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Targeting gene transcription: a new strategy to down-regulate c-erbB-2 expression in mammary carcinoma
1Gene Transcription Laboratory, Hammersmith Hospital, London, UK.
Abstract:
Overexpression of the c-erbB-2 proto-oncogene in mammary carcinoma is frequently associated with amplification of the c-erbB-2 gene, but it also occurs from single-copy gene. Studies in mammary-derived cell lines have shown that, whether or not the gene is amplified, there is a 6- to 8-fold increase in the accumulation of c-erbB-2 mRNA per gene copy in overexpressing cells. We have recently shown that this phenomenon is due to increased activity of the c-erbB-2 promoter mediated by the binding of a novel transcription factor, OB2-1, which is present at higher levels in overexpressing cells than in low expressors. OB2-1 activity therefore represents a novel therapeutic target for the down-regulation of c-erbB-2 levels in human cells. As a prototype for this strategy, we show here that the drug sodium aurothiomalate is able to inhibit the DNA-binding activity of OB2-1 in vitro and also to interfere with c-erbB-2 promoter activity in cell-based transfection assays. In addition, endogenous c-erbB-2 immunoreactivity was reduced in cells treated with aurothiomalate as compared with the levels observed in control cells.
Insights
Overexpression of the c-erbB-2 gene in breast cancer involves increased promoter activity driven by the transcription factor OB2-1. The drug sodium aurothiomalate inhibits OB2-1, reducing c-erbB-2 levels and offering a potential therapeutic strategy.
Area of Science:
- Oncology
- Molecular Biology
- Pharmacology
Background:
- Overexpression of the c-erbB-2 proto-oncogene in mammary carcinoma is linked to gene amplification or single-copy gene events.
- Mammary-derived cell lines show a 6- to 8-fold increase in c-erbB-2 mRNA per gene copy in overexpressing cells, regardless of gene amplification.
- This phenomenon is attributed to increased c-erbB-2 promoter activity mediated by the transcription factor OB2-1.
Purpose of the Study:
- To investigate OB2-1 as a novel therapeutic target for down-regulating c-erbB-2 levels in human cells.
- To evaluate the efficacy of sodium aurothiomalate in inhibiting OB2-1 activity and c-erbB-2 expression.
Main Methods:
- In vitro inhibition of OB2-1 DNA-binding activity by sodium aurothiomalate.
- Cell-based transfection assays to assess interference with c-erbB-2 promoter activity.
- Measurement of endogenous c-erbB-2 immunoreactivity in cells treated with aurothiomalate.
Main Results:
- Sodium aurothiomalate demonstrated inhibition of OB2-1 DNA-binding activity in vitro.
- The drug interfered with c-erbB-2 promoter activity in cell-based assays.
- Aurothiomalate treatment led to reduced endogenous c-erbB-2 immunoreactivity compared to controls.
Conclusions:
- OB2-1 activity is a viable therapeutic target for controlling c-erbB-2 levels in human cells.
- Sodium aurothiomalate shows potential as a drug to down-regulate c-erbB-2 expression by targeting OB2-1.
- These findings support a novel strategy for managing c-erbB-2-related conditions in breast cancer.