BACKGROUND: Medullary thyroid carcinoma (MTC), a rare type of thyroid cancer, is a big challenge in clinical treatment. However, the pathogenesis of MTC remains poorly understand. MicroRNAs (miRNAs) were previously demonstrated to be involved in the pathogenesis of MTC, however, the roles of majority of miRNAs in MTC are still undetermined.

MATERIAL AND METHODS: Two GEO miRNA expression profiles (GSE40807, GSE97070) were downloaded, and the differentially expressed miRNAs (DEmiRNAs) of GSE40807 and GSE97070 were analyzed by bioinformatics methods. Expressions of miRNAs were detected by quantitative real-time polymerase chain reaction; cell proliferation was examined through Cell Counting Kit-8, colony formation and in vivo tumor growth assays; the interaction between miRNA and mRNA was verified by dual-luciferase reporter assay; functional analysis of target genes was performed using the Database for Annotation, Visualization and Integrated Discovery (DAVID, www.david.ncifcrf.gov) software.

RESULTS: Ten miRNAs were identified to be dysregulated in both GSE40807 and GSE97070 datasets, and miR-31-3p showed the highest change fold (Log fold change=–3.460625 in GSE40807 and Log fold change=–0.07084374 in GSE97070). MiR-31-3p expression was significantly downregulated in MTC, and low miR-31-3p expression showed a poor prognosis relative to high miR-31-3p expression (P<0.05). Functionally, miR-31-3p inhibited MTC cell proliferation in vitro and in vivo. Functional analysis also showed that the target genes of miR-31-3p were involved in numerous of biochemical processes and pathways, of which Ras signaling pathway was selected for further study. RASA2, overexpressed in MTC, were negatively regulated by miR-31-3p. In addition, we found that knockdown of RASA2 inhibited MTC cell proliferation.

CONCLUSIONS: Reduced expression level of miR-31-3p might play a key role in the tumorigenesis of MTC by targeting critical pathways, especially Ras signaling pathway.

Keywords: Carcinoma, Medullary, Gene Targeting, Carcinoma, Neuroendocrine, Down-Regulation, High-Throughput Nucleotide Sequencing, RNA, Messenger, ras GTPase-Activating Proteins