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

Abstract

Summary Leukemia-Associated RhoGEF (LARG) is highly expressed in platelets, which are essential for maintaining normal hemostasis. We studied the function of LARG in murine and human megakaryocytes and platelets with Larg knockout, 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 2 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.

MicroRNA-214-3p Regulates Hypoxia-Mediated Pulmonary Artery Smooth Muscle Cell Proliferation and Migration by Targeting ARHGEF12

“…The RhoA/RhoA kinase signaling pathway plays an important role the pathogenesis of PH, and inhibiting the RhoA/RhoA kinase pathway is a promising therapy for the treatment of PH [11,24]. Guanine exchange factors (GEF) are known to couple Gα subunits and Rho signaling, and there are multiple GEFs that can potentially function in platelet signal transduction from Gα subunits to RhoA [25]. Leukemia-associated RhoGEF (ARHGEF12) plays a critical role in the RhoA/RhoA kinase pathway [25].…”

“…Guanine exchange factors (GEF) are known to couple Gα subunits and Rho signaling, and there are multiple GEFs that can potentially function in platelet signal transduction from Gα subunits to RhoA [25]. Leukemia-associated RhoGEF (ARHGEF12) plays a critical role in the RhoA/RhoA kinase pathway [25]. However, the role of ARHGEF12 in PH is not yet clear.…”

Potentiation of receptor responses induced by prolonged binding of Gα 13 and leukemia‐associated RhoGEF

“…Gqmediated responses require much higher concentrations of U‐46619 (1). Considering that U‐46619‐activated TPαRs couple equally well with Gq and G 13 (41), together with the observation that LARG is involved in the Gα 13 mediated platelet response (42), it seems likely that the high agonist sensitivity of the Gα 13 response originates in its high‐affinity interaction with LARG.…”

Turning Platelets Off and On: Role of RhoGAPs and RhoGEFs in Platelet Activity

“…Therefore, ARHGEF12 may be responsible for RhoA activity in resting platelets only (67). In contrast, Zou et al (68) reported ARHGEF12 was necessary for RhoA activation in platelets. MLC phosphorylation by ROCK (downstream of RhoA-GTP) was abolished, albeit in a global ARHGEF12 knockout mouse model.…”