title: Protein tyrosine phosphatase alpha regulates Fyn activity and Cbp/PAG phosphorylation in thymocyte lipid rafts.
abstract: A role for the receptor protein tyrosine phosphatase alpha (PTPalpha) in immune cell function and regulation of Src family kinases was investigated using thymocytes from PTPalpha-deficient mice. PTPalpha-null thymocytes develop normally, but unstimulated PTPalpha-/- cells exhibit increased tyrosine phosphorylation of specific proteins, increased Fyn activity, and hyperphosphorylation of Cbp/PAG that promotes its association with C-terminal Src kinase. Elevated Fyn activity in the absence of PTPalpha is due to enhanced phosphorylation of Fyn tyrosines 528 and 417. Some PTPalpha is localized in lipid rafts of thymocytes, and raft-associated Fyn is specifically activated in PTPalpha-/- cells. PTPalpha is not a Cbp/PAG phosphatase, because it is not required for Cbp/PAG dephosphorylation in unstimulated or anti-CD3-stimulated thymocytes. Together, our results indicate that PTPalpha, likely located in lipid rafts, regulates the activity of raft Fyn. In the absence of PTPalpha this population of Fyn is activated and phosphorylates Cbp/PAG to enhance association with C-terminal Src kinase. Although TCR-mediated tyrosine phosphorylation was apparently unaffected by the absence of PTPalpha, the long-term proliferative response of PTPalpha-/- thymocytes was reduced. These findings indicate that PTPalpha is a component of the complex Src family tyrosine kinase regulatory network in thymocytes and is required to suppress Fyn activity in unstimulated cells in a manner that is not compensated for by the major T cell PTP and SFK regulator, CD45.
authors.affiliation: Department of Pediatrics, University of British Columbia, Vancouver, Canada.
authors.forename: Lola
authors.initials: L
authors.lastname: Maksumova
authors.forename: Hoa T
authors.initials: HT
authors.lastname: Le
authors.forename: Farkhad
authors.initials: F
authors.lastname: Muratkhodjaev
authors.forename: Dominique
authors.initials: D
authors.lastname: Davidson
authors.forename: André
authors.initials: A
authors.lastname: Veillette
authors.forename: Catherine J
authors.initials: CJ
authors.lastname: Pallen
mesh_terms: D000818:Animals; D000081247:CSK Tyrosine-Protein Kinase; D049109:Cell Proliferation; D004789:Enzyme Activation; D036341:Intercellular Signaling Peptides and Proteins; D017493:Leukocyte Common Antigens; D021962:Membrane Microdomains / Q000201:enzymology / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D017027:Protein Tyrosine Phosphatases / Q000172:deficiency / Q000502:physiology*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D051076:Proto-Oncogene Proteins c-fyn / Q000378:metabolism*; D054630:Receptor-Like Protein Tyrosine Phosphatases, Class 4; D011956:Receptors, Cell Surface / Q000502:physiology; D013950:Thymus Gland / Q000166:cytology* / Q000648:ultrastructure; D019061:src-Family Kinases
chemical_list: D036341:Intercellular Signaling Peptides and Proteins; D008565:Membrane Proteins; C408344:Pag protein, mouse; C498709:Pag1 protein, mouse; D010750:Phosphoproteins; D011956:Receptors, Cell Surface; D011505:Protein-Tyrosine Kinases; D000081247:CSK Tyrosine-Protein Kinase; C494960:Fyn protein, mouse; D051076:Proto-Oncogene Proteins c-fyn; D019061:src-Family Kinases; D017493:Leukocyte Common Antigens; D017027:Protein Tyrosine Phosphatases; C516843:Ptpra protein, mouse; D054630:Receptor-Like Protein Tyrosine Phosphatases, Class 4