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 phenoty pe is the pivotal event in hepatic wound healing and fibrosis. Rat HSCs act ivated in vitro express JunD, Fra2, and FosB as the predominant AP-1 DNA-bi nding proteins, and all three associate with an AP-I sequence that is essen tial 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. J unD activity was required for TIMP-1 gene promoter activity, whereas overex pression of Fra2 or FosB caused a repression of promoter activity. The abil ity 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 an d also required JunD activity; however, expression of JunD/eb1 homodimers r esulted in transcriptional repression, Mutagenesis of the IL-6 promoter sho wed that an AP-1 DNA-binding site previously reported to be an activator of transcription in fibroblasts functions as a suppressor of promoter activit y in HSCs, We conclude that JunD activates IL-6 gene transcription as a het erodimer and operates at an alternative DNA-binding site in the promoter. T he relevance of these findings to events occurring in the injured Liver was addressed by showing that AP-I DNA-binding complexes are induced during HS C activation and contain JunD as the predominant Jun family protein. JunD i s therefore an important transcriptional regulator of genes responsive to J un homo- and heterodimers in activated HSCs.