Diarylurea compounds inhibit caspase activation by preventing the formation of the active 700-kilodalton apoptosome complex.
The release of mitochondrial proapoptotic proteins into the cytosol is the key event in apoptosis signaling, leading to the activation of caspases. Once in the cytosol, cytochrome c triggers the formation of a caspase-activating protein complex called the apoptosome, whereas Smac/Diablo and Omi/htra2 antagonize the caspase inhibitory effect of inhibitor of apoptosis proteins (IAPs). Here, we identify diarylurea compounds as effective inhibitors of the cytochrome c-induced formation of the active, approximately 700-kDa apoptosome complex and caspase activation. Using diarylureas to inhibit the formation of the apoptosome complex, we demonstrated that cytochrome c, rather than IAP antagonists, is the major mitochondrial caspase activation factor in tumor cells treated with tumor necrosis factor. Thus, we have identified a novel class of compounds that inhibits apoptosis by blocking the activation of the initiator caspase 9 by directly inhibiting the formation of the apoptosome complex. This mechanism of action is different from that employed by the widely used tetrapeptide inhibitors of caspases or known endogenous apoptosis inhibitors, such as Bcl-2 and IAPs. Thus, these compounds provide a novel specific tool to investigate the role of the apoptosome in mitochondrion-dependent death paradigms.
Lademann
Ulrik
U
Apoptosis Laboratory, Institute of Cancer Biology, Danish Cancer Society, DK-2100 Copenhagen, Denmark.
Cain
Kelvin
K
Gyrd-Hansen
Mads
M
Brown
David
D
Peters
Dan
D
Jäättelä
Marja
M
D017209:Apoptosis / Q000502:physiology*; D053477:Apoptotic Protease-Activating Factor 1; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D045744:Cell Line, Tumor; D045304:Cytochromes c / Q000378:metabolism; D003838:Deoxyadenine Nucleotides / Q000378:metabolism; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000378:metabolism*; D053222:Fas Ligand Protein; D006801:Humans; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins / Q000378:metabolism; D015394:Molecular Structure; D008970:Molecular Weight; D011506:Proteins / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D014508:Urea / Q000737:chemistry* / Q000378:metabolism*
C506592:APAF1 protein, human; D053477:Apoptotic Protease-Activating Factor 1; D061945:Caspase Inhibitors; D003838:Deoxyadenine Nucleotides; D004791:Enzyme Inhibitors; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins; D011506:Proteins; D014409:Tumor Necrosis Factor-alpha; D014508:Urea; D045304:Cytochromes c; D020169:Caspases; C026600:2'-deoxyadenosine triphosphate