JunD is a profibrogenic transcription factor regulated by Jun N-terminal kinase-independent phosphorylation

JunD is implicated in the regulation of hepatic stellate cell (HSC) activation and liver fibrosis via its transcriptional regulation of the tissue inhibitor of metalloproteinases-1 (TIMP-1) gene. In the present study we found in vivo evidence of a role for JunD in fibrogenesis. Expression of JunD was demonstrated in alpha-SMA-positive activated HSCs of fibrotic rodents and human livers. The junD −/− mice were protected from carbon tetrachloride–induced fibrosis. The livers of injured junD −/− mice displayed significantly reduced formation of fibrotic crosslinked collagen and a smaller number of alpha-SMA-positive HSCs compared with those of wild-type (wt) mice. Hepatic TIMP-1 mRNA expression in injured junD −/− mice was 78% lower and in culture activated junD −/− HSCs was 50%-80% lower than that in wt mice. In examining the signal transduction mechanisms that regulate JunD-dependent TIMP-1 expression, we found a role for phosphorylation of the Ser100 residue of JunD but ruled out JNK as a mediator of this event, suggesting ERK1/2 is utilized. In conclusion , a signaling pathway for the development of fibrosis involves the regulation of TIMP-1 expression by phosphorylated JunD. Supplementary material for this article can be found on the HEPATOLOGY website (http://interscience.wiley.com/jpages/0270-9139/suppmat/index.html).