MicroRNA-34a (miR-34a) is a master regulator of signaling networks that maintain normal physiology and disease and is currently in development as a miRNA-based therapy for cancer. Prior studies have reported low miR-34a expression in osteosarcoma (OS); however, the molecular mechanisms underlying miR-34a activity in OS are not well defined. Therefore, this study evaluated the role of miR-34a in regulating signal transduction pathways that influence cell death in OS. Levels of miR-34a were attenuated in human OS cells and xenografts of the Pediatric Preclinical Testing Consortium (PPTC). Bioinformatics predictions identified stathmin 1 (STMN1) as a potential miR-34a target. Biotin pulldown assay and luciferase reporter analysis confirmed miR-34a target interactions within the STMN1 mRNA 3'UTR. Overexpression of miR-34a in OS cells suppressed STMN1 expression and reduced cell growth in vitro. Restoration of miR-34a led to microtubule destabilization and increased betaIII-tubulin expression, with corresponding G1/G2 phase cell cycle arrest and apoptosis. Knockdown of the Sp1 transcription factor, by siRNA silencing, also upregulated βIII-tubulin expression in OS cells, suggesting miR-34a indirectly affects Sp1. Validating the coordinating role of miR-34a in microtubule destabilization, when miR-34a was combined with either microtubule inhibitors or chemotherapy, STMN1 phosphorylation was suppressed and there was greater cytotoxicity in OS cells. These results demonstrate that miR-34a directly represses STMN1 gene and protein expression and upregulates betaIII-tubulin, leading to disruption of the microtubule network and cell death. Implications: The miR-34a/STMN1/betaIII-tubulin axis maintains the microtubule cytoskeleton in osteosarcoma, and combining miR-34a with microtubule inhibitors can be investigated as a novel therapeutic strategy.
- Received October 24, 2016.
- Revision received February 28, 2017.
- Accepted March 2, 2017.
- Copyright ©2017, American Association for Cancer Research.