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Cytochrome c-mediated apoptosis in cells lacking mitochondrial DNA. Signaling pathway involving release and caspase 3
1Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
Abstract:
Mitochondria serve as a pivotal component of the apoptotic cell death machinery. However, cells that lack mitochondrial DNA (rho(0) cells) retain apparently normal apoptotic signaling. In the present study, we examined mitochondrial mechanisms of apoptosis in rho(0) osteosarcoma cells treated with staurosporine. Immunohistochemistry revealed that rho(0) 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 (Deltapsi(m)). After mitochondrial loss of cytochrome c, rho(0) cells underwent little change in glutathione (GSH) redox potential whereas a dramatic oxidation in GSH/glutathione disulfide (GSSG) pool occurred in parental rho(+) 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.
Insights
Mitochondria are key to apoptosis. Even without mitochondrial DNA, cells show normal cytochrome c release, but lose the associated intracellular oxidation, highlighting the respiratory chain's role in redox signaling during cell death.
Area of Science:
- Cell Biology
- Biochemistry
- Apoptosis Research
Background:
- Mitochondria are central to programmed cell death (apoptosis).
- Mitochondrial DNA-deficient (rho(0)) cells exhibit seemingly normal apoptotic signaling.
- The precise role of mitochondria in apoptosis-associated redox changes remains unclear.
Purpose of the Study:
- To investigate mitochondrial mechanisms of apoptosis in rho(0) osteosarcoma cells.
- To determine if mitochondrial DNA is essential for cytochrome c release and redox signaling during staurosporine-induced apoptosis.
Main Methods:
- Utilized rho(0) and parental rho(+) osteosarcoma cells.
- Induced apoptosis using staurosporine.
- Performed immunohistochemistry for cytochrome c localization.
- Assessed caspase 3 activation and mitochondrial membrane potential (Deltapsi(m)).
- Measured glutathione (GSH) and glutathione disulfide (GSSG) redox potential.
Main Results:
- rho(0) cells retained normal mitochondrial cytochrome c distribution despite respiratory deficiency.
- Staurosporine treatment triggered cytochrome c release, caspase 3 activation, and Deltapsi(m) loss in rho(0) cells.
- rho(0) cells showed minimal change in GSH redox potential, unlike rho(+) cells which exhibited significant oxidation.
Conclusions:
- Mitochondrial cytochrome c release as an apoptotic signal is preserved in cells lacking mitochondrial DNA.
- The mitochondrial respiratory chain is the primary source of intracellular oxidation during apoptosis.
- mtDNA is not required for initiating apoptosis but is crucial for the associated redox signaling cascade.