Regulation of Utrophin Promoter in Muscle

描述(申请人提供)：utroin(dystrophin相关蛋白)与dystrophin具有广泛的序列同源性和组织基序，被认为是dystrophin的常染色体同源物。事实上，转基因过表达utroin可以在功能上取代缺失的dystrophin分子，并逆转MDX(营养不良)小鼠肌肉营养不良的病理生理。虽然utroin基因广泛表达，但在发育、再生和成熟的骨骼肌中都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，中营养素在突触或神经肌肉接头(NMJ)处丰富。肌纤维中中性粒细胞营养素的空间分布在很大程度上与烟碱型乙酰胆碱受体(NACHR)的分布相似，特别是它们受到运动神经释放的生长和分化因子(如hereglin)的影响。NACHR和utroin在NMJ的选择性浓缩部分是因为它们的信息优先在突触下核转录，而不是沿着肌纤维长度散布的核。最近，我们和其他人证明了轴突相关生长因子hereglin利用ERK(MAP Kinase)信号通路促进GABPA/b转录因子复合体与utroin启动子的N-Box基序结合，从而激活启动子并增加培养的肌肉细胞中utroin基因的表达。 目前关于肌肉中心促性腺激素表达调控的假说是依赖N-box的突触下核团中促性腺激素的区段化转录。我们假设存在额外的反式作用因子，并调节utroin启动子。我们还假设，这些反式作用因子和信号通路之间的协同作用在促性腺激素启动子的调控中发挥作用。在我们的初步研究中，我们已经确定了其他反式作用因子，它们的信号通路，并描述了它们在促性腺激素启动子调控中的协同作用；我们还在体内研究了HERG介导的小鼠肌肉中促性腺激素启动子的激活。在这项提案中，我们计划扩大这些研究，以更好地了解骨骼肌中促性腺激素启动子调控的分子机制。

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.