title: X-linked thrombocytopenia causing mutations in WASP (L46P and A47D) impair T cell chemotaxis.
abstract: BACKGROUND
  Mutation in the Wiskott-Aldrich syndrome Protein (WASP) causes Wiskott-Aldrich syndrome (WAS), X-linked thrombocytopenia (XLT) and X-linked congenital neutropenia (XLN). The majority of missense mutations causing WAS and XLT are found in the WH1 (WASP Homology) domain of WASP, known to mediate interaction with WIP (WASP Interacting Protein) and CIB1 (Calcium and Integrin Binding).
  
  
  RESULTS
  We analyzed two WASP missense mutants (L46P and A47D) causing XLT for their effects on T cell chemotaxis. Both mutants, WASPRL46P and WASPRA47D (S1-WASP shRNA resistant) expressed well in JurkatWASP-KD T cells (WASP knockdown), however expression of these two mutants did not rescue the chemotaxis defect of JurkatWASP-KD T cells towards SDF-1α. In addition JurkatWASP-KD T cells expressing these two WASP mutants were found to be defective in T cell polarization when stimulated with SDF-1α. WASP exists in a closed conformation in the presence of WIP, however both the mutants (WASPRL46P and WASPRA47D) were found to be in an open conformation as determined in the bi-molecular complementation assay. WASP protein undergoes proteolysis upon phosphorylation and this turnover of WASP is critical for T cell migration. Both the WASP mutants were found to be stable and have reduced tyrosine phosphorylation after stimulation with SDF-1α.
  
  
  CONCLUSIONS
  Thus our data suggest that missense mutations WASPRL46P or WASPRA47D affect the activity of WASP in T cell chemotaxis probably by affecting the turnover of the protein.
authors.forename: Neeraj
authors.initials: N
authors.lastname: Jain
authors.forename: Jun Hou
authors.initials: JH
authors.lastname: Tan
authors.forename: Shijin
authors.initials: S
authors.lastname: Feng
authors.forename: Bhawana
authors.initials: B
authors.lastname: George
authors.affiliation: School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore 637551, Singapore. thirumaran@ntu.edu.sg.
authors.forename: Thirumaran
authors.initials: T
authors.lastname: Thanabalu
mesh_terms: D019943:Amino Acid Substitution; D054377:Chemokine CXCL12 / Q000235:genetics / Q000378:metabolism; D002633:Chemotaxis; D040181:Genetic Diseases, X-Linked / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D019169:Jurkat Cells; D020125:Mutation, Missense; D010766:Phosphorylation / Q000235:genetics; D059748:Proteolysis; D013601:T-Lymphocytes; D013921:Thrombocytopenia / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D051316:Wiskott-Aldrich Syndrome Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: C515255:CXCL12 protein, human; D054377:Chemokine CXCL12; C495767:WAS protein, human; D051316:Wiskott-Aldrich Syndrome Protein