Mislocalization of the E3 Ligase, beta-Transducin Repeat-containing Protein 1 (beta-TrCP1), in Glioblastoma Uncouples Negative Feedback between the Pleckstrin Homology Domain Leucine-rich Repeat Protein Phosphatase 1 (PHLPP1) and Akt

Noel A. Warfel, Matt Niederst, Michael W. Stevens, Paul M. Brennan, Margaret C. Frame, Alexandra C. Newton*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

The PH domain leucine-rich repeat protein phosphatase, PHLPP, plays a central role in controlling the amplitude of growth factor signaling by directly dephosphorylating and thereby inactivating Akt. The cellular levels of PHLPP1 have recently been shown to be enhanced by its substrate, activated Akt, via modulation of a phosphodegron recognized by the E3 ligase beta-TrCP1, thus providing a negative feedback loop to tightly control cellular Akt output. Here we show that this feedback loop is lost in aggressive glioblastoma but not less aggressive astrocytoma. Overexpression and pharmacological studies reveal that loss of the feedback loop does not result from a defect in PHLPP1 protein or in the upstream kinases that control its phosphodegron. Rather, the defect arises from altered localization of beta-TrCP1; in astrocytoma cell lines and in normal brain tissue the E3 ligase is predominantly cytoplasmic, whereas in glioblastoma cell lines and patient-derived tumor neurospheres, the E3 ligase is confined to the nucleus and thus spatially separated from PHLPP1, which is cytoplasmic. Restoring the localization of beta-TrCP1 to the cytosol of glioblastoma cells rescues the ability of Akt to regulate PHLPP1 stability. Additionally, we show that the degradation of another beta-TrCP1 substrate, beta-catenin, is impaired and accumulates in the cytosol of glioblastoma cell lines. Our findings reveal that the cellular localization of beta-TrCP1 is altered in glioblastoma, resulting in dysregulation of PHLPP1 and other substrates such as beta-catenin.

Original languageEnglish
Pages (from-to)19777-19788
Number of pages12
JournalJournal of Biological Chemistry
Volume286
Issue number22
DOIs
Publication statusPublished - 3 Jun 2011

Keywords

  • beta-Transducin Repeat-Containing Proteins
  • Ubiquitin-Protein Ligases
  • Glioblastoma
  • Active Transport, Cell Nucleus
  • Nuclear Proteins
  • Humans
  • Enzyme Stability
  • beta Catenin
  • Proto-Oncogene Proteins c-akt
  • Cell Line, Tumor
  • Cell Nucleus
  • Phosphoprotein Phosphatases

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