The Circadian Clock Protein CRY1 Is a Negative Regulator of HIF-11

The circadian clock and the hypoxia signaling pathway are regulated by an integrated interplay of positive and negative feedback limbs that incorporate energy homeostasis and carcinogenesis. We show that the negative circadian regulator CRY1 is also a negative regulator of hypoxiainducible factor (HIF). Mechanistically, CRY1 interacts with the basic helixloop-helix domain of HIF-1α via its tail region. Subsequently, CRY1 reduces HIF-1α half-life and binding of HIFs to target gene promoters. This appeared to be CRY1 specific since genetic disruption of CRY1 but not CRY2 affected the hypoxia response. Further, CRY1-deficiency could induce cellular HIF levels, proliferation and migration, which could be reversed by CRISPR/Cas9 or shRNA mediated HIF knock-out. Altogether, our study provides a mechanistic explanation for genetic association studies linking a disruption of the circadian clock with hypoxia-associated processes such as carcinogenesis.