EPIDERMAL GROWTH-FACTOR RECEPTOR ACTIVATION IN ANDROGEN-INDEPENDENT BUT NOT ANDROGEN-STIMULATED GROWTH OF HUMAN PROSTATIC-CARCINOMA CELLS

These studies were undertaken to assess the relative expression and au tocrine activation of the epidermal growth factor receptor (EGFR) in n ormal and transformed prostatic epithelial cells and to determine whet her EGFR activation plays a functional role in androgen-stimulated gro wth of prostate cancer cells in vitro. EGFR expression was determined by Western blot analysis and ELISA immunoassays. Immunoprecipitation o f radiophosphorylated EGFR and evaluation of tyrosine phosphorylation was used to assess EGFR activation. The human androgen-independent pro state cancer cell lines PC3 and DU145 exhibited higher levels of EGFR expression and autocrine phosphorylation than normal human prostatic e pithelial cells or the human androgen-responsive prostate cancer cell line LNCaP. PC3 and DU145 cells also showed higher levels of autonomou s growth under serum-free defined conditions, Normal prostatic epithel ial cells expressed EGFR but did not exhibit detectable levels of EGFR phosphorylation when cultured in the absence of exogenous EGF. Additi on of EGF stimulated EGFR phosphorylation and induced proliferation of normal cells. LNCaP cells exhibited autocrine phosphorylation of EGFR but did not undergo significant proliferation when cultured in the ab sence of exogenous growth factors. A biphasic growth curve was observe d when LNCaP cells were cultured with dihydrotestosterone (DHT). Maxim um proliferation occurred at 1 nM DHT with regression of the growth re sponse at DHT concentrations greater than 1 nM. However, neither EGFR expression nor phosphorylation was altered in LNCaP cells after androg en stimulation. In addition, DHT-stimulated growth of LNCaP cells was not inhibited by anti-EGFR. These studies show that autocrine activati on of EGFR is a common feature of prostatic carcinoma cells in contras t to normal epithelial cells. However, EGFR activation does not appear to play a functional role in androgen-stimulated growth of LNCaP cell s in vitro.