The monomeric G proteins AGS1 and Rhes selectively influence Gαi-dependent signaling to modulate N-type (CaV2.2) calcium channels

Abstract

Activator of G protein Signaling 1 (AGS1) and Ras homologue enriched in striatum (Rhes) define a new group of Ras-like monomeric G proteins whose signaling properties and physiological roles are just beginning to be understood. Previous results suggest that AGS1 and Rhes exhibit distinct preferences for heterotrimeric G proteins, with AGS1 selectively influencing Gαi and Rhes selectively influencing Gαs. Here, we demonstrate that AGS1 and Rhes trigger nearly identical modulation of N-type Ca2+channels (CaV2.2) by selectively altering Gαi-dependent signaling. Whole-cell currents were recorded from HEK293 cells expressing CaV2.2 and Gαi- or Gαs-coupled receptors. AGS1 and Rhes reduced basal current densities and triggered tonic voltage-dependent (VD) inhibition of CaV2.2. Additionally, each protein attenuated agonist-initiated channel inhibition through Gαi-coupled receptors without reducing channel inhibition through a Gαs-coupled receptor. The above effects of AGS1 and Rhes were blocked by pertussis toxin (PTX) or by expression of a Gβγ-sequestering peptide (masGRK3ct). Transfection with HRas, KRas2, Rap1A-G12V, Rap2B, Rheb2, or Gem failed to duplicate the effects of AGS1 and Rhes on CaV2.2. Our data provide the first demonstration that AGS1 and Rhes exhibit similar if not identical signaling properties since both trigger tonic Gβγ signaling and both attenuate receptor-initiated signaling by the Gβγ subunits of PTX-sensitive G proteins. These results are consistent with the possibility that AGS1 and Rhes modulate Ca2+influx through CaV2.2 channels under more physiological conditions and thereby influence Ca2+-dependent events such as neurosecretion.