Disruption of transforming growth factor-β signaling by curcumin induces gene expression of peroxisome proliferator-activated receptor-γ in rat hepatic stellate cells
Disruption of transforming growth factor-β signaling by curcumin induces gene expression of peroxisome proliferator-activated receptor-γ in rat hepatic stellate cells
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DOI：
10.1152/ajpgi.00200.2006
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发表时间：
2007-01-01
影响因子：
4.5
通讯作者：
Chen, Anping
中科院分区：
文献类型：
--
作者：
Zheng, Shizhong;Chen, Anping
肝星状细胞（HSC）是肝纤维化的主要效应因子，其激活伴随着基因表达的顺序改变，包括转化生长因子- β (tgf - β)受体的增加和过氧化物酶体增殖物激活受体- γ (ppar - γ)的急剧减少。他们之间的关系仍然模糊不清。我们之前已经证明姜黄素在活化的HSC中诱导ppar - γ的基因表达，导致细胞增殖减少，诱导细胞凋亡和抑制细胞外基质基因的表达。潜在的分子机制在很大程度上是未知的。我们最近观察到，刺激ppar - γ激活可抑制活化HSC中tgf - β受体的基因表达，导致tgf - β信号通路中断。这一观察结果支持了我们的假设，即在HSC中ppar - γ激活和tgf - β信号之间存在拮抗关系。在本研究中，我们进一步假设tgf - β信号可能负向调节活化的HSC中ppar - γ的基因表达。本报告表明，外源性tgf - β 1抑制活化的HSC中ppar - γ的基因表达，姜黄素预处理可能通过中断tgf - β信号通路来消除ppar - γ的表达。转染实验进一步表明，显性负型tgf - β受体阻断tgf - β信号传导可增加ppar - γ基因启动子活性。启动子缺失试验、位点定向诱变和凝胶转移试验定位ppar - γ基因启动子中的两个Smad结合元件（SBEs），作为姜黄素反应元件，负向调节传代HSC启动子活性。Smad3/4蛋白复合物特异性地与SBEs结合。Smad4的过表达可以剂量依赖性地消除姜黄素对ppar - γ基因启动子和tgf - β信号传导的抑制作用。综上所述，这些结果表明，姜黄素阻断tgf - β信号通路可诱导体外活化HSC中ppar - γ的基因表达。我们的研究为姜黄素在诱导ppar - γ基因表达和抑制HSC活化中的分子机制提供了新的见解。
Activation of hepatic stellate cells (HSC), the major effectors of hepatic fibrogenesis, is coupled with sequential alterations in gene expression, including an increase in receptors for transforming growth factor-beta (TGF-beta) and a dramatic reduction in the peroxisome proliferator-activated receptor-gamma (PPAR-gamma). The relationship between them remains obscure. We previously demonstrated that curcumin induced gene expression of PPAR-gamma in activated HSC, leading to reducing cell proliferation, inducing apoptosis and suppressing expression of extracellular matrix genes. The underlying molecular mechanisms are largely unknown. We recently observed that stimulation of PPAR-gamma activation suppressed gene expression of TGF-beta receptors in activated HSC, leading to the interruption of TGF-beta signaling. This observation supported our assumption of an antagonistic relationship between PPAR-gamma activation and TGF-beta signaling in HSC. In this study, we further hypothesize that TGF-beta signaling might negatively regulate gene expression of PPAR-gamma in activated HSC. The present report demonstrates that exogenous TGF-beta 1 inhibits gene expression of PPAR-gamma in activated HSC, which is eliminated by the pretreatment with curcumin likely by interrupting TGF-beta signaling. Transfection assays further indicate that blocking TGF-beta signaling by dominant negative type II TGF-beta receptor increases the promoter activity of PPAR-gamma gene. Promoter deletion assays, site-directed mutageneses, and gel shift assays localize two Smad binding elements (SBEs) in the PPAR-gamma gene promoter, acting as curcumin response elements and negatively regulating the promoter activity in passaged HSC. The Smad3/4 protein complex specifically binds to the SBEs. Overexpression of Smad4 dose dependently eliminates the inhibitory effects of curcumin on the PPAR-gamma gene promoter and TGF-beta signaling. Taken together, these results demonstrate that the interruption of TGF-beta signaling by curcumin induces gene expression of PPAR-gamma in activated HSC in vitro. Our studies provide novel insights into the molecular mechanisms of curcumin in the induction of PPAR-gamma gene expression and in the inhibition of HSC activation.