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Regulatory effects of a Mnk2-eIF4E feedback loop during mTORC1 targeting of human medulloblastoma cells

Frank Eckerdt1, Elspeth Beauchamp2, Jonathan Bell1

  • 1Robert H. Lurie Comprehensive Cancer Center and Division of Hematology- Oncology, Feinberg School of Medicine, Northwestern University, Chicago, IL,USA.

Oncotarget
|September 7, 2014
PubMed

Insights

mTOR inhibitor resistance in medulloblastoma involves a Mnk2-mediated feedback loop. Targeting this loop sensitizes cells to mTOR inhibitors, suggesting combination therapies for improved treatment.

Area of Science:

  • Oncology
  • Molecular Biology
  • Cellular Metabolism

Background:

  • The mechanistic target of rapamycin (mTOR) pathway regulates cell metabolism and proliferation, making it a key target in cancer therapy.
  • Resistance to mTOR inhibitors is a significant challenge in treating malignant cells, including medulloblastoma.
  • The precise mechanisms underlying mTOR inhibitor resistance are not fully elucidated.

Purpose of the Study:

  • To investigate the mechanisms of resistance to mTOR inhibitors in medulloblastoma cells.
  • To identify potential therapeutic strategies to overcome this resistance.
  • To explore the role of feedback regulatory loops in medulloblastoma cell survival.

Main Methods:

  • Utilized rapamycin to inhibit mTORC1 in medulloblastoma cells.
  • Investigated the phosphorylation of eukaryotic translation-initiation factor 4E (eIF4E).
  • Assessed the role of Mnk1 and Mnk2 kinases in the feedback loop using pharmacological inhibitors and siRNA.
  • Evaluated the effects of combined mTOR and Mnk inhibition on cell proliferation and anchorage-independent growth.

Main Results:

  • mTORC1 inhibition by rapamycin activates a negative feedback loop involving Mnk2-mediated eIF4E phosphorylation in medulloblastoma cells.
  • This eIF4E phosphorylation acts as a survival mechanism, contributing to resistance against mTOR inhibitors.
  • Targeting Mnk1/2 or specifically knocking down Mnk2 sensitizes medulloblastoma cells to mTOR inhibition.
  • Combination treatment suppressed malignant cell proliferation and anchorage-independent growth.

Conclusions:

  • A Mnk2-dependent feedback loop contributes to medulloblastoma resistance to mTOR inhibitors.
  • Pharmacological targeting of Mnk1/2 kinases can overcome resistance to mTOR inhibitors.
  • Combination therapy with mTOR and Mnk inhibitors holds promise for medulloblastoma treatment.

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