Cytosolic domain of SIDT2 carries an arginine-rich motif that binds to RNA/DNA and is important for the direct transport of nucleic acids into lysosomes
Cytosolic domain of SIDT2 carries an arginine-rich motif that binds to RNA/DNA and is important for the direct transport of nucleic acids into lysosomes
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DOI：
10.1080/15548627.2020.1712109
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发表时间：
2020-01-18
期刊：
影响因子：
13.3
通讯作者：
Kabuta, Tomohiro
中科院分区：
文献类型：
--
作者：
Hase, Katsunori;Contu, Viorica Raluca;Kabuta, Tomohiro
RNA自噬和DNA自噬（RDA）是非常规的自噬途径，其中核酸直接通过溶酶体膜运输，然后在溶酶体内降解。我们以前已经表明，双位蛋白LAMP2C和推定的RNA转运蛋白SIDT2，这两种溶酶体膜蛋白，介导核酸直接转运到溶酶体中，LAMP2C与核酸相互作用，并在RDA期间作为受体发挥作用。由于SIDT2介导的RDA发生在缺乏LAMP2C的分离的溶酶体中，因此在本研究中，我们测试了SIDT2本身也可以与核酸相互作用的假设。我们的研究结果表明，SIDT2直接结合RNA和DNA通过一个富含精氨酸的基序（ARM）位于其主要胞质结构域，和破坏这个基序显着损害SIDT2介导的RNA自噬活性。我们还发现，SIDT2与HTT（亨廷顿蛋白）转录本的外显子1通过ARM以CAG依赖的方式相互作用。此外，SIDT2的过表达促进HTT mRNA的降解，并降低多聚谷氨酰胺扩增的HTT聚集体的水平，这是亨廷顿病的标志。此外，在细胞水平上对LAMP2C和SIDT2功能的比较分析显示，这两种蛋白质对RNA自噬活性发挥协同作用，并且介导SIDT2和LAMP2C与RNA相互作用的ARM对于协同作用是必需的。总之，我们的研究结果指出了SIDT2的核酸结合能力对于其通过脂质双层转运核酸的功能的重要性，并表明了RN自噬激活在降低致病毒性蛋白表达水平方面的潜在应用。
RNautophagy and DNautophagy (RDA) are unconventional autophagic pathways where nucleic acids are directly transported through the lysosomal membrane, then degraded inside lysosomes. We have previously shown that bitopic protein LAMP2C and putative RNA transporter SIDT2, both lysosomal membrane proteins, mediate the direct transport of nucleic acids into lysosomes and that LAMP2C interacts with the nucleic acids and functions as a receptor during RDA. Because SIDT2-mediated RDA occurs in isolated lysosomes that lack LAMP2C, in this study, we tested the hypothesis that SIDT2 itself could also interact with the nucleic acids. Our results show that SIDT2 directly binds RNA and DNA through an arginine-rich motif (ARM) located within its main cytosolic domain, and disruption of this motif dramatically impairs SIDT2-mediated RNautophagic activity. We also found that SIDT2 interacts with exon 1 of HTT (huntingtin) transcript through the ARM in a CAG-dependent manner. Moreover, overexpression of SIDT2 promoted degradation of HTT mRNA and reduced the levels of polyglutamine-expanded HTT aggregates, hallmarks of Huntington disease. In addition, a comparative analysis of LAMP2C and SIDT2 functions at the cellular level revealed that the two proteins exert a synergistic effect on RNautophagic activity and that the ARMs which mediate the interactions of SIDT2 and LAMP2C with RNA are essential for the synergy. Together, our results point out the importance of nucleic acid-binding capacity of SIDT2 for its function in translocating nucleic acids through the lipid bilayer and suggests a potential application of RNautophagy activation to reduce the expression levels of disease-causing toxic proteins.