Cullin mediated protein turnover in skeletal and cardiac muscles

7.项目总结/摘要 Cullin介导的骨骼肌和心肌蛋白质周转 蛋白质的调节性降解是细胞存活的重要机制。积累 聚集体/包涵体中的未降解蛋白，或（突变）蛋白的过早降解， 通常与疾病的发展有关，如心脏和骨骼肌肌病。 心肌和骨骼肌细胞含有多达四种用于降解肌纤维的蛋白水解系统， 蛋白质：半胱天冬酶和钙蛋白酶，泛素-蛋白酶体系统（UPS）和自噬 系统大多数细胞蛋白质的降解是通过UPS实现的，并且需要标记 底物蛋白通过泛素化（多泛素化）通过酶级联。底物识别 其随后的遍在化涉及E3-遍在蛋白连接酶和E2-遍在蛋白的协同作用 结合酶。有趣的是，参与肌肉蛋白泛素化的几种成分是 沿着肌原纤维定位，如MuRF蛋白家族的肌肉特异性E3连接酶。虽然数量可观， 人们的注意力一直集中在这些肌肉特异性UPS组件上，关于其作用的信息有限。 更普遍表达的E3-连接酶在肌肉蛋白质周转，以及它们是否可能发挥更多的作用， 肌病的发展和进展的因果作用。 在研究肌原纤维蛋白的obscurin家族的同时，我们发现了几个以前 Cullin-RING蛋白是泛素E3连接酶的一个大家族。此外，我们发现， 这些Cullin蛋白中的一些表现出与肌肉特异性E3-连接酶相当的肌原纤维定位。 这些有趣的结果，以及观察到cullin-RING连接酶在扩张的 心肌病（MLP敲除小鼠）和骨骼肌肌病（obscurin敲除）使我们发现了 假设cullin-3及其相关蛋白可能在肌肉蛋白质周转中发挥更大的作用， 此前预计。 拟议的研究项目调查了cullin蛋白对肌肉特异性蛋白的生物学作用， 周转，以及它们与obscurin蛋白家族的肌原纤维蛋白的联系，通过体内 分析心脏和骨骼肌生理学和功能的方法， 在分子水平上表征cullin-3、其结合伴侣以及它们与obscurin蛋白的结合。 初步研究表明，该项目的结果可能不仅对骨骼肌有影响， 肌病，如肢带型肌营养不良症（2 J型），通过与obscurin蛋白的联系，但也为 心肌病，因为cullin蛋白及其一些结合伴侣在动物中显著改变， 扩张型心肌病模型（MLP敲除）。

7. Project Summary/Abstract Cullin mediated protein turnover in skeletal and cardiac muscles The regulated degradation of proteins is an important mechanism for the survival of cells. Accumulation of undegraded proteins in aggrosomes/inclusion bodies, or the premature degradation of (mutant) proteins is often associated with development of diseases, like cardiac and skeletal muscle myopathies. Cardiac and skeletal muscle cells contain up to four proteolytic systems for the degradation of myofbrillar proteins: the caspase and calpain proteases, the ubiquitin-proteasome system (UPS), and the autophagy system. Degradation of most cellular proteins is achieved by way of the UPS and requires tagging of substrate proteins by ubiquitin (poly-ubiquitylation) through an enzymatic cascade. Recognition of substrate and its subsequent ubiquitylation involves the concerted action of E3-ubiquitin ligases and E2-ubiquitin conjugating enzymes. Intriguingly, several components involved in the ubiquitylation of muscle proteins are localized along myofibrils, like the muscle specific E3-ligases of the MuRF protein family. While considerable attention has been focused on these muscle specific UPS components, there is limited information on the role of the more ubiquitously expressed E3-ligases in muscle protein turnover, and whether they may play a more causal role for the development and progression of myopathies. While investigating the obscurin family of myofibrillar proteins, we identified several previously uncharacterized links to cullin-RING proteins, a large family of ubiquitin E3-ligases. Moreover we found that some of these cullin proteins exhibit a myofibrillar localization, comparable to muscle specific E3-ligases. These intriguing results, and the observation that cullin-RING ligases are altered in models for dilated cardiomyopathy (MLP knockout mouse) and skeletal muscle myopathy (obscurin knockout) led us to the hypothesis that cullin-3 and its associated proteins may play a greater role for muscle protein turnover than previously anticipated. The proposed research project investigates the biological role of cullin proteins for muscle specific protein- turnover, and their links to myofibrillar proteins of the obscurin protein family, through a combination of in vivo approaches that analyze cardiac and skeletal muscle physiology and function, with in vitro methods that characterize cullin-3, its binding partners, and their association to obscurin proteins at the molecular level. Preliminary studies indicate that results from this project may have ramifications not only for skeletal muscle myopathies, like the limb-girdle muscular dystrophy (type 2J) through links with obscurin proteins, but also for cardiomyopathies, since cullin proteins, and some of their binding partners are significantly altered in animal models for dilated cardiomyopathy (MLP knockout).