Mechanism of internalization of the cytolethal distending toxin of Actinobacillus actinomycetemcomitans.
Cytolethal distending toxin (CDT), which is encoded by three genes, cdtA, cdtB and cdtC, is now recognized to have a growing list of biological actions, including inhibition of cell cycle progression, promotion of apoptosis and stimulation of cytokine secretion. It appears that internalization of CDT is essential, at least for cell cycle blockade. Using purified recombinant CDT proteins from the periodontopathic bacterium Actinobacillus actinomycetemcomitans, the authors investigated which combination of toxin proteins produce cell cycle inhibition and which bound and/or entered into host cells. No evidence was found that CdtB bound to HEp-2 human epithelial cells. In contrast, both CdtA and CdtC bound to these cells. Induction of cell cycle arrest required that cells be exposed to both CdtB and CdtC. Pre-exposure of cells to CdtC for as little as 10 min, followed by removal of the free CdtC and addition of exogenous CdtB, resulted in the inhibition of cell cycle progression, suggesting that CdtB could bind to cell-surface-located CdtC. Using various methods to follow internalization of the CDT proteins it was concluded that CdtC acts to bind CdtB at the cell surface and transports it into the cell as a complex via an endosomal pathway blockable by monensin and brefeldin A.
Akifusa
Sumio
S
Division of Microbial Diseases, Eastman Dental Institute, University College London, 256 Gray's Inn Road, London WC1X 8LD, UK.
Heywood
Wendy
W
Division of Microbial Diseases, Eastman Dental Institute, University College London, 256 Gray's Inn Road, London WC1X 8LD, UK.
Nair
Sean P
SP
Division of Microbial Diseases, Eastman Dental Institute, University College London, 256 Gray's Inn Road, London WC1X 8LD, UK.
Stenbeck
Gudrun
G
Bone and Mineral Centre, University College London, 5 University Street, London WC1E 6JJ, UK.
Henderson
Brian
B
Division of Microbial Diseases, Eastman Dental Institute, University College London, 256 Gray's Inn Road, London WC1X 8LD, UK.
D016976:Aggregatibacter actinomycetemcomitans / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity*; D001427:Bacterial Toxins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D020126:Brefeldin A / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism; D006801:Humans; D008985:Monensin / Q000494:pharmacology; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism
D001427:Bacterial Toxins; D011994:Recombinant Proteins; C067044:cytolethal distending toxin; C447141:cytolethal distending toxin, Actinobacillus actinomycetemcomitans; D020126:Brefeldin A; D008985:Monensin