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Identification of Cyclin-dependent Kinase 1 Specific Phosphorylation Sites by an In Vitro Kinase Assay
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Stabilization of Mdm2 via decreased ubiquitination is mediated by protein kinase B/Akt-dependent phosphorylation

Jianhua Feng1, Rastislav Tamaskovic, Zhongzhou Yang

  • 1Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, Basel CH-4058, Switzerland.

The Journal of Biological Chemistry
|June 1, 2004
PubMed

Insights

Protein kinase B (PKB) controls the stability of Mdm2, a protein that regulates p53. PKB phosphorylates Mdm2, preventing its degradation and influencing the p53 signaling pathway in cancer cells.

Area of Science:

  • Molecular Biology
  • Cellular Signaling
  • Cancer Research

Background:

  • The tumor suppressor p53 is often inactivated when the phosphatidylinositide 3'-OH kinase/protein kinase B (PKB)Akt pathway is active.
  • Mdm2, an E3 ubiquitin ligase, regulates intracellular p53 levels.

Purpose of the Study:

  • To investigate the role of PKB in regulating Mdm2 stability and its impact on the p53 signaling pathway.
  • To elucidate the mechanism by which PKB affects Mdm2.

Main Methods:

  • Investigated Mdm2 self-ubiquitination and phosphorylation in response to PKB activation.
  • Utilized human embryonic kidney 293 and COS-1 cells, as well as PKBalpha-deficient mouse embryonic fibroblasts.
  • Assessed Mdm2 degradation, p53 and p21(Cip1) levels, and apoptosis induction after UV irradiation.

Main Results:

  • PKB phosphorylates Mdm2 on Ser(166) and Ser(188), inhibiting its self-ubiquitination and degradation.
  • PKB activation stabilizes Mdm2 protein levels, while its inhibition leads to Mdm2 proteasomal degradation.
  • PKBalpha deficiency in mouse embryonic fibroblasts resulted in increased p53 and p21(Cip1), leading to elevated apoptosis.
  • PKB activation correlated with Mdm2 phosphorylation and stability in human tumor cells.

Conclusions:

  • PKB plays a crucial role in regulating the Mdm2-p53 signaling pathway by controlling Mdm2 stability.
  • PKB-mediated phosphorylation of Mdm2 is a key mechanism for stabilizing Mdm2 and influencing p53 tumor suppressor activity.
  • Targeting the PKB-Mdm2 interaction could offer therapeutic strategies for cancers with activated PKB/Akt signaling.

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