A critical role for PKC zeta in endothelin-1-induced uterine contractions at the end of pregnancy

Integrative analysis of noncoding mutations identifies the druggable genome in preterm birth

Preterm birth affects ~10% of pregnancies in the US. Despite familial associations, identifying at-risk genetic loci has been challenging. We built deep learning and graphical models to score mutational effects at base resolution via integrating the pregnant myometrial epigenome and large-scale patient genomes with spontaneous preterm birth (sPTB) from European and African American cohorts. We uncovered previously unidentified sPTB genes that are involved in myometrial muscle relaxation and inflammatory responses and that are regulated by the progesterone receptor near labor onset. We studied genomic variants in these genes in our recruited pregnant women administered progestin prophylaxis. We observed that mutation burden in these genes was predictive of responses to progestin treatment for preterm birth. To advance therapeutic development, we screened ~4000 compounds, identified candidate molecules that affect our identified genes, and experimentally validated their therapeutic effects on regulating labor. Together, our integrative approach revealed the druggable genome in preterm birth and provided a generalizable framework for studying complex diseases.

The Link Between Human Menstruation and Placental Delivery: A Novel Evolutionary Interpretation: Menstruation and fetal placental detachment share common evolved physiological processes dependent on progesterone withdrawal

A new interpretation of human menstruation is presented, resulting from a cross-disciplinary investigation of evolution, developmental biology, and physiology. A process evolutionarily associated with childbirth expresses itself as menstruation in women for whom frequent and continual failure to conceive has become the default situation. In humans and Old World primates, contractile uterine spiral arterioles evolved as the complement of the highly invasive hemochorionic placenta and is the selected phenotype. Placental progesterone withdrawal during the last stage of birth leads to arrested blood flow through maternal spiral arterioles, allowing detachment of the deciduous placenta with minimal maternal hemorrhage. In nonpregnant females, progesterone withdrawal from a degenerating corpus luteum initiates menstruation and stops blood flow through uterine spiral arterioles. Both events share similar physiological mechanisms and sequences. This explanation may improve our understanding of a recurrent event experienced by half of the human population and for a quarter of their adult reproductive life.

Control of endothelin-a receptor expression by progesterone is enhanced by synergy with Gata2

The endothelin-A receptor (Ednra) is involved in several physiological, pathological, and developmental pathways. Known for its function in vasoconstriction after being activated by endothelin-1, Ednra also controls cephalic neural crest cell development and appears to play a role in several pathologies, including cancer and periodontitis. However, the mechanisms regulating Ednra expression have not been identified despite its important functions. In this study, we investigated the role progesterone plays in Ednra gene expression in vivo and in vitro. In mice, pregnancy promotes Ednra expression in the heart, kidney, lung, uterus, and placenta, and the up-regulation is mediated by progesterone. We determined that the conserved region between -5.7 and -4.2 kb upstream of the mouse Ednra gene is necessary for the progesterone response. We also found that progesterone mediates Ednra activation through progesterone receptor B activation by its recruitment to PRE6, one of the 6 progesterone response elements found in that locus. However, gene activation by means of a GATA2 site was also necessary for the progesterone response. The Gata2 transcription factor enhances the progesterone response mediated by the progesterone receptor B. Together these results indicate that progesterone regulates Ednra expression by synergizing with Gata2 activity, a previously unknown mechanism. This mechanism may have an impact on pathologies involving the endothelin signaling.

Isoform α of PKC may contribute to the maintenance of pregnancy myometrial quiescence in humans

We postulate that protein kinase C α (PKCα) may contribute to the maintenance of pregnancy myometrial quiescence in humans. We studied the changes in myometrial PKCα gene products (messenger RNA [mRNA] and protein) in 4 groups of women: preterm not in labor (PT-NL), preterm in labor (PT-L), term not in labor (T-NL), and term in labor (T-L). The degree of PKCα activation was studied by comparing the levels of particulate (active) PKCα with the total PKCα protein levels and by measuring PKCα activity in the cytosolic and particulate fractions. Protein kinase Cα abundance (mRNA and protein) did not increase during myometrial quiescence (PT-NL), whereas the level of PKCα activity significantly increased during quiescence. The activity of PKCα significantly decreased in the T-NL, T-L, and PT-L groups. These findings suggest that PKCα plays a significant role in the maintenance of myometrial quiescence and that PKCα activity must decrease at the end of pregnancy allowing myometrial activation. Additionally, our data demonstrate an association between reduced PKCα activity and preterm labor, which merits further investigation.

Thrombin promotes actin stress fiber formation in RPE through Rho/ROCK-mediated MLC phosphorylation

The retinal pigment epithelium (RPE) forms the outer blood-retina barrier (BRB). Most retinal diseases involve BRB breakdown, whereupon thrombin contained in serum directly contacts the RPE. Thrombin is known to promote actin stress fiber formation, an important determinant in eye diseases involving the epithelial-mesenchymal transition (EMT) and migration of RPE cells, such as proliferative vitreoretinopathy. We analyzed thrombin effect on signaling pathways leading to myosin light chain (MLC) phosphorylation and actin stress fiber formation in primary cultures of rat RPE cells, in order to support a role for thrombin in RPE transdifferentiation. MLC phosphorylation was measured by Western blot; actin cytoskeleton was visualized using immunofluorescent phalloidin, and Rho GTPase activation was assessed by ELISA. We showed that thrombin/PAR-1 induces the time- and dose-dependent phosphorylation of MLC through the activation of Rho/ROCK and myosin light chain kinase (MLCK). ROCK increased phospho-MLC by phosphorylating MLC and by inhibiting MLC phosphatase. Thrombin effect was abolished by the ROCK inhibitor Y-27632, whereas MLCK inhibitor ML-7 and PLC-β inhibitor U73122 attenuated MLC phosphorylation by ≈50%, suggesting the activation of MLCK by PLC-β-mediated calcium increase. Additionally, thrombin-induced MLC phosphorylation was blocked by the inhibitory PKCζ pseudosubstrate, wortmannin, and LY294002, indicating IP(3)/PKCζ involvement in the control of MLC phosphorylation. Moreover, we demonstrated that thrombin effect on MLC induces actin stress fiber formation, since this effect was prevented by inhibiting the pathways leading to MLC phosphorylation. We conclude that thrombin stimulation of MLC phosphorylation and actin stress fiber formation may be involved in thrombin-induced RPE cell transformation subsequent to BRB dysfunction.

A genetic association study of maternal and fetal candidate genes that predispose to preterm prelabor rupture of membranes (PROM)

OBJECTIVE

We sought to determine whether maternal/fetal single-nucleotide polymorphisms (SNPs) in candidate genes are associated with preterm prelabor rupture of membranes (pPROM).

STUDY DESIGN

A case-control study was conducted in patients with pPROM (225 mothers and 155 fetuses) and 599 mothers and 628 fetuses with a normal pregnancy; 190 candidate genes and 775 SNPs were studied. Single locus/haplotype association analyses were performed; false discovery rate was used to correct for multiple testing (q* = 0.15).

RESULTS

First, a SNP in tissue inhibitor of metalloproteinase 2 in mothers was significantly associated with pPROM (odds ratio, 2.12; 95% confidence interval, 1.47-3.07; P = .000068), and this association remained significant after correction for multiple comparisons. Second, haplotypes for Alpha 3 type IV collagen isoform precursor in the mother were associated with pPROM (global P = .003). Third, multilocus analysis identified a 3-locus model, which included maternal SNPs in collagen type I alpha 2, defensin alpha 5 gene, and endothelin 1.

CONCLUSION

DNA variants in a maternal gene involved in extracellular matrix metabolism doubled the risk of pPROM.

Cellulite: Is there a role for injectables?

BACKGROUND

Cellulite describes the cutaneous dimpling of the thighs, buttocks, and hips that is seen predominately in women. Current evidence suggests that structural differences in fat architecture between the sexes account for its appearance. Mesotherapy, a method of delivering medication locally with the use of numerous cutaneous injections, has recently become a popular method to purportedly treat the condition.

METHODS

An overview of cellulite and adipocyte physiology, with a literature review and appraisal of compounds commonly used in mesotherapy.

RESULTS

Experimental studies using individual mesotherapy ingredients for other conditions suggest a number of mechanisms, including lipolysis, disrupting connective tissue and augmenting circulation, which may theoretically improve cellulite. Peer-reviewed studies have not evaluated whether these effects translate clinically.

CONCLUSIONS

Until further studies are performed, patients considering mesotherapy for cellulite must be aware that the substances currently being injected to treat this cosmetically disturbing, but medically benign, condition have not been thoroughly evaluated for safety or efficacy.

Modulation of human uterine smooth muscle cell collagen contractility by thrombin, Y-27632, TNF alpha and indomethacin

BACKGROUND

Preterm labour occurs in approximately 10% of pregnancies and is a major cause of infant morbidity and mortality. However, the pathways involved in regulating contractility in normal and preterm labour are not fully elucidated. Our aim was to utilise a human myometrial contractility model to investigate the effect of a number of uterine specific contractility agents in this system. Therefore, we investigated the contractile response of human primary uterine smooth muscle cells or immortalised myometrial smooth muscle cells cultured within collagen lattices, to known mediators of uterine contractility, which included thrombin, the ROCK-1 inhibitor Y-27632, tumour necrosis factor alpha (TNF alpha) and the non-steroidal anti-inflammatory indomethacin.

METHODS

Cell contractility was calculated over time, with the collagen gel contraction assay, utilising human primary uterine smooth muscle cells (hUtSMCs) and immortalised myometrial smooth muscle cells (hTERT-HM): a decrease in collagen gel area equated to an increase in contractility. RNA was isolated from collagen embedded cells and gene expression changes were analysed by real time fluorescence reverse transcription polymerase chain reaction. Scanning electron and fluorescence microscopy were employed to observe cell morphology and cell collagen gel interactions. Statistical analysis was performed using ANOVA followed by Tukey's post hoc tests.

RESULTS

TNF alpha increased collagen contractility in comparison to the un-stimulated collagen embedded hUtSMC cells, which was inhibited by indomethacin, while indomethacin alone significantly inhibited contraction. Thrombin augmented the contractility of uterine smooth muscle cell and hTERT-HM collagen gels, this effect was inhibited by the thrombin specific inhibitor, hirudin. Y-27632 decreased both basal and thrombin-induced collagen contractility in the hTERT-HM embedded gels. mRNA expression of the thrombin receptor, F2R was up-regulated in hUtSMCs isolated from collagen gel lattices, following thrombin-stimulated contractility.

CONCLUSION

TNF alpha and thrombin increased uterine smooth muscle cell collagen contractility while indomethacin had the opposite effect. Thrombin-induced collagen contractility resulted in F2R activation which may in part be mediated by the ROCK-1 pathway. This study established the in vitro human myometrial model as a viable method to assess the effects of a range of uterotonic or uterorelaxant agents on contractility, and also permits investigation of the complex regulatory pathways involved in mediating myometrial contractility at labour.

Surfactant protein A signaling pathways in human uterine smooth muscle cells

The present study investigated the ability of surfactant associated protein A1 (SFTPA1), a major component of lung surfactant, to bind and serve as a signal in human cultured myometrial cells. By using ligand blot analysis with 125I-SFTPA1, we consistently identified two myometrial SFTPA1 interacting proteins (55 and 200 kDa). We found that the SFTPA1 immunoreactive protein was present in myometrial cells. We also showed by indirect immunofluorescence the nuclear translocation of RELA (also known as NFkappaB p65 subunit) after activation of myometrial cells by SFTPA1. Neutralization of TLR4 did not reverse this effect. Moreover, SFTPA1 rapidly activated mitogen-activated protein kinase 1/3 (MAPK1/3) and protein kinase C zeta (PRKCZ). The prolonged treatment of myometrial cells with SFTPA1 upregulated PTGS2 (COX2) protein levels. We next evaluated whether SFTPA1 affected the actin dynamic. Stimulation of myometrial cells with SFTPA1 markedly enhanced the intensity of the filamentous-actin pool stained with fluorescein isothiocyanate-phalloidin. Inhibition of PRKC or Rho-associated, coiled-coil containing protein kinase 1 (ROCK) reduced the SFTPA1-mediated stress fiber formation. Our data support the hypothesis that human myometrial cells express functional SFTPA1 binding sites and respond to SFTPA1 to initiate activation of signaling events related to human parturition.

Endothelin-1 signalling in vascular smooth muscle: pathways controlling cellular functions associated with atherosclerosis

Atherosclerosis is the primary ischaemic vascular condition underlying a majority of cardiovascular disease related deaths. Endothelin-1 is a vasoactive peptide agent upregulated in atherosclerosis and in conjunction with its G protein-coupled receptors exerts diverse actions on all cells of the vasculature in particular vascular smooth muscle cells (VSMC). The effects of endothelin-1 include cell proliferation, migration and contraction, and the induction of extracellular matrix components and growth factors. VSMC as the major component of the neointima in atherosclerotic plaques accordingly play a key role in atherogenesis. In this review we examine classic and novel signalling pathways activated by endothelin-1 in VSMC (including phospholipase C, adenylate cyclase, Rho kinase, transactivation of receptor tyrosine kinases, mitogen activated protein kinase cascades and beta-arrestin) and their likely impact on the development and progression of atherosclerosis.

Protein kinase C-zeta regulation of GLUT4 translocation through actin remodeling in CHO cells

Actin remodeling plays a crucial role in insulin-induced translocation of glucose transporter 4 (GLUT4) from the cytoplasm to the plasma membrane and subsequent glucose transport. Protein kinase C (PKC) zeta has been implicated in this translocation process, although the exact mechanism remains unknown. In this study, we investigated the effect of PKCzeta on actin cytoskeleton and translocation of GLUT4 in CHO-K1 cells expressing myc-tagged GLUT4. Insulin stimulated the phosphorylation of PKCzeta at Thr410 with no apparent effect on its protein expression. Moreover, insulin promoted colocalization of PKCzeta and actin that could be abolished by Latrunculin B. The overexpression of PKCzeta mimicked the insulin-induced change in actin cytoskeleton and translocation of GLUT4. These effects were also completely abrogated by Latrunculin B treatment. Using cell-permeable pseudosubstrate (PS) inhibitor of PKCzeta, the response to insulin could be alleviated. Our results strongly suggest that PKCzeta mediates the stimulatory effect of insulin on GLUT4 translocation through its interaction with actin cytoskeleton.

Protein kinase C and human uterine contractility

Abnormalities in uterine contractility are thought to contribute to several clinical problems, including preterm labor. A better understanding of the mechanisms controlling uterine activity would make it possible to propose more appropriate and effective management practices than those currently in use. Recent advances point to a role of the protein kinase C (PRKC) family in the regulation of uterine smooth muscle contraction at the end of pregnancy. In this review, we highlight recent work that explores the involvement of individual PRKC isoforms in cellular process, with an emphasis on the properties of PRKCZ isoform.

Exogenous sphingosine 1-phosphate and sphingosine kinase activated by endothelin-1 induced myometrial contraction through differential mechanisms

Sphingosine 1-phosphate (S1P), a bioactive sphingolipid involved in diverse biological processes, is generated by sphingosine kinase (SphK) and acts via intracellular and/or extracellular mechanisms. We used biochemical, pharmacological, and physiological approaches to investigate in rat myometrium the contractile effect of exogenous S1P and the possible contribution of SphK in endothelin-1 (ET-1)-mediated contraction. S1P stimulated uterine contractility (EC50 = 1 μM and maximal response = 5 μM) by a pertussis toxin-insensitive and a phospholipse C (PLC)-independent pathway. Phosphorylated FTY720, which interacts with all S1P receptors, except S1P2 receptors, failed to mimic S1P contractile response, indicating that the effects of S1P involved S1P2 receptors that are expressed in myometrium. Contraction mediated by S1P and ET-1 required extracellular calcium and Rho kinase activation. Inhibition of SphK reduced ET-1-mediated contraction. ET-1, via ETA receptors coupled to pertussis toxin-insensitive G proteins, stimulated SphK1 activity and induced its translocation to the membranes. Myometrial contraction triggered by ET-1 is consecutive to the sequential activation of PLC, protein kinase C, SphK1 and Rho kinase. Prolonged exposure of the myometrium to S1P downregulated S1P2 receptors and abolished the contraction induced by exogenous S1P. However, in these conditions, the tension triggered by ET-1 was not reduced, indicating that SphK activated by ET-1 contributed to its contractile effect via a S1P2 receptor-independent process. Our findings demonstrated that exogenous S1P and SphK activity regulated myometrial contraction and may be of physiological relevance in the regulation of uterine motility during gestation and parturition.

Atypical protein kinase C in glucose metabolism

Type 2 diabetes mellitus is a multigenic disease with evident genetic predisposition, and complex pathogenesis in which environmental and genetic factors interact. The disorder of body utilization glucose is a crucial reason for causing diabetes. Atypical PKCs, belonging to Ser/Thr protein kinase, have many important biological functions in vivo, and may be involved in the pathogenesis of diabetes mellitus. APKCs participate in glucose metabolism by regulating glucose transport and absorption, glycogen synthesis, and insulin secretion. The exact mechanism by which aPKCs participate in glucose metabolism remains unclear. So far, the clarification of which will be helpful for the prevention and cure of type 2 diabetes.

Natural nutrient mixture effectively reduces collagen matrix contraction driven by human uterine smooth muscle cells

AIM

Abnormal uterine myometrial contractility causes preterm delivery, contributing to perinatal morbidity and mortality. Disturbances in hormonal regulation and inflammation-related processes have been attributed a role in the pathophysiological mechanisms of uterine contractility. We investigated the effects of natural nutrients on uterine tissue contractility in vitro.

METHODS

We used an in vitro model of collagen I gel contraction driven by embedded cultured human uterine smooth muscle cells (SMC). The effects of tested compounds were evaluated using their capacity to affect gel contraction (measured by reduction in gel area during 24-h incubation in serum free medium). Cellular expression of matrix metalloproteinases (MMP) was followed by gel zymography.

RESULTS

Collagen gel contraction driven by uterine SMC was significantly stimulated by potassium chloride, pituitary hormone oxytocin and by inflammatory cytokine alpha-tumor necrosis factor (TNF-alpha). Accelerated gel contraction was accompanied by elevated secretion of MMP-2 and MMP-9 into cell culture media. Among a variety of purified bioflavonoids and polyphenol-enriched plant extracts tested for their ability to counteract uterine SMC-dependent collagen gel contraction, the strongest effects were demonstrated by epigallocatechin gallate and green tea leaf extract, respectively. The addition of ascorbic acid and the amino acids lysine, arginine, cysteine and proline to green tea extract further increased its effectiveness. A reduction in gel contraction correlated with decreased MMP expression.

CONCLUSION

Based on these findings, we found that nutrients can effectively counteract uterine myometrial contraction and MMP activity in vitro, suggesting that pathophysiological mechanisms of abnormal uterine myometrial contractility can be counteracted by a combination of naturally occurring nutrients. These mechanisms might involve extracellular matrix remodeling.

Gene and protein expression in the myometrium in pregnancy and labor

Microarray technologies widen our comprehension of the major structural and metabolic transformations which affect the myometrium from the very beginning of pregnancy until parturition. The results are coherent with the mass of information which was accumulated previously, primarily on the basis of studies of selected critical factors. They highlight the activation of precise signaling pathways, some of which may have been previously under evaluated. The remodelling and maturation processes that the myometrium undergoes in pregnancy appear clearly as phenomena which last during the full course of gestation. Comparatively, the onset of labor is perhaps the phenomenon which remains the least well described by these methods of analysis. Nevertheless, genomic studies constitute a necessary first step of orientation and help establishing new links between the generic signaling pathways that are activated during the normal or pathological gestation. These studies also represent an indicative step that will have to be paralleled, in the future, with the results of the systematic proteomic analysis of the myometrium.

Role of atypical protein kinase C isozymes and NF-κB in IL-1β-induced expression of cyclooxygenase-2 in human myometrial smooth muscle cells

Increased myometrial expression of cyclooxygenase-2 (Cox-2) at term results from elevated local levels of inflammatory cytokines, and its inhibition provides a potential route for intervention in human pre-term labor. We have identified a role for atypical protein kinase C (PKC) isozymes in IL-1beta-induced Cox-2 expression in human myometrial smooth muscle cells (HMSMC). The PKC inhibitor GF109203X (10 microM) inhibited IL-1beta-induced Cox-2 protein and RNA expression, which were also reduced by MAPK and nuclear factor kappaB (NF-kappaB) inhibitors. GF109203X did not affect MAPK activities, and neither did it replicate the effect of p38 MAPK inhibition on Cox-2 mRNA stability, suggesting that PKC operates through an independent mechanism. The effect of GF109203X remained intact after depletion of conventional and novel PKC isozymes by phorbol ester pre-treatment. In contrast LY379196 (10 microM), which at micromolar concentrations inhibits all but atypical PKCs, did not affect Cox-2 expression. A peptide corresponding to the pseudosubstrate sequence of atypical PKCs blocked Cox-2 protein expression, whereas the sequence from conventional PKCs was ineffective. GF109203X did not affect NF-kappaB binding to nuclear proteins, but strongly reduced NF-kappaB-dependent transcription in luciferase reporter assays. Our findings indicate that IL-1beta-induced Cox-2 expression in HMSMC in culture requires p38-MAPK-mediated mRNA stabilization and an independent activation of Cox-2 transcription which is dependent on the action of atypical PKCs, probably through direct stimulation of the transactivating activity of NF-kappaB.

Protein kinases in vascular smooth muscle tone--role in the pulmonary vasculature and hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV) is an adaptive mechanism that in the normal animal diverts blood away from poorly ventilated areas of the lung, thereby maintaining optimal ventilation-perfusion matching. In global hypoxia however, such as in respiratory disease or at altitude, it causes detrimental increases in pulmonary vascular resistance and pulmonary artery (PA) pressure. The precise intracellular pathways and mechanisms underlying HPV remain unclear, although it is now recognised that both an elevation in smooth muscle intracellular [Ca2+] and a concomitant increase in Ca2+ sensitivity are involved. Several key intracellular protein kinases have been proposed as components of the signal transduction pathways leading to development of HPV, specifically Rho kinase, non-receptor tyrosine kinases (NRTK), p38 mitogen activated protein (MAP) kinase, and protein kinase C (PKC). All of these have been implicated to a greater or lesser extent in pathways leading to Ca2+ sensitisation, and in some cases regulation of intracellular [Ca2+] as well. In this article, we review the role of these key protein kinases in the regulation of vascular smooth muscle (VSM) constriction, applying what is known in the systemic circulation to the pulmonary circulation and HPV. We conclude that the strongest evidence for direct involvement of protein kinases in the mechanisms of HPV concerns a central role for Rho kinase in Ca2+ sensitisation, and a potential role for Src-family kinases in both modulation of Ca2+ entry via capacitative Ca2+ entry (CCE) and activation of Rho kinase, though others are likely to have indirect or modulatory influences. In addition, we speculate that Src family kinases may provide a central interface between the proposed hypoxia-induced generation of reactive oxygen species by mitochondria and both the elevation in intracellular [Ca2+] and Rho kinase mediated Ca2+ sensitisation.

A role for PKCζ in the LPS-induced translocation NF-κB p65 subunit in cultured myometrial cells

Human myometrial cells respond to the endotoxin lipopolysaccharide (LPS) by activation of protein kinase C (PKC) zeta and nuclear translocation of the p65 subunit of NF-kB. Our first objective was to determine the expression of TLR4 in cultured myometrial cells. Positive immunoreactivity observed for TLR4 suggests that myometrial cells have the potential to respond to LPS. To confirm that LPS signals via TLR4, the ability of an anti-TLR4 neutralizing antibody to block LPS-induced translocation of p65 was demonstrated. To determine whether LPS-induced nuclear translocation of p65 is mediated through the PKC pathway, myometrial cells were treated with various inhibitors of the PKC isoforms already characterized in human myometrium. Neither the selective conventional PKC inhibitor nor the inhibitor of PKCdelta affected NF-kB activation. By contrast, we found that treatment of myometrial cells with an antisense against PKCzeta affect LPS-induced nuclear translocation of the p65 subunit of NF-kB. Accordingly, our data support the notion that PKCzeta is essential for LPS-induced NF-kB p65 subunit nuclear translocation in human myometrial cells.

Relaxin stimulates protein kinase C zeta translocation: requirement for cyclic adenosine 3',5'-monophosphate production

Relaxin is a polypeptide hormone that activates the leucine-rich repeat containing G protein-coupled receptors, LGR7 and LGR8. In an earlier study, we reported that relaxin produces a biphasic time course and the second wave of cAMP is highly sensitive to phosphoinositide-3 kinase inhibitors (LY294002 and wortmannin). LY294002 inhibits relaxin-mediated increases in cAMP production by 40-50% across a large range of relaxin concentrations. Here we show that protein kinase C zeta (PKCzeta) is a component of relaxin signaling in THP-1 cells. Sphingomyelinase increases cAMP production due to the release of ceramide, a direct activator of PKCzeta. Chelerythrine chloride (a general PKC inhibitor) inhibits relaxin induced cAMP production to the same degree (approximately 40%) as LY294002. Relaxin stimulates PKCzeta translocation to the plasma membrane in THP-1, MCF-7, pregnant human myometrial 1-31, and mouse mesangial cells, as shown by immunocytochemistry. PKCzeta translocation is phosphoinositide-3 kinase dependent and independent of cAMP production. Antisense PKCzeta oligodeoxynucleotides (PKCzeta-ODNs) deplete both PKCzeta transcript and protein levels in THP-1 cells. PKCzeta-ODNs abolish relaxin-mediated PKCzeta translocation and inhibit relaxin stimulation of cAMP by 40%, as compared with mock and random ODN controls. Treatment with LY294002 in the presence of PKCzeta-ODNs results in little further inhibition. In summary, we present a novel role for PKCzeta in relaxin-mediated stimulation of cAMP.

Contribution of phospholipase D in endothelin-1-mediated extracellular signal-regulated kinase activation and proliferation in rat uterine leiomyoma cells

Endothelin (ET)-1 is a mitogenic factor in numerous cell types, including rat myometrial cells. In the present study, we investigated the potential role of ET-1 in the proliferation of tumoral uterine smooth muscle cells (ELT-3 cells). We found that ET-1 exerted a more potent mitogenic effect in ELT-3 cells than in normal myometrial cells, as indicated by the increase in [3H]thymidine incorporation, cell number, and bromodeoxyuridine incorporation. The ET-1 was more efficient than platelet-derived growth factor and epidermal growth factor to stimulate proliferation. The ET-1-mediated cell proliferation was inhibited in the presence of U0126, a specific inhibitor of (mitogen-activated protein kinase ERK kinase), indicating that extracellular signal-regulated kinase (ERK) activation is involved. Additionally, ET-1 induced the activation of phospholipase (PL) D, leading to the synthesis of phosphatidic acid (PA). The ET-1-induced activation of PLD was twofold higher in ELT-3 cells compared to that in normal cells. The two cell types expressed mRNA for PLD1a and PLD2, whereas PLD1b was expressed only in ELT-3 cells. The exposure of cells to butan-1-ol reduced ET-1-mediated production of PA by PLD and partially inhibited ERK activation and DNA synthesis. Addition of exogenous PLD or PA in the medium reproduced the effect of ET-1 on ERK activation and cell proliferation. Collectively, these data indicate that ET-1 is a potent mitogenic factor in ELT-3 cells via a signaling pathway involving a PLD-dependent activation of ERK. This highlights the potential role of ET-1 in the development of uterine leiomyoma, and it reinforces the role of PLD in tumor growth.

Trans-inactivation of receptor tyrosine kinases by novel angiotensin II AT2 receptor-interacting protein, ATIP

Negative regulation of mitogenic pathways is a fundamental process that remains poorly characterized. The angiotensin II AT2 receptor is a rare example of a 7-transmembrane domain receptor that negatively cross-talks with receptor tyrosine kinases to inhibit cell growth. In the present study, we report the molecular cloning of a novel protein, ATIP1 (AT2-interacting protein), which interacts with the C-terminal tail of the AT2 receptor, but not with those of other receptors such as angiotensin AT1, bradykinin BK2, and adrenergic beta(2) receptor. ATIP1 defines a family of at least four members that possess the same domain of interaction with the AT2 receptor, contain a large coiled-coil region, and are able to dimerize. Ectopic expression of ATIP1 in eukaryotic cells leads to inhibition of insulin, basic fibroblast growth factor, and epidermal growth factor-induced ERK2 activation and DNA synthesis, and attenuates insulin receptor autophosphorylation, in the same way as the AT2 receptor. The inhibitory effect of ATIP1 requires expression, but not ligand activation, of the AT2 receptor and is further increased in the presence of Ang II, indicating that ATIP1 cooperates with AT2 to transinactivate receptor tyrosine kinases. Our findings therefore identify ATIP1 as a novel early component of growth inhibitory signaling cascade.