Goswami S K, Siddiqui M A
Department of Anatomy and Cell Biology, SUNY Health Science Center at Brooklyn 11203, USA.
Cell Mol Biol Res. 1995;41(3):199-205.
MyoD-mediated activation of skeletal muscle genes, which is dependent upon the consensus E-box sequence, involves, at least in one group of muscle genes, another transcription factor, the myocyte enhancer factor-2 (MEF-2). Since the cardiac myosin light chain-2 (MLC-2) gene promoter lacks the functional E-box but contains the activator MEF-2 site, we tested the effect of ectopic expression of MyoD on cardiac MLC-2 promoter function. Here, we demonstrate that either transient or stable expression of MyoD in otherwise nonpermissive C3H10T1/2 fibroblast cells can promote the expression of MLC-2/CAT. Deletion and site-specific mutation analysis demonstrate that the MEF-2 site (Element B) in the MLC-2 promoter is the target of activation by MyoD. Gel mobility shift assay using nuclear extracts from the normal and MyoD-transfected fibroblast cells did not show a difference in the major MEF-2 binding complexes, except for one complex of fast-moving mobility, which suggested that new MEF-2-like regulatory proteins are induced by MyoD.
肌分化因子（MyoD）介导的骨骼肌基因激活依赖于共有E盒序列，至少在一组肌肉基因中，还涉及另一种转录因子——肌细胞增强因子2（MEF-2）。由于心肌肌球蛋白轻链2（MLC-2）基因启动子缺乏功能性E盒，但含有激活因子MEF-2位点，我们测试了异位表达MyoD对心肌MLC-2启动子功能的影响。在此，我们证明，在原本不允许的C3H10T1/2成纤维细胞中，MyoD的瞬时或稳定表达均可促进MLC-2/CAT的表达。缺失和位点特异性突变分析表明，MLC-2启动子中的MEF-2位点（元件B）是MyoD激活的靶点。使用正常和成肌分化因子转染的成纤维细胞的核提取物进行凝胶迁移率变动分析，结果显示，除了一种迁移速度较快的复合物外，主要的MEF-2结合复合物并无差异，这表明MyoD可诱导新的MEF-2样调节蛋白。
