Extracellular signal-regulated kinase and AP-1 pathways are involved in reactive oxygen species-induced urokinase plasminogen activator receptor expression in human gastric cancer cells

Overexpression of urokinase plasminogen activator receptor (uPAR) is known to correlate closely with tumor cell invasion and metastasis. In gastric cancer, however, the mechanism for induction of uPAR remains to be elucidated. In this study, to investigate the effect of reactive oxygen species (ROS) on uPAR expression and the underlying signal pathways in human gastric cancer AGS cells, phenazine methosulfate (PMS) and H2O2 were used as ROS generator. PMS and H2O2 induced the uPAR expression in time- and concentration-dependent manner. PMS and H2O2 also induced the activation of extracellular signal-regulated kinases (Erk)-1/2. A specific inhibitor of MEK-1 (PD980590) was found to suppress the PMS-induced uPAR expression and the uPAR promoter activity. Expression of vectors encoding a mutated-type MEK-1 resulted in decreases in the uPAR promoter activity. Electrophoretic mobility shift assay revealed that PMS increased time-dependently the DNA binding activity of AP-1. Transient transfection studies using AP-1 decoy confirmed that the activation of AP-1 is involved in PMS-induced uPAR upregulation. The AGS cells pretreated with PMS showed a remarkably enhanced invasiveness and this effect was partially abrogated by uPAR neutralizing antibodies. The above results suggest that ROS induces uPAR expression via Erk-1/2 and AP-1 signaling pathways and, in turn, stimulates the cell invasiveness in human gastric cancer AGS cells.