Characterization of a 23-kDa protein associated with CD40.
CD40 is a 45-kDa glycoprotein member of the tumor necrosis factor receptor (TNFR) family expressed on B cells, thymic epithelial cells, dendritic cells, and some carcinoma cells. The unique capacity of CD40 to trigger immunoglobulin isotype switching is dependent on the activation of protein-tyrosine kinases, yet CD40 possesses no kinase domain and no known consensus sequences for binding to protein-tyrosine kinases. Recently, an intracellular protein (CD40bp/LAP-1/CRAF-1) which belongs to the family of TNFR-associated proteins was reported to associate with CD40. We describe a 23-kDa cell surface protein (p23) which is specifically associated with CD40 on B cells and on urinary bladder transitional carcinoma cells. Protein microsequencing revealed that p23 shows no homology to any known protein. A rabbit antibody raised against a peptide derived from p23 recognized a 23-kDa protein in CD40 immunoprecipitates. In contrast to CD40bp/LAP-1/CRAF-1, p23 was not associated with TNFR p80 (CD120b). These findings suggest that p23 is a novel member of the CD40 receptor complex.
Morio
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Division of Immunology, Children's Hospital, Boston, MA, USA.
Hanissian
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S
Geha
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RS
D001402:B-Lymphocytes / Q000737:chemistry*; D019013:CD40 Antigens / Q000378:metabolism*; D002277:Carcinoma / Q000737:chemistry*; D002478:Cells, Cultured; D015180:Electrophoresis, Gel, Two-Dimensional; D006801:Humans; D017578:Immunoglobulin Class Switching; D008565:Membrane Proteins / Q000737:chemistry / Q000276:immunology / Q000378:metabolism*; D011233:Precipitin Tests; D011485:Protein Binding; D017421:Sequence Analysis; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D001749:Urinary Bladder Neoplasms / Q000737:chemistry*
D019013:CD40 Antigens; D008565:Membrane Proteins