title: Rac regulates collagen-induced HSP27 phosphorylation via p44/p42 MAP kinase in human platelets.
abstract: We previously reported that the collagen-induced phosphorylation of heat shock protein (HSP) 27 via p44/p42 mitogen-activated protein (MAP) kinase is sufficient to induce the secretion of platelet-derived growth factor (PDGF)-AB and the release of soluble CD40 ligand (sCD40L) from human platelets. It has been shown that Rac, which belongs to the Rho family of small GTPases, is involved in the collagen-induced platelet aggregation. In this study, we investigated the role of Rac in the collagen-stimulated release of PDGF-AB and sCD40L in human platelets. Human blood was donated from healthy volunteers and platelet-rich plasma was obtained from the blood samples. The samples were then treated with 1.0 µg/ml collagen for 0, 1, 3, or 5 min and Rac1 activity was determined using the Rac1 Activation Assay kit. We found that collagen stimulated the activation of Rac in human platelets in a time-dependent manner. However, pre-treatment with NSC23766, a selective inhibitor of Rac-guanine nucleotide exchange factor interaction, reduced the collagen-induced platelet aggregation. NSC23766 markedly attenuated not only the collagen-induced p44/p42 MAP kinase phosphorylation, but also the phosphorylation of HSP27 at three serine residues (Ser-15, Ser-78 and Ser-82). In addition, the collagen‑induced release of PDGF-AB and sCD40L was significantly suppressed by NSC23766 in a dose-dependent manner. These results strongly suggest that Rac regulates the collagen-induced HSP27 phosphorylation via p44/p42 MAP kinase in human platelets, resulting in the stimulation of PDGF-AB secretion and the release of sCD40L.
authors.affiliation: Department of Emergency and Disaster Medicine, Gifu University Graduate School of Medicine, Gifu 501-1194, Japan.
authors.forename: Yasunari
authors.initials: Y
authors.lastname: Kageyama
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Doi
authors.forename: Shigeru
authors.initials: S
authors.lastname: Akamatsu
authors.forename: Gen
authors.initials: G
authors.lastname: Kuroyanagi
authors.forename: Akira
authors.initials: A
authors.lastname: Kondo
authors.forename: Jun
authors.initials: J
authors.lastname: Mizutani
authors.forename: Takanobu
authors.initials: T
authors.lastname: Otsuka
authors.forename: Haruhiko
authors.initials: H
authors.lastname: Tokuda
authors.forename: Osamu
authors.initials: O
authors.lastname: Kozawa
authors.forename: Shinji
authors.initials: S
authors.lastname: Ogura
mesh_terms: D000634:Aminoquinolines / Q000494:pharmacology; D001792:Blood Platelets / Q000378:metabolism*; D023201:CD40 Ligand / Q000378:metabolism; D003094:Collagen / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D055551:HSP27 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D064368:Healthy Volunteers; D006360:Heat-Shock Proteins; D006801:Humans; D019950:Mitogen-Activated Protein Kinase 1 / Q000235:genetics / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000235:genetics / Q000378:metabolism*; D018832:Molecular Chaperones; D010766:Phosphorylation; D010974:Platelet Aggregation; D010982:Platelet-Derived Growth Factor / Q000378:metabolism; D053657:Platelet-Rich Plasma / Q000378:metabolism; D011743:Pyrimidines / Q000494:pharmacology; D020830:rac1 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D000634:Aminoquinolines; D055551:HSP27 Heat-Shock Proteins; C057725:HSPB1 protein, human; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; C487513:NSC 23766; D010982:Platelet-Derived Growth Factor; D011743:Pyrimidines; C095477:platelet-derived growth factor AB; D023201:CD40 Ligand; D003094:Collagen; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020830:rac1 GTP-Binding Protein