Smads 2 and 3 are differentially activated by transforming growth factor-β (TGF-β) in quiescent and activated hepatic stellate cells -: Constitutive nuclear localization of Smads in activated cells is TGF-β-independent
Smads 2 and 3 are differentially activated by transforming growth factor-β (TGF-β) in quiescent and activated hepatic stellate cells -: Constitutive nuclear localization of Smads in activated cells is TGF-β-independent
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DOI：
10.1074/jbc.m207728200
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发表时间：
2003-03-28
影响因子：
4.8
通讯作者：
Wells, RG
中科院分区：
文献类型：
--
作者：
Liu, CH;Gaça, MDA;Wells, RG
肝星状细胞是主要的细胞类型。负责肝纤维化中的基质沉积，经历转分化为纤维化的肌成纤维细胞的过程。这些细胞在体外培养时经历了类似的转分化过程，是促纤维化药物转化生长因子-β(TGF-β)的主要靶点。我们研究了转化生长因子-β下游信号分子Smads 2、3和4在体外培养1、4和7天的肝星状细胞(HSC)中的激活情况，分别具有静止型、中间型和完全转分化表型。Smad4的总水平不会随着HSC的转分化而改变，而Smad4的总水平不会随着HSC的转分化而改变，而且这种蛋白存在于细胞核和胞浆中，而不依赖于转化生长因子-β或核输出抑制剂瘦素B的处理。转化生长因子-β主要在早期培养的细胞中介导Smad2的激活，在转分化细胞中主要介导Smad3的激活。Smad2信号转导所需的连接蛋白SarA在转分化过程中消失。此外，第7天的细胞表现出结构性的磷酸化和Smad2的核定位，这不受转化生长因子-β中和抗体、I型转化生长因子-β受体激酶抑制剂或激活素中和抗体的影响。这些结果表明，在静止期和体外转分化的肝星状细胞中，转化生长因子-β介导的信号通路存在本质差异。
Hepatic stellate cells are the primary cell type. responsible for matrix deposition in liver fibrosis, undergoing a process of transdifferentiation into fibrogenic myofibroblasts. These cells, which undergo a similar transdifferentiation process when cultured in vitro, are a major target of the profibrogenic agent transforming growth factor-beta (TGF-beta). We have studied activation of the TGF-beta downstream signaling molecules Smads 2, 3, and 4 in hepatic stellate cells (HSC) cultured in vitro for 1, 4, and 7 days, with quiescent, intermediate, and fully transdifferentiated phenotypes, respectively. Total levels of Smad4, common to multiple TGF-beta superfamily signaling pathways, do not change as HSC transdifferentiate, and the protein is found in both nucleus and cytoplasm, independent of treatment with TGF-beta or the nuclear export inhibitor leptomycin B. TGF-beta mediates activation of Smad2 primarily in early cultured cells and that of Smad3 primarily in transdifferentiated cells. The linker protein SARA, which is required for Smad2 signaling, disappears with transdifferentiation. Additionally, day 7 cells demonstrate constitutive phosphorylation and nuclear localization of Smad 2, which is not affected by pretreatment with TGF-beta-neutralizing antibodies, a type I TGF-beta receptor kinase inhibitor, or activin-neutralizing antibodies. These results demonstrate essential differences between TGF-beta-mediated signaling pathways in quiescent and in vitro transdifferentiated hepatic stellate cells.