Disruption of HIF1Α translational control attenuates the HIF-dependent hypoxic response and solid tumour formation in vivo

ABSTRACT Adaptation to reduced oxygen availability is mediated by the hypoxia-inducible factor (HIF) family of transcription factors. The activity and availability of HIF proteins is primarily driven by the stability of the HIF alpha subunits. However, it is becoming increasingly apparent that preferential translation of HIF1α mRNA is also necessary for full activation of the HIF1-dependent hypoxic response. Consequently, the mechanisms controlling HIF1α translation are of equivalent importance to the proline hydroxylase-dependent degradation pathways. Here we investigate the role of the 5’UTR of the HIF1α mRNA in controlling preferential translation of endogenous HIF1α in hypoxic cells. CRISPR/Cas9-mediated genetic deletion of the 5’ UTR of HIF1α results in reduced HIF1α levels following hypoxia, without alteration in mRNA or protein stability. HIF1α mRNA lacking the 5’UTR was efficiently translated in adequately oxygenated cells but this was inhibited during hypoxia, consistent with the global block on protein synthesis. The HIF1α translational defect observed in cells missing the 5’UTR led to reduced viability in hypoxic conditions in vitro and an impaired ability to form solid tumours in murine xenografts. Prevention of preferential HIF1α translation limits the duration and intensity of the HIF-dependent hypoxic response and disrupts the formation of solid tumours. Together these results demonstrate the importance of translation control over HIF1α and suggest that strategies to inhibit preferential HIF1α protein translation in hypoxic cancer cells will be an effective strategy to limit the growth of solid hypoxic tumours.