Incorporation of 5-chlorocytosine into mammalian DNA results in heritable gene silencing and altered cytosine methylation patterns

Victoria Valinluck Lao, Jason L. Herring, Cherine H. Kim, Agus Darwanto, Ubaldo Soto, Lawrence Sowers

Research output: Contribution to journalArticle

33 Citations (Scopus)

Abstract

Cytosine methylation patterns are essential for the proper control of gene expression in higher vertebrates. Although alterations in methylation patterns are frequently observed in human tumors, neither the mechanisms for establishing methylation patterns during normal development nor the mechanisms leading to pathological alterations of methylation patterns are currently known. While epidemiological studies have implicated inflammation in cancer etiology, a mechanistic link has yet to be established. Investigations of inflammation-mediated DNA damage may have provided important new insights. Our in vitro studies revealed that the inflammation-mediated DNA damage product, 5-chlorocytosine, could direct fraudulent methylation of previously unmethylated CpG sites. The purpose of this study was to recapitulate our in vitro findings by introducing 5-chlorocytosine residues into the DNA of replicating mammalian cells and to examine its impact on gene expression and cytosine methylation patterns. CHO-K1 cells hemizygous for the hprt gene were electroporated with the triphosphates of cytosine [2′-deoxycytidine-5′-triphosphate (dCTP)], 5-methylcytosine [5-methyl-2′-deoxycytidine-5′-triphosphate (MedCTP)] and 5′-chloro-2′-deoxycytidine-5′-triphosphate (CldCTP), and then selected with 6-thioguanine for silencing the hprt gene. Both modified nucleotides, MedCTP and CldCTP, but not unmodified dCTP, silenced hprt gene expression. Subsequent bisulfite pyrosequencing of CpG sites within the hprt promoter region of the selected cells confirmed hypermethylation, although global methylation levels as measured by gas chromatography-mass spectrometry did not change. Modified nucleotide-induced gene silencing could be reversed with 5-aza-2′-deoxycytidine indicating an epigenetic rather than mutagenic alteration. These results provide further evidence that the inflammation damage product 5-chlorocytosine could be a link between inflammation and cancer development.

Original languageEnglish (US)
Pages (from-to)886-893
Number of pages8
JournalCarcinogenesis
Volume30
Issue number5
DOIs
StatePublished - 2009
Externally publishedYes

Fingerprint

Cytosine
Gene Silencing
Methylation
DNA
Inflammation
decitabine
Gene Expression
DNA Damage
Nucleotides
5-Methylcytosine
Thioguanine
Neoplasms
CHO Cells
5-chlorocytosine
Genetic Promoter Regions
Epigenomics
Gas Chromatography-Mass Spectrometry
Vertebrates
Epidemiologic Studies
2'-deoxycytidine 5'-triphosphate

ASJC Scopus subject areas

  • Cancer Research

Cite this

Incorporation of 5-chlorocytosine into mammalian DNA results in heritable gene silencing and altered cytosine methylation patterns. / Lao, Victoria Valinluck; Herring, Jason L.; Kim, Cherine H.; Darwanto, Agus; Soto, Ubaldo; Sowers, Lawrence.

In: Carcinogenesis, Vol. 30, No. 5, 2009, p. 886-893.

Research output: Contribution to journalArticle

Lao, Victoria Valinluck ; Herring, Jason L. ; Kim, Cherine H. ; Darwanto, Agus ; Soto, Ubaldo ; Sowers, Lawrence. / Incorporation of 5-chlorocytosine into mammalian DNA results in heritable gene silencing and altered cytosine methylation patterns. In: Carcinogenesis. 2009 ; Vol. 30, No. 5. pp. 886-893.
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