The GRAF family member oligophrenin1 is a RhoGAP with BAR domain and regulates Rho GTPases in platelets.
OBJECTIVE
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.


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.


CONCLUSIONS
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.
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
Margitta
M
Elvers
Sandra
S
Beck
Anna
A
Fotinos
Melanie
M
Ziegler
Meinrad
M
Gawaz
D000199:Actins / Q000378:metabolism; D000818:Animals; D001792:Blood Platelets / Q000166:cytology / Q000378:metabolism*; D002448:Cell Adhesion; D002478:Cells, Cultured; D006224:Cricetinae; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D003599:Cytoskeleton / Q000378:metabolism; D020690:GTPase-Activating Proteins / Q000378:metabolism*; D051097:Glial Cell Line-Derived Neurotrophic Factor Receptors / Q000378:metabolism; D038901:X-Linked Intellectual Disability / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D009687:Nuclear Proteins / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism; D020741:rho GTP-Binding Proteins / Q000378:metabolism*
D000199:Actins; D003598:Cytoskeletal Proteins; D020690:GTPase-Activating Proteins; C494988:Gfra1 protein, mouse; D051097:Glial Cell Line-Derived Neurotrophic Factor Receptors; D009687:Nuclear Proteins; C498439:Ophn1 protein, mouse; D020764:cdc42 GTP-Binding Protein; D020741:rho GTP-Binding Proteins