The platelet α2β1 integrin functions as both an adhesion and signaling receptor upon exposure to collagen. Recent studies have indicated that α2β1 function can be activated via inside-out signaling, similar to the prototypical platelet integrin αIIbβ3. However, signaling molecules that regulate α2β1 activation in platelets are not well defined. A strong candidate molecule is the small GTPase Rap1b, the dominant platelet isoform of Rap1, which regulates αIIbβ3 activation
