Abstract 4698: Mechanism of glucose deprivation-induced sensitization of tumor cells to receptor-mediated apoptosis: Downregulation of intracellular superoxide anion and cFLIP
Authors: Hirpara Jayshree L. , Subramaniam Kothandaraman , Seah Serena , Loh Thomas , Goh Boon Cher , Pervaiz Shazib 
Published: June 2012

Abstract
One hallmark of cancer cells is their ability to switch their metabolism from oxidative phosphorylation to glycolysis. This is accomplished via an increase in glucose uptake and high rate of glycolysis. Therefore, one attractive strategy for a favorable anti-cancer response would be to deprive cancer cells of this essential nutrient. Here we investigated the effect of glucose withdrawal on death receptor-induced apoptosis in human leukemia cells overexpressing Bcl-2. Interestingly, subjecting Bcl-2 overexpressing cancer cells to a 30-60 minutes of glucose deprivation significantly increased sensitivity to CD95 (Fas/Apo1)-induced apoptosis. We have previously reported that death signaling in cancer cells is regulated by the cellular redox status in that a slight increase in superoxide anion (O2-) inhibited apoptotic signaling1. Of note, we also reported the ability of Bcl-2 and other oncogenes such as Rac1 to inhibit apoptosis via generating a pro-oxidant intracellular milieu. In line with those findings, we report here that glucose withdrawal resulted in a significant decrease in intracellular O2- and triggered strong activation of caspases 8, 9, and 3, translocation of Bax to the mitochondria and subsequent release of cytochrome C, independent of Bcl-2 expression. More importantly, we identified the death inhibitory protein cFLIP as a target of glucose withdrawal induced sensitization to death receptor induced apoptosis; glucose withdrawal decreased the expression and promoter activity of cFLIP, which correlated with increased caspase 8 activation. In order to provide evidence to link O2- to death inhibition, intracellular O2- levels were manipulated by incubation with PMA (62.5ng/ml), paraquat (50uM), or upon transient transfection with the constutively active form of the GTP binding protein Rac1 (RacV12) or a variety of functional mutants of Rac1, namely H103A, K166E, H40 and L37, and the effect on glucose withdrawal induced apoptosis was assessed. Indeed, increasing O2- strongly inhibited death signaling in cancer cells via an effect on the promoter activity and transcription of cFLIP, whereas blocking NADHP oxidase repressed cFLIP expression and facilitated death execution. This finding suggest that the glycolytic pathway may be important in sensitizing tumor cells to death receptor ligand by inhibiting cFLIP and facilitating the activation of initiator caspase-8 via a drop in intracellular O2-.
1 Clement, M-V., Hirpara, J.L., and Pervaiz, S. Decrease in intracellular superoxide sensitizes Bcl-2 overexpressing tumor cells to receptor- and drug-induced apoptosis independent of the mitochondria. Cell Death Diff. 10(11):1273-85, 2003.
This work is supported by research grants to S.P. from the NMRC, Singapore.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4698. doi:10.1158/1538-7445.AM2011-4698