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Fbxw5 suppresses nuclear c-Myb activity via DDB1-Cul4-Rbx1 ligase-mediated sumoylation

Chie Kanei-Ishii1, Teruaki Nomura, Ayako Egoh

  • 1Laboratory of Molecular Genetics, RIKEN Tsukuba Institute, 3-1-1 Koyadai, Tsukuba, Ibaraki 305-0074, Japan.

Biochemical and Biophysical Research Communications
|August 23, 2012
PubMed

Insights

Fbxw5 enhances sumoylation of nuclear c-Myb, a process that suppresses its activity. This suggests E3 ligases regulate c-Myb through sumoylation and ubiquitination.

Area of Science:

  • Molecular Biology
  • Cellular Biology
  • Oncogenesis

Background:

  • The c-myb proto-oncogene product (c-Myb) is a transcription factor regulated by post-translational modifications.
  • Wnt-1 signaling leads to c-Myb degradation via ubiquitination mediated by Fbxw7α and the SCF complex.

Purpose of the Study:

  • To investigate the role of Fbxw5 in the regulation of c-Myb.
  • To determine if Fbxw5 influences c-Myb sumoylation and cellular localization.

Main Methods:

  • Co-immunoprecipitation assays to assess protein interactions.
  • Western blotting to detect ubiquitination and sumoylation.
  • Reporter assays to measure promoter trans-activation.
  • Confocal microscopy to observe protein localization.

Main Results:

  • Fbxw5 enhances the sumoylation of nuclear c-Myb through the DDB1-Cul4A-Rbx1 complex.
  • The Fbxw5-DDB1-Cul4A-Rbx1 complex exhibits dual SUMO/ubiquitin ligase activity.
  • Fbxw5 promotes the localization of c-Myb to nuclear dot-like domains.
  • Fbxw5 suppresses the trans-activation activity of wild-type c-Myb but not sumoylation-deficient v-Myb.

Conclusions:

  • Fbxw5 acts as a negative regulator of c-Myb activity via sumoylation.
  • Multiple E3 ligases, including Fbxw5, control c-Myb function through sumoylation and ubiquitination.
  • The viral Myb oncoprotein (v-Myb) evades these regulatory mechanisms.

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