Multivesicular bodies associate with components of miRNA effector complexes and modulate miRNA activity

Nat Cell Biol. 2009 Sep;11(9):1143-9. doi: 10.1038/ncb1929. Epub 2009 Aug 16.

Abstract

In animals, P-bodies or GW-bodies appear to cause the congregation of proteins involved in microRNA (miRNA)-mediated post-transcriptional silencing. The localization of P-bodies does not overlap with that of known organelles and are thus considered independent of lipid bilayers. Nonetheless, an miRNA effector protein, argonaute 2 (AGO2), was initially identified as membrane-associated, and some miRNAs have been found in secreted vesicles (exosomes) that derive from endo-lysosomal compartments called multivesicular bodies (MVBs). Proteins can be sorted in a ubiquitin-dependent manner into MVBs by three heteromeric subcomplexes, collectively termed ESCRT (endosomal sorting complex required for transport), to be further secreted in exosomes and/or degraded by the lysosome. Here we show that GW-bodies containing GW182 and AGO2, two main components of the RNA-induced silencing complex (RISC), are distinct from P-bodies due to their congregation with endosomes and MVBs. Moreover, miRNAs and miRNA-repressible mRNAs are enriched at these cellular membranes, suggesting that endosomes and/or MVBs are sites of miRNA-loaded RISC (miRISC) accumulation and, possibly, action. We further show that purified exosome-like vesicles secreted by MVBs are considerably enriched in GW182, but not P-body components, AGO2 or miRNA-repressible mRNA. Moreover, cells depleted of some ESCRT components show compromised miRNA-mediated gene silencing and over-accumulate GW182, which associates with ubiquitylated proteins. Therefore, GW182, possibly in association with a fraction of miRNA-loaded AGO2, is sorted into MVBs for secretion and/or lysosomal degradation. We propose that this process promotes continuous assembly or disassembly of membrane-associated miRISCs, which is possibly required for miRNA loading or target recognition and subsequent silencing.

Publication types

  • Research Support, Non-U.S. Gov't
  • Comment

MeSH terms

  • Argonaute Proteins
  • Autoantigens / metabolism
  • Cell Line
  • Endoribonucleases / metabolism
  • Endosomes / metabolism*
  • Endosomes / ultrastructure
  • Eukaryotic Initiation Factor-2 / metabolism
  • Exosomes / metabolism
  • Exosomes / ultrastructure
  • Gene Knockdown Techniques
  • Humans
  • MicroRNAs / metabolism*
  • Protein Transport
  • RNA-Binding Proteins
  • Trans-Activators / metabolism

Substances

  • AGO2 protein, human
  • Argonaute Proteins
  • Autoantigens
  • Eukaryotic Initiation Factor-2
  • MicroRNAs
  • RNA-Binding Proteins
  • Trans-Activators
  • autoantigen GW182, human
  • Endoribonucleases
  • DCP1A protein, human