β-Catenin and NF-κB cooperate to regulate the uPA/uPAR system in cancer cells

Expression of the urokinase plasminogen activator (uPA) and urokinase plasminogen activator receptor (uPAR) has recently been shown to be directly regulated by the Wnt/beta-catenin signaling pathway in colon cancer cells, through beta-catenin binding to T-cell factor binding element motifs present in their gene promoters. In our study, we present evidence that inhibition of beta-catenin causes upregulation of uPA/uPAR gene expression enhancing invasive potential. Using MCF-7, MDA-MB- 231 (breast cancer cells) and SW480 (colon cancer cells), we found that siRNA-mediated silencing of beta-catenin increased uPA, uPAR and plasminogen activator inhibitor-1 (PAI-1) expression at the mRNA and protein levels. This increase was responsible for the observed enhanced invasive capacity of MDA-MB- 231 and SW480 cancer cells. In addition, beta-catenin stabilization and accumulation by lithium chloride treatment, a well-known inhibitor of glycogen synthase kinase-3 beta (GSK-3 beta), or by beta-catenin/T-cell factor-4 expression vectors transfection led to a decrease in uPA, uPAR and PAI-1 mRNA expression in the studied cancer models. Treatment of beta-catenin siRNA-transfected cells with a specific inhibitor of nuclear factor-kappaB (NF-kappa B), SN50, significantly reduced enhancement of uPA, uPAR and PAI-1 expression and cancer cell invasion, observed in beta-catenin siRNA-transfected cells. Furthermore, beta-catenin siRNA-treated cells exhibited NF-kappa B nuclear accumulation. These data suggest that beta-catenin regulates the uPA/uPAR system in cooperation with NF-kappa B transcription factor, which constitutes a novel mechanism of regulation.