title: Tyrosine phosphorylation of CD45 phosphotyrosine phosphatase by p50csk kinase creates a binding site for p56lck tyrosine kinase and activates the phosphatase.
abstract: Src family protein tyrosine kinases (PTKs) play an essential role in antigen receptor-initiated lymphocyte activation. Their activity is largely regulated by a negative regulatory tyrosine which is a substrate for the activating action of the CD45 phosphotyrosine phosphatase (PTPase) or, conversely, the suppressing action of the cytosolic p50csk PTK. Here we report that CD45 was phosphorylated by p50csk on two tyrosine residues, one of them identified as Tyr-1193. This residue was not phosphorylated by T-cell PTKs p56lck and p59fyn. Tyr-1193 was phosphorylated in intact T cells, and phosphorylation increased upon treatment with PTPase inhibitors, indicating that this tyrosine is a target for a constitutively active PTK. Cotransfection of CD45 and csk into COS-1 cells caused tyrosine phosphorylation of CD45 in the intact cells. Tyrosine-phosphorylated CD45 bound p56lck through the SH2 domain of the kinase. Finally, p50csk-mediated phosphorylation of CD45 caused a severalfold increase in its PTPase activity. Our results show that direct tyrosine phosphorylation of CD45 can affect its activity and association with Src family PTKs and that this phosphorylation could be mediated by p50csk. If this is also true in the intact cells, it adds a new dimension to the physiological function of p50csk in T lymphocytes.
authors.affiliation: Department of Biochemistry, University of Helsinki, Finland.
authors.forename: M
authors.initials: M
authors.lastname: Autero
authors.forename: J
authors.initials: J
authors.lastname: Saharinen
authors.forename: T
authors.initials: T
authors.lastname: Pessa-Morikawa
authors.forename: M
authors.initials: M
authors.lastname: Soula-Rothhut
authors.forename: C
authors.initials: C
authors.lastname: Oetken
authors.forename: M
authors.initials: M
authors.lastname: Gassmann
authors.forename: M
authors.initials: M
authors.lastname: Bergman
authors.forename: K
authors.initials: K
authors.lastname: Alitalo
authors.forename: P
authors.initials: P
authors.lastname: Burn
authors.forename: C G
authors.initials: CG
authors.lastname: Gahmberg
mesh_terms: D000595:Amino Acid Sequence; D015703:Antigens, CD / Q000378:metabolism*; D001665:Binding Sites; D000081247:CSK Tyrosine-Protein Kinase; D002478:Cells, Cultured; D004789:Enzyme Activation; D006801:Humans; D007700:Kinetics; D017493:Leukocyte Common Antigens / Q000378:metabolism*; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D008954:Models, Biological; D008969:Molecular Sequence Data; D010449:Peptide Mapping; D010455:Peptides / Q000138:chemical synthesis / Q000378:metabolism; D010748:Phosphopeptides / Q000302:isolation & purification / Q000378:metabolism; D010766:Phosphorylation; D019000:Phosphotyrosine; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D013601:T-Lymphocytes / Q000201:enzymology*; D014162:Transfection; D014357:Trypsin; D014443:Tyrosine / Q000031:analogs & derivatives / Q000032:analysis / Q000378:metabolism; D019061:src-Family Kinases
chemical_list: D015703:Antigens, CD; D010455:Peptides; D010748:Phosphopeptides; D019000:Phosphotyrosine; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D000081247:CSK Tyrosine-Protein Kinase; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D019061:src-Family Kinases; C000631346:CSK protein, human; D017493:Leukocyte Common Antigens; D017027:Protein Tyrosine Phosphatases; D014357:Trypsin