Effects of ataluren readthrough on the proliferation of PAECs. Live cell counts show that ataluren treatment leads to growth suppression of R321X (A) and restores BMP-mediated growth repression in response to BMP9 (B) (post hoc P values versus control at 72-h: R321X + ataluren, P < 0.001; R294X + ataluren + BMP9 versus control + BMP9, P = 0.42). In cell proliferation assays using XTT: (C) untreated PAECs from heritable PAH (HPAH) proliferate significantly faster than controls (*post hoc pairwise P values at 72 h; all P < 0.001); (D) BMP9 treatment slows proliferation in all cells, but HPAH cases still proliferate faster than untreated control cells (*P < 0.001); (E) Ataluren treatment significantly represses the growth of R321X and R294X cells, but has no effect on Δex1–8 cells (*P < 0.001); (F) BMP9 induction after ataluren treatment shows restoration of BMP growth repression in R321X and R294X, but not Δex1–8 cells. Means (±SD) of triplicate wells are shown.