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Annexin A6 inhibits Ras signalling in breast cancer cells

S Vilá de Muga1, P Timpson, L Cubells

  • 1Departament de Biologia Cellular, Facultat de Medicina, Universitat de Barcelona, Barcelona, Spain.

Oncogene
|October 14, 2008
PubMed

Insights

Annexin A6 (AnxA6) downregulation in breast cancer impacts Ras signaling. AnxA6 re-expression in EGFR-overexpressing cells restores p120GAP function, inhibiting Ras/MAPK activity and proliferation.

Area of Science:

  • Molecular Biology
  • Cancer Research
  • Cell Signaling

Background:

  • Epidermal growth factor receptor (EGFR) overexpression drives Ras activation in breast cancer.
  • Regulation of Ras inactivation by GTPase-activating proteins (GAPs) like p120GAP is poorly understood in hyperactive Ras contexts.
  • Annexin A6 (AnxA6) has been implicated in modulating Ras signaling.

Purpose of the Study:

  • To investigate the role of AnxA6 in the regulation of Ras signaling in EGFR-overexpressing and estrogen receptor (ER)-negative breast cancer cells.
  • To determine if AnxA6 influences the membrane recruitment and function of p120GAP.
  • To explore the therapeutic potential of targeting the AnxA6-p120GAP-Ras axis.

Main Methods:

  • Cell culture of EGFR-overexpressing and ER-negative breast cancer lines (e.g., MDA-MB-436).
  • Ectopic expression and knockdown of AnxA6 and p120GAP.
  • Analysis of Ras/MAPK pathway activity, cell proliferation assays (anchorage-independent growth).
  • Co-immunoprecipitation and Fluorescence Resonance Energy Transfer (FRET) microscopy to study protein interactions and localization.

Main Results:

  • AnxA6 is downregulated in several EGFR-overexpressing, ER-negative breast cancer cells.
  • AnxA6 overexpression promotes calcium- and EGF-inducible membrane targeting of p120GAP.
  • Overexpression of p120GAP, but not a mutant lacking the AnxA6-binding domain, inhibits Ras/MAPK activity in MDA-MB-436 cells.
  • AnxA6 knockdown increases Ras activity and anchorage-independent cell proliferation.
  • AnxA6 interacts with H-Ras in a calcium- and EGF-inducible manner and localizes near active H-Ras.

Conclusions:

  • AnxA6 plays a crucial role in regulating p120GAP-mediated Ras inactivation in EGFR-overexpressing, ER-negative breast cancer.
  • AnxA6 association with H-Ras complexes may facilitate p120GAP recruitment and function.
  • Restoring AnxA6 levels could be a potential therapeutic strategy for specific breast cancer subtypes.

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