G-protein-coupled receptor-mediated activation of rap GTPases: characterization of a novel Galphai regulated pathway.
Ras proteins mediate the proliferative effects of G-protein-coupled receptors (GPCRs), but the role of Rap proteins in GPCR signaling is unclear. We have developed a novel cellular proliferation assay for examining signal transduction to Rap utilizing Ras-rap chimeras that respond selectively to Rap-specific exchange factors, but which stimulate cellular proliferation through Ras effectors. Both the D1 dopamine receptor (Gs-coupled) and the 5HT1E serotonin receptor (Gi-coupled) mediated cellular proliferation in a Ras/rap chimera-dependent manner. Responses to both receptors were PKA-independent. Both receptors activated Ras/rap and full-length Rap as measured by activation-specific probes. Pertussis toxin blocked Ras/rap-dependent responses to 5HT1E but not D1. Ras/rap-dependent responses to both receptors were insensitive to beta-gamma scavengers. Responses to 5HT1E, but not D1, were sensitive to inhibition by a dominant-negative C3G fragment, by the Src-like kinase inhibitors PP1 and PP2, and by a dominant-negative mutant of Src. Very similar data were obtained for two other Gi-coupled receptors, the D2 dopamine receptor and the alpha2C adrenergic receptor. A constitutively active mutant of Galphai2 also mediated Ras/rap-dependent responses. These data indicate that GPCRs coupled to pertussis-toxin-sensitive G-proteins activate Rap through a Galpha subunit, C3G, and Src-dependent pathway.
Weissman
Jacques T
JT
ACADIA Pharmaceuticals Inc., 3911 Sorrento Valley Blvd, San Diego, CA 92121, USA.
Ma
Jian-Nong
JN
Essex
Anthony
A
Gao
Yan
Y
Burstein
Ethan S
ES
D000818:Animals; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D004789:Enzyme Activation; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000502:physiology*; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000502:physiology; D051379:Mice; D041681:NIH 3T3 Cells; D010766:Phosphorylation; D043562:Receptors, G-Protein-Coupled / Q000502:physiology*; D020668:rap GTP-Binding Proteins / Q000378:metabolism*; D018631:ras Proteins / Q000502:physiology
D043562:Receptors, G-Protein-Coupled; D017868:Cyclic AMP-Dependent Protein Kinases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D019205:GTP-Binding Protein alpha Subunits, Gs; D020668:rap GTP-Binding Proteins; D018631:ras Proteins