8月28日,，國際知名學(xué)術(shù)期刊The Journal of Biological Chemistry刊登了上海生命科學(xué)研究院生物化學(xué)與細(xì)胞生物學(xué)研究所丁小燕實(shí)驗(yàn)室的研究論文,，研究人員通過免疫共沉淀等方法發(fā)現(xiàn)了轉(zhuǎn)錄因子Tbx6的一個新的相互作用蛋白--Smad6。進(jìn)一步的研究發(fā)現(xiàn)Smad6通過增加Tbx6泛素化修飾,，進(jìn)而抑制Tbx6的轉(zhuǎn)錄活性。
T-box基因家族是近十年來新發(fā)現(xiàn)的一類在胚胎早期發(fā)育和遺傳性疾病中起重要作用的轉(zhuǎn)錄調(diào)控因子,。近十年的研究表明,，作為T-box基因家族成員之一的Tbx6參與了中胚層細(xì)胞的特化和肌肉的發(fā)生過程。Myf-5和MyoD是成肌調(diào)控因子（myogenic regulatory factors,，MRFs）家族中的兩個重要成員,，它們的活化是肌肉前體細(xì)胞分化的作用。BMP（bone morphogenetic protein）信號通過負(fù)向調(diào)控Myf-5和MyoD的轉(zhuǎn)錄,，有效抑制肌肉前體細(xì)胞的分化,，但具體的分子機(jī)制尚不清楚。
生化與細(xì)胞所博士生陳躍磊等人發(fā)現(xiàn)Tbx6蛋白與BMP信號的下游分子Smad6之間存在直接的蛋白相互作用,。缺失突變實(shí)驗(yàn)發(fā)現(xiàn),，Smad6通過其C端MH2結(jié)構(gòu)域與Tbx6的第90-180位氨基酸發(fā)生蛋白相互作用。Smad6招募E3連接酶Smurf1后能有效增強(qiáng)Tbx6蛋白的泛素化降解，從而實(shí)現(xiàn)對Tbx6下游基因的轉(zhuǎn)錄抑制,。同時,，他們還建立了小鼠TT-D6間充質(zhì)干細(xì)胞系體外誘導(dǎo)分化形成軟骨細(xì)胞的模型，發(fā)現(xiàn)TT-D6細(xì)胞中內(nèi)源的Smad6和Tbx6蛋白也存在著相互作用,。利用siRNA降低內(nèi)源Smad6蛋白的表達(dá)后,，能增加細(xì)胞內(nèi)Tbx6的蛋白含量，并且解除了BMP信號對成肌調(diào)控因子的抑制作用,。他們的研究提出了一個全新的假說,，即BMP信號通過下游分子Smad6與Tbx6相互作用后降解Tbx6蛋白，進(jìn)而實(shí)現(xiàn)對成肌調(diào)控因子Myf-5的轉(zhuǎn)錄抑制,。這也為更好地闡釋BMP信號如何調(diào)控細(xì)胞分化過程提供了一個新的分子機(jī)制,。上述研究成果得到國際同行評審專家和雜志編輯的好評，
該項(xiàng)研究工作得到了國家科技部,、國家自然基金委 ,、中國科學(xué)院的經(jīng)費(fèi)支持。（生物谷Bioon.com）
生物谷推薦原始出處：
J. Biol. Chem., Vol. 284, Issue 35, 23481-23490, August 28, 2009
Smad6 Inhibits the Transcriptional Activity of Tbx6 by Mediating Its Degradation*
Yue-Lei Chen, Bin Liu, Zhen-Ning Zhou, Rui-Ying Hu, Cong Fei, Zhi-Hui Xie, and Xiaoyan Ding1
From the From the Laboratory of Molecular Cell Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Graduate School of the Chinese Academy of Sciences, Shanghai 200031, China
ABSTRACT
Members of the bone morphogenetic protein (BMP) and T-box gene families play several critical roles in the early embryonic development and tissue homeostasis. Although BMP proteins are the upstream regulators of T-box genes, few studies have investigated the molecular mechanisms between these two protein families. Here, we report that Tbx6 interacts directly with Smad6, an inhibitory Smad that antagonizes the BMP signal. This interaction is mediated through the Mad homology 2 (MH2) domain of Smad6 and residues 90–180 of Tbx6. We demonstrate that Smad6 facilitates the degradation of Tbx6 protein through recruitment of Smurf1, a ubiquitin E3 ligase. Consequently, Smad6 reduces Tbx6-mediated Myf-5 gene activation. Furthermore, specific knockdown of endogenous Smad6 and Smurf1 by small interfering RNA increases the protein levels of Tbx6 and enhance the expression of Tbx6 target genes. Collectively, these findings reveal that Smad6 serves as a critical mediator of BMP signal via a functional interaction with Tbx6, thus regulating the activation of Tbx6 downstream genes during cell differentiation.
