title: The proteasome regulates collagen-induced platelet aggregation via nuclear-factor-kappa-B (NFĸB) activation.
abstract: BACKGROUND
  Platelets possess critical hemostatic functions in the system of thrombosis and hemostasis, which can be affected by a multitude of external factors. Previous research has shown that platelets have the capacity to synthesize proteins de novo and more recently a multicatalytic protein complex, the proteasome, has been discovered in platelets. Due to its vital function for cellular integrity, the proteasome has become a therapeutic target for anti-proliferative drug therapies in cancer. Clinically thrombocytopenia is a frequent side-effect, but the aggregatory function of platelets also appears to be affected. Little is known however about underlying regulatory mechanisms and functional aspects of proteasome inhibition on platelets. Our study aims to investigate the role of the proteasome in regulating collagen-induced platelet aggregation and its interaction with NFkB in this context.
  
  
  METHODS
  Using fluorescence activity assays, platelet aggregometry and immunoblotting, we investigate regulatory interactions of the proteasome and Nuclear-factor-kappa-B (NFkB) in collagen-induced platelet aggregation.
  
  
  RESULTS
  We show that collagen induces proteasome activation in platelets and collagen-induced platelet aggregation can be reduced with proteasome inhibition by the specific inhibitor epoxomicin. This effect does not depend on Rho-kinase/ROCK activation or thromboxane release, but rather depends on NFkB activation. Inhibition of the proteasome prevented cleavage of NFκB-inhibitor protein IκBα and decreased NFκB activity after collagen stimulation. Inhibition of the NFκB-pathway in return reduced collagen-induced platelet proteasome activity and cleavage of proteasome substrates.
  
  
  CONCLUSIONS
  This work offers novel explanations how the proteasome influences collagen-dependent platelet aggregation by involving non-genomic functions of NFkB.
authors: Walter Brendel-Zentrum, Ludwig-Maximilians Universitaet Muenchen, Schillerstr. 44, 80336 Muenchen, Gemany; Medizinische Klinik und Poliklinik I, Klinikum der Universitaet Muenchen, Ziemssenstr. 1, 80336 Muenchen, Germany.
authors: Katharina
authors: K
authors: Grundler
authors: Walter Brendel-Zentrum, Ludwig-Maximilians Universitaet Muenchen, Schillerstr. 44, 80336 Muenchen, Gemany.
authors: Raffaela
authors: R
authors: Rotter
authors: Walter Brendel-Zentrum, Ludwig-Maximilians Universitaet Muenchen, Schillerstr. 44, 80336 Muenchen, Gemany.
authors: Sloane
authors: S
authors: Tilley
authors: Medizinische Klinik und Poliklinik I, Klinikum der Universitaet Muenchen, Ziemssenstr. 1, 80336 Muenchen, Germany.
authors: Joachim
authors: J
authors: Pircher
authors: Medizinische Klinik und Poliklinik I, Klinikum der Universitaet Muenchen, Ziemssenstr. 1, 80336 Muenchen, Germany.
authors: Thomas
authors: T
authors: Czermak
authors: Medizinische Klinik und Poliklinik I, Klinikum der Universitaet Muenchen, Ziemssenstr. 1, 80336 Muenchen, Germany.
authors: Mustaf
authors: M
authors: Yakac
authors: Walter Brendel-Zentrum, Ludwig-Maximilians Universitaet Muenchen, Schillerstr. 44, 80336 Muenchen, Gemany.
authors: Erik
authors: E
authors: Gaitzsch
authors: Medizinische Klinik und Poliklinik I, Klinikum der Universitaet Muenchen, Ziemssenstr. 1, 80336 Muenchen, Germany; DZHK (German Center for Cardiovascular Research) partner site Munich Heart Alliance, Munich, Germany.
authors: Steffen
authors: S
authors: Massberg
authors: Klinikum Starnberg, Osswaldstr.1, 82319 Starnberg, Germany.
authors: Florian
authors: F
authors: Krötz
authors: MediCenter Germering, Hartstr. 52, 82110 Germering, Germany.
authors: Hae-Young
authors: HY
authors: Sohn
authors: Walter Brendel-Zentrum, Ludwig-Maximilians Universitaet Muenchen, Schillerstr. 44, 80336 Muenchen, Gemany; DZHK (German Center for Cardiovascular Research) partner site Munich Heart Alliance, Munich, Germany.
authors: Ulrich
authors: U
authors: Pohl
authors: Walter Brendel-Zentrum, Ludwig-Maximilians Universitaet Muenchen, Schillerstr. 44, 80336 Muenchen, Gemany.
authors: Hanna
authors: H
authors: Mannell
authors: Medizinische Klinik und Poliklinik I, Klinikum der Universitaet Muenchen, Ziemssenstr. 1, 80336 Muenchen, Germany. Electronic address: bjoern.kraemer@med.uni-muenchen.de.
authors: Bjoern F
authors: BF
authors: Kraemer
mesh_terms: D001792:Blood Platelets / Q000166:cytology / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D003094:Collagen / Q000378:metabolism*; D006801:Humans; D016328:NF-kappa B / Q000378:metabolism*; D010974:Platelet Aggregation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D016328:NF-kappa B; D003094:Collagen; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; D002118:Calcium
keywords: Collagen pathway; NFĸB; Nuclear-factor-kappa-B; Platelet aggregation; Proteasome