DNA-damaging agents cause inactivation of translational regulators linked to mTOR signalling.
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).
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Department of Anatomy & Physiology, Medical Sciences Institute/Wellcome Trust Building Complex, University of Dundee, Dow Street, Dundee, DD1 5EH, UK.
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D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002460:Cell Line; D004249:DNA Damage; D005047:Etoposide / Q000494:pharmacology*; D051379:Mice; D008969:Molecular Sequence Data; D009153:Mutagens / Q000494:pharmacology*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D014176:Protein Biosynthesis / Q000187:drug effects*; D011494:Protein Kinases; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects*; D058570:TOR Serine-Threonine Kinases
D009153:Mutagens; D011500:Protein Synthesis Inhibitors; D005047:Etoposide; D011494:Protein Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); C546843:mTOR protein, mouse; C546845:mTOR protein, rat; D058570:TOR Serine-Threonine Kinases