Hypoxia and the metabolic phenotype of prostate cancer cells
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Cancer cells have the ability to survive when oxygen is limiting, and upregulate the pathway of fatty acid synthesis, owing in part to alterations in their metabolism. I compared the metabolic phenotypes of the prostate cancer cell lines LNCaP, DU145, and PC3 assessing energy metabolism, and metabolic gene expression. I also explored the plasticity of the metabolic phenotype following passage, selection and in vivo growth. Finally, I explored the sensitivity of the fatty acid synthesis pathway to low oxygen. LNCaP cells had a more oxidative phenotype based on oxygen consumption, lactate production, enzyme assays, and mRNA levels. While DU145 and PC3 cells were more glycolytic, they were unresponsive to dichloroacetate (DCA), and dinitrophenol (DNP), stimulators of oxygen consumption. Mitochondrial dysfunction in the PC3 and DU145 cells may explain this phenomenon, for they possessed normal cardiolipin levels but lower mitochondrial enzyme activities (cytochrome oxidase (COX), citrate synthase (CS)). When LNCaP cells were subjected to high passage, with and without clonal selection, the derived lines acquired a dysfunctional oxidative phenotype, becoming more glycolytic. Clonal selection appeared to have the most dramatic effect on cellular metabolism. This finding is supported by decreased oxygen consumption, increased lactate production, and a reduction in the activity of the oxidative enzymes CS and COX in the clonally selected LNCaP-luc cell line. Similar to the DU145 and PC3 cells, NAO fluorescence indicates that the oxidative impairment in these LNCaP-derived lines may be due to a reduction in mitochondrial activity. The pattern of metabolic gene expression iii seen in vitro was unaffected when LNCaP cells were grown as subcaspular and muscle xenografts in immunodeficient mice, though xenografts did exhibit indications of an hypoxic response (elevated VEGF mRNA). Oxygen deprivation in vitro increased mRNA for HIF and responsive genes but not SREBP responsive genes. Similarly, oxygen deprivation had no influence on triglyceride levels in any of the lines suggesting that the SREBP axis may not be directly modulated by oxygen levels. Collectively these studies demonstrate differences in the metabolism of these prostate cancer models, with important ramifications of therapeutic strategies involving metabolic targets.