INTERLEUKIN-6 AND EPIDERMAL GROWTH-FACTOR PROMOTE ANCHORAGE-INDEPENDENT GROWTH OF IMMORTALIZED HUMAN PROSTATIC EPITHELIAL-CELLS TREATED WITH N-METHYL-N-NITROSOUREA

BACKGROUND. Epidermal growth factor (EGF) and interleukin (IL)-6 are i mplicated in the growth of benign and malignant prostatic epithelial c ells. We investigated the role of EGF and IL-6 during the process of p rostate carcinogenesis. METHODS. Using growth in soft agar as an index of transformation, we examined the effect of EGF and IL-6 on the enha ncement of N-methyl-N-nitrosourea (MNU)-initiated transformation of im mortalized, nontumorigenic prostatic epithelial cell Lines (PWR-1E and RWPE-1) developed in our laboratory. The effect of EGF and IL-6 on th e growth of MNU-induced transformants isolated from soft agar was asse ssed both in monolayer culture and in a soft agar. RESULTS. After al h r exposure to N-methyl-N-nitrosourea (50 mu g/ml), cells (5 x 10(4)) w ere grown in soft agar in the presence of EGF (5 ng/mI) or IL-6 (10 or 100 ng/ml). Addition of EGF or IL-6 significantly increased colony fo rmation in soft agar of both immortalized prostatic epithelial cell li nes initiated with MNU (P < 0.001-0.05). Only a very small number of c olonies was observed with the parental cell lines PWR-1E and RWPE-1 no t exposed to MNU, and their numbers increased by the addition of EGF o r IL-6. All of the transformants, derived by exposure to MNU and isola ted from soft agar, exhibited a higher cell growth potential in monola yer cultures than did their parental cell lines. Furthermore, as compa red to the parental cell lines, growth response of MNU-transformants t o 5 alpha-dihydrotestosterone (5 alpha-DHT), EGF, or IL-6 in monolayer culture was better in 5 of 8, 6 of 8, and 7 of 8 cell lines, respecti vely. All of the MNU-transformants exhibited a far higher colony-formi ng efficiency in soft agar than did the parental cell Lines. However, the degree of responsiveness to EGF or IL-6 in soft agar varied among the MNU-transformants. CONCLUSIONS. The results of the present study s uggest that IL-6 and EGF may enhance prostate carcinogenesis in vitro by preferentially stimulating the growth of transformed cells. (C) 199 8 Wiley-Liss, Inc.