Differential modulation of mu‐opioid receptor signaling to adenylyl cyclase by regulators of G protein signaling proteins 4 or 8 and 7 in permeabilised C6 cells is Gα subtype dependent

Abstract

J. Neurochem. (2009) 112, 1026–1034. Abstract Regulators of G protein signaling (RGS) proteins act as GTPase‐accelerating protein to negatively modulate G protein signaling and are defined by a conserved RGS domain with considerable amino acid diversity. To determine the effects of specific, purified RGS proteins on mu‐opioid signaling, C6 cells stably expressing a mu‐opioid receptor were rendered permeable to proteins by treatment with digitonin. Mu‐opioid inhibition of forskolin‐stimulated adenylyl cyclase by [d‐Ala2,N‐Me‐Phe4,Gly‐ol]‐enkephalin (DAMGO), a mu‐specific opioid peptide, remained fully intact in permeabilized cells. Purified RGS domain of RGS4 added to permeabilized cells resulted in a twofold loss in DAMGO potency but had no effect in cells expressing RGS‐insensitive G proteins. The inhibitory effect of DAMGO was reduced to the same extent by purified RGS4 and RGS8. In contrast, the RGS domain of RGS7 had no effect and inhibited the action of RGS8 as a result of weak physical association with Gαi2 and minimal GTPase‐accelerating protein activity in C6 cell membranes. These data suggest that differences in conserved RGS domains of specific RGS proteins contribute to differential regulation of opioid signaling to adenylyl cyclase and that a permeabilized cell model is useful for studying the effects of specific RGS proteins on aspects of G protein‐coupled receptor signaling.

The role of regulator of G protein signaling 4 in delta-opioid receptor-mediated behaviors

“…For example, RGS4 was shown to regulate the rewarding effects of morphine and the antinociceptive effects of the MOPr agonists methadone and fentanyl but not morphine (Han et al 2010). In addition, in heterologous expression systems, RGS4 can regulate MOPr signaling (Leonidas et al 2009; Talbot et al 2010). Together, these data suggest that RGS4 proteins may have the capacity to regulate MOPr-mediated signaling and behaviors as long as the appropriate proteins are co-expressed in the necessary cells and/or circuits.…”

RGS inhibition at Gα i2 selectively potentiates 5-HT1A–mediated antidepressant effects

“…RGS proteins primarily function as GTPase accelerating proteins (GAPS) that bind to and rapidly deactivate Gα subunits, thereby greatly limiting the lifetime of active Gα and Gβγ signaling molecules. Thus, RGS proteins are the principle negative regulators of Gαi/o-mediated signaling (4)(5)(6), and evidence suggests that they participate in shaping behavioral responses stemming from several types of dopaminergic, opioidergic, and serotonergic neurotransmission (7)(8)(9)(10). However, because of the large number of RGS proteins, defining the regulatory contribution of each has proven difficult, in part because of functional redundancy.…”

μ-Opioid receptors and regulators of G protein signaling (RGS) proteins: From a symposium on new concepts in mu-opioid pharmacology

“…The RGS4 knockout mouse model provides a good example. This mouse shows little if any phenotypic behavioral responses to morphine compared with wild-type littermates (Grillet et al, 2005; Han et al, 2010), yet profound effects of RGS4 on morphine signaling in vitro have been reported (Georgoussi et al, 2006; Xie et al, 2007; Talbot et al, 2010b). Conversely, the discrete localization of many RGS proteins, especially in the central nervous system (Gold et al, 1997), together with the complex nature of certain RGS protein families, does indicate potential selectivity for certain receptors and their cognate heterotrimeric G proteins.…”