85-kDa cytosolic phospholipase A2 mediates peroxisome proliferator-activated receptor γ activation in human lung epithelial cells

The 85-kDa cytosolic phospholipase A(2) (cPLA(2)) plays an important role in the control of arachidonic acid metabolism. This study was designed to investigate the possible contributions of cPLA(2) and group IIA secretory phospholipase A2 (sPLA(2)) in the regulation of peroxisome proliferator-activated receptor (PPAR)-mediated gene transcription in human airway epithelial cells. Primary normal human bronchial epithelial cells and human lung epithelial cell lines BEAS 2B, A549, and NCI-H292 all express PPARgamma and -beta. Overexpression of cPLA(2) in BEAS 213 cells and primary bronchial epithelial cells resulted in a significant increase of PPARgamma-mediated reporter activity. In contrast, overexpression of group IIA sPLA(2), had no effect on PPARgamma activation. The PPARgamma activity in A549 cells was significantly inhibited by the cPLA(2) inhibitor arachidonyltrifluoromethyl ketone but not by the sPLA2 inhibitor LY311727 and the iPLA(2) inhibitor HELSS. Activation of cPLA(2) by the calcium ionophore, A23187, induced a dose-dependent increase of PPAR activity in normal human bronchial epithelial cells and in the A549 cells. Electrophoretic mobility shift assays show that the binding between PPAR isolated from A549 cells and peroxisome proliferator response element (PPRE) is enhanced by A23187 but partially blocked by the cPLA2 inhibitors arachidonyltrifluoromethyl ketone and methyl arachidonyl fluorophosphate. Finally, NS 398, a COX-2 inhibitor, partially blocked the A23187 effect on PPAR activity and binding to the PPRE suggesting involvement of COX-2 metabolites in PPRE activation. The above results demonstrate a novel function of cPLA, in the control of PPARgamma activation in human lung epithelial cells.