AKAP95-mediated Nuclear Anchoring of PKA Mediates Cortisol-induced Expression in Human Amnion Fibroblasts

Phosphorylation of the transcription factors cyclic adenosine monophosphate response element-binding protein (CREB) and signal transducer and activator of transcription 3 (STAT3) by protein kinase A (PKA) is required for the cortisol-induced production of cyclooxygenase-2 (COX-2) and prostaglandin E (PGE) in human amnion fibroblasts, which critically mediates human parturition (labor). We found that PKA was confined in the nucleus by A-kinase-anchoring protein 95 (AKAP95) in amnion fibroblasts and that this localization was key to the cortisol-induced expression of , the gene encoding COX-2. Cortisol increased the abundance of nuclear PKA by stimulating the expression of the gene encoding AKAP95. Knockdown of AKAP95 not only reduced the amounts of nuclear PKA and phosphorylated CREB but also attenuated the induction of expression in primary human amnion fibroblasts treated with cortisol, whereas the phosphorylation of STAT3 in response to cortisol was not affected. The abundances of AKAP95, phosphorylated CREB, and COX-2 were markedly increased in human amnion tissue after labor compared to those in amnion tissues from cesarean sections without labor. These results highlight an essential role for PKA that is anchored in the nucleus by AKAP95 in the phosphorylation of CREB and the consequent induction of COX-2 expression by cortisol in amnion fibroblasts, which may be important in human parturition.