Sirtuin-7 Inhibits the Activity of Hypoxia-inducible Factors

Hypoxia-inducible factor (HIF) 1 and HIF-2 are heterodimeric proteins composed of an oxygen-regulated HIF-1 alpha or HIF-2 alpha subunit, respectively, and a constitutively expressed HIF-1 beta subunit, which mediate adaptive transcriptional responses to hypoxia. Here, we report that Sirt7 (sirtuin-7) negatively regulates HIF-1 alpha and HIF-2 alpha protein levels by a mechanism that is independent of prolyl hydroxylation and that does not involve proteasomal or lysosomal degradation. The effect of Sirt7 was maintained in the presence of the sirtuin inhibitor nicotinamide and upon deletion or mutation of its deacetylase domain, indicating a non-catalytic function. Knockdown of Sirt7 led to an increase in HIF-1 alpha and HIF-2 alpha protein levels and an increase in HIF-1 and HIF-2 transcriptional activity. Thus, we identify a novel molecular function of Sirt7 as a negative regulator of HIF signaling.