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Analysis of the transcriptional program induced by Raf in epithelial cells
A Schulze1, K Lehmann, H B Jefferies
1Signal Transduction Laboratory, Imperial Cancer Research Fund, London WC2A 3PX, UK.
Abstract:
Activation of the Raf/MAP kinase pathway is a critical event in tumorigenesis induced by RAS and other oncogenes, a major role of this signaling system being the regulation of cellular transcription factors. To address the contribution of MAP kinase mediated transcriptional changes to the transformed phenotype, we used an inducible form of Raf to analyze early changes in the transcription of some 6000 genes following activation of the kinase in a normal human breast epithelial cell line. Of the more than 120 significant changes in mRNA level detected, genes promoting cell proliferation, invasiveness, and angiogenesis featured prominently. Some of the most strongly induced genes encoded growth factors of the EGF family: Autocrine activation of the EGF receptor was shown to be responsible for the ability of Raf activation to protect these cells from apoptosis induced by detachment of cells from extracellular matrix (anoikis), which is a critical component of the transformed phenotype.
Insights
Activating the Raf/MAP kinase pathway drives cancer by altering gene transcription. This pathway promotes cell proliferation, invasion, and angiogenesis, and protects cells from anoikis (detachment-induced apoptosis).
Area of Science:
- Molecular Biology
- Cellular Signaling
- Oncology
Background:
- The Raf/MAP kinase pathway is crucial in tumorigenesis, particularly in RAS-driven cancers.
- This pathway regulates cellular transcription factors, influencing cell behavior and phenotype.
- Understanding MAP kinase-mediated transcriptional changes is key to understanding oncogenesis.
Purpose of the Study:
- To investigate the contribution of MAP kinase-mediated transcriptional changes to the transformed phenotype.
- To analyze early transcriptional alterations following Raf activation in human breast epithelial cells.
Main Methods:
- Utilized an inducible form of Raf to activate the pathway.
- Analyzed changes in mRNA levels of approximately 6000 genes.
- Investigated the role of Epidermal Growth Factor (EGF) family growth factors and EGF receptor signaling.
Main Results:
- Over 120 significant mRNA level changes were detected upon Raf activation.
- Genes involved in cell proliferation, invasiveness, and angiogenesis were prominently upregulated.
- Autocrine activation of the EGF receptor mediated resistance to anoikis.
Conclusions:
- MAP kinase pathway activation profoundly alters cellular transcription, promoting key aspects of the transformed phenotype.
- Upregulation of EGF family genes and subsequent EGF receptor activation contribute to anoikis resistance.
- Targeting the Raf/MAP kinase pathway and its downstream effectors holds therapeutic potential in cancer treatment.