Inhibition of Ca2+ signalling by the sphingosine 1-phosphate receptor S1P1

The lysophospholipid, sphingosine I-phosphate (S I P), regulates a multitude of cellular functions by activating specific G protein-coupled receptors (GPCRs) (S1P(1-5), plus three newly identified S1P receptors). The G(i)-coupled S1P(1) receptor inhibits adenylyl cyclase, stimulates mitogen-activated protein kinases (MAP kinases) and cell migration, and is required for blood vessel maturation. Here, we report that S I P I inhibits Ca2+ signalling in a number of cell types. In HEK-293 cells, which endogenously express S1P(1-3), overexpression of S1P(1) reduced intracellular free Ca2+. concentration ([Ca2+](i)) increases induced by various receptor agonists as well as thapsigargin. The inhibitory Ca2+ signalling of S1P(1) was blocked by pertussis toxin (PTX) and the protein kinase C (PKC) inhibitor, Go6976, and imitated by phorbol ester and overexpression of classical PKC isoforms. Activation of S1P(1) stably expressed in RH7777 cells, which endogenously do not express S1P receptors, also inhibited Ca2+ signalling, without mediating Ca2+ mobilization on its own. It is concluded that the widely expressed S1P receptor S1P(2) inhibits Ca2+ signalling, most likely via G(i) proteins and classical PKC isoforms. Co-expression of S1P(1) with S1P(3), but not S1P(2) reversed the inhibitory effect of S1P(1), furthermore suggesting a specific interplay of S1P receptor subtypes usually found within a single cell type. (C) 2003 Elsevier Science Inc. All rights reserved.