HIFs are heterodimeric proteins composed of an alpha subunit (HIF-α) and a beta subunit (HIF-β). The HIF-α subunit is oxygen-sensitive, while the HIF-β subunit, also known as ARNT (Aryl Hydrocarbon Receptor Nuclear Translocator), is constitutively expressed. There are three main isoforms of the HIF-α subunit: HIF-1α, HIF-2α, and HIF-3α, each with distinct but overlapping roles.
