Down-Regulation of miR-218-2 and Its Host Gene SLIT3 Cooperate to Promote Invasion and Progression of Thyroid Cancer

Abstract

The functional relationships between intronic microRNAs (miRNAs) and their host genes in thyroid cancer remain unclear. miR-218, a miRNA down-regulated in several kinds of cancers and associated with multiple cancer phenotypes, is transcribed from 2 loci located on chromosomes 4p15.31 (miR-218-1) and 5q35.1 (miR-218-2) within the introns of SLIT2 and SLIT3, respectively. The aim of our work was to investigate the expression and the roles of miR-218-1 and miR-218-2, as well as their host genes SLIT2 and SLIT3 in thyroid carcinogenesis. The expression of miR-218-1 and miR-218-2, as well as their host genes SLIT2 and SLIT3, in a panel of normal and neoplastic human thyroid tissues was assessed by quantitative RT-PCR. We restored the expression of miR-218-2 and SLIT3 in thyroid cancer cells and evaluated their effects on cell invasion, migration, and proliferation. We found that miR-218-2 and its host gene SLIT3 were down-regulated concomitantly in thyroid cancer. Synergistic inhibitory effects of miR-218-2 with SLIT3 on thyroid cancer cell invasion, migration, and proliferation were observed. Moreover, the effects of miR-218-2 on thyroid cancer cells were due, at least partially, to targeting PDGFRA and PLCG1. These results implicate the involvement of miR-218-2 and its host gene SLIT3 in thyroid cancer cell invasion, migration, and proliferation. Our findings highlight the functional associations of intronic miRNAs and their host genes in thyroid carcinogenesis.