title: RASA3 is a critical inhibitor of RAP1-dependent platelet activation.
abstract: The small GTPase RAP1 is critical for platelet activation and thrombus formation. RAP1 activity in platelets is controlled by the GEF CalDAG-GEFI and an unknown regulator that operates downstream of the adenosine diphosphate (ADP) receptor, P2Y12, a target of antithrombotic therapy. Here, we provide evidence that the GAP, RASA3, inhibits platelet activation and provides a link between P2Y12 and activation of the RAP1 signaling pathway. In mice, reduced expression of RASA3 led to premature platelet activation and markedly reduced the life span of circulating platelets. The increased platelet turnover and the resulting thrombocytopenia were reversed by concomitant deletion of the gene encoding CalDAG-GEFI. Rasa3 mutant platelets were hyperresponsive to agonist stimulation, both in vitro and in vivo. Moreover, activation of Rasa3 mutant platelets occurred independently of ADP feedback signaling and was insensitive to inhibitors of P2Y12 or PI3 kinase. Together, our results indicate that RASA3 ensures that circulating platelets remain quiescent by restraining CalDAG-GEFI/RAP1 signaling and suggest that P2Y12 signaling is required to inhibit RASA3 and enable sustained RAP1-dependent platelet activation and thrombus formation at sites of vascular injury. These findings provide insight into the antithrombotic effect of P2Y12 inhibitors and may lead to improved diagnosis and treatment of platelet-related disorders.
authors.forename: Lucia
authors.initials: L
authors.lastname: Stefanini
authors.forename: David S
authors.initials: DS
authors.lastname: Paul
authors.forename: Raymond F
authors.initials: RF
authors.lastname: Robledo
authors.forename: E Ricky
authors.initials: ER
authors.lastname: Chan
authors.forename: Todd M
authors.initials: TM
authors.lastname: Getz
authors.forename: Robert A
authors.initials: RA
authors.lastname: Campbell
authors.forename: Daniel O
authors.initials: DO
authors.lastname: Kechele
authors.forename: Caterina
authors.initials: C
authors.lastname: Casari
authors.forename: Raymond
authors.initials: R
authors.lastname: Piatt
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: Caron
authors.forename: Nigel
authors.initials: N
authors.lastname: Mackman
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Weyrich
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Parrott
authors.forename: Yacine
authors.initials: Y
authors.lastname: Boulaftali
authors.forename: Mark D
authors.initials: MD
authors.lastname: Adams
authors.forename: Luanne L
authors.initials: LL
authors.lastname: Peters
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Bergmeier
mesh_terms: D000818:Animals; D016922:Cellular Senescence; D000077144:Clopidogrel; D020690:GTPase-Activating Proteins / Q000235:genetics / Q000502:physiology*; D020662:Guanine Nucleotide Exchange Factors / Q000172:deficiency; D006487:Hemostasis; D008231:Lymphopenia / Q000235:genetics; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D015539:Platelet Activation / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000502:physiology; D058925:Receptors, Purinergic P2Y12 / Q000502:physiology; D012501:Saphenous Vein / Q000293:injuries; D013156:Splenectomy; D013921:Thrombocytopenia / Q000235:genetics / Q000601:surgery; D034061:Thrombopoiesis; D013988:Ticlopidine / Q000031:analogs & derivatives / Q000494:pharmacology; D020827:rap1 GTP-Binding Proteins / Q000037:antagonists & inhibitors* / Q000502:physiology
chemical_list: D020690:GTPase-Activating Proteins; D020662:Guanine Nucleotide Exchange Factors; C548577:P2ry12 protein, mouse; D010975:Platelet Aggregation Inhibitors; C583390:RASA3 protein, mouse; C485927:Rasgrp2 protein, mouse; D058925:Receptors, Purinergic P2Y12; D000077144:Clopidogrel; C514862:Akt1 protein, mouse; D051057:Proto-Oncogene Proteins c-akt; D020827:rap1 GTP-Binding Proteins; D013988:Ticlopidine