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Overexpression of transforming growth factor beta type I receptor abolishes malignant phenotype of a rat bladder
1Department of Pathology, Northwestern University Medical School, Chicago, Illinois 60611, USA.
Abstract:
Transforming growth factor beta1 (TGF-beta1), a potent growth inhibitor of bladder carcinoma cells, elicits its effects by binding to cell surface receptors. LMC19, a highly invasive and metastatic rat bladder carcinoma cell line, was insensitive to the growth-suppressive effect of TGF-beta1, and it expressed undetectable levels of TGF-beta type I receptor (TbetaRI) mRNA by reverse transcription-PCR and its protein by Western blot analysis. To evaluate the effect of TbetaRI in reducing the malignant phenotype, we transfected LMC19 with an expression vector containing human TbetaRI cDNA. Stable transfection with the expression vector yielded five transfectants that expressed the introduced TbetaRI mRNA. The binding activity of TGF-beta1 to TbetaRI was restored in all of the transfectants. The growth of the transfectants on a plastic surface was markedly inhibited in the presence of TGF-beta1 in the culture medium (P < 0.001), whereas the control cells (parental and transfectant with only neo gene) remained TGF-beta1 insensitive. The colony-forming efficiency of the transfectants was strongly reduced in soft agar medium containing 5% FCS (P < 0.001) and was restored by the addition of a neutralizing anti-TGF-beta antibody. Furthermore, none of the transfectants tested formed tumors in athymic nude mice, whereas the control cells did so in all mice tested. These findings indicate that introduction of TbetaRI can revert a malignant phenotype to a less aggressive (even benign) phenotype in a rat bladder carcinoma cell line that lacks TbetaRI, and that reduced expression of TbetaRI may be associated with the development and progression of bladder carcinomas.
Insights
Restoring TGF-beta type I receptor (TbetaRI) expression in bladder cancer cells reversed their malignant traits. This suggests TbetaRI is crucial for controlling tumor growth and metastasis in bladder carcinoma.
Area of Science:
- Oncology
- Molecular Biology
- Cell Biology
Background:
- Transforming growth factor beta1 (TGF-beta1) inhibits bladder carcinoma cell growth via cell surface receptors.
- LMC19, a rat bladder carcinoma cell line, is invasive, metastatic, and lacks TGF-beta type I receptor (TbetaRI).
Purpose of the Study:
- To investigate the role of TbetaRI in reverting the malignant phenotype of bladder carcinoma cells.
- To determine if restoring TbetaRI expression can reduce invasiveness, metastasis, and tumor formation.
Main Methods:
- Transfection of LMC19 cells with human TbetaRI cDNA.
- Analysis of TbetaRI mRNA and protein expression.
- Assessment of TGF-beta1 binding and growth inhibition.
- Evaluation of colony-forming efficiency in soft agar.
- Tumorigenicity studies in athymic nude mice.
Main Results:
- Transfected cells expressed TbetaRI, restoring TGF-beta1 binding and growth inhibition.
- Colony formation in soft agar was significantly reduced in transfectants.
- Transfected cells failed to form tumors in nude mice, unlike control cells.
Conclusions:
- Introduction of TbetaRI can revert the malignant phenotype of TbetaRI-deficient bladder carcinoma cells.
- Reduced TbetaRI expression may be linked to bladder carcinoma development and progression.