Basic Study on Toxic Activity of Cytolethal Distending Toxin of Actinobacillus actinomycetemcomitans

Abstract

Cytolethal distending toxin (CDT) of Actinobacillus actinomycetemcomitans is a protein toxin that induces irreversible cell cycle arrest, cellular distention and subsequent cell death in mammalian cells. In this study susceptibility to human cells (HeLa cell and normal fibroblast TIG-7) of the A. actinomycetemcomitans CDT produced by recombinant E. coli cells was estimated by morphological change of the cells and a ratio of cell death. When influence to cell morphology by CDT-treatment was examined, HeLa cells was round at 2 days and distended about over 5-fold in size at 4 days. In contrast, morphology of TIG-7 cells did not change at 2 days after CDT-treatment and showed slight distension at 4 days. But cell cycle arrest was observed in both types of the cells after CDT-treatment. When relationship between amount of CDT for treatment and cell number was examined, amounts of CDT did not affect the cell number of HeLa and TIG-7 cells. However, viability of HeLa and TIG-7 cells was obviously distinct, the viability of HeLa cells was less than 5% at 7 days after treatment and that of TIG-7 was about 20%. In addition, viable TIG-7 cells continued to be alive even after subsequent spread although the cells were not growing. These results suggested that CDT produced by A. actinomycetemcomitans might act as a factor that facilitates bacterial infection to the cells by inducing prolonged cell cycle arrest to host cells.