siRNA-mediated GNB4 knockdown, however, suppressed proliferation of 182R-6 and TAMR-1 cells in the presence of antiestrogen drugs, and induced S-phase arrest of 182R-6 cells and apoptosis of TAMR-1 cells (Fig. 6a and b), further validating a crucial role of GNB4 in the development of antiestrogen resistance of breast cancer cells. Here, GNB4 is linked to breast cancer.