RGS7 and RGS8 Differentially Accelerate G Protein-mediated Modulation of K+ Currents

Abstract

The recently discovered family of RGS (regulators of G protein signaling) proteins acts as GTPase activating proteins which bind to ␣ 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 G␣ o , G␣ i3 , and G␣ z . 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.Numerous extracellular signals such as hormones, neurotransmitters, and odors stimulate seven transmembrane-spanning receptors that activate heterotrimeric G proteins. These G proteins function as signal transducing molecules by regulating cellular effectors including enzymes and ion channels (1, 2). The regulatory mechanisms that control G protein signaling have not been fully studied. Recently, a new family of regulators of G protein signaling (RGS) 1 was identified in organisms ranging from yeast to mammals (3, 4). Genetic screenings for negative regulators for pheromone response pathway in yeast identified a protein, Sst2 (5). By genetic and biochemical analyses, Sst2 was revealed to interact directly with G protein ␣ subunit (6). In the last few years, full or partial sequences of 22 RGS proteins have been identified in mammals. All of them share a conserved RGS domain of ϳ120 amino acids (7-15). It has been shown that several RGS proteins (RGS1, RGS3, RGS4, GAIP) attenuate G protein signaling in cultures (9,16,17). Biochemical studies have demonstrated that some RGS members (RGS1, RGS4, RGS10, GAIP, RGSr/RGS16, RET-RGS1) function as GTPase-activating proteins (GAPs) for the Gi family of ␣ subunit, including G␣ o , G␣ i , and transducin (10, 14, 18 -20). Hence, these characterized RGS proteins are proposed to down-regulate G protein signaling in vivo by enhancing the rate of G␣ GTP hydrolysis. However, whether other RGS proteins regulate G protein signalings in a similar manner remains to be established.Because there are many G protein signaling pathways which regulate important functions such as neural transmission in the brain, it is possible that certain RGS proteins might determine a mode of G protein signaling that control neural functions. We searched RGS proteins specifically ...

The R7 Subfamily of RGS Proteins Assists Tachyphylaxis and Acute Tolerance at μ-Opioid Receptors

“…The GAP activities of the RGS6/b5 and RGS11/b5 complexes also appear specific for Goa-GTP (Snow et al, 1998;Posner et al, 1999). However, R7 proteins have been shown to bind to activated Goa, Gi3a, and Gza subunits in rat and mouse brain membrane fractions (Saitoh et al, 1999: Rose et al, 2000Sánchez-Blázquez et al, 2003). It is therefore possible that to show GAP activity on Ga-GTP subunitsFdistinct from GoaFR7/b5 complexes require the assistance of as yet unidentified auxiliary proteins.…”

Regulator of G Protein Signaling 8 (RGS8) Requires Its NH2 Terminus for Subcellular Localization and Acute Desensitization of G Protein-gated K+ Channels

“…Bar, 10 m. that RGS8 speeds up the activation and deactivation kinetics of GIRK upon receptor stimulation. We also reported the RGS8-induced acute desensitization of the receptor-activated GIRK current (11,12). Here, we examined the functional role of the NH 2 -terminal domain, which determines subcellular localization, in the RGS8-mediated modulation of on-off kinetics of GIRK current.…”

“…The acute desensitization of receptor-activated GIRK observed with RGS8 was not apparent with RGS7. Thus, RGS7 and RGS8 were shown to accelerate G protein-mediated modulation of GIRK current differentially (12). What is the structural basis for the weaker off acceleration and reduced desensitization in the case of RGS7?…”

“…We isolated cDNA of RGS8 and identified it as a RGS protein induced in differentiated P19 cells (11). In addition, since RGS7 had been reported to be expressed predominantly in the brain (5), we also isolated a full-length cDNA of RGS7 (12). Biochemical studies indicated that RGS8 binds to G␣ o and G␣ i3 , and that RGS7 binds to G␣ o , G␣ i3 , and G␣ z .…”

Gene-trapped mouse embryonic stem cell-derived cardiac myocytes and human genetics implicate AKAP10 in heart rhythm regulation

“…Interestingly, Akap10 contains two domains with homology to ''regulator of G protein signaling'' (RGS) proteins (13, 18) (SI Fig. 4C), which could alter G protein signaling (19)(20)(21)(22)(23)(24)(25). Because the Akap10 mutant has a dominant effect physiologically, the mutant allele may be interfering with the WT allele.…”