Structure-function analysis of the human integrin VLA-4 (alpha 4/beta 1). Correlation of proteolytic alpha 4 peptides with alpha 4 epitopes and sites of ligand interaction.
The structure-function relationship of the human integrin VLA-4 (alpha 4/beta 1; CD49d/CD29), has been studied in the human B-cell line Ramos by immunochemical and functional analysis. Ramos cells expressed the 150-kDa non-proteolyzed form of the alpha 4 chain, which could be digested upon mild trypsin treatment to generate the 80- and 65-kDa proteolyzed forms, as well as alpha 4 polypeptides of 55 and 50 kDa. In addition, treatment of Ramos cells with high doses of pronase predominantly yielded the 55- and 50-kDa alpha 4 peptides. The trypsin-generated 80- and 65-kDa alpha 4 polypeptides, but not the 55- and 50-kDa fragments, were able to associate with the beta 1 chain. Distinct anti-VLA-4 mAb against four different alpha 4 epitopes, referred to as epitopes A, B1, B2, and C, recognized the 150-kDa alpha 4 chain both associated or non-associated with the beta 1 chain. The alpha 4 proteolytic forms of 80, 65 and 50 kDa were precipitated by the anti-alpha 4 mAb directed against the four different alpha 4 epitopes. On the other hand, the 55-kDa alpha 4 peptide was present in precipitates from anti-alpha 4 mAb specific for epitopes A, B1 and C, but absent in precipitates from the anti-alpha 4 mAb specific for epitope B2. The different adhesive capacities of the VLA-4 integrin, namely the interaction with a 38-kDa fibronectin fragment containing the CS-1 region of plasma fibronectin (Fn-38), the binding to the vascular cell adhesion molecule-1 (VCAM-1), or the ability to mediate the anti-alpha 4-induced cell aggregation, were not altered on VLA-4 from cells upon mild trypsin treatment, when compared to non-treated cells. However, the 55- and 50-kDa alpha 4 forms generated by high-dose pronase cell treatment, failed to mediate cell interaction with Fn-38 or VCAM-1 ligands, and cell aggregation could not be triggered through VLA-4 under these conditions.
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Sección de Inmunología, Hospital de la Princesa, Universidad Autónoma de Madrid, Spain.
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García-Pardo
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Sánchez-Madrid
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D000911:Antibodies, Monoclonal; D000936:Antigen-Antibody Complex; D001402:B-Lymphocytes; D002448:Cell Adhesion; D002449:Cell Aggregation; D002460:Cell Line; D000939:Epitopes / Q000032:analysis*; D005353:Fibronectins / Q000502:physiology; D006801:Humans; D039001:Integrin alpha Chains; D008024:Ligands; D010446:Peptide Fragments / Q000276:immunology; D016029:Receptors, Very Late Antigen / Q000276:immunology* / Q000378:metabolism
D000911:Antibodies, Monoclonal; D000936:Antigen-Antibody Complex; C063493:CDw49d; D000939:Epitopes; D005353:Fibronectins; D039001:Integrin alpha Chains; D008024:Ligands; D010446:Peptide Fragments; D016029:Receptors, Very Late Antigen