Abstract
Transforming growth factor (TGF)‑β3 has previously been reported to antagonize hepatic fibrosis in vivo and in vitro. The present study aimed to investigate the mechanism underlying the involvement of TGF‑β3 in hepatic fibrosis. Short hairpin (sh)RNA‑cAMP-responsive element binding protein (CREB) 1 and small interfering (si)RNA‑Smad3 were utilized to silence the expression of CREB1 and Smad3 in hepatic stellate cells (HSCs), whereas the vector pRSV‑CREB1 was used to induce CREB1 overexpression in HSCs. Cells were treated with or without exogenous TGF‑β3 or TGF‑β1, and mRNA and protein expression levels were assessed using reverse transcription‑quantitative polymerase chain reaction and western blot analysis. Untreated cells served as the control group. Exogenous TGF‑β3 increased Smad7 mRNA and protein expression levels in rat HSCs, and CREB1 and Smad3 appeared to be implicated in the mechanism of Smad7. CREB1 knockdown inhibited the TGF‑β3‑induced upregulation of Smad7, whereas its overexpression potentiated the Smad7 upregulation in HSCs; conversely, CREB1 manipulations had no effect on Smad7 expression under basal conditions. In addition, TGF‑β3‑induced Smad7 upregulation was blocked when the activity of p38, a kinase upstream of CREB1, was inhibited. Furthermore, silencing Smad3 resulted in decreased Smad7 expression under basal conditions and in TGF‑β3‑stimulated cells. Notably, Smad7 expression appeared to also be induced by exogenous TGF‑β1, independent of CREB1. The present study demonstrated that TGF‑β3 increased Smad7 expression in HSCs, whereas CREB1 and Smad3 appeared to participate in the mechanism of induction. Smad3 is the key regulator whereas CREB‑1 acts as a co‑regulator. These results suggested that this mechanism may underlie the antagonizing effects of TGF‑β3 on hepatic fibrosis.