Regulation of endogenous CYGB expression in human hepatic stellate cells

Background: Cytoglobin (CYGB) belongs to the mammalian globin family and is localized in hepatic stellate cells (HSCs) in the liver. Besides its gas-binding ability, CYGB may be relevant in hepatic fibrosis and cancer due to... [ view full abstract ]

Background: Cytoglobin (CYGB) belongs to the mammalian globin family and is localized in hepatic stellate cells (HSCs) in the liver. Besides its gas-binding ability, CYGB may be relevant in hepatic fibrosis and cancer due to its anti-oxidative properties. We investigate a mechanism by which endogenous factors regulates CYGB expression in HSCs. Methods: Human HSC cell line, HHSteCs, and human primary-cultured HSCs isolated from intact human liver were employed in this study. Messenger RNA and protein levels were determined using quantitative PCR and western blotting. Bile duct ligation (BDL) was performed on C57Bl/6J mice. Results: Here we report that fibroblast growth factor 2 (FGF2) is a key factor for CYGB induction in human HSCs through JNK-c-Jun signaling; induction of CYGB by FGF2 was inhibited by sic-JUN and augmented by pCMFlag-hcJUN vector transfection. ChIP analyses revealed the augmented binding of phospho-c-JUN to its consensus motif (5’-TGAC/GTCA), located at -218 to - 222 bases from transcription initiation site in CYGB promoter, under FGF2 stimulation. Additionally, FGF2 induced quiescent-like phenotype of HSCs in part via ERK pathway. In BDL mice, FGF2 administration ameliorated liver fibrosis with significant reduction of activated HSCs. In contrast, TGF-β1, a well-known fibrosis inducer, was identified as the potent suppressor of CYGB via Smad2, but not via Smad3 pathways. Binding of Smad2 to a transcription factor SP1 was critical for suppressing CYGB gene by TGF-β1. Conclusion: FGF2 and TGF-β1 are potent regulators of CYGB gene expression and induce deactivation and activation, respectively, of human HSCs through different intracellular signaling pathways.