The Apoptotic Regulatory Protein ARC (Apoptosis Repressor with Caspase Recruitment Domain) Prevents Oxidant Stress-mediated Cell Death by Preserving Mitochondrial Function

ARC is an apoptotic regulatory protein expressed almost exclusively in myogenic cells. It contains a caspase recruitment domain (CARD) through which it has been shown to block the activation of some initiator caspases. Because ARC also blocks caspase-independent events associated with apoptosis, such as hypoxia-induced cytochrome c release, we examined its role in cell death triggered by exposure to hydrogen peroxide (H₂O₂) in the myogenic cell line, H9c2. Cell death in this model was caspase-independent and characterized by dose-dependent reduction in ARC expression accompanied by disruption of the mitochondrial membrane potential (Δψ_m) and loss of plasma membrane integrity, typical of necrotic cell death. Ectopic expression of ARC prevented both H₂O₂-induced mitochondrial dysfunction and cell death without affecting the stress kinase response, suggesting that ARCs protective effects were downstream of early signaling events and not due to quenching of H₂O₂. ARC was also effective in blocking H₂O₂-induced loss of membrane integrity and/or disruption of Δψ_m in two human cell lines in which it is not normally expressed. These results demonstrate that, in addition to its ability to block caspase-dependent and -independent events in apoptosis, ARC also prevents necrosis-like cell death via the preservation of mitochondrial function.