COMPLEMENT ACTIVATES PHOSPHOLIPASES AND PROTEIN-KINASES IN GLOMERULAREPITHELIAL-CELLS

Background. In rat membranous nephropathy, complement C5b-9 induces gl omerular epithelial cell (GEC) injury and proteinuria, which in some m odels is partially mediated by eicosanoids. In cultured rat GEC, subly tic C5b-9 injures plasma membranes and releases arachidonic acid (AA) and eicosanoids, due to activation of cytosolic phospholipase A(2) (cP LA(2)). In this study, we address the role of protein kinases in cPLA( 2) activation. Methods. GEC were stably transfected with cDNAs of wild -type (wt) cPLA(2) and serine(505)-->alanine mutant (cPLA(2)-SA505), w hich lacks the mitogen-activated protein kinase (MAPK) phosphorylation site. Results. Complement stimulated protein kinase C (PKC) activity in GEC, and activated p42 (but not p38) MAPK. Overexpression of either cPLA(2)-wt or cPLA(2)-SA505 markedly amplified the release of [H-3]AA by C5b-9. Depletion of PKC blocked the complement-dependent activatio n of cPLA(2)-wt or cPLA(2)-SA505, but inhibition of the p42 MAPK pathw ay had no effect. Epidermal growth factor was a strong activator of p4 2 MAPK, but stimulated PKC activity weakly. Unlike complement, activat ion of cPLA(2)-wt by epidermal growth factor was dependent on PKC, and was augmented significantly by p42 MAPK. Stable overexpression of pho spholipase C-gamma 1 in GEC amplified C5b-9-induced production of [H-3 ]inositol phosphates and [H-3]diacylglycerol, an endogenous activator of PKC, and complement stimulated tyrosine phosphorylation of phosphol ipase C-gamma 1. Conclusions. C5b-9 induces activation of cPLA(2) that is dependent on the diacylglycerol-PKC pathway. The role of p42 MAPK in cPLA(2) activation becomes redundant in the presence of relatively potent PKC activation.