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Click-code-seq mapping of oxidized guanines in cells exposed to DNMT1 inhibitor GSK-3484862. Click-code-seq mapping of oxidized guanines and abasic sites in plasmids with site-specific DNA modifications.

ABSTRACT: By relating the numbers of oxidized guanines in different sequence contexts to the abundance of these contexts in the human genome, we observed that the probability of guanine to be or remain oxidized is low if this guanine is preceded by cytosine (CpG sites) compared to other nucleotides. As CpG sites are substrates of epigenetic cytosine methylation, we investigated the influence of cytosine methylation status on guanine oxidation level in CpG sites. For this, we exposed HAP1 and U2OS cells for three days to GSK-3484862, a novel DNA methyltransferase 1 (DNMT1) inhibitor causing the degradation of this enzyme within 24 hours and having low cellular toxicity. Using Infinium MethylationEPIC v2.0 array, we observed a drastic hypomethylation after the exposure in both cell lines such that the peak of highly methylated CpG sites (beta values 0.8–1) found in vehicle (DMSO) exposed cells is absent in GSK-3484862-exposed cells. In contrast, the oxidation level of guanines in the CpG sites profiled by the array did not change in response to the inhibitor and was virtually constant across CpG sites with different methylation levels. In addition, on the level of all CpG sites in the genome, guanine-oxidation did not differ between DMSO and GSK-3484862 exposures. Thus, in CpG sites, guanine oxidation level likely does not depend on cytosine methylation status. As a control for the click-code-seq protocol, we successfully called 8-oxoG incorporated at specific sites in a plasmid (~25 fmol) that was mixed with ~28-times bigger amount of the unmodified vector. As a control for click-code-seq detection of abasic sites, we inserted uracils in a plasmid, converted them to abasic sites by uracil-DNA glycosylase (UDG) and successfully called them in the expected locations.

ORGANISM(S): Escherichia coli Homo sapiens

PROVIDER: GSE295218 | GEO | 2025/08/22

REPOSITORIES: GEO

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Project description:DNA methylation plays a vital role in genome dynamics and, in the human genome, occurs predominantly at cytosine guanine dinucleotide (CpG) sites. The diploid haploid human genome analysed here contains around 2060 million CpG sites (methylome) where DNA methylation can vary, affecting many biological processes in health and disease. Using whole-genome bisulfite sequencing, we report the essentially complete (92.6282%) methylome of human peripheral blood mononuclear cells (PBMC) which constitute an important source for clinical blood tests world-wide. We find the majority of CpG sites (68.4% at false positive rate of 0.46%) and only <0.2% of non-CpG sites to be methylated, demonstrating that non-CpG cytosine methylation is negligible in human PBMC. Analysis of the PBMC methylome revealed a rich landscape of epigenomic data for 20 distinct features including regulatory, protein-coding, RNA gene coding, non-coding and repeat sequences. Alu element mobility, for instance, was found to negatively correlate with their methylation levels, emphasizing the critical role of DNA methylation in genome stability. Integration of our methylome data with the previously determined genome sequence of the same Asian individual analysed here, enabled a first assessment of allele-specific methylation (ASM) differences between the two haploid methylomes of any individual. Using a conservative cut-off (p <0.001), we identified 599 haploid differentially methylated regions (hDMRs) covering 287 genes. Of these, 76 genes had hDMRs within 2kb of their transcriptional start sites of which >80% displayed allele-specific expression (ASE) after random testing using TA clone sequencing of the same PBMC sample. These data show, that ASM is a recurrent phenomenon and highly correlated with ASE, suggesting that imprinting may be more common than previously thought. Our study not only provides a comprehensive resource for future epigenomic research but also demonstrates a paradigm of large-scale epigenomics studies through new sequencing technology. We report the essentially complete (92.6282%) methylome of human peripheral blood mononuclear cells (PBMC) which constitute an important source for clinical blood tests world-wide.

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Click-code-seq mapping of oxidized guanines in cells exposed to DNMT1 inhibitor GSK-3484862. Click-code-seq mapping of oxidized guanines and abasic sites in plasmids with site-specific DNA modifications.

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