MicroRNA-34a: a novel tumor suppressor in p53-mutant glioma cell line U251.

BACKGROUND AND AIMS: Previous studies showed that microRNA-34 (miR-34a) family was found to be a direct target of p53, functioning downstream of the p53 pathway as tumor suppressors. MiR-34a was identified to represent the status of p53 and participate in initiation and progress of cancers. We undertook this study to investigate the role of miR-34a in glioma cells.

METHODS: Expression levels of miR-34a in glioma cell lines and normal brains were detected using qRT-PCR. Human U251 glioma cells were transfected with miR-34a mimics, and the effects of miR-34a restoration were assessed by MTT assays, cell cycle analysis, caspase-3 activation, and in vitro migration and invasion assays. A computational search revealed a conserved target site of miR-34a within the 3'-untranslated region of SIRT1. Luciferase reporter assay was performed to examine the effects of miR-34a on expression of potential target gene SIRT1, and mRNA and protein expression of SIRT1 after miR-34a transfection were detected by qRT-PCR and Western blot analysis.

RESULTS: MiR-34a expression was markedly reduced in p53-mutant cells U251 compared with A172 and SHG-44 cells expressing wild-type p53 and normal brains. Overexpression of miR-34a in U251 cells resulted in inhibition of cell growth and arrest in G0-G1 phase and induced apoptosis. Also, restoration of miR-34a significantly reduced in vitro migration and invasion capabilities. Reporter assays indicated that SIRT1 was a direct target of miR-34a. In U251 cells, overexpression of miR-34a decreased SIRT1 protein levels but not mRNA expressions, which demonstrated miR-34a-induced SIRT1 inhibition occurred at the posttranscriptional level.

CONCLUSIONS: Our results demonstrate that miR-34a acts as a tumor suppressor in p53-mutant glioma cells U251, partially through regulating SIRT1.