, peripheral blood leukocytes, skin, and in two prostate cancer cell lines: LNCaP and PC-3. The transcript seems to encode a 10.5-kDa nuclear protein. The PRAC2 gene is located on chromosome 17 at position 17q21, between the Hoxb-13 gene and the recently discovered PRAC gene.

CONCLUSIONS

Because of the higher expression of PRAC2 in prostate and its proximity to Hoxb-13, PRAC2 may have a function in prostate growth and development.

Genome-wide screening for complete genetic loss in prostate cancer by comparative hybridization onto cDNA microarrays

We demonstrate that comparative genomic hybridization (CGH) onto cDNA microarrays may be used to carry out genome-wide screens for regions of genetic loss, including homozygous (complete) deletions that may represent the possible location of tumour suppressor genes in human cancer. Screening of the prostate cancer cell lines LNCaP, PC3 and DU145 allowed the mapping of specific regions where genome copy number appeared altered and led to the identification of two novel regions of complete loss at 17q21.31 (500 kb spanning STAT3) and at 10q23.1 (50-350 kb spanning SFTPA2) in the PC3 cell line.

BRCA1 and prostate cancer

The breast cancer susceptibility gene BRCA1 on chromosome 17q21 encodes an 1863 amino acid protein that is important for normal embryonic development. Germline mutations of this gene are linked to a significantly increased lifetime risk for breast and/or ovarian cancer, and recent studies suggest that the same may be true for prostate cancer. Several activities that may contribute to the tumor suppressor function of BRCA1 have been identified via in vitro and experimental animal studies. These include (i) regulation of cell proliferation; (ii) participation in DNA repair/recombination processes related to the maintenance of genomic integrity; (iii) induction of apoptosis in damaged cells; and (iv) regulation of transcription. A second breast cancer susceptibility gene (BRCA2) operates in some of the same molecular pathways as BRCA1, and mutations of this gene predispose to breast and ovarian cancer and probably to other tumor types, including prostate cancer. Finally, recent studies from our laboratory suggest that BRCA1 modulates proliferation, chemosensitivity, repair of DNA strand breaks, apoptosis induction, and expression of certain key cellular regulatory proteins (including BRCA2 and p300) in human prostate cancer cells. These activities are consistent with a putative prostate tumor suppressor function of BRCA1.

PRAC: A novel small nuclear protein that is specifically expressed in human prostate and colon

BACKGROUND

The database of human Expressed Sequence Tags (dbEST) provides a potential source for identification of tissue-specific genes. This database contains sequences that originate from cDNA libraries from particular tumors, organs or cell types. In this report, we have used the EST database to identify PRAC, a novel gene specifically expressed in human Prostate, prostate cancer, Rectum And distal Colon.

METHODS

Using a computer based analysis, a cluster of sequence homologous ESTs was identified which contained ESTs derived only from human prostate cDNA libraries. The tissue specificity was examined by multiple tissue RNA dot blots and RT-PCR. The PRAC transcript and protein was identified using Northern blot analysis, RACE-PCR, primer extension, and western blot.

RESULTS

PRAC encode a 382 nucleotide RNA found in prostate, rectum, distal colon, and in three prostate cancer cell lines; LNCaP, PC-3 and DU145. This transcript encodes a 6 kDa nuclear protein. The PRAC gene is located on chromosome 17 at position 17q21, about 4 kbp downstream from the homeodomain Hoxb-13 gene.

CONCLUSIONS

Our data proves that the EST database can be a useful tool for discovery of prostate-specific genes. The nuclear localization, identification of potential phosphorylation sites, and possible cotranscription with the Hoxb-13 gene suggest that PRAC may have a regulatory role in the nucleus.

Identification of nucleolar protein No55 as a tumour-associated autoantigen in patients with prostate cancer

Four different genes were identified by immunoscreening of a cDNA expression library from the human prostate cancer cell line DU145 with allogeneic sera from four prostate cancer patients. A cDNA encoding the nucleolar protein No55 was further analysed and shown to be expressed at the mRNA level in several normal tissues, including ovaries, pancreas and prostate and in human prostate cancer cell lines PC-3, PC-3m and LNCaP. By reverse transcriptase/polymerase chain reaction, expression of No55 was several-fold higher in two out of nine prostate cancer primary tumours and two out of two metastatic lesions, compared to normal prostate tissue. Antibodies to No55 were detected in sera from seven out of 47 prostate cancer patients but not in sera from 20 healthy male controls. Sequence analysis of the No55 open reading frame from normal and tumour tissues revealed no tumour-specific mutations. The No55 gene was located to chromosome 17q21, a region reported to be partially deleted in prostate cancer. Considering the immunogenicity of the No55 protein in the tumour host, the expression profile and chromosomal localization of the corresponding gene, studies evaluating No55 as a potential antigen for immunological studies in prostate cancer may be warranted.

Identification of genetic markers for prostatic cancer progression

Despite the high incidence of prostate cancer, only limited data are available on genes or chromosomes specifically involved in its initiation and progression. We have applied comparative genomic hybridization to routinely processed, paraffin-embedded, tissues at different times in prostatic tumor progression to screen the tumor genome for gains and losses. Our panel included specimens derived from 56 different patients: 23 patients with primary, prostate-confined carcinomas; 18 patients with regional lymph node metastases; and 15 patients with distant metastases. Chromosome arms that most frequently showed losses, included 13q (55%), 8p (48%), 6q (43%), 5q (32%), 16q (25%), 18q (20%), 2q (18%), 4q (18%), 10q (18%), and Y (16%). Gains were often seen of chromosome arms 8q (36%), 17q (23%), Xq (23%), 7q (21%), 3q (18%), 9q (18%), 1q (16%), Xp (16%). Furthermore, specific high-level amplifications, eg, of 1q21, 1q25, and Xq12 to q13, were found in metastatic cancers. A significant accumulation of genetic changes in distant metastases was observed, eg, loss of 10q (p = 0.03) and gain of 7q (p = 0.03) sequences. In addition, investigation of a potential biomarker identified in previous studies by our group, ie, extra copies of #7 and/or #8, revealed a high prevalence of 7pq and/or 8q gain in the distant metastases (p = 0.02). Importantly, gains were observed more frequently in tumors derived from progressors after radical prostatectomy, than in nonprogressors (mean time of follow-up, 74 months). Specifically, gain of chromosome 7pq and/or 8q sequences appeared an accurate discriminator between the progressors and nonprogressors. Multivariate analysis showed a significant correlation between progressive disease and the number of chromosomes with gains. This correlation also held true when stage (p = 0.007) or grade (p = 0.002) were taken into account. Likewise, this applied for gain of chromosome 7pq and/or 8q sequences (p = 0.03 and p = 0.005 for stage or grade, respectively). Additionally, an increase in the number of chromosomes with gains per case was related to a decrease in biochemical progression-free survival (Ptrend <0.001). More specifically, the gain of 7pq and/or 8q sequences markedly reduced the biochemical progression-free survival (p < 0.001). In conclusion, this study has, firstly, documented the spectrum of chromosomal alterations in subsequent stages of prostate cancer, a number of which had not been described previously. It allowed us to identify chromosomal regions related to advanced tumor stage, ie, loss of 10q24 and gain of 7q11.2 and/or 7q31 sequences. Secondly, gain of 7pq and/or 8q was identified as a potential genetic discriminator between progressors and nonprogressors after radical surgery.