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 factor receptor (EGFR) and its ligands in chemically induced mouse bladder cancer. Bladder tumours were induced in C57Bl/6 and B6D2F1 mice by treatment with the carcinogen, N:-butyl-N:-(4-hydroxybutyl) nitrosamine (BBN). The levels of mRNA for EGFR and its ligands were analysed by reverse transcription-polymerase chain reaction (RT-PCR) in bladder tumours and in normal bladder urothelia. EGFR mRNA was detected in all tumours, transforming growth factor alpha (TGFalpha) mRNA levels were similar to those in normal bladder urothelia or were decreased and mRNA levels for amphiregulin, heparin-binding epidermal growth factor-like factor (HB-EGF) and betacellulin were significantly higher than those in normal urothelia. Seven cell lines were derived from chemically induced tumours. These cell lines were able to grow in serum-free conditions. All the cell lines tested expressed the genes encoding EGFR and at least one of its ligands. Proliferation of these cell lines was inhibited by AG1478, a specific EGFR tyrosine kinase inhibitor, strongly suggesting that EGFR was involved in cell growth. As expected, EGFR was found to be phosphorylated in serum-free medium, this phosphorylation being inhibited by AG1478. Conditioned medium of a bladder cancer cell line had EGFR-stimulating activity and an antibody directed against EGFR inhibited proliferation 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 results suggest that EGFR plays a critical role in bladder tumour progression.

Tumour suppressive properties of fibroblast growth factor receptor 2-IIIb in human bladder cancer.

FGFRs (fibroblast growth factor receptors) are encoded by four genes (FGFR1-4). Alternative splicing results in various receptor isoforms. The FGFR2-IIIb variant is present in a wide variety of epithelia, including the bladder epithelium. Recently, we have shown that FGFR2-IIIb is downregulated in a subset of transitional cell carcinomas of the bladder, and that this downregulation is associated with a poor prognosis. We investigated possible tumour suppressive properties of FGFR2-IIIb by transfecting two human bladder tumour cell lines, J82 and T24, which have no endogenous FGFR2-IIIb expression, with FGFR2-IIIb cDNA. No stable clones expressing FGFR2-IIIb were isolated with the J82 cell line. For the T24 cell line, stable transfectants expressing FGFR2-IIIb had reduced growth in vitro and formed fewer tumours in nude mice which, in addition, grew more slowly. The potential mechanisms leading to decreased FGFR2-IIIb mRNA levels were also investigated. The 5' region of the human FGFR2 gene was isolated and found to contain a CpG island which was partially methylated in more than half the cell lines and tumours which do not express FGFR2-IIIb. No homozygous deletion was identified in any of the tumours or cell lines with reduced levels of FGFR2-IIIb. Mutational analysis of the entire coding region of FGFR2-IIIb at the transcript level was performed in 33 bladder tumours. In addition to normal FGFR2-IIIb mRNA, abnormal transcripts were detected in two tumour samples. These abnormal mRNAs resulted from exon skipping which affected the region encoding the kinase domain. Altogether, these results show that FGFR2-IIIb has tumour growth suppressive properties in bladder carcinomas and suggest possible mechanisms of FGFR2 gene inactivation.

Messenger RNA for enzymes of ornithine and polyamine metabolism are selectively underexpressed in kidney of 5/6 nephrectomized rats.

Altered nitrogen metabolism is a feature of chronic renal failure (CRF). The present study examined changes in renal expression of mRNA for enzymes involved in ornithine and polyamine metabolism, i.e. ornithine aminotransferase (OAT), ornithine decarboxylase (ODC), and S-adenosylmethionine synthetase (S-ADMase), during the early phase of renal insufficiency in rats after 5/6 nephrectomy (Nx). Involvement of androgens, the most potent stimulators of renal ODC, in these changes, was also evaluated inasmuch as testoseronemia is known to be significantly decreased in male uremic subjects. The abundance of mRNA was evaluated by quantitative Northern analysis of total RNA extracted from the remnant kidney of male or female Nx rats. The level mRNA for ODC was depressed by 76, 83, and 79%, that for OAT by 60, 76 and 63%, and that for S-ADMase by 37, 58 and 30%, at, respectively, 2, 7 and 35 days after Nx, in both male and female rats. ODC but not OAT enzyme activity was decreased. The expression of glyceraldehyde-3-phosphate dehydrogenase was only slightly lowered and that of c-myc was unaltered. Renal polyamine content of the remnant kidney was unchanged. It is concluded that in CRF: (1) intrarenal ornithine metabolism and polyamine biosynthesis are greatly impaired; (2) decreased androgens are not involved in these changes; (3) increased ODC is not a prerequisite for kidney hypertrophy; (4) extrarenal polyamines accumulation into the remnant likely compensates for defective renal biosynthesis.

Decreased expression of keratinocyte growth factor receptor in a subset of human transitional cell bladder carcinomas.

Growth factors and growth factor receptors are involved in tumor progression. The fibroblast growth factor receptor 2 gene encodes distinct isoforms. The isoforms which bind KGF (keratinocyte growth factor or FGF-7) are called KGF-R or FGFR2b. KGF-R is expressed in different epithelia and is involved in the control of epithelial-mesenchymal interactions. Expression of KGF-R mRNA was examined in normal human bladder and transitional cell carcinoma of the bladder (TCC) by semi-quantitative RT-PCR using TFIID and GAPDH as internal standards. In normal bladder, the KGF-R mRNA was detected in the urothelium but not in the underlying stroma. In TCCs, the level of KGF-R mRNA was generally either normal or low. Eighteen out of 54 TCCs had a KGF-R mRNA level below 30% of that found in normal urothelium. This decrease in KGF-R mRNA was not accompanied by an increase in BEK (FGFR2c) mRNA, the other major splice variant of the fibroblast growth factor receptor 2 gene. Expression of the KGF-R was also monitored by immunohistochemistry using a functional KGF-immunoglobulin chimera. The receptor was uniformly expressed throughout the normal urothelium except for the umbrella cells. Immunoreactivity for KGF-R was found to be negative in tumors with low levels of KGF-R mRNA, while the peritumoral normal urothelium was positive. Among patients with muscle invasive tumors, those exhibiting a low level of KGF-R mRNA had a significantly higher proportion of cancer deaths. Our results suggest that decreased expression of KGF-R can be considered as a marker of tumor progression in muscle invasive TCCs.