Epidermal growth factor induces bladder cancer cell proliferation through activation of the androgen receptor

Androgen receptor (AR) signals have been suggested to contribute to bladder tumorigenesis and cancer progression. Activation of epidermal growth factor receptor (EGFR) also leads to stimulation of bladder tumor growth. However, crosstalk between AR and EGFR pathways in bladder cancer remains uncharacterized. We have recently shown that androgens activate the EGFR pathway in bladder cancer cells. The purpose of this study was to investigate the effects of EGF on AR activity in bladder cancer. EGF increased AR transcriptional activity by 1.2-, 1.9- and 2.0-fold in UMUC3, 5637-AR and J82-AR cell lines, respectively, over mock treatment and a specific EGFR inhibitor, PD168393, antagonized the EGF effect. Combined treatment of EGF and dihydrotestosterone (DHT) further induced AR transactivation while an AR antagonist, hydroxyflutamide (HF), abolished the effect of not only DHT but also EGF. In growth assays, EGF alone/DHT alone/EGF+DHT increased cell numbers by 16/12/19%, 6/14/18% and 30/12/38% in UMUC3-control-shRNA, 5637-AR and J82-AR, respectively, whereas the effects of EGF were marginal or less significant in UMUC3-AR-shRNA (8%) or AR-negative 5637-V (