Caspase activation precedes PTP opening in TNF-alpha-induced apoptosis in L929 cells.

In this work, we studied the apoptotic pathway in murine fibrosarcoma cells L929 exposed to tumor necrosis factor alpha (TNF-alpha). DNA fragmentation, activation of caspases, cytochrome c release and poly (ADP-ribose) polymerase cleavage were demonstrated. We showed that the proapoptotic proteins Bid and Bax as well as caspase 8 are involved in the initiation of this apoptotic pathway triggered by TNF-alpha. Indeed, inhibition of caspase 8 could prevent TNF-alpha-induced DNA fragmentation. Furthermore, Bid and Bax translocation into mitochondria were already evidenced after 6 h. In contrast, permeability transition pore inhibitors did not prevent the DNA fragmentation induced by TNF-alpha. In addition, these events were not associated with changes in the mitochondrial membrane potential nor with the loss of ATP, which only occurred after 16 h. Taken together, these results underline the fact that TNF-alpha is able to induce caspase-dependent apoptosis in L929 in the absence of permeability transition pore opening.