TWIST1 and idiopathic pulmonary arterial hypertension: In addition, (4) PDGFB promoter region has putative TWIST1 binding site, (5) p16INK4A knockdown decreased TWIST1 and PDGFB expression in a hypoxia-induced pulmonary hypertension model and IPAH patient cells (Figures 2–4), (6) significantly differentially expressed genes of healthy vs. IPAH patient lungs that interacted with TWIST1 also interacted with PDGFB (Supplementary Figure 1A).