RGS2-Mediated Regulation of Gqα

Anti-angiogenic mechanisms and serotonergic dysfunction in the Rgs2 knockout model for the study of psycho-obstetric risk

Psychiatric and obstetric diseases are growing threats to public health and share high rates of co-morbidity. G protein-coupled receptor signaling (e.g., vasopressin, serotonin) may be a convergent psycho-obstetric risk mechanism. Regulator of G Protein Signaling 2 (RGS2) mutations increase risk for both the gestational disease preeclampsia and for depression. We previously found preeclampsia-like, anti-angiogenic obstetric phenotypes with reduced placental Rgs2 expression in mice. Here, we extend this to test whether conserved cerebrovascular and serotonergic mechanisms are also associated with risk for neurobiological phenotypes in the Rgs2 KO mouse. Rgs2 KO exhibited anxiety-, depression-, and hedonic-like behaviors. Cortical vascular density and vessel length decreased in Rgs2 KO; cortical and white matter thickness and cell densities were unchanged. In Rgs2 KO, serotonergic gene expression was sex-specifically changed (e.g., cortical Htr2a, Maoa increased in females but all serotonin targets unchanged or decreased in males); redox-related expression increased in paraventricular nucleus and aorta; and angiogenic gene expression was changed in male but not female cortex. Whole-cell recordings from dorsal raphe serotonin neurons revealed altered 5-HT1A receptor-dependent inhibitory postsynaptic currents (5-HT1A-IPSCs) in female but not male KO neurons. Additionally, serotonin transporter blockade by the SSRI sertraline increased the amplitude and time-to-peak of 5-HT1A-IPSCs in KO neurons to a greater extent than in WT neurons in females only. These results demonstrate behavioral, cerebrovascular, and sertraline hypersensitivity phenotypes in Rgs2 KOs, some of which are sex-specific. Disruptions may be driven by vascular and cell stress mechanisms linking the shared pathogenesis of psychiatric and obstetric disease to reveal future targets.

Spatiotemporal Optical Control of Gαq-PLCβ Interactions

Cells experience time-varying and spatially heterogeneous chemokine signals in vivo, activating cell surface proteins including G protein-coupled receptors (GPCRs). The Gαq pathway activation by GPCRs is a major signaling axis with broad physiological and pathological significance. Compared with other Gα members, GαqGTP activates many crucial effectors, including PLCβ (Phospholipase Cβ) and Rho GEFs (Rho guanine nucleotide exchange factors). PLCβ regulates many key processes, such as hematopoiesis, synaptogenesis, and cell cycle, and is therefore implicated in terminal-debilitating diseases, including cancer, epilepsy, Huntington's Disease, and Alzheimer's Disease. However, due to a lack of genetic and pharmacological tools, examining how the dynamic regulation of PLCβ signaling controls cellular physiology has been difficult. Since activated PLCβ induces several abrupt cellular changes, including cell morphology, examining how the other pathways downstream of Gq-GPCRs contribute to the overall signaling has also been difficult. Here we show the engineering, validation, and application of a highly selective and efficient optogenetic inhibitor (Opto-dHTH) to completely disrupt GαqGTP-PLCβ interactions reversibly in user-defined cellular-subcellular regions on optical command. Using this newly gained PLCβ signaling control, our data indicate that the molecular competition between RhoGEFs and PLCβ for GαqGTP determines the potency of Gq-GPCR-governed directional cell migration.

Phosphodiesterases Mediate the Augmentation of Myogenic Constriction by Inhibitory G Protein Signaling and is Negatively Modulated by the Dual Action of RGS2 and 5

G protein regulation by regulators of G protein signaling (RGS) proteins play a key role in vascular tone maintenance. The loss of Gi/o and Gq/11 regulation by RGS2 and RGS5 in non-pregnant mice is implicated in augmented vascular tone and decreased uterine blood flow (UBF). RGS2 and 5 are closely related and co-expressed in uterine arteries (UA). However, whether and how RGS2 and 5 coordinate their regulatory activities to finetune G protein signaling and regulate vascular tone are unclear. Here, we determined how the integrated activity of RGS2 and 5 modulates vascular tone to promote UBF. Using ultrasonography and pressure myography, we examined uterine hemodynamics and myogenic tone (MT) of UA of wild type (WT), Rgs2-/-, Rgs5-/-, and Rgs2/5 dbKO mice. We found that MT was reduced in Rgs5-/- relative to WT or Rgs2-/- UA. Activating Gi/o with dopamine increased, whereas exogenous cAMP decreased MT in Rgs5-/- UA to levels in WT UA. Dual deletion of Rgs2 and 5 abolished the reduced MT due to the absence of Rgs5 and enhanced dopamine-induced Gi/o effects in Rgs2/5 dbKO UA. Conversely, and as in WT UA, Gi/o inhibition with pertussis toxin or exogenous cAMP decreased MT in Rgs2/5 dbKO to levels in Rgs5-/- UA. Inhibition of phosphodiesterases (PDE) concentration-dependently decreased and normalized MT in all genotypes, and blocked dopamine-induced MT augmentation in Rgs2-/-, Rgs5-/-, and Rgs2/5 dbKO UA. We conclude that Gi/o augments UA MT in the absence of RGS2 by a novel mechanism involving PDE-mediated inhibition of cAMP-dependent vasodilatation..

Spatiotemporal optical control of Gαq-PLCβ interactions

Cells experience time-varying and spatially heterogeneous chemokine signals in vivo, activating cell surface proteins, including G protein-coupled receptors (GPCRs). The Gαq pathway activation by GPCRs is a major signaling axis with a broad physiological and pathological significance. Compared to other Gα members, GαqGTP activates many crucial effectors, including PLCβ (Phospholipase Cβ) and Rho GEFs (Rho guanine nucleotide exchange factors). PLCβ regulates many key processes, such as hematopoiesis, synaptogenesis, and cell cycle, and is therefore implicated in terminal - debilitating diseases, including cancer, epilepsy, Huntington's Disease, and Alzheimer's Disease. However, due to a lack of genetic and pharmacological tools, examining how the dynamic regulation of PLCβ signaling controls cellular physiology has been difficult. Since activated PLCβ induces several abrupt cellular changes, including cell morphology, examining how the other pathways downstream of Gq-GPCRs contribute to the overall signaling has also been difficult. Here we show the engineering, validation, and application of a highly selective and efficient optogenetic inhibitor (Opto-dHTH) to completely disrupt GαqGTP-PLCβ interactions reversibly in user-defined cellular-subcellular regions on optical command. Using this newly gained PLCβ signaling control, our data indicate that the molecular competition between RhoGEFs and PLCβ for GαqGTP determines the potency of Gq-GPCR-governed directional cell migration.

Transcriptome-Level Interactions between Budesonide and Formoterol Provide Insight into the Mechanism of Action of Inhaled Corticosteroid/Long-Acting β 2-Adrenoceptor Agonist Combination Therapy in Asthma

In 2019, the Global Initiative for Asthma treatment guidelines were updated to recommend that inhaled corticosteroid (ICS)/long-acting β ₂-adrenoceptor agonist (LABA) combination therapy should be a first-in-line treatment option for asthma. Although clinically superior to ICS, mechanisms underlying the efficacy of this combination therapy remain unclear. We hypothesized the existence of transcriptomic interactions, an effect that was tested in BEAS-2B and primary human bronchial epithelial cells (pHBECs) using formoterol and budesonide as representative LABA and ICS, respectively. In BEAS-2B cells, formoterol produced 267 (212 induced; 55 repressed) gene expression changes (≥2/≤0.5-fold) that were dominated by rapidly (1 to 2 hours) upregulated transcripts. Conversely, budesonide induced 370 and repressed 413 mRNAs, which occurred predominantly at 6-18 hours and was preceded by transcripts enriched in transcriptional regulators. Significantly, genes regulated by both formoterol and budesonide were over-represented in the genome; moreover, budesonide plus formoterol induced and repressed 609 and 577 mRNAs, respectively, of which ∼one-third failed the cutoff criterion for either treatment alone. Although induction of many mRNAs by budesonide plus formoterol was supra-additive, the dominant (and potentially beneficial) effect of budesonide on formoterol-induced transcripts, including those encoding many proinflammatory proteins, was repression. Gene ontology analysis of the budesonide-modulated transcriptome returned enriched terms for transcription, apoptosis, proliferation, differentiation, development, and migration. This "functional" ICS signature was augmented in the presence of formoterol. Thus, LABAs modulate glucocorticoid action, and comparable transcriptome-wide interactions in pHBECs imply that such effects may be extrapolated to individuals with asthma taking combination therapy. Although repression of formoterol-induced proinflammatory mRNAs should be beneficial, the pathophysiological consequences of other interactions require investigation. SIGNIFICANCE STATEMENT: In human bronchial epithelial cells, formoterol, a long-acting β ₂-adrenoceptor agonist (LABA), enhanced the expression of inflammatory genes, and many of these changes were reduced by the glucocorticoid budesonide. Conversely, the ability of formoterol to enhance both gene induction and repression by budesonide provides mechanistic insight as to how adding a LABA to an inhaled corticosteroid may improve clinical outcomes in asthma.

DNA Methylation Regulates RGS2-induced S100A12 Expression in Airway Epithelial Cells

RGS2 is a key modulator of stress in human airway epithelial cells, especially of hyperresponsiveness and mucin hypersecretion, both of which are features of cystic fibrosis (CF). Because its expression can be modulated through the DNA methylation pathway, we hypothesize that RGS2 is downregulated by DNA hypermethylation in CF airway epithelial cells. This downregulation would then lead to an enhanced inflammatory response. We demonstrated RGS2 transcript and protein downregulation in cultured airway epithelial cells from patients with CF and validated our findings in two CF epithelial cell lines. A methylated DNA immunoprecipitation array showed the presence of methylated cytosine on 13 gene promoters in CF. Among these genes, we confirmed that the RGS2 promoter was hypermethylated by using bisulfite conversion coupled with a methylation-specific PCR assay. Finally, we showed that downregulation of RGS2 in non-CF cells increased the expression of S100A12, a proinflammatory marker. These results highlight the importance of epigenetic regulation in gene expression in CF and show that RGS2 might modulate the inflammatory response in CF through DNA methylation control.

Genetic Analysis of Rare Human Variants of Regulators of G Protein Signaling Proteins and Their Role in Human Physiology and Disease

Regulators of G protein signaling (RGS) proteins modulate the physiologic actions of many neurotransmitters, hormones, and other signaling molecules. Human RGS proteins comprise a family of 20 canonical proteins that bind directly to G protein-coupled receptors/G protein complexes to limit the lifetime of their signaling events, which regulate all aspects of cell and organ physiology. Genetic variations account for diverse human traits and individual predispositions to disease. RGS proteins contribute to many complex polygenic human traits and pathologies such as hypertension, atherosclerosis, schizophrenia, depression, addiction, cancers, and many others. Recent analysis indicates that most human diseases are due to extremely rare genetic variants. In this study, we summarize physiologic roles for RGS proteins and links to human diseases/traits and report rare variants found within each human RGS protein exome sequence derived from global population studies. Each RGS sequence is analyzed using recently described bioinformatics and proteomic tools for measures of missense tolerance ratio paired with combined annotation-dependent depletion scores, and protein post-translational modification (PTM) alignment cluster analysis. We highlight selected variants within the well-studied RGS domain that likely disrupt RGS protein functions and provide comprehensive variant and PTM data for each RGS protein for future study. We propose that rare variants in functionally sensitive regions of RGS proteins confer profound change-of-function phenotypes that may contribute, in newly appreciated ways, to complex human diseases and/or traits. This information provides investigators with a valuable database to explore variation in RGS protein function, and for targeting RGS proteins as future therapeutic targets.

Analysis of the Indacaterol-Regulated Transcriptome in Human Airway Epithelial Cells Implicates Gene Expression Changes in the Adverse and Therapeutic Effects of β2-Adrenoceptor Agonists

The contribution of gene expression changes to the adverse and therapeutic effects of β₂-adrenoceptor agonists in asthma was investigated using human airway epithelial cells as a therapeutically relevant target. Operational model-fitting established that the long-acting β₂-adrenoceptor agonists (LABA) indacaterol, salmeterol, formoterol, and picumeterol were full agonists on BEAS-2B cells transfected with a cAMP-response element reporter but differed in efficacy (indacaterol ≥ formoterol > salmeterol ≥ picumeterol). The transcriptomic signature of indacaterol in BEAS-2B cells identified 180, 368, 252, and 10 genes that were differentially expressed (>1.5- to <0.67-fold) after 1-, 2-, 6-, and 18-hour of exposure, respectively. Many upregulated genes (e.g., AREG, BDNF, CCL20, CXCL2, EDN1, IL6, IL15, IL20) encode proteins with proinflammatory activity and are annotated by several, enriched gene ontology (GO) terms, including cellular response to interleukin-1, cytokine activity, and positive regulation of neutrophil chemotaxis The general enriched GO term extracellular space was also associated with indacaterol-induced genes, and many of those, including CRISPLD2, DMBT1, GAS1, and SOCS3, have putative anti-inflammatory, antibacterial, and/or antiviral activity. Numerous indacaterol-regulated genes were also induced or repressed in BEAS-2B cells and human primary bronchial epithelial cells by the low efficacy LABA salmeterol, indicating that this genomic effect was neither unique to indacaterol nor restricted to the BEAS-2B airway epithelial cell line. Collectively, these data suggest that the consequences of inhaling a β₂-adrenoceptor agonist may be complex and involve widespread changes in gene expression. We propose that this genomic effect represents a generally unappreciated mechanism that may contribute to the adverse and therapeutic actions of β₂-adrenoceptor agonists in asthma.

Intracellular interactions of umeclidinium and vilanterol in human airway smooth muscle

Background

Intracellular mechanisms of action of umeclidinium (UMEC), a long-acting muscarinic receptor antagonist, and vilanterol (VI), a long-acting β₂-adrenoceptor (β₂R) agonist, were investigated in target cells: human airway smooth-muscle cells (ASMCs).

Materials and methods

ASMCs from tracheas of healthy lung-transplant donors were treated with VI, UMEC, UMEC and VI combined, or control compounds (salmeterol, propranolol, ICI 118.551, or methacholine [MCh]). Cyclic adenosine monophosphate (cAMP) was measured using an enzyme-linked immunosorbent assay, intracellular free calcium ([Ca²⁺]_i) using a fluorescence assay, and regulator of G-protein signaling 2 (RGS2) messenger RNA using real-time quantitative polymerase chain reaction.

Results

VI and salmeterol (10⁻¹²–10⁻⁶ M) induced cAMP production from ASMCs in a concentration-dependent manner, which was greater for VI at all concentrations. β₂R antagonism by propranolol or ICI 118.551 (10⁻¹²–10⁻⁴ M) resulted in concentration-dependent inhibition of VI-induced cAMP production, and ICI 118.551 was more potent. MCh (5×10⁻⁶ M, 30 minutes) attenuated VI-induced cAMP production (P<0.05), whereas pretreatment with UMEC (10⁻⁸ M, 1 hour) restored the magnitude of VI-induced cAMP production. ASMC stimulation with MCh (10⁻¹¹–5×10⁻⁶ M) resulted in a concentration-dependent increase in [Ca²⁺]_i, which was attenuated with UMEC pretreatment. Reduction of MCh-induced [Ca²⁺]_i release was greater with UMEC + VI versus UMEC. UMEC enhanced VI-induced RGS2 messenger RNA expression.

Conclusion

These data indicate that UMEC reverses cholinergic inhibition of VI-induced cAMP production, and is a more potent muscarinic receptor antagonist when in combination with VI versus either alone.

Protective Roles for RGS2 in a Mouse Model of House Dust Mite-Induced Airway Inflammation

The GTPase-accelerating protein, regulator of G-protein signalling 2 (RGS2) reduces signalling from G-protein-coupled receptors (GPCRs) that signal via Gαq. In humans, RGS2 expression is up-regulated by inhaled corticosteroids (ICSs) and long-acting β2-adrenoceptor agonists (LABAs) such that synergy is produced in combination. This may contribute to the superior clinical efficacy of ICS/LABA therapy in asthma relative to ICS alone. In a murine model of house dust mite (HDM)-induced airways inflammation, three weeks of intranasal HDM (25 μg, 3×/week) reduced lung function and induced granulocytic airways inflammation. Compared to wild type animals, Rgs2-/- mice showed airways hyperresponsiveness (increased airways resistance and reduced compliance). While HDM increased pulmonary inflammation observed on hematoxylin and eosin-stained sections, there was no difference between wild type and Rgs2-/- animals. HDM-induced mucus hypersecretion was also unaffected by RGS2 deficiency. However, inflammatory cell counts in the bronchoalveolar lavage fluid of Rgs2-/- animals were significantly increased (57%) compared to wild type animals and this correlated with increased granulocyte (neutrophil and eosinophil) numbers. Likewise, cytokine and chemokine (IL4, IL17, IL5, LIF, IL6, CSF3, CXCLl, CXCL10 and CXCL11) release was increased by HDM exposure. Compared to wild type, Rgs2-/- animals showed a trend towards increased expression for many cytokines/chemokines, with CCL3, CCL11, CXCL9 and CXCL10 being significantly enhanced. As RGS2 expression was unaffected by HDM exposure, these data indicate that RGS2 exerts tonic bronchoprotection in HDM-induced airways inflammation. Modest anti-inflammatory and anti-remodelling roles for RGS2 are also suggested. If translatable to humans, therapies that maximize RGS2 expression may prove advantageous.

Understanding how long-acting β2 -adrenoceptor agonists enhance the clinical efficacy of inhaled corticosteroids in asthma - an update

In moderate-to-severe asthma, adding an inhaled long-acting β₂ -adenoceptor agonist (LABA) to an inhaled corticosteroid (ICS) provides better disease control than simply increasing the dose of ICS. Acting on the glucocorticoid receptor (GR, gene NR3C1), ICSs promote anti-inflammatory/anti-asthma gene expression. In vitro, LABAs synergistically enhance the maximal expression of many glucocorticoid-induced genes. Other genes, including dual-specificity phosphatase 1(DUSP1) in human airways smooth muscle (ASM) and epithelial cells, are up-regulated additively by both drug classes. Synergy may also occur for LABA-induced genes, as illustrated by the bronchoprotective gene, regulator of G-protein signalling 2 (RGS2) in ASM. Such effects cannot be produced by either drug alone and may explain the therapeutic efficacy of ICS/LABA combination therapies. While the molecular basis of synergy remains unclear, mechanistic interpretations must accommodate gene-specific regulation. We explore the concept that each glucocorticoid-induced gene is an independent signal transducer optimally activated by a specific, ligand-directed, GR conformation. In addition to explaining partial agonism, this realization provides opportunities to identify novel GR ligands that exhibit gene expression bias. Translating this into improved therapeutic ratios requires consideration of GR density in target tissues and further understanding of gene function. Similarly, the ability of a LABA to interact with a glucocorticoid may be suboptimal due to low β₂ -adrenoceptor density or biased β₂ -adrenoceptor signalling. Strategies to overcome these limitations include adding-on a phosphodiesterase inhibitor and using agonists of other Gs-coupled receptors. In all cases, the rational design of ICS/LABA, and derivative, combination therapies requires functional knowledge of induced (and repressed) genes for therapeutic benefit to be maximized.

RGS2 squelches vascular Gi/o and Gq signaling to modulate myogenic tone and promote uterine blood flow

Uterine artery blood flow (UABF) is critical to maintaining uterine perfusion in nonpregnant states and for uteroplacental delivery of nutrients and oxygen to the fetus during pregnancy. Impaired UABF is implicated in infertility and several pregnancy complications including fetal growth restriction, small for gestational age, and preeclampsia. The etiology of abnormal UABF is not known. Here, we determined whether deficiency or loss of RGS2, a GTPase-activating protein for Gq/11 and Gi/o class G proteins, affects UABF in nonpregnant mice. We used Doppler ultrasonography to assess UABF in wild type (WT), Rgs2 heterozygous (Rgs2+/-), and homozygous knockout (Rgs2-/-) mice. Video microscopy was used for ex vivo examination of uterine artery myogenic tone and fura-2 imaging for in vitro assessment of internal stores Ca(2+) release. We found that baseline UABF velocity was markedly decreased while impedance measured as resistive index (WT = 0.58 ± 0.04 vs. Rgs2-/- = 0.71 ± 0.03, P < 0.01) and pulsatile index (WT = 0.90 ± 0.06 vs. Rgs2-/- = 1.25 ± 0.11, P < 0.01) was increased in Rgs2-/- mice. Uterine artery tone was augmented in Rgs2+/- and Rgs2-/- mice, which was normalized to WT levels following Gi/o and Gq inactivation. Conversely, blockade of ryanodine receptors increased WT myogenic tone to RGS2 mutant levels. The data together indicate that RGS2 deficiency decreases UABF by increasing myogenic tone at least partly through prolonged G protein activation. Mutations that decrease vascular RGS2 expression may be a predisposition to decreased uterine blood flow. Targeting G protein signaling therefore might improve uterine and uteroplacental underperfusion disorders.

Regulation of Renal Hemodynamics and Function by RGS2

Regulator of G protein signaling 2 (RGS2) controls G protein coupled receptor (GPCR) signaling by acting as a GTPase-activating protein for heterotrimeric G proteins. Certain Rgs2 gene mutations have been linked to human hypertension. Renal RGS2 deficiency is sufficient to cause hypertension in mice; however, the pathological mechanisms are unknown. Here we determined how the loss of RGS2 affects renal function. We examined renal hemodynamics and tubular function by monitoring renal blood flow (RBF), glomerular filtration rate (GFR), epithelial sodium channel (ENaC) expression and localization, and pressure natriuresis in wild type (WT) and RGS2 null (RGS2-/-) mice. Pressure natriuresis was determined by stepwise increases in renal perfusion pressure (RPP) and blood flow, or by systemic blockade of nitric oxide synthase with L-NG-Nitroarginine methyl ester (L-NAME). Baseline GFR was markedly decreased in RGS2-/- mice compared to WT controls (5.0 ± 0.8 vs. 2.5 ± 0.1 μl/min/g body weight, p<0.01). RBF was reduced (35.4 ± 3.6 vs. 29.1 ± 2.1 μl/min/g body weight, p=0.08) while renal vascular resistance (RVR; 2.1 ± 0.2 vs. 3.0 ± 0.2 mmHg/μl/min/g body weight, p<0.01) was elevated in RGS2-/- compared to WT mice. RGS2 deficiency caused decreased sensitivity and magnitude of changes in RVR and RBF after a step increase in RPP. The acute pressure–natriuresis curve was shifted rightward in RGS2-/- relative to WT mice. Sodium excretion rate following increased RPP by L-NAME was markedly decreased in RGS2-/- mice and accompanied by increased translocation of ENaC to the luminal wall. We conclude that RGS2 deficiency impairs renal function and autoregulation by increasing renal vascular resistance and reducing renal blood flow. These changes impair renal sodium handling by favoring sodium retention. The findings provide a new line of evidence for renal dysfunction as a primary cause of hypertension.

MicroRNA hsa-miR-4717-5p regulates RGS2 and may be a risk factor for anxiety-related traits

Regulator of G-protein Signaling 2 (RGS2) is a key regulator of G-protein-coupled signaling pathways involved in fear and anxiety. Data from rodent models and genetic analysis of anxiety-related traits and disorders in humans suggest down-regulation of RGS2 expression to be a risk factor for anxiety. Here we investigated, whether genetic variation in microRNAs mediating posttranscriptional down-regulation of RGS2 may be a risk factor for anxiety as well. 75 microRNAs predicted to regulate RGS2 were identified by four bioinformatic algorithms and validated experimentally by luciferase reporter gene assays. Specificity was confirmed for six microRNAs (hsa-miR-1271-5p, hsa-miR-22-3p, hsa-miR-3591-3p, hsa-miR-377-3p, hsa-miR-4717-5p, hsa-miR-96-5p) by disrupting their seed sequence at the 3' untranslated region of RGS2. Hsa-miR-4717-5p showed the most robust effect on RGS2 and regulated two other candidate genes of anxiety disorders (CNR1 and IKBKE) as well. Two SNPs (rs150925, rs161427) within and 1,000 bp upstream of the hostgene of hsa-miR-4717-5p (MIR4717) show a minor allele frequency greater than 0.05. Both were in high linkage disequilibrium (r(2) = 1, D' = 1) and both major (G) alleles showed a trend for association with panic disorder with comorbid agoraphobia in one of two patient/control samples (combined n(patients) = 497). Dimensional anxiety traits, as described by Anxiety Sensitivity Index (ASI) and Agoraphobic Cognitions Questionnaire (ACQ) were significantly higher among carriers of both major (G) alleles in a combined patient/control sample (n(combined) = 831). Taken together, data indicate that MIR4717 regulates human RGS2 and contributes to the genetic risk towards anxiety-related traits.

RGS2 ggenetic variation: association analysis with panic disorder and dimensional as well as intermediate phenotypes of anxiety

Accumulating evidence from mouse models points to the G protein-coupled receptor RGS2 (regulator of G-protein signaling 2) as a promising candidate gene for anxiety in humans. Recently, RGS2 polymorphisms were found to be associated with various anxiety disorders, e.g., rs4606 with panic disorder (PD), but other findings have been negative or inconsistent concerning the respective risk allele. To further examine the role of RGS2 polymorphisms in the pathogenesis of PD, we genotyped rs4606 and five additional RGS2 tag single nucleotide polymorphisms (SNPs; rs16834831, rs10801153, rs16829458, rs1342809, rs1890397) in two independent PD samples, comprising 531 matched case/control pairs. The functional SNP rs4606 was nominally associated with PD when both samples were combined. The upstream SNP rs10801153 displayed a Bonferroni-resistant significant association with PD in the second and the combined sample (P = 0.006 and P = 0.017). We furthermore investigated the effect of rs10801153 on dimensional anxiety traits, a behavioral avoidance test (BAT), and an index for emotional processing in the respective subsets of the total sample. In line with categorical results, homozygous risk (G) allele carriers displayed higher scores on the Agoraphobic Cognitions Questionnaire (ACQ; P = 0.015) and showed significantly more defensive behavior during fear provoking situations (P = 0.001). Furthermore, significant effects on brain activation in response to angry (P = 0.013), happy (P = 0.042) and neutral faces (P = 0.032) were detected. Taken together, these findings provide further evidence for the potential role of RGS2 as a candidate gene for PD.

Potential mechanisms to explain how LABAs and PDE4 inhibitors enhance the clinical efficacy of glucocorticoids in inflammatory lung diseases

Inhaled glucocorticoids acting via the glucocorticoid receptor are a mainstay treatment option for individuals with asthma. There is a consensus that the remedial actions of inhaled glucocorticoids are due to their ability to suppress inflammation by modulating gene expression. While inhaled glucocorticoids are generally effective in asthma, there are subjects with moderate-to-severe disease in whom inhaled glucocorticoids fail to provide adequate control. For these individuals, asthma guidelines recommend that a long-acting β₂-adrenoceptor agonist (LABA) be administered concurrently with an inhaled glucocorticoid. This so-called “combination therapy” is often effective and clinically superior to the inhaled glucocorticoid alone, irrespective of dose. LABAs, and another class of drug known as phosphodiesterase 4 (PDE4) inhibitors, may also enhance the efficacy of inhaled glucocorticoids in chronic obstructive pulmonary disease (COPD). In both conditions, these drugs are believed to work by elevating the concentration of cyclic adenosine-3',5'-monophosphate (cAMP) in target cells and tissues. Despite the success of inhaled glucocorticoid/LABA combination therapy, it remains unclear how an increase in cAMP enhances the clinical efficacy of an inhaled glucocorticoid. In this report, we provide a state-of-the-art appraisal, including unresolved and controversial issues, of how cAMP-elevating drugs and inhaled glucocorticoids interact at a molecular level to deliver enhanced anti-inflammatory benefit over inhaled glucocorticoid monotherapy. We also speculate on ways to further exploit this desirable interaction. Critical discussion of how these two drug classes regulate gene transcription, often in a synergistic manner, is a particular focus. Indeed, because interplay between glucocorticoid receptor and cAMP signaling pathways may contribute to the superiority of inhaled glucocorticoid/LABA combination therapy, understanding this interaction may provide a logical framework to rationally design these multicomponent therapeutics that was not previously possible.

Superiority of combined phosphodiesterase PDE3/PDE4 inhibition over PDE4 inhibition alone on glucocorticoid- and long-acting β2-adrenoceptor agonist-induced gene expression in human airway epithelial cells

Glucocorticoids, also known as corticosteroids, induce effector gene transcription as a part of their anti-inflammatory mechanisms of action. Such genomic effects can be significantly enhanced by long-acting β2-adrenoceptor agonists (LABAs) and may contribute to the clinical superiority of inhaled corticosteroid (ICS)/LABA combinations in asthma and chronic obstructive pulmonary disease (COPD) over ICSs alone. Using models of cAMP- and glucocorticoid-induced transcription in human bronchial epithelial BEAS-2B cells, we show that combining inhibitors of phosphodiesterase (PDE) 3 and PDE4 provides greater benefits compared with inhibiting either PDE alone. In respect to cAMP-dependent transcription, inhibitors of PDE3 (siguazodan, cilostazol) and PDE4 (rolipram, GSK256066, roflumilast N-oxide) each sensitized to the LABA, formoterol. This effect was magnified by dual PDE3 and PDE4 inhibition. Siguazodan plus rolipram was also more effective at inducing cAMP-dependent transcription than either inhibitor alone. Conversely, the concentration-response curve describing the enhancement of dexamethasone-induced, glucocorticoid response element-dependent transcription by formoterol was displaced to the left by PDE4, but not PDE3, inhibition. Overall, similar effects were described for bona fide genes, including RGS2, CD200, and CRISPLD2. Importantly, the combination of siguazodan plus rolipram prolonged the duration of gene expression induced by formoterol, dexamethasone, or dexamethasone plus formoterol. This was most apparent for RGS2, a bronchoprotective gene that may also reduce the proinflammatory effects of constrictor mediators. Collectively, these data provide a rationale for the use of PDE3 and PDE4 inhibitors in the treatment of COPD and asthma where they may enhance, sensitize, and prolong the effects of LABA/ICS combination therapies.

UV light activates a Gαq/11-coupled phototransduction pathway in human melanocytes

UV light stimulates a phosphoinositide signaling pathway in human melanocytes similar to those elicited by light in the eye.

While short exposure to solar ultraviolet radiation (UVR) can elicit increased skin pigmentation, a protective response mediated by epidermal melanocytes, chronic exposure can lead to skin cancer and photoaging. However, the molecular mechanisms that allow human skin to detect and respond to UVR remain incompletely understood. UVR stimulates a retinal-dependent signaling cascade in human melanocytes that requires GTP hydrolysis and phospholipase C β (PLCβ) activity. This pathway involves the activation of transient receptor potential A1 (TRPA1) ion channels, an increase in intracellular Ca²⁺, and an increase in cellular melanin content. Here, we investigated the identity of the G protein and downstream elements of the signaling cascade and found that UVR phototransduction is Gα_q/11 dependent. Activation of Gα_q/11/PLCβ signaling leads to hydrolysis of phosphatidylinositol (4,5)-bisphosphate (PIP₂) to generate diacylglycerol (DAG) and inositol 1, 4, 5-trisphosphate (IP₃). We found that PIP₂ regulated TRPA1-mediated photocurrents, and IP₃ stimulated intracellular Ca²⁺ release. The UVR-elicited Ca²⁺ response appears to involve both IP₃-mediated release from intracellular stores and Ca²⁺ influx through TRPA1 channels, showing the fast rising phase of the former and the slow decay of the latter. We propose that melanocytes use a UVR phototransduction mechanism that involves the activation of a Gα_q/11-dependent phosphoinositide cascade, and resembles light phototransduction cascades of the eye.

Induction of regulator of G-protein signaling 2 expression by long-acting β2-adrenoceptor agonists and glucocorticoids in human airway epithelial cells

In asthma and chronic obstructive pulmonary disease (COPD) multiple mediators act on Gαq-linked G-protein-coupled receptors (GPCRs) to cause bronchoconstriction. However, acting on the airway epithelium, such mediators may also elicit inflammatory responses. In human bronchial epithelial BEAS-2B cells (bronchial epithelium + adenovirus 12-SV40 hybrid), regulator of G-protein signaling (RGS) 2 mRNA and protein were synergistically induced in response to combinations of long-acting β2-adrenoceptor agonist (LABA) (salmeterol, formoterol) plus glucocorticoid (dexamethasone, fluticasone propionate, budesonide). Equivalent responses occurred in primary human bronchial epithelial cells. Concentrations of glucocorticoid plus LABA required to induce RGS2 expression in BEAS-2B cells were consistent with the levels achieved therapeutically in the lungs. As RGS2 is a GTPase-activating protein that switches off Gαq, intracellular free calcium ([Ca(2+)]i) flux was used as a surrogate of responses induced by histamine, methacholine, and the thromboxane receptor agonist U46619 [(Z)-7-[(1S,4R,5R,6S)-5-[(E,3S)-3-hydroxyoct-1-enyl]-3-oxabicyclo[2.2.1]heptan-6-yl]hept-5-enoic acid]. This was significantly attenuated by salmeterol plus dexamethasone pretreatment, or RGS2 overexpression, and the protective effect of salmeterol plus dexamethasone was abolished by RGS2 RNA silencing. Although methacholine and U46619 induced interleukin-8 (IL-8) release and this was inhibited by RGS2 overexpression, the repression of U46619-induced IL-8 release by salmeterol plus dexamethasone was unaffected by RGS2 knockdown. Given a role for Gαq-mediated pathways in inducing IL-8 release, we propose that RGS2 acts redundantly with other effector processes to repress IL-8 expression. Thus, RGS2 expression is a novel effector mechanism in the airway epithelium that is induced by glucocorticoid/LABA combinations. This could contribute to the efficacy of glucocorticoid/LABA combinations in asthma and COPD.

Amino-terminal cysteine residues differentially influence RGS4 protein plasma membrane targeting, intracellular trafficking, and function

Regulator of G-protein signaling (RGS) proteins are potent inhibitors of heterotrimeric G-protein signaling. RGS4 attenuates G-protein activity in several tissues. Previous work demonstrated that cysteine palmitoylation on residues in the amino-terminal (Cys-2 and Cys-12) and core domains (Cys-95) of RGS4 is important for protein stability, plasma membrane targeting, and GTPase activating function. To date Cys-2 has been the priority target for RGS4 regulation by palmitoylation based on its putative role in stabilizing the RGS4 protein. Here, we investigate differences in the contribution of Cys-2 and Cys-12 to the intracellular localization and function of RGS4. Inhibition of RGS4 palmitoylation with 2-bromopalmitate dramatically reduced its localization to the plasma membrane. Similarly, mutation of the RGS4 amphipathic helix (L23D) prevented membrane localization and its G(q) inhibitory function. Together, these data suggest that both RGS4 palmitoylation and the amphipathic helix domain are required for optimal plasma membrane targeting and function of RGS4. Mutation of Cys-12 decreased RGS4 membrane targeting to a similar extent as 2-bromopalmitate, resulting in complete loss of its G(q) inhibitory function. Mutation of Cys-2 did not impair plasma membrane targeting but did partially impair its function as a G(q) inhibitor. Comparison of the endosomal distribution pattern of wild type and mutant RGS4 proteins with TGN38 indicated that palmitoylation of these two cysteines contributes differentially to the intracellular trafficking of RGS4. These data show for the first time that Cys-2 and Cys-12 play markedly different roles in the regulation of RGS4 membrane localization, intracellular trafficking, and G(q) inhibitory function via mechanisms that are unrelated to RGS4 protein stabilization.

β2-Adrenoceptor agonist-induced RGS2 expression is a genomic mechanism of bronchoprotection that is enhanced by glucocorticoids

In asthma and chronic obstructive pulmonary disease, activation of G(q)-protein-coupled receptors causes bronchoconstriction. In each case, the management of moderate-to-severe disease uses inhaled corticosteroid (glucocorticoid)/long-acting β(2)-adrenoceptor agonist (LABA) combination therapies, which are more efficacious than either monotherapy alone. In primary human airway smooth muscle cells, glucocorticoid/LABA combinations synergistically induce the expression of regulator of G-protein signaling 2 (RGS2), a GTPase-activating protein that attenuates G(q) signaling. Functionally, RGS2 reduced intracellular free calcium flux elicited by histamine, methacholine, leukotrienes, and other spasmogens. Furthermore, protection against spasmogen-increased intracellular free calcium, following treatment for 6 h with LABA plus corticosteroid, was dependent on RGS2. Finally, Rgs2-deficient mice revealed enhanced bronchoconstriction to spasmogens and an absence of LABA-induced bronchoprotection. These data identify RGS2 gene expression as a genomic mechanism of bronchoprotection that is induced by glucocorticoids plus LABAs in human airway smooth muscle and provide a rational explanation for the clinical efficacy of inhaled corticosteroid (glucocorticoid)/LABA combinations in obstructive airways diseases.

Control of striatal signaling by g protein regulators

Signaling via heterotrimeric G proteins plays a crucial role in modulating the responses of striatal neurons that ultimately shape core behaviors mediated by the basal ganglia circuitry, such as reward valuation, habit formation, and movement coordination. Activation of G protein-coupled receptors (GPCRs) by extracellular signals activates heterotrimeric G proteins by promoting the binding of GTP to their α subunits. G proteins exert their effects by influencing the activity of key effector proteins in this region, including ion channels, second messenger enzymes, and protein kinases. Striatal neurons express a staggering number of GPCRs whose activation results in the engagement of downstream signaling pathways and cellular responses with unique profiles but common molecular mechanisms. Studies over the last decade have revealed that the extent and duration of GPCR signaling are controlled by a conserved protein family named regulator of G protein signaling (RGS). RGS proteins accelerate GTP hydrolysis by the α subunits of G proteins, thus promoting deactivation of GPCR signaling. In this review, we discuss the progress made in understanding the roles of RGS proteins in controlling striatal G protein signaling and providing integration and selectivity of signal transmission. We review evidence on the formation of a macromolecular complex between RGS proteins and other components of striatal signaling pathways, their molecular regulatory mechanisms and impacts on GPCR signaling in the striatum obtained from biochemical studies and experiments involving genetic mouse models. Special emphasis is placed on RGS9-2, a member of the RGS family that is highly enriched in the striatum and plays critical roles in drug addiction and motor control.

SDF1-induced antagonism of axonal repulsion requires multiple G-protein coupled signaling components that work in parallel

SDF1 reduces the responsiveness of axonal growth cones to repellent guidance cues in a pertussis-toxin-sensitive, cAMP-dependent manner. Here, we show that SDF1's antirepellent effect can be blocked in embryonic chick dorsal root ganglia (DRGs) by expression of peptides or proteins inhibiting either Gα_i, Gα_q, or Gβγ. SDF1 antirepellent activity is also blocked by pharmacological inhibition of PLC, a common effector protein for Gα_q. We also show that SDF1 antirepellent activity can be mimicked by overexpression of constitutively active Gα_i, Gα_q, or Gα_s. These results suggest a model in which multiple G protein components cooperate to produce the cAMP levels required for SDF1 antirepellent activity.

Variant in RGS2 moderates posttraumatic stress symptoms following potentially traumatic event exposure

Polymorphisms in the RGS2 (regulator of G-protein signaling 2) gene were found to be associated with anxious behavior in mice and anxiety in humans. We examined whether rs4606, a single nucleotide polymorphism (SNP) of RGS2, and social support moderated risk for PTSD in an epidemiologic sample. The study examines 607 adults from the 2004 Florida Hurricanes study who returned buccal DNA samples via mail. rs4606 was associated with increased symptoms of posthurricane PTSD symptoms under conditions of high hurricane exposure and low social support (P<.05). Further, this polymorphism was associated with lifetime PTSD symptoms under conditions of lifetime exposure to a potentially traumatic event, and low social support (P<.001). These gene by environment interactions remained significant after adjustment for sex, ancestry, and age. RGS2 rs4606 modifies risk of postdisaster and lifetime PTSD symptoms under conditions of high stressor exposure. This is the first demonstration of gene-environment interaction for this locus.

RGS2 and generalized anxiety disorder in an epidemiologic sample of hurricane-exposed adults

BACKGROUND

Generalized anxiety disorder (GAD) is a common and sometimes disabling condition often associated with stressful life events that involve significant loss or danger. The disorder appears moderately heritable. Polymorphisms in the RGS2 (regulator of G-protein signaling 2) gene were recently associated with anxious behavior in mice and panic disorder and trait anxiety in humans. We examined whether rs4606, a single nucleotide polymorphism (SNP) in the 3' UTR of RGS2, was associated with GAD in an epidemiologic sample of adults exposed to the 2004 Florida Hurricanes.

METHODS

The sample for the current study is 607 adults from the 2004 Florida Hurricane Study who returned buccal DNA samples via mail. Participants were selected via random digit dial procedures and interviewed via telephone about hurricane exposure, social support, and GAD symptoms. The outcome measure was DSM-IV diagnosis of GAD derived from structured interviews.

RESULTS

RGS2 SNP rs4606 was significantly associated with GAD in this sample. In logistic regression analyses, each C allele was associated with a 100% (P=.026) increased risk of GAD after controlling for age, sex, ancestry, hurricane exposure, and social support.

CONCLUSIONS

These findings are consistent with a previously published study showing a higher prevalence of the C allele among panic disorder patients than controls. This study points toward a relevant polymorphism for GAD at the 3' end of the RGS2 gene; and suggests that studying a recently disaster-exposed sample is both feasible and may improve power to find gene-disorder associations.

Variation in RGS2 is associated with suicidal ideation in an epidemiological study of adults exposed to the 2004 Florida hurricanes

This study examined whether rs4606, a single nucleotide polymorphism (SNP) in the translated region at the 3' end of RGS2, was related to suicidal ideation in an epidemiologic sample of adults living in areas affected by the 2004 Florida hurricanes. An epidemiologic sample of residents of Florida was recruited via random digit-dial procedures after the 2004 Florida hurricanes; participants were interviewed about suicidal ideation, hurricane exposure, and social support. Participants who returned buccal DNA samples via mail (n = 607) were included here. Rs4606 in RGS2 was associated with increased symptoms of current suicidal ideation (p < 0.01). Each "C" allele was associated with 5.59 times increased risk of having current ideation. No gene-by-environment interactions were found, perhaps due to low power. RGS2 rs4606 is related to risk of current suicidal ideation in stressor-exposed adults.

Assembly of high order G alpha q-effector complexes with RGS proteins

Transmembrane signaling through G alpha(q)-coupled receptors is linked to physiological processes such as cardiovascular development and smooth muscle function. Recent crystallographic studies have shown how G alpha(q) interacts with two activation-dependent targets, p63RhoGEF and G protein-coupled receptor kinase 2 (GRK2). These proteins bind to the effector-binding site of G alpha(q) in a manner that does not appear to physically overlap with the site on G alpha(q) bound by regulator of G-protein signaling (RGS) proteins, which function as GTPase-activating proteins (GAPs). Herein we confirm the formation of RGS-G alpha(q)-GRK2/p63RhoGEF ternary complexes using flow cytometry protein interaction and GAP assays. RGS2 and, to a lesser extent, RGS4 are negative allosteric modulators of Galpha(q) binding to either p63RhoGEF or GRK2. Conversely, GRK2 enhances the GAP activity of RGS4 but has little effect on that of RGS2. Similar but smaller magnitude responses are induced by p63RhoGEF. The fact that GRK2 and p63RhoGEF respond similarly to these RGS proteins supports the hypothesis that GRK2 is a bona fide G alpha(q) effector. The results also suggest that signal transduction pathways initiated by GRK2, such as the phosphorylation of G protein-coupled receptors, and by p63RhoGEF, such as the activation of gene transcription, can be regulated by RGS proteins via both allosteric and GAP mechanisms.

Association of RGS2 gene polymorphisms with suicide and increased RGS2 immunoreactivity in the postmortem brain of suicide victims

Regulators of G-protein signaling are a family of proteins that negatively regulate the intracellular signaling of G protein-coupled receptors, such as the serotonin receptor. Recent studies have suggested that one of these proteins, the regulator of G-protein signaling 2 (RGS2), plays an important part in anxiety and/or aggressive behavior. To explore the involvement of the RGS2 gene in the vulnerability to suicide, we screened Japanese suicide victims for sequence variations in the RGS2 gene and carried out an association study of RGS2 gene polymorphisms with suicide victims. In the eight identified polymorphisms that were identified by mutation screening, we genotyped four common single-nucleotide polymorphisms (SNPs) in the RGS2 gene, and found significant differences in the distribution of the SNP3 (C+2971G, rs4606) genotypes and alleles of the SNP2 (C-395G, rs2746072) and the SNP3 between completed suicides and the controls. The distribution of the haplotype was also significantly different between the two groups (global p<0.0001). Furthermore, RGS2 immunoreactivity significantly increased in the amygdala and the prefrontal cortex (Brodmann area 9 (BA9)) of the postmortem brain of the suicide subjects. These findings suggest that RGS2 is genetically involved in the biological susceptibility to suicide in the Japanese population.

Alternative translation initiation of human regulators of G-protein signaling-2 yields a set of functionally distinct proteins

The regulator of G-protein signaling (RGS2) contains a characteristic RGS domain flanked by short amino and carboxyl terminal sequences. The RGS domain mediates inhibition of Galpha(q) and Galpha(i) signaling, whereas the amino terminal domain (NTD) directs interaction with adenylyl cyclases, G-protein-coupled receptors, and other signaling partners. Here, we identify a set of novel RGS2 protein products that differ with respect to their amino terminal architecture and functional characteristics. An RGS2 expression reporter cassette revealed four distinct open reading frames (ORFs) that can be expressed from the RGS2 NTD. We hypothesized that alternative translation initiation from four AUG codons corresponding to amino acid positions 1, 5, 16, and 33 could produce the observed RGS2 expression profile. Selective disruption of each AUG confirmed that alternate sites of translation initiation accounted for each of the observed products. Proteins derived from ORFs 1 to 4 showed no difference in Galpha(q) inhibitory potential or recruitment from the nucleus in response to Galpha(q) signaling. By contrast, RGS2 products initiating from methionines at positions 16 (ORF3) and 33 (ORF4) were impaired as inhibitors of type V adenylyl cyclase (ACV) compared with full-length RGS2. We predicted that regulation of the RGS2 expression profile would allow cells to adapt to changing signaling conditions. Consistent with this model, activation of Galpha(s)/ACV but not Galpha(q) signaling increased the relative abundance of the full-length RGS2 protein, suggesting that alternative translation initiation of RGS2 is part of a novel negative feedback control pathway for adenylyl cyclase signaling.

Unique hydrophobic extension of the RGS2 amphipathic helix domain imparts increased plasma membrane binding and function relative to other RGS R4/B subfamily members

RGS2 and RGS5 are inhibitors of G-protein signaling belonging to the R4/B subfamily of RGS proteins. We here show that RGS2 is a much more potent attenuator of M1 muscarinic receptor signaling than RGS5. We hypothesize that this difference is mediated by variation in their ability to constitutively associate with the plasma membrane (PM). Compared with full-length RGS2, the RGS-box domains of RGS2 and RGS5 both show reduced PM association and activity. Prenylation of both RGS-box domains increases activity to RGS2 levels, demonstrating that lipid bilayer targeting increases RGS domain function. Amino-terminal domain swaps confirm that key determinants of localization and function are found within this important regulatory domain. An RGS2 amphipathic helix domain mutant deficient for phospholipid binding (L45D) shows reduced PM association and activity despite normal binding to the M1 muscarinic receptor third intracellular loop and activated Galpha(q). Replacement of a unique dileucine motif adjacent to the RGS2 helix with corresponding RGS5 residues disrupts both PM localization and function. These data suggest that RGS2 contains a hydrophobic extension of its helical domain that imparts high efficiency binding to the inner leaflet of the lipid bilayer. In support of this model, disruption of membrane phospholipid composition with N-ethylmaleimide reduces PM association of RGS2, without affecting localization of the M1 receptor or Galpha(q). Together, these data indicate that novel features within the RGS2 amphipathic alpha helix facilitate constitutive PM targeting and more efficient inhibition of M1 muscarinic receptor signaling than RGS5 and other members of the R4/B subfamily.

Spinophilin/neurabin reciprocally regulate signaling intensity by G protein-coupled receptors

Spinophilin (SPL) and neurabin (NRB) are structurally similar scaffolding proteins with several protein binding modules, including actin and PP1 binding motifs and PDZ and coiled-coil domains. SPL also binds regulators of G protein signaling (RGS) proteins and the third intracellular loop (3iL) of G protein-coupled receptors (GPCRs) to reduce the intensity of Ca(2+) signaling by GPCRs. The role of NRB in Ca(2+) signaling is not known. In the present work, we used biochemical and functional assays in model systems and in SPL(-/-) and NRB(-/-) mice to show that SPL and NRB reciprocally regulate Ca(2+) signaling by GPCRs. Thus, SPL and NRB bind all members of the R4 subfamily of RGS proteins tested (RGS1, RGS2, RGS4, RGS16) and GAIP. By contract, SPL, but not NRB, binds the 3iL of the GPCRs alpha(1B)-adrenergic (alpha(1B)AR), dopamine, CCKA, CCKB and the muscarinic M3 receptors. Coexpression of SPL or NRB with the alpha(1B)AR in Xenopus oocytes revealed that SPL reduces, whereas NRB increases, the intensity of Ca(2+) signaling by alpha(1B)AR. Accordingly, deletion of SPL in mice enhanced binding of RGS2 to NRB and Ca(2+) signaling by alphaAR, whereas deletion of NRB enhanced binding of RGS2 to SPL and reduced Ca(2+) signaling by alphaAR. This was due to reciprocal modulation by SPL and NRB of the potency of RGS2 to inhibit Ca(2+) signaling by alphaAR. These findings suggest a novel mechanism of regulation of GPCR-mediated Ca(2+) signaling in which SPL/NRB forms a functional pair of opposing regulators that modulates Ca(2+) signaling intensity by GPCRs by determining the extent of inhibition by the R4 family of RGS proteins.

G protein-coupled receptors control NMDARs and metaplasticity in the hippocampus

Long-term potentiation (LTP) and long-term depression (LTD) are the major forms of functional synaptic plasticity observed at CA1 synapses of the hippocampus. The balance between LTP and LTD or "metaplasticity" is controlled by G-protein coupled receptors (GPCRs) whose signal pathways target the N-methyl-D-asparate (NMDA) subtype of excitatory glutamate receptor. We discuss the protein kinase signal cascades stimulated by Galphaq and Galphas coupled GPCRs and describe how control of NMDAR activity shifts the threshold for the induction of LTP.

Analysis of the dissociated steroid RU24858 does not exclude a role for inducible genes in the anti-inflammatory actions of glucocorticoids

Although repression of inflammatory gene expression makes glucocorticoids powerful anti-inflammatory agents, side effects limit usage and drive the search for improved glucocorticoid receptor (GR) ligands. In A549 pulmonary cells, dexamethasone and the prototypical dissociated ligand RU24858 (Mol Endocrinol 11:1245-1255, 1997) repress interleukin (IL)-1beta-induced expression of cyclooxygenase (COX)-2 and IL-8. Although RU24858 is a weaker GR ligand, both glucocorticoids showed similar efficacies on transrepression of nuclear factor kappaB (NF-kappaB)-dependent transcription, whereas RU24858 yielded less than 12% of the response to dexamethasone on a classic glucocorticoid response element (GRE) reporter (transactivation). Modest NF-kappaB-dependent transrepression ( approximately 40%), along with analysis of IL-8 transcription rate and the accumulation of unspliced nuclear RNA, indicates that transrepression does not fully account for the repression of genes such as IL-8. This was confirmed by the finding that mRNA degradation is increased by both dexamethasone and RU24858. Analysis of IL-1beta-induced steady-state mRNA levels for IL-8 and COX-2 show that dexamethasone- and RU24858-dependent repression of these genes is attenuated by inhibitors of transcription and protein synthesis. Because similar effects were observed with respect to COX-2 and IL-8 protein expression, we conclude that glucocorticoid-dependent gene expression is necessary for repression by both glucocorticoids. Despite RU24858 being defective at classic GRE-dependent transactivation, both dexamethasone and RU24858 induced the expression of potentially anti-inflammatory genes and metabolic genes, suggesting the importance of nontraditional glucocorticoid-dependent gene expression. Thus, classic transactivation- and transrepressionbased screens for anti-inflammatory "dissociated" GR ligands may be flawed because they may not reflect the effects on real glucocorticoid-inducible genes.

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.

Application of RGS box proteins to evaluate G-protein selectivity in receptor-promoted signaling

Regulator of G-protein signaling (RGS) domains bind directly to GTP-bound Galpha subunits and accelerate their intrinsic GTPase activity by up to several thousandfold. The selectivity of RGS proteins for individual Galpha subunits has been illustrated. Thus, the expression of RGS proteins can be used to inhibit signaling pathways activated by specific G protein-coupled receptors (GPCRs). This article describes the use of specific RGS domain constructs to discriminate among G(i/o), Gq-and G(12/13)-mediated activation of phospholipase C (PLC) isozymes in COS-7 cells. Overexpression of the N terminus of GRK2 (amino acids 45-178) or p115 RhoGEF (amino acids 1-240) elicited selective inhibition of Galphaq- or Galpha(12/13)-mediated signaling to PLC activation, respectively. In contrast, RGS2 overexpression was found to inhibit PLC activation by both G(i/o)- and Gq-coupled GPCRs. RGS4 exhibited dramatic receptor selectivity in its inhibitory actions; of the G(i/o)- and Gq-coupled GPCRs tested (LPA1, LPA2, P2Y1, S1P3), only the Gq-coupled lysophosphatidic acid-activated LPA2 receptor was found to be inhibited by RGS4 overexpression.