STAT3 activation increases KLF5 expression. A) STAT3 inhibition by siRNA decreases KLF5 RNA expression measured by qRT-PCR in human PAH-PASMC and protein expressions were measured by Western blot. B) STAT3 activation (i.e. PY705-STAT3/STAT3 ratio) and KLF5 expression were measured in control cells with or without stimulation (ET-1, PDGF, IL-6), by Western blot. Our results show that ET1, PDGF and IL6 stimulations induce STAT3 activation and upregulation of KLF5 expression. qRT-PCR results were normalized to 18S gene expression and protein expression measured by Western blot were normalized to SM-actin (*, P < 0.05; **, P < 0.01).