The frequency of germ-line mutations in the breast cancer predisposition genes BRCA1 and BRCA2 in familial prostate cancer. The Cancer Research Campaign/British Prostate Group United Kingdom Familial Prostate Cancer Study Collaborators.

Predisposition to prostate cancer has a genetic component, and there are reports of familial clustering of breast and prostate cancer. Two highly penetrant genes that predispose individuals to breast cancer (BRCA1 and BRCA2) are known to confer an increased risk of prostate cancer of about 3-fold and 7-fold, respectively, in breast cancer families. Blood DNA from affected individuals in 38 prostate cancer clusters was analyzed for germ-line mutations in BRCA1 and BRCA2 to assess the contribution of each of these genes to familial prostate cancer. Seventeen DNA samples were each from an affected individual in families with three or more cases of prostate cancer at any age; 20 samples were from one of affected sibling pairs where one was < or = 67 years at diagnosis. No germ-line mutations were found in BRCA1. Two germ-line mutations in BRCA2 were found, and both were seen in individuals whose age at diagnosis was very young (< or = 56 years) and who were members of an affected sibling pair. One is a 4-bp deletion at base 6710 (exon 11) in a man who had prostate cancer at 54 years, and the other is a 2-bp deletion at base 5531 (exon 11) in a man who had prostate cancer at 56 years. In both cases, the wild-type allele was lost in the patient's prostate tumor at the BRCA2 locus. However, intriguingly, in neither case did the affected brother also carry the mutation. Germ-line mutations in BRCA2 may therefore account for about 5% of prostate cancer in familial clusters.

Frequent loss of BRCA1 mRNA and protein expression in sporadic ovarian cancers.

Germline mutations in the BRCA1 gene cause inherited susceptibility to breast and ovarian cancers. However, somatic mutations of BRCA1 are rare in sporadic breast and ovarian tumours. To establish whether BRCA1 is altered during the development of sporadic ovarian cancer by mechanisms other than somatic mutation, we have analysed 57 sporadic epithelial ovarian tumours for BRCA1 protein and RNA expression. Reduced or absent protein expression was observed in 90% of tumours. Decreased protein expression was significantly associated with a reduction in the levels of RNA expression. Somatic mutations of BRCA1 and LOH at the BRCA1 locus were detected in 3.5% and 44% of informative tumours, respectively; there was no significant correlation between the levels of protein and RNA expression and the DNA mutation and/or LOH status. Together, these data suggest that expression of BRCA1 is down-regulated at the level of transcription during the development of sporadic ovarian cancers.

Mutation analysis of the c-mos proto-oncogene in human ovarian teratomas.

Female transgenic mice lacking a functional c-mos proto-oncogene develop ovarian teratomas, indicating that c-mos may behave as a tumour-suppressor gene for this type of tumour. We have analysed the entire coding region of the c-MOS gene in a series of human ovarian teratomas to determine whether there are any cancer-causing alterations. DNA from twenty teratomas was analysed by single-strand conformational analysis (SSCA) and heteroduplex analysis (HA) to screen for somatic and germline mutations. In nine of these tumours the entire gene was also sequenced. A previously reported polymorphism and a single new sequence variant were identified, neither of which we would predict to be disease-causing alterations. These results suggest that mutations in the coding region of the c-MOS gene do not play a significant role in the genesis of human ovarian teratomas.

Aberrant splicing of the TSG101 and FHIT genes occurs frequently in multiple malignancies and in normal tissues and mimics alterations previously described in tumours.

Intragenic deletions of TSG101, the human homolog of a mouse gene (tsg101) that acts to suppress malignant cell growth, were reported in human breast tumours. We screened TSG101 for somatic mutations in DNA and RNA samples isolated from a variety of common human malignancies, EBV-immortalised B-cells, and normal lung parenchyma. Intragenic TSG101 deletions in RNA transcripts were frequently found in all types of samples. Analysis of DNA failed to show genomic rearrangements corresponding to transcripts containing deletions in the same samples. The breakpoints of most transcript deletions coincide with genuine or cryptic splice site sequences, suggesting that they result from alternative or aberrant splicing. A similar spectrum of transcript deletions has previously been described in the putative tumour suppressor gene FHIT. We analysed FHIT in the same series of RNA samples and detected truncated FHIT transcripts frequently in both tumour and normal tissues. In addition, transcripts from TSG101, FHIT and seven other genes were analysed in RNA isolated from normal peripheral blood lymphocytes. Large TSG101 and FHIT intragenic transcript deletions were detected and these appeared to be the predominant transcript in 'aged' lymphocytes. Similar alterations were not detected in transcripts of the other genes which were analysed. Our findings demonstrate that truncated TSG101 and FHIT transcripts are commonly detected in both normal and malignant tissues and that a significant fraction of these are likely to be the result of aberrant splicing. While we cannot exclude that alterations in TSG101 and FHIT occur during cancer development, our data indicate that in this context the commonly observed transcript abnormalities are misleading.