Transcriptional control by mediators and their physiological significance

为了了解依赖于介体的转录调控，我们进行了以下4个方面的研究：1)转录因子上的辅活化子和辅抑制子之间的切换：我们发现，转录因子c-Myb竞争性地与可控子CBP和包括Ski在内的多个核心抑制子结合。此外，P53还结合并招募辅抑制子mSin3A到c-Myb。抑制细胞周期调节基因的转录2)通过特定的信号调节介质：我们证明了Wnt信号激活了作为辅助抑制因子的HIPK2激酶，并导致NLK激酶与c-Myb的结合。NLK直接磷酸化c-Myb及其蛋白酶体依赖的降解。在A-Myb的情况下，HIPK2将组体甲基转移酶招募到A-Myb，但不诱导A-Myb的降解。3)介质的生理作用：通过对Ski基因敲除小鼠的分析，我们发现Ski是Gli3的辅助抑制因子，Gli3在刺猬信号通路中发挥作用。我们还发现shn-2基因敲除小鼠的脂肪细胞分化存在缺陷。Shn-2作为一种平台蛋白，介导共激活因子和多种转录因子之间的相互作用，协同诱导PPAR-2基因的转录，这对脂肪细胞的分化是必不可少的。4)转录调控中的核结构分析：我们鉴定了调控转录因子亚核定位的因子，这些转录因子在发育中起着重要的作用。

To understand the mediator-dependent transcriptional control, the following 4 aspects of research were performed.1) Switching between coactivators and corepressrs on the transcription factor: We found that transcription factor c-Myb competitively binds to the cocativator CBP and to multiple corespressors, including Ski.Further, p53 binds to and recruit corepressor mSin3A to c-Myb. leading to repression of transcription of the cell-cycle regulator genes.2) Regulation of mediators by specific signaling: We demonstrated that Wnt signal activates the HIPK2 kinase, which acts as a corepressor, and leads to binding of NLK kinase to c-Myb. NLK directly phosphorylates c-Myb and its proteasome-dependent degradation. In the case of A-Myb, HIPK2 recruites histome methyltransferase to A-Myb, but does not induce the A-Myb degradation.3) Physiological role of mediators : By analysis of Ski knockout mice, we found that Ski acts as a corepressor of Gli3, which functions in the hedgehog signaing pathway. We also found that the Shn-2 knockout mice have the defective adipocyte differentiation. Shn-2 acts as a platform protein and mediates the interaction between coactivators and multiple transcription factors to synergistically induce transcription of the PPAR□2 gene, which is essential for the adipocyte differentiation.4) Analysis of the nuclear architecture in transcriptional control : We identified the factor that regulates the subnuclear localization of transcription factors, which play an important role in development.