Purpose: Several microRNAs (miRNAs) that are aberrantly expressed in glioblastoma multiforme (GBM) play a significant role in GBM formation and progression. The expression profile and functions of miR-559 in GBM remain unclear. Here, we quantified the expression and investigated the involvement of miR-559 in the oncogenicity of GBM cells in vitro and in vivo. Material and methods: Reverse-transcription quantitative polymerase chain reaction (RT-qPCR) was carried out to determine miR-559 expression in GBM tissues and cell lines. A series of functional assays was performed to evaluate the effects of miR-559 overexpression on GBM cell proliferation, apoptosis, migration, and invasion in vitro and on GBM tumor growth in vivo. The regulatory mechanisms of miR-559 action in GBM cells were then explored. Results: The expression of miR‑559 was lower in GBM tissues and cell lines and significantly correlated with the Karnofsky performance score and tumor size among patients with GBM. Exogenous miR‑559 expression inhibited GBM cell proliferation, migration, and invasion and promoted apoptosis. MiR-559 overexpression decreased tumor growth in vivo. Mechanistic experiments confirmed metadherin ( MTDH ) as a direct target gene of miR-559 in GBM. Silencing of MTDH induced effects similar to those of miR-559 upregulation in GBM cells, whereas MTDH expression restoration attenuated the antitumor effects of miR‑559 in GBM cells. Protein kinase B (AKT) in the phosphatase and tensin homolog (PTEN)–AKT signaling pathway was found to be deactivated in GBM cells after upregulation of miR-559 both in vitro and in vivo. Conclusion: MiR-559 acts as a tumor suppressor in GBM cells in vitro and in vivo, at least in part through the downregulation of MTDH and inhibition of AKT in the PTEN–AKT pathway. Therefore, targeting the miR-559–MTDH axis may be a promising therapeutic strategy for patients with GBM.

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