title: Wiskott-Aldrich syndrome protein (WASp) controls the delivery of platelet transforming growth factor-β1.
abstract: Platelets are immunologically competent cells containing cytokines such as TGF-β1 that regulate cell-mediated immunity. However, the mechanisms underlying cytokine secretion from platelets are undefined. The Wiskott-Aldrich syndrome protein (WASp) regulates actin polymerization in nucleated hematopoietic cells but has other role(s) in platelets. WASp-null (WASp(-/-)) platelets stimulated with a PAR-4 receptor agonist had increased TGF-β1 release compared with WT platelets; inhibiting WASp function with wiskostatin augmented TRAP-induced TGF-β1 release in human platelets. TGF-β1 release is dissociated from α-granule secretion (P-selectin up-regulation) and occurs more gradually, with ∼10-15% released after 30-60 min. Blockade of Src family kinase-mediated WASp Tyr-291/Tyr-293 phosphorylation increased TGF-β1 release, with no additive effect in WASp(-/-) platelets, signifying that phosphorylation is critical for WASp-limited TGF-β1 secretion. Inhibiting F-actin assembly with cytochalasin D enhanced secretion in WT platelets and further increased TGF-β1 release in WASp(-/-) platelets, indicating that WASp and actin assembly independently regulate TGF-β1 release. A permeabilized platelet model was used to test the role of upstream small GTPases in TGF-β1 release. N17Cdc42, but not Rac1 mutants, increased TGF-β1 secretion and abrogated WASp phosphorylation. We conclude that WASp function restricts TGF-β1 secretion in a Cdc42- and Src family kinase-dependent manner and independently of actin assembly.
authors.affiliation: From the Division of Translational Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02115.
authors.forename: Hugh
authors.initials: H
authors.lastname: Kim
authors.forename: Hervé
authors.initials: H
authors.lastname: Falet
authors.forename: Karin M
authors.initials: KM
authors.lastname: Hoffmeister
authors.forename: John H
authors.initials: JH
authors.lastname: Hartwig
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000819:agonists / Q000378:metabolism; D001792:Blood Platelets / Q000276:immunology / Q000378:metabolism*; D002227:Carbazoles / Q000378:metabolism; D005109:Extracellular Matrix / Q000235:genetics*; D006801:Humans; D007111:Immunity, Cellular / Q000235:genetics*; D051379:Mice; D011412:Propanolamines / Q000378:metabolism; D015398:Signal Transduction; D053773:Transforming Growth Factor beta1 / Q000235:genetics / Q000378:metabolism*; D051316:Wiskott-Aldrich Syndrome Protein / Q000235:genetics* / Q000378:metabolism; D020764:cdc42 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism; D019061:src-Family Kinases / Q000235:genetics / Q000378:metabolism
chemical_list: D000199:Actins; D051017:Apoptosis Regulatory Proteins; D002227:Carbazoles; D011412:Propanolamines; D053773:Transforming Growth Factor beta1; D051316:Wiskott-Aldrich Syndrome Protein; C101296:prostate apoptosis response-4 protein; C489942:wiskostatin; D019061:src-Family Kinases; D020764:cdc42 GTP-Binding Protein
keywords: Cytokine; Extracellular Matrix; Platelets; Signal Transduction; Signaling