X-Linked thrombocytopenia causing mutations in WASP (L46P and A47D) impair T cell chemotaxis.

[wiskott-aldrich syndrome]

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 WH 1 (WASP Homology ) domain of WASP , known to mediate interaction with WIP (WASP Interacting Protein ) and CIB 1 (Calcium and Integrin Binding ).We analyzed two WASP missense mutants (L 46 P and A 47 D ) causing XLT for their effects on T cell chemotaxis . Both mutants , WASPRL 46 P and WASPRA 47 D (S 1 -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-1 α . In addition JurkatWASP-KD T cells expressing these two WASP mutants were found to be defective in T cell polarization when stimulated with SDF-1 α . WASP exists in a closed conformation in the presence of WIP , however both the mutants (WASPRL 46 P and WASPRA 47 D ) 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-1 α .Thus our data suggest that missense mutations WASPRL 46 P or WASPRA 47 D affect the activity of WASP in T cell chemotaxis probably by affecting the turnover of the protein .