Despite major advances in diagnosis and therapy there have been no improvements in the survival of patients with primary malignant brain tumors. Gliomas are the most common primary brain tumors in humans and glioblastoma multiforme (GBM) is the most aggressive of these tumors. GBMs are highly resistant to radiation and chemotherapy and nearly all patients with GBM die of their disease with a median survival of one year. In addition to genetic alterations, tumor hypoxia may play a role in the malignant progression of gliomas. This may be because tumor hypoxia induces the expression of angiogenic and cell survival-promoting cytokines and enhances the glycolytic capability of cancer cells. Hypoxia activates gene expression via the transcription factor HIF-1 which can also be turned on by certain growth factors. We have identified a novel biochemical pathway by which glycolytic metabolites such as lactate and pyruvate stabilize HIF-1alpha protein levels independently of hypoxia. Since the majority of hypoxia-independent activators of HIF- 1 also enhance glycolysis, this pathway may provide a mechanism accounting for their actions. Our recent discovery of autocrine erythropoietin signaling in human cancer also points to a major role for hypoxia in enhancing the survival of cancer cells via mechanisms not previously appreciated. The research proposed here will explore the relationship between hypoxia, altered gene expression, cell metabolism and cell survival. Our hypothesis is that hypoxia-induced changes in the ,qlycolytic metabolism of cancer cells results in the self-sustaining activation of HIF-1alpha regulated genes, even in the absence of persisting hypoxia. We will test our hypothesis by pursuing four aims:
Specific Aim #1 : Determine the mechanism by which glycolytic metabolites regulate HIF-1alpha protein stability.
Specific Aim #2 : Test the hypothesis that hypoxia-independent activators of HIF-1alpha act via regulation of glycolysis.
Specific Aim #3 : Determine whether hypoxic selection of treatment-resistant glioma cells results from the self-sustaining activation of HIF-1alpha regulated genes.
Specific Aim #4 : Test the hypothesis that erythropoietin signaling plays a prominent role in the hypoxia-induced selection of glioma cells with diminished apoptotic potential.
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