Identification of a combinatorial epitope expressed by the integrin alpha 4 beta 1 heterodimer involved in the regulation of cell adhesion.
The alpha 4 integrin subunit can associate with either the beta 1- or beta 7-integrin subunit to form two unique adhesion receptors alpha 4 beta 1 and alpha 4 beta 7. We developed a monoclonal antibody (mAb 19H8) that immunoprecipitated alpha 4 beta 1, induced homotypic leukocyte aggregation, and blocked the binding of cells to a synthetic peptide corresponding to the CS-1 peptide region of fibronectin. Aggregation cross-blocking analysis suggested that mAb 19H8 belonged to the group of mAbs that react with the B2 epitope of the alpha 4 subunit (alpha 4.B2 epitope); however, unlike the alpha 4.B2-specific mAb L25, mAb 19H8 did not immunoprecipitate alpha 4 beta 7. In addition, mAb 19H8 did not bind to beta 1-positive cells unless transfected with alpha 4 cDNA. These results indicated that mAb 19H8 was not specific for an individual alpha 4, beta 1, or beta 7 subunit but reacted with an epitope formed from the association of alpha 4 with beta 1. Separating the alpha 4 from the beta 1 subunit, by removing divalent cations or by treatment with high pH, disrupted mAb 19H8 binding. In contrast, the alpha 4-specific mAb L25 and the beta 1-specific mAb 18D3 could react with their respective subunits without subunit association. Therefore, mAb 19H8 defined a novel regulatory epitope expressed by the integrin alpha 4 beta 1.
Bednarczyk
J L
JL
Department of Immunology, University of Texas M. D. Anderson Cancer Center, Houston 77030.
Szabo
M C
MC
Wygant
J N
JN
Lazarovits
A I
AI
McIntyre
B W
BW
D000911:Antibodies, Monoclonal / Q000378:metabolism / Q000494:pharmacology; D002051:Burkitt Lymphoma; D002448:Cell Adhesion; D002449:Cell Aggregation; D002460:Cell Line; D000939:Epitopes / Q000032:analysis; D005353:Fibronectins / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D039041:Integrin alpha4beta1; D016023:Integrins / Q000032:analysis / Q000096:biosynthesis*; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive; D008214:Lymphocytes / Q000502:physiology; D016029:Receptors, Very Late Antigen / Q000032:analysis / Q000096:biosynthesis; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; D000939:Epitopes; D005353:Fibronectins; D039041:Integrin alpha4beta1; D016023:Integrins; D016029:Receptors, Very Late Antigen