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

Androgen receptor (AR) signals have been suggested to contribute to bladdertumorigenesis and cancer progression. Activation of epidermal growth factor receptor(EGFR) also leads to stimulation of bladder tumor growth. However, crosstalk betweenAR and EGFR pathways in bladder cancer remains uncharacterized. We have recentlyshown that androgens activate the EGFR pathway in bladder cancer cells. The purposeof this study was to investigate the effects of EGF on AR activity in bladdercancer. EGF increased AR transcriptional activity by 1.2-, 1.9- and 2.0-fold inUMUC3, 5637-AR and J82-AR cell lines, respectively, over mock treatment and aspecific EGFR inhibitor, PD168393, antagonized the EGF effect. Combined treatmentof EGF and dihydrotestosterone (DHT) further induced AR transactivation whilean AR antagonist, hydroxyflutamide (HF), abolished the effect of not only DHTbut also EGF. In growth assays, EGF alone/DHT alone/EGF+DHT increased cell numbersby 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 inUMUC3-AR-shRNA (8%) or AR-negative 5637-V (<1%) and J82-V (17%) cells. HF treatmentat least partially counteracted the EGF effect on the growth of AR-positive cells.Western blotting demonstrated that EGF, especially in the presence of DHT, upregulatedthe expression of the p160 coactivator TIF2 and HF again blocked this stimulation.Co-immunoprecipitation revealed the association between AR and estrogen receptor(ER)-β or Src in UMUC3 cells and stronger associations with EGF treatment, implyingthe involvement of the AR/ER/Src complex in EGF-increased AR transactivation andcell growth. Current results, thus, suggest that EGF promotes bladder cancer cellproliferation via modulation of AR signals. Taken together with our previous findings,crosstalk between EGFR and AR pathways can play an important role in the progressionof bladder cancer.