Smad Ubiquitination Regulatory Factor 1 (Smurf1) Promotes Thyroid Cancer Cell Proliferation and Migration via Ubiquitin-Dependent Degradation of Kisspeptin-1

Background/Aims: Thyroid cancer is the most common malignancy in human endocrine system. Smad ubiquitination regulatory factor 1 (Smurf1) is an E3 ubiquitin-protein ligase in ubiquitin-proteasome pathway (UPP) system. This study aimed to investigate the effects of Smurf1 on thyroid cancer proliferation and metastasis, as well as underlying potential mechanism. Methods: The expression levels of Smurf1 in thyroid tumor tissues and thyroid cancer cells were detected by western blotting and qRT-PCR. Then, the effects of up-regulation or down-regulation of Smurf1 on thyroid cancer cell viability, migration, invasion, proliferation and apoptosis were measured using trypan blue exclusion assay, two-chamber migration (invasion) assay, cell colony formation assay and Guava Nexin assay, respectively. The ubiquitination of kisspeptin-1 (KISS-1) was assessed by protein ubiquitination assay. Finally, the effects of KISS-1 overexpression on activity of nuclear factor-kappa B (NF-κB) signaling pathway, as well as thyroid cancer cell viability, migration, invasion, proliferation and apoptosis were also detected, respectively. Results: Smurf1 was highly expressed in thyroid tumor tissues and thyroid cancer cells. Up-regulation of Smurf1 promoted the viability, migration, invasion and proliferation of thyroid cancer cells. Knockdown of Smurf1 had opposite effects. Moreover, smurf1 promoted the ubiquitination of KISS-1. Overexpression of KISS-1 inactivated NF-κB pathway, suppressed thyroid cancer cell viability, migration, invasion and proliferation, and induced cell apoptosis. Conclusion: Up-regulation of Smurf1 exerted important roles in thyroid cancer formation and development by promoting thyroid cancer proliferation and metastasis. The ubiquitin-dependent degradation of KISS-1 induced by Smurf1 and the activation of NF-κB signaling pathway might be involved in this process. Smurf1 could be an effective therapy target and biomarker for thyroid cancer treatment