RGS17/RGSZ2, a novel regulator of Gi/o, Gz, and Gq signaling

Abstract

To identify novel regulators of Gαo, the most abundant G-protein in brain, we used yeast two-hybrid screening with constitutively active Gαo as bait and identified a new regulator of G-protein signaling (RGS) protein, RGS17 (RGSZ2), as a novel human member of the RZ (or A) subfamily of RGS proteins. RGS17 contains an aminoterminal cysteine-rich motif and a carboxyl-terminal RGS domain with highest homology to hRGSZ1- and hRGS-Gα-interacting protein. RGS17 RNA was strongly expressed as multiple species in cerebellum and other brain regions. The interactions between hRGS17 and active forms of Gαi1-3, Gαo, Gαz, or Gαq but not Gαs were detected by yeast two-hybrid assay, in vitro pull-down assay, and co-immunoprecipitation studies. Recombinant RGS17 acted as a GTPase-activating protein (GAP) on free Gαi2 and Gαo under pre-steady-state conditions, and on M2-muscarinic receptor-activated Gαi1, Gαi2, Gαi3, Gαz, and Gαo in steady-state GTPase assays in vitro. Unlike RGSZ1, which is highly selective for Gz, RGS17 exhibited limited selectivity for Go among Gi/G o proteins. All RZ family members reduced dopamine-D2/ Gαi-mediated inhibition of cAMP formation and abolished thyrotropin-releasing hormone receptor/Gαq-mediated calcium mobilization. RGS17 is a new RZ member that preferentially inhibits receptor signaling via Gi/o, Gz, and Gq over Gs to enhance cAMP-dependent signaling and inhibit calcium signaling. Differences observed between in vitro GAP assays and whole-cell signaling suggest additional determinants of the G-protein specificity of RGS GAP effects that could include receptors and effectors.