c-Myc activates BRCA1 gene expression through distal promoter elements in breast cancer cells

c-Myc was depleted using c-Myc-specific siRNAs in cultured breast cancer cells. BRCA1 mRNA expression and BRCA1 protein expression were determined by quantitative RT-PCR and western blot, respectively and BRCA1 promoter activities were examined under these conditions. DNA sequence analysis was conducted to search for high similarity to E boxes in the BRCA1 promoter region. The association of c-Myc with the BRCA1 promoter in vivo was tested by a chromatin immunoprecipitation assay. We investigated the function of the c-Myc binding site in the BRCA1 promoter region by a promoter assay with nucleotide substitutions in the putative E boxes. BRCA1-dependent DNA repair activities were measured by a GFP-reporter assay.Depletion of c-Myc was found to be correlated with reduced expression levels of BRCA1 mRNA and BRCA1 protein. Depletion of c-Myc decreased BRCA1 promoter activity, while ectopically expressed c-Myc increased BRCA1 promoter activity. In the distal BRCA1 promoter, DNA sequence analysis revealed two tandem clusters with high similarity, and each cluster contained a possible c-Myc binding site. c-Myc bound to these regions in vivo. Nucleotide substitutions in the c-Myc binding sites in these regions abrogated c-Myc-dependent promoter activation. Furthermore, breast cancer cells with reduced BRCA1 expression due to depletion of c-Myc exhibited impaired DNA repair activity.The distal BRCA1 promoter region is associated with c-Myc and contributes to BRCA1 gene activation.The human breast cancer susceptibility gene 1 product, BRCA1 is involved in important cellular processes, including DNA repair, and loss of BRCA1 can result in genomic instability. Loss of BRCA1 expression occurs in a subset of breast cancer cases, and inherited mutations of the BRCA1 gene account for about 5% of all breast cancer cases [1-8]. The regulation of BRCA1 expression has been studied extensively, including investigations of alternative mechanisms for reduced expression of BRCA1 in sporadi