The bacterial cytolethal distending toxin (CDT) triggers a G2 cell cycle checkpoint in mammalian cells without preliminary induction of DNA strand breaks

Oncogene. 1999 Nov 4;18(46):6296-304. doi: 10.1038/sj.onc.1203007.


The bacterial cytolethal distending toxin (CDT) was previously shown to arrest the tumor-derived HeLa cell line in the G2-phase of the cell cycle through inactivation of CDK1, a cyclin-dependent kinase whose state of activation determines entry into mitosis. We have analysed the effects induced in HeLa cells by CDT, in comparison to those induced by etoposide, a prototype anti-tumoral agent that triggers a G2 cell cycle checkpoint by inducing DNA damage. Both CDT and etoposide inhibit cell proliferation and induces the formation of enlarged mononucleated cells blocked in G2. In both cases, CDK1 from arrested cells could be reactivated both in vitro by dephosphorylation by recombinant Cdc25B phosphatase and in vivo by caffeine. However, the cell cycle arrest triggered by CDT, unlike etoposide, did not originate from DNA strand breaks as demonstrated in the single cell gel electrophoresis assay and by the absence of slowing down of S phase in synchronized cells. Together with additional observations on synchronized HeLa cells, our results suggest that CDT triggers a G2 cell cycle checkpoint that is initiated during DNA replication and that is independent of DNA damage.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents, Phytogenic / pharmacology
  • Bacterial Toxins / pharmacology*
  • CDC2 Protein Kinase / metabolism
  • Caffeine / pharmacology
  • Cell Division / drug effects
  • DNA Damage*
  • DNA Replication / drug effects*
  • DNA, Neoplasm / drug effects
  • Etoposide / pharmacology
  • G2 Phase / drug effects*
  • HeLa Cells / drug effects
  • Humans
  • Neoplasm Proteins / metabolism
  • Phosphorylation / drug effects
  • Protein Processing, Post-Translational / drug effects
  • Recombinant Fusion Proteins / pharmacology
  • S Phase / drug effects
  • cdc25 Phosphatases / pharmacology


  • Antineoplastic Agents, Phytogenic
  • Bacterial Toxins
  • DNA, Neoplasm
  • Neoplasm Proteins
  • Recombinant Fusion Proteins
  • cytolethal distending toxin
  • Caffeine
  • Etoposide
  • CDC2 Protein Kinase
  • cdc25 Phosphatases