A Role of CREB in BRCA1 Constitutive Promoter Activity and Aromatase Basal Expression

Aromatase is the rate-limiting enzyme in estrogen biosynthesis and a key target in breast cancer treatment. Its ovary-specific promoter, PII, is induced in response to protein kinase A (PKA) activation. It has been proposed that breast cancer susceptibility gene 1, BRCA1, is involved in negative regulation of aromatase PII activity. Surprisingly, inhibition of PKA pathway by inhibitor H89 elevates basal aromatase expression while abolishes cAMP-mediated aromatase induction in an ovarian granulosa cell line, KGN. In this report, we decipher the mechanism by which the PKA pathway negatively regulates aromatase basal expression. We show that PKA pathway plays a positive role in the expression of BRCA1. H89 effectively reduces endogenous BRCA1 mRNA levels as well as reporter gene expression from a BRCA1 promoter. Mutation of a cAMP-responsive element (CRE) in the BRCA1 promoter reduces BRCA1 expression. Chromatin immunoprecipitation (ChIP) shows that CRE-binding protein, CREB, binds to the BRCA1 promoter. Furthermore, knockdown of CREB in KGN cells leads to decreased BRCA1 level as well as elevated basal aromatase mRNA expression. These data demonstrate that both the CRE site in the BRCA1 promoter and CREB are required for BRCA1 constitutive expression. Our study suggests that PKA pathway exerts its negative impact on basal aromatase expression indirectly by contributing to the constitutive expression of BRCA1.