PARP1 and cancer: While the precise mechanisms by which B18L mediates the killing of cancer cells is unknown, several lines of evidence indicate that B18L induces membranolytic effects, negatively regulates Src•Erk1/2 signaling and activates the extrinsic and mitochondrial apoptotic pathways, as evidenced by its cleavage of Cas3, Bid and PARP (Figure 8).