Paclitaxel is a potent anti-tumor drug used in the treatment of breast cancer. It induces de-centralization of the microtubular system in tumor cells, blocking cell division. In the search for dissemination to a secondary site, cancer cells are capable of degrading most components of the extracellular matrix via an extracellular proteolytic cascade, including urokinase-type plasminogen activator (uPA) and the matrix metalloproteinases (MMPs). In the present study, the effects of paclitaxel and nocodazole, 2 drugs known to affect microtubules with opposite mechanisms of action, have been tested for their effect on the secretion of uPA and MMPs in cultures of F3II mouse mammary-tumor cells. Tumor-derived uPA activity significantly increased after pre-treatment of tumor cells for 24 hr with micromolar concentrations of paclitaxel (4 microM), while decreasing after pre-treatment with nocodazole (1 microM). A similar modulation was found for MMP-9 by zymographic analysis. Immunofluorescence and Western-blot analysis confirmed the formation of parallel microtubule fragments in paclitaxel-treated cells and almost complete de-polymerization of microtubules in nocodazole-treated ones. Our data suggest that, through opposite actions on microtubule organization and dynamics, paclitaxel and nocodazole exert inverse modulation of tumor-derived proteolytic activity in mammary tumor cells.
Copyright 1999 Wiley-Liss, Inc.