Institute for Research in Biomedicine (IRB Barcelona), The Barcelona Institute of Science and Technology, Baldiri Reixac, 10, 08028, Barcelona, Spain.
EMBL Grenoble, 71 Avenue des Martyrs, CS 90181, 38042, Grenoble, Cedex 9, France.
Nat Commun. 2017 Dec 12;8(1):2070. doi: 10.1038/s41467-017-02054-6.
Smad transcription factors activated by TGF-β or by BMP receptors form trimeric complexes with Smad4 to target specific genes for cell fate regulation. The CAGAC motif has been considered as the main binding element for Smad2/3/4, whereas Smad1/5/8 have been thought to preferentially bind GC-rich elements. However, chromatin immunoprecipitation analysis in embryonic stem cells showed extensive binding of Smad2/3/4 to GC-rich cis-regulatory elements. Here, we present the structural basis for specific binding of Smad3 and Smad4 to GC-rich motifs in the goosecoid promoter, a nodal-regulated differentiation gene. The structures revealed a 5-bp consensus sequence GGC(GC)|(CG) as the binding site for both TGF-β and BMP-activated Smads and for Smad4. These 5GC motifs are highly represented as clusters in Smad-bound regions genome-wide. Our results provide a basis for understanding the functional adaptability of Smads in different cellular contexts, and their dependence on lineage-determining transcription factors to target specific genes in TGF-β and BMP pathways.
Smad 转录因子被 TGF-β 或 BMP 受体激活后，与 Smad4 形成三聚体复合物，靶向特定基因以调节细胞命运。CAGAC 基序被认为是 Smad2/3/4 的主要结合元件，而 Smad1/5/8 则被认为优先结合富含 GC 的元件。然而，胚胎干细胞中的染色质免疫沉淀分析显示 Smad2/3/4 与富含 GC 的顺式调控元件广泛结合。在这里，我们展示了 Smad3 和 Smad4 与 goosecoid 启动子中富含 GC 基序特异性结合的结构基础，goosecoid 启动子是一个受 nodal 调控的分化基因。这些结构揭示了一个 5 个碱基对的保守序列 GGC(GC)|(CG)，是 TGF-β 和 BMP 激活的 Smads 以及 Smad4 的结合位点。这些 5GC 基序在全基因组范围内的 Smad 结合区域中以簇的形式高度代表。我们的结果为理解 Smads 在不同细胞环境中的功能适应性及其对谱系决定转录因子的依赖性提供了基础，以靶向 TGF-β 和 BMP 途径中的特定基因。
