Activation of a High Affinity Gi Protein-coupled Plasma Membrane Receptor by Sphingosine-1-phosphate

Abstract

Sphingosine-1-phosphate (SPP) has attracted much attention as a possible second messenger controlling cell proliferation and motility and as an intracellular Ca(2+)-releasing agent. Here, we present evidence that SPP activates a G protein-coupled receptor in the plasma membrane of various cells, leading to increase in cytoplasmic Ca2+ concentration ([Ca2+]i), inhibition of adenylyl cyclase, and opening of G protein-regulated potassium channels. In human enbryonic kidney (HEK) cells, SPP potently (EC50, 2 nM) and rapidly increased [Ca2+]i in a pertussis toxin-sensitive manner. Pertussis toxin-sensitive increase in [Ca2+]i was also observed with sphingosylphosphorylcholine (EC50, 460 nM), whereas other sphingolipids, including ceramide-1-phosphate, N-palmitoyl-sphingosine, psychosine, and D-erythro-sphingosine at micromolar concentrations did not or only marginally increased [Ca2+]i. Furthermore, SPP inhibited forskolin-stimulated cAMP accumulation in HEK cells and increased binding of guanosine 5'3-O-(thio) triphosphate to HEK cell membranes. Rapid [Ca2+]i responses were also observed in human transitional bladder carcinoma (J82) cells, monkey COS-1 cells, mouse NIH 3T3 cells, Chinese hamster ovary (CHO-K1) cells, and rat C6 glioma cells, whereas human HL-60 leukemia cells and human erythroleukemia cells failed to respond to SPP. In guinea pig atrial myocytes, SPP activated Gi protein-regulated inwardly rectifying potassium channels. Activation of these channels occurred strictly when SPP was applied at the extracellular face of atrial myocyte plasma membrane as measured in cell-attached and inside-out patch clamp current recordings. We conclude that SPP, in addition to its proposed direct action on intracellular Ca2+ stores, interacts with a high affinity Gi protein-coupled receptor in the plasma membrane of apparently many different cell types.