Margitta Elvers1, Sandra Beck, Anna Fotinos, Melanie Ziegler, Meinrad Gawaz. 1. Medizinische Klinik III, Department of Cardiology and Cardiovascular Medicine, Eberhard Karls University, Tübingen, Otfried-Müller Str. 10, 72076 Tübingen, Germany. margitta.elvers@med.uni-tuebingen.de
Abstract
AIMS: Platelet adhesion and aggregation is essential for haemostasis and thrombosis. Cytoskeletal reorganization of activated platelets plays a crucial role in these processes and implies activation of Rho GTPases. Rho GTPases are regulated by GTPase-activating proteins (GAPs) that stimulate GTP hydrolysis to terminate Rho signalling. In this study, we explored the regulation of Rho GTPases in platelets. METHODS AND RESULTS: Oligophrenin1 (OPHN1) is a RhoGAP-regulating cytoplasmic protein that has been investigated in patients with X-linked mental retardation. Here, we identified OPHN1 in mouse platelets where it co-localizes to actin-rich regions and Rho GTPases. OPHN1 exhibits strong GTPase-stimulating activity towards RhoA, Cdc42, and Rac1 and regulates cell adhesion and spreading. Furthermore, OPHN1 controls RhoA-mediated stress fibre and focal adhesion formation as well as filopodia and lamellipodia development. The analysis of different domains of OPHN1 revealed distinct functions in Rho hydrolysis. The C-terminus of OPHN1 displays an essential unit for Rho regulation, whereas the PH domain is a regulatory unit of OPHN1 controlling GAP function. The N-terminal BAR (Bin/amphiphysin/Rvs)-like domain is involved in GAP regulation but not in cytoskeleton rearrangements or Rho regulation and acts as a guidance domain to direct this GAP to its substrate. CONCLUSION: Our results suggest that OPHN1 is a powerful regulator of Rho GTPase activity in platelets that is critical for the reorganization of the cytoskeleton, which is a major process required for stable platelet adhesion and thrombus formation to occur.
AIMS: Platelet adhesion and aggregation is essential for haemostasis and thrombosis. Cytoskeletal reorganization of activated platelets plays a crucial role in these processes and implies activation of Rho GTPases. Rho GTPases are regulated by GTPase-activating proteins (GAPs) that stimulate GTP hydrolysis to terminate Rho signalling. In this study, we explored the regulation of Rho GTPases in platelets. METHODS AND RESULTS:Oligophrenin1 (OPHN1) is a RhoGAP-regulating cytoplasmic protein that has been investigated in patients with X-linked mental retardation. Here, we identified OPHN1 in mouse platelets where it co-localizes to actin-rich regions and Rho GTPases. OPHN1 exhibits strong GTPase-stimulating activity towards RhoA, Cdc42, and Rac1 and regulates cell adhesion and spreading. Furthermore, OPHN1 controls RhoA-mediated stress fibre and focal adhesion formation as well as filopodia and lamellipodia development. The analysis of different domains of OPHN1 revealed distinct functions in Rho hydrolysis. The C-terminus of OPHN1 displays an essential unit for Rho regulation, whereas the PH domain is a regulatory unit of OPHN1 controlling GAP function. The N-terminal BAR (Bin/amphiphysin/Rvs)-like domain is involved in GAP regulation but not in cytoskeleton rearrangements or Rho regulation and acts as a guidance domain to direct this GAP to its substrate. CONCLUSION: Our results suggest that OPHN1 is a powerful regulator of Rho GTPase activity in platelets that is critical for the reorganization of the cytoskeleton, which is a major process required for stable platelet adhesion and thrombus formation to occur.
Authors: Antonija Jurak Begonja; Fred G Pluthero; Worawit Suphamungmee; Silvia Giannini; Hilary Christensen; Richard Leung; Richard W Lo; Fumihiko Nakamura; William Lehman; Markus Plomann; Karin M Hoffmeister; Walter H A Kahr; John H Hartwig; Hervé Falet Journal: Blood Date: 2015-04-02 Impact factor: 22.113
Authors: Bart-Jan de Kreuk; Antje Schaefer; Eloise C Anthony; Simon Tol; Mar Fernandez-Borja; Dirk Geerts; Jos Pool; Lothar Hambach; Els Goulmy; Peter L Hordijk Journal: PLoS One Date: 2013-09-23 Impact factor: 3.240