The intracellular domain of p55 tumor necrosis factor receptor induces apoptosis which requires different caspases in naive and neuronal PC12 cells

Apoptosis is induced in cells via distinct pathways, which may differ according to various stimuli and different cell types. One apoptotic stimulus is the activation of receptors such as the p55 tumor necrosis factor (TNF) receptor. These receptors transduce their apoptotic signals via a cytoplasmic region termed the death domain. Here we investigated the apoptotic pathway induced by overexpression of the intracellular domain of p55 TNF receptor (p55-IC) in a neuronal model system consisting of PC12 cells. Using the tetracycline-regulated transactivator system, which allows controlled gene expression, we show that overexpression of p55-IC induces apoptosis in both naive and neuronal PC12 cells. The apoptosis-inducing effect of p55-IC is blocked by the expression of bcl-2, suggesting that p55-IC induces apoptosis in PC 12 cells via a pathway controlled by bcl-2. The need for caspases in the p55-IC-induced cell death effect in naive and neuronal PC12 cells was studied by examining the effects of broad-spectrum and specific inhibitors of caspases as well as expression of antisense caspase-2 RNA. The broad-spectrum caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone blocked p55-IC-induced cell death in both naive and neuronal cells, suggesting that caspases are needed for this process in both cell types. Caspase-1like proteases are most probably not involved in the process since neither expression of crmA nor treatment with the caspase-l-specific peptide inhibitor Ac-Try-Val-Ala-Asp-aldehyde had any protective effect. Interestingly, expression of antisense caspase-2 RNA blocked the p55-IC- induced cell death in naive but not in neuronal PC12 cells, whereas the caspase-3like specific inhibitor Ac-Asp-Glu-Val-Asp-aldehyde partially inhibited this death in neuronal but not in naive cells. These results suggest that the apoptosisinducing effect of p55-IC requires different caspases in naive and neuronal PC12 cells.