Mammalian S-phase checkpoint integrity is dependent on transformation status and purine deoxyribonucleosides

C. Stephen Downes, Csanád Z. Bachrati, S. Jayne Devlin, Massimo Tommasino, Timothy J.R. Cutts, James V. Watson, István Raskó, Robert T. Johnson

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In eukaryotic cells arrested in S-phase, checkpoint controls normally restrain mitosis until after replication. We have identified an array of previously unsuspected factors that modulate this restraint, using transformed hamster cells in which cycle controls are known to be altered in S-phase arrest. Arrested cells accumulate cyclin B, the regulatory partner of the mitotic p34(cdc2) kinase, which is normally not abundant until late G2 phase; treatment of arrested cells with caffeine produces rapid S-phase condensation. We show here that such S-phase checkpoint slippage, as visualised through caffeine-dependent S-phase condensation, correlates with rodent origin and transformed status, is opposed by reverse transformation, and is favoured by c-src and opposed by wnt1 overexpression. Slippage is also dependent on a prolonged replicative arrest, and is favoured by arrest with hydroxyurea, which inhibits ribonucleotide reductase, This last is a key enzyme in deoxyribonucleotide synthesis, recently identified as a determinant of malignancy. Addition of deoxyribonucleosides shows that rapid S-phase condensation is suppressed by a novel checkpoint mechanism: purine (but not pyrimidine) deoxyribonucleosides, like reverse transformation, suppress cyclin B/p34(cdc2) activation by caffeine, but not cyclin B accumulation. Thus, ribonucleotide reductase has an unexpectedly complex role in mammalian cell cycle regulation: not only is it regulated in response to cycle progression, but its products can also reciprocally influence cell cycle control kinase activation.

Original languageEnglish
Pages (from-to)1089-1096
Number of pages8
JournalJournal of cell science
Issue number6
Publication statusPublished - Apr 12 2000



  • Caffeine
  • Cell cycle checkpoint
  • Premature mitosis
  • Ribonucleotide reductase

ASJC Scopus subject areas

  • Cell Biology

Cite this

Downes, C. S., Bachrati, C. Z., Devlin, S. J., Tommasino, M., Cutts, T. J. R., Watson, J. V., Raskó, I., & Johnson, R. T. (2000). Mammalian S-phase checkpoint integrity is dependent on transformation status and purine deoxyribonucleosides. Journal of cell science, 113(6), 1089-1096.