PARP1 and breast carcinoma: As shown in Figure 3A, treatment of human breast cancer MDA-MB-231 and SK-BR-3 cells with 10 μM of proteasome inhibitor MG-132 resulted in an accumulation of endogenous PARP1 in a time-dependent manner (Figure 3A), indicating that PARP1 undergoes proteasome-dependent degradation.