Antagonism between G_oα and G_qα in Caenorhabditis elegans: the RGS protein EAT-16 is necessary for G_oα signaling and regulates G_qα activity

Abstract

To elucidate the cellular role of the heterotrimeric G protein G_o, we have taken a molecular genetic approach inCaenorhabditis elegans. We screened for suppressors of activated GOA-1 (G_oα) that do not simply decrease its expression and found mutations in only two genes, sag-1 andeat-16. Animals defective in either gene display a hyperactive phenotype similar to that of goa-1 loss-of-function mutants. Double-mutant analysis indicates that both sag-1 andeat-16act downstream of, or parallel to, Goα and negatively regulate EGL-30 (G_qα) signaling. eat-16encodes a regulator of G protein signaling (RGS) most similar to the mammalian RGS7 and RGS9 proteins and can inhibit endogenous mammalian G_q/G_(11) in COS-7 cells. Animals defective in both sag-1 and eat-16 are inviable, but reducing function in egl-30 restores viability, indicating that the lethality of the eat-16; sag-1 double mutant is due to excessive G_qα activity. Analysis of these mutations indicates that the G_o and G_q pathways function antagonistically in C. elegans, and that G_oα negatively regulates the G_q pathway, possibly via EAT-16 or SAG-1. We propose that a major cellular role of G_o is to antagonize signaling by G_q.