Expression of urokinase-type plasminogen activator, its receptor and type-1 plasminogen activator inhibitor is differently regulated by inhibitors of protein synthesis in human cancer cell lines

Abstract

Expression of the various components of the plasminogen activation system is under tight regulation by hormones, cytokines, and growth factors under physiologic conditions. Like early-response genes, these components are modulated by inhibitors of protein synthesis in some cell lines. To clarify the specific expression and regulation of mRNAs for urokinase (uPA), its receptor (uPAR), and type-1 plasminogen activator inhibitor (PAI-1), I analyzed RNA from four human cancer cell lines by RNA blotting after treatment with cycloheximide, anisomycin, emetine or puromycin. These inhibitors, all of which induced translational arrest, induced a very diverse response in the various transcripts, suggesting that the inhibitors mediate their effects through different molecular mechanisms. Dose-response analysis showed that, in A549 cells, anisomycin strongly induced uPAR and PAI-1 mRNA at concentrations that did not cause complete inhibition of protein synthesis, whereas cycloheximide induced these transcripts in a dose-dependent manner only at concentrations sufficient to inhibit total protein synthesis by >90%. Puromycin induced the 3.4-kb transcript of PAI-1 mRNA in A549 and RD cells, whereas it decreased the expression of both the 3.4-kb and 2.4-kb PAI-1 transcripts in HT-1080 cells. Different time patterns of induction for uPA, uPAR and PAI-1 mRNA suggest that even in the same cell type, inhibitors of protein synthesis mediate their effects on various genes through different mechanisms. Thus, induction of uPA, uPAR and PAI-1 transcripts by inhibitors of protein synthesis was dependent on the gene, the cell line, and the type of inhibitor, and inhibition of protein synthesis per se was not sufficient for induction of these transcripts.