Expression of the cyclic AMP-dependent transcription factors, CREB, CREM and ATF2, in the human myometrium during pregnancy and labour

Abstract

Elevated concentrations of cyclic AMP (cAMP) in the human myometrium may promote uterine quiescence during pregnancy by protein kinase A (PKA)-mediated phosphorylation and subsequent inactivation of myosin light-chain kinase, as well as by the phosphorylation and activation of cAMP-dependent transcription factors. In this context, we show that the altered expression of cAMP response-element binding protein (CREB), cAMP response-element modulator protein (CREM) and activating transcription factor 2 (ATF2) are implicated in the maintenance of myometrial quiescence during fetal maturation and the switch to uterine activation at term. Using electrophoretic mobility shift and super shift assays, as well as immunoblotting of paired myometrial tissue samples from non-pregnant, pregnant non-labouring and spontaneous labouring women, we defined the patterns of expression of various isoforms of these proteins in the human uterus. Here, we report spatio-temporal changes in the expression of a 43 kDa form of CREB, a 28 kDa CREM-like protein, and a novel 28 kDa ATF2-like protein which are differentially expressed, depending on the gestational state of the uterus. Changes in the pattern of expression of these potent transcription factors may have an important role in the control of uterine activity throughout pregnancy.

Identification of human myometrial target genes of the c-Jun NH2-terminal kinase (JNK) pathway: the role of activating transcription factor 2 (ATF2) and a novel spliced isoform ATF2-small

“…Our previous results indicate that in vivo, at some point during pregnancy, expression of ATF2 is downregulated in the myometrium whereas ATF2-sm becomes spatially expressed with greater levels detected in the fundus compared with the lower uterine segment (Bailey et al 2000). These events may consequently have major effects on the genes observed to be regulated by these proteins in this study.…”

“…It is therefore interesting to note the increased expression of oestrogen receptor 2 (ESR2/ESR-beta) with over-expression of ATF2, and to compare this to the detected increase in expression of the alternative oestrogen receptor 1 (ESR1/ESR-alpha) associated with over-expression of the ATF2-related bZIP transcription factor CREB in myometrial cells (Bailey et al 2004), which has been found to be prevalent in the non-pregnant myometrium but almost absent in pregnant non-labouring and spontaneous labouring tissue (Bailey et al 2000). Interestingly, a significant minority of genes found to be affected by the over-expression of ATF2 and ATF2-sm in myometrial cells in this study are also affected by CREB (Bailey et al 2004): 25% of the genes affected by ATF2, and 38% of the genes affected by ATF2-sm.…”

“…However, in addition to the well characterized 60 000 mol wt ATF2 protein, we also reported the existence of a novel putative splice-variant designated ATF2-small (ATF2-sm) (Bailey et al 2000), showing potent trans-activation properties. To our knowledge, this is the first alternatively-spliced variant of ATF2 to be identified in human tissue.…”

Synergistic effects of PDGF-BB and cAMP-elevating agents on expression of connexin43 in mesangial cells

“…As shown in PDGF activates Cx43 promoter in the presence of cAMP. Previous studies have demonstrated the presence of activator protein-1 (AP-1) and CRE in the promoter region of Cx43 (2,7,24). Because PDGF and IBMX are well-known activators of AP-1 and CRE, respectively, the agents may upregulate Cx43 via activation of these regulatory elements.…”

Regulation of GTP-binding Protein (Gαs) Expression in Human Myometrial Cells

“…It is clear, however, that components of the cAMP/protein kinase A (PKA) pathway are differentially expressed in the human myometrium during pregnancy (41)(42)(43)(44)(45)(46)(47): central to this is the GTP-binding protein G␣ s . Indeed, signaling through G␣ s is thought to facilitate promotion of myometrial quiescence, and G␣ s protein levels have been shown to be reduced at the onset of labor (41,42).…”