Metabolic profiling of hypoxia-inducible factor-1β-deficient and wild type Hepa-1 cells: Effects of hypoxia measured by<sup>1</sup>H magnetic resonance spectroscopy
Troy H., Chung YL., Mayr M., Ly L., Williams K., Stratford I., Harris A., Griffiths J., Stubbs M.
HIF-1 is upregulated across a broad range of cancers and modulates tumor progression through genes including those for glycolytic enzymes and glucose transporters. Hepa-1 cell lines that were either wild type (WT), or deficient in HIF-1β (c4) were studied by metabolic profiling. Western blots indicated that the HIF-1β deficient c4 cells failed to translocate the HIF-1α-β complex to the nucleus under hypoxia whereas both HIF-1α and HIF-1β accumulated in the nuclei of Hepa-1 WT cells after 18 h exposure to hypoxia (1% O 2 , 5% CO 2 , N 2 ). Reporter gene assays showed that, compared to WT cells, c4 cells were unable to activate transcription from the PGK and LDH HRE regulated promoters. ELISA assays showed similar VEGF secretion by both cell types under normoxia and a 1.6-fold increase in WT cells under hypoxia. Metabolite profiles (by 1 H MR spectroscopy) under normoxia (95% air, 5% CO 2 ) showed similar lactate content and secretion whilst hypoxia caused lactate to increase ∼2.5-fold in both deficient and WT cells. In addition phosphocholine (PC), NTP (by 31 P MRS) and glycine were significantly lower in c4 than WT cells under normoxia. Although the immunoblotting and transcription assays indicated loss of activation of HIF-1β, the c4 cells were still able to upregulate glycolysis in hypoxia (as shown by the lactate data). We conclude that there are mechanisms other than HIF-1β transcription that may up-regulate glycolysis in HIF-1 deficient Hepa-1 cells. © Springer Science+Business Media, Inc. 2006.