Yang Liuqing, Gal Jozsef, Chen Jing, Zhu Haining
Department of Molecular and Cellular Biochemistry, College of Medicine, University of Kentucky, Lexington, KY 40536.
Department of Molecular and Cellular Biochemistry, College of Medicine, University of Kentucky, Lexington, KY 40536
Proc Natl Acad Sci U S A. 2014 Dec 16;111(50):17809-14. doi: 10.1073/pnas.1414004111. Epub 2014 Dec 1.
Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease. Fused in sarcoma (FUS) is a DNA/RNA binding protein and mutations in FUS cause a subset of familial ALS. Most ALS mutations are clustered in the C-terminal nuclear localization sequence of FUS and consequently lead to the accumulation of protein inclusions in the cytoplasm. It remains debatable whether loss of FUS normal function in the nucleus or gain of toxic function in the cytoplasm plays a more critical role in the ALS etiology. Moreover, the physiological function of FUS in the nucleus remains to be fully understood. In this study, we found that a significant portion of nuclear FUS was bound to active chromatin and that the ALS mutations dramatically decreased FUS chromatin binding ability. Functionally, the chromatin binding is required for FUS transcription activation, but not for alternative splicing regulation. The N-terminal QGSY (glutamine-glycine-serine-tyrosine)-rich region (amino acids 1-164) mediates FUS self-assembly in the nucleus of mammalian cells and the self-assembly is essential for its chromatin binding and transcription activation. In addition, RNA binding is also required for FUS self-assembly and chromatin binding. Together, our results suggest a functional assembly of FUS in the nucleus under physiological conditions, which is different from the cytoplasmic inclusions. The ALS mutations can cause loss of function in the nucleus by disrupting this assembly and chromatin binding.
肌萎缩侧索硬化症（ALS）是一种进行性神经退行性疾病。肉瘤融合蛋白（FUS）是一种DNA/RNA结合蛋白，FUS的突变导致一部分家族性ALS。大多数ALS突变聚集在FUS的C末端核定位序列中，从而导致蛋白质包涵体在细胞质中积累。FUS在细胞核中的正常功能丧失或在细胞质中的毒性功能获得在ALS病因中哪个起更关键的作用仍存在争议。此外，FUS在细胞核中的生理功能仍有待充分了解。在本研究中，我们发现很大一部分核FUS与活性染色质结合，并且ALS突变显著降低了FUS与染色质的结合能力。在功能上，染色质结合是FUS转录激活所必需的，但不是可变剪接调控所必需的。N末端富含QGSY（谷氨酰胺-甘氨酸-丝氨酸-酪氨酸）的区域（氨基酸1-164）介导FUS在哺乳动物细胞核中的自我组装，并且这种自我组装对于其染色质结合和转录激活至关重要。此外，RNA结合对于FUS的自我组装和染色质结合也是必需的。总之，我们的结果表明在生理条件下FUS在细胞核中存在功能性组装，这与细胞质包涵体不同。ALS突变可通过破坏这种组装和染色质结合导致细胞核功能丧失。
