Search

TET2 is shown to associate with OGT, which catalyses O-GlcNAcylation, and the two enzymes are found together at transcription start sites; TET2 facilitates the activity of OGT in O-GlcNAcylation of histone 2B, and epigenetic modifications to both DNA and histones by TET2 and OGT may be important in gene transcription regulation. Enzymes of the TET family catalyse the oxidation of 5-methylcytosine, the 'fifth base' in DNA, into derivatives such as 5-hydroxymethylcytosine, and can influence gene expression. Here, Xiaochun Yu and colleagues show that TET2 associates with O-linked β-N-acetylglucosamine transferase (OGT), an enzyme that catalyses O-GlcNAcylation, and that the two proteins are found concurrently at transcriptional start sites. TET2 facilitates the activity of OGT in O-GlcNAcylation of histone H2B, a histone mark associated with active genes. Thus as well as influencing histone modifications, TET2 can affect DNA modifications of potential importance in transcription regulation Ten eleven translocation (TET) enzymes, including TET1, TET2 and TET3, convert 5-methylcytosine to 5-hydroxymethylcytosine1 and regulate gene transcription2,3,4,5. However, the molecular mechanism by which TET family enzymes regulate gene transcription remains elusive5,6. Using protein affinity purification, here we search for functional partners of TET proteins, and find that TET2 and TET3 associate with O-linked β-N-acetylglucosamine (O-GlcNAc) transferase (OGT), an enzyme that by itself catalyses the addition of O-GlcNAc onto serine and threonine residues (O-GlcNAcylation) in vivo7,8. TET2 directly interacts with OGT, which is important for the chromatin association of OGT in vivo. Although this specific interaction does not regulate the enzymatic activity of TET2, it facilitates OGT-dependent histone O-GlcNAcylation. Moreover, OGT associates with TET2 at transcription start sites. Downregulation of TET2 reduces the amount of histone 2B Ser 112 GlcNAc marks in vivo, which are associated with gene transcription regulation. Taken together, these results reveal a TET2-dependent O-GlcNAcylation of chromatin. The double epigenetic modifications on both DNA and histones by TET2 and OGT coordinate together for the regulation of gene transcription.

Protein ubiquitination is a crucial component of the DNA damage response. To study the mechanism of the DNA damage-induced ubiquitination pathway, we analyzed the impact of the loss of two E3 ubiquitin ligases, RNF8 and Chfr. Notably, DNA damage-induced activation of ATM kinase is suppressed in cells deficient in both RNF8 and Chfr (double-knockout, or DKO), and DKO mice develop thymic lymphomas that are nearly diploid but harbor clonal chromosome translocations. Moreover, DKO mice and cells are hypersensitive to ionizing radiation. We present evidence that RNF8 and Chfr synergistically regulate histone ubiquitination to control histone H4 Lys16 acetylation through MRG15-dependent acetyltransferase complexes. Through these complexes, RNF8 and Chfr affect chromatin relaxation and modulate ATM activation and DNA damage response pathways. Collectively, our findings demonstrate that two chromatin-remodeling factors, RNF8 and Chfr, function together to activate ATM and maintain genomic stability in vivo.