title: The T-cell antigen CD5 acts as a receptor and substrate for the protein-tyrosine kinase p56lck.
abstract: CD5 is a T-cell-specific antigen which binds to the B-cell antigen CD72 and acts as a coreceptor in the stimulation of T-cell growth. CD5 associates with the T-cell receptor zeta chain (TcR zeta)/CD3 complex and is rapidly phosphosphorylated on tyrosine residues as a result of TcR zeta/CD3 ligation. However, despite this, the mechanism by which CD5 generates intracellular signals is unclear. In this study, we demonstrate that CD5 is coupled to the protein-tyrosine kinase p56lck and can act as a substrate for p56lck. Coexpression of CD5 with p56lck in the baculovirus expression system resulted in the phosphorylation of CD5 on tyrosine residues. Further, anti-CD5 and anti-p56lck coprecipitated each other in a variety of detergents, including Nonidet P-40 and Triton X-100. Anti-CD5 also precipitated the kinase from various T cells irrespective of the expression of TcR zeta/CD3 or CD4. No binding between p59fyn(T) and CD5 was detected in T cells. The binding of p56lck to CD5 induced a 10- to 15-fold increase in p56lck catalytic activity, as measured by in vitro kinase analysis. In vivo labelling with 32P(i) also showed a four- to fivefold increase in Y-394 occupancy in p56lck when associated with CD5. The use of glutathione S-transferase-Lck fusion proteins in precipitation analysis showed that the SH2 domain of p56lck could recognize CD5 as expressed in the baculovirus expression system. CD5 interaction with p56lck represents a novel variant of a receptor-kinase complex in which receptor can also serve as substrate. The CD5-p56lck interaction is likely to play roles in T-cell signalling and T-B collaboration.
authors.affiliation: Division of Tumor Immunology, Dana-Farber Cancer Institute, Boston, Massachusetts 02115.
authors.forename: M
authors.initials: M
authors.lastname: Raab
authors.forename: M
authors.initials: M
authors.lastname: Yamamoto
authors.forename: C E
authors.initials: CE
authors.lastname: Rudd
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015703:Antigens, CD / Q000096:biosynthesis / Q000378:metabolism*; D016367:Baculoviridae; D001665:Binding Sites; D017252:CD3 Complex / Q000378:metabolism; D018956:CD5 Antigens; D002460:Cell Line; D005822:Genetic Vectors; D006801:Humans; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D008969:Molecular Sequence Data; D009036:Moths; D010449:Peptide Mapping; D010766:Phosphorylation; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases / Q000096:biosynthesis / Q000378:metabolism*; D013379:Substrate Specificity; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism*; D014162:Transfection; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000031:analogs & derivatives / Q000032:analysis / Q000378:metabolism
chemical_list: D015703:Antigens, CD; D017252:CD3 Complex; D018956:CD5 Antigens; D019000:Phosphotyrosine; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck)