Bragg D C, Camp S M, Kaufman C A, Wilbur J D, Boston H, Schuback D E, Hanson P I, Sena-Esteves M, Breakefield X O
Department of Cell Biology and Physiology, Washington University School of Medicine, St Louis, MO 63110, USA.
Neuroscience. 2004;125(3):651-61. doi: 10.1016/j.neuroscience.2004.01.053.
TorsinA is a novel protein identified in the search for mutations underlying the human neurologic movement disorder, early onset torsion dystonia. Relatively little is understood about the normal function of torsinA or the physiological effects of the codon deletion associated with most cases of disease. Overexpression of wild-type torsinA in cultured cells by DNA transfection results in a reticular distribution of immunoreactive protein that co-localizes with endoplasmic reticulum resident chaperones, while the dystonia-related mutant form accumulates within concentric membrane whorls and nuclear-associated membrane stacks. In this study we examined the biogenesis of mutant torsinA-positive membrane inclusions using tetracycline-regulated herpes simplex virus amplicon vectors. At low expression levels, mutant torsinA was localized predominantly around the nucleus, while at high levels it was also concentrated within cytosolic spheroid inclusions. In contrast, the distribution of wild-type torsinA did not vary, appearing diffuse and reticular at all expression levels. These observations are consistent with descriptions of inducible membrane synthesis in other systems in which cytosolic membrane whorls are derived from multilayered membrane stacks that first form around the nuclear envelope. These results also suggest that formation of mutant torsinA-positive inclusions occurs at high expression levels in culture, whereas the perinuclear accumulation of the mutant protein is present even at low expression levels that are more likely to resemble those of the endogenous protein. These nuclear-associated membrane structures enriched in mutant torsinA may therefore be of greater relevance to understanding how the dystonia-related mutation compromises cellular physiology.
扭转蛋白A是在寻找人类神经运动障碍——早发性扭转性肌张力障碍潜在突变过程中发现的一种新型蛋白质。对于扭转蛋白A的正常功能或与大多数疾病病例相关的密码子缺失的生理影响，人们了解相对较少。通过DNA转染在培养细胞中过表达野生型扭转蛋白A会导致免疫反应性蛋白呈网状分布，并与内质网驻留伴侣蛋白共定位，而与肌张力障碍相关的突变形式则积聚在同心膜涡旋和核相关膜堆叠中。在本研究中，我们使用四环素调控的单纯疱疹病毒扩增子载体研究了突变型扭转蛋白A阳性膜内含物的生物发生。在低表达水平时，突变型扭转蛋白A主要定位于细胞核周围，而在高表达水平时，它也集中在胞质球状内含物中。相比之下，野生型扭转蛋白A的分布没有变化，在所有表达水平下均呈弥漫性和网状。这些观察结果与其他系统中诱导性膜合成的描述一致，在这些系统中，胞质膜涡旋源自首先在核膜周围形成的多层膜堆叠。这些结果还表明，突变型扭转蛋白A阳性内含物的形成发生在培养物的高表达水平，而突变蛋白的核周积累即使在更可能类似于内源性蛋白的低表达水平时也存在。因此，这些富含突变型扭转蛋白A的核相关膜结构可能与理解肌张力障碍相关突变如何损害细胞生理学更相关。
