Regulation of Utrophin Promoter in Muscle

描述（由申请人提供）：Utrophin（肌营养不良蛋白相关蛋白）与肌营养不良蛋白具有广泛的序列同源性和组织基序，被认为是肌营养不良蛋白的常染色体同源物。事实上，转基因过表达的肌营养蛋白可以在功能上替代缺失的肌营养不良蛋白分子，逆转mdx（营养不良）小鼠肌肉中的营养不良病理生理。肌营养因子基因虽然普遍表达，但在发育、再生和成熟骨骼肌中具有高度调控的亚细胞分布。在成熟的肌纤维（细长的多核细胞）中，肌营养蛋白在突触或神经肌肉连接处（NMJ）富集。肌纤维中肌营养因子的空间分布与烟碱乙酰胆碱受体（nACHR）的分布在很大程度上相似，特别是它们受运动神经释放的生长和分化因子（如heregulin）的影响。nACHR和肌营养蛋白在NMJ发生选择性富集，部分原因是它们的信息优先在亚突触核而不是沿肌纤维长度分散的核上转录。我们和其他人最近证明，神经突相关生长因子heregulin利用ERK （MAP激酶）信号通路促进GABPa/b转录因子复合物与肌营养因子启动子的N-Box基元结合，从而激活启动子并增加肌营养因子基因在培养肌肉细胞中的表达。

DESCRIPTION (provided by applicant): Utrophin (dystrophin related protein) shares extensive sequence homology and organizational motifs with dystrophin, and is considered to be the autosomal homolog of dystrophin. Indeed, transgenic over expression of utrophin can functionally substitute for the missing dystrophin molecule and reverse the dystrophic patho-physiology in the muscles of mdx (dystrophic) mice. The utrophin gene, while ubiquitously expressed, has a highly regulated sub-cellular distribution during development, regeneration as well as in mature skeletal muscle. In mature myofibers (elongated multi-nucleated cells), utrophin is enriched at the synapse or neuromuscular junction (NMJ). The spatial distribution of utrophin in myofibers parallels the distribution of nicotinic acetylcholine receptors (nACHR) to a remarkable degree, in particular, the manner in which they are influenced by the release of growth and differentiation factors (e.g. heregulin) from motor nerves. Selective enrichment of nACHR and utrophin at the NMJ occurs, in part, due to their messages being preferentially transcribed at sub-synaptic nuclei rather than nuclei scattered along the length of the myofiber. We and others, recently demonstrated that the neurite-associated growth factor heregulin utilizes the ERK (MAP kinase) signaling pathway to promote the binding of the GABPa/b transcription factor complex to the N-Box motif of the utrophin promoter, thus activating the promoter and increasing utrophin gene expression in cultured muscle cells. Current hypotheses on the regulation of utrophin expression in muscle center on N-box dependent compartmentalized transcription of utrophin at sub-synaptic nuclei. We hypothesize that additional trans-acting factors exist and regulate the utrophin promoter. We also hypothesize that co-operability among these trans-acting factors and signaling pathways plays a role in utrophin promoter regulation. In our preliminary studies, we have identified additional trans-acting factors, their signaling pathways and describe their co-operability in utrophin promoter regulation; we have also studied heregulin mediated utrophin promoter activation in mouse muscle, in vivo. In this proposal we plan to extend these studies to better understand the molecular mechanisms of utrophin promoter regulation in skeletal muscle.