JunD regulates transcription of the tissue inhibitor of metalloproteinases-1 and interleukin-6 genes in activated hepatic stellate cells.
Activation of hepatic stellate cells (HSCs) to a myofibroblast-like phenotype is the pivotal event in hepatic wound healing and fibrosis. Rat HSCs activated in vitro express JunD, Fra2, and FosB as the predominant AP-1 DNA-binding proteins, and all three associate with an AP-1 sequence that is essential for activity of the tissue inhibitor of metalloproteinases-1 (TIMP-1) promoter. In this study, we used expression vectors for wild-type, dominant-negative, and forced homodimeric (Jun/eb1 chimeric factors) forms of JunD and other Fos and Jun proteins to determine the requirement for JunD in the transcriptional regulation of the TIMP-1 and interleukin-6 (IL-6) genes. JunD activity was required for TIMP-1 gene promoter activity, whereas overexpression of Fra2 or FosB caused a repression of promoter activity. The ability of homodimeric JunD/eb1 to elevate TIMP-1 promoter activity supports a role for JunD homodimers as the major AP-1-dependent transactivators of the TIMP-1 gene. IL-6 promoter activity was induced upon activation of HSCs and also required JunD activity; however, expression of JunD/eb1 homodimers resulted in transcriptional repression. Mutagenesis of the IL-6 promoter showed that an AP-1 DNA-binding site previously reported to be an activator of transcription in fibroblasts functions as a suppressor of promoter activity in HSCs. We conclude that JunD activates IL-6 gene transcription as a heterodimer and operates at an alternative DNA-binding site in the promoter. The relevance of these findings to events occurring in the injured liver was addressed by showing that AP-1 DNA-binding complexes are induced during HSC activation and contain JunD as the predominant Jun family protein. JunD is therefore an important transcriptional regulator of genes responsive to Jun homo- and heterodimers in activated HSCs.
Smart
D E
DE
Liver Group, Division of Infection, Inflammation, and Repair, University of Southampton, Southampton General Hospital, Southampton SO16 6YD, United Kingdom.
Vincent
K J
KJ
Arthur
M J
MJ
Eickelberg
O
O
Castellazzi
M
M
Mann
J
J
Mann
D A
DA
D000818:Animals; D002251:Carbon Tetrachloride; D002478:Cells, Cultured; D019281:Dimerization; D022781:Hepatocytes / Q000378:metabolism*; D015850:Interleukin-6 / Q000096:biosynthesis / Q000235:genetics*; D008103:Liver Cirrhosis / Q000139:chemically induced / Q000378:metabolism; D008297:Male; D009154:Mutation; D011401:Promoter Regions, Genetic; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics / Q000502:physiology*; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D019715:Tissue Inhibitor of Metalloproteinase-1 / Q000235:genetics*; D015534:Trans-Activators / Q000502:physiology; D018808:Transcription Factor AP-1 / Q000378:metabolism; D014158:Transcription, Genetic
D015850:Interleukin-6; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger; D019715:Tissue Inhibitor of Metalloproteinase-1; D015534:Trans-Activators; D018808:Transcription Factor AP-1; D002251:Carbon Tetrachloride