Comparison of intrinsic activities of the putative sphingosine 1- phosphate receptor subtypes to regulate several signaling pathways in their cDNA-transfected Chinese hamster ovary cells

Abstract

We examined the actions of sphingosine 1-phosphate (S1P) on signaling pathways in Chinese hamster ovary cells transfected with putative SIP receptor subtypes, i.e. Edg-1, AGR16/H218 (Edg-5), and Edg-3. Among these receptor-transfected cells, there was no significant difference in the expressing numbers of the S1P receptors and their affinities to S1P, which were estimated by [3H]S1P binding to the cells. In vector-transfected cells, S1P slightly increased cytosolic Ca2+ concentration ([Ca2+](i)) in association with inositol phosphate production, reflecting phospholipase C activation; the S1P-induced actions were markedly enhanced in the Edg-3- transfected cells and moderately so in the AGR16-transfected cells. In comparison with vector-transfected cells, the S1P-induced [Ca2+](i) increase was also slightly enhanced in the Edg-1-transfected cells. In all cases, the inositol phosphate and Ca2+ responses to SIP were partially inhibited by pertussis toxin (PTX). S1P also significantly increased cAMP content in a PTX-insensitive manner in all the transfected cells; the rank order of their intrinsic activity of SIP receptor subtypes was AGR16 > Edg-3 > Edg-1. In the presence of forskolin, however, SIP significantly inhibited cAMP accumulation at a lower concentration (1-100 nM) of SIP in a manner sensitive to PTX in the Edg. 1-transfected cells but not in either the Edg-3 or AGR16-transfected cells. As for cell migration activity evaluated by cell number across the filter of blind Boyden chamber, Edg-1 and Edg-3 were equally potent, but AGR16 was ineffective. Thus, S1P receptors may couple to both PTX-sensitive and -insensitive G-proteins, resulting in the selective regulation of the phospholipase C-Ca2+ system, adenylyl cyclase-cAMP system, and cell migration activity, according to the receptor subtype.