Leukemia-associated Rho guanine-nucleotide exchange factor is not critical for RhoA regulation, yet is important for platelet activation and thrombosis in mice.
BACKGROUND
RhoA is an important regulator of platelet responses downstream of Gα13 , yet we still know little about its regulation in platelets. Leukemia-associated Rho guanine-nucleotide exchange factor (GEF [LARG]), a RhoA GEF, is highly expressed in platelets and may constitute a major upstream activator of RhoA. To this end, it is important to determine the role of LARG in platelet function and thrombosis.


RESULTS
Using a platelet-specific gene knockout, we show that the absence of LARG results in a marked reduction in aggregation and dense-granule secretion in response to the thromboxane mimetic U46619 and proteinase-activated receptor 4-activating peptide, AYPGKF, but not to adenosine diphosphate. In a ferric chloride thrombosis model in vivo, this translated into a defect, under mild injury conditions. Importantly, agonist-induced RhoA activation was not affected by the absence of LARG, although basal activity was reduced, suggesting that LARG may play a housekeeper role in regulating constitutive RhoA activity.


CONCLUSIONS
LARG plays an important role in platelet function and thrombosis in vivo. However, although LARG may have a role in regulating the resting activation state of RhoA, its role in regulating platelet function may principally be through RhoA-independent pathways, possibly through other Rho family members.
School of Physiology & Pharmacology, University of Bristol, Bristol, UK.
C M
CM
Williams
School of Physiology & Pharmacology, University of Bristol, Bristol, UK.
M T
MT
Harper
School of Physiology & Pharmacology, University of Bristol, Bristol, UK.
R
R
Goggs
School of Physiology & Pharmacology, University of Bristol, Bristol, UK.
T G
TG
Walsh
Max Planck Institute for Heart and Lung Research, Bad Nauheim, Germany.
S
S
Offermanns
School of Physiology & Pharmacology, University of Bristol, Bristol, UK.
A W
AW
Poole
D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid / Q000494:pharmacology; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D015550:Cell Degranulation / Q000187:drug effects; D002712:Chlorides / Q000633:toxicity; D003433:Crosses, Genetic; D005290:Ferric Compounds / Q000633:toxicity; D055786:Gene Knockout Techniques; D051379:Mice; D018345:Mice, Knockout; D009842:Oligopeptides / Q000494:pharmacology; D009928:Organ Specificity; D015539:Platelet Activation / Q000502:physiology*; D010974:Platelet Aggregation; D064067:Rho Guanine Nucleotide Exchange Factors / Q000097:blood / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D013927:Thrombosis / Q000097:blood* / Q000139:chemically induced; D020741:rho GTP-Binding Proteins / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein / Q000378:metabolism*
C577223:Arhgef12 protein, mouse; D002712:Chlorides; D005290:Ferric Compounds; D009842:Oligopeptides; D064067:Rho Guanine Nucleotide Exchange Factors; C455901:alanyl-tyrosyl-prolyl-glycyl-lysyl-phenylalanine; D000244:Adenosine Diphosphate; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; C526380:RhoA protein, mouse; D020741:rho GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein; C024555:ferric chloride
Larg protein, mouse; RhoA protein, mouse; gene knockout; mouse; platelets; thrombosis