Ratovitski Tamara, Arbez Nicolas, Stewart Jacqueline C, Chighladze Ekaterine, Ross Christopher A
a Division of Neurobiology; Department of Psychiatry; Johns Hopkins University School of Medicine ; CMSC 8-121; Baltimore , MD , USA.
Cell Cycle. 2015;14(11):1716-29. doi: 10.1080/15384101.2015.1033595.
Abnormal protein interactions of mutant huntingtin (Htt) triggered by polyglutamine expansion are thought to mediate Huntington's disease (HD) pathogenesis. Here, we explored a functional interaction of Htt with protein arginine methyltransferase 5 (PRMT5), an enzyme mediating symmetrical dimethylation of arginine (sDMA) of key cellular proteins, including histones, and spliceosomal Sm proteins. Gene transcription and RNA splicing are impaired in HD. We demonstrated PRMT5 and Htt interaction and their co-localization in transfected neurons and in HD brain. As a result of this interaction, normal (but to a lesser extend mutant) Htt stimulated PRMT5 activity in vitro. SDMA of histones H2A and H4 was reduced in the presence of mutant Htt in primary cultured neurons and in HD brain, consistent with a demonstrated reduction in R3Me2s occupancy at the transcriptionally repressed promoters in HD brain. SDMA of another PRMT5 substrate, Cajal body marker coilin, was also reduced in the HD mouse model and in human HD brain. Finally, compensation of PRMT5 deficiency by ectopic expression of PRMT5/MEP50 complexes, or by the knock-down of H4R3Me2 demethylase JMJD6, reversed the toxic effects of mutant Htt in primary cortical neurons, suggesting that PRMT5 deficiency may mediate, at least in part, HD pathogenesis. These studies revealed a potential new mechanism for disruption of gene expression and RNA processing in HD, involving a loss of normal function of Htt in facilitation of PRMT5, supporting the idea that epigenetic regulation of gene transcription may be involved in HD and highlighting symmetric dimethylation of arginine as potential new therapeutic target.
由多聚谷氨酰胺扩增引发的突变型亨廷顿蛋白（Htt）的异常蛋白相互作用被认为介导了亨廷顿舞蹈病（HD）的发病机制。在此，我们探究了Htt与蛋白精氨酸甲基转移酶5（PRMT5）的功能相互作用，PRMT5是一种介导包括组蛋白和剪接体Sm蛋白在内的关键细胞蛋白精氨酸对称二甲基化（sDMA）的酶。HD中基因转录和RNA剪接受损。我们证明了PRMT5与Htt在转染神经元和HD脑内的相互作用及其共定位。这种相互作用的结果是，正常（但程度较轻的突变型）Htt在体外刺激了PRMT5的活性。在原代培养神经元和HD脑中，突变型Htt存在时组蛋白H2A和H4的sDMA减少，这与HD脑中转录抑制启动子处R3Me2s占有率的降低一致。另一种PRMT5底物、 Cajal体标记物卷曲螺旋蛋白的sDMA在HD小鼠模型和人类HD脑中也减少。最后，通过异位表达PRMT5/MEP50复合物或敲低H4R3Me2去甲基化酶JMJD6来补偿PRMT5缺陷，可逆转突变型Htt在原代皮质神经元中的毒性作用，这表明PRMT5缺陷可能至少部分介导了HD的发病机制。这些研究揭示了HD中基因表达和RNA加工破坏的一种潜在新机制，涉及Htt在促进PRMT5正常功能方面的丧失，支持了基因转录的表观遗传调控可能参与HD的观点，并突出了精氨酸对称二甲基化作为潜在新治疗靶点的作用。
