HCN2 and breast cancer: Western blot employed to determine the expression of endogenous HCN2, HCN3, BRCA1, BRCA2, and RAD51, confirmed that either HCN2 or HCN3 was overexpressed in the breast cancer cells (Fig. 1E, F), whilst HEK293 had low expression in both of HCN2 and HCN3 (Fig. 1E, F).