title: Lymphoid susceptibility to the Aggregatibacter actinomycetemcomitans cytolethal distending toxin is dependent upon baseline levels of the signaling lipid, phosphatidylinositol-3,4,5-triphosphate.
abstract: The Aggregatibacter actinomycetemcomitans cytolethal distending toxin (Cdt) induces G2 arrest and apoptosis in lymphocytes and other cell types. We have shown that the active subunit, CdtB, exhibits phosphatidylinositol-3,4,5-triphosphate (PIP3) phosphatase activity and depletes lymphoid cells of PIP3. Hence we propose that Cdt toxicity results from depletion of this signaling lipid and perturbation of phosphatidylinositol-3-kinase (PI-3K)/PIP3/Akt signaling. We have now focused on the relationship between cell susceptibility to CdtB and differences in the status of baseline PIP3 levels. Our studies demonstrate that the baseline level of PIP3, and likely the dependence of cells on steady-state activity of the PI-3K signaling pathway for growth and survival, influence cell susceptibility to the toxic effects of Cdt. Jurkat cells with known defects in both PIP3 degradative enzymes, PTEN and SHIP1, not only contain high baseline levels of PIP3, pAkt, and pGSK3β, but also exhibit high sensitivity to Cdt. In contrast, HUT78 cells, with no known defects in this pathway, contain low levels of PIP3, pAkt, and pGSK3β and likely minimal dependence on the PI-3K signaling pathway for growth and survival, and exhibit reduced susceptibility to Cdt. These differences in susceptibility to Cdt cannot be explained by differential toxin binding or internalization of the active subunit. Indeed, we now demonstrate that Jurkat and HUT78 cells bind toxin at comparable levels and internalize relatively equal amounts of CdtB. The relevance of these observations to the mode of action of Cdt and its potential role as a virulence factor is discussed.
authors: Department of Pathology, University of Pennsylvania School of Dental Medicine, Philadelphia, PA, USA.
authors: B J
authors: BJ
authors: Shenker
authors: Department of Pathology, University of Pennsylvania School of Dental Medicine, Philadelphia, PA, USA.
authors: L P
authors: LP
authors: Walker
authors: Department of Pathology, University of Pennsylvania School of Dental Medicine, Philadelphia, PA, USA.
authors: A
authors: A
authors: Zekavat
authors: Department of Biochemistry, University of Pennsylvania School of Dental Medicine, Philadelphia, PA, USA.
authors: K
authors: K
authors: Boesze-Battaglia
mesh_terms: D016976:Aggregatibacter actinomycetemcomitans / Q000378:metabolism*; D001427:Bacterial Toxins / Q000235:genetics / Q000276:immunology / Q000378:metabolism* / Q000494:pharmacology / Q000633:toxicity; D002478:Cells, Cultured; D006790:Host-Parasite Interactions; D006801:Humans; D019169:Jurkat Cells; D008214:Lymphocytes / Q000382:microbiology / Q000502:physiology; D051059:PTEN Phosphohydrolase / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D018129:Phosphatidylinositol Phosphates / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D001427:Bacterial Toxins; D051059:PTEN Phosphohydrolase; D019869:Phosphatidylinositol 3-Kinases; D018129:Phosphatidylinositol Phosphates; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases; C067044:cytolethal distending toxin; C447141:cytolethal distending toxin, Actinobacillus actinomycetemcomitans; C494929:PTEN protein, human; C000606430:INPP5D protein, human
keywords: bacterial toxins; host-parasite interactions; lymphocytes; phosphatidylinositol-3-kinase signaling