Submitted on September 20, 2007
Accepted on May 19, 2008
Cytosolic phospholipase A2
activation induced by S1P is mediated by the S1P3 receptor in lung epithelial cells
Li-Yuan Chen1, Grzegorz Woszczek1, Sahrudaya Nagineni1, Carolea Logun1, and James H. Shelhamer1*
1 Critical Care Medicine Department, National Institutes of Health, Bethesda, Maryland, United States
* To whom correspondence should be addressed. E-mail: jshelhamer{at}mail.nih.gov.
Cytosolic phospholipase A2
(cPLA2) 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 cPLA2 in these events in A549 human lung epithelial cells. S1P induced AA release rapidly within 5 minutes in a dose and time dependent manner. S1P-induced AA release was inhibited by the cPLA2 inhibitors, methyl arachidonyl fluorophosphonate (MAFP) and pyrrolidine derivative, by siRNA-mediated down-regulation of cPLA2, and by inhibition of S1P-induced calcium flux, suggesting a significant role of cPLA2 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 cPLA2 activation. Our data suggest that S1P acting through S1P3, calcium flux, and Rho kinase activates cPLA2 and releases AA in lung epithelial cells. An understanding of S1P-induced cPLA2 activation mechanisms in epithelial cells may provide potential targets to control inflammatory processes in the lung.
