Role of Bcl-2 in the arachidonate-mediated survival signaling preventing mitochondrial permeability transition-dependent U937 cell necrosis induced by peroxynitrite

Antisense technology was successfully employed to selectively reduce the expression of Bcl-2 in U937 cells, while leaving their redox status intact. These cells displayed enhanced sensitivity to mitochondrial permeability transition (MPT)-dependent apoptosis induced by arsenite and underwent a rapid, MPT-dependent necrotic response after exposure to otherwise nontoxic concentrations of peroxynitrite. Several lines of evidence consistently indicate that these low concentrations of peroxynitrite nevertheless commit cells to MPT, which is, however, prevented by a survival signaling in which arachidonic acid, protein kinase Cα (PKCα), and Bcl-2 are sequentially involved. Bcl-2, however, was not the direct target of PKCα but most likely Bad, a protein involved in the regulation of Bcl-2 activity via heterodimerization. Further studies revealed that Bcl-2 does not afford protection in cells challenged with intrinsically toxic concentrations of peroxynitrite. This was due to depletion of GSH, an event leading to loss of the anti-MPT function of Bcl-2. Collectively, these results demonstrate a role of Bcl-2 in monocyte survival signaling preventing MPT-dependent necrosis induced by peroxynitrite, and provide an explanation for the reported observation that Bcl-2 fails to prevent necrosis mediated by intrinsically toxic levels of peroxynitrite.