Osteosarcoma (OS) is one of the most common malignant bone tumors in children and adolescents, accounting for approximately 5% of all pediatric tumors and 20% of all bone cancers [1,2]. Approximately 10–20% OS patients have lung metastasis, which is the leading cause of death [3]. The 5-year survival rate of OS patients without lung metastasis is approximately 60–70%, which dramatically decreases to 10–20% in OS patients with lung metastasis [4,5]. Currently, there are no effective therapeutic strategies to inhibit lung metastasis in OS patients. In addition, despite the increasing frequency of clinical trials with OS as an indication, the survival rate of osteosarcoma has not significantly improved in the past 20 years [6,7]. Therefore, there is an urgent need to develop effective drugs for OS patients with lung metastasis.

Epithelial-mesenchymal transition (EMT) is a biological process in which epithelial cells lose their polarity and cell-cell adhesion, and instead develop a mesenchymal phenotype to obtain increased motility and invasiveness [8,9]. EMT has been reported to be an essential process for the migratory and invasive abilities of various malignant tumors [[10], [11], [12]]. In addition, mounting evidence has shown the crucial role of EMT in tumors of mesenchymal origin, such as OS [13,14]. Therefore, inhibiting EMT may be an effective treatment strategy for OS metastasis.

Tumor necrosis factor superfamily member 11 (TNFRSF11A; also known as RANK) and its ligand TNFSF11 (also known as RANKL) are required for normal physiological processes, such as osteoclast differentiation, bone remodeling, and lymph node formation [15,16]. Several studies have reported dysregulation of the RANK/RANKL pathway in a number of cancers [17]. Furthermore, RANK-regulated pathways have been reported to enhance cancer development and metastasis [18]. Our previous study showed that RANKL increases migration and invasion by inducing EMT in RANK-expressing breast cancer cells [19]. However, it remains unclear whether the RANK/RANKL axis is involved in migration, invasion, and metastasis by inducing EMT in OS cells.

In this study, we showed that OS cell lines possess a high level of RANK protein when compared with normal cells. Furthermore, the RANK/RANKL axis promotes migration, invasion, and metastasis of OS cells by inducing EMT. In terms of mechanism, the interaction of RANK and RANKL induced EMT by activating the nuclear factor-kappa B (NF-κB) pathway. Importantly, dimethyl fumarate (DMF), an NF-κB inhibitor, suppressed the migration and invasion of OS cells by inhibiting the EMT process. This study may provide new targets for future therapeutic interventions against tumor metastasis.