Abstract
As an important type of programmed cell death, apoptosis plays a critical role in lepidopteran insects in response to various internal and external stresses. It is controlled by a network of genes such as those encoding the inhibitor of apoptosis proteins. However, there are few studies on apoptosis-related genes in Spodoptera frugiperda. In this study, an orthologue to the Drosophila reaper gene, named Sf-IBM1, was identified from S. frugiperda, and a full-length sequence was obtained by reverse transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends PCR (RACE-PCR). The expression pattern of Sf-IBM1 was determined in different developmental stages and various tissues. Apoptotic stimuli including azadirachtin, camptothecin, and ultraviolet radiation (UV) induced the expression of Sf-IBM1 at both transcript and protein levels. Overexpression of Sf-IBM1 induced apoptosis in Sf9 cells, and the Sf-IBM1 protein was localized in mitochondria. The apoptosis induced by Sf-IBM1 could be blocked by the caspase universal inhibitor carbobenzoxy-valyl-alanyl-aspartyl-[O-methyl]-fluoromethylketone (Z-VAD-FMK) and Sf-IAP1. Our results provide valuable information that should contribute to a better understanding of the molecular events that lead to apoptosis in lepidopterans.
Highlights
Apoptosis is a highly conserved cellular process in metazoans and is responsible for eliminating supernumerary, deleterious, or defective cells
We found that overexpression of Sf-IBM1 induced apoptosis in Sf9 cells by activating the mitochondrial apoptosis pathway, and apoptosis was inhibited by the caspase general inhibitor carbobenzoxy-valyl-alanyl-aspartyl-[O-methyl]-fluoromethylketone (Z-VAD-FMK) completely
To explore whether a gene homologous to RHG exists in S. frugiperda, we searched a transcriptome of Sf9 cells and identified a truncate unigene annotated as the Reaper homolog IBM1
Summary
Apoptosis is a highly conserved cellular process in metazoans and is responsible for eliminating supernumerary, deleterious, or defective cells. IAPs can bind to both initiator and effector caspases directly and degrade activated caspases through the E3 ubiquitin ligase activity, resulting in inhibition of apoptosis [11]. IAP antagonists compete with caspases by binding to the BIR domains of IAPs with different affinities via IBM directly [15]. The IAP antagonists can function as positive regulators of apoptosis by inducing the auto-ubiquitylation of DIAP1 in Drosophila [16]. We found that overexpression of Sf-IBM1 induced apoptosis in Sf9 cells by activating the mitochondrial apoptosis pathway, and apoptosis was inhibited by the caspase general inhibitor carbobenzoxy-valyl-alanyl-aspartyl-[O-methyl]-fluoromethylketone (Z-VAD-FMK) completely. Our results indicate that Sf-IBM1 plays a pro-apoptotic role in Sf9 cells and has functional similarity to an RHG family protein in Drosophila
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