MiR-181d acts as a tumor suppressor in glioma by targeting K-ras and Bcl-2

Recently, several microRNAs (miRNAs) were reported to be involved in the modulation of glioma development. The aim of our study was to determine the effect of miR-181d on the growth of glioma and to investigate whether this growth is modulated by targeting K-ras and Bcl-2. Real-time PCR was used to analyze the expression of miR-181d in human glioma samples and glioma cell lines. Apoptosis, cell cycle, and proliferation (MTT) assays were performed to assess the phenotypic changes in glioma cells. Immunohistochemistry was used to determine the expression of K-ras and Bcl-2 in glioma tissues, and a luciferase reporter assay was carried out to confirm whether K-ras and Bcl-2 are direct targets of miR-181d. Western blotting was used to identify the potential signaling pathways affected glioma cell growth by miR-181d. In vivo, xenograft tumors were examined for an anti-glioma effect of miR-181d. MiR-181d was down-regulated in human glioma samples and up-regulated in transfected glioma cells. Ectopic expression of miR-181d suppressed proliferation and triggered cell cycle arrest and apoptosis in glioma cell lines. K-ras and Bcl-2 were identified as direct targets of miR-181d and were up-regulated in glioma samples. The results showed evidence linking the tumor suppressor activity of miR-181d in glioma cells with the K-ras-related PI3K/AKT and MAPK/ERK pathways. Furthermore, xenograft tumors from miR-181d-treated U251 cells were suppressed in vivo. MiR-181d may act as a glioma suppressor by targeting K-ras and Bcl-2.