title: Differentiation of human monocytic cell lines confers susceptibility to Bacillus anthracis lethal toxin.
abstract: Anthrax lethal toxin (LT) is comprised of protective antigen and lethal factor. Lethal factor enters mammalian cells in a protective antigen-dependent process and cleaves mitogen-activated protein kinase kinases. Although LT has no observable effect on many cell types, it causes necrosis in macrophages derived from certain mouse strains and apoptosis in activated mouse macrophages. In this study, we observed that LT treatment of three different human monocytic cell lines U-937, HL-60 and THP-1 did not induce cell death. Cells did become susceptible to the toxin, however, after differentiation into a macrophage-like state. Treatment with LT resulted in decreased phosphorylation of p38, ERK1/2 and JNK in both undifferentiated and differentiated HL-60 cells, suggesting that the change in susceptibility does not result from differences in toxin delivery or substrate cleavage. Death of differentiated HL-60 cells was accompanied by chromosome condensation and DNA fragmentation, but was not inhibited by the pan-caspase inhibitor Z-VAD-FMK. In addition, we observed that the macrophage differentiation process could be inhibited by LT. Our results indicate that LT-mediated death of mouse and human macrophages may occur through distinct processes and that the differentiation state of human cells can determine susceptibility or resistance to LT.
authors.affiliation: Department of Laboratory Medicine and Pathobiology, University of Toronto M5S 1A8, ON, Canada.
authors.forename: Altaf
authors.initials: A
authors.lastname: Kassam
authors.forename: Sandy D
authors.initials: SD
authors.lastname: Der
authors.forename: Jeremy
authors.initials: J
authors.lastname: Mogridge
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000942:Antigens, Bacterial / Q000633:toxicity*; D001408:Bacillus anthracis; D001427:Bacterial Toxins / Q000633:toxicity*; D016923:Cell Death; D002454:Cell Differentiation / Q000502:physiology*; D002460:Cell Line; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004247:DNA / Q000378:metabolism; D053938:DNA Fragmentation; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D048670:MAP Kinase Kinase 4; D008264:Macrophages / Q000187:drug effects*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D009000:Monocytes / Q000166:cytology / Q000187:drug effects*; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D000942:Antigens, Bacterial; D001427:Bacterial Toxins; D015853:Cysteine Proteinase Inhibitors; D014409:Tumor Necrosis Factor-alpha; C030325:anthrax toxin; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D004247:DNA; D048031:JNK Mitogen-Activated Protein Kinases; D048052:Mitogen-Activated Protein Kinase 3; D048051:p38 Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases