APOPTOSIS INDUCED BY INHIBITORS OF THE PLASMA-MEMBRANE NADH-OXIDASE INVOLVES BCL-2 AND CALCINEURIN

Activation of the plasma membrane NADH-oxidoreductase (PMOR) system by addition of growth factors or extracellular electron accepters stimul ates cellular proliferation, We now show that the vanilloids capsaicin , dihydrocapsaicin, and resiniferatoxin are inhibitors of the NADH-oxi dase activity of the PMOR system and that both these and two previousl y identified PMOR inhibitors (chloroquine and retinoic acid) induce ap optosis in human B-cell and mouse myeloid cell lines. At the optimal c oncentration, PMOR inhibitors can induce between 50 and 70% of apoptos is in mouse myeloid and human B-cell lines within 8-12 h, provided the se cell lines do not express Bcl-2. The immunosuppressants cyclosporin A and fujimycin (tacrolimus) inhibit PMOR inhibitor-induced apoptosis . By using combinations of these immunosuppressants and excess amounts of their nonimmunosuppressive analogues, we demonstrate that in human B-cell lines the Bcl-2-sensitive apoptotic pathway triggered by PMOR inhibitors involves signaling through the protein phosphatase calcineu rin. We suggest that the PMOR system is a redox sensor that can, depen ding on the ambient redox environment and the availability of growth f actors, regulate plasma membrane calcium fluxes and signal for apoptos is through calcineurin. Bcl-2, a protein that is thought to inhibit ap optosis by regulating reactive oxygen species and calcium fluxes in th e cell, inhibits this apoptotic pathway.