The modulation of myogenic regulatory factor transactivation activity by Bhlhe40
| Autor: | Sheng-Pin Hsiao, 蕭勝斌 |
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| Rok vydání: | 2011 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 100 The differentiation of functional skeletal muscle cells is characterized by the acquirement of contractile filaments, cell cycle exit, and fusion of myoblasts to form voluntarily contractible multinucleated myotubes. This process is critically regulated by a family of basic helix-loop-helix (bHLH) transcription factors, including MyoD, Myf-5, Myogenin and MRF4, called as myogenic regulatory factors (MRFs) that work together with myocyte enhancer factors (MEF2s) to activate the expression of muscle-specific genes required for myogenic differentiation. In this study, we found that the expression level of Bhlhe40, a ubiquitously expressed bHLH transcriptional repressor, was up-regulated during terminal myogenic differentiation and it could repress the MRF-activated transcription of PGC-1α, M-cadherin, and Myogenin by directly binding to their promoters in vitro and in vivo. Furthermore, we found that Bhlhe40-mediated repression of MRF transactivational activity could be relieved by over-expression of P/CAF, an essential coactivator of MRFs. We demonstrated that Bhlhe40 repressed MRF-activated M-cadherin transcription through a HDAC independent pathway and the DNA binding activity of Bhlhe40 was required but not sufficient to repress the M-cadherin expression. We also found that Bhlhe40-mediated repression of M-cadherin promoter activity may not only through its direct binding to the E3-box in the M-cadherin proximal promoter but also could be mediated by unknown bHLH proteins. We are currently identifying the unknown proteins and observing the interaction among MRFs, Bhlhe40, P/CAF, and other co-factors (co-activators or co-repressors) acting on muscle-specific gene promoters. Based on our observations on the regulation of PGC-1α and M-cadherin transcription, we speculate that the specificity of MyoD targeting and transactivation can be significantly determined by the E-boxes and their binding proteins adjacent to the MyoD binding sites. We are currently identifying genome-wide targeting sites of both MyoD and Bhlhe40 to prove this hypothesis. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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