INTERLEUKIN-1 AND ENDOTHELIN STIMULATE DISTINCT SPECIES OF DIGLYCERIDES THAT DIFFERENTIALLY REGULATE PROTEIN-KINASE-C IN MESANGIAL CELLS

Diglycerides are phospholipid-derived second messengers that serve as cofactors for protein kinase C activation. We have previously shown th at, in rat glomerular mesangial cells, the cytokine, interleulrin-1 al pha, and the vasoactive peptide, endothelin, generate diglycerides fro m unique phospholipid precursors. However, neither the molecular speci es of these diglycerides nor their biological actions were determined. It is now hypothesized that interleukin-1- and endothelin-treated mes angial cells form distinct molecular species of diglycerides which may serve different roles as intracellular signaling molecules. Diglyceri de molecular species were resolved and quantified by TLC and high perf ormance liquid chromatography as diglyceride-[C-14]acetate derivatives . Endothelin stimulates predominantly ester linked species (diacylglyc erols) in contrast to interleukin-1 which stimulates only ether-linked species (alkyl, acyl- and alkenyl,acylglycerols). In support of these data, interleukin-1-treated mesangial cells hydrolyze ethanolamine pl asmalogens, vinyl ether-linked phospholipids. It has been reported tha t ether-linked, in contrast to ether-linked, diglyceride species do no t activate protein kinase C activity. Thus, we next assessed membrane protein kinase C activity in endothelin- or interleukin-1-treated mesa ngial cells. Even though interleukin-1 has no effect upon basal protei n kinase C activity, this cytokine, through the formation of ether-lin ked diglyceride second messengers, inhibits endothelin, platelet-activ ating factor, or arginine vasopressin-stimulated protein kinase C acti vity. We further demonstrate that ether-linked diacylglycerols but not alkyl,acyl- or alkenyl,acylglycerols substitute for phorbol esters in a cell-free protein kinase C assay, In addition, alkenyl,acylglycerol s inhibit diacylglycerol-stimulated immunoprecipitated protein kinase C alpha activity in vitro and total protein kinase C activity in perme abilized mesangial cells ex vivo. Taken together, these data suggest t hat interleukin-1-induced formation of ether-linked diglycerides may p hysiologically serve to down-regulate receptor-mediated protein kinase C activity and that individual molecular species of diglycerides may serve different roles as intracellular signaling molecules.