Cloning and characterization of insect genes involved in programmed cell death

Two insect Inhibitor of Apoptosis Proteins (IAPs), SfIAP and BmIAP, were cloned respectively from Sf-21 cells derived from Spodoptera frugiperda (fall armyworm) and BmN cells derived from Bombyx mori (silkworm), hosts of insect baculoviruses. These two IAPs contain two baculoviral IAP repeat (BIR) domains followed by a RING domain. They share striking amino acid similarity with baculoviral IAPs, CpIAP and OpIAP, suggesting that baculoviral IAPs may be host-derived genes. SfIAP and BmIAP block programmed cell death (apoptosis) in Sf-21 cells induced by p35-deficient Autographa californica nucleopolyhedrovirus (AcMNPV). In mammalian cells these two IAPs and baculoviral CpIAP suppress Bax-induced but not Fas-induced apoptosis. Further biochemical data suggest that these IAPs are specific inhibitors of human caspase-9. These results suggest that suppression of apoptosis by lepidopteran and baculoviral IAPs may involve inhibition of insect upstream initiator caspases in the conserved mitochondrial pathway for apoptosis. Peptides representing the IAP-binding domain of the cell death protein Grim from Drosophila melanogaster abrogated human caspase suppression by SfIAP and CpIAP, implying evolutionary conservation of the functions of IAPs and their inhibitors.;A homologue of human Bcl family member (DBok) was cloned from Drosophila melanogaster. The predicted structure of DBok is similar to the pore-forming Bcl family members. DBok induces apoptosis in both insect and mammalian cells, which is suppressible by Mcl-1, an anti-apoptotic human Bcl-2 family member. Moreover, DBok targets mitochondria and triggers cytochrome-c release through a caspase-independent mechanism. These characteristics of DBok reveal evolutionary conservation of cell death mechanism in flies and humans.