Expression of BRCA1 Transcripts and Protein in Sporadic Ovarian Cancer

Park, C S; Kim, J K

Abstract

Recently the breast cancer susceptibility (BRCA1) gene on chromosome 17q has been isolated and identified as a tumor supressor gene that is mutated in many cases of inherited breast and ovarian cancer. Most of these mutations result in truncation and presumed inactivation of the BRCA1 protein. Many sporadic breast and ovarian cancers show LOH of chromosome 17q markers and it was assumed that BRCA1 would be also important in sporadic cancers. However, the function and the role of BRCA1 gene has not been elucidated, especially in sporadic ovarian cancers. In order to elucidate the role of BRCA1 in carcinogenesis of sporadic ovarian cancer, transcripts for BRCA1 gene were analysed in normal ovary tissues and sporadic ovarian cancer tissues using northern blot, RT-PCR, and in situ hybridization. Localization of BRCA1 protein in normal ovarian tissues and ovarian cancer tissues was determined by immunohistochemistry using BRCA1 Ab (K18). The pattern and level of BRCA1 protein was analysed by western blotting using BRCA1 Ab (6B4). By northern blot analysis, a 7.8 kb BRCA1 transcript was identified in various normal adult and fetal tissues. However,7.8 kb and 4.3 kb BRCA1 transcripts were detected in breast and ovarian cancer cell lines. The exon 11 truncated form of BRCA1 was detected in 3 of 8 (37.5%) ovarian cancer tissues by RT-PCR analysis and confirmed by in situ hybridization. In western blot analysis, BRCA1 protein was identified as a 220 kD protein and 87 kD of truncated protein product in normal ovary tissues and ovarian cancer tissues, however 87 kD of truncated protein product was strongly expressed in 4 of 10 (40%) ovarian cancer tissues. BRCA1 protein was localized in nucleus of normal breast epithelium and benign ovarian tumor epithelium and mainly in cytoplasm in 7 of 16 (44%) ovarian cancer tissues by immunohistochemistry. In conclusion, these findings suggest that the mutated BRCA1 gene (truncation of exon 11) may be involved in the carcinogenesis of sporadic ovarian cancers.