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Regulation of DNA methylation by the Ras signaling pathway
A R MacLeod1, J Rouleau, M Szyf
1Department of Pharmacology and Therapeutics, McGill University, Montreal, PQ Canada.
Abstract:
We demonstrate that DNA methylation in an adrenocortical tumor cell line, Y1, is controlled by the Ras signaling pathway. Forced expression of a cDNA encoding human GAP120 (hGAP), a down-modulator of Ras activity or delta 9-Jun a transdominant negative mutant of Jun, in Y1 cells reverts the transformed morphology of the cells and results in a reduction in the level of DNA methylation, DNA methyltransferase (MeTase) mRNA, and enzymatic activity. Introduction of an oncogenic Ha-ras into the GAP transfectants results in reversion to a transformed morphology and an increase in the levels of DNA methylation and DNA MeTase activity. Transient transfection CAT assays demonstrate that the expression of DNA MeTase promoter in Y1 cells is regulated by Ras and AP-1. These results establish a molecular link between a major signaling pathway involved in tumorigenesis and DNA methylation.
Insights
The Ras signaling pathway controls DNA methylation in adrenocortical tumors. Inhibiting Ras reduces DNA methylation and reverses tumor cell transformation, linking Ras signaling to cancer development.
Area of Science:
- Molecular Biology
- Cancer Research
- Epigenetics
Background:
- The Ras signaling pathway is a critical regulator of cell growth and differentiation.
- Aberrant Ras signaling is implicated in numerous human cancers, including adrenocortical tumors.
- DNA methylation is an epigenetic mechanism that plays a vital role in gene regulation and has been linked to cancer development.
Purpose of the Study:
- To investigate the role of the Ras signaling pathway in regulating DNA methylation in adrenocortical tumor cells.
- To elucidate the molecular mechanisms connecting Ras signaling to DNA methylation and tumorigenesis.
Main Methods:
- Utilized the Y1 adrenocortical tumor cell line.
- Employed forced expression of human GAP120 (hGAP) and a dominant-negative Jun mutant to modulate Ras activity.
- Introduced an oncogenic Ha-ras gene to assess its effect on cellular morphology and DNA methylation.
- Performed transient transfection CAT assays to analyze DNA methyltransferase (MeTase) promoter activity.
Main Results:
- Down-modulation of Ras activity using hGAP or dominant-negative Jun reversed the transformed phenotype of Y1 cells.
- Ras inhibition led to decreased DNA methylation levels, DNA methyltransferase (MeTase) mRNA, and enzymatic activity.
- Introduction of oncogenic Ha-ras restored the transformed morphology and increased DNA methylation and MeTase activity.
- Ras and AP-1 were found to regulate the expression of the DNA MeTase promoter.
Conclusions:
- The Ras signaling pathway is a key regulator of DNA methylation in adrenocortical tumor cells.
- These findings establish a direct molecular link between a major tumorigenic signaling pathway and epigenetic modifications like DNA methylation.
- This provides novel insights into the mechanisms of cancer development and potential therapeutic targets.