Differential Coupling of the Sphingosine 1-Phosphate Receptors Edg-1, Edg-3, and H218/Edg-5 to the Gi, Gq, and G12 Families of Heterotrimeric G Proteins

Abstract

Sphingosine 1-phosphate (S1P) is one of several bioactive phospholipids that exert profound mitogenic and morphogenic actions. Originally characterized as a second messenger, S1P is now recognized to achieve many of its effects through cell surface, G protein-coupled receptors. We used a subunit-selective [(35)S]GTPgammaS binding assay to investigate whether the variety of actions exerted through Edg-1, a recently identified receptor for S1P, might be achieved through multiple G proteins. We found, employing both Sf9 and HEK293 cells, that Edg-1 activates only members of the G(i) family, and not G(s), G(q), G(12), or G(13). We additionally established that Edg-1 activates G(i) in response not only to S1P but also sphingosylphosphorylcholine; no effects of lysophosphatidic acid through Edg-1 were evident. Our assays further revealed a receptor(s) for S1P endogenous to HEK293 cells that mediates activation of G(13) as well as G(i). Because several of the biological actions of S1P are assumed to proceed through the G(12/13) family, we tested whether Edg-3 and H218/Edg-5, two other receptors for S1P, might have a broader coupling profile than Edg-1. Indeed, Edg-3 and H218/Edg-5 communicate not only with G(i) but also with G(q) and G(13). These studies represent the first characterization of S1P receptor activity through G proteins directly and establish fundamental differences in coupling.