title: MHC class I ligation of human T cells activates the ZAP70 and p56lck tyrosine kinases, leads to an alternative phenotype of the TCR/CD3 zeta-chain, and induces apoptosis.
abstract: Cross-linking of MHC class I (MHC-I) molecules on human T cells induces signal-transduction events, including activation of tyrosine kinases, tyrosine phosphorylation of phospholipase C-gamma 1, and elevation of the intracellular free calcium concentration. In this study, we demonstrate that the ZAP70 tyrosine kinase is tyrosine phosphorylated in Jurkat T cells and in purified peripheral T cells after MHC-I ligation. The tyrosine-phosphorylated ZAP70 kinase exhibits a particular phenotype with low affinities for proteins at 21, 40, 60, and 120 kDa, proteins normally co-precipitated with ZAP70 after TCR/CD3 stimulation. The phosphorylation of ZAP70 after MHC-I ligation was dependent on TCR/CD3 surface expression. One of the natural substrates for ZAP70 is the zeta-chain dimer of the TCR/CD3 complex. MHC-I cross-linking induces a phosphorylated zeta-protein that migrates as a dimer at 42 kDa in SDS-PAGE and differs from the 38-kDa phosphorylated zeta-protein dimer induced by TCR/CD3 cross-linking. Furthermore, we demonstrate that the p56lck tyrosine kinase is tyrosine phosphorylated following MHC-I ligation, and that a p56lck-negative Jurkat T cell mutant does not induce phosphorylation of the zeta-chain and the ZAP70 kinase following MHC-I ligation. Previous studies have demonstrated that lack or diminished activation of ZAP70 is involved in the induction of anergy or apoptosis in T cells. Likewise, MHC-I cross-linking of Jurkat T cells results in growth arrest and induction of apoptosis that is strongly inhibited by herbimycin A, suggesting an essential role of tyrosine kinase activity in the process leading to apoptosis.
authors.affiliation: Department of Medical Anatomy, Panum Institute, University of Copenhagen, Denmark.
authors.forename: S
authors.initials: S
authors.lastname: Skov
authors.forename: S
authors.initials: S
authors.lastname: Bregenholt
authors.forename: M H
authors.initials: MH
authors.lastname: Claesson
mesh_terms: D000911:Antibodies, Monoclonal / Q000378:metabolism; D017209:Apoptosis / Q000276:immunology*; D016227:Benzoquinones; D002455:Cell Division / Q000276:immunology; D004789:Enzyme Activation / Q000276:immunology; D006680:HLA Antigens / Q000378:metabolism*; D015395:Histocompatibility Antigens Class I / Q000378:metabolism*; D006801:Humans; D016130:Immunophenotyping; D019169:Jurkat Cells; D047029:Lactams, Macrocyclic; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D008565:Membrane Proteins / Q000145:classification*; D008970:Molecular Weight; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011809:Quinones / Q000633:toxicity; D017260:Receptor-CD3 Complex, Antigen, T-Cell / Q000276:immunology*; D011948:Receptors, Antigen, T-Cell / Q000145:classification* / Q000378:metabolism; D017828:Rifabutin / Q000031:analogs & derivatives; D013601:T-Lymphocytes / Q000378:metabolism*; D051746:ZAP-70 Protein-Tyrosine Kinase; D019061:src-Family Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D016227:Benzoquinones; D006680:HLA Antigens; D015395:Histocompatibility Antigens Class I; D047029:Lactams, Macrocyclic; D008565:Membrane Proteins; D011809:Quinones; D017260:Receptor-CD3 Complex, Antigen, T-Cell; D011948:Receptors, Antigen, T-Cell; C054979:antigen T cell receptor, zeta chain; D017828:Rifabutin; C020754:herbimycin; D011505:Protein-Tyrosine Kinases; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D051746:ZAP-70 Protein-Tyrosine Kinase; C497261:ZAP70 protein, human; D019061:src-Family Kinases