The actin cytoskeleton facilitates complement-mediated activation of cytosolic phospholipase A2.

Cytosolic PLA(2)-alpha (cPLA(2)) and metabolites of arachidonic acid (AA) are key mediators of complement-dependent glomerular epithelial cell (GEC) injury. Assembly of C5b-9 increases cytosolic Ca(2+) concentration and results in transactivation of receptor tyrosine kinases and activation of PLC-gamma 1 and the 1,2-diacylglycerol (DAG)-PKC pathway. Ca(2+) and PKC are essential for membrane association and increased catalytic activity of cPLA(2). This study addresses the role of the actin cytoskeleton in cPLA(2) activation. Depolymerization of F-actin by cytochalasin D or latrunculin B reduced complement-dependent [(3)H]AA release, as well as the complement-induced increase in cPLA(2) activity. These effects were due to inhibition of [(3)H]DAG production and PKC activation, implying interference with PLC. Complement-dependent [(3)H]AA release was also reduced by jasplakinolide, a compound that stabilizes F-actin and organizes actin filaments at the cell periphery, and calyculin A, which induces condensation of actin filaments at the plasma membrane. The latter drugs did not affect [(3)H]DAG production, suggesting their inhibitory actions were downstream of PKC. Neither cytochalasin D, latrunculin B, nor calyculin A affected association of cPLA(2) with microsomal membranes, and cytochalasin D and latrunculin B did not alter the localization of the endoplasmic reticulum. Stable transfection of constitutively active RhoA induced formation of stress fibers, stabilized F-actin, and attenuated the complement-induced increase in [(3)H]AA. Thus in GEC, cPLA(2) activation is dependent, in part, on actin remodeling. By regulating complement-mediated activation of cPLA(2), the actin cytoskeleton may contribute to the pathophysiology of GEC injury.