CLIC4 and Arf6 are activated by angiotensin II44,45 and mediate the effects of TGF-β.6,46 We noted a marked upregulation of CLIC4 and Arf6 signaling in ECFCs from idiopathic PAH patients (5- and 10-fold increase, respectively), suggesting potential importance of this pathway in the human condition. This evidence concerns the gene ARF6 and pulmonary arterial hypertension.