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mtDNA-depleted U937 cells are sensitive to TNF and Fas-mediated cytotoxicity
1Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Zaragoza, Spain.
Abstract:
It has been proposed that TNF cytotoxicity is mediated by reactive oxygen intermediates generated by uncoupling of mitochondrial respiration. We have compared sensitive U937 cells and derived cell lines depleted of mtDNA for their ability to undergo TNF- and Fas-induced apoptosis. Cells lacking around 98% of mtDNA were still sensitive to TNF-induced apoptosis. U937 cells devoid of mtDNA (U937-rho degree) were resistant to TNF, but this was due to the loss of its 55 kDa receptor. U937-rho degree cells were also resistant to docosahexaenoic acid, which causes U937 cell death by lipid peroxidation. These cells were sensitive to anti-Fas toxicity. The results indicate that TNF and Fas-induced toxicity occurs by a mechanism mostly independent of mitochondrial free radical generation.
Insights
Tumor necrosis factor (TNF) and Fas-induced apoptosis are largely independent of mitochondrial reactive oxygen species. Depleting mitochondrial DNA (mtDNA) did not prevent TNF-induced apoptosis, indicating alternative pathways are involved.
Area of Science:
- Cellular biology
- Immunology
- Biochemistry
Background:
- Mitochondrial respiration and reactive oxygen intermediates (ROIs) have been implicated in tumor necrosis factor (TNF)-induced cytotoxicity.
- Understanding the precise mechanisms of TNF and Fas-induced apoptosis is crucial for developing targeted therapies.
Purpose of the Study:
- To investigate the role of mitochondrial reactive oxygen intermediates in TNF- and Fas-induced apoptosis.
- To compare the sensitivity of cells with varying mitochondrial DNA (mtDNA) content to TNF and Fas signaling.
Main Methods:
- Utilized U937 cells and derived cell lines with significantly depleted mtDNA (rho degree).
- Assessed sensitivity to TNF, Fas, and docosahexaenoic acid-induced cell death.
- Analyzed TNF receptor expression in mtDNA-depleted cells.
Main Results:
- Cells lacking approximately 98% of mtDNA remained sensitive to TNF-induced apoptosis.
- U937 cells completely devoid of mtDNA (rho degree) were resistant to TNF due to loss of the 55 kDa receptor, not impaired signaling.
- These mtDNA-deficient cells were sensitive to Fas-induced apoptosis and docosahexaenoic acid-induced cell death.
Conclusions:
- TNF and Fas-induced apoptosis predominantly occur through mechanisms independent of mitochondrial free radical generation.
- Mitochondrial integrity is not essential for mediating TNF and Fas apoptotic signaling pathways.