p2y5 is an orphan G protein-coupled receptor that is closely related to the fourth lysophosphatidic acid (LPA) receptor, LPA 4 . Here we report that p2y5 is a novel LPA receptor coupling to the G 13 -Rho signaling pathway. "LPA receptor-null" RH7777 and B103 cells exogenously expressing p2y5 showed [ 3 H]LPA binding, LPA-induced [35 S]guanosine 5-3-O-(thio)triphosphate binding, Rho-dependent alternation of cellular morphology, and G s/13 chimeric protein-mediated cAMP accumulation. LPA-induced contraction of human umbilical vein endothelial cells was suppressed by small interfering RNA knockdown of endogenously expressed p2y5. We also found that 2-acyl-LPA had higher activity to p2y5 than 1-acyl-LPA. A recent study has suggested that p2y5 is an LPA receptor essential for human hair growth. We confirmed that p2y5 is a functional LPA receptor and propose to designate this receptor LPA 6 .Lysophosphatidic acid (LPA 3 ; 1-or 2-acyl-sn-glycero-3-phosphate) is a naturally occurring lipid mediator with diverse biological activities (1, 2). LPA plays important roles in many biological processes, such as the nervous system (3), tumor metastasis (4), wound healing (5), cardiovascular functions (6), and reproduction (7), through its specific G protein-coupled receptors (GPCRs). At least five subtypes of LPA receptors have been identified. Three receptors (LPA 1 (8), LPA 2 (9), and LPA 3 (10, 11)) share about 50% amino acid sequence identities, and form the Edg (endothelial differentiation gene) family together with the GPCRs for sphingosine 1-phosphate. Two additional LPA receptors, p2y9/LPA 4 (12) and GPR92/LPA 5 (13, 14), which show small similarities with the Edg family GPCRs, were recently identified. These LPA receptors, by coupling with different sets of G proteins, transduce various responses in many cell types. Depending on the functional coupling of a given LPA receptor to the G proteins, LPA activates diverse signaling cascades involving phosphoinositide 3-kinase, phospholipase C, mitogen-activated protein kinase, Rho-family GTPase, and adenylyl cyclase (2).The fact that p2y5 shares the highest sequence homology with p2y9/LPA 4 among all GPCRs (12) strongly suggested that LPA is a ligand for p2y5. However, we could not detect LPAinduced Ca 2ϩ mobilization or cAMP level changes in p2y5-overexpressing cells at the time of the identification of p2y9/ LPA 4 as the fourth LPA receptor in our laboratory (12). In the course of the further analysis of p2y5-overexpressing cells, we found that p2y5 actually responded to LPA with activation of the G 13 -Rho signaling pathway. Our results confirm the identification of p2y5 as an LPA receptor and extend the knowledge of the functional roles of LPA.
EXPERIMENTAL PROCEDURESLipids-1-Oleoyl-LPA, 1-palmitoyl-LPA, 1-stearoyl-LPA, 1-myristoyl-LPA, and 1-arachidonoyl-LPA were purchased from Avanti Polar Lipids (Alabaster, AL). 1-Linoleoyl-LPA was from Echelon Biosciences (Salt Lake City, UT). These lipids were stored at Ϫ30°C (10 mM stock in 50% ethanol). Alkyl-OMPT (10 mM stock in d...