IL-6 and IL-6 receptor modulation by IFN-gamma and tumor necrosis factor-alpha in human monocytic cell line (THP-1). Priming effect of IFN-gamma.
The present work is a detailed study of the mechanism of IFN-gamma- and TNF-alpha-triggered IL-6 secretion and IL-6 gene expression in human monocytic THP-1 cells and of the effect of these cytokines on the expression of IL-6 surface receptor and IL-6R gene. Although TNF-alpha was shown to stimulate IL-6 expression in fibroblasts in monocytic THP-1 cells, IFN-gamma is required for TNF to induce IL-6 expression. The results reported here demonstrate that combined treatment of THP-1 cells with IFN-gamma + TNF-alpha induced IL-6 mRNA expression, whereas no significant induction was obtained by either cytokine alone. Nuclear run-on transcription assay showed that the increased level of IL-6 mRNA induced by IFN-gamma + TNF-alpha was associated with induction of gene transcription. Sequential stimulation of THP-1 cells by IFN-gamma and subsequently by TNF-alpha did not allow IL-6 gene induction, suggesting that IFN-gamma and TNF-alpha induced or activated different signaling factors which should act together to trigger IL-6 gene transcription. IFN-gamma pretreatment followed by IFN-gamma + TNF-alpha restimulation led to superinduction of the IL-6 gene expression with a concomitant increase in IL-6-secreted activity. This priming effect of IFN-gamma is dependent on active protein synthesis. Biochemical characterization of IL-6 proteins secreted by THP-1 cells by Western blotting and affinity chromatography allowed identification of a major IL-6 molecular species of 42 kDa and a minor one of 23 kDa. Furthermore, we showed here that IFN-gamma increased the IL-6R mRNA level with a concomitant increase in IL-6-specific binding to surface receptors. On the contrary, treatment with IFN-gamma + TNF-alpha reduced the level of IL-6R mRNA and IL-6 binding to THP-1 cells probably due to a ligand-mediated effect. Taken together, results reported here provide evidence that functional interaction between IFN-gamma and TNF-alpha is involved in the regulation of IL-6 and IL-6R expression in monocytic cells. Control of IL-6 production and IL-6R expression may be one of the important homeostatic properties of IFN-gamma.
Unité 196 INSERM, Institut Curie, Section de Biologie, Paris, France.
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J
Sanceau
J
J
Wijdenes
M
M
Revel
J
J
Wietzerbin
D002460:Cell Line; D003513:Cycloheximide / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects*; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology*; D015850:Interleukin-6 / Q000235:genetics* / Q000378:metabolism; D008070:Lipopolysaccharides; D009000:Monocytes / Q000187:drug effects / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D011971:Receptors, Immunologic / Q000032:analysis / Q000235:genetics*; D019947:Receptors, Interleukin-6; D014158:Transcription, Genetic; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D015850:Interleukin-6; D008070:Lipopolysaccharides; D012333:RNA, Messenger; D011971:Receptors, Immunologic; D019947:Receptors, Interleukin-6; D014409:Tumor Necrosis Factor-alpha; D007371:Interferon-gamma; D003513:Cycloheximide