Structure-function Studies On A Cancer Cell-specific Cell Adhesion Protein

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Very often polypeptides are cleaved after translation from mRNA.Typical examples are signal peptides, which are necessary for protein secretion or targeting proteins to various membranes. There are also peptides called "propeptides", whose functions are usually not known. We had previously investigated physiological functions of propolypeptide of von Willebrand factor (pp-vWF,-100kDa), and elucidated the interaction between pp-vWF and collagen in molecular terms. In the present investigation we have extended this study and found that pp-vWF is incorporated into extra cellular matrix, and that it serves as a cell adhesion protein. Our initial observation suggested that it specifically mediated the adhesion of melanoma cells. Using our monoclonal antibodies against pp-vWF and technique of protease digestion, we found that the domain responsible for the cell adhesion resided in the central 8-kDa region. Using genetic engineering and synthetic peptide techniques we have narrowed down the domain to 15 amino acid segment Asp395-Gln409. Using this peptide as the ligand, we have devised affinity chromatography and isolated the receptor for the cell adhesion, which was identified as alpha4beta1 integrin, VLA-4. This point was further confirmed by transfection of the cDNA of this integrin into animal cells and testing the cell adhesion to pp-vWF.VLA-4 is found not only in melanoma cells but also various blood cells such as lymphocytes. We indeed confirmed the adhesion of lymphocyte Molt-3 to pp-vWF.In conclusion, we speculate that pp-vWF is involved not only in metastasis of melanoma but also in adhesion of lymphocytes to the site of inflammation.