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Suppression of Egr-1 transcription through targeting of the serum response factor by oncogenic H-Ras

Soon Young Shin1, Young Yil Bahk, Jesang Ko

  • 1Division of Molecular & Life Science, College of Science & Technology, Hanyang University, Ansan, Korea.

The EMBO Journal
|February 4, 2006
PubMed

Insights

Oncogenic H-Ras suppresses the tumor suppressor Egr-1 by activating PI3K signaling, which degrades SRF protein. Inhibiting PI3K restores Egr-1 expression, revealing a novel mechanism in NIH3T3 fibroblasts.

Area of Science:

  • Molecular biology
  • Cellular signaling
  • Cancer research

Background:

  • Early growth response gene 1 (Egr-1) is a crucial regulator of cell growth, differentiation, and apoptosis.
  • Loss of Egr-1 expression is linked to tumor development, but the underlying mechanisms remain unclear.
  • Oncogenic H-Ras is frequently implicated in cancer progression.

Purpose of the Study:

  • To investigate the molecular mechanism by which oncogenic H-Ras suppresses Egr-1 expression.
  • To elucidate the role of phosphoinositide 3-kinase (PI3K) signaling in this process.
  • To identify potential therapeutic targets for restoring Egr-1 function in Ras-driven cancers.

Main Methods:

  • Utilized NIH3T3 fibroblast cell lines expressing oncogenic H-Ras.
  • Investigated the impact of oncogenic H-Ras on Egr-1 gene expression and promoter activity.
  • Assessed the role of PI3K signaling using specific inhibitors.
  • Analyzed the levels and binding activity of serum response factor (SRF) protein.

Main Results:

  • Chronic expression of oncogenic H-Ras downregulated growth factor-induced Egr-1 transcription in NIH3T3 cells.
  • PI3K signaling was essential for oncogenic H-Ras-mediated Egr-1 suppression.
  • Aberrant PI3K activation accelerated proteolysis of SRF protein, reducing its binding to the Egr-1 promoter's serum response element (SRE).
  • Inhibition of PI3K signaling restored SRF and Egr-1 levels.

Conclusions:

  • Prolonged activation of oncogenic H-Ras suppresses the tumor suppressor Egr-1 via the PI3K pathway.
  • This suppression occurs through accelerated proteolysis of SRF, leading to reduced Egr-1 transcription.
  • Targeting the PI3K pathway may offer a strategy to counteract Egr-1 loss in Ras-driven cancers.

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