Mizuide Masafumi, Hara Takane, Furuya Toshio, Takeda Masafumi, Kusanagi Kiyoshi, Inada Yuri, Mori Masatomo, Imamura Takeshi, Miyazawa Keiji, Miyazono Kohei
Department of Biochemistry, The Cancer Institute of the Japanese Foundation for Cancer Research (JFCR), Tokyo 170-8455, Japan.
J Biol Chem. 2003 Jan 3;278(1):531-6. doi: 10.1074/jbc.C200596200. Epub 2002 Nov 7.
c-Ski and SnoN are transcriptional co-repressors that inhibit transforming growth factor-beta signaling through interaction with Smad proteins. Among receptor-regulated Smads, c-Ski and SnoN bind more strongly to Smad2 and Smad3 than to Smad1. Here, we show that c-Ski and SnoN bind to the "SE" sequence in the C-terminal MH2 domain of Smad3, which is exposed on the N-terminal upper side of the toroidal structure of the MH2 oligomer. The "QPSMT" sequence, located in the vicinity of SE, supports the interaction with c-Ski and SnoN. Sequences similar to SE and QPSMT are found in Smad2, but not in Smad1. The N-terminal MH1 domain and linker region of Smad3 protrude from the N-terminal upper side of the MH2 oligomer toroid. Smurf2 induces ubiquitin-dependent degradation of SnoN, since it appears to be located close to SnoN through binding to the linker region of Smad2. In contrast, transcription factors Mixer and FoxH3 (FAST1) bind to the bottom side of the Smad3 MH2 toroid; therefore, c-Ski does not affect the interaction of Smads with these transcription factors. Our findings thus demonstrate the stoichiometry of how multiple molecules can associate with the Smad oligomers and how the Smad-interacting proteins functionally interact with each other.
c-Ski和SnoN是转录共抑制因子，它们通过与Smad蛋白相互作用来抑制转化生长因子-β信号通路。在受体调节型Smad蛋白中，c-Ski和SnoN与Smad2和Smad3的结合比与Smad1的结合更强。在此，我们表明c-Ski和SnoN与Smad3 C末端MH2结构域中的“SE”序列结合，该序列暴露于MH2寡聚体环形结构的N末端上侧。位于SE附近的“QPSMT”序列支持与c-Ski和SnoN的相互作用。在Smad2中发现了与SE和QPSMT相似的序列，但在Smad1中未发现。Smad3的N末端MH1结构域和连接区从MH2寡聚体环形结构的N末端上侧突出。Smurf2诱导SnoN的泛素依赖性降解，因为它似乎通过与Smad2的连接区结合而靠近SnoN。相比之下，转录因子Mixer和FoxH3（FAST1）与Smad3 MH2环形结构的底部结合；因此，c-Ski不影响Smad与这些转录因子的相互作用。我们的研究结果因此证明了多个分子如何与Smad寡聚体结合以及Smad相互作用蛋白如何在功能上相互作用的化学计量关系。
