Pro-urokinase up-regulates the expression of urokinase-type plasminogen activator (u-PA) in human pulmonary arterial endothelial cells

Exogenous Urokinase Inhibits Proteasomal Degradation of Its Cognate Urokinase Plasminogen Activator Receptor

Acute pulmonary embolism (APE) is a debilitating condition with high incidence and mortality rates. APE is widely treated with the serine protease urokinase or urokinase-type plasminogen activator (uPA) that functions by resolving blood clots via catalyzing the conversion of plasminogen to plasmin. Treatment with recombinant uPA has been shown to increase endogenous expression of uPA and its cognate receptor, uPAR; however, the mechanisms for this induction are not known. Using an in vitro hypoxia/reoxygenation model in bronchial epithelial BEAS-2B cells, we show that induction of hypoxia/reoxygenation induces apoptosis and increases secretion of tumor necrosis factor–alpha, brain natriuretic peptide, and fractalkine, which are attenuated when treated with exogenous uPA. Induction of hypoxia/reoxygenation resulted in decreased expression of uPAR on cell surface without any significant changes in its messenger RNA expression, highlighting post-transcriptional regulatory mechanisms. Determination of uPAR protein half-life using cycloheximide showed treatment with uPA significantly increased its half-life (209.6 ± 0.2 min from 48.2 ± 2.3 min). Hypoxia/reoxygenation promoted the degradation of uPAR. Inhibition of proteasome-mediated degradation using MG-132 and lactacystin revealed that uPAR was actively degraded when hypoxia/reoxygenation was induced and that it was reversed when treated with exogenous uPA. Determination of the proteolytic activity of 20S proteasome showed a global increase in ubiquitin–proteasome activation without an increase in proteasome content in cells subjected to hypoxia/reoxygenation. Our results cumulatively reveal that uPAR is actively degraded following hypoxia/reoxygenation, and the degradation was significantly weakened by exogenous uPA treatment. Given the importance of the uPA/uPAR axis in a multitude of pathophysiological contexts, these findings provide important yet undefined mechanistic insights.

MicroRNA 449a can Attenuate Protective Effect of Urokinase Against Pulmonary Embolism

Acute pulmonary embolism (APE) is a disabling diseases with high incidence rate and mortality rate. Although with high specificity, D-Dimer lacks specificity to assess APE, hence additional diagnostic and prognostic biomarkers are necessary. APE is widely treated with serine protease urokinase or urokinase-type plasminogen activator (uPA), which act as a catalyst for conversion of plasminogen to plasmin to resolve blood clots. However, it is unknown the role of differential expression of microRNAs (miRNAs) in protective effect of uPA against APE. Hence, we performed miRNA profiling in a hypoxia/reoxygenation (H/R) model of bronchial epithelial BEAS-2B cells in vitro and a APE mice model in vivo. Our analysis revealed that miR-34a-5p, miR-324-5p, miR-331-3p are upregulated with H/R or APE induction, whereas miR-429, miR-491-5p, and miR-449a are downregulated. The differential expression of the miRNAs was attenuated to levels comparable to control by treatment with uPA both in vitro and in vivo. In situ target prediction and analysis of potential functions of the target genes showed that the enrichment of biological processes and pathways were related to cell growth, proliferation, and inflammation. Ectopic overexpression of miR-449a using a mimic completely attenuated the protective effect of uPA in the H/R model in vitro. These results provide a group of miRNAs that could be used as markers, and the modulation of these miRNAs might have potential therapeutic benefits in patients with APE, which need to be validated in additional studies in humans.