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DNA-damaging agents cause inactivation of translational regulators linked to mTOR signalling

A R Tee1, C G Proud

  • 1Department of Anatomy & Physiology, Medical Sciences Institute/Wellcome Trust Building Complex, University of Dundee, Dow Street, Dundee, DD1 5EH, UK.

Oncogene
|June 29, 2000
PubMed

Insights

DNA-damaging agents inhibit the mammalian target of rapamycin (mTOR) signaling pathway independently of caspases. This inhibition occurs before apoptosis and is reversible until cells enter cell death.

Area of Science:

  • Cellular biology
  • Molecular oncology
  • Biochemistry

Background:

  • DNA-damaging agents like etoposide induce cell cycle arrest or apoptosis.
  • The mammalian target of rapamycin (mTOR) pathway regulates cell growth and survival.
  • Understanding the interplay between DNA damage response and mTOR signaling is crucial for cancer therapy.

Purpose of the Study:

  • To investigate the effect of DNA-damaging agents on mTOR signaling.
  • To determine whether mTOR inhibition is caspase-dependent or independent.
  • To elucidate the timing of mTOR inhibition relative to apoptosis.

Main Methods:

  • Treatment of Swiss 3T3 and RAT-1 cells with etoposide, cisplatin, and mitomycin-C.
  • Analysis of p70 S6 kinase and eukaryotic initiation factor (eIF) 4E-binding protein 1 (4E-BP1) phosphorylation status.
  • Assessment of apoptosis using caspase-3 activity assays and FACS analysis.
  • Inhibition studies using the general caspase inhibitor Z-VAD.FMK.

Main Results:

  • Etoposide treatment led to dephosphorylation of p70 S6 kinase and 4E-BP1 in a caspase-independent manner.
  • mTOR signaling inhibition preceded apoptosis and was observed with other DNA-damaging agents.
  • 4E-BP1 cleavage during apoptosis was caspase-dependent.
  • Insulin could activate mTOR signaling prior to apoptosis but not during cell death.

Conclusions:

  • DNA-damaging agents trigger caspase-independent inhibition of mTOR signaling.
  • mTOR pathway inhibition is an early event in the response to DNA damage, preceding apoptosis.
  • Irreversible mTOR inhibition occurs upon entry into apoptosis, suggesting a role in cell death commitment.

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