Alpha 4 beta 1 recognition of the Hep II domain of fibronectin is constitutive on some hemopoietic cells but requires activation on others [corrected].
Leukocyte adhesion to the carboxyl-terminal region of fibronectin, a major component of extracellular matrices, involves recognition of the CS-1 site and the Hep II domain. We have previously shown that cultured T and B lymphoid cells constitutively attach via the alpha 4 beta 1 integrin to a 38-kDa fibronectin fragment that contains CS-1 and Hep II, and to a 58-kDa fragment that contains Hep II only. In this report we have studied the adhesion of other hemopoietic cells to the CS-1 and Hep II regions of fibronectin. Cultured monocytic cells and peripheral blood T lymphocytes constitutively bound to the 38-kDa fragment indicating that alpha 4 beta 1 was functional. These cells, however, were unable to bind to the 58-kDa fragment. On lymphoid cells both fragments were shown to bind to very close regions of alpha 4 beta 1 as indicated by the inhibition pattern of mAb to various alpha 4 epitopes, and by the good inhibitory capacity of soluble 38-kDa fragment on cell adhesion to 58-kDa fragment. These results suggested that alpha 4 beta 1 is present on certain cell populations as a partially active form able to recognize the "high affinity" ligand CS-1 but not the "low affinity" ligand Hep II. Binding of monocytic cells and peripheral blood T lymphocytes to the Hep II domain could be induced by several agents: first, long (48-h) and short (20-min) treatment with phorbol esters; second, cell incubation with the divalent cation Mn2+; third, and most effective, cell incubation with the mAb TS2/16, which is directed to the beta 1 integrin subunit. Binding to the 58-kDa fragment in all three cases was completely inhibited by mAb anti-alpha 4, thus confirming the involvement of alpha 4 beta 1 in the recognition of the Hep II domain. No major changes on alpha 4 beta 1 surface expression were observed after these treatments as determined by immunofluorescence analyses. Our results indicate that hemopoietic cells may differentially bind the CS-1 and Hep II ligands in fibronectin depending on the activation state of alpha 4 beta 1, a fact that may be relevant for the migration and function of leukocytes.
Sánchez-Aparicio
P
P
Unidad de Inmunología, Centro de Investigaciones Biológicas, CSIC, Madrid, Spain.
Ferreira Júnior
O C
OC
Garcia-Pardo
A
A
D000911:Antibodies, Monoclonal / Q000276:immunology; D001665:Binding Sites; D002448:Cell Adhesion; D002454:Cell Differentiation; D002460:Cell Line; D005353:Fibronectins / Q000378:metabolism*; D006801:Humans; D039041:Integrin alpha4beta1; D016023:Integrins / Q000502:physiology*; D008345:Manganese / Q000494:pharmacology; D009000:Monocytes / Q000502:physiology*; D010446:Peptide Fragments / Q000378:metabolism*; D013601:T-Lymphocytes / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D000911:Antibodies, Monoclonal; D005353:Fibronectins; D039041:Integrin alpha4beta1; D016023:Integrins; D010446:Peptide Fragments; D008345:Manganese; D013755:Tetradecanoylphorbol Acetate