Vol. 57, Issue 4, 792-796, April 2000

Down-Regulation of Ceramide Production Abrogates Ionizing Radiation-Induced Cytochrome c Release and Apoptosis

Steven J. Chmura, Edwardine Nodzenski, Surender Kharbanda, Pramod Pandey, Jose Quintans, Donald W. Kufe, and Ralph R. Weichselbaum

Department of Radiation and Cellular Oncology, Division of Biological Sciences, University of Chicago, and the Pritzker School of Medicine, Chicago, Illinois (S.J.C., E.N., J.Q., R.R.W.); Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts (S.K., P.P., D.W.K.)

Previous work has demonstrated that down-regulation of ceramide production after selection of cells with N-oleoylethanolamine (OE), an inhibitor of ceramidase, results in resistance to DNA damage-induced apoptosis. We report here that acute exposure of WEHI-231 cells (murine B-cell lymphoma) to OE activates neutral sphingomyelinase, induces ceramide production and increases intracellular reactive oxygen species. OE exposure also induces mitochondrial permeability, cytochrome c release, and apoptosis. Cells selected for resistance to OE exhibit little if any change in reactive oxygen species and cytochrome c release when exposed either to OE or to toxic doses of ceramide. Importantly, the OE resistant cells are also resistant to ionizing radiation-induced cytochrome c release and apoptosis. These findings demonstrate that down-regulation of neutral sphingomyelinase activity is associated with decreased DNA-damage-induced apoptosis. In addition, the data suggests that agents that modify extranuclear targets responsible for ceramide production select for cells resistant to ionizing radiation-induced apoptosis through alterations in mitochondrial function.