title: Importin 8 regulates the transport of mature microRNAs into the cell nucleus.
abstract: Mature microRNAs (miRNAs), ∼ 22-nucleotide noncoding RNAs regulating target gene expression at the post-transcriptional level, have been recently shown to be transported into the nucleus where they modulate the biogenesis of other miRNAs or their own expression. However, the mechanism that governs the transport of mature miRNAs from cytoplasm to nucleus remains unknown. Here, we report that importin 8 (IPO8), a member of the karyopherin β (also named the protein import receptor importin β) family, plays a critical role in mediating the cytoplasm-to-nucleus transport of mature miRNAs. Specifically knocking down IPO8 but not other karyopherin β family proteins via siRNA significantly decreases the nuclear transport of various known nucleus-enriched miRNAs without affecting their total cellular levels. IPO8-mediated nuclear transport of mature miRNAs is also dependent on the association of IPO8 with the Argonaute 2 (Ago2) complex. Cross-immunoprecipitation and Western blot analysis show that IPO8 is physically associated with Ago2. Knocking down IPO8 via siRNA markedly decreases the nuclear transport of Ago2 but does not affect the total cellular Ago2 level. Furthermore, dissociating the binding of miRNAs with Ago2 by trypaflavine strongly reduces the IPO8-mediated nuclear transport of miRNAs.
authors.affiliation: Jiangsu Engineering Research Center for MicroRNA Biology and Biotechnology, State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, Jiangsu 210093, China.
authors.forename: Yao
authors.initials: Y
authors.lastname: Wei
authors.affiliation: Jiangsu Engineering Research Center for MicroRNA Biology and Biotechnology, State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, Jiangsu 210093, China. Electronic address: bixuehan2005@163.com.
authors.forename: Limin
authors.initials: L
authors.lastname: Li
authors.affiliation: Jiangsu Engineering Research Center for MicroRNA Biology and Biotechnology, State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, Jiangsu 210093, China.
authors.forename: Dong
authors.initials: D
authors.lastname: Wang
authors.affiliation: Jiangsu Engineering Research Center for MicroRNA Biology and Biotechnology, State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, Jiangsu 210093, China. Electronic address: cyzhang@nju.edu.cn.
authors.forename: Chen-Yu
authors.initials: CY
authors.lastname: Zhang
authors.affiliation: Jiangsu Engineering Research Center for MicroRNA Biology and Biotechnology, State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, Jiangsu 210093, China. Electronic address: kzen@nju.edu.cn.
authors.forename: Ke
authors.initials: K
authors.lastname: Zen
mesh_terms: D021581:Active Transport, Cell Nucleus; D000818:Animals; D060565:Argonaute Proteins / Q000378:metabolism*; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D003599:Cytoskeleton / Q000378:metabolism; D053263:Gene Regulatory Networks; D051379:Mice; D035683:MicroRNAs / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D011485:Protein Binding; D034741:RNA, Small Interfering / Q000378:metabolism; D028901:alpha Karyopherins / Q000737:chemistry / Q000502:physiology*
chemical_list: C526735:Ago2 protein, mouse; D060565:Argonaute Proteins; C553637:Kpna7 protein, mouse; D035683:MicroRNAs; D034741:RNA, Small Interfering; D028901:alpha Karyopherins
keywords: MicroRNA; Nuclear Transport; Polymerase Chain Reaction (PCR); RNA Processing; siRNA