Lipopolysaccharide tolerance in murine peritoneal macrophages induces downregulation of the lipopolysaccharide signal transduction pathway through mitogen-activated protein kinase and nuclear factor-kappaB cascades, but not lipopolysaccharide-incorporation steps.
Endotoxin/lipopolysaccharide (LPS) tolerance, a hyporesponsive state to endotoxin or LPS stimulation, was induced in murine peritoneal macrophages by previous exposure of macrophages to LPS. Expression of tumor necrosis factor (TNF)-alpha and interleukin (IL)-6 mRNA in response to LPS stimulation was suppressed in LPS-tolerant macrophages. Tyrosine phosphorylations in response to LPS of 40-45-kDa proteins in non-tolerant macrophages were also suppressed in LPS-tolerant macrophages. These proteins corresponded to two members of the mitogen-activated protein kinase (MAPK) family, ERK and p38. In addition to these proteins, another MAPK family protein, JNK, was also suppressed in LPS-tolerant macrophages. Activation of Raf-1, located in the upstream portion of ERK cascades, was also suppressed by LPS-tolerance induction. These suppressions in LPS-tolerant macrophages were exhibited against stimulation by an LPS agonist like taxol, but not towards stimulation by an unrelated activator like phorbol ester (PMA). Activation of the transcription factor NF-kappaB, which is supposed to be one of the components of another important pathway for transduction of LPS-stimulated cytokine producing signals, was strongly suppressed and degradation of IkappaB, an inhibitor of NF-kappaB, was also severely diminished in LPS-tolerant macrophages. Although a monosaccharide lipid A analog, GLA-58, was able to stimulate macrophages to activate ERK proteins without cytokine production, pretreatment of macrophages with this compound suppressed both LPS-stimulated activation of ERK and cytokine production. Furthermore, downregulation of LPS-uptake in LPS-tolerant macrophages was not observed. Based on all these findings, LPS tolerance might be caused by the previous activation of some components on LPS-signaling pathways. This may then induce a refractory state in key LPS-signal transducer molecules located downstream of the cell membrane LPS receptor and upstream of the branching point in intracellular cascades for activation of MAPK and NF-kappaB, probably in some initial steps of intracellular signaling.
Tominaga
K
K
Department of Microbiology, Jichi Medical School, Tochigi-ken 329-0498, Japan. ktominag@nils.go.jp
Saito
S
S
Matsuura
M
M
Nakano
M
M
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015536:Down-Regulation; D004361:Drug Tolerance; D015850:Interleukin-6 / Q000378:metabolism; D008070:Lipopolysaccharides / Q000378:metabolism / Q000494:pharmacology*; D017737:Macrophages, Peritoneal / Q000187:drug effects* / Q000378:metabolism; D051379:Mice; D008809:Mice, Inbred C3H; D019950:Mitogen-Activated Protein Kinase 1; D016328:NF-kappa B / Q000378:metabolism*; D017239:Paclitaxel; D010766:Phosphorylation / Q000187:drug effects; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism
D015850:Interleukin-6; D008070:Lipopolysaccharides; D016328:NF-kappa B; D014409:Tumor Necrosis Factor-alpha; D014443:Tyrosine; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D013755:Tetradecanoylphorbol Acetate; D017239:Paclitaxel