The monomeric G proteins AGS1 and Rhes selectively influence Galphai-dependent signaling to modulate N-type (CaV2.2) calcium channels.
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 Galphai and Rhes selectively influencing Galphas. Here, we demonstrate that AGS1 and Rhes trigger nearly identical modulation of N-type Ca(2+) channels (Ca(V)2.2) by selectively altering Galphai-dependent signaling. Whole-cell currents were recorded from HEK293 cells expressing Ca(V)2.2 and Galphai- or Galphas-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 Galphai-coupled receptors without reducing channel inhibition through a Galphas-coupled receptor. The above effects of AGS1 and Rhes were blocked by pertussis toxin (PTX) or by expression of a Gbetagamma-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 Gbetagamma signaling and both attenuate receptor-initiated signaling by the Gbetagamma subunits of PTX-sensitive G proteins. These results are consistent with the possibility that AGS1 and Rhes modulate Ca(2+) influx through Ca(V)2.2 channels under more physiological conditions and thereby influence Ca(2+)-dependent events such as neurosecretion.
Thapliyal
Ashish
A
Dept. of Biology, Utah State Univ., 5305 Old Main Hill, Logan, UT 84322, USA.
Bannister
Roger A
RA
Hanks
Christopher
C
Adams
Brett A
BA
D000818:Animals; D020864:Calcium Channels, N-Type / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002460:Cell Line; D018679:Cholinergic Agonists / Q000494:pharmacology; D005090:Exodeoxyribonucleases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000187:drug effects / Q000378:metabolism*; D044387:GTP-Binding Protein beta Subunits / Q000378:metabolism; D044388:GTP-Binding Protein gamma Subunits / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008564:Membrane Potentials; D037342:Pertussis Toxin / Q000494:pharmacology; D010750:Phosphoproteins; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D011817:Rabbits; D043585:Receptor, Muscarinic M2 / Q000819:agonists / Q000378:metabolism; D018343:Receptors, Adrenergic, beta-2 / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D014162:Transfection
D020864:Calcium Channels, N-Type; D002217:Carbachol; D018679:Cholinergic Agonists; D005090:Exodeoxyribonucleases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D019204:GTP-Binding Proteins; D037342:Pertussis Toxin; D010750:Phosphoproteins; D011506:Proteins; D043585:Receptor, Muscarinic M2; D018343:Receptors, Adrenergic, beta-2; C118981:G-protein Beta gamma; C429526:three prime repair exonuclease 1; C486702:RASD2 protein, human