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 acceptors stimulates cellular proliferation. We now show that the vanilloids capsaicin, dihydrocapsaicin, and resiniferatoxin are inhibitors of the NADH-oxidase activity of the PMOR system and that both these and two previously identified PMOR inhibitors (chloroquine and retinoic acid) induce apoptosis in human B-cell and mouse myeloid cell lines. At the optimal concentration, PMOR inhibitors can induce between 50 and 70% of apoptosis in mouse myeloid and human B-cell lines within 8-12 h, provided these 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 calcineurin. We suggest that the PMOR system is a redox sensor that can, depending on the ambient redox environment and the availability of growth factors, regulate plasma membrane calcium fluxes and signal for apoptosis through calcineurin. Bcl-2, a protein that is thought to inhibit apoptosis by regulating reactive oxygen species and calcium fluxes in the cell, inhibits this apoptotic pathway.