title: Smad6 inhibits the transcriptional activity of Tbx6 by mediating its degradation.
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.
authors: 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.
authors: Yue-Lei
authors: YL
authors: Chen
authors: Bin
authors: B
authors: Liu
authors: Zhen-Ning
authors: ZN
authors: Zhou
authors: Rui-Ying
authors: RY
authors: Hu
authors: Cong
authors: C
authors: Fei
authors: Zhi-Hui
authors: ZH
authors: Xie
authors: Xiaoyan
authors: X
authors: Ding
mesh_terms: D000818:Animals; D002460:Cell Line; D015536:Down-Regulation; D006801:Humans; D051379:Mice; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D051905:Smad6 Protein / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020825:T-Box Domain Proteins; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism
chemical_list: D051905:Smad6 Protein; D020825:T-Box Domain Proteins; C102932:Tbx6 protein, mouse; D014157:Transcription Factors; C492381:Smurf1 protein, mouse; D044767:Ubiquitin-Protein Ligases