Importin 8 is a gene silencing factor that targets argonaute proteins to distinct mRNAs

Cell. 2009 Feb 6;136(3):496-507. doi: 10.1016/j.cell.2008.12.023. Epub 2009 Jan 22.


Small regulatory RNAs including small interfering RNAs (siRNAs) and microRNAs (miRNAs) guide Argonaute (Ago) proteins to specific target RNAs leading to mRNA destabilization or translational repression. Here, we report the identification of Importin 8 (Imp8) as a component of miRNA-guided regulatory pathways. We show that Imp8 interacts with Ago proteins and localizes to cytoplasmic processing bodies (P bodies), structures involved in RNA metabolism. Furthermore, we detect Ago2 in the nucleus of HeLa cells, and knockdown of Imp8 reduces the nuclear Ago2 pool. Using immunoprecipitations of Ago2-associated mRNAs followed by microarray analysis, we further demonstrate that Imp8 is required for the recruitment of Ago protein complexes to a large set of Ago2-associated target mRNAs, allowing for efficient and specific gene silencing. Therefore, we provide evidence that Imp8 is required for cytoplasmic miRNA-guided gene silencing and affects nuclear localization of Ago proteins.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Active Transport, Cell Nucleus
  • Argonaute Proteins
  • Cell Line
  • Cytoplasmic Granules / metabolism
  • Eukaryotic Initiation Factor-2 / metabolism*
  • Gene Silencing
  • HeLa Cells
  • Humans
  • Intranuclear Inclusion Bodies / metabolism
  • MicroRNAs / metabolism
  • RNA, Messenger / metabolism*
  • beta Karyopherins / metabolism*


  • AGO2 protein, human
  • Argonaute Proteins
  • Eukaryotic Initiation Factor-2
  • IPO8 protein, human
  • MicroRNAs
  • RNA, Messenger
  • beta Karyopherins

Associated data

  • GEO/GSE14054