Cancer-associated Fibroblasts Release Exosomal CBFB That Dictate an Aggressive Bone Metastasis Phenotype in Breast Cancer 

Abstract

Background: Breast cancer up to date remains the one of the most prevalent female malignancies in the world. Better prognostic and therapeutic biomarkers are urgently required for these patients. Circulating exosomes are shown to participate in tumorigenesis including distance metastasis and of prognostic/therapeutic potential. Methods: Sera from control health, primary breast cancer, and bone metastatic breast cancer patients were collected. The Exosome were isolated from collected sera and culture medium from previously steps, and a standard procedure was performed. We utilized MDA-MB-436-derived xenograft mouse model to demonstrate that silencing CBFB (core binding factor subunit β) significantly reduced bone-metastasis in association with reduced expression of OPN, IL-6, Runx2 and OPN as well as reduced exosomes containing CBFB.Results: We found that circulating exosomes (Exos), from bone metastatic patients with breast cancer, were enriched with CBFB. Fibroblasts co-cultured with Exos showed increased α-SMA, vimentin expression and increased secretion of IL-6 and OPN; non-metastatic breast cancer cells co-cultured with Exos exhibited increased markers including vimentin, snail1, CXCR4 and Runx2. Subsequent analysis revealed that these Exos were enriched with bone metastasis associated maker CBFB. Gene-silencing experiments metastatic MDA-MB-436 and MDA-MB-157 cells, demonstrated that CBFB significantly reduced metastatic potential, reflected by the suppression of vimentin, CXCR4, snail1 and Runx2, CD44 and OPN. In contrary, CBFB-overexpression resulted in the increased metastasis associated genes in non-metastatic T47D and MCF7 cells. The CBFB-enriched exosomes derived from MDA-MB-436 enhanced metastatic phenotypes of low metastatic potential breast cancer cell lines. Conclusion: We demonstrated the essential roles of CBFB in the promotion of bone metastasis in breast cancer cells. The suppression of CBFB led to the decreased tumor burden and bone metastasis in association with decreased markers of bone metastasis including CXCR4, Snail, CD44, OPN, Runx2 and IL-6.