Our cell growth determinations using both MTT and BrdU assays as well as siRNA transfections illustrate that when the action of either PLK1 or FOXM1 is blocked, not only is the proliferation of PAH HPASMC inhibited but also that of normal HPASMC (Figs 1 and 2). This evidence concerns the gene FOXM1 and pulmonary arterial hypertension.