Adaptation to chronic
hypoxia occurs through changes in
protein expression, which are controlled by
hypoxia-inducible factor 1α (HIF1α) and are necessary for
cancer cell survival. However, the mechanisms that enable
cancer cells to adapt in early
hypoxia, before the HIF1α-mediated transcription programme is fully established, remain poorly understood. Here we show in human
breast cancer cells, that within 3 h of
hypoxia exposure, glycolytic flux increases in a HIF1α-independent manner but is limited by NAD+ availability. Glycolytic
ATP maintenance and cell survival in early
hypoxia rely on reserve
lactate dehydrogenase A capacity as well as the activity of
glutamate-oxoglutarate
transaminase 1 (GOT1), an
enzyme that fuels
malate dehydrogenase 1 (MDH1)-derived NAD+. In addition, GOT1 maintains low α-ketoglutarate levels, thereby limiting
prolyl hydroxylase activity to promote HIF1α stabilisation in early
hypoxia and enable robust HIF1α target gene expression in later
hypoxia. Our findings reveal that, in normoxia, multiple
enzyme systems maintain cells in a primed state ready to support increased glycolysis and HIF1α stabilisation upon
oxygen limitation, until other adaptive processes that require more time are fully established.