The tumor suppressor and transcriptional regulator p53 has been associated with both apoptotic and autophagic cell death processes. Vaseva et al. identified a previously unknown role for p53 in necrotic cell death. Oxidative stress can cause necrosis in ischemic tissue by stimulating the sudden opening of the mitochondrial permeability transition pore (PTP), which is enhanced by cyclophilin D (CypD). Adding purified p53 to mitochondria isolated from mouse embryo fibroblasts (MEFs) and preloaded with the fluorescent dye calcein induced loss of signal, indicating opening of the PTP. Immunoprecipitation experiments with HCT116 cell lysates and with purified proteins showed that p53 interacted with CypD but not with other PTP components. Microscopy and fractionation showed that p53 localized to the mitochondria of MEFs upon treatment with H2O2 to induce oxidative stress. Treatment of MEFs with H2O2 also induced opening of the PTP, observed as loss of calcein fluorescence. H2O2 induced necrosis of wild-type MEFs, but not those deficient in p53 or CypD, as revealed by electron microscopy and by the release of the necrotic marker protein HMGB1 into the culture medium. Adenoviral delivery of a chimeric p53 (Lp53) that was targeted exclusively to the mitochondrial matrix (and that bypassed the nucleus and was devoid of transcriptional activity) induced PTP opening and necrosis in H2O2-treated wild-type but not CypD-deficient MEFs. Deletion of the genes encoding the proapoptotic proteins Bax and Bak from MEFs had no effect on PTP opening or necrosis in response to the combination of oxidative stress and adenoviral delivery of Lp53. In a mouse model for ischemic stroke, the brains of heterozygous mice missing one p53 allele had smaller areas of damage than those from wild-type mice, suggesting that p53 contributes to cell death induced by ischemia. The results of Vaseva et al. suggest that p53 participates in necrosis by directly interacting with CypD to open the PTP in response to oxidative stress.
A. V. Vaseva, N. D. Marchenko, K. Ji, S. E. Tsirka, S. Holzmann, U. M. Moll, p53 opens the mitochondrial permeability transition pore to trigger necrosis. Cell 149, 1536–1548 (2012). [Online Journal]