Kinetic analysis of smad nucleocytoplasmic shuttling reveals a mechanism for transforming growth factor β-dependent nuclear accumulation of Smads
Kinetic analysis of smad nucleocytoplasmic shuttling reveals a mechanism for transforming growth factor β-dependent nuclear accumulation of Smads
复制标题
DOI：
10.1128/mcb.25.22.9845-9858.2005
复制
发表时间：
2005-11-01
影响因子：
5.3
通讯作者：
Hill, CS
中科院分区：
文献类型：
--
作者：
Schmierer, B;Hill, CS
在转化生长因子 β (TGF-β) 刺激下，Smad 会在细胞核中积聚，并在细胞核中调节基因表达。通过对与增强型绿色荧光蛋白或光激活绿色荧光蛋白融合的 Smad2 和 Smad4 进行荧光扰动实验，我们在体内定量研究了 Smad 核质穿梭动力学。我们获得了 Smad2 导入和导出的速率常数，并表明 Smad2 在未诱导细胞中的细胞质定位反映了其核导出比导入更快。我们发现TGF-β诱导的Smad2核积累是由Smad2从细胞核输出率显着下降引起的，这与Smad2和Smad4的核迁移率的强烈下降有关。 TGF-β诱导的核积累既不涉及细胞质滞留的释放，也不涉及Smad2导入率的增加。因此，Smad2 的 TGF-β 依赖性核积累完全是由磷酸化复合 Smad2 的选择性核捕获引起的。所提出的机制将 Smad2 的信号依赖性核积累与其连续核质循环特性相协调。
Upon transforming growth factor beta (TGF-beta) stimulation, Smads accumulate in the nucleus, where they regulate gene expression. Using fluorescence perturbation experiments on Smad2 and Smad4 fused to either enhanced green fluorescent protein or photoactivatable green fluorescent protein, we have studied the kinetics of Smad nucleocytoplasmic shuttling in a quantitative manner in vivo. We have obtained rate constants for import and export of Smad2 and show that the cytoplasmic localization of Smad2 in uninduced cells reflects its nuclear export being more rapid than import. We find that TGF-beta-induced nuclear accumulation of Smad2 is caused by a pronounced drop in the export rate of Smad2 from the nucleus, which is associated with a strong decrease in nuclear mobility of Smad2 and Smad4. TGF-beta-induced nuclear accumulation involves neither a release from c)cytoplasmic retention nor an increase in Smad2 import rate. Hence, TGF-beta-dependent nuclear accumulation of Smad2 is caused exclusively by selective nuclear trapping of phosphorylated, complexed Smad2. The proposed mechanism reconciles signal-dependent nuclear accumulation of Smad2 with its continuous nucleocytoplasmic cycling properties.