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Evidence that phosphorylation by the mitotic kinase Cdk1 promotes ICER monoubiquitination and nuclear delocalization

Elisabeth Mémin1, Megan Genzale, Marni Crow

  • 1Department of Biochemistry and Molecular Biology, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark, NJ 07103, USA.

Experimental Cell Research
|July 20, 2011
PubMed

Insights

Prostate cancer cells lack the Inducible cAMP Early Repressor (ICER) protein in their nuclei. This study reveals that monoubiquitination of ICER by cdk1 causes its cytosolic localization, explaining its abnormal expression in tumors.

Area of Science:

  • Molecular biology
  • Cellular biology
  • Cancer research

Background:

  • The transcriptional repressor Inducible cAMP Early Repressor (ICER) is absent in prostate cancer cell nuclei, unlike normal cells.
  • The underlying molecular mechanisms for ICER's altered expression in prostate cancer are not well understood.

Purpose of the Study:

  • To elucidate the molecular mechanisms behind the abnormal subcellular localization of ICER in prostate cancer cells.
  • To investigate the post-translational modifications of ICER and their effect on its cellular distribution.

Main Methods:

  • Western blotting to detect ICER phosphorylation and ubiquitination.
  • Immunoprecipitation assays to identify interacting proteins.
  • Confocal microscopy to visualize ICER localization within cells.
  • Site-directed mutagenesis to identify phosphorylation and ubiquitination sites.

Main Results:

  • ICER is phosphorylated by the mitotic kinase cdk1.
  • Phosphorylation of ICER targets it for monoubiquitination.
  • Monoubiquitinated ICER exhibits cytosolic localization, distinct from unphosphorylated, phosphorylated, or polyubiquitinated forms.
  • These findings suggest a mechanism for ICER's abnormal cytosolic localization in human prostate tumors.

Conclusions:

  • CDK1-mediated phosphorylation and subsequent monoubiquitination of ICER lead to its cytosolic mislocalization.
  • This mechanism provides a potential explanation for the absence of nuclear ICER in prostate cancer cells.
  • Targeting this pathway could offer new therapeutic strategies for prostate cancer.

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