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Studying TGF-β Signaling and TGF-β-induced Epithelial-to-mesenchymal Transition in Breast Cancer and Normal Cells
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Ligand release-independent transactivation of epidermal growth factor receptor by transforming growth factor-beta

C-K Joo1, H-S Kim, J-Y Park

  • 1Laboratory of Visual Science, Korea Eye Tissue and Gene Bank, College of Medicine, The Catholic University of Korea, Seoul, Korea.

Oncogene
|July 20, 2007
PubMed

Insights

Transforming growth factor-beta (TGF-beta) activates epidermal growth factor receptor (EGFR) independently of Smad proteins. This novel pathway involves Src family kinases, reactive oxygen species, and E-cadherin, diversifying TGF-beta signaling.

Area of Science:

  • Cellular signaling pathways
  • Molecular biology
  • Cancer research

Background:

  • Transforming growth factor-beta (TGF-beta) elicits diverse cellular responses.
  • While Smad proteins mediate many TGF-beta signals, non-Smad pathways are increasingly recognized.
  • Understanding alternative TGF-beta signaling mechanisms is crucial for deciphering complex cellular processes.

Purpose of the Study:

  • To investigate the non-Smad signaling pathways activated by TGF-beta1.
  • To determine the role of epidermal growth factor receptor (EGFR) transactivation in TGF-beta1 signaling.
  • To elucidate the upstream regulators and downstream effectors of EGFR transactivation by TGF-beta1.

Main Methods:

  • Immunoprecipitation and immunofluorescence staining to detect EGFR phosphorylation.
  • Cell-based assays to assess the roles of Src family kinases (SFKs), reactive oxygen species (ROS), and E-cadherin.
  • Gene expression analysis of c-Fos and c-Jun.
  • Stable cell line transfection and blocking assays.

Main Results:

  • TGF-beta1 induces EGFR transactivation, evidenced by tyrosine phosphorylation.
  • EGFR transactivation is dependent on SFKs and ROS generation via NADPH oxidase, but not metalloproteases or EGF-like ligand release.
  • ROS production requires SFK signaling and de novo protein synthesis.
  • E-cadherin-mediated cell-cell interactions are essential for EGFR transactivation.
  • EGFR transactivation regulates c-Fos and c-Jun expression through the extracellular signal-regulated kinase (ERK) pathway.

Conclusions:

  • TGF-beta1 can activate EGFR independently of Smad proteins and ligand release.
  • This non-Smad pathway, involving SFKs, ROS, and E-cadherin, diversifies TGF-beta signaling.
  • EGFR transactivation represents a novel mechanism for TGF-beta-mediated gene expression, potentially impacting cellular behavior and disease.

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