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

Neeraj Jain,Bhawana George,Shijin Feng,Thirumaran Thanabalu,Jun Hou Tan

doi:10.1186/s12929-014-0091-1

Abstract

BackgroundMutation 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).ResultsWe 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.ConclusionThus 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12929-014-0091-1) contains supplementary material, which is available to authorized users.

Highlights

Mutation in the Wiskott-Aldrich syndrome Protein (WASP) causes Wiskott-Aldrich syndrome (WAS), X-linked thrombocytopenia (XLT) and X-linked congenital neutropenia (XLN)
We found that 41.3% of WASPR L46P-RFP or 44.4% of WASPR A47D-RFP expressing JurkatWASP-KD T cells migrated to the lower well compared to 57.5% of WASPR-RFP expressing cells suggesting that WASPR L46P or WASPR A47D mutants are unable to rescue the impaired chemotaxis of JurkatWASP-KD T cells towards SDF-1α (Figure 3D)
Most of the missense mutations causing WAS/XLT are found in the WH1 domain of WASP [10] and it has been suggested that loss of interaction with WIP is causal for the disease [19]

Summary

Introduction

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). Wiskott-Aldrich Syndrome (WAS) is a rare X-linked recessive disorder characterized by eczema, thrombocytopenia (low platelet count, small size platelets), recurrent infections, autoimmune disorders and malignancies [1,2]. It was first described in two brothers with chronic bloody diarrhea [3] and subsequently the X-linked pattern of inheritance and platelet abnormalities were characterized [4]. WASP is a proline-rich adaptor with a WH1 (WASP homology) domain at the N-terminal which mediates (XLN) is caused by missense mutations in the GBD of WASP (L270P, S272P, I294T) which destroy the autoinhibitory conformation of WASP and enhanced its actin polymerization activity [15,16]

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Conclusion