Background. Interleukin (IL)-6 is produced by enterocytes in response to sepsis and after treatment with IL-1β. The IL-6 promoter contains binding sites for multiple transcription factors, including nuclear factor-κB and C/EBP. The anti-inflammatory cytokine IL-10 downregulates nuclear factor-κB activity, but its effects on C/EBP activation and IL-6 production in the enterocyte are not known. Methods. Caco-2 cells were treated with IL-1β, IL-10, or a combination of the cytokines. C/EBP DNA binding activity was determined by electrophoretic mobility shift assay and IL-6 levels by enzyme-linked immunosorbent assay. IL-6 promoter activation was assessed by luciferase assay. Results. IL-10 treatment of cultured Caco-2 cells resulted in increased C/EBP DNA binding activity. Supershift analysis revealed upregulated DNA binding activity of C/EBP-β but not C/EBP-δ. To examine if the increased DNA binding reflected gene activation, cells were transfected with a wild-type IL-6 promoter luciferase construct or with a mutated C/EBP binding site. IL-10 potentiated IL-1β-induced IL-6 promoter activity. Replacing the wild-type promoter with the promoter containing a mutated C/EBP DNA binding sequence blocked the effect of IL-10. When cells were treated with 0.5 ng/mL of IL-1β for 24 hours, IL-6 production increased, and this response to IL-1β was potentiated several-fold by IL-10. Conclusions. IL-10 may activate the IL-6 gene in stimulated enterocytes by upregulating the expression and activity of C/EBP.
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