PAI-1 is a novel component of the miR-17~92 signaling that regulates pulmonary artery smooth muscle cell phenotypes

We have previously reported that miR-17~92 is critically involved in the pathogenesis of pulmonary hypertension (PH). We also identified two novel mR-17/20a direct targets PDLIM5 and PHD2 and elucidated the signaling pathways by which PDLIM5 and PHD2 regulate functions of pulmonary artery smooth muscle cells (PASMC). In addition, we have shown that plasminogen activator inhibitor-1 (PAI-1) is also downregulated in PASMC that overexpress miR-17~92. However, it is unclear whether PAI-1 is a direct target of miR-17~92 and whether it plays a role in regulating PASMC phenotype. In this study, we have identified PAI-1 as a novel target of miR-19a/b, two members of the miR-17~92 cluster. We found that the 3’-untranslated region (UTR) of PAI-1 contains a miR-19a/b binding site and that miR-19a/b can target this site to suppress PAI-1 protein expression. MiR-17/20a, two other members of miR-17~92 may also indirectly suppress PAI-1 expression through PDLIM5. PAI-1 is a negative regulator of miR-17~92-mediated PASMC proliferation. Silencing of PAI-1 induces Smad2/Calponin signaling in PASMC, suggesting that PAI-1 is a negative regulator of PASMC contractile phenotype. We also found that PAI-1 is essential for the metabolic gene expression in PASMC. Furthermore, although there is no significant change in PAI-1 levels in PASMC isolated from IPAH and APHA patients, PAI-1 is downregulated in hypoxia/Sugen-induced hypertensive rat lungs. These results suggest that miR-17~92 regulates PASMC contractile phenotype and proliferation coordinately and synergistically by direct and indirect targeting of PAI-1.