Methylation of DNA Ligase 1 by G9a/GLP Recruits UHRF1 to Replicating DNA and Regulates DNA Methylation

Abstract

DNA methylation is an essential epigenetic mark in mammals that has to be re-established after each round of DNA replication. The protein UHRF1 is essential for this process; it has been proposed that the protein targets newly replicated DNA by cooperatively binding hemi-methylated DNA and H3K9me2/3, but this model leaves a number of questions unanswered. Here, we present evidence for a direct recruitment of UHRF1 by the replication machinery via DNA ligase 1 (LIG1). A histone H3K9-like mimic within LIG1 is methylated by G9a and GLP and, compared with H3K9me2/3, more avidly binds UHRF1. Interaction with methylated LIG1 promotes the recruitment of UHRF1 to DNA replication sites and is required for DNA methylation maintenance. These results further elucidate the function of UHRF1, identify a non-histone target of G9a and GLP, and provide an example of a histone mimic that coordinates DNA replication and DNA methylation maintenance.

UHRF1 Licensed Self-Renewal of Active Adult Neural Stem Cells

“…The process of recognition of hemimethylated DNA involves catalytic and recognition loops that interact with both grooves containing the methylated cytosine and the unmethylated cytosine that is everted from the double helix. However, UHRF1 which recruits DNMT1 is the actual protein that “recognizes” hemimethylated sites through its SRA domain and in addition, can also be recruited to replicating DNA through the replication machinery In concordance, UHRF1 has been observed by immunohistochemistry in replication foci . By using iPOND, we place UHRF1 within the replication fork itself and furthermore show that UHRF1‐deficient neural progenitors display whole genome hypomethylation illustrating its importance for maintenance methylation.…”

Dual Targeting of Histone Methyltransferase G9a and DNA‐Methyltransferase 1 for the Treatment of Experimental Hepatocellular Carcinoma

“…Reduction of G9a levels may be significant to the antitumoral effects of CM‐272, as G9a has also been described as a transcriptional coactivator of cancer‐related genes independent of its catalytic activity . The concomitant downregulation of DNMT1 and UHRF1 proteins upon CM‐272 treatment found in HCC cells could be secondary to G9a depletion, as all these proteins physically interact in multimeric functional complexes that may mediate the relative stability of their components . Nevertheless, this issue merits further investigation.…”

“…H3K9 mono‐ and di‐methylation is catalyzed by the HMT G9a, also known as euchromatic histone‐lysine methyltransferase 2 (EHMT2) . G9a physically interacts with DNMT1, contributing to DNA methylation during cell replication . G9a expression is dysregulated in cancer, contributing to cell growth, survival, adaptation to hypoxia, and metastasis .…”

EHMT1/GLP; Biochemical Function and Association with Brain Disorders

“…UHRF1 was also shown to bind to H3K9me2/3 through its tandem Tudor domain and appears to bind DNMT1 to mediate DNA methylation maintenance in an H3K9me2/3 dependent manner [27]. A recent paper however has increased the current understanding of this process; DNA ligase 1 (LIG1), a novel target of GLP is methylated on its H3K9 mimic, UHRF1 then binds to the mimic, and in turn this binding leads to the recruitment of UHRF1 to hemi-methylated sites, mediating its activity [29] (Figure 1). UHRF1 was also found to more readily bind to the LIG1 mimic compared to H3K9me2/3.…”