Bidirectional modulation of HIF-2 activity through chemical ligands.

Abstract

Hypoxia-inducible factor-2 (HIF-2) is a heterodimeric transcription factor formed through dimerization between an oxygen-sensitive subunit HIF-2α subunit and its obligate partner subunit ARNT. Enhanced HIF-2 activity drives some cancers, while reduced activity causes anemia in chronic kidney disease. Therefore, modulation of HIF-2 activity via direct-binding ligands could provide many new therapeutic benefits. Here, we explored HIF-2α chemical ligands using combined crystallographic, biophysical, and cell-based functional studies. We found chemically unrelated antagonists to employ the same mechanism of action. Their binding displaced residue M252 from inside the HIF-2α PAS-B pocket toward the ARNT subunit to weaken heterodimerization. We also identified first-in-class HIF-2α agonists and found they significantly displaced pocket residue Y281. Its dramatic side-chain movement increases heterodimerization stability and transcriptional activity. Our findings show that despite binding to the same HIF-2α PAS-B pocket, ligands can manifest as inhibitors versus activators by mobilizing different pocket residues to allosterically alter HIF-2α-ARNT heterodimerization.