Complement C5b-9 activates cytosolic phospholipase A2 in glomerular epithelial cells.
In rat membranous nephropathy, complement C5b-9 induces glomerular epithelial cell (GEC) injury and proteinuria, which, in some models, is partially mediated by eicosanoids. By analogy, sublytic C5b-9 injures plasma membranes and releases arachidonic acid (AA) and eicosanoids in cultured rat GEC. In this study, we demonstrate that, in GEC, sublytic C5b-9 stably increased the activity of a high-molecular-mass cytosolic phospholipase A2 (PLA2), which we identified as "cPLA2." This increase was abolished with inhibitors of protein kinase C. C5b-9 did not affect low-molecular-mass membrane-associated or secretory PLA2 activities. In GEC that stably overexpress cPLA2 activity and protein (produced by transfection of cPLA2 cDNA), immunoblot analysis showed that sublytic C5b-9 induced a decreased mobility of cPLA2, consistent with cPLA2 phosphorylation. Incubation of cPLA2-transfected GEC with sublytic C5b-9 significantly increased production of free AA and prostaglandin E2, whereas, in control GEC, the C5b-9-induced changes in free AA and prostaglandin E2 were small. Furthermore, both C5b-9-dependent sublytic cytotoxicity and cytolysis were enhanced in GEC overexpressing cPLA2, compared with control cells. Thus C5b-9 increased cPLA2 activity, probably via phosphorylation involving a protein kinase C-dependent pathway. Phospholipid hydrolysis by cPLA2 resulted in release of substrate for eicosanoid synthesis and in enhancement of C5b-9-dependent GEC injury. Both processes may facilitate glomerular damage in membranous nephropathy.
Cybulsky
A V
AV
Department of Medicine, Royal Victoria Hospital, McGill University, Montreal, Quebec, Canada.
Monge
J C
JC
Papillon
J
J
McTavish
A J
AJ
D000818:Animals; D002478:Cells, Cultured; D015938:Complement Membrane Attack Complex / Q000494:pharmacology*; D003600:Cytosol / Q000201:enzymology*; D004789:Enzyme Activation; D004848:Epithelium / Q000201:enzymology; D007678:Kidney Glomerulus / Q000201:enzymology*; D008970:Molecular Weight; D010741:Phospholipases A / Q000737:chemistry / Q000378:metabolism*; D054467:Phospholipases A2; D010743:Phospholipids / Q000378:metabolism; D010766:Phosphorylation; D051381:Rats
D015938:Complement Membrane Attack Complex; D010743:Phospholipids; D010741:Phospholipases A; D054467:Phospholipases A2