title: Minimal role of base excision repair in TET-induced global DNA demethylation in HEK293T cells.
abstract: Oxidation of 5-methylcytosine by TET family proteins can induce DNA replication-dependent (passive) DNA demethylation and base excision repair (BER)-based (active) DNA demethylation. The balance of active vs. passive TET-induced demethylation remains incompletely determined. In the context of large scale DNA demethylation, active demethylation may require massive induction of the DNA repair machinery and thus compromise genome stability. To study this issue, we constructed a tetracycline-controlled TET-induced global DNA demethylation system in HEK293T cells. Upon TET overexpression, we observed induction of DNA damage and activation of a DNA damage response; however, BER genes are not upregulated to promote DNA repair. Depletion of TDG (thymine DNA glycosylase) or APEX1 (apurinic/apyrimidinic endonuclease 1), two key BER enzymes, enhances rather than impairs global DNA demethylation, which can be explained by stimulated proliferation. By contrast, growth arrest dramatically blocks TET-induced global DNA demethylation. Thus, in the context of TET-induction in HEK293T cells, the DNA replication-dependent passive mechanism functions as the predominant pathway for global DNA demethylation. In the same context, BER-based active demethylation is markedly restricted by limited BER upregulation, thus potentially preventing a disastrous DNA damage response to extensive active DNA demethylation.
authors.affiliation: a Fels Institute for Cancer Research and Molecular Biology; Temple University ; Philadelphia , PA USA.|b Department of Epigenetics and Molecular Carcinogenesis ; The University of Texas MD Anderson Cancer Center ; Houston , TX USA.
authors.forename: Chunlei
authors.initials: C
authors.lastname: Jin
authors.affiliation: c Department of Cancer Biology ; The University of Texas MD Anderson Cancer Center ; Houston , TX USA.
authors.forename: Taichun
authors.initials: T
authors.lastname: Qin
authors.affiliation: b Department of Epigenetics and Molecular Carcinogenesis ; The University of Texas MD Anderson Cancer Center ; Houston , TX USA.
authors.forename: Michelle Craig
authors.initials: MC
authors.lastname: Barton
authors.affiliation: a Fels Institute for Cancer Research and Molecular Biology; Temple University ; Philadelphia , PA USA.
authors.forename: Jaroslav
authors.initials: J
authors.lastname: Jelinek
authors.affiliation: a Fels Institute for Cancer Research and Molecular Biology; Temple University ; Philadelphia , PA USA.
authors.forename: Jean-Pierre J
authors.initials: JP
authors.lastname: Issa
mesh_terms: D049109:Cell Proliferation; D004249:DNA Damage; D019175:DNA Methylation; D004260:DNA Repair; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase / Q000172:deficiency; D057809:HEK293 Cells; D006801:Humans; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D044502:Thymine DNA Glycosylase / Q000172:deficiency
chemical_list: D011518:Proto-Oncogene Proteins; D006899:Mixed Function Oxygenases; C462539:TET1 protein, human; D044502:Thymine DNA Glycosylase; C085108:APEX1 protein, human; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase
keywords: DNA damage; DNA demethylation pathway; DNA replication; TET genes; base excision repair