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PP2A interaction with Rb2/p130 mediates translocation of Rb2/p130 into the nucleus in all-trans retinoic acid-treated

Enkhtsetseg Purev1, Dianne R Soprano, Kenneth J Soprano

  • 1Department of Microbiology and Immunology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.

Journal of Cellular Physiology
|September 22, 2010
PubMed

Insights

All-trans retinoic acid (ATRA) suppresses ovarian cancer growth by stabilizing Rb2/p130 protein. This involves PP2A phosphatase dephosphorylating Rb2/p130, enabling nuclear transport and cell-cycle arrest.

Area of Science:

  • Molecular Biology
  • Cancer Research
  • Cell Biology

Background:

  • All-trans retinoic acid (ATRA) is known to inhibit the growth of CAOV3 ovarian carcinoma cells.
  • Rb2/p130, a tumor suppressor protein, is implicated in this growth suppression.
  • The precise molecular mechanisms underlying ATRA's effect on Rb2/p130 accumulation require further elucidation.

Purpose of the Study:

  • To investigate the mechanism by which ATRA increases Rb2/p130 protein accumulation in CAOV3 cells.
  • To identify the specific interactions and modifications of Rb2/p130 involved in ATRA-mediated cell-cycle arrest.
  • To explore the role of protein phosphatase 2A (PP2A) in regulating Rb2/p130 stability and function.

Main Methods:

  • Treatment of CAOV3 cells with ATRA.
  • Western blotting to assess protein levels and phosphorylation status.
  • Co-immunoprecipitation to study protein-protein interactions.
  • Site-directed mutagenesis to investigate the role of specific residues.
  • Analysis of protein localization using immunofluorescence.

Main Results:

  • ATRA treatment increases Rb2/p130 protein stability through dephosphorylation mediated by PP2A.
  • PP2A directly interacts with the C-terminus of Rb2/p130, dephosphorylating S1080 and T1097 residues near nuclear localization signals (NLS).
  • Dephosphorylated Rb2/p130 binds to importin α and importin β, facilitating nuclear transport.
  • Mutating S1080 and T1097 prevents nuclear localization of Rb2/p130, causing cytoplasmic retention.

Conclusions:

  • ATRA induces G0/G1 cell-cycle arrest in CAOV3 cells by recruiting PP2A to Rb2/p130.
  • This interaction leads to dephosphorylation of key residues, promoting Rb2/p130 nuclear import via importins.
  • Nuclear Rb2/p130 then inhibits cell-cycle progression, contributing to ATRA's anti-cancer effects.

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