The Wiskott-Aldrich syndrome (WAS) is an X-chromosome-linked recessive disease characterized by eczema, thrombocytopenia, and immunodeficiency (1). WAS is an immunodeficiency disorder with the most severe pathology in the T lymphocytes and platelets. The disease arises from mutations in the gene encoding the WAS protein (WASP). T lymphocytes of affected males with WAS exhibit a severe disturbance of the actin cytoskeleton, suggesting that the WASP could regulate its organization. Data suggest that the WASP might function as a signal transduction adaptor downstream of Cdc42, and in affected males, the cytoskeletal abnormalities may result from a defect in Cdc42 signaling (2). WASP is a key regulator of the Arp2/3 complex and the actin cytoskeleton in hematopoietic cells. WASP is capable of forming an auto-inhibited conformation, which can be disrupted by binding of Cdc42 and phosphatidylinositol 4,5-bisphosphate, leading to its activation. Stimulation of the collagen receptor on platelets and crosslinking the B-cell receptor induce tyrosine phosphorylation of WASP (3).

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