Quantitative proteomics of Bombyx mori after BmNPV challenge

K64 acetylation of heat shock protein 90 suppresses nucleopolyhedrovirus replication in Bombyx mori

HSP90 is a highly conserved chaperone that facilitates the proliferation of many viruses, including silkworm (bombyx mori) nucleopolyhedrovirus (BmNPV), but the underlying regulatory mechanism was unclear. We found that suppression of HSP90 by 17-AAG, a HSP90-specific inhibitor, significantly reduced the expression of BmNPV capsid protein gp64 and viral genome replication, whereas overexpression of B. mori HSP90(BmHSP90) promoted BmNPV replication. Furthermore, in a recent study of the lysine acetylome of B. mori infected with BmNPV, we focused on the reduced viral proliferation due to changes of BmHSP90 lysine acetylation. Site-directed introduction of acetylated (K/Q) or deacetylated (K/R) mimic mutations into BmHSP90 revealed that lysine 64 (K64) acetylation activated the JAK/STAT pathway and reduced BmHSP90 ATPase activity, leading to diminished chaperone activity and ultimately inhibiting BmNPV proliferation. In this study, a single lysine 64 acetylation change of BmHSP90 was elucidated as a model of posttranslational modifications occurring in the wake of host-virus interactions, providing novel insights into potential antiviral strategies.

Insect Cell-Based Models: Cell Line Establishment and Application in Insecticide Screening and Toxicology Research

During the past decades, research on insect cell culture has grown tremendously. Thousands of lines have been established from different species of insect orders, originating from several tissue sources. These cell lines have often been employed in insect science research. In particular, they have played important roles in pest management, where they have been used as tools to evaluate the activity and explore the toxic mechanisms of insecticide candidate compounds. This review intends to first briefly summarize the progression of insect cell line establishment. Then, several recent studies based on insect cell lines coupled with advanced technologies are introduced. These investigations revealed that insect cell lines can be exploited as novel models with unique advantages such as increased efficiency and reduced cost compared with traditional insecticide research. Most notably, the insect cell line-based models provide a global and in-depth perspective to study the toxicology mechanisms of insecticides. However, challenges and limitations still exist, especially in the connection between in vitro activity and in vivo effectiveness. Despite all this, recent advances have suggested that insect cell line-based models promote the progress and sensible application of insecticides, which benefits pest management.

Baculovirus LEF-11 interacts with BmIMPI to induce cell cycle arrest in the G2/M phase for viral replication

Viruses arrest the host cell cycle and using multiple functions of host cells is an important approach for their replication. Baculovirus arrests infected insect cells at both the late S and G2/M phase, but the strategy employed by baculovirus is not clearly understood. Our research suggests that the Bombyx mori nucleopolyhedrovirus (BmNPV) could arrest the cell cycle in the G2/M phase to promote virus replication, and also that the viral protein LEF-11 could inhibit host cell proliferation and arrest the cell cycle by inhibiting the cell cycle checkpoint proteins BmCyclinB and BmCDK1. Furthermore, we found that LEF-11 interacts with BmIMPI to regulate cell proliferation, but not by direct interaction with BmCyclinB or BmCDK1. In addition, our findings showed that BmIMPI was important and necessary for LEF-11 induced cell cycle arrest in the G2/M phase. Moreover, BmIMPI was found to interact with BmCyclinB and BmCDK1, and down-regulate the expression of BmCyclinB and BmCDK1 to compromise the cell cycle and cell proliferation. Taken together, the data presented demonstrated that baculovirus LEF-11 regulates BmIMPI to inhibit host cell proliferation and provide a new insight into the molecular mechanisms employed by viruses to induce cell cycle arrest.

SUMOylation Regulates BmNPV Replication by Moderating PKIP Intracellular Localization

SUMOylation is a reversible covalent process between a small ubiquitin-like modifier (SUMO) and its target protein and has become a crucial regulator of protein functions. Here, we report that Bombyx mori nucleopolyhedrovirus (BmNPV) may take advantage of the host SUMOylation system to enhance its own replication, similar to many other viruses. Both the knockdown of BmSUMO by RNAi and chemical blocking by ginkgolic acid both impaired BmNPV replication. Using site mutation and pull-down assays, we found that lysine K70 of the protein kinase-interacting protein (PKIP), which is conserved in all Alphabaculoviruses, was modified by SUMO. Mutation of K70 in PKIP led to its translocation from the cytoplasm to the nucleus. Knockout and rescue experiments showed that the rescue of PKIP mutant virus with wild-type PKIP restored BmNPV replication to the normal level, but this was not true for the K70R mutation. Altogether, these results show that SUMOylation of PKIP plays a key role in BmNPV replication.

Deacetylation of BmAda3 is required for cell apoptosis caused by Bombyx mori nucleopolyhedrovirus infection

Silkworm is not only an ideal insect model with a biological significance, but it is also crucially important in sericulture and bioreactors. Bombyx mori nucleopolyhedrovirus (BmNPV) is a principal pathogen of silkworm. However, the molecular mechanism underlying BmNPV invasion is still unclear. Based on our previous acetylome research findings of B. mori after BmNPV infection, here, we focused on silkworm alteration/deficiency in activation-3 (BmAda3). The acetylation of K124 and K128 were significantly reduced (0.66-fold) upon the virus challenge. Due to the interaction between Ada3 and P53, acetylation-mimic K124Q/K128Q and deacetylation-mimic K124R/K128R mutants of BmAda3 were constructed to explore the roles exerted by the acetylation modification of BmAda3 on P53. Yeast two-hybrid and IP results revealed that both BmAda3 and its deacetylation mutants (K124R/K128R) interacted with P53. Interestingly, we found that the deacetylation mutants (K124R/K128R) of BmAda3 significantly promoted the stability of P53. Since P53 is a proapoptotic factor, cell apoptosis was detected. We established that the deacetylation of BmAda3 at K124/K128 facilitated cellular apoptosis during BmNPV infection. Finally, viral proliferation was analyzed, and the results indicated that virus generation was reduced by K124/K128 deacetylation. Our report, based on the deacetylation of two lysine sites 124/128 of BmAda3, shows possible regulatory pathways of BmNPV proliferation and provides novel insights into the development of antiviral agents.

The Antiviral Molecule 5-Pyridoxolactone Identified Post BmNPV Infection of the Silkworm, Bombyx mori

Bombyx mori nucleopolyhedrovirus (BmNPV) is a pathogen that causes great economic losses in sericulture. Many genes play a role in viral infection of silkworms, but silkworm metabolism in response to BmNPV infection is unknown. We studied BmE cells infected with BmNPV. We performed liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS)-based non-targeted metabolomics analysis of the cytosolic extract and identified 36, 76, 138, 101, 189, and 166 different molecules at 3, 6, 12, 24, 48, and 72 h post BmNPV infection (hpi) compared with 0 hpi. Compounds representing different areas of metabolism were increased in cells post BmNPV infection. These areas included purine metabolism, aminoacyl−tRNA biosynthesis, and ABC transporters. Glycerophosphocholine (GPC), 2-hydroxyadenine (2-OH-Ade), gamma-glutamylcysteine (γ-Glu-Cys), hydroxytolbutamide, and 5-pyridoxolactone glycerophosphocholine were continuously upregulated in BmE cells post BmNPV infection by heat map analysis. Only 5-pyridoxolactone was found to strongly inhibit the proliferation of BmNPV when it was used to treat BmE cells. Fewer infected cells were detected and the level of BmNPV DNA decreased with increasing 5-pyridoxolactone in a dose-dependent manner. The expression of BmNPV genes ie1, helicase, GP64, and VP39 in BmE cells treated with 5-pyridoxolactone were strongly inhibited in the BmNPV infection stage. This suggested that 5-pyridoxolactone may suppress the entry of BmNPV. The data in this study characterize the metabolism changes in BmNPV-infected cells. Further analysis of 5-pyridoxolactone, which is a robust antiviral molecule, may increase our understanding of antiviral immunity.

Proteomic Identification of Bombyx mori Organelles Using the Engineered Ascorbate Peroxidase APEX and Development of Silkworm Organelle Proteome Database (SilkOrganPDB)

Silkworm Bombyx mori is an economically important insect and a lepidopteran model. Organelle proteome is vital to understanding gene functions; however, it remains to be identified in silkworm. Here, using the engineered ascorbate peroxidase APEX, we constructed transgenic B. mori embryo cells (BmE) expressing APEX-NLS, COX4-APEX, APEX-Rev, and APEX-KDEL in nucleus, mitochondrial matrix (MM), cytosol, and endoplasmic reticulum (ER), and isolated the biotin-labeled proteins using streptavidin-affinity purification, respectively. The isolated proteins were determined using LC-MS/MS and annotated by searching B. mori genomes downloaded from GenBank, SilkBase, SilkDB 2.0, and SilkDB 3.0, resulting in 842, 495, 311, and 445 organelle proteins identified, respectively. We mapped the 296 MM proteins annotated in the GenBank data to mitochondrial protein databases of the fly, human, and mouse, and found that 140 (47%) proteins are homologous to 80 fly proteins, and 65 (22%) proteins match to 31 and 29 human and mouse proteins, respectively. Protein orthology was predicted in multiple insects using OrthoMCL, producing 460 families containing 839 proteins we identified. Out of 460 families, 363 were highly conserved and found in all insects, leaving only three proteins without orthology in other insects, indicating that the identified proteins are highly conserved and probably play important roles in insects. A gene ontology enrichment analysis by clusterProfiler revealed that the nucleus proteins significantly enriched in cellular component terms of nucleus and nucleolus, the MM proteins markedly enriched in molecular function terms of nucleotide binding, and the cytosol proteins mainly enriched in biological process terms of small molecule metabolism. To facilitate the usage and analysis of our data, we developed an open-access database, Silkworm Organelle Proteome Database (SilkOrganPDB), which provides multiple modules for searching, browsing, downloading, and analyzing these proteins, including BLAST, HMMER, Organelle Proteins, Protein Locations, Sequences, Gene Ontology, Homologs, and Phylogeny. In summary, our work revealed the protein composition of silkworm BmE organelles and provided a database resource helpful for understanding the functions and evolution of these proteins.

Deacetylation of HSC70-4 Promotes Bombyx mori Nucleopolyhedrovirus Proliferation via Proteasome-Mediated Nuclear Import

Silkworm (Bombyx mori) is a model organism with great agricultural economic value that plays a crucial role in biological studies. B. mori nucleopolyhedrovirus (BmNPV) is a major viral pathogen found in silkworms, which leads to huge silk loss annually. In a recent lysine acetylome of silkworm infected with BmNPV, we focused on the heat shock cognate protein 70-4 (HSC70-4) lysine acetylation change due to the consequent nuclear accumulation and viral structure assembly. In this study, the genome replication, proliferation, and production of budded viruses (BVs) were arrested by HSP/HSC70 inhibitor treatment. However, HSC70-4 overexpression enhanced BmNPV reproduction. Furthermore, site-direct mutagenesis for acetylated mimic (K/Q) or deacetylated mimic (K/R) mutants of HSC70-4 demonstrated that lysine 77 (K77) deacetylation promotes HSC70-4 stability, viral DNA duplication, and HSC70-4 nuclear entry upon BmNPV challenge, and the nuclear propulsion of HSC70-4 after viral stimulus might be dependent on the interaction with the carboxyl terminus of HSC70-interacting protein (CHIP, an E3 ubiquitin ligase), followed by ubiquitin-proteasome system assistance. In this study, single lysine 77 deacetylation of HSC70-4 was deemed a part of the locomotive pathway for facilitating BmNPV proliferation and provided novel insights into the antiviral strategic development.

Metabolic Characterisation of the Midgut of Bombyx mori Varieties after BmNPV Infection Using GC-MS-Based Metabolite Profiling

Bombyx mori nucleopolyhedrovirus (BmNPV) is a silkworm disease that is especially harmful to cocoon production and seriously restricts sericultural development. Our laboratory successfully cultivated a new highly BmNPV-resistant silkworm variety, Huakang 2; however, its mechanism of BmNPV resistance remains unclear. To understand its resistance mechanism, we conducted a metabolomic and transcriptomic study of the midgut of silkworm varieties, Baiyu N and Baiyu after BmNPV infection. We identified 451 differential metabolites, which were mostly comprised of small molecules, such as saccharides, acids, amines, alcohols, and glycosides. We found that the primary differences in disease resistance between the silkworm varieties are metabolic-pathways, tryptophan metabolism, oxidative phosphorylation, ABC-transporters, beta-alanine metabolism, and phenylalanine metabolism. Combined analysis with transcriptomic data suggested that tryptophan metabolism and oxidative phosphorylation are closely related to the silkworms' BmNPV resistance. We hypothesize that the roles of the two metabolic pathways in the BmNPV resistance mechanism might be the following: Oxidative phosphorylation generates a large amount of adenosine triphosphate (ATP) in response to BmNPV infection to provide silkworms the energy required for establishing BmNPV resistance. Tryptophan metabolism then activates the aryl hydrocarbon receptor (AhR) through the exogenous virus BmNPV, which activates the silkworm's immune system to defeat BmNPV infections.

Quantitative proteomics analysis provides insight into the biological role of Hsp90 in BmNPV infection in Bombyx mori

Heat shock protein 90, an essential chaperone responsible for the correct maturation of key proteins, has been confirmed to facilitate Bombyx mori nucleopolyhedrovirus (BmNPV) proliferation but the mechanism is not clear. In this study, we use quantitative proteomics analysis to investigate the mechanism of Hsp90 in BmNPV replication. In total, 195 differentially expressed proteins (DEPs) were identified with 136 up-regulated proteins and 59 down-regulated proteins. The protein expression level of small heat shock proteins, immune-related proteins, cellular DNA repair-related proteins and zinc finger proteins is significantly enhanced while that of protein kinases is declined. KEGG pathway analysis reveals that DEPs are involved in longevity regulating pathway, mTOR signaling pathway, FoxO signaling pathway and Toll and Imd signaling pathway. Based on the DEPs results, we speculate that inhibition of Hsp90 suppresses the BmNPV infection may because it could not only stimulate the host innate immune, induce small heat shock proteins expression to maintain the cellular proteostasis but activate host transcription factors to bind to virus DNA or protein and subsequently hinder virus replication. The results will help understand the roles of Hsp90 in BmNPV infection and shed light on new clue to illustrate the molecular mechanism of silkworm-virus interaction. SIGNIFICANCE: This is the first report on Hsp90 roles in BmNPV infection based on proteomic analysis. Our findings may provide new clue and research orientation to illustrate the molecular mechanism of silkworm-virus interaction and a set of BmHsp90 candidate clients, which may involve in BmNPV infection in BmN cells.

Label-free proteomic analysis of silkworm midgut infected by Bombyx mori nuclear polyhedrosis virus

Bombyx mori nuclear polyhedrosis virus (BmNPV) is the most damaging virus for the production of silkworm cocoons. Antivirus research continues to be an important aspect of the silkworm industry. Two-dimensional electrophoresis and mass spectrometry have been applied for analyzing the midgut proteome of BmNPV-infected silkworms. In recent years, the isobaric tags for relative and absolute quantitation (iTRAQ) method has frequently been used when studying interaction between BmNPV and Bombyx mori, and useful information has been obtained. In this study, midgut proteins of BmNPV-infected silkworms were extracted from silkworm variety NIL·LVR with anti-BmNPV activity at 48 h, and proteome analysis was carried out using the label-free method. 2196 proteins were identified. Among them, there were 85 differentially expressed proteins, 45 upregulated proteins (immune-activated proteins), 28 downregulated proteins, and six proteins were specific for the BmNPV group and another six specific for control group. Many of the immune-activated proteins have been reported to have innate immune functions, and the downregulated proteins are involved in apoptosis or abnormal cell viability. In conclusion, this study provides evidence for host defense against BmNPV infection by both innate immunity and apoptosis, revealing the potential function of the midgut after oral infection of BmNPV in Bombyx mori. SIGNIFICANCE: Bombyx mori nuclear polyhedrosis virus (BmNPV) has a great impact on the sericulture industry. However, the mechanism of resistance to BmNPV has not been fully elucidated. The silkworm midgut is not only the major organ for food digestion and nutrient absorption but also an immune organ serving as the first line of defense against microbial invasion and proliferation. Here we combined label-free quantitative proteomic, bioinformatics, quantitative real-time PCR and SDS-PAGE analyses and found that BmNPV invasion causes complex protein alterations in the larval midgut of NIL·LVR with anti-BmNPV activity. The results showed that many upregulated differentially expressed proteins have been reported to have innate immune functions and the downregulation proteins are involved in apoptosis or abnormal cell viability. These findings provide evidence for host defense against BmNPV infection by both innate immunity and apoptosis, and reveals the potential function of the midgut after infection of BmNPV in Bombyx mori.