Interleukin-6 represses the transcription of the CCAAT/enhancer binding protein-alpha gene in hepatoma cells by inhibiting its ability to autoactivate the proximal promoter region.
The cytokine interleukin-6 (IL-6) plays key roles in the immune and inflammatory responses, acute-phase reaction and hematopoiesis. Such biological actions of IL-6 are characterised by both the activation and the inhibition of gene transcription. Unfortunately, in contrast to gene activation, the mechanism by which IL-6 suppresses transcription remains largely unclear. We have, therefore, investigated this aspect using the Xenopus laevis CCAAT/enhancer binding protein-alpha (C/EBPalpha) gene promoter as a model. We show by transient transfection assays of various promoter-luciferase DNA constructs into hepatoma cells that a C/EBP recognition sequence in the proximal promoter region is essential for the IL-6-mediated repression. Electrophoretic mobility shift assays showed that C/EBPalpha was the major protein that bound to this site and, consistent with its expression pattern, the binding was reduced when the cells were exposed to IL-6. Co-transfection assays revealed for the first time that the ability of C/EBPalpha, but not C/EBPbeta or Sp1, to transactivate the promoter was decreased dramatically when the cells were incubated with IL-6. These studies, therefore, identify a novel mechanism for IL-6-mediated repression of gene transcription that involves a reduction in C/EBPalpha-mediated activation.
Foka
Pelagia
P
Cardiff School of Biosciences, Cardiff University, Museum Avenue, PO Box 911, Cardiff CF10 3US, UK.
Irvine
Scott A
SA
Kockar
Feray
F
Ramji
Dipak P
DP
D000818:Animals; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism*; D006528:Carcinoma, Hepatocellular / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D015850:Interleukin-6 / Q000494:pharmacology*; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011485:Protein Binding / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020218:Response Elements / Q000235:genetics; D017384:Sequence Deletion / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects*; D015533:Transcriptional Activation; D014982:Xenopus laevis / Q000235:genetics*
D022763:CCAAT-Enhancer-Binding Protein-alpha; D015850:Interleukin-6; D012333:RNA, Messenger