HIF1A (hypoxia inducible factor 1 subunit alpha; HGNC:4910, NCBI Gene ID 3091) is a human locus mapped to chromosome band 14q23.2 that encodes oxygen-labile basic helix-loop-helix-PAS transcription factor subunit HIF-1alpha (826 aa). HIF1A acts in normoxic PHD1–3 prolyl hydroxylation (Pro402/Pro564) & VHL ubiquitylation vs. hypoxic heterodimerization with ARNT -> VEGFA, EPO, GLUT1 & LDHA/PDK1 glycolysis, together with VEGFA (Primary Angiogenic Target Gene of HIF-1alpha), EPO (Erythropoietin Hypoxia Response Element Target Gene), and LDHA (Anaerobic Glycolysis Target Gene of HIF-1alpha). Encodes the oxygen-sensitive alpha subunit of hypoxia-inducible factor 1 (HIF-1), the master transcriptional regulator of cellular adaptation to hypoxia, angiogenesis, and glycolysis.
Normoxic PHD1–3 prolyl hydroxylation (Pro402/Pro564) & VHL ubiquitylation vs. hypoxic heterodimerization with ARNT -> VEGFA, EPO, GLUT1 & LDHA/PDK1 glycolysis
Clinical / Therapeutic Role
2019 Nobel Prize oxygen-sensing pathway; targeted by HIF-PHD stabilizers (daprodustat, vadadustat) for renal anemia & HIF-2alpha inhibitor belzutifan in VHL tumors
Gene Structure & Expression
Genomic Organization & Cytogenetic Locus: 15-exon gene on chromosome 14q23.2 encoding an 826-amino-acid polypeptide composed of an N-terminal basic helix-loop-helix (bHLH) DNA-binding domain, tandem Per-Arnt-Sim (PAS-A and PAS-B) heterodimerization domains, a central Oxygen-Dependent Degradation Domain (ODDD, residues 401–603 carrying conserved prolines Pro402 and Pro564), and two transactivation domains (N-TAD and C-TAD, where Asn803 is hydroxylated by FIH-1 / HIF1AN).
Cellular & Tissue Expression Profile: Constitutively transcribed and translated across all nucleated human cells (driven in part by growth factor PI3K-AKT1-mTORC1 signaling), with protein half-life controlled strictly by cellular O2 tension.
Molecular Function & Pathways
Biochemical & Physiological Mechanism: Under normoxia (normal O2, 2-oxoglutarate, Fe2+, and ascorbate), prolyl hydroxylase domain enzymes PHD1, PHD2 (EGLN1), and PHD3 split molecular O2 to hydroxylate Pro402 and Pro564 of HIF-1alpha—creating a high-affinity binding site for the von Hippel-Lindau (VHL) E3 ubiquitin ligase complex, which polyubiquitylates HIF-1alpha for proteasomal destruction within <5 minutes, while Factor Inhibiting HIF-1 (FIH-1) hydroxylates Asn803 to block p300/CBP coactivator binding; when tissue O2 falls below ~2–5% (hypoxia, ischemia, high altitude, or solid tumors), PHD and FIH-1 enzymes arrest, allowing HIF-1alpha to accumulate, enter the nucleus, heterodimerize with constitutive HIF-1beta (ARNT), and bind 5-prime-RCGTG-3-prime Hypoxia Response Elements (HREs) to activate >100 genes—including VEGFA (angiogenesis), EPO (erythropoiesis), SLC2A1/GLUT1, HK2, LDHA, and PDK1 (which shifts metabolism from mitochondrial OXPHOS to anaerobic glycolysis, opposed by SIRT6).
Clinical & Therapeutic Significance
Human Genetic Variants & Disease Phenotypes: Discovery of the HIF-PHD-VHL oxygen-sensing mechanism by Gregg Semenza (who purified and cloned HIF1A in 1995), William Kaelin, and Peter Ratcliffe was awarded the 2019 Nobel Prize in Physiology or Medicine; in aging skeletal muscle, declining nuclear NAD+ reduces SIRT1 activity and causes pseudohypoxic stabilization of HIF-1alpha, which sequesters c-MYC and disrupts TFAM-dependent nuclear-mitochondrial communication.
Therapeutic & Clinical Pharmacology: Oral small-molecule 2-oxoglutarate-competitive PHD inhibitors (daprodustat, vadadustat, roxadustat) stabilize endogenous HIF-1alpha/HIF-2alpha to treat anemia of chronic kidney disease, whereas hypoxia-addicted clear-cell renal cell carcinomas (which lack VHL) are treated with the FDA-approved HIF-2alpha PAS-B pocket inhibitor belzutifan (Welireg).