RETINOIC ACID MODULATES EXTRACELLULAR UROKINASE-TYPE PLASMINOGEN-ACTIVATOR ACTIVITY IN DU-145 HUMAN PROSTATIC-CARCINOMA CELLS

Effects of all-trans retinoic acid (RA) on the net enzymatic activity of secreted, extracellular urokinase type plasminogen activator (u-PA) in DU-145 human prostatic carcinoma cells were examined to assess the potential use of retinoids in human prostate cancer prevention and tr eatment. u-PA is associated with tumor progression involving invasion and metastasis. Based on a chromogenic substrate assay, results show t hat DU-145 cells secrete five times more u-PA than normal human prosta tic epithelium. DU-145 cells were treated with 0.1 to 10 mu M RA for 4 8 h. This short treatment of cells with RA did not inhibit growth, Aft er a 48-h treatment of cultures with RA, serum-free conditioned medium was analyzed for u-PA activity by SDS-PAGE zymography. Two major band s of u-PA with M(r) of similar to 54,000 (high molecular weight u-PA) and similar to 33,000 (low molecular weight u-PA) were detected. Plasm inogen-dependent catalytic activity of these bands could be specifical ly inhibited with antibody to u-PA, confirming that these bands repres ent u-PA. A 48 h treatment with 1.0 mu M RA reduced u-PA activity in c onditioned medium to 51.6% of control. A 50% reduction in free u-PA an tigen level, as compared to control, was further demonstrated at 1.0 m u M RA by Western blot analysis and densitometry. These results show t hat RA can decrease the net extracellular urokinase activity produced by prostatic carcinoma cells, It is proposed that these effects of RA may have important implications not only in the chemoprevention of pro state cancer, by inhibition of promotion of prostatic intraepithelial neoplasia to invasive carcinoma, but also in tumor progression during invasion and metastasis, by decreasing extracellular matrix degradatio n, as shown in our accompanying article.