EP2 and EP4 Receptors Regulate Aromatase Expression in Human Adipocytes and Breast Cancer Cells EVIDENCE OF A BRCA 1 AND p300 EXCHANGE.

Cytochrome P450 aromatase (aromatase), a product of the CYP19 gene, catalyzes the synthesis of estrogens from androgens. Because aromatase-dependent estrogen biosynthesis has been linked to hormone-dependent breast carcinogenesis, it is important to elucidate the mechanisms that regulate CYP19 gene expression. The main objective of this study was to identify the receptors (EP) for prostaglandin E2 (PGE2) that mediate the induction of CYP19 transcription in human adipocytes and breast cancer cells. Treatment with PGE2 induced aromatase, an effect that was mimicked by either EP2 or EP4 agonists. Antagonists of EP2 or EP4 or small interference RNA-mediated down-regulation of these receptors suppressed PGE2-mediated induction of aromatase. PGE2 via EP2 and EP4 stimulated the cAMP->protein kinase A pathway resulting in enhanced interaction between P-CREB, p300, and the aromatase promoter I.3/II. Overexpressing a mutant form of p300 that lacks histone acetyltransferase activity suppressed PGE2-mediated induction of aromatase promoter activity. PGE2 via EP2 and EP4 also caused a reduction in both the amounts of BRCA1 and the interaction between BRCA1 and the aromatase promoter I.3/II. Activation of the aromatase promoter by PGE2 was suppressed by overexpressing wild-type BRCA1. Silencing of EP2 or EP4 also blocked PGE2-mediated induction of the progesterone receptor, a prototypic estrogen-response gene. In a mouse model, overexpressing COX-2 in the mammary gland, a known inducer of PGE2 synthesis, led to increased aromatase mRNA and activity and reduced amounts of BRCA1; these effects were reversed by knocking out EP2. Taken together, these results suggest that PGE2 via EP2 and EP4 activates the cAMP->PKA->CREB pathway leading to enhanced CYP19 transcription and increased aromatase activity. Reciprocal changes in the interaction between BRCA1, p300, and the aromatase promoter I.3/II contributed to the inductive effects of PGE2. [ABSTRACT FROM AUTHOR]