Bcl-2 protects peroxynitrite-treated thymocytes from poly(ADP-ribose) synthase (PARS)-independent apoptotic but not from PARS-mediated necrotic cell death

In thymocytes, peroxynitrite induces poly(ADP-ribose) synthetase (PARS) act ivation, which results in necrotic cell death. In the absence of PARS, howe ver, peroxynitrite-treated thymocytes die by apoptosis. Because Bcl-2 has b een reported to inhibit not only apoptotic but also some forms of necrotic cell death, here we have investigated how Bcl-2 regulates the peroxynitrite -induced apoptotic and necrotic cell death. We have found that Bcl-2 did no t provide protection against peroxynitrite-induced necrotic death, as chara cterized by propidium iodide uptake, mitochondrial membrane potential decre ase, secondary superoxide production, and cardiolipin loss. In the presence of a PARS inhibitor. peroxynitrite-treated thymocytes from Bcl-2 transgeni c mice showed no caspase activation or DNA fragmentation and displayed smal ler mitochondrial membrane potential decrease. These data show that Bcl-2 p rotects thymocytes from peroxynitrite-induced apoptosis at a step proximal to mitochondrial alterations but fails to prevent PARS-mediated necrotic ce ll death. Activation of tissue transglutaminase (tTG) occurs in various for ms of apoptosis. Peroxynitrite did not induce transglutaminase activity in thymocytes and did not have a direct inhibitory effect on the purified tTG. Basal tTG was not different in Bcl-2 transgenic and wild type cells. (C) 2 000 Elsevier Science Inc.