Abstract: Objective To investigate the role of long non-coding RNA LINC00339 in the migration and invasion of thyroid cancer (TC) cells and its molecular mechanism. Methods Thyroid cancer cell line KTC-1 was divided into sh-NC group, sh-LINC00339 group, NC mimic group, miR-15b-5p mimic group, NC inhibitor group, miR-15b-5p inhibitor group, sh-LINC00339+NC inhibitor group, sh-LINC00339+miR-15b-5p inhibitor group, miR-15b-5p mimic+pcDNA-NC group, miR-15b-5p mimic+pcDNA-E2F3 group, sh-LINC00339+pcDNA-NC group and sh-LINC00339+ pcDNA-E2F3 group. Three holes were set in each group. The expression levels of LINC00339, miR-15b-5p and E2F3 mRNA were detected by RT-qPCR. Wound healing assay and Transwell assay were used to evaluate the ability of cell migration and invasion. Tumor sphere formation assay was used to detect the characteristics of stem cells. Western blot was used to detect the protein expression of stemness-related markers. Results Compared with normal thyroid cells, the expression of LINC00339 and E2F3 in TC cell lines was up-regulated, and the expression of miR-15b-5p was down-regulated (P＜0.05). Interfering with LINC00339 can reduce the expression of E2F3, inhibit cell migration, invasion and stem cell characteristics, and up-regulate miR-15b-5p. Inhibition of miR-15b-5p partially reversed these effects (P＜0.05). Over-expression of miR-15b-5p could inhibit E2F3 expression and cell migration, invasion and stem cell characteristics, while over-expression of E2F3 could restore these effects (P＜0.05). Conclusions LINC00339 is highly expressed in TC cell lines, which can relieve the inhibitory effect of miR-15b-5p on E2F3 by targeting down-regulation of miR-15b-5p expression, thereby inducing the stem cell characteristics of TC cell lines and promoting cell migration and invasion.

Key words: LINC00339, miR-15b-5p, E2F transcription factor 3, thyroid carcinoma, cell stemness