Hypertension and prolonged vasoconstrictor signaling in RGS2-deficient mice

Regulators of G-protein signalling are modulated by bacterial lipopeptides and lipopolysaccharide

Regulators of G-protein signalling accelerate the GTPase activity of G(alpha) subunits, driving G proteins in their inactive GDP-bound form. This property defines them as GTPase activating proteins. Here the effect of different Toll-like receptor agonists on RGS1 and RGS2 expression in murine bone marrow-derived macrophages and J774 cells was analysed. After stimulation with TLR2/1 or TLR2/6 lipopeptide ligands and the TLR4/MD2 ligand lipopolysaccharide, microarray analyses show only modulation of RGS1 and RGS2 among all the regulators of G-protein signalling tested. Real-time PCR confirmed modulation of RGS1 and RGS2. In contrast to RGS2, which was always downregulated, RGS1 mRNA was upregulated during the first 30 min after stimulation, followed by downregulation. Similar results were also found in the murine macrophage cell line J774. The ligand for intracellular TLR9 modulates RGS1 and RGS2 in a similar manner. However, the TLR3 ligand poly(I:C) permanently upregulates RGS1 and RGS2 expression indicating a different modulation by the MyD88- and TRIF-signalling pathway. This was confirmed using MyD88(-/-) and TRIF(-/-) bone marrow-derived macrophages. Modulation of RGS1 and RGS2 by Toll-like receptor ligands plays an important role during inflammatory and immunological reactions after bacterial and viral infection.

Regulator of G-protein signaling 4 suppresses LPS-induced MUC5AC overproduction in the airway

Mucus overproduction and airway obstruction are common features in airway mucosal inflammation. The mechanism by which LPS induces MUC5AC overexpression, however, has not been fully explored. The aims of this study were twofold: first, to examine the ATP-dependent mechanism by which LPS induces MUC5AC gene expression, and second, to identify specific molecules that could suppress LPS-induced MUC5AC expression at a G-protein-coupled receptor level. Here, we suggest that LPS from Pseudomonas aeruginosa induces MUC5AC overproduction by both an ATP-dependent pathway and an ATP-independent pathway. In addition, we showed that Regulator of G-protein signaling (RGS) 4 plays as a suppressor for ATP-induced MUC5AC expression by interacting with G alpha q in a GTP-dependent manner in vivo. These results give additional insights into the molecular mechanism of negative regulation of mucin overproduction and enhance our understanding of mucus hypersecretion during airway mucosal inflammation.

Regulator of G-protein signalling expression and function in ovarian cancer cell lines

Regulator of G-protein signalling (RGS)(2) proteins critically regulate signalling cascades initiated by G-protein coupled receptors (GPCRs) by accelerating the deactivation of heterotrimeric G-proteins. Lysophosphatidic acid (LPA) is the predominant growth factor that drives the progression of ovarian cancer by activating specific GPCRs and G-proteins expressed in ovarian cancer cells. We have recently reported that RGS proteins endogenously expressed in SKOV-3 ovarian cancer cells dramatically attenuate LPA stimulated cell signalling. The goal of this study was twofold: first, to identify candidate RGS proteins expressed in SKOV-3 cells that may account for the reported negative regulation of G-protein signalling, and second, to determine if these RGS protein transcripts are differentially expressed among commonly utilized ovarian cancer cell lines and non-cancerous ovarian cell lines. Reverse transcriptase-PCR was performed to determine transcript expression of 22 major RGS subtypes in RNA isolated from SKOV-3, OVCAR-3 and Caov-3 ovarian cancer cell lines and non-cancerous immortalized ovarian surface epithelial (IOSE) cells. Fifteen RGS transcripts were detected in SKOV-3 cell lines. To compare the relative expression levels in these cell lines, quantitative real time RT-PCR was performed on select transcripts. RGS19/GAIP was expressed at similar levels in all four cell lines, while RGS2 transcript was detected at levels slightly lower in ovarian cancer cells as compared to IOSE cells. RGS4 and RGS6 transcripts were expressed at dramatically different levels in ovarian cancer cell lines as compared to IOSE cells. RGS4 transcript was detected in IOSE at levels several thousand fold higher than its expression level in ovarian cancer cells lines, while RGS6 transcript was expressed fivefold higher in SKOV-3 cells as compared to IOSE cells, and over a thousand fold higher in OVCAR-3 and Caov-3 cells as compared to IOSE cells. Functional studies of RGS 2, 6, and 19/GAIP were performed by measuring their effects on LPA stimulated production of inositol phosphates. In COS-7 cells expressing individual exogenous LPA receptors, RGS2 and RSG19/GAIP attenuated signalling initiated by LPA1, LPA2, or LPA3, while RGS6 only inhibited signalling initiated by LPA2 receptors. In SKOV-3 ovarian cancer cells, RGS2 but not RGS6 or RGS19/GAIP, inhibited LPA stimulated inositol phosphate production. In contrast, in CAOV-3 cells RGS19/GAIP strongly attenuated LPA signalling. Thus, multiple RGS proteins are expressed at significantly different levels in cells derived from cancerous and normal ovarian cells and at least two candidate RGS transcripts have been identified to account for the reported regulation of LPA signalling pathways in ovarian cancer cells.

S1P receptor signalling and RGS proteins; expression and function in vascular smooth muscle cells and transfected CHO cells

Sphingosine-1-phosphate (S1P) signalling via G protein-coupled receptors is important for the regulation of cell function and differentiation. Specific Regulators of G protein Signalling (RGS) proteins modulate the function of these receptors in many cell types including vascular smooth muscle cells (VSMCs). Therefore, we investigated the role of altered expression levels of RGS proteins in S1P receptor function in VSMCs and transfected CHO cells. The mRNA expression of the S1P(1) receptor, RGS4 and RGS16 were down-regulated in VSMCs during phenotypic modulation induced by culturing, whereas mRNA levels of RGS2, RGS3, S1P(2) and S1P(3) receptors were unchanged. Interestingly, the expression level of RGS5 was transiently up-regulated. Despite major alterations in RGS levels, S1P-induced calcium elevation in VSMCs was not altered. Co-transfection of RGS2, RGS3, RGS4, RGS5 and RGS16 into CHO-Flp-In cells stably expressing the S1P(1) or S1P(3) receptor did not modify S1P-induced inhibition of cAMP accumulation to a major extent. Similar results were obtained with SEW2871, a selective S1P(1) receptor agonist. However, the inhibition of cAMP accumulation by the agonist FTY720-P via the S1P(1) receptor was significantly decreased by co-transfection with RGS5. These results indicate that mRNA of the S1P(1) receptor, RGS4, RGS5 and RGS16 is differentially regulated during phenotypic modulation. However, major alterations in RGS protein expression have only limited effect on S1P receptor function.

Role of the Multidomain Protein Spinophilin in Blood Pressure and Cardiac Function Regulation

Spinophilin controls intensity/duration of G protein-coupled receptor signaling and thereby influences synaptic activity. We hypothesize that spinophilin affects blood pressure through central mechanisms. We measured blood pressure and heart rate in SPL-deficient (SPL −/− ), heterozygous SPL-deficient (SPL +/− ), and wild-type (SPL +/+ ) mice by telemetry combined with fast Fourier transformation. We also assessed peripheral vascular reactivity and performed echocardiography. SPL −/− had higher mean arterial pressure than SPL +/− and SPL +/+ (121±2, 112±1, and 113±1 mm Hg). Heart rate was inversely related to spinophilin expression (SPL −/− 565±0.4, SPL +/− 541±5, SPL +/+ 525±8 bpm). The blood pressure response to prazosin, trimethapane, and the heart rate response to metoprolol were stronger in SPL −/− than SPL +/+ mice, whereas heart rate response to atropine was attenuated in SPL −/− . Mesenteric artery vasoreactivity after angiotensin II, phenylephrine, and the thromboxane mimetic (U46619) as well as change in heart rate, stroke volume, and cardiac output after dobutamine were similar in SPL −/− and SPL +/+ . Baroreflex sensitivity was attenuated in SPL −/− compared with SPL +/− and SPL +/+ , which was confirmed by pharmacological testing. Heart rate variability parameters were attenuated in SPL −/− mice. We suggest that an increase in central sympathetic outflow participates in blood pressure and heart rate increases in SPL −/− mice. The elevated blood pressure in SPL −/− mice was associated with attenuated baroreflex sensitivity and decreased parasympathetic activity. Our study is the first to show a role for the spinophilin gene in blood pressure regulation.

Regulator of G-protein signaling subtype 4 mediates antihypertrophic effect of locally secreted natriuretic peptides in the heart

BACKGROUND

Mice lacking guanylyl cyclase-A (GC-A), a natriuretic peptide receptor, have pressure-independent cardiac hypertrophy. However, the mechanism underlying GC-A-mediated inhibition of cardiac hypertrophy remains to be elucidated. In the present report, we examined the role of regulator of G-protein signaling subtype 4 (RGS4), a GTPase activating protein for G(q) and G(i), in the antihypertrophic effects of GC-A.

METHODS AND RESULTS

In cultured cardiac myocytes, treatment of atrial natriuretic peptide stimulated the binding of guanosine 3',5'-cyclic monophosphate-dependent protein kinase (PKG) I-alpha to RGS4, PKG-dependent phosphorylation of RGS4, and association of RGS4 and Galpha(q). In contrast, blockade of GC-A by an antagonist, HS-142-1, attenuated the phosphorylation of RGS4 and association of RGS4 and Galpha(q). Moreover, overexpressing a dominant negative form of RGS4 diminished the inhibitory effects of atrial natriuretic peptide on endothelin-1-stimulated inositol 1,4,5-triphosphate production, [(3)H]leucine incorporation, and atrial natriuretic peptide gene expression. Furthermore, expression and phosphorylation of RGS4 were significantly reduced in the hearts of GC-A knockout (GC-A-KO) mice compared with wild-type mice. For further investigation, we constructed cardiomyocyte-specific RGS4 transgenic mice and crossbred them with GC-A-KO mice. The cardiac RGS4 overexpression in GC-A-KO mice significantly reduced the ratio of heart to body weight (P<0.001), cardiomyocyte size (P<0.01), and ventricular calcineurin activity (P<0.05) to 80%, 76%, and 67% of nontransgenic GC-A-KO mice, respectively. It also significantly suppressed the augmented cardiac expression of hypertrophy-related genes in GC-A-KO mice.

CONCLUSIONS

These results provide evidence that GC-A activates cardiac RGS4, which attenuates Galpha(q) and its downstream hypertrophic signaling, and that RGS4 plays important roles in GC-A-mediated inhibition of cardiac hypertrophy.

Structural diversity in the RGS domain and its interaction with heterotrimeric G protein alpha-subunits

Regulator of G protein signaling (RGS) proteins accelerate GTP hydrolysis by Galpha subunits and thus facilitate termination of signaling initiated by G protein-coupled receptors (GPCRs). RGS proteins hold great promise as disease intervention points, given their signature role as negative regulators of GPCRs-receptors to which the largest fraction of approved medications are currently directed. RGS proteins share a hallmark RGS domain that interacts most avidly with Galpha when in its transition state for GTP hydrolysis; by binding and stabilizing switch regions I and II of Galpha, RGS domain binding consequently accelerates Galpha-mediated GTP hydrolysis. The human genome encodes more than three dozen RGS domain-containing proteins with varied Galpha substrate specificities. To facilitate their exploitation as drug-discovery targets, we have taken a systematic structural biology approach toward cataloging the structural diversity present among RGS domains and identifying molecular determinants of their differential Galpha selectivities. Here, we determined 14 structures derived from NMR and x-ray crystallography of members of the R4, R7, R12, and RZ subfamilies of RGS proteins, including 10 uncomplexed RGS domains and 4 RGS domain/Galpha complexes. Heterogeneity observed in the structural architecture of the RGS domain, as well as in engagement of switch III and the all-helical domain of the Galpha substrate, suggests that unique structural determinants specific to particular RGS protein/Galpha pairings exist and could be used to achieve selective inhibition by small molecules.

Regulation of G protein-coupled receptor signalling: focus on the cardiovascular system and regulator of G protein signalling proteins

G protein-coupled receptors (GPCRs) are involved in many biological processes. Therefore, GPCR function is tightly controlled both at receptor level and at the level of signalling components. Well-known mechanisms by which GPCR function can be regulated comprise desensitization/resensitization processes and GPCR up- and downregulation. GPCR function can also be regulated by several proteins that directly interact with the receptor and thereby modulate receptor activity. An additional mechanism by which receptor signalling is regulated involves an emerging class of proteins, the so-called regulators of G protein signalling (RGS). In this review we will describe some of these control mechanisms in more detail with some specific examples in the cardiovascular system. In addition, we will provide an overview on RGS proteins and the involvement of RGS proteins in cardiovascular function.

Regulator of G-protein signalling 2 mRNA is differentially expressed in mammary epithelial subpopulations and over-expressed in the majority of breast cancers

Introduction

To understand which signalling pathways become deregulated in breast cancer, it is necessary to identify functionally significant gene expression patterns in the stem, progenitor, transit amplifying and differentiated cells of the mammary epithelium. We have previously used the markers 33A10, CD24 and Sca-1 to identify mouse mammary epithelial cell subpopulations. We now investigate the relationship between cells expressing these markers and use gene expression microarray analysis to identify genes differentially expressed in the cell populations.

Methods

Freshly isolated primary mouse mammary epithelial cells were separated on the basis of staining with the 33A10 antibody and an α-Sca-1 antibody. The populations identified were profiled using gene expression microarray analysis. Gene expression patterns were confirmed on normal mouse and human mammary epithelial subpopulations and were examined in a panel of breast cancer samples and cell lines.

Results

Analysis of the separated populations demonstrated that Sca-1^- 33A10^High stained cells were estrogen receptor α (Esr1)^- luminal epithelial cells, whereas Sca-1⁺ 33A10^Low/- stained cells were a mix of nonepithelial cells and Esr1⁺ epithelial cells. Analysis of the gene expression data identified the gene Rgs2 (regulator of G-protein signalling 2) as being highly expressed in the Sca-1^- 33A10^Low/- population, which included myoepithelial/basal cells. RGS2 has previously been described as a regulator of angiotensin II receptor signalling. Gene expression analysis by quantitative real-time RT-PCR of cells separated on the basis of CD24 and Sca-1 expression confirmed that Rgs2 was more highly expressed in mouse myoepithelial/basal mammary cells than luminal cells. This expression pattern was conserved in normal human breast cells. Functional analysis demonstrated RGS2 to be a modulator of oxytocin receptor signalling. The potential significance of RGS2 expression in breast cancer was demonstrated by semi-quantitative RT-PCR analysis, data mining and quantitative real-time RT-PCR approaches, which showed that RGS2 was expressed in the majority of solid breast cancers at much higher levels than in normal human mammary cells.

Conclusion

Molecular analysis of prospectively isolated mammary epithelial cells identified RGS2 as a modulator of oxytocin receptor signalling, which is highly expressed in the myoepithelial cells. The RGS2 gene, but not the oxytocin receptor, was also shown to be over-expressed in the majority of breast cancers, identifying the product of this gene, or the pathway(s) it regulates, as potentially significant therapeutic targets.

RGS2 C1114G polymorphism and body weight gain in hypertensive patients

RGS2 is a negative regulator of Galpha protein signaling and promotes adipocyte differentiation. Recently, we described a polymorphism at the C1114G locus with the G allele associated with hypertension in a cross-sectional study. The aim of the present study was to assess whether the RGS2 C1114G is predictive of overweight in young subjects with grade I hypertension. We genotyped at the RGS2 C1114G locus 406 (male, n = 294; female, n = 112) white hypertensive subjects (age, 33 +/- 9 years) never treated for hypertension and at low cardiovascular risk. Median follow-up was 7.85 years. At baseline, male patients carrying the RGS2 1114G allele had higher body mass index (BMI) than patients with CC genotype (26.1 +/- 0.3 vs 25.3 +/- 0.3 kg/m2, P < .05). The frequency of male patients with BMI > or = 25 was similar between the patients with G allele and those with CC genotype (55.1% vs 47.8%, P = not significant). No significant difference between the 2 groups was observed with regard to physical activity, blood pressure, and heart rate. At the end of follow-up, BMI was higher in male patients with G allele compared with patients with CC genotype (26.8 +/- 0.3 vs 25.8 +/- 0.2 kg/m2, P < .01); and the frequency of male patients with BMI >25 kg/m2 was greater in the former (69.0% vs 52.2%, P < .01). According to Cox regression, allele G was a significant predictor of developing overweight or obesity during follow-up. These epidemiologic relations were not significant in female patients. In young male patients with grade I hypertension, RGS2 1114G allele is associated with increased BMI and with greater risk of developing overweight or obesity. The RGS2 1114G allele may be considered a genetic marker that predicts an individual's predisposition to gaining weight.

Rgs5 targeting leads to chronic low blood pressure and a lean body habitus

RGS5 is a potent GTPase-activating protein for G(ialpha) and G(qalpha) that is expressed strongly in pericytes and is present in vascular smooth muscle cells. To study the role of RGS5 in blood vessel physiology, we generated Rgs5-deficient mice. The Rgs5(-/-) mice developed normally, without obvious defects in cardiovascular development or function. Surprisingly, Rgs5(-/-) mice had persistently low blood pressure, lower in female mice than in male mice, without concomitant cardiac dysfunction, and a lean body habitus. The examination of the major blood vessels revealed that the aortas of Rgs5(-/-) mice were dilated compared to those of control mice, without altered wall thickness. Isolated aortic smooth muscle cells from the Rgs5(-/-) mice exhibited exaggerated levels of phosphorylation of vasodilator-stimulated phosphoprotein and extracellular signal-regulated kinase in response to stimulation with either sodium nitroprusside or sphingosine 1-phosphate. The results of this study, along with those of previous studies demonstrating that RGS5 stability is under the control of nitric oxide via the N-end rule pathway, suggest that RGS5 may balance vascular tone by attenuating vasodilatory signaling in vivo in opposition to RGS2, another RGS (regulator of G protein signaling) family member known to inhibit G protein-coupled receptor-mediated vasoconstrictor signaling. Blocking the function or the expression of RGS5 may provide an alternative approach to treat hypertension.

G12-G13-LARG-mediated signaling in vascular smooth muscle is required for salt-induced hypertension

The tone of vascular smooth muscle cells is a primary determinant of the total peripheral vascular resistance and hence the arterial blood pressure. Most forms of hypertension ultimately result from an increased vascular tone that leads to an elevated total peripheral resistance. Regulation of vascular resistance under normotensive and hypertensive conditions involves multiple mediators, many of which act through G protein-coupled receptors on vascular smooth muscle cells. Receptors that mediate vasoconstriction couple with the G-proteins G(q)-G11 and G12-G13 to stimulate phosphorylation of myosin light chain (MLC) via the Ca2+/MLC kinase- and Rho/Rho kinase-mediated signaling pathways, respectively. Using genetically altered mouse models that allow for the acute abrogation of both signaling pathways by inducible Cre/loxP-mediated mutagenesis in smooth muscle cells, we show that G(q)-G11-mediated signaling in smooth muscle cells is required for maintenance of basal blood pressure and for the development of salt-induced hypertension. In contrast, lack of G12-G13, as well as of their major effector, the leukemia-associated Rho guanine nucleotide exchange factor (LARG), did not alter normal blood pressure regulation but did block the development of salt-induced hypertension. This identifies the G12-G13-LARG-mediated signaling pathway as a new target for antihypertensive therapies that would be expected to leave normal blood pressure regulation unaffected.

RGS5, RGS4, and RGS2 expression and aortic contractibility are dynamically co-regulated during aortic banding-induced hypertrophy

Overexpression of regulator of G protein signaling 5 (RGS5) in arteries over veins is the most striking difference observed using microarray analysis. The obvious question is what arterial function might require RGS5. Based on functions of homologous proteins in regulating cardiac mass and G-protein-coupled receptor (GPCR) signaling, we proposed that RGS5 and vascular expressed RGS2 and RGS4 could participate in regulating arterial hypertrophy. We used the suprarenal abdominal aorta banding model to induce hypertension and hypertrophy. All 3 RGS messages were expressed in unmanipulated aorta with RGS5 predominating. After 2 days, thoracic aorta lost expression of RGS5, 4, and 2. At 1 week, all three returned to normal, and at 28 days, they increased many fold above normal. Valsartan blockade of angiotensin II (angII)/angII type 1 receptor signaling prevented upregulation of RGS messages but only delayed mass increases, implying wall mass regulation involves both angII-dependent and angII-independent pathways. The abdominal aorta showed less dramatic expression changes in RGS5 and 4, but not 2. Again, those changes were delayed by valsartan treatment with no mass changes. Thoracic aorta contraction to GPCR agonists was examined in aortic explant rings to identify vessel wall physiological changes. In 2-day aorta, the response to Galphaq/i agonists increased above normal, while 28-day aorta had attenuated induced contraction via Galphaq/i agonist, implicating a connection between RGS message levels and changes in GPCR-induced contraction. In vitro overexpression studies showed RGS5 inhibits angII-induced signaling in smooth muscle cells. This study is the first experimental evidence that changes in RGS expression and function correlate with vascular remodeling.

Endogenous RGS proteins attenuate Galpha(i)-mediated lysophosphatidic acid signaling pathways in ovarian cancer cells

Lysophosphatidic acid is a bioactive phospholipid that is produced by and stimulates ovarian cancer cells, promoting proliferation, migration, invasion, and survival. Effects of LPA are mediated by cell surface G-protein coupled receptors (GPCRs) that activate multiple heterotrimeric G-proteins. G-proteins are deactivated by Regulator of G-protein Signaling (RGS) proteins. This led us to hypothesize that RGS proteins may regulate G-protein signaling pathways initiated by LPA in ovarian cancer cells. To determine the effect of endogenous RGS proteins on LPA signaling in ovarian cancer cells, we compared LPA activity in SKOV-3 ovarian cancer cells expressing G(i) subunit constructs that are either insensitive to RGS protein regulation (RGSi) or their RGS wild-type (RGSwt) counterparts. Both forms of the G-protein contained a point mutation rendering them insensitive to inhibition with pertussis toxin, and cells were treated with pertussis toxin prior to experiments to eliminate endogenous G(i/o) signaling. The potency and efficacy of LPA-mediated inhibition of forskolin-stimulated adenylyl cyclase activity was enhanced in cells expressing RGSi G(i) proteins as compared to RGSwt G(i). We further showed that LPA signaling that is subject to RGS regulation terminates much faster than signaling thru RGS insensitive G-proteins. Finally, LPA-stimulated SKOV-3 cell migration, as measured in a wound-induced migration assay, was enhanced in cells expressing Galpha(i2) RGSi as compared to cells expressing Galpha(i2) RGSwt, suggesting that endogenous RGS proteins in ovarian cancer cells normally attenuate this LPA effect. These data establish RGS proteins as novel regulators of LPA signaling in ovarian cancer cells.

Vascular microarray profiling in two models of hypertension identifies caveolin-1, Rgs2 and Rgs5 as antihypertensive targets

BACKGROUND

Hypertension is a complex disease with many contributory genetic and environmental factors. We aimed to identify common targets for therapy by gene expression profiling of a resistance artery taken from animals representing two different models of hypertension. We studied gene expression and morphology of a saphenous artery branch in normotensive WKY rats, spontaneously hypertensive rats (SHR) and adrenocorticotropic hormone (ACTH)-induced hypertensive rats.

RESULTS

Differential remodeling of arteries occurred in SHR and ACTH-treated rats, involving changes in both smooth muscle and endothelium. Increased expression of smooth muscle cell growth promoters and decreased expression of growth suppressors confirmed smooth muscle cell proliferation in SHR but not in ACTH. Differential gene expression between arteries from the two hypertensive models extended to the renin-angiotensin system, MAP kinase pathways, mitochondrial activity, lipid metabolism, extracellular matrix and calcium handling. In contrast, arteries from both hypertensive models exhibited significant increases in caveolin-1 expression and decreases in the regulators of G-protein signalling, Rgs2 and Rgs5. Increased protein expression of caveolin-1 and increased incidence of caveolae was found in both smooth muscle and endothelial cells of arteries from both hypertensive models.

CONCLUSION

We conclude that the majority of differences in gene expression found in the saphenous artery taken from rats with two different forms of hypertension reflect distinctive morphological and physiological alterations. However, changes in common to caveolin-1 expression and G protein signalling, through attenuation of Rgs2 and Rgs5, may contribute to hypertension through augmentation of vasoconstrictor pathways and provide potential targets for common drug development.

R4 RGS proteins: regulation of G-protein signaling and beyond

The regulators of G-protein signaling (RGS) proteins were initially characterized as inhibitors of signal transduction cascades initiated by G-protein-coupled receptors (GPCR) because of their ability to increase the intrinsic GTPase activity of heterotrimeric G proteins. This GTPase accelerating protein (GAP) activity enhances G protein deactivation and promotes desensitization. However, in addition to this signature trait, emerging data have revealed an expanding network of proteins, lipids, and ions that interact with RGS proteins and confer additional regulatory functions. This review highlights recent advances in our understanding of the physiological functions of one subfamily of RGS proteins with a high degree of homology (B/R4) gleaned from recent studies of knockout mice or cells with reduced RGS expression. We also discuss some of the newly appreciated interactions of RGS proteins with cellular factors that suggest RGS control of several components of G-protein-mediated pathways, as well as a diverse array of non-GPCR-mediated biological responses.

Genetic determinants of emotionality and stress response in AcB/BcA recombinant congenic mice and in silico evidence of convergence with cardiovascular candidate genes

Genomic loci bearing stress-related phenotypes were dissected in recombinant congenic strains (RCS) of mice with C57BL/6J (B6) and A/J progenitors. Adult male mice from 14 A/J and 22 B6 background lines were evaluated for emotional reactivity in open-field (OF) and elevated plus-maze tests. Core temperature was monitored by radio telemetry during immobilization and on standard as well as salt-enriched diets. In addition, urinary electrolytes were measured. Genome-wide linkage analysis of the parameters revealed over 20 significant quantitative trait loci (QTL). The highest logarithm of odds (LOD) scores were within the previously-reported OF emotionality locus on Chr 1 (LOD = 4.6), in the dopa decarboxylase region on Chr 11 for the plus-maze (LOD = 4.7), and within a novel region of calmodulin 1 on Chr 12 for Ca++ excretion after a 24-h salt load (LOD = 4.6). RCS stress QTL overlapped with several candidate loci for cardiovascular (CV) disease. In silico evidence of functional polymorphisms by comparative sequence analysis of progenitor strains assisted to ascertain this convergence. The anxious BcA70 strain showed down regulation of Atp1a2 gene expression in the heart (P < 0.001) and brain (P < 0.05) compared with its parental B6 strain, compatible with the enhanced emotionality described in knock out animals for this gene, also involved in the salt-sensitive component of hypertension. Functional polymorphisms in regulatory elements of candidate genes of the CV/inflammatory/immune systems support the hypothesis of genetically-altered environmental susceptibility in CV disease development.

Regulation of RGS2 and Second Messenger Signaling in Vascular Smooth Muscle Cells by cGMP-dependent Protein Kinase

RGS2, a GTPase-activating protein (GAP) for G(q)alpha, regulates vascular relaxation and blood pressure. RGS2 can be phosphorylated by type Ialpha cGMP-dependent protein kinase (cGKIalpha), increasing its GAP activity. To understand how RGS2 and cGKIalpha regulate vascular smooth muscle signaling and function, we identified signaling pathways that are controlled by cGMP in an RGS2-dependent manner and discovered new mechanisms whereby cGK activity regulates RGS2. We show that RGS2 regulates vasoconstrictor-stimulated Ca(2+) store release, capacitative Ca(2+) entry, and noncapacitative Ca(2+) entry and that RGS2 is required for cGMP-mediated inhibition of vasoconstrictor-elicited phospholipase Cbeta activation, Ca(2+) store release, and capacitative Ca(2+) entry. RGS2 is degraded in vascular smooth muscle cells via the proteasome. Inhibition of cGK activity blunts RGS2 degradation. However, inactivation of the cGKIalpha phosphorylation sites in RGS2 does not stabilize the protein, suggesting that cGK activity regulates RGS2 degradation by other mechanisms. cGK activation promotes association of RGS2 with the plasma membrane by a mechanism requiring its cGKIalpha phosphorylation sites. By regulating GAP activity, plasma membrane association, and degradation, cGKIalpha therefore may control a cycle of RGS2 activation and inactivation. By diminishing cGK activity, endothelial dysfunction may impair RGS2 activation, thereby blunting vascular relaxation and contributing to hypertension.

Group VIA phospholipase A2 (iPLA2beta) participates in angiotensin II-induced transcriptional up-regulation of regulator of g-protein signaling-2 in vascular smooth muscle cells

Rgs2 (regulator of G-protein signaling-2)-deficient mice exhibit severe hypertension, and genetic variations of RGS2 occur in hypertensive patients. RGS2 mRNA up-regulation by angiotensin II (Ang II) in vascular smooth muscle cells (VSMC) is a potentially important negative feedback mechanism in blood pressure homeostasis, but how it occurs is unknown. Here we demonstrate that group VIA phospholipase A2 (iPLA2beta) plays a pivotal role in Ang II-induced RGS2 mRNA up-regulation in VSMC by three independent approaches, including pharmacologic inhibition with a bromoenol lactone suicide substrate, suppression of iPLA2beta expression with antisense oligonucleotides, and genetic deletion in iPLA2beta-null mice. Selective inhibition of iPLA2beta by each of these approaches abolishes Ang II-induced RGS2 mRNA up-regulation. Furthermore, using adenovirus-mediated gene transfer, we demonstrate that restoration of iPLA2beta-expression in iPLA2beta-null VSMC reconstitutes the ability of Ang II to up-regulate RGS2 mRNA expression. In contrast, Ang II-induced vasodilator-stimulated phosphoprotein phosphorylation and Ang II receptor expression are unaffected. Moreover, in wild-type but not iPLA2beta-null VSMC, Ang II stimulates iPLA2 enzymatic activity significantly. Both arachidonic acid and lysophosphatidylcholine, products of iPLA2beta action, induce RGS2 mRNA up-regulation. Inhibition of lipoxygenases, particularly 15-lipoxygenase, and cyclooxygenases, but not cytochrome P450-dependent epoxygenases inhibits Ang II- or AA-induced RGS2 mRNA expression. Moreover, RGS2 protein expression is also up-regulated by Ang II, and this is attenuated by bromoenol lactone. Disruption of the Ang II/iPLA2beta/RGS2 feedback pathway in iPLA2beta-null cells potentiates Ang II-induced vasodilator-stimulated phosphoprotein and Akt phosphorylation in a time-dependent manner. Collectively, our results demonstrate that iPLA2beta participates in Ang II-induced transcriptional up-regulation of RGS2 in VSMC.

Regulator of G protein signalling 2 ameliorates angiotensin II-induced hypertension in mice

Angiotensin II (Ang II) activates signalling pathways predominantly through the G-protein-coupled Ang II type 1 receptor (AT(1)R). The regulator of G protein signalling 2 (RGS2) is a negative G protein regulator. We hypothesized that RGS2 deletion changes blood pressure regulation by increasing the response to Ang II. To address this issue, we infused Ang II (0.5 mg kg(-1) day(-1)) chronically into conscious RGS2-deleted (RGS2(-/-)) and wild-type (RGS2(+/+)) mice, measured mean arterial blood pressure and heart rate (HR) with telemetry and assessed vasoreactivity and gene expression of AT(1A), AT(1B) and AT(2) receptors. Angiotensin II infusion increased blood pressure more in RGS2(-/-) than in RGS2(+/+) mice, while HR was not different between the groups, indicating a resetting of the baroreceptor reflex. Urinary catecholamine excretion was similar in Ang II-infused RGS2(-/-) and RGS2(+/+) mice, indicating a minor role of sympathetic tone for blood pressure differences. Myogenic tone and vasoreactivity in response to Ang II, endothelin-1 and phenylephrine were increased in isolated renal interlobar arterioles of RGS2(-/-) mice compared with RGS2(+/+) mice. The AT(1A), AT(1B) and AT(2) receptor gene expression was not different between RGS2(-/-) and RGS2(+/+) mice. Our findings suggest that RGS2 deletion promotes Ang II-dependent hypertension primarily through an increase of myogenic tone and vasoreactivity, probably by sensitization of AT(1) receptors.

Phosphorylation of Ser166 in RGS5 by protein kinase C causes loss of RGS function

RGS5 is a member of regulators of G protein signaling (RGS) proteins that attenuate heterotrimeric G protein signaling by functioning as GTPase-activating proteins (GAPs). We investigated phosphorylation of RGS5 and the resulting change of its function. In 293T cells, transiently expressed RGS5 was phosphorylated by endogenous protein kinases in the basal state. The phosphorylation was enhanced by phorbol 12-myristate 13-acetate (PMA) and endothelin-1 (ET-1), and suppressed by protein kinase C (PKC) inhibitors, H7, calphostin C and staurosporine. These results suggest involvement of PKC in phosphorylation of RGS5. In in vitro experiments, PKC phosphorylated recombinant RGS5 protein at serine residues. RGS5 protein phosphorylated by PKC showed much lower binding capacity for and GAP activity toward Galpha subunits than did the unphosphorylated RGS5. In cells expressing RGS5, the inhibitory effect of RGS5 on ET-1-induced Ca(2+) responses was enhanced by staurosporine. Mass spectrometric analysis of the phosphorylated RGS5 revealed that Ser166 was one of the predominant phosphorylation sites. Substitution of Ser166 by aspartic acid abolished the binding capacity to Galpha subunits and the GAP activity, and markedly reduced the inhibitory effect on ET-1-induced Ca(2+) responses. These results indicate that phosphorylation at Ser166 of RGS5 by PKC causes loss of the function of RGS5 in G protein signaling. Since this serine residue is conserved in RGS domains of many RGS proteins, the phosphorylation at Ser166 by PKC might act as a molecular switch and have functional significance.

Sympathetic nerve traffic and circulating norepinephrine levels in RGS2-deficient mice

Regulator of G protein signaling 2 (RGS2-/-) deficient mice feature an increased resting blood pressure and an excessive pressor response to stress. We measured renal sympathetic nerve activity (RSNA) directly to test the hypothesis that RSNA is increased in RGS2-/- mice, compared to RGS2+/+ mice. Seventeen mice (RGS2-/-, n=9; RGS2+/+, n=8) were anesthetized with isoflurane. We cannulated the left jugular vein for drug administration. Renal sympathetic nerve activity (RSNA) was recorded using bipolar electrodes. Arterial blood pressure (BP) from the femoral artery, ECG (needle electrodes), and RSNA were recorded (sample rate 10 kHz) simultaneously. RSNA was analysed off-line using a modified wavelet de-noising technique and the classical discriminator method. RSNA detected during phenylephrine bolus injections or after the animals death was subtracted from baseline values. Mean arterial blood pressure, norepinephrine plasma levels, the responsiveness to vasoactive drugs, and the sympathetic baroreflex gain were similar in anesthetized RGS2+/+ and RGS2-/- animals. RSNA was lower in RGS2-/- mice compared to wild-type controls (wavelet: spike rate in Hz: RGS2+/+ 25.5+/-5.1; RGS2-/- 17.4+/-4.0; discriminator method: RGS2+/+ 41.4+/-5.7, RGS2-/- 22.0+/-4.3, p<0.05). Thus, the expected result proved not to be the case. Our data suggest a mismatch between sympathetic nerve traffic and plasma norepinephrine concentrations. This observation may depend on altered coupling between electrical nerve activity and norepinephrine release and/or a changed norepinephrine uptake in RGS2-/- mice.

-391 C to G substitution in the regulator of G-protein signalling-2 promoter increases susceptibility to the metabolic syndrome in white European men: consistency between molecular and epidemiological studies

BACKGROUND

The regulator of G-protein signalling-2 (RGS2) is a key factor in adipogenesis. We hypothesized that the metabolic syndrome, of which obesity is an important component, might be related to genetic variation in RGS2.

METHODS AND RESULTS

We screened the human RGS2 gene. We tested the functionality of a common genetic variant in vitro, ex vivo, and in epidemiological study involving six European populations. The C to G substitution at position -391 in the RGS2 promoter was associated with enhanced RGS2 expression in vitro in transfected 3T3-L1 adipocytes and Chinese hamster cells and ex vivo in adipocytes from male, but not female, volunteers. In 2732 relatives from 512 families and 348 unrelated individuals, randomly recruited from six European populations, the prevalence of GG homozygosity was 54.1%. The metabolic syndrome score, a composite of six continuous traits making up this clinical entity, was 0.27 standardized units higher (P < 0.001) in 795 GG homozygous men compared with 683 men carrying the C allele. Transmission of the -391 G allele to male offspring was associated with a 0.20 unit increase in the score (P=0.039). These epidemiological relations were not significant in 1602 women.

CONCLUSIONS

The C to G substitution at position -391 in the RGS2 promoter increases RGS2 expression in adipocytes and is associated with the metabolic syndrome in white European men. Further experimental and clinical research should establish whether this common polymorphism might be a target for preventive or therapeutic intervention.

Gαq-TRPC6-mediated Ca2+ Entry Induces RhoA Activation and Resultant Endothelial Cell Shape Change in Response to Thrombin

RhoA activation and increased intracellular Ca(2+) concentration mediated by the activation of transient receptor potential channels (TRPC) both contribute to the thrombin-induced increase in endothelial cell contraction, cell shape change, and consequently to the mechanism of increased endothelial permeability. Herein, we addressed the possibility that TRPC signals RhoA activation and thereby contributes in actinomyosin-mediated endothelial cell contraction and increased endothelial permeability. Transduction of a constitutively active Galphaq mutant in human pulmonary arterial endothelial cells induced RhoA activity. Preventing the increase in intracellular Ca2+ concentration by the inhibitor of Galphaq or phospholipase C and the Ca2+ chelator, BAPTA-AM, abrogated thrombin-induced RhoA activation. Depletion of extracellular Ca2+ also inhibited RhoA activation, indicating the requirement of Ca2+ entry in the response. RhoA activation could not be ascribed to storeoperated Ca2+ (SOC) entry because SOC entry induced with thapsigargin or small interfering RNA-mediated inhibition of TRPC1 expression, the predominant SOC channel in these endothelial cells, failed to alter RhoA activity. However, activation of receptor-operated Ca2+ entry by oleoyl-2-acetyl-sn-glycerol, the membrane permeable analogue of the Galphaq-phospholipase C product diacylglycerol, induced RhoA activity. Receptor-operated Ca2+ activation was mediated by TRPC6 because small interfering RNA-induced TRPC6 knockdown significantly reduced Ca2+ entry. TRPC6 knockdown also prevented RhoA activation, myosin light chain phosphorylation, and actin stress fiber formation as well as inter-endothelial junctional gap formation in response to either oleoyl-2-acetyl-sn-glycerol or thrombin. TRPC6-mediated RhoA activity was shown to be dependent on PKCalpha activation. Our results demonstrate that Galphaq activation of TRPC6 signals the activation of PKCalpha, and thereby induces RhoA activity and endothelial cell contraction.

The expression patterns of RGS transcripts in platelets

Regulators of G protein signalling (RGS) are involved in the negative regulation of cell activation processes and are involved in the pathophysiology of cardiovascular diseases. To get some further evidence for a role of RGS proteins in platelets, we determined the expression profile of RGS-specific mRNA in rat platelets using reverse transcription-polymerase chain reaction (RT-PCR) with a poly dT18 primer and transcript-specific primers. We found that RGS2, RGS3, RGS5, RGS6, RGS10, RGS14, RGS16 and RGS18, Leukemia-associated Rho-GEF factor (LARG), and Galpha interacting protein (GAIP) were differentially expressed in platelets. The highest expression rate was found for RGS18 (about 1.3 fold when compared to GAPDH), followed by LARG, RGS6, RGS10 and RGS16 (0.7 to 0.95), whereas expression rates for RGS2, RGS3, RGS5, RGS14, and GAIP were in a range of 0.1 to 0.3. Our results suggest that G-protein-coupled receptor-mediated signalling in platelet may be regulated mainly by RGS 18, 16, 10, 6, and LARG.

Endogenous RGS proteins modulate SA and AV nodal functions in isolated heart: implications for sick sinus syndrome and AV block

G protein-coupled receptors play a pivotal role in regulating cardiac automaticity. Their function is controlled by regulator of G protein signaling (RGS) proteins acting as GTPase-activating proteins for Galpha subunits to suppress Galpha(i) and Galpha(q) signaling. Using knock-in mice in which Galpha(i2)-RGS binding and negative regulation are disrupted by a genomic Galpha(i2)G184S (GS) point mutation, we recently (Fu Y, Huang X, Zhong H, Mortensen RM, D'Alecy LG, Neubig RR. Circ Res 98: 659-666, 2006) showed that endogenous RGS proteins suppress muscarinic receptor-mediated bradycardia. To determine whether this was due to direct regulation of cardiac pacemakers or to alterations in the central nervous system or vascular responses, we examined isolated, perfused hearts. Isoproterenol-stimulated beating rates of heterozygote (+/GS) and homozygote (GS/GS) hearts were significantly more sensitive to inhibition by carbachol than were those of wild type (+/+). Even greater effects were seen in the absence of isoproterenol; the potency of muscarinic-mediated bradycardia was enhanced fivefold in GS/GS and twofold in +/GS hearts compared with +/+. A(1)-adenosine receptor-mediated bradycardia was unaffected. In addition to effects on the sinoatrial node, +/GS and GS/GS hearts show significantly increased carbachol-induced third-degree atrioventricular (AV) block. Atrial pacing studies demonstrated an increased PR interval and AV effective refractory period in GS/GS hearts compared with +/+. Thus loss of the inhibitory action of endogenous RGS proteins on Galpha(i2) potentiates muscarinic inhibition of cardiac automaticity and conduction. The severe carbachol-induced sinus bradycardia in Galpha(i2)G184S mice suggests a possible role for alterations of Galpha(i2) or RGS proteins in sick sinus syndrome and pathological AV block.

Genetics of arterial hypertension and hypotension

Human hypertension affects affects more than 20% of the adult population in industrialized countries, and it is implicated in millions of deaths worldwide each year from stroke, heart failure and ischemic heart disease. Available evidence suggests a major genetic impact on blood pressure regulation. Studies in monogenic hypertension revealed that renal salt and volume regulation systems are predominantly involved in the genesis of these disorders. Mutations here affect the synthesis of mineralocorticoids, the function of the mineralocorticoid receptor, epithelial sodium channels and their regulation by a new class of kinases, termed WNK kinases. It has been learned from monogenic hypotension that almost all ion transporters involved in the renal uptake of Na(+) have a major impact on blood pressure regulation. For essential hypertension as a complex disease, many candidate genes have been analysed. These include components of the renin-angiotensin-aldosterone system, adducin, beta-adrenoceptors, G protein subunits, regulators of G protein signalling (RGS) proteins, Rho kinases and G protein receptor kinases. At present, the individual impact of common polymorphisms in these genes on the observed blood pressure variation, on risk for stroke and as predictors of antihypertensive responses remains small and clinically irrelevant. Nevertheless, these studies have greatly augmented our knowledge on the regulation of renal functions, cellular signal transduction and the integration of both. Together, this provides the basis for the identification of novel drug targets and, hopefully, innovative antihypertensive drugs.

Inhibition of Gαq-dependent PLC-β1 activity by PKG and PKA is mediated by phosphorylation of RGS4 and GRK2

In smooth muscle of the gut, Gq-coupled receptor agonists activate preferentially PLC-β1 to stimulate phosphoinositide (PI) hydrolysis and inositol 1,4,5-trisphosphate (IP3) generation and induce IP3-dependent Ca2+ release. Inhibition of Ca2+ mobilization by cAMP- (PKA) and cGMP-dependent (PKG) protein kinases reflects inhibition of PI hydrolysis by both kinases and PKG-specific inhibitory phosphorylation of IP3 receptor type I. The mechanism of inhibition of PLC-β1-dependent PI hydrolysis has not been established. Neither Gq nor PLC-β1 was directly phosphorylated by PKA or PKG in gastric smooth muscle cells. However, both kinases 1) phosphorylated regulator of G protein signaling 4 (RGS4) and induced its translocation from cytosol to plasma membrane, 2) enhanced ACh-stimulated association of RGS4 and Gαq·GTP and intrinsic Gαq·GTPase activity, and 3) inhibited ACh-stimulated PI hydrolysis. RGS4 phosphorylation and inhibition of PI hydrolysis were blocked by selective PKA and PKG inhibitors. Expression of RGS4(S52A), which lacks a PKA/PKG phosphorylation site, blocked the increase in GTPase activity and the decrease in PI hydrolysis induced by PKA and PKG. Blockade of PKA-dependent effects was only partial. Selective phosphorylation of G protein-coupled receptor kinase 2 (GRK2), which contains a RGS domain, by PKA augmented ACh-stimulated GRK2:Gαq·GTP association; both effects were blocked in cells expressing GRK2(S685A), which lacks a PKA phosphorylation site. Inhibition of PI hydrolysis induced by PKA was partly blocked in cells expressing GRK2(S685A) and completely blocked in cells coexpressing GRK2(S685A) and RGS4(S52A) or Gαq(G188S), a Gαq mutant that binds GRK2 but not RGS4. The results demonstrate that inhibition of PLC-β1-dependent PI hydrolysis by PKA is mediated via stimulatory phosphorylation of RGS4 and GRK2, leading to rapid inactivation of Gαq·GTP. PKG acts only via phosphorylation of RGS4.

Up-regulation of endogenous RGS2 mediates cross-desensitization between Gs and Gq signaling in osteoblasts

Regulator of G protein signaling (RGS) proteins limit G protein signals. In this study, we investigated the role of RGS2 in the control of G protein signaling cascades in osteoblasts, the cells responsible for bone formation. Expression of RGS2 was up-regulated in primary cultures of mouse calvarial osteoblasts by parathyroid hormone-related peptide (PTHrP)-(1-34), which stimulates G(s) signaling. RGS2 was also up-regulated by extracellular ATP, which selectively activates G(q), as well as by forskolin and phorbol myristate acetate, which activate targets downstream of G(s) and G(q), respectively. To assess the role of endogenous RGS2, we characterized G(s) and G(q) signaling in osteoblasts derived from wild type and rgs2(-/-) mice. Under control conditions, nucleotide-stimulated calcium release, endothelin-stimulated accumulation of inositol phosphates, and PTHrP-stimulated cAMP accumulation were equivalent in osteoblasts isolated from wild type and rgs2(-/-) mice. Thus, basal levels of endogenous RGS2 do not appear to regulate G(s) or G(q) signaling in osteoblasts. Interestingly, forskolin treatment of wild type but not rgs2(-/-) osteoblasts suppressed both endothelin-stimulated accumulation of inositol phosphates and nucleotide-stimulated calcium release, indicating that up-regulation of RGS2 by G(s) signaling desensitizes G(q) signals. Furthermore, pretreatment with ATP suppressed PTHrP-dependent cAMP accumulation in wild type but not rgs2(-/-) osteoblasts, implying that up-regulation of RGS2 by G(q) signaling desensitizes G(s) signals. Our findings demonstrate that endogenously expressed RGS2 can limit G(s) signaling. Moreover, up-regulation of RGS2 contributes to cross-desensitization of G(s)- and G(q)-coupled signals.

RGS2 is regulated by angiotensin II and functions as a negative feedback of aldosterone production in H295R human adrenocortical cells

Regulator of G protein signaling (RGS) proteins interact with Galpha-subunits of heterotrimeric G proteins, accelerating the rate of GTP hydrolysis and finalizing the intracellular signaling triggered by the G protein-coupled receptor-ligand interaction. Angiotensin (Ang) II interacts with its G protein-coupled receptor in zona glomerulosa adrenal cells and triggers a cascade of intracellular signals that regulates steroidogenesis and proliferation. We studied Ang II-mediated regulation of RGS2, the role of RGS2 in steroidogenesis, and the intracellular signal events involved in H295R human adrenal cells. We report that both H295R cells and human adrenal gland express RGS2 mRNA. In H295R cells, Ang II caused a rapid and transient increase in RGS2 mRNA levels quantified by real-time RT-PCR. Ang II effects were mimicked by calcium ionophore A23187 and blocked by calcium channel blocker nifedipine. Ang II effects also were blocked by calmodulin antagonists (W-7 and calmidazolium) and calcium/calmodulin-dependent kinase antagonist KN-93. RGS2 overexpression by retroviral infection in H295R cells caused a decrease in Ang II-stimulated aldosterone secretion but did not modify cortisol secretion. In reporter assays, RGS2 decreased Ang II-mediated aldosterone synthase up-regulation. These results suggest that Ang II up-regulates RGS2 mRNA by the calcium/calmodulin-dependent kinase pathway in H295R cells. RGS2 overexpression specifically decreases aldosterone secretion through a decrease in Ang II-mediated aldosterone synthase-induced expression. In conclusion, RGS2 expression is induced by Ang II to terminate the intracellular signaling cascade generated by Ang II. RGS2 alterations in expression levels or functionality could be implicated in deregulations of Ang II signaling and abnormal aldosterone secretion by the adrenal gland.

Reduced expression of regulator of G-protein signaling 2 (RGS2) in hypertensive patients increases calcium mobilization and ERK1/2 phosphorylation induced by angiotensin II

CONTEXT

RGS2 (regulators of G-protein signaling) is a negative regulator of Galphaq protein signaling, which mediates the action of several vasoconstrictors. RGS2-deficient mouse line exhibits a hypertensive phenotype and a prolonged response to vasoconstrictors.

OBJECTIVE

To compare RGS2 expression in peripheral blood mononuclear cells (PBMs) and cultured fibroblasts from normotensive subjects and hypertensive patients.

METHODS

PBMs were isolated from 100 controls and 150 essential hypertensives. Additionally, fibroblasts were isolated from skin biopsy of 11 normotensives and 12 hypertensives and cultured up to the third passage. Quantitative mRNA and protein RGS2 expression were performed by real-time quantitative reverse transcriptase-polymerase chain reaction and by immunoblotting, respectively. Free Ca measurement was performed in monolayers of 24-h serum-deprived cells, using FURA-2 AM. Phosphorylation of the extracellular signal-regulated kinases ERK1/2 was measured by immunoblotting. Polymorphism (C1114G) in the 3' untranslated region of the RGS2 gene was investigated by direct sequencing and real-time polymerase chain reaction (PCR).

RESULTS

RGS2 mRNA expression was significantly lower in PBM and in fibroblasts from hypertensives, in comparison to normotensives. C1114G polymorphism was associated with RGS2 expression, with the lowest values in GG hypertensives. The 1114G allele frequency was increased in hypertensives compared with normotensives. Angiotensin II-stimulated intracellular Ca increase and ERK1/2 phosphorylation were higher in fibroblasts from hypertensive patients compared with control subjects, and in those with the G allele, independently of the blood pressure status. The angiotensin II-stimulated Ca mobilization and ERK1/2 phosphorylation were negatively correlated with RGS2 mRNA expression.

CONCLUSION

Low expression of RGS2 contributes to increased G-protein-coupled signaling in hypertensive patients. The allele G is associated with low RGS2 expression and blood pressure increase in humans.

Bigenic mouse models of focal segmental glomerulosclerosis involving pairwise interaction of CD2AP, Fyn, and synaptopodin

Focal segmental glomerulosclerosis (FSGS) is the most common primary glomerular diagnosis resulting in end-stage renal disease. Defects in several podocyte proteins have been implicated in the etiology of FSGS, including podocin, alpha-actinin-4, CD2-associated protein (CD2AP), and TRPC6. Despite our growing understanding of genes involved in the pathogenesis of focal segmental sclerosis, the vast majority of patients with this disease, even those with a familial linkage, lack a clear genetic diagnosis. Here, we tested whether combinations of genetic heterozygosity (bigenic heterozygosity) that alone do not result in clinical kidney disease could function together to enhance susceptibility to glomerular damage and FSGS. Combinations of Cd2ap heterozygosity and heterozygosity of either synaptopodin (Synpo) or Fyn proto-oncogene (Fyn) but not kin of IRRE like 1 (Neph1) resulted in spontaneous proteinuria and in FSGS-like glomerular damage. These genetic interactions were also reflected at a functional level, as we found that CD2AP associates with Fyn and Synpo but not with Neph1. This demonstrates that bigenic heterozygosity can lead to FSGS and suggests that combined mutations in 2 or multiple podocyte genes may be a common etiology for glomerular disease.

Endogenous RGS Proteins and Gα Subtypes Differentially Control Muscarinic and Adenosine-Mediated Chronotropic Effects

Cardiac automaticity is controlled by G protein-coupled receptors, such as adrenergic, muscarinic, and adenosine receptors. The strength and duration of G protein signaling is attenuated by regulator of G protein signaling (RGS) proteins acting as GTPase-activating proteins for Galpha subunits; however, little is known about the role of endogenous RGS proteins in cardiac function. We created point mutations in Galpha subunits that disrupt Galpha-RGS binding and introduced them into embryonic stem (ES) cells by homologous recombination. Spontaneously contacting cardiocytes derived from the ES cells were used to evaluate the role of endogenous RGS proteins in chronotropic regulation. The RGS-insensitive GalphaoG184S homozygous knock-in (GalphaoGS/GS) cells demonstrated enhanced adenosine A1 and muscarinic M2 receptor-mediated bradycardic responses. In contrast, Galphai2GS/GS cells showed enhanced responses to M2 but not A1 receptors. Similarly M2 but not A1 bradycardic responses were dramatically enhanced in Galphai2GS/GS mice. Blocking G protein-coupled inward rectifying K+ (GIRK) channels largely abolished the mutation-induced enhancement of the M2 receptor-mediated response but had a minimal effect on A1 responses. The Galphas-dependent stimulation of beating rate by the beta2 adrenergic receptor agonist procaterol was significantly attenuated in GalphaoGS/GS and nearly abolished in Galphai2GS/GS cells because of enhanced signaling via a pertussis toxin sensitive mechanism. Thus, endogenous RGS proteins potently reduce the actions of Galpha(i/o)-linked receptors on cardiac automaticity. Furthermore, M2 and A1 receptors differentially use Galphai2 and Galphao and associated downstream effectors. Thus, alterations in RGS function may play a role in pathophysiological processes and RGS proteins could represent novel cardiovascular therapeutic targets.

Polymorphisms and Haplotypes of the Regulator of G Protein Signaling-2 Gene in Normotensives and Hypertensives

Regulator of G protein signaling (RGS) proteins stimulate the GTPase activity of Galpha subunits of heterotrimeric G proteins, thereby negatively regulating G protein-coupled receptor signaling. RGS2, which preferentially alters Galphaq-mediated signaling, may be important for cardiovascular health, because knockout of RGS2 in mice is associated with altered smooth muscle relaxation and hypertension. In this study, we determined genetic variation in the human RGS2 gene by sequencing DNA in normotensive and hypertensive populations of whites (n=128) and blacks (n=122). We identified 14 single nucleotide polymorphisms and 2 two-base insertion/deletions (in/del; 1891 to 1892 TC and 2138 to 2139 AA). Although most of the genetic variants were found at low allelic frequency, in particular in coding regions, the 1891 to 1892 TC and 2138 to 2139 AA intronic in/del were in linkage disequilibrium and were associated with hypertension in blacks (P<0.05). We defined several haplotypes for the RGS2 gene, certain of which showed striking differences between whites and blacks. Additionally, 2 haplotypes had significantly different frequencies between hypertensive and normotensive black groups (P<0.05). We conclude that RGS2 is genetically conserved within coding regions but that the intronic in/del define ethnicity-specific haplotypes. Moreover, certain RGS2 variants that occur at greater frequency in hypertensive blacks may serve as ethnicity-specific genetic variants for this disease.

Selective Loss of Fine Tuning of Gq/11 Signaling by RGS2 Protein Exacerbates Cardiomyocyte Hypertrophy

Alterations in cardiac G protein-mediated signaling, most prominently G(q/11) signaling, are centrally involved in hypertrophy and heart failure development. Several RGS proteins that can act as negative regulators of G protein signaling are expressed in the heart, but their functional roles are still poorly understood. RGS expression changes have been described in hypertrophic and failing hearts. In this study, we report a marked decrease in RGS2 (but not other major cardiac RGS proteins (RGS3-RGS5)) that occurs prior to hypertrophy development in different models with enhanced G(q/11) signaling (transgenic expression of activated Galpha(q)(*) and pressure overload due to aortic constriction). To assess functional consequences of selective down-regulation of endogenous RGS2, we identified targeting sequences for effective RGS2 RNA interference and used lipid-based transfection to achieve uptake of fluorescently labeled RGS2 small interfering RNA in >90% of neonatal and adult ventricular myocytes. Endogenous RGS2 expression was dose-dependently suppressed (up to 90%) with no major change in RGS3-RGS5. RGS2 knockdown increased phenylephrine- and endothelin-1-induced phospholipase Cbeta stimulation in both cell types and exacerbated the hypertrophic effect (increase in cell size and radiolabeled protein) in neonatal myocytes, with no major change in G(q/11)-mediated ERK1/2, p38, or JNK activation. Taken together, this study demonstrates that endogenous RGS2 exerts functionally important inhibitory restraint on G(q/11)-mediated phospholipase Cbeta activation and hypertrophy in ventricular myocytes. Our findings point toward a potential pathophysiological role of loss of fine tuning due to selective RGS2 down-regulation in G(q/11)-mediated remodeling. Furthermore, this study shows the feasibility of effective RNA interference in cardiomyocytes using lipid-based small interfering RNA transfection.

Vascular tone control in humans: Insights from studies in Bartter's/Gitelman's syndromes

Studies in patients with Bartter's and Gitelman's syndromes performed in the last 10 years have provided important insights into the mechanistic details of relevant pathways of angiotensin II signaling and vascular tone regulation, therefore making these syndromes a good human model to gain insight into the mechanisms responsible for maintaining/controlling vascular tone. Extensive studies of patients with Bartter's/Gitelman's syndromes have, in fact, shown biochemical abnormalities of angiotensin II short- and long-term cell signaling, which depict a mirror image of those found in hypertension. The information obtained from the study of this human model of altered vascular tone regulation show that it can be used to gather more general data and/or confirm mechanistic details of the cellular and biochemical events involved in the pathophysiology of vascular tone control and to shed light on the multiplicity of the angiotensin II signaling-related mechanisms responsible for the pathophysiology of hypertension and its long-term complication such as cardiovascular remodeling and atherogenesis.

Regulator of G-protein signaling 2 (RGS2) inhibits androgen-independent activation of androgen receptor in prostate cancer cells

Hormones acting through G protein-coupled receptors (GPCRs) can cause androgen-independent activation of androgen receptor (AR) in prostate cancer cells. Regulators of G-protein signaling (RGS) proteins, through their GTPase activating protein (GAP) activities, inhibit GPCR-mediated signaling by inactivating G proteins. Here, we identified RGS2 as a gene specifically downregulated in androgen-independent prostate cancer cells. Expression of RGS2, but not other RGS proteins, abolished androgen-independent AR activity in androgen-independent LNCaP cells and CWR22Rv1 cells. In LNCaP cells, RGS2 inhibited G(q)-coupled GPCR signaling. Expression of exogenous wild-type RGS2, but not its GAP-deficient mutant, significantly reduced AR activation by constitutively activated G(q)Q209L mutant whereas silencing endogenous RGS2 by siRNA enhanced G(q)Q209L-stimulated AR activity. RGS2 had no effect on RGS-insensitive G(q)Q209L/G188S-induced AR activation. Furthermore, extracellular signal-regulated kinase 1/2 (ERK1/2) was found to be involved in RGS2-mediated regulation of androgen-independent AR activity. In addition, RGS2 functioned as a growth suppressor for androgen-independent LNCaP cells whereas androgen-sensitive LNCaP cells with RGS2 silencing had a growth advantage under steroid-reduced conditions. Finally, RGS2 expression level was significantly decreased in human prostate tumor specimens. Taken together, our results suggest RGS2 as a novel regulator of AR signaling and its repression may be an important step during prostate tumorigenesis and progression.

Is RGS-2 a new drug development target in cardiovascular disease?

Hypertension is the most common cardiovascular disease. The regulator of G-protein signalling (RGS) proteins modify the activity of G proteins, and mice deficient in RGS-2 are hypertensive. On vascular smooth muscle, RGS-2 is involved in cross-talk between the nitric oxide (NO)-relaxation pathway and thrombin-contraction pathway. RGS-2 binds to the cGMP-dependent protein kinase I-alpha from the NO relaxation pathway to terminate protease-activated receptor-1 signalling. It has been suggested that RGS-2 is a new drug development target for hypertension. Mice deficient in RGS-2 also have impaired antiviral immunity. It is difficult to envisage how RGS-2 could be targeted to have effects on the cardiovascular system without affecting immunity. Also, it is not clear whether or not targeting RGS-2 will have advantages over targeting receptors. Only an increased understanding of the physiological and pathological role of RGS-2 will help us resolve these issues.

Genetic variations of regulator of G-protein signaling 2 in hypertensive patients and in the general population

OBJECTIVES

Mice deficient in the regulator of G-protein signaling 2 (RGS2) exhibit a strong hypertensive phenotype. We studied whether genetic variations in RGS2 are implicated in hypertension or other phenotypes in Japanese hypertensive individuals and the general population.

METHODS

We sequenced all exons of RGS2 and the promoter region in 953 and 48 hypertensive individuals, respectively. Genotyping by the TaqMan polymerase chain reaction method was performed for six missense or frameshift mutations and common single nucleotide polymorphisms in the general population, with a sample size of 1872 individuals (862 men and 1011 women).

RESULTS

We identified five novel missense mutations (Q2L; n = 2, Q2R; n = 1, M5V; n = 1, R44H; n = 2, Q78H; n = 1) and one novel frameshift mutation (1925-1926insT; n = 2) in a heterozygous state, in addition to 33 variations including five common single nucleotide polymorphisms. Six missense/frameshift mutations and three common single nucleotide polymorphisms (-638A > G, 1026T > A, 1891-1892delTC) were successfully genotyped in the general population. Mutations Q2L (n = 2), M5V (n = 1), and 1925-1926insT (n = 2) were only identified in hypertensive subjects. Six out of seven individuals with the R44H mutation, which occurs in the amphipathic alpha-helical domain of RGS2, had hypertension. The results showed a significant association of two common single nucleotide polymorphisms, 1026T > A [TT versus TA + AA: odds ratio (OR) 1.33; 95% confidence interval (CI) 1.02-1.74; P = 0.035] and 1891-1892delTC (I: insertion allele, D: deletion allele, II versus ID + DD: OR 1.47; 95% CI 1.09-1.97; P = 0.012), with hypertension in women by multivariate logistic regression analysis.

CONCLUSION

Our results suggest that genetic variations in RGS2 contribute partly to the hypertensive phenotype.

NO-dependent blood pressure regulation in RGS2-deficient mice

The regulator of G protein signaling (RGS) 2, a GTPase-activating protein, is activated via the nitric oxide (NO)-cGMP pathway and thereby may influence blood pressure regulation. To test that notion, we measured mean arterial blood pressure (MAP) and heart rate (HR) with telemetry in N(omega)-nitro-l-arginine methyl ester (l-NAME, 5 mg l-NAME/10 ml tap water)-treated RGS2-deficient (RGS2(-/-)) and RGS2-sufficient (RGS2(+/+)) mice and assessed autonomic function. Without l-NAME, RGS2(-/-) mice showed during day and night a similar increase of MAP compared with controls. l-NAME treatment increased MAP in both strains. nNOS is involved in this l-NAME-dependent blood pressure increase, since 7-nitroindazole increased MAP by 8 and 9 mmHg (P < 0.05) in both strains. The l-NAME-induced MAP increase of 14-15 mmHg during night was similar in both strains. However, the l-NAME-induced MAP increase during the day was smaller in RGS2(-/-) than in RGS2(+/+) (11 +/- 1 vs. 17 +/- 2 mmHg; P < 0.05). Urinary norepinephrine and epinephrine excretion was higher in RGS2(-/-) than in RGS2(+/+) mice. The MAP decrease after prazosin was more pronounced in l-NAME-RGS2(-/-). HR variability parameters [root mean square of successive differences (RMSSD), low-frequency (LF) power, and high-frequency (HF) power] and baroreflex sensitivity were increased in RGS2(-/-). Atropine and atropine plus metoprolol markedly reduced RMSSD, LF, and HF. Our data suggest an interaction between RGS2 and the NO-cGMP pathway. The blunted l-NAME response in RGS2(-/-) during the day suggests impaired NO signaling. The MAP increases during the active phase in RGS2(-/-) mice may be related to central sympathetic activation and increased vascular adrenergic responsiveness.

Multi-tasking RGS proteins in the heart: the next therapeutic target?

Regulator of G-protein-signaling (RGS) proteins play a key role in the regulation of G-protein-coupled receptor (GPCR) signaling. The characteristic hallmark of RGS proteins is a conserved approximately 120-aa RGS region that confers on these proteins the ability to serve as GTPase-activating proteins (GAPs) for G(alpha) proteins. Most RGS proteins can serve as GAPs for multiple isoforms of G(alpha) and therefore have the potential to influence many cellular signaling pathways. However, RGS proteins can be highly regulated and can demonstrate extreme specificity for a particular signaling pathway. RGS proteins can be regulated by altering their GAP activity or subcellular localization; such regulation is achieved by phosphorylation, palmitoylation, and interaction with protein and lipid-binding partners. Many RGS proteins have GAP-independent functions that influence GPCR and non-GPCR-mediated signaling, such as effector regulation or action as an effector. Hence, RGS proteins should be considered multifunctional signaling regulators. GPCR-mediated signaling is critical for normal function in the cardiovascular system and is currently the primary target for the pharmacological treatment of disease. Alterations in RGS protein levels, in particular RGS2 and RGS4, produce cardiovascular phenotypes. Thus, because of the importance of GPCR-signaling pathways and the profound influence of RGS proteins on these pathways, RGS proteins are regulators of cardiovascular physiology and potentially novel drug targets as well.

Selective inhibition of alpha1A-adrenergic receptor signaling by RGS2 association with the receptor third intracellular loop

Regulators of G-protein signaling (RGS) proteins act directly on Galpha subunits to increase the rate of GTP hydrolysis and to terminate signaling. However, the mechanisms involved in determining their specificities of action in cells remain unclear. Recent evidence has raised the possibility that RGS proteins may interact directly with G-protein-coupled receptors to modulate their activity. By using biochemical, fluorescent imaging, and functional approaches, we found that RGS2 binds directly and selectively to the third intracellular loop of the alpha1A-adrenergic receptor (AR) in vitro, and is recruited by the unstimulated alpha1A-AR to the plasma membrane in cells to inhibit receptor and Gq/11 signaling. This interaction was specific, because RGS2 did not interact with the highly homologous alpha1B- or alpha1D-ARs, and the closely related RGS16 did not interact with any alpha1-ARs. The N terminus of RGS2 was required for association with alpha1A-ARs and inhibition of signaling, and amino acids Lys219, Ser220, and Arg238 within the alpha1A-AR i3 loop were found to be essential for this interaction. These findings demonstrate that certain RGS proteins can directly interact with preferred G-protein-coupled receptors to modulate their signaling with a high degree of specificity.