title: TET1 regulates hypoxia-induced epithelial-mesenchymal transition by acting as a co-activator.
abstract: BACKGROUND
  Hypoxia induces the epithelial-mesenchymal transition, EMT, to promote cancer metastasis. In addition to transcriptional regulation mediated by hypoxia-inducible factors, HIFs, other epigenetic mechanisms of gene regulation, such as histone modifications and DNA methylation, are utilized under hypoxia. However, whether DNA demethylation mediated by TET1, a DNA dioxygenase converting 5-methylcytosine, 5mC, into 5-hydroxymethylcytosine, 5hmC, plays a role in hypoxia-induced EMT is largely unknown.
  
  
  RESULTS
  We show that TET1 regulates hypoxia-responsive gene expression. Hypoxia/HIF-2α regulates the expression of TET1. Knockdown of TET1 mitigates hypoxia-induced EMT. RNA sequencing and 5hmC sequencing identified the set of TET1-regulated genes. Cholesterol metabolic process genes are among the genes that showed high prevalence and statistical significance. We characterize one of the genes, INSIG1 (insulin induced gene 1), to confirm its expression and the 5hmC levels in its promoter. Knockdown of INSIG1 also mitigates hypoxia-induced EMT. Finally, TET1 is shown to be a transcriptional co-activator that interacts with HIF-1α and HIF-2α to enhance their transactivation activity independent of its enzymatic activity. TET1 acts as a co-activator to further enhance the expression of INSIG1 together with HIF-2α. We define the domain in HIF-1α that interacts with TET1 and map the domain in TET1 that confers transactivation to a 200 amino acid region that contains a CXXC domain. The TET1 catalytically inactive mutant is capable of rescuing hypoxia-induced EMT in TET1 knockdown cells.
  
  
  CONCLUSIONS
  These findings demonstrate that TET1 serves as a transcription co-activator to regulate hypoxia-responsive gene expression and EMT, in addition to its role in demethylating 5mC.
authors.forename: Ya-Ping
authors.initials: YP
authors.lastname: Tsai
authors.forename: Hsiao-Fan
authors.initials: HF
authors.lastname: Chen
authors.forename: Sung-Yuan
authors.initials: SY
authors.lastname: Chen
authors.forename: Wei-Chung
authors.initials: WC
authors.lastname: Cheng
authors.forename: Hsei-Wei
authors.initials: HW
authors.lastname: Wang
authors.forename: Zih-Jie
authors.initials: ZJ
authors.lastname: Shen
authors.forename: Chunxiao
authors.initials: C
authors.lastname: Song
authors.forename: Shu-Chun
authors.initials: SC
authors.lastname: Teng
authors.forename: Chuan
authors.initials: C
authors.lastname: He
authors.forename: Kou-Juey
authors.initials: KJ
authors.lastname: Wu
mesh_terms: D044503:5-Methylcytosine / Q000378:metabolism; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism*; D020134:Catalytic Domain; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D058750:Epithelial-Mesenchymal Transition; D015972:Gene Expression Regulation, Neoplastic; D057809:HEK293 Cells; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics* / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D006899:Mixed Function Oxygenases; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000099162:Endothelial PAS Domain-Containing Protein 1
chemical_list: D044503:5-Methylcytosine; D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D006899:Mixed Function Oxygenases; D011518:Proto-Oncogene Proteins; D000099162:Endothelial PAS Domain-Containing Protein 1; C497442:HIF1A protein, human; C108626:INSIG1 protein, human; C462539:TET1 protein, human