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

Thapliyal A, Bannister RA, Hanks C, Adams BA. The monomeric G proteins AGS1 and Rhes selectively influence G alpha i-dependent signaling to modulate N-type (Ca(V)2.2) calcium channels. Am J Physiol Cell Physiol 295: C1417-C1426, 2008. First published September 24, 2008; doi: 10.1152/ajpcell.00341.2008.-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 G alpha i and Rhes selectively influencing G alpha s. Here, we demonstrate that AGS1 and Rhes trigger nearly identical modulation of N-type Ca2+ channels (Ca(V)2.2) by selectively altering G alpha i-dependent signaling. Whole-cell currents were recorded from HEK293 cells expressing Ca(V)2.2 and G alpha i- or G alpha s-coupled receptors. AGS1 and Rhes reduced basal current densities and triggered tonic voltage-dependent (VD) inhibition of Ca(V)2.2. Additionally, each protein attenuated agonist-initiated channel inhibition through G alpha i-coupled receptors without reducing channel inhibition through a G alpha s-coupled receptor. The above effects of AGS1 and Rhes were blocked by pertussis toxin (PTX) or by expression of a G beta gamma-sequestering peptide (masGRK3ct). Transfection with HRas, KRas2, Rap1A-G12V, Rap2B, Rheb2, or Gem failed to duplicate the effects of AGS1 and Rhes on Ca(V)2.2. Our data provide the first demonstration that AGS1 and Rhes exhibit similar if not identical signaling properties since both trigger tonic G beta gamma signaling and both attenuate receptor-initiated signaling by the G beta gamma subunits of PTX-sensitive G proteins. These results are consistent with the possibility that AGS1 and Rhes modulate Ca2+ influx through Ca(V)2.2 channels under more physiological conditions and thereby influence Ca2+-dependent events such as neurosecretion.