Interleukin-6 promotes the dedifferentiation of papillary thyroid cancer cells

Radioiodine treatment is a fundamental therapy for patients with papillary thyroid cancer (PTC). Sodium/iodide symporter (NIS)-mediated iodine uptake is a prerequisite for the efficacy of radioiodine therapy. Interleukin-6 (IL-6) is a pro-tumor cytokine, but its regulation of NIS expression in PTC has not been elucidated. In this study, we found that IL-6 enhanced the proliferation ability of PTC cells. Moreover, the negative association between IL-6 and NIS expression in thyroid cancer tissues was demonstrated. IL-6 downregulated thyroid-specific genes such as NIS, thyroid peroxidase, and thyroid-stimulating hormone receptor and thyroid-specific transcription factors including thyroid transcription factor-1 (TTF-1) and paired box protein-8 (PAX-8). The inhibitory effects of IL-6 on NIS expression were alleviated by mitogen-activated protein kinase and Janus kinase inhibitors. Depletion of c-Jun or STAT3 also rescued IL-6-induced NIS downregulation, with STAT3 depletion exerting a stronger effect. TTF-1 protein expression was also restored by depleting c-Jun or STAT3. STAT3 depletion, but not c-Jun depletion, alleviated the inhibitory effect of IL-6 on PAX-8 expression. Moreover, the downregulation of NIS by IL-6 was rescued by overexpressing TTF-1 and PAX-8. Tocilizumab, an IL-6 receptor blocker, did not have any cytostatic activity in PTC cells, and it also failed to induce redifferentiation in vitro . However, we found that the drug blocked the inhibitory effect of IL-6 on NIS expression. In summary, IL-6 inhibits NIS transcription in PTC cells by activating mitogen-activated protein kinase and Janus kinase signaling.