miR-29a suppresses growth and metastasis in papillary thyroid carcinoma by targeting AKT3.

MicroRNA-29a (miR-29a) has been reported to play important roles in tumor initiation, development, and metastasis in various cancers. However, the biological function and potential mechanisms of miR-29a in papillary thyroid carcinoma (PTC) remain unclear. In the present study, we discovered that miR-29a was frequently downregulated in PTC tissues, and its expression was significantly associated with tumor size, TNM stage, and lymph node metastasis. Functional assays showed that overexpression of miR-29a markedly suppressed PTC cell proliferation, migration, and invasion and promoted PTC apoptosis and cell cycle arrest at G0/G1 phase. In vivo, miR-29a overexpression decreased tumor growth in a xenograft mouse model. Luciferase reporter assay showed that miR-29a can directly bind to the 3' untranslated region (UTR) of AKT3 in PTC cells. Overexpreesion of miR‑29a obviously decreased AKT3 expression, thereby suppressing phosphatidylinositol 3-kinase (PI3K)/AKT pathway activation. We also confirmed that AKT3 expression was increased in PTC tissue and was inversely correlated miR-29a expression in PTC tissues. In addition, downregulation of AKT3 by siRNA mimicked the effects of miR-29a overexpression, and upregulation of AKT3 partially reversed the inhibitory effects of miR-29a. These results suggested that miR-29a could act as a tumor suppressor in PTC by targeting AKT3 and that miR-29a may potentially serve as an anti-tumor agent in the treatment of PTC.