Albany 2015:Book of Abstracts
June 9-13 2015
©Adenine Press (2012)
Cytosine demethylation through off-target base excision repair
Cytosine methylation in CpG dinucleotides is a well-known way of gene activity regulation at the level of transcription, forming the basis of many cases of epigenetic inheritance, the transfer of information on the gene activity from parent cells or organisms to their progeny. Although a large body of literature is devoted to the appearance of epigenetic methylation marks in DNA, much less is known about their removal.
It has been recently shown that oxoGua, one of the most widespread oxidative DNA lesions, is a key element in the gene activation by ERÎ± (Perillo et al., 2008) and c-Myc transcripti on factors (Amente et al., 2010). This damage is removed from DNA by DNA glycosylase OGG1 and AP endonuclease APEX1, and the nicks appearing in DNA ultimately lead, through a still unknown mechanism, to local chromatin decondensation and transcription activation. We have shown that in the course of OGG1-initiated repair of oxoGua, APEX1 can remove mCyt 5' to the oxoGua base from DNA. To unequivocally establish that a new pathway of active demethylation may be based on such non-targeted DNA, using substrates mimicking various repair intermediates (AP sites, gap, etc.) we have characterized the ability of the human BER nuclease APEX1 to remove mCyt from DNA.
Excision of mCyt nucleotide from DNA repair intermediates by the 3'-->5'-exonuclease activity of APEX1 has been demonstrated. The presence of an AP site at the 5'-terminus at the nick formed by the sequential action of DNA glycosylases and APEX1 was shown to stimulate the APEX1 activity towards mCyt at the 3'-terminus of the nick. Thus our data in conjunction with previous work suggest principal possibility of active demethylation during the repair of base lesions adjacent to methylcytosine.
This work was supported by Russian Science Foundation #14-24-00093. A. E. was supported by stipend of the President of the Russian Federation.
Perillo B., Ombra M.N., Bertoni A., Cuozzo C., Sacchetti S., Sasso A., Chiariotti L., Malorni A., Abbondanza C., Avvedimento E.V. (2008). DNA oxidation as triggered by H3K9me2 demethylation drives estrogen-induced gene expression. Science, 319 (5860), 202-206.
SB RAS Institute of Chemical Biology and Fundamental Medicine