Induction of urokinase-type plasminogen activator by anticancer agents in RC-K8 human lymphoma cells

We have shown that the anthracycline antibiotics induce u-PA through the gene expression in which reactive oxygen species (ROS) may be involved. Here, we examined the effects of other ROS inducible anticancer agents, such as mitomycin C (MMC), cisplatin and camptothecin (CPT) on the u-PA expression in RC-K8 human lymphoma cells. u-PA activities were quantitatively measured using a synthetic chromogenic substrate S-2444. All of these agents, especially CPT and SN38, the active metabolite of CPT, increased u-PA accumulation in the conditioned medium in a dose-dependent manner. The peak induction was observed at the sublethal concentrations. The u-PA induction by CPT was also confirmed by the fibrin-zymography. No specific activation of metalloproteinases, MMP-2 and MMP-9, was shown by the gelatin-zymography. Northern blotting using Rl-labeled u-PA cDNA probe revealed that CPT and SN38 increased u-PA mRNA levels. Electrophoretic mobility shift assay revealed that the nuclear protein binding to Rel-related protein-binding element, present in the u-PA promoter, was activated after CPT stimulation. Bindings to AP-1 and CREB elements were not activated. These data suggest that CPT induces u-PA probably through u-PA gene expression by activating NF-kB transcriptional factor. Therefore, the sublethal doses of these anticancer agents may influence many aspects of tumor growth and invasiveness through activating u-PA/plasmin system.