establishment-viral-infection-analysis-host-virus-interaction

Establishment of Viral Infection and Analysis of Host-Virus Interaction in <em>Drosophila Melanogaster</em>

Virus spreading is a major cause of epidemic diseases. Thus, understanding the interaction between the virus and the host is very important to extend our ...

Guangzhou Women and Children's medical center

Chinese Academy of Sciences

Guangzhou Women and Children's Medical Center

Uncovering the mystery of Ebola virus entry: Lock and key.

Immune homeostasis is a prerequisite to protective immunity against gastrointestinal infections. In Drosophila, immune deficiency (IMD) signalling (tumour necrosis factor receptor/interleukin-1 receptor, TNFR/IL-1R in mammals) is indispensable for intestinal immunity against invading bacteria. However, how this local antimicrobial immune response contributes to inflammatory regulation remains poorly defined. Here, we show that flies lacking intestinal Bap180 (a subunit of the chromatin-remodelling switch/sucrose non-fermentable (SWI/SNF) complex) are susceptible to infection as a result of hyper-inflammation rather than bacterial overload. Detailed analysis shows that Bap180 is induced by the IMD-Relish response to both enteropathogenic and commensal bacteria. Upregulated Bap180 can feed back to restrain overreactive IMD signalling, as well as to repress the expression of the pro-inflammatory gene eiger (TNF), a critical step to prevent excessive tissue damage and elongate the lifespan of flies, under pathological and physiological conditions, respectively. Furthermore, intestinal targeting of Baf180 renders mice susceptible to a more aggressive infectious colitis caused by Citrobacter rodentium. Together, Bap180 and Baf180 serve as a conserved transcriptional repressor that is critical for the maintenance of innate immune homeostasis in the intestines.

Bap180/Baf180 is required to maintain homeostasis of intestinal innate immune response in Drosophila and mice.

The metabolic intermediate of acetaminophen (APAP) can cause severe hepatocyte necrosis, which triggers aberrant immune activation of liver non-parenchymal cells (NPC). Overzealous hepatic inflammation determines the morbidity and mortality of APAP-induced liver injury (AILI). Interleukin-1 receptor (IL-1R) signaling has been shown to play a critical role in various inflammatory conditions, but its precise role and underlying mechanism in AILI remain debatable. Herein, we show that NLRP3 inflammasome activation of IL-1β is dispensable to AILI, whereas IL-1α, the other ligand of IL-1R1, accounts for hepatic injury by a lethal dose of APAP. Furthermore, Kupffer cells function as a major source of activated IL-1α in the liver, which is activated by damaged hepatocytes through TLR4/MyD88 signaling. Finally, IL-1α is able to chemoattract and activate CD11bGr-1 myeloid cells, mostly neutrophils and inflammatory monocytes, to amplify deteriorated inflammation in the lesion. Therefore, this work identifies that MyD88-dependent activation of IL-1α in Kupffer cells plays a central role in the immunopathogenesis of AILI and implicates that IL-1α is a promising therapeutic target for AILI treatment.

Macrophage-derived IL-1α promotes sterile inflammation in a mouse model of acetaminophen hepatotoxicity.

HCV infection can decrease NAD/NADH ratio, which could convert lipid metabolism to favor HCV replication. In hepatocytes, quinolinate phosphoribosyl transferase (QPRT) catabolizes quinolinic acid (QA) to nicotinic acid mononucleotide (NAMN) for de novo NAD synthesis. However, whether and how HCV modulates QPRT hence the lipogenesis is unknown. In this work, we found QPRT was reduced significantly in livers of patients or humanized C/O mice with persistent HCV infection. Mechanistic studies indicated that HCV NS3/4A promoted proteasomal degradation of QPRT through Smurf2, an E3 ubiquitin-protein ligase, in Huh7.5.1 cells. Furthermore, QPRT enzymatic activity involved in suppression of HCV replication in cells. Activation of QPRT with clofibrate (CLO) or addition of QPRT catabolite NAD both inhibited HCV replication in cells, probably through NAD-dependent Sirt1 inhibition of cellular lipogenesis. More importantly, administration of CLO, a hypolipidemic drug used in clinics, could significantly reduce the viral load in HCV infected C/O mice. Take together, these results suggested that HCV infection triggered proteasomal degradation of QPRT and consequently reduced de novo NAD synthesis and lipogenesis, in favor of HCV replication. Hepatic QPRT thus likely served as a cellular factor that dampened productive HCV replication.

Quinolinate Phosphoribosyltransferase is an Antiviral Host Factor Against Hepatitis C Virus Infection.

In order to establish productive infection and dissemination, viruses usually evolve a number of strategies to hijack and/or subvert the host defense systems. However, host factors utilized by the virus to facilitate infection remain poorly characterized. In this work, we found that  deficient in  (), a highly conserved subunit of the kinetochore complex regulating chromosome congression (1), became resistant to  (DCV) infection, evidenced in increased survival rates and reduced viral loads, compared to the wild-type control. Mechanistic analysis further showed that Bub1 also functioned in the cytoplasm and was essentially involved in clathrin-dependent endocytosis of DCV and other pathogens, thus limiting pathogen entry. DCV infection potentially had strengthened the interaction between Bub1 and the clathrin adaptor on the cell membrane. Furthermore, the conserved function of Bub1 was also verified in a mammalian cell line. Thus, our data demonstrated a previously unknown function of Bub1 that could be hijacked by pathogens to facilitate their infection and spread. In this work, we identify for the first time that the nuclear protein Bub1 (budding uninhibited by benzimidazoles 1), a highly conserved subunit of the kinetochore complex regulating chromosome congression, has a novel and important function on the cell membrane to facilitate the virus to enter host cells. Bub1 deficiency empowers the host to have the ability to resist viral infection in  and a human cell line. Bub1 is involved in the virus entry step through regulating endocytosis. The DCV capsid protein can recruit Bub1, and DCV infection can strengthen the interaction between Bub1 and a clathrin-dependent endocytosis component. The restricted entry of vesicular stomatitis virus (VSV) and  in -deficient flies and cell lines was also observed. Therefore, our data implicate a previously unknown function of Bub1 that can be hijacked by pathogens to facilitate their entry, and Bub1 may serve as a potential antiviral therapy target for limiting viral entry.

Bub1 Facilitates Virus Entry through Endocytosis in a Model of Drosophila Pathogenesis.

B cells can present antigens to CD4 T cells, but it is thought that dendritic cells (DCs) are the primary initiators of naive CD4 T cell responses. Nanoparticles, including virus-like particles (VLPs), are attractive candidates as carriers for vaccines and drug delivery. Using RNA phage Qβ-derived VLP (Qβ-VLP) as a model antigen, we found that antigen-specific B cells were the dominant antigen-presenting cells that initiated naive CD4 T cell activation. B cells were sufficient to induce T follicular helper cell development in the absence of DCs. Qβ-specific B cells promoted CD4 T cell proliferation and differentiation via cognate interactions and through Toll-like receptor signaling-mediated cytokine production. Antigen-specific B cells were also involved in initiating CD4 T cell responses during immunization with inactivated influenza virus. These findings have implications for the rational design of nanoparticles as vaccine candidates, particularly for therapeutic vaccines that aim to break immune tolerance.

Article	Year
Uncovering the mystery of Ebola virus entry: Lock and key. Science China. Life sciences\| PubMed ID: 26965522	2016
Bap180/Baf180 is required to maintain homeostasis of intestinal innate immune response in Drosophila and mice. Nature microbiology\| PubMed ID: 28418397	2017
Macrophage-derived IL-1α promotes sterile inflammation in a mouse model of acetaminophen hepatotoxicity. Cellular & molecular immunology\| PubMed ID: 28504245	2018
Quinolinate Phosphoribosyltransferase is an Antiviral Host Factor Against Hepatitis C Virus Infection. Scientific reports\| PubMed ID: 28724915	2017
Bub1 Facilitates Virus Entry through Endocytosis in a Model of Drosophila Pathogenesis. Journal of virology\| PubMed ID: 29976667	2018
B Cells Are the Dominant Antigen-Presenting Cells that Activate Naive CD4 T Cells upon Immunization with a Virus-Derived Nanoparticle Antigen. Immunity\| PubMed ID: 30291027	2018

Hong Tang

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