Cytochrome c Release,Mitochondrial Membrane Depolarization,Caspase-3 Activation,and Bax-α Cleavage During IFN-α-Induced Apoptosis in Daudi B Lymphoma Cells

Abstract

Interferon-α (IFN-α) displays antitumor action by inducing direct cytotoxicity against tumor cells in addition to generation of cytotoxic cells. The IFN-α-induced direct cytotoxicity is at least partly due to induction of apoptosis. In the present study, we examined signaling pathways implicated in IFN-α-induced apoptosis in Daudi cells. Release of cytochrome c from mitochondria to cytosol was found after 12 h incubation with IFN-α, followed by a decline in mitochondrial membrane potential (Δψ_m) and procaspase-3 activation at 24 and 36 h, respectively. Cleavage of endogenous Bax-α (21 kDa), generating an 18-kDa fragment (p18 Bax-α), was found at 36 h. Although the endogenous p21 Bax-α was located in both cytosol and mitochondrial membranes, the p18 Bax-α resided only on mitochondrial membranes. IFN-α-induced apoptosis occurred 48 h after stimulation, with a further increase in proportion up to 72 h. Pretreatment with pancaspase inhibitor Z-VAD-fmk substantially inhibited the IFN-α-mediated Bax-α cleavage and apoptosis, but not the decline in Δψ_m, suggesting the possibility that caspase-3 activation is implicated in the Bax-α cleavage, probably leading to amplification of the apoptotic processes. Our results suggest that modulation of endogenous p21 Bax-α is implicated in IFN-α-induced apoptosis.