Sphingosine-1-phosphate mediates COX-2 expression and PGE₂/IL-6 secretion via c-Src-Dependent AP-1 activation

Sphingosine-1-phosphate (S1P) has been shown to regulate cyclooxygenase-2 (COX-2)/prostaglandin E₂ (PGE₂) expression and IL-6 secretion in various respiratory diseases. However, the mechanisms underlying S1P-induced COX-2 expression and PGE₂ production in human tracheal smooth muscle cells (HTSMCs) remain unclear. Here we demonstrated that S1P markedly induced COX-2 expression. S1P also induced PGE₂ and IL-6 secretion which were reduced by the inhibitors of COX-2 (NS-398 and celecoxib). Pretreatment with the inhibitor of S1PR1 (W123), S1PR3 (CAY10444), c-Src (PP1), PYK2 (PF431396), MEK1/2 (U0126), p38 MAPK (SB202190), JNK1/2 (SP600125), or AP-1 (Tanshinone IIA) and transfection with siRNA of S1PR1, S1PR3, c-Src, PYK2, p38, p42, JNK2, c-Jun, or c-Fos reduced S1P-induced COX-2 expression and PGE₂/IL-6 secretion. Moreover, S1P induced c-Src, PYK2, p42/p44 MAPK, JNK1/2, p38 MAPK, and c-Jun phosphorylation. We observed that S1P-induced p42/p44 MAPK and JNK1/2, but not p38 MAPK activation was mediated via a c-Src/PYK2-dependent pathway. S1P also enhanced c-Fos, but not c-Jun mRNA and protein expression and the AP-1 promoter activity. S1P-induced c-Fos mRNA and protein expression, c-Jun phosphorylation, and AP-1 promoter activity was reduced by W123, CAY10444, PP1, PF431396, U0126, SP600125, or SB202190. These results demonstrated that S1P-induced COX-2 expression and PGE₂/IL-6 generation was mediated through S1PR1/3/c-Src/PYK2/p42/p44 MAPK- or JNK1/2- and S1PR1/3/c-Src/p38 MAPK-dependent AP-1 activation.