Prostaglandin receptor EP2 is responsible for cyclooxygenase-2 induction by prostaglandin E2 in mouse skin

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Abstract
The EP2 prostanoid receptor is one of the four subtypes of receptors for prostaglandin E 2 (PGE 2 ). We previously reported that deletion of EP2 led to resistance to chemically induced mouse skin carcinogenesis, whereas overexpression of EP2 resulted in enhanced tumor development. The purpose of this study was to investigate the underlying molecular mechanisms. We found that EP2 knockout mice had reduced cyclooxygenase-2 (COX-2) expression after 12- O -tetradecanoylphorbol-13-acetate (TPA) treatment compared with wild-type (WT) mice. Further, primary keratinocytes from EP2 transgenic mice had increased COX-2 expression after either TPA or PGE 2 treatment and COX-2 expression was blocked by 10 μM SQ 22,536, an adenylate cyclase inhibitor. EP2 knockout mice had significantly decreased, whereas EP2 transgenic mice had significantly increased PGE 2 production in response to a single treatment of TPA. Cyclic AMP response element-binding protein (CREB) phosphorylation was elevated to a greater extent in keratinocytes from EP2 transgenic mice compared with those of WT mice following PGE 2 treatment. A protein kinase A (PKA) inhibitor reduced PGE 2 -mediated CREB phosphorylation in keratinocytes from EP2 transgenic mice. Furthermore, we found that there was no CREB phosphorylation in EP2 knockout mice following PGE 2 treatment. PGE 2 -induced DNA synthesis (cell proliferation) was significantly decreased in keratinocytes from EP2 knockout mice following pretreatment with 10 μM SQ 22,536. Taken together, EP2 activation of the PKA/CREB-signaling pathway is responsible for keratinocyte proliferation and our findings reveal a positive feedback loop between COX-2 and PGE 2 that is mediated by the EP2 receptor.

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