CXCR4 and breast carcinoma: But in case of gp120/CXCR4-mediated apoptosis, the signaling pathway seems to be Gαi protein-independent, at least in T-cells (196, 197), whereas gp120/CXCR4-induced apoptosis of breast cancer cells (194) and hepatocytes (193) depends on Gαi protein involvement.