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Structure‐function analysis of the human integrin VLA‐4 (α4/β1)
Author(s) -
Pulido Rafael,
Campanero Miguel R.,
García-Pardo Angeles,
Sánchez-Madrid Francisco
Publication year - 1991
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(91)81356-d
Subject(s) - epitope , fibronectin , trypsin , integrin , microbiology and biotechnology , monoclonal antibody , pronase , chemistry , cell adhesion , biochemistry , biology , antibody , cell , immunology , enzyme
The structure‐function relationship of the human integrin VLA‐4 (α4/β1; 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 α4 chain, which could be digested upon mild trypsin treatment to generate the 80‐ and 65‐kDa proteolyzed forms, as well as α4 polypeptides of 55 and 50 kDa. In addition, treatment of Ramos cells with high doses of pronase predominantly yielded the 55‐ and 50‐kDa α4 peptides. The trypsin‐generated 80‐ and 65‐kDa α4 polypeptides, but not the 55‐ and 50‐kDa fragments, were able to associate with the β1 chain. Distinct anti‐VLA‐4 mAb against four different α4 epitopes, referred to as epitopes A, B1, B2, and C, recognized the 150‐kDa α4 chain both associated or non‐associated with the β1 chain. The α4 proteolytic forms of 80, 65 and 50 kDa were precipitated by the anti‐α4 mAb directed against the four different α4 epitopes. On the other hand, the 55‐kDa α4 peptide was present in precipitates from anti‐α4 mAb specific for epitopes A, B1 and C, but absent in precipitates from the anti‐α4 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‐α4‐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 α4 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.