Prostacyclin receptor regulates contraction‐associated proteins and contractile proteins in pregnant human myometrium via PKA/cAMP and the transcription factors GATA‐6 and myocardin

Abstract

Objective: Levels of the smooth muscle relaxant prostacyclin increase prior to labor. We investigated the role of prostacyclin in myometrial activation.Methods: Myometrial tissue was obtained from term pregnant women during cesarean delivery and treated with vehicle or the prostacyclin receptor (IP) agonist iloprost in organ or cell culture models. siRNA was transfected using a Nucleofector. Contraction‐associated protein (CAP) and contractile protein expression were analyzed by immunoblotting or RT‐PCR.Results: Iloprost induced expression of the CAPs COX‐2 and connexin‐43, and the contractile proteins smooth muscle‐myosin heavy chain, h‐caldesmon, and calponin in organ culture and/or cell culture. COX‐2 activity increased as measured by PGF2αrelease. Iloprost activated cAMP/PKA, and siRNA against PKA reduced iloprost‐induced CAP and contractile protein expression, while 8‐Br‐cAMP mimicked the effect. siRNA against the transcription factors GATA‐6 or myocardin inhibited iloprost‐induced SM‐MHC and COX‐2.Conclusions: IP activation of cAMP/PKA induces CAPs and contractile proteins in human myometrium, perhaps by regulating GATA‐6 and myocardin. Prostacyclin may provide positive feedback, linking CAPs and contractile proteins, by increasing COX‐2 activity. These mechanisms may be involved in the conversion of the human uterus from quiescent to an actively contracting labor phenotype.This work was supported by grants from the NIH NHLBI and an NIH NCI training grant