Calphostin C-mediated translocation and integration of Bax into mitochondria induces cytochrome c release before mitochondrial dysfunction

Calphostin C-mediated apoptosis in glioma cells was reported previously to be associated with down-regulation of Bcl-2 and Bcl-x(L). In this study, we report that 100 nM calphostin C also induces translocation and integration of monomeric Bax into mitochondrial membrane, followed by cytochrome c release into cytosol and subsequent decrease of mitochondrial inner membrane potential (Delta Psi m) before activation of caspase-3, The integration of monomeric Bax was associated with acquirement of alkali-resistance. The translocated monomeric Bax was partly homodimerized after cytochrome c release and decrease of Delta Psi m, The translocation and homodimerization of Bax, cytochrome c release, and decrease of Delta Psi m were not blocked by 100 mu M z-VAD.fmk, a pan-caspase inhibitor, but the homodimerization of Bax and decrease of Delta Psi m were inhibited by 10 mu M oligomycin, a mitochondrial F0F1-ATPase inhibitor. Therefore, it would be assumed that mitochondrial release of cytochrome c results from translocation and integration of Bax and is independent of permeability transition of mitochondria and caspase activation, representing a critical step in calphostin C-induced cell death.