Purpose: Previous studies have revealed that microRNA-665 (miR-665) is dysregulated in a variety of human cancers. However, little is known regarding its expression profiles and functions in retinoblastoma (RB). Therefore, the aims of our study were to evaluate miR-665 expression in RB and determine the precise roles of miR-665 in the progression of RB.
Patients and methods: Herein, RT-qPCR was used to determine miR-665 expression levels in RB tissues and cell lines, and a series of functional experiments were performed to explore the influence of miR-665 on RB cell proliferation, colony formation, apoptosis, migration, and invasion as well as tumor growth. The molecular mechanisms underlying the tumor-suppressive action of miR-665 in RB were also explored.
Results: We found that miR-665 was markedly reduced in RB tissues and cell lines and that lower miR-665 expression was strongly associated with tumor size, TNM stage, and differentiation in patients with RB. Exogenous expression of miR-665 suppressed cell proliferation, colony formation, migration, and invasion, and induced cell apoptosis in RB cells, while silencing miR-665 expression had the opposite effects. In addition, upregulation of miR-665 decreased the tumor growth of RB cells in vivo. High-mobility group box 1 (HMGB1 ) was identified as a direct target of miR-665 in RB cells, and decreasing the expression of HMGB1  simulated the regulatory effects of miR-665 overexpression in RB cells, while knockdown of HMGB1  expression counteracted the miR-665-mediated antitumor effects in RB cells. Moreover, miR-665 was shown to regulate the Wnt/β-catenin signaling pathway by targeting HMGB1  in vitro and in vivo.
Conclusion: Taken together, our in vitro and in vivo results suggest that miR-665 acts as a tumor-suppressive miRNA in RB by directly targeting HMGB1  and inactivating the Wnt/β-catenin pathway. Hence, this miRNA is a candidate prognostic biomarker and therapeutic target in patients with RB.
Keywords: microRNA-665, retinoblastoma, high-mobility group box 1, Wnt/β-catenin pathway, oncogenicity