p63RhoGEF couples Gα(q/11)-mediated signaling to Ca2+ sensitization of vascular smooth muscle contractility

Lymphatic vessels and the renin-angiotensin-system

The lymphatic system is an integral part of the circulatory system and plays an important role in the fluid homeostasis of the human body. Accumulating evidence has recently suggested the involvement of lymphatic dysfunction in the pathogenesis of cardio-reno-vascular (CRV) disease. However, how the sophisticated contractile machinery of lymphatic vessels is modulated and, possibly impaired in CRV disease, remains largely unknown. In particular, little attention has been paid to the effect of the renin-angiotensin-system (RAS) on lymphatics, despite the high concentration of RAS mediators that these tissue-draining vessels are exposed to and the established role of the RAS in the development of classic microvascular dysfunction and overt CRV disease. We herein review recent studies linking RAS to lymphatic function and/or plasticity and further highlight RAS-specific signaling pathways, previously shown to drive adverse arterial remodeling and CRV organ damage that have potential for direct modulation of the lymphatic system.

Dual thick and thin filament linked regulation of stretch- and L-NAME-induced tone in young and senescent murine basilar artery

Stretch-induced vascular tone is an important element of autoregulatory adaptation of cerebral vasculature to maintain cerebral flow constant despite changes in perfusion pressure. Little is known as to the regulation of tone in senescent basilar arteries. We tested the hypothesis, that thin filament mechanisms in addition to smooth muscle myosin-II regulatory-light-chain-(MLC20)-phosphorylation and non-muscle-myosin-II, contribute to regulation of stretch-induced tone. In young BAs (y-BAs) mechanical stretch does not lead to spontaneous tone generation. Stretch-induced tone in y-BAs appeared only after inhibition of NO-release by L-NAME and was fully prevented by treatment with 3 μmol/L RhoA-kinase (ROK) inhibitor Y27632. L-NAME-induced tone was reduced in y-BAs from heterozygous mice carrying a point mutation of the targeting-subunit of the myosin phosphatase, MYPT1 at threonine696 (MYPT1-T696A/+). In y-BAs, MYPT1-T696A-mutation also blunted the ability of L-NAME to increase MLC20-phosphorylation. In contrast, senescent BAs (s-BAs; >24 months) developed stable spontaneous stretch-induced tone and pharmacological inhibition of NO-release by L-NAME led to an additive effect. In s-BAs the MYPT1-T696A mutation also blunted MLC20-phosphorylation, but did not prevent development of stretch-induced tone. In s-BAs from both lines, Y27632 completely abolished stretch- and L-NAME-induced tone. In s-BAs phosphorylation of non-muscle-myosin-S1943 and PAK1-T423, shown to be down-stream effectors of ROK was also reduced by Y27632 treatment. Stretch- and L-NAME tone were inhibited by inhibition of non-muscle myosin (NM-myosin) by blebbistatin. We also tested whether the substrate of PAK1 the thin-filament associated protein, caldesmon is involved in the regulation of stretch-induced tone in advanced age. BAs obtained from heterozygotes Cald1+/− mice generated stretch-induced tone already at an age of 20–21 months old BAs (o-BA). The magnitude of stretch-induced tone in Cald1+/− o-BAs was similar to that in s-BA. In addition, truncation of caldesmon myosin binding Exon2 (CaD-▵Ex2−/−) did not accelerate stretch-induced tone. Our study indicates that in senescent cerebral vessels, mechanisms distinct from MLC20 phosphorylation contribute to regulation of tone in the absence of a contractile agonist. While in y-and o-BA the canonical pathways, i.e., inhibition of MLCP by ROK and increase in pMLC20, predominate, tone regulation in senescence involves ROK regulated mechanisms, involving non-muscle-myosin and thin filament linked mechanisms involving caldesmon.

Epoxyeicosatrienoic Acid and Prostanoid Crosstalk at the Receptor and Intracellular Signaling Levels to Maintain Vascular Tone

Epoxyeicosatrienoic acids (EETs) are signaling lipids produced by the cytochrome P450-(CYP450)-mediated epoxygenation of arachidonic acid. EETs have numerous biological effects on the vascular system, but aspects including their species specificity make their effects on vascular tone controversial. CYP450 enzymes require the 450-reductase (POR) for their activity. We set out to determine the contribution of endothelial CYP450 to murine vascular function using isolated aortic ring preparations from tamoxifen-inducible endothelial cell-specific POR knockout mice (ecPOR^-/-). Constrictor responses to phenylephrine were similar between control (CTR) and ecPOR^-/- mice. Contrastingly, sensitivity to the thromboxane receptor agonist U46619 and prostaglandin E2 (PGE2) was increased following the deletion of POR. Ex vivo incubation with a non-hydrolyzable EET (14,15-EE-8(Z)-E, EEZE) reversed the increased sensitivity to U46619 to the levels of CTR. EETs had no effect on vascular tone in phenylephrine-preconstricted vessels, but dilated vessels contracted with U46619 or PGE2. As U46619 acts through RhoA-dependent kinase, this system was analyzed. The deletion of POR affected the expression of genes in this pathway and the inhibition of Rho-GTPase with SAR407899 decreased sensitivity to U46619. These data suggest that EET and prostanoid crosstalk at the receptor level and that lack of EET production sensitizes vessels to vasoconstriction via the induction of the Rho kinase system.

Inhibition of Human Prostate and Bladder Smooth Muscle Contraction, Vasoconstriction of Porcine Renal and Coronary Arteries, and Growth-Related Functions of Prostate Stromal Cells by Presumed Small Molecule Gαq/11 Inhibitor, YM-254890

Introduction: Lower urinary tract symptoms (LUTS) involve benign prostatic hyperplasia (BPH) and overactive bladder (OAB). Standard-of-care medical treatment includes α1-blockers and antimuscarinics for reduction of prostate and detrusor smooth muscle tone, respectively, and 5α-reductase inhibitors (5-ARI) to prevent prostate growth. Current medications are marked by high discontinuation rates due to unfavourable balance between efficacy and treatment-limiting side effects, ranging from dry mouth for antimuscarinics to cardiovascular dysregulation and a tendency to fall for α1-blockers, which results from hypotension, due to vasorelaxation. Agonist-induced smooth muscle contractions are caused by activation of receptor-coupled G-proteins. However, little is known about receptor- and organ-specific differences in coupling to G-proteins. With YM-254890, a small molecule inhibitor with presumed specificity for Gαq/11 became recently available. Here, we investigated effects of YM-254890 on prostate, bladder and vascular smooth muscle contraction, and on growth-related functions in prostate stromal cells.

Methods: Contractions of human prostate and detrusor tissues, porcine renal and coronary arteries were induced in an organ bath. Proliferation (EdU assay), growth (colony formation), apoptosis and cell death (flow cytometry), viability (CCK-8) and actin organization (phalloidin staining) were studied in cultured human prostate stromal cells (WPMY-1).

Results: Contractions by α1-adrenergic agonists, U46619, endothelin-1, and neurogenic contractions were nearly completely inhibited by YM-254890 (30 nM) in prostate tissues. Contractions by cholinergic agonists, U46619, endothelin-1, and neurogenic contractions were only partly inhibited in detrusor tissues. Contractions by α1-adrenergic agonists, U46619, endothelin-1, and neurogenic contractions were strongly, but not fully inhibited in renal arteries. Contractions by cholinergic agonists were completely, but by U46619 and endothelin-1 only strongly inhibited, and neurogenic contractions reduced by half in coronary arteries. YM-254890 had no effect on agonist-independent contractions induced by highmolar (80 mM) potassium chloride (KCl). Neurogenic detrusor contractions were fully sensitive to tetrodotoxin. In WPMY-1 cells, YM-254890 caused breakdown of actin polymerization and organization, and obvious, but clearly limited decreases of proliferation rate, colony formation and viability, and slightly increased apoptosis.

Conclusion: Intracellular post-receptor signaling pathways are shared by Gαq-coupled contractile receptors in multiple smooth muscle-rich organs, but to different extent. While inhibition of Gαq/11 causes actin breakdown, anti-proliferative effects were detectable but clearly limited. Together this may aid in developing future pharmaceutical targets for LUTS and antihypertensive medication.

Endogenous Anti-Cancer Candidates in GPCR, ER Stress, and EMT

The majority of cellular responses to external stimuli are mediated by receptors such as G protein-coupled receptors (GPCRs) and systems including endoplasmic reticulum stress (ER stress). Since GPCR signalling is pivotal in numerous malignancies, they are widely targeted by a number of clinical drugs. Cancer cells often negatively modulate GPCRs in order to survive, proliferate and to disseminate. Similarly, numerous branches of the unfolded protein response (UPR) act as pro-survival mediators and are involved in promoting cancer progression via mechanisms such as epithelial to mesenchymal transition (EMT). However, there are a few proteins among these groups which impede deleterious effects by orchestrating the pro-apoptotic phenomenon and paving a therapeutic pathway. The present review exposes and discusses such critical mechanisms and some of the key processes involved in carcinogenesis.

Histamine-induced biphasic activation of RhoA allows for persistent RhoA signaling

The small GTPase RhoA is a central signaling enzyme that is involved in various cellular processes such as cytoskeletal dynamics, transcription, and cell cycle progression. Many signal transduction pathways activate RhoA—for instance, Gα_q-coupled Histamine 1 Receptor signaling via Gα_q-dependent activation of RhoGEFs such as p63. Although multiple upstream regulators of RhoA have been identified, the temporal regulation of RhoA and the coordination of different upstream components in its regulation have not been well characterized. In this study, live-cell measurement of RhoA activation revealed a biphasic increase of RhoA activity upon histamine stimulation. We showed that the first and second phase of RhoA activity are dependent on p63 and Ca²⁺/PKC, respectively, and further identified phosphorylation of serine 240 on p115 RhoGEF by PKC to be the mechanistic link between PKC and RhoA. Combined approaches of computational modeling and quantitative measurement revealed that the second phase of RhoA activation is insensitive to rapid turning off of the receptor and is required for maintaining RhoA-mediated transcription after the termination of the receptor signaling. Thus, two divergent pathways enable both rapid activation and persistent signaling in receptor-mediated RhoA signaling via intricate temporal regulation.

The small GTPase RhoA is a central signaling enzyme that is involved in various cellular processes such as cytoskeletal dynamics, transcription, and cell cycle progression. This study shows that histamine induces biphasic activation of RhoA via two divergent signaling pathways, allowing for intricate regulation of cellular processes.

Inhibition of neurogenic and thromboxane A2 -induced human prostate smooth muscle contraction by the integrin α2β1 inhibitor BTT-3033 and the integrin-linked kinase inhibitor Cpd22

INTRODUCTION

Prostate smooth muscle contraction is critical for etiology and treatment of lower urinary tract symptoms in benign prostatic hyperplasia (BPH). Integrins connect the cytoskeleton to membranes and cells to extracellular matrix, what is essential for force generation in smooth muscle contraction. Integrins are composed of different subunits and may cooperate with integrin-linked kinase (ILK). Here, we examined effects of inhibitors for different integrin heterodimers and ILK on contraction of human prostate tissues.

METHODS

Prostate tissues were obtained from radical prostatectomy. Integrins and ILK were detected by Western blot, real-time polymerase chain reaction (RT-PCR), and double fluorescence staining. Smooth muscle contractions of prostate strips were studied in an organ bath. Contractions were compared after application of solvent (controls), the ILK inhibitor Cpd22 (N-methyl-3-(1-(4-(piperazin-1-yl)phenyl)-5-(4'-(trifluoromethyl)-[1,1'-biphenyl]-4-yl)-1H-pyrazol-3-yl)propanamide), the integrin α2β1 inhibitor BTT-3033 (1-(4-fluorophenyl)-N-methyl-N-[4[[(phenylamino)carbonyl]amino]phenyl]-1H-pyrazole-4-sulfonamide), or the integrin α4β1/α9β1 inhibitor BOP (N-(benzenesulfonyl)- l-prolyl- l-O-(1-pyrrolidinylcarbonyl)tyrosine sodium salt).

RESULTS

Western blot analyses of prostate tissues using antibodies raised against integrins α2b, α4, α9, β1, and ILK revealed bands matching the expected sizes of corresponding antigens. Expression of integrins and ILK was confirmed by RT-PCR. Individual variations of expression levels occurred independently from divergent degree of BPH, reflected by different contents of prostate-specific antigen. Double fluorescence staining of prostate sections using antibodies raised against integrins α2 and β1, or against ILK resulted in immunoreactivity colocalizing with calponin, suggesting localization in prostate smooth muscle cells. Electric field stimulation (EFS) induced frequency-dependent contractions, which were inhibited by Cpd22 (3 µM) and BTT-3033 (1 µM) (inhibition around 37% by Cpd22 and 46% by BTT-3033 at 32 Hz). The thromboxane A₂ analog U46619-induced concentration-dependent contractions, which were inhibited by Cpd22 and BTT-3033 (around 67% by Cpd22 and 39% by BTT-3033 at 30 µM U46619). Endothelin-1 induced concentration-dependent contractions, which were not affected by Cpd22 or BTT-3033. Noradrenaline and the α₁ -adrenergic agonists methoxamine and phenylephrine-induced concentration-dependent contractions, which were not or very slightly inhibited by Cpd22 and BTT-3033. BOP did not change EFS- or agonist-induced contraction.

CONCLUSIONS

Integrin α2β1 and ILK inhibitors inhibit neurogenic and thromboxane A₂ -induced prostate smooth muscle contraction in human BPH. A role for these targets for prostate smooth muscle contraction may appear possible.

Epigenetically upregulated GEFT-derived invasion and metastasis of rhabdomyosarcoma via epithelial mesenchymal transition promoted by the Rac1/Cdc42-PAK signalling pathway

Background

Metastasis of rhabdomyosarcoma (RMS) is the primary cause of tumour-related deaths. Previous studies have shown that overexpression of the guanine nucleotide exchange factor T (GEFT) is correlated with a poorer RMS prognosis, but the mechanism remains largely unexplored.

Methods

We focused on determining the influence of the GEFT-Rho-GTPase signalling pathway and the epithelial–mesenchymal transition (EMT) or mesenchymal–epithelial transition (MET) on RMS progression and metastasis by using RMS cell lines, BALB/c nude mice and cells and molecular biology techniques.

Findings

GEFT promotes RMS cell viability, migration, and invasion; GEFT also inhibits the apoptosis of RMS cells and accelerates the growth and lung metastasis of RMS by activating the Rac1/Cdc42 pathways. Interestingly, GEFT upregulates the expression levels of N-cadherin, Snail, Slug, Twist, Zeb1, and Zeb2 and reduces expression level of E-cadherin. Thus, GEFT influences the expression of markers for EMT and MET in RMS cells via the Rac1/Cdc42-PAK1 pathways. We also found that the level of GEFT gene promoter methylation in RMS is lower than that in normal striated muscle tissue. Significant differences were observed in the level of GEFT gene methylation in different histological subtypes of RMS.

Interpretation

These findings suggest that GEFT accelerates the tumourigenicity and metastasis of RMS by activating Rac1/Cdc42-PAK signalling pathway-induced EMT; thus, it may serve as a novel therapeutic target.

Fund

This work was supported by grants from the National Natural Science Foundation of China (81660441, 81460404, and 81160322) and Shihezi University Initiative Research Projects for Senior Fellows (RCZX201447). Funders had no role in the design of the study, data collection, data analysis, interpretation, or the writing of this report.

Structural design principles that underlie the multi-specific interactions of Gαq with dissimilar partners

Gα_q is a ubiquitous molecular switch that activates the effectors phospholipase-C-β3 (PLC-β3) and Rho guanine-nucleotide exchange factors. Gα_q is inactivated by regulators of G protein signaling proteins, as well as by PLC-β3. Gα_q further interacts with G protein-coupled receptor kinase 2 (GRK2), although the functional role of this interaction is debated. While X-ray structures of Gα_q bound to representatives of these partners have revealed details of their interactions, the mechanistic basis for differential Gα_q interactions with multiple partners (i.e., Gα_q multi-specificity) has not been elucidated at the individual residue resolution. Here, we map the structural determinants of Gα_q multi-specificity using structure-based energy calculations. We delineate regions that specifically interact with GTPase Activating Proteins (GAPs) and residues that exclusively contribute to effector interactions, showing that only the Gα_q “Switch II” region interacts with all partners. Our analysis further suggests that Gα_q-GRK2 interactions are consistent with GRK2 functioning as an effector, rather than a GAP. Our multi-specificity analysis pinpoints Gα_q residues that uniquely contribute to interactions with particular partners, enabling precise manipulation of these cascades. As such, we dissect the molecular basis of Gα_q function as a central signaling hub, which can be used to target Gα_q-mediated signaling in therapeutic interventions.

Druggable targets in the Rho pathway and their promise for therapeutic control of blood pressure

The prevalence of high blood pressure (also known as hypertension) has steadily increased over the last few decades. Known as a silent killer, hypertension increases the risk for cardiovascular disease and can lead to stroke, heart attack, kidney failure and associated sequela. While numerous hypertensive therapies are currently available, it is estimated that only half of medicated patients exhibit blood pressure control. This signifies the need for a better understanding of the underlying cause of disease and for more effective therapies. While blood pressure homeostasis is very complex and involves the integrated control of multiple body systems, smooth muscle contractility and arterial resistance are important contributors. Strong evidence from pre-clinical animal models and genome-wide association studies indicate that smooth muscle contraction and BP homeostasis are governed by the small GTPase RhoA and its downstream target, Rho kinase. In this review, we summarize the signaling pathways and regulators that impart tight spatial-temporal control of RhoA activity in smooth muscle cells and discuss current therapeutic strategies to target these RhoA pathway components. We also discuss known allelic variations in the RhoA pathway and consider how these polymorphisms may affect genetic risk for hypertension and its clinical manifestations.

Targeting G protein-coupled receptor signalling by blocking G proteins

G protein-coupled receptors (GPCRs) are the largest class of drug targets, largely owing to their druggability, diversity and physiological efficacy. Many drugs selectively target specific subtypes of GPCRs, but high specificity for individual GPCRs may not be desirable in complex multifactorial disease states in which multiple receptors may be involved. One approach is to target G protein subunits rather than the GPCRs directly. This approach has the potential to achieve broad efficacy by blocking pathways shared by multiple GPCRs. Additionally, because many GPCRs couple to multiple G protein signalling pathways, blocking specific G protein subunits can 'bias' GPCR signals by inhibiting only a subset of these signals. Molecules that target G protein α or βγ-subunits have been developed and show strong efficacy in multiple preclinical disease models and biased inhibition of G protein signalling. In this Review, we discuss the development and characterization of G protein α and βγ-subunit ligands and the preclinical evidence that this exciting new approach has potential for therapeutic efficacy in a number of indications, such as pain, thrombosis, asthma and heart failure.

Role of age, Rho-kinase 2 expression, and G protein-mediated signaling in the myogenic response in mouse small mesenteric arteries

The myogenic response (MR) and myogenic tone (MT) in resistance vessels is crucial for maintaining peripheral vascular resistance and blood flow autoregulation. Development of MT involves G protein-coupled receptors, and may be affected by aging.

AIMS

(1) to estimate the mesenteric blood flow in myogenically active small mesenteric arteries; (2) to investigate the signaling from Gαq/11 and/or Gα12 activation to MT development; (3) to investigate the role of Rho-kinase 2 and aging on MT in mesenteric resistance arteries.

METHODS

we used pressure myography, quantitative real-time PCR, and immunolocalization to study small (<200 μm) mesenteric arteries (SMA) from young, mature adult, and middle aged mice.

RESULTS

Poiseuille flow calculations indicated autoregulation of blood flow at 60-120 mm Hg arterial pressure. Gαq/11 and Gα12 were abundantly expressed at the mRNA and protein levels in SMA. The Gαq/11 inhibitor YM-254890 suppressed MT development, and the Phosholipase C inhibitors U73122 and ET-18-OCH3 robustly inhibited it. We found an age-dependent increase in ROCK2 mRNA expression, and in basal MT. The specific ROCK2 inhibitor KD025 robustly inhibited MT in SMAs in all mice with an age-dependent variation in KD025 sensitivity. The inhibitory effect of KD025 was not prevented by the L-type Ca2+ channel activator BayK 8644. KD025 reversibly inhibited MT and endothelin-1 vasoconstriction in small pial arteries from Göttingen minipigs.

CONCLUSIONS

MT development in SMAs occurs through a Gαq/11 /PLC/Ca2+ -dependent pathway, and is maintained via ROCK2-mediated Ca2+ sensitization. Increased MT at mature adulthood can be explained by increased ROCK2 expression/activity.

Gαq/p63RhoGEF interaction in RhoA/Rho kinase signaling: investigation in Gitelman's syndrome and implications with hypertension

PURPOSE

Gitelman's syndrome (GS) presents normo-hypotension and absence of cardiovascular-renal remodeling despite high angiotensin II (Ang II), activation of renin-angiotensin-aldosterone system and is a human model of endogenous antagonism of Ang II signaling, opposite to hypertension. GS's clinical presentation leads to questions regarding what features might be responsible. One area of investigation involves Ang II signaling. In hypertensive patients, RhoA/Rho kinase (RhoA/ROCK) pathway activation by Ang II is involved in hypertension development/maintenance and induction of long-term consequences (cardiovascular-renal remodeling), while GS has reduced p63RhoGEF gene and protein levels and ROCK activity. Ang II signaling is mediated by Gαq, which interacts with p63RhoGEF via the α6-αN linker connecting p63RhoGEF's DH and PH domains acting as a conformational switch to activate RhoA/ROCK signaling.

METHODS

We have investigated in GS patients, the presence of mutations in either p63RhoGEF's α6-αN linker domain and in Gαq's Ala253, Trp263, and Tyr356 residues, crucial for p63RhoGEF-Gαq interplay.

RESULTS

No mutations have been found in specific aminoacids of p63RhoGEF α6-αN linker and Gαq, key for p63RhoGEF/Gαq interplay.

CONCLUSIONS

Gitelman's syndrome normo/hypotension and lack of cardiovascular-renal remodeling are not due to mutations of p63RhoGEF α6-αN linker and Gαq interactions. This opens the way for investigations on different coding and no-coding regions (p63RhoGEF and Gαq promoters) and on altered transcriptional/post-transcriptional regulation. Clarification of how these biochemical/molecular mechanisms work/interact would provide insights into mechanisms involved in the GS's Ang II signaling fine tuning, in human physiology/pathophysiology in general and could also identify significant targets for intervention in the treatments of hypertension.

Inhibition of smooth muscle contraction and ARF6 activity by the inhibitor for cytohesin GEFs, secinH3, in the human prostate

Prostate smooth muscle contraction is critical for etiology and treatment of male lower urinary tract symptoms (LUTS) and is promoted by small monomeric GTPases (RhoA and Rac). GTPases may be activated by guanosine nucleotide exchange factors (GEFs). GEFs of the cytohesin family may indirectly activate Rac, or ADP ribosylation factor (ARF) GTPases directly. Here we investigated the expression of cytohesin family GEFs and effects of the cytohesin inhibitor Sec7 inhibitor H3 (secinH3) on smooth muscle contraction and GTPase activities in human prostate tissues. Of all four cytohesin isoforms, cytohesin-1 and -2 showed the highest expression in real-time PCR. Western blot and fluorescence staining suggested that cytohesin-2 may be the predominant isoform in prostate smooth muscle cells. Contractions induced by norepinephrine, the α₁-adrenoceptor agonist phenylephrine, the thromboxane A₂ analog U-46619 , and endothelin-1 and -3, as well as neurogenic contractions induced by electric field stimulation (EFS), were reduced by secinH3 (30 µM). Inhibition of EFS-induced contractions appeared to have efficacy similar to that of inhibition by the α₁-adrenoceptor antagonist tamsulosin (300 nM). Combined application of secinH3 plus tamsulosin caused larger inhibition of EFS-induced contractions than tamsulosin alone. Pull-down assays demonstrated inhibition of the small monomeric GTPase ARF6 by secinH3, but no inhibition of RhoA or Rac1. In conclusion, we suggest that a cytohesin-ARF6 pathway takes part in smooth muscle contraction. This may open attractive new possibilities in medical treatment of male LUTS.

Inhibition of hyaluronan synthesis attenuates pulmonary hypertension associated with lung fibrosis

BACKGROUND AND PURPOSE

Group III pulmonary hypertension (PH) is a highly lethal and widespread lung disorder that is a common complication in idiopathic pulmonary fibrosis (IPF) where it is considered to be the single most significant predictor of mortality. While increased levels of hyaluronan have been observed in IPF patients, hyaluronan-mediated vascular remodelling and the hyaluronan-mediated mechanisms promoting PH associated with IPF are not fully understood.

EXPERIMENTAL APPROACH

Explanted lung tissue from patients with IPF with and without a diagnosis of PH was used to identify increased levels of hyaluronan. In addition, an experimental model of lung fibrosis and PH was used to test the capacity of 4-methylumbeliferone (4MU), a hyaluronan synthase inhibitor to attenuate PH. Human pulmonary artery smooth muscle cells (PASMC) were used to identify the hyaluronan-specific mechanisms that lead to the development of PH associated with lung fibrosis.

KEY RESULTS

In patients with IPF and PH, increased levels of hyaluronan and expression of hyaluronan synthase genes are present. Interestingly, we also report increased levels of hyaluronidases in patients with IPF and IPF with PH. Remarkably, our data also show that 4MU is able to inhibit PH in our model either prophylactically or therapeutically, without affecting fibrosis. Studies to determine the hyaluronan-specific mechanisms revealed that hyaluronan fragments result in increased PASMC stiffness and proliferation but reduced cell motility in a RhoA-dependent manner.

CONCLUSIONS AND IMPLICATIONS

Taken together, our results show evidence of a unique mechanism contributing to PH in the context of lung fibrosis.

Relaxing Responses to Hydrogen Peroxide and Nitric Oxide in Human Pericardial Resistance Arteries Stimulated with Endothelin-1

In human pericardial resistance arteries, effects of the endothelium-dependent vasodilator bradykinin are mediated by NO during contraction induced by K⁺ or the TxA₂ analogue U46619 and by H₂ O₂ during contraction by endothelin-1 (ET-1), respectively. We tested the hypotheses that ET-1 reduces relaxing effects of NO and increases those of H₂ O₂ in resistance artery smooth muscle of patients with cardiovascular disease. Arterial segments, dissected from the parietal pericardium of 39 cardiothoracic surgery patients, were studied by myography during amplitude-matched contractions induced by K⁺ , the TXA₂ analogue U46619 or ET-1. Effects of the NO donor Na-nitroprusside (SNP) and of exogenous H₂ O₂ were recorded in the absence and presence of inhibitors of cyclooxygenases, NO synthases and small and intermediate conductance calcium-activated K⁺ channels. During contractions induced by either of the three stimuli, the potency of SNP did not differ and was not modified by the inhibitors. In vessels contracted with ET-1, the potency of H₂ O₂ was on average and in terms of interindividual variability considerably larger than in K⁺ -contracted vessels. Both differences were not statistically significant in the presence of inhibitors of mechanisms of endothelium-dependent vasodilatation. In resistance arteries from patients with cardiovascular disease, ET-1 does not selectively modify smooth muscle relaxing responses to NO or H₂ O₂ . Furthermore, the candidate endothelium-derived relaxing factor H₂ O₂ also acts as an endothelium-dependent vasodilator.

ROK and Arteriolar Myogenic Tone Generation: Molecular Evidence in Health and Disease

The myogenic response is an inherent property of resistance arteries that warrants a relatively constant blood flow in response to changes in perfusion pressure and protect delicate organs from vascular insufficiencies and excessive blood flow. This fundamental phenomenon has been extensively studied aiming to elucidate the underlying mechanisms triggering smooth muscle contraction in response to intraluminal pressure elevation, particularly, Rho-associated kinase (ROK)-mediated Ca²⁺-independent mechanisms. The size of the resistance arteries limits the capacity to examine changes in protein phosphorylation/expression levels associated with ROK signaling. A highly sensitive biochemical detection approach was beneficial in examining the role of ROK in different force generation mechanisms along the course of myogenic constriction. In this mini review, we summarize recent results showing direct evidence for the contribution of ROK in development of myogenic response at the level of mechanotransduction, myosin light chain phosphatase inhibition and dynamic actin cytoskeleton reorganization. We will also present evidence that alterations in ROK signaling could underlie the progressive loss in myogenic response in a rat model of type 2 diabetes.

GPR78 promotes lung cancer cell migration and metastasis by activation of Gαq-Rho GTPase pathway

GPR78 is an orphan G-protein coupled receptor (GPCR) that is predominantly expressed in human brain tissues. Currently, the function of GPR78 is unknown. This study revealed that GPR78 was expressed in lung cancer cells and functioned as a novel regulator of lung cancer cell migration and metastasis. We found that knockdown of GPR78 in lung cancer cells suppressed cell migration. Moreover, GPR78 modulated the formation of actin stress fibers in A549 cells, in a RhoA- and Rac1-dependent manner. At the molecular level, GPR78 regulated cell motility through the activation of Gαq-RhoA/Rac1 pathway. We further demonstrated that in vivo, the knockdown of GPR78 inhibited lung cancer cell metastasis. These findings suggest that GPR78 is a novel regulator for lung cancer metastasis and may serve as a potential drug target against metastatic human lung cancer. [BMB Reports 2016; 49(11): 623-628].

Kinetics of recruitment and allosteric activation of ARHGEF25 isoforms by the heterotrimeric G-protein Gαq

Rho GTPases are master regulators of the eukaryotic cytoskeleton. The activation of Rho GTPases is governed by Rho guanine nucleotide exchange factors (GEFs). Three RhoGEF isoforms are produced by the gene ARHGEF25; p63RhoGEF⁵⁸⁰, GEFT and a recently discovered longer isoform of 619 amino acids (p63RhoGEF⁶¹⁹). The subcellular distribution of p63RhoGEF⁵⁸⁰ and p63RhoGEF⁶¹⁹ is strikingly different in unstimulated cells, p63RhoGEF⁵⁸⁰ is located at the plasma membrane and p63RhoGEF⁶¹⁹ is confined to the cytoplasm. Interestingly, we find that both P63RhoGEF⁵⁸⁰ and p63RhoGEF⁶¹⁹ activate RhoGTPases to a similar extent after stimulation of Gαq coupled GPCRs. Furthermore, we show that p63RhoGEF⁶¹⁹ relocates to the plasma membrane upon activation of Gαq coupled GPCRs, resembling the well-known activation mechanism of RhoGEFs activated by Gα_12/13. Synthetic recruitment of p63RhoGEF⁶¹⁹ to the plasma membrane increases RhoGEF activity towards RhoA, but full activation requires allosteric activation via Gαq. Together, these findings reveal a dual role for Gαq in RhoGEF activation, as it both recruits and allosterically activates cytosolic ARHGEF25 isoforms.

Heme Oxygenases in Cardiovascular Health and Disease

Heme oxygenases are composed of two isozymes, Hmox1 and Hmox2, that catalyze the degradation of heme to carbon monoxide (CO), ferrous iron, and biliverdin, the latter of which is subsequently converted to bilirubin. While initially considered to be waste products, CO and biliverdin/bilirubin have been shown over the last 20 years to modulate key cellular processes, such as inflammation, cell proliferation, and apoptosis, as well as antioxidant defense. This shift in paradigm has led to the importance of heme oxygenases and their products in cell physiology now being well accepted. The identification of the two human cases thus far of heme oxygenase deficiency and the generation of mice deficient in Hmox1 or Hmox2 have reiterated a role for these enzymes in both normal cell function and disease pathogenesis, especially in the context of cardiovascular disease. This review covers the current knowledge on the function of both Hmox1 and Hmox2 at both a cellular and tissue level in the cardiovascular system. Initially, the roles of heme oxygenases in vascular health and the regulation of processes central to vascular diseases are outlined, followed by an evaluation of the role(s) of Hmox1 and Hmox2 in various diseases such as atherosclerosis, intimal hyperplasia, myocardial infarction, and angiogenesis. Finally, the therapeutic potential of heme oxygenases and their products are examined in a cardiovascular disease context, with a focus on how the knowledge we have gained on these enzymes may be capitalized in future clinical studies.

Endothelin-1 shifts the mediator of bradykinin-induced relaxation from NO to H2 O2 in resistance arteries from patients with cardiovascular disease

BACKGROUND AND PURPOSE

We tested the hypothesis that in resistance arteries from cardiovascular disease (CVD) patients, effects of an endothelium-dependent vasodilator depend on the contractile stimulus.

EXPERIMENTAL APPROACH

Arteries dissected from parietal pericardium of cardiothoracic surgery patients were studied by myography and imaging techniques. Segments were sub-maximally contracted by K(+) , the TxA2 analogue U46619 or endothelin-1 (ET-1).

KEY RESULTS

Relaxing effects of Na-nitroprusside were comparable, but those of bradykinin (BK) were bigger in the presence of ET-1 compared with K(+) or U46619. BK-induced relaxation was (i) abolished by L-NAME in K(+) -contracted arteries, (ii) partly inhibited by L-NAME in the presence of U46619 and (iii) not altered by indomethacin, L-NAME plus inhibitors of small and intermediate conductance calcium-activated K(+) channels, but attenuated by catalase, in ET-1-contracted arteries. This catalase-sensitive relaxation was unaffected by inhibitors of NADPH oxidases or allopurinol. Exogenous H2 O2 caused a larger relaxation of ET-1-induced contractions than those evoked by K(+) or U46619 in the presence of inhibitors of other endothelium-derived relaxing factors. Catalase-sensitive staining of cellular ROS with CellROX Deep Red was significantly increased in the presence of both 1 μM BK and 2 nM ET-1 but not either peptide alone.

CONCLUSIONS AND IMPLICATIONS

In resistance arteries from patients with CVD, exogenous ET-1 shifts the mediator of relaxing responses to the endothelium-dependent vasodilator BK from NO to H2 O2 and neither NADPH oxidases, xanthine oxidase nor NOS appear to be involved in this effect. This might have consequences for endothelial dysfunction in conditions where intra-arterial levels of ET-1 are enhanced.

Understanding the mechanisms of angiotensin II signaling involved in hypertension and its long-term sequelae: insights from Bartter's and Gitelman's syndromes, human models of endogenous angiotensin II signaling antagonism

Angiotensin II (Ang II) plays a key role in hypertension, renal and cardiovascular pathophysiology via intracellular pathways that involve the activation of a multiplicity of signaling mechanisms. Although experimental and genetic animal models have been developed and used to explore Ang II signaling's role in hypertension, a complete understanding of the processes mediating Ang II signaling in hypertension in humans remains elusive. One impediment is that these animal models do not exhibit all the traits of human hypertension, making it impossible to extrapolate from them to humans. To overcome this issue, we have used patients with Bartter's and Gitelman's syndromes, a human model of endogenously blunted and blocked Ang II signaling that presents a constellation of clinical findings which manifest themselves as the opposite of hypertension. This article reviews the aspects of the pathophysiology of human hypertension and its short and long term sequelae, and uses the results of our studies in Bartter's and Gitelman's syndromes along with those of others to gain better insight and understanding of the role of Ang II signaling in these processes.

RhoA signaling and blood pressure: The consequence of failing to “Tone it Down”

Uncontrolled high blood pressure is a major risk factor for heart attack, stroke, and kidney failure and contributes to an estimated 25% of deaths worldwide. Despite numerous treatment options, estimates project that reasonable blood pressure (BP) control is achieved in only about half of hypertensive patients. Improvements in the detection and management of hypertension will undoubtedly be accomplished through a better understanding of the complex etiology of this disease and a more comprehensive inventory of the genes and genetic variants that influence BP regulation. Recent studies (primarily in pre-clinical models) indicate that the small GTPase RhoA and its downstream target, Rho kinase, play an important role in regulating BP homeostasis. Herein, we summarize the underlying mechanisms and highlight signaling pathways and regulators that impart tight spatial-temporal control of RhoA activity. We also discuss known allelic variations in the RhoA pathway and consider how these polymorphisms may affect genetic risk for hypertension and its clinical manifestations. Finally, we summarize the current (albeit limited) clinical data on the efficacy of targeting the RhoA pathway in hypertensive patients.

p63RhoGEF regulates auto- and paracrine signaling in cardiac fibroblasts

Cardiac remodeling, a hallmark of heart disease, is associated with intense auto- and paracrine signaling leading to cardiac fibrosis. We hypothesized that the specific mediator of Gq/11-dependent RhoA activation p63RhoGEF, which is expressed in cardiac fibroblasts, plays a role in the underlying processes. We could show that p63RhoGEF is up-regulated in mouse hearts subjected to transverse aortic constriction (TAC). In an engineered heart muscle model (EHM), p63RhoGEF expression in cardiac fibroblasts increased resting and twitch tensions, and the dominant negative p63ΔN decreased both. In an engineered connective tissue model (ECT), p63RhoGEF increased tissue stiffness and its knockdown as well as p63ΔN reduced stiffness. In 2D cultures of neonatal rat cardiac fibroblasts, p63RhoGEF regulated the angiotensin II (Ang II)-dependent RhoA activation, the activation of the serum response factor, and the expression and secretion of the connective tissue growth factor (CTGF). All these processes were inhibited by the knockdown of p63RhoGEF or by p63ΔN likely based on their negative influence on the actin cytoskeleton. Moreover, we show that p63RhoGEF also regulates CTGF in engineered tissues and correlates with it in the TAC model. Finally, confocal studies revealed a closely related localization of p63RhoGEF and CTGF in the trans-Golgi network.

α5-Integrin-mediated cellular signaling contributes to the myogenic response of cerebral resistance arteries

The myogenic response of resistance arterioles and small arteries involving constriction in response to intraluminal pressure elevation and dilation on pressure reduction is fundamental to local blood flow regulation in the microcirculation. Integrins have garnered considerable attention in the context of initiating the myogenic response, but evidence indicative of mechanotransduction by integrin adhesions, for example established changes in tyrosine phosphorylation of key adhesion proteins, has not been obtained to substantiate this interpretation. Here, we evaluated the role of integrin adhesions and associated cellular signaling in the rat cerebral arterial myogenic response using function-blocking antibodies against α5β1-integrins, pharmacological inhibitors of focal adhesion kinase (FAK) and Src family kinase (SFK), an ultra-high-sensitivity western blotting technique, site-specific phosphoprotein antibodies to quantify adhesion and contractile filament protein phosphorylation, and differential centrifugation to determine G-actin levels in rat cerebral arteries at varied intraluminal pressures. Pressure-dependent increases in the levels of phosphorylation of FAK (FAK-Y397, Y576/Y577), SFK (SFK-Y416; Y527 phosphorylation was reduced), vinculin-Y1065, paxillin-Y118 and phosphoinositide-specific phospholipase C-γ1 (PLCγ1)-Y783 were detected. Treatment with α5-integrin function-blocking antibodies, FAK inhibitor FI-14 or SFK inhibitor SU6656 suppressed the changes in adhesion protein phosphorylation, and prevented pressure-dependent phosphorylation of the myosin targeting subunit of myosin light chain phosphatase (MYPT1) at T855 and 20kDa myosin regulatory light chains (LC20) at S19, as well as actin polymerization that are necessary for myogenic constriction. We conclude that mechanotransduction by integrin adhesions and subsequent cellular signaling play a fundamental role in the cerebral arterial myogenic response.

Mechanistic approach to the pathophysiology of target organ damage in hypertension from studies in a human model with characteristics opposite to hypertension: Bartter's and Gitelman's syndromes

INTRODUCTION

Extensive studies using Bartter's/Gitelman's syndrome patients have provided insights into the angiotensin II (Ang II) signaling pathways involved in the regulation of vascular tone and cardiovascular-renal remodeling. The renin-angiotensin-aldosterone system is activated in these syndromes, however, patients do not develop hypertension and cardiovascular remodeling and clinically manifest conditions opposite to hypertension. The short- and the long-term signaling of Ang II remains an important matter of investigation to shed light on mechanisms responsible for the pathophysiology of hypertension and its long-term complications. The long-term signaling of Ang II is involved in the pathophysiology of cardiovascular-renal remodeling and inflammatory responses in which the balance between RhoA/Rho kinase pathway and NO system plays a crucial role.

METHODS AND RESULTS

In this brief review, the results of our studies in Bartter's and Gitelman's syndromes are reported on these processes.

CONCLUSIONS

The information obtained from these studies can clarify, confirm or be used to extend the biochemical mechanisms responsible for the pathophysiology of hypertension and its long-term complications and could offer further chances to identify additional potential significant targets of therapy.

Angiotensin II and Cardiovascular-Renal Remodelling in Hypertension: Insights from a Human Model Opposite to Hypertension

Insights into the Angiotensin II (Ang II) signalling pathways have been provided by extensive studies using Bartter's/Gitelman's syndromes patients. These syndromes are characterized by activation of the renin-angiotensin-aldosterone system but do not develop hypertension and cardiovascular remodelling, therefore represent a mirror image of hypertension and clinically manifest themselves as the opposite of hypertension. The short and the long-term signalling of Ang II remain an important matter of investigation to shed light on mechanisms responsible for the pathophysiology of hypertension and its long-term complications, such as cardiovascular remodelling and atherogenesis. In particular the long-term signalling of Ang II is involved in the pathophysiology of cardiovascular-renal remodelling, inflammatory and hypertrophic responses in which the relationship between RhoA/Rho kinase pathway and NO system plays a crucial role. This review reports the results of our studies in Bartter's and Gitelman's syndromes to get better insight these processes and the role of Ang II signaling. The information obtained from the studies in Bartter's/Gitelman's patients can, in fact, clarify, confirm or be used to gather more general data on the biochemical mechanisms responsible for the pathophysiology of hypertension and its long-term complications and could contribute to identify additional potential significant targets of therapy.

Signaling pathways that control rho kinase activity maintain the embryonic epicardial progenitor state

This study identifies signaling pathways that play key roles in the formation and maintenance of epicardial cells, a source of progenitors for coronary smooth muscle cells (SMCs). After epithelial to mesenchymal transition (EMT), mesenchymal cells invade the myocardium to form coronary SMCs. RhoA/Rho kinase activity is required for EMT and for differentiation into coronary SMCs, whereas cAMP activity is known to inhibit EMT in epithelial cells by an unknown mechanism. We use outgrowth of epicardial cells from E9.5 isolated mouse proepicardium (PE) explants, wild type and Epac1 null E12.5 mouse heart explants, adult rat epicardial cells, and immortalized mouse embryonic epicardial cells as model systems to identify signaling pathways that regulate RhoA activity to maintain the epicardial progenitor state. We demonstrate that RhoA activity is suppressed in the epicardial progenitor state, that the cAMP-dependent Rap1 GTP exchange factor (GEF), Epac, known to down-regulate RhoA activity through activation of Rap1 GTPase activity increased, that Rap1 activity increased, and that expression of the RhoA antagonistic Rnd proteins known to activate p190RhoGAP increased and associated with p190RhoGAP. Finally, EMT is associated with increased p63RhoGEF and RhoGEF-H1 protein expression, increased GEF-H1 activity, with a trend in increased p63RhoGEF activity. EMT is suppressed by partial silencing of p63RhoGEF and GEF-H1. In conclusion, we have identified new signaling molecules that act together to control RhoA activity and play critical roles in the maintenance of coronary smooth muscle progenitor cells in the embryonic epicardium. We suggest that their eventual manipulation could promote revascularization after myocardial injury.

A molecular signature in the pannexin1 intracellular loop confers channel activation by the α1 adrenoreceptor in smooth muscle cells

Both purinergic signaling through nucleotides such as ATP (adenosine 5'-triphosphate) and noradrenergic signaling through molecules such as norepinephrine regulate vascular tone and blood pressure. Pannexin1 (Panx1), which forms large-pore, ATP-releasing channels, is present in vascular smooth muscle cells in peripheral blood vessels and participates in noradrenergic responses. Using pharmacological approaches and mice conditionally lacking Panx1 in smooth muscle cells, we found that Panx1 contributed to vasoconstriction mediated by the α1 adrenoreceptor (α1AR), whereas vasoconstriction in response to serotonin or endothelin-1 was independent of Panx1. Analysis of the Panx1-deficient mice showed that Panx1 contributed to blood pressure regulation especially during the night cycle when sympathetic nervous activity is highest. Using mimetic peptides and site-directed mutagenesis, we identified a specific amino acid sequence in the Panx1 intracellular loop that is essential for activation by α1AR signaling. Collectively, these data describe a specific link between noradrenergic and purinergic signaling in blood pressure homeostasis.

Involvement of Rho GTPases and their regulators in the pathogenesis of hypertension

Proper regulation of arterial blood pressure is essential to allow permanent adjustment of nutrient and oxygen supply to organs and tissues according to their need. This is achieved through highly coordinated regulation processes controlling vascular resistance through modulation of arterial smooth muscle contraction, cardiac output, and kidney function. Members of the Rho family of small GTPases, in particular RhoA and Rac1, have been identified as key signaling molecules playing important roles in several different steps of these regulatory processes. Here, we review the current state of knowledge regarding the involvement of Rho GTPase signaling in the control of blood pressure and the pathogenesis of hypertension. We describe how knockout models in mouse, genetic, and pharmacological studies in human have been useful to address this question.

Increased level of p63RhoGEF and RhoA/Rho kinase activity in hypertensive patients

OBJECTIVE

p63RhoGEF, a guanine nucleotide exchange factor, has been reported 'in vitro' as key mediator of the angiotensin II-induced RhoA/Rho kinase activation leading to vasoconstriction and cardiovascular remodeling. We assessed p63RhoGEF gene and protein expression and RhoA/Rho kinase activity in essential hypertensive and Bartter's and Gitelman's syndrome patients, a human model opposite to hypertension; the latter have, in fact, increased plasma angiotensin II, activation of the renin-angiotensin system, yet normotension/hypotension, reduced peripheral resistance and lack of cardiovascular remodeling due to an endogenously blunted angiotensin II type 1 receptor signaling.

METHODS

Mononuclear cell p63RhoGEF gene and protein expression and the phosphorylation status of the myosin phosphatase target protein-1 (MYPT-1), marker of Rho kinase activity, were assessed in essential hypertensive patients, Bartter's/Gitelman's patients and healthy individuals by quantitative real-time PCR and western blot.

RESULTS

p63RhoGEF mRNA and protein level and MYPT-1 phosphorylation status were higher in hypertensive patients and lower in Bartter's/Gitelman's patients compared with healthy individuals: p63RhoGEF mRNA level: 0.59 ± 0.17 ΔΔCt vs. 0.37 ± 0.17 vs. 0.20 ± 0.19, analysis of variance (ANOVA): P <0.016; p63RhoGEF protein level 1.35 ± 0.14 vs. 1.09 ± 0.05 vs. 0.90 ± 0.09 densitometric units, ANOVA: P <0.0001; MYPT-1: 1.39 ± 0.34 vs. 1.01 ± 0.12 vs. 0.81 ± 0.06, ANOVA: P < 0.0001. p63RhoGEF mRNA was significantly correlated with both SBP and DBP in both hypertensive patients (R = 0.79, P < 0.02 and R = 0.78, P < 0.02) and in Bartter's syndrome/Gitelman's syndrome patients (R = 0.87, P < 0.001 and R = 0.86, P < 0.001), respectively.

CONCLUSION

Increased p63RhoGEF mRNA and protein level and Rho kinase activity are shown for the first time in essential hypertensive patients, whereas the opposite was found in Bartter's/Gitelman's patients, a human model opposite to hypertension. These results combined with other 'in-vitro' studies strongly support the crucial importance of p63RhoGEF in Ang II-mediated signaling involved in the regulation of blood pressure and its long-term complications in humans.

Herbal Prescription, DSGOST, Prevents Cold-Induced RhoA Activation and Endothelin-1 Production in Endothelial Cells

Herbal prescription, Danggui-Sayuk-Ga-Osuyu-Saenggang-tang (DSGOST), has long been used to treat Raynaud's phenomenon (RP) in traditional Chinese medicine (TCM). However, a biological mechanism by which DSGOST ameliorates RP is yet deciphered. In this study, we demonstrate that DSGOST inhibits cold-induced activation of RhoA, in both vascular smooth muscle cells (VSMC) and endothelial cells (EC), and blocks endothelin-1-mediated paracrine path for cold response on vessels. While cold induced RhoA activity in both cell types, DSGOST pretreatment prevented cold-induced RhoA activation. DSGOST inhibition of cold-induced RhoA activation further blocked α2c-adrenoreceptor translocation to the plasma membrane in VSMC. In addition, DSGOST inhibited endothelin-1-mediated RhoA activation and α2c-adrenoreceptor translocation in VSMC. Meanwhile, DSGOST inhibited cold-induced or RhoA-dependent phosphorylation of FAK, SRC, and ERK. Consistently, DSGOST inhibited cold-induced endothelin-1 expression in EC. Therefore, DSGOST prevents cold-induced RhoA in EC and blocks endothelin-1-mediated paracrine path between EC and VSMC. In conclusion, our data suggest that DSGOST is beneficial for treating RP-like syndrome.

Dynamics of Gαq-protein-p63RhoGEF interaction and its regulation by RGS2

Some G-protein-coupled receptors regulate biological processes via Gα12/13- or Gαq/11-mediated stimulation of RhoGEFs (guanine-nucleotide-exchange factors). p63RhoGEF is known to be specifically activated by Gαq/11 and mediates a major part of the acute response of vascular smooth muscle cells to angiotensin II treatment. In order to gain information about the dynamics of receptor-mediated activation of p63RhoGEF, we developed a FRET-based assay to study interactions between Gαq-CFP and Venus-p63RhoGEF in single living cells. Upon activation of histaminergic H1 or muscarinic M3 receptors, a robust FRET signal occurred that allowed for the first time the analysis of the kinetics of this interaction in detail. On- and off-set kinetics of Gαq-p63RhoGEF interactions closely resembled the kinetics of Gαq activity. Analysis of the effect of RGS2 (regulator of G-protein signalling 2) on the dynamics of Gαq activity and their interaction with p63RhoGEF showed that RGS2 is able to accelerate both deactivation of Gαq proteins and dissociation of Gαq and p63RhoGEF to a similar extent. Furthermore, we were able to detect activation-dependent FRET between RGS2 and p63RhoGEF and observed a reduced p63RhoGEF-mediated downstream signalling in the presence of RGS2. In summary, these observations support the concept of a functional activation-dependent p63RhoGEF-Gαq-RGS2 complex.

Overexpression of GEFT, a Rho family guanine nucleotide exchange factor, predicts poor prognosis in patients with rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is one of the most common soft-tissue sarcomas in children and adolescents with poor prognosis. Yet, there is lack of effective prognostic biomarkers for RMS. The present study, therefore, aimed to explore potential biomarkers for RMS based on our previous findings using array comparative genomic hybridization. We investigated guanine nucleotide exchange factor, GEFT, at expression level in 45 RMS patients and 36 normal striated muscle controls using immunohistochemistry using tissue microarrays. The expression rate of GEFT in RMS samples (42/45, 93.33%) was significantly higher (P<0.05) than that in normal controls (5/36, 13.89%). Moreover, the overexpression rate of GEFT in RMS (31/45, 68.89%) was also significantly higher (P<0.05) than that in normal controls (0/36, 0.00%). Increased expression of GEFT correlated significantly with advanced disease stages (stages III/IV) (P=0.001), lymph node metastasis (P=0.019), and distant metastasis (P=0.004), respectively, in RMS patients. In addition, RMS patients having overexpressed GEFT experienced worse overall survival (OS) than those having low levels of GEFT (P=0.001). GEFT overexpression was determined to be an independent prognostic factor for poor OS in RMS patients (hazard ratio: 3.491, 95% confidence interval: 1.121-10.871, P=0.004). In conclusion, these observations provide the first evidence of GEFT overexpression in RMS and its correlations with disease aggressiveness and metastasis. These findings suggest that GEFT may serve as a promising biomarker predicting poor prognosis in RMS patients, thus implying its potential as a therapeutic target.

Signaling efficiency of Gαq through its effectors p63RhoGEF and GEFT depends on their subcellular location

The p63RhoGEF and GEFT proteins are encoded by the same gene and both members of the Dbl family of guanine nucleotide exchange factors. These proteins can be activated by the heterotrimeric G-protein subunit Gαq. We show that p63RhoGEF is located at the plasma membrane, whereas GEFT is confined to the cytoplasm. Live-cell imaging studies yielded quantitative information on diffusion coefficients, association rates and encounter times of GEFT and p63RhoGEF. Calcium signaling was examined as a measure of the signal transmission, revealing more efficient signaling through the membrane-associated p63RhoGEF. A rapamycin dependent recruitment system was used to dynamically alter the subcellular location and concentration of GEFT, showing efficient signaling through GEFT only upon membrane recruitment. Together, our results show efficient signal transmission through membrane located effectors, and highlight a role for increased concentration rather than increased encounter times due to membrane localization in the Gαq mediated pathways to p63RhoGEF and PLCβ.

Rho-kinase: regulation, (dys)function, and inhibition

In a variety of normal and pathological cell types, Rho-kinases I and II (ROCKI/II) play a pivotal role in the organization of the nonmuscle and smooth muscle cytoskeleton and adhesion plaques as well as in the regulation of transcription factors. Thus, ROCKI/II activity regulates cellular contraction, motility, morphology, polarity, cell division, and gene expression. Emerging evidence suggests that dysregulation of the Rho-ROCK pathways at different stages is linked to cardiovascular, metabolic, and neurodegenerative diseases as well as cancer. This review focuses on the current status of understanding the multiple functions of Rho-ROCK signaling pathways and various modes of regulation of Rho-ROCK activity, thereby orchestrating a concerted functional response.

Interactions between thromboxane A₂, thromboxane/prostaglandin (TP) receptors, and endothelium-derived hyperpolarization

Endothelium-dependent smooth muscle hyperpolarization (EDH) increasingly predominates over endothelium-derived nitric oxide (NO) as a participant in vasodilation as vessel size decreases. Its underlying nature is highly variable between vessel types, species, disease states, and exact experimental conditions, and is variably mediated by one or more transferable endothelium-derived hyperpolarizing factors and/or the electrotonic spread of endothelial hyperpolarization into the media via gap junctions. Although generally regarded (and studied) as a mechanism that is independent of NO and prostanoids, evidence has emerged that the endothelium-derived contracting factor and prostanoid thromboxane A2 can modulate several signalling components central to EDH, and therefore potentially curtail vasodilation through mechanisms that are distinct from those putatively involved in direct smooth muscle contraction. Notably, vascular production of thromboxane A2 is elevated in a number of cardiovascular disease states that promote endothelial dysfunction. This review will therefore discuss the mechanisms through which thromboxane A2 interacts with and modulates EDH, and will also consider the implications of such cross-talk in vasodilator control in health and disease.

A new non-canonical pathway of Gα(q) protein regulating mitochondrial dynamics and bioenergetics

Contrary to previous assumptions, G proteins do not permanently reside on the plasma membrane, but are constantly monitoring the cytoplasmic surfaces of the plasma membrane and endomembranes. Here, we report that the Gαq and Gα11 proteins locate at the mitochondria and play a role in a complex signaling pathway that regulates mitochondrial dynamics. Our results provide evidence for the presence of the heteromeric G protein (Gαq/11βγ) at the outer mitochondrial membrane and for Gαq at the inner membrane. Both localizations are necessary to maintain the proper equilibrium between fusion and fission; which is achieved by altering the activity of mitofusin proteins, Drp1, OPA1 and the membrane potential at both the outer and inner mitochondrial membranes. As a result of the absence of Gαq/11, there is a decrease in mitochondrial fusion rates and a decrease in overall respiratory capacity, ATP production and OXPHOS-dependent growth. These findings demonstrate that the presence of Gαq proteins at the mitochondria serves as a physiological function: stabilizing elongated mitochondria and regulating energy production in Drp1 and Opa1 dependent mechanisms. This thereby links organelle dynamics and physiology.

Altered reactivity of resistance vasculature contributes to hypertension in elastin insufficiency

Elastin (Eln) insufficiency in mice and humans is associated with hypertension and altered structure and mechanical properties of large arteries. However, it is not known to what extent functional or structural changes in resistance arteries contribute to the elevated blood pressure that is characteristic of Eln insufficiency. Here, we investigated how Eln insufficiency affects the structure and function of the resistance vasculature. A functional profile of resistance vasculature in Eln(+/-) mice was generated by assessing small mesenteric artery (MA) contractile and vasodilatory responses to vasoactive agents. We found that Eln haploinsufficiency had a modest effect on phenylephrine-induced vasoconstriction, whereas ANG II-evoked vasoconstriction was markedly increased. Blockade of ANG II type 2 receptors with PD-123319 or modulation of Rho kinase activity with the inhibitor Y-27632 attenuated the augmented vasoconstriction, whereas acute Y-27632 administration normalized blood pressure in Eln(+/-) mice. Sodium nitroprusside- and isoproterenol-induced vasodilatation were normal, whereas ACh-induced vasodilatation was severely impaired in Eln(+/-) MAs. Histologically, the number of smooth muscle layers did not change in Eln(+/-) MAs; however, an additional discontinuous layer of Eln appeared between the smooth muscle layers that was absent in wild-type arteries. We conclude that high blood pressure arising from Eln insufficiency is due partly to permanent changes in vascular tone as a result of increased sensitivity of the resistance vasculature to circulating ANG II and to impaired vasodilatory mechanisms arising from endothelial dysfunction characterized by impaired endothelium-dependent vasodilatation. Eln insufficiency causes augmented ANG II-induced vasoconstriction in part through a novel mechanism that facilitates contraction evoked by ANG II type 2 receptors and altered G protein signaling.

Strike a pose: Gαq complexes at the membrane

The heterotrimeric G protein Gαq is a central player in signal transduction, relaying signals from activated G-protein-coupled receptors (GPCRs) to effectors and other proteins to elicit changes in intracellular Ca(2+), the actin cytoskeleton, and gene transcription. Gαq functions at the intracellular surface of the plasma membrane, as do its best-characterized targets, phospholipase C-β, p63RhoGEF, and GPCR kinase 2 (GRK2). Recent insights into the structure and function of these signaling complexes reveal several recurring themes, including complex multivalent interactions between Gαq, its protein target, and the membrane, that are likely essential for allosteric control and maximum efficiency in signal transduction. Thus, the plasma membrane is not only a source of substrates but also a key player in the scaffolding of Gαq-dependent signaling pathways.

The P2Y6 receptor mediates Clostridium difficile toxin-induced CXCL8/IL-8 production and intestinal epithelial barrier dysfunction

C. difficile is a Gram-positive spore-forming anaerobic bacterium that is the leading cause of nosocomial diarrhea in the developed world. The pathogenesis of C. difficile infections (CDI) is driven by toxin A (TcdA) and toxin B (TcdB), secreted factors that trigger the release of inflammatory mediators and contribute to disruption of the intestinal epithelial barrier. Neutrophils play a key role in the inflammatory response and the induction of pseudomembranous colitis in CDI. TcdA and TcdB alter cytoskeletal signaling and trigger the release of CXCL8/IL-8, a potent neutrophil chemoattractant, from intestinal epithelial cells; however, little is known about the surface receptor(s) that mediate these events. In the current study, we sought to assess whether toxin-induced CXCL8/IL-8 release and barrier dysfunction are driven by the activation of the P2Y₆ receptor following the release of UDP, a danger signal, from intoxicated Caco-2 cells. Caco-2 cells express a functional P2Y₆ receptor and release measurable amounts of UDP upon exposure to TcdA/B. Toxin-induced CXCL8/IL-8 production and release were attenuated in the presence of a selective P2Y₆ inhibitor (MRS2578). This was associated with inhibition of TcdA/B-induced activation of NFκB. Blockade of the P2Y₆ receptor also attenuated toxin-induced barrier dysfunction in polarized Caco-2 cells. Lastly, pretreating mice with the P2Y₆ receptor antagonists (MSR2578) attenuated TcdA/B-induced inflammation and intestinal permeability in an intrarectal toxin exposure model. Taken together these data outline a novel role for the P2Y₆ receptor in the induction of CXCL8/IL-8 production and barrier dysfunction in response to C. difficile toxin exposure and may provide a new therapeutic target for the treatment of CDI.

Agonist-induced Ca2+ sensitization in smooth muscle: redundancy of Rho guanine nucleotide exchange factors (RhoGEFs) and response kinetics, a caged compound study

Many agonists, acting through G-protein-coupled receptors and Gα subunits of the heterotrimeric G-proteins, induce contraction of smooth muscle through an increase of [Ca(2+)]i as well as activation of the RhoA/RhoA-activated kinase pathway that amplifies the contractile force, a phenomenon known as Ca(2+) sensitization. Gα12/13 subunits are known to activate the regulator of G-protein signaling-like family of guanine nucleotide exchange factors (RhoGEFs), which includes PDZ-RhoGEF (PRG) and leukemia-associated RhoGEF (LARG). However, their contributions to Ca(2+)-sensitized force are not well understood. Using permeabilized blood vessels from PRG(-/-) mice and a new method to silence LARG in organ-cultured blood vessels, we show that both RhoGEFs are activated by the physiologically and pathophysiologically important thromboxane A2 and endothelin-1 receptors. The co-activation is the result of direct and independent activation of both RhoGEFs as well as their co-recruitment due to heterodimerization. The isolated recombinant C-terminal domain of PRG, which is responsible for heterodimerization with LARG, strongly inhibited Ca(2+)-sensitized force. We used photolysis of caged phenylephrine, caged guanosine 5'-O-(thiotriphosphate) (GTPγS) in solution, and caged GTPγS or caged GTP loaded on the RhoA·RhoGDI complex to show that the recruitment and activation of RhoGEFs is the cause of a significant time lag between the initial Ca(2+) transient and phasic force components and the onset of Ca(2+)-sensitized force.

Small G Proteins in the Cardiovascular System: Physiological and Pathological Aspects

Small G proteins exist in eukaryotes from yeast to human and constitute the Ras superfamily comprising more than 100 members. This superfamily is structurally classified into five families: the Ras, Rho, Rab, Arf, and Ran families that control a wide variety of cell and biological functions through highly coordinated regulation processes. Increasing evidence has accumulated to identify small G proteins and their regulators as key players of the cardiovascular physiology that control a large panel of cardiac (heart rhythm, contraction, hypertrophy) and vascular functions (angiogenesis, vascular permeability, vasoconstriction). Indeed, basal Ras protein activity is required for homeostatic functions in physiological conditions, but sustained overactivation of Ras proteins or spatiotemporal dysregulation of Ras signaling pathways has pathological consequences in the cardiovascular system. The primary object of this review is to provide a comprehensive overview of the current progress in our understanding of the role of small G proteins and their regulators in cardiovascular physiology and pathologies.

GPR116, an adhesion G-protein-coupled receptor, promotes breast cancer metastasis via the Gαq-p63RhoGEF-Rho GTPase pathway

Adhesion G-protein-coupled receptors (GPCR), which contain adhesion domains in their extracellular region, have been found to play important roles in cell adhesion, motility, embryonic development, and immune response. Because most adhesion molecules with adhesion domains have vital roles in cancer metastasis, we speculated that adhesion GPCRs are potentially involved in cancer metastasis. In this study, we identified GPR116 as a novel regulator of breast cancer metastasis through expression and functional screening of the adhesion GPCR family. We found that knockdown of GPR116 in highly metastatic (MDA-MB-231) breast cancer cells suppressed cell migration and invasion. Conversely, ectopic GPR116 expression in poorly metastatic (MCF-7 and Hs578T) cells promoted cell invasion. We further showed that knockdown of GPR116 inhibited breast cancer cell metastasis in two mammary tumor metastasis mouse models. Moreover, GPR116 modulated the formation of lamellipodia and actin stress fibers in cells in a RhoA- and Rac1-dependent manner. At a molecular level, GPR116 regulated cell motility and morphology through the Gαq-p63RhoGEF-RhoA/Rac1 pathway. The biologic significance of GPR116 in breast cancer is substantiated in human patient samples, where GPR116 expression is significantly correlated with breast tumor progression, recurrence, and poor prognosis. These findings show that GPR116 is crucial for the metastasis of breast cancer and support GPR116 as a potential prognostic marker and drug target against metastatic human breast cancer.