The inhibitor of apoptosis gene (iap-3) of Anticarsia gemmatalis multicapsid nucleopolyhedrovirus (AgMNPV) encodes a functional IAP

Abstract

Programmed cell death or apoptosis is one of the defense mechanisms used by insect cells in response to baculovirus infection. Baculoviruses harbour antiapoptotic genes to prevent apoptosis and to maintain the normal course of infection. In this work, we showed that, like other baculoviruses, Anticarsia gemmatalis multicapsid nucleopolyhedrovirus (AgMNPV) has a functional inhibitor of apoptosis gene (iap-3). The iap-3 gene was cloned, sequenced and its transcription confirmed by RT-PCR. The putative iap-3 gene of the baculovirus AgMNPV has 864 nucleotides and codes an ORF of 287 amino acids. We have found two BIR motifs (baculoviral iap repeats) at the amino-terminal region and a carboxi-terminal RING finger motif. The IAP-3 protein of AgMNPV is closely related to IAP-3 proteins of baculoviruses and lepidopteran IAPs, with most amino acid identity (75%) with the IAP-3 protein of CfDefNPV (Choristoneura fumiferana DEF nucleopolyhedrovirus). Transcriptional analysis of the AgMNPV iap-3 gene showed that iap-3-specific transcripts could be detected early and late in the infection. The iap-3 gene of AgMNPV was shown to encode a functional IAP since insect cells transfected with increasing amounts of a plasmid containing the iap-3 of AgMNPV showed increased resistance to apoptosis induced by a AgMNPV mutant virus.

Viral IAPs, then and now

“…IAP-3 homologs that have been shown to have anti-apoptotic activity include those of CpGV [6], OpMNPV [8], Anticarsia gemmatalis MNPV [35], Hyphantria cunea NPV (HycuNPV) [36], and Helicoverpa armigera NPV (HearNPV) [37]. However, the Epiphyas postvittana MNPV (EppoM-NPV) IAP-3 is unable to inhibit apoptosis [38], and IAP-3 and IAP-2 from Lymantria dispar MNPV (LdMNPV) induced apoptosis when overexpressed [39].…”

Function analysis and application of IAP1/2 of Autographa californica multiple nucleopolyhedrovirus

“…In most of the baculoviruses, IAP3 has an antiapoptosis function. [9][10][11][12][13] IAPs have 1-3 baculovirus IAP repeats (BIRs) in the N-terminal region and a RING nger domain in the C-terminal region. BIRs are unique to IAPs and consist of $70 amino acids with the signature sequence CX 2 CX 16 HX 6 C, which coordinate a zinc ion and mediate protein-protein interaction.…”

The BIR and BIR-like domains of Bombyx mori nucleopolyhedrovirus IAP2 protein are required for efficient viral propagation

“…Baculovirus genomes commonly contain multiple iap genes that belong to different groups. Although IAP3 proteins from most baculoviruses inhibit apoptosis [6,7,[10][11][12], the roles of most other IAPs, including IAP2, remain unknown.…”