Cell adhesion is a fundamental consideration in tumor cell metastasis. Understanding the molecular basis of cellular recognition and adhesion could lead to novel forms of therapeutic intervention. Their research focus has been to understand a role for cell surface proteoglycan in modulating integrin-mediated tumor cell adhesion. As a model system, they have identified a role for cell surface chondroitin sulfate proteoglycan (CSPG) in modulating the function of alpha4beta1 integrin on melanoma cells. alpha4beta1 integrin can mediate tumor cell arrest in the vasculature due to its ability to bind to fibronectin and to VCAM, which is expressed on the surface of cytokine-activated endothelial cells. This integrin also modulates protease production and tumor cell invasion. Removal of cell surface chondroitin sulfate reduces alpha4 beta1 integrin mediated melanoma adhesion and ligand binding, suggesting that cell surface CSPG can affect the affinity state of the integrin. Furthermore, cell surface CSPG also affects alpha4 beta1 integrin-mediated cell spreading and focal contact formation by modulating intracellular signaling pathways. Collectively, the results suggest a model in which cell surface CSPG can enhance the function of alpha4 beta1 integrin by both direct and indirect interactions. To begin to test this model, they have synthesized several synthetic peptides from the extracellular domain of the alpha4 integrin subunit that could serve as potential integrin/proteoglycan binding sites. One synthetic peptide, termed SG-1, as well anti-SG-1 antibodies, will inhibit alpha4 beta1 integrin-mediated cell adhesion. Furthermore, the SG-1 peptide binds cell surface CSPG by affinity chromatography, suggesting that it may inhibit alpha4 beta1 integrin function by interferring with direct interactions between alpha4 beta1 integrin and cell surface CSPG. Preliminary evidence also suggests that the two recpetors may constitutively associate at low levels on the cell surface, and that this association may be enhanced in the process of cell adhesion to ligands that bind both CSPG and alpha4 beta1 integrin. In this proposal, they will therefore evaluate the mechanisms by which cell surface CSPG functionally enhances alpha4 beta1 integrin-mediated adhesion and spreading and they will determine if this enhancement is due, in part, to a direct association of the two cell surface receptors. They believe that this may be representative of a more generalized mechanism of integrin-mediated cell adhesion. The overall goal in these studies is to define the molecular mechanisms that regulate CSPG/alpha4beta1 integrin interactions and to evaluate their importance in tumor cell adhesion, invasion and metastasis.
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