Characterization of the dipeptide repeat protein in the molecular pathogenesis of c9FTD/ALS
Characterization of the dipeptide repeat protein in the molecular pathogenesis of c9FTD/ALS
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DOI：
10.1093/hmg/ddu576
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发表时间：
2015-03-15
影响因子：
3.5
通讯作者：
Suzuki, Norihiro
中科院分区：
文献类型：
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作者：
Yamakawa, Mai;Ito, Daisuke;Suzuki, Norihiro
GGGGCC六核苷酸重复序列在9号染色体开放阅读框72(C9orf72)基因非编码区的扩增是额颞叶痴呆(FTD)和肌萎缩侧索硬化症(ALS)最常见的原因。最近，有报道称，重复相关的非ATG(RAN)翻译的一种非传统机制源于C9orf72的扩增。C9FTD/ALS患者脑组织中存在C9orf72重复序列的正、反义转录本，即甘氨酸-丙氨酸(PolyGA)、甘氨酸-丙氨酸(Poly-GP)、甘氨酸-精氨酸(Poly-GR)、脯氨酸-精氨酸(Poly-PR)和脯氨酸-丙氨酸(PolyPA)的二肽重复蛋白(DRP)。然而，RAN翻译的多肽的病理意义仍不清楚。我们合成了编码100个重复的DRP的cDNA，没有GGGGCC重复，并评估了这些蛋白质对体内培养细胞和皮质神经元的影响。我们的结果表明，PolyGA蛋白在神经细胞中形成了高度聚集的泛素/p62阳性包涵体。相反，高度碱性的蛋白质Poly-GR和PR也形成了独特的泛素/p62阴性细胞质内含物，与RNA颗粒的成分共同定位。细胞毒性评价显示，过表达的多聚GA、多聚糖蛋白和多聚GR增加了泛素-蛋白酶体系统(UPS)底物，包括TDP-43，并增强了对蛋白酶体抑制剂的敏感性，表明这些DRP具有细胞毒性，可能是通过UPS功能障碍实现的。提示毒性DRPs的功能获得机制可能参与了C9FTD/ALS的发病机制，DRPs可能成为治疗C9FTD/ALS的新靶点。
The expansion of the GGGGCC hexanucleotide repeat in the non-coding region of the chromosome 9 open-reading frame 72 (C9orf72) gene is the most common cause of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) (c9FTD/ALS). Recently, it was reported that an unconventional mechanism of repeat-associated non-ATG (RAN) translation arises from C9orf72 expansion. Sense and anti-sense transcripts of the expanded C9orf72 repeat, i.e. the dipeptide repeat protein (DRP) of glycine-alanine (poly-GA), glycine-proline (poly-GP), glycine-arginine (poly-GR), proline-arginine (poly-PR) and proline-alanine (poly-PA), are deposited in the brains of patients with c9FTD/ALS. However, the pathological significance of RAN-translated peptides remains unknown. We generated synthetic cDNAs encoding 100 repeats of DRP without a GGGGCC repeat and evaluated the effects of these proteins on cultured cells and cortical neurons in vivo. Our results revealed that the poly-GA protein formed highly aggregated ubiquitin/p62-positive inclusion bodies in neuronal cells. In contrast, the highly basic proteins poly-GR and PR also formed unique ubiquitin/p62-negative cytoplasmic inclusions, which co-localized with the components of RNA granules. The evaluation of cytotoxicity revealed that overexpressed poly-GA, poly-GP and poly-GR increased the substrates of the ubiquitin-proteasome system (UPS), including TDP-43, and enhanced the sensitivity to a proteasome inhibitor, indicating that these DRPs are cytotoxic, possibly via UPS dysfunction. The present data indicate that a gain-of-function mechanism of toxic DRPs possibly contributes to pathogenesis in c9FTD/ALS and that DRPs may serve as novel therapeutic targets in c9FTD/ALS.