Localization of human BRCA1 and its loss in high-grade, non-inherited breast carcinomas

Abstract

Although the link between the BRCA1 tumour-suppressor gene and hereditary breast and ovarian cancer is established, the role, if any, of BRCA1 in non-familial cancers is unclear. BRCA1 mutations are rare in sporadic cancers, but loss of BRCA1 resulting from reduced expression or incorrect subcellular localization is postulated to be important in non-familial breast and ovarian cancers. Epigenetic loss, however, has not received general acceptance due to controversy regarding the subcellular localization of BRCA1 proteins, reports of which have ranged from exclusively nuclear, to conditionally nuclear, to the ER/golgi, to cytoplasmic invaginations into the nucleus. In an attempt to resolve this issue, we have comprehensively characterized 19 anti-BRCA1 antibodies. These reagents detect a 220-kD protein localized in discrete nuclear foci in all epithelial cell lines, including those derived from breast malignancies. Immunohistochemical staining of human breast specimens also revealed BRCA1 nuclear foci in benign breast, invasive lobular cancers and low-grade ductal carcinomas. Conversely, BRCA1 expression was reduced or undetectable in the majority of high-grade, ductal carcinomas, suggesting that absence of BRCA1 may contribute to the pathogenesis of a significant percentage of sporadic breast cancers.

BRCA1 and BRCA2 as molecular targets for phytochemicals indole-3-carbinol and genistein in breast and prostate cancer cells

“…Evidence of a role for BRCA1 in sporadic mammary carcinogenesis supports this idea. Thus, BRCA1 expression is decreased or absent in a significant proportion of sporadic breast and ovarian cancer cases, in part because of hypermethylation of the BRCA1 promoter on CpG islands (Wilson et al, 1999;Rice et al, 2000). A significant fraction of sporadic breast cancers (46%) were found to be haploinsufficient for BRCA1 (Staff et al, 2003).…”

Gene replacement with the human BRCA1 locus: tissue specific expression and rescue of embryonic lethality in mice

“…In addition to inherited mutations, other means of regulating BRCA1 function may be important in sporadic tumors. The gene is down-regulated at the transcriptional level in sporadic cancer (Catteau et al, 1999;Mancini et al, 1998;Wilson et al, 1999) and the BRCA1 protein becomes mislocalized following infection with certain transforming viruses (Maul et al, 1998). There are currently no models which allow testing for the consequences of individual mutations in the human BRCA1 gene in an intact animal system.…”

“…Testis is a site of signi®cant BRCA1 expression (Lane et al, 1995;Scully et al, 1997b) due to a presumed role for the protein in homologous strand exchange (Snouwaert et al, 1999;Zabludo et al, 1996). Antibodies were the generous gift of Drs C Wilson and D Slamon (UCLA School of Medicine, Los Angeles, CA, USA) and have been described elsewhere (Wilson et al, 1997(Wilson et al, , 1999. None of the antibodies used in this experiment cross-reacted with extracts derived from mice.…”

“…The anti-BRCA1 antisera used have been characterized extensively as described (Wilson et al, 1997(Wilson et al, , 1999. 115 is a rabbit polyclonal antibody useful for immuno-precipitation and SD118 is a mouse monoclonal antibody useful for immuno-blot analysis.…”

A role for BRCA1 in sporadic breast cancer

“…Hence, three strands of evidence confirm our results to be correct and reproducible under different fixation conditions. Previous work has suggested that MS13 staining is predominantly nuclear and represents the full-length protein (Wilson et al, 1999). However, recent immunoblotting data from the same group (http://www.med.ucla.edu/ora/manuscripts.htm) showed MS13 to detect the D11b splice variant in the cytoplasm as well as the full-length BRCA1 species in the nucleus.…”