Involvement of epidermal growth factor receptor in chemically induced mouse bladder tumour progression

This study was designed to investigate the role of the epidermal growth fac tor receptor (EGFR) and its ligands in chemically induced mouse bladder can cer. Bladder tumours were induced in C57BI/6 and B6D2F1 mice by treatment w ith the carcinogen, N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN). The level s of mRNA for EGFR and its ligands were analysed by reverse transcription-p olymerase chain reaction (RT-PCR) in bladder tumours and in normal bladder urothelia, EGFR mRNA was detected in all tumours, transforming growth facto r alpha (TGF alpha) mRNA levels were similar to those in normal bladder uro thelia or were decreased and mRNA levels for amphiregulin, heparin-binding epidermal growth factor-like factor (HB-EGF) and betacellulin were signific antly higher than those in normal urothelia, Seven cell lines were derived from chemically induced tumours, These cell lines were able to grow in seru m-free conditions. All the cell lines tested expressed the genes encoding E GFR and at least one of its ligands, Proliferation of these cell lines was inhibited by AG1478, a specific EGFR tyrosine kinase inhibitor, strongly su ggesting that EGFR was involved in cell growth, As expected, EGFR was found to be phosphorylated in serum-free medium, this phosphorylation being inhi bited by AG1478, Conditioned medium of a bladder cancer cell line had EGFR- stimulating activity and an antibody directed against EGFR inhibited prolif eration by 45 %, This suggests that tumour cell growth is stimulated by an autocrine loop involving EGFR and secreted growth factors. AG1478 decreased the expression of genes for amphiregulin, HB-EGF and betacellulin, showing that EGFR activation induces up-regulation of the EGFR ligands, These resu lts suggest that EGFR plays a critical role in bladder tumour progression.