The long-term objective of these experiments is to determine the mechanisms by which the expression of a particular glycosyltransferase and its homologs, termed GIcNAc-T V (GnT-V), regulates cell adhesion and tumor progression. Studies have documented an association between specific changes in N-linked oligosaccharides with beta(1,6) branches and oncogenic transformation, increased tumor cell invasiveness, and metastatic potential. Elevation of beta (1,6) branches has also been documented in the progression of human mammary and colon carcinomas. The synthesis of this N-linked oligosaccharide branch is catalyzed by GIcNAc-T V, and the activity of this enzyme is selectively increased after transformation by several oncogenes, and utilizing a mouse model of mammary tumor oncogenesis and progression, elimination of the N-linked beta (1,6) branches branch clearly inhibits tumor invasion and metastasis. Both integrin-based adhesion to the matrix glycoprotein, fibronectin, and N-cadherin-based cell-cell adhesion, as well as the corresponding intracellular signaling pathways are reduced after GnT-V over-expression and increased after eliminating the expression of the enzyme, suggesting mechanisms by which tumor progression can be regulated. A new homolog of GnT-V has been identified in brain tissue and termed GnT-VB.
Aim I will focus on determining how changes in GnT-V activity modulate integrin- and cadherin-based adhesion. In addition, a mouse model of tumor progression will be utilized to study glycan structural changes on adhesion receptors and their signaling pathways in the presence and absence GnT-V activity to test if changes can be detected in vivo.
Aim II will focus on investigating the regulation and function of GnT-VB. Brain glycoproteins that are endogenous acceptors will be identified, and techniques for expression of siRNA will be used to test if GnT-VB expression in vivo during brain development functions to regulate cell migration/adhesion. GnT-VB null mice and GnT-V/GnT-VB double null mice will be generated.
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