Tubeimosides are pan-coronavirus and filovirus inhibitors that can block their fusion protein binding to Niemann-Pick C1.

SARS-CoV-2 and filovirus enter cells via the cell surface angiotensin-converting enzyme 2 (ACE2) or the late-endosome Niemann-Pick C1 (NPC1) as a receptor. Here, we screened 974 natural compounds and identified Tubeimosides I, II, and III as pan-coronavirus and filovirus entry inhibitors that target NPC1. Using in-silico, biochemical, and genomic approaches, we provide evidence that NPC1 also binds SARS-CoV-2 spike (S) protein on the receptor-binding domain (RBD), which is blocked by Tubeimosides. Importantly, NPC1 strongly promotes productive SARS-CoV-2 entry, which we propose is due to its influence on fusion in late endosomes. The Tubeimosides' antiviral activity and NPC1 function are further confirmed by infection with SARS-CoV-2 variants of concern (VOC), SARS-CoV, and MERS-CoV. Thus, NPC1 is a critical entry co-factor for highly pathogenic human coronaviruses (HCoVs) in the late endosomes, and Tubeimosides hold promise as a new countermeasure for these HCoVs and filoviruses.

IL-27 signaling negatively regulates FcɛRI-mediated mast cell activation and allergic response.

IL-27 is a member of the IL-12 family, exerting both anti- and pro-inflammatory activity in a cell-dependent and disease context-specific manner. Antigen-mediated cross-linking of IgE on mast cells triggers a signaling cascade that results in mast cell degranulation and proinflammatory cytokine production, which are key effectors in allergic reactions. Here, we show that the activation of mast cells is negatively regulated by IL-27 signaling. We found that mice lacking IL-27Rα (WSX-1) displayed increased sensitivity to IgE-mediated skin allergic response and chronic airway inflammation. The bone marrow-derived mast cells (BMMCs) of IL-27Rα-deficient mouse showed greater high-affinity receptor Fc epsilon RI (FcεRI)-mediated activation with significantly enhanced degranulation and cytokine production. Mechanistically, the dysregulated signaling in IL-27Rα-/- mast cells is associated with increased activation of Grb2-PLC-γ1-SLP-76, PI3K/Akt/IκBα signaling and decreased phosphorylation level of SH2 domain-containing protein phosphatase1 (SHP1). Furthermore, IL-27 treatment could inhibit mast cell activation directly, and retrovirus-based IL-27 expression in lung attenuated the airway inflammation in mice. Collectively, our findings reveal that IL-27 signaling negatively regulates mast cell activation and its mediated allergic response.

H7N9 virus infection triggers lethal cytokine storm by activating gasdermin E-mediated pyroptosis of lung alveolar epithelial cells.

The H7N9 influenza virus emerged in China in 2013, causing more than 1560 human infections, 39% of which were fatal. A 'cytokine storm' in the lungs of H7N9 patients has been linked to a poor prognosis and death; however, the underlying mechanism that triggers the cytokine storm is unknown. Here, we found that efficient replication of the H7N9 virus in mouse lungs activates gasdermin E (GSDME)-mediated pyroptosis in alveolar epithelial cells, and that the released cytosolic contents then trigger a cytokine storm. Knockout of Gsdme switched the manner of death of A549 and human primary alveolar epithelial cells from pyroptosis to apoptosis upon H7N9 virus infection, and Gsdme knockout mice survived H7N9 virus lethal infection. Our findings reveal that GSDME activation is a key and unique mechanism for the pulmonary cytokine storm and lethal outcome of H7N9 virus infection and thus opens a new door for the development of antivirals against the H7N9 virus.

Opposite effects of miR-155 in the initial and later stages of lipopolysaccharide (LPS)-induced inflammatory response.

Although microRNA-155 (miR-155) is considered a pro-inflammatory mediator, cumulative evidence indicates that it also has anti-inflammatory effects in macrophages and dendritic cells. In this study, we identified the dramatic expression changes of more than half of potential miR-155-targeted genes upon lipopolysaccharide (LPS) stimulation; 223 genes were down-regulated and 85 genes were up-regulated, including suppressor of cytokine signaling 1 (SOCS1) and transforming growth factor-ß-activated kinase 1-binding protein 2 (TAB2), two well-known genes involved in miR-155-mediated regulation of the Toll-like receptor 4 (TLR4) signaling pathway. We also found that miR-155 acted as an anti-inflammatory mediator in the initial stage of LPS-induced inflammatory response mainly through repressing TAB2 protein translation, and as a pro-inflammatory mediator by down-regulating SOCS1 in the later stage. Meanwhile, overexpression of TAB2 3' untranslated region (UTR) in macrophages promoted the development of endotoxin tolerance by competing for binding with miR-155, which resulted in an elevated expression level of SOCS1 protein. These findings provide new insights for understanding the regulatory mechanisms in fine-tuning of LPS-induced innate immune response.

LRCH1 deficiency enhances LAT signalosome formation and CD8+ T cell responses against tumors and pathogens.

CD8+ T cells play pivotal roles in eradicating pathogens and tumor cells. T cell receptor (TCR) signaling is vital for the optimal activation of CD8+ T cells. Upon TCR engagement, the transmembrane adapter protein LAT (linker for activation of T cells) recruits other key signaling molecules and forms the "LAT signalosome" for downstream signal transduction. However, little is known about which functional partners could restrain the formation of the LAT signalosome and inhibit CD8+ cytotoxic T lymphocyte (CTL)-mediated cytotoxicity. Here we have demonstrated that LRCH1 (leucine-rich repeats and calponin homology domain containing 1) directly binds LAT, reduces LAT phosphorylation and interaction with GRB2, and also promotes the endocytosis of LAT. Lrch1-/- mice display better protection against influenza virus and Listeria infection, with enhanced CD8+ T cell proliferation and cytotoxicity. Adoptive transfer of Lrch1-/- CD8+ CTLs leads to increased B16-MO5 tumor clearance in vivo. Furthermore, knockout of LRCH1 in human chimeric antigen receptor (CAR) T cells that recognize the liver tumor-associated antigen glypican-3 could improve CAR T cell migration and proliferation in vitro. These findings suggest LRCH1 as a potential translational target to improve T cell immunotherapy against infection and tumors.

TRIM35 mediates protection against influenza infection by activating TRAF3 and degrading viral PB2.

Tripartite motif (TRIM) family proteins are important effectors of innate immunity against viral infections. Here we identified TRIM35 as a regulator of TRAF3 activation. Deficiency in or inhibition of TRIM35 suppressed the production of type I interferon (IFN) in response to viral infection. Trim35-deficient mice were more susceptible to influenza A virus (IAV) infection than were wild-type mice. TRIM35 promoted the RIG-I-mediated signaling by catalyzing Lys63-linked polyubiquitination of TRAF3 and the subsequent formation of a signaling complex with VISA and TBK1. IAV PB2 polymerase countered the innate antiviral immune response by impeding the Lys63-linked polyubiquitination and activation of TRAF3. TRIM35 mediated Lys48-linked polyubiquitination and proteasomal degradation of IAV PB2, thereby antagonizing its suppression of TRAF3 activation. Our in vitro and in vivo findings thus reveal novel roles of TRIM35, through catalyzing Lys63- or Lys48-linked polyubiquitination, in RIG-I antiviral immunity and mechanism of defense against IAV infection.

Targeting 7-Dehydrocholesterol Reductase Integrates Cholesterol Metabolism and IRF3 Activation to Eliminate Infection.

Recent work suggests that cholesterol metabolism impacts innate immune responses against infection. However, the key enzymes or the natural products and mechanisms involved are not well elucidated. Here, we have shown that upon DNA and RNA viral infection, macrophages reduced 7-dehydrocholesterol reductase (DHCR7) expression. DHCR7 deficiency or treatment with the natural product 7-dehydrocholesterol (7-DHC) could specifically promote phosphorylation of IRF3 (not TBK1) and enhance type I interferon (IFN-I) production in macrophages. We further elucidated that viral infection or 7-DHC treatment enhanced AKT3 expression and activation. AKT3 directly bound and phosphorylated IRF3 at Ser385, together with TBK1-induced phosphorylation of IRF3 Ser386, to achieve IRF3 dimerization. Deletion of DHCR7 and the DHCR7 inhibitors including AY9944 and the chemotherapy drug tamoxifen promoted clearance of Zika virus and multiple viruses in vitro or in vivo. Taken together, we propose that the DHCR7 inhibitors and 7-DHC are potential therapeutics against emerging or highly pathogenic viruses.

Rapid Evolution of H7N9 Highly Pathogenic Viruses that Emerged in China in 2017.

H7N9 low pathogenic influenza viruses emerged in China in 2013 and mutated to highly pathogenic strains in 2017, resulting in human infections and disease in chickens. To control spread, a bivalent H5/H7 inactivated vaccine was introduced in poultry in September 2017. To monitor virus evolution and vaccine efficacy, we collected 53,884 poultry samples across China from February 2017 to January 2018. We isolated 252 H7N9 low pathogenic viruses, 69 H7N9 highly pathogenic viruses, and one H7N2 highly pathogenic virus, of which two low pathogenic and 14 highly pathogenic strains were collected after vaccine introduction. Genetic analysis of highly pathogenic strains revealed nine genotypes, one of which is predominant and widespread and contains strains exhibiting high virulence in mice. Additionally, some H7N9 and H7N2 viruses carrying duck virus genes are lethal in ducks. Thus, although vaccination reduced H7N9 infections, the increased virulence and expanded host range to ducks pose new challenges.

H7N9 virulent mutants detected in chickens in China pose an increased threat to humans.

Certain low pathogenic avian influenza viruses can mutate to highly pathogenic viruses when they circulate in domestic poultry, at which point they can cause devastating poultry diseases and severe economic damage. The H7N9 influenza viruses that emerged in 2013 in China had caused severe human infections and deaths. However, these viruses were nonlethal in poultry. It is unknown whether the H7N9 viruses can acquire additional mutations during their circulation in nature and become lethal to poultry and more dangerous for humans. Here, we evaluated the evolution of H7N9 viruses isolated from avian species between 2013 and 2017 in China and found 23 different genotypes, 7 of which were detected only in ducks and were genetically distinct from the other 16 genotypes that evolved from the 2013 H7N9 viruses. Importantly, some H7N9 viruses obtained an insertion of four amino acids in their hemagglutinin (HA) cleavage site and were lethal in chickens. The index strain was not lethal in mice or ferrets, but readily obtained the 627K or 701N mutation in its PB2 segment upon replication in ferrets, causing it to become highly lethal in mice and ferrets and to be transmitted efficiently in ferrets by respiratory droplet. H7N9 viruses bearing the HA insertion and PB2 627K mutation have been detected in humans in China. Our study indicates that the new H7N9 mutants are lethal to chickens and pose an increased threat to human health, and thus highlights the need to control and eradicate the H7N9 viruses to prevent a possible pandemic.

E3 ligase FBXW7 is critical for RIG-I stabilization during antiviral responses.

Viruses can escape from host recognition by degradation of RIG-I or interference with the RIG-I signalling to establish persistent infections. However, the mechanisms by which host cells stabilize RIG-I protein for avoiding its degradation are largely unknown. We report here that, upon virus infection, the E3 ubiquitin ligase FBXW7 translocates from the nucleus into the cytoplasm and stabilizes RIG-I. FBXW7 interacts with SHP2 and mediates the degradation and ubiquitination of SHP2, thus disrupting the SHP2/c-Cbl complex, which mediates RIG-I degradation. When infected with VSV or influenza A virus, FBXW7 conditional knockout mice (Lysm+FBXW7f/f) show impaired antiviral immunity. FBXW7-deficient macrophages have decreased RIG-I protein levels and type-I interferon signalling. Furthermore, PBMCs from RSV-infected children have reduced FBXW7 mRNA levels. Our results identify FBXW7 as an important interacting partner for RIG-I. These findings provide insights into the function of FBXW7 in antiviral immunity and its related clinical significance.

Inhibition of ERα/ERK/P62 cascades induces "autophagic switch" in the estrogen receptor-positive breast cancer cells exposed to gemcitabine.

Several clinical trials revealed that estrogen receptor (ER) status had relevance to the response of mammary malignancy to chemotherapy. Autophagy has emerged as an important cellular mechanism of tumor cells in response to anticancer therapy. The aim of this study is to investigate whether gemcitabine induces autophagy, and more importantly, whether such autophagy is functional relevant to the therapeutic effects of gemcitabine in breast cancer cells in relation to the ER status. In our study, autophagy was induced both in ER+ MCF-7 and ER- MDA-MB-231 cells by gemcitabine markedly, while the autophagy plays distinct roles - cytoprotective in ER- MDA-MB-231 and cytotoxic in ER+ MCF-7 cells. Gemcitabine treatment leads to the activation of ERα-ERK-P62 signal pathway in MCF-7 cells which may augment the autophagic degradation, thus results in the excessive activation of autophagy and irreversible autophagic cell death eventually. Inhibition of ERα-ERK-P62 cascades in MCF-7 cells by small interfering RNA or PD98059 impairs the autophagic degradation, and leads to "autophagic switch" - from cytotoxic autophagy to cytoprotection. Moreover, stable overexpression of ERα in the ER- BCap37 breast cancer cell line enhances the gemcitabine-induced autophagy flux and switches the autophagic cytoprotection in ER- BCap37 to cytotoxicity effect in ER+ BCap37 cells. Our study firstly demonstrated that ER status influences gemcitabine efficacy via modulating the autophagy in breast cancer cells.

MicroRNA-223 Promotes Type I Interferon Production in Antiviral Innate Immunity by Targeting Forkhead Box Protein O3 (FOXO3).

Effective recognition of viral infection and subsequent triggering of antiviral innate immune responses are essential for the host antiviral defense, which is tightly regulated by multiple regulators, including microRNAs. Previous reports have shown that some microRNAs are induced during virus infection and participate in the regulation of the innate antiviral response. However, whether the type I IFN response is regulated by miR-223 is still unknown. Here, we reported that vesicular stomatitis virus (VSV) infection induced significant up-regulation of miR-223 in murine macrophages. We observed that miR-223 overexpression up-regulated type I IFN expression levels in VSV-infected macrophages. We also demonstrated that miR-223 directly targets FOXO3 to regulate the type I IFN production. Furthermore, type I IFN, which is triggered by VSV infection, is responsible for the up-regulation of miR-223, thus forming a positive regulatory loop for type I IFN production. Our results uncovered a novel mechanism of miR-223-mediated regulation of type I IFN production in the antiviral innate immunity for the first time.

Interleukin 33 in tumor microenvironment is crucial for the accumulation and function of myeloid-derived suppressor cells.

Tumor-induced, myeloid-derived suppressor cells (MDSCs)-mediated immune dysfunction is an important mechanism that leads to tumor immune escape and the inefficacy of cancer immunotherapy. Importantly, tumor-infiltrating MDSCs have much stronger ability compared to MDSCs in the periphery. However, the mechanisms that tumor microenvironment induces the accumulation and function of MDSCs are poorly understood. Here, we report that Interleukin-33 (IL-33) - a cytokine which can be abundantly released in tumor tissues both in 4T1-bearing mice and breast cancer patients, is crucial for facilitating the expansion of MDSCs. IL-33 in tumor microenvironment reduces the apoptosis and sustains the survival of MDSCs through induction of autocrine secretion of GM-CSF, which forms a positive amplifying loop for MDSC accumulation. This is in conjunction with IL-33-driven induction of arginase-1 expression and activation of NF-κB and MAPK signaling in MDSCs which augments their immunosuppressive ability, and histone modifications were involved in IL-33 signaling in MDSCs. In ST2-/- mice, the defect of IL-33 signaling in MDSCs attenuates the immunosuppressive and pro-tumoral capacity of MDSCs. Our results identify IL-33 as a critical mediator that contributes to the abnormal expansion and enhanced immunosuppressive function of MDSCs within tumor microenvironment, which can be potentially targeted to reverse MDSC-mediated tumor immune evasion.

The cytoprotective role of gemcitabine-induced autophagy associated with apoptosis inhibition in triple-negative MDA-MB-231 breast cancer cells.

Triple-negative breast cancer (TNBC), which is estrogen receptor (ER)-negative, progesterone receptor­negative and is also negative for HER2 expression, remains a great clinical challenge due to its strong resistance to chemotherapy at the late stage of treatment and relatively unfavorable prognosis. Gemcitabine has been approved by the FDA/SFDA for use as a first-line therapeutic drug against advanced or metastatic breast cancer. Therefore, the clarification of the mechanisms underlying gemcitabine-acquired resistance is of particular importance for the optimal management of TNBC. A number of studies have revealed that autophagy, which has been found to protect cancer cells from anti-cancer drug-induced death, may contribute to the development of drug resistance. However, the association between autophagy and gemcitabine treatment in TNBC cells has yet to be defined. Our study clearly demonstrates that gemcitabine is able to induce mTOR-independent autophagy in human triple­negative MDA-MB-231 breast cancer cells. In addition, we demonstrate that autophagy protects MDA-MB-231 cells from gemcitabine-induced cell growth inhibition and apoptosis, indicating that gemcitabine can activate autophagy to impair the sensitivity of MDA-MB­231 cells. Furthermore, as shown by our results, the inhibition of gemcitabine-induced autophagy by chloroquine shifts the expression of the p53 protein, Bcl-2 family proteins and the relative Bax/Bcl-xL ratio in favor of promoting apoptosis. These results reveal that the inhibition of apoptosis may be one of the mechanisms of autophagy-induced cytoprotection in gemcitabine-treated MDA-MB-231 cells. The apoptotic and autophagic processes constitute a mutual inhibition system and jointly seal the fate of TNBC cells that are exposed to gemcitabine. Thus, our study suggests that the combination of an autophagic inhibitor and gemcitabine as a therapeutic strategy may represent a promising approach with greater clinical efficacy for patients with TNBC. However, extended preclinical trials are required to further determine the positive effects of the inhibition of autophagy on the efficacy of gemcitabine.