WASP and N-WASP in human platelets differ in sensitivity to protease calpain.
Mutations of Wiskott-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.
Shcherbina
A
A
Center for Blood Research and the Department of Pediatrics, Harvard Medical School, Boston, MA 02115, USA.
Miki
H
H
Kenney
D M
DM
Rosen
F S
FS
Takenawa
T
T
Remold-O'Donnell
E
E
D001792:Blood Platelets / Q000378:metabolism* / Q000648:ultrastructure; D002118:Calcium / Q000378:metabolism; D002154:Calpain / Q000378:metabolism*; D002474:Cell-Free System; D004151:Dipeptides / Q000378:metabolism; D005260:Female; D006367:HeLa Cells / Q000378:metabolism; D006801:Humans; D008297:Male; D009419:Nerve Tissue Proteins / Q000097:blood / Q000502:physiology*; D015539:Platelet Activation; D011506:Proteins / Q000032:analysis / Q000502:physiology*; D011554:Pseudopodia / Q000648:ultrastructure; D012680:Sensitivity and Specificity; D013379:Substrate Specificity; D014923:Wiskott-Aldrich Syndrome / Q000097:blood*; D051316:Wiskott-Aldrich Syndrome Protein; D051317:Wiskott-Aldrich Syndrome Protein, Neuronal
D004151:Dipeptides; D009419:Nerve Tissue Proteins; D011506:Proteins; C495767:WAS protein, human; C495771:WASL protein, human; D051316:Wiskott-Aldrich Syndrome Protein; D051317:Wiskott-Aldrich Syndrome Protein, Neuronal; C071482:calpeptin; D002154:Calpain; D002118:Calcium