EVIDENCE THAT INHIBITION OF PHORBOL ESTER-INDUCED SUPEROXIDE ANION FORMATION BY CYCLOSPORINE-A IN PHAGOCYTES IS NOT MEDIATED BY DIRECT INHIBITION OF PROTEIN-KINASE-C

Cyclosporin A (CsA) has been reported to inhibit phorbol myristate ace tate (PMA)-induced superoxide anion (O-2(-)) formation in human neutro phils and murine macrophages. We found that CsA inhibited O-2(-) forma tion in HL-60 cells induced by PMA (30 nM) and phorbol dibutyrate (200 nM) with a half-maximal effect at 1 and 0.75 mu M, respectively. One possible target of CsA action is protein kinase C (PKC) [EC 2.7.1.37] since phorbol eaters activate this kinase. However, CsA did not inhibi t PMA-mediated reduction of histamine-induced rises in cytosolic Ca2concentration in, and PMA-induced differentiation of, HL-60 cells and platelet aggregation. CsA did not reduce the activity of various recom binant c-PKC isoenzymes (alpha, beta 1 and gamma), n-PKC isoenzymes (d elta and epsilon), an a-PKC isoenzyme (zeta) nor of PKC purified from rat brain in vitro. These data show that CsA inhibits phorbol eater-in duced O-2(-) formation in HL-60 cells but not other phorbol ester-medi ated events and that inhibition by CsA of O-2(-) formation cannot read ily be attributed to direct PKC inhibition. We also show that CsA does not change the activity of nucleoside diphosphate kinase [EC 2.7.4.6] in HL-60 membranes nor the latter's physical properties.