title: Tumor necrosis factor alpha enhances Actinobacillus actinomycetemcomitans leukotoxin-induced HL-60 cell apoptosis by stimulating lymphocyte function-associated antigen 1 expression.
abstract: We demonstrated previously that Actinobacillus actinomycetemcomitans leukotoxin (Ltx) is greatly able to induce apoptotic signaling in cells that are positive for lymphocyte function-associated antigen 1 (LFA-1), a cell receptor of Ltx. We investigated in this study whether inflammatory cytokines can regulate apoptosis of human leukemic HL-60 cells induced by Ltx. Of the cytokines tested, tumor necrosis factor alpha (TNF-alpha) significantly enhanced the Ltx-induced cell apoptosis. Northern and Western blotting analyses showed that TNF-alpha enhanced the expression of CD11a in the cells at both the mRNA and protein levels but did not do so for CD18 expression. TNF-alpha also enhanced the binding of Ltx to the cells. We also observed by measuring the mitochondrial transmembrane potential and the generation of superoxide anion that the cytokine enhanced Ltx-induced apoptosis in HL-60 cells. In addition, interleukin-1beta significantly enhanced Ltx-induced cell apoptosis, although the enhancing activity was lower than that of TNF-alpha. These stimulatory effects of both cytokines were also observed for human polymorphonuclear leukocytes. The ability of TNF-alpha to increase cell susceptibility to Ltx could be inhibited by preincubation of the cells with a monoclonal antibody against TNF receptor 1 but not by preincubation of the cells with a monoclonal antibody against anti-TNF receptor 2. Furthermore, the results of an assay of caspase 3 intracellular activity (PhiPhiLuxG1D2) showed that Ltx-induced caspase 3 activation was completely neutralized by CD18 antibody treatment, although significant neutralization was also observed with anti-CD11a antibody. Taken together, the results of the present study indicate that TNF-alpha acts as a potent stimulator of Ltx-induced HL-60 cell apoptosis via TNF receptor 1-mediated upregulation of LFA-1 expression.
authors.affiliation: Department of Preventive Dentistry, Kyushu University Faculty of Dental Science, Fukuoka 812-8582, Japan. nyama@dent.kyushu-u.ac.jp
authors.forename: Noboru
authors.initials: N
authors.lastname: Yamaguchi
authors.forename: Chie
authors.initials: C
authors.lastname: Kubo
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Masuhiro
authors.forename: Edward T
authors.initials: ET
authors.lastname: Lally
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Koga
authors.forename: Shigemasa
authors.initials: S
authors.lastname: Hanazawa
mesh_terms: D016976:Aggregatibacter actinomycetemcomitans / Q000472:pathogenicity* / Q000502:physiology; D017209:Apoptosis; D005098:Exotoxins / Q000502:physiology*; D018922:HL-60 Cells; D006801:Humans; D007375:Interleukin-1 / Q000494:pharmacology; D007963:Leukocytes, Mononuclear; D016169:Lymphocyte Function-Associated Antigen-1 / Q000378:metabolism*; D018124:Receptors, Tumor Necrosis Factor / Q000378:metabolism; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology / Q000502:physiology*; D015854:Up-Regulation
chemical_list: D005098:Exotoxins; D007375:Interleukin-1; D016169:Lymphocyte Function-Associated Antigen-1; D018124:Receptors, Tumor Necrosis Factor; D014409:Tumor Necrosis Factor-alpha; C018579:leukotoxin