Breakthroughs and Views
O-GlcNAc: a regulatory post-translational modification

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Abstract

β-N-Acetylglucosamine (O-GlcNAc) is a regulatory post-translational modification of nuclear and cytosolic proteins. The enzymes for its addition and removal have recently been cloned and partially characterized. While only about 80 mammalian proteins have been identified to date that carry this modification, it is clear that this represents just a small percentage of the modified proteins. O-GlcNAc has all the properties of a regulatory modification including being dynamic and inducible. The modification appears to modulate transcriptional and signal transduction events. There are also accruing data that O-GlcNAc plays a role in apoptosis and neurodegeneration. A working model is emerging that O-GlcNAc serves as a metabolic sensor that attenuates a cell’s response to extracellular stimuli based on the energy state of the cell. In this review, we will focus on the enzymes that add/remove O-GlcNAc, the functional impact of O-GlcNAc modification, and the current working model for O-GlcNAc as a nutrient sensor.

Section snippets

The enzymes

A soluble O-GlcNAc transferase (OGT) was first purified and characterized in 1990 [14] but it would be another seven years before the enzyme was cloned [8], [9]. The 110 kDa polypeptide has two domains: an N-terminus with 11.5 tetratricopeptide repeats (TPRs) and a putative catalytic C-terminus. TPRs are known protein–protein association domains [15]. The enzyme functions as a trimer with the polypeptide chains interacting via the TPRs [10]. The enzyme transfers N-acetylglucosamine from

Transcription/translation

A large number of transcription factors are modified by O-GlcNAc as well as the C-terminal domain (CTD) of RNA polymerase II [20]. Glycosylation of the CTD induces a conformational change in the CTD that could have a variety of functional consequences [21]. Recent data have shown that in vitro glycosylation of the CTD of RNA polymerase II prevents the required phosphorylation for elongation [22]. Thus it has been proposed that O-GlcNAc may modify RNA polymerase II that is in the preinitiation

Neurodegenration

There is considerable indirect evidence that O-GlcNAc may play a role in neurodegenerative disorders. It is well established that glucose metabolism is reduced in the aging neurons. A reduction in glucose flux results in lower UDP-GlcNAc levels and presumably lower levels of O-GlcNAc modified proteins. There are a variety of O-GlcNAc modified proteins that are enriched in brain neurons including tau, β-amyloid precursor protein, neurofilaments, microtubule-associated proteins, clathrin assembly

Signal transduction

While the attractive model of O-GlcNAc participating in signal transduction events has been proposed for more than a decade [41], only recently have data emerged implicating O-GlcNAc in specific signal transduction cascades. The hexosamine biosynthetic pathway (HSP), which converts fructose-6-phosphate to UDP-GlcNAc (see Fig. 1), the donor sugar nucleotide for OGT, has been implicated in type II diabetes, specifically in insulin resistance and glucose toxicity [43], [44]. Very compelling

Working model and future directions

The current nutritional sensor model of O-GlcNAc has been reviewed elsewhere [56]. Briefly, the model proposes that cells are not blindly responding to extracellular stimuli but instead are taking into account their own energy stores. O-GlcNAc, which appears to be highly responsive to nutrient state, modifies signaling components, cytoskeletal components, and the transcriptional and translational machinery. Thus, O-GlcNAc modification could be modulating the proteins that are present and their

Acknowledgements

We thank members of the Hart laboratory and Karen M. Wells for critical reading of the manuscript. The “O-GlcNAc field” is rapidly expanding and thus it is likely that we failed to acknowledge the contributions of some of our colleagues (for this we apologize). This work was supported by NIH Grants CA42486, DK38418, and HD13563 to GWH.

References (78)

  • L. Wells et al.

    Dynamic O-glycosylation of nuclear and cytosolic proteins: further characterization of the nucleocytoplasmic β-N-acetylglucosaminidase, O-GlcNAcase

    J. Biol. Chem.

    (2002)
  • R.S. Haltiwanger et al.

    Enzymatic addition of O-GlcNAc to nuclear and cytoplasmic proteins. Identification of a uridine diphospho-N-acetylglucosamine:peptide β-N-acetylglucosaminyltransferase

    J. Biol. Chem.

    (1990)
  • X. Yang et al.

    Recruitment of O-GlcNAc transferase to promoters by corepressor mSin3A: coupling protein O-GlcNAcylation to transcriptional repression

    Cell

    (2002)
  • F.I. Comer et al.

    O-Glycosylation of nuclear and cytosolic proteins. Dynamic interplay between O-GlcNAc and O-phosphate

    J. Biol. Chem.

    (2000)
  • F.I. Comer et al.

    O-GlcNAc and the control of gene expression

    Biochim. Biophys. Acta

    (1999)
  • X. Cheng et al.

    Glycosylation of the murine estrogen receptor-α

    J. Steroid Biochem. Mol. Biol.

    (2000)
  • B. Datta et al.

    Glycosylation of eukaryotic peptide chain initiation factor 2 (eIF-2)-associated 67-kDa polypeptide (p67) and its possible role in the inhibition of eIF-2 kinase-catalyzed phosphorylation of the eIF-2 α-subunit

    J. Biol. Chem.

    (1989)
  • R. Datta et al.

    Protection of translation initiation factor eIF2 phosphorylation correlates with eIF2-associated glycoprotein p67 levels and requires the lysine-rich domain I of p67

    Biochimie

    (2001)
  • C.S. Arnold et al.

    The microtubule-associated protein tau is extensively modified with O-linked N-acetylglucosamine

    J. Biol. Chem.

    (1996)
  • D.L. Dong et al.

    Glycosylation of mammalian neurofilaments. Localization of multiple O-linked N-acetylglucosamine moieties on neurofilament polypeptides L and M

    J. Biol. Chem.

    (1993)
  • M. Ding et al.

    High molecular weight microtubule-associated proteins contain O-linked-N-acetylglucosamine

    J. Biol. Chem.

    (1996)
  • J.E. Murphy et al.

    Clathrin assembly protein AP-3 is phosphorylated and glycosylated on the 50-kDa structural domain

    J. Biol. Chem.

    (1994)
  • P.J. Yao et al.

    Reduced O-glycosylated clathrin assembly protein AP180: implication for synaptic vesicle recycling dysfunction in Alzheimer’s disease

    Neurosci. Lett.

    (1998)
  • S. Marshall et al.

    Discovery of a metabolic pathway mediating glucose-induced desensitization of the glucose transport system. Role of hexosamine biosynthesis in the induction of insulin resistance

    J. Biol. Chem.

    (1991)
  • H. Yki-Jarvinen et al.

    Insulin and glucosamine infusions increase O-linked N-acetyl-glucosamine in skeletal muscle proteins in vivo

    Metabolism

    (1998)
  • R.S. Haltiwanger et al.

    Modulation of O-linked N-acetylglucosamine levels on nuclear and cytoplasmic proteins in vivo using the peptide O-GlcNAc-β-N-acetylglucosaminidase inhibitor O-(2-acetamido-2-deoxy-d-glucopyranosylidene)amino-N-phenylcarbamate

    J. Biol. Chem.

    (1998)
  • M. Nakamura et al.

    Excessive hexosamines block the neuroprotective effect of insulin and induce apoptosis in retinal neurons

    J. Biol. Chem.

    (2001)
  • F.I. Comer et al.

    Characterization of a mouse monoclonal antibody specific for O-linked N-acetylglucosamine

    Anal. Biochem.

    (2001)
  • K. Kamemura et al.

    Dynamic interplay between O-glycosylation and O-phosphorylation of nucleocytoplasmic proteins: alternative glycosylation/phosphorylation of THR-58, a known mutational hot spot of c-Myc in lymphomas, is regulated by mitogens

    J. Biol. Chem.

    (2002)
  • B.K. Hayes et al.

    Specific isolation of O-linked N-acetylglucosamine glycopeptides from complex mixtures

    Anal. Biochem.

    (1995)
  • K.D. Greis et al.

    Selective detection and site-analysis of O-GlcNAc-modified glycopeptides by β-elimination and tandem electrospray mass spectrometry

    Anal. Biochem.

    (1996)
  • L. Wells et al.

    Mapping sites of O-GlcNAc modification using affinity tags for serine and threonine post-translational modifications

    Mol. Cell Proteomics

    (2002)
  • W.G. Kelly et al.

    RNA polymerase II is a glycoprotein. Modification of the COOH-terminal domain by O-GlcNAc

    J. Biol. Chem.

    (1993)
  • S.P. Jackson et al.

    O-glycosylation of eukaryotic transcription factors: implications for mechanisms of transcriptional regulation

    Cell

    (1988)
  • A.J. Reason et al.

    Localization of O-GlcNAc modification on the serum response transcription factor

    J. Biol. Chem.

    (1992)
  • S. Lichtsteiner et al.

    A glycosylated liver-specific transcription factor stimulates transcription of the albumin gene

    Cell

    (1989)
  • N.O. Ku et al.

    Identification and mutational analysis of the glycosylation sites of human keratin 18

    J. Biol. Chem.

    (1995)
  • J. Hagmann et al.

    The cytoskeletal protein talin is O-glycosylated

    J. Biol. Chem.

    (1992)
  • M. Inaba et al.

    O-N-acetyl-d-glucosamine moiety on discrete peptide of multiple protein 4.1 isoforms regulated by alternative pathways

    J. Biol. Chem.

    (1989)
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