Introduction. Sphingosine 1-phosphate (S1P) is a bioactive lysophospholipid, derived from activated platelet, that is known to induce diverse cellular responses through at least five G-protein-coupled receptors on various cell types. Abnormal platelet and coagulation activation is often seen in patients with gastric cancer. However, neither the effects of this platelet-derived mediator S1P nor the distribution of S1P receptors on the gastric cancer cell are fully understood. The aim of this study was to examine the possible role of S1P and its receptors in the progression of gastric cancer. Materials and methods. We characterized the expression profiles of S1P receptors in nine human gastric cancer cell lines and evaluated the relationship between the responses to S1P and its receptor expression on cell migration by modified Boyden chamber and cell proliferation by MTS assay. Results. Northern blotting analysis has revealed that S1P2 was expressed in all gastric cancer cell lines to varying degrees, and S1P3 was expressed in four cell lines. S1P1 expression was weak, and no significant expression of either S1P4 or S1P5 was detected. The addition of S1P markedly stimulated the migration of MKN1 and HCG-27 that dominantly expressed S1P3, and the effect was potently inhibited by pertussis toxin or wortmannin. In contrast, S1P significantly inhibited the migration of AZ-521 that expressed S1P2 exclusively. This indicates that the balance between S1P2- and S1P3-mediated signals might be critical in determining the metastatic response of gastric cancer cells to S1P. S1P elicited weak but significant antiproliferative effects on all of the three cell lines, although the effects were not major. In these cells, S1P induced extracellular signal-regulated kinase (ERK) phosphorylation with transient Akt dephosphorylation that may cause the weak effects on proliferation. Conclusions. Our results suggest that the S1P receptor expression may critically determine the biological behavior of gastric cancers and thus therapeutic interventions directed at each S1P receptor might be clinically effective in preventing metastasis in gastric cancer. (c) 2006 Elsevier Inc. All rights reserved.