Brennan T J, Olson E N
Department of Biochemistry and Molecular Biology, University of Texas, MD Anderson Cancer Center, Houston 77030.
Genes Dev. 1990 Apr;4(4):582-95. doi: 10.1101/gad.4.4.582.
Myogenin is a member of a family of muscle-specific factors that can activate the muscle differentiation program in nonmyogenin cells. Using antibodies directed against unique domains of myogenin, we show in the present study that myogenin resides in the nucleus of differentiated muscle cells. Myogenin translated in vitro does not exhibit detectable DNA binding activity; however, when dimerized with the ubiquitous enhancer-binding factor E12, it acquires high affinity for an element in the core of the muscle creatine kinase (MCK) enhancer that is conserved among many muscle-specific genes. Antibody disruption experiments show that myogenin, synthesized during differentiation of the BC3H1 and C2 muscle cell lines, is part of a complex that binds to the same site in the MCK enhancer as myogenin-E12 translated in vitro. Mutagenesis of the myogenin-E12-binding site in the MCK enhancer abolishes binding of the heterodimer and prevents trans-activation of the enhancer by myogenin. The properties of myogenin suggest that its functions as a sequence-specific DNA-binding factor that interacts directly with muscle-specific genes during myogenesis. The dependence of myogenin on E12 for high-affinity DNA binding activity also suggests that the susceptibility of various cell types to the actions of myogenin may be influenced by the cellular factors with which it may interact.
肌细胞生成素是肌肉特异性因子家族的一员，它能够在非肌细胞生成素细胞中激活肌肉分化程序。在本研究中，我们使用针对肌细胞生成素独特结构域的抗体，证明了肌细胞生成素存在于分化的肌肉细胞核中。体外翻译的肌细胞生成素未表现出可检测到的DNA结合活性；然而，当与普遍存在的增强子结合因子E12二聚化时，它对肌肉肌酸激酶（MCK）增强子核心中的一个元件具有高亲和力，该元件在许多肌肉特异性基因中保守。抗体破坏实验表明，在BC3H1和C2肌肉细胞系分化过程中合成的肌细胞生成素是一种复合物的一部分，该复合物与体外翻译的肌细胞生成素-E12结合到MCK增强子中的同一位点。MCK增强子中肌细胞生成素-E12结合位点的诱变消除了异二聚体的结合，并阻止了肌细胞生成素对增强子的反式激活。肌细胞生成素的特性表明，它在肌生成过程中作为一种序列特异性DNA结合因子，直接与肌肉特异性基因相互作用。肌细胞生成素对E12的高亲和力DNA结合活性的依赖性还表明，各种细胞类型对肌细胞生成素作用的敏感性可能受与其相互作用的细胞因子影响。
