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Genome-wide maps of rH2A.X in wildtype and DNMT3b-KO HCT116 lines

ABSTRACT: Dysfunction of DNA methyltransferase 3b (DNMT3b) causes centromere instability but the underlying mechanism is unclear. We found that enforced expression of RNase H1 that removes R-loops, nucleic structures comprising an DNA-RNA hybrid, was sufficient to abolish DNA double-strand breaks (DSBs) at (peri-)centromeric sites in immunodeficiency-centromeric instability-facial anomalies (ICF) patient cells carrying DNMT3b mutation. However, ICF cells had lower steady-state level of centromeric R-loops than normal cells. Simultaneous knockdown of two DNA endonucleases, XPG and XPF, restored centromeric R-loops in ICF cells while reducing DSBs and chromosome segregation error. This suggests that (peri-)centromeric R-loops are more vulnerable to XPG or XPF in ICF cells, thus increasing centromeric breaks. This mechanism is recapitulated in DNMT3b-knockout HCT116 cells. Moreover, we present evidence for the choice of alternative end-joining (alt-EJ) repair of (peri-)centromeric breaks in ICF cells. Thus, DNA cleavages of (peri-)centromeric R-loops and mutagenic alt-EJ repair undermine centromere stability in DNMT3b defective cells.

ORGANISM(S): Homo sapiens

PROVIDER: GSE142376 | GEO | 2022/06/12

REPOSITORIES: GEO

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Project description:Immunodeficiency, centromeric instability and facial anomalies syndrome (ICF) is a rare autosomal recessive disease, characterized by severe hypomethylation in pericentromeric regions of chromosomes (1, 16 and 9), marked immunodeficiency and facial anomalies. The majority of ICF patients present mutations in the DNMT3B gene, affecting the DNA methyltransferase activity of the protein. In the present study, we have used the Infinium 450K DNA methylation array to evaluate the methylation level of 450,000 CpGs in lymphoblastoid cell lines and untrasformed fibroblasts derived from ICF patients and healthy donors. Our results demonstrate that ICF-specific DNMT3B variants A603T/STP807ins and V699G/R54X cause global DNA hypomethylation compared to wild-type protein. We identified 181 novel differentially methylated positions (DMPs) including subtelomeric and intrachromosomic regions, outside the classical ICF-related pericentromeric hypomethylated positions. Interestingly, these sites were mainly located in intergenic regions and inside the CpG islands. Among the identified hypomethylated CpG-island associated genes, we confirmed the overexpression of three selected genes, BOLL, SYCP2 and NCRNA00221, in ICF compared to healthy controls, which are normally expressed in germ line and silenced in somatic tissues. In conclusion, this study contributes in clarifying the direct relationship between DNA methylation defect and gene expression impairment in ICF syndrome, identifying novel direct target genes of DNMT3B. A high percentage of the DMPs are located in the subtelomeric regions, indicating a specific role of DNMT3B in methylating these chromosomal sites. Therefore, we provide further evidence that hypomethylation in specific non-pericentromeric regions of chromosomes might be involved in the molecular pathogenesis of ICF syndrome. The detection of DNA hypomethylation at BOLL, SYCP2 and NCRNA00221 may pave the way for the development of specific clinical biomarkers with the aim to facilitate the identification of ICF patients.

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Genome-wide maps of rH2A.X in wildtype and DNMT3b-KO HCT116 lines

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