MicroRNA‑936 inhibits the malignant phenotype of retinoblastoma by directly targeting HDAC9 and deactivating the PI3K/AKT pathway

MicroRNA936 (miR936) has been reported to play important roles in the progression of nonsmall cell lung cancer and glioma. However, the expression and functions of miR936 in retinoblastoma (RB) remain elusive and need to be further elucidated. Herein, the aims were to measure miR936 expression in RB, identify the functional importance of miR936 in the oncogenicity of RB, and investigate the underlying molecular mechanisms. Reversetranscription quantitative PCR was carried out to determine miR936 expression in RB tissues and cell lines. Cell proliferation, colony formation, apoptosis, migration, and invasion in vitro and tumor growth in vivo were examined respectively by Cell Counting Kit8, colony formation, flow cytometric, and Transwell migration and invasion assays and a subcutaneous heterotopic xenograft experiment. The potential target of miR936 was predicted by bioinformatic analysis and was subsequently validated by luciferase reporter assay, reversetranscription quantitative PCR, and western blotting. miR936 expression was weak in both RB tissues and cell lines and was correlated with differentiation, lymph node metastasis and TNM staging in RB. RB cell proliferation, colony formation, migration, and invasion in vitro and tumor growth in vivo were attenuated by exogenous miR936, whereas apoptosis was enhanced by miR936 overexpression. Further molecular investigation identified histone deacetylase 9 (HDAC9) as a direct target gene of miR936 in RB cells. HDAC9 depletion had effects similar to those of miR936 overexpression in RB cells. Recovery of HDAC9 expression counteracted the tumorsuppressive action of miR936 on the oncogenicity of RB cells. Ectopic miR936 expression deactivated the PI3K/AKT pathway in RB cells in vitro and in vivo by decreasing HDAC9 expression. Downregulated miR936 is related to poor prognosis in RB, and its upregulation inhibits RB aggressiveness via direct targeting of HDAC9 mRNA and thereby inactivation of the PI3K/AKT pathway.