title: Aberrant TCR-mediated signaling in CD45-null thymocytes involves dysfunctional regulation of Lck, Fyn, TCR-zeta, and ZAP-70.
abstract: CD45 is a transmembrane phosphotyrosine phosphatase expressed on all nucleated hemopoietic cells. Targeting of CD45 exon 9 has generated a mouse line completely lacking CD45 expression (CD45-null) in which there are severe abnormalities in T cell development. Defects in TCR-mediated signals underlying these abnormalities have now been investigated using CD45-null T cells. No T cell proliferation was detected in response to a CD3 mAb. In thymocytes the p56(lck) and p59(fyn) tyrosine kinases were hyperphosphorylated, and p56(lck) was in its inactive conformation. Both basal and TCR-stimulated tyrosine phosphorylation of TCR-zeta and CD3-epsilon were much reduced, and TCR stimulation induced an abnormal p18 phosphoisomer of TCR-zeta previously noted in T cells stimulated by altered peptide ligands. These defects were associated with the failure of ZAP-70 kinase recruitment to the TCR-zeta chain. TCR coupling to the tyrosine phosphorylation of several proteins, including HS1 and p120(cbl), was also much reduced. However, TCR-induced signaling was not ablated, and significant inositol phosphate and calcium signals were observed in CD45-null thymocytes. Our molecular analysis suggests that the threshold for TCR signal transduction is greatly increased in CD45-null T cells, thus explaining the profound defects in thymic development.
authors.affiliation: Department of Immunology, The Babraham Institute, Cambridge, United Kingdom.
authors.forename: J D
authors.initials: JD
authors.lastname: Stone
authors.forename: L A
authors.initials: LA
authors.lastname: Conroy
authors.forename: K F
authors.initials: KF
authors.lastname: Byth
authors.forename: R A
authors.initials: RA
authors.lastname: Hederer
authors.forename: S
authors.initials: S
authors.lastname: Howlett
authors.forename: Y
authors.initials: Y
authors.lastname: Takemoto
authors.forename: N
authors.initials: N
authors.lastname: Holmes
authors.forename: D R
authors.initials: DR
authors.lastname: Alexander
mesh_terms: D000818:Animals; D017493:Leukocyte Common Antigens / Q000032:analysis*; D008213:Lymphocyte Activation / Q000502:physiology; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D008565:Membrane Proteins / Q000502:physiology*; D051379:Mice; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D051076:Proto-Oncogene Proteins c-fyn; D011948:Receptors, Antigen, T-Cell / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology; D013601:T-Lymphocytes / Q000276:immunology*; D014443:Tyrosine / Q000378:metabolism; D051746:ZAP-70 Protein-Tyrosine Kinase; D019061:src-Family Kinases / Q000502:physiology*
chemical_list: D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D011948:Receptors, Antigen, T-Cell; C054979:antigen T cell receptor, zeta chain; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; C494960:Fyn protein, mouse; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D051076:Proto-Oncogene Proteins c-fyn; D051746:ZAP-70 Protein-Tyrosine Kinase; C497262:Zap70 protein, mouse; D019061:src-Family Kinases; D017493:Leukocyte Common Antigens