The cytolethal distending toxin from the chancroid bacterium Haemophilus ducreyi induces cell-cycle arrest in the G2 phase

The patent cyolethal distending toxin produced by Haemophilus ducreyi is a putative virulence factor in the pathogenesis of chancroid. We studied its action on eukaryotic cells, with the long-term goal of understanding the pa thophysiology of the disease. Intoxication of cultured human epithelial-lik e cells, human keratinocytes, and hamster fibroblasts was irreversible, and appeared as a gradual distention of three- to fivefold the size of control cells. Organized actin assemblies appeared concomitantly with cell enlarge ment, promoted by a mechanism that probably does not involve small GTPases of the Rho protein family. Intoxicated cells did not proliferate. Similar t o cells treated with other cyolethal distending toxins, these cells accumul ated in the G2 phase of the cell cycle, demonstrating an increased level of the tyrosine phosphorylated (inactive) form of the cyclin-dependent kinase p34(cdc2). DNA synthesis was not affected until several hours after this i ncrease, suggesting that the toxin acts directly on some kinase/phosphatase in the signaling network controlling the p34(cdc2) activity. We propose th at this toxin has an important role both in the generation of chancroid ulc ers and in their slow healing. The toxin may also be an interesting new too l for molecular studies of the eukaryotic cell- cycle machinery.