The +ACA BRCA1 Promoter is Functionally Deficient and Subject to FAC1 Repression

Abstract

We previously identified a +ACA insertional polymorphism at ‐600 bp in the BRCA1 promoter that creates a FAC1 transcriptional repressor binding site (AACAACAC). FAC1‐negative NIH‐3T3 cells were transfected with luciferase vectors containing the 847 bp wild‐type (WT) or 850 bp +ACA minimal BRCA1 promoter sequence. The WT BRCA1 promoter‐driven luciferase construct produced 64,448 ± 9125 units of luciferase activity (relative light units) and the +ACA BRCA1 promoter‐driven luciferase construct produced 30,567 ± 2568 units. This result indicates that the +ACA BRCA1 promoter is functionally deficient compared to the WT BRCA1 promoter (53% reduction, p=0.004). Exogenous FAC1 protein did not significantly alter the luciferase activity from the WT BRCA1 promoter. In contrast, we observed a 79% reduction in luciferase activity from the +ACA BRCA1 promoter in the presence of FAC1 (p<0.0001). The FAC1‐mediated repression of the +ACA BRCA1 promoter reflects a 90% decrease in activity compared to the WT BRCA1 promoter (p<0.0001). Thus, the +ACA BRCA1 promoter is functionally deficient and subject to repression (silencing) by FAC1. Individuals that are homozygous for the +ACA polymorphism will exhibit compromised BRCA1 function and may become BRCA1‐null in response to FAC1 activation. These studies identify an alternative mechanism for loss of BRCA1 leading to breast cancer susceptibility. Support: NIH CA78343.