Year: 2014

Extracellular vesicles, such as exosomes and microvesicles, have recently been discovered to contain different types of regulatory RNA such as long non-coding RNA (lncRNA).   The lncRNA are a group of diverse non-coding genes that are being increasingly implicated in biological processes, but they remain poorly characterized and understood.   Their role in cancers such as hepatocellular cancer (HCC) has been increasingly recognized. We have discovered that some lncRNA that contain highly conserved sequences, termed ultraconserved RNA (ucRNA), are transcribed and altered in HCC.   We examined the role of extracellular vesicles in mediating intercellular transfer of these lncRNA and influencing tumor cell behavior.  We found that lncRNA could be isolated in extracellular vesicles secreted from cultured HCC cells and then internalized by other cell types.  By profiling RNA expression in these extracellular vesicles and their donor cells, we identified and then cloned a ucRNA highly expressed and enriched in extracellular vesicles. This novel lncRNA, termed TUC339, was found to modulate tumor cell growth and adhesion. Suppression of TUC339 with siRNA reduced HCC cell proliferation, clonogenic growth and anchorage independent growth. Inversely, enforced expression of TUC339 increased cell proliferation, thus representing a functional mechanism by which intercellular transfer of TUC339 can promote HCC growth and spread. We conclude that these findings support the existence of selective mechanisms for lncRNA export from cells and implicate the transfer of lncRNA via extracellular vesicles as a mechanism by which tumor cells can modulate their local cellular environment.


Kogure T, Yan IK, Lin WL, Patel T. (2013) Extracellular Vesicle-Mediated Transfer of a Novel Long Noncoding RNA TUC339: A Mechanism of Intercellular Signaling in Human Hepatocellular Cancer. Genes Cancer  4(7-8), 261-72.


It has long been clear that while many microRNAs are present in the extracellular environment outside of microvesicles, there are many microRNAs that are preferentially packaged into exosomes as they are exported from cells.  A major scientific question has been what features of a microRNA cause it to be packaged into microvesicles, and specifically into exosomes.  The mechanisms that control the specific loading of RNA species into exosomes have remained obscure. This paper reports on three aspects of one such mechanism.  First, a heterogeneous nuclear ribonucleoprotein, hnRNPA2B1, specifically binds exosome-bound miRNAs and directly controls their loading into exosomes.  Second, the protein recognizes specific sequence motifs present in the mature miRNA targets and not in other microRNAs. Third, when purified from exosomes, the protein is sumoylated, and sumoylation is required for its binding to export-targeted miRNAs. The authors showed that altering expression level of the protein, its sumoylation level, or presence of the sequence motifs in the target miRNA all changed the level of enrichment of the miRNAs in exosomes versus a control condition. Thus, the authors identified not only the information used in channeling miRNAs into export pathways, but also a protein involved in the targeting and a mechanism (sumoylation) that regulates this process.  This appears to be a significant advance in our understanding of the fundamental mechanisms that determine the spectrum and packaging of at least one kind of extracellular RNA.

Villarroya-Beltri, C. et al. Sumoylated hnRNPA2B1 controls the sorting of miRNAs into exosomes through binding to specific motifs. Nat. Commun. (2013) 4: 2980, PMID:24356509, doi:10.1038/ncomms3980.

Proposed mechanism for sorting miRNAs into exosomes through binding to sumoylated hnRNPA2B1.

Proposed mechanism for sorting miRNAs into exosomes through binding to sumoylated hnRNPA2B1.