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Adenovirus E1A down-regulates the EGF receptor via repression of its promoter
M Prudenziati1, M Sirito, H van Dam
1Laboratory of Molecular Genetics, G. Gaslini Institute, Genoa, Italy.
Abstract:
The epidermal growth factor receptor (EGF-R), after activation by its ligands, stimulates a cascade of intracellular events leading to cellular proliferation. Its expression is increased in various forms of cancer as a consequence of altered regulation. Our objective was to study potential negative regulators of EGF-R expression; we investigated the effect of adenovirus E1A proteins. E1A proteins can exert both positive and negative effects on cell growth, depending on the cell type and cellular context, and have anti-tumorigenic features on human cancer cells. We show that human cell lines stably transformed with the adenovirus E1 region show significantly reduced expression of EGF-R protein and mRNA compared to their control, non-E1A-expressing counterparts. Furthermore, the promoter activity of EGF-R can be specifically repressed by E1A in transient co-transfection analysis in multiple cell types. Transfections with deleted promoter fragments and constructs containing short fragments of the putative E1A-responsive region fused to a heterologous promoter indicate that E1A-responsive elements are contained in a promoter region (from -150 to -76). Analysis of E1A mutants showed that both E1A gene products, 12S and 13S, repress EGF-R promoter activity and that full repression requires the presence of an intact CR1 domain.
Insights
Adenovirus E1A proteins significantly reduce epidermal growth factor receptor (EGF-R) expression and promoter activity in human cancer cells. This finding highlights E1A as a potential negative regulator of EGF-R, impacting cellular proliferation.
Area of Science:
- Molecular Biology
- Oncology
- Virology
Background:
- Epidermal growth factor receptor (EGF-R) signaling drives cellular proliferation and is often dysregulated in cancer.
- Adenovirus E1A proteins are known to influence cell growth and possess anti-tumorigenic properties.
Purpose of the Study:
- To investigate the potential of adenovirus E1A proteins as negative regulators of EGF-R expression.
- To elucidate the mechanism by which E1A affects EGF-R expression and promoter activity.
Main Methods:
- Stable transformation of human cell lines with the adenovirus E1 region.
- Quantitative analysis of EGF-R protein and mRNA levels.
- Transient co-transfection assays with EGF-R promoter constructs and E1A mutants.
- Deletion analysis of the EGF-R promoter to identify E1A-responsive elements.
Main Results:
- Adenovirus E1A expression led to significantly reduced EGF-R protein and mRNA levels in human cell lines.
- E1A proteins specifically repressed EGF-R promoter activity across multiple cell types.
- E1A-responsive elements were localized to the -150 to -76 region of the EGF-R promoter.
- Both 12S and 13S E1A isoforms repressed EGF-R promoter activity, with full repression dependent on the CR1 domain.
Conclusions:
- Adenovirus E1A proteins act as potent negative regulators of EGF-R expression.
- E1A-mediated repression of EGF-R occurs at the transcriptional level via specific promoter elements.
- The findings suggest a potential therapeutic strategy targeting EGF-R in cancer using E1A or its functional domains.