Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
RNA. 2011 Jun;17(6):1057-65. doi: 10.1261/rna.2596511. Epub 2011 Apr 7.
Systemic RNAi in Caenorhabditis elegans requires the widely conserved transmembrane protein SID-1 to transport RNAi silencing signals between cells. When expressed in Drosophila S2 cells, C. elegans SID-1 enables passive dsRNA uptake from the culture medium, suggesting that SID-1 functions as a channel for the transport of double-stranded RNA (dsRNA). Here we show that nucleic acid transport by SID-1 is specific for dsRNA and that addition of dsRNA to SID-1 expressing cells results in changes in membrane conductance, which indicate that SID-1 is a dsRNA gated channel protein. Consistent with passive bidirectional transport, we find that the RNA induced silencing complex (RISC) is required to prevent the export of imported dsRNA and that retention of dsRNA by RISC does not seem to involve processing of retained dsRNA into siRNAs. Finally, we show that mimics of natural molecules that contain both single- and double-stranded dsRNA, such as hairpin RNA and pre-microRNA, can be transported by SID-1. These findings provide insight into the nature of potential endogenous RNA signaling molecules in animals.
在秀丽隐杆线虫中，系统性 RNAi 需要广泛保守的跨膜蛋白 SID-1 在细胞间运输 RNAi 沉默信号。当在果蝇 S2 细胞中表达时，秀丽隐杆线虫 SID-1 能够从培养基中被动摄取双链 RNA（dsRNA），这表明 SID-1 作为双链 RNA（dsRNA）运输的通道发挥作用。在这里，我们表明 SID-1 的核酸运输是特异性的 dsRNA，并且向表达 SID-1 的细胞中添加 dsRNA 会导致膜电导发生变化，这表明 SID-1 是一种 dsRNA 门控通道蛋白。与被动双向运输一致，我们发现 RNA 诱导沉默复合物（RISC）是防止导入的 dsRNA 输出所必需的，并且 RISC 保留 dsRNA 似乎不涉及将保留的 dsRNA 加工成 siRNA。最后，我们表明，含有单链和双链 dsRNA 的天然分子类似物，如发夹 RNA 和前 microRNA，可以被 SID-1 转运。这些发现为动物中潜在的内源性 RNA 信号分子的性质提供了深入了解。
