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Characterization of PTEN mutations in brain cancer reveals that pten mono-ubiquitination promotes protein stability

Jr-M Yang1, P Schiapparelli2,3, H-N Nguyen1

  • 1Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD, USA.

Oncogene
|March 7, 2017
PubMed

Insights

Mutations in the PTEN tumor suppressor can disrupt its cellular localization and stability without affecting its enzymatic activity, offering new therapeutic targets for brain cancers like glioblastoma.

Area of Science:

  • Oncology
  • Molecular Biology
  • Biochemistry

Background:

  • PTEN (Phosphatase and tensin homolog) is a crucial tumor suppressor that counteracts PI3K/AKT signaling.
  • PTEN mutations are frequent in cancers, particularly glioblastoma, often leading to loss of function.
  • Current understanding suggests PTEN deficiency stems mainly from reduced expression or enzymatic inactivity.

Purpose of the Study:

  • To investigate novel mechanisms of PTEN dysfunction in glioblastoma beyond loss of expression or enzymatic activity.
  • To identify specific PTEN mutations affecting its localization and stability.
  • To explore therapeutic strategies targeting PTEN regulation in brain tumors.

Main Methods:

  • Analysis of PTEN in primary malignant glioblastoma cells from 16 patients.
  • Cellular and biochemical assays to assess PTEN localization, lipid phosphatase activity, and ubiquitination.
  • Structural modeling to understand the impact of mutations on PTEN conformation.
  • Investigation of the effects of mono-ubiquitination on mutant PTEN stability and localization.

Main Results:

  • Identified PTEN mutations in glioblastoma that impair plasma membrane and nuclear localization without altering lipid phosphatase activity.
  • Demonstrated that two specific mutations disrupt intramolecular PTEN interactions, leading to an open conformation.
  • Observed that these mutations enhance PTEN polyubiquitination and decrease protein stability.
  • Found that promoting PTEN mono-ubiquitination enhances the stability and nuclear localization of mutant PTEN.

Conclusions:

  • Discovered a molecular mechanism for cancer-associated PTEN defects involving impaired localization and stability.
  • Established that PTEN mutations can disrupt its conformation and increase susceptibility to degradation.
  • Proposed that targeting PTEN mono-ubiquitination represents a potential therapeutic avenue for brain cancers.

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