Disease relevance of Epas1

• Cre-mediated removal of the inserted gene recovered normal HLF expression and retinal neovascularization in HLF(kd/kd) mice [1].
• HLF/HIF-2alpha is a key factor in retinopathy of prematurity in association with erythropoietin [1].
• To investigate the role of HLF in adult pathological angiogenesis, we generated HLF-knockdown (HLF(kd/kd)) mice by inserting a neomycin gene sandwiched between two loxP sequences into exon 1 of the HLF gene [1].
• EPAS1-null as well as heterozygous mice have impaired renal erythropoietin induction in response to hypoxia [2].
• We previously reported that mice lacking wild-type HIF-2alpha, encoded by the EPAS1 gene, exhibit pancytopenia [2].

High impact information on Epas1

• We report that mice lacking the HIF family member HIF-2alpha (encoded by Epas1) have a syndrome of multiple-organ pathology, biochemical abnormalities and altered gene expression patterns [3].
• Multiple organ pathology, metabolic abnormalities and impaired homeostasis of reactive oxygen species in Epas1-/- mice [3].
• Prenatal or postnatal treatment of Epas1-/- mice with a superoxide dismutase (SOD) mimetic reversed several aspects of the null phenotype [3].
• Transfection analyses showed that HIF-2alpha could efficiently transactivate the promoters of the primary AOEs [3].
• Using a genetic "knock-in" strategy, we demonstrate that targeted replacement of the oxygen-regulated transcription factor HIF-1alpha with HIF-2alpha results in expanded expression of HIF-2alpha-specific target genes including Oct-4, a transcription factor essential for maintaining stem cell pluripotency [4].

Chemical compound and disease context of Epas1

• We report here that the C-terminal transactivation domain of HLF is phosphorylated on multiple sites and that phosphorylation on threonine 844 of HLF is necessary for the transcriptional activation function of the protein independently of the hypoxia condition [5].
• Importantly, HIF-1alpha Pro-564 and HIF-2alpha Pro-531 hydroxylation is diminished with the treatment of hypoxia, cobalt chloride, desferrioxamine, or dimethyloxalyglycine, regardless of the E3 ubiquitin ligase activity of the von Hippel-Lindau (VHL) tumor suppressor gene [6].
• We recently showed that Hypoxia inducible factor-2alpha (HIF-2alpha) plays several supporting roles in adipose differentiation and adipocytes functions including regulation of glucose uptake followed by lipid synthesis [7].
• As elevated bronchoalveolar lavage (BAL) fluid histamine levels are noted in patients with pulmonary fibrosis (PF), we assayed BAL fluid from 16 patients with PF for the presence of a histamine releasing factor (HRF) [8].

Biological context of Epas1

• Whole mount in situ hybridization experiments demonstrated that HLF mRNA was expressed in vascular endothelial cells at the middle stages (9.5 and 10.5 days postcoitus) of mouse embryo development, where HIF1alpha mRNA was almost undetectable [9].
• The HIF1alpha-like factor (HLF) encoded by the isolated cDNA bound the hypoxia-response element (HRE) found in enhancers of genes for erythropoietin, vascular endothelial growth factor (VEGF), and various glycolytic enzymes, and activated transcription of a reporter gene harboring the HRE [9].
• In lung development around parturition, HLF mRNA expression was markedly enhanced, whereas that of HIF1alpha mRNA remained apparently unchanged at a much lower level [9].
• The deletion of the DNA binding and carboxyl-terminal transactivation domains of HIF-2alpha, respectively, created dominant negative mutants that suppressed transactivation by the wild type protein and failed to synergize with Ets-1 [10].
• A tandem HIF-2alpha/Ets binding site was identified within the Flk-1 promoter that acted as a strong enhancer element [10].

Anatomical context of Epas1

• The high expression level of HLF mRNA in the O2 delivery system of developing embryos and adult organs suggests that in a normoxic state, HLF regulates gene expression of VEGF, various glycolytic enzymes, and others driven by the HRE sequence, and may be involved in development of blood vessels and the tubular system of lung [9].
• In contrast, HIF-2alpha was present in endothelial cells, bronchial epithelial cells, and type II cells from E18 to P28 [11].
• In addition, smooth muscle cells of the uterus, neurons, brown adipose tissue and various epithelial tissues express HRF mRNA as well [12].
• In the present study we describe mRNA cloning and mRNA expression pattern of mouse HIF-related factor (HRF), a novel close relative of HIF-1 alpha which is expressed most prominently in brain capillary endothelial cells and other blood vessels as well as in bronchial epithelium in the embryo and the adult [12].
• HIF-2alpha regulates Oct-4: effects of hypoxia on stem cell function, embryonic development, and tumor growth [4].

Associations of Epas1 with chemical compounds

• Transcriptionally active heterodimer formation of an Arnt-like PAS protein, Arnt3, with HIF-1a, HLF, and clock [13].
• In addition, we engineered HEK293 cells to express stabilized forms of HIF-1alpha or HIF-2alpha via a tetracycline-regulated promoter [14].
• Taken together, these results suggest that EPAS1 plays several supporting roles in maintaining specific aspects of adipogenesis and adipocyte function including regulation of glucose uptake followed by lipid synthesis [15].
• Using pharmacological, molecular, and genetic approaches, we also observed that although progesterone primarily up-regulates uterine HIF-1alpha expression, estrogen transiently stimulates that of HIF-2alpha [16].
• Here, employing a novel hydroxylation-specific antibody, we directly show that proline 564 of HIF-1alpha and proline 531 of HIF-2alpha are hydroxylated under normoxia [6].
• Additional experiments indicate that the ETS transcription factor ELK is required for HIF-2alpha to activate specific target genes such as Cited-2, EPO, and PAI-1 [17].

Physical interactions of Epas1

• HIF-2alpha may function through ephrin A1 as the expression of ephrin A1 and related genes was markedly reduced in kd/kd ECs, and HIF-2alpha specifically bound a hypoxia-response element sequence in the ephrin A1 promoter [18].

Regulatory relationships of Epas1

• HIF-2alpha regulates murine hematopoietic development in an erythropoietin-dependent manner [2].
• These and other data indicate that HIF-2alpha promotes tumor growth more effectively than HIF-1alpha in multiple contexts [19].

Other interactions of Epas1

• Treatment of EPAS1-null mice with exogenous erythropoietin reverses the hematopoietic and other defects [2].
• These results suggest that the interaction between HIF-2alpha and endothelial Ets factors is required for the full transcriptional activation of Flk-1 in endothelial cells and may therefore represent a future target for the manipulation of angiogenesis [10].
• Thus, HIMF and HIF-2alpha were temporally and spatially coexpressed in the developing lung [11].
• The recent cloning of ARNT and HIF1(homologues (ARNT2 and HIF2 alpha) indicates that at least six distinct bHLH-PAS heterodimeric combinations can occur in response to a number of environmental stimuli [20].
• In electrophoretic mobility studies, CHF1 inhibited the binding of the ARNT/EPAS1 heterodimer to its target site [21].
• Under very stringent conditions, we ablate Hif-2alpha after birth and compare the effect of acute global deletion of Hif-2alpha and Hif-1alpha [22].

Analytical, diagnostic and therapeutic context of Epas1

• Together with the results from intraperitoneal injection of Epo into HLF(kd/kd) mouse, this suggests that Epo is one of the target genes of HLF responsible for experimental ROP [1].
• We have studied the role of the basic helix-loop-helix-PAS transcription factor EPAS-1/hypoxia-inducible factor 2alpha in vascular development by gene targeting [23].
• To address this discrepancy, and to identify specific HIF-2alpha target genes, we used DNA microarray analysis to evaluate hypoxic gene induction in cells expressing HIF-2alpha but not HIF-1alpha [14].
• Immunohistochemistry of newborn kidney demonstrated widespread expression of HIF-1beta protein in nuclei of glomeruli and all tubular segments, whereas HIF-2alpha protein expression was more restricted and localized chiefly to podocytes of developing glomeruli and developing tubules [24].
• The expression of HIF-1alpha and HIF-2alpha mRNAs in newborn mouse kidney was confirmed by RT-PCR and Northern blot analysis [24].

References