Nutrient-driven O-GlcNAc cycling - think globally but act locally.
ABSTRACT Proper cellular functioning requires that cellular machinery behave in a spatiotemporally regulated manner in response to global changes in nutrient availability. Mounting evidence suggests that one way this is achieved is through the establishment of physically defined gradients of O-GlcNAcylation (O-linked addition of N-acetylglucosamine to serine and threonine residues) and O-GlcNAc turnover. Because O-GlcNAcylation levels are dependent on the nutrient-responsive hexosamine signaling pathway, this modification is uniquely poised to inform upon the nutritive state of an organism. The enzymes responsible for O-GlcNAc addition and removal are encoded by a single pair of genes: both the O-GlcNAc transferase (OGT) and the O-GlcNAcase (OGA, also known as MGEA5) genes are alternatively spliced, producing protein variants that are targeted to discrete cellular locations where they must selectively recognize hundreds of protein substrates. Recent reports suggest that in addition to their catalytic functions, OGT and OGA use their multifunctional domains to anchor O-GlcNAc cycling to discrete intracellular sites, thus allowing them to establish gradients of deacetylase, kinase and phosphatase signaling activities. The localized signaling gradients established by targeted O-GlcNAc cycling influence many important cellular processes, including lipid droplet remodeling, mitochondrial functioning, epigenetic control of gene expression and proteostasis. As such, the tethering of the enzymes of O-GlcNAc cycling appears to play a role in ensuring proper spatiotemporal responses to global alterations in nutrient supply.
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ABSTRACT: O-GlcNAc transferase (OGT) is an essential mammalian enzyme responsible for transferring a single GlcNAc moiety from UDP-GlcNAc to specific serine/threonine residues of hundreds of nuclear and cytoplasmic proteins. This modification is dynamic and has been implicated in numerous signaling pathways. An unexpected second function for OGT as a protease involved in cleaving the epigenetic regulator HCF-1 has also been reported. Recent structural and biochemical studies that provide insight into the mechanism of glycosylation and HCF-1 cleavage will be described, with outstanding questions highlighted.Journal of Biological Chemistry 10/2014; DOI:10.1074/jbc.R114.604405 · 4.60 Impact Factor
Article: Epigenetics and Metabolism.[Show abstract] [Hide abstract]
ABSTRACT: The molecular signatures of epigenetic regulation and chromatin architectures are fundamental to genetically determined biological processes. Covalent and post-translational chemical modification of the chromatin template can sensitize the genome to changing environmental conditions to establish diverse functional states. Recent interest and research focus surrounds the direct connections between metabolism and chromatin dynamics, which now represents an important conceptual challenge to explain many aspects of metabolic dysfunction. Several components of the epigenetic machinery require intermediates of cellular metabolism for enzymatic function. Furthermore, changes to intracellular metabolism can alter the expression of specific histone methyltransferases and acetyltransferases conferring widespread variations in epigenetic modification patterns. Specific epigenetic influences of dietary glucose and lipid consumption, as well as undernutrition, are observed across numerous organs and pathways associated with metabolism. Studies have started to define the chromatin-dependent mechanisms underlying persistent and pathophysiological changes induced by altered metabolism. Importantly, numerous recent studies demonstrate that gene regulation underlying phenotypic determinants of adult metabolic health is influenced by maternal and early postnatal diet. These emerging concepts open new perspectives to combat the rising global epidemic of metabolic disorders. © 2015 American Heart Association, Inc.Circulation Research 02/2015; 116(4):715-736. DOI:10.1161/CIRCRESAHA.116.303936 · 11.09 Impact Factor
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ABSTRACT: TET proteins oxidize 5-methylcytosine (mC) to 5-hydroxymethylcytosine (hmC), 5-formylcytosine (fC) and 5-carboxylcytosine (caC) and thus provide a possible means for active DNA demethylation in mammals. Although their catalytic mechanism is well characterized and the catalytic dioxygenase domain is highly conserved, the function of the regulatory regions - the N-terminus and the low complexity insert between the two parts of the dioxygenase domains - is only poorly understood. Here, we demonstrate that TET proteins are subject to a variety of PTMs that mostly occur at these regulatory regions. We mapped TET modification sites at amino acid resolution and show for the first time that TET1, TET2, and TET3 are highly phosphorylated. The glycosyltransferase OGT, which we identified as a strong interactor of all three TET proteins, catalyzes the addition of an N-acetylglucosamine (GlcNAc) group to serine and threonine residues of TET proteins and thereby decreases both the number of phosphorylation sites as well as the site occupancy. Interestingly, the different TET proteins display unique PTM patterns and some modifications occur in distinct combinations. In summary, our results provide a novel potential mechanism for TET protein regulation based on a dynamic interplay of phosphorylation and O-GlcNAcylation at the N-terminus and the low complexity insert region. Our data suggest strong crosstalk between the modification sites that could allow rapid adaption of TET protein localization, activity, or targeting due to changing environmental conditions as well as in response to external stimuli. Copyright © 2015, The American Society for Biochemistry and Molecular Biology.Journal of Biological Chemistry 01/2015; 290(8). DOI:10.1074/jbc.M114.605881 · 4.60 Impact Factor