RHOA and idiopathic pulmonary arterial hypertension: The activity of the G protein RhoA and its downstream target ROCK are increased in both IPAH and animal PAH models, particularly because of serotonylation- (Guilluy et al., 2009) and superoxide-mediated (Resta et al., 2010) activation of RhoA which results in constitutive Ca2+ hypersensitivity.