Cytochrome c-mediated apoptosis in cells lacking mitochondrial DNA. Signaling pathway involving release and caspase 3 activation is conserved

Mitochondria serve as a pivotal component of the apoptotic cell death machinery. However, cells that lack mitochondrial DNA (ρ⁰ cells) retain apparently normal apoptotic signaling. In the present study, we examined mitochondrial mechanisms of apoptosis in ρ⁰ osteosarcoma cells treated with staurosporine. Immunohistochemistry revealed that ρ⁰ cells maintained a normal cytochrome c distribution in mitochondria even though these cells were deficient in respiration. Upon staurosporine treatment, cytochrome c was released concomitantly with activation of caspase 3 and loss of mitochondrial membrane potential (Aψ(m)). After mitochondrial loss of cytochrome c, ρ⁰ cells underwent little change in glutathione (GSH) redox potential whereas a dramatic oxidation in GSH/glutathione disulfide (GSSG) pool occurred in parental ρ⁺ cells. These results show that mitochondrial signaling of apoptosis via cytochrome c release was preserved in cells lacking mtDNA. However, intracellular oxidation that normally accompanies apoptosis was lost, indicating that the mitochondrial respiratory chain provides the major source of redox signaling in apoptosis.