Export of microRNAs and microRNA-protective protein by mammalian cells

By Kai Wang, Shile Zhang, Jessica A. Weber, D. Baxter, D. Galas. Nucleic Acids Research, 2010

1,010 citations recorded by the source corpus.

The discovery of microRNAs (miRNAs) as a new class of regulators of gene expression has triggered an explosion of research activities, but has left many unanswered questions about how this regulation functions and how it is integrated with other regulatory mechanisms. A number of miRNAs have been found to be present in plasma and other body fluids of humans and mice in surprisingly high concentrations. This observation was unexpected in two respects: first, the fact that these molecules are present at all outside the cell at significant concentrations and second, that these molecules appear to be stable outside of the cell. In light of this it has been suggested that the biological function of miRNAs may also extend outside of the cell and mediate cell–cell communication. We report here that after serum deprivation several human cell lines tested promptly export a substantial amount of miRNAs into the culture medium and the export process is largely energy dependent. The exported miRNAs are found both within and outside of the 16.5 and 120 K centrifugation pellets which contain most of the known cell-derived vesicles, the microvesicles and exosomes. We have identified some candidate proteins involved in this system, and one of these proteins may also play a role in protecting extracellular miRNAs from degradation. Our results point to a hitherto unrecognized and uncharacterized miRNA trafficking system in mammalian cells that is consistent with the cell–cell communication hypothesis.

Subfields: Cancer Research, Molecular Biology

View Paper: https://www.semanticscholar.org/paper/f5a1881e60669626f377478f2870ae37735e3fa1

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Citations in the corpus

Exosomes: current knowledge of their composition, biological functions, and diagnostic and therapeutic potentials. (2012, background): “[31] found that large number of miRNAs are contained within extracellular protein complexes rather than exosomes (biological roles for these are yet to be understood).”
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MicroRNA: Biogenesis, Function and Role in Cancer (2010, background): “The predominant hypothesis suggests that miRNAs (more likely pre-miRNAs) are circulating in exosomes that are shed from normal or tumor-derived cells [354].”
Cardiac fibroblast-derived microRNA passenger strand-enriched exosomes mediate cardiomyocyte hypertrophy. (2014, neutral): “Circulating miRNAs are actively transported, either by the inclusion in microvesicles/exosomes (9, 11, 12) or by binding to RNA-binding proteins (21, 22), allowing protection from ribonuclease-dependent degradation.”
Argonaute2 complexes carry a population of circulating microRNAs independent of vesicles in human plasma (2011, background): “In addition, cultured fibroblasts secrete nucleophosmin 1, which is able to protect miRNA from degradation in vitro (29).”
Exosome Secretion: Molecular Mechanisms and Roles in Immune Responses (2011, background): “larger secreted membrane vesicles (40), and that miRNAs”
Comparing the MicroRNA Spectrum between Serum and Plasma (2012, background): “During the coagulation process, blood cells are exposed to a ‘‘stressful environment’’ which may ‘‘stimulate’’ the release of certain miRNAs and other RNAs, as was observed when cells were exposed in vitro to serum-free conditions [7].”
Exosome-Mediated Transfer of miR-133b from Multipotent Mesenchymal Stromal Cells to Neural Cells Contributes to Neurite Outgrowth (2012, neutral): “miRNAs are exported from cells both within and outside the exosomes [53, 54].”
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Deep sequencing of RNA from immune cell-derived vesicles uncovers the selective incorporation of small non-coding RNA biotypes with potential regulatory functions (2012, background): “Although the majority of circulating miRNAs in human plasma and serum were found to co-fractionate with proteins such as Argonaute2 (Ago2) and nucleophosmin, which have been suggested to protect miRNAs from degradation in RNase-rich environments (22,23), it is currently unknown if vesicle-free RNAs ”
Obstacles and opportunities in the functional analysis of extracellular vesicle RNA – an ISEV position paper (2017, background): “same miRNA is present at significant levels in both large and small EVs derived from A549 cells.[21] In immune cells, the miRNA content of EVs was shown to differ by immune cell type when comparing EVs from B- or T-cell lines and primary dendritic cells (DC).”