Identification of p2y9/GPR23 as a novel G protein-coupled receptor for lysophosphatidic acid, structurally distant from the Edg family

Lysophosphatidic acid (LPA) is a bioactive lipid mediator with diverse physiological and pathological actions on many types of cells. LPA has been widely considered to elicit its biological functions through three types of G protein-coupled receptors, Edg-2 (endothelial cell differentiation gene-2)/LPA(1)/vzg-1 (ventricular zone gene-1), Edg-4/LPA(2), and Edg-7/LPA(3). We identified an orphan G protein-coupled receptor, p2y(9)/GPR23, as the fourth LPA receptor (LPA(4)). Membrane fractions of RH7777 cells transiently expressing p2y(9)/GPR23 displayed a specific binding for 1-oleoyl-LPA with a K-d value of around 45 nM. Competition binding and reporter gene assays showed that p2y(9)/GPR23 preferred structural analogs of LPA with a rank order of 1-oleoyl- > 1-stearoyl- > 1-palmitoyl- > 1-myristoyl- > 1-alkyl- > 1-alkenyl-LPA. In Chinese hamster ovary cells expressing p2y(9)/GPR23, 1-oleoyl- LPA induced an increase in intracellular Ca2+ concentration and stimulated adenylyl cyclase activity. Quantitative real-time PCR demonstrated that mRNA of p2y(9)/GPR23 was significantly abundant in ovary compared with other tissues. Interestingly, p2y(9)/GPR23 shares only 20-24% amino acid identities with Edg-2/LPA1, Edg-4/LPA(2), and Edg-7/LPA(3), and phylogenetic analysis also shows that p2y(9)/GPR23 is far distant from the Edg family. These facts suggest that p2y(9)/GPR23 has evolved from different ancestor sequences from the Edg family.