Macrophage-derived exosomes mediate osteosarcoma cell behavior by activating AKT signaling

Osteosarcoma is the most common type of bone tumor, which severely threatens the health of adolescents and young adults. Tumor-infiltrating macrophages have been shown to mediate cancer progression via extracellular vesicles. However, their potential mechanisms in osteosarcoma progression and in drug-resistance are still not yet known. The macrophage cell line THP1 was stimulated by phorbol myristate acetate (PMA) to secrete exosomes. The exosomes isolated from THP1 were characterized via transmission electron microscopy (TEM), nanoparticle tracking analysis (NTA) and by a western blot. Cell proliferation was determined using CCK-8. A transwell assay and flow cytometry were conducted to detect cell migration and apoptosis, respectively. The expression levels of AKT and its phosphorylation status were determined using a western blot. PMA-treated activated THP1 cells secreted an abundance of exosomes with the characteristics of being less than 200 nm in diameter, and showing the robust expression of exosome markers CD63 and CD81. The THP1-derived exosomes promoted cell proliferation, migration and drug-resistance to the chemical drug docetaxel in both osteosarcoma cell lines MG63 and 143B. The inhibition of the generation of exosomes by the knockdown of ALIX clearly suppressed the cell proliferation, migration and drug-resistance. Mechanistically, the THP1-derived exosomes activated AKT signaling by inducing the increased expression of the phosphorylated AKT at serine 473 (p-AKT). The AKT inhibitor MK2206 significantly abolished exosome-mediated cell proliferation and drug-resistance in osteosarcoma cells. In summary, our data demonstrated that macrophage-derived exosomes promoted osteosarcoma progression and drug-resistance by activating AKT signaling that could be used as a potential molecular target for osteosarcoma treatment.