Abstract
TET2 recruits O-GlcNAc transferase to chromatin and promotes histone H2B O-GlcNAcylation.
Major finding: TET2 recruits O-GlcNAc transferase to chromatin and promotes histone H2B O-GlcNAcylation.
Concept: TET2, OGT, and O-GlcNAc enrichment at transcription start sites was associated with increased expression.
Impact: Inactivating TET2 mutations may lead to reduced histone O-GlcNAcylation and gene silencing.
Recurrent somatic loss-of-function mutations in ten eleven translocation 2 (TET2) have been identified in myeloid cancers. TET enzymes convert 5-methylcytosine to 5-hydroxymethylcytosine, but the molecular mechanisms by which they regulate gene expression remain incompletely understood. To gain insight into the role of the TET family in transcription, Chen and colleagues used affinity purification and mass spectrometry to identify TET-interacting proteins. TET2 and TET3 specifically bound O-linked β-N-acetylglucosamine (O-GlcNAc) transferase (OGT), which catalyzes the addition of a monosaccharide glucose derivative to proteins, both in vitro and in mouse embryonic stem (ES) cells. O-GlcNAcylation of specific amino acids mediates functions of many cellular proteins and is thought to link nutrient sensing to cell signaling. OGT did not glycosylate 5-hydroxymethylcytosine, and its coexpression had no effect on TET2-dependent 5-methylcytosine conversion in vitro. However, TET2 knockdown in ES cells dramatically reduced the levels of chromatin-bound OGT and histone O-GlcNAcylation, particularly at serine-112 of histone H2B. This modification is believed to promote H2B lysine 120 monoubiquitination and transcriptional activation by serving as a scaffold for ubiquitin ligase binding. Genome-wide chromatin immunoprecipitation sequencing analysis showed a marked overlap among TET2, OGT, and H2B serine-112 O-GlcNAc, particularly at transcription start sites associated with highly expressed genes. TET2 loss strongly suppressed OGT recruitment and H2B serine-112 O-GlcNAcylation at target gene promoters in association with transcriptional downregulation. Of note, a TET2 enzymatic mutant incapable of 5-methylcytosine conversion restored H2B O-GlcNAcylation and partially rescued TET2 and OGT gene expression, suggesting that TET2-mediated gene expression is partly dependent on histone O-GlcNAcylation. Loss of this epigenetic modification may therefore play a role in cancers harboring inactivating TET2 mutations.