Rosmarinic acid exerts an anticancer effect on osteosarcoma cells by inhibiting DJ-1 via regulation of the PTEN-PI3K-Akt signaling pathway

Background: Osteosarcoma is the most common type of primary malignant bone tumor. This disease has exhibited a progressively lower survival rate over the past several decades, which has resulted in it becoming a main cause of death in humans. Rosmarinic acid (RA), a water-soluble polyphenolic phytochemical, exerts powerful anticancer effects against multiple types of cancer; however, its potential effects on osteosarcoma remain unknown. Hence, the present study investigated the efficacy of RA against osteosarcoma and aimed to clarify the mechanisms underlying this process. Methods: The effects of RA on cell viability, apoptosis, cell cycle distribution, migration, invasion, and signaling molecules were analyzed by CCK-8 assay, flowcytometric analysis, wound healing assay, Transwell assay, proteomic analysis, and use of shRNAs. Results: RA exerted anti-proliferation and pro-apoptotic effects on U2OS and MG63 osteosarcoma cells. Apoptosis was induced via extrinsic and intrinsic pathways by increasing the Bax/Bcl-2 ratio, triggering the intracellular production of reactive oxygen species (ROS), reducing the mitochondrial membrane potential (MMP), and upregulating the cleavage rates of caspase-8, caspase-9, and caspase-3. Additionally, RA suppressed the migration and invasion of osteosarcoma cells by inhibiting the expression levels of matrix metalloproteinase-2 and -9 (MMP-2 and -9), which are associated with a weakening of the epithelial-mesenchymal transition (EMT). Moreover, proteomic analyses identified DJ-1 as a potential target for RA. Several studies have indicated an oncogenic role for DJ-1 using knockdowns via the lentiviral-mediated transfection of shRNA, which caused the conspicuous suppression of cell proliferation, migration, and invasion as well as the arrest of cell cycle progression. At the molecular level, the expression levels of DJ-1, p-PI3K, and p-Akt were reduced, whereas the protein levels of phosphatase and tensin homologue (PTEN) were increased. Conclusion: In conjunction with the high levels of DJ-1 expression in osteosarcoma tissues and cell lines, the present results suggested that RA exhibited anticancer effects in osteosarcoma cells by inhibiting DJ-1 via regulation of the PTEN-PI3K-Akt signaling pathway. Therefore, DJ-1 might be a biological target for RA in osteosarcoma cells.