Lauren Ball, PhD
Director of Mass Spectrometry Facility
Co-Director, Graduate Program
2003 Ph.D., Medical University of South Carolina
Office: CRI 311
Role of O-GlcNAc Glycosylation in the Regulation of Insulin/IGF-1 Receptor Signal Transduction Pathways
The O-linked glycosylation of serine and threonine residues by a single monosaccharide, beta-N-acetylglucosamine (O-GlcNAc), is a dynamic and reversible posttranslational modification occurring on nuclear and cytoplasmic proteins. This modification regulates protein function in a manner analogous to S/T phosphorylation and furthermore may compete with S/T phosphorylation. The enzymes catalyzing the incorporation and removal of GlcNAc from proteins, O-GlcNAc transferase and O-GlcNAcase, respectively, are located in the nucleus and cytoplasm and are ubiquitously distributed in tissues. Many proteins are O-GlcNAc modified including transcription factors, oncogenes, tumor suppressors, heat shock proteins, nuclear pore proteins, and intracellular signaling molecules. Global protein O-GlcNAc modification increases with nutrient excess, cellular stress, and hormonal stimulation and dysregulation of this modification has been implicated in diabetes, cancer, and neurodegenerative disease.
The sugar donor for O-GlcNAc modification, UDP-GlcNAc, is generated by the metabolism of glucose through the hexosamine biosynthetic pathway. Under normal conditions 2-3% of the glucose entering the cell is committed to this pathway. However, in states of nutrient excess, such as type II diabetes, UDP-GlcNAc levels and the extent of protein O-GlcNAc modification rise. Thus, hyperglycemia-induced O-GlcNAc modification has been proposed to contribute to the microvascular complications (nephropathy, neuropathy, and retinopathy) associated with diabetes and may exacerbate diabetic periodontal disease.
We are interested in the role of O-GlcNAc modification of insulin receptor substrate proteins in the regulation of insulin receptor and insulin-like growth factor (IGF-1) receptor signaling pathways. Insulin receptor substrate-1 (IRS-1), a central molecule in the insulin/IGF-1 receptor pathways, mediates many of the metabolic and mitogenic effects of insulin and IGF-1. The phenotypic characteristics of transgenic animals deficient in IRS-1 reflect defects in both the insulin and IGF-1 receptor signaling pathways. These animals exhibit retarded growth, impaired endothelial-dependent vascular relaxation, peripheral insulin resistance of skeletal muscle and adipose tissue, and a decreased capacity for bone healing. A human polymorphism of IRS-1 has been linked to insulin resistance, endothelial dysfunction, and an increased risk for breast, prostate, and colorectal cancers. Following insulin or IGF-1 receptor stimulation, IRS-1 is phosphorylated by the receptor tyrosine kinases within distinct protein interaction motifs. These motifs provide a platform for interaction of IRS-1 with a number of downstream effectors including PI3Kinase, Grb2, and SHP-2. These interactions are further modulated by S/T kinases which are involved in positive or negative feedback regulation at the level of IRS-1. We are currently investigating the influence of O-GlcNAc modification on the phosphorylation state and the interactions of IRS-1 with binding partners.
In the laboratory, we use tandem mass spectrometry to identify the exact sites of protein O-GlcNAc modification and phosphorylation. Mass spectrometry provides a powerful tool for the identification and quantification of posttranslational modifications and the discovery of unanticipated protein-protein interactions. We are interested in developing proteomic methods to facilitate the isolation and identification of O-GlcNAcylated proteins to further examine the role of this modification in the regulation of protein function and its contribution to the development or progression of human disease. Elucidation of the mechanisms by which O-GlcNAc modification regulates signal transduction pathways may reveal novel targets of therapeutic intervention applicable to many human diseases.
Recent Publications | Additional Publications
1. Klein AL, Berkaw MN, Buse MG, Ball LE. O-linked N-acetylglucosamine modification of insulin receptor substrate-1 occurs in close proximity to multiple SH2 domain binding motifs. Mol Cell Proteomics. 2009 Dec;8(12):2733-45. Epub 2009 Aug 11. PubMed PMID: 19671924; PubMed Central PMCID: PMC2816021.
2. Robinson KA, Ball LE, Buse MG. Reduction of O-GlcNAc protein modification does not prevent insulin resistance in 3T3-L1 adipocytes. Am J Physiol Endocrinol Metab. 2007 Mar;292(3):E884-90. Epub 2006 Nov 22. PubMed PMID: 17122093; PubMed Central PMCID: PMC2366901.
3. Ball LE, Berkaw MN, Buse MG. Identification of the major site of O-linked beta-N-acetylglucosamine modification in the C terminus of insulin receptor substrate-1. Mol Cell Proteomics. 2006 Feb;5(2):313-23. Epub 2005 Oct 22. PubMed PMID: 16244361; PubMed Central PMCID: PMC2435407.