Role of mitochondria in TNF-induced apoptosis; induction of apoptosis through inhibition of complex I

The involvement of mitochondria in the cell death response has been implicated, but the precise mechanisms has not been defined. Here we demonstrate that mitochondria play a critical role in TNF-induced apoptosis by using three different approaches. First, we generated mitochondrial respiration-free cells from ML-la cells and showed that TNF-induced apoptosis was completely abrogated. The restoration of normal mitochondria to respiration-free cells recovered the apoptotic response. The second approach was to examine the effect of TNF on mitochondrial respiration. We showed that treatment with TNF or a fusion protein containing intracellular domain of the p60 TNF receptor caused MRC complex I dysfunction. In the third approach, we used specific inhibitors of MRC complexes to demonstrate the apoptosis-inducing mechanism in mitochondria. Rotenone, an inhibitor of MRC complex I, but not inhibitors of other complexes, induced apoptosis in ML-la cells but not in respiration-free cells. These results clearly indicate that TNF can induce MRC complex I dysfunction leading to apoptosis.