The retinoblastoma gene functions as a growth and tumor suppressor in human bladder carcinoma cells
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R Takahashi1, T Hashimoto, H J Xu
1Center for Biotechnology, Woodlands, TX 77381.
Abstract:
The product of the human retinoblastoma gene (RB) is a nuclear phosphoprotein that is thought to function as a tumor suppressor. Mutations of RB frequently occur in human bladder carcinoma. To investigate the significance of the functional loss of this gene in bladder cancer, an RB expression plasmid (pBARB) under control of the human beta-actin promoter was transfected into the bladder carcinoma cell line HTB9, which lacks RB expression. Marker-selected transfectants that expressed RB protein were identified by immunoblotting and immunohistochemical staining. In selected clones, stable RB expression has persisted over 1 yr under standard culture conditions with 10% serum. However, RB expression caused major alterations of HTB9 growth properties both in vitro and in vivo. RB+ transfectants lacked the ability to form colonies in semi-solid medium, and their growth rate was significantly decreased in 3% serum. In addition, the tumorigenicity of these transfectants was markedly decreased. Tumors that formed in nude mice were much smaller and had a longer latency period but were indistinguishable microscopically from those produced by parental cells. Slower growing tumors were RB+, as measured by nuclear staining of their RB protein and by a normal RB protein pattern on immunoblots. These findings support the concept that the RB gene acts as both a growth and tumor suppressor in bladder cancer cells.
Insights
Restoring the retinoblastoma gene (RB) in bladder cancer cells suppressed their growth and tumor formation. This suggests RB functions as a critical tumor suppressor in bladder carcinoma.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- The human retinoblastoma gene (RB) product is a nuclear phosphoprotein functioning as a tumor suppressor.
- RB gene mutations are common in human bladder carcinoma, indicating its potential role in cancer development.
Purpose of the Study:
- To investigate the significance of RB functional loss in bladder cancer.
- To determine if restoring RB expression can inhibit bladder cancer cell growth and tumorigenicity.
Main Methods:
- Transfection of an RB expression plasmid (pBARB) into RB-deficient bladder carcinoma cell line HTB9.
- Selection and characterization of transfectants stably expressing RB protein using immunoblotting and immunohistochemical staining.
- Assessment of in vitro growth properties (colony formation, growth rate) and in vivo tumorigenicity in nude mice.
Main Results:
- Stable RB expression was achieved and maintained in HTB9 cells.
- RB expression significantly reduced HTB9 cell growth rate and colony formation in semi-solid medium.
- Tumorigenicity in nude mice was markedly decreased, with smaller tumors and longer latency periods observed in RB-expressing transfectants.
- Slower growing tumors consistently expressed RB protein.
Conclusions:
- The RB gene functions as both a growth and tumor suppressor in bladder cancer cells.
- Restoration of RB expression can inhibit the proliferation and tumorigenic potential of bladder cancer cells.
- These findings highlight the critical role of RB in bladder cancer pathogenesis and suggest its therapeutic potential.