OTUB1 Is a Key Regulator of RIG-I-Dependent Immune Signaling and Is Targeted for Proteasomal Degradation by Influenza A NS1.

Deubiquitylases (DUBs) regulate critical signaling pathways at the intersection of host immunity and viral pathogenesis. Although RIG-I activation is heavily dependent on ubiquitylation, systematic analyses of DUBs that regulate this pathway have not been performed. Using a ubiquitin C-terminal electrophile, we profile DUBs that function during influenza A virus (IAV) infection and isolate OTUB1 as a key regulator of RIG-I-dependent antiviral responses. Upon infection, OTUB1 relocalizes from the nucleus to mitochondrial membranes together with RIG-I, viral PB2, and NS1. Its expression depends on competing effects of interferon stimulation and IAV-triggered degradation. OTUB1 activates RIG-I via a dual mechanism of K48 polyubiquitin hydrolysis and formation of an E2-repressive complex with UBCH5c. We reconstitute this mechanism in a cell-free system comprising [35S]IRF3, purified RIG-I, mitochondrial membranes, and cytosol expressing OTUB1 variants. A range of IAV NS1 proteins trigger proteasomal degradation of OTUB1, antagonizing the RIG-I signaling cascade and antiviral responses

Mechanisms of pathogenic avian influenza-induced immune responses in human cells

abstracttocpublished_or_final_versionPaediatrics and Adolescent MedicineMasterMaster of Philosoph

Avian influenza A viral genetic determinants of cytokine hyper-induction in primary human macrophages

published_or_final_versionMicrobiologyDoctoralDoctor of Philosoph

Interaction of Influenza A Nucleoprotein with Host hnRNP-C Is Implicated in Viral Replication

The host interactome of influenza viral proteins is ever-expanding. In this work, we report the identification of host heterogeneous nuclear ribonucleoprotein C (hnRNP-C) as an interacting partner of influenza A virus nucleoprotein (NP). We confirmed that this interaction exists across different influenza A subtypes and strains. Using biochemical methods, we determined that hnRNP-C interacts with NP via its C-terminal auxiliary domain. Further, we determined that the hnRNP-C is a negative regulator of influenza viral growth. Its interaction with NP is implicated in the promotion of host cell apoptosis during viral infection. It is the first time that the interaction between influenza nucleoprotein and host heterogeneous nuclear ribonucleoprotein C is characterized in detail. Overall, these findings not only characterize the interaction between NP and its host interacting partner hnRNP-C but also clarify the functional significance of this interaction. This work may lead to a new therapeutic target for the development of anti-influenza drugs

Lack of neutralizing antibodies against influenza A viruses in adults during the 2022/2023 winter season – a serological study using retrospective samples collected in Hong Kong

Objectives: Since the onset of the COVID-19 pandemic in 2020, there has been a significant decline in seasonal influenza infection cases in Hong Kong. However, this decline has also resulted in reduced opportunities for the development of influenza-specific antibodies in the community. The levels of antibodies required for protection against recently circulating influenza A viruses in the post-COVID-19 era remain unclear. Methods: This study involved the analysis of paired plasma samples collected from 479 healthy adults in Hong Kong in 2021 and 2022. The neutralizing titers of plasma against influenza A (H1N1) and (H3N2) viruses circulating before and after the COVID-19 outbreak were determined using a microneutralization assay. Results: The H1N1 and H3N2 vaccine strains selected for the 2022/23 season were found to be closely related to the recently circulating viruses. However, in the samples collected in 2022, only 14.61% and 0.42% showed a neutralization titer (MN50) ≥1:20 against H1N1 A/Wisconsin/588/2019 (H1/Wis19) and H3N2 A/Darwin/6/2021 (H3/Dar21), respectively. Notably, participants who reported receiving annual flu vaccinations exhibited a higher seropositive rate for H1/Wis19 compared to those who had never received the flu vaccine (28.06% vs. 5.30%). Conclusion: Our results indicate that adults in Hong Kong generally lack neutralizing antibodies against circulating influenza A viruses, particularly H3N2. These findings underscore the importance of promoting flu vaccination in the post-COVID-19 era

PB2-Q591K Mutation Determines the Pathogenicity of Avian H9N2 Influenza Viruses for Mammalian Species.

Influenza A subtype H9N2 is widespread and prevalent in poultry. It has repeatedly transmitted zoonotically to cause mild influenza-like illness in humans and is regarded as a potential pandemic candidate. In additon, the six internal genes of H7N9 and H10N8 viruses which caused infection in human in China as well as some of the highly pathogenic H5N1 strains are origined from H9N2. Previous studies have shown that the mammalian adaptation PB2-Q591K contributes to the pathogenicity of H5N1 and H7N9 viruses. However, the role of the PB2-Q591K mutation in H9N2 subtype is still not well understood.To define and compare the individual role of PB2-Q591K substitution in the PB2 gene segment of H9N2 in relation to polymerase activity, replication competence and the pathogenicity using in vitro and in vivo models.The PB2-Q591K mutation in H9N2 virus enhanced the polymerase activity and virus replication in human NHBE cells when compared to the wild type strain. Mice infected with the PB2 mutant showed significant weight loss, higher virus replication and immune responses in the lungs.Our evidences suggest that the PB2-Q591K, in addition to the -E627K mutation in H9N2 enhanced the pathogenicity in mammalian host

Serum Cytokine Profiles in Patients with Dengue Fever at the Acute Infection Phase

Background. Dengue virus (DENV) is transmitted by mosquito and has been circulating in Guangdong, China, for over 30 years. Dengue infection causes mild to severe disease symptoms in human. Cytokine profiles were suggested to be crucial especially during the acute stage in the dengue infection. Aim. To determine the cytokine profiles at the acute stage in patients with primary or secondary dengue infection in Guangzhou city in the 2014 outbreak. Methods. We investigated 23 inflammatory cytokines in serum collected from dengue-infected patients and analyzed their correlations with their clinical indexes. Results. The concentrations of CXCL9, IP-10, CXCL11, IL-8, IL-10, and CCL2 in serum were significantly higher in the groups of DENV-infected patients during the first two weeks than those of control group while CCL17 and CXCL5 showed lower expression level in the patients. Among these cytokines, CXCL9, CCL17, and CXCL5 showed statistical difference between the groups of primary and secondary infections. The platelet count and lactate dehydrogenase were correlated with the level of CCL17 and MIP-1α/CXCL5, respectively, in the group of secondary infection. Conclusions. We determined the cytokine profiles in serum of the patients during the 2014 dengue outbreak. The expression of specific cytokines was associated with the secondary infection