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Modulation of EGFR gene transcription by secondary structures, a polymorphic repetitive sequence and mutations--a
F Gebhardt1, H Bürger, B Brandt
1Institute for Clinical Chemistry, University of Muenster, Germany.
Abstract:
The epidermal growth factor receptor (EGFR) plays a crucial role in growth, differentiation and motility of normal as well as tumor cells. The transduction of extracellular signals to the cytoplasm via the receptor not only depends on ligand binding, but is also determined by the receptor density on the cell surface. Therefore, in terms of cancer diagnosis and therapeutic approaches targeting EGFR it is decisive to know how the expression level of EGFR is controlled. We found that transcription activity declines with increasing numbers of CA dinucleotides of a highly polymorphic CA repeat in the first intron epidermal growth factor receptor gene. In vivo data from cultured cell lines support these findings, although other regulation mechanisms can compensate this effect. In addition, we showed that RNA elongation terminates at a site closely downstream of the simple sequence repeat (SSR) and that there are two separate major transcription start sites. Model calculations for the helical DNA conformation revealed a high bendability in the EGFR polymorphic region, especially if the CA stretch is extended. These data suggest that the CA-SSR can act like a joint bringing the promoter in proximity to a putative repressor protein bound downstream of the CA-SSR. The data suggest that this polymorphism is a marker for cancer linking genetic and epigenetic risk. Furthermore in breast cancer, heterozygous tumours with short CA-SSR showed an elevated EGFR-expression in contrast to tumours with longer CA-SSR. Tumours with loss of heterozygosity in intron 1 of egfr revealed an increased EGFR expression if the longer allele was lost. Moreover, deceased egfr gene dosages were significantly correlated to poor prognosis in breast cancer.
Insights
A highly polymorphic CA repeat in the epidermal growth factor receptor (EGFR) gene influences its transcription. Shorter repeats correlate with higher EGFR expression, impacting breast cancer prognosis and potentially serving as a cancer risk marker.
Area of Science:
- Genetics
- Molecular Biology
- Cancer Research
Background:
- Epidermal growth factor receptor (EGFR) is vital for cell growth and motility.
- EGFR signaling is crucial in both normal and tumor cells.
- Controlling EGFR expression is key for cancer diagnosis and therapy.
Purpose of the Study:
- To investigate the regulatory mechanisms controlling EGFR gene expression.
- To determine the role of a polymorphic CA repeat in the first intron of the EGFR gene.
- To explore the association between EGFR expression, this polymorphism, and breast cancer prognosis.
Main Methods:
- Analysis of transcription activity in relation to CA dinucleotide repeat length.
- In vivo studies using cultured cell lines.
- DNA conformation modeling to assess helical properties.
- Correlation analysis of EGFR expression, CA-SSR polymorphism, and clinical data in breast cancer patients.
Main Results:
- Transcription activity of the EGFR gene decreases with increasing length of the CA dinucleotide repeat.
- RNA elongation termination occurs downstream of the CA repeat.
- The CA repeat exhibits high DNA bendability, suggesting a role in regulating transcription.
- Shorter CA repeats are associated with elevated EGFR expression in heterozygous breast tumors.
- Loss of heterozygosity in tumors with longer alleles leads to increased EGFR expression.
- Reduced EGFR gene dosage correlates with poor prognosis in breast cancer.
Conclusions:
- The polymorphic CA repeat in the EGFR gene acts as a regulatory element influencing transcription.
- This polymorphism may serve as a marker for cancer risk, linking genetic and epigenetic factors.
- EGFR gene dosage and CA-SSR length are significant prognostic indicators in breast cancer.