To examine the effect of TM-PUMA on cell viability, we expressed an empty vector, WT-PUMA or TM-PUMA in two different HER2-overexpressing breast cancer cell lines, namely BT-474 (Figure 5e) and MDA-MB-453 (Figure 5f) cells, and monitored the ability of these cells to form colonies. Here, ERBB2 is linked to breast cancer.