We have previously reported that propolypeptide of von Willebrand factor (pp-vWF) promotes melanoma cell adhesion in a ␤1 integrin-dependent manner. In this report, we identified the ␣ subunit of the cell adhesion receptor for pp-vWF as ␣4. Human leukemia cell lines that express ␣4␤1 integrin (very late antigen-4, VLA-4), but not cell lines which lack VLA-4, attached well to pp-vWF substrate and these adhesions were completely inhibited by anti-␣4 integrin monoclonal antibody HP2/1. Adhesion of mouse melanoma expressing ␣4 integrin was also inhibited by anti-mouse ␣4 mAb PS/2. Furthermore, transfection of human ␣4 cDNA into ␣4 ؊ Chinese hamster ovary cells resulted in an acquisition of adhesive activity to pp-vWF, indicating that pp-vWF is a ligand for VLA-4 integrin. Using a recombinant fragment of pp-vWF, the cell attachment site was shown to be located within amino acid residues 376 -455 of ppvWF. A series of synthetic peptides covering this region were tested for the ability to promote cell attachment and a 15-residue peptide designated T2-15 (DCQDHSF-SIVIETVQ, residues numbered 395-409) promoted VLA-4 dependent cell adhesion. The peptide was also capable of inhibiting cell adhesion to pp-vWF, suggesting that this sequence represents the cell attachment site. By affinity chromatography using peptide T2-15-Sepharose, it was found that ␣4␤1 integrin complex from extracts of surface iodinated B16 cells specifically bound to the peptide. These results strongly suggest that pp-vWF is a novel physiological ligand for VLA-4.Propolypeptide of von Willebrand factor (pp-vWF), 1 which is also called von Willebrand antigen II (1), is an unusually large propolypeptide (ϳ100 kDa) produced only in endothelial cells and megakaryocytes together with blood coagulation protein von Willebrand factor (2). It is processed from a large precursor of vWF (prepro-vWF) during biosynthesis and stored in the granule of both endothelial cells and platelets independent from mature vWF (3, 4). We have been investigating the biological functions of pp-vWF and found that pp-vWF bound to collagen and inhibited collagen-induced platelet aggregation in contrast to the mature vWF (5, 6). Furthermore, we have found that pp-vWF serves as a substrate for transglutaminase and is specifically cross-linked to laminin (7), suggesting a possibility that it acts as transient matrix protein upon secretion from platelets and endothelial cells at the site of vascular injury. In a previous paper (8), we reported that pp-vWF promoted the attachment and spreading of melanoma cells. The receptor responsible for this adhesion was the ␤1 class of integrin but the corresponding ␣ subunit could not be identified.Integrins are heterodimeric transmembrane proteins consisting of ␣ and ␤ subunits and mediate cell adhesion to extracellular matrix proteins as well as cell-cell interactions (9 -12). To date more than 15 ␣ subunits and 8 ␤ subunits have been identified and combination of ␣ and ␤ subunits determines the ligand specificity of individual integrins. Integrin-m...

Participants in this study had an increased ratio of silent brain infarction compared with Japanese healthy controls, accompanied with higher ratios of diabetes and low HDL cholesterol.

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