An early effect of the dysregulated growth that occurs in cancer is the accumulation of malignant cells in excess of the physiologic numbers that can be supported by the existing vascular system. Therefore, developing tumors are subject to a combination of oxygen limitation and nutrient deprivation. In nontransformed cells, either hypoxia or nutrient deprivation leads to the initiation of apoptosis. Our initial studies suggest that apoptosis in response to hypoxia/glucose deprivation is initiated by the proapoptotic effects of Bax and Bak. Nevertheless, few tumors carrying mutations in both Bax and Bak have been observed. Therefore, to survive hypoxia/glucose deprivation tumor cells must suppress the ability of Bax and Bak to initiate apoptosis. The goals of this project are to determine how apoptotic regulatory genes that have been implicated in carcinogenesis contribute to the cellular response to hypoxia/nutrient deprivation.
Three specific aims are envisioned: 1) determine the molecular mechanisms by which Bax and Bak activation occur under conditions of hypoxia or glucose withdrawal; 2) determine the role of the Akt/PI3 kinase/PTEN/TOR pathway in the susceptibility to apoptosis during hypoxia and nutrient deprivation and determine the interrelationship between this metabolic control pathway and the metabolic sensing pathway mediated by AMPK; and 3) identify genes involved in prolonged adaptation to metabolic stress and determine whether they can contribute to the malignant phenotype of transformed cells. There are obvious synergies between this project and Project 2 in studying the molecular response to hypoxia. Where appropriate, we will collaborate with the other projects in investigating the roles of genes implicated in intracellular adaptation to metabolic stress to determine the contributions of these genes to the regulation of apoptosis (this project) and cellular adaptation to ER stress and hypoxia (Projects 2, 3). Specific areas where we expect synergy between the studies proposed here and those proposed in the other projects include studies of the genes transcriptionally induced in response to oxygen limitation by HIF-1alpha (Project 2) and the substrates PERK and related elF2alpha kinases (Project 3). Through these combined studies we expect to learn how known apoptotic genes are regulated transcriptionally and post transcriptionally in response to hypoxiaJnutrient deprivation, discover additional genes involved in apoptotic regulation, and ultimately use this information to design novel treatment strategies that specifically stimulate apoptosis of transformed tumor cells under conditions of nutrient or oxygen limitation.
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