Rap1b is critical for glycoprotein VI-mediated but not ADP receptor-mediated alpha2beta1 activation. J Thromb Haemost 2009 Apr;7(4):693-700
Date
02/05/2009Pubmed ID
19192113Pubmed Central ID
PMC2904080DOI
10.1111/j.1538-7836.2009.03289.xScopus ID
2-s2.0-63049104047 (requires institutional sign-in at Scopus site) 16 CitationsAbstract
BACKGROUND: The platelet alpha2beta1 integrin functions as both an adhesion and signaling receptor upon exposure to collagen. Recent studies have indicated that alpha2beta1 function can be activated via inside-out signaling, similar to the prototypical platelet integrin alphaIIbbeta3. However, signaling molecules that regulate alpha2beta1 activation in platelets are not well defined. A strong candidate molecule is the small GTPase Rap1b, the dominant platelet isoform of Rap1, which regulates alphaIIbbeta3 activation.
OBJECTIVES: We hypothesized that Rap1b positively regulates alpha2beta1 during agonist-induced platelet activation.
METHODS: To test whether Rap1b activates alpha2beta1 downstream of glycoprotein (GP)VI or other platelet receptors, we stimulated platelets purified from Rap1b-/- or wild-type mice with diverse agonists and measured alpha2beta1 activation using fluorescein isothiocyanate-labeled monomeric collagen. We also examined the role of Rap1b in outside-in signaling pathways by analyzing adhesion and spreading of Rap1b-/- or wild-type platelets on monomeric, immobilized collagen. Finally, we monitored the activation status of related Rap GTPases to detect changes in signaling pathways potentially associated with Rap1b-mediated events.
RESULTS: Rap1b-/- platelets displayed comparable ADP-induced or thrombin-induced alpha2beta1 activation as wild-type platelets, but reduced convulxin-dependent alpha2beta1 activation. Rap1b-/- platelets exhibited increased spreading on immobilized collagen but similar adhesion to immobilized collagen compared to wild-type platelets. Rap1b-/- platelets also showed Rap1a and Rap2 activation upon agonist stimulation, possibly revealing functional compensation among Rap family members.
CONCLUSIONS: Rap1b is required for maximal GPVI-induced but not ADP-induced activation of alpha2beta1 in murine platelets.
Author List
Wang Z, Holly SP, Larson MK, Liu J, Yuan W, Chrzanowska-Wodnicka M, White GC 2nd, Parise LVAuthors
Magdalena Chrzanowska PhD Professor in the Pharmacology and Toxicology department at Medical College of WisconsinGilbert C. White MD Professor in the Medicine department at Medical College of Wisconsin
MESH terms used to index this publication - Major topics in bold
AnimalsBlood Platelets
Cell Shape
Collagen
Integrin alpha2beta1
Mice
Mice, Knockout
Platelet Adhesiveness
Platelet Membrane Glycoproteins
Receptors, Purinergic P2
Signal Transduction
rap GTP-Binding Proteins
