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Identification of Cyclin-dependent Kinase 1 Specific Phosphorylation Sites by an In Vitro Kinase Assay
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Calcineurin-mediated dephosphorylation of c-Jun Ser-243 is required for c-Jun protein stability and cell

C-C Huang1, J-M Wang, U Kikkawa

  • 1Department of Pharmacology, College of Medicine, Tainan, Taiwan.

Oncogene
|October 24, 2007
PubMed

Insights

Calcineurin (CaN) stabilizes the proto-oncogene c-Jun by dephosphorylating it at Ser-243, increasing c-Jun’s role in tumor progression. This interaction is enhanced in cervical cancer tissues, suggesting CaN as a therapeutic target.

Area of Science:

  • Oncology
  • Molecular Biology
  • Biochemistry

Background:

  • The proto-oncogene c-Jun is crucial for tumor progression.
  • Calcineurin (CaN), a serine/threonine phosphatase, dephosphorylates c-Jun at Ser-243, enhancing c-Jun and Sp1 interaction and gene expression.

Purpose of the Study:

  • To investigate the interaction between c-Jun and CaN in living cells.
  • To elucidate the role of CaN-mediated dephosphorylation of c-Jun at Ser-243 in regulating c-Jun protein stability and tumorigenic potential.

Main Methods:

  • Fluorescence resonance energy transfer (FRET) assay to detect c-Jun and CaN interaction in living cells.
  • Analysis of c-Jun protein stability using wild-type and Ser-243 mutant (c-Jun-S243A).
  • Assessment of c-Jun ubiquitination and stability upon silencing of endogenous CaN expression.
  • Analysis of c-Jun, CaN, and phospho-Ser-243 expression in clinical cervical cancer tissue samples.

Main Results:

  • c-Jun and CaN interact in the nucleus, mediated by CaN's calmodulin-binding domain.
  • CaN-mediated dephosphorylation at c-Jun Ser-243 increases c-Jun protein stability; c-Jun-S243A mutant shows longer half-life than wild-type c-Jun.
  • Silencing CaN increases c-Jun ubiquitination and decreases its stability.
  • Enhanced c-Jun and CaN expression, with decreased phospho-Ser-243, observed in 46% of cervical cancer tissues.

Conclusions:

  • CaN stabilizes c-Jun by dephosphorylating it at Ser-243.
  • This stabilization enhances c-Jun's tumorigenic ability.
  • The c-Jun/CaN pathway is dysregulated in cervical cancer, highlighting its potential as a therapeutic target.

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