Background: Abnormal expression of miR-199a-3p, which has similar effects to oncogenes or tumor suppressor genes, can occur in various malignant tumors and is closely linked with tumor cell proliferation, invasion, and metastasis. However, its expression and effects in endometrial endometrioid adenocarcinoma (EEC) are still unclear. This study was designed to identify the impact of miR-199a-3p on the proliferation of EEC cells and its role in the carcinogenesis of EEC.

Methods: The expression levels of miR-199a-3p in EEC and paired adjacent nontumor tissues were analyzed by real-time polymerase chain reaction. The effects of miR-199a-3p on proliferation, cell cycle and apoptosis in EEC cells were analyzed in Ishikawa cells transfected with miR-199a-3p mimics and inhibitors. The target genes of miR-199a-3p were predicted using bioinformatics methods. The extent of regulation of the predicted target genes by miR-199a-3p was determined using luciferase reporter assays, Western blotting, and quantitative polymerase chain reaction. The EEC cells were pretreated with target gene-specific inhibitors to further identify the relationship between the effects of miR-199a-3p and the predicted target genes.

Results: Compared with the adjacent tissues and normal endometrium, reduced expression of miR-199a-3p was found in human EEC specimens. Compared with the control group transfected with control microRNA mimics, the proliferative capacity of EEC cells transfected with miR-199a-3p mimics was inhibited, whereas cells transfected with miR-199a-3p inhibitors showed increased proliferation. The inhibitory effect was associated with increased cell populations at the G1-phase, and decreased cell populations at the S-phase. The results demonstrated that miR-199a-3p could inhibit the protein expression of mammalian target of rapamycin (mTOR) by targeted binding to the mTOR-3' untranslated region. Inhibition of EEC cell proliferation by miR-199a-3p was mediated by its targeted regulation of mTOR.

Conclusions: MiR-199a-3p inhibits tumor cell proliferation through negative regulation of mTOR expression. Restoration of intracellular miR-199a-3p levels may serve as a potential option for EEC treatment.