Lipopolysaccharide inhibits TNF-induced apoptosis: role of nuclear factor-kappaB activation and reactive oxygen intermediates.
LPS, a component of the cell wall in Gram-negative bacteria, induces inflammation and septic shock syndrome by stimulating various inflammatory cytokines including TNF. How LPS affects the TNF-mediated cellular responses, however, is not understood. In this study, the effect of LPS on TNF-mediated apoptosis in human histiocytic lymphoma U-937 cells was investigated. We found that treatment of cells with LPS completely abolished TNF-mediated cytotoxicity and activation of caspase-3. LPS-chelating antibiotic, polymyxin B, suppressed the antiapoptotic activity, indicating the specificity of the effect. Within minutes, LPS through CD14 induced the activation of NF-kappaB, degradation of IkappaBalpha (inhibitory subunit of NF-kappaB) and IkappaBbeta, and nuclear translocation of p65. An antioxidant, pyrrolidine dithiocarbamate, which blocked LPS-induced NF-kappaB activation, also abolished the antiapoptotic effects of LPS at the same time. Besides TNF, the apoptosis induced by taxol and okadaic acid was also sensitive to LPS-induced NF-kappaB activation, whereas that induced by H2O2, doxorubicin, daunomycin, vincristine, and vinblastine was NF-kappaB insensitive. Tumor cells that constitutively expressed NF-kappaB also showed resistance to the apoptotic effects of TNF, taxol, and okadaic acid, but sensitivity to all other agents, indicating the critical role of NF-kappaB in blocking apoptosis induced by certain agents. Overall, these results indicate that LPS induces resistance to the apoptotic effects of TNF and other agents, and that NF-kappaB activation, whether induced or constitutive, inhibits this apoptosis.
Manna
S K
SK
Cytokine Research Laboratory, Department of Molecular Oncology, University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
Aggarwal
B B
BB
D017209:Apoptosis / Q000187:drug effects*; D001483:Base Sequence; D001693:Biological Transport, Active / Q000187:drug effects; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D006090:Gram-Negative Bacteria / Q000472:pathogenicity; D006801:Humans; D020672:I-kappa B Proteins; D008070:Lipopolysaccharides / Q000494:pharmacology* / Q000633:toxicity; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000378:metabolism*; D009838:Oligodeoxyribonucleotides / Q000235:genetics / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism*; D051996:Transcription Factor RelA; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*