The Haemophilus ducreyi Cytolethal Distending Toxin Induces Cell Cycle Arrest and Apoptosis via the DNA Damage Checkpoint Pathways

Abstract

The cytolethal distending toxins (CDTs) induce cell cycle arrest by a mechanism still not well characterized. We demonstrate that the effect of the Haemophilus ducreyi CDT (HdCDT) is cell type-specific: B cell lines underwent apoptosis, epithelial cells and keratinocytes arrested exclusively in G 2 , whereas normal fibroblasts arrested both in G 1 and G 2 . We studied normal keratinocytes and fibroblasts, which are relevant for understanding the pathogenicity of H. ducreyi. The response to HdCDT resembles the checkpoint response activated by ionizing radiation. Both responses were characterized by an early induction of the p53 gene and the cyclindependent kinase inhibitor p21 in fibroblasts, and activation of the chk2 kinase in epithelial cells. In the Ataxia Telangiectasia-mutated gene (ATM)-deficient lymphoblastoid cell lines, intoxication was significantly delayed compared with ATM wild type cells, and was associated with a slower kinetic of p53 stabilization, suggesting that the early response to HdCDT is ATM-dependent. Activation of ATM-dependent pathways was further confirmed by the ability of caffeine to partially override the HdCDT-mediated cell cycle arrest. Our data shed new light on the mechanism of action of this novel family of bacterial toxins, limiting the target candidates to DNA or molecules directly involved in activation of checkpoint responses.

A CdtA-CdtC Complex Can Block Killing of HeLa Cells by Haemophilus ducreyi Cytolethal Distending Toxin

“…The CdtB protein from several different bacterial pathogens has been shown to possess DNase activity (7,8,10,13,17) when introduced into or expressed within eukaryotic cells, and there seems to be a reasonable consensus that a functional CdtB molecule is essential for expression of toxicity by CDT (15). This property of DNase activity inherent in the CdtB protein is consistent with reports of CDT causing arrest of different cell types in the G 2 /M or G 1 and G 2 phases of the cell cycle (3,5,10,15,24,29,30).…”

Differential effect of the cytolethal distending toxin of Actinobacillus actinomycetemcomitans on co-cultures of human oral cells

“…Eukaryotic cells that are sensitive to the toxin are usually arrested at the G 0 /G 1 or G 2 /M phase of the growth cycle (Comayras et al, 1997;Whitehouse et al, 1998;Cortes-Bratti et al, 1999;Shenker et al, 1999). CDT triggers the block in cell-cycle progression through the action of a DNase I-like nuclease (CdtB) that causes double-strand breaks in the host-cell DNA (Elwell & Dreyfus, 2000;LaraTejero & Galán, 2000;Cortes-Bratti et al, 2001;Frisan et al, 2003;Hassane et al, 2003).…”

Prevalence of cdtABC genes encoding cytolethal distending toxin among Haemophilus ducreyi and Actinobacillus actinomycetemcomitans strains

“…The H. ducreyi cytolethal distending toxin (HdCDT) has been shown to inhibit proliferation, induce cell enlargement and cause death of a number of human cells and cell lines, e.g., HEp-2, HeLa, HaCaT, T cells, B cells and human ®broblasts [7±13]. It has been shown to induce a cell cycle arrest not only in the G2/M phase, but also in the G1 phase [14,15]. cdt genes have also been identi®ed in strains of Escherichia coli [16±18], some Shigella [19], Campylobacter [20±22] and Helicobacter [23] species and in the oral pathogen Actinobacillus actinomycetemcomitans [24±26].…”