Diablo homolog, mitochondrial (DIABLO) is also known as direct IAP-binding protein with low pI and second mitochondria-derived activator of caspase (SMAC), which can interact with BIRC2/c-IAP1, BIRC3/c-IAP2, XIAP/BIRC4, BIRC6/bruce and BIRC7/livin. Acting by opposing the inhibitory activity of inhibitor of apoptosis proteins (IAP),DIABLO can also promote apoptosis by activating caspases in the cytochrome c/Apaf-1/caspase-9 pathway. Also, DIABLO inhibits the activity of BIRC6/bruce by inhibiting its binding to caspases. Furthermore, DIABLO is defective in the capacity to down-regulate the XIAP/BIRC4 abundance.