Transcriptional control by mediators and their physiological significance

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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.