Department of Biology, York University, Toronto, ON, M3J 1P3, Canada.
Muscle Health Research Centre (MHRC), York University, Toronto, ON, M3J 1P3, Canada.
Cell Death Dis. 2019 May 16;10(6):387. doi: 10.1038/s41419-019-1615-0.
Recent reports indicate that Smad7 promotes skeletal muscle differentiation and growth. We previously documented a non-canonical role of nuclear Smad7 during myogenesis, independent of its role in TGF-β signaling. Here further characterization of the myogenic function of Smad7 revealed β-catenin as a Smad7 interacting protein. Biochemical analysis identified a Smad7 interaction domain (SID) between aa575 and aa683 of β-catenin. Reporter gene analysis and chromatin immunoprecipitation demonstrated that Smad7 and β-catenin are cooperatively recruited to the extensively characterized ckm promoter proximal region to facilitate its muscle restricted transcriptional activation in myogenic cells. Depletion of endogenous Smad7 and β-catenin in muscle cells reduced ckm promoter activity indicating their role during myogenesis. Deletion of the β-catenin SID substantially reduced the effect of Smad7 on the ckm promoter and exogenous expression of SID abolished β-catenin function, indicating that SID functions as a trans dominant-negative regulator of β-catenin activity. β-catenin interaction with the Mediator kinase complex through its Med12 subunit led us to identify MED13 as an additional Smad7-binding partner. Collectively, these studies document a novel function of a Smad7-MED12/13-β-catenin complex at the ckm locus, indicating a key role of this complex in the program of myogenic gene expression underlying skeletal muscle development and regeneration.
最近的报告表明，Smad7 促进骨骼肌的分化和生长。我们之前记录了核 Smad7 在成肌过程中的一种非经典作用，独立于其在 TGF-β信号中的作用。在这里，Smad7 的成肌功能的进一步表征揭示了 β-catenin 是 Smad7 的相互作用蛋白。生化分析确定了β-catenin 的 aa575 和 aa683 之间的 Smad7 相互作用结构域（SID）。报告基因分析和染色质免疫沉淀表明，Smad7 和 β-catenin 被协同招募到广泛表征的 ckm 启动子近端区域，以促进其在成肌细胞中的肌肉受限转录激活。在肌肉细胞中耗尽内源性 Smad7 和 β-catenin 降低了 ckm 启动子活性，表明它们在成肌过程中的作用。β-catenin SID 的缺失大大降低了 Smad7 对 ckm 启动子的影响，而 SID 的外源性表达则消除了 β-catenin 的功能，表明 SID 作为 β-catenin 活性的反式显性负调控因子发挥作用。β-catenin 通过其 Med12 亚基与 Mediator 激酶复合物的相互作用，使我们鉴定出 MED13 是 Smad7 的另一个结合伴侣。总之，这些研究证明了 Smad7-MED12/13-β-catenin 复合物在 ckm 基因座上的一种新功能，表明该复合物在骨骼肌发育和再生的成肌基因表达程序中起关键作用。
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