GJA1 and breast cancer: In a first approach, a model system was designed consisting of (a) SkBr3 cells as a drug-sensitive breast cancer cell line with reduced Cx43 expression and increased Cx43 plaques formation [27], (b) primary human internal mammary artery endothelial cells (HIMAECs) relevant for angiogenesis, (c) BJ fibroblasts representing connective tissue in the tumor environment.