Normal Arp2/3 complex activation in platelets lacking WASp.
Arp2/3 complex is believed to induce de novo nucleation of actin filaments at the edge of motile cells downstream of WASp family proteins. In this study, the signaling pathways leading to Arp2/3 complex activation, actin assembly, and shape change were investigated in platelets isolated from patients with Wiskott-Aldrich Syndrome (WAS), that is, who lack WASp, and in WASp-deficient mouse platelets. WASp-deficient human and mouse platelets elaborate filopodia, spread lamellae, and assemble actin, identical to control WASp-expressing platelets. Human platelets contain 2 microM Arp2/3 complex, or 8600 molecules/cell. Arp2/3 complex redistributes to the edge of the lamellae and to the Triton X-100-insoluble actin cytoskeleton of activated WASp-deficient platelets. Furthermore, the C-terminal CA domain of N-WASp, which sequesters Arp2/3 complex, inhibits by half the actin nucleation capacity of octylglucoside-permeabilized and activated WAS platelets, similar to its effect in WASp-expressing cells. Along with WASp, platelets express WAVE-2 as a physiologic activator of Arp2/3 complex and a small amount of N-WASp. Taken together, our findings show that platelets activate Arp2/3 complex, assemble actin, and change shape in the absence of WASp, indicating a more specialized role for WASp in these cells.
Department of Medicine, Division of Hematology, Brigham and Women's Hospital, Harvard Medical School, 221 Longwood Avenue, LMRC 301, Boston, MA 02115, USA. hfalet@rics.bwh.harvard.edu
Hervé
H
Falet
Karin M
KM
Hoffmeister
Ralph
R
Neujahr
John H
JH
Hartwig
D051377:Actin-Related Protein 2; D051378:Actin-Related Protein 3; D000199:Actins / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D001792:Blood Platelets / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D048429:Cell Size / Q000187:drug effects; D003598:Cytoskeletal Proteins / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D006801:Humans; D051379:Mice; D010973:Platelet Adhesiveness / Q000187:drug effects; D011485:Protein Binding; D011506:Proteins / Q000235:genetics / Q000494:pharmacology*; D015398:Signal Transduction; D014923:Wiskott-Aldrich Syndrome / Q000097:blood / Q000378:metabolism*; D051316:Wiskott-Aldrich Syndrome Protein
C495926:ACTR2 protein, human; C495928:ACTR3 protein, human; D051377:Actin-Related Protein 2; D051378:Actin-Related Protein 3; D000199:Actins; C495927:Actr2 protein, mouse; C495929:Actr3 protein, mouse; D003598:Cytoskeletal Proteins; D011506:Proteins; C495767:WAS protein, human; C495768:Was protein, mouse; D051316:Wiskott-Aldrich Syndrome Protein