Apoptosis shifts to necrosis via intermediate types of cell death by a mechanism depending on c-myc and bcl-2 expression

Hypoxic and chemical hypoxia (antimycin A) commits cultured rat fibroblasts (Rat-1) towards apoptosis, necrosis or an intermediate form of cell death (aponecrosis) depending on the degree of hypoxia. Aponecrosis also occurs in vivo. Here, we demonstrate that c-myc and bcl-2, two proto-oncogenes known to lower or to enhance, respectively, the apoptotic threshold, also affect the type of cell death: apoptosis shifts to aponecrosis and aponecrosis to necrosis, depending on c-myc or bcl-2 expression and the antimycin A concentration (100–400 M). In cells with basal gene expression, apoptosis shifts to aponecrosis/necrosis at 300 M antimycin A (middle hypoxia). Overexpression of c-myc markedly increases cumulative cell death in response to antimycin A and lowers the antimycin A concentration required to shift apoptosis to aponecrosis/necrosis from 300 M to 100 M (low hypoxia). Overexpression of bcl-2 elicits the opposite effect, decreasing cumulative cell death in response to antimycin A and raising the drug concentration required to shift apoptosis to aponecrosis/necrosis to 400 M (high hypoxia). The passage from one to the other form of cell death involves various aponecrotic features with observed intermediate aspects between apoptosis and necrosis, a progressive increase in necrotic features being correlated with an increase in antimycin A concentration. The mechanism underlying the various effects of c-myc and bcl-2 on cell-death type has been related to the ability of these genes to counteract, to various extents, the ATP decrease occurring in response to different degrees of chemical hypoxia.The first two authors contributed equally to this workThis work was supported by grants from the Associazione Italiana per la Ricerca sul Cancro (AIRC, Milano), CNR/MIUR (Grant Progetto Finalizzato Oncologia), Ente Cassa di Risparmio di Firenze and Ministero dellIstruzione, dellUniversità e della Ricerca (MIUR, Cofin 2003). Andrea Lapucci is supported by a fellowship from the Federazione Italiana per la Ricerca sul Cancro (FIRC, Milano)