Exosomal miR-675 from metastatic osteosarcoma promotes cell migration and invasion by targeting CALN1

Highlights: • Metastatic OS-derived exosomes induce the migration and invasion of osteoblast. • The expression of miR-675 is higher in metastatic OS-derived exosomes. • Exosomal miR-675 regulate the migration and invasion of osteoblast by down-regulating the expression of CALN1. • The expression of exosomal miR-675 is higher in metastatic OS patients' serum sample. Exosomal microRNAs(miRNAs) transfer from tumor to stromal cells is reportedly associated with cancer progression and metastasis in various epithelial cancers. However, the role of exosomal miRNA in the metastasis of osteosarcoma(OS) -the most common bone malignancy-still largely remains unknown. In this study, we purified exosomes with a median size close to 100 nm from cell culture media as well as patient serum, and proved that exosomes derived from the metastatic, but not the non-metastatic OS cells increase the migration and invasion of non-malignant fibroblast cells (hFOB1.19) in vitro. Furthermore, the differential miRNA cargo between metastatic and non-metastatic OS is identified by small RNA sequencing and RT-PCR validation, we found a highly expression of exosomal, but not cellular miR-675 level in the metastatic OS cell-lines compared with non-metastatic counterparts. Meanwhile, we also found that exosomal miR-675 could down-regulate CALN1 expression in recipient cell, which may influence the invasion and migration of hFOB1.19. Finally, the up regulation serum exosomal miR-675 and down regulation of CALN1 in tumor specimen was also found to be associated with the metastatic phenotype in OS patients. Our findings indicate that the exosomal miR-675 is a gene associated with OS and serum exosomal miR-675 expression may serve as a novel biomarker for the metastasis of OS.