The alpha 4 beta 1 fibronectin ligands CS-1, Hep II, and RGD induce different intracellular events in B lymphoid cells. Comparison with the effects of the endothelial ligand VCAM-1.
The lymphocyte integrin alpha 4 beta 1 is the receptor for the Hep II domain and CS-1 site in fibronectin (Fn) as well as for VCAM-1. We recently showed that upon activation with anti-beta 1 mAb TS2/16, alpha 4 beta 1 also recognizes the RGD Fn sequence. To determine the physiological role of these multiple interactions, we have now studied some intracellular events induced by "resting" and activated alpha 4 beta 1 binding to its different ligands. Analyses of actin and tubulin reorganization upon adhesion of B lymphoid cells to Fn fragments or VCAM-1 showed that VCAM-1, a 38 kDa fragment (Hep II+CS-1), and the CS-1 synthetic peptide induced formation of transient cytoplasmic projections; however, cells attached to a 58 kDa (Hep II) or 80 kDa (RGD) fragments remained rounded. Using transfilter assays, we showed that VCAM-1, 38 kDa and CS-1 also induced dose-dependent B cell migration mediated by alpha 4 beta 1. Furthermore, these three ligands, but not the 80 kDa fragment or a synthetic peptide (H1) containing a sequence from Hep II shown to bind alpha 4 beta 1, induced tyrosine phosphorylation of a 110 kDa protein. Activation of alpha 4 beta 1 with TS2/16 inhibited the cytoplasmic protrusions and cell migration but did not affect the pattern of phosphorylation. Our results indicate that the various alpha 4 beta 1 ligands induce different cellular responses. Most importantly they show that alpha 4 beta 1 interaction with CS-1 is sufficient to trigger intracellular events in B cells. Furthermore, they suggest a regulation by the activation form of the receptor as well as by the ligand in events involving lymphocyte adhesion and migration.
Domínguez-Jiménez
C
C
Departmento de Inmunología, Centro de Investigaciones Biológicas, CSIC, Madrid, Spain.
Sánchez-Aparicio
P
P
Albar
J P
JP
García-Pardo
A
A
D000595:Amino Acid Sequence; D001402:B-Lymphocytes / Q000378:metabolism*; D002448:Cell Adhesion; D002460:Cell Line; D002465:Cell Movement; D048429:Cell Size; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D005353:Fibronectins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D039041:Integrin alpha4beta1; D016023:Integrins / Q000378:metabolism*; D008024:Ligands; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D016201:Receptors, Lymphocyte Homing / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D019010:Vascular Cell Adhesion Molecule-1 / Q000235:genetics / Q000378:metabolism*
D003598:Cytoskeletal Proteins; D005353:Fibronectins; D039041:Integrin alpha4beta1; D016023:Integrins; D008024:Ligands; D010446:Peptide Fragments; D016201:Receptors, Lymphocyte Homing; D011994:Recombinant Proteins; D019010:Vascular Cell Adhesion Molecule-1; C105547:MARK1 protein, human; D017346:Protein Serine-Threonine Kinases