Sphingosine 1-phosphate induces cyclooxygenase-2 via Ca2+-dependent, but MAPK-independent mechanism in rat vascular smooth muscle cells

The effects of sphingosine 1-phosphate (S1P) on prostaglandin I2 (PGI2) production and cyclooxygenase (COX) expression in cultured rat vascular smooth muscle cells (VSMCs) were investigated. S1P stimulated PGI2 production in a concentration-dependent manner, which was completely suppressed by NS-398, a selective COX-2 inhibitor, as determined by radioimmunoassay. S1P stimulated COX-2 protein and mRNA expressions in a concentration- and time-dependent manner, while it had no effect on COX-1 expression. S1P2 and S1P3 receptors mRNA were abundantly expressed in rat VSMCs. Suramin, an antagonist of S1P3 receptor, almost completely inhibited S1P-induced COX-2 expression. Pretreatment of VSMCs with pertussis toxin (PTX) partially, but significantly inhibited S1P-induced PGI2 production and COX-2 expression. S1P also activated extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (MAPK). However, neither PD 98059, a selective inhibitor of ERK activation, nor SB 203580, a selective inhibitor of p38 MAPK, had a significant inhibitory effect on S1P-induced COX-2 expression, suggesting that the MAPK activation does not play main roles in S1P-induced COX-2 induction. S1P-induced COX-2 expression was inhibited by PP2, an inhibitor of Src-family tyrosine kinase, Ca2+ depletion, and GF 109203X, an inhibitor of protein kinase C (PKC). These results suggest that S1P stimulates COX-2 induction in rat VSMCs through mechanisms involving Ca2+-dependent PKC and Src-family tyrosine kinase activation via S1P3 receptor coupled to PTX-sensitive and -insensitive G proteins.