Apoptosis In Sf9 Cells Research Articles

Evaluation of insecticidal potential of organochemicals on SF9 cell line

BackgroundOrganophosphates and Pyrethroids are the most widely used pesticides worldwide and are known to have significant toxicity on the nervous system of the target pest. Assessment for combined toxicity of Organophosphate and Pyrethroid on Sf9 (Spodoptera frugiperda) cells is less explored. The present study demonstrates and compares the two organochemicals whose trade names are Ammo and Profex, for its cytotoxic potential on the insect Sf9 cells. Ammo and Profex were selected as the test chemicals as toxicity of these insecticides at molecular and cellular level is poorly understood.ResultsThe results of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide assay demonstrated that Ammo and Profex exhibited significant cytotoxicity to Sf9 cells in a time- and dose-dependent manner. In our study, the IC50 value was obtained by MTT assay and the sub-lethal concentrations (IC50/20-17.5 µg/ml, IC50/10-35 µg/ml, and IC50/5–70 µg/ml for Ammo and IC50/20-20 µg/ml, IC50/10-40 µg/ml, and IC50/5-80 µg/ml for Profex) were selected for further tests. Acridine orange/ethidium bromide staining proved the apoptotic cell death on exposure of both the insecticides confirming its toxic potential. Furthermore, antioxidant status was assessed using DCF-DA staining and both the insecticides resulted into an increased reactive oxygen species (ROS) generation. A dose- and time-dependent significant (p < 0.05) alterations in lipid peroxidase (LPO), glutathione (GSH) and catalase (CAT) activity were observed.ConclusionThe results showed that both Ammo and Profex triggered apoptosis in Sf9 cells through an intrinsic mitochondrial pathway via the generation of ROS. Of the two insecticides, Ammo was found to be more toxic compared to Profex. The present study is important to evaluate the environmental safety and risk factors of Organochemicals’ exposure to crops and livestock.

Pro-Apoptotic Function Analysis of the Reaper Homologue IBM1 in Spodoptera frugiperda.

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.

Mitochondria and Lysosomes Participate in Vip3Aa-Induced Spodoptera frugiperda Sf9 Cell Apoptosis.

Vip3Aa, a soluble protein produced by certain Bacillus thuringiensis strains, is capable of inducing apoptosis in Sf9 cells. However, the apoptosis mechanism triggered by Vip3Aa is unclear. In this study, we found that Vip3Aa induces mitochondrial dysfunction, as evidenced by signs of collapse of mitochondrial membrane potential, accumulation of reactive oxygen species, release of cytochrome c, and caspase-9 and -3 activation. Meanwhile, our results indicated that Vip3Aa reduces the ability of lysosomes in Sf9 cells to retain acridine orange. Moreover, pretreatment with Z-Phe-Tyr-CHO (a cathepsin L inhibitor) or pepstatin (a cathepsin D inhibitor) increased Sf9 cell viability, reduced cytochrome c release, and decreased caspase-9 and -3 activity. In conclusion, our findings suggested that Vip3Aa promotes Sf9 cell apoptosis by mitochondrial dysfunction, and lysosomes also play a vital role in the action of Vip3Aa.

Neochamaejasmin A extracted from Stellera chamaejasme L. induces apoptosis involving mitochondrial dysfunction and oxidative stress in Sf9 cells

To explore the toxicity mechanisms of neochamaejasmin A (NCA), extracted from Stellera chamaejasme L., we first evaluated its cytotoxicity on the Spodoptera frugiperda (Sf9) cell line. The results confirmed that NCA inhibited Sf9 cell survival in both a dose- and time-dependent manner. Then, intracellular biochemical assays showed that NCA induced apoptosis in Sf9 cells. Evidence of apoptosis was confirmed by morphological changes and the activation of caspases-3/9. We also observed that NCA induced apoptosis via mitochondrial-dependent intrinsic apoptotic pathway by upregulating cytochrome c and proapoptotic protein (Bax) and downregulating the mitochondrial membrane potential (MMP) and antiapoptotic protein (Bcl-2). Moreover, we found a dose-dependent increase in reactive oxygen species (ROS), accumulation of lipid peroxidation product and an inactivation of the antioxidant enzymes in treated cells. Additionally, the cleavage of PARP and G2/M arrest were also detected in Sf9 cells exposed to NCA. These findings provide critical information that NCA effectively induced apoptosis in Sf9 cells through mitochondrial pathways.

Harmine induced apoptosis in Spodoptera frugiperda Sf9 cells by activating the endogenous apoptotic pathways and inhibiting DNA topoisomerase I activity

Harmine, a useful botanical compound, has demonstrated insecticidal activity against some pests. However, harmine's mechanism of action has not been thoroughly elucidated to date. To preliminarily explore harmine's insecticidal mechanisms, the cytotoxicity of harmine against Spodoptera frugiperda Sf9 cells was comprehensively investigated. Our results indicated that harmine induced apoptosis in Sf9 cells, as evidenced by cellular and nuclear morphological changes, DNA laddering and increases in caspase-3-like activities. In addition, activation of the mitochondrial apoptotic pathway by harmine was confirmed by the generation of ROS, opening of mitochondrial permeability transition pores (MPTPs), increase in cytosolic Ca2+, changes in mRNA expression levels of genes involved in the mitochondrial apoptotic pathway and increase and release of Cytochrome c. Furthermore, lysosomal membrane permeabilization, release of cathepsin L from the lysosome into the cytosol and cleavage of caspase-3 were also triggered, which indicated that lysosomes were involved in this physiological process. Moreover, the effect of harmine on DNA topoisomerase I activity was investigated by in vivo and molecular docking experiments. These data not only verified that harmine induced apoptosis via comprehensive activation of the mitochondrial and lysosomal pathways and inhibition of DNA topoisomerase I activity in Sf9 cells but also revealed a mechanism of harmine insecticidal functions for pest control.

DnaJ homolog subfamily A member1 (DnaJ1) is a newly discovered anti-apoptotic protein regulated by azadirachtin in Sf9 cells

BackgroundAzadirachtin, one of the most promising botanical insecticides, has been widely used for pest control. Azadirachtin induces apoptosis in insect cell lines, including Sf9, SL-1 and BTI-Tn-5B1–4. Mitochondrial and lysosomal pathways are likely involved in the azadirachtin-induced apoptosis, however, detailed molecular mechanisms remain largely undefined.ResultsAzadirachtin-induced apoptosis in Sf9 cells was verified by morphological observation, Hoechst 33258 staining, and a Caspase-3-based analysis. Comparative two-dimensional gel electrophoresis (2-DE) coupled with a linear ion trap quadrupole (LTQ)-MS/MS analysis identified 12 prominent, differentially expressed proteins following azadirachtin treatment. These differentially expressed genes are involved in regulating cytoskeleton development, signal transduction, gene transcription, and cellular metabolism. Knockdown gene expression of a gene encoding a DnaJ homolog enhanced apoptosis induced by azadirachtin in Sf9 cells.ConclusionAzadirachtin treatment induces apoptosis in Sf9 cells and affects expression of multiple genes with functions in cytoskeleton development, signal transduction, gene regulation, and cellular metabolisms. Azadirachtin induces apoptosis at least partially by down-regulation of Sf-DnaJ in Sf9 cells.

Evidence for a radiation-responsive \u2018p53 gateway\u2019 contributing significantly to the radioresistance of lepidopteran insect cells

Recently, we have demonstrated that microRNA-31 (miR-31) overexpression is inherent to radiation-induced cell death in the highly radioresistant Sf9 insect cells, and regulates pro-apoptotic Bax translocation to mitochondria. In the present study, we report that at sub-lethal radiation doses for Sf9 cells, miR-31 is significantly downregulated and is tightly regulated by an unusual mechanism involving p53. While ectopic overexpression of a well-conserved Sfp53 caused typical apoptosis, radiation-induced p53 accumulation observed selectively at sub-lethal doses failed to induce cell death. Further investigation of this paradoxical response revealed an intriguing phenomenon that sub-lethal radiation doses result in accumulation of a ‘hyper-phosphorylated’ Sfp53, which in turn binds to miR-31 genomic location and suppresses its expression to prevent cell death. Interestingly, priming cells with sub-lethal doses even prevented the apoptosis induced by lethal radiation or ectopic Sfp53 overexpression. On the other hand, silencing p53 increased radiation-induced cell death by inhibiting miR-31 downregulation. This study thus shows the existence of a unique radiation-responsive ‘p53 gateway’ preventing miR-31-mediated apoptosis in Sf9 cells. Since Sfp53 has a good functional homology with human p53, this study may have significant implications for effectively modulating the mammalian cell radioresistance.

Transcriptome analysis of Spodoptera frugiperda Sf9 cells reveals putative apoptosis-related genes and a preliminary apoptosis mechanism induced by azadirachtin

As an important botanical pesticide, azadirachtin demonstrates broad insecticidal activity against many agricultural pests. The results of a previous study indicated the toxicity and apoptosis induction of azadirachtin in Spodoptera frugiperda Sf9 cells. However, the lack of genomic data has hindered a deeper investigation of apoptosis in Sf9 cells at a molecular level. In the present study, the complete transcriptome data for Sf9 cell line was accomplished using Illumina sequencing technology, and 97 putative apoptosis-related genes were identified through BLAST and KEGG orthologue annotations. Fragments of potential candidate apoptosis-related genes were cloned, and the mRNA expression patterns of ten identified genes regulated by azadirachtin were examined using qRT-PCR. Furthermore, Western blot analysis showed that six putative apoptosis-related proteins were upregulated after being treated with azadirachtin while the protein Bcl-2 were downregulated. These data suggested that both intrinsic and extrinsic apoptotic signal pathways comprising the identified potential apoptosis-related genes were potentially active in S. frugiperda. In addition, the preliminary results revealed that caspase-dependent or caspase-independent apoptotic pathways could function in azadirachtin-induced apoptosis in Sf9 cells.

Characterization of an inhibitor of apoptosis gene (BmSurvivin-2) from the silkworm, Bombyx mori

The inhibitor of apoptosis proteins (IAP) plays an important role in maintaining the balance between cell proliferation and cell death. Here, we describe an IAP named BmSurvivin-2 isolated from tissues of Bombyx mori that contains only one baculoviral IAP repeat (BIR) domain and lacks a really interesting new gene (RING) finger domain. Cell viability and DNA fragment analysis showed that over-expression of BmSurvivin-2 could inhibit actinomycin D (ActD)-induced apoptosis in Sf9 cells, and its anti-apoptotic activity was dependent on its N-terminal BIR domain. Real-time PCR analyses indicated that BmSurvivin-2 mRNA was expressed in all tissues of silkworm and the highest expression level was found in testis and head. Expression of BmSurvivin-2 was found to gradually increase during the wandering stage of silkworm and decreased after wandering. Similar to deterin but not survivin, BmSurvivin-2 was primarily located in the cytoplasm. All these results provide insight into the role of a novel IAP in the silkworm, B. mori.

The expression and purification of WSSV134 from white spot syndrome virus and its inhibitory effect on caspase activity from Penaeus monodon

WSSV134 or VP36A protein of white spot syndrome virus was previously reported to be able to reduce apoptosis in Sf-9 cells transfected with caspase of Penaeus monodon (PmCasp). The protein was therefore believed to have a role in supporting the survival of WSSV inside the host cells during infection. However, the anti-apoptosis activity of WSSV134 involved in the inhibition of PmCasp is still unclear. In this study, we produced a recombinant WSSV134 (rWSSV134) and tested for its ability to inhibit PmCasp in vitro. The results from a caspase inhibition assay revealed that rWSSV134 could inhibit PmCasp in a dose-dependent manner. Since WSSV134 was predicted to contain three potential caspase binding sites, corresponding to the D54, D104 and D259, we then employed site-directed mutagenesis to investigate the involvement of these sites in PmCasp inhibition. D54A and D259A mutants could still inhibit PmCasp while D104A mutant lacks this activity. Our results confirmed that the WSSV134 is an inhibitor for PmCasp and that residue D104 is important for PmCasp inhibition.

Vip3Aa induces apoptosis in cultured Spodoptera frugiperda (Sf9) cells

The vegetative insecticidal proteins (Vip) secreted by many Bacillus thuringiensis strains during their vegetative growth stage are regarded as second generation insecticidal proteins, as they share no sequence or structural homology with known crystal insecticidal proteins (Cry) and have a broad insecticidal spectrum. Compared with insecticidal crystal proteins (ICPs), the insecticidal mechanisms of Vips have been little studied. Here we investigated the mechanism responsible for Vip3Aa toxicity in cultured insect cells. Using, flow cytometry analyzes, TUNEL staining and DNA fragmentation assays, we show that Vip3Aa can induce apoptosis in Spodoptera frugiperda (Sf9) cells and cause cells to arrest at the G2/M phase. We also show that Vip3Aa can disrupt mitochondrial membrane potential (ΔΨm), leading to the activation of Sf-caspase-1, suggesting that a mitochondrial mediated and caspase dependent pathway may be involved in Vip3Aa-induced apoptosis in Sf9 cells.

Staurosporine shows insecticidal activity against Mythimna separata Walker (Lepidoptera: Noctuidae) potentially via induction of apoptosis

Staurosporine (STS), a wide-spectrum kinase inhibitor, is widely used in studies of apoptosis in mammalian cells. However, its physiological and mechanistic effects have never been clearly defined in insect cells, and other applications of STS have rarely been reported. The present study reveals the insecticidal activity of STS on larvae of Mythimna separata Walker, and the apoptotic mechanism induced by STS on lepidopteran Sf9 cell lines. We demonstrate that the viability of Sf9 cells is inhibited by STS in a time- and concentration-dependent manner. Intracellular biochemical assays show that STS-induced apoptosis of Sf9 cells coincides with a decrease in the mitochondrial membrane potential, the release of cytochrome c into the cytosol, a significant increase of the Bax/Bcl-2 ratio, and a marked activation of caspase-9 and caspase-3. These results indicate that a mitochondrial-dependent intrinsic pathway contributes to STS induced caspase-3 activation and apoptosis in Sf9 cells which is homologous to the mechanisms in mammalian cells. This study contributes to our understanding of the mechanism of insect cell apoptosis and suggests a possible new application of STS as a potential insecticide against Lepidopteran insect pests in agriculture.

Azadirachtin-induced apoptosis involves lysosomal membrane permeabilization and cathepsin L release in Spodoptera frugiperda Sf9 cells

Azadirachtin as a kind of botanical insecticide has been widely used in pest control. We previously reported that azadirachtin could induce apoptosis of Spodoptera litura cultured cell line Sl-1, which involves in the up-regulation of P53 protein. However, the detailed mechanism of azadirachtin-induced apoptosis is not clearly understood in insect cultured cells. The aim of the present study was to address the involvement of lysosome and lysosomal protease in azadirachtin-induced apoptosis in Sf9 cells. The result confirmed that azadirachtin indeed inhibited proliferation and induced apoptosis. The lysosomes were divided into different types as time-dependent manner, which suggested that changes of lysosomes were necessarily physiological processes in azadirachtin-induced apoptosis in Sf9 cells. Interestingly, we noticed that azadirachtin could trigger lysosomal membrane permeabilization and cathepsin L releasing to cytosol. Z-FF-FMK (a cathepsin L inhibitor), but not CA-074me (a cathepsin B inhibitor), could effectively hinder the apoptosis induced by azadirachtin in Sf9 cells. Meanwhile, the activity of caspase-3 could also be inactivated by the inhibition of cathepsin L enzymatic activity induced by Z-FF-FMK. Taken together, our findings suggest that azadirachtin could induce apoptosis in Sf9 cells in a lysosomal pathway, and cathepsin L plays a pro-apoptosis role in this process through releasing to cytosol and activating caspase-3.

The mitochondria-mediate apoptosis of Lepidopteran cells induced by azadirachtin.

Mitochondria have been shown to play an important role in apoptosis using mammalian cell lines. However, this seems not to be the case in Drosophila, an insect model organism; thus more in-depth studies of insect cell apoptosis are necessary. In the present study, mitochondrial involvement during azadirachtin- and camptothecin-induced apoptosis in Spodoptera frugiperda Sf9 cells (isolated from Spodoptera frugiperda pupal ovarian tissue) was investigated. The results showed that both azadirachtin and camptothecin could induce apoptosis in Sf9 cells. Reactive oxygen species (ROS) generation, activation of mitochondrial permeability transition pores (MPTPs) and loss of mitochondrial membrane potential (MMP) were observed very early during apoptosis and were followed subsequently by the release of cytochrome-c from the mitochondria. Furthermore, the results also revealed that the opening of MPTPs and the loss of MMP induced by azadirachtin could be significantly inhibited by the permeability transition pore (PTP) inhibitor cyclosporin A (CsA), which was used to identify the key role of mitochondria in the apoptosis of Sf9 cells. However, in camptothecin-treated Sf9 cells, CsA could not suppress the opening of MPTPs and the loss of MMP when apoptosis was induced. The data from caspase-3 and caspase-9 activity assays and detection of apoptosis by morphological observation and flow cytometry also uncovered the different effect of CsA on the two botanical apoptosis inducers. Although different mechanisms of apoptosis induction exist, our study revealed that mitochondria play a crucial role in insect cell line apoptosis.

SfDronc, an initiator caspase involved in apoptosis in the fall armyworm Spodoptera frugiperda

Initiator caspases are the first caspases that are activated following an apoptotic stimulus, and are responsible for cleaving and activating downstream effector caspases, which directly cause apoptosis. We have cloned a cDNA encoding an ortholog of the initiator caspase Dronc in the lepidopteran insect Spodoptera frugiperda. The SfDronc cDNA encodes a predicted protein of 447 amino acids with a molecular weight of 51 kDa. Overexpression of SfDronc induced apoptosis in Sf9 cells, while partial silencing of SfDronc expression in Sf9 cells reduced apoptosis induced by baculovirus infection or by treatment with UV or actinomycin D. Recombinant SfDronc exhibited several expected biochemical characteristics of an apoptotic initiator caspase: 1) SfDronc efficiently cleaved synthetic initiator caspase substrates, but had very little activity against effector caspase substrates; 2) mutation of a predicted cleavage site at position D340 blocked autoprocessing of recombinant SfDronc and reduced enzyme activity by approximately 10-fold; 3) SfDronc cleaved the effector caspase Sf-caspase-1 at the expected cleavage site, resulting in Sf-caspase-1 activation; and 4) SfDronc was strongly inhibited by the baculovirus caspase inhibitor SpliP49, but not by the related protein AcP35. These results indicate that SfDronc is an initiator caspase involved in caspase-dependent apoptosis in S. frugiperda, and as such is likely to be responsible for the initiator caspase activity in S. frugiperda cells known as Sf-caspase-X.

Cloning and Characterization of the Caspase Family Member BmDronc from Bombyx mori (Lepidoptera: Bombycidae) Embryo Cells

Abstract Caspases are a family of cysteinyl aspartate proteinases known for their essential roles in the regulation of apoptosis. To date, ≈20 caspases have been identified, although few have been cloned and characterized in Bombyx mori (L.). Two caspase-9 variants from the B. mori embryo cell line (BmE), designated BmDroncL and BmDroncS, were cloned. BmDroncL has three classic domains: a caspase recruitment domain and large and small subunits, and is a homologue of Drosophila Dronc, human caspase-9, Aedes Dronc, and fish caspase-9, whereas BmDroncS lacks the large subunit. Instantaneous expression of BmDroncL caused typical apoptosis in Sf-9 cells. Moreover, BmDronc gene expression increased markedly during the silkworm metamorphosis at the larva-pupa and pupa-moth stages, which suggested that BmDronc plays a crucial role during B. mori metamorphosis.

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

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.

PKC activation contributes to caspase-mediated eIF2α phosphorylation and cell death

Back ground Stress-induced phosphorylation of the alpha-subunit of eukaryotic initiation factor 2 (eIF2α), involved in translation, promotes cell suicide or survival. Since multiple signaling pathways are implicated in cell death, the present study has analyzed the importance of PKC activation in the stress-induced eIF2α phosphorylation, caspase activation and cell death in the ovarian cells of Spodoptera frugiperda ( Sf9) and in their extracts. Methods Cell death is analyzed by flow cytometry. Caspase activation is measured by Ac-DEVD-AFC hydrolysis and also by the cleavage of purified recombinant PERK, an endoplasmic reticulum-resident eIF2α kinase. Status of eIF2α phosphorylation and cytochrome c levels are analyzed by western blots. Results PMA, an activator of PKC, does not promote cell death or affect eIF2α phosphorylation. However, PMA enhances late stages of UV-irradiation or cycloheximide-induced caspase activation, eIF2α phosphorylation and apoptosis in Sf9 cells. PMA also enhances cytochrome c-induced caspase activation and eIF2α phosphorylation in cell extracts. These changes are mitigated more efficiently by caspase inhibitor, z-VAD-fmk, than by calphostin, an inhibitor of PKC. In contrast, tunicamycin-induced eIF2α phosphorylation that does not lead to caspase activation or cell death is unaffected by PMA, z-VAD-fmk or by calphostin. Conclusions While caspase activation is a cause and consequence of eIF2α phosphorylation, PKC activation that follows caspase activation further enhances caspase activation, eIF2α phosphorylation, and cell death in Sf9 cells. General significance Caspases can activate multiple signaling pathways to enhance cell death.

TheCampoletis sonorensisichnovirus vankyrin protein P-vank-1 inhibits apoptosis in insect Sf9 cells

The Campoletis sonorensis ichnovirus (CsIV) vankyrin genes encode proteins containing truncated ankyrin repeat domains with sequence homology to the inhibitory domains of NF-kappaB transcription factor inhibitors, IkappaBs. The CsIV vankyrin proteins are thought to be involved in the suppression of NF-kappaB activity during immune response and/or developmental events in the parasitized host. Here we report that when P-vank-1 was expressed stably from Sf9 cells, prolonged survival of these cells was observed after baculovirus infection, UV irradiation, and treatment with the apoptosis-inducing chemical camptothecin compared to untransformed Sf9 cells. Furthermore, P-vank-1 inhibited nuclear and internucleosomal degradation and caspase activity after induction of apoptosis in Sf9 cells stably expressing P-vank-1. This is the first report of a polydnavirus protein with anti-apoptotic function.

Induction of apoptosis in SF21 cell line by conditioned medium of the entomopathogenic fungus, Nomuraea rileyi, through Sf‐caspase‐1 signaling pathway

The apoptosis in SF-21 cell line can be induced by the conditioned medium (CM) of the entomopathogenic fungus, Nomuraea rileyi, based on changes in morphology and formation of apoptotic bodies in cultured cells, and with the onset of DNA fragmentation as shown by TUNEL staining and agarose electrophoresis. Moreover, the induction of apoptosis in SF-21 cells was inhibited by adding the inhibitor of effector caspase, viz. z-DEVD-fmk, to the CM, indicating that Sf-caspase-1 is involved in this apoptosis. Similarly, the inhibitor of initiator caspase, viz., z-VAD-fmk, inhibited apoptosis. Therefore, both initiator and effector caspases are possibly involved in the apoptosis of SF-21 cells. In addition, we detected Sf-caspase-1 activity in the process of apoptosis in SF-21 cells, suggesting that the effector caspase in SF-21 is similar to that found in mammalian cells. Our results also indicated that the apoptosis found in this line is accomplished through a Sf-caspase-1 signaling pathway.