MicroRNA-363-3p inhibits papillary thyroid carcinoma progression by targeting PIK3CA.

MicroRNA-363-3p (miR-363-3p) reportedly plays crucial roles in tumor development and progression in many types of cancers. However, its role in papillary thyroid carcinoma (PTC) remain largely unclear. We therefore investigated the function and underlying mechanism of miR-363-3p in PTC. Here, we found that miR-363-3p was significantly downregulated in human PTC tissue samples and cell lines, and that miR-363-3p levels are negatively correlated with advanced clinical stage and lymph node metastasis. In addition to suppressing tumor growth in vivo, restoration of miR-363-3p in TPC-1 cells significantly inhibits proliferation, migration, and invasion and induced apoptosis in vitro. Mechanistically, miR-363-3p was verified to directly bind to 3'UTR of the phosphoinositide-3-kinase catalytic subunit alpha (PIK3CA) mRNA, and reduce its expression at both mRNA and protein levels, which further inhibits phosphatidylinositol 3-kinase/Akt signaling pathway. PIK3CA expression was also found to be increased in human PTC tissues, and were inversely correlated with miR-363-3p. Furthermore, restoration of PIK3CA partially rescued the miR-363-3p-induced inhibition effect on TPC-1 cell proliferation, migration and invasion. Taken together, these findings indicated for the first time that miR-363-3p functions as a tumor suppressor in PTC, and its suppressive effect is mediated by repressing PIK3CA.