Abstract
Long noncoding RNA cancer susceptibility candidate 2 (CASC2) has been reported to play an anticancer role in papillary thyroid cancer (PTC). Radioiodine (131I) is a common option for the treatment of PTC. However, the role and mechanism of CASC2 in 131I sensitivity remain unclear. In this study, 131I-resistant cells were constructed through continuous treatment of 131I. The expression levels of CASC2 and miR-155 were measured by qRT-PCR. The IC50 of 131I was analyzed by cell viability using MTT assay. Flow cytometry was conducted to determine cell apoptosis induced by 131I. The association between CASC2 and miR-155 was evaluated by luciferase assay and RNA immunoprecipitation. A mouse xenograft model was built to explore the effect of CASC2 on the growth of 131I-resistant PTC cells in vivo. Results showed that CASC2 expression was decreased in PTC tissues and cells, and low expression of CASC2 was associated with poor outcome of patients. CASC2 level was reduced in 131I-resistant cells. Knockdown of CASC2 inhibited 131I sensitivity in thyroid cancer cells. Overexpression of CASC2 enhanced 131I sensitivity in constructed resistant PTC cells. CASC2 was a decoy of miR-155, and CASC2-mediated promotion of 131I sensitivity was weakened by decreasing miR-155. Abundance of CASC2 inhibited the growth of 131I-resistant cells in vivo. As a conclusion, CASC2 increases 131I sensitivity in PTC by sponging miR-155, providing a novel target for the treatment of thyroid cancer patients with 131I resistance.