Viral protease cleavage of MAVS in genetically modified mice with hepatitis A virus infection

The CARD14sh-BCL10-MALT1 complex regulates MAVS-mediated antiviral response in keratinocytes

The Mitochondrial Antiviral Signaling Protein (MAVS) is a key adaptor in antiviral immunity, mediating type I interferon responses downstream of RIG1 and TLR3. While MAVS regulation is essential for antiviral defense, its modulation in keratinocytes is poorly understood. Here, we examine the role of the CARD14-BCL10-MALT1 (CBM) complex, a skin-specific signaling module, in controlling MAVS-dependent antiviral responses. We identify CARD14short as a dual regulator that activates NF-κB while inhibiting IRF3 signaling. Psoriasis-associated CARD14 mutations are less efficient in restricting IRF3 activation and cytokine production upon Poly (I:C) stimulation, highlighting a potential mechanism in psoriasis pathogenesis. BCL10 is essential for MAVS-induced IRF3 activation, while MALT1 limits IRF3 signaling by promoting MAVS cleavage, K48-linked ubiquitination, and proteasomal degradation. Genetic and chemical inhibition of MALT1 enhances IRF3 activation and type I IFN expression. These findings reveal a MAVS-CBM regulatory network linking innate immunity to epithelial homeostasis.

Limited impact of hepatitis A virus 3C protease-mediated cleavage on the functions of NEMO in human hepatocytes

NF-κB essential modulator (NEMO) is critically involved in the induction of interferons (IFNs) and pro-inflammatory cytokines. Hepatitis A virus (HAV) 3C protease was recently identified to cleave NEMO in non-hepatic cells. This study aimed at understanding efficiency and function of HAV 3C-mediated NEMO cleavage in hepatocytes. HAV 3C protease and its precursor 3CD strongly affected NEMO abundance in ectopic expression models, which was not observed in HAV replicon cells and upon HAV infection. Using a cleavage-resistant NEMO mutant, we found that specific cleavage by 3C only marginally contributed to NEMO degradation, whereas the magnitude of the effect was due to cytotoxic effects induced by 3C activity. Cleavage efficiency generally did not suffice to disrupt the type I IFN or NF-κB signaling pathways. Knockout of NEMO indeed abrogated both pathways, whereas efficient knockdown had limited the impact on NEMO-mediated signaling, suggesting that low levels of NEMO are sufficient to maintain antiviral responses in hepatocytes. NEMO cleavage was barely detectable in a cell line harboring a persistent HAV replicon or in HAV-infected cells. HAV infection induced a robust innate immune response, which was not affected by efficient knockdown of NEMO, arguing for a limited potential contribution of NEMO cleavage to innate immune counteraction. Overall, our data suggest that HAV 3C is capable of partially cleaving NEMO as reported. However, since minute expression levels of NEMO were sufficient for induction of innate immunity, inefficient NEMO cleavage by HAV is unlikely to contribute to dampening of innate immune responses in hepatocytes.IMPORTANCEHepatitis A virus (HAV) establishes acute infections of the liver, which are always cleared, while a number of mechanisms have been identified contributing to immune escape. Among those, proteolytic cleavage of NF-κB essential modulator (NEMO) by HAV has been suggested to counteract innate immune responses. This study demonstrates that the HAV 3C protease cleaves NEMO inefficiently and does not result in substantial disruption of antiviral signaling. Importantly, NEMO remains capable of inducing an effective immune response in hepatocytes even at low expression levels. Our findings suggest a limited role for NEMO cleavage in HAV's interaction with host immunity and call for a revision of our understanding of HAV counteraction mechanisms.

Hepatovirus translation requires PDGFA-associated protein 1, an eIF4E-binding protein regulating endoplasmic reticulum stress responses

The overexpression and misfolding of viral proteins in the endoplasmic reticulum (ER) may cause cellular stress, thereby inducing a cytoprotective, proteostatic host response involving phosphorylation of eukaryotic translation initiation factor 2 subunit alpha (eIF2α). Here, we show that hepatitis A virus, a positive-strand RNA virus responsible for infectious hepatitis, adopts a stress-resistant, eIF2α-independent mechanism of translation to ensure the synthesis of viral proteins within the infected liver. Cap-independent translation directed by the hepatovirus internal ribosome entry site and productive hepatovirus infection of mice both require platelet-derived growth factor subunit A (PDGFA)-associated protein 1 (PDAP1), a small phosphoprotein of unknown function with eIF4E-binding activity. PDAP1 also interacts with eIF1A and is essential for translating stress-resistant host messenger RNAs that evade the proteostatic response to ER stress and that encode proteins promoting the survival of stressed cells.

Natural-Target-Mimicking Translocation-Based Fluorescent Sensor for Detection of SARS-CoV-2 PLpro Protease Activity and Virus Infection in Living Cells

Papain-like protease PLpro, a domain within a large polyfunctional protein, nsp3, plays key roles in the life cycle of SARS-CoV-2, being responsible for the first events of cleavage of a polyprotein into individual proteins (nsp1-4) as well as for the suppression of cellular immunity. Here, we developed a new genetically encoded fluorescent sensor, named PLpro-ERNuc, for detection of PLpro activity in living cells using a translocation-based readout. The sensor was designed as follows. A fragment of nsp3 protein was used to direct the sensor on the cytoplasmic surface of the endoplasmic reticulum (ER) membrane, thus closely mimicking the natural target of PLpro. The fluorescent part included two bright fluorescent proteins-red mScarlet I and green mNeonGreen-separated by a linker with the PLpro cleavage site. A nuclear localization signal (NLS) was attached to ensure accumulation of mNeonGreen into the nucleus upon cleavage. We tested PLpro-ERNuc in a model of recombinant PLpro expressed in HeLa cells. The sensor demonstrated the expected cytoplasmic reticular network in the red and green channels in the absence of protease, and efficient translocation of the green signal into nuclei in the PLpro-expressing cells (14-fold increase in the nucleus/cytoplasm ratio). Then, we used PLpro-ERNuc in a model of Huh7.5 cells infected with the SARS-CoV-2 virus, where it showed robust ER-to-nucleus translocation of the green signal in the infected cells 24 h post infection. We believe that PLpro-ERNuc represents a useful tool for screening PLpro inhibitors as well as for monitoring virus spread in a culture.

The intersection of virus infection and liver disease: A comprehensive review of pathogenesis, diagnosis, and treatment

Liver disease represents a significant global burden, placing individuals at a heightened risk of developing cirrhosis and liver cancer. Viral infections act as a primary cause of liver diseases on a worldwide scale. Infections involving hepatitis viruses, notably hepatitis B, C, and E viruses, stand out as the most prevalent contributors to acute and chronic intrahepatic adverse outcome, although the hepatitis C virus (HCV) can be effectively cured with antiviral drugs, but no preventative vaccination developed. Hepatitis B virus (HBV) and HCV can lead to both acute and chronic liver diseases, including liver cirrhosis and hepatocellular carcinoma (HCC), which are principal causes of worldwide morbidity and mortality. Other viruses, such as Epstein-Barr virus (EBV) and cytomegalovirus (CMV), are capable of causing liver damage. Therefore, it is essential to recognize that virus infections and liver diseases are intricate and interconnected processes. A profound understanding of the underlying relationship between virus infections and liver diseases proves pivotal in the effective prevention, diagnosis, and treatment of these conditions. In this review, we delve into the mechanisms by which virus infections induce liver diseases, as well as explore the pathogenesis, diagnosis, and treatment of liver diseases. This article is categorized under: Infectious Diseases > Biomedical Engineering.

Recent advances in hepatitis A virus research and clinical practice guidelines for hepatitis A virus infection in Japan

In 2018, there was a hepatitis A outbreak in Japan, and hepatitis A virus (HAV) infection is considered a sexually transmitted disease. In general, patients with hepatitis A should be given attention, and this disease should be prevented more than ever. The Japan Agency for Medical Research and Development (AMED) Hepatitis A and E viruses (HAV and HEV) Study Group has worked on the project to create "Recent Advances in Hepatitis A Virus (HAV) Research and Clinical Practice Guidelines for HAV Infection in Japan". The group consists of expert hepatologists and virologists who gathered at virtual meeting on August 5, 2023. Data about the pathogenesis, infection routes, diagnosis, complications, several factors for the severities, vaccination, and current and future treatments for hepatitis A were discussed and debated for a draft version. The participants assessed the quality of cited studies. The finalized recommendations are presented in this review. The recent advances in HAV research and clinical practice for HAV infection in Japan, have been reviewed by the AMED HAV and HEV Study Group.