Shi Y, Hata A, Lo R S, Massagué J, Pavletich N P
Cellular Biochemistry and Biophysics Program, Memorial Sloan-Kettering Cancer Center, New York 10021, USA.
Nature. 1997 Jul 3;388(6637):87-93. doi: 10.1038/40431.
The Smad4/DPC4 tumour suppressor is inactivated in nearly half of pancreatic carcinomas and to a lesser extent in a variety of other cancers. Smad4/DPC4, and the related tumour suppressor Smad2, belong to the SMAD family of proteins that mediate signalling by the TGF-beta/activin/BMP-2/4 cytokine superfamily from receptor Ser/Thr protein kinases at the cell surface to the nucleus. SMAD proteins, which are phosphorylated by the activated receptor, propagate the signal, in part, through homo- and hetero-oligomeric interactions. Smad4/DPC4 plays a central role as it is the shared hetero-oligomerization partner of the other SMADs. The conserved carboxy-terminal domains of SMADs are sufficient for inducing most of the ligand-specific effects, and are the primary targets of tumorigenic inactivation. We now describe the crystal structure of the C-terminal domain (CTD) of the Smad4/DPC4 tumour suppressor, determined at 2.5 A resolution. The structure reveals that the Smad4/DPC4 CTD forms a crystallographic trimer through a conserved protein-protein interface, to which the majority of the tumour-derived missense mutations map. These mutations disrupt homo-oligomerization in vitro and in vivo, indicating that the trimeric assembly of the Smad4/DPC4 CTD is critical for signalling and is disrupted by tumorigenic mutations.
Smad4/DPC4肿瘤抑制因子在近半数的胰腺癌中失活，在其他多种癌症中失活程度较小。Smad4/DPC4以及相关的肿瘤抑制因子Smad2属于SMAD蛋白家族，该家族介导从细胞表面的受体丝氨酸/苏氨酸蛋白激酶到细胞核的TGF-β/激活素/BMP-2/4细胞因子超家族的信号传导。被激活的受体磷酸化的SMAD蛋白部分通过同型和异型寡聚体相互作用来传递信号。Smad4/DPC4起着核心作用，因为它是其他SMAD蛋白共同的异型寡聚化伙伴。SMAD蛋白保守的羧基末端结构域足以诱导大多数配体特异性效应，并且是致瘤失活的主要靶点。我们现在描述了Smad4/DPC4肿瘤抑制因子C末端结构域（CTD）的晶体结构，分辨率为2.5埃。该结构表明，Smad4/DPC4 CTD通过一个保守的蛋白质-蛋白质界面形成晶体学三聚体，大多数肿瘤来源的错义突变都定位在这个界面上。这些突变在体外和体内破坏了同型寡聚化，表明Smad4/DPC4 CTD的三聚体组装对于信号传导至关重要，并且会被致瘤突变破坏。
