The role of mitogen-activated protein kinase in oxytocin-induced contraction of uterine smooth muscle in pregnant rat

A novel deleterious oxytocin variant is associated with the lower twinning ratio in Awassi ewes

This study aimed to assess the possible association of oxytocin (OXT) gene with reproductive traits in two groups of Awassi ewes that differ in their reproductive potentials. Sheep were genotyped using PCR-single-stranded conformation polymorphism approach. Three genotypes were detected in exon 2, CC, CA, and AA, and a novel SNP was identified with a missense effect on oxytocin (c.188C > A → p.Arg55Leu). A significant (p < 0.01) association of p.Arg55Leu with the twinning rate was found as ewes with AA and CA genotypes exhibited, respectively a lower twinning ratio than those with the wild-type CC genotype. The deleterious impact of p.Arg55Leu was demonstrated by all in silico tools that were utilized to assess the effect of this variant on the structure, function, and stability of oxytocin. Molecular docking showed that p.Arg55Leu caused a dramatic alteration in the binding of oxytocin with its receptor and reduced the number of interacted amino acids between them. Our study suggests that ewes with AA and CA genotypes showed a lower reproductive performance due to the presence of p.Arg55Leu, which caused damaging impacts on oxytocin and is binding with the OXT receptor. The utilization of the p.Arg55Leu could be useful for improving Awassi reproductive potential.

The MAP kinase ERK5/MAPK7 is a downstream effector of oxytocin signaling in myometrial cells

The hormone oxytocin (OT) has pleiotropic activities both in the central nervous system as well as in peripheral tissues, including uterotonic effects on the myometrium during parturition. OT effects are mediated by a single transmembrane receptor, belonging to the GPCR (G protein-coupled receptor) superfamily and coupled primarily to Gq- and Gi-containing heterotrimeric G proteins. Upon receptor stimulation, one well-studied downstream effect is activation of the ERK1/2 MAP (mitogen-activated protein) kinase, and studies have shown that induction of COX-2 by OT in the myometrium required ERK1/2 activity. Many studies investigating the role of ERK1/2 in myometrial tissue were based on the use of chemical inhibitors that, to varying degrees, also inhibited ERK5/MAPK7. Here we report that OT activates ERK5 in a human myometrial cell line in a dose- and time-dependent manner through the activation of Gi/o heterotrimers. Using complementary approaches, we demonstrate that OT-induced COX-2 induction and the concomitant release of PGF2α into the media are primarily ERK5-dependent and to a much lesser extent ERK1/2-dependent. Moreover, in contrast to ERK1/2 activation, ERK5 activation is downstream of Gi/o activation. Here, we also found that ERK5 impacted both basal and to a lesser extent, OT-mediated myometrial cell contraction in vitro. Finally, tracking both ERK1/2 and ERK5 activity during different stages of gestation in rat myometrium, we showed that they followed distinct patterns starting at the onset of labor corresponding to the highest COX-2 expression levels. Overall, our results reveal an important, hitherto unrecognized role for ERK5 in myometrial cell contraction involving induction of COX-2. This novel pathway is likely to play an important role in supporting uterine contractions during parturition.

Oxytocin antagonism prevents pregnancy-associated aortic dissection in a mouse model of Marfan syndrome

Women with Marfan syndrome (MFS) are at high risk for pregnancy-associated aortic dissection. Pathogenic models that singularly invoke hemodynamic stress are difficult to reconcile with predominant postnatal occurrence of aortic tear, often occurring weeks to months after delivery. In consideration of events that peak at term, are sustained after delivery, and might synergize with previously defined signaling pathways implicated in aneurysm progression, we examined the hormone oxytocin, which initiates uterine contraction and milk letdown for the duration of lactation through phosphorylation of extracellular signal-regulated kinase (ERK). In a mouse model of MFS that shows highly penetrant postnatal aortic dissection, risk was strongly attenuated by preventing lactation or use of an oxytocin receptor antagonist. Survival correlated inversely with the extent of ERK activation in the aortic wall, and strong protection was observed upon attenuation of ERK phosphorylation using an inhibitor of ERK kinase (MEK) or the U.S. Food and Drug Administration-approved medication hydralazine, offering potential therapeutic strategies for pregnancy-associated vascular catastrophe in the setting of MFS.

The Oxytocin Receptor: From Intracellular Signaling to Behavior

The many facets of the oxytocin (OXT) system of the brain and periphery elicited nearly 25,000 publications since 1930 (see FIGURE 1 , as listed in PubMed), which revealed central roles for OXT and its receptor (OXTR) in reproduction, and social and emotional behaviors in animal and human studies focusing on mental and physical health and disease. In this review, we discuss the mechanisms of OXT expression and release, expression and binding of the OXTR in brain and periphery, OXTR-coupled signaling cascades, and their involvement in behavioral outcomes to assemble a comprehensive picture of the central and peripheral OXT system. Traditionally known for its role in milk let-down and uterine contraction during labor, OXT also has implications in physiological, and also behavioral, aspects of reproduction, such as sexual and maternal behaviors and pair bonding, but also anxiety, trust, sociability, food intake, or even drug abuse. The many facets of OXT are, on a molecular basis, brought about by a single receptor. The OXTR, a 7-transmembrane G protein-coupled receptor capable of binding to either Gαior Gαqproteins, activates a set of signaling cascades, such as the MAPK, PKC, PLC, or CaMK pathways, which converge on transcription factors like CREB or MEF-2. The cellular response to OXT includes regulation of neurite outgrowth, cellular viability, and increased survival. OXTergic projections in the brain represent anxiety and stress-regulating circuits connecting the paraventricular nucleus of the hypothalamus, amygdala, bed nucleus of the stria terminalis, or the medial prefrontal cortex. Which OXT-induced patterns finally alter the behavior of an animal or a human being is still poorly understood, and studying those OXTR-coupled signaling cascades is one initial step toward a better understanding of the molecular background of those behavioral effects.

Seasonal Expression of Oxytocin and Oxytocin Receptor in the Scented Gland of Male Muskrat (Ondatra zibethicus)

Oxytocin (OT) can modulate multiple physiological functions via binding to the widely distributed oxytocin receptor (OTR). In this study, we investigated the seasonal expressions of OT, OTR and extracellular signal regulated kinase (ERK1/2) signaling pathway components in the scented gland of muskrat during the breeding and non-breeding seasons. Histologically, glandular cells, interstitial cells and excretory tubules were identified in the breeding season scented glands, whereas epithelial cells were sparse in the non-breeding season. Immunohistochemical results showed that OTR was present in epithelial cells and interstitial cells while OT, pERK1/2, ERK1/2 and c-fos were expressed in epithelial cells and glandular cells. The protein and mRNA expressions of OTR, OT and c-fos were significantly higher in the scented gland in the breeding season than in the non-breeding season. Importantly, the levels of OT in scented glands and serum were measured by hormone assays, and their concentrations were both significantly higher in the breeding season than in the non-breeding season. Moreover, bioinformatics analysis showed that the predicted targets of the differentially expressed microRNAs might include the genes encoding OTR, ERK1/2 and c-fos. These findings suggested that OT may regulate the function of muskrat scented glands by the locally expressed receptors.

Advances in the role of oxytocin receptors in human parturition

Oxytocin (OT) is a neurohypophysial hormone which has been found to play a central role in the regulation of human parturition. The most established role of oxytocin/oxytocin receptor (OT/OTR) system in human parturition is the initiation of uterine contractions, however, recent evidence have demonstrated that it may have a more complex role including initiation of inflammation, regulation of miRNA expression, as well as mediation of other non-classical oxytocin actions via receptor crosstalk with other G protein-coupled receptors (GPCRs). In this review we highlight both established and newly emerging roles of OT/OTR system in human parturition and discuss the expanding potential for OTRs as pharmacological targets in the management of preterm labour.

Neuroendocrinology of pregnancy and parturition

During pregnancy, the maternal brain drives a series of adaptive mechanisms that are fundamental for allowing fetal growth and development, protecting both mother and fetus from adverse programming and timing of parturition. This neuroendocrine concept is even more complex as fetal brain and placenta also participate as regulators of maternal-placental-fetal physiology. The placenta is now seen as a neuroendocrine organ, acting as a source of several neuroactive factors that may exert their biologic effects either locally or by entering maternal and fetal circulation, thus acting in an autocrine, paracrine, and endocrine manner. A variety of hypothalamic neurohormones (GnRH, GHRH, somatostatin, CRH, oxytocin) are expressed in the placenta. When stress occurs during pregnancy, the maternal, fetal, and placental hypothalamic-pituitary-adrenal (HPA) axes are activated to stimulate a series of responses contributing to maintain physiologic conditions while at the same time avoiding the adverse effects of stress on the mother and offspring. However, when stress is excessive, a number of obstetric complications may occur, such as preterm birth, pre-eclampsia and intrauterine growth restriction, related to an impairment of the placental adaptive response.

Functional interactions between the oxytocin receptor and the β2-adrenergic receptor: implications for ERK1/2 activation in human myometrial cells

The Gq-coupled oxytocin receptor (OTR) and the Gs-coupled β(2)-adrenergic receptor (β(2)AR) are both expressed in myometrial cells and mediate uterine contraction and relaxation, respectively. The two receptors represent important pharmacological targets as OTR antagonists and β(2)AR agonists are used to control pre-term uterine contractions. Despite their physiologically antagonistic effects, both receptors activate the MAP kinases ERK1/2, which has been implicated in uterine contraction and the onset of labor. To determine the signalling pathways involved in mediating the ERK1/2 response, we assessed the effect of blockers of specific G protein-associated pathways. In human myometrial hTERT-C3 cells, inhibition of Gαi as well as inhibition of the Gαq/PKC pathway led to a reduction of both OTR- and β(2)AR-mediated ERK1/2 activation. The involvement of Gαq/PKC in β(2)AR-mediated ERK1/2 induction was unexpected. To test whether the emergence of this novel signalling mechanism was dependent on OTR expression in the same cell, we conducted experiments in HEK 293 cells that were transfected with the β(2)AR alone or co-transfected with the OTR. Using this approach, we found that β(2)AR-mediated ERK1/2 responses became sensitive to PKC inhibition only in cells co-transfected with the OTR. Inhibitor studies indicated the involvement of an atypical PKC isoform in this process. We confirmed the specific involvement of PKCζ in this pathway by assessing PKCζ translocation to the cell membrane. Consistent with our inhibitor studies, we found that β(2)AR-mediated PKCζ translocation was dependent on co-expression of OTR. The present demonstration of a novel β(2)AR-coupled signalling pathway that is dependent on OTR co-expression is suggestive of a molecular interaction between the two receptors.

Neuroendocrine mechanisms in pregnancy and parturition

The complex mechanisms controlling human parturition involves mother, fetus, and placenta, and stress is a key element activating a series of physiological adaptive responses. Preterm birth is a clinical syndrome that shares several characteristics with term birth. A major role for the neuroendocrine mechanisms has been proposed, and placenta/membranes are sources for neurohormones and peptides. Oxytocin (OT) is the neurohormone whose major target is uterine contractility and placenta represents a novel source that contributes to the mechanisms of parturition. The CRH/urocortin (Ucn) family is another important neuroendocrine pathway involved in term and preterm birth. The CRH/Ucn family consists of four ligands: CRH, Ucn, Ucn2, and Ucn3. These peptides have a pleyotropic function and are expressed by human placenta and fetal membranes. Uterine contractility, blood vessel tone, and immune function are influenced by CRH/Ucns during pregnancy and undergo major changes at parturition. Among the others, neurohormones, relaxin, parathyroid hormone-related protein, opioids, neurosteroids, and monoamines are expressed and secreted from placental tissues at parturition. Preterm birth is the consequence of a premature and sustained activation of endocrine and immune responses. A preterm birth evidence for a premature activation of OT secretion as well as increased maternal plasma CRH levels suggests a pathogenic role of these neurohormones. A decrease of maternal serum CRH-binding protein is a concurrent event. At midgestation, placental hypersecretion of CRH or Ucn has been proposed as a predictive marker of subsequent preterm delivery. While placenta represents the major source for CRH, fetus abundantly secretes Ucn and adrenal dehydroepiandrosterone in women with preterm birth. The relevant role of neuroendocrine mechanisms in preterm birth is sustained by basic and clinic implications.

A comparative genome analysis of gene expression reveals different regulatory mechanisms between mouse and human embryo pre-implantation development

BACKGROUND

Pre-implantation development is a crucial step in successful implantation and pregnancy in mammals. It has been studied in depth, but mostly in laboratory animal models. Less is known about the regulatory mechanism involved in the pre-implantation development in humans and about the comparative aspects.

METHODS

Here, we employed the microarray datasets from the public database library of GEO and applied comparative analysis of genome wide temporal gene expression data based on statistical analysis and functional annotation for both mouse and human, demonstrating the discordance between the regulatory mechanisms of both mouse and human pre-implantation development.

RESULTS

There were differences between mouse and human pre-implantation development both in the global gene expression pattern and in the expression changes of individual genes at each stage, including different major transient waves of transcription profiles and some stage-specific genes and significantly related pathways. There also appeared to be different functional changes from one stage to another between mouse and human.

CONCLUSIONS

The analysis presented here lead to interesting and complementary conclusions that the regulatory mechanism of human pre-implantation development is not completely the same as the mouse. Not as the fact that 1-cell to 2-cell stage is important for mouse pre-implantation development, the 4-cell stage and 8-cell stage are both essential for human. Unlike in mouse, of which most of pathways found were related to energy, RNA and protein metabolism, the identified pathways in human were mostly disease-related and associated with human pre-implantation embryonic development. All of these suggest that a further comparative analysis should be required for applying the result of mouse expression data to human research or therapy, particularly in pre-implantation developments. Our study provides several potential targets of genes and pathways for studying the regulatory mechanism of human pre-implantation development using mouse model.

Preterm labour. Biochemical and endocrinological preparation for parturition

Preterm delivery is a common obstetric problem occurring in about 1 in 10 of all births. Preterm babies have a high risk of morbidity and mortality. Such births account for 75% of all major neonatal problems. At the other end of the spectrum, prolonged pregnancy is also a subject of concern because it too is associated with increased fetal morbidity and mortality. Despite extensive research, the mechanisms that control the length of human pregnancy and signal the onset of labour have not been fully determined. This chapter will discuss basic principles in the biology of parturition and the regulation of contraction-associated proteins including the oxytocin receptor. The major pathways regulating contractions and the transcriptional regulation of the main genes that are known to be involved in the onset of labour and parturition will be examined. Some new potentially therapeutic strategies for the biochemical management of preterm labour will be discussed.

In vitro and in vivo pharmacological characterization of ethyl-4-[trans-4-[((2S)-2-hydroxy-3-[4-hydroxy-3[(methylsulfonyl)amino]-phenoxy]propyl) amino]cyclohexyl]benzoate hydrochloride (SAR150640), a new potent and selective human beta3-adrenoceptor agonist for the treatment of preterm labor

Ethyl-4-[trans-4-[((2S)-2-hydroxy-3-[4-hydroxy-3[(methylsulfonyl)amino] phenoxy]propyl) amino]cyclohexyl]benzoate hydrochloride (SAR150640) was characterized as a new potent and selective beta(3)-adrenoceptor agonist for the treatment of preterm labor. SAR150640 and its major metabolite, the corresponding acid 4-[trans-4-[((2S)-2-hydroxy-3-[4-hydroxy-3[(methylsulfonyl) amino] phenoxy]propyl)amino]cyclohexyl]benzoic acid (SSR500400), showed high affinity for beta(3)-adrenoceptors (K(i) = 73 and 358 nM) and greater potency than (-)-isoproterenol in increasing cAMP production in membrane preparations from human neuroblastoma cells (SKNMC), which express native beta(3)-adrenoceptors (pEC(50) = 6.5, 6.2, and 5.1, respectively). SAR150640 and SSR500400 also increased cAMP production in membrane preparations from human uterine smooth muscle cells (UtSMC), which also express native beta(3)-adrenoceptors (pEC(50) = 7.7 and 7.7, respectively). In these cells, SAR150640 dose-dependently inhibited oxytocin-induced intracellular Ca(2+) mobilization and extracellular signal-regulated kinase 1/2 phosphorylation. SAR150640 and SSR500400 had no beta(1)- or beta(2)-agonist or antagonist activity in guinea pig atrium and trachea, or in human isolated atrium and bronchus preparations. Both compounds concentration-dependently inhibited spontaneous contractions in human near-term myometrial strips, with greater potency than salbutamol and 4-[3-[(1,1-dimethylethyl)-amino]-2-hydroxypropoxy]-1,3-dihydro-2H-benzimidazol-2-one hydrochloride (CGP12177) (pIC(50) = 6.4, 6.8, 5.9, and 5.8, respectively), but with similar potency to (-)-isoproterenol and atosiban (oxytocin/vasopressin V(1)a receptor antagonist). SAR150640 also inhibited the contractions induced by oxytocin and prostaglandin F(2alpha). In vivo, after intravenous administration, SAR150640 (1 and 6 mg/kg), but not atosiban (6 mg/kg), dose-dependently inhibited myometrial contractions in conscious unrestrained female cynomolgus monkeys, with no significant effects on heart rate or blood pressure. In contrast, salbutamol (50 and 250 microg/kg) had no inhibitory effect on uterine contractions, but it dose-dependently increased heart rate. These findings indicate a potential for the therapeutic use of SAR150640 in mammals during preterm labor.

Focal adhesion signaling is required for myometrial ERK activation and contractile phenotype switch before labor

In late pregnancy rapidly increasing fetal growth dramatically increases uterine wall tension. This process has been implicated in the activation of the myometrium for labor, but the mechanisms involved are unclear. Here, we tested, using a rat model, the hypothesis that gestation-dependent stretch, via activation of focal adhesion signaling, contributes to the published activation of myometrial ERK at the end of pregnancy. Consistent with this hypothesis, we show here that ERK is targeted to adhesion plaques during late pregnancy. Furthermore, myometrial stretch triggers a dramatic increase in myometrial contractility and ERK and caldesmon phosphorylation, confirming the presence of stretch sensitive myometrial signaling element. Screening by anti-phosphotyrosine immunoblotting for focal adhesion signaling in response to stretch reveals a significant increase in the tyrosine phosphorylated bands identified as focal adhesion kinase (FAK), A-Raf, paxillin, and Src. Pretreatment with PP2, a Src inhibitor, significantly suppresses the stretch-induced increases in FAK, paxillin, Src, ERK and caldesmon phosphorylation and myometrial contractility. Thus, focal adhesion-Src signaling contributes to ERK activation and promotes contraction in late pregnancy. These results point to focal adhesion signaling molecules as potential targets in the modulation of the myometrial contractility and the onset of labor.

Spatial and temporal expression of the myometrial mitogen-activated protein kinases p38 and ERK1/2 in the human uterus during pregnancy and labor

OBJECTIVE

We have recently identified a novel putative spliced variant of the activating transcription factor 2 (ATF2) in the human myometrium during pregnancy and labor. This protein, termed ATF2-sm like full-length ATF2, acts as a potent transactivator of cyclic adenosine monophosphate response element (CRE)-containing promoter reporter genes. Similarly, employing microarray gene profiling in myometrial cells, we have shown ATF2-sm to affect the expression of several specific myometrial genes associated with regulating uterine activity during pregnancy and labor. At some point after conception this transcription factor becomes spatially expressed within the body of the uterus, with significantly higher levels detected in the upper (corpus) compared to the lower uterine segment. Because ATF2 species are the primary substrate for phosphorylation by the mitogen-activated protein kinases (MAPKs) p38 and ERK1/2, the purpose of the current investigation was to define the expression levels of these kinases in upper and lower segment myometrium during pregnancy and labor to see if they also correlated with expression of ATF2-sm.

METHODS

Paired myometrial samples were collected from the upper (corpus) and lower uterine segments from term nonlaboring and spontaneously laboring women undergoing elective and emergency cesarean deliveries, respectively. Non-pregnant myometrial samples were collected from premenopausal women having hysterectomies for benign gynecologic disorders. The MAPKs p38 and ERK1/2 present in individual myometrial homogenates were resolved using sodium dodecyl sulfate polacrylamide gel electropheresis (SDS-PAGE) with subsequent Western blotting with specific antibodies and scanning densitometry. Expression of the individual MAPKs in myometrial tissues was confirmed in situ using immunohistochemistry.

RESULTS

In non-pregnant tissues, p38 and ERK1/2 expression was uniform throughout the uterus. In term pregnant nonlaboring and spontaneously laboring samples expression of p38 and ERK1 was significantly elevated in the upper uterine segment compared to the lower segment, respectively. In contrast, there was no difference in ERK2 expression.

CONCLUSION

The data from this study indicate that both p38 and ERK1 are spatially regulated in different uterine regions during pregnancy/labor and suggest that they may be involved in regulating the activity of ATF2 isoforms and their subsequent effects on myometrial function.

Urocortins in human reproduction

Data on biological effects and localization of corticotropin-releasing factor (CRF), a neuropeptide structurally and biologically related to urocortins, have triggered the study on expression of urocortins and their function in human reproductive tissues. Ovary, endometrium, placenta and fetal membranes (amnion and chorion), myometrium, and prostate are sources of urocortin 1 and, they also express urocortin binding sites (receptors and CRF-binding protein), thus suggesting that these tissues are also targets of urocortin 1. The current concept thus is that urocortin 1 may affect the physiology of human reproduction through paracrine/autocrine actions. In particular, in vitro data have shown that urocortin 1 plays a major role in human placenta: it stimulates the secretion of ACTH, prostaglandins and activin A from cultured human placental cells, and regulates placental vessel resistance to blood flow. Furthermore, when incubated in myometrial strips, urocortins stimulate uterine contractility, by activating specific intracellular pathways. Taken together, these findings do suggest an important role of urocortins in the physiology of pregnancy and parturition.

ERK-mediated uterine artery contraction: role of thick and thin filament regulatory pathways

We have demonstrated that extracellular signal-regulated kinase (ERK) plays an important role in the regulation of uterine artery contraction. The present study tested the hypothesis that ERK regulates thick and thin filament regulatory pathways in the uterine artery. Isometric tension, intracellular free Ca2+ concentration ([Ca2+]i), and 20-kDa myosin light chain (LC20) phosphorylation were measured simultaneously in uterine arteries isolated from near-term (140 days gestation) pregnant sheep. Phenylephrine produced time-dependent increases in [Ca2+]i and LC20 phosphorylation that preceded the contraction, which were inhibited by the MEK (ERK) inhibitor PD-098059. In addition, PD-098059 decreased the intercept of the regression line of LC20 phosphorylation vs. [Ca2+]i but increased the rate of tension development vs. LC20 phosphorylation. In contrast to phenylephrine, phorbol 12,13-bibutyrate (PDBu) produced contractions without changing [Ca2+]i or LC20 phosphorylation. PD-098059 potentiated PDBu-induced contractions without affecting [Ca2+]i and LC20 phosphorylation. PDBu produced time-dependent increases in phosphorylation of p42 and p44 ERK and ERK-dependent phosphorylation of caldesmon at Ser789 in the uterine artery. PD-098059 blocked PDBu-mediated phosphorylation of p42 and p44 ERK and caldesmon. The results indicate that ERK may regulate force by a dual regulation of thick and thin filaments in uterine artery smooth muscle. ERK potentiates the thick filament regulatory pathway by enhancing LC20 phosphorylation via increases in [Ca2+]i and Ca2+ sensitivity of LC20 phosphorylation. In contrast, ERK attenuates the thin filament regulatory pathway and suppresses contractions independent of changes in LC20 phosphorylation in the uterine artery.

Role of ERK1/2 in uterine contractility and preterm labor in rats

The present study tested the hypothesis that ERK activation is an essential step in the onset of labor in a rat model of preterm labor. The administration of RU-486, an antiprogesterone agent, to rats induced preterm delivery 22.2 +/- 0.24 h after treatment. Changes in basal signaling events were studied in myometrial tissue from CO(2)-euthanized rats. Rats treated with RU-486 displayed a dramatically increased in vitro uterine contractility compared with gestational stage-matched, sham-treated rats. In vitro contractility was not significantly different from that during spontaneous labor. During RU-486-induced preterm labor, as previously described for spontaneous labor, ERK phosphorylation levels increased, as did phosphorylation of caldesmon at Ser(789), an ERK phosphorylation site. Also, a small but significant increase in 20-kDa myosin light chain phosphorylation was seen at a constant intracellular pCa of 7. When rats were chronically treated with an agent that prevents ERK activation, U-0126, the onset of RU-486-induced preterm labor was delayed in a statistically significant manner. Chronic in vivo treatment with U-0126 also significantly inhibited the RU-486-induced increase in in vitro contractility and ERK and caldesmon phosphorylation but did not alter the RU-486-induced increase in 20-kDa myosin light chain phosphorylation. These data indicate that ERK activation is a component of the multiple events leading to the development of labor in this rat model. We suggest that the ERK pathway could possibly be used to identify targets for the development of a novel class of tocolytic agents.

Urocortin II is expressed in human pregnant myometrial cells and regulates myosin light chain phosphorylation: potential role of the type-2 corticotropin-releasing hormone receptor in the control of myometrial contractility

The family of CRH-related peptides are suggested to play important roles in the control of myometrial contractility during pregnancy and labor. In this study we investigated the expression of urocortin II (UCN II) in human myometrium and its ability to phosphorylate intracellular components that can be involved in modulating myometrial contractility. Using RT-PCR and fluorescent in situ hybridization, we demonstrated that UCN II and type-2 CRH receptor (CRH-R2) mRNAs were expressed in human nonpregnant and pregnant myometrium. Immunofluorescent studies confirmed protein expression of UCN II in human pregnant myometrial cells, whereas chemical cross-linking studies with radiolabeled UCN II confirmed the presence of CRH-R2 sites with an apparent molecular mass of 50 kDa. Treatment of primary human myometrial cells with UCN II to specifically activate CRH-R2 resulted in a dose-dependent increase of myosin light chain (MLC(20)) phosphorylation. Activation of protein kinase C (PKC) and ERK1/2 was required for the UCN II-induced activation of MLC(20), because treatment of myometrial cells with inhibitors of MAPK kinase 1 (U0126) and PKC (bisindolylmaleimide) inhibited the UCN II-induced phosphorylation of MLC(20). Furthermore, the UCN II effect on MLC(20) was dependent on RhoA translocation to the membrane and subsequent activation of RhoA-associated kinase, as shown by the use of the specific inhibitors exoenzyme C3 and Y27632. Collectively, our data suggest a distinctive role for CRH-R2- specific agonists like UCN II in the control of myometrial contractility during human pregnancy involving sequential activation of PKC, MAPK kinase 1, ERK1/2, RhoA, and RhoA-associated kinase, leading to the MLC(20) phosphorylation.

Role of pp60(c-src) and p(44/42) MAPK in ANG II-induced contraction of rat tonic gastrointestinal smooth muscles

We examined the role of mitogen-activated protein kinase (p(44/42) MAPK) in ANG II-induced contraction of lower esophageal sphincter (LES) and internal anal sphincter (IAS) smooth muscles. Studies were performed in the isolated smooth muscles and cells (SMC). ANG II-induced changes in the levels of phosphorylation of different signal transduction and effector proteins were determined before and after selective inhibitors. ANG II-induced contraction of the rat LES and IAS SMC was inhibited by genistein, PD-98059 [a specific inhibitor of MAPK kinases (MEK 1/2)], herbimycin A (a pp60(c-src) inhibitor), and antibodies to pp60(c-src) and p(120) ras GTPase-activating protein (p(120) rasGAP). ANG II-induced contraction of the tonic smooth muscles was accompanied by an increase in tyrosine phosphorylation of p(120) rasGAP. These were attenuated by genistein but not by PD-98059. ANG II-induced increase in phosphorylations of p(44/42) MAPKs and caldesmon was attenuated by both genistein and PD-98059. We conclude that pp60(c-src) and p(44/42) MAPKs play an important role in ANG II-induced contraction of LES and IAS smooth muscles.

ET-1 stimulates ERK signaling pathway through sequential activation of PKC and Src in rat myometrial cells

In this study, we analyzed in rat myometrial cells the signaling pathways involved in the endothelin (ET)-1-induced extracellular signal-regulated kinase (ERK) activation required for the induction of DNA synthesis. We found that inhibition of protein kinase C (PKC) by Ro-31-8220 abolished ERK activation. Inhibition of phospholipase C (PLC) by U-73122 or of phosphoinositide (PI) 3-kinase by wortmannin partially reduced ERK activation. A similar partial inhibition was observed after treatment with pertussis toxin or PKC downregulation by phorbol ester treatment. The effect of wortmannin was additive with that produced by PKC downregulation but not with that due to pertussis toxin. These results suggest that both diacylglycerol-sensitive PKC, activated by PLC products, and diacylglycerol-insensitive PKC, possibly activated by a G(i)-PI 3-kinase-dependent process, are involved in ET-1-induced ERK activation. These two pathways were found to be activated mainly through the ET(A) receptor subtype. ET-1 and phorbol ester stimulated Src activity in a PKC-dependent manner, both responses being abolished in the presence of Ro-31-8220. Inhibition of Src kinases by PP1 abrogated phorbol ester- and ET-1-induced ERK activation. Finally, ET-1 activated Ras in a PP1- and Ro-31-8220-sensitive manner. Altogether, our results indicate that ET-1 induces ERK activation in rat myometrial cells through the sequential stimulation of PKC, Src, and Ras.

ERK MAP kinases regulate smooth muscle contraction in ovine uterine artery: effect of pregnancy

The present study investigated the potential role of extracellular signal-regulated kinase (ERK) in uterine artery contraction and tested the hypothesis that pregnancy upregulated ERK-mediated function in the uterine artery. Isometric tension in response to phenylephrine (PE), serotonin (5-HT), phorbol 12,13-dibutyrate (PDBu), and KCl was measured in the ring preparation of uterine arteries obtained from nonpregnant and near-term (140 days gestation) pregnant sheep. Inhibiting ERK activation with PD-98059 did not change the KCl-evoked contraction but significantly inhibited the contraction to 5-HT in both nonpregnant and pregnant uterine arteries. PD-98059 did not affect PE-induced contraction in the uterine arteries of nonpregnant sheep but significantly decreased it in the uterine arteries of pregnant sheep. In accordance, PE stimulated activation of ERK in uterine arteries of pregnant sheep, which was blocked by PD-98059. PD-98059-mediated inhibition of the PE-induced contraction was associated with a decrease in both intracellular Ca(2+) concentration and Ca(2+) sensitivity of contractile proteins in the uterine arteries of pregnant sheep. PDBu-mediated contraction was significantly less in pregnant than in nonpregnant uterine arteries. PD-98059 had no effect on PDBu-induced contraction in nonpregnant but significantly increased it in pregnant uterine arteries. In addition, PD-98059 significantly enhanced PDBu-stimulated protein kinase C activity. The results indicate that ERK plays an important role in the regulation of uterine artery contractility, and its effect is agonist dependent. More importantly, pregnancy selectively enhances the role of ERK in alpha(1)-adrenoceptor-mediated contractions and its effect in suppressing protein kinase C-mediated contraction in the uterine artery.

Characterising the corticotropin-releasing hormone (CRH) receptors mediating CRH and urocortin actions during human pregnancy and labour

The mechanism of human labour remains unresolved. One of the most important regulatory signals, however, appears to be corticotropin-releasing hormone (CRH), a hypothalamic peptide that controls the body's response to stress, which is also produced by the placenta and intrauterine tissues during pregnancy. CRH belongs to a family of peptides that includes urocortin, which shares sequence homology with CRH and is also expressed by the placenta and intrauterine tissues. During human pregnancy circulating CRH appears to have five main target tissues: the myometrium, the placenta, the fetal membranes, the fetal adrenal cortex and the vasculature. In these tissues CRH plays a role in the control of myometrial contractility,placenta vasodilation, peptide and prostaglandin production and adrenal steroidogenesis and probably many more, yet unidentified processes. The actions of CRH in these tissues are mediated via specific G-protein coupled membrane-bound receptors. These receptors have different functional characteristics, depending on where they are expressed and on the stage of pregnancy. In addition, their function depends upon other intracellular signals via communication between signalling cascades. These findings led us to propose a hypothesis for a dual role of CRH and other CRH-like peptides during pregnancy and labour.

Phorbol ester differentially regulates oxytocin receptor binding activity in hypothalamic cultured neurons and astrocytes

Hypothalamic cultured neurons and astrocytes were used to investigate the cellular mechanisms underlying the oxytocin receptor-mediated downregulation through a possible involvement of protein kinase C (PKC). For this purpose, the effects of PKC activators, inhibitor and of OT on OT receptor binding activity were compared in both cultures. In neurons, phorbol-myristate-acetate (PMA), a potent PKC activator, increased the binding of an OT receptor antagonist whereas in astrocytes, a decrease was observed. Pre-treatment of the cells with bisindolylmaleimide (10(-4) M), a PKC inhibitor, prevented the PMA-induced up- and downregulation. In contrast, receptor downregulation resulting from treatment of both cells with OT (10(-9) M) was not affected by the PKC inhibitor. On the other hand, when PMA (10(-7) M) was tested along with OT (10(-9) M), a subsequent decrease in ligand binding was observed in astrocytes. In neurons, PMA attenuated the OT-induced downregulation. Structural analysis of neuron and astrocyte OT receptor mRNA by RT-PCR, subcloning and sequencing, demonstrated identical sequence to rat uterine receptor. In conclusion, these data suggest that activation of PKC has opposite effect on OT receptor binding activity in neurons and astrocytes but they do not support the involvement of PKC in the OT-induced downregulation.

Mitogen-activated protein kinase inhibitors suppress prostaglandin F(2alpha)-induced myosin-light chain phosphorylation and contraction in iris sphincter smooth muscle

The purpose of this study was to investigate the potential role of mitogen-activated protein (MAP) kinase in contraction by monitoring MAP kinase phosphorylation (activation) and contraction during agonist stimulation of cat iris sphincter smooth muscle. Changes in tension in response to prostaglandin F(2alpha), latanoprost, a prostaglandin F(2alpha) analog used as an anti-glaucoma drug, and carbachol were recorded isometrically, and MAP kinase activation was monitored by Western blot using a phosphospecific p42/p44 MAP kinase antibody. We found that treatment of the muscle with 2'-Amino-3'-methoxyflavone (PD98059) (10 microM), a specific inhibitor of MAP kinase kinase (MEK), inhibited significantly prostaglandin F(2alpha)- and latanoprost-induced phosphorylation and contraction, but had little effect on those evoked by carbachol. Prostaglandin F(2alpha) increased MAP kinase phosphorylation in a concentration-dependent manner with EC(50) value of 1.1 x 10(-8) M and increased contraction with EC(50) of 0.92 x 10(-9) M. The MAP kinase inhibitors PD98059, Apigenin and 1,4-Diamino-2,3-dicyano-1, 4bis(2-aminophenylthio)butadiene (UO126) inhibited prostaglandin F(2alpha)-induced contraction in a concentration-dependent manner with IC(50) values of 2.4, 3.0 and 4.8 microM, respectively. PD98059 had no effect on prostaglandin F(2alpha)- or on carbachol-stimulated inositol-1,4,5-trisphosphate (IP(3)) production. In contrast, the MAP kinase inhibitor inhibited prostaglandin F(2alpha)-induced myosin-light chain (MLC) phosphorylation, but had no effect on that of carbachol. N-[2-(N-(4-Chloro-cinnamyl)-N-methylaminomethyl)phenyl]-N-[2- hydroxyethyl]-4-methoxybenzenesulfonamide (KN-93) (10 microM), a Ca(2+)-calmodulin-dependent protein kinase inhibitor, and Wortmannin (10 microM), an MLC kinase inhibitor, inhibited significantly (by 80%) prostaglandin F(2alpha)- and carbachol-induced contraction. It can be concluded that in this smooth muscle p42/p44 MAP kinases are involved in the mechanism of prostaglandin F(2alpha)-, but not in that of carbachol, induced contraction. In addition, these data clearly indicate that the stimulation of the iris sphincter with prostaglandin F(2alpha) and carbachol activate two distinct pathways, the MAP kinase pathway and the Ca(2+) mobilization pathway.

Pharmacology of oxytocin and prostaglandins

Significant advances have been made in the last 20 years in our knowledge about the subcellular events occurring during myometrial contractions and cervical ripening and in the mechanism of action of oxytocin and prostaglandins. These advances have been instrumental in furthering our understanding of the mechanism of action of inhibitors of uterine contractility and have opened the door to clinical trials of agents such as specific COX-II inhibitors that may have the potential to inhibit labor without serious maternal or fetal side effects. There is still a long way to go, however, before all the complex actions of oxytocin and prostaglandins can be understood at a subcellular level, particularly the mechanism of action of prostaglandins in the process of cervical ripening.

Pharmacologic characterization of the oxytocin receptor in human uterine smooth muscle cells

[(3)H]-oxytocin was used to characterize the oxytocin receptor found in human uterine smooth muscle cells (USMC). Specific binding of [(3)H]-oxytocin to USMC plasma membranes was dependent upon time, temperature and membrane protein concentration. Scatchard plot analysis of equilibrium binding data revealed the existence of a single class of high-affinity binding sites with an apparent equilibrium dissociation constant (K(d)) of 0.76 nM and a maximum receptor density (B(max)) of 153 fmol mg(-1) protein. The Hill coefficient (n(H)) did not differ significantly from unity, suggesting binding to homogenous, non-interacting receptor populations. Competitive inhibition of [(3)H]-oxytocin binding showed that oxytocin and vasopressin (AVP) receptor agonists and antagonists displaced [(3)H]-oxytocin in a concentration-dependent manner. The order of potencies for peptide agonists and antagonists was: oxytocin>[Asu(1,6)]-oxytocin>AVP= atosiban>d(CH(2))(5)Tyr(Me)AVP>[Thr(4),Gly(7)]-oxytocin>dDAVP, and for nonpeptide antagonists was: L-371257>YM087>SR 49059>OPC-21268>SR 121463A>OPC-31260. Oxytocin significantly induced concentration-dependent increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) and hyperplasia in USMC. The oxytocin receptor antagonists, atosiban and L-371257, potently and concentration-dependently inhibited oxytocin-induced [Ca(2+)](i) increase and hyperplasia. In contrast, the V(1A) receptor selective antagonist, SR 49059, and the V(2) receptor selective antagonist, SR 121463A, did not potently inhibit oxytocin-induced [Ca(2+)](i) increase and hyperplasia. The potency order of antagonists in inhibiting oxytocin-induced [Ca(2+)](i) increase and hyperplasia was similar to that observed in radioligand binding assays. In conclusion, these data provide evidence that the high-affinity [(3)H]-oxytocin binding site found in human USMC is a functional oxytocin receptor coupled to [Ca(2+)](i) increase and cell growth. Thus human USMC may prove to be a valuable tool in further investigation of the physiologic and pathophysiologic roles of oxytocin in the uterus. British Journal of Pharmacology (2000) 129, 131 - 139

Oxytocin activates mitogen-activated protein kinase and up-regulates cyclooxygenase-2 and prostaglandin production in human myometrial cells

OBJECTIVE

The objective of our study was to test the hypothesis that oxytocin promotes prostaglandin production by up-regulating cyclooxygenase-2 via activation of mitogen-activated protein kinase cascade in human myometrial cells.

STUDY DESIGN

Confluent cultures of human myometrial cells obtained from uterine specimens of premenopausal women undergoing hysterectomy were serum starved for 48 hours before oxytocin stimulation. Prostacyclin levels, as 6-keto-prostaglandin F(1) (alpha), were measured by radioimmunoassay, and the cellular cyclooxygenase-2 protein content was determined by Western blot. Mitogen-activated protein kinase activity was assessed by measuring the phosphorylation of myelin basic protein.

RESULTS

In a time- and dose-dependent manner oxytocin promoted prostacyclin production in human myometrial cells. Maximal responses were observed after 8 hours of stimulation at a dose of 100 nmol/L. This effect was mainly due to the expression of cyclooxygenase-2 protein. Within 5 minutes oxytocin significantly stimulated mitogen-activated protein kinase, as compared with the expression in untreated controls. The maximal increase in enzyme activity (2.5-fold) was obtained at 45 minutes. A selective inhibitor of mitogen-activated protein kinase activation (PD98059), as well as herbimycin, a tyrosine kinase inhibitor, and the transcriptional blocker actinomycin D, suppressed oxytocin-induced cyclooxygenase-2 expression and prostacyclin production. The stimulatory action of oxytocin was also sensitive to inhibition by pertussis toxin but appeared to be independent of protein kinase C activation.

CONCLUSION

Our data indicate a largely unrecognized signal transduction mechanism for oxytocin, involving G-protein-coupled activation of mitogen-activated protein kinase and cyclooxygenase-2 gene expression, leading to increased prostaglandin production in human myometrial cells. This signaling pathway complements the rapid activation of the phosphoinositide cycle and may be responsible for sustained release of prostaglandins in uterine tissues, promoting labor and parturition.

Mitogen-activated protein kinase cascade is involved in endothelin-1-induced rat puerperal uterine contraction

The regulation of mitogen-activated protein (MAP) kinase by endothelin-1 (ET-1) in cultured rat puerperal uterine myometrial cells was investigated. ET-1 caused the rapid stimulation of MAP kinase activity. ET-1-induced MAP kinase activation is neither extracellular Ca2+- nor intracellular Ca2+-dependent. ET-1 stimulation also led to an increase in phosphorylation of son-of-sevenless (SOS), and transfection of dominant negative SOS attenuated the ET-1-induced MAP kinase activity. Phorbol-12-myristate 13-acetate (PMA) also induced the MAP kinase activity, but pretreatment of the cultured cells with PMA, to down-regulate protein kinase C (PKC), did not abolish the activation of MAP kinase by ET-1. In addition, down-regulation of PKC had no effect on ET-1-induced SOS phosphorylation. Pertussis toxin, which inactivates Gi/Go proteins, blocked the ET-1-induced MAP kinase activation but not the PMA-induced MAP kinase activation. The results suggested that MAP kinase is acutely activated by ET-1 through a pertussis toxin-sensitive G protein and SOS, not through the PMA-sensitive PKC. In addition, although reverse-transcriptase PCR assays detected messenger RNA for both ET- 1 receptor subtypes in cultured rat puerperal uterine myometrial cells, ET-1-induced MAP kinase activity and uterine contraction were blocked by treatment with BQ485, an antagonist selective for an ET type A receptor (but not by BQ788, an ET type B receptor antagonist). Ritodrine, which is known to relax uterine muscle contraction, attenuated ET-1-induced MAP kinase activity. We further examined the role of MAP kinase pathway in uterine contraction using an inhibitor of MEK activity, PD098059. This inhibitor completely inhibited the ET-1-induced MAP kinase activation and partially, but significantly, inhibited the ET-1-induced uterine contraction. These results indicate that ET-1-induced MAP kinase signaling cascade may play an important role in the ET-1-induced uterine contraction.

MAP kinases and vascular smooth muscle function

The mitogen-activated protein (MAP) kinase family members are ubiquitously expressed protein kinases activated in response to a variety of extracellular stimuli and shown to be involved in cell growth, transformation, differentiation and apoptosis. MAP kinases have been implicated in both growth and apoptosis of vascular smooth muscle cells (VSMC) which suggests that they play important roles in cardiovascular diseases such as essential hypertension, atherosclerosis, and restenosis followed angioplasty. The MAP kinases are themselves components of specific kinase cascades characterized by activation by specific stimuli, families of related serine and threonine kinases and downstream substrates that include other kinases, transcription factors, membrane receptors and other cell mediators. Cross-talk among the different MAP kinases results in direct modulation of signal transduction. In addition, increased expression and activation of MAP kinase phosphatases plays an important role in MAP kinase inactivation. Our laboratory has used angiotensin II (AngII), a potent activator of all MAP kinases in VSMC, to study mechanisms by which MAP kinases are regulated by vasoactive peptides. In this review, we describe the mechanisms by which AngII activates MAP kinases, and potential roles for MAP kinases in AngII-dependent effects on VSMC function.

A role for MAP kinase in differentiated smooth muscle contraction evoked by alpha-adrenoceptor stimulation

The purpose of this study was to investigate the potential role of mitogen-activated protein (MAP) kinase in smooth muscle contraction by monitoring MAP kinase activation, caldesmon phosphorylation, and contractile force during agonist stimulation. Isometric tension in response to KCl and phenylephrine (PE) was measured from strips of ferret aorta. MAP kinase activation was monitored by Western blot using a phosphospecific p44/p42 MAP kinase antibody. Caldesmon phosphorylation was assessed using specific phosphocaldesmon antibodies. We report here that treatment of smooth muscle strips with PD-098059, a specific inhibitor of MAP kinase kinase, did not detectably modify the KCl-evoked contraction but significantly inhibited the contraction to PE in the absence of extracellular Ca2+. In this experimental condition, where the contraction occurs in the absence of increases in 20-kDa myosin light chain phosphorylation, PD-098059 also inhibited significantly MAP kinase and caldesmon phosphorylation. Collectively, these results demonstrate a direct cause-and-effect relationship between MAP kinase activation and Ca2+-independent smooth muscle contraction and support the concept of caldesmon phosphorylation as the missing link between both events.

Norepinephrine stimulates mitogen-activated protein kinase activity in GT1-1 gonadotropin-releasing hormone neuronal cell lines

The GT1-1 GnRH neuronal cell lines exhibit highly differentiated properties of GnRH neurons. We have used GT1-1 cells to study the roles of norepinephrine (NE), membrane depolarization, calcium influx, and phorbol esters in the regulation of mitogen-activated protein (MAP) kinase. NE, which is known to stimulate the release of GnRH, induced MAP kinase activity, the tyrosine phosphorylation of MAP kinase, and MAP kinase kinase activity. Forskolin led to activation of MAP kinase comparable with that induced by NE, and a selective inhibitor of cAMP-dependent protein kinase, H8, attenuated the NE-induced activation of MAP kinase. On the other hand, elimination of extracellular calcium by EGTA completely blocked NE-induced tyrosine phosphorylation of MAP kinase, and a selective inhibitor of calcium/calmodulin-dependent protein kinase, KN-62, attenuated the NE-induced activation of MAP kinase. Furthermore, depolarization of GT1-1 cells with 75 mM KCl, 10 microM BayK 8644, or 1 microM calcium ionophore (A23187) induced rapid tyrosine phosphorylation of MAP kinase. The omission of calcium from the extracellular medium completely abolished these effects of tyrosine phosphorylation of MAP kinase. Phorbol 12-myristate 13-acetate (PMA) also induced MAP kinase activity, but pretreatment of the cultured cells with PMA to down-regulate protein kinase C did not abolish the activation of MAP kinase by NE. In addition, although phosphorylation of Raf-1 kinase was stimulated by PMA, this phosphorylation was not induced by either NE or A23187. These results demonstrate that NE activates MAP kinase directly in GT1-1 cells, and that the effect of NE is mediated by increase in the cAMP level and by calcium influx, but not by PMA-sensitive protein kinase C or Raf-1 kinase.

Role of mitogen-activated protein kinase pathway in prostaglandin F2alpha-induced rat puerperal uterine contraction

In this study, prostaglandin (PG) F2alpha was found to activate mitogen-activated protein (MAP) kinase and MAP kinase kinase (MEK) in cultured rat puerperal uterine myometrial cells. PGF2alpha stimulation also led to an increase in phosphorylation of raf-1, son of sevenless (SOS), and Shc. Furthermore, we examined the mechanism by which PGF2alpha induced MAP kinase phosphorylation. Both pertussis toxin (10 ng/ml), which inactivates Gi/Go proteins, and expression of a peptide derived from the carboxyl terminus of the beta-adrenergic receptor kinase 1 (betaARK1), which specifically blocks signaling mediated by the betagamma subunits of G proteins, blocked the PGF2alpha-induced activation of MAP kinase. Ritodrine (1 microM), which is known to relax uterine muscle contraction, attenuated PGF2alpha-induced tyrosine phosphorylation of MAP kinase. Moreover, to examine the role of MAP kinase pathway in uterine contraction, an inhibitor of MEK activity, PD098059, was used. Although MEK inhibitor had no effect on PGF2alpha-induced calcium mobilization, this inhibitor partially inhibited PGF2alpha-induced uterine contraction. These results provide evidence that PGF2alpha stimulates the MAP kinase signaling pathway in cultured rat puerperal uterine myometrial cells through Gbetagamma protein, suggesting that this new pathway may play an important role in the biological action of PGF2alpha on these cells.