Tumor Microvesicle MicroRNAs: Profiling, Trafficking and Role in Cell Invasion

The communication between cancer cells and the tumor microenvironments is critical for metastasis. Emerging evidence indicates that tumor-derived extracellular vesicles play an important role in mediating such intercommunication by intercellular transport of bioactive materials. Accumulating evidence has shown that the aberrant release of tumor-derived microvesicles (TMVs), a subtype of extracellular vesicles released by tumor cells, correlates with the onset and progression of cancers. This study investigated the miRNA content of TMVs and delineated a mechanism through which active ARF6 promotes miRNA abundance in TMVs.

First, the miRNA content in TMVs shed from melanoma cells was characterized. A small set of miRNAs was selectively enriched in TMVs, although TMV miRNA profiles are representative of the miRNA profiles of their cells of origin. In addition, the data presented here indicated that TMV miR-21 plays a central role in promoting cell invasion in recipient tumor cells. We also demonstrate that there is a set of miRNAs enriched in TMVs shed from breast, melanoma, and prostate cancer cell lines, that may represent a prototype of a potential general miRNA signature. Moreover, our data indicated that the signature miRNAs have a guanine-rich motif.

Previous research has shown that ARF6 activation promotes the shedding of TMVs. Here we showed a mechanism through which ARF6 regulates the trafficking of pre-miRNAs to TMVs. This is facilitated by formation of a complex consisting of pre-miRNA, ARF6-GTP, Exportin-5 (XPO5), and Cytohesin-3 (GRP1). Disruption of this complex results in the release of TMVs lacking pre-miRNA and mature miRNAs. Additionally, we demonstrated that GRP1 serves as a scaffolding protein and its depletion disrupts the formation and trafficking of the complex. Finally, by interrogating the Cancer Genome Atlas database, we showed that GRP1 expression negatively correlates with poor prognosis for breast, colorectal, melanoma, and ovarian cancer patients. Together, these studies suggest that TMV miRNA holds great potential to be used as biomarkers for cancer diagnosis and the miRNA trafficking regulators such as GRP1 is a prospective therapeutic target.