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A nucleolar isoform of the Fbw7 ubiquitin ligase regulates c-Myc and cell size

Markus Welcker1, Amir Orian, Jonathan E Grim

  • 1Divisions of Clinical Research, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA.

Current Biology : CB
|October 23, 2004
PubMed

Insights

The Fbw7 tumor suppressor targets proteins like cyclin E and c-Myc for degradation. Fbw7 loss disrupts cell growth and division, potentially driving cancer by increasing c-Myc levels, especially in the nucleolus.

Area of Science:

  • Cell Biology
  • Molecular Oncology
  • Tumor Suppression

Background:

  • Fbw7 (also known as hCdc4) is a crucial tumor suppressor.
  • It acts as a substrate recognition component for SCF ubiquitin ligases.
  • Fbw7 targets key proteins like cyclin E, Notch, c-Jun, and c-Myc for ubiquitination and degradation.

Purpose of the Study:

  • To investigate the role of Fbw7 isoforms in cellular processes.
  • To understand the subcellular localization and function of Fbw7 isoforms.
  • To elucidate the impact of Fbw7 loss on c-Myc regulation and cell growth.

Main Methods:

  • Analysis of Fbw7 protein isoforms (Fbw7alpha, Fbw7beta, Fbw7gamma).
  • Determination of subcellular localization signals for each isoform.
  • Investigation of Fbw7gamma's interaction with c-Myc in the nucleolus.
  • Cell size measurements following Fbw7 knockdown.

Main Results:

  • Fbw7 isoforms (alpha, beta, gamma) localize to distinct subcellular compartments.
  • Fbw7gamma is found in the nucleolus and regulates nucleolar c-Myc accumulation.
  • Fbw7 knockdown leads to increased cell size, linked to nucleolar c-Myc levels.
  • Fbw7 loss in cancer may promote oncogenesis via dysregulated c-Myc.

Conclusions:

  • The nucleolar Fbw7gamma isoform plays a specific role in regulating c-Myc.
  • Interactions between Fbw7gamma and c-Myc in the nucleolus control cell growth.
  • Fbw7 inactivation in cancer can lead to c-Myc activation and uncontrolled cell proliferation.

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