Cyclic AMP Effectors Regulate Myometrial Oxytocin Receptor Expression.
The factors that initiate human labor are poorly understood. We have tested the hypothesis that a decline in cAMP/protein kinase A (PKA) function leads to the onset of labor. Initially, we identified myometrial cAMP/PKA-responsive genes (six up-regulated and five down-regulated genes) and assessed their expression in myometrial samples taken from different stages of pregnancy and labor. We found that the oxytocin receptor (OTR) was one of the cAMP-repressed genes, and, given the importance of OTR in the labor process, we studied the mechanisms involved in greater detail using small interfering RNA, chemical agonists, and antagonists of the cAMP effectors. We found that cAMP-repressed genes, including OTR, increased with the onset of labor. Our in vitro studies showed that cAMP acting via PKA reduced OTR expression but that in the absence of PKA, cAMP acts via exchange protein activated by cAMP (EPAC) to increase OTR expression. In early labor myometrial samples, PKA levels and activity declined and Epac1 levels increased, perhaps accounting for the increase in myometrial OTR mRNA and protein levels at this time. In vitro exposure of myometrial cells to stretch and IL-1β increased OTR levels and reduced basal and forskolin-stimulated cAMP and PKA activity, as judged by phospho-cAMP response element-binding protein levels, but neither stretch nor IL-1β had any effect on PKA or EPAC1 levels. In summary, there is a reduction in the activity of the cAMP/PKA pathway with the onset of human labor potentially playing a critical role in regulating OTR expression and the transition from myometrial quiescence to activation.
Chelsea and Westminster Hospital (A.Y., N.S., K.L., S.R.S., M.R.J.), London SW10 9NH, United Kingdom; and Institute of Reproductive and Developmental Biology (A.Y., N.S., K.L., S.R.S., M.R.J.), London W12 0NN, United Kingdom.
Angela
A
Yulia
Chelsea and Westminster Hospital (A.Y., N.S., K.L., S.R.S., M.R.J.), London SW10 9NH, United Kingdom; and Institute of Reproductive and Developmental Biology (A.Y., N.S., K.L., S.R.S., M.R.J.), London W12 0NN, United Kingdom.
Natasha
N
Singh
Chelsea and Westminster Hospital (A.Y., N.S., K.L., S.R.S., M.R.J.), London SW10 9NH, United Kingdom; and Institute of Reproductive and Developmental Biology (A.Y., N.S., K.L., S.R.S., M.R.J.), London W12 0NN, United Kingdom.
Kaiyu
K
Lei
Chelsea and Westminster Hospital (A.Y., N.S., K.L., S.R.S., M.R.J.), London SW10 9NH, United Kingdom; and Institute of Reproductive and Developmental Biology (A.Y., N.S., K.L., S.R.S., M.R.J.), London W12 0NN, United Kingdom.
Suren R
SR
Sooranna
Chelsea and Westminster Hospital (A.Y., N.S., K.L., S.R.S., M.R.J.), London SW10 9NH, United Kingdom; and Institute of Reproductive and Developmental Biology (A.Y., N.S., K.L., S.R.S., M.R.J.), London W12 0NN, United Kingdom.
Mark R
MR
Johnson
D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism; D005260:Female; D015870:Gene Expression / Q000187:drug effects / Q000235:genetics; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D053583:Interleukin-1beta / Q000494:pharmacology; D007743:Labor, Obstetric / Q000235:genetics / Q000378:metabolism*; D009215:Myometrium / Q000187:drug effects / Q000378:metabolism*; D011247:Pregnancy; D034741:RNA, Small Interfering / Q000235:genetics; D018045:Receptors, Oxytocin / Q000235:genetics / Q000378:metabolism*
D020662:Guanine Nucleotide Exchange Factors; D053583:Interleukin-1beta; C116122:RAPGEF3 protein, human; D034741:RNA, Small Interfering; D018045:Receptors, Oxytocin; D005576:Colforsin; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases