title: CD45 regulation of tyrosine phosphorylation and enzyme activity of src family kinases.
abstract: Previous analyses have suggested that the CD45 tyrosine phosphatase activates src family tyrosine kinases p56lck and p59fyn by dephosphorylating regulatory COOH-terminal residues. We have examined the status of p56lck and p59fyn in murine and human CD45- T cell lines. Surprisingly, despite the fact that p56lck and p59fyn were spontaneously hyperphosphorylated, the tyrosine kinase activity of both enzymes was increased in CD45- versus CD45+ cells. In vitro exposure of hyperphosphorylated p56lck to CD45 decreased enzyme activity to near-basal levels. Lck from CD45- cells was hyperphosphorylated on the cyanogen bromide digestion fragment that contains the negative regulatory residue Tyr-505, and the identity of this site of phosphorylation was confirmed by trypsin digestion followed by high performance liquid chromatography. Loss of CD45 results, therefore, in a paradoxical hyperphosphorylation of the COOH-terminal tyrosine and increased src family kinase enzymatic activity.
authors.affiliation: Laboratory of Immune Cell Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: C M
authors.initials: CM
authors.lastname: Burns
authors.forename: K
authors.initials: K
authors.lastname: Sakaguchi
authors.forename: E
authors.initials: E
authors.lastname: Appella
authors.forename: J D
authors.initials: JD
authors.lastname: Ashwell
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003488:Cyanogen Bromide; D006801:Humans; D017493:Leukocyte Common Antigens / Q000378:metabolism*; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D051379:Mice; D008969:Molecular Sequence Data; D015688:Oncogene Protein pp60(v-src) / Q000737:chemistry / Q000378:metabolism*; D010449:Peptide Mapping; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051076:Proto-Oncogene Proteins c-fyn; D013601:T-Lymphocytes / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D011518:Proto-Oncogene Proteins; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; C494957:FYN protein, human; C494960:Fyn protein, mouse; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D015688:Oncogene Protein pp60(v-src); D051076:Proto-Oncogene Proteins c-fyn; D017493:Leukocyte Common Antigens; D003488:Cyanogen Bromide