Cross-talk between cytosolic phospholipase A2α (cPLA2α) and secretory phospholipase A2 (sPLA2) in hydrogen peroxide-induced arachidonic acid release in murine mesangial cells -: sPLA2 regulates cPLA2α activity that is responsible for arachidonic acid release

Oxidant stress and phospholipase A(2) (PLA(2)) activation have been implicated in numerous proinflammatory responses of the mesangial cell (MC). We investigated the cross-talk between group IValpha cytosolic PLA(2) (cPLA(2)alpha) and secretory PLA(2)s (sPLA(2)s) during H2O2-induced arachidonic acid (AA) release using two types of murine MC: (i) MC+/+, which lack group IIa and V PLA(2)s, and (ii) MC-/-, which lack groups IIa, V, and IValpha PLA(2)s. H2O2-induced AA release was greater in MC+/+ compared with MC-/-. It has been argued that cPLA(2)alpha plays a regulatory role enhancing the activity of sPLA(2)s, which act on phospholipids to release fatty acid. Group IIa, V, or IValpha PLA(2)s were expressed in MC-/- or MC+/+ using recombinant adenovirus vectors. Expression of cPLA(2)alpha in H2O2-treated MC-/- increased AA release to a level approaching that of H2O2-treated MC+/+. Expression of either group IIa PLA(2) or V PLA(2) enhanced AA release in MC+/+ but had no effect on AA release in MC-/-. When sPLA(2) and cPLA(2)alpha are both present, the effect of H2O2 is manifested by preferential release of AA compared with oleic acid. Inhibition of the ERK and protein kinase C signaling pathways with the MEK-1 inhibitor, U0126, and protein kinase C inhibitor, GF 1092030x, respectively, and chelating intracellular free calcium with 1,2-bis(2-aminophenoyl)ethane-N,N,N',N'-tetraacetic acid-AM, which also reduced ERK1/2 activation, significantly reduced H2O2-induced AA release in MC+/+ expressing either group IIa or V PLA(2)s. By contrast, H2O2-induced AA release was not enhanced when ERK1/2 was activated by infection of MC+/+ with constitutively active MEK1-DD. We conclude that the effect of group IIa and V PLA(2)s on H2O2-induced AA release is dependent upon the presence of cPLA(2)alpha and the activation of PKC and ERK1/2. Group IIa and V PLA(2)s are regulatory and cPLA(2)alpha is responsible for AA release.