AIF suppresses chemical stress-induced apoptosis and maintains the transformed state of tumor cells

• Published in: The EMBO journal 2005-08, Vol.24 (15), p.2815-2826
• Main Authors: Urbano, Alexander, Lakshmanan, Umayal, Choo, Poh Heok, Kwan, Jair Chau, Ng, Poh Yong, Guo, Ke, Dhakshinamoorthy, Saravanakumar, Porter, Alan
• Format: Article
• Language: English
• Subjects: AIF; Animals; Antioxidants; apoptosis; Apoptosis - physiology; Apoptosis Inducing Factor; Cell Line, Tumor; Cell Transformation, Neoplastic - genetics; Cell Transformation, Neoplastic - metabolism; Cell Transformation, Neoplastic - pathology; colon cancer; DNA Damage; Electron Transport Complex I - metabolism; Electron Transport Complex I - physiology; EMBO07; EMBO24; Flavoproteins - physiology; Humans; Membrane Proteins - deficiency; Membrane Proteins - physiology; Mice; Mice, Nude; Mitochondria - enzymology; Multienzyme Complexes - metabolism; NADH oxidase; NADH, NADPH Oxidoreductases - metabolism; NIH 3T3 Cells; Oxidative Stress - physiology; Reactive Oxygen Species - metabolism; Superoxides - metabolism; tumorigenesis
• ISSN: 0261-4189; 1460-2075
• DOI: 10.1038/sj.emboj.7600746

Apoptosis‐inducing factor (AIF) exhibits reactive oxygen species (ROS)‐generating NADH oxidase activity of unknown significance, which is dispensable for apoptosis. We knocked out the aif gene in two human colon carcinoma cell lines that displayed lower mitochondrial complex I oxidoreductase activity and produced less ROS, but showed increased sensitivity to peroxide‐ or drug‐induced apoptosis. AIF knockout cells failed to form tumors in athymic mice or grow in soft agar. Only AIF with intact NADH oxidase activity restored complex I activity and anchorage‐independent growth of aif knockout cells, and induced aif ‐transfected mouse NIH3T3 cells to form foci. AIF knockdown in different carcinoma cell types resulted in lower superoxide levels, enhanced apoptosis sensitivity and loss of tumorigenicity. Antioxidants sensitized AIF‐expressing cells to apoptosis, but had no effect on tumorigenicity. In summary, AIF‐mediated resistance to chemical stress involves ROS and probably also mitochondrial complex I. AIF maintains the transformed state of colon cancer cells through its NADH oxidase activity, by mechanisms that involve complex I function. On both counts, AIF represents a novel type of cancer drug target.