The Gbeta5-RGS7 complex selectively inhibits muscarinic M3 receptor signaling via the interaction between the third intracellular loop of the receptor and the DEP domain of RGS7

The association of GNB5 with Alzheimer disease revealed by genomic analysis restricted to variants impacting gene function

Disease-associated variants identified from genome-wide association studies (GWASs) frequently map to non-coding areas of the genome such as introns and intergenic regions. An exclusive reliance on gene-agnostic methods of genomic investigation could limit the identification of relevant genes associated with polygenic diseases such as Alzheimer disease (AD). To overcome such potential restriction, we developed a gene-constrained analytical method that considers only moderate- and high-risk variants that affect gene coding sequences. We report here the application of this approach to publicly available datasets containing 181,388 individuals without and with AD and the resulting identification of 660 genes potentially linked to the higher AD prevalence among Africans/African Americans. By integration with transcriptome analysis of 23 brain regions from 2,728 AD case-control samples, we concentrated on nine genes that potentially enhance the risk of AD: AACS, GNB5, GNS, HIPK3, MED13, SHC2, SLC22A5, VPS35, and ZNF398. GNB5, the fifth member of the heterotrimeric G protein beta family encoding Gβ5, is primarily expressed in neurons and is essential for normal neuronal development in mouse brain. Homozygous or compound heterozygous loss of function of GNB5 in humans has previously been associated with a syndrome of developmental delay, cognitive impairment, and cardiac arrhythmia. In validation experiments, we confirmed that Gnb5 heterozygosity enhanced the formation of both amyloid plaques and neurofibrillary tangles in the brains of AD model mice. These results suggest that gene-constrained analysis can complement the power of GWASs in the identification of AD-associated genes and may be more broadly applicable to other polygenic diseases.

Molecular Influence of Resiniferatoxin on the Urinary Bladder Wall Based on Differential Gene Expression Profiling

Resiniferatoxin (RTX) is a potent capsaicin analog used as a drug for experimental therapy to treat neurogenic disorders associated with enhanced nociceptive transmission, including lower urinary tract symptoms. The present study, for the first time, investigated the transcriptomic profile of control and RTX-treated porcine urinary bladder walls. We applied multistep bioinformatics and discovered 129 differentially expressed genes (DEGs): 54 upregulated and 75 downregulated. Metabolic pathways analysis revealed five significant Kyoto Encyclopedia of Genes and Genomes (KEGG) items ('folate biosynthesis', 'metabolic pathways', 'sulfur relay system', 'sulfur metabolism' and 'serotonergic synapse') that were altered after RTX intravesical administration. A thorough analysis of the detected DEGs indicated that RTX treatment influenced the signaling pathways regulating nerve growth, myelination, axon specification, and elongation. Many of the revealed DEGs are involved in the nerve degeneration process; however, some of them were implicated in the initiation of neuroprotective mechanisms. Interestingly, RTX intravesical installation was followed by changes in the expression of genes involved in synaptic plasticity and neuromodulation, including 5-HT, H2S, glutamate, and GABA transmission. The obtained results suggest that the toxin may exert a therapeutic, antinociceptive effect not only by acting on TRPV1 receptors.

Structure of the class C orphan GPCR GPR158 in complex with RGS7-Gβ5

GPR158, a class C orphan GPCR, functions in cognition, stress-induced mood control, and synaptic development. Among class C GPCRs, GPR158 is unique as it lacks a Venus flytrap-fold ligand-binding domain and terminates Gαi/o protein signaling through the RGS7-Gβ5 heterodimer. Here, we report the cryo-EM structures of GPR158 alone and in complex with one or two RGS7-Gβ5 heterodimers. GPR158 dimerizes through Per-Arnt-Sim-fold extracellular and transmembrane (TM) domains connected by an epidermal growth factor-like linker. The TM domain (TMD) reflects both inactive and active states of other class C GPCRs: a compact intracellular TMD, conformations of the two intracellular loops (ICLs) and the TMD interface formed by TM4/5. The ICL2, ICL3, TM3, and first helix of the cytoplasmic coiled-coil provide a platform for the DHEX domain of one RGS7 and the second helix recruits another RGS7. The unique features of the RGS7-binding site underlie the selectivity of GPR158 for RGS7.

Subtype-dependent regulation of Gβγ signalling

G protein-coupled receptors (GPCRs) transmit information to the cell interior by transducing external signals to heterotrimeric G protein subunits, Gα and Gβγ subunits, localized on the inner leaflet of the plasma membrane. Though the initial focus was mainly on Gα-mediated events, Gβγ subunits were later identified as major contributors to GPCR-G protein signalling. A broad functional array of Gβγ signalling has recently been attributed to Gβ and Gγ subtype diversity, comprising 5 Gβ and 12 Gγ subtypes, respectively. In addition to displaying selectivity towards each other to form the Gβγ dimer, numerous studies have identified preferences of distinct Gβγ combinations for specific GPCRs, Gα subtypes and effector molecules. Importantly, Gβ and Gγ subtype-dependent regulation of downstream effectors, representing a diverse range of signalling pathways and physiological functions have been found. Here, we review the literature on the repercussions of Gβ and Gγ subtype diversity on direct and indirect regulation of GPCR/G protein signalling events and their physiological outcomes. Our discussion additionally provides perspective in understanding the intricacies underlying molecular regulation of subtype-specific roles of Gβγ signalling and associated diseases.

Structural organization of a major neuronal G protein regulator, the RGS7-Gβ5-R7BP complex

Signaling by the G-protein-coupled receptors (GPCRs) plays fundamental role in a vast number of essential physiological functions. Precise control of GPCR signaling requires action of regulators of G protein signaling (RGS) proteins that deactivate heterotrimeric G proteins. RGS proteins are elaborately regulated and comprise multiple domains and subunits, yet structural organization of these assemblies is poorly understood. Here, we report a crystal structure and dynamics analyses of the multisubunit complex of RGS7, a major regulator of neuronal signaling with key roles in controlling a number of drug target GPCRs and links to neuropsychiatric disease, metabolism, and cancer. The crystal structure in combination with molecular dynamics and mass spectrometry analyses reveals unique organizational features of the complex and long-range conformational changes imposed by its constituent subunits during allosteric modulation. Notably, several intermolecular interfaces in the complex work in synergy to provide coordinated modulation of this key GPCR regulator.

The Newly Synthesized Pyrazole Derivative 5-(1-(3 Fluorophenyl)-1H-Pyrazol-4-yl)-2H-Tetrazole Reduces Blood Pressure of Spontaneously Hypertensive Rats via NO/cGMO Pathway

The search for new antihypertensive drugs has grown in recent years because of high rate of morbidity among hypertensive patients and several side effects that are associated with the first-line medications. The current study sought to investigate the antihypertensive effect of a newly synthesized pyrazole derivative known as 5-(1-(3 fluorophenyl)-1H-pyrazol-4-yl)-2H-tetrazole (LQFM-21). Spontaneously hypertensive rats (SHR) were used to evaluate the effect of LQFM-21 on mean arterial pressure (MAP), heart rate (HR), renal vascular conductance (RVC), arterial vascular conductance (AVC), baroreflex sensitivity (BRS) index, and vascular reactivity. Acute intravenous (iv) administration of LQFM-21 (0.05, 0.1, 0.2, and 0.4 mg kg^-1) reduced MAP and HR, and increased RVC and AVC. Chronic oral administration of LQFM-21 (15 mg kg^-1) for 15 days reduced MAP without altering BRS. The blockade of muscarinic receptors and nitric oxide synthase by intravenous infusion of atropine and L-NAME, respectively, attenuated cardiovascular effects of LQFM-21. In addition, ex vivo experiments showed that LQFM-21 induced an endothelium-dependent relaxation in isolated aortic rings from SHR. This effect was blocked by guanylyl cyclase inhibitor (ODQ) and L-NAME. These findings suggest the involvement of muscarinic receptor and NO/cGMP pathway in the antihypertensive and vasodilator effects of LQFM-21.

Overexpression of regulator of G protein signaling 11 promotes cell migration and associates with advanced stages and aggressiveness of lung adenocarcinoma

Regulator of G protein signaling 11 (RGS11), a member of the R7 subfamily of RGS proteins, is a well-characterized GTPase-accelerating protein that is involved in the heterotrimeric G protein regulation of the amplitude and kinetics of receptor-promoted signaling in retinal bipolar and nerve cells. However, the role of RGS11 in cancer is completely unclear. Using subtractive hybridization analysis, we found that RGS11 was highly expressed in the lymph-node metastatic tissues and bone-metastatic tumors obtained from patients with lung adenocarcinoma. Characterization of the clinicopathological features of 91 patients showed that around 57.1% of the tumor samples displayed RGS11 overexpression that was associated with primary tumor status, nodal metastasis and increased disease stages. Its high expression was an independent predictive factor for poor prognosis of these patients. Cotransfection of guanine nucleotide-binding protein beta-5 (GNB5) markedly increased RGS11 expression. Enhancement or attenuation of RGS11 expression pinpointed its specific role in cell migration, but not in cell invasion and proliferation. Signaling events initiated by the RGS11–GNB5 coexpression activated the c-Raf/ERK/FAK-mediated pathway through upregulation of the Rac1 activity. Consistently, increasing the cell invasiveness of the transfectants by additional cotransfection of the exogenous urokinase–plasminogen activator gene caused a significant promotion in cell invasion in vitro and in vivo, confirming that RGS11 functions in cell migration, but requires additional proteolytic activity for cell and tissue invasion. Collectively, overexpression of RGS11 promotes cell migration, participates in tumor metastasis, and correlates the clinicopathological conditions of patients with lung adenocarcinoma.

Regulator of G-protein signaling Gβ5-R7 is a crucial activator of muscarinic M3 receptor-stimulated insulin secretion

In pancreatic β cells, muscarinic cholinergic receptor M3 (M3R) stimulates glucose-induced secretion of insulin. Regulator of G-protein signaling (RGS) proteins are critical modulators of GPCR activity, yet their role in β cells remains largely unknown. R7 subfamily RGS proteins are stabilized by the G-protein subunit Gβ5, such that the knockout of the Gnb5 gene results in degradation of all R7 subunits. We found that Gnb5 knockout in mice or in the insulin-secreting MIN6 cell line almost completely eliminates insulinotropic activity of M3R. Moreover, overexpression of Gβ5-RGS7 strongly promotes M3R-stimulated insulin secretion. Examination of this noncanonical mechanism in Gnb5^-/- MIN6 cells showed that cAMP, diacylglycerol, or Ca²⁺ levels were not significantly affected. There was no reduction in the amplitude of free Ca²⁺ responses in islets from the Gnb5^-/- mice, but the frequency of Ca²⁺ oscillations induced by cholinergic agonist was lowered by more than 30%. Ablation of Gnb5 impaired M3R-stimulated phosphorylation of ERK1/2. Stimulation of the ERK pathway in Gnb5^-/- cells by epidermal growth factor restored M3R-stimulated insulin release to near normal levels. Identification of the novel role of Gβ5-R7 in insulin secretion may lead to a new therapeutic approach for improving pancreatic β-cell function.-Wang, Q., Pronin, A. N., Levay, K., Almaca, J., Fornoni, A., Caicedo, A., Slepak, V. Z. Regulator of G-protein signaling Gβ5-R7 is a crucial activator of muscarinic M3 receptor-stimulated insulin secretion.

Regulation of neurite morphogenesis by interaction between R7 regulator of G protein signaling complexes and G protein subunit Gα13

The R7 regulator of G protein signaling family (R7-RGS) critically regulates nervous system development and function. Mice lacking all R7-RGS subtypes exhibit diverse neurological phenotypes, and humans bearing mutations in the retinal R7-RGS isoform RGS9-1 have vision deficits. Although each R7-RGS subtype forms heterotrimeric complexes with Gβ₅ and R7-RGS-binding protein (R7BP) that regulate G protein-coupled receptor signaling by accelerating deactivation of G_i/o α-subunits, several neurological phenotypes of R7-RGS knock-out mice are not readily explained by dysregulated G_i/o signaling. Accordingly, we used tandem affinity purification and LC-MS/MS to search for novel proteins that interact with R7-RGS heterotrimers in the mouse brain. Among several proteins detected, we focused on Gα₁₃ because it had not been linked to R7-RGS complexes before. Split-luciferase complementation assays indicated that Gα₁₃ in its active or inactive state interacts with R7-RGS heterotrimers containing any R7-RGS isoform. LARG (leukemia-associated Rho guanine nucleotide exchange factor (GEF)), PDZ-RhoGEF, and p115RhoGEF augmented interaction between activated Gα₁₃ and R7-RGS heterotrimers, indicating that these effector RhoGEFs can engage Gα₁₃·R7-RGS complexes. Because Gα₁₃/R7-RGS interaction required R7BP, we analyzed phenotypes of neuronal cell lines expressing RGS7 and Gβ₅ with or without R7BP. We found that neurite retraction evoked by Gα_12/13-dependent lysophosphatidic acid receptors was augmented in R7BP-expressing cells. R7BP expression blunted neurite formation evoked by serum starvation by signaling mechanisms involving Gα_12/13 but not Gα_i/o These findings provide the first evidence that R7-RGS heterotrimers interact with Gα₁₃ to augment signaling pathways that regulate neurite morphogenesis. This mechanism expands the diversity of functions whereby R7-RGS complexes regulate critical aspects of nervous system development and function.

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.

Fine Mapping of the Body Fat QTL on Human Chromosome 1q43

Introduction

Evidence for linkage and association of obesity-related quantitative traits to chromosome 1q43 has been reported in the Quebec Family Study (QFS) and in populations of Caribbean Hispanic ancestries yet no specific candidate locus has been replicated to date.

Methods

Using a set of 1,902 single nucleotide polymorphisms (SNPs) genotyped in 525 African American (AA) and 391 European American (EA) women enrolled in the NIEHS uterine fibroid study (NIEHS-UFS), we generated a fine association map for the body mass index (BMI) across a 2.3 megabase-long interval delimited by RGS7 (regulator of G-protein signaling 7) and PLD5 (Phospholipase D, member 5). Multivariable-adjusted linear regression models were fitted to the data to evaluate the association in race-stratified analyses and meta-analysis.

Results

The strongest associations were observed in a recessive genetic model and peaked in the 3’ end of RGS7 at intronic rs261802 variant in the AA group (p = 1.0 x 10⁻⁴) and in meta-analysis of AA and EA samples (p = 9.0 x 10⁻⁵). In the EA group, moderate associations peaked at rs6429264 (p = 2.0 x 10⁻³) in the 2 Kb upstream sequence of RGS7. In the reference populations for the European ancestry in the 1,000 genomes project, rs6429264 occurs in strong linkage disequilibrium (D’ = 0.94) with rs1341467, the strongest candidate SNP for total body fat in QFS that failed genotyping in the present study. Additionally we report moderate associations at the 3’ end of PLD5 in meta-analysis (3.2 x 10⁻⁴ ≤ p ≤ 5.8 x 10⁻⁴).

Conclusion

We report replication data suggesting that RGS7, a gene abundantly expressed in the brain, might be a putative body fat QTL on human chromosome 1q43. Future genetic and functional studies are required to substantiate our observations and to potentially link them to the neurobehavioral phenotypes associated with the RGS7 region.

Regulator of G Protein Signaling 7 (RGS7) Can Exist in a Homo-oligomeric Form That Is Regulated by Gαo and R7-binding Protein

RGS (regulator of G protein signaling) proteins of the R7 subfamily (RGS6, -7, -9, and -11) are highly expressed in neurons where they regulate many physiological processes. R7 RGS proteins contain several distinct domains and form obligatory dimers with the atypical Gβ subunit, Gβ5 They also interact with other proteins such as R7-binding protein, R9-anchoring protein, and the orphan receptors GPR158 and GPR179. These interactions facilitate plasma membrane targeting and stability of R7 proteins and modulate their activity. Here, we investigated RGS7 complexes using in situ chemical cross-linking. We found that in mouse brain and transfected cells cross-linking causes formation of distinct RGS7 complexes. One of the products had the apparent molecular mass of ∼150 kDa on SDS-PAGE and did not contain Gβ5 Mass spectrometry analysis showed no other proteins to be present within the 150-kDa complex in the amount close to stoichiometric with RGS7. This finding suggested that RGS7 could form a homo-oligomer. Indeed, co-immunoprecipitation of differentially tagged RGS7 constructs, with or without chemical cross-linking, demonstrated RGS7 self-association. RGS7-RGS7 interaction required the DEP domain but not the RGS and DHEX domains or the Gβ5 subunit. Using transfected cells and knock-out mice, we demonstrated that R7-binding protein had a strong inhibitory effect on homo-oligomerization of RGS7. In contrast, our data indicated that GPR158 could bind to the RGS7 homo-oligomer without causing its dissociation. Co-expression of constitutively active Gαo prevented the RGS7-RGS7 interaction. These results reveal the existence of RGS protein homo-oligomers and show regulation of their assembly by R7 RGS-binding partners.

Orphan Receptor GPR158 Is an Allosteric Modulator of RGS7 Catalytic Activity with an Essential Role in Dictating Its Expression and Localization in the Brain

Regulators of G protein signaling control the duration and extent of signaling via G protein-coupled receptor (GPCR) pathways by accelerating the GTP hydrolysis on G protein α subunits thereby promoting termination of GPCR signaling. A member of this family, RGS7, plays a critical role in the nervous system where it regulates multiple neurotransmitter GPCRs that mediate vision, memory, and the action of addictive drugs. Previous studies have established that in vivo RGS7 forms mutually exclusive complexes with the membrane protein RGS7-binding protein or the orphan receptor GPR158. In this study, we examine the impact of GPR158 on RGS7 in the brain. We report that knock-out of GPR158 in mice results in marked post-transcriptional destabilization of RGS7 and substantial loss of its association with membranes in several brain regions. We further identified the RGS7-binding site in the C terminus of GPR158 and found that it shares significant homology with the RGS7-binding protein. The proximal portion of the GPR158 C terminus additionally contained a conserved sequence that was capable of enhancing RGS7 GTPase-activating protein activity in solution by an allosteric mechanism acting in conjunction with the regulators of the G protein signaling-binding domain. The distal portion of the GPR158 C terminus contained several phosphodiesterase E γ-like motifs and selectively recruited G proteins in their activated state. The results of this study establish GPR158 as an essential regulator of RGS7 in the native nervous system with a critical role in controlling its expression, membrane localization, and catalytic activity.

Helix 8 and the i3 loop of the muscarinic M3 receptor are crucial sites for its regulation by the Gβ5-RGS7 complex

The muscarinic M3 receptor (M3R) is a Gq-coupled receptor and is known to interact with many intracellular regulatory proteins. One of these molecules is Gβ5-RGS7, the permanently associated heterodimer of G protein β-subunit Gβ5 and RGS7, a regulator of G protein signaling. Gβ5-RGS7 can attenuate M3R-stimulated release of Ca²⁺ from intracellular stores or enhance the influx of Ca²⁺ across the plasma membrane. Here we show that deletion of amino acids 304–345 from the central portion of the i3 loop renders M3R insensitive to regulation by Gβ5-RGS7. In addition to the i3 loop, interaction of M3R with Gβ5-RGS7 requires helix 8. According to circular dichroism spectroscopy, the peptide corresponding to amino acids 548–567 in the C-terminus of M3R assumes an α-helical conformation. Substitution of Thr553 and Leu558 with Pro residues disrupts this α-helix and abolished binding to Gβ5-RGS7. Introduction of the double Pro substitution into full-length M3R (M3R^TP/LP) prevents trafficking of the receptor to the cell surface. Using atropine or other antagonists as pharmacologic chaperones, we were able to increase the level of surface expression of the TP/LP mutant to levels comparable to that of wild-type M3R. However, M3R-stimulated calcium signaling is still severely compromised. These results show that the interaction of M3R with Gβ5-RGS7 requires helix 8 and the central portion of the i3 loop.

G protein beta 5 is targeted to D2-dopamine receptor-containing biochemical compartments and blocks dopamine-dependent receptor internalization

G beta 5 (Gbeta5, Gβ5) is a unique G protein β subunit that is thought to be expressed as an obligate heterodimer with R7 regulator of G protein signaling (RGS) proteins instead of with G gamma (Gγ) subunits. We found that D2-dopamine receptor (D2R) coexpression enhances the expression of Gβ5, but not that of the G beta 1 (Gβ1) subunit, in HEK293 cells, and that the enhancement of expression occurs through a stabilization of Gβ5 protein. We had previously demonstrated that the vast majority of D2R either expressed endogenously in the brain or exogenously in cell lines segregates into detergent-resistant biochemical fractions. We report that when expressed alone in HEK293 cells, Gβ5 is highly soluble, but is retargeted to the detergent-resistant fraction after D2R coexpression. Furthermore, an in-cell biotin transfer proximity assay indicated that D2R and Gβ5 segregating into the detergent-resistant fraction specifically interacted in intact living cell membranes. Dopamine-induced D2R internalization was blocked by coexpression of Gβ5, but not Gβ1. However, the same Gβ5 coexpression levels had no effect on agonist-induced internalization of the mu opioid receptor (MOR), cell surface D2R levels, dopamine-mediated recruitment of β-arrestin to D2R, the amplitude of D2R-G protein coupling, or the deactivation kinetics of D2R-activated G protein signals. The latter data suggest that the interactions between D2R and Gβ5 are not mediated by endogenously expressed R7 RGS proteins.

DEP domains: structurally similar but functionally different

The Dishevelled, EGL-10 and pleckstrin (DEP) domain is a globular protein domain that is present in about ten human protein families with well-defined structural features. A picture is emerging that DEP domains mainly function in the spatial and temporal control of diverse signal transduction events by recruiting proteins to the plasma membrane. DEP domains can interact with various partners at the membrane, including phospholipids and membrane receptors, and their binding is subject to regulation.

Differential effects of the Gβ5-RGS7 complex on muscarinic M3 receptor-induced Ca2+ influx and release

The G protein β subunit Gβ5 uniquely forms heterodimers with R7 family regulators of G protein signaling (RGS) proteins (RGS6, RGS7, RGS9, and RGS11) instead of Gγ. Although the Gβ5-RGS7 complex attenuates Ca(2+) signaling mediated by the muscarinic M3 receptor (M3R), the route of Ca(2+) entry (i.e., release from intracellular stores and/or influx across the plasma membrane) is unknown. Here, we show that, in addition to suppressing carbachol-stimulated Ca(2+) release, Gβ5-RGS7 enhanced Ca(2+) influx. This novel effect of Gβ5-RGS7 was blocked by nifedipine and 2-aminoethoxydiphenyl borate. Experiments with pertussis toxin, an RGS domain-deficient mutant of RGS7, and UBO-QIC {L-threonine,(3R)-N-acetyl-3-hydroxy-L-leucyl-(aR)-a-hydroxybenzenepropanoyl-2,3-idehydro-N-methylalanyl-L-alanyl-N-methyl-L-alanyl-(3R)-3-[[(2S,3R)-3-hydroxy-4- methyl-1-oxo-2-[(1-oxopropyl)amino]pentyl]oxy]-L-leucyl-N,O-dimethyl-,(7→1)-lactone (9CI)}, a novel inhibitor of Gq, showed that Gβ5-RGS7 modulated a Gq-mediated pathway. These studies indicate that Gβ5-RGS7, independent of RGS7 GTPase-accelerating protein activity, couples M3R to a nifedipine-sensitive Ca(2+) channel. We also compared the action of Gβ5-RGS7 on M3R-induced Ca(2+) influx and release elicited by different muscarinic agonists. Responses to Oxo-M [oxotremorine methiodide N,N,N,-trimethyl-4-(2-oxo-1-pyrrolidinyl)-2-butyn-1-ammonium iodide] were insensitive to Gβ5-RGS7. Pilocarpine responses consisted of a large release and modest influx components, of which the former was strongly inhibited whereas the latter was insensitive to Gβ5-RGS7. McN-A-343 [(4-hydroxy-2-butynyl)-1-trimethylammonium-3-chlorocarbanilate chloride] was the only compound whose total Ca(2+) response was enhanced by Gβ5-RGS7, attributed to, in part, by the relatively small Ca(2+) release this partial agonist stimulated. Together, these results show that distinct agonists not only have differential M3R functional selectivity, but also confer specific sensitivity to the Gβ5-RGS7 complex.

A physiologically required G protein-coupled receptor (GPCR)-regulator of G protein signaling (RGS) interaction that compartmentalizes RGS activity

G protein-coupled receptors (GPCRs) can interact with regulator of G protein signaling (RGS) proteins. However, the effects of such interactions on signal transduction and their physiological relevance have been largely undetermined. Ligand-bound GPCRs initiate by promoting exchange of GDP for GTP on the Gα subunit of heterotrimeric G proteins. Signaling is terminated by hydrolysis of GTP to GDP through intrinsic GTPase activity of the Gα subunit, a reaction catalyzed by RGS proteins. Using yeast as a tool to study GPCR signaling in isolation, we define an interaction between the cognate GPCR (Mam2) and RGS (Rgs1), mapping the interaction domains. This reaction tethers Rgs1 at the plasma membrane and is essential for physiological signaling response. In vivo quantitative data inform the development of a kinetic model of the GTPase cycle, which extends previous attempts by including GPCR-RGS interactions. In vivo and in silico data confirm that GPCR-RGS interactions can impose an additional layer of regulation through mediating RGS subcellular localization to compartmentalize RGS activity within a cell, thus highlighting their importance as potential targets to modulate GPCR signaling pathways.

Macromolecular composition dictates receptor and G protein selectivity of regulator of G protein signaling (RGS) 7 and 9-2 protein complexes in living cells

Regulator of G protein signaling (RGS) proteins play essential roles in the regulation of signaling via G protein-coupled receptors (GPCRs). With hundreds of GPCRs and dozens of G proteins, it is important to understand how RGS regulates selective GPCR-G protein signaling. In neurons of the striatum, two RGS proteins, RGS7 and RGS9-2, regulate signaling by μ-opioid receptor (MOR) and dopamine D2 receptor (D2R) and are implicated in drug addiction, movement disorders, and nociception. Both proteins form trimeric complexes with the atypical G protein β subunit Gβ5 and a membrane anchor, R7BP. In this study, we examined GTPase-accelerating protein (GAP) activity as well as Gα and GPCR selectivity of RGS7 and RGS9-2 complexes in live cells using a bioluminescence resonance energy transfer-based assay that monitors dissociation of G protein subunits. We showed that RGS9-2/Gβ5 regulated both Gi and Go with a bias toward Go, but RGS7/Gβ5 could serve as a GAP only for Go. Interestingly, R7BP enhanced GAP activity of RGS7 and RGS9-2 toward Go and Gi and enabled RGS7 to regulate Gi signaling. Neither RGS7 nor RGS9-2 had any activity toward Gz, Gs, or Gq in the absence or presence of R7BP. We also observed no effect of GPCRs (MOR and D2R) on the G protein bias of R7 RGS proteins. However, the GAP activity of RGS9-2 showed a strong receptor preference for D2R over MOR. Finally, RGS7 displayed an four times greater GAP activity relative to RGS9-2. These findings illustrate the principles involved in establishing G protein and GPCR selectivity of striatal RGS proteins.

GIRK channel modulation by assembly with allosterically regulated RGS proteins

G-protein-activated inward-rectifying K(+) (GIRK) channels hyperpolarize neurons to inhibit synaptic transmission throughout the nervous system. By accelerating G-protein deactivation kinetics, the regulator of G-protein signaling (RGS) protein family modulates the timing of GIRK activity. Despite many investigations, whether RGS proteins modulate GIRK activity in neurons by mechanisms involving kinetic coupling, collision coupling, or macromolecular complex formation has remained unknown. Here we show that GIRK modulation occurs by channel assembly with R7-RGS/Gβ5 complexes under allosteric control of R7 RGS-binding protein (R7BP). Elimination of R7BP occludes the Gβ5 subunit that interacts with GIRK channels. R7BP-bound R7-RGS/Gβ5 complexes and Gβγ dimers interact noncompetitively with the intracellular domain of GIRK channels to facilitate rapid activation and deactivation of GIRK currents. By disrupting this allosterically regulated assembly mechanism, R7BP ablation augments GIRK activity. This enhanced GIRK activity increases the drug effects of agonists acting at G-protein-coupled receptors that signal via GIRK channels, as indicated by greater antinociceptive effects of GABA(B) or μ-opioid receptor agonists. These findings show that GIRK current modulation in vivo requires channel assembly with allosterically regulated RGS protein complexes, which provide a target for modulating GIRK activity in neurological disorders in which these channels have crucial roles, including pain, epilepsy, Parkinson's disease and Down syndrome.

Subcellular localization of regulator of G protein signaling RGS7 complex in neurons and transfected cells

The R7 family of regulators of G protein signaling (RGS) is involved in many functions of the nervous system. This family includes RGS6, RGS7, RGS9, and RGS11 gene products and is defined by the presence of the characteristic first found in Disheveled, Egl-10, Pleckstrin (DEP), DEP helical extension (DHEX), Gγ-like, and RGS domains. Herein, we examined the subcellular localization of RGS7, the most broadly expressed R7 member. Our immunofluorescence studies of retinal and dorsal root ganglion neurons showed that RGS7 concentrated at the plasma membrane of cell bodies, in structures resembling lamellipodia or filopodia along the processes, and at the dendritic tips. At the plasma membrane of dorsal root ganglia neurons, RGS7 co-localized with its known binding partners R7 RGS binding protein (R7BP), Gαo, and Gαq. More than 50% of total RGS7-specific immunofluorescence was present in the cytoplasm, primarily within numerous small puncta that did not co-localize with R7BP. No specific RGS7 or R7BP immunoreactivity was detected in the nuclei. In transfected cell lines, ectopic RGS7 had both diffuse cytosolic and punctate localization patterns. RGS7 also localized in centrosomes. Structure-function analysis showed that the punctate localization was mediated by the DEP/DHEX domains, and centrosomal localization was dependent on the DHEX domain.

Fluorescence-based assay probing regulator of G protein signaling partner proteins

The regulator of G protein signaling (RGS) proteins are one of the essential modulators for the G protein system. Besides regulating G protein signaling by accelerating the GTPase activity of Gα subunits, RGS proteins are implicated in exerting other functions; they are also known to be involved in several diseases. Moreover, the existence of a single RGS protein in plants and its seven-transmembrane domain found in 2003 triggered efforts to unveil detailed structural and functional information of RGS proteins. We present a method for real-time examination of the protein-protein interactions between RGS and Gα subunits. AtRGS1 from plants and RGS4 from mammals were site-directedly labeled with the fluorescent probe Lucifer yellow on engineered cysteine residues and used to interact with different Gα subunits. The physical interactions can be revealed by monitoring the real-time fluorescence changes (8.6% fluorescence increase in mammals and 27.6% in plants); their correlations to functional exertion were shown with a GTPase accelerating activity assay and further confirmed by measurement of K(d). We validate the effectiveness of this method and suggest its application to the exploration of more RGS signaling partner proteins in physiological and pathological studies.

Genetic ablation of Pannexin1 protects retinal neurons from ischemic injury

Pannexin1 (Panx1) forms large nonselective membrane channel that is implicated in paracrine and inflammatory signaling. In vitro experiments suggested that Panx1 could play a key role in ischemic death of hippocampal neurons. Since retinal ganglion cells (RGCs) express high levels of Panx1 and are susceptible to ischemic induced injury, we hypothesized that Panx1 contributes to rapid and selective loss of these neurons in ischemia. To test this hypothesis, we induced experimental retinal ischemia followed by reperfusion in live animals with the Panx1 channel genetically ablated either in the entire mouse (Panx1 KO), or only in neurons using the conditional knockout (Panx1 CKO) technology. Here we report that two distinct neurotoxic processes are induced in RGCs by ischemia in the wild type mice but are inactivated in Panx1KO and Panx1 CKO animals. First, the post-ischemic permeation of RGC plasma membranes is suppressed, as assessed by dye transfer and calcium imaging assays ex vivo and in vitro. Second, the inflammasome-mediated activation of caspase-1 and the production of interleukin-1β in the Panx1 KO retinas are inhibited. Our findings indicate that post-ischemic neurotoxicity in the retina is mediated by previously uncharacterized pathways, which involve neuronal Panx1 and are intrinsic to RGCs. Thus, our work presents the in vivo evidence for neurotoxicity elicited by neuronal Panx1, and identifies this channel as a new therapeutic target in ischemic pathologies.

cAMP regulates DEP domain-mediated binding of the guanine nucleotide exchange factor Epac1 to phosphatidic acid at the plasma membrane

Epac1 is a cAMP-regulated guanine nucleotide exchange factor for the small G protein Rap. Upon cAMP binding, Epac1 undergoes a conformational change that results in its release from autoinhibition. In addition, cAMP induces the translocation of Epac1 from the cytosol to the plasma membrane. This relocalization of Epac1 is required for efficient activation of plasma membrane-located Rap and for cAMP-induced cell adhesion. This translocation requires the Dishevelled, Egl-10, Pleckstrin (DEP) domain, but the molecular entity that serves as the plasma membrane anchor and the possible mechanism of regulated binding remains elusive. Here we show that Epac1 binds directly to phosphatidic acid. Similar to the cAMP-induced Epac1 translocation, this binding is regulated by cAMP and requires the DEP domain. Furthermore, depletion of phosphatidic acid by inhibition of phospholipase D1 prevents cAMP-induced translocation of Epac1 as well as the subsequent activation of Rap at the plasma membrane. Finally, mutation of a single basic residue within a polybasic stretch of the DEP domain, which abolishes translocation, also prevents binding to phosphatidic acid. From these results we conclude that cAMP induces a conformational change in Epac1 that enables DEP domain-mediated binding to phosphatidic acid, resulting in the tethering of Epac1 at the plasma membrane and subsequent activation of Rap.

Membrane attachment is key to protecting transducin GTPase-activating complex from intracellular proteolysis in photoreceptors

The members of the R7 regulator of G-protein signaling (RGS) protein subfamily are versatile regulators of G-protein signaling throughout the nervous system. Recent studies indicate that they are often found in complexes with membrane anchor proteins that serve as versatile modulators of their activity, intracellular targeting, and stability. One striking example is the interplay between the membrane anchor R9AP and the RGS9-1 · Gβ5 GTPase-activating complex responsible for the rapid inactivation of the G-protein transducin in vertebrate photoreceptor cells during their recovery from light excitation. The amount of this complex in photoreceptors sets their temporal resolution and is precisely regulated by the expression level of R9AP, which serves to protect the RGS9-1 and Gβ5 subunits from intracellular proteolysis. In this study, we investigated the mechanism by which R9AP performs its protective function in mouse rods and found that it is entirely confined to recruiting RGS9-1 · Gβ5 to cellular membranes. Furthermore, membrane attachment of RGS9-1 · Gβ5 is sufficient for its stable expression in rods even in the absence of R9AP. Our second finding is that RGS9-1 · Gβ5 possesses targeting information that specifies its exclusion from the outer segment and that this information is neutralized by association with R9AP to allow outer segment targeting. Finally, we demonstrate that the ability of R9AP · RGS9-1 · Gβ5 to accelerate GTP hydrolysis on transducin is independent of its means of membrane attachment, since replacing the transmembrane domain of R9AP with a site for lipid modification did not impair the catalytic activity of this complex.

β-arrestin2 plays permissive roles in the inhibitory activities of RGS9-2 on G protein-coupled receptors by maintaining RGS9-2 in the open conformation

Together with G protein-coupled receptor (GPCR) kinases (GRKs) and β-arrestins, RGS proteins are the major family of molecules that control the signaling of GPCRs. The expression pattern of one of these RGS family members, RGS9-2, coincides with that of the dopamine D(3) receptor (D(3)R) in the brain, and in vivo studies have shown that RGS9-2 regulates the signaling of D2-like receptors. In this study, β-arrestin2 was found to be required for scaffolding of the intricate interactions among the dishevelled-EGL10-pleckstrin (DEP) domain of RGS9-2, Gβ5, R7-binding protein (R7BP), and D(3)R. The DEP domain of RGS9-2, under the permission of β-arrestin2, inhibited the signaling of D(3)R in collaboration with Gβ5. β-Arrestin2 competed with R7BP and Gβ5 so that RGS9-2 is placed in the cytosolic region in an open conformation which is able to inhibit the signaling of GPCRs. The affinity of the receptor protein for β-arrestin2 was a critical factor that determined the selectivity of RGS9-2 for the receptor it regulates. These results show that β-arrestins function not only as mediators of receptor-G protein uncoupling and initiators of receptor endocytosis but also as scaffolding proteins that control and coordinate the inhibitory effects of RGS proteins on the signaling of certain GPCRs.

Targeted deletion of one or two copies of the G protein β subunit Gβ5 gene has distinct effects on body weight and behavior in mice

We investigated the physiological role of Gβ5, a unique G protein β subunit that dimerizes with regulators of G protein signaling (RGS) proteins of the R7 family instead of Gγ. Gβ5 is essential for stability of these complexes, so that its knockout (KO)causes degradation of the entire Gβ5-R7 family. We report that the Gβ5-KO mice remain leaner than the wild type (WT) throughout their lifetime and are resistant to a high-fat diet. They have a 5-fold increase in locomotor activity, increased thermogenesis, and lower serum insulin, all of which correlate with a higher level of secreted epinephrine. Heterozygous (HET) mice are 2-fold more active than WT mice. Surprisingly, with respect to body weight, the HET mice display a phenotype opposite to that of the KO mice: by the age of 6 mo, they are ≥ 15% heavier than the WT and have increased adiposity, insulin resistance, and liver steatosis. These changes occur in HET mice fed a normal diet and without apparent hyperphagia, mimicking basic characteristics of human metabolic syndrome. We conclude that even a partial reduction in Gβ5-R7 level can perturb normal animal metabolism and behavior. Our data on Gβ5 haploinsufficient mice may explain earlier observations of genetic linkage between R7 family mutations and obesity in humans.

Type 5 G protein beta subunit (Gbeta5) controls the interaction of regulator of G protein signaling 9 (RGS9) with membrane anchors

The R7 family of regulators of G protein signaling (RGS) proteins, comprising RGS6, RGS7, RGS9, and RGS11, regulate neuronal G protein signaling pathways. All members of the R7 RGS form trimeric complexes with the atypical G protein β subunit, Gβ5, and membrane anchor R7BP or R9AP. Association with Gβ5 and membrane anchors has been shown to be critical for maintaining proteolytic stability of the R7 RGS proteins. However, despite its functional importance, the mechanism of how R7 RGS forms complexes with Gβ5 and membrane anchors remains poorly understood. Here, we used protein-protein interaction, co-localization, and protein stability assays to show that association of RGS9 with membrane anchors requires Gβ5. We further establish that the recruitment of R7BP to the complex requires an intact interface between the N-terminal lobe of RGS9 and protein interaction surface of Gβ5. Site-directed mutational analysis reveals that distinct molecular determinants in the interface between Gβ5 and N-terminal Dishevelled, EGL-10, Pleckstrin/DEP Helical Extension (DEP/DHEY) domains are differentially involved in R7BP binding and proteolytic stabilization. On the basis of these findings, we conclude that Gβ5 contributes to the formation of the binding site to the membrane anchors and thus is playing a central role in the assembly of the proteolytically stable trimeric complex and its correct localization in the cell.

Regulator of G protein signaling proteins as drug targets: current state and future possibilities

Regulators of G protein signaling (RGS) proteins have emerged in the past two decades as novel drug targets in many areas of research. Their importance in regulating signaling via G protein-coupled receptors has become evident as numerous studies have been published on the structure and function of RGS proteins. A number of genetic models have also been developed, demonstrating the potential clinical importance of RGS proteins in various disease states, including central nervous system disorders, cardiovascular disease, diabetes, and several types of cancer. Apart from their classical mechanism of action as GTPase-activating proteins (GAPs), RGS proteins can also serve other noncanonical functions. This opens up a new approach to targeting RGS proteins in drug discovery as the view on the function of these proteins is constantly evolving. This chapter summarizes the latest development in RGS protein drug discovery with special emphasis on noncanonical functions and regulatory mechanisms of RGS protein expression. As more reports are being published on this group of proteins, it is becoming clear that modulation of GAP activity might not be the only way to therapeutically target RGS proteins.

Thinking outside of the "RGS box": new approaches to therapeutic targeting of regulators of G protein signaling

Regulators of G protein signaling (RGS) proteins are emerging as potentially important drug targets. The mammalian RGS protein family has more than 20 members and they share a common ∼120-residue RGS homology domain or "RGS box." RGS proteins regulate signaling via G protein-coupled receptors by accelerating GTPase activity at active α subunits of G proteins of the G(q) and G(i/o) families. Most studies searching for modulators of RGS protein function have been focused on inhibiting the GTPase accelerating protein activity. However, many RGS proteins contain additional domains that serve other functions, such as interactions with proteins or subcellular targeting. Here, we discuss a rationale for therapeutic targeting of RGS proteins by regulation of expression or allosteric modulation to permit either increases or decreases in RGS function. Several RGS proteins have reduced expression or function in pathophysiological states, so strategies to increase RGS function would be useful. Because several RGS proteins are rapidly degraded by the N-end rule pathway, finding ways to stabilize them may prove to be an effective way to enhance RGS protein function.

RNA interference screen for RGS protein specificity at muscarinic and protease-activated receptors reveals bidirectional modulation of signaling

Regulator of G protein signaling (RGS) proteins are considered key modulators of G protein-coupled receptor (GPCR)-mediated signal transduction. These proteins act directly on Galpha subunits in vitro to increase their intrinsic rate of GTP hydrolysis; this activity is central to the prevailing view of RGS proteins as negative regulators of agonist-initiated GPCR signaling. However, the specificities of action of particular RGS proteins toward specific GPCRs in an integrated cellular context remain unclear. Here, we developed a medium-throughput assay to address this question in a wholly endogenous context using RNA interference. We performed medium-throughput calcium mobilization assays of agonist-stimulated muscarinic acetylcholine and protease-activated receptors in human embryonic kidney 293 (HEK293) cells transfected with individual members of a "pooled duplex" short interfering RNA library targeting all conventional human RGS transcripts. Only knockdown of RGS11 increased both carbachol-mediated calcium mobilization and inositol phosphate accumulation. Surprisingly, we found that knockdown of RGS8 and RGS9, but not other conventional RGS proteins, significantly decreased carbachol-mediated calcium mobilization, whereas only RGS8 knockdown decreased protease-activated receptor-1 (PAR-1)-mediated calcium mobilization. Loss of responsiveness toward carbachol and PAR-1 agonist peptide upon RGS8 knockdown appears due, at least in part, to a loss in respective receptor cell surface expression, although this is not the case for RGS9 knockdown. Our data suggest a cellular role for RGS8 in the stable surface expression of M3 muscarinic acetylcholine receptor and PAR-1, as well as a specific and opposing set of functions for RGS9 and RGS11 in modulating carbachol responsiveness similar to that seen in Caenorhabditis elegans.

Molecular organization of the complex between the muscarinic M3 receptor and the regulator of G protein signaling, Gbeta(5)-RGS7

The complex of the regulator of G protein signaling (RGS), Gbeta(5)-RGS7, can inhibit signal transduction via the M3 muscarinic acetylcholine receptor (M3R). RGS7 consists of three distinct structural entities: the DEP domain and its extension DHEX, the Ggamma-like (GGL) domain, which is permanently bound to Gbeta subunit Gbeta(5), and the RGS domain responsible for the interaction with Galpha subunits. Inhibition of the M3R by Gbeta(5)-RGS7 is independent of the RGS domain but requires binding of the DEP domain to the third intracellular loop of the receptor. Recent studies identified the dynamic intramolecular interaction between the Gbeta(5) and DEP domains, which suggested that the Gbeta(5)-RGS7 dimer could alternate between the "open" and "closed" conformations. Here, we identified point mutations that weaken DEP-Gbeta(5) binding, presumably stabilizing the open state, and tested their effects on the interaction of Gbeta(5)-RGS7 with the M3R. We found that these mutations facilitated binding of Gbeta(5)-RGS7 to the recombinant third intracellular loop of the M3R but did not enhance its ability to inhibit M3R-mediated Ca(2+) mobilization. This led us to the idea that the M3R can effectively induce the Gbeta(5)-RGS7 dimer to open; such a mechanism would require a region of the receptor distinct from the third loop. Indeed, we found that the C-terminus of M3R interacts with Gbeta(5)-RGS7. Truncation of the C-terminus rendered the M3R insensitive to inhibition by wild-type Gbeta(5)-RGS7; however, the open mutant of Gbeta(5)-RGS7 was able to inhibit signaling by the truncated M3R. The GST fusion of the M3R C-tail could not bind to wild-type Gbeta(5)-RGS7 but could associate with its open mutant as well as with the separated recombinant DEP domain or Gbeta(5). Taken together, our data are consistent with the following model: interaction of the M3R with Gbeta(5)-RGS7 causes the DEP domain and Gbeta(5) to dissociate from each other and bind to the C-tail, and the DEP domain also binds to the third loop, thereby inhibiting M3R-mediated signaling.

RGS4 is a negative regulator of insulin release from pancreatic beta-cells in vitro and in vivo

Therapeutic strategies that augment insulin release from pancreatic beta-cells are considered beneficial in the treatment of type 2 diabetes. We previously demonstrated that activation of beta-cell M(3) muscarinic receptors (M3Rs) greatly promotes glucose-stimulated insulin secretion (GSIS), suggesting that strategies aimed at enhancing signaling through beta-cell M3Rs may become therapeutically useful. M3R activation leads to the stimulation of G proteins of the G(q) family, which are under the inhibitory control of proteins known as regulators of G protein signaling (RGS proteins). At present, it remains unknown whether RGS proteins play a role in regulating insulin release. To address this issue, we initially demonstrated that MIN6 insulinoma cells express functional M3Rs and that RGS4 was by far the most abundant RGS protein expressed by these cells. Strikingly, siRNA-mediated knockdown of RGS4 expression in MIN6 cells greatly enhanced M3R-mediated augmentation of GSIS and calcium release. We obtained similar findings using pancreatic islets prepared from RGS4-deficient mice. Interestingly, RGS4 deficiency had little effect on insulin release caused by activation of other beta-cell GPCRs. Finally, treatment of mutant mice selectively lacking RGS4 in pancreatic beta-cells with a muscarinic agonist (bethanechol) led to significantly increased plasma insulin and reduced blood glucose levels, as compared to control littermates. Studies with beta-cell-specific M3R knockout mice showed that these responses were mediated by beta-cell M3Rs. These findings indicate that RGS4 is a potent negative regulator of M3R function in pancreatic beta-cells, suggesting that RGS4 may represent a potential target to promote insulin release for therapeutic purposes.

RSBP-1 is a membrane-targeting subunit required by the Galpha(q)-specific but not the Galpha(o)-specific R7 regulator of G protein signaling in Caenorhabditis elegans

Regulator of G protein signaling (RGS) proteins inhibit G protein signaling by activating Galpha GTPase activity, but the mechanisms that regulate RGS activity are not well understood. The mammalian R7 binding protein (R7BP) can interact with all members of the R7 family of RGS proteins, and palmitoylation of R7BP can target R7 RGS proteins to the plasma membrane in cultured cells. However, whether endogenous R7 RGS proteins in neurons require R7BP or membrane localization for function remains unclear. We have identified and knocked out the only apparent R7BP homolog in Caenorhabditis elegans, RSBP-1. Genetic studies show that loss of RSBP-1 phenocopies loss of the R7 RGS protein EAT-16, but does not disrupt function of the related R7 RGS protein EGL-10. Biochemical analyses find that EAT-16 coimmunoprecipitates with RSBP-1 and is predominantly plasma membrane-associated, whereas EGL-10 does not coimmunoprecipitate with RSBP-1 and is not predominantly membrane-associated. Mutating the conserved membrane-targeting sequence in RSBP-1 disrupts both the membrane association and function of EAT-16, demonstrating that membrane targeting by RSBP-1 is essential for EAT-16 activity. Our analysis of endogenous R7 RGS proteins in C. elegans neurons reveals key differences in the functional requirements for membrane targeting between members of this protein family.

Structure, function, and localization of Gβ5-RGS complexes

Members of the R7 subfamily of regulator of G protein signaling (RGS) proteins (RGS6, 7, 9, and 11) exist as heterodimers with the G protein beta subunit Gβ5. These protein complexes are only found in neurons and are defined by the presence of three domains: DEP/DHEX, Gβ5/GGL, and RGS. This article summarizes published work in the following areas: (1) the functional significance of structural organization of Gβ5-R7 complexes, (2) regional distribution of Gβ5-R7 in the nervous system and regulation of R7 family expression, (3) subcellular localization of Gβ5-R7 complexes, and (4) novel binding partners of Gβ5-R7 proteins. The review points out some contradictions between observations made by different research groups and highlights the importance of using alternative experimental approaches to obtain conclusive information about Gβ5-R7 function in vivo.

The R7 RGS protein family: multi-subunit regulators of neuronal G protein signaling

G protein-coupled receptor signaling pathways mediate the transmission of signals from the extracellular environment to the generation of cellular responses, a process that is critically important for neurons and neurotransmitter action. The ability to promptly respond to rapidly changing stimulation requires timely inactivation of G proteins, a process controlled by a family of specialized proteins known as regulators of G protein signaling (RGS). The R7 group of RGS proteins (R7 RGS) has received special attention due to their pivotal roles in the regulation of a range of crucial neuronal processes such as vision, motor control, reward behavior, and nociception in mammals. Four proteins in this group, RGS6, RGS7, RGS9, and RGS11, share a common molecular organization of three modules: (i) the catalytic RGS domain, (ii) a GGL domain that recruits G beta(5), an outlying member of the G protein beta subunit family, and (iii) a DEP/DHEX domain that mediates interactions with the membrane anchor proteins R7BP and R9AP. As heterotrimeric complexes, R7 RGS proteins not only associate with and regulate a number of G protein signaling pathway components, but have also been found to form complexes with proteins that are not traditionally associated with G protein signaling. This review summarizes our current understanding of the biology of the R7 RGS complexes including their structure/functional organization, protein-protein interactions, and physiological roles.