Axin1 prevents Salmonella invasiveness and inflammatory response in intestinal epithelial cells

Axin1's mystique in manipulating microbiome amidst colitis

Classically, Axin1 is considered a regulator of Wnt/β-catenin signaling. However, Axin1's roles in host-microbial interactions have been unknown. Our recent study has demonstrated that deletion of intestinal epithelial Axin1 in epithelial cells and Paneth cells protects the host against colitis by enhancing Akkermansia muciniphila. Loss of intestinal epithelial or Paneth cell Axin1 results in increased Wnt/β-catenin signaling, proliferation, and cell migration. This is associated with morphologically altered goblet and Paneth cells, including increased Muc2 and decreased lysozyme. Axin1 deletion specifically enriched Akkermansia muciniphila. Akkermansia muciniphila in Axin1 knockout mice is the driver of protection against DSS-induced inflammation. Here, we feature several significant conceptual changes, such as differences between Axin1 and Axin2, Axin1 in innate immunity and microbial homeostasis, and Axin1 reduction of Akkermansia muciniphila. We discuss an important trend in the field related to Paneth cells and tissue-specific Axin1 manipulation of microbiome in health and inflammation.

Roles of host SUMOylation in bacterial pathogenesis

Bacteria frequently interfere with the post-translational modifications of host cells to facilitate their survival and growth after invasion. SUMOylation, a reversible post-translational modification process, plays an important role in biological life activities. In addition to being critical to host cell metabolism and survival, SUMOylation also regulates gene expression and cell signal transmission. Moreover, SUMOylation in eukaryotic cells can be used by a variety of bacterial pathogens to advance bacterial invasion. In this minireview, we focused on the role and mechanism of host SUMOylation in the pathogenesis of six important clinical bacterial pathogens (Listeria monocytogenes, Shigella flexneri, Salmonella Typhimurium, Klebsiella pneumoniae, Staphylococcus aureus, and Escherichia coli). Taken together, this review provided new insights for understanding the unique pathogen-host interaction based on host SUMOylation and provided a novel perspective on the development of new strategies to combat bacterial infections in the future.

Axin1: A novel scaffold protein joins the antiviral network of interferon

Acute respiratory infection by influenza virus is a persistent and pervasive public health problem. Antiviral innate immunity initiated by type I interferon (IFN) is the first responder to pathogen invasion and provides the first line of defense. We discovered that Axin1, a scaffold protein, was reduced during influenza virus infection. We also found that overexpression of Axin1 and the chemical stabilizer of Axin1, XAV939, reduced influenza virus replication in lung epithelial cells. This effect was also observed with respiratory syncytial virus and vesicular stomatitis virus. Axin1 boosted type I IFN response to influenza virus infection and activated JNK/c-Jun and Smad3 signaling. XAV939 protected mice from influenza virus infection. Thus, our studies provide new mechanistic insights into the regulation of the type I IFN response and present a new potential therapeutic of targeting Axin1 against influenza virus infection.

Plasma biomarkers for systemic inflammation in COVID-19 survivors

BACKGROUND

While the majority of COVID-19 patients fully recover from the infection and become asymptomatic, a significant proportion of COVID-19 survivors experience a broad spectrum of symptoms lasting weeks to months post-infection, a phenomenon termed "post-acute sequelae of COVID-19 (PASC)." The aim of this study is to determine whether inflammatory proteins are dysregulated and can serve as potential biomarkers for systemic inflammation in COVID-19 survivors.

METHODS

We determined the levels of inflammatory proteins in plasma from 22 coronavirus disease 2019 (COVID-19) long haulers (COV-LH), 22 COVID-19 asymptomatic survivors (COV-AS), and 22 healthy subjects (HS) using an Olink proteomics assay and assessed the results by a beads-based multiplex immunoassay.

RESULTS

Compared to HS, we found that COVID-19 survivors still exhibited systemic inflammation, as evidenced by significant changes in the levels of multiple inflammatory proteins in plasma from both COV-LH and COV-AS. CXCL10 was the only protein that significantly upregulated in COV-LH compared with COV-AS and HS.

CONCLUSIONS

Our results indicate that several inflammatory proteins remain aberrantly dysregulated in COVID-19 survivors and CXCL10 might serve as a potential biomarker to typify COV-LH. Further characterization of these signature inflammatory molecules might improve the understanding of the long-term impacts of COVID-19 and provide new targets for the diagnosis and treatment of COVID-19 survivors with PASC.

Impact of bacterial infection and intestinal microbiome on colorectal cancer development

ABSTRACT

Accumulating evidence suggests that intestinal bacteria play an important role in the pathogenesis of colorectal cancer (CRC). Due to the complexity of the intestinal microbiome, identification of the specific causative microbial agents in CRC remains challenging, and the search for the causative microbial agents is intense. However, whether bacteria or their products can induce inflammation that results in tumorigenesis or directly causes CRC in humans is still not clear. This review will mainly focus on the progress of bacterial infection and CRC, and introduce the microbial contribution to the hallmarks of cancer. This article uses Salmonella and its chronic infection as an example to investigate a single pathogen and its role in the development of CRC, based on laboratory and epidemiological evidence. The bacterial infection leads to an altered intestinal microbiome. The review also discusses the dysfunction of the microbiome and the mechanism of host-microbial interactions, for example, bacterial virulence factors, key signaling pathways in the host, and microbial post-translational modifications in the tumorigenesis. Colonic carcinogenesis involves a progressive accumulation of mutations in a genetically susceptible host leading to cellular autonomy. Moving forward, more human data are needed to confirm the direct roles of bacterial infection in CRC development. Insights into the inhibiting infection will help to prevent cancer and develop strategies to restore the balance between host and microorganisms.

Paneth Cell Alertness to Pathogens Maintained by Vitamin D Receptors

BACKGROUND AND AIMS

Vitamin D exerts a regulatory role over mucosal immunity via the vitamin D receptor (VDR). Although Paneth cells and their products are known to regulate the commensal and pathogenic microbiota, the role that VDRs in Paneth cells play in these responses is unknown.

METHODS

We identified the decreased intestinal VDR significantly correlated with reduction of an inflammatory bowel disease risk gene ATG16L1 and Paneth cell lysozymes in patients with Crohn's disease. We generated Paneth cell-specific VDR knockout (VDR^ΔPC) mice to investigate the molecular mechanisms.

RESULTS

Lysozymes in the Paneth cells were significantly decreased in the VDR^ΔPC mice. Isolated VDR^ΔPC Paneth cells exhibited weakened inhibition of pathogenic bacterial growth and displayed reduced autophagic responses. VDR^ΔPC mice had significantly higher inflammation after Salmonella infections. VDR^ΔPC mice also showed high susceptibility to small intestinal injury induced by indomethacin, a nonsteroidal anti-inflammatory drug. Co-housing of VDR^ΔPC and VDR^lox mice made the VDR^ΔPC less vulnerable to dextran sulfate sodium colitis, suggesting the transmission of protective bacterial from the VDR^lox mice. Thus, a lack of VDR in Paneth cells leads to impaired antibacterial activities and consequently increased inflammatory responses. Genetically and environmentally regulated VDRs in the Paneth cells may set the threshold for the development of chronic inflammation, as observed in inflammatory bowel diseases.

CONCLUSIONS

We provide new insights into the tissue-specific functions of VDRs in maintaining Paneth cell alertness to pathogens in intestinal disorders. Targeting the VDR affects multiple downstream events within Paneth cells that inhibit intestinal inflammation and establish host defense against enteropathogens.

Wnt Signaling: Pathogen Incursion and Immune Defense

Wnt ligands interact with the transmembrane cell surface receptors Frizzled and ROR/RYK to initiate complex signaling cascades that are crucial for cell physiology and the proper functioning of the immune system. Wnt signaling is instrumental in maintaining immune surveillance and during infections by pathogenic microbes helps mount host resistance to infection. Some pathogens, however, utilize Wnt signaling to build a niche for their survival. The goal of this review is to summarize current and developing concepts about the tug of war between Wnt signaling and pathogens for deployment of host resources, focusing mostly on macrophages and cytoskeletal actin dynamics. An additional objective is to outline the interrelation between Wnt signaling and the host microbiota, which is vital for immune defense, discussing in the same perspective, how Wnt signaling could be differentiating pathogen from non-pathogen.

The WNT Framework in Shaping Immune Cell Responses During Bacterial Infections

A large proportion of the world is inflicted with health concerns arising from infectious diseases. Moreover, there is a widespread emergence of antibiotic resistance among major infectious agents, partially stemming from their continuous dialog with the host, and their enormous capacity to remodel the latter toward a secure niche. Among the several infection-driven events, moderation of WNT signaling pathway has been identified to be strategically tuned during infections to govern host-pathogen interactions. Primarily known for its role in arbitrating early embryonic developmental events; aberrant activation of the WNT pathway has also been associated with immunological consequences during diverse patho-physiological conditions. Here, we review the different mechanisms by which components of WNT signaling pathways are exploited by discrete bacterial agents for their pathogenesis. Furthermore, recent advances on the cross-talk of WNT with other signaling pathways, the varied modes of WNT-mediated alteration of gene expression, and WNT-dependent post-transcriptional and post-translational regulation of the immune landscape during distinct bacterial infections would be highlighted.

Vitamin D Receptor Deletion Leads to the Destruction of Tight and Adherens Junctions in Lungs

Vitamin D deficiency has been linked to various inflammatory diseases in lungs, including pneumonia, asthma and chronic obstructive pulmonary disease. However, the mechanisms by which vitamin D and vitamin D receptor reduce inflammation in lung diseases remain poorly understood. In this study, we investigated the expression and cell-specific distribution of tight and adherens junctions in the lungs of vitamin D receptor-deficient (VDR^-/-) mice. Our results demonstrated that mRNA and protein levels of claudin-2, claudin-4 and claudin-12 were significantly decreased in the lungs of VDR^-/- mice. Other tight and adherens junction proteins, such as ZO-1, occludin, claudin-10, β-catenin, and VE-cadherin, showed significant differences in expression in the lungs of VDR^-/- and wild-type mice. These data suggest that altered expression of tight and adherens junction molecules, especially of claudin-2, -4, -10, -12, and -18, after chronic pneumonia caused by VDR deletion could increase lung permeability.Therefore, VDR may play an important role in maintaining pulmonary barrier integrity. Further studies should confirm whether vitamin D/VDR is beneficial for the prevention or treatment of lung diseases.

Individual variations in cardiovascular-disease-related protein levels are driven by genetics and gut microbiome

Despite a growing body of evidence, the role of the gut microbiome in cardiovascular diseases (CVDs) is still unclear. Here we present a systems-genome-wide and metagenome-wide association study on plasma concentrations of 92 CVD-related proteins in the population cohort Lifelines-DEEP. We identified genetic components for 73 proteins and microbial associations for 41 proteins, of which 31 were associated to both. The genetic and microbial factors identified mostly exert additive effects and collectively explain up to 76.6% of inter-individual variation (17.5% on average). Genetics contributes most to concentrations of immune-related proteins, while the gut microbiome contributes most to proteins involved in metabolism and intestinal health. We found several host-microbe interactions that impact proteins involved in epithelial function, lipid metabolism and central nervous system function. This study reveals important evidence for a joint genetic and microbial effect in cardiovascular disease and provides directions for future applications in personalized medicine.

Novel Regulatory Roles of Wnt1 in Infection-Associated Colorectal Cancer

Salmonella infection is a major public health concern, and colonization in humans can be chronic and increases the risk of cancers. Wnt signaling is a key pathway for intestinal renewal and development, inflammation, and tumorigenesis. In the current study, we report a novel role of Wnt1 in infection and colon cancer using cell culture models, a Salmonella-colitis colon cancer model, and human samples. In contrast to the bacteria-induced increases in Wnt2 and Wnt11, Salmonella colonization significantly reduced the level of Wnt1 in intestinal epithelial cells in vivo and in vitro. The bacterial AvrA protein is known to activate the canonical Wnt pathway. Wnt1 expression level was downregulated by AvrA-expressing Salmonella but stabilized by AvrA-deficient Salmonella in the intestine of Salmonella-colitis mice. In a chronic Salmonella-infected cancer model, the Wnt1 protein level was decreased in the AvrA+ infected group. Thus, we further assessed the functional role of Wnt1 downregulation in the inflammatory response and colorectal cancer (CRC) progression. Moreover, downregulation of Wnt1 by the Crispr-Cas9 method promoted cancer cell invasion and migration. Interestingly, we found that Wnt1 was downregulated in human CRC tissue, and Wnt1 downregulation may be correlated with cancer progression. Our study provides insights into mechanisms by which enteric bacteria regulate Wnt1 expression and potentially contribute to infection-associated colon cancer.

Vitamin D receptor is a novel transcriptional regulator for Axin1

BACKGROUND

Axin1 is a scaffold protein in the β-catenin destruction complex, which, if disrupted, contributes to pathogenesis of various human diseases, including colorectal carcinogenesis and inflammatory bowel diseases (IBD). We have previously demonstrated that Salmonella infection promotes the degradation and plasma sequestration of Axin1, leading to bacterial invasiveness and inflammatory responses. Vitamin D and the vitamin D receptor (VDR) appear to be important regulators of IBD and colon cancer. Although VDR and Axin1 are all involved in intestinal inflammation, it remains unclear whether these processes are related or function independently. In the current study, we hypothesize that VDR is an important regulator for the maintenance of physiological level of Axin1.

METHODS

Using the intestinal epithelial conditional VDR knockout mouse model (VDR^ΔIEC) and cultured cell lines, influences of VDR status on the expression of Axin1 was evaluated by Western blots and real-time PCR. Loss- and gain-of-function assays were used to investigate the regulation of VDR on Axin1 at the transcriptional and translational levels. Cells were treated with cycloheximide or actinomycin for molecular mechanistic studies. Candidate genomic VDR binding sites for Axin1 were tested by chromatin immunoprecipitation (ChIP) assay. Physical interactions among VDR, Axin1, and β-catenin were tested by immunoprecipitation. Cellular localization of Axin1 with different VDR status was determined by fractionation and immunohistochemistry.

RESULTS

We found that VDR deletion led to lower protein and mRNA levels of Axin1, whereas knockdown of Axin1 did not change the expression level of VDR protein. Immunoprecipitation data did not support physical interaction between VDR and Axin1. The VDR regulation of Axin1 was through a VDR genomic binding site for Axin1 gene on the regulatory region. Fractionation data showed that cytosolic Axin1 was significantly reduced due to VDR deletion, leaving the nuclear fraction unchanged. In ileum, Axin1 was distributed in the cytosol of apical epithelium and crypts.

CONCLUSION

VDR is important for the maintenance of physiological level of Axin1. The discovery of Axin1 as a VDR target gene provides novel and fundamental insights into the interactions between the VDR and β-catenin signaling pathways.

Administration of defined microbiota is protective in a murine Salmonella infection model

Salmonella typhimurium is a major cause of diarrhea and causes significant morbidity and mortality worldwide, and perturbations of the gut microbiota are known to increase susceptibility to enteric infections. The purpose of this study was to investigate whether a Microbial Ecosystem Therapeutic (MET-1) consisting of 33 bacterial strains, isolated from human stool and previously used to cure patients with recurrent Clostridium difficile infection, could also protect against S. typhimurium disease. C57BL/6 mice were pretreated with streptomycin prior to receiving MET-1 or control, then gavaged with S. typhimurium. Weight loss, serum cytokine levels, and S. typhimurium splenic translocation were measured. NF-κB nuclear staining, neutrophil accumulation, and localization of tight junction proteins (claudin-1, ZO-1) were visualized by immunofluorescence. Infected mice receiving MET-1 lost less weight, had reduced serum cytokines, reduced NF-κB nuclear staining, and decreased neutrophil infiltration in the cecum. MET-1 also preserved cecum tight junction protein expression, and reduced S. typhimurium translocation to the spleen. Notably, MET-1 did not decrease CFUs of Salmonella in the intestine. MET-1 may attenuate systemic infection by preserving tight junctions, thereby inhibiting S. typhimurium from gaining access to the systemic circulation. We conclude that MET-1 may be protective against enteric infections besides C. difficile infection.

STK4 regulates TLR pathways and protects against chronic inflammation-related hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is frequently associated with pathogen infection-induced chronic inflammation. Large numbers of innate immune cells are present in HCCs and can influence disease outcome. Here, we demonstrated that the tumor suppressor serine/threonine-protein kinase 4 (STK4) differentially regulates TLR3/4/9-mediated inflammatory responses in macrophages and thereby is protective against chronic inflammation-associated HCC. STK4 dampened TLR4/9-induced proinflammatory cytokine secretion but enhanced TLR3/4-triggered IFN-β production via binding to and phosphorylating IL-1 receptor-associated kinase 1 (IRAK1), leading to IRAK1 degradation. Notably, macrophage-specific Stk4 deletion resulted in chronic inflammation, liver fibrosis, and HCC in mice treated with a combination of diethylnitrosamine (DEN) and CCl4, along with either LPS or E. coli infection. STK4 expression was markedly reduced in macrophages isolated from human HCC patients and was inversely associated with the levels of IRAK1, IL-6, and phospho-p65 or phospho-STAT3. Moreover, serum STK4 levels were specifically decreased in HCC patients with high levels of IL-6. In STK4-deficient mice, treatment with an IRAK1/4 inhibitor after DEN administration reduced serum IL-6 levels and liver tumor numbers to levels similar to those observed in the control mice. Together, our results suggest that STK4 has potential as a diagnostic biomarker and therapeutic target for inflammation-induced HCC.

Salmonella Engages Host MicroRNAs To Modulate SUMOylation: a New Arsenal for Intracellular Survival

Posttranslational modifications (PTMs) can alter many fundamental properties of a protein. One or combinations of them have been known to regulate the dynamics of many cellular pathways and consequently regulate all vital processes. Understandably, pathogens have evolved sophisticated strategies to subvert these mechanisms to achieve instantaneous control over host functions. Here, we present the first report of modulation by intestinal pathogen Salmonella enterica serovar Typhimurium (S. Typhimurium) of host SUMOylation, a PTM pathway central to all fundamental cellular processes. Both in cell culture and in a mouse model, we observed that S. Typhimurium infection led to a dynamic SUMO-conjugated proteome alteration. The intracellular survival of S. Typhimurium was dependent on SUMO status as revealed by reduced infection and Salmonella-induced filaments (SIFs) in SUMO-upregulated cells. S. Typhimurium-dependent SUMO modulation was seen as a result of depletion of crucial SUMO pathway enzymes Ubc-9 and PIAS1, at both the protein and the transcript levels. Mechanistically, depletion of Ubc-9 relied on upregulation of small noncoding RNAs miR30c and miR30e during S. Typhimurium infection. This was necessary and sufficient for both down-modulation of Ubc-9 and a successful infection. Thus, we demonstrate a novel strategy of pathogen-mediated perturbation of host SUMOylation, an integral mechanism underlying S. Typhimurium infection and intracellular survival.

Salmonella-infected crypt-derived intestinal organoid culture system for host-bacterial interactions

The in vitro analysis of bacterial-epithelial interactions in the intestine has been hampered by a lack of suitable intestinal epithelium culture systems. Here, we report a new experimental model using an organoid culture system to study pathophysiology of bacterial-epithelial interactions post Salmonella infection. Using crypt-derived mouse intestinal organoids, we were able to visualize the invasiveness of Salmonella and the morphologic changes of the organoids. Importantly, we reported bacteria-induced disruption of epithelial tight junctions in the infected organoids. In addition, we showed the inflammatory responses through activation of the NF-κB pathway in the organoids. Moreover, our western blot, PCR, and immunofluorescence data demonstrated that stem cell markers (Lgr5 and Bmi1) were significantly decreased by Salmonella infection (determined using GFP-labeled Lgr5 organoids). For the first time, we created a model system that recapitulated a number of observations from in vivo studies of the Salmonella-infected intestine, including bacterial invasion, altered tight junctions, inflammatory responses, and decreased stem cells. We have demonstrated that the Salmonella-infected organoid culture system is a new experimental model suitable for studying host-bacterial interactions.

The Wnt/β-catenin signaling pathway controls the inflammatory response in infections caused by pathogenic bacteria

Innate immunity against pathogenic bacteria is critical to protect host cells from invasion and infection as well as to develop an appropriate adaptive immune response. During bacterial infection, different signaling transduction pathways control the expression of a wide range of genes that orchestrate a number of molecular and cellular events to eliminate the invading microorganisms and regulate inflammation. The inflammatory response must be tightly regulated because uncontrolled inflammation may lead to tissue injury. Among the many signaling pathways activated, the canonical Wnt/β-catenin has been recently shown to play an important role in the expression of several inflammatory molecules during bacterial infections. Our main goal in this review is to discuss the mechanism used by several pathogenic bacteria to modulate the inflammatory response through the Wnt/β-catenin signaling pathway. We think that a deep insight into the role of Wnt/β-catenin signaling in the inflammation may open new venues for biotechnological approaches designed to control bacterial infectious diseases.

A Wnt/β-catenin negative feedback loop represses TLR-triggered inflammatory responses in alveolar epithelial cells

Increasing evidence has demonstrated that the epithelial cells in the lung play crucial roles in regulating certain inflammatory responses by modulating Wnt signaling during microbial infection. However, the anti-microbial functions of Wnt signaling in alveolar epithelial cells remain elusive. In this report, we show that Wnt/β-catenin signaling is repressed in A549 alveolar epithelial cells during a Toll-like receptor ligand stimulation with Mycobacterium bovis Bacillus Calmette-Guerin (BCG) or lipopolysaccharide (LPS). In addition to activating TLR signaling, a stimulation of BCG or LPS led to the up-regulation of a Wnt receptor Frizzled-1, cytosolic GSK3β and Axin, and the down-regulation of nuclear β-catenin, lymphoid enhancer factor 1 and transcription factor 4. While an enhancement of β-catenin activity suppressed the TLR signal response, and substantially led to alleviate the TLR ligand-induced pro-inflammatory responses. Importantly, gain and loss of function studies by overexpressing or silencing of TLR signaling adaptor, myeloid differentiation primary response gene 88 (MyD88) further demonstrated an inverse relationship between TLR signaling and canonical Wnt signaling in A549 cells. These data imply that Wnt/β-catenin signaling acts as a negative feedback loop to suppress inflammation in alveolar epithelial cells, and averts cell injury from excessive inflammatory reactions. This study thus reveals a novel immunoregulatory mechanism in alveolar epithelial cells in response to bacterial infection.

Host-microbiota interaction and intestinal stem cells in chronic inflammation and colorectal cancer

Inflammatory bowel disease (IBD) and colorectal cancer (CRC) are the major diseases of the lower gastrointestinal tract. The intestinal epithelium plays a critical role in the host's interactions with the large communities of resident luminal bacteria. Epithelial cells recognize the bacterial components via pattern-recognition receptors. Toll-like receptors (TLRs) are a major class of pattern-recognition receptors that are present on intestinal epithelial cells, including putative stem cells. Stem cells are responsible for tissue homeostasis and regeneration after injury including IBD. Stem cells are also implicated in the pathogenesis of CRC. In susceptible individuals, disruption of normal homeostatic balance between the host's mucosal cells and enteric microflora is believed to result in aberrant immune responses against the resident commensal bacteria, leading to IBD. Microbiological analyses have revealed that the composition and localization of microbiota is altered in CRC and IBD. It is plausible that stem cells directly sense and respond to microbiota. This review aims to summarize the current knowledge on the effect of microbiota and TLR signaling on intestinal stem cells. It also describes how TLR signaling could affect the stem cell regulatory pathways.

β-Catenin promotes host resistance against Pseudomonas aeruginosa keratitis

OBJECTIVE

To explore the role of β-catenin in Pseudomonas aeruginosa (PA) keratitis.

METHODS

Western-blot and immunostaining assay were used to determine the β-catenin protein expression in C57BL/6 (B6) corneas and in in vitro cultured murine cells including macrophage-like RAW264.7 cells, bone marrow-derived neutrophils and A6(1) corneal epithelial cells. B6 mice were subconjunctivally injected with lentivirus expressing active mutant of β-catenin (β-cat-lentivirus) vs appropriate control (Ctl-lentivirus), and then infected with PA. Pro-inflammatory cytokine levels were examined using real-time PCR and ELISA, and bacterial burden was assessed using plate count assays both in vivo and in vitro.

RESULTS

β-Catenin protein expression was decreased in B6 corneas, murine macrophage-like RAW264.7 cells, mouse bone marrow-derived neutrophils and mouse A6(1) corneal epithelial cells after PA infection. Over-expression of β-catenin in B6 corneas significantly reduced the severity of corneal disease after PA infection, by decreasing pro-inflammatory cytokine expression and bacterial burden. In vitro data further demonstrated that over-expression of β-catenin suppressed pro-inflammatory cytokine production but enhanced bacterial clearance in macrophages and neutrophils.

CONCLUSIONS

β-Catenin reduces the severity of PA keratitis by decreasing corneal inflammation and bacterial burden.

Axin expression enhances herpes simplex virus type 1 replication by inhibiting virus-mediated cell death in L929 cells

Herpes simplex virus type 1 (HSV-1) replicates in various cell types and induces early cell death, which limits viral replication in certain cell types. Axin is a scaffolding protein that regulates Wnt signalling and participates in various cellular events, including cellular proliferation and cell death. The effects of axin expression on HSV-1 infection were investigated based on our initial observation that Wnt3a treatment or axin knockdown reduced HSV-1 replication. L929 cells expressed the axin protein in a doxycycline-inducible manner (L-axin) and enhanced HSV-1 replication in comparison to control cells (L-EV). HSV-1 infection induced cell death as early as 6 h after infection through the necrotic pathway and required de novo protein synthesis in L929 cells. Subsequent analysis of viral protein expression suggested that axin expression led to suppression of HSV-1-induced premature cell death, resulting in increased late gene expression. In analysis of axin deletion mutants, the regulators of the G-protein signalling (RGS) domain were involved in the axin-mediated enhancement of viral replication and reduction in cell death. These results suggest that viral replication enhancement might be mediated by the axin RGS domain.