ERBB2 and breast cancer: As shown in Figure 2, A and B, overexpression of DPAGT1, but not the enzyme-dead mutant DPAGT1-N185A (21), dramatically increased the level of p95HER2 in HER2+ breast cancer cells and the HER2-ECD level in the conditional medium, which was abolished by DPAGT1 inhibition with tunicamycin (TM).