RAS­stimulated release of exosomal miR­494­3p promotes the osteolytic bone metastasis of breast cancer cells.

ABSTRACT

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 exosome­mediated osteoclastogenic miRNAs and to elucidate their functional role in bone microenvironment remodeling in vitro and in vivo. Exosomes derived from RAS­activated breast cancer cells promoted RANKL­induced osteoclastogenesis; however, RAS inhibition abolished this effect. miR­494­3p, miR­4508 and miR­6869­5p were identified as osteoclastogenic miRNAs in the exosomes secreted by RAS­activated breast cancer cells. The levels of these osteoclastogenic miRNAs in the sera of patients with human epidermal growth factor receptor 2­positive luminal breast cancer were significantly higher than those in the sera of patients with triple­negative breast cancer. miR­494­3p exhibited both osteoclastogenic and anti­osteoblastogenic activity. Treatment with a miR­494­3p inhibitor abolished the exosome­mediated increase in RANKL­induced osteoclastogenesis. Treatment with a miR­494­3p mimic enhanced RANKL­induced osteoclast formation; however, treatment with its inhibitor suppressed this effect by targeting leucine­rich repeat­containing G­protein coupled receptor 4 in osteoclast precursors. Furthermore, miR­494­3p inhibited bone morphogenetic protein 2­induced osteoblast formation by targeting semaphorin 3A. In a mouse model, exosomes derived from breast cancer cells promoted osteolytic bone lesions; however, treatment with a miR­494­3p 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 exosome­mediated transfer of osteoclastogenic miRNAs, including miR­494­3p to bone cells.