Association of BAP31 with CD11b/CD18. Potential role in intracellular trafficking of CD11b/CD18 in neutrophils.
The beta2 integrin CD11b/CD18 is an integral membrane protein that is present in the plasma membrane and secondary granules of neutrophils and functions as a major adhesion molecule. Upon cellular activation, there is translocation of intracellular pools of CD11b/CD18 to the plasma membrane in concert with enhanced cellular adhesion. Although ... much is known about the function of CD11b/CD18, how this protein is transported within the cell is less well defined. Here we report that CD11b/CD18 specifically binds to BAP31, a member of a novel class of sorting proteins regulating cellular anterograde transport. Through experiments aimed at identifying CD11b/CD18-binding proteins, we produced a monoclonal antibody termed E1B2 that recognizes a 28-kDa membrane protein that co-precipitates with CD11b/CD18. Microsequence analysis of the E1B2 antigen revealed that it is BAP31. Co-association of CD11b/CD18 and BAP31 was confirmed in co-immunoprecipitation and protein binding assays. Additional experiments revealed that the binding of BAP31 to CD11b/CD18 was not dependent on divalent cations nor mediated by the I-domain of CD11b. Using glutathione S-transferase fusion chimeras, we determined that binding of CD11b/CD18 to BAP31 is mediated through interactions with the cytoplasmic tail of BAP31. Immunolocalization studies revealed colocalization of BAP31 and CD11b/CD18 within neutrophil secondary granules. Subcellular fractionation studies in polymorphonuclear leukocytes (PMN) revealed similar patterns of redistribution of BAP31 and CD11b/CD18 from fractions enriched in secondary granules to the plasma membrane following stimulation with formylmethionylleucylphenylalanine (fMLP). Given the known sorting properties of BAP31, these findings suggest that BAP31 may play a role in regulating intracellular trafficking of CD11b/CD18 in neutrophils.
Mesh Terms:
Amino Acid Sequence, Antigens, CD11b, Antigens, CD18, Biological Transport, Cell Adhesion, Cell Line, Cell Membrane, Cells, Cultured, Glutathione Transferase, HL-60 Cells, Humans, Immunohistochemistry, Immunoprecipitation, Membrane Proteins, Molecular Sequence Data, N-Formylmethionine Leucyl-Phenylalanine, Neutrophils, Protein Binding, Protein Structure, Tertiary, Protein Transport, Recombinant Fusion Proteins, Secretory Vesicles, Subcellular Fractions
Amino Acid Sequence, Antigens, CD11b, Antigens, CD18, Biological Transport, Cell Adhesion, Cell Line, Cell Membrane, Cells, Cultured, Glutathione Transferase, HL-60 Cells, Humans, Immunohistochemistry, Immunoprecipitation, Membrane Proteins, Molecular Sequence Data, N-Formylmethionine Leucyl-Phenylalanine, Neutrophils, Protein Binding, Protein Structure, Tertiary, Protein Transport, Recombinant Fusion Proteins, Secretory Vesicles, Subcellular Fractions
J. Biol. Chem.
Date: Oct. 22, 2004
PubMed ID: 15294914
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