HIF1
哺乳動物細胞を低酸素環境で培養した際に細胞やあ個体の恒常性を維持するために働く転写因子。
HIF1αとHIF1βのヘテロダイマーである。
低酸素に対する細胞の応答（エネルギー代謝、血管新生、アポトーシスを司る遺伝子発現の調節を含む）の主役である。
HIF1αは通常のコンディションでは迅速にプロテオソームで分解されるが、低酸素で安定化する。
HIF1の活性は酸素濃度によってユビキチン化され分解されるHIF1αの濃度で調節される。
低酸素により、タンパク合成は全体として抑制される。
VEGFの転写は転写開始の1kbp上流にある低酸素応答エレメントにHIF1が結合することで増加する。
他に、HIF1が調節に関与する遺伝子はエネルギー代謝、鉄代謝、血管新生、細胞増殖など多岐にわたる。
酸素存在下で、VHLタンパクを含むE3ユビキチンリガーゼによってHIFは分解される。
この際のVHLとHIFの相互作用にHIF1の特定のプロリンの水酸化が関与する。（HIFalpha prolyl-hydroxylase）
Hypoxia-inducible factor 1-alpha
Short name=HIF-1-alpha
Short name=HIF1-alpha
Alternative name(s):
ARNT-interacting protein
Basic-helix-loop-helix-PAS protein MOP1
Class E basic helix-loop-helix protein 78
Short name=bHLHe78
Member of PAS protein 1
PAS domain-containing protein 8
Gene names
Name: HIF1A
Synonyms: BHLHE78, MOP1, PASD8
Function
Functions as a master transcriptional regulator of the adaptive response to hypoxia. Under hypoxic conditions, activates the transcription of over 40 genes, including erythropoietin, glucose transporters, glycolytic enzymes, vascular endothelial growth factor, HILPDA, and other genes whose protein products increase oxygen delivery or facilitate metabolic adaptation to hypoxia. Plays an essential role in embryonic vascularization, tumor angiogenesis and pathophysiology of ischemic disease. Binds to core DNA sequence 5'-[AG]CGTG-3' within the hypoxia response element (HRE) of target gene promoters. Activation requires recruitment of transcriptional coactivators such as CREBPB and EP300. Activity is enhanced by interaction with both, NCOA1 or NCOA2. Interaction with redox regulatory protein APEX seems to activate CTAD and potentiates activation by NCOA1 and CREBBP. Involved in the axonal distribution and transport of mitochondria in neurons during hypoxia. Ref.16 Ref.21 Ref.23 Ref.30 Ref.34 Ref.35 Ref.36 Ref.42 Ref.43
Subunit structure
Interacts with the HIF1A beta/ARNT subunit; heterodimerization is required for DNA binding. Interacts with COPS5; the interaction increases the transcriptional activity of HIF1A through increased stability By similarity. Interacts with EP300 (via TAZ-type 1 domains); the interaction is stimulated in response to hypoxia and inhibited by CITED2. Interacts with CREBBP (via TAZ-type 1 domains). Interacts with NCOA1, NCOA2, APEX and HSP90. Interacts (hydroxylated within the ODD domain) with VHLL (via beta domain); the interaction, leads to polyubiquitination and subsequent HIF1A proteasomal degradation. During hypoxia, sumoylated HIF1A also binds VHL; the interaction promotes the ubiquitination of HIF1A. Interacts with SENP1; the interaction desumoylates HIF1A resulting in stabilization and activation of transcription. Interacts (Via the ODD domain) with ARD1A; the interaction appears not to acetylate HIF1A nor have any affect on protein stability, during hypoxia. Interacts with RWDD3; the interaction enhances HIF1A sumoylation. Interacts with TSGA10 By similarity. Interacts with RORA (via the DNA binding domain); the interaction enhances HIF1A transcription under hypoxia through increasing protein stability. Interaction with PSMA7 inhibits the transactivation activity of HIF1A under both normoxic and hypoxia-mimicking conditions. Interacts with USP20. Interacts with GNB2L1/RACK1; promotes HIF1A ubiquitination and proteasome-mediated degradation. Interacts (via N-terminus) with USP19. Ref.11 Ref.15 Ref.16 Ref.17 Ref.18 Ref.19 Ref.21 Ref.22 Ref.24 Ref.29 Ref.31 Ref.32 Ref.33 Ref.34 Ref.35 Ref.37 Ref.38 Ref.39 Ref.40 Ref.45 Ref.46
Subcellular location
Cytoplasm. Nucleus. Note: Cytoplasmic in normoxia, nuclear translocation in response to hypoxia. Colocalizes with SUMO1 in the nucleus, under hypoxia. Ref.13
Tissue specificity
Expressed in most tissues with highest levels in kidney and heart. Overexpressed in the majority of common human cancers and their metastases, due to the presence of intratumoral hypoxia and as a result of mutations in genes encoding oncoproteins and tumor suppressors.
Induction
Under reduced oxygen tension. Induced also by various receptor-mediated factors such as growth factors, cytokines, and circulatory factors such as PDGF, EGF, FGF2, IGF2, TGFB1, HGF, TNF, IL1B/interleukin-1 beta, angiotensin-2 and thrombin. However, this induction is less intense than that stimulated by hypoxia. Repressed by HIPK2 and LIMD1. Ref.41 Ref.47
Domain
Contains two independent C-terminal transactivation domains, NTAD and CTAD, which function synergistically. Their transcriptional activity is repressed by an intervening inhibitory domain (ID). Ref.12 Ref.14 Ref.15
Post-translational modification
In normoxia, is hydroxylated on Pro-402 and Pro-564 in the oxygen-dependent degradation domain (ODD) by EGLN1/PHD1 and EGLN2/PHD2. EGLN3/PHD3 has also been shown to hydroxylate Pro-564. The hydroxylated prolines promote interaction with VHL, initiating rapid ubiquitination and subsequent proteasomal degradation. Deubiquitinated by USP20. Under hypoxia, proline hydroxylation is impaired and ubiquitination is attenuated, resulting in stabilization.
In normoxia, is hydroxylated on Asn-803 by HIF1AN, thus abrogating interaction with CREBBP and EP300 and preventing transcriptional activation. This hydroxylation is inhibited by the Cu/Zn-chelator, Clioquinol.
S-nitrosylation of Cys-800 may be responsible for increased recruitment of p300 coactivator necessary for transcriptional activity of HIF-1 complex.
Requires phosphorylation for DNA-binding. Phosphorylation at Ser-247 by CSNK1D/CK1 represses kinase activity and impairs ARNT binding. Phosphorylation by GSK3-beta and PLK3 promote degradation by the proteasome.
Sumoylated; with SUMO1 under hypoxia. Sumoylation is enhanced through interaction with RWDD3. Desumoylation by SENP1 leads to increased HIF1A stability and transriptional activity By similarity. Ref.30 Ref.36 Ref.37
Ubiquitinated; in normoxia, following hydroxylation and interaction with VHL. Lys-532 appears to be the principal site of ubiquitination. Clioquinol, the Cu/Zn-chelator, inhibits ubiquitination through preventing hydroxylation at Asn-803. Ref.14 Ref.20 Ref.21 Ref.23 Ref.32 Ref.35 Ref.39
The iron and 2-oxoglutarate dependent 3-hydroxylation of asparagine is (S) stereospecific within HIF CTAD domains.
Sequence similarities
Contains 1 bHLH (basic helix-loop-helix) domain.
Contains 1 PAC (PAS-associated C-terminal) domain.
Contains 2 PAS (PER-ARNT-SIM) domains.
