Regulation of pyruvate dehydrogenase phosphorylation by hypoxia (572.4)

Pyruvate dehydrogenase (PDH), a mitochondrial enzyme, converts pyruvate formed by glycolysis into acetyl‐CoA, thus feeding the Krebs cycle. PDH can be inactivated by phosphorylation via pyruvate dehydrogenase kinase (PDK1), which is activated under hypoxic conditions. The levels of PDH (total and phosphorylated protein) , PDK1 and Hypoxia Inducible Factor (HIF‐1α and HIF‐2α) were analysed in human colon cancer cells HCT116 wild type and SCO2‐/‐ (deficient in complex IV of the respiratory chain) grown under 20.9% and 3% O2. Surprisingly, under normoxia the levels of active non‐phosphorylated PDH were substantially higher in the low respiring HCT116 SCO2‐/‐ cells. Under continuous hypoxia WT cells exhibited lower intracellular O2 coupled to the significant elevation of HIF‐α and PDK1 protein levels. A proportion of the inactive phospho‐PDH increased in both cell lines. Interestingly, in SCO2‐/‐ cells the level of phospho‐PDH became higher than in WT cells. Our data on PDH phosphorylation state indicates that regulation of the enzyme activity under normoxia and hypoxia can occur in a manner independent of HIF‐signalling, mitochondrial respiration and the demand of the Krebs cycle in acetyl‐CoA. Grant Funding Source : EU FP7 Marie Curie ITN Program “Chebana”, 733 grant agreement no. 264772.