Characterization of Lysophosphatidic Acid and Sphingosine-1-Phosphate- Mediated Signal Transduction in Rat Cortical Oligodendrocytes NAICHEN YU,* KAREN D. LARIOSA-WILLINGHAM, FEN-FEN LIN, MICHAEL WEBB, AND TADIMETI S. RAO Molecular Neuroscience, Merck Research Laboratories, San Diego, California KEY WORDS lysophospholipid receptors; lysophosphatidic acid; sphingosine-1- phosphate; oligodendrocytes; receptors; G-protein; MAP kinase; pro- tein kinase C; phospholipase C; calcium ABSTRACT Lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) have been proposed to play a key role in oligodendrocyte maturation and myelinogenesis. In this study, we examined lysophospholipid receptor gene expression in differentiated rat oligodendrocyte cultures and signaling downstream of lysophospholipid receptor activa- tion by LPA and S1P. Differentiated oligodendrocytes express mRNAs encoding lyso- phospholipid receptors with the relative abundance of lpa1  s1p5  s1p1 = s1p2 = lpa3  s1p3. LPA and S1P transiently increased phosphorylation of extracellular signal- regulated kinase (ERK) with EC 50 values of 956 and 168 nM, respectively. LPA- and S1P-induced ERK phosphorylation was dependent on the activation of mitogen-acti- vated protein kinase (MAPK), phospholipase C (PLC), and protein kinase C (PKC), but was insensitive to pertussis toxin (PTX). LPA increased intracellular calcium levels in oligodendrocytes and these increases were partially blocked by a PLC inhibitor but not by PTX. In contrast, S1P was not found to induce measurable changes of intracellular calcium. These results taken together suggest that lysophospholipid receptor activation involves receptor coupling to heterotrimeric G q subunits with consequent activation of PLC, PKC, and MAPK pathways leading to ERK phosphorylation. © 2003 Wiley-Liss, Inc. INTRODUCTION Lysophosphatidic acid (LPA) and sphingosine-1- phosphate (S1P) are endogenous bioactive phospho- lipid agonists of a family of G-protein-coupled lysophos- pholipid receptors (lpR), previously described as endothelial differentiation gene (Edg) receptors. So far, eight members of the family have been discovered in mammalian cells: lpa1, lpa2, and lpa3 receptors for LPA (formerly known as Edg-2, Edg-4, and Edg-7, re- spectively), and s1p1, s1p2, s1p3, s1p4, and s1p5 recep- tors for S1P [formerly known as Edg-1, Edg-5, Edg-3, Edg-6, and Edg-8, respectively; for reviews of nomen- clature, see Chun et al. (2002)]. LPA induces a variety of biological actions, including proliferation, differentiation, survival, and chemotaxis (Moolenaar, 1995; Tokumura, 1995). LPA receptors couple to three out of four primary classes of hetero- meric G-proteins, G i/o ,G q , and G 12/13 , but not to G s . Activation of LPA receptors results in wide spectrum of intracellular events, such as increases in inositol phos- phates and intracellular calcium (An et al., 1998), in- hibition of adenylyl cyclase (Hecht et al., 1996; Tigyi et al., 1996; Arimura et al., 1998), activation of kinases such as protein kinase C (PKC) (Seewald et al., 1999; Kim et al., 2000; Paolucci et al., 2000; Rui et al., 2000), *Correspondence to: Dr. Naichen Yu, Merck Research Laboratories, 3535 General Atomics Court, Building 1, San Diego, CA 92121. E-mail: naichen_yu@merck.com Received 16 January 2003; Accepted 28 May 2003 DOI 10.1002/glia.10297 GLIA 45:17–27 (2004) © 2003 Wiley-Liss, Inc.