| Abstract: |
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. PGE 2 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 PGE 2-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. © 2008 by The American Society for Biochemistry and Molecular Biology, Inc. |
| Keywords: |
signal transduction; controlled study; protein expression; unclassified drug; human cell; genetics; nonhuman; protein function; animal cell; mouse; animal; metabolism; animals; mice; animal tissue; breast cancer; gene expression; protein kinases; protein protein interaction; animal experiment; animal model; small interfering rna; enzymology; enzyme activity; cell line, tumor; breast neoplasms; brca1 protein; transgenic mouse; mice, transgenic; rna; gene expression regulation; gene expression regulation, neoplastic; biosynthesis; cyclooxygenase 2; breast tumor; cancer cell; nucleic acids; prostaglandin e2; tumor cell line; transcription; cyclic amp; down regulation; experimental neoplasm; mouse models; prostaglandin e; biochemistry; brca1 protein, human; mammary gland; cytochrome p450; aromatase; enzyme induction; cyclic amp responsive element binding protein; gene expression regulation, enzymologic; cyclic amp dependent protein kinase; biochemical engineering; mammary neoplasms, animal; prostaglandin synthesis; dinoprostone; e1a associated p300 protein; protein p300; pka; adipocyte; breast cancer cells; adipocytes; promoter activities; e1a-associated p300 protein; synthesis of; flow interactions; fetal monitoring; receptors, prostaglandin e; histone acetyl transferases; inductive effects; mammary glands; progesterone receptors; response genes; small interference rnas; histone acetyltransferase; prostaglandin e receptor; prostaglandin receptor blocking agent; prostaglandin receptor stimulating agent; ep300 protein, human; ep4 receptor; prostaglandin ep2 receptor
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