title: CD50 (ICAM-3) is phosphorylated on tyrosine and is associated with tyrosine kinase activity in human neutrophils.
abstract: CD50 (ICAM-3) is expressed at a high level on resting blood granulocytes, monocytes, and lymphocytes. The constitutive high expression of CD50 on resting leukocytes suggests that it is an important LFA-1 ligand in the initiation of the immune/inflammatory response. Using a radiolabeling technique initially designed to detect ecto-protein kinase activity, we found that CD50 mAbs immunoprecipitated a approximately 125- to 170-kDa phosphoprotein from human neutrophils. Phosphorylation was increased after stimulation with the chemotactic agent FMLP, platelet-activating factor, 12-O-tetradecanoyl-phorbol-13-acetate, and the calcium ionophore A23187. This increase in phosphorylation was transient with the maximal phosphorylation, being observed by 1 min. Phosphoamino acid analysis revealed that CD50 contained predominantly phosphotyrosine. Although this assay system was designed initially to detect ecto-protein kinase activity, subsequent studies have shown that membrane proteins can be phosphorylated on the cytoplasmic domain under these conditions. When CD50 was immunoprecipitated from solubilized neutrophils, protein tyrosine kinase activity associated with CD50 was detected in the immunoprecipitate. The data suggest that phosphorylation of CD50 on tyrosine by an associated tyrosine kinase plays a role in the function of CD50.
authors.affiliation: Department of Medicine, University of Minnesota Medical School, Minneapolis.
authors.forename: K M
authors.initials: KM
authors.lastname: Skubitz
authors.forename: K
authors.initials: K
authors.lastname: Ahmed
authors.forename: K D
authors.initials: KD
authors.lastname: Campbell
authors.forename: A P
authors.initials: AP
authors.lastname: Skubitz
mesh_terms: D015703:Antigens, CD; D000943:Antigens, Differentiation; D015815:Cell Adhesion Molecules / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D018375:Neutrophil Activation / Q000502:physiology; D009504:Neutrophils / Q000201:enzymology* / Q000276:immunology*; D011233:Precipitin Tests; D011505:Protein-Tyrosine Kinases / Q000097:blood*; D015854:Up-Regulation / Q000502:physiology
chemical_list: D015703:Antigens, CD; D000943:Antigens, Differentiation; D015815:Cell Adhesion Molecules; C483616:ICAM3 protein, human; D011505:Protein-Tyrosine Kinases