The transforming growth factor–β (TGF-β) superfamily of cytokines regulates various biological processes, including cell proliferation, immune responses, autophagy, and senescence. Dysregulation of TGF-β signaling causes various diseases, such as cancer and fibrosis. SMAD2 and SMAD3 are core transcription factors involved in TGF-β signaling, and they form heterotrimeric complexes with SMAD4 (SMAD2-SMAD2-SMAD4, SMAD3-SMAD3-SMAD4, and SMAD2-SMAD3-SMAD4) in response to TGF-β signaling. These heterotrimeric complexes interact with cofactors to control the expression of TGF-β–dependent genes. SMAD2 and SMAD3 may promote or repress target genes depending on whether they form complexes with other transcription factors, coactivators, or corepressors; therefore, the selection of specific cofactors is critical for the appropriate activity of these transcription factors. To reveal the structural basis by which SMAD2 and SMAD3 select cofactors, we determined the crystal structures of SMAD3 in complex with the transcription factor FOXH1 and SMAD2 in complex with the transcriptional corepressor SKI. The structures of the complexes show that the MAD homology 2 (MH2) domains of SMAD2 and SMAD3 have multiple hydrophobic patches on their surfaces. The cofactors tether to various subsets of these patches to interact with SMAD2 and SMAD3 in a cooperative or competitive manner to control the output of TGF-β signaling.

细胞因子的转化生长因子-β（TGF-β）超家族调节各种生物过程，包括细胞增殖，免疫反应，自噬和衰老。TGF-β信号转导的失调会导致多种疾病，例如癌症和纤维化。SMAD2和SMAD3是参与TGF-β信号传导的核心转录因子，它们响应TGF-β信号传导而与SMAD4（SMAD2-SMAD2-SMAD4，SMAD3-SMAD3-SMAD4和SMAD2-SMAD3-SMAD4）形成异源三聚体复合物。这些异源三聚体复合物与辅因子相互作用，以控制TGF-β依赖性基因的表达。SMAD2和SMAD3可能促进或抑制靶基因，这取决于它们是否与其他转录因子，共激活因子或共抑制因子形成复合物。所以，特定辅因子的选择对于这些转录因子的适当活性至关重要。为了揭示SMAD2和SMAD3选择辅因子的结构基础，我们确定了与转录因子FOXH1和SMAD2与转录共抑制因子SKI复杂的SMAD3的晶体结构。配合物的结构表明SMAD2和SMAD3的MAD同源2（MH2）域在它们的表面上有多个疏水补丁。辅因子束缚于这些补丁的各个子集，以协同或竞争方式与SMAD2和SMAD3相互作用，以控制TGF-β信号的输出。我们确定了与转录因子FOXH1结合的SMAD3的晶体结构和与转录共抑制因子SKI结合的SMAD2的晶体结构。配合物的结构表明SMAD2和SMAD3的MAD同源2（MH2）域在它们的表面上有多个疏水补丁。辅因子束缚于这些补丁的各个子集，以协同或竞争方式与SMAD2和SMAD3相互作用，以控制TGF-β信号的输出。我们确定了与转录因子FOXH1结合的SMAD3的晶体结构和与转录共抑制因子SKI结合的SMAD2的晶体结构。配合物的结构表明SMAD2和SMAD3的MAD同源2（MH2）域在它们的表面上有多个疏水补丁。辅因子束缚于这些补丁的各个子集，以协同或竞争方式与SMAD2和SMAD3相互作用，以控制TGF-β信号的输出。