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

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.

Exosomes as intercellular signalosomes and pharmacological effectors

“…In that respect two major components of the RNA-Induced Silencing Complex (RISC) have been shown to associate with MVB and to be sorted into exosomes [24].…”

Cell-Cell Communication Via Extracellular Membrane Vesicles and Its Role in the Immune Response

“…As for mRNAs, only a selected set of miRNAs are present in exosomes, and therefore the profile of exosomal miRNAs is distinct from that of cellular miRNAs. Exosomal miRNAs are also fully functional; they can modify the levels of target mRNAs and proteins when they successfully penetrate into the cytoplasm of the recipient cells (Gibbings et al, 2009;Rabinowits et al, 2009;Rana et al, 2013).…”

“…The ESCRT complex, a key component of the cellular machinery required to sort cytosolic proteins to the late endosomes, acts by associating with ubiquitinated proteins. Thus, the process of sorting cellular miRNAs into exosomes is hypothesized to occur as ubiquitinated RISC complexes interact with the ESCRT complexes in the late endosome (Gibbings et al, 2009). …”

“…Direct evidence that miRNAs transferred to immune cells may change biological properties of the recipient cells are scarce. However, one study has shown the effect of EBV-derived miRNAs in a highly artificial system (Gibbings et al, 2009;Rabinowits et al, 2009;Rana et al, 2013). The impact of miRNA transfer via exosomes is therefore one of many future research endeavors.…”

MicroRNA and autophagy—C. elegans joins the crew

“…In the first study, Bardehle et al used in vivo two-photon laser-scanning microscopy to monitor individual astrocytes for up to 28 days after a stab wound to the somatosensory cortex [7]. To visualize single cells, astrocytes were labelled using different lines: GLAST CreERT2 /eGFP or Confetti reporter, labelling 60-80% of all astrocytes; Aldh1l1-eGFP mice, labelling all astrocytes; and hGFAP-eGFP mice, labelling only those astrocytes with the highest GFAP expression.…”