Gbeta5 prevents the RGS7-Galphao interaction through binding to a distinct Ggamma-like domain found in RGS7 and other RGS proteins.
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The G protein beta subunit Gbeta5 deviates significantly from the other four members of Gbeta-subunit family in amino acid sequence and subcellular localization. To detect the protein targets of Gbeta5 in vivo, we have isolated a native Gbeta5 protein complex from the retinal cytosolic fraction and identified the protein tightly associated with Gbeta5 as the regulator of G protein signaling (RGS) protein, RGS7. Here we show that complexes of Gbeta5 with RGS proteins can be formed in vitro from the recombinant proteins. The reconstituted Gbeta5-RGS dimers are similar to the native retinal complex in their behavior on gel-filtration and cation-exchange chromatographies and can be immunoprecipitated with either anti-Gbeta5 or anti-RGS7 antibodies. The specific Gbeta5-RGS7 interaction is determined by a distinct domain in RGS that has a striking homology to Ggamma subunits. Deletion of this domain prevents the RGS7-Gbeta5 binding, although the interaction with Galpha is retained. Substitution of the Ggamma-like domain of RGS7 with a portion of Ggamma1 changes its binding specificity from Gbeta5 to Gbeta1. The interaction of Gbeta5 with RGS7 blocked the binding of RGS7 to the Galpha subunit Galphao, indicating that Gbeta5 is a specific RGS inhibitor. (+info)
Regulators of G protein signaling exhibit distinct patterns of gene expression and target G protein specificity in human lymphocytes.
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The newly recognized regulators of G protein signaling (RGS) attenuate heterotrimeric G protein signaling pathways. We have cloned an IL-2-induced gene from human T cells, cytokine-responsive gene 1, which encodes a member of the RGS family, RGS16. The RGS16 protein binds Gialpha and Gqalpha proteins present in T cells, and inhibits Gi- and Gq-mediated signaling pathways. By comparison, the mitogen-induced RGS2 inhibits Gq but not Gi signaling. Moreover, the two RGS genes exhibit marked differences in expression patterns. The IL-2-induced expression of the RGS16 gene in T cells is suppressed by elevated cAMP, whereas the RGS2 gene shows a reciprocal pattern of regulation by these stimuli. Because the mitogen and cytokine receptors that trigger expression of RGS2 and RGS16 in T cells do not activate heterotrimeric G proteins, these RGS proteins and the G proteins that they regulate may play a heretofore unrecognized role in T cell functional responses to Ag and cytokine activation. (+info)
RGS7 and RGS8 differentially accelerate G protein-mediated modulation of K+ currents.
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The recently discovered family of RGS (regulators of G protein signaling) proteins acts as GTPase activating proteins which bind to alpha subunits of heterotrimeric G proteins. We previously showed that a brain-specific RGS, RGS8 speeds up the activation and deactivation kinetics of the G protein-coupled inward rectifier K+ channel (GIRK) upon receptor stimulation (Saitoh, O., Kubo, Y., Miyatani, Y., Asano, T., and Nakata, H. (1997) Nature 390, 525-529). Here we report the isolation of a full-length rat cDNA of another brain-specific RGS, RGS7. In situ hybridization study revealed that RGS7 mRNA is predominantly expressed in Golgi cells within granule cell layer of cerebellar cortex. We observed that RGS7 recombinant protein binds preferentially to Galphao, Galphai3, and Galphaz. When co-expressed with GIRK1/2 in Xenopus oocytes, RGS7 and RGS8 differentially accelerate G protein-mediated modulation of GIRK. RGS7 clearly accelerated activation of GIRK current similarly with RGS8 but the acceleration effect of deactivation was significantly weaker than that of RGS8. These acceleration properties of RGS proteins may play important roles in the rapid regulation of neuronal excitability and the cellular responses to short-lived stimulations. (+info)
Modulation of renal tubular cell function by RGS3.
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The recently discovered family of regulators of G protein signaling (RGS) accelerates the intrinsic GTPase activity of certain Galpha subunits, thereby terminating G protein signaling. Particularly high mRNA levels of one family member, RGS3, are found in the adult kidney. To establish the temporal and spatial renal expression pattern of RGS3, a polyclonal antiserum was raised against the COOH terminus of RGS3. Staining of mouse renal tissue at different gestational stages revealed high levels of RGS3 within the developing and mature tubular epithelial cells. We tested whether RGS3 can modulate tubular migration, an important aspect of tubular development, in response to G protein-mediated signaling. Several mouse intermedullary collecting duct (mIMCD-3) cell lines were generated that expressed RGS3 under the control of an inducible promoter. Lysophosphatidic acid (LPA) is a potent chemoattractant that mediates its effects through heterotrimeric G proteins. We found that induction of RGS3 significantly reduced LPA-mediated cell migration in RGS3-expressing mIMCD-3 clones, whereas chemotaxis induced by hepatocyte growth factor remained unaffected by RGS3. Our findings suggest that RGS3 modulates tubular functions during renal development and in the adult kidney. (+info)
Region-specific regulation of RGS4 (Regulator of G-protein-signaling protein type 4) in brain by stress and glucocorticoids: in vivo and in vitro studies.
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The present study demonstrates that the regulator of G-protein-signaling protein type 4 (RGS4) is differentially regulated in the locus coeruleus (LC) and the paraventricular nucleus (PVN) of the hypothalamus by chronic stress and glucocorticoid treatments. Acute or chronic administration of corticosterone to adult rats decreased RGS4 mRNA levels in the PVN but increased these levels in the LC. Similarly, chronic unpredictable stress decreased RGS4 mRNA levels in the PVN but had a strong trend to increase these levels in the LC. Chronic stress also decreased RGS4 mRNA levels in the pituitary. The molecular mechanisms of RGS4 mRNA regulation were further investigated in vitro in the LC-like CATH.a cell line and the neuroendocrine AtT20 cell line using the synthetic corticosterone analog dexamethasone. Consistent with the findings in vivo, dexamethasone treatment caused a dose- and time-dependent decrease in RGS4 mRNA levels in AtT20 cells but a dose- and time-dependent increase in CATH.a cells. RGS4 mRNA regulation seen in these two cell lines seems to be attributable, at least in part, to opposite changes in mRNA stability. The differential regulation of RGS4 expression in the LC and in key relays of the hypothalamic-pituitary-adrenal axis could contribute to the brain's region-specific and long-term adaptations to stress. (+info)
A PDZ protein regulates the distribution of the transmembrane semaphorin, M-SemF.
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M-SemF is a membrane-associated, neurally enriched member of the semaphorin family of axon guidance signals. We considered whether the cytoplasmic domain of M-SemF might possess a signaling function and/or might control the distribution of M-SemF on the cell surface. We identify a PDZ-containing neural protein as an M-SemF cytoplasmic domain-associated protein (SEMCAP-1). SEMCAP-2 is a closely related nonneuronal protein. SEMCAP-1 has recently also been identified as GIPC, by virtue of its interaction with the RGS protein GAIP in vitro (De Vries, L., Lou, X., Zhao, G., Zheng, B., and Farquhar, M. G. (1998) Proc. Natl. Acad. Sci. U. S. A. 95, 12340-12345). Expression studies support the notion that SEMCAP-1(GIPC) interacts with M-SemF, but not GAIP, in brain. Lung SEMCAP-2 and SEMCAP-1(GIPC) are potential partners for both GAIP and M-SemF. The protein interaction requires the single PDZ domain of SEMCAP-1(GIPC) and the carboxyl-terminal four residues of M-SemF, ESSV. While SEMCAP-1(GIPC) also interacts with SemC, it does not interact with other proteins containing a class I PDZ binding motif, nor does M-SemF interact with other class I PDZ proteins. Co-expression of SEMCAP-1(GIPC) induces the redistribution of dispersed M-SemF into detergent-resistant aggregates in HEK293 cells. Thus, SEMCAP-1(GIPC) appears to regulate the subcellular distribution of M-SemF in brain, and SEMCAPs could link M-SemF to G protein signal transduction pathways. (+info)
Regulators of G protein signaling proteins as determinants of the rate of desensitization of presynaptic calcium channels.
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Norepinephrine inhibits omega-conotoxin GVIA-sensitive presynaptic Ca2+ channels in chick dorsal root ganglion neurons through two pathways, one mediated by Go and the other by Gi. These pathways desensitize at different rates. We have found that recombinant Galpha interacting protein (GAIP) and regulators of G protein signaling (RGS)4 selectively accelerate the rate of desensitization of Go- and Gi-mediated pathways, respectively. Blockade of endogenous RGS proteins using antibodies raised against Galpha interacting protein and RGS4 slows the rate of desensitization of these pathways in a selective manner. These results demonstrate that different RGS proteins may interact with Gi and Go selectively, giving rise to distinct time courses of transmitter-mediated effects. (+info)
New roles for RGS2, 5 and 8 on the ratio-dependent modulation of recombinant GIRK channels expressed in Xenopus oocytes.
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1. The activation of G protein-regulated inward rectifying potassium (GIRK) channels is modulated by G protein-coupled receptors (GPCRs) via the G protein betagamma subunits and is accelerated by regulators of G protein signalling (RGS). In the present study we investigated the ratio dependence of receptor-mediated activation and deactivation and the influence of new members of the RGS protein family on GIRK currents by coexpressing the recombinant protein subunits in Xenopus oocytes and further analysis of the whole cell currents. 2. The activation of GIRK channels by the muscarinic acetylcholine receptor M2 (M2 mAChR) is strongly dependent on the ratio of receptor to channel in Xenopus oocytes. The increase and on-rate of the amplified current is affected by this ratio. An excess of receptor over channel is necessary for current amplification, while the reverse excess of channel over receptor abolishes the effect. 3. The speed of receptor-mediated activation of GIRK currents is accelerated for a high ratio of receptor to channel, while the time of deactivation is independent of this ratio. 4. Coexpression of RGS2, 5 and 8 accelerates the speed for ACh-mediated activation and deactivation of GIRK1/2 and GIRK1/4 currents. Thereby the receptor/channel/RGS ratio determines the amount of current amplification. 5. Bordetella pertussis toxin completely abolished ACh-mediated current amplification of GIRK channels coexpressed with or without RGS2. 6. Two single point mutations in the RGS2 protein (RGS2(N109S) and RGS2(L180F)) reduced the acceleration of current amplification after ACh application on GIRK1/4 channels compared with RGS2 wild-type protein. (+info)