Journal
BLOOD
Volume 98, Issue 10, Pages 2988-2991Publisher
AMER SOC HEMATOLOGY
DOI: 10.1182/blood.V98.10.2988
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Funding
- NHLBI NIH HHS [HL59561, P01 HL059561] Funding Source: Medline
- NIAID NIH HHS [R01 AI039574, AI39574] Funding Source: Medline
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Mutations of Wiskoft-Aldrich syndrome protein (WASP) underlie the severe thrombocytopenia and immunodeficiency of the Wiskott-Aldrich syndrome. WASP, a specific blood cell protein, and its close homologue, the broadly distributed N-WASP, function in dynamic actin polymerization processes. Here it is demonstrated that N-WASP is expressed along with WASP, albeit at low levels, in human blood cells. The presence of approximately 160 nmol/L rapidly acting N-WASP molecules may explain the normal capacity of WASP-negative patient platelets for early agonist-induced aggregation and filopodia formation. Ex vivo experiments revealed a significant difference between WASP and N-WASP in sensitivity to calpain, the Ca++-dependent protease activated in agonist-stimulated platelets. Through the use of a series of calpain-containing broken cell systems, it is shown that WASP is cleaved in a Ca++-dependent reaction inhibitable by calpeptin and E64d and that N-WASP is not cleaved, suggesting that the cleavage of WASP by calpain functions in normal platelets as part of a Ca++-dependent switch mechanism that terminates the surface projection phase of blood cell activation processes. (C) 2001 by The American Society of Hematology.
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