Cytosolic phospholipase A2α activation induced by S1P is mediated by the S1P3 receptor in lung epithelial cells

Abstract

Cytosolic phospholipase A2α (cPLA2α) activation is a regulatory step in the control of arachidonic acid (AA) liberation for eicosanoid formation. Sphingosine 1-phosphate (S1P) is a bioactive lipid mediator involved in the regulation of many important proinflammatory processes and has been found in the airways of asthmatic subjects. We investigated the mechanism of S1P-induced AA release and determined the involvement of cPLA2α in these events in A549 human lung epithelial cells. S1P induced AA release rapidly within 5 min in a dose- and time-dependent manner. S1P-induced AA release was inhibited by the cPLA2α inhibitors methyl arachidonyl fluorophosphonate (MAFP) and pyrrolidine derivative, by small interfering RNA-mediated downregulation of cPLA2α, and by inhibition of S1P-induced calcium flux, suggesting a significant role of cPLA2α in S1P-mediated AA release. Knockdown of the S1P3 receptor, the major S1P receptor expressed on A549 cells, inhibited S1P-induced calcium flux and AA release. The S1P-induced calcium flux and AA release was associated with sphingosine kinase 1 (Sphk1) expression and activity. Furthermore, Rho-associated kinase, downstream of S1P3, was crucial for S1P-induced cPLA2α activation. Our data suggest that S1P acting through S1P3, calcium flux, and Rho kinase activates cPLA2α and releases AA in lung epithelial cells. An understanding of S1P-induced cPLA2α activation mechanisms in epithelial cells may provide potential targets to control inflammatory processes in the lung.