5A. Baseline HER2 phosphorylation in different cell lines. Cell lysates were harvested from different cells. Phosphorylated HER2 and total HER2 were examined by immunoblotting with primary antibodies. Immunoblotting for β-actin was determined for loading control. 5B. Inhibitory effects of the HER2 inhibitor and the c-Src inhibitor on cells with elevated HER2 phosphorylation. Sk-Br-3, BT474, T47D:C42, and MDA-MB-231 cells were seeded in 24-well plates in triplicate. After one day, the cells were treated with vehicle (0.1%DMSO), lapatinib (1μM), and PP2 (5μM) in 10% SFS medium. The cells were harvested after 7 days treatment and total DNA was determined as above. 5C. S phase changes after lapatinib and PP2 treatment. Sk-Br-3 and MDA-MB-231 cells were treated with vehicle (0.1% DMSO), lapatinib (1μM), and PP2 (5μM) for 24h. Cells were harvested and fixed with 75% EtOH. Cell cycles were analyzed through flow cytometery. 5D. Blocking HER2 phosphorylation after lapatinib treatment. Sk-Br-3 and BT474 cells were treated with vehicle (0.1%DMSO) and lapatinib (1μM) for 24h. HER2 phosphorylation was examined by immunoblotting with primary antibody. Immunoblotting for total HER2 was determined for loading control.