miR-181c-containing exosomes from brain-metastatic breast cancer cells can be transferred to endothelial cells of the BBB to destroy the BBB by inhibiting 3-phosphoinositide-dependent protein kinase 1 (PDPK1) expression and altering actin dynamics, which can facilitate brain metastasis of breast cancer cells (Tominaga et al., 2015). Here, PDPK1 is linked to breast cancer.