Glucose metabolism and cell death in cancer

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A key barrier that leukemic cells overcome in cancer progression is dependence on cytokine growth factors for survival. We have shown that prior to commitment to cell death, growth factor-deprivation of normal lymphoid cells results in cellular atrophy with decreased glucose metabolism, activation of autophagy, and proteolytic degradation of the anti-apoptotic Bcl-2 family member, Mcl1. In contrast, leukemic cells or cells with activated forms of the oncogenic kinase, Akt/PKB, resist atrophy and cell death, are highly glycolytic, and maintain Mcl1 even in the absence of growth factors. The role of this increased glucose metabolism is unknown. We show that increased glucose metabolism characteristic of cancer activates an anti-apoptotic nutrient signaling pathway. This glucose-stimulated signaling pathway involves inhibitory phosphorylation of glycogen synthase kinase-3ff//? (GSK3) by protein kinase C (PKC), which prevents degradation of Mcl1. McM stabilization appears critical as enhanced glucose metabolism failed to provide a survival advantage in Mel 1-deficient cells. The means by which glucose hydrolysis promotes PKC activity and regulates of McM remain uncertain. Glucose metabolism is also required for oncogenic Akt to prevent cell death in the absence of growth factor and the pentose phosphate pathway (PPP), in particular, may be important. In contrast, we show that Bcl-xL supports growth factor-independent survival in the absence of glucose and instead must rely on autophagy to both maintain mitochondrial metabolites and attenuate cell death. We hypothesize that the increased glucose utilization of cancer cells initiates cell metabolism and survival pathways that impact both mitochondrial and alternative cell death pathways and may play important roles in cancer cell resistance to death. We propose to: (1) Identify the mechanism of anti-apoptotic glucose-mediated signal transduction to activate PKC and stabilize McM; (2) Examine the role of glucose metabolism in cells expressing oncogenic Akt to determine the role that the PPP or alternative metabolic pathways play in regulation of Mcl1 and cell death; and (3) Establish the role of increased glucose metabolism on autophagy as a source of cell metabolism and survival in cytokine withdrawal. These studies will identify mechanisms by which cell metabolism may regulate cell death and how the highly glycolytic nature of cancer cells may affect these pathways to better understand cancer cell survival mechanisms.