Inhibition of microRNA-14 contributes to actinomycin-D-induced apoptosis in the Sf9 insect cell line

Activity and Mechanism of Action of Antifungal Peptides from Microorganisms: A Review

Harmful fungi in nature not only cause diseases in plants, but also fungal infection and poisoning when people and animals eat food derived from crops contaminated with them. Unfortunately, such fungi are becoming increasingly more resistant to traditional synthetic antifungal drugs, which can make prevention and control work increasingly more difficult to achieve. This means they are potentially very harmful to human health and lifestyle. Antifungal peptides are natural substances produced by organisms to defend themselves against harmful fungi. As a result, they have become an important research object to help deal with harmful fungi and overcome their drug resistance. Moreover, they are expected to be developed into new therapeutic drugs against drug-resistant fungi in clinical application. This review focuses on antifungal peptides that have been isolated from bacteria, fungi, and other microorganisms to date. Their antifungal activity and factors affecting it are outlined in terms of their antibacterial spectra and effects. The toxic effects of the antifungal peptides and their common solutions are mentioned. The mechanisms of action of the antifungal peptides are described according to their action pathways. The work provides a useful reference for further clinical research and the development of safe antifungal drugs that have high efficiencies and broad application spectra.

MicroRNA-Mediated Host-Pathogen Interactions Between Bombyx mori and Viruses

MicroRNAs (miRNAs), small non-coding RNAs of about 22 nucleotides, have been reported to regulate gene expression at the posttranscriptional level and are involved in several biological processes such as immunity, development, metabolism, and host-pathogen interactions. Apart from miRNAs encoded by the host, miRNAs produced by pathogens also regulate host genes to facilitate virus replication and evasion of the host defense responses. In recent years, accumulated studies suggest that viral infections alter the host miRNAs expression profile, and both cellular and viral miRNAs may play vital roles in host-pathogen interactions. Bombyx mori, one of the critical lepidopteran model species, is an economically important insect for silk production. The mechanism of interaction between B. mori and its pathogens and their regulation by miRNAs has been extensively studied. Therefore, in this review, we aim to highlight the recent information and understanding of the virus-encoding miRNAs and their functions in modulating viral and host (B. mori) genes. Additionally, the response of B. mori derived miRNAs to viral infection is also discussed. A detailed critical view about miRNAs’ regulatory roles in B. mori-virus interactions will help us understand molecular networks and develop a sustainable antiviral strategy.

Identification and Functional Analysis of Apoptotic Protease Activating Factor-1 (Apaf-1) from Spodoptera litura

Apoptotic protease activating factor-1 (Apaf-1) is an adaptor molecule, essential for activating initiator caspase and downstream effector caspases, which directly cause apoptosis. In fruit flies, nematodes, and mammals, Apaf-1 has been extensively studied. However, the structure and function of Apaf-1 in Lepidoptera remain unclear. This study identified a novel Apaf-1 from Spodoptera litura, named Sl-Apaf-1. Sl-Apaf-1 contains three domains: a CARD domain, as well as NOD and WD motifs, and is very similar to mammalian Apaf-1. Interference of Sl-apaf-1 expression in SL-1 cells blocked apoptosis induced by actinomycin D. Overexpression of Sl-apaf-1 significantly enhances apoptosis induced by actinomycin D in Sf9/SL-1/U2OS cells, suggesting that the function of Sl-Apaf-1 is evolutionarily conserved. Furthermore, Sl-Apaf-1 could interact with Sl-caspase-5 (a homologue of mammalian caspase-9) and yielded a binding affinity of 1.37 × 10⁶ M^-1 according isothermal titration calorimetry assay. Initiator caspase (procaspase-5) of S. litura could be activated by Sl-Apaf-1 (without WD motif) in vitro, and the activated Sl-caspase-5 could cleave Sl-procaspase-1 (a homologue of caspase-3 in mammals), which directly caused apoptosis. This study demonstrates the key role of Sl-Apaf-1 in the apoptosis pathway, suggesting that the apoptosis pathway in Lepidopteran insects and mammals is conserved.

Small regulatory noncoding RNAs in Drosophila melanogaster: biogenesis and biological functions

RNA interference (RNAi) is an important phenomenon that has diverse genetic regulatory functions at the pre- and posttranscriptional levels. The major trigger for the RNAi pathway is double-stranded RNA (dsRNA). dsRNA is processed to generate various types of major small noncoding RNAs (ncRNAs) that include microRNAs (miRNAs), small interfering RNAs (siRNAs) and PIWI-interacting RNAs (piRNAs) in Drosophila melanogaster (D. melanogaster). Functionally, these small ncRNAs play critical roles in virtually all biological systems and developmental pathways. Identification and processing of dsRNAs and activation of RNAi machinery are the three major academic interests that surround RNAi research. Mechanistically, some of the important biological functions of RNAi are achieved through: (i) supporting genomic stability via degradation of foreign viral genomes; (ii) suppressing the movement of transposable elements and, most importantly, (iii) post-transcriptional regulation of gene expression by miRNAs that contribute to regulation of epigenetic modifications such as heterochromatin formation and genome imprinting. Here, we review various routes of small ncRNA biogenesis, as well as different RNAi-mediated pathways in D. melanogaster with a particular focus on signaling pathways. In addition, a critical discussion of the most relevant and latest findings that concern the significant contribution of small ncRNAs to the regulation of D. melanogaster physiology and pathophysiology is presented.

Modulation of antiviral immunity by the ichnovirus HdIV in Spodoptera frugiperda

Polydnaviruses (PDVs) are obligatory symbionts found in thousands of endoparasitoid species and essential for successful parasitism. The two genera of PDVs, ichnovirus (IV) and bracovirus (BV), use different sets of virulence factors to ensure successful parasitization of the host. Previous studies have shown that PDVs target apoptosis, one of the innate antiviral responses in many host organisms. However, IV and BV have been shown to have opposite effects on this process. BV induces apoptosis in host cells, whereas some IV proteins have been shown to have anti-apoptotic activity. The different biological contexts in which the assays were performed may account for this difference. In this study, we evaluated the interplay between apoptosis and the ichnovirus HdIV from the parasitoid Hyposoter didymator, in the HdIV-infected hemocytes and fat bodies of S. frugiperda larvae, and in the Sf9 insect cell line challenged with HdIV. We found that HdIV induced cell death in hemocytes and fat bodies, whereas anti-apoptotic activity was observed in HdIV-infected Sf9 cells, with and without stimulation with viral PAMPs or chemical inducers. We also used an RT-qPCR approach to determine the expression profiles of a set of genes known to encode key components of the other main antiviral immune pathways described in insects. The analysis of immune gene transcription highlighted differences in antiviral responses to HdIV as a function of host cell type. However, all these antiviral pathways appeared to be neutralized by low levels of expression for the genes encoding the key components of these pathways, in all biological contexts. Finally, we investigated the effect of HdIV on the general antiviral defenses of the lepidopteran larvae in more detail, by studying the survival of S. frugiperda co-infected with HdIV and the entomopathogenic densovirus JcDV. Coinfected S. frugiperda larvae have increased resistance to JcDV at an early phase of infection, whereas HdIV effects enhance the virulence of the virus at later stages of infection. Overall, these results reveal complex interactions between HdIV and its cellular environment.

Genome-wide identification, expression profiling, and target gene analysis of microRNAs in the Onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), vectors of tospoviruses (Bunyaviridae)

Thrips tabaci Lindeman is an important polyphagous insect pest species estimated to cause losses of more than U.S. $1 billion worldwide annually. Chemical insecticides are of limited use in the management of T. tabaci due to the thigmokinetic behavior and development of resistance to insecticides. There is an urgent need to find alternative management strategies. Small noncoding RNAs (sncRNAs) especially microRNAs (miRNAs) hold great promise as key regulators of gene expression in a wide range of organisms. MiRNAs are a group of endogenously originated sncRNA known to regulate gene expression in animals, plants, and protozoans. In this study, we explored these RNAs in T. tabaci using deep sequencing to provide a basis for future studies of their biological and physiological roles in governing gene expression. Apart from snoRNAs and piRNAs, our study identified nine novel and 130 known miRNAs from T. tabaci. Functional classification of the targets for these miRNAs predicted that majority are involved in regulating transcription, translation, signal transduction and genetic information processing. The higher expression of few miRNAs (such as tta-miR-281, tta-miR-184, tta-miR-3533, tta-miR-N1, tta-miR-N7, and tta-miR-N9) in T. tabaci pupal and adult stages reflected their possible role in larval and adult development, metamorphosis, parthenogenesis, and reproduction. This is the first exploration of the miRNAome in T. tabaci, which not only provides insights into their possible role in insect metamorphosis, growth, and development but also offer an important resource for future pest management strategies.

The genomic features of parasitism, Polyembryony and immune evasion in the endoparasitic wasp Macrocentrus cingulum

BACKGROUND

Parasitoid wasps are well-known natural enemies of major agricultural pests and arthropod borne diseases. The parasitoid wasp Macrocentrus cingulum (Hymenoptera: Braconidae) has been widely used to control the notorious insect pests Ostrinia furnacalis (Asian Corn Borer) and O. nubilalis (European corn borer). One striking phenomenon exhibited by M. cingulum is polyembryony, the formation of multiple genetically identical offspring from a single zygote. Moreover, M. cingulum employs a passive parasitic strategy by preventing the host's immune system from recognizing the embryo as a foreign body. Thus, the embryos evade the host's immune system and are not encapsulated by host hemocytes. Unfortunately, the mechanism of both polyembryony and immune evasion remains largely unknown.

RESULTS

We report the genome of the parasitoid wasp M. cingulum. Comparative genomics analysis of M. cingulum and other 11 insects were conducted, finding some gene families with apparent expansion or contraction which might be linked to the parasitic behaviors or polyembryony of M. cingulum. Moreover, we present the evidence that the microRNA miR-14b regulates the polyembryonic development of M. cingulum by targeting the c-Myc Promoter-binding Protein 1 (MBP-1), histone-lysine N-methyltransferase 2E (KMT2E) and segmentation protein Runt. In addition, Hemomucin, an O-glycosylated transmembrane protein, protects the endoparasitoid wasp larvae from being encapsulated by host hemocytes. Motif and domain analysis showed that only the hemomucin in two endoparasitoids, M. cingulum and Venturia canescens, possessing the ability of passive immune evasion has intact mucin domain and similar O-glycosylation patterns, indicating that the hemomucin is a key factor modulating the immune evasion.

CONCLUSIONS

The microRNA miR-14b participates in the regulation of polyembryonic development, and the O-glycosylation of the mucin domain in the hemomucin confers the passive immune evasion in this wasp. These key findings provide new insights into the polyembryony and immune evasion.

MicroRNA-14 regulates larval development time in Bombyx mori

MicroRNAs (miRNA) regulate multiple physiological processes including development and metamorphosis in insects. In the current study, we demonstrate that a conserved invertebrate miRNA-14 (miR-14) plays an important role in ecdysteroid regulated development in the silkworm Bombyx mori, a lepidopteran model insect. Ubiquitous transgenic overexpression of miR-14 using the GAL4/UAS system resulted in delayed silkworm larval development and smaller body size of larva and pupa with decrease in ecdysteriod titers. On the contrary, miR-14 disruption using the transgenic CRISPR/Cas9 system led to a precocious wandering stage with increase in ecdysteriod titers. We identified that the hormone receptor E75 (E75) and the ecdysone receptor isoform B (ECR-B), which both serve as essential mediators in the ecdysone signaling pathway, as putative target genes of miR-14 by in silico target prediction. Dual-luciferase reporter assays confirmed the binding of miR-14 to the 3'UTRs of E75 and ECR-B in a mammalian HEK293T cell line. Furthermore, transcription levels of E75 and ECR-B were significantly affected in both miR-14 overexpression and knockout transgenic animals. Taken together, our data suggested that the canonical invertebrate miR-14 is a general regulator in maintaining ecdysone homeostasis for normal development and metamorphosis in B. mori.

Radioresistant Sf9 insect cells readily undergo an intrinsic mode of apoptosis in response to histone deacetylase (HDAC) inhibition

Insect cell lines have been utilized as an important higher eukaryotic model system to decipher stress responses and cell death mechanisms. Lepidopteran Sf9 cells (derived from the ovaries of Spodoptera frugiperda) display nearly 100 times higher resistance to ionizing radiation in contrast to mammalian cells, which is partly contributed by an unusually high HDAC activity. However, their response to HDAC inhibition remains to be evaluated. In the present study, the effects of HDAC inhibitor (NaBt) on Sf9 cellular/nuclear morphology, cell cycle progression, DNA damage/repair, redox status, and mitochondrial perturbations were evaluated. NaBt-induced apoptosis was evident at 18 h in Sf9 cells at 2 mM concentration, primarily through mitochondrial induction of oxidative stress and subsequent DNA damage. Cell cycle analysis revealed appearance of sub-G1 DNA content at 12 h onwards and DNA fragmentation by 18 h. Initial few hours of treatment caused significant loss in MMP through oxidation of mitochondrial inner membrane protein, i.e., cardiolipin. HDAC inhibition-mediated apoptosis was associated with increased Bax/Bcl2 ratio, mitochondrial cytochrome-c release, and caspase-3 activation. The study thus infers that Sf9 cells, which can withstand very high radiation doses, are quite sensitive to the increase in the chromatin acetylation levels. In addition, HDAC inhibition also sensitized Sf9 cells to radiation-induced DNA damage, further corroborating our recent finding that chromatin compactness contributes significantly to their radioresistance. Therefore, the study demonstrates prominence of prevailing DNA/chromatin protective mechanisms in Lepidopteran insect cells.

Evidence for microRNA-31 dependent Bim-Bax interaction preceding mitochondrial Bax translocation during radiation-induced apoptosis

Downregulation of microRNA-31 has been linked with enhanced stress resistance, while its overexpression leads to cell death. In this study, we found mediatory role of microRNA-31 in γ-radiation-induced apoptosis in a model insect cell line Sf9 carrying well-conserved apoptotic machinery. Mature microRNA-31 is perfectly conserved amongst insects; hence we used biotinylated probes designed from Bombyx mori sequence for its successful detection in Sf9 cells. Target identification using Bombyx mori 3′UTRs predicted miR-31′s potential role in Lepidopteran apoptosis, which prompted us to investigate alterations in its expression during radiation-induced cell death. We found significant overexpression of Sf-miR-31 following lethal dose (1,000Gy–3,000Gy) irradiation. Its mediatory role was finally confirmed as antisense-microRNA-31 could successfully inhibit radiation-induced cytochrome-c release, caspase-3 activation and apoptosis. While Bax/Bcl-2 expression remained unchanged, lethal radiation doses induced Bim overexpression and direct Bim-Bax interaction (co-immunoprecipitation) which is not yet unequivocally demonstrated during apoptosis. Quite important, these events were found to be dependent on radiation-induced miR-31 overexpression, as antisense-miR-31 inhibited both the responses and resulted in significant inhibition of cell death. Pro-apoptotic role of miR-31 was further confirmed when miR-31 mimic induced apoptosis involving similar Bim/Bax alterations. Therefore, our study reveals an important mediatory role of miR-31 in radiation-induced cell death.

Radioresistant Sf9 insect cells undergo an atypical form of Bax-dependent apoptosis at very high doses of γ-radiation

PURPOSE

To investigate the underlying mechanisms of cell-death at extremely high doses of radiation in radioresistant Spodoptera frugiperda-9 (Sf9) insect cells.

MATERIALS AND METHODS

Morphology, cell proliferation and DNA-fragmentation analysis was performed at 500-2000 Gy. Changes in intracellular reactive oxygen species (ROS), mitochondrial membrane potential (MMP), cardiolipin oxidation and Annexin-V externalization were studied using flow-cytometry. Cytochrome-c release was measured using immunofluorescence microscopy. Inhibitors of apoptosis, i.e., Bongkrekic acid (BKA), Caspase-9 inhibitor (C9i), 5-(4-fluorosulfonylbenzoyl) adenosine hydrochloride (FSBA) and Cyclosporin-A (CsA) were used to dissect apoptotic mechanism at many classical steps. Caspase-3 activity was measured using a caspase-activity assay kit.

RESULTS

A dose-dependent induction of typical apoptosis was observed at extremely high doses, marked by extensive apoptotic body formation. However, certain atypical responses such as cellular hypertrophy and the lack of phosphatidylserine-externalization were observed during the initial hours after radiation. Loss of mitochondrial membrane potential observed at 48 h following a 2000 Gy dose was accompanied by an increase in ROS that caused significant cardiolipin oxidation leading to cytochrome-c release, caspase activation and internucleosomal DNA fragmentation. Inhibitors of B-cell lymphoma-2 (Bcl-2)-associated X protein (Bax)-mediated cytochrome-c release, apoptosome formation and caspase-9 effectively prevented radiation-induced apoptosis, strongly suggesting the role of Bax-dependent cell death mechanism.

CONCLUSIONS

Our study demonstrates that the Sf9 insect cells display good homology with human cells in the mitochondria-dependent events during radiation-induced apoptosis, although doses eliciting similar responses were 50-200 times higher than human cells. Factors upstream to mitochondrial damage remain pertinent for a thorough understanding of this extreme radioresistance displayed by lepidopteran cells.

Involvement of microRNAs in infection of silkworm with bombyx mori cytoplasmic polyhedrosis virus (BmCPV)

Bombyx mori cytoplasmic polyhedrosis virus (BmCPV) is one of the most important pathogens of silkworm. MicroRNAs (miRNAs) have been demonstrated to play key roles in regulating host-pathogen interaction. However, there are limited reports on the miRNAs expression profiles during insect pathogen challenges. In this study, four small RNA libraries from BmCPV-infected midgut of silkworm at 72 h post-inoculation and 96 h post-inoculation and their corresponding control midguts were constructed and deep sequenced. A total of 316 known miRNAs (including miRNA*) and 90 novel miRNAs were identified. Fifty-eight miRNAs displayed significant differential expression between the infected and normal midgut (P value < = 0.01 and fold change > = 2.0 or < = 0.5), among which ten differentially expressed miRNA were validated by qRT-PCR method. Further bioinformatics analysis of predicted target genes of differentially expressed miRNAs showed that the miRNA targets were involved in stimulus and immune system process in silkworm.

MicroRNA 17-92 expressed by a transposone-based vector changes expression level of cell-cycle-related genes

The miR-17-92 cluster is composed of seven miRNAs (microRNAs; miR-17-5p, miR-17-3p, miR-18a, miR-19a, miR-20a, miR-19b-1 and miR-92a-1). Previous studies have indicated that this cluster is involved in cell proliferation and their overexpression has been seen in several types of cancer. We have assessed the overexpression effects of miR-17-92 on the expression of several genes associated with cell-cycle regulation. The human miR-17-92 gene was cloned into a transposone-based vector, piggyBac and transfected into HEK-293T [HEK-293 cells (human embryonic kidney cells) expressing the large T-antigen of SV40 (simian virus 40)] cell line. Gene expression analysis indicated that up-regulation of this cluster causes significant changes in the expression of several cell-cycle related genes, including CDK2 (cyclin-dependent kinase 2), cyclin-D2, c-Myc and CREB (cAMP-response-element-binding protein). Other methods of transcripts assessment confirmed miR-17-92 overexpression enhances cell proliferation.

Insect microRNAs: biogenesis, expression profiling and biological functions

MicroRNAs (miRNA) are a class of endogenous regulatory RNA molecules 21-24 nucleotides in length that modulate gene expression at the post-transcriptional level via base pairing to target sites within messenger RNAs (mRNA). Typically, the miRNA "seed sequence" (nucleotides 2-8 at the 5' end) binds complementary seed match sites within the 3' untranslated region of mRNAs, resulting in either translational inhibition or mRNA degradation. MicroRNAs were first discovered in Caenorhabditis elegans and were shown to be involved in the timed regulation of developmental events. Since their discovery in the 1990s, thousands of potential miRNAs have since been identified in various organisms through small RNA cloning methods and/or computational prediction, and have been shown to play functionally important roles of gene regulation in invertebrates, vertebrates, plants, fungi and viruses. Numerous functions of miRNAs identified in Drosophila melanogaster have demonstrated a great significance of these regulatory molecules. However, elucidation of miRNA roles in non-drosophilid insects presents a challenging and important task.

Lack of effective anti-apoptotic activities restricts growth of Parachlamydiaceae in insect cells

The fundamental role of programmed cell death in host defense is highlighted by the multitude of anti-apoptotic strategies evolved by various microbes, including the well-known obligate intracellular bacterial pathogens Chlamydia trachomatis and Chlamydia (Chlamydophila) pneumoniae. As inhibition of apoptosis is assumed to be essential for a successful infection of humans by these chlamydiae, we analyzed the anti-apoptotic capacity of close relatives that occur as symbionts of amoebae and might represent emerging pathogens. While Simkania negevensis was able to efficiently replicate within insect cells, which served as model for metazoan-derived host cells, the Parachlamydiaceae (Parachlamydia acanthamoebae and Protochlamydia amoebophila) displayed limited intracellular growth, yet these bacteria induced typical features of apoptotic cell death, including formation of apoptotic bodies, nuclear condensation, internucleosomal DNA fragmentation, and effector caspase activity. Induction of apoptosis was dependent on bacterial activity, but not bacterial de novo protein synthesis, and was detectable already at very early stages of infection. Experimental inhibition of host cell death greatly enhanced parachlamydial replication, suggesting that lack of potent anti-apoptotic activities in Parachlamydiaceae may represent an important factor compromising their ability to successfully infect non-protozoan hosts. These findings highlight the importance of the evolution of anti-apoptotic traits for the success of chlamydiae as pathogens of humans and animals.