title: Cross-linking of T-cell surface molecules CD4 and CD8 stimulates phosphorylation of the lck tyrosine protein kinase at the autophosphorylation site.
abstract: p56lck, a lymphocyte-specific tyrosine protein kinase, binds to the cytoplasmic tails of the T-cell surface molecules CD4 and CD8. Cross-linking of CD4 expressed on the surface of murine thymocytes, splenocytes, and CD4+ T-cell lines induced tyrosine phosphorylation of p56lck dramatically. Cross-linking of CD8 stimulated tyrosine phosphorylation of p56lck strongly in murine L3 and GA4 cells, slightly in splenocytes, but not detectably in thymocytes. Differing effects of cross-linking on in vitro tyrosine kinase activity of p56lck were observed. An increase in the in vitro kinase activity of p56lck, when assayed with [Val5]-angiotensin II as an exogenous substrate, was found to accompany cross-linking of CD4 in three cell lines. No stimulation of the in vitro kinase activity, however, was observed after cross-linking of CD8 in L3 cells. The phosphorylation of p56lck at Tyr-394, the autophosphorylation site, was stimulated by cross-linking in all cell lines examined. Tyr-394 was the predominant site of increased tyrosine phosphorylation in two leukemic cell lines. In the other two cell lines, the phosphorylation of both Tyr-394 and an inhibitory site, Tyr-505, was found to increase. In contrast to cross-linking with antibodies, no striking increase in the tyrosine phosphorylation of p56lck was stimulated by antigenic stimulation. Therefore, the effect of antibody-induced aggregation of CD4 and CD8 on the tyrosine phosphorylation of p56lck differs, at least quantitatively, from what occurs during antigen-induced T-cell activation.
authors.affiliation: Molecular Biology and Virology Laboratory, Salk Institute, San Diego, California 92138.
authors.forename: K X
authors.initials: KX
authors.lastname: Luo
authors.forename: B M
authors.initials: BM
authors.lastname: Sefton
mesh_terms: D000818:Animals; D000945:Antigens, Differentiation, T-Lymphocyte / Q000502:physiology*; D015153:Blotting, Western; D015704:CD4 Antigens / Q000502:physiology*; D016827:CD8 Antigens; D002460:Cell Line; D003432:Cross-Linking Reagents; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D051379:Mice; D008970:Molecular Weight; D010449:Peptide Mapping; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011940:Receptor Aggregation; D015398:Signal Transduction; D013154:Spleen / Q000166:cytology; D013601:T-Lymphocytes / Q000502:physiology*
chemical_list: D000945:Antigens, Differentiation, T-Lymphocyte; D015704:CD4 Antigens; D016827:CD8 Antigens; D003432:Cross-Linking Reagents; D011505:Protein-Tyrosine Kinases; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck)