Functional analysis of the inhibitor of apoptosis (iap) gene carried by the entomopoxvirus of Amsacta moorei

The entomopoxvirus from Amsacta moorei (AmEPV) contains none of the commonly recognized vertebrate poxvirus apoptotic suppressor genes. However, AmEPV carries a single inhibitor of apoptosis (iap) gene (AMViap) not present in vertebrate poxviruses. The AMViap gene was active when coexpressed with the Drosophila proapoptotic gene hid in Ld652 cells and can rescue cells from apoptosis as shown by increased number of surviving cells and reduced levels of caspase-3-like activity. We also showed that expression of the AMViap gene rescued polyhedron production in Autographa californica M nucleopolyhedrovirus (AcMNPV)Deltap35-infected Sf9 cells during an otherwise abortive infection induced by apoptosis. Surprisingly, deletion of the AMViap gene from the AmEPV genome led to only a modest (10-fold) loss of virion production in infected Ld652 cells, indicating that the AMViap gene is nonessential for virus replication under these conditions. However, infection of Ld652 cells by AmEPV lacking a functional iap gene led to a more rapid induction of cytotoxicity and increased levels of caspase-3-like activity. Similar results were observed and were more pronounced in infected Sf9 and S2 cells. The purified AMVIAP protein also inhibits the enzymatic activities of human caspase-9 and caspase-3 in vitro. Our results indicate that while the AMViap gene was active in controlling apoptosis through the intrinsic pathway, the virus likely encodes additional proteins that also regulate apoptosis.