To elucidate whether this EPAC1/ERK1/2 pathway mediates CAD phosphorylation by PDGF-BB, PAH pericytes were pretreated with the EPAC inhibitor, ESI-09 (1 μM, 20 min) or the MEK inhibitor, PD98059 (10 μM, 20 min). Here, MAPK3 is linked to pulmonary arterial hypertension.