The stability and antiapoptotic activity of Bm30K-3 can be improved by lysine acetylation in the silkworm, Bombyx mori

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.

The acetyltransferase BmCBP changes the acetylation modification of BmSP3 and affects its protein expression in silkworm, Bombyx mori

BACKGROUND

Protein acetylation is an important post-translational modification (PTM) that widely exists in organisms. As a reversible PTM, acetylation modification can regulate the function of proteins with high efficiency. In the previous study, the acetylation sites of silkworm proteins were identified on a large scale by nano-HPLC/MS/MS (nanoscale high performance liquid chromatography-tandem secondary mass spectrometry), and a total of 11 acetylation sites were discovered on Bombyx mori nutrient-storage protein SP3 (BmSP3). The purpose of this study was to investigate the effect of acetylation level on BmSP3.

METHODS AND RESULTS

In this study, the acetylation of BmSP3 was further verified by immunoprecipitation (IP) and Western blotting. Then, it was confirmed that acetylation could up-regulate the expression of BmSP3 by improving its protein stability in BmN cells. Co-IP and RNAi experiments showed acetyltransferase BmCBP could bind to BmSP3 and catalyze its acetylation modification, then regulate the expression of BmSP3. Furthermore, the knock-down of BmCBP could improve the ubiquitination level of BmSP3. Both acetylation and ubiquitination occur on the side chain of lysine residues, therefore, we speculated that the acetylation of BmSP3 catalyzed by BmCBP could competitively inhibit its ubiquitination modification and improve its protein stability by inhibiting ubiquitin-mediated proteasome degradation pathway, and thereby increase the expression and intracellular accumulation.

CONCLUSIONS

BmCBP catalyzes the acetylation of BmSP3 and may improve the stability of BmSP3 by competitive ubiquitination. This conclusion provides a new functional basis for the extensive involvement of acetylation in the regulation of nutrient storage and utilization in silkworm, Bombyx mori.

Determination of Key Components in the Bombyx mori p53 Apoptosis Regulation Network Using Y2H-Seq

The apoptosis pathway is highly conserved between invertebrates and mammals. Although genes encoding the classical apoptosis pathway can be found in the silkworm genome, the regulatory pathway and other apoptotic network genes have yet to be confirmed. Consequently, characterizing these genes and their underlying mechanisms could provide critical insights into the molecular basis of organ apoptosis and remodeling. A homolog of p53, a key apoptosis regulator in vertebrates, has been identified and cloned from Bombyx mori (Bmp53). This study confirmed via gene knockdown and overexpression that Bmp53 directly induces cell apoptosis and regulates the morphology and development of individuals during the metamorphosis stage. Furthermore, yeast two-hybrid sequencing (Y2H-Seq) identified several potential apoptotic regulatory interacting proteins, including the MDM2-like ubiquitination regulatory protein, which may represent an apoptosis factor unique to Bmp53 and which differs from that in other Lepidoptera. These results provide a theoretical basis for analyzing the various biological processes regulated by Bmp53 interaction groups and thus provide insight into the regulation of apoptosis in silkworms. The global interaction set identified in this study also provides a basic framework for future studies on apoptosis-dependent pupation in Lepidoptera.

BmCBP Catalyzes the Acetylation of BmApoLp-II Protein and Regulates Its Stability in Silkworm, Bombyx mori

Acetylation is an important and reversible post-translational modification (PTM) of protein, which is involved in many cellular physiological processes. In previous studies, lots of nutrient storage proteins were found to be highly acetylated in silkworms, and acetylation can improve the stability of these proteins. However, the related acetyltransferase was not involved. In the present work, a Bombyx mori nutrient storage protein, apolipophorin II (BmApoLp-II), was further confirmed to be acetylated, and the acetylation could improve its protein expression. Furthermore, RNAi and Co-IP showed that the acetyltransferase BmCBP was found to catalyze the acetylation modification of BmApoLp-II, and thus affect its protein expression. Meanwhile, it was proved that acetylation could improve the stability of the BmApoLp-II protein by completing its ubiquitination. These results lay a foundation for further study on the mechanism of regulating nutrition storage and hydrolysis utilization of storage proteins by BmCBP and the acetylation in the silkworm Bombyx mori.

Haemolymph metabolomic differences in silkworms (Bombyx mori L.) under mulberry leaf and two artificial diet rearing methods

The new technology of silkworm (Bombyx mori L.) artificial feed breeding has many characteristics and advantages. This study assessed silkworm rearing with mulberry leaf at all instars (MF) as the control, and used metabolomics to explore the differences in haemolymph metabolism of fifth instar silkworms under two modes of rearing with an artificial diet at all instars (AF) and rearing with an artificial diet during first to third instars and mulberry leaf during the fourth and fifth instars (AMF). The results show that, compared with silkworms of the MF group, the amount and fold change of various metabolites were higher in the haemolymph of AF group silkworms, and the metabolism of amino acids and uric acid, carbohydrates, lipids, and vitamins were changed. These changes may be the reasons for the poor performance of the AF silkworms. However, the amount and fold change of the various metabolites of silkworms in the AMF group were lower, and some metabolic pathways were more active. The amount of material and energy supply were greater. These changes could explain the high efficiency growth of body weight of silkworms after the conversion from artificial diet rearing to mulberry leaf rearing. These findings provide an important theoretical basis for the optimisation of artificial diet rearing technology for silkworms.

The Acetylation Modification of SP1 Regulates the Protein Stability in Silkworm

Acetylation is a highly conservative and reversible post-translational modification. Acetylation modification can regulate gene expression by altering protein function and is widely identified in an increasing number of species. Previously, the acetylated proteome of silkworm was identified by combining acetylated polypeptide enrichment with nano-HPLC/MS/MS; the identification revealed that the SP proteins (SPs) were high acetylated. In this study, the acetylation of SP1, one of the SPs, was further confirmed using immunoprecipitation (IP) and Western blotting. Then, we found the acetylation could upregulate SP1 protein expression by enhancing the protein stability. Further research found that the acetylation of SP1 protein can competitively inhibit its ubiquitination and thus improve the stability and cell accumulation of SP1 protein by inhibiting the ubiquitin-mediated proteasome degradation pathway. This result provides a basis for acetylation to regulate the nutrient storage and utilization of silkworm.

The acetylation modification regulates the stability of Bm30K-15 protein and its mechanism in silkworm, Bombyx mori

The 30 K proteins are the major silkworm hemolymph proteins and are involved in a variety of physiological processes, such as nutrient and energy storage, embryogenesis, immune response, and inhibition of apoptosis. The Bm30K-15 protein is one of the 30 K proteins and is abundant in the hemolymph of fifth instar silkworm larva. We previously found that the Bm30K-15 protein can be acetylated. In the present study, we found that acetylation can improve the protein stability of Bm30K-15. Further exploration confirmed that the increase in protein stability by acetylation was caused by competition between acetylation and ubiquitination. In summary, these findings aim to provide insight into the effect of acetylation modification on the protein level and stability of the Bm30K-15 and the possible molecular mechanism of its existence in silkworm, Bombyx mori.

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.