DNA-damaging Agents Cause Inactivation of Translational Regulators Linked to mTOR Signalling

Oncogene. 2000 Jun 15;19(26):3021-31. doi: 10.1038/sj.onc.1203622.

Abstract

Treatment of cells with DNA-damaging agents, such as etoposide, can cause growth arrest or apoptosis. Treatment of Swiss 3T3 or RAT-1 cells with etoposide led to the dephosphorylation of both p70 S6 kinase and eukaryotic initiation factor (eIF) 4E-binding protein 1 (4E-BP1), resulting in decreased p70 S6 kinase activity and an increase in 4E-BP1 binding to eIF4E. These effects were not prevented by the general caspase inhibitor, Z-VAD.FMK. These findings indicate caspase-independent inhibition of signalling pathways that involve the mammalian target of rapamycin (mTOR). Similar effects were observed in response to two other DNA-damaging agents, cisplatin and mitomycin-C. These events preceded apoptosis, which was assessed by caspase-3 activity assays and FACS analysis. This shows that inhibition of mTOR signalling is not a consequence of apoptosis, although it may play a role in the events that precede cell death. 4E-BP1 was cleaved during apoptosis yielding a fragment that retained the ability to bind eIF4E. Cleavage of 4E-BP1 was inhibited by treatment of the cells with Z-VAD.FMK, indicating it is caspase-dependent. Insulin elicited full activation of p70 S6 kinase and phosphorylation of 4E-PB1 in etoposide-treated cells prior to the onset of apoptosis, but not during cell death. This suggests that mTOR signalling becomes irreversibly inhibited only after entry into apoptosis. Oncogene (2000).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3T3 Cells
  • Amino Acid Sequence
  • Animals
  • Apoptosis / drug effects
  • Cell Line
  • DNA Damage*
  • Etoposide / pharmacology*
  • Mice
  • Molecular Sequence Data
  • Mutagens / pharmacology*
  • Phosphotransferases (Alcohol Group Acceptor) / metabolism*
  • Protein Biosynthesis / drug effects*
  • Protein Kinases*
  • Protein Synthesis Inhibitors / pharmacology
  • Rats
  • Signal Transduction / drug effects*
  • TOR Serine-Threonine Kinases

Substances

  • Mutagens
  • Protein Synthesis Inhibitors
  • Etoposide
  • Protein Kinases
  • Phosphotransferases (Alcohol Group Acceptor)
  • TOR Serine-Threonine Kinases
  • mTOR protein, mouse
  • mTOR protein, rat