Roles for the MH2 domain of Smad7 in the specific inhibition of transforming growth factor-β superfamily signaling
Roles for the MH2 domain of Smad7 in the specific inhibition of transforming growth factor-β superfamily signaling
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DOI：
10.1074/jbc.m313977200
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发表时间：
2004-07-23
影响因子：
4.8
通讯作者：
Miyazono, K
中科院分区：
文献类型：
--
作者：
Mochizuki, T;Miyazaki, H;Miyazono, K
转化生长因子-β（TGF-β）超家族的细胞因子的信号由抑制性Smads（I-Smads）负调节。Smad 7抑制TGF-β和骨形态发生蛋白（BMP）的信号传导，而Smad 6抑制TGF-β信号的效果较差。I-Smads具有氨基末端N结构域和羧基末端Mad同源2（MH 2）结构域。N结构域是Smad 7特异性抑制TGF-β信号传导所必需的，而I-Smads的MH 2结构域通过与I型受体相互作用参与TGF-β超家族信号的抑制。在这里，我们已经确定了四个基本的氨基酸残基（赖氨酸-312，赖氨酸-316，赖氨酸-401，和精氨酸-409）的Smad 7 MH 2结构域的基本表面发挥重要作用，在与I型受体的相互作用。四个碱性氨基酸残基突变为酸性残基（K312 E，K316 E，K401 E和R409 E）消除了Smad 7与TGF-β I型受体的相互作用，抑制了TGF-β诱导的Smad 2磷酸化和转录反应，并诱导了非洲爪蟾早期胚胎内源性激活素/Nodal信号的靶基因。Smad 7的K401 E和R409 E突变体也不能与BMP I型受体（BMPR-I）相互作用，抑制BMP诱导的Smad 5磷酸化和转录，有效抑制爪蟾早期胚胎内源性BMP信号。然而，K312 E和K316 E突变体能够与BMPR-I相互作用，并保留抑制BMP信号传导的能力。因此，Smad 7的MH 2结构域通过与I型受体的差异相互作用在TGF-β超家族信号的特异性抑制中起重要作用。
Signals by cytokines of the transforming growth factor-beta( TGF-beta) superfamily are negatively regulated by inhibitory Smads ( I-Smads). Smad7 inhibits signaling by both TGF-beta and bone morphogenetic proteins (BMPs), whereas Smad6 inhibits TGF-beta signals less effectively. I-Smads have amino-terminal N domains and carboxyl-terminal Mad homology 2 (MH2) domains. The N domains are essential for specific inhibition of TGF-beta signaling by Smad7, whereas the MH2 domains of I-Smads are involved in the inhibition of TGF-beta superfamily signals through interaction with type I receptors. Here, we have identified four basic amino acid residues (Lys-312, Lys-316, Lys-401, and Arg-409) in the basic surface of the Smad7 MH2 domain that play important roles in interaction with type I receptors. Mutations of the four basic amino acid residues to acidic residues (K312E, K316E, K401E, and R409E) abolished the interaction of Smad7 with TGF-beta type I receptors, inhibition of Smad2 phosphorylation and transcriptional responses induced by TGF-beta, and induction of target genes of endogenous activin/Nodal signals in Xenopus early embryos. The K401E and R409E mutants of Smad7 were also unable to interact with BMP type I receptors ( BMPR-I), repress the Smad5 phosphorylation and transcription induced by BMP, and effectively inhibit endogenous BMP signals in Xenopus early embryos. However, the K312E and K316E mutants were able to interact with BMPR-I and retained the ability to inhibit BMP signaling. Thus, the MH2 domain of Smad7 plays important roles in specific inhibition of TGF-beta superfamily signals through differential interaction with type I receptors.