Talin-1 is the principal platelet Rap1 effector of integrin activation

• Published in: Blood 2020-09, Vol.136 (10), p.1180-1190
• Main Authors: Lagarrigue, Frederic, Paul, David S., Gingras, Alexandre R., Valadez, Andrew J., Sun, Hao, Lin, Jenny, Cuevas, Monica N., Ablack, Jailal N., Lopez-Ramirez, Miguel Alejandro, Bergmeier, Wolfgang, Ginsberg, Mark H.
• Format: Article
• Language: English
• Subjects: Animals; Female; Integrin beta1 - genetics; Integrin beta1 - metabolism; Integrin beta3 - genetics; Integrin beta3 - metabolism; Life Sciences; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Platelet Activation; Platelet Aggregation; Platelets and Thrombopoiesis; Point Mutation; Protein Domains; rap GTP-Binding Proteins - physiology; rap1 GTP-Binding Proteins - physiology; Signal Transduction; Talin - physiology; Thrombopoiesis
• ISSN: 0006-4971; 1528-0020; 1528-0020
• DOI: 10.1182/blood.2020005348

Ras-related protein 1 (Rap1) is a major convergence point of the platelet-signaling pathways that result in talin-1 binding to the integrin β cytoplasmic domain and consequent integrin activation, platelet aggregation, and effective hemostasis. The nature of the connection between Rap1 and talin-1 in integrin activation is an important remaining gap in our understanding of this process. Previous work identified a low-affinity Rap1-binding site in the talin-1 F0 domain that makes a small contribution to integrin activation in platelets. We recently identified an additional Rap1-binding site in the talin-1 F1 domain that makes a greater contribution than F0 in model systems. Here we generated mice bearing point mutations, which block Rap1 binding without affecting talin-1 expression, in either the talin-1 F1 domain (R118E) alone, which were viable, or in both the F0 and F1 domains (R35E,R118E), which were embryonic lethal. Loss of the Rap1–talin-1 F1 interaction in platelets markedly decreases talin-1–mediated activation of platelet β1- and β3-integrins. Integrin activation and platelet aggregation in mice whose platelets express only talin-1(R35E, R118E) are even more impaired, resembling the defect seen in platelets lacking both Rap1a and Rap1b. Although Rap1 is important in thrombopoiesis, platelet secretion, and surface exposure of phosphatidylserine, loss of the Rap1–talin-1 interaction in talin-1(R35E, R118E) platelets had little effect on these processes. These findings show that talin-1 is the principal direct effector of Rap1 GTPases that regulates platelet integrin activation in hemostasis. •Blockade of Rap1 binding to talin-1 F0 and F1 domains phenocopies the defects in integrin activation observed in platelets lacking Rap1a/b.•Rap1–talin-1 interaction in platelets is crucial for hemostasis, with minor impact on granule secretion. [Display omitted]