title: Hypoxia-Mediated Epigenetic Regulation of Stemness in Brain Tumor Cells.
abstract: Activation of pluripotency regulatory circuit is an important event in solid tumor progression and the hypoxic microenvironment is known to enhance the stemness feature of some cells. The distinct population of cancer stem cells (CSCs)/tumor initiating cells exist in a niche and augment invasion, metastasis, and drug resistance. Previously, studies have reported global hypomethylation and site-specific aberrant methylation in gliomas along with other epigenetic modifications as important contributors to genomic instability during glioma progression. Here, we have demonstrated the role of hypoxia-mediated epigenetic modifications in regulating expression of core pluripotency factors, OCT4 and NANOG, in glioma cells. We observe hypoxia-mediated induction of demethylases, ten-eleven-translocation (TET) 1 and 3, but not TET2 in our cell-line model. Immunoprecipitation studies reveal active demethylation and direct binding of TET1 and 3 at the Oct4 and Nanog regulatory regions. Tet1 and 3 silencing assays further confirmed induction of the pluripotency pathway involving Oct4, Nanog, and Stat3, by these paralogues, although with varying degrees. Knockdown of Tet1 and Tet3 inhibited the formation of neurospheres in hypoxic conditions. We observed independent roles of TET1 and TET3 in differentially regulating pluripotency and differentiation associated genes in hypoxia. Overall, this study demonstrates an active demethylation in hypoxia by TET1 and 3 as a mechanism of Oct4 and Nanog overexpression thus contributing to the formation of CSCs in gliomas. Stem Cells 2017;35:1468-1478.
authors.affiliation: Department of Genetics, University of Delhi South Campus, New Delhi, India.
authors.forename: Pankaj
authors.initials: P
authors.lastname: Prasad
authors.affiliation: Department of Genetics, University of Delhi South Campus, New Delhi, India.
authors.forename: Shivani Arora
authors.identifier: 0000-0001-9734-3488
authors.initials: SA
authors.lastname: Mittal
authors.affiliation: Department of Genetics, University of Delhi South Campus, New Delhi, India.
authors.forename: Jonita
authors.initials: J
authors.lastname: Chongtham
authors.affiliation: Stem Cell Facility, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: Sujata
authors.initials: S
authors.lastname: Mohanty
authors.affiliation: Department of Genetics, University of Delhi South Campus, New Delhi, India.
authors.forename: Tapasya
authors.initials: T
authors.lastname: Srivastava
mesh_terms: D001932:Brain Neoplasms / Q000235:genetics* / Q000473:pathology*; D002454:Cell Differentiation / Q000235:genetics; D015687:Cell Hypoxia / Q000235:genetics; D045744:Cell Line, Tumor; D000073399:DNA Demethylation; D049308:Dioxygenases / Q000378:metabolism; D044127:Epigenesis, Genetic; D015972:Gene Expression Regulation, Neoplastic; D055785:Gene Knockdown Techniques; D056426:Genetic Loci; D005910:Glioma / Q000473:pathology; D006801:Humans; D006899:Mixed Function Oxygenases / Q000378:metabolism; D008954:Models, Biological; D014411:Neoplastic Stem Cells / Q000378:metabolism* / Q000473:pathology*; D039904:Pluripotent Stem Cells / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D018874:Spheroids, Cellular / Q000378:metabolism
chemical_list: D011518:Proto-Oncogene Proteins; D006899:Mixed Function Oxygenases; C462539:TET1 protein, human; C578792:TET3 protein, human; D049308:Dioxygenases
keywords: Cancer stem cells; Demethylation; Genomic instability; Glioma; Hypoxia; Ten-eleven-translocation (TET)