Rap1 binding to the talin 1 F0 domain makes a minimal contribution to murine platelet GPIIb-IIIa activation

Blood Adv. 2018 Sep 25;2(18):2358-2368. doi: 10.1182/bloodadvances.2018020487.

Abstract

Activation of platelet glycoprotein IIb-IIIa (GPIIb-IIIa; integrin αIIbβ3) leads to high-affinity fibrinogen binding and platelet aggregation during hemostasis. Whereas GTP-bound Rap1 GTPase promotes talin 1 binding to the β3 cytoplasmic domain to activate platelet GPIIb-IIIa, the Rap1 effector that regulates talin association with β3 in platelets is unknown. Rap1 binding to the talin 1 F0 subdomain was proposed to forge the talin 1-Rap1 link in platelets. Here, we report a talin 1 point mutant (R35E) that significantly reduces Rap1 affinity without a significant effect on its structure or expression. Talin 1 head domain (THD) (R35E) was of similar potency to wild-type THD in activating αIIbβ3 in Chinese hamster ovary cells. Coexpression with activated Rap1b increased activation, and coexpression with Rap1GAP1 reduced activation caused by transfection of wild-type THD or THD(R35E). Furthermore, platelets from Tln1R35E/R35E mice showed similar GPIIb-IIIa activation to those from wild-type littermates in response to multiple agonists. Tln1R35E/R35E platelets exhibited slightly reduced platelet aggregation in response to low doses of agonists; however, there was not a significant hemostatic defect, as judged by tail bleeding times. Thus, the Rap1-talin 1 F0 interaction has little effect on platelet GPIIb-IIIa activation and hemostasis and cannot account for the dramatic effects of loss of Rap1 activity on these platelet functions.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blood Cell Count
  • Blood Platelets / metabolism*
  • CHO Cells
  • Cricetulus
  • Female
  • Male
  • Mice
  • Mice, Transgenic
  • Models, Molecular
  • Mutation
  • Platelet Function Tests
  • Platelet Glycoprotein GPIIb-IIIa Complex / agonists*
  • Protein Conformation
  • Protein Interaction Domains and Motifs*
  • Talin / chemistry
  • Talin / genetics
  • Talin / metabolism*
  • rap1 GTP-Binding Proteins / metabolism*

Substances

  • Platelet Glycoprotein GPIIb-IIIa Complex
  • Talin
  • talin protein, mouse
  • rap1 GTP-Binding Proteins