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

Abstract

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.

Physical interaction of apoptosis-inducing factor with DNA and RNA

“…Within mitochondria, AIF is required for the maturation and/or maintenance of the complex I of the respiratory chain (Vahsen et al, 2004). This effect depends on its redox activity (Urbano et al, 2005). Indeed, AIF is a flavoprotein that can oxidize NADH and NADPH in vitro (Miramar et al, 2001) and may participate in the detoxification of reactive oxygen species (Klein et al, 2002) and in the maintenance of glutathione levels (Cande et al, 2004b), although the mechanisms of this antioxidant activity remain to be determined.…”

“…Thus, mutations that affect the redox activity of AIF compromise mitochondrial metabolism (Urbano et al, 2005), yet do not affect its acute proapoptotic activity (Loeffler et al, 2001). Conversely, mutations that affect the translocation of AIF into the nucleus or its DNA binding do not compromise its capacity to sustain the activity of the respiratory chain and cellular redox homeostasis (Cande et al, 2004b;Urbano et al, 2005).…”

“…Nonetheless, the role of AIF in cancer biology is ambiguous. On the one hand, AIF is required for the growth of colon carcinoma cells (Urbano et al, 2005). On the other hand, AIF is required for experimental apoptosis induction, for instance in radiation-resistant human T-cell lymphoma (Park et al, 2005) or in lung or cervix carcinoma (Gallego et al, 2004;Kang et al, 2004).…”

Cavitation of embryoid bodies requires optimal oxidative phosphorylation and AIF

“…10 In mammalian cells, removal of AIF can reduce apoptosis in some particular settings, although there is no general apoptosis defect. 2,8,9 Thus, knockdown of AIF protects differentiated PC12 cells against the neurotoxin 1-methyl-4-phenylpyridinium, 12 Jurkat T lymphoma cells against a combination of g-irradiation and phytosphingosin, 13 16 and Raji B lymphoma cells against UV irradiation. 17 Microinjection of AIF-neutralizing antibodies can also reduce the neurotoxic effects of NMDA in primary murine cortical cultures, 18 the lethal effects of PARP-1 activators in several cellular systems, 19 as well as the proapoptotic effects of staurosporin on non-small cell lung carcinoma cells.…”

“…4 AIF can also participate in apoptotic chromatinolysis, presumably by recruiting catabolic enzymes to the so-called degradosome. 7 The AIF gene has been knocked out or knocked down in several species including in human cell lines, 8 mice, 9 Caenorhabditis elegans 10 and Saccharomyces cerevisiae. 11 In yeast, the knockout of AIF leads to a partial resistance to oxidative stress and influences replicative aging.…”