RAS-stimulated release of exosomal miR-494-3p promotes the osteolytic bone metastasis of breast cancer cells

RAS activation is a key determinant of breast cancer progression and metastasis. However, the role of the interaction among exosomes, RAS and microRNAs (miRNAs/miRs) in the osteolytic bone metastasis of breast cancer remains unclear. Therefore, the present study aimed to examine the role of activated RAS (KRAS, HRAS and NRAS) in the release of exosome-mediated osteoclastogenic miRNAs and to elucidate their functional role in bone microenvironment remodeling in vitro and in vivo. Exosomes derived from RAS-activated breast cancer cells promoted RANKL-induced osteoclastogenesis; however, RAS inhibition abolished this effect. miR-494-3p, miR-4508 and miR-6869-5p were identified as osteoclastogenic miRNAs in the exosomes secreted by RAS-activated breast cancer cells. The levels of these osteoclastogenic miRNAs in the sera of patients with human epidermal growth factor receptor 2-positive luminal breast cancer were significantly higher than those in the sera of patients with triple-negative breast cancer. miR-494-3p exhibited both osteoclastogenic and anti-osteoblastogenic activity. Treatment with a miR-494-3p inhibitor abolished the exosome-mediated increase in RANKL-induced osteoclastogenesis. Treatment with a miR-494-3p mimic enhanced RANKL-induced osteoclast formation; however, treatment with its inhibitor suppressed this effect by targeting leucine-rich repeat-containing G-protein coupled receptor 4 in osteoclast precursors. Furthermore, miR-494-3p inhibited bone morphogenetic protein 2-induced osteoblast formation by targeting semaphorin 3A. In a mouse model, exosomes derived from breast cancer cells promoted osteolytic bone lesions; however, treatment with a miR-494-3p inhibitor significantly suppressed this effect. On the whole, the present study provides a novel mechanism, demonstrating that the RAS activation of breast cancer cells induces osteolytic bone metastasis by stimulating the exosome-mediated transfer of osteoclastogenic miRNAs, including miR-494-3p to bone cells.