Cancer cells require several adaptations to survive. Two key adaptations include the ability to evade apoptosis and metabolic rearrangement. Despite an obvious requirement for these two pathways to intersect, very little evidence exists supporting this convergence. We have observed that the small pro-apoptotic protein, Noxa, is capable of regulating separate metabolic pathways and therefore may represent an intersection between metabolism and apoptosis. Previous work in our lab showed that Noxa overexpressing cells increase glucose consumption and decrease glycolytic carbon flux into the citric acid cycle (TCA). Noxa expressing cells also increase the flux of glutamine derived carbon into the TCA, independent of the glycolytic role described above. We had shown previously that in the cytoplasm Noxa is phosphorylated and recruited into large multi- protein complexes in the presence of glucose. Found within these complexes is the pro-survival binding partner of Noxa, Mcl-1, and the glycolytic enzyme GAPDH. We observed that GAPDH in complex with Mcl-1 is post-translationally modified in response to glucose in a manner that is likely to inhibit its glycolytic activity. Our data suggest Noxa regulates glycolysis indirectly through Mcl-1 and GAPDH. Mitochondrial Noxa, on the other hand, may play a critical role in regulating how glutamine and ?-ketoglutarate are utilized. We observed that in cells lacking Noxa, the glutamine derived TCA intermediate ?-ketoglutarate accumulated in the mitochondria and increased mitochondrial respiration prior to causing massive apoptosis. Importantly, these mitochondrial metabolic effects of Noxa were independent of its apoptotic function, as a mutant deficient for apoptosis rescued sensitivity to ?-ketoglutarate. The studies proposed here will address Noxa's broad role in metabolism by investigating the mechanism underlying its regulation of the two pathways described above.
Specific Aim 1 will investigate the metabolic consequences of the Mcl-1/GAPDH/Noxa axis. Protein complexes and, specifically, interactions between Mcl-1 and GAPDH will be disrupted by genetic manipulation, and biochemical assays and targeted metabolomics will be used to interrogate the metabolic effects of the disruption.
Specific Aim 2 will examine Noxa's role in mitochondrial ?-ketoglutarate utilization, focusing on the malate/aspartate shuttle. The ability of specific metabolite treatments to sensitize cells or t rescue potential deficiencies in the malate/aspartate shuttle, either in the absence of Noxa or in the presence of its non-apoptotic mutant, will be examined to understand how Noxa affects this pathway. The results of these studies will offer valuable insight into both apoptosis evasion and metabolic alterations in cancer as we examine the convergence of these pathways through the Bcl-2 family protein, Noxa. More significantly, understanding the crosstalk between apoptosis and metabolic rearrangement could lead to the discovery of therapeutic targets capable of simultaneously disrupting two critical pillars of cancer.
Cancer cells acquire many adaptations during their development. Two key adaptations exhibited by tumor cells are evasion of death and metabolic alteration. This project will investigate the convergence of these two adaptations into one molecule, thereby revealing a significant therapeutic target.