Tumor-promoting mechanisms of macrophage-derived extracellular vesicles-enclosed microRNA-660 in breast cancer progression

Introduction: Breast cancer metastasis is the main cause of cancer-related death in women worldwide. Current therapies have remarkably improved the prognosis of breast cancer patients but still fail to manage metastatic breast cancer. Here, the present study was set to explore the role of microRNA (miR)-660 from tumor-associated macrophages (TAMs) in breast cancer, particularly in metastasis.

Materials and methods: We collected breast cancer tissues and isolated their polarized macrophages as well as extracellular vesicles (EVs), in which we measured the expression of miR-660, Kelch-like Protein 21 (KLHL21), and nuclear factor-κB (NF-κB) p65. Breast cancer cells were transfected with miR-660 mimic, miR-660 inhibitor, and sh-KLHL21 and then the cells were co-cultured with EVs or TAMs followed by detection of invasion and migration. Finally, mouse model of breast cancer was established to detect the effect of miR-660 or KLHL21 on metastasis by measuring the lymph node metastasis (LNM) foci in femur and lung.

Results: KLHL21 was poorly expressed, whereas miR-660 was highly expressed in breast cancer tissues and cells. Of note, low KLHL21 expression or high miR-660 expression was related to poor overall survival. EVs-contained miR-660 was identified to bind to KLHL21, reducing the binding between KLHL21 and inhibitor kappa B kinase β (IKKβ) to activate the NF-κB p65 signaling pathway. Interestingly, EV-loaded miR-660 from TAMs could be internalized by breast cancer cells. Moreover, silencing of KLHL21 increased the number of lung LNM foci in vivo, while EVs-contained miR-660 promoted cancerous cell invasion and migration.

Discussion: Taken altogether, our work shows that TAMs-EVs-shuttled miR-660 promotes breast cancer progression through KLHL21-mediated IKKβ/NF-κB p65 axis.