Actinobacillus actinomycetemcomitans Immunosuppressive Protein Is a Member of the Family of Cytolethal Distending Toxins Capable of Causing a G sub(2) Arrest in Human T Cells

• Published in: The Journal of immunology (1950) 1999-04, Vol.162 (8), p.4773-4780
• Main Authors: Shenker, B J, McKay, T, Datar, S, Miller, M, Chowhan, R, Demuth, D
• Format: Article
• Language: English
• Subjects: Actinobacillus actinomycetemcomitans
• ISSN: 0022-1767

We have previously shown that Actinobacillus actinomycetecomitans produces an immunosuppressive factor (ISF) capable of impairing human lymphocyte function by perturbing cell cycle progression. We now report that ISF is the product of the cdtB gene, one of three genes encoding the family of cytolethal distending toxins (Cdt). The ISF polypeptide exhibits greater than or equal to 95% identity with Hemophilus ducreyi CdtB protein and less than or equal to 60% homology with Escherichia coli or Campylobacter jejuni CdtB. Pretreatment of PHA-activated lymphocytes with 5-25 ng ISF results in G sub(2) arrest of CD4 super(+) and CD8 super(+) T cells. Similarly, treatment of HeLa cells results in G sub(2) arrest and cell elongation and distension. However, lymphocytes are at least 5 times more sensitive to ISF than HeLa cells and do not undergo the elongation and distension that characterizes interactions of Cdts with cell lines. ISF-treated lymphocytes express normal cyclin A and B1 levels, but contain reduced levels of cell cycle-dependent kinase-1 (Cdk1). Additionally, the majority of Cdk1 is in the hyperphosphorylated, inactive, form. In contrast, PHA-induced G sub(2) cells contain elevated levels of the hypophosphorylated, active Cdk1. Failure of ISF-treated cells to dephosphorylate Cdk1 is not associated with decreased availability of Cdc25. These studies suggest that the CdtB protein alone is capable of inducing G sub(2) arrest in lymphocytes and cell cycle arrest, elongation, and distension of HeLa cells. Our studies also suggest that lymphocytes may be primary targets for A. actinomycetemcomitans CdtB (ISF) and possibly for other Cdt family members as well. Thus, Cdts may function to impair host immunity and contribute to the pathogenesis of disease associated with Cdt-producing organisms.