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 LVAuthor
Gilbert C. White MD Professor in the Medicine department at Medical College of WisconsinMESH 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
