Activator of G protein signaling 3 null mice: I. Unexpected alterations in metabolic and cardiovascular function

A Genome-Wide Association Study Suggests New Susceptibility Loci for Primary Antiphospholipid Syndrome

OBJECTIVE

Primary antiphospholipid syndrome (PAPS) is a rare autoimmune disease characterized by the presence of antiphospholipid antibodies and the occurrence of thrombotic events and pregnancy complications. Our study aimed to identify novel genetic susceptibility loci associated with PAPS.

METHODS

We performed a genome-wide association study comprising 5,485 individuals (482 affected individuals) of European ancestry. Significant and suggestive independent variants from a meta-analysis of approximately 7 million variants were evaluated for functional and biological process enrichment. The genetic risk variability for PAPS in different populations was also assessed. Hierarchical clustering, Mahalanobis distance, and Dirichlet Process Mixtures with uncertainty clustering methods were used to assess genetic similarities between PAPS and other immune-mediated diseases.

RESULTS

We revealed genetic associations with PAPS in a regulatory locus within the HLA class II region near HLA-DRA and in STAT1-STAT4 with a genome-wide level of significance; 34 additional suggestive genetic susceptibility loci for PAPS were also identified. The disease risk allele near HLA-DRA is associated with overexpression of HLA-DRB6, HLA-DRB9, HLA-DQA2, and HLA-DQB2 in immune cells, vascular tissue, and nervous tissue. This association is independent of the association between PAPS and HLA-DRB1*1302. Functional analyses highlighted immune-related pathways in PAPS-associated loci. The comparison with other immune-mediated diseases revealed a close genetic relatedness to neuromyelitis optica, systemic sclerosis, and Sjögren syndrome, suggesting co-localized causal variations close to STAT1-STAT4, TNPO3, and BLK.

CONCLUSION

This study represents a comprehensive large-scale genetic analysis for PAPS and provides new insights into the genetic basis and pathophysiology of this rare disease.

Properties of biomolecular condensates defined by Activator of G-protein Signaling 3

Activator of G-protein signaling 3 (AGS3; also known as GPSM1), a receptor-independent activator of G-protein signaling, oscillates among defined subcellular compartments and biomolecular condensates (BMCs) in a regulated manner that is likely related to the functional diversity of the protein. We determined the influence of cell stress on the cellular distribution of AGS3 and core material properties of AGS3 BMCs. Cellular stress (oxidative, pHi and thermal) induced the formation of AGS3 BMCs in HeLa and COS-7 cells, as determined by fluorescent microscopy. Oxidative stress-induced AGS3 BMCs were distinct from G3BP1 stress granules and from RNA processing BMCs defined by the P-body protein Dcp1a. Immunoblots indicated that cellular stress shifted AGS3, but not the stress granule protein G3BP1 to a membrane pellet fraction following cell lysis. The stress-induced generation of AGS3 BMCs was reduced by co-expression of the signaling protein Gαi3, but not the AGS3-binding partner DVL2. Fluorescent recovery following photobleaching of individual AGS3 BMCs indicated that there are distinct diffusion kinetics and restricted fluidity for AGS3 BMCs. These data suggest that AGS3 BMCs represent a distinct class of stress granules that serve as a previously unrecognized signal processing node.

A genome-wide association study suggests new susceptibility loci for primary antiphospholipid syndrome

Objectives

Primary antiphospholipid syndrome (PAPS) is a rare autoimmune disease characterized by the presence of antiphospholipid antibodies and the occurrence of thrombotic events and pregnancy complications. Our study aimed to identify novel genetic susceptibility loci associated with PAPS.

Methods

We performed a genome-wide association study comprising 5,485 individuals (482 affected individuals) of European ancestry. Significant and suggestive independent variants from a meta-analysis of approximately 7 million variants were evaluated for functional and biological process enrichment. The genetic risk variability for PAPS in different populations was also assessed. Hierarchical clustering, Mahalanobis distance, and Dirichlet Process Mixtures with uncertainty clustering methods were used to assess genetic similarities between PAPS and other immune-mediated diseases.

Results

We revealed genetic associations with PAPS in a regulatory locus within the HLA class II region near HLA-DRA and in STAT4 with a genome-wide level of significance. 34 additional suggestive genetic susceptibility loci for PAPS were also identified. The disease risk allele in the HLA class II locus is associated with overexpression of HLA-DRB6 , HLA-DRB9 , HLA-DPB2 , HLA-DQA2 and HLA-DQB2 , and is independent of the association between PAPS and HLA-DRB1*1302 . Functional analyses highlighted immune and nervous system related pathways in PAPS-associated loci. The comparison with other immune-mediated diseases revealed a close genetic relatedness to neuromyelitis optica, systemic sclerosis, and Sjögren's syndrome, suggesting colocalized causal variations close to STAT4 , TNPO3 , and BLK .

Conclusions

This study represents a comprehensive large-scale genetic analysis for PAPS and provides new insights into the genetic basis and pathophysiology of this rare disease.

G-protein signaling modulator 1 promotes colorectal cancer metastasis by PI3K/AKT/mTOR signaling and autophagy

BACKGROUND

Colorectal cancer is the second most common malignant tumor worldwide. A deeper insight into the mechanisms underlying colorectal cancer metastasis is urgently needed. G-protein signaling modulator 1 and autophagy play critical roles in tumor migration and invasion. However, the biological functions and regulatory networks of G-protein signaling modulator 1 and autophagy have not yet been fully studied.

METHODS

We performed immunohistochemistry and clinic-pathological characteristic analysis in 328 human colorectal cancer specimens to identify the clinical role of G-protein signaling modulator 1 in colorectal cancer. An in vitro coculture system and a tumor metastasis mouse model were used to explore the biological function of G-protein signaling modulator 1 on tumor metastasis. Autophagic flux detection like GFP-LC3B signal immunofluorescence and electron microscope observation of autophagic vesicles and confocal microscope detection were used to gain insights into the underlying role of G-protein signaling modulator 1 in autophagy.

RESULTS

We found that G-protein signaling modulator 1 was abundantly expressed in colorectal cancer tissues and was associated with lymph node metastasis and poor prognosis. Furthermore, our bioinformatic and functional studies demonstrated that G-protein signaling modulator 1 significantly promoted cell migration and invasion, both in vitro and in vivo. Mechanistically, we demonstrated that G-protein signaling modulator 1 could promote colorectal cancer cell migration and invasion and inhibit autophagy and by activating the PI3K/AKT/mTOR pathway.

CONCLUSIONS

We proposed that G-protein signaling modulator 1 promotes colorectal cancer metastasis by modulating autophagy through the PI3K/AKT/mTOR pathway.

GPSM1 impairs metabolic homeostasis by controlling a pro-inflammatory pathway in macrophages

G-protein-signaling modulator 1 (GPSM1) exhibits strong genetic association with Type 2 diabetes (T2D) and Body Mass Index in population studies. However, how GPSM1 carries out such control and in which types of cells are poorly understood. Here, we demonstrate that myeloid GPSM1 promotes metabolic inflammation to accelerate T2D and obesity development. Mice with myeloid-specific GPSM1 ablation are protected against high fat diet-induced insulin resistance, glucose dysregulation, and liver steatosis via repression of adipose tissue pro-inflammatory states. Mechanistically, GPSM1 deficiency mainly promotes TNFAIP3 transcription via the Gα_i3/cAMP/PKA/CREB axis, thus inhibiting TLR4-induced NF-κB signaling in macrophages. In addition, we identify a small-molecule compound, AN-465/42243987, which suppresses the pro-inflammatory phenotype by inhibiting GPSM1 function, which could make it a candidate for metabolic therapy. Furthermore, GPSM1 expression is upregulated in visceral fat of individuals with obesity and is correlated with clinical metabolic traits. Overall, our findings identify macrophage GPSM1 as a link between metabolic inflammation and systemic homeostasis.

Dynamic transcriptome analysis of the muscles in high-fat diet-induced obese zebrafish (Danio rerio) under 5-HT treatment

Peripheral 5-hydroxytryptamine (5-HT, also called serotonin) is reportedly a potential therapeutic target in obesity-related metabolic diseases due to its regulatory role in energy homeostasis in mammals. However, information on the detailed effect of peripheral 5-HT on the energy metabolism in fishes, especially the lipid metabolism, and the underlying mechanism remains elusive. In this study, a diet-induced obesity model was developed in the zebrafish (Danio rerio), a prototypical animal model for metabolic disorders. The zebrafish were fed a high-fat diet for 8 weeks and were simultaneously injected with PBS, 0.1 mM and 10 mM 5-HT, intraperitoneally. The body weight was significantly lower in the zebrafish injected with 0.1 mM 5-HT (P < 0.05), however, there was no change in body length (P > 0.05) at the end of the 8-week treatment. The muscle tissues from the zebrafish treated with PBS and 5-HT were collected for transcriptomic analysis and the RNA-seq revealed 1134, 3713, and 2535 genes were screened out compared to the muscular DEGs among three groups. The enrichment analysis revealed DEGs to be significantly associated with multiple metabolic pathways, including ribosome, oxidative phosphorylation, proteasome, PPAR signaling pathway, and ferroptosis. Additionally, the qRT-PCR validated 12 DEGs out of which 10 genes exhibited consistent trends. Taken together, this data provided useful information on the transcriptional characteristics of the muscle tissue in the obese zebrafish exposed to 5-HT, offering important insights into the regulatory effect of peripheral 5-HT in teleosts, as well as novel approaches for preventing and treating obesity-related metabolic dysfunction.

Histological and transcriptomic analysis of adipose and muscle of dairy calves supplemented with 5-hydroxytryptophan

In mammals, peripheral serotonin is involved in regulating energy balance. Herein, we characterized the transcriptomic profile and microstructure of adipose and muscle in pre-weaned calves with increased circulating serotonin. Holstein bull calves (21 ± 2 days old) were fed milk replacer supplemented with saline (CON, 8 mL/day n = 4) or 5-hydroxytryptophan (5-HTP, 90 mg/day, n = 4) for 10 consecutive days. Calves were euthanized on d10 to harvest adipose and muscle for RNA-Sequencing and histological analyses. Twenty-two genes were differentially expressed in adipose, and 33 in muscle. Notably, Interferon gamma inducible protein-47 was highly expressed and upregulated in muscle and adipose (avg. log FC = 6.5). Enriched pathways in adipose tissue revealed serotonin’s participation in lipid metabolism and PPAR signaling. In muscle, enriched pathways were related to histone acetyltransferase binding, Jak-STAT signaling, PI3K-Akt signaling and cell proliferation. Supplementation of 5-HTP increased cell proliferation and total cell number in adipose and muscle. Adipocyte surface area was smaller and muscle fiber area was not different in the 5-HTP group. Manipulating the serotonin pathway, through oral supplementation of 5-HTP, influences signaling pathways and cellular processes in adipose and muscle related to endocrine and metabolic functions which might translate into improvements in calf growth and development.

DIAPH3 deficiency links microtubules to mitotic errors, defective neurogenesis, and brain dysfunction

Diaphanous (DIAPH) three (DIAPH3) is a member of the formin proteins that have the capacity to nucleate and elongate actin filaments and, therefore, to remodel the cytoskeleton. DIAPH3 is essential for cytokinesis as its dysfunction impairs the contractile ring and produces multinucleated cells. Here, we report that DIAPH3 localizes at the centrosome during mitosis and regulates the assembly and bipolarity of the mitotic spindle. DIAPH3-deficient cells display disorganized cytoskeleton and multipolar spindles. DIAPH3 deficiency disrupts the expression and/or stability of several proteins including the kinetochore-associated protein SPAG5. DIAPH3 and SPAG5 have similar expression patterns in the developing brain and overlapping subcellular localization during mitosis. Knockdown of SPAG5 phenocopies DIAPH3 deficiency, whereas its overexpression rescues the DIAHP3 knockdown phenotype. Conditional inactivation of Diaph3 in mouse cerebral cortex profoundly disrupts neurogenesis, depleting cortical progenitors and neurons, leading to cortical malformation and autistic-like behavior. Our data uncover the uncharacterized functions of DIAPH3 and provide evidence that this protein belongs to a molecular toolbox that links microtubule dynamics during mitosis to aneuploidy, cell death, fate determination defects, and cortical malformation.

AGS3-dependent trans-Golgi network membrane trafficking is essential for compaction in mouse embryos

Activator of G-protein signaling 3 (AGS3, also known as GPSM1) regulates the trans-Golgi network. The AGS3 GoLoco motif binds to Gαi and thereby regulates the transport of proteins to the plasma membrane. Compaction of early embryos is based on the accumulation of E-cadherin (Cdh1) at cell-contacted membranes. However, how AGS3 regulates the transport of Cdh1 to the plasma membrane remains undetermined. To investigate this, AGS3 was knocked out using the Cas9-sgRNA system. Both trans-Golgi network protein 46 (TGN46, also known as TGOLN2) and transmembrane p24-trafficking protein 7 (TMED7) were tracked in early mouse embryos by tagging these proteins with a fluorescent protein label. We observed that the majority of the AGS3-edited embryos were developmentally arrested and were fragmented after the four-cell stage, exhibiting decreased accumulation of Cdh1 at the membrane. The trans-Golgi network and TMED7-positive vesicles were also dispersed and were not polarized near the membrane. Additionally, increased Gαi1 (encoded by GNAI1) expression could rescue AGS3-overexpressed embryos. In conclusion, AGS3 reinforces the dynamics of the trans-Golgi network and the transport of TMED7-positive cargo containing Cdh1 to the cell-contact surface during early mouse embryo development.

Intersection of two key signal integrators in the cell: activator of G-protein signaling 3 and dishevelled-2

Activator of G-protein signaling 3 (AGS3, encoded by GPSM1) was discovered as a one of several receptor-independent activators of G-protein signaling, which are postulated to provide a platform for divergence between canonical and noncanonical G-protein signaling pathways. Similarly, Dishevelled (DVL) proteins serve as a point of divergence for β-catenin-dependent and -independent signaling pathways involving the family of Frizzled (FZD) ligands and cell-surface WNT receptors. We recently discovered the apparent regulated localization of dishevelled-2 (DVL2) and AGS3 to distinct cellular puncta, suggesting that the two proteins interact as part of various cell signaling systems. To address this hypothesis, we asked the following questions: (1) do AGS3 signaling pathways influence the activation of β-catenin (CTNNB1)-regulated transcription through the WNT-Frizzled-Dishevelled axis, and (2) is the AGS3 and DVL2 interaction regulated? The interaction of AGS3 and DVL2 was regulated by protein phosphorylation, subcellular distribution, and a cell-surface G-protein-coupled receptor. These data, and the commonality of functional system impacts observed for AGS3 and DVL2, suggest that the AGS3-DVL2 complex presents an unexpected path for functional integration within the cell.This article has an associated First Person interview with the first author of the paper.

Gαi2 Signaling Regulates Inflammasome Priming and Cytokine Production by Biasing Macrophage Phenotype Determination

Macrophages exist as innate immune subsets that exhibit phenotypic heterogeneity and functional plasticity. Their phenotypes are dictated by inputs from the tissue microenvironment. G-protein-coupled receptors are essential in transducing signals from the microenvironment, and heterotrimeric Gα signaling links these receptors to downstream effectors. Several Gα_i-coupled G-protein-coupled receptors have been implicated in macrophage polarization. In this study, we use genetically modified mice to investigate the role of Gα_i2 on inflammasome activity and macrophage polarization. We report that Gα_i2 in murine bone marrow-derived macrophages (BMDMs) regulates IL-1β release after activation of the NLRP3, AIM2, and NLRC4 inflammasomes. We show this regulation stems from the biased polarity of Gα_i2 deficient (Gnai2 ^-/-) and RGS-insensitive Gα_i2 (Gnai2 ^G184S/G184S) BMDMs. We determined that although Gnai2 ^G184S/G184S BMDMs (excess Gα_i2 signaling) have a tendency toward classically activated proinflammatory (M1) phenotype, Gnai2^-/- BMDMs (Gα_i2 deficient) are biased toward alternatively activated anti-inflammatory (M2) phenotype. Finally, we find that Gα_i2-deficient macrophages have increased Akt activation and IFN-β production but defects in ERK1/2 and STAT3 activation after LPS stimulation. Gα_i2-deficient macrophages also exhibit increased STAT6 activation after IL-4 stimulation. In summary, our data indicates that excess Gα_i2 signaling promotes an M1 macrophage phenotype, whereas Gα_i2 signaling deficiency promotes an M2 phenotype. Understanding Gα_i2-mediated effects on macrophage polarization may bring to light insights regarding disease pathogenesis and the reprogramming of macrophages for the development of novel therapeutics.

Role of G-proteins and phosphorylation in the distribution of AGS3 to cell puncta

Activator of G-protein signaling 3 (AGS3, also known as GPSM1) exhibits broad functional diversity and oscillates among different subcellular compartments in a regulated manner. AGS3 consists of a tetratricopeptide repeat (TPR) domain and a G-protein regulatory (GPR) domain. Here, we tested the hypothesis that phosphorylation of the AGS3 GPR domain regulates its subcellular distribution and functionality. In contrast to the cortical and/or diffuse non-homogeneous distribution of wild-type (WT) AGS3, an AGS3 construct lacking all 24 potential phosphorylation sites in the GPR domain localized to cytosolic puncta. This change in localization was revealed to be dependent upon phosphorylation of a single threonine amino acid (T602). The punctate distribution of AGS3-T602A was rescued by co-expression of Gα_i and Gα_o but not Gα_s or Gα_q Following treatment with alkaline phosphatase, both AGS3-T602A and WT AGS3 exhibited a gel shift in SDS-PAGE as compared to untreated WT AGS3, consistent with a loss of protein phosphorylation. The punctate distribution of AGS3-T602A was lost in an AGS3-A602T conversion mutant, but was still present upon T602 mutation to glutamate or aspartate. These results implicate dynamic phosphorylation as a discrete mechanism to regulate the subcellular distribution of AGS3 and associated functionality.

Cortical progenitor biology: key features mediating proliferation versus differentiation

The cerebral cortex is a highly organized structure whose development depends on diverse progenitor cell types, namely apical radial glia, intermediate progenitors, and basal radial glia cells, which are responsible for the production of the correct neuronal output. In recent years, these progenitor cell types have been deeply studied, particularly basal radial glia and their role in cortical expansion and gyrification. We review here a broad series of factors that regulate progenitor behavior and daughter cell fate. We first describe the different neuronal progenitor types, emphasizing the differences between lissencephalic and gyrencephalic species. We then review key factors shown to influence progenitor proliferation versus differentiation, discussing their roles in progenitor dynamics, neuronal production, and potentially brain size and complexity. Although spindle orientation has been considered a critical factor for mode of division and daughter cell output, we discuss other features that are emerging as crucial for these processes such as organelle and cell cycle dynamics. Additionally, we highlight the importance of adhesion molecules and the polarity complex for correct cortical development. Finally, we briefly discuss studies assessing progenitor multipotency and its possible contribution to the production of specific neuronal populations. This review hence summarizes recent aspects of cortical progenitor cell biology, and pinpoints emerging features critical for their behavior.

Regulation of Chemokine Signal Integration by Activator of G-Protein Signaling 4 (AGS4)

Activator of G-protein signaling 4 (AGS4)/G-protein signaling modulator 3 (Gpsm3) contains three G-protein regulatory (GPR) motifs, each of which can bind Gαi-GDP free of Gβγ We previously demonstrated that the AGS4-Gαi interaction is regulated by seven transmembrane-spanning receptors (7-TMR), which may reflect direct coupling of the GPR-Gαi module to the receptor analogous to canonical Gαβγ heterotrimer. We have demonstrated that the AGS4-Gαi complex is regulated by chemokine receptors in an agonist-dependent manner that is receptor-proximal. As an initial approach to investigate the functional role(s) of this regulated interaction in vivo, we analyzed leukocytes, in which AGS4/Gpsm3 is predominantly expressed, from AGS4/Gpsm3-null mice. Loss of AGS4/Gpsm3 resulted in mild but significant neutropenia and leukocytosis. Dendritic cells, T lymphocytes, and neutrophils from AGS4/Gpsm3-null mice also exhibited significant defects in chemoattractant-directed chemotaxis and extracellular signal-regulated kinase activation. An in vivo peritonitis model revealed a dramatic reduction in the ability of AGS4/Gpsm3-null neutrophils to migrate to primary sites of inflammation. Taken together, these data suggest that AGS4/Gpsm3 is required for proper chemokine signal processing in leukocytes and provide further evidence for the importance of the GPR-Gαi module in the regulation of leukocyte function.

Choose Delicately and Reuse Adequately: The Newly Revealed Process of Autophagy

Autophagy is a degradation system for intracellular components. One of the roles of autophagy is the prompt removal of damaged organelles. Another unique role is to supply resources that maintain metabolism in response to the cellular nutritional state. Precise management of all the components in the autophagic system is essential for cellular health. Especially important are the selectivity of target cargos for autophagy, and the coordination of autophagy with the lysosomal catabolic process. This review outlines our current understanding of autophagy and discusses potential therapeutic perspectives. Emphasis will be given to lysosomal function as a central controller of metabolism, and to selective autophagy as a key mechanism for the efficient removal of dysfunctional organelles.

Activator of G-Protein Signaling 3-Induced Lysosomal Biogenesis Limits Macrophage Intracellular Bacterial Infection

Many intracellular pathogens cause disease by subverting macrophage innate immune defense mechanisms. Intracellular pathogens actively avoid delivery to or directly target lysosomes, the major intracellular degradative organelle. In this article, we demonstrate that activator of G-protein signaling 3 (AGS3), an LPS-inducible protein in macrophages, affects both lysosomal biogenesis and activity. AGS3 binds the Gi family of G proteins via its G-protein regulatory (GoLoco) motif, stabilizing the Gα subunit in its GDP-bound conformation. Elevated AGS3 levels in macrophages limited the activity of the mammalian target of rapamycin pathway, a sensor of cellular nutritional status. This triggered the nuclear translocation of transcription factor EB, a known activator of lysosomal gene transcription. In contrast, AGS3-deficient macrophages had increased mammalian target of rapamycin activity, reduced transcription factor EB activity, and a lower lysosomal mass. High levels of AGS3 in macrophages enhanced their resistance to infection by Burkholderia cenocepacia J2315, Mycobacterium tuberculosis, and methicillin-resistant Staphylococcus aureus, whereas AGS3-deficient macrophages were more susceptible. We conclude that LPS priming increases AGS3 levels, which enhances lysosomal function and increases the capacity of macrophages to eliminate intracellular pathogens.

Cell Division Modes and Cleavage Planes of Neural Progenitors during Mammalian Cortical Development

During mammalian brain development, neural progenitor cells undergo symmetric proliferative divisions followed by asymmetric neurogenic divisions. The division mode of these self-renewing progenitors, together with the cell fate of their progeny, plays critical roles in determining the number of neurons and, ultimately, the size of the adult brain. In the past decade, remarkable progress has been made toward identifying various types of neuronal progenitors. Recent technological advances in live imaging and genetic manipulation have enabled us to link dynamic cell biological events to the molecular mechanisms that control the asymmetric divisions of self-renewing progenitors and have provided a fresh perspective on the modes of division of these progenitors. In addition, comparison of progenitor repertoires between species has provided insight into the expansion and the development of the complexity of the brain during mammalian evolution.

B Lymphocyte-Specific Loss of Ric-8A Results in a Gα Protein Deficit and Severe Humoral Immunodeficiency

Resistance to inhibitors of cholinesterase 8A (Ric-8A) is a highly evolutionarily conserved cytosolic protein initially identified in Caenorhabditis elegans, where it was assigned a regulatory role in asymmetric cell divisions. It functions as a guanine nucleotide exchange factor for Gαi, Gαq, and Gα12/13 and as a molecular chaperone required for the initial association of nascent Gα subunits with cellular membranes in embryonic stem cell lines. To test its role in hematopoiesis and B lymphocytes specifically, we generated ric8 (fl/fl) vav1-cre and ric8 (fl/fl) mb1-cre mice. The major hematopoietic cell lineages developed in the ric8 (fl/fl) vav1-cre mice, notwithstanding severe reduction in Gαi2/3, Gαq, and Gα13 proteins. B lymphocyte-specific loss of Ric-8A did not compromise bone marrow B lymphopoiesis, but splenic marginal zone B cell development failed, and B cells underpopulated lymphoid organs. The ric8 (fl/fl) mb1-cre B cells exhibited poor responses to chemokines, abnormal trafficking, improper in situ positioning, and loss of polarity components during B cell differentiation. The ric8 (fl/fl) mb1-cre mice had a severely disrupted lymphoid architecture and poor primary and secondary Ab responses. In B lymphocytes, Ric-8A is essential for normal Gα protein levels and is required for B cell differentiation, trafficking, and Ab responses.

Heterotrimeric G protein-mediated signaling and its non-canonical regulation in the heart

Heterotrimeric guanine nucleotide-binding proteins (G proteins) regulate a multitude of signaling pathways in mammalian cells by transducing signals from G protein-coupled receptors (GPCRs) to effectors, which in turn regulate cellular function. In the myocardium, G protein signaling occurs in all cardiac cell types and is centrally involved in the regulation of heart rate, pump function, and vascular tone and in the response to hemodynamic stress and injury. Perturbations in G protein-mediated signaling are well known to contribute to cardiac hypertrophy, failure, and arrhythmias. Most of the currently used drugs for cardiac and other diseases target GPCR signaling. In the canonical G protein signaling paradigm, G proteins that are located at the cytoplasmic surface of the plasma membrane become activated after an agonist-induced conformational change of GPCRs, which then allows GTP-bound Gα and free Gβγ subunits to activate or inhibit effector proteins. Research over the past two decades has markedly broadened the original paradigm with a GPCR-G protein-effector at the cell surface at its core by revealing novel binding partners and additional subcellular localizations for heterotrimeric G proteins that facilitate many previously unrecognized functional effects. In this review, we focus on non-canonical and epigenetic-related mechanisms that regulate heterotrimeric G protein expression, activation, and localization and discuss functional consequences using cardiac examples where possible. Mechanisms reviewed involve microRNAs, histone deacetylases, chaperones, alternative modes of G protein activation, and posttranslational modifications. Some of these newly characterized mechanisms may be further developed into novel strategies for the treatment of cardiac disease and beyond.

Genetic Determinants of Type 2 Diabetes in Asians

Type 2 diabetes (T2D) has become a major health problem throughout the world and the epidemic is particularly severe in Asian countries. Compared with European populations, Asians tend to develop diabetes at a younger age and at much higher incidence rates given the same amount of weight gain. Genome-wide association studies (GWAS) have identified over 70 loci associated with T2D. Although the majority of GWAS results were conducted in populations of European ancestry, recent GWAS in Asians have made important contributions to the identification of T2D susceptibility loci. These studies not only confirmed T2D susceptibility loci initially identified in European populations, but also identified novel susceptibility loci that provide new insights into the pathophysiology of diseases. In this article, we review GWAS results of T2D conducted in East and South Asians and compare them to those of European populations. Currently identified T2D genetic variants do not appear to explain the phenomenon that Asians are more susceptible to T2D than European populations, suggesting further studies in Asian populations are needed.

Overexpression of activator of G-protein signaling 3 decreases the proliferation of esophageal squamous cell carcinoma

BACKGROUND

Activator of G-protein Signaling 3 (AGS3, also known as GPSM1), is related to cell cycle progression. We investigated the expression of AGS3 in human esophageal squamous cell carcinoma (ESCC) and the therapeutic effect of chemotherapy drugs.

METHODS

Immunohistochemistry and Western blot analysis were performed for AGS3 in 85ESCC samples. The data were correlated with clinicopathological features. The univariate and multivariate survival analyses were also performed to determine its prognostic significance. The effect of overexpression of AGS3 on proliferation of esophageal carcinoma TE1 cells was analyzed by serum starvation.

RESULTS

AGS3 was down regulated in ESCC as compared with the adjacent normal tissue. Low expression of AGS3 was associated with tumor grade (P=0.002), and AGS3 was negatively correlated with proliferation marker Ki-67 (P<0.01). Univariate analysis showed that AGS3 expression did have a remarkable prediction for poor prognosis (P=0.004), while in vitro, the expression of AGS3 was down regulated with release from serum starvation of TE1 cells.

CONCLUSIONS

This study shows that AGS3 is an important regulator of ESCC proliferation.

Localization and expression profile of Group I and II Activators of G-protein Signaling in the kidney

Activators of G-protein Signaling (AGS) are a family of accessory proteins that were discovered as modulators of heterotrimeric G-protein subunits. The primary aim of the present study was to localize Group I and II AGS proteins and determine the renal expression profile using immunohistochemistry and quantitative RT-PCR, respectively, during normal and injured states of the kidney. Group I AGS1 was found to be predominantly localized to the proximal tubule, Group II AGS3 and AGS5 were exclusively localized to the distal tubular segments, and Group II AGS6 was ubiquitously expressed in every nephron segment of the rodent kidney. In rat kidneys following ischemia-reperfusion injury (IRI), Group I AGS1 mRNA was dramatically increased after 24 h by fivefold (P < 0.05), whereas Group II AGS3 and AGS4 mRNA was significantly decreased at the same time point (P < 0.05). No significant change in the transcript levels were detected at other time points for any of the AGS genes between control and IRI groups. In polycystic diseased kidneys, mRNA levels for AGS3, AGS4 and AGS6 was significantly increased (P < 0.05) by 75-80 % in PCK rat kidneys. The identification of Group I and II AGS mRNA and protein in the kidney may provide insight into the potential mechanism of action during normal and varying states of renal disease or injury.

Activator of G protein signaling 3 forms a complex with resistance to inhibitors of cholinesterase-8A without promoting nucleotide exchange on Gα(i3)

Activator of G protein signaling 3 (AGS3) is a guanine nucleotide dissociation inhibitor (GDI) which stabilizes the Gα(i/o) subunits as an AGS3/Gα(i/o)-GDP complex. It has recently been demonstrated in reconstitution experiments that the AGS3/Gα(i/o)-GDP complex may act as a substrate of resistance to inhibitors of cholinesterase 8A (Ric-8A), a guanine exchange factor (GEF) for heterotrimeric Gα proteins. Since the ability of Ric-8A to activate Gα(i/o) subunits that are bound to AGS3 in a cellular environment has not been confirmed, we thus examined the effect of Ric-8A on cAMP accumulation in HEK293 cells expressing different forms of AGS3 and Gα(i3). Co-immunoprecipitation assays indicate that full-length AGS3 and its N- and C-terminal truncated mutants can interact with Ric-8A in HEK293 cells. Yeast two-hybrid assay further confirmed that Ric-8A can directly bind to AGS3S, a short form of AGS3 which is endogenously expressed in heart. However, Ric-8A failed to facilitate Gα(i)-induced suppression of adenylyl cyclase, suggesting that it may not serve as a GEF for AGS3/Gα(i/o)-GDP complex in a cellular environment.

Defective chemokine signal integration in leukocytes lacking activator of G protein signaling 3 (AGS3)

Activator of G-protein signaling 3 (AGS3, gene name G-protein signaling modulator-1, Gpsm1), an accessory protein for G-protein signaling, has functional roles in the kidney and CNS. Here we show that AGS3 is expressed in spleen, thymus, and bone marrow-derived dendritic cells, and is up-regulated upon leukocyte activation. We explored the role of AGS3 in immune cell function by characterizing chemokine receptor signaling in leukocytes from mice lacking AGS3. No obvious differences in lymphocyte subsets were observed. Interestingly, however, AGS3-null B and T lymphocytes and bone marrow-derived dendritic cells exhibited significant chemotactic defects as well as reductions in chemokine-stimulated calcium mobilization and altered ERK and Akt activation. These studies indicate a role for AGS3 in the regulation of G-protein signaling in the immune system, providing unexpected venues for the potential development of therapeutic agents that modulate immune function by targeting these regulatory mechanisms.

Activators of G protein signaling exhibit broad functionality and define a distinct core signaling triad

Activators of G protein signaling (AGS), initially discovered in the search for receptor-independent activators of G protein signaling, define a broad panel of biologic regulators that influence signal transfer from receptor to G-protein, guanine nucleotide binding and hydrolysis, G protein subunit interactions, and/or serve as alternative binding partners for Gα and Gβγ independently of the classic heterotrimeric Gαβγ. AGS proteins generally fall into three groups based upon their interaction with and regulation of G protein subunits: group I, guanine nucleotide exchange factors (GEF); group II, guanine nucleotide dissociation inhibitors; and group III, entities that bind to Gβγ. Group I AGS proteins can engage all subclasses of G proteins, whereas group II AGS proteins primarily engage the Gi/Go/transducin family of G proteins. A fourth group of AGS proteins with selectivity for Gα16 may be defined by the Mitf-Tfe family of transcription factors. Groups I-III may act in concert, generating a core signaling triad analogous to the core triad for heterotrimeric G proteins (GEF + G proteins + effector). These two core triads may function independently of each other or actually cross-integrate for additional signal processing. AGS proteins have broad functional roles, and their discovery has advanced new concepts in signal processing, cell and tissue biology, receptor pharmacology, and system adaptation, providing unexpected platforms for therapeutic and diagnostic development.

Normal autophagic activity in macrophages from mice lacking Gαi3, AGS3, or RGS19

In macrophages autophagy assists antigen presentation, affects cytokine release, and promotes intracellular pathogen elimination. In some cells autophagy is modulated by a signaling pathway that employs Gαi3, Activator of G-protein Signaling-3 (AGS3/GPSM1), and Regulator of G-protein Signaling 19 (RGS19). As macrophages express each of these proteins, we tested their importance in regulating macrophage autophagy. We assessed LC3 processing and the formation of LC3 puncta in bone marrow derived macrophages prepared from wild type, Gnai3(-/-), Gpsm1(-/-), or Rgs19(-/-) mice following amino acid starvation or Nigericin treatment. In addition, we evaluated rapamycin-induced autophagic proteolysis rates by long-lived protein degradation assays and anti-autophagic action after rapamycin induction in wild type, Gnai3(-/-), and Gpsm1(-/-) macrophages. In similar assays we compared macrophages treated or not with pertussis toxin, an inhibitor of GPCR (G-protein couple receptor) triggered Gαi nucleotide exchange. Despite previous findings, the level of basal autophagy, autophagic induction, autophagic flux, autophagic degradation and the anti-autophagic action in macrophages that lacked Gαi3, AGS3, or RGS19; or had been treated with pertussis toxin, were similar to controls. These results indicate that while Gαi signaling may impact autophagy in some cell types it does not in macrophages.

The G protein regulator AGS-3 allows C. elegans to alter behaviors in response to food deprivation

Behavioral responses to food deprivation are a fundamental aspect of nervous system function in all animals. In humans, these behavioral responses prevent dieting from being an effective remedy for obesity. Several signaling molecules in the mammalian brain act through G proteins of the Gα_i/o family to mediate responses to food restriction. The mechanisms for neural response to food deprivation may be conserved across species, allowing the power of genetic model organisms to generate insights relevant to the problem of human obesity. In a recent study, we found that C. elegans uses Gα_o signaling to mediate a number of behavioral changes that occur after food deprivation. Food deprivation causes biochemical changes in the G Protein Regulator (GPR) domain protein AGS-3 and AGS-3, together with the guanine nucleotide exchange factor RIC-8, activates Gα_o signaling to alter food-seeking behavior. These proteins are all conserved in the human brain. Thus the study of behavioral responses to food deprivation in C. elegans may reveal the details of conserved molecular mechanisms underlying neural responses to food deprivation.

Translocation of activator of G-protein signaling 3 to the Golgi apparatus in response to receptor activation and its effect on the trans-Golgi network

Group II activators of G-protein signaling play diverse functional roles through their interaction with Gαi, Gαt, and Gαo via a G-protein regulatory (GPR) motif that serves as a docking site for Gα-GDP. We recently reported the regulation of the AGS3-Gαi signaling module by a cell surface, seven-transmembrane receptor. Upon receptor activation, AGS3 reversibly dissociates from the cell cortex, suggesting that it may function as a signal transducer with downstream signaling implications, and this question is addressed in the current report. In HEK-293 and COS-7 cells expressing the α2A/D-AR and Gαi3, receptor activation resulted in the translocation of endogenous AGS3 and AGS3-GFP from the cell cortex to a juxtanuclear region, where it co-localized with markers of the Golgi apparatus (GA). The agonist-induced translocation of AGS3 was reversed by the α2-AR antagonist rauwolscine. The TPR domain of AGS3 was required for agonist-induced translocation of AGS3 from the cell cortex to the GA, and the translocation was blocked by pertussis toxin pretreatment or by the phospholipase Cβ inhibitor U73122. Agonist-induced translocation of AGS3 to the GA altered the functional organization and protein sorting at the trans-Golgi network. The regulated movement of AGS3 between the cell cortex and the GA offers unexpected mechanisms for modulating protein secretion and/or endosome recycling events at the trans-Golgi network.

Genome-wide transcriptome analysis between small-tail Han sheep and the Surabaya fur sheep using high-throughput RNA sequencing

The small-tail Han sheep and the Surabaya fur sheep are two local breeds in north China, which are characterized by high-fecundity and low-prolificacy breed respectively. Significant genetic differences between these two breeds have provided increasing interests in the identification and utilization of major prolificacy genes in these sheep. High prolificacy is a complex trait, and it is difficult to comprehensively identify the candidate genes related to this trait using the single molecular biology technique. To understand the molecular mechanisms of fecundity and provide more information about high prolificacy candidate genes in high- and low-fecundity sheep, we explored the utility of next-generation sequencing technology in this work. A total of 1.8 Gb sequencing reads were obtained and resulted in more than 20 000 contigs that averaged ∼300 bp in length. Ten differentially expressed genes were further verified by quantitative real-time RT-PCR to confirm the reliability of RNA-seq results. Our work will provide a basis for the future research of the sheep reproduction.

Drosophila neuroblasts: a model for stem cell biology

Drosophila neuroblasts, the stem cells of the developing fly brain, have emerged as a key model system for neural stem cell biology and have provided key insights into the mechanisms underlying asymmetric cell division and tumor formation. More recently, they have also been used to understand how neural progenitors can generate different neuronal subtypes over time, how their cell cycle entry and exit are coordinated with development, and how proliferation in the brain is spared from the growth restrictions that occur in other organs upon starvation. In this Primer, we describe the biology of Drosophila neuroblasts and highlight the most recent advances made using neuroblasts as a model system.

G-protein signaling modulator 1 deficiency accelerates cystic disease in an orthologous mouse model of autosomal dominant polycystic kidney disease

Polycystic kidney diseases are the most common genetic diseases that affect the kidney. There remains a paucity of information regarding mechanisms by which G proteins are regulated in the context of polycystic kidney disease to promote abnormal epithelial cell expansion and cystogenesis. In this study, we describe a functional role for the accessory protein, G-protein signaling modulator 1 (GPSM1), also known as activator of G-protein signaling 3, to act as a modulator of cyst progression in an orthologous mouse model of autosomal dominant polycystic kidney disease (ADPKD). A complete loss of Gpsm1 in the Pkd1(V/V) mouse model of ADPKD, which displays a hypomorphic phenotype of polycystin-1, demonstrated increased cyst progression and reduced renal function compared with age-matched cystic Gpsm1(+/+) and Gpsm1(+/-) mice. Electrophysiological studies identified a role by which GPSM1 increased heteromeric polycystin-1/polycystin-2 ion channel activity via Gβγ subunits. In summary, the present study demonstrates an important role for GPSM1 in controlling the dynamics of cyst progression in an orthologous mouse model of ADPKD and presents a therapeutic target for drug development in the treatment of this costly disease.

Regulation of the G-protein regulatory-Gαi signaling complex by nonreceptor guanine nucleotide exchange factors

Group II activators of G-protein signaling (AGS) serve as binding partners for Gα(i/o/t) via one or more G-protein regulatory (GPR) motifs. GPR-Gα signaling modules may be differentially regulated by cell surface receptors or by different nonreceptor guanine nucleotide exchange factors. We determined the effect of the nonreceptor guanine nucleotide exchange factors AGS1, GIV/Girdin, and Ric-8A on the interaction of two distinct GPR proteins, AGS3 and AGS4, with Gα(il) in the intact cell by bioluminescence resonance energy transfer (BRET) in human embryonic kidney 293 cells. AGS3-Rluc-Gα(i1)-YFP and AGS4-Rluc-Gα(i1)-YFP BRET were regulated by Ric-8A but not by Gα-interacting vesicle-associated protein (GIV) or AGS1. The Ric-8A regulation was biphasic and dependent upon the amount of Ric-8A and Gα(i1)-YFP. The inhibitory regulation of GPR-Gα(i1) BRET by Ric-8A was blocked by pertussis toxin. The enhancement of GPR-Gα(i1) BRET observed with Ric-8A was further augmented by pertussis toxin treatment. The regulation of GPR-Gα(i) interaction by Ric-8A was not altered by RGS4. AGS3-Rluc-Gα(i1)-YFP and AGS4-Rluc-G-Gα(i1)-YFP BRET were observed in both pellet and supernatant subcellular fractions and were regulated by Ric-8A in both fractions. The regulation of the GPR-Gα(i1) complex by Ric-8A, as well as the ability of Ric-8A to restore Gα expression in Ric8A(-/-) mouse embryonic stem cells, involved two helical domains at the carboxyl terminus of Ric-8A. These data indicate a dynamic interaction between GPR proteins, Gα(i1) and Ric-8A, in the cell that influences subcellular localization of the three proteins and regulates complex formation.

The G-protein regulator LGN modulates the activity of the NO receptor soluble guanylate cyclase

sGC (soluble guanylate cyclase) is the main mediator of NO signalling. Biochemical and physiological studies suggest that, besides NO, in vivo regulation of sGC involves direct interaction with other proteins. Using yeast two-hybrid screening, we identified that the multidomain LGN (Leu-Gly-Asn repeat-enriched protein) interacts with both α1 and β1 sGC subunits. LGN and sGC co-localized in the cell cytoplasm, and the LGN-sGC complex was co-immunoprecipitated from cells expressing both proteins and from native tissues. Their interaction requires the N-terminal tetratricopeptide repeats of LGN, but does not require the N-terminal portions of α1 or β1 sGC subunits. Overexpression of LGN decreases the activity of cellular sGC, whereas knockdown of LGN mRNA and protein correlated with increased sGC activity. Although purified LGN interacts directly with purified sGC, the inhibitory effect in vitro is observed only after supplementation of cell lysate to the reaction. Although resting sGC and sGC activated by the stimulator BAY41-2272 have very similar LGN-IC50 values to the NO-stimulated sGC, they have a much higher Hill coefficient, suggesting co-operative binding with respect to LGN in the low-activated state of sGC. AGS3 (activator of G-protein signalling 3), the closest LGN homologue, also inhibits sGC. The interaction of sGC with these scaffolding proteins may expand the cross-talk between NO/cGMP signalling and other cellular pathways and tailor sGC function to specific tissues or signals.

Group II activators of G-protein signalling and proteins containing a G-protein regulatory motif

Beyond the core triad of receptor, Gαβγ and effector, there are multiple accessory proteins that provide alternative modes of signal input and regulatory adaptability to G-protein signalling systems. Such accessory proteins may segregate a signalling complex to microdomains of the cell, regulate the basal activity, efficiency and specificity of signal propagation and/or serve as alternative binding partners for Gα or Gβγ independent of the classical heterotrimeric Gαβγ complex. The latter concept led to the postulate that Gα and Gβγ regulate intracellular events distinct from their role as transducers for cell surface seven-transmembrane span receptors. One general class of such accessory proteins is defined by AGS proteins or activators of G-protein signalling that refer to mammalian cDNAs identified in a specific yeast-based functional screen. The discovery of AGS proteins and related entities revealed a number of unexpected mechanisms for regulation of G-protein signalling systems and expanded functional roles for this important signalling system.

Mouse inscuteable induces apical-basal spindle orientation to facilitate intermediate progenitor generation in the developing neocortex

Neurons in the mammalian neocortex arise from asymmetric divisions of progenitors residing in the ventricular zone. While in most progenitor divisions, the mitotic spindle is parallel to the ventricular surface, some progenitors reorient the spindle and divide in oblique orientations. Here, we use conditional deletion and overexpression of mouse Inscuteable (mInsc) to analyze the relevance of spindle reorientation in cortical progenitors. Mutating mInsc almost abolishes oblique and vertical mitotic spindles, while mInsc overexpression has the opposite effect. Our data suggest that oblique divisions are essential for generating the correct numbers of neurons in all cortical layers. Using clonal analysis, we demonstrate that spindle orientation affects the rate of indirect neurogenesis, a process where progenitors give rise to basal progenitors, which in turn divide symmetrically into two differentiating neurons. Our results indicate that the orientation of progenitor cell divisions is important for correct lineage specification in the developing mammalian brain.

Structural basis for interaction between the conserved cell polarity proteins Inscuteable and Leu-Gly-Asn repeat-enriched protein (LGN)

Interaction between the mammalian cell polarity proteins mInsc (mammalian homologue of Inscuteable) and Leu-Gly-Asn repeat-enriched protein (LGN), as well as that between their respective Drosophila homologues Inscuteable and Partner of Inscuteable (Pins), plays crucial roles in mitotic spindle orientation, a process contributing to asymmetric cell division. Here, we report a crystal structure of the LGN-binding domain (LBD) of human mInsc complexed with the N-terminal tetratricopeptide repeat (TPR) motifs of human LGN at 2.6-Å resolution. In the complex, mInsc-LBD adopts an elongated structure with three binding modules--an α-helix, an extended region, and a β-sheet connected with a loop--that runs antiparallel to LGN along the concave surface of the superhelix formed by the TPRs. Structural analysis and structure-based mutagenesis define residues that are critical for mInsc-LGN association, and reveal that the activator of G-protein signaling 3 (AGS3)-binding protein Frmpd1 [4.1/ezrin/radixin/moesin (FERM) and PSD-95/Dlg/ZO-1 (PDZ) domain-containing protein 1] and its relative Frmpd4 interact with LGN via a region homologous to a part of mInsc-LBD, whereas nuclear mitotic apparatus protein (NuMA) and the C terminus of LGN recognize the TPR domain in a manner different from that by mInsc. mInsc binds to LGN with the highest affinity (K(D) ≈ 2.4 nM) and effectively replaces the Frmpd proteins, NuMA, and the LGN C terminus, suggesting the priority of mInsc in binding to LGN. We also demonstrate, using mutant proteins, that mInsc-LGN interaction is vital for stabilization of LGN and for intracellular localization of mInsc.

AGS-3 alters Caenorhabditis elegans behavior after food deprivation via RIC-8 activation of the neural G protein G αo

Proteins containing the G protein regulator (GPR) domain bind the major neural G protein Gα(o) in vitro. However, the biological functions of GPR proteins in neurons remain undefined, and based on the in vitro activities of GPR proteins it is unclear whether these proteins activate or inhibit G protein signaling in vivo. We found that the conserved GPR domain protein AGS-3 activates Gα(o) signaling in vivo to allow Caenorhabditis elegans to alter several behaviors after food deprivation, apparently so that the animals can more effectively seek food. AGS-3 undergoes a progressive change in its biochemical fractionation upon food deprivation, suggesting that effects of food deprivation are mediated by modifying this protein. We analyzed one C. elegans food-regulated behavior in depth; AGS-3 activates Gα(o) in the ASH chemosensory neurons to allow food-deprived animals to delay response to the aversive stimulus octanol. Genetic epistasis experiments show the following: (1) AGS-3 and the guanine nucleotide exchange factor RIC-8 act in ASH in a mutually dependent fashion to activate Gα(o); (2) this activation requires interaction of the GPR domains of AGS-3 with Gα(o); and (3) Gα(o)-GTP is ultimately the signaling molecule that acts in ASH to delay octanol response. These results identify a biological role for AGS-3 in response to food deprivation and indicate the mechanism for its activation of Gα(o) signaling in vivo.

Resistance to age-related, normal body weight gain in RGS2 deficient mice

RGS2 (regulator of G protein signaling 2) is known to limit signals mediated via Gq- and Gs-coupled GPCRs (G protein coupled receptors), and it has been implicated in the differentiation of several cells types. The physiology of RGS2 knockout mice (rgs2(-/-)) has been studied in some detail, however, a metabolic phenotype has not previously been reported. We observed that old (21-24month) rgs2(-/-) mice weigh much less than wild-type C57BL/6 controls, and exhibit greatly reduced fat deposits, decreased serum lipids, and low leptin levels. Lower weight was evident as early as four weeks and continued throughout life. Younger adult male rgs2(-/-) mice (4-8months) were found to show similar strain-related differences as the aged animals, as well improved glucose clearance and insulin sensitivity, and enhanced beta-adrenergic and glucagon signaling in isolated hepatocytes. In addition, rgs2(-/-) pre-adipocytes had reduced levels of differentiation markers (Peroxisome proliferator-activated receptor γ (PPARγ); lipoprotein lipase (Lpl); CCAAT/enhancer binding protein α (CEBPα)) and also rgs2(-/-) white adipocytes were small relative to controls, suggesting altered adipogenesis. In wild-type animals, RGS2 mRNA was decreased in brown adipose tissue after cold exposure (7 h at 4 °C) but increased in white adipose tissue in response to a high fat diet, also suggesting a role in lipid storage. No differences between strains were detected with respect to food intake, energy expenditure, GPCR-stimulated lipolysis, or adaptive thermogenesis. In conclusion this study points to RGS2 as being an important regulatory factor in controlling body weight and adipose function.

Identification of transcription factor E3 (TFE3) as a receptor-independent activator of Gα16: gene regulation by nuclear Gα subunit and its activator

Receptor-independent G-protein regulators provide diverse mechanisms for signal input to G-protein-based signaling systems, revealing unexpected functional roles for G-proteins. As part of a broader effort to identify disease-specific regulators for heterotrimeric G-proteins, we screened for such proteins in cardiac hypertrophy using a yeast-based functional screen of mammalian cDNAs as a discovery platform. We report the identification of three transcription factors belonging to the same family, transcription factor E3 (TFE3), microphthalmia-associated transcription factor, and transcription factor EB, as novel receptor-independent activators of G-protein signaling selective for Gα(16). TFE3 and Gα(16) were both up-regulated in cardiac hypertrophy initiated by transverse aortic constriction. In protein interaction studies in vitro, TFE3 formed a complex with Gα(16) but not with Gα(i3) or Gα(s). Although increased expression of TFE3 in heterologous systems had no influence on receptor-mediated Gα(16) signaling at the plasma membrane, TFE3 actually translocated Gα(16) to the nucleus, leading to the induction of claudin 14 expression, a key component of membrane structure in cardiomyocytes. The induction of claudin 14 was dependent on both the accumulation and activation of Gα(16) by TFE3 in the nucleus. These findings indicate that TFE3 and Gα(16) are up-regulated under pathologic conditions and are involved in a novel mechanism of transcriptional regulation via the relocalization and activation of Gα(16).

Loss of activator of G-protein signaling 3 impairs renal tubular regeneration following acute kidney injury in rodents

The intracellular mechanisms underlying renal tubular epithelial cell proliferation and tubular repair following ischemia-reperfusion injury (IRI) remain poorly understood. In this report, we demonstrate that activator of G-protein signaling 3 (AGS3), an unconventional receptor-independent regulator of heterotrimeric G-protein function, influences renal tubular regeneration following IRI. In rat kidneys exposed to IRI, there was a temporal induction in renal AGS3 protein expression that peaked 72 h after reperfusion and corresponded to the repair and recovery phase following ischemic injury. Renal AGS3 expression was localized predominantly to the recovering outer medullary proximal tubular cells and was highly coexpressed with Ki-67, a marker of cell proliferation. Kidneys from mice deficient in the expression of AGS3 exhibited impaired renal tubular recovery 7 d following IRI compared to wild-type AGS3-expressing mice. Mechanistically, genetic knockdown of endogenous AGS3 mRNA and protein in renal tubular epithelial cells reduced cell proliferation in vitro. Similar reductions in renal tubular epithelial cell proliferation were observed following incubation with gallein, a selective inhibitor of Gβγ subunit activity, and lentiviral overexpression of the carboxyl-terminus of G-protein-coupled receptor kinase 2 (GRK2ct), a scavenger of Gβγ subunits. In summary, these data suggest that AGS3 acts through a novel receptor-independent mechanism to facilitate renal tubular epithelial cell proliferation and renal tubular regeneration.

Structural determinants of affinity enhancement between GoLoco motifs and G-protein alpha subunit mutants

GoLoco motif proteins bind to the inhibitory G(i) subclass of G-protein α subunits and slow the release of bound GDP; this interaction is considered critical to asymmetric cell division and neuro-epithelium and epithelial progenitor differentiation. To provide protein tools for interrogating the precise cellular role(s) of GoLoco motif/Gα(i) complexes, we have employed structure-based protein design strategies to predict gain-of-function mutations that increase GoLoco motif binding affinity. Here, we describe fluorescence polarization and isothermal titration calorimetry measurements showing three predicted Gα(i1) point mutations, E116L, Q147L, and E245L; each increases affinity for multiple GoLoco motifs. A component of this affinity enhancement results from a decreased rate of dissociation between the Gα mutants and GoLoco motifs. For Gα(i1)(Q147L), affinity enhancement was seen to be driven by favorable changes in binding enthalpy, despite reduced contributions from binding entropy. The crystal structure of Gα(i1)(Q147L) bound to the RGS14 GoLoco motif revealed disorder among three peptide residues surrounding a well defined Leu-147 side chain. Monte Carlo simulations of the peptide in this region showed a sampling of multiple backbone conformations in contrast to the wild-type complex. We conclude that mutation of Glu-147 to leucine creates a hydrophobic surface favorably buried upon GoLoco peptide binding, yet the hydrophobic Leu-147 also promotes flexibility among residues 511-513 of the RGS14 GoLoco peptide.

Regulation of the AGS3·G{alpha}i signaling complex by a seven-transmembrane span receptor

G-protein signaling modulators (GPSM) play diverse functional roles through their interaction with G-protein subunits. AGS3 (GPSM1) contains four G-protein regulatory motifs (GPR) that directly bind Gα(i) free of Gβγ providing an unusual scaffold for the "G-switch" and signaling complexes, but the mechanism by which signals track into this scaffold are not well understood. We report the regulation of the AGS3·Gα(i) signaling module by a cell surface, seven-transmembrane receptor. AGS3 and Gα(i1) tagged with Renilla luciferase or yellow fluorescent protein expressed in mammalian cells exhibited saturable, specific bioluminescence resonance energy transfer indicating complex formation in the cell. Activation of α(2)-adrenergic receptors or μ-opioid receptors reduced AGS3-RLuc·Gα(i1)-YFP energy transfer by over 30%. The agonist-mediated effects were inhibited by pertussis toxin and co-expression of RGS4, but were not altered by Gβγ sequestration with the carboxyl terminus of GRK2. Gα(i)-dependent and agonist-sensitive bioluminescence resonance energy transfer was also observed between AGS3 and cell-surface receptors typically coupled to Gα(i) and/or Gα(o) indicating that AGS3 is part of a larger signaling complex. Upon receptor activation, AGS3 reversibly dissociates from this complex at the cell cortex. Receptor coupling to both Gαβγ and GPR-Gα(i) offer additional flexibility for systems to respond and adapt to challenges and orchestrate complex behaviors.

Receptor-regulated interaction of activator of G-protein signaling-4 and Galphai

Activator of G-protein signaling-4 (AGS4), via its three G-protein regulatory motifs, is well positioned to modulate G-protein signal processing by virtue of its ability to bind Galpha(i)-GDP subunits free of Gbetagamma. Apart from initial observations on the biochemical activity of the G-protein regulatory motifs of AGS4, very little is known about the nature of the AGS4-G-protein interaction, how this interaction is regulated, or where the interaction takes place. As an initial approach to these questions, we evaluated the interaction of AGS4 with Galpha(i1) in living cells using bioluminescence resonance energy transfer (BRET). AGS4 and Galpha(i1) reciprocally tagged with either Renilla luciferase (RLuc) or yellow fluorescent protein (YFP) demonstrated saturable, specific BRET signals. BRET signals observed between AGS4-RLuc and Galpha(i1)-YFP were reduced by G-protein-coupled receptor activation, and this agonist-induced reduction in BRET was blocked by pertussis toxin. In addition, specific BRET signals were observed for AGS4-RLuc and alpha(2)-adrenergic receptor-Venus, which were Galpha(i)-dependent and reduced by agonist, indicating that AGS4-Galpha(i) complexes are receptor-proximal. These data suggest that AGS4-Galpha(i) complexes directly couple to a G-protein-coupled receptor and may serve as substrates for agonist-induced G-protein activation.

Identification of a deubiquitinating enzyme as a novel AGS3-interacting protein

Activator of G protein Signaling 3 (AGS3) is a receptor-independent G protein activator that has been implicated in multiple biological events such as brain development, neuroplasticity and addiction, cardiac function, Golgi structure/function, macroautophagy and metabolism. However, how AGS3 is regulated is little known. We demonstrate here that AGS3 interacts with a ubiquitin specific protease USP9x, and this interaction is at least partially mediated through the C-terminal G protein regulatory domain of AGS3. Knockdown of USP9x causes a moderate reduction in the level of AGS3. In contrast, overexpression of either USP9x or its deubiquitinating domain UCH increases the amount of AGS3, whereas expression of the mutant UCH domain that lacks deubiquitinating activity does not have the same effect. As previously observed in AGS3 knockdown cells, the localization of several marker proteins of the late Golgi compartments is disturbed in cells depleted of USP9x. Taken together, our study suggests that USP9x can modulate the level of a subpopulation of AGS3, and this modulation plays a role in regulating the structure of the late Golgi compartments. Finally, we have found that levels of AGS3 and USP9x are co-regulated in the prefrontal cortex of rats withdrawn from repeated cocaine treatment. In conjunction with the above data, this observation indicates a potential role of USP9X in the regulation of the AGS3 level during cocaine-induced neuroplasticity.

Distribution of activator of G-protein signaling 3 within the aggresomal pathway: role of specific residues in the tetratricopeptide repeat domain and differential regulation by the AGS3 binding partners Gi(alpha) and mammalian inscuteable

AGS3, a receptor-independent activator of G-protein signaling, is involved in unexpected functional diversity for G-protein signaling systems. AGS3 has seven tetratricopeptide (TPR) motifs upstream of four G-protein regulatory (GPR) motifs that serve as docking sites for Gialpha-GDP. The positioning of AGS3 within the cell and the intramolecular dynamics between different domains of the proteins are likely key determinants of their ability to influence G-protein signaling. We report that AGS3 enters into the aggresome pathway and that distribution of the protein is regulated by the AGS3 binding partners Gialpha and mammalian Inscuteable (mInsc). Gialpha rescues AGS3 from the aggresome, whereas mInsc augments the aggresome-like distribution of AGS3. The distribution of AGS3 to the aggresome is dependent upon the TPR domain, and it is accelerated by disruption of the TPR organizational structure or introduction of a nonsynonymous single-nucleotide polymorphism. These data present AGS3, G-proteins, and mInsc as candidate proteins involved in regulating cellular stress associated with protein-processing pathologies.