PARP-1 interactions with cell death proteases. PARP-1 cleavage by various suicidal proteases like caspases, calpain, cathepsins and granzymes liberates fragments with specific molecular weights and are shown in this schematic representation. Importantly, 21-kD and 55-kD PARP-1 fragments generated by caspase 3/7 and Gra-A respectively function as an inhibitor of PARP-1 activity and might also play important roles in reducing necrosis and/or parthanatos. Further, PARP-1 and PARP-1 fragment's involvement in various forms of cell death e.g. autophagy, necrosis and parthanatos are also indicated.