Distinct oligomeric states of SMAD proteins in the transforming growth factor-β pathway
Distinct oligomeric states of SMAD proteins in the transforming growth factor-β pathway
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DOI：
10.1074/jbc.m005799200
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发表时间：
2000-12-29
影响因子：
4.8
通讯作者：
Massagué, J
中科院分区：
文献类型：
--
作者：
Jayaraman, L;Massagué, J
蛋白质相互作用对于SMAD作为转化生长因子-β（TGF-β）信号介体的功能至关重要。SMAD 2或SMAD 3的TGF-β受体磷酸化导致它们与SMAD 4结合并在细胞核中积累，其中SMAD复合物结合决定靶基因选择的辅因子。我们提供的证据表明，在基础状态下，SMADs 2，3和4形成单独的，截然不同的复合物。SMAD 2主要以单体形式存在，而密切相关的SMAD 3以多种寡聚状态存在。这种差异是由于SMAD 2的MH 1结构域中的独特结构元件，其在基础状态下抑制蛋白质-蛋白质相互作用。与SMAD 2和SMAD 3相反，SMAD 4在基础状态下主要被发现为同源寡聚体，最有可能是三聚体。在用TGF-β刺激细胞后，SMAD蛋白参与大小范围从SMAD 2-SMAD 4异二聚体到>650 kDa的组装体的多种复合物。后者显示出对JUNB和胶原蛋白7的TGF-β响应元件的最高DNA结合亲和力。这些观察结果，所有验证与内源性SMAD蛋白，修改以前的模型关于组装和活性的SMAD复合物在TGF-β途径。
Protein interactions are critical for the function of SMADs as mediators of transforming growth factor-beta (TGF-beta) signals. TGF-beta receptor phosphorylation of SMAD2 or SMAD3 causes their association with SMAD4 and accumulation in the nucleus where the SMAD complex binds cofactors that determine the choice of target genes. We provide evidence that in the basal state, SMADs 2, 3, and 4 form separate, strikingly different complexes. SMAD2 is found mostly as monomer, whereas the closely related SMAD3 exists in multiple oligomeric states. This difference is due to a unique structural element in the MH1 domain of SMAD2 that inhibits protein-protein interactions in the basal state. In contrast to SMAD2 and SMAD3, SMAD4 in the basal state is found mostly as a homo-oligomer, most likely a trimer. Upon cell stimulation with TGF-beta, SMAD proteins become engaged in a multitude of complexes ranging in size from SMAD2-SMAD4 heterodimers to assemblies of >650 kDa, The latter display the highest DNA binding affinity for the TGF-beta -response elements of JUNB and collagen 7. These observations, all validated with endogenous SMAD proteins, modify previous models regarding the assembly and activity of SMAD complexes in the TGF-beta pathway.