The catalytic activity of the CD45 membrane-proximal phosphatase domain is required for TCR signaling and regulation.
Cell surface expression of CD45, a receptor-like protein tyrosine phosphatase (PTPase), is required for T cell antigen receptor (TCR)-mediated signal transduction. Like the majority of transmembrane PTPases, CD45 contains two cytoplasmic phosphatase domains, whose relative in vivo function is not known. Site-directed mutagenesis of the individual catalytic residues of the two CD45 phosphatase domains indicates that the catalytic activity of the membrane-proximal domain is both necessary and sufficient for restoration of TCR signal transduction in a CD45-deficient cell. The putative catalytic activity of the distal phosphatase domain is not required for proximal TCR-mediated signaling events. Moreover, in the context of a chimeric PTPase receptor, the putative catalytic activity of the distal phosphatase domain is not required for ligand-induced negative regulation of PTPase function. We also demonstrate that the phosphorylation of the C-terminal tyrosine of Lck, a site of negative regulation, is reduced only when CD45 mutants with demonstrable in vitro phosphatase activity are introduced into the CD45-deficient cells. These results demonstrate that the phosphatase activity of CD45 is critical for TCR signaling, and for regulating the levels of C-terminal phosphorylated Lck molecules.
Desai
D M
DM
Howard Hughes Medical Institute, Department of Medicine, University of California at San Francisco 94143-0724.
Sap
J
J
Silvennoinen
O
O
Schlessinger
J
J
Weiss
A
A
D000595:Amino Acid Sequence; D002384:Catalysis; D004252:DNA Mutational Analysis; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism; D017493:Leukocyte Common Antigens / Q000235:genetics / Q000378:metabolism*; D008024:Ligands; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D008969:Molecular Sequence Data; D010766:Phosphorylation; D017354:Point Mutation; D011499:Protein Processing, Post-Translational; D017027:Protein Tyrosine Phosphatases / Q000235:genetics / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D013329:Structure-Activity Relationship; D014443:Tyrosine / Q000378:metabolism
D008024:Ligands; D011948:Receptors, Antigen, T-Cell; D011993:Recombinant Fusion Proteins; D014443:Tyrosine; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D017493:Leukocyte Common Antigens; D017027:Protein Tyrosine Phosphatases