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Effect of CpG-rich sequences in transformation and tumorigenesis by polyomavirus
A Renzo1, L Bouchard, C J Mongeau
1Department of Microbiology, University of Sherbrooke, Quebec, Canada.
Abstract:
To address the question of the role of CpG-rich sequences in gene expression, we investigated the effect of an HTF island on the activity of the polyomavirus middle T (pmt) oncogene. pmt is less transformant and less tumorigenic when it is introduced into cultured cells or newborn rats in the presence of an HTF island. Transformed cells carrying pmt in the vicinity of the HTF island have a propensity to revert at a relatively high rate of about 2 X 10(-3) per cell per generation by a mechanism probably involving methylation of some CpG sites in the island. Our results suggest that HTF islands can function as transcriptional silencers.
Insights
CpG-rich sequences, known as HTF islands, can silence gene expression. Introducing the polyomavirus middle T (pmt) oncogene near an HTF island reduced its transforming and tumorigenic activity, suggesting a gene-silencing role for these islands.
Area of Science:
- Molecular Biology
- Epigenetics
- Cancer Research
Background:
- CpG-rich sequences, or HTF islands, are prevalent in gene promoter regions.
- The precise role of HTF islands in regulating gene expression remains an area of active investigation.
- The polyomavirus middle T (pmt) oncogene is a well-characterized tool for studying cellular transformation.
Purpose of the Study:
- To investigate the influence of HTF islands on the gene expression and oncogenic activity of the polyomavirus middle T (pmt) oncogene.
- To determine if HTF islands can modulate the transforming and tumorigenic potential of an oncogene.
Main Methods:
- Introduction of the pmt oncogene into cultured cells and newborn rats in the presence and absence of an HTF island.
- Assessment of the transforming and tumorigenic activity of the pmt oncogene under different conditions.
- Analysis of the reversion rate in transformed cells and investigation of potential mechanisms, including CpG site methylation.
Main Results:
- The pmt oncogene exhibited reduced transforming and tumorigenic activity when co-introduced with an HTF island.
- Transformed cells containing pmt near an HTF island showed a significant reversion rate (approximately 2 x 10^-3 per cell per generation).
- CpG site methylation within the HTF island is implicated as a likely mechanism for this reversion.
Conclusions:
- HTF islands can function as transcriptional silencers, inhibiting oncogene activity.
- CpG methylation within HTF islands plays a crucial role in mediating this gene-silencing effect.
- These findings contribute to understanding the epigenetic regulation of gene expression and its implications in cancer.