Transcriptional control by mediators and their physiological significance

为了了解介体依赖的转录调控，我们从以下4个方面进行了研究：1）转录因子在辅激活子和辅抑制子之间的转换：我们发现转录因子c-Myb竞争性地与辅激活子CBP和多个辅抑制子（包括Ski）结合，p53与辅抑制子mSin 3A结合并募集到c-Myb。导致细胞周期调节基因转录的抑制。2）通过特异性信号传导调节介质：我们证明了Wnt信号激活作为辅阻遏物的HIPK 2激酶，并导致NLK激酶与c-Myb结合。NLK直接磷酸化c-Myb及其蛋白酶体依赖性降解。在A-Myb的情况下，HIPK 2募集组织组甲基转移酶到A-Myb，但不诱导A-Myb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Hedgehog信号通路中Gli 3的辅阻遏物。我们还发现Shn-2基因敲除小鼠存在脂肪细胞分化缺陷。Shn-2作为一个平台蛋白，介导共激活因子和多个转录因子之间的相互作用，协同诱导PPAR□2基因的转录，这是脂肪细胞分化所必需的。4）转录调控中的核结构分析：我们鉴定了调节转录因子亚核定位的因子，这些转录因子在发育中起重要作用。

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.