Novel exon 12 mutations in the HIF2A gene associated with erythrocytosis.
Percy MJ
et al.
Blood 2008 Jun;111(11)5400-5402
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.
Blood 2008 Jun;111(11)5400-5402
Abstract: Erythrocytosis can arise from deregulation of the erythropoietin (Epo) axis resulting from defects in the oxygen-sensing pathway. Epo synthesis is controlled by the hypoxia inducible factor (HIF) complex, composed of an alpha and a beta subunit. There are 2 main alpha subunits, HIF-1 alpha and HIF-2 alpha. Recently, a HIF-2 alpha Gly537Trp mutation was identified in a family with erythrocytosis. This raises the possibility of HIF2A mutations being associated with other cases of erythrocytosis. We now report a subsequent analysis of HIF2A in a cohort of 75 erythrocytosis patients and identify 4 additional patients with novel heterozygous Met535Val and Gly537Arg mutations. All patients presented at a young age with elevated serum Epo. Mutations at Gly-537 account for 4 of 5 HIF2A mutations associated with erythrocytosis. These findings support the importance of HIF-2 alpha in human Epo regulation and warrant investigation of HIF2A in patients with unexplained erythrocytosis.
Characterization of a subset of the basic-helix-loop-helix-PAS superfamily that interacts with components of the dioxin signaling pathway.
Hogenesch JB
et al.
J Biol Chem 1997 Mar;272(13)8581-8593
Hogenesch JB, Chan WK, Jackiw VH, Brown RC, Gu YZ, Pray-Grant M, Perdew GH, Bradfield CA.
J Biol Chem 1997 Mar;272(13)8581-8593
Abstract: In an effort to better understand the mechanism of toxicity of 2,3,7, 8-tetrachlorodibenzo-p-dioxin, we employed an iterative search of human expressed sequence tags to identify novel basic-helix-loop-helix-PAS (bHLH-PAS) proteins that interact with either the Ah receptor (AHR) or the Ah receptor nuclear translocator (ARNT). We characterized five new "members of the PAS superfamily," or MOPs 1-5, that are similar in size and structural organization to the AHR and ARNT. MOPs 1-4 have N-terminal bHLH and PAS domains and C-terminal variable regions. MOP5 contained the characteristic PAS domain and a variable C terminus; it is possible that the cDNA contains a bHLH domain, but the entire open reading frame has yet to be completed. Coimmunoprecipitation studies, yeast two-hybrid analysis, and transient transfection experiments demonstrated that MOP1 and MOP2 dimerize with ARNT and that these complexes are transcriptionally active at defined DNA enhancer sequences in vivo. MOP3 was found to associate with the AHR in vitro but not in vivo. This observation, coupled with the fact that MOP3 formed tighter associations with the 90-kDa heat shock protein than the human AHR, suggests that MOP3 may be a conditionally active bHLH-PAS protein that requires activation by an unknown ligand. The expression profiles of the AHR, MOP1, and MOP2 mRNAs, coupled with the observation that they all share ARNT as a common dimeric partner, suggests that the cellular pathways mediated by MOP1 and MOP2 may influence or respond to the dioxin signaling pathway.
Endothelial PAS domain protein 1 (EPAS1), a transcription factor selectively expressed in endothelial cells.
Tian H
et al.
Genes Dev 1997 Jan;11(1)72-82
Tian H, McKnight SL, Russell DW.
Genes Dev 1997 Jan;11(1)72-82
Abstract: Here we describe the cloning and characterization of a PAS domain transcription factor termed endothelial PAS-1 (EPAS1). This protein shares 48% sequence identity with hypoxia inducible factor (HIF-1alpha) and lesser similarity with other members of the basic helix-loop-helix/PAS domain family of transcription factors. Like HIF-1alpha, EPAS1 binds to and activates transcription from a DNA element originally isolated from the erythropoietin gene and containing the sequence 5'-GCCCTACGTGCTGTCTCA-3'. Activation by both HIF-1alpha and EPAS1 is stimulated by hypoxic conditions. EPAS1 forms a heterodimeric complex with the aryl hydrocarbon nuclear transporter prior to transcriptional activation of target genes. EPAS1 expression is limited to the endothelium of mouse embryos and, in agreement with its cell type-specific expression pattern, is capable of specifically activating the transcription of the endothelial tyrosine kinase gene Tie-2. These observations raise the possibility that EPAS1 may represent an important regulator of vascularization, perhaps involving the regulation of endothelial cell gene expression in response to hypoxia.