Comparative analysis of human and rat S1P5 (edg8):: differential expression profiles and sensitivities to antagonists

Five guanine nucleotide-binding protein-coupled receptors (S1P(1-5)) for the lysophospholipid mediator sphingosine 1-phosphate (SIP) have thus far been described. Whereas tissue distribution and functional properties of the human S1P(1-4) genes are well characterized, only limited functional and expression data are available for S1P(5), todate. Northern blot analysis indicated that human SIP5 (hSIP(5)) is an alternatively spliced gene, with a 5.4-kb transcript that is predominantly expressed in peripheral tissues, and a 2.4-kb transcript expressed in brain, spleen, and peripheral blood leucocytes. In contrast, rat S1P(5) (rS1P(5)) was exclusively detected in brain and skin. Expression of hS1P(5) and rS1P(5) in mammalian CHO-K1 or HEK293 cells conferred onto the cells the ability to mobilize intracellular calcium as determined by a functional Fluorometric Imaging Plate Reader assay, when challenged with S 1 P and dihydro S1P, respectively. Applying a lipid library with 200 bioactive lipids in a functional Fluorometric Imaging Plate Reader assay did not reveal additional agonists. However, both receptors exhibited differential sensitivity towards the S1P- and lysophosphatidic acid-receptor antagonist, suramin: rSIP(5)-mediated intracellular calcium mobilization was partly inhibited by suramin (IC50: 5800 muM), whereas hS1P(5) was completely antagonized (IC50: 130 muM). Both receptors were sensitive towards inhibition with the related drug (8,8'-(carbonylbis(imino-3,1-phenylene))bis(1,3,5-naphthalenetrisulfonic acid)) but IC50 values differed significantly (340 muM for hS1P(5), 4000 muM for rS1P(5)). In addition, rS1P(5) displayed antiproliferative effects in transfected CHO-K1 and HEK293 cells in contrast to hS1P(5). Taken together, our data imply that differences between hS1P(5) and rS1P(5) will be an important point to be considered in the development of selective receptor antagonists. (C) 2002 Elsevier Science Inc. All rights reserved.