A human gene encoding a putative basic helix-loop-helix phosphoprotein whose mRNA increases rapidly in cycloheximide-treated blood mononuclear cells

Germline deletion of Rgs2 and/or Rgs5 in male mice does not exacerbate left ventricular remodeling induced by subchronic isoproterenol infusion

Sympathoexcitation is a hallmark of heart failure, with sustained β-adrenergic receptor (βAR)-G protein signaling activation. βAR signaling is modulated by regulator of G protein signaling (RGS) proteins. Previously, we reported that Gαi/o regulation by RGS2 or RGS5 is key to ventricular rhythm regulation, while the dual loss of both RGS proteins results in left ventricular (LV) dilatation and dysfunction. Here, we tested whether sustained βAR stimulation with isoproterenol (ISO, 30 mg/kg/day, 3 days) exacerbates LV remodeling in male mice with germline deletion of Rgs2 and/or Rgs5. Rgs2 KO and Rgs2/5 dbKO mice showed LV dilatation at baseline, which was unchanged by ISO. Rgs2 or Rgs5 deletion decreased Rgs1 expression, whereas Rgs5 deletion increased Rgs4 expression. ISO induced cardiac hypertrophy and interstitial fibrosis in Rgs2/5 dbKO mice without increasing cardiomyocyte size or LV dilation but increased expression of cardiac fetal gene Nppa, α-actinin, and Ca2+-/calmodulin-dependent kinase II. Single Rgs2 and Rgs5 KO mice had markedly increased CD45+ cells, whereas tissue from Rgs5 KO mice showed increased CD68+ cells, as revealed by immunohistochemistry. The results together indicate that ventricular remodeling due to Rgs2 and/or Rgs5 deletion is associated with augmented myocardial immune cell presence but is not exacerbated by sustained βAR stimulation.

CMV-encoded GPCRs in infection, disease, and pathogenesis

G protein coupled receptors (GPCRs) are seven-transmembrane domain proteins that modulate cellular processes in response to external stimuli. These receptors represent the largest family of membrane proteins, and in mammals, their signaling regulates important physiological functions, such as vision, taste, and olfaction. Many organisms, including yeast, slime molds, and viruses encode GPCRs. Cytomegaloviruses (CMVs) are large, betaherpesviruses, that encode viral GPCRs (vGPCRs). Human CMV (HCMV) encodes four vGPCRs, including UL33, UL78, US27, and US28. Each of these vGPCRs, as well as their rodent and primate orthologues, have been investigated for their contributions to viral infection and disease. Herein, we discuss how the CMV vGPCRs function during lytic and latent infection, as well as our understanding of how they impact viral pathogenesis.

Rodent Models of Audiogenic Epilepsy: Genetic Aspects, Advantages, Current Problems and Perspectives

Animal models of epilepsy are of great importance in epileptology. They are used to study the mechanisms of epileptogenesis, and search for new genes and regulatory pathways involved in the development of epilepsy as well as screening new antiepileptic drugs. Today, many methods of modeling epilepsy in animals are used, including electroconvulsive, pharmacological in intact animals, and genetic, with the predisposition for spontaneous or refractory epileptic seizures. Due to the simplicity of manipulation and universality, genetic models of audiogenic epilepsy in rodents stand out among this diversity. We tried to combine data on the genetics of audiogenic epilepsy in rodents, the relevance of various models of audiogenic epilepsy to certain epileptic syndromes in humans, and the advantages of using of rodent strains predisposed to audiogenic epilepsy in current epileptology.

Effect of the regulator of G-protein signaling 2 on the proliferation and invasion of oral squamous cell carcinoma cells and its molecular mechanism

OBJECTIVES

This study aims to investigate the effect of the regulator of G-protein signaling 2 (RGS2) on the proliferation and invasion of oral squamous cell carcinoma (OSCC) cells and its potential molecular mechanism. Metho⁃ds The expression status and clinical significance of RGS2 in head and neck squamous cell carcinomas and matched adjacent normal tissues were evaluated using TCGA database. Three OSCC cell lines (i.e., SCC-9, Cal27, and Fadu) were overexpressed with RGS2, and the effect of RGS2 on cell proliferation and invasion was determined using the Transwell, clone formation, and cell counting kit (CCK)-8 assays. Moreover, the yeast two-hybrid scree-ning and co-immunoprecipitation (Co-IP) assays were conducted to detect the correlation of RGS2, four and a half LIM domains protein 1 (FHL1), and damage DNA-binding protein 1 (DDB1).

RESULTS

The expression level of RGS2 in OSCC was significantly lower than that in matched adjacent normal tissues (P=0.023). The high RGS2 expression level was negatively correlated with lymphovascular invasion (P<0.001). After transfection with lentiv-RGS2, the expression of RGS2 was increased, and the invasion and proliferation abilities of OSCC cell lines were evidently inhibited. FHL1 could competitively bind with RGS2, which decreased the integration of DDB1 and RGS2, inhibited the ubiquitination process of RGS2, and maintained the stability of the RGS2 protein.

CONCLUSIONS

RGS2 plays an important role in the inhibition of OSCC proliferation and invasion. The structure stability of RGS2 is competitively regulated by FHL1 and DDB1.

Proteolytic degradation of regulator of G protein signaling 2 facilitates temporal regulation of Gq/11 signaling and vascular contraction

Regulator of G protein signaling 2 (RGS2) controls signaling by receptors coupled to the G_q/11 class heterotrimeric G proteins. RGS2 deficiency causes several phenotypes in mice and occurs in several diseases, including hypertension in which a proteolytically unstable RGS2 mutant has been reported. However, the mechanisms and functions of RGS2 proteolysis remain poorly understood. Here we addressed these questions by identifying degradation signals in RGS2, and studying dynamic regulation of G_q/11-evoked Ca²⁺ signaling and vascular contraction. We identified a novel bipartite degradation signal in the N-terminal domain of RGS2. Mutations disrupting this signal blunted proteolytic degradation downstream of E3 ubiquitin ligase binding to RGS2. Analysis of RGS2 mutants proteolyzed at various rates and the effects of proteasome inhibition indicated that proteolytic degradation controls agonist efficacy by setting RGS2 protein expression levels, and affecting the rate at which cells regain agonist responsiveness as synthesis of RGS2 stops. Analyzing contraction of mesenteric resistance arteries supported the biological relevance of this mechanism. Because RGS2 mRNA expression often is strikingly and transiently up-regulated and then down-regulated upon cell stimulation, our findings indicate that proteolytic degradation tightly couples RGS2 transcription, protein levels, and function. Together these mechanisms provide tight temporal control of G_q/11-coupled receptor signaling in the cardiovascular, immune, and nervous systems.

The evolution of regulators of G protein signalling proteins as drug targets - 20 years in the making: IUPHAR Review 21

Regulators of G protein signalling (RGS) proteins are celebrating the 20th anniversary of their discovery. The unveiling of this new family of negative regulators of G protein signalling in the mid-1990s solved a persistent conundrum in the G protein signalling field, in which the rate of deactivation of signalling cascades in vivo could not be replicated in exogenous systems. Since then, there has been tremendous advancement in the knowledge of RGS protein structure, function, regulation and their role as novel drug targets. RGS proteins play an important modulatory role through their GTPase-activating protein (GAP) activity at active, GTP-bound Gα subunits of heterotrimeric G proteins. They also possess many non-canonical functions not related to G protein signalling. Here, an update on the status of RGS proteins as drug targets is provided, highlighting advances that have led to the inclusion of RGS proteins in the IUPHAR/BPS Guide to PHARMACOLOGY database of drug targets.

Summertime dosage-dependent hypersensitivity to an angiotensin II receptor blocker

Background

Summertime dips in blood pressure (BP), both in normotensive and hypertensive subjects, are well known. However, the dips are small and are not related to particular forms or doses of antihypertensive medication. Nevertheless it is the practice in some quarters to decrease antihypertensive medication in summer, and/or to increase in winter. Large scale studies being inconclusive, there are calls for long-term examination of the relationship between environmental temperature and blood pressure in single individuals under medication.

Case presentation

While analyzing data from a subject whose BP had been controlled for a decade with the angiotensin-II receptor blocker losartan, an extreme, dosage-dependent, summertime dip came to light. Downward dosage adjustment appeared essential and may have prevented hypotension-related pathology.

Conclusion

The benefits of aggressive medication (the “J curve” phenomenon) being debated, the possibility of seasonal hypersensitivity, perhaps explicable in terms of differential signaling by countervailing receptors, should be taken into account when considering dosage adjustments in hypertensive subjects.

Regulator of G Protein Signaling 2: A Versatile Regulator of Vascular Function

Regulators of G protein signaling (RGS) proteins of the B/R4 family are widely expressed in the cardiovascular system where their role in fine-tuning G protein signaling is critical to maintaining homeostasis. Among members of this family, RGS2 and RGS5 have been shown to play key roles in cardiac and smooth muscle function by tightly regulating signaling pathways that are activated through Gq/11 and Gi/o classes of heterotrimeric G proteins. This chapter reviews accumulating evidence supporting a key role for RGS2 in vascular function and the implication of changes in RGS2 function and/or expression in the pathogenesis of blood pressure disorders, particularly hypertension. With such understanding, RGS2 and the signaling pathways it controls may emerge as novel targets for developing next-generation antihypertensive drugs/agents.

The RGS2 (-391, C>G) genetic variation correlates to antihypertensive drug responses in Chinese patients with essential hypertension

OBJECTIVE

Regulators of G-protein signaling protein 2 (RGS2) play an irreplaceable role in the control of normal blood pressure (BP). One RGS2 (-391, C>G) genetic variation markedly changes its mRNA expression levels. This study explored the relationship between this genetic variation and the responses to antihypertensive drugs in Chinese patients with essential hypertension.

METHODS

Genetic variations of RGS2 were successfully identified in 367 specimens using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assays. All patients were treated with conventional doses of antihypertensives after a 2-week run-in period and followed-up according to our protocol. A general linear model multivariate analysis of variance (ANOVA) was used for the data analysis.

RESULTS

A significant difference in the mean systolic BP change was observed between RGS2 (-391, C>G) CC/CG (n = 82) and GG (n = 38) genotype carriers (-13.6 vs. -19.9 mmHg, P = 0.043) who were treated with candesartan, irbesartan or imidapril at the end of 6 weeks. In addition, the patients' BP responses to α,β-adrenergic receptor blockers exhibited an age-specific association with the RGS2 (-391, C>G) genetic variation at the end of 4 weeks.

CONCLUSION

The RGS2 (-391, C>G) genetic polymorphism may serve as a biomarker to predict a patient's response to antihypertensive drug therapy, but future studies need to confirm this.

Phenotype-independent effects of retroviral transduction in human dental pulp stem cells

An immortalized human dental pulp stem cell (DPSC) line of an odontoblastic phenotype is established to circumvent the normal programmed senescence and to maintain the cell line's usefulness as a tool for further study of cellular activity. DPSCs are isolated from human dental pulp tissues and transfected using hTERT. The influence of this process on the DPSC phenotype and the mRNA expression of oncogenes involved in cellular senescence is investigated. The results reveal an absence of altered DPSC morphology and phenotype following the exogenous introduction of the hTERT gene, which is coupled with a significant reduction in p16 mRNA expression. This provides insight into how to circumvent in vitro dental pulp stem cell death following the exogenous introduction of hTERT.

RGS2 is a component of the cellular stress response

Regulator of G protein signaling (RGS) proteins are GTPase accelerating proteins for heterotrimeric G protein α-subunits. RGS2 has recently been shown to have additional G protein-independent functions including control of ion channel currents, microtubule polymerization, and protein synthesis. Cellular levels of RGS2 mRNA and protein are upregulated in response to various forms of stress suggesting that it may be a stress-adaptive protein; however, direct evidence to support this notion has remained elusive. In this report, we show that thermal stress upregulates RGS2 expression and this serves to arrest de novo protein synthesis. The latter is an established cellular response to stress. Inhibiting the stress-induced RGS2 upregulation by way of siRNA knockdown diminished the repression of global protein synthesis. The collective results of our study implicate RGS2 upregulation as a cellular mechanism of controlling de novo protein synthesis in response to stress. This work provides greater insight into the stress proteome and the role of RGS2.

Anthrax lethal toxin-induced gene expression changes in mouse lung

A major virulence factor of Bacillus anthracis is the anthrax Lethal Toxin (LeTx), a bipartite toxin composed of Protective Antigen and Lethal Factor. Systemic administration of LeTx to laboratory animals leads to death associated with vascular leakage and pulmonary edema. In this study, we investigated whether systemic exposure of mice to LeTx would induce gene expression changes associated with vascular/capillary leakage in lung tissue. We observed enhanced susceptibility of A/J mice to death by systemic LeTx administration compared to the C57BL/6 strain. LeTx-induced groups of both up- and down-regulated genes were observed in mouse lungs 6 h after systemic administration of wild type toxin compared to lungs of mice exposed to an inactive mutant form of the toxin. Lungs of the less susceptible C57BL/6 strain showed 80% fewer differentially expressed genes compared to lungs of the more sensitive A/J strain. Expression of genes known to regulate vascular permeability was modulated by LeTx in the lungs of the more susceptible A/J strain. Unexpectedly, the largest set of genes with altered expression was immune specific, characterized by the up-regulation of lymphoid genes and the down-regulation of myeloid genes. Transcripts encoding neutrophil chemoattractants, modulators of tumor regulation and angiogenesis were also differentially expressed in both mouse strains. These studies provide new directions for the investigation of vascular leakage and pulmonary edema induced by anthrax LeTx.

Regulators of G-protein signaling and their Gα substrates: promises and challenges in their use as drug discovery targets

Because G-protein coupled receptors (GPCRs) continue to represent excellent targets for the discovery and development of small-molecule therapeutics, it is posited that additional protein components of the signal transduction pathways emanating from activated GPCRs themselves are attractive as drug discovery targets. This review considers the drug discovery potential of two such components: members of the "regulators of G-protein signaling" (RGS protein) superfamily, as well as their substrates, the heterotrimeric G-protein α subunits. Highlighted are recent advances, stemming from mouse knockout studies and the use of "RGS-insensitivity" and fast-hydrolysis mutations to Gα, in our understanding of how RGS proteins selectively act in (patho)physiologic conditions controlled by GPCR signaling and how they act on the nucleotide cycling of heterotrimeric G-proteins in shaping the kinetics and sensitivity of GPCR signaling. Progress is documented regarding recent activities along the path to devising screening assays and chemical probes for the RGS protein target, not only in pursuits of inhibitors of RGS domain-mediated acceleration of Gα GTP hydrolysis but also to embrace the potential of finding allosteric activators of this RGS protein action. The review concludes in considering the Gα subunit itself as a drug target, as brought to focus by recent reports of activating mutations to GNAQ and GNA11 in ocular (uveal) melanoma. We consider the likelihood of several strategies for antagonizing the function of these oncogene alleles and their gene products, including the use of RGS proteins with Gα(q) selectivity.

Expression, purification and characterization of yellow grouper Epinephelus awoara regulator of G protein signaling 16 protein

Regulators of G-protein signaling (RGS) proteins are a family of proteins, which accelerate GTPase-activity intrinsic to the alpha subunits of heterotrimeric G-proteins and play crucial roles in the physiological control of G-protein signaling. Here, yellow grouper RGS16 protein was expressed in Escherichia coli and purified by Ni-NTA affinity chromatography. The expression level of the fusion protein was up to 30% of the total cellular protein.Western blotting analysis showed that a band with the molecular mass of about 21 Kda was detected. The purified recombinant protein was used to prepare polyclonal antibody, and antiserum obtained was highly specific with the titer of over 1:32,000. Additionally, RGS16 protein was expressed in the Tn-5B1-4 insect cells. Western blotting analysis revealed that the expressed protein had immunoreactivity.

Rgs2 mediates pro-angiogenic function of myeloid derived suppressor cells in the tumor microenvironment via upregulation of MCP-1

Background

Tumor growth is intimately linked with stromal interactions. Myeloid derived suppressor cells (MDSCs) are dramatically elevated in cancer patients and tumor bearing mice. MDSCs modulate the tumor microenvironment through attenuating host immune response and increasing vascularization.

Methodology/Principal Findings

In searching for molecular mediators responsible for pro-tumor functions, we found that regulator of G protein signaling-2 (Rgs2) is highly increased in tumor-derived MDSCs compared to control MDSCs. We further demonstrate that hypoxia, a common feature associated with solid tumors, upregulates the gene expression. Genetic deletion of Rgs2 in mice resulted in a significant retardation of tumor growth, and the tumors exhibit decreased vascular density and increased cell death. Interestingly, deletion of Rgs2 in MDSCs completely abolished their tumor promoting function, suggesting that Rgs2 signaling in MDSCs is responsible for the tumor promoting function. Cytokine array profiling identified that Rgs2−/− tumor MDSCs produce less MCP-1, leading to decreased angiogenesis, which could be restored with addition of recombinant MCP-1.

Conclusion

Our data reveal Rgs2 as a critical regulator of the pro-angiogenic function of MDSCs in the tumor microenvironment, through regulating MCP-1 production.

KLF4 is a novel candidate tumor suppressor gene in pancreatic ductal carcinoma

Ductal pancreatic carcinoma (DPC) is a deadly disease with an incidence of 9 cases in 100,000 people per year and a mortality rate close to 100%. Allelic losses in the long arm of chromosome 9 are commonly encountered in many human malignancies but no data are yet available about DPC. We screened 40 laser-microdissected DPC samples and 6 pre-invasive lesions for 9 microsatellite mapping markers of region 9q21.3 through 9q34.2. A small overlapping region of deletion, spanning 8 million base pairs, was identified between D9S127 and D9S105. Two genes, RSG3 and KLF4, mapped to 9q31.1 through 9q32, were further investigated. A highly significant association was found between KLF4 gene expression levels and genomic status. Similarly, absence of immunohistochemical expression of KLF4 protein was found in 86.8% cases of DPC (33/38). Overexpression of KLF4 in a human pancreatic carcinoma cell line induced a significant decrease in the proliferation associated with up-regulation of p21 and the down-regulation of cyclin D1. In conclusion, we identified a novel oncosuppressor region located at the 9q 31.1-3 locus that is lost in DPC at high frequency. Loss of KLF4 expression is closely related to the genomic loss, and its restoration inhibits cancer cell proliferation, suggesting a key suppressor role in pancreatic tumorigenesis.

Analysis of RGS2 expression and prognostic significance in stage II and III colorectal cancer

The role of RGS2 (regulator of G-protein signalling 2) has been studied in several tumours. The purpose of the present study is to investigate the correlations between clinicopathological factors and patients' survival time and RGS2 expression in stage II and III CRC (colorectal cancer) patients. Real-time quantitative PCR was performed in 36 CRC tissues with recurrence and 28 without recurrence, and in three CRC-metastasis-derived cell lines (SW620, LoVo and Colo205) and 3 primary-CRC-derived ones (SW480, Caco-2 and HCT116) to examine RGS2 mRNA expression. In addition, to provide visualized evidence for RGS2 mRNA expression, random CRC samples were also performed with RT–PCR (reverse transcription–PCR). RGS2 protein was detected by immunostaining in 118 paraffin-embedded specimens, and the correlations between clinicopathological factors and survival time and RGS2 expression were analysed. We found that RGS2 mRNA was down-regulated both in CRC tissues with recurrence and metastasis-derived cell lines, and the expression level of RGS2 was unrelated to gender, age, tumour grade, or lymphovascular or perineural invasion. However, it was positively related to disease-free survival time (P<0.05). Furthermore, low RGS2 expression indicated a poorer survival rate (P<0.05, log-rank test). Multivariate analysis also showed that weak RGS2 protein expression was an independent adverse prognosticator in CRC (P<0.05). Taken together, we suggested that down-regulation of RGS2 might play an important role in CRC metastasis and predict poor prognosis in stage II and III CRC patients.

Regulator of G protein-signaling proteins and addictive drugs

Regulator of G protein-signaling (RGS) proteins are a family of more than 30 intracellular proteins that negatively modulate intracellular signaling of receptors in the G protein-coupled receptor family. This family includes receptors for opioids, cannabinoids, and dopamine that mediate the acute effects of addictive drugs or behaviors and chronic effects leading to the development of addictive disease. Members of the RGS protein family, by negatively modulating receptor signaling, influence the intracellular processes that lead to addiction. In turn, addictive drugs control the expression levels of several RGS proteins. This review will consider the distribution and mechanisms of action of RGS proteins, particularly the R4 and R7 families that have been implicated in the actions of addictive drugs, how knowledge of these proteins is contributing to an understanding of addictive processes, and whether specific RGS proteins could provide targets for the development of medications to manage and/or treat addiction.

Molecular and functional analysis of the stem cell compartment of chronic myelogenous leukemia reveals the presence of a CD34- cell population with intrinsic resistance to imatinib

We show the molecular and functional characterization of a novel population of lineage-negative CD34-negative (Lin(-)CD34(-)) hematopoietic stem cells from chronic myelogenous leukemia (CML) patients at diagnosis. Molecular karyotyping and quantitative analysis of BCR-ABL transcript demonstrated that approximately one-third of CD34(-) cells are leukemic. CML Lin(-)CD34(-) cells showed kinetic quiescence and limited clonogenic capacity. However, stroma-dependent cultures induced CD34 expression on some cells and cell cycling, and increased clonogenic activity and expression of BCR-ABL transcript. Lin(-)CD34(-) cells showed hematopoietic cell engraftment rate in 2 immunodeficient mouse strains similar to Lin-CD34(+) cells, whereas endothelial cell engraftment was significantly higher. Gene expression profiling revealed the down-regulation of cell-cycle arrest genes and genes involved in antigen presentation and processing, while the expression of genes related to tumor progression, such as angiogenic factors, was strongly up-regulated compared with normal counterparts. Phenotypic analysis confirmed the significant down-regulation of HLA class I and II molecules in CML Lin(-)CD34(-) cells. Imatinib mesylate did not reduce fusion transcript levels, BCR-ABL kinase activity, and clonogenic efficiency of CML Lin(-)CD34(-) cells in vitro. Moreover, leukemic CD34(-) cells survived exposure to BCR-ABL inhibitors in vivo. Thus, we identified a novel CD34(-) leukemic stem cell subset in CML with peculiar molecular and functional characteristics.

Translational control by RGS2

The regulator of G protein signaling (RGS) proteins are a family of guanosine triphosphatase (GTPase)-accelerating proteins. We have discovered a novel function for RGS2 in the control of protein synthesis. RGS2 was found to bind to eIF2Bepsilon (eukaryotic initiation factor 2B epsilon subunit) and inhibit the translation of messenger RNA (mRNA) into new protein. This effect was not observed for other RGS proteins tested. This novel function of RGS2 is distinct from its ability to regulate G protein-mediated signals and maps to a stretch of 37 amino acid residues within its conserved RGS domain. Moreover, RGS2 was capable of interfering with the eIF2-eIF2B GTPase cycle, which is a requisite step for the initiation of mRNA translation. Collectively, this study has identified a novel role for RGS2 in the control of protein synthesis that is independent of its established RGS domain function.

Structure and function of regulator of G protein signaling homology domains

All regulator of G protein signaling (RGS) proteins contain a conserved domain of approximately 130 amino acids that binds to activated heterotrimeric G protein α subunits (Gα) and accelerates their rate of GTP hydrolysis. Homologous domains are found in at least six other protein families, including a family of Rho guanine nucleotide exchange factors (RhoGEFs) and the G protein-coupled receptor kinases (GRKs). Although some of the RhoGEF and GRK RGS-like domains can also bind to activated Gα subunits, they do so in distinct ways and with much lower levels of GTPase activation. In other protein families, the domains have as of yet no obvious relationship to heterotrimeric G protein signaling. These RGS homology (RH) domains are now recognized as mediators of extraordinarily diverse protein-protein interactions. Through these interactions, they play roles that range from enzyme to molecular scaffold to signal transducing module. In this review, the atomic structures of RH domains from RGS proteins, Axins, RhoGEFs, and GRKs are compared in light of what is currently known about their functional roles.

Expansion of signal transduction by G proteins. The second 15 years or so: from 3 to 16 alpha subunits plus betagamma dimers

The first 15 years, or so, brought the realization that there existed a G protein coupled signal transduction mechanism by which hormone receptors regulate adenylyl cyclases and the light receptor rhodopsin activates visual phosphodiesterase. Three G proteins, Gs, Gi and transducin (T) had been characterized as alphabetagamma heterotrimers, and Gsalpha-GTP and Talpha-GTP had been identified as the sigaling arms of Gs and T. These discoveries were made using classical biochemical approaches, and culminated in the purification of these G proteins. The second 15 years, or so, are the subject of the present review. This time coincided with the advent of powerful recombinant DNA techniques. Combined with the classical approaches, the field expanded the repertoire of G proteins from 3 to 16, discovered the superfamily of seven transmembrane G protein coupled receptors (GPCRs) -- which is not addressed in this article -- and uncovered an amazing repertoire of effector functions regulated not only by alphaGTP complexes but also by betagamma dimers. Emphasis is placed in presenting how the field developed with the hope of conveying why many of the new findings were made.

-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.

Chronic olanzapine treatment causes differential expression of genes in frontal cortex of rats as revealed by DNA microarray technique

Recent emerging biochemical data indicate that several important neuroregulatory genes and proteins may be involved in the etiology of schizophrenia and bipolar disorder. Additionally, the same genes appear to be targets of several psychotropic medications that are used to treat these disorders. Recent DNA microarray studies show that genes involved in synaptic neurotransmission, signal transduction, and glutamate/GABA regulation may be differentially regulated in brains of subjects with schizophrenia. We hypothesized that chronic administration of olanzapine to rats would alter expression of various genes that may be involved in the etiology of schizophrenia and mood disorders. Rats were administered olanzapine (N=20, 2 mg/kg/day) or sterile saline intraperitoneally (N=20) daily for 21 days. Control and olanzapine-treated frontal cortices were analyzed using cDNA microarray technology. The results showed significant downregulation of 31 genes and upregulation of 38 genes by greater than two-fold in the drug-treated brains vs controls. Our results provide evidence for altered regulation of genes involved with signal transduction and cell communication, metabolism and energy pathways, transport, immune response, nucleic acid metabolism, and neuronal growth factors. Real-time quantitative RT-PCR analysis verified the direction and magnitude of change in six genes of interest: calbindin 3, homer 1, regulator of G-protein signaling (RGS) 2, pyruvate kinase, Reelin and insulin 2. Western blotting showed significant upregulation in protein products for Reelin 410 and Reelin 180 kDa and downregulation for NMDA3B and RGS2. Our results show for the first time that olanzapine causes changes in levels of several important genes that may be involved in the etiology and treatment of schizophrenia and other psychiatric disorders.

Palmitoylation and its effect on the GTPase-activating activity and conformation of RGS2

Regulator of G protein signaling (RGS) proteins act as negative regulators of G protein coupled signaling by accelerating the GTPase activity of the G proteins alpha subunits. Reversible palmitoylation, a common post-translational modification for various components of the G protein-coupled signaling pathway, plays an important role in the modulation of protein activity. RGS2 appears to act selectively to increase the GTPase activity of Gqalpha when single turnover assays are preformed in solution. However, less attention has been paid to the effects of palmitoylation of RGS2 on its conformation and GTPase-activating activity. Studies of palmitoylation on a series of RGS2 mutants in which alanine was substituted for cysteine revealed cysteine 106, 116 and 199 to be multiple putative palmitoylation sites in RGS2, the efficiency of palmitate incorporation being about 60% at each individual palmitoylation site. Palmitoylation of RGS2 inhibited the GTPase-activating activity toward a GTPase-deficient R183C mutant of Gqalpha in vitro, but mutation of cysteine 116 eliminated the inhibition of palmitoylation on GTPase-activating activity of RGS2. The effect of palmitoylation on conformation of RGS2 was examined by monitoring spectra of the intrinsic fluorescence and Circular Dichroism. The results suggested that GTPase-activating activity change of RGS2 might be related to conformational change of RGS2 upon palmitoylation. Taken together, these results provided clear and strong experimental evidence for palmitoylation sites in RGS2 as well as for effect of palmitoylation on the GTPase-activating activity and conformation of RGS2.

Investigating RGS proteins in yeast

Regulator of G protein signalling (RGS) proteins are vital in the adaptation of cells to stimulation via G protein-coupled receptors. Yeast have been integral in elucidating the important role that RGS proteins play within cellular processes. In addition to extensive characterisation of the endogenous RGS proteins, these organisms have enabled the identification and analysis of numerous mammalian homologues. The simplicity and plasticity of the yeast pheromone-response pathway has facilitated studies which would have been impossible in mammalian systems and it is certain that yeast will continue to have a great impact on this field of research in the future.

Respiratory failure due to differentiation arrest and expansion of alveolar cells following lung-specific loss of the transcription factor C/EBPalpha in mice

The leucine zipper family transcription factor CCAAT enhancer binding protein alpha (C/EBPalpha) inhibits proliferation and promotes differentiation in various cell types. In this study, we show, using a lung-specific conditional mouse model of C/EBPalpha deletion, that loss of C/EBPalpha in the respiratory epithelium leads to respiratory failure at birth due to an arrest in the type II alveolar cell differentiation program. This differentiation arrest results in the lack of type I alveolar cells and differentiated surfactant-secreting type II alveolar cells. In addition to showing a block in type II cell differentiation, the neonatal lungs display increased numbers of proliferating cells and decreased numbers of apoptotic cells, leading to epithelial expansion and loss of airspace. Consistent with the phenotype observed, genes associated with alveolar maturation, survival, and proliferation were differentially expressed. Taken together, these results identify C/EBPalpha as a master regulator of airway epithelial maturation and suggest that the loss of C/EBPalpha could also be an important event in the multistep process of lung tumorigenesis. Furthermore, this study indicates that exploring the C/EBPalpha pathway might have therapeutic benefits for patients with respiratory distress syndromes.

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.

Expression of regulator of G protein signalling proteins in natural killer cells, and their modulation by Ly49A and Ly49D

The small GTPase accelerators regulator of G protein signalling (RGS) proteins are important regulators of proximal signalling from G protein coupled receptors. Although natural killer (NK) cells express a number of G-protein coupled receptors, expression of RGS proteins has not been investigated. We analysed the expression of RGS proteins in rat NK cells, and detected mRNA for RGS1, RGS2, RGS5, RGS8, RGS16, and RGS18. Interestingly, when we included a panel of different leucocyte subsets, we found that RGS8 was selectively expressed by NK cells. NK cells are under control of both activating and inhibitory receptors and, utilizing a xenogeneic system where the mouse activating Ly49D or inhibitory Ly49A receptors were transfected into the rat RNK-16 cell line, the potential regulation of RGS proteins by single NK cell receptors was studied. We found that ligation of Ly49D led to a rapid and transient increase in message for RGS2, while Ly49A ligation up-regulated RGS2, RGS16, and RGS18 mRNA. Both receptors also induced a prolonged increase in RGS2 endogenous protein levels. These findings suggest that RGS proteins may be influenced by or involved in NK cell receptor events, suggesting a crosstalk between G-protein coupled receptors and NK cell receptors.

Influenza A virus infection causes alterations in expression of synaptic regulatory genes combined with changes in cognitive and emotional behaviors in mice

Epidemiological studies have indicated a link between certain neuropsychiatric diseases and exposure to viral infections. In order to examine long-term effects on behavior and gene expression in the brain of one candidate virus, we have used a model involving olfactory bulb injection of the neuro-adapted influenza A virus strain, WSN/33, in C57Bl/6 mice. Following this olfactory route of invasion, the virus targets neurons in the medial habenular, midline thalamic and hypothalamic nuclei as well as monoaminergic neurons in the brainstem. The mice survive and the viral infection is cleared from the brain within 12 days. When tested 14-20 weeks after infection, the mice displayed decreased anxiety in the elevated plus-maze and impaired spatial learning in the Morris water maze test. Elevated transcriptional activity of two genes encoding synaptic regulatory proteins, regulator of G-protein signaling 4 and calcium/calmodulin-dependent protein kinase IIalpha, was found in the amygdala, hypothalamus and cerebellum. It is of particular interest that the gene encoding RGS4, which has been related to schizophrenia, showed the most pronounced alteration. This study indicates that a transient influenza virus infection can cause persistent changes in emotional and cognitive functions as well as alterations in the expression of genes involved in the regulation of synaptic activities.

MK-801 alters RGS2 levels and adenylyl cyclase sensitivity in the rat striatum

The present report examines the effects of acute NMDA antagonism on Regulator of G Protein Signaling 2 (RGS2) expression and adenylyl cyclase sensitivity in the rat striatum. MK-801 and phencyclidine rapidly down-regulate RGS2 mRNA. The down-regulation of RGS2 by MK-801 was dose dependent and transient. Because previous reports showed that RGS2 attenuates activity of adenylyl cyclase, RGS2 protein level and sensitivity of adenylyl cyclase to forskolin was tested 2 h after administration of MK-801 (1 mg/kg). In striatal membranes of these rats, RGS2 protein level was 17% lower and forskolin-stimulated cAMP production 38% higher than in controls. These findings reveal a cross-talk between NMDA receptors and adenylyl cyclase and suggest a general cross-talk mechanism by which RGS proteins transcriptionally regulated by ionotropic receptors can alter signaling properties of metabotropic receptors.

RGS2-Mediated Regulation of Gqα

Regulators of G-protein signaling (RGS) proteins are GTPase-activating proteins (GAPs) that attenuate signaling by heterotrimeric G proteins. In RGS2, three unique residues within the G-protein-binding (RGS) domain have been shown to direct its selective inhibition of Gqalpha function. The function of RGS2 as a regulator of Gq is also dependent on regulatory sequences in its amino-terminal domain that direct its localization to the plasma membrane. This work details various approaches that have been used to characterize the relative contribution of the RGS and regulatory domains in RGS2 to its function as a regulator of Gq signaling. Specifically, assays describing (i) the identification of alpha subunit binding partners for RGS2 (ii) the characterization of RGS2-mediated inhibition of Gq-dependent phosphatidylinositol signaling in tissue culture models, and (iii) the measurement of Gq-dependent calcium responses in vascular smooth muscle cells from RGS2-deficient mice are presented. Results from these studies have been used to demonstrate the high relative potency of RGS2 for the regulation of Gq signaling at the biochemical, cellular, and physiologic level.

Role of regulator of G protein signaling 16 in inflammation-induced T lymphocyte migration and activation

Chemokine-induced T lymphocyte recruitment to the lung is critical for allergic inflammation, but chemokine signaling pathways are incompletely understood. Regulator of G protein signaling (RGS)16, a GTPase accelerator (GTPase-activating protein) for Galpha subunits, attenuates signaling by chemokine receptors in T lymphocytes, suggesting a role in the regulation of lymphocyte trafficking. To explore the role of RGS16 in T lymphocyte-dependent immune responses in a whole-organism model, we generated transgenic (Tg) mice expressing RGS16 in CD4(+) and CD8(+) cells. rgs16 Tg T lymphocytes migrated to CC chemokine ligand 21 or CC chemokine ligand 12 injection sites in the peritoneum, but not to CXC chemokine ligand 12. In a Th2-dependent model of allergic pulmonary inflammation, CD4(+) lymphocytes bearing CCR3, CCR5, and CXCR4 trafficked in reduced numbers to the lung after acute inhalation challenge with allergen (OVA). In contrast, spleens of sensitized and challenged Tg mice contained increased numbers of CD4(+)CCR3(+) cells producing more Th2-type cytokines (IL-4, IL-5, and IL-13), which were associated with increased airway hyperreactivity. Migration of Tg lymphocytes to the lung parenchyma after adoptive transfer was significantly reduced compared with wild-type lymphocytes. Naive lymphocytes displayed normal CCR3 and CXCR4 expression and cytokine responses, and compartmentation in secondary lymphoid organs was normal without allergen challenge. These results suggest that RGS16 may regulate T lymphocyte activation in response to inflammatory stimuli and migration induced by CXCR4, CCR3, and CCR5, but not CCR2 or CCR7.

Chick RGS2L demonstrates concentration-dependent selectivity for pertussis toxin-sensitive and -insensitive pathways that inhibit L-type Ca2+ channels

In neuronal cells, the influx of Ca2+ ions through voltage-dependent L-type calcium (L) channels couples excitation to multiple cellular functions. In addition to voltage, several neurotransmitters, hormones and cytokines regulate L channel gating via binding to G-protein-coupled receptors. Intracellular molecules that modify G-protein activity - such as regulator of G-protein-signalling (RGS) proteins - are therefore potential candidates for regulating Ca2+ influx through L channels. Here we show that a novel RGS2 splice variant from chick dorsal root ganglion (DRG) neurons, RGS2L, reduces bradykinin (BK)-mediated inhibition of neuronal L channels and accelerates recovery from inhibition. Chick RGS2 reduces the inhibition mediated by both the pertussis toxin (PTX)-sensitive (Gi/o-coupled) and the PTX-insensitive (presumably Gq/11-coupled) pathways. However, we demonstrate for the first time in a living cell that the extent of coupling to each pathway varies with RGS2L concentration. A low concentration of recombinant chick RGS2L (10 nM) preferentially reduces the inhibition mediated by the PTX-insensitive pathway, whereas a 100-fold higher concentration attenuates both PTX-sensitive- and PTX-insensitive-mediated components equally. Our data suggest that factors promoting RGS2L gene induction may regulate Ca2+ influx through L channels by recruiting low-affinity interactions with Gi/o that are absent at basal RGS2L levels.

Gene array and protein expression profiles suggest post-transcriptional regulation during CD8+ T cell differentiation

Peripheral CD8(+) T cells circulate in a quiescent naive state until they are primed by specific antigen and differentiate into effector cells. In the effector state, CD8(+) T cells acquire cytolytic activity and produce increased levels of cytokines such as interferon-gamma. They also exhibit increased T cell receptor sensitivity, decreased CD28 dependence, and become inhibitable by CTLA-4 and other negative regulatory pathways. We hypothesized that one mechanism by which these two states are regulated is via differential expression of specific genes. To this end, basal gene expression profiles of naive and effector 2C TCR transgenic x RAG2(-/-) CD8(+) T cells were analyzed using Affymetrix arrays representing 11,000 genes. Of the 177 differentially expressed known genes, 68 were expressed at higher levels in effector cells, but 109 were more abundant in naive cells, supporting the notion that the naive state is not passive. Expression of genes related to metabolism, actin cytoskeletal dynamics, and effector function increased with priming, whereas expression of putative anti-proliferative genes decreased. Semiquantitative reverse transcription-PCR was utilized as a secondary validation for selected transcripts, and Western blot analysis was used to examine protein expression for molecules of interest. Surprisingly, for 24 genes examined, 12 showed discordant protein versus mRNA expression. In summary, our study indicates that: 1) not only does the expression of some genes in naive CD8(+) T cells become up-regulated upon priming, but the expression of other genes is down-regulated as well and 2) the complexities of T cell differentiation include regulation at the post-transcriptional level.

Striatal gene expression of RGS2 and RGS4 is specifically mediated by dopamine D1 and D2 receptors: clues for RGS2 and RGS4 functions

Of all partners involved in G-protein coupled receptor (GPCR) signalling, the regulator of G-protein signalling (RGS) proteins are the only ones showing fast gene expression changes after various stimuli. These expression changes can offer feedback regulation to GPCR signalling as RGS accelerate the return of G-proteins to their inactive form and exert regulatory functions on intracellular effectors. However, it is not yet known which RGS regulate which receptor transduction pathways in the brain. To start to answer this question, we studied the influence of specific agonists and antagonists of the dopamine D1 and D2 receptors on the gene expression of the five most abundant RGS in the striatum: RGS2, RGS4, RGS8, RGS9 and RGS10. Only changes in RGS2 and RGS4 mRNA levels were observed. The D1 agonist SKF82958 and D2 antagonist haloperidol caused an up-regulation of RGS2 (+ 38.0% and + 41.6%, respectively). The D1 antagonist SCH23390 and D2 agonist quinpirole caused a down-regulation of RGS2 (- 25.0% and - 35.0%) and an up-regulation of RGS4 (+ 57.2% and + 52.5%). D1 and D2 receptors exert opposite effects on RGS2 expression, as they do on cAMP levels, suggesting a cAMP-mediated transcription of RGS2. This was confirmed by the unique induction of RGS2 (+ 111.1%) observed in the periventricular zone of the striatum after intracerebroventricular injection of forskolin. RGS4 was up-regulated only when RGS2 was down-regulated. This suggests that both RGS exert distinct functions. Considering the coupling of D1 and D2 receptors to the intracellular effector adenylate cyclase 5 (AC5) through their respective Galpha subunits in the striatum, our data allow us to suggest that RGS2 regulates the D1/Galphaolf/AC5 pathway and RGS4 the D2/Galphao/AC5 pathway.

Detailed localization of regulator of G protein signaling 2 messenger ribonucleic acid and protein in the rat brain

Regulator of G protein signaling (RGS) proteins are a recently identified family of proteins which dampen G protein-coupled receptor-mediated signaling by accelerating the intrinsic GTPase activity of Galpha subunits of heterotrimeric G proteins. More than 20 different RGSs have been identified and at least 10 are expressed in the CNS. The present study describes in detail the localization in the rat brain of one member of this family, RGS2. The distribution of RGS2 mRNA and protein has been studied in parallel by performing in situ hybridization and immunoautoradiography on adjacent rat brain sections. Our localization study reveals that RGS2 mRNA and protein are widely expressed in the brain. Protein and mRNA are mostly colocalized such as in neocortex, piriform cortex, caudate-putamen, septum, hippocampus, locus coeruleus. Some mismatches were also observed such as presence of mRNA but not protein in the paraventricular nucleus, the substantia nigra pars compacta and the red nucleus, suggesting that RGS2 protein is present in neuronal projections. Previous reports describing an induction of RGS2 mRNA in the rat striatum after psychostimulants (amphetamine, cocaine) led us to focus on the distribution of RGS2 in the basal ganglia circuitry. The absence of RGS2 mRNA and protein in the globus pallidus suggests that RGS2 would play its regulatory role more in the direct (striatonigral) than in the indirect (striatopallidal) striatal output pathway. In addition, to delineate the implication of RGS2 in pre- and/or postsynaptic functions in the basal ganglia, we performed lesions of the nigrostriatal pathway by 6-hydroxydopamine (6-OHDA) and striatal quinolinic acid lesions. The 6-OHDA lesion did not modify RGS2 mRNA or protein levels in the caudate-putamen whereas the intrastriatal quinolinic acid infusion caused a marked reduction of RGS2 mRNA and protein in the lesioned zone. These data indicate that RGS2 is predominantly expressed in intrinsic striatal neurons. Moreover, the absence of detectable change in RGS2 expression after injections of 6-OHDA suggests also that RGS2 is not primarily involved in the hypersensitization of postsynaptic dopamine receptors observed after lesion of the nigrostriatal pathway.

Opposite modulation of regulators of G protein signalling-2 RGS2 and RGS4 expression by dopamine receptors in the rat striatum

The role of dopaminergic transmission on striatal mRNA levels of regulators of G protein signalling proteins RGS 2-12 was evaluated by quantitative in situ hybridisation. A single injection of L-dopa (50 mg/kg i.p.) significantly increased the RGS2 mRNA level (by 25%), an effect that was specifically abolished by the D1 dopamine receptor antagonist R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (R(+)-SCH23390), but not changed by S(-)-eticlopride. Interestingly, the administration of this D2 dopamine receptor antagonist alone markedly enhanced the expression of RGS2 (by 71%), which suggests a constitutive inhibition of RGS2 expression by D2 dopamine receptors. Opposite results were obtained concerning the regulation of RGS4 since L-dopa alone was without effect whereas co-administration of L-dopa and R(+)-SCH23390 significantly enhanced the RGS4 mRNA levels (by 38%). In conclusion, D1 and D2 dopamine receptors appear to mediate opposite regulatory effects on RGS2 and RGS4 expression in the striatum.

Analysis of regulator of G-protein signaling-2 (RGS-2) expression and function in osteoblastic cells

Regulator of G-protein signaling-2 (RGS-2) belongs to a novel family of GTPase-activating proteins that rapidly turn-off G-protein coupled receptor signaling. RGS proteins contain a characteristic RGS domain by which they interact with the alpha-subunit of G-proteins and drive them into their inactive GDP-bound forms. Previously, we have reported that RGS-2 mRNA is rapidly and transiently increased by PTH in rat bone and in osteoblast cultures in vitro. In this study, we further explored the molecular basis for the regulation of RGS-2 by cloning and functionally characterizing the RGS-2 gene promoter. We cloned 2.3- and 2.8-kb fragments of the 5'-flanking regions of the rat and mouse RGS-2 genes, respectively, and generated a stable clone of UMR106 osteoblastic cells containing the rat RGS-2 promoter driving the beta-gal reporter gene (p2.3RGS-2-beta-gal). Treatment of the stable clone with PTH resulted in a maximal 2.2- to 3.6-fold increase in promoter activity at 8 h, reminiscent of the early response observed with endogenous RGS-2 mRNA regulation. Further, PTH (1-38), (1-31), PTHrP (1-34), and forskolin, which elevate cAMP levels, stimulated the promoter, while PTH (3-34) and (7-34), which do not readily stimulate cAMP accumulation, and PMA that directly activates protein kinase C, had no effect on promoter activity. Taken together, these results implicate the involvement of the Galpha(s)-adenylate cyclase-protein kinase A pathway in stimulating RGS-2 expression. Maintenance of a hyperphosphorylated state via the inhibition of type 2A protein phosphatases by okadaic acid, resulted in a strong dose-dependent increase in transcriptional activity of the RGS-2 promoter as well as that of the endogenous RGS-2 gene. Furthermore, overexpression of the osteoblast-specific transcription factor Runx2 also led to a stimulation of RGS-2 promoter activity. Functional analysis using RGS-2 overexpression suggests the potential negative regulatory effects of RGS-2 on PTH- and forskolin-induced cAMP production in osteoblastic cells. In summary, our data suggest that PTH treatment results in a direct transcriptional stimulation of RGS-2 that in turn may play a role in modulating the duration/intensity of PTH receptor signaling.

Regulator of G-protein signaling protein 2 modulates purinergic calcium and ciliary beat frequency responses in airway epithelia

In ciliated airway epithelial cells, purinergic stimulation increases both intracellular calcium ([Ca(2+)](i)) and ciliary beat frequency (CBF). Because regulator of G-protein signaling protein 2 (RGS2) terminates Galphaq-mediated phospholipase C activation, we examined its role in regulating purinergic signaling in human and ovine airway epithelial cells. RT-PCR of both human and ovine epithelial cell RNA yielded fragments of expected size ( approximately 491 bp) and sequence, confirming RGS2 message. Immunofluorescence demonstrated RGS2 protein expression in cultured airway epithelial cells of both species. Overexpression of an EGFP-RGS2 fusion protein (increasing RGS2 protein levels 1.8 times control, n = 28 cells) resulted in a reduced [Ca(2+)](i) and CBF response to 10 micro M ATP (human: 58 +/- 9% and 49 +/- 8% lower, respectively; n = 8 measurements, 4 cells; ovine: 56 +/- 12% and 53 +/- 16% lower, respectively; n = 5 measurements, 4 cells). Reducing RGS2 protein levels using antisense oligonucleotides increased the response of both [Ca(2+)](i) and CBF to ATP in human cells by 57 +/- 10% and 47 +/- 11%, respectively (n = 10 measurements, 6 cells), and in ovine cells by 88 +/- 13% and 48 +/- 9%, respectively (n = 10 measurements, 5 cells). These data provide functional evidence that RGS2 modulates purinergic signaling in human and ovine ciliated airway epithelial cells.

Structure, chromosomal localization and expression of the mouse regulator of G-protein signaling10 gene (mRGS10)

Regulator of G-protein signaling (RGS) proteins negatively regulate signaling pathways involving seven transmembrane receptors and heterotrimeric G proteins. The purpose of this study was to determine the chromosomal localization, structure and expression profile of the gene coding for mouse regulator of G-protein signaling10 (mRGS10). Fluorescence in situ hybridization analysis indicated that mRGS10 maps to band F3-F4 of the mouse chromosome 7. Sequence analysis revealed that the RGS10 gene encompasses six exons spanning more than 40 kb of genomic DNA. The RGS domain is encoded by exons 3-6; alternative splicing of the first exons allows the generation of two isoforms in the mouse system which differ in their N-terminal portion. Thus, mRGS10 encodes two intracellular proteins of 167 and 181 amino-acids which are highly homologous to the human and rat polypeptides. The deduced amino-acid sequences of mouse RGS10 show 92% sequence identity to their orthologues from human. The mRGS10 gene is expressed predominantly in brain and testis but it is also found in heart, lung, bone marrow, lymph node and spleen. Differential display between mature B lymphocytes and marginal zone B cells, as well as reverse transcription-polymerase chain reaction and Northern blot, showed that mRGS10 is differentially transcribed during B-cell differentiation. Finally, mRGS10 protein was detected in plasma cells of secondary lymphoid organs by immunofluorescence.

Interferon beta-1a counteracts effects of activation on the expression of G-protein-coupled receptor kinases 2 and 3, beta-arrestin-1, and regulators of G-protein signalling 2 and 16 in human mononuclear leukocytes

Activation regulates the responsiveness of G-protein-coupled receptors (GPCRs) on T cells, and modifications in the activity of GPCRs characterize lymphocytes from some immune disorders such as multiple sclerosis (MS) and rheumatoid arthritis (RA). Some lines of evidence suggest that such an effect is connected with the altered expression of some GPCRs regulatory proteins. Herein we demonstrate that phitoemagglutinin (PHA)-induced activation leads to differential expression of G-protein-coupled receptor kinase (GRK) 2, GRK3, beta-arrestin-1, regulators of G-protein signalling (RGS) 2, and RGS16 and decreases responsiveness of mononuclear leukocytes (MNL) to the beta-adrenergic agonist isoproterenol. Interferon beta-1a (IFN beta-1a), which is known to ameliorate the course of MS, counteracts the activation-induced effects on the expression of these GPCR regulatory proteins in MNL. Furthermore, IFN beta-1a quenches the effects of PHA on the isoproterenol-induced accumulation of cyclic AMP (cAMP). We suggest that regulation of GPCRs responsiveness may be a relevant property of IFN beta-1a in MS.

Functional characterization of the G protein regulator RGS13

The signaling cascades evoked by G protein-coupled receptors are a predominant mechanism of cellular communication. The regulators of G protein signaling (RGS) comprise a family of proteins that attenuate G protein-mediated signal transduction. Here we report the characterization of RGS13, the smallest member of the RGS family, which has been cloned from human lung. RGS13 has been found most abundantly in human tonsil, followed by thymus, lung, lymph node, and spleen. RGS13 is a GTPase-activating protein for Galpha(i) and Galpha(o) but not Galpha(s). RGS13 binds Galpha(q) in the presence of aluminum magnesium fluoride, suggesting that it bears GTPase-activating protein activity toward Galpha(q). RGS13 blocks MAPK activity induced by Galpha(i)- or Galpha(q)-coupled receptors. RGS13 also attenuates GTPase-deficient Galpha(q) (Galpha(q)QL) mediated cAMP response element activation but not transcription evoked by constitutively active Galpha(12) or Galpha(13). Surprisingly, RGS13 inhibits cAMP generation elicited by stimulation of the beta(2)-adrenergic receptor. These data suggest that RGS13 may regulate Galpha(i)-, Galpha(q)-, and Galpha(s)-coupled signaling cascades.

Parathyroid hormone induces RGS-2 expression by a cyclic adenosine 3',5'-monophosphate-mediated pathway in primary neonatal murine osteoblasts

Parathyroid hormone (PTH) is a promising anabolic agent for the treatment of osteoporosis. However, PTH is also potently catabolic. To help delineate the molecular mediators of PTH's opposing effects on skeletal metabolism, we have examined PTH-induced regulator of G-protein signaling-2 (RGS-2) expression and function in murine osteoblasts. RGS proteins are GTPase-activating proteins (GAPs) that regulate GTP-binding protein-coupled receptor (GPCR) signaling by enhancing the intrinsic GTPase activity of Galpha subunits. We found that 10 nmol/L PTH maximally induced RGS-2 mRNA in murine MC3T3-E1 cells, rat Py1a and ROS-17/2.8 cells, primary mouse osteoblasts (MOB cells), and mouse calvariae organ culture at 1-2 h posttreatment. PTH signaling through its receptor, PTHR1, is coupled to cAMP-protein kinase A (PKA), protein kinase C (PKC), and calcium signaling pathways. We examined the effect of selective signaling agonists and antagonists on RGS-2 expression in MOB cells to determine which pathway(s) mediates PTH-induced RGS-2 expression. Although selective activation of all three pathways led to RGS-2 expression, cAMP-PKA activation with 10 nmol/L PTH and 10 micromol/L forskolin elicited the strongest induction. Similarly, RGS-2 mRNA expression was most strongly inhibited by the PKA inhibitor, H89 (10-30 micromol/L). The phorbol ester, PMA (1 micromol/L), which activates the PKC pathway, and ionomycin (1 micromol/L), which activates the calcium pathway, produced small but detectable elevations in RGS-2 mRNA levels. Overnight treatment with 1 micromol/L PMA to deplete PKC did not affect subsequent RGS-2 induction by PTH, but significantly inhibited PMA-induced RGS-2 expression. Treatment with 1-100 nmol/L PTH(3-34), which does not activate cAMP-PKA signaling, did not induce RGS-2 expression. MOB cells pretreated with 3 microg/mL cycloheximide produced sustained RGS-2 mRNA levels 2 h after 10 nmol/L PTH treatment. Actinomycin D (5 microg/mL) completely blocked 10 nmol/L PTH-induced RGS-2 expression. Finally, we tested the effect of RGS-2 overexpression on PTH- and fluprostenol-induced interleukin (IL)-6 promoter activity in MOB cells. PTH induces IL-6 through PKA activation, whereas fluprostenol induces IL-6 through PKC activation. We found that RGS-2 overexpression significantly inhibited IL-6 promoter activity following fluprostenol treatment, but not following PTH treatment. We conclude that RGS-2 is a PTH-induced primary response gene in murine osteoblasts that is induced mainly through the cAMP-PKA pathway and specifically inhibits Galphaq-coupled receptors.

Heterotrimeric G protein signaling: role in asthma and allergic inflammation

Asthma and rhinitis are pathophysiologic conditions associated with a prototypical allergic response to inhaled allergens consisting of both neuromechanical and inflammatory components. Heptahelical receptors that bind guanosine triphosphate-binding proteins (G proteins), referred to as G protein-coupled receptors (GPCRs), have been intimately linked with asthma and allergic inflammation for many years. G protein signaling mediates responses throughout the immune, nervous, and muscular systems that might contribute to the pathogenesis of allergic processes and asthma. For example, GPCR agonists or antagonists are used as therapies for asthma either by promoting airway smooth muscle relaxation (beta2 adrenergic receptor agonists) or by inhibiting inflammation in the nasal mucosa and airways (cysteinyl leukotriene receptor antagonists). The focus of this review is to explore how downstream signaling cascades elicited by GPCR activation contribute to the allergic phenotype and the mechanism by which pharmaceuticals alter signaling to generate a therapeutic effect. We also discuss physiologic modulators of G protein signaling, such as regulator of G protein signaling proteins and G protein receptor kinases, inasmuch as they represent potential new therapeutic targets in the treatment of atopy and other inflammatory conditions.