In sporadic breast cancer, no mutations of the BRCA1 gene have been reported so far, whereas BRCA1 mRNA is markedly decreased in invasive breast cancer. To elucidate the contribution of the BRCA1 gene in sporadic breast cancer, we quantified the BRCA1 protein, using [ 125 I] labeling of wholecell proteins, lentil-lectin affinity chromatography, immunoprecitation by anti-BRCA1 antibodies (C-20, D-20, I-20 and K-18), purification of the immune complex by protein A affinity chromatography and chromato-focusing. As loss of 1 allele may lead to a decreased expression of the gene, 10 tumors were previously checked for loss of heterozygosity (LOH) of the BRCA1 gene, using 3 intragenic microsatellite markers. Our results indicated that the BRCA1 gene product was decreased in the 4 tumors with LOH compared with matched normal breast tissues. Reduced amounts of BRCA1 protein were also detected in 3 of 6 tumors without LOH. Our quantitative method allowed us to demonstrate that the BRCA1 protein level was decreased in sporadic invasive breast carcinomas with or without LOH of the BRCA1 gene, implying multiple mechanisms of BRCA1 expression downregulation in these tumors. Our data suggest that the amount of BRCA1 protein present may play an important role in human sporadic breast carcinoma. Int. J. Cancer 80:823-826, 1999. Wiley-Liss, Inc.While familial breast cancer or familial breast/ovarian cancer often accompanies germ-line mutations of the BRCA1 gene (Miki et al., 1994), there is no evidence of BRCA1 mutations in sporadic breast cancer and BRCA1 mutations in sporadic ovarian cancer are rare (Futreal et al., 1994, Merajver et al., 1995. However BRCA1 gene transcription is markedly reduced in invasive breast tumors relative to normal breast epithelium, ductal carcinoma in situ (Thompson et al., 1995) and breast cancer cell lines (Ribieras et al., 1997), suggesting a role for BRCA1 in sporadic tumors. So far, BRCA1 gene expression in tumor tissues and cell lines has been monitored mainly at the mRNA level, by either Northern blot (Marquis et al., 1995), ribonuclease protection assay (Thompson et al., 1995) or competitive RT-PCR (Ribieras et al., 1997). In this study, we evaluated the relative amount of BRCA1 protein in ductal invasive carcinomas, using a strategy of biochemical purification previously devised in our laboratory for measureing HLA-DR antigen amounts (Bernard et al., 1984(Bernard et al., , 1985 and adapted for the BRCA1 protein (Bernard-Gallon et al., 1997).As loss of 1 allele might lead to reduced expression of the corresponding gene, we searched for loss of heterozygosity (LOH) of the BRCA1 gene, using 3 intragenic microsatellite markers. The BRCA1 protein was then quantified in the 2 groups of tumors, with and without LOH, and compared in tumors and normal matched tissues. Our results show that the amount of BRCA1 protein was decreased in all tumors with LOH as well as in a majority of ductal invasive carcinomas without LOH. MATERIAL AND METHODS Patient samplesTen sporadic invasive ductal breast carcinomas...

Any factor affecting BRCA gene regulation may be of interest in the prevention of breast tumourigenesis. We studied the influence of dietary docosahexaenoic acid (DHA), a major ˆ-3 fatty acid present in marine products, on rat autochthonous mammary tumourigenesis. DHAsupplementation significantly reduced the incidence of tumours (30%, P=0.007) and led to a 60% increase (P=0.02) in BRCA1 protein level. Since DHA influences the product of a major tumour suppressor gene, this finding may contribute to the observation that high-fish consumption reduces the risk of breast cancer.

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