PARP1 and cancer: As shown in Figure 4, knockdown of either ERK3 (siCtrl/shERK3), TDP2 (siTDP2/shGIPZ) or both (siTDP2/shERK3) greatly increased the levels of cleaved PARP-1, suggesting that ERK3 and TDP2 also protects cancer cells against etoposide-induced apoptosis.