The inhibitors of apoptosis of Epiphyas postvittana nucleopolyhedrovirus

Abstract

In this study, four inhibitor of apoptosis genes ( iaps ) in the genome of Epiphyas postvittana nucleopolyhedrovirus (EppoMNPV) that are homologous to iap-1 , iap-2 , iap-3 and iap-4 genes of other baculoviruses have been identified. All four iap genes were sequenced and the iap-1 and iap-2 genes were shown to be functional inhibitors of apoptosis. The iap-1 , iap-2 and iap-3 genes contain two baculovirus apoptosis inhibitor repeat motifs and a C 3 HC 4 RING finger-like motif. The activity of the iap genes was tested by transient expression in Spodoptera frugiperda (Sf-21) cells treated with the apoptosis-inducing agents actinomycin D, cycloheximide, anisomycin, tumour necrosis factor-α and UV light. The iap-2 gene prevented apoptosis induced by all agents tested, indicating activity towards a conserved component(s) of multiple apoptotic pathways. However, the iap-2 gene was unable to function in the absence of a gene immediately upstream of iap-2 that has homology to the orf69 gene of Autographa californica MNPV. The use of a CMV promoter rescued the apoptosis inhibition activity of the iap-2 gene, indicating that the upstream orf69 homologue is associated with expression of iap-2 . The iap-1 gene was able to delay the onset of apoptosis caused by all of the induction agents tested but, unlike iap-2 , was unable to prevent the development of an apoptotic response upon prolonged exposure of cells to the apoptosis induction agents. No anti-apoptotic activity was observed for the iap-3 and iap-4 genes of EppoMNPV.