Nuclear and cytoplasmic glycosylation.

We recently described a major new form of protein glycosylation (termed O-GlcNAc) that is found in all multicellular organisms, including plants, animals and viruses that infect them. O-GlcNAc is ubiquitous, abundant and highly-dynamic, suggesting a regulatory role analogous to phosphorylation. O-GlcNAc is found on a myriad of nuclear and cytoplasmic proteins including chromatin proteins, RNA polymerase II and its transcription factors, oncogene proteins, heat shock proteins, nuclear pore proteins, viral proteins, and cytoskeletal proteins. A major thrust of our lab is to elucidate the biosynthesis, removal, attachments sites, and functions of this novel post-translational modification.

Glycosylation and cancer.
Recently we found that many nuclear oncogenes, such as c-myc and adenovirus E1A or tumor suppressors are glycosylated by O-GlcNAc. Steroid receptors, such as the estrogen receptor are also glycosylated. O-GlcNAc appears to have a 'yin-yang' relationship with phosphorylation of these proteins. For example, c-myc is dynamically glycosylated on Thr-58, also a major site for GSK3 kinase action and the highest mutation 'hot-spot' in lymphomas. Much effort in the lab is directed at elucidating the roles these O-GlcNAc modifications in cancer. Glycosylation and neurobiology. Many of the proteins involved in synaptic transmission or cytoskeletal proteins important to nerve function and disease, such as glycosylated by O-GlcNAc. We are investigating the role of O-GlcNAc and its relation to phosphorylation of these proteins.

Nuclear glycosylation and diabetes.
We are investigating the roles of nuclear and cytoplasmic glycosylation in mediating the toxicity of hyperglycemia and the role of transcription factor glycosylation in the control of the expression of the insulin gene. The O-GlcNAc transferase and O-GlcNAc-proteins are greatly enriched in the insulin-producing (-cells of the pancreas.

Publications:

Zachara NE, Cheung WD, Hart GW. (2004) Nucleocytoplasmic glycosylation, O-GlcNAc: identification and site mapping. Methods Mol Biol.;284:175-94.
PubMed Abstract

O'Donnell N, Zachara NE, Hart GW, Marth JD. (2004) Ogt-dependent X-chromosome-linked protein glycosylation is a requisite modification in somatic cell function and embryo viability. Mol Cell Biol. Feb;24(4):1680-90.
PubMed Abstract

Zachara NE, Hart GW. (2004) O-GlcNAc modification: a nutritional sensor that modulates proteasome function. Trends Cell Biol. May;14(5):218-21.
PubMed Abstract

Liu, F., Iqbal, K., Grundke-Iqbal, K., Hart, G., and Gong, C.(2004). O-GlcNAcylation regulates phosphorylation of tau: a novel mechanism involved in Alzheimer’s disease. Proc. Natl. Acad. Sci. 101, 10804-10809.
PubMed Abstract

Zachara NE, Hart GW. (2004) O-GlcNAc a sensor of cellular state: the role of nucleocytoplasmic glycosylation in modulating cellular function in response to nutrition and stress. Biochim Biophys Acta. Jul 6;1673(1-2):13-28. Review.
PubMed Abstract

Natasha E. Zachara, Niall O'Donnell, Win D. Cheung, Jessica J. Mercer, Jamey D. Marth, and Gerald W. Hart (2004) Dynamic O-GlcNAc Dynanic O-GlcNAc Modification of Nucleocytoplasmic Proteins in Response to Stress: A Survival Response of Mammalian Cells. J. Biol. Chem. 279, 30133-30142.
PubMed Abstract

Donnell, N., Zachara, N., Hart, G., and Marth, J., (2004). Ogt-Dependent X-Chromosome-Linked Intracellular Protein Glycosylation is Essential for Mammalian Viability and Cellular Metabolism. Mol. Cell Biochem. 24, 1680-1690.
PubMed Reference

Whelan, S., and Hart, G., (2004). O-Linked N-Acetylglucosamine (O-GlcNAc) in Encyclopedia of Genetics, Genomics, Proteomics and Bioinformatics, John Wiley & Sons edited by Pauline Rudd.

Wells L, Kreppel LK, Comer FI, Wadzinski BE, Hart GW. (2004) O-GlcNAc transferase is in a functional complex with protein phosphatase 1 catalytic subunits. J Biol Chem. Sep 10;279(37):38466-70. Epub 2004 Jul 7.
PubMed Abstract

Chad Slawson, Natasha E. Zachara, Keith Vosseller, Win Den Cheung, M. Daniel Lane, and Gerald W. Hart (2005) Perturbations in O-GlcNAc Protein Modification Cause Severe Defects in Mitotic Progression and Cytokinesis. J.Biol. Chem. 280, 32944-32956.
PubMed Reference

Vosseller K, Hansen KC, Chalkley RJ, Trinidad JC, Wells L, Hart GW, Burlingame AL. (2005) Quantitative analysis of both protein expression and serine / threonine post-translational modifications through stable isotope labeling with dithiothreitol. Proteomics. Feb;5(2):388-98.
PubMed Abstract

Stephen A. Whelan and Gerald W. Hart (2006) Identification of O-GlcNAc Sites on Proteins. Methods in Enzymology, M. Fukuda, editor 415, 113-133.
PubMed Reference

Natasha E. Zachara & Gerald W. Hart (2006) Cell Signaling, the Essential Role of O-GlcNAc! Biochimic Biophysica ACTA 1761, 599-617.
PubMed Reference

Zihao Wang and Gerald W. Hart Dynamic Interplay Between O-GlcNAcylation and GSK3-Dependent Phosphorylation. Molecular & Cellular Proteomics MCP Papers On-Line. Published on May 16, 2007 as Manuscript M600453-MCP200

Gerald W. Hart, Michael P. Housley and Chad Slawson Cycling of O-Linked b-N-Acetylglucosamine on Nucleocytoplasmic Proteins. (2007) Nature 446, 1017-1022(26 April 2007) doi:10.1038/nature05815.
PubMed Reference