Tumor-Derived miR-378a-3p-Containing Extracellular Vesicles Promote Osteolysis by Activating a Dyrk1a/Nfatc1/Angptl2 Axis for Bone Metastasis

Background: The majority of the deaths of prostate cancer (PCa) are caused by progression to bone metastatic PCa. The importance of extracellular vesicles (EVs) in the formation of the pre-metastatic niche has been demonstrated in recent years. However, whether and how tumor-derived EVs interact with bone marrow macrophages (BMMs) to release EV-delivered microRNAs to promote osteolysis and to activate pre-metastatic niche formation for PCa bone metastasis remain unclear. Methods Bioinformatics and qRT-PCR analyses were used to screen microRNAs and to identify the elevated expression of miR-378a-3p in both serum-derived EVs from PCa patients and in culture medium-derived EVs from PCa cell lines. Functional assays in vitro and in vivo were performed to investigate the functions of miR-378a-3p during PCa progression. IF staining and Dual-luciferase reporter, co-IP, western blot, RIP and ChIP assays were conducted to reveal the underlying mechanism. Results We found that EV-mediated release of miR-378a-3p from tumor cells was upregulated in bone-metastatic PCa which keeps a low intracellular concentration of miR-378a-3p, to promote proliferation and the MAOA-mediated epithelial-to-mesenchymal transition (EMT) in PCa cells. In addition, we demonstrated that the enrichment of miR-378a-3p in tumor derived EVs was induced by overexpression of hnRNPA2B1 as a transfer chaperone. After miR-378a-3p-enriched EVs were taken in by BMMs, elevated intracellular concentration of miR-378a-3p promoted osteolytic progression by targeting the Dyrk1a/Nfatc1 pathway. Mechanistically, inhibition of Dyrk1a by miR-378a-3p improved the nuclear translocation of Nfatc1 to promote expression of the downstream target gene Angptl2. As a feedback, increased secretion of Angptl2 into the tumor environment promoted PCa progression. Conclusions Our findings indicate that tumor-derived miR-378a-3p-containing EVs play a significant role in promoting prostate cancer bone metastasis by activating a Dyrk1a/Nfatc1/Angptl2 axis in BMMs to induce osteolytic progression, which implicates that miR-378a-3p may be a potential predictor of metastatic PCa. Moreover, reducing the release of miR-378a-3p-containing EVs or inhibiting the recruitment of miR-378a-3p into tumor-derived EVs might be a potential therapeutic strategy for PCa metastasis.