Activation of ERK5 in angiotensin II-induced hypertrophy of human aortic smooth muscle cells

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.

Cortistatin exerts antiproliferation and antimigration effects in vascular smooth muscle cells stimulated by Ang II through suppressing ERK1/2, p38 MAPK, JNK and ERK5 signaling pathways

Background

Vascular remodeling, that contributes to cardiovascular diseases such as hypertension develops by anomalous proliferation and migration of vascular smooth muscle cells (VSMCs). Cortistatin (CST), a newly discovered biological peptide, has been acknowledged for its protective effects against cardiovascular diseases. Whether CST has an inhibitory regulation role in angiotensin II (Ang II)-induced proliferation and migration of VSMCs and what molecular mechanisms may participate in the CST inhibition process are still unknown.

Methods

VSMCs were divided into control group, Ang II (10^-7 M) group, Ang II + PD98059 (5×10^-5 M) group, Ang II + SB203580 (10^-5 M) group, Ang II + SP600125 (10^-5 M) group, Ang II + XMD17-109 (10^-6 M) group, Ang II + CST (10^-8 M) group and Ang II + CST (10^-7 M) group. Cell proliferation was detected by western blotting and cell counting kit-8 (CCK8) analysis. Migration of VSMCs was measured by Transwell assay.

Results

Compared with control group, Ang II upregulated the expression levels of proliferating cell nuclear antigen (PCNA) and osteopontin (OPN) and downregulated that of α-smooth muscle actin (α-SMA), increased the proliferation rate as shown by CCK8 and VSMC migration as shown by Transwell assay in cultured VSMCs of the Ang II group. Meanwhile, in Ang II-cultured VSMCs, we found activation of extracellular signal-regulated kinase (ERK) 1/2, p38 MAP kinase (p38 MAPK), c-Jun N-terminal kinase (JNK), and ERK5 pathways by western blotting at different time points. However, the proliferation and migration stimulated by Ang II were partly reversed by drug inhibitors of the four pathways, namely, PD98059, SB203580, SP600125 and XMD17-109. When Ang II-stimulated VSMCs were cultured with CST pretreatment, we found that proliferation and migration were greatly suppressed as well as that the ERK1/2, p38 MAPK, JNK and ERK5 pathways were deactivated by CST.

Conclusions

The accumulated data suggest that CST may play a protective role in Ang II-promoted proliferation and migration of VSMCs via inhibiting the mitogen-activated protein kinase (MAPK) family pathways, providing a new orientation of CST in protecting against cardiovascular diseases.

Role of cytochrome P450-mediated arachidonic acid metabolites in the pathogenesis of cardiac hypertrophy

A plethora of studies have demonstrated the expression of cytochrome P450 (CYP) and soluble epoxide hydrolase (sEH) enzymes in the heart and other cardiovascular tissues. In addition, the expression of these enzymes is altered during several cardiovascular diseases (CVDs), including cardiac hypertrophy (CH). The alteration in CYP and sEH expression results in derailed CYP-mediated arachidonic acid (AA) metabolism. In animal models of CH, it has been reported that there is an increase in 20-hydroxyeicosatetraenoic acid (20-HETE) and a decrease in epoxyeicosatrienoic acids (EETs). Further, inhibiting 20-HETE production by CYP ω-hydroxylase inhibitors and increasing EET stability by sEH inhibitors have been proven to protect against CH as well as other CVDs. Therefore, CYP-mediated AA metabolites 20-HETE and EETs are potential key players in the pathogenesis of CH. Some studies have investigated the molecular mechanisms by which these metabolites mediate their effects on cardiomyocytes and vasculature leading to pathological CH. Activation of several intracellular signaling cascades, such as nuclear factor of activated T cells, nuclear factor kappa B, mitogen-activated protein kinases, Rho-kinases, Gp130/signal transducer and activator of transcription, extracellular matrix degradation, apoptotic cascades, inflammatory cytokines, and oxidative stress, has been linked to the pathogenesis of CH. In this review, we discuss how 20-HETE and EETs can affect these signaling pathways to result in, or protect from, CH, respectively. However, further understanding of these metabolites and their effects on intracellular cascades will be required to assess their potential translation to therapeutic approaches for the prevention and/or treatment of CH and heart failure.

Protein kinase C (PKC)ζ-mediated Gαq stimulation of ERK5 protein pathway in cardiomyocytes and cardiac fibroblasts

Gq-coupled G protein-coupled receptors (GPCRs) mediate the actions of a variety of messengers that are key regulators of cardiovascular function. Enhanced Gα(q)-mediated signaling plays an important role in cardiac hypertrophy and in the transition to heart failure. We have recently described that Gα(q) acts as an adaptor protein that facilitates PKCζ-mediated activation of ERK5 in epithelial cells. Because the ERK5 cascade is known to be involved in cardiac hypertrophy, we have investigated the potential relevance of this pathway in cardiovascular Gq-dependent signaling using both cultured cardiac cell types and chronic administration of angiotensin II in mice. We find that PKCζ is required for the activation of the ERK5 pathway by Gq-coupled GPCR in neonatal and adult murine cardiomyocyte cultures and in cardiac fibroblasts. Stimulation of ERK5 by angiotensin II is blocked upon pharmacological inhibition or siRNA-mediated silencing of PKCζ in primary cultures of cardiac cells and in neonatal cardiomyocytes isolated from PKCζ-deficient mice. Moreover, upon chronic challenge with angiotensin II, these mice fail to promote the changes in the ERK5 pathway, in gene expression patterns, and in hypertrophic markers observed in wild-type animals. Taken together, our results show that PKCζ is essential for Gq-dependent ERK5 activation in cardiomyocytes and cardiac fibroblasts and indicate a key cardiac physiological role for the Gα(q)/PKCζ/ERK5 signaling axis.

Protein kinase C epsilon-dependent extracellular signal-regulated kinase 5 phosphorylation and nuclear translocation involved in cardiomyocyte hypertrophy with angiotensin II stimulation

Angiotensin II (Ang II) plays a critical role in hypertrophy of cardiomyocytes; however, the molecular mechanism, especially the signaling cascades, in cardiomyocytes remains unclear. In the present study, we examined the mechanism of Ang II in hypertrophy of cardiomyocytes. Ang II rapidly stimulated phosphorylation of protein kinase C epsilon (PKCepsilon) in a time- and dose-dependent manner via Ang II receptor-1 (AT(1)). Furthermore, Ang II-induced extracellular signal-regulated kinase 5 (ERK5) phosphorylation and translocation was mediated through a signal pathway that involves AT(1) and PKCepsilon, which resulted in transcriptional activation of myocyte enhancer factor-2C (MEF2C) and hypertrophy. Consequently, inhibiting PKCepsilon or ERK5 by small interfering RNA (siRNA) significantly attenuated Ang II-induced MEF2C activation and hypertrophy of rat cardiomyocytes. These data provide evidence that PKCepsilon-dependent ERK5 phosphorylation and nucleocytoplasmic traffic mediates Ang II-induced MEF2C activation and cardiomyocyte hypertrophy. PKCepsilon and ERK5 may be potential targets in the treatment of pathological vascular hypertrophy associated with the enhanced renin-angiotensin system.

Mechanisms of protein kinase A anchoring

The second messenger cyclic adenosine monophosphate (cAMP), which is produced by adenylyl cyclases following stimulation of G-protein-coupled receptors, exerts its effect mainly through the cAMP-dependent serine/threonine protein kinase A (PKA). Due to the ubiquitous nature of the cAMP/PKA system, PKA signaling pathways underlie strict spatial and temporal control to achieve specificity. A-kinase anchoring proteins (AKAPs) bind to the regulatory subunit dimer of the tetrameric PKA holoenzyme and thereby target PKA to defined cellular compartments in the vicinity of its substrates. AKAPs promote the termination of cAMP signals by recruiting phosphodiesterases and protein phosphatases, and the integration of signaling pathways by binding additional signaling proteins. AKAPs are a heterogeneous family of proteins that only display similarity within their PKA-binding domains, amphipathic helixes docking into a hydrophobic groove formed by the PKA regulatory subunit dimer. This review summarizes the current state of information on compartmentalized cAMP/PKA signaling with a major focus on structural aspects, evolution, diversity, and (patho)physiological functions of AKAPs and intends to outline newly emerging directions of the field, such as the elucidation of AKAP mutations and alterations of AKAP expression in human diseases, and the validation of AKAP-dependent protein-protein interactions as new drug targets. In addition, alternative PKA anchoring mechanisms employed by noncanonical AKAPs and PKA catalytic subunit-interacting proteins are illustrated.

Hypertrophic response to angiotensin II is mediated by protein kinase D-extracellular signal-regulated kinase 5 pathway in human aortic smooth muscle cells

Angiotensin II plays a critical role in hypertrophy of vascular smooth muscle cells, however, the molecular underpinnings remain unclear. The present study indicated that AT1/PKC/PKD pathway was able to regulate downstream ERK5, affecting pro-hypertrophic responses to Ang II. Ang II-stimulated phosphorylation of ERK5 in a time- and dose-dependent manner in human aortic smooth muscle cells (HASMCs). The pharmacological inhibitors for AT1 and PKCs significantly inhibited Ang II-induced ERK5 activation, suggesting the involvement of the AT1/PKC pathway. In particular, PKD was critical for Ang II-induced ERK5 activation since silencing PKD by siRNA markedly inhibited Ang II-induced ERK5 activation. Consequently, we found that Losartan, Gö 6983 and PKD siRNA significantly attenuated ERK5 activated translocation and hypertrophy of HASMCs by Ang II. Taken together, we demonstrated for the first time that Ang II activates ERK5 via the AT1/PKC/PKD pathway and revealed a critical role of ERK5 in Ang II-induced HASMCs hypertrophy.