Post-translational modifications of histones and the dynamic DNA methylation cycle are finely regulated by a myriad of chromatin-binding factors and chromatin-modifying enzymes. Epigenetic modifications ensure local changes in the architecture of chromatin, thus controlling the accessibility of the machinery of transcription, replication or DNA repair to the chromatin. Over the past decade, the nutrient-sensor enzyme-GlcNAc transferase (OGT) has emerged as a modulator of chromatin remodeling. In mammals, OGT acts either directly through dynamic and reversible O-GlcNAcylation of histones and chromatin effectors, or in an indirect manner through its recruitment into chromatin-bound multiprotein complexes. In particular, there is an increasing amount of evidence of a cross-talk between OGT and the DNA dioxygenase ten-eleven translocation proteins that catalyze active DNA demethylation. Conversely, the stability of OGT itself can be controlled by the histone lysine-specific demethylase 2 (LSD2). Finally, a few studies have explored the role of -GlcNAcase (OGA) in chromatin remodeling. In this review, we summarize the recent findings on the link between OGT, OGA and chromatin regulators in mammalian cellular models, and discuss their relevance in physiological and pathological conditions.

O-GlcNAcylation (O-linked beta-N-acetylglucosaminylation) is a widespread PTM confined within the nuclear, the cytosolic, and the mitochondrial compartments of eukaryotes. Recently, O-GlcNAcylation has been also detected in the close vicinity of plasma membranes particularly in lipid microdomains. The detection of this PTM can be easily done if appropriate controls and precautions are taken using a wide variety of tools including lectins, antibodies, or click-chemistry-based methods. In contrast, the identification of the proteins bearing O-GlcNAc moieties and the localization of the precise sites of O-GlcNAcylation remain challenging. This is due to the lability of the glycosidic bond between hydroxyl group of serine or threonine and N-acetylglucosamine using conventional fragmentation techniques such as CID. To tentatively overcome this technical limitation, electron-capture dissociation, or electron-transfer dissociation MS/MS are now used. Thanks to these breakthroughs, a large number of O-GlcNAc sites have been identified to date but these methodologies remain far from being used in routine.

O-GlcNAcylation of proteins is governed by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA). The homeostasis of O-GlcNAc cycling is regulated during cell cycle progression and is essential for proper cellular division. We previously reported the O-GlcNAcylation of the minichromosome maintenance proteins MCM2, MCM3, MCM6 and MCM7. These proteins belong to the MCM2–7 complex which is crucial for the initiation of DNA replication through its DNA helicase activity. Here we show that the six subunits of MCM2–7 are O-GlcNAcylated and that O-GlcNAcylation of MCM proteins mainly occurs in the chromatin-bound fraction of synchronized human cells. Moreover, we identify stable interaction between OGT and several MCM subunits. We also show that down-regulation of OGT decreases the chromatin binding of MCM2, MCM6 and MCM7 without affecting their steady-state level. Finally, OGT silencing or OGA inhibition destabilizes MCM2/6 and MCM4/7 interactions in the chromatin-enriched fraction. In conclusion, OGT is a new partner of the MCM2–7 complex and O-GlcNAcylation homeostasis might regulate MCM2–7 complex by regulating the chromatin loading of MCM6 and MCM7 and stabilizing MCM/MCM interactions.Electronic supplementary materialThe online version of this article (10.1007/s00018-018-2874-0) contains supplementary material, which is available to authorized users.

Cyclin D1 is the regulatory partner of the cyclin-dependent kinases (CDKs) CDK4 or CDK6. Once associated and activated, the cyclin D1/CDK complexes drive the cell cycle entry and G1 phase progression in response to extracellular signals. To ensure their timely and accurate activation during cell cycle progression, cyclin D1 turnover is finely controlled by phosphorylation and ubiquitination. Here we show that the dynamic and reversible O- linked β-N-Acetyl-glucosaminylation ( O -GlcNAcylation) regulates also cyclin D1 half-life. High O -GlcNAc levels increase the stability of cyclin D1, while reduction of O -GlcNAcylation strongly decreases it. Moreover, elevation of O -GlcNAc levels through O -GlcNAcase (OGA) inhibition significantly slows down the ubiquitination of cyclin D1. Finally, biochemical and cell imaging experiments in human cancer cells reveal that the O -GlcNAc transferase (OGT) binds to and glycosylates cyclin D1. We conclude that O -GlcNAcylation promotes the stability of cyclin D1 through modulating its ubiquitination.

In multicellular organisms, cell proliferation must be tightly coordinated with other developmental processes to form functional tissues and organs. Despite significant advances in our understanding of how the cell cycle is controlled by conserved cell‐cycle regulators (CCRs), how the cell cycle is coordinated with cell differentiation in metazoan organisms and how CCRs contribute to this process remain poorly understood. Here, we review the emerging roles of metazoan CCRs as intracellular proliferation‐differentiation coordinators in multicellular organisms. We illustrate how major CCRs regulate cellular events that are required for cell fate acquisition and subsequent differentiation. To this end, CCRs employ diverse mechanisms, some of which are separable from those underpinning the conventional cell‐cycle‐regulatory functions of CCRs. By controlling cell‐type‐specific specification/differentiation processes alongside the progression of the cell cycle, CCRs enable spatiotemporal coupling between differentiation and cell proliferation in various developmental contexts in vivo. We discuss the significance and implications of this underappreciated role of metazoan CCRs for development, disease and evolution.