Identification and functional analysis of the putative anti-apoptotic gene iap4 of Spodoptera litura nucleopolyhedrovirus

Abstract

Baculoviruses possess two types of anti-apoptotic genes, p35 and inhibitor of apoptosis (iap). In this study, we cloned a novel IAP family member, Splt-IAP4, from Spodoptera litura nucleopolyhedrovirus (SpltNPV). ScanProsite analysis of Splt-IAP4 amino acid sequence show that it contain a baculovirus IAP repeat (BIR) motif at the N-terminal portion from 18 to 61 amino acid and a Zinc finger RING motif near its C-terminus. Baculovirus IAPs could be divided into five types from IAP1 to IAP5 according to amino acid sequence homology, so the Splt-IAP4 was grouped into IAP4 because of containing a single BIR motif. Alignment of the six IAP4s in sequenced baculovirus genomes indicated that the Splt-IAP4 gene shared 74% amino acid sequence similarity with Spodoptera littoralis NPV (SpliNPV) IAP4 higher than other baculovirus IAP4 proteins, suggesting evolutionary conservation. In transient expression assay, Splt-IAP4 was not able to suppress apoptosis induced by a mutant AcMNPV deficient in p35 (vAcAnh) infection and rescue the mutant virus replication from apoptosis in Sf-9 cells. Cell viabilities analysis showed that Splt-IAP4 could not inhibit or delay the apoptosis of Sf-9 cells induced by vAcAnh infection. In summary, Splt-IAP4 had no anti-apoptotic function during vAcAnh-infected Sf-9 cells.

Viral IAPs, then and now

“…Three IAP-4 genes have been tested for their ability to inhibit apoptosis [38,48,49]; IAP-4 from Spodoptera littoralis NPV was reported to be able to delay, but not block, apoptosis, while the other reports failed to find any evidence of anti-apoptotic activity. To my knowledge only one IAP-5 gene, from CpGV, has been tested for anti-apoptotic activity; it was reported to not be able to inhibit apoptosis on its own, but it was able to stimulate protection by CpGV IAP-3 [50].…”