Blockade of the PI-3K signalling pathway by the Aggregatibacter actinomycetemcomitans cytolethal distending toxin induces macrophages to synthesize and secrete pro-inflammatory cytokines.
The Aggregatibactor actinomycetemcomitans cytolethal distending toxin (Cdt) induces G2 arrest and apoptosis in lymphocytes; these toxic effects are due to the active subunit, CdtB, which functions as a phosphatidylinositol-3,4,5-triphosphate (PIP3) phosphatase. We now extend our investigation and demonstrate that Cdt is able to perturb human macrophage function. THP-1- and monocyte-derived macrophages were found not to be susceptible to Cdt-induced apoptosis. Nonetheless, the toxin was capable of binding to macrophages and perturbing PI-3K signalling resulting in decreased PIP3 levels and reduced phosphorylation of Akt and GSK3β; these changes were accompanied by concomitant alterations in kinase activity. Exposure of monocytes and macrophages to Cdt resulted in pro-inflammatory cytokine production including increased expression and release of IL-1β, TNFα and IL-6. Furthermore, treatment of cells with either TLR-2, -3 or -4 agonists in the presence of Cdt resulted in an augmented pro-inflammatory response relative to agonist alone. GSK3β inhibitors blocked the Cdt-induced pro-inflammatory cytokine response suggesting a pivotal role for PI-3K blockade, concomitant decrease in GSK3β phosphorylation and increased kinase activity. Collectively, these studies provide new insight into the virulence potential of Cdt in mediating the pathogenesis of disease caused by Cdt-producing organisms.
Department of Pathology, University of Pennsylvania School of Dental Medicine, 240 South 40th Street, Philadelphia, PA, 19104-6030, USA.
Bruce J
BJ
Shenker
Lisa P
LP
Walker
Ali
A
Zekavat
Mensur
M
Dlakić
Kathleen
K
Boesze-Battaglia
D016976:Aggregatibacter actinomycetemcomitans / Q000276:immunology*; D001427:Bacterial Toxins / Q000276:immunology*; D016207:Cytokines / Q000276:immunology*; D053583:Interleukin-1beta / Q000378:metabolism; D015850:Interleukin-6 / Q000378:metabolism; D008264:Macrophages / Q000276:immunology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
D001427:Bacterial Toxins; D016207:Cytokines; D053583:Interleukin-1beta; D015850:Interleukin-6; D019869:Phosphatidylinositol 3-Kinases; D014409:Tumor Necrosis Factor-alpha; C067044:cytolethal distending toxin