Endocrine Abstracts

Background: MiRNAs transported by exosomes play a role in various processes of tumorigenesis and tumor progression. They can function as oncogenes able to structurally and biologically change the tumor microenvironment (TME) therefore playing a crucial role in cell-to-cell communication during tumor development and allowing cancer cells to become invasive and disseminate from the primary site to distant locations.We aimed to identify the exosome miRNAs that may be involved in thyroid cancer development and progression and to investigate their functional effects.

Methods: We searched for the presence of specific miRNA profiles in exosomes secreted by a non-tumorigenic thyroid cell line (Nthy-ori-3-1) and two papillary thyroid cancer cell lines (TPC1 and K1) and compared them with intracellular miRNA profile of each cell line. Exosomes isolated from the cells’ conditioned medium were characterized by dynamic light scattering and the expression of exosome-specific markers. We evaluated the expression of 46 miRNAs by Real-Time PCR using custom TaqMan Array cards on RNA from exosomes of each cell line. Mienturnet web tool was used for the microRNA-target enrichment and network-based analysis.

Results: Exosomes secreted by thyroid cancer cell lines were enriched in five miRNAs (miR21-5p, miR221-3p, miR22-3p, miR31-5p, and miR-let7i-3p) compared to normal cell lines, with higher levels observed in more aggressive K1 compared to less aggressive TPC1 cell lines. The levels of exosome miRNAs reflected those of intracellular miRNAs. The microRNA-target enrichment analysis revealed that VEGFA−VEGFR2 Signaling Pathway, ATM-dependent DNA damage response, EGF/EGFR Signaling Pathway, and PI3K−AKT−mTOR signaling pathway may be the most affected cellular processes. Finally, Network-based analysis found seven genes (ICAM1, FOXO3, SELE, ETS1, RECK, PTEN and TIMP3) which are targets of at least three identified miRNAs. Notably, ICAM1, target of 4 out 5 identified exosome miRNAs, is known to be the most important adhesion molecule involved in the extravasation of leukocytes into the surrounding tissue.

Conclusion: We identified five exosomal miRNAs that may be involved in thyroid cancer development and progression by playing paracrine effects on the tumor microenvironment. The findings of “in silico” analysis suggest a potential role even in angiogenesis, promotion and immune-surveillance impairment. Further studies will be performed to define the effects of these exosomal miRNAs.