Composition and function of AP-1 transcription complexes during muscle cell differentiation
Composition and function of AP-1 transcription complexes during muscle cell differentiation
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DOI：
10.1074/jbc.m110891200
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发表时间：
2002-05-10
影响因子：
4.8
通讯作者：
McDermott, JC
中科院分区：
文献类型：
--
作者：
Andreucci, JJ;Grant, D;McDermott, JC
激活蛋白-1（AP-1）在肌肉细胞中的作用目前尚不明确。虽然一些研究提出AP-1抑制肌生成，但其他研究表明AP-1在此过程中起积极作用。我们测试了这种变化是否可能是由于分化细胞中AP-1亚基组成的不同特性。使用Western分析，我们发现c-Jun，Fra-2和JunD在整个分化过程中表达。磷酸酶测定表明，JunD和Fra-2在肌细胞中被磷酸化，并且每种至少有两种亚型在肌细胞中表达。电泳迁移率变动分析结合抗体supershifts表明的外观Fra-2作为一个主要组成部分的AP-1 DNA结合复合物在分化细胞。在这种情况下，似乎Fra-2与c-Jun和JunD异二聚化。在报告基因测定中研究c-jun增强子，我们观察到肌肉转录因子MEF 2A和MyoD可以有助于c-jun增强子的稳健转录激活。在分化的肌细胞中，MEF 2位点的突变降低了c-jun增强子的反式激活，并且MEF 2A是与该顺式元件结合的主要MEF 2同种型。与C2 C12肌细胞中的生长条件相比，在分化条件下含有报告基因（TRE-Luc）的AP-1位点的转录激活增强。进一步的研究表明，含有A-P-1复合物的Fra-2可以反式激活MyoD增强子/启动子。因此，含有Fra-2和c-Jun或JunD的A-P-1复合物与肌肉分化一致，表明AP-1在肌发生期间的功能依赖于其亚基组成。
The role of activating protein-1 (AP-1) in muscle cells is currently equivocal. While some studies propose that AP-1 is inhibitory for myogenesis, others implicate a positive role in this process. We tested whether this variation may be due to different properties of the AP-1 subunit composition in differentiating cells. Using Western analysis we show that c-Jun, Fra-2, and JunD are expressed throughout the time course of differentiation. Phosphatase assays indicate that JunD and Fra-2 are phosphorylated in muscle cells and that at least two isoforms of each are expressed in muscle cells. Electrophoretic mobility shift assays combined with antibody supershifts indicate the appearance of Fra-2 as a major component of the AP-1 DNA binding complex in differentiating cells. In this context it appears that Fra-2 heterodimerizes with c-Jun and JunD. Studying the c-jun enhancer in reporter gene assays we observed that the muscle transcription factors MEF2A and MyoD can contribute to robust transcriptional activation of the c-jun enhancer. In differentiating muscle cells mutation of the MEF2 site reduces transactivation of the c-jun enhancer and MEF2A is the predominant MEF2 isoform binding to this cis element. Transcriptional activation of an AP-1 site containing reporter gene (TRE-Luc) is enhanced under differentiation conditions compared with growth conditions in C2C12 muscle cells. Further studies indicate that Fra-2 containing A-P-1 complexes can transactivate the MyoD enhancer/promoter. Thus, an A-P-1 complex containing Fra-2 and c-Jun or JunD is consistent with muscle differentiation, indicating that AP-1 function during myogenesis is dependent on its subunit composition.