miR-215-5p is an anticancer gene in multiple myeloma by targeting RUNX1 and deactivating the PI3K/AKT/mTOR pathway

This study examined the underlying mechanism of miR-215-5p in multiple myeloma (MM) at the molecular level. miR-215-5p was upregulated in bone marrow specimens of patients with MM and MM cell lines through real-time polymerase chain reaction, and downregulation of miR-215-5p was related to poor survival of patients with MM. The results of Western blot assay showed that the PI3K/AKT/mTOR signaling pathway was activated in bone marrow specimens of patients with MM. miR-215-5p was found to negatively correlate with runt-related transcription factor 1 (RUNX1) expression in MM clinical bone marrow samples. Therefore, to test the probable mechanisms of the regulation of MM cell proliferation and apoptosis, a miR-215-5p mimics/inhibitors/negative control was transfected into MM cells. The targets of miR-215-5p were estimated using four bioinformatics databases (including miRDB, miRTarBase, Starbase, and Targetscan). Furthermore, enrichment analyses of gene ontology and Kyoto Encyclopedia of Genomes pathway were carried out at the Enrichr website. Cell viability was detected using the MTT method, while apoptosis and cell cycle were measured using flow cytometry. RUNX1, CDK2, CDC25B, cleaved-caspase-3, cleaved-PARP, p-PI3K, PI3K, p-AKT, AKT, p-mTOR as well as mTOR protein were also investigated using Western blot analysis. According to our findings, miR-215-5p overexpression could induce apoptosis while rendering cell cycle arrest at G1 phase and reducing the proliferation of cells. Meanwhile, miRNA-215-5p could negatively regulate messengerRNA and protein levels of RUNX1 in MM cells. In addition, there was a similar effect in cell proliferation and apoptosis after miR-215-5p mimics or siRNA-RUNX1 transfection. miR-215-5p inhibition inhibited apoptosis while increased the phosphorylation levels of PI3K, AKT, and mTOR proteins, whereas, miR-215-5p overexpression increased cell proliferation. Therefore, miR-215-5p inhibited MM cell apoptosis via targeting RUNX1 and suppressing the activation of the PI3K/AKT/mTOR pathway.