Leukaemia-associated Rho guanine nucleotide exchange factor (LARG) plays an agonist specific role in platelet function through RhoA activation

Thromb Haemost. 2016 Aug 30;116(3):506-16. doi: 10.1160/TH15-11-0848. Epub 2016 Jun 23.


Leukemia-Associated RhoGEF (LARG) is highly expressed in platelets, which are essential for maintaining normal haemostasis. We studied the function of LARG in murine and human megakaryocytes and platelets with Larg knockout (KO), shRNA-mediated knockdown and small molecule-mediated inhibition. We found that LARG is important for human, but not murine, megakaryocyte maturation. Larg KO mice exhibit macrothrombocytopenia, internal bleeding in the ovaries and prolonged bleeding times. KO platelets have impaired aggregation, α-granule release and integrin α2bβ3 activation in response to thrombin and thromboxane, but not to ADP. The same agonist-specific reductions in platelet aggregation occur in human platelets treated with a LARG inhibitor. Larg KO platelets have reduced RhoA activation and myosin light chain phosphorylation, suggesting that Larg plays an agonist-specific role in platelet signal transduction. Using two different in vivo assays, Larg KO mice are protected from in vivo thrombus formation. Together, these results establish that LARG regulates human megakaryocyte maturation, and is critical for platelet function in both humans and mice.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Bleeding Time
  • Blood Platelets / drug effects
  • Blood Platelets / metabolism*
  • Gene Knockdown Techniques
  • Humans
  • Megakaryocytes / cytology
  • Megakaryocytes / metabolism
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Myosin Light Chains / blood
  • Platelet Function Tests
  • Rho Guanine Nucleotide Exchange Factors / antagonists & inhibitors
  • Rho Guanine Nucleotide Exchange Factors / blood*
  • Rho Guanine Nucleotide Exchange Factors / deficiency
  • Rho Guanine Nucleotide Exchange Factors / genetics
  • Thrombin / metabolism
  • Thrombin / pharmacology
  • Thrombopoiesis / genetics
  • Thrombopoiesis / physiology
  • Thromboxanes / blood
  • Thromboxanes / pharmacology
  • rho GTP-Binding Proteins / agonists
  • rho GTP-Binding Proteins / blood*
  • rhoA GTP-Binding Protein / agonists
  • rhoA GTP-Binding Protein / blood*


  • ARHGEF12 protein, human
  • Arhgef12 protein, mouse
  • Myosin Light Chains
  • Rho Guanine Nucleotide Exchange Factors
  • Thromboxanes
  • RHOA protein, human
  • Thrombin
  • RhoA protein, mouse
  • rho GTP-Binding Proteins
  • rhoA GTP-Binding Protein