[EPAS1_HUMAN] Defects in EPAS1 are the cause of familial erythrocytosis type 4 (ECYT4) [MIM:611783]. ECYT4 is an autosomal dominant disorder characterized by increased serum red blood cell mass, elevated hemoglobin concentration and hematocrit, and normal platelet and leukocyte counts.
[EPAS1_HUMAN] Transcription factor involved in the induction of oxygen regulated genes. Binds to core DNA sequence 5'-[AG]CGTG-3' within the hypoxia response element (HRE) of target gene promoters. Regulates the vascular endothelial growth factor (VEGF) expression and seems to be implicated in the development of blood vessels and the tubular system of lung. May also play a role in the formation of the endothelium that gives rise to the blood brain barrier. Potent activator of the Tie-2 tyrosine kinase expression. Activation seems to require recruitment of transcriptional coactivators such as CREBPB and probably EP300. Interaction with redox regulatory protein APEX seems to activate CTAD. [ARNT_HUMAN] Required for activity of the Ah (dioxin) receptor. This protein is required for the ligand-binding subunit to translocate from the cytosol to the nucleus after ligand binding. The complex then initiates transcription of genes involved in the activation of PAH procarcinogens. The heterodimer with HIF1A or EPAS1/HIF2A functions as a transcriptional regulator of the adaptive response to hypoxia.
The aryl hydrocarbon receptor nuclear translocator (ARNT) is a promiscuous bHLH-PAS (Per-ARNT-Sim) protein that forms heterodimeric transcriptional regulator complexes with several other bHLH-PAS subunits to control a variety of biological pathways, some of which are centrally involved in disease initiation and/or progression. One of these is the hypoxia response pathway, which allows eukaryotic cells to respond to low oxygen tension via the formation of a heterodimeric complex between ARNT and another bHLH-PAS protein, the hypoxia-inducible factor alpha (HIF-alpha). We have previously shown that the C-terminal PAS domains of an HIF-alpha isoform (HIF-2alpha) and ARNT interact in vitro, and that mutations in the solvent-exposed beta-sheet surface of the HIF-2alpha domain not only disrupt this interaction, but also greatly attenuate the hypoxia response in living cells. Here, we have solved the solution structure of the corresponding PAS domain of ARNT and show that it utilizes a very similar interface for the interaction with the HIF-2alpha PAS domain. We also show that this domain self-associates in a concentration-dependent manner, and that the interface used in this homodimeric complex is very similar to that used in the formation of heterodimer. In addition, using experimentally derived NMR restraints, we used the program HADDOCK to calculate a low-resolution model of the complex formed in solution by these two PAS domains, and confirm the validity of this model using site-directed spin labeling to obtain long-range distance information in solution. With this information, we propose a model for the mode of multi-PAS domain interaction in bHLH-PAS transcriptional activation complexes.
Structural basis of ARNT PAS-B dimerization: use of a common beta-sheet interface for hetero- and homodimerization.,Card PB, Erbel PJ, Gardner KH J Mol Biol. 2005 Oct 28;353(3):664-77. Epub 2005 Sep 6. PMID:16181639
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↑ Furlow PW, Percy MJ, Sutherland S, Bierl C, McMullin MF, Master SR, Lappin TR, Lee FS. Erythrocytosis-associated HIF-2alpha mutations demonstrate a critical role for residues C-terminal to the hydroxylacceptor proline. J Biol Chem. 2009 Apr 3;284(14):9050-8. doi: 10.1074/jbc.M808737200. Epub 2009, Feb 10. PMID:19208626 doi:10.1074/jbc.M808737200
↑ Percy MJ, Beer PA, Campbell G, Dekker AW, Green AR, Oscier D, Rainey MG, van Wijk R, Wood M, Lappin TR, McMullin MF, Lee FS. Novel exon 12 mutations in the HIF2A gene associated with erythrocytosis. Blood. 2008 Jun 1;111(11):5400-2. doi: 10.1182/blood-2008-02-137703. Epub 2008, Mar 31. PMID:18378852 doi:10.1182/blood-2008-02-137703
↑ Percy MJ, Furlow PW, Lucas GS, Li X, Lappin TR, McMullin MF, Lee FS. A gain-of-function mutation in the HIF2A gene in familial erythrocytosis. N Engl J Med. 2008 Jan 10;358(2):162-8. doi: 10.1056/NEJMoa073123. PMID:18184961 doi:10.1056/NEJMoa073123
↑ Percy MJ, Chung YJ, Harrison C, Mercieca J, Hoffbrand AV, Dinardo CL, Santos PC, Fonseca GH, Gualandro SF, Pereira AC, Lappin TR, McMullin MF, Lee FS. Two new mutations in the HIF2A gene associated with erythrocytosis. Am J Hematol. 2012 Apr;87(4):439-42. doi: 10.1002/ajh.23123. Epub 2012 Feb 24. PMID:22367913 doi:10.1002/ajh.23123
↑ Card PB, Erbel PJ, Gardner KH. Structural basis of ARNT PAS-B dimerization: use of a common beta-sheet interface for hetero- and homodimerization. J Mol Biol. 2005 Oct 28;353(3):664-77. Epub 2005 Sep 6. PMID:16181639 doi:10.1016/j.jmb.2005.08.043