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Yeast As a Chassis for Developing Functional Assays to Study Human P53

Published on: August 4, 2019

Activation of p53-dependent growth suppression in human cells by mutations in PTEN or PIK3CA

Jung-Sik Kim1, Carolyn Lee, Challice L Bonifant

  • 1Lombardi Comprehensive Cancer Center, Georgetown University School of Medicine, 3970 Reservoir Road NW, NRB E304, Washington, DC 20057, USA.

Molecular and Cellular Biology
|October 25, 2006
PubMed

Insights

Activating PI3K signaling through PTEN or PIK3CA mutations upregulates p53, a tumor suppressor. This p53 activation halts cell growth, acting as a brake against cancer development driven by PI3K pathway overactivation.

Area of Science:

  • Molecular Biology
  • Cancer Research
  • Cell Signaling

Background:

  • Phosphatidylinositol 3-kinase (PI3K) signaling is frequently dysregulated in human cancers.
  • PTEN and PIK3CA are key regulators of the PI3K pathway, with mutations often leading to pathway activation.
  • The tumor suppressor p53 plays a critical role in cell cycle control and tumor suppression.

Purpose of the Study:

  • To identify genes regulated by activated PI3K signaling.
  • To investigate the role of p53 in mediating the cellular response to PI3K pathway activation.
  • To determine if PI3K pathway activation by PTEN loss or PIK3CA mutation leads to p53 activation and subsequent growth suppression.

Main Methods:

  • Microarray analysis and quantitative reverse transcription-PCR in PTEN-deficient human cancer cells.
  • Gene depletion studies using stable shRNA to assess the role of p53.
  • Western blot analysis to examine protein stabilization.
  • Retroviral expression of oncogenic PIK3CA and targeted gene deletion in human cell lines.

Main Results:

  • PTEN deletion upregulated numerous p53 effectors, including p21, GDF15, PIG3, NOXA, and PLK2.
  • p53 stabilization was observed in PTEN-deficient cells via an Akt1-dependent mechanism.
  • PTEN depletion in normal cells induced p53 upregulation and senescence, which was rescued by p53 depletion.
  • Oncogenic PIK3CA activated p53, upregulated p53 targets, and synergized with p53 depletion to promote anchorage-independent growth.
  • Targeted deletion of oncogenic PIK3CA reduced p53 levels and p53-regulated gene expression.

Conclusions:

  • Activation of PI3K signaling by PTEN loss or PIK3CA mutations leads to p53 activation in human cells.
  • p53 acts as a critical mediator of growth suppression in response to PI3K pathway hyperactivation.
  • p53 functions as a tumor suppressor by inhibiting proliferation driven by oncogenic PI3K signaling.

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