title: Characterization of the Rac guanine nucleotide exchange factor P-Rex1 in platelets.
abstract: BACKGROUND
  Blood platelets undergo a carefully regulated change in shape to serve as the primary mediators of hemostasis and thrombosis. These processes manifest through platelet spreading and aggregation and are dependent on platelet actin cytoskeletal changes orchestrated by the Rho GTPase family member Rac1. To elucidate how Rac1 is regulated in platelets, we captured Rac1-interacting proteins from platelets and identified Rac1-associated proteins by mass spectrometry.
  
  
  RESULTS
  Here, we demonstrate that Rac1 captures the Rac guanine nucleotide exchange factor P-Rex1 from platelet lysates. Western blotting experiments confirmed that P-Rex1 is expressed in platelets and associated with Rac1. To investigate the functional role of platelet P-Rex1, platelets from P-Rex1-/--deficient mice were treated with platelet agonists or exposed to platelet activating surfaces of fibrinogen, collagen and thrombin. Platelets from P-Rex1-/- mice responded to platelet agonists and activating surfaces similarly to wild type platelets.
  
  
  CONCLUSIONS
  These findings suggest that P-Rex1 is not required for Rac1-mediated platelet activation and that the GEF activities of P-Rex1 may be more specific to GPCR chemokine receptor mediated processes in immune cells and tumor cells.
authors: Department of Biomedical Engineering, Oregon Health & Science University, 3303 SW Bond Avenue, Mail Code CH13B, Portland, OR 97239 USA. aslanj@ohsu.edu.
authors: Joseph E
authors: JE
authors: Aslan
authors: Alex M
authors: AM
authors: Spencer
authors: Cassandra P
authors: CP
authors: Loren
authors: Jiaqing
authors: J
authors: Pang
authors: Heidi C
authors: HC
authors: Welch
authors: Daniel L
authors: DL
authors: Greenberg
authors: Owen Jt
authors: OJ
authors: McCarty