PKA and AKIP1 interact to mediate cAMP-driven COX-2 expression: A potentially pivotal interaction in preterm and term labour.

Angela Yulia,Kaiyu Lei,Danijela Markovic,Natasha Singh,Suren R Sooranna,Mark R Johnson,Alice J Varley,Kang Sun

doi:10.1371/journal.pone.0252720

Abstract

Previously, we showed that cAMP increased COX-2 expression in myometrial cells via MAPK. Here, we have extended these observations, using primary myometrial cell cultures to show that the cAMP agonist, forskolin, enhances IL-1β-driven COX-2 expression. We then explored the role of A-kinase interacting protein (AKIP1), which modulates the effect of PKA on p65 activation. AKIP1 knockdown reversed the effect of forskolin, such that its addition inhibited IL-1β-induced COX-2 mRNA expression and reduced the IL-1β-induced increase in nuclear levels of p65 and c-jun. Forskolin alone and with IL-1β increased IκBα mRNA expression suggesting that in the context of inflammation and in the presence of AKIP1, cAMP enhances p65 activation. AKIP1 knockdown reversed these changes. Interestingly, AKIP1 knockdown had minimal effect on the ability of forskolin to repress either basal OTR expression or IL-1β-stimulated OTR mRNA expression. AKIP1 was up-regulated by IL-1β, but not stretch and was repressed by cAMP. The mRNA expression of AKIP1 increased in early labour in tandem with an increase in COX-2 mRNA and protein. AKIP1 protein levels were also increased with inflammation and stretch-induced preterm labour. Our results identify a second important cAMP effector-switch occurring at term in human myometrium and suggest that a hitherto unrecognized interaction may exist between AKIP1, NFκB and AP-1. These data add to the proposition that cAMP acts as a key regulator of human myometrial contractility.

Highlights

The factors controlling the onset of human labour remain unclear and until we understand the mechanisms involved it is unlikely that we will reduce the high rates of spontaneous preterm labour or improve our ability to induce labour when it is necessary
NFκB activation has been suggested to play a key role in labour onset, repressing progesterone activity and driving the expression of prostaglandin synthetic enzymes, including cyclooxygenase-2 COX-2, oxytocin receptor (OTR) and pro-inflammatory chemokines involved in both preterm and term labour [9,10,11,12,13]
We show in primary myometrial cell cultures that when levels of the protein kinase A (PKA)-interacting protein, A kinase interacting protein 1 (AKIP1), are low, that Cyclic AMP (cAMP) inhibits inflammation driven COX-2 expression

Summary

Introduction

The factors controlling the onset of human labour remain unclear and until we understand the mechanisms involved it is unlikely that we will reduce the high rates of spontaneous preterm labour or improve our ability to induce labour when it is necessary. Cyclic AMP (cAMP) is an important second messenger in many cell types regulating many essential processes in a range of tissues. It acts via a number of intermediaries including protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac) to modulate target molecule activation and alter cell function. NFκB activation has been suggested to play a key role in labour onset, repressing progesterone activity and driving the expression of prostaglandin synthetic enzymes, including cyclooxygenase-2 COX-2, oxytocin receptor (OTR) and pro-inflammatory chemokines involved in both preterm and term labour [9,10,11,12,13]. Despite the fact that cAMP/PKA appears to repress NFκB activation, we recently showed that cAMP enhances COX-2 expression in myometrial cells via a mitogen-activated protein kinase (MAPK)-dependent pathway [14]

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