Paradoxical Stimulation of Cyclooxygenase-2 Expression by Glucocorticoids via a Cyclic AMP Response Element in Human Amnion Fibroblasts

• Published in: Molecular endocrinology (Baltimore, Md.) Vol. 23; no. 11; pp. 1839 - 1849
• Main Authors: Zhu, X. O, Yang, Z, Guo, C. M, Ni, X. T, Li, J. N, Ge, Y. C, Myatt, L, Sun, K
• Format: Journal Article
• Language: English
• Published: United States Endocrine Society 01.11.2009; Oxford University Press
• Subjects: Amnion - cytology; Base Sequence; Cyclic AMP - metabolism; Cyclic AMP Response Element-Binding Protein - metabolism; Cyclooxygenase 2 - biosynthesis; Enzyme Inhibitors - pharmacology; Fibroblasts - metabolism; Gene Expression Regulation, Enzymologic; Glucocorticoids - metabolism; Hormone Antagonists - pharmacology; Humans; MAP Kinase Signaling System; Mifepristone - pharmacology; Molecular Sequence Data; Original Research; Phosphorylation; Response Elements
• ISSN: 0888-8809; 1944-9917
• DOI: 10.1210/me.2009-0201

Human amnion fibroblasts produce abundant prostaglandins toward the end of gestation, which is one of the major events leading to parturition. In marked contrast to its well-described antiinflammatory effect, glucocorticoids have been shown to up-regulate cyclooxygenase-2 (COX-2) expression in human amnion fibroblasts. The mechanisms underlying this paradoxical induction of COX-2 by glucocorticoids have not been resolved. Using cultured human amnion fibroblasts, we found that the induction of COX-2 mRNA expression by cortisol was a glucocorticoid receptor (GR)-dependent process requiring ongoing transcription. Upon transfection of a COX-2 promoter-driven reporter gene into the amnion fibroblasts, cortisol stimulated the COX-2 promoter activity. This was abolished by mutagenesis of a cAMP response element (CRE) at −53 to approximately −59bp as well as by cotransfection of a plasmid expressing dominant-negative CRE-binding protein (CREB). The phosphorylation level of CREB-1 was significantly increased by cortisol treatment of the amnion fibroblasts, whereas the effect was attenuated either by the protein kinase A inhibitor H89 or the p38 -MAPK inhibitor SB203580. The induction of the COX-2 promoter activity and the phosphorylation of CREB-1 were also blocked by the GR antagonist RU486. Chromatin immunoprecipitation (ChIP) assay revealed that the binding of CREB-1 to the CRE of the COX-2 promoter was increased by cortisol treatment of the amnion fibroblasts. In conclusion, cortisol, via binding to GR, stimulated COX-2 expression by increasing phosphorylated CREB-1 binding to the CRE of the COX-2 gene. Cortisol may phosphorylate CREB-1 by activating either protein kinase A or p38-MAPK in the amnion fibroblasts. Cortisol induces COX-2 by increasing phosphorylated CREB via PKA or p38-MAPK and its binding to the CRE of the COX-2 gene in human amnion fibroblasts.