Survivin in breast cancer-derived exosomes activates fibroblasts by up-regulating SOD1, whose feedback promotes cancer proliferation and metastasis.

Cancer-associated fibroblasts (CAFs) play a critical role in the coevolution of breast tumor cells and their microenvironment by modifying cellular compartments and regulating cancer cell functions via stromal-epithelial dialogue. However, the relationship and interaction between stromal and epithelial cells is still poorly understood. Herein, we revealed that breast cancer cells have a stronger ability to activate fibroblasts and transform them into myofibroblasts (CAF-like) than normal breast epithelial cells, and this stronger ability occurs through paracrine signaling. In turn, myofibroblasts promote the proliferation, epithelial-to-mesenchymal transition (EMT), and stemness of breast cancer cells. Detailed regulatory mechanisms showed that, compared with normal cells, Survivin is overexpressed in breast cancer cells and secreted extracellularly in the form of exosomes, which are then internalized by fibroblasts. Breast cancer cell-derived survivin up-regulates SOD1 expression in fibroblasts and then converts them into myofibroblasts, conversely inducing breast cancer progression in vitro and in vivo Thus, our results indicate that survivin acts as an activator of the tumor microenvironment and that SOD1 up-regulation in fibroblasts can promote breast cancer progression. These results suggest that targeting survivin and SOD1 may be a potential therapeutic strategy for breast cancer.