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

This study was designed to investigate the role of the tumours has been demonstrated by a series of epidemiology epidermal growth factor receptor (EGFR) and its ligands studies (2). More than 50% of bladder carcinomas are thought in chemically induced mouse bladder cancer. Bladder to be associated with cigarette smoking or exposure to industrial tumours were induced in C57Bl/6 and B6D2F1 mice by carcinogens (3–5). The carcinogens specifically implicated treatment with the carcinogen, N-butyl-N-(4-hydroxybutyl) include aromatic amines and nitrosamines, many of which nitrosamine (BBN). The levels of mRNA for EGFR and its have been detected in human urine. ligands were analysed by reverse transcription–polymerase Growth factors and their receptors regulate normal cell chain reaction (RT–PCR) in bladder tumours and in proliferation and differentiation and may be involved in any normal bladder urothelia. EGFR mRNA was detected in of the several steps in neoplastic development and progression. all tumours, transforming growth factor α (TGFα) mRNA The mechanisms by which growth factor receptors participate levels were similar to those in normal bladder urothelia or in malignant transformation include receptor activation by were decreased and mRNA levels for amphiregulin, hep- mutation, autocrine and paracrine growth loops, changes in arin-binding epidermal growth factor-like factor (HB-EGF) signalling and regulatory pathways and, possibly, receptor and betacellulin were significantly higher than those in trans-activation (6–11). normal urothelia. Seven cell lines were derived from chem- Epidermal growth factor receptor (EGFR), also called ErbB1, ically induced tumours. These cell lines were able to grow was the first identified member of the subfamily of tyrosine in serum-free conditions. All the cell lines tested expressed kinase receptors that includes ErbB2/Neu, ErbB3 and ErbB4 the genes encoding EGFR and at least one of its ligands. (12). The ligands of the EGFR belong to the epidermal growth Proliferation of these cell lines was inhibited by AG1478, a factor (EGF)/transforming growth factor α (TGFα) family, specific EGFR tyrosine kinase inhibitor, strongly suggesting which includes EGF, TGFα, amphiregulin, heparin-binding that EGFR was involved in cell growth. As expected, EGFR EGF-like factor (HB-EGF), betacellulin (BTC) and epiregulin was found to be phosphorylated in serum-free medium, this (13–15). Over-expression of EGFR—as a result of gene phosphorylation being inhibited by AG1478. Conditioned amplification, increased transcription rate and/or protein stabilmedium of a bladder cancer cell line had EGFR-stimulating ization—has been reported in a wide spectrum of human activity and an antibody directed against EGFR inhibited cancers including non-small cell lung cancer, head and neck proliferation by 45%. This suggests that tumour cell growth squamous carcinomas, glioblastoma multiforme and cancers is stimulated by an autocrine loop involving EGFR and of the breast, pancreas (9,16,17) and bladder (18–20). In several secreted growth factors. AG1478 decreased the expression tumour types, including bladder carcinoma, overexpression of of genes for amphiregulin, HB-EGF and betacellulin, showEGFR has been shown to be correlated with poor prognosis. ing that EGFR activation induces up-regulation of the Overexpression of EGFR by tumour cells is also often accomEGFR ligands. These results suggest that EGFR plays a panied by the production of one or more of the ligands by the