Russo Arianna, Scardigli Raffaella, La Regina Federico, Murray Melissa E, Romano Nicla, Dickson Dennis W, Wolozin Benjamin, Cattaneo Antonino, Ceci Marcello
Department of Ecology and Biology, Tuscia University, Viterbo 01100, Italy.
Institute of Translational Pharmacology, National Council of Research, Rome 00133, Italy.
Hum Mol Genet. 2017 Apr 15;26(8):1407-1418. doi: 10.1093/hmg/ddx035.
TDP-43 is a well known RNA binding protein involved in the pathogenesis of Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Lobar Dementia (FTLD). In physiological conditions, TDP-43 mainly localizes in the nucleus and shuttles, at least in neurons, to the cytoplasm to form TDP-43 RNA granules. In the nucleus, TDP-43 participates to the expression and splicing of RNAs, while in the cytoplasm its functions range from transport to translation of specific mRNAs. However, if loss or gain of these TDP-43 functions are affected in ALS/FTLD pathogenesis is not clear. Here, we report that TDP-43 localizes on ribosomes not only in primary neurons but also in SH-SY5Y human neuroblastoma cells. We find that binding of TDP-43 to the translational machinery is mediated by an interaction with a specific ribosomal protein, RACK1, and that an increase in cytoplasmic TDP-43 represses global protein synthesis, an effect which is rescued by overexpression of RACK1. Ribosomal loss of RACK1, which excludes TDP-43 from the translational machinery, remarkably reduces formation of TDP-43 cytoplasmic inclusions in neuroblastoma cells. Finally, we corroborate the interaction between TDP-43 and RACK1 on polyribosomes of neuroblastoma cells with mis-localization of RACK1 on TDP-43 positive cytoplasmic inclusions in motor neurons of ALS patients. In conclusions, results from this study suggest that TDP-43 represents a translational repressor not only for specific mRNAs but for overall translation and that its binding to polyribosomes through RACK1 may promote, under conditions inducing ALS pathogenesis, the formation of cytoplasmic inclusions.
TDP-43是一种众所周知的RNA结合蛋白，参与肌萎缩侧索硬化症（ALS）和额颞叶痴呆（FTLD）的发病机制。在生理条件下，TDP-43主要定位于细胞核，并至少在神经元中穿梭至细胞质以形成TDP-43 RNA颗粒。在细胞核中，TDP-43参与RNA的表达和剪接，而在细胞质中，其功能范围从特定mRNA的运输到翻译。然而，这些TDP-43功能的丧失或获得在ALS/FTLD发病机制中是否受到影响尚不清楚。在这里，我们报告TDP-43不仅在原代神经元中，而且在SH-SY5Y人神经母细胞瘤细胞中定位于核糖体。我们发现TDP-43与翻译机制的结合是由与一种特定核糖体蛋白RACK1的相互作用介导的，并且细胞质中TDP-43的增加会抑制整体蛋白质合成，RACK1的过表达可挽救这种效应。RACK1从核糖体上缺失，将TDP-43排除在翻译机制之外，显著减少了神经母细胞瘤细胞中TDP-43细胞质包涵体的形成。最后，我们通过ALS患者运动神经元中RACK1在TDP-43阳性细胞质包涵体上的错误定位，证实了神经母细胞瘤细胞多核糖体上TDP-43与RACK1之间的相互作用。总之，这项研究的结果表明，TDP-43不仅是特定mRNA的翻译抑制因子，也是整体翻译的抑制因子，并且在诱导ALS发病机制的条件下，其通过RACK1与多核糖体的结合可能促进细胞质包涵体的形成。
