DNA adduct 8-hydroxyl-2′-deoxyguanosine (8-hydroxyguanine) affects function of human DNA methyltransferase

Abstract

8-Hydroxyl-2'-deoxyguanosine (also referred to as 8-hydroxyguanine [8-OH-dG] or 7,8-dihydro-8-oxoguanine), a common DNA adduct resulting from injury to DNA via reactive oxygen species, affects the in vitro methylation of nearby cytosine moieties by the human DNA methyltransferase. The exact position of 8-OH-deoxyguanosine relative to a CpG dinucleotide appears important to this effect. Our data indicate that 8-OH-deoxyguanosine diminishes the ability of the methyltransferase to methylate a target cytosine when the 8-OH-deoxyguanosine is one or two nucleotides 3' from the cytosine, on the same strand. On the other hand 8-OH-deoxyguanosine does not diminish the ability of the enzyme to respond to a methyl director (5-methylcytosine) when the 8-OH-deoxyguanosine is on the same strand but one or two nucleotides 3' from the methyl director. Differences in methylation rates as great as 13-fold have been detected using various 8-OH-deoxyguanosine-containing oligonucleotides as substrates in methylation assays. Our findings suggest that oxidative damage of parental strand guanines would permit normal copying of methylation patterns through maintenance methylation, while oxidative damage of guanines in the nascent strand DNA would inhibit such methylation.

Fractionated Low-Dose Radiation Exposure Leads to Accumulation of DNA Damage and Profound Alterations in DNA and Histone Methylation in the Murine Thymus

“…Presence of DNA lesions has been reported to affect the methylation ability of DNA methyltransferases (35,36). Furthermore, during repair, DNA synthesis polymerases incorporate cytidine but not methyl cytidine; thus, the elevated levels of DNA lesions seen in this study and activation of DNA repair may be one of the factors contributing to decrease in DNA methylation.…”

“…Radiation is a potent damaging agent that induces double-strand breaks and other lesions in DNA, activating a battery of DNA repair mechanisms. Because DNA lesions can interfere with activity of DNA methyltransferases (35,36), and during repair DNA synthesis polymerases incorporate cytidine but not methyl cytidine, the presence of DNA lesions and activation of DNA repair mechanisms may result in DNA hypomethylation. In light of these considerations, we measured the levels of DNA damage (radiation-induced strand breaks) in the thymus tissue of animals subjected to acute and fractionated low-dose radiation exposure.…”

Age and Organ Dependent Spontaneous Generation of Nuclear 8-Hydroxydeoxyguanosine in Male Fischer 344 Rats

“…These then alter the expression of specific genes, largely influence a variety of signal transduction pathways responsible for the maintenance and regulation of cellular functions, and in turn cause a variety of disorders (Anisimov, 1998;Finkel, 1999;Gameley and Kiyubin, 1999;Hampton et al, 1998;Hogg, 1998). The hypomethylation of specific genes is a particular example of such epigenetic changes, because ROS are among its main mediators (Cerda and Weitzman, 1997), while the presence of 8-OHdG per se inhibits DNA methylation (Turk et al, 1995;Weitzman et al, 1994). The hypomethylation occurs in an organ-and gene-specific and age-dependent manner and has been shown to play one of the central roles in both senescence and carcinogenesis (Anisimov, 1998;Christman, 1995;Poirier, 1994).…”

Exposure to estrogen and ionizing radiation causes epigenetic dysregulation, activation of mitogen-activated protein kinase pathways, and genome instability in the mammary gland of ACI rats

“…It has been demonstrated previously that DNA damage can interfere with the methylating ability of DNA methyltransferases by stalling DNA methyltransferase at sites of lesions. 53,54 Furthermore, during DNA repair synthesis, polymerases incorporate cytidine but not methylcytidine, thus the presence of DNA lesions and activation of DNA repair Figure 1. White bars, controls; gray, e 2 -exposed animals; striped, IR-exposed animals; black, e 2 + IR, exposed animals.…”