Effect of integrin beta 2 subunit truncations on LFA-1 (CD11a/CD18) and Mac-1 (CD11b/CD18) assembly, surface expression, and function.
LFA-1 (CD11a/CD18) and Mac-1 (CD11b/CD18) are members of the beta2 integrins involved in leukocyte function during immune and inflammatory responses. We aimed to determine a minimized beta2 subunit that forms functional LFA-1 and Mac-1. Using a series of truncated beta2 variants, we showed that the subregion Q23-D300 of the beta2 subunit is sufficient to combine with the alphaL and alphaM subunits intracellularly. However, only the beta2 variants terminating after Q444 promote cell surface expression of LFA-1 and Mac-1. Thus, the major cysteine-rich region and the three highly conserved cysteine residues at positions 445, 447, and 449 of the beta2 subunit are not required for LFA-1 and Mac-1 surface expression. The surface-expressed LFA-1 variants are constitutively active with respect to ICAM-1 adhesion and these variants express the activation reporter epitope of the mAb 24. In contrast, surface-expressed Mac-1, both the wild type and variants, require 0. 5 mM MnCl2 for adhesion to denatured BSA. These results suggest that the role of the beta2 subunit in LFA-1- and Mac-1-mediated adhesion may be different.
Tan
S M
SM
Medical Research Council Immunochemistry Unit, Department of Biochemistry, University of Oxford, Oxford, United Kingdom.
Hyland
R H
RH
Al-Shamkhani
A
A
Douglass
W A
WA
Shaw
J M
JM
Law
S K
SK
D000818:Animals; D018821:CD18 Antigens / Q000235:genetics* / Q000502:physiology; D019556:COS Cells; D003545:Cysteine / Q000235:genetics / Q000502:physiology; D003593:Cytoplasm / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D019281:Dimerization; D014644:Genetic Variation; D005822:Genetic Vectors / Q000138:chemical synthesis; D006801:Humans; D008024:Ligands; D016169:Lymphocyte Function-Associated Antigen-1 / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D016177:Macrophage-1 Antigen / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D008565:Membrane Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D010446:Peptide Fragments / Q000235:genetics / Q000502:physiology; D011499:Protein Processing, Post-Translational / Q000276:immunology; D017384:Sequence Deletion; D012995:Solubility; D014162:Transfection
D018821:CD18 Antigens; D008024:Ligands; D016169:Lymphocyte Function-Associated Antigen-1; D016177:Macrophage-1 Antigen; D008565:Membrane Proteins; D010446:Peptide Fragments; D003545:Cysteine