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Characterization of the Rac guanine nucleotide exchange factor P-Rex1 in platelets

Joseph E Aslan1*, Alex M Spencer2, Cassandra P Loren1, Jiaqing Pang1, Heidi C Welch3, Daniel L Greenberg2 and Owen JT McCarty1

Author Affiliations

1 Department of Biomedical Engineering, Oregon Health & Science University, 3303 SW Bond Avenue, Mail Code CH13B, Portland, OR 97239 USA

2 Department of Medicine, School of Medicine, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, OR, 97239 USA

3 Inositide Laboratory, The Babraham Institute, Babraham Research Campus, Cambridge, CB22 3AT, UK

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Journal of Molecular Signaling 2011, 6:11  doi:10.1186/1750-2187-6-11

Published: 1 September 2011



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.


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.


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.

platelet signaling; cytoskeletal remodeling; GEF; small GTPase