RESEARCH ARTICLE Sphingosine-1-Phosphate Induces the Migration of Thyroid Follicular Carcinoma Cells through the MicroRNA-17/PTK6/ERK1/2 Pathway

Sphingosine-1-phosphate (S1P) is a bioactive lipid known to play a role in tumorigenesis and cancer progression. However, the molecular mechanisms of S1P regulated migration of papillary thyroid cancer cells are still unknown. In this study, we showed that S1P induced PTK6 mRNA and protein expression in two thyroid follicular cancer cell lines (ML-1 and FTC-133). Further studies demonstrated that induced PTK6 and its downstream signal component (ERK1/2) are involved in S1P-induced migration. Upon investigating the mecha-nisms behind this event, we found that miR-17 inhibited the expression of PTK6 through di-rect binding to its 3’-UTR. Through overexpression and knockdown studies, we found that miR-17 can significantly inhibit S1P-induced migration in thyroid follicular cancer cells. Inter-estingly, overexpression or knockdown of PTK6 or ERK1/2 effectively removed the inhibi-tion of S1P-induced migration by miR-17. Furthermore, we showed that S1P decreased miR-17 expression levels. Meanwhile, in papillary thyroid cancers, miR-17 is downregulated and negatively associated with clinical staging, whereas PTK6 is upregulated and positively associated with clinical stages. Collectively, our work defines a novel signaling pathway im-plicated in the control of thyroid cancer migration