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Early response to ErbB2 over-expression in polarized Caco-2 cells involves partial segregation from ErbB3 by

Amber B Pfister1, Robert C Wood, Pedro J I Salas

  • 1Department of Pharmaceutical Sciences, Bill Gatton College of Pharmacy, East Tennessee State University, Johnson City, Tennessee 37614, USA.

Journal of Cellular Biochemistry
|July 1, 2010
PubMed

Insights

Over-expressing ErbB2 (Epidermal Growth Factor Receptor 2) in polarized cells relocates it to the apical surface, activating a survival pathway via Bcl-2, not the canonical Erk pathway. This apical ErbB2 signaling is blocked by Herceptin.

Area of Science:

  • Molecular Cell Biology
  • Cancer Research
  • Epithelial Biology

Background:

  • ErbB2 (Epidermal Growth Factor Receptor 2) over-expression in cancers drives signaling, promoting cell survival, proliferation, and metastasis.
  • Polarized epithelial cells (Caco-2, MDCK) are models for studying molecular trafficking and receptor localization.
  • Normally, ErbB2 and ErbB3 share basolateral localization in these cells without over-expression.

Purpose of the Study:

  • To investigate the impact of ErbB2 over-expression on its localization and signaling pathways in polarized Caco-2 and MDCK cells.
  • To determine if ErbB2 relocalization affects downstream signaling cascades.
  • To assess the role of subcellular localization in regulating ErbB2 activity in polarized epithelia.

Main Methods:

  • Transient transfection to over-express ErbB2 in Caco-2 and MDCK cells.
  • Biotinylation of apical and basolateral surfaces to track receptor localization.
  • Immunofluorescence and confocal microscopy for visualizing receptor distribution.
  • Immunoprecipitation to confirm protein-protein interactions (phosphotyrosine binding Grb2).
  • Treatment with anti-ErbB2 monoclonal antibody Herceptin.

Main Results:

  • ErbB2 over-expression caused ErbB2, but not ErbB3, to relocalize to the apical surface, without disrupting cell polarity.
  • Apical ErbB2, but not basolateral ErbB2, was activated at tyrosine 1139, binding to Grb2.
  • This interaction initiated a survival pathway via Bcl-2, bypassing the canonical Grb2-Ras-Raf-Erk pathway.
  • Herceptin, applied apically, abrogated the effects of over-expressed ErbB2.

Conclusions:

  • Subcellular localization of ErbB2 is critical for regulating its signaling in polarized epithelia.
  • Apical ErbB2 over-expression activates a distinct downstream cascade involving Bcl-2, promoting cell survival.
  • Targeting apical ErbB2 with antibodies like Herceptin can inhibit its oncogenic signaling.

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