The Robust Restriction of Zika Virus by Type-I Interferon in A549 Cells Varies by Viral Lineage and Is Not Determined by IFITM3

The Antiviral Potential of AdipoRon, an Adiponectin Receptor Agonist, Reveals the Ability of Zika Virus to Deregulate Adiponectin Receptor Expression

Zika virus (ZIKV) is a pathogenic member of the flavivirus family, with several unique characteristics. Unlike any other arbovirus, ZIKV can be transmitted sexually and maternally, and thus produce congenital syndromes (CZS) due to its neurotropism. This challenges the search for safe active molecules that can protect pregnant women and their fetuses. In this context, and in the absence of any existing treatment, it seemed worthwhile to test whether the known cytoprotective properties of adiponectin and its pharmacological analog, AdipoRon, could influence the outcome of ZIKV infection. We showed that both AdipoRon and adiponectin could significantly reduce the in vitro infection of A549 epithelial cells, a well-known cell model for flavivirus infection studies. This effect was particularly observed when a pre-treatment was carried out. Conversely, ZIKV revealed an ability to downregulate adiponectin receptor expression and thereby limit adiponectin signaling.

Caveats of Using Overexpression Approaches to Screen Cellular Host IFITM Proteins for Antiviral Activity

Ectopic protein overexpression in immortalised cell lines is a commonly used method to screen host factors for their antiviral activity against different viruses. However, the question remains as to what extent such artificial protein overexpression recapitulates endogenous protein function. Previously, we used a doxycycline-inducible overexpression system, in conjunction with approaches to modulate the expression of endogenous protein, to demonstrate the antiviral activity of IFITM1, IFITM2, and IFITM3 against influenza A virus (IAV) but not parainfluenza virus-3 (PIV-3) in A549 cells. We now show that constitutive overexpression of the same IFITM constructs in A549 cells led to a significant restriction of PIV-3 infection by all three IFITM proteins. Variable IFITM mRNA and protein expression levels were detected in A549 cells with constitutive versus inducible overexpression of each IFITM. Our findings show that overexpression approaches can lead to levels of IFITM1, IFITM2, and IFITM3 that significantly exceed those achieved through interferon stimulation of endogenous protein. We propose that exceedingly high levels of overexpressed IFITMs may not accurately reflect the true function of endogenous protein, thus contributing to discrepancies when attributing the antiviral activity of individual IFITM proteins against different viruses. Our findings clearly highlight the caveats associated with overexpression approaches used to screen cellular host proteins for antiviral activity.

Inhibiting cardiac autophagy suppresses Zika virus replication

Zika Virus (ZIKV) infection is a global threat. Other than the congenital neurological disorders it causes, ZIKV infection has been reported to induce cardiac complications. However, the precise treatment plans are unclear. Thus, illustrating the pathogenic mechanism of ZIKV in the heart is critical to providing effective prevention and treatment of ZIKV infection. The mechanism of autophagy has been reported recently in Dengue virus infection. Whether or not autophagy participates in ZIKV infection and its role remains unrevealed. This study successfully established the in vitro cardiomyocytes and in vivo mouse models of ZIKV infection to investigate the involvement of autophagy in ZIKV infection. The results showed that ZIKV infection is both time and gradient-dependent. The key autophagy protein, LC3B, increased remarkably after ZIKV infection. Meanwhile, autophagic flux was detected by immunofluorescence. Applying autophagy inhibitors decreased the LC3B levels. Furthermore, the number of viral copies was quantified to evaluate the influence of autophagy during infection. We found that autophagy was actively involved in the ZIKV infection and the inhibition of autophagy could effectively reduce the viral copies, suggesting a potential intervention strategy for reducing ZIKV infection and the undesired complications caused by ZIKV.

RIG-I and MDA5 are modulated by bone morphogenetic protein (BMP6) and are essential for restricting Zika virus infection in human Sertoli cells

Sexual transmission of Zika virus (ZIKV) is associated with virus persistence in the testes and shedding in the seminal fluid for months after recovery. We previously demonstrated that ZIKV can establish long-term replication without causing cytotoxicity in human Sertoli cells (SC), responsible for maintaining the immune privileged compartment of seminiferous tubules. Functional gene expression analyses also predicted activation of multiple virus sensing pathways including TLR3, RIG-I, and MDA5. Here, we elucidated which of the RNA virus sensing receptors play a decisive role in restricting ZIKV replication. We show that both poly I:C and IFN-β treatment induced a robust antiviral state and reduced ZIKV replication significantly, suggesting that virus sensing and antiviral signaling are functional in SC. Silencing of TLR3, 7, and 9 did not affect virus replication kinetics; however, both RIG-I and MDA5 played a synergistic role in inducing an anti-ZIKV response. Further, the impact of SC-specific immunosuppressive pathways that collectively regulate SC function, specifically the TGF-β superfamily members, TGF-β, Activin A, and BMP6, on ZIKV replication was investigated. While ZIKV did not modulate the expression of TGF-β and Activin A, BMP6 signaling was suppressed at later stages of infection. Notably, treatment with BMP6 increased IFN-β, p-IRF3, and p-STAT1 levels, and expression of key interferon-stimulated genes including MDA5, suggesting that BMP6 enhances antiviral response in SC. Collectively, this study further delineates the key role of the RIG-I-like receptors in sensing ZIKV in SC, and reveals a novel role of BMP6 in modulating innate immune and antiviral response in the testes.

Targeting the EGFR-ERK axis using the compatible solute ectoine to stabilize CFTR mutant F508del

Mutations in the CFTR gene lead to cystic fibrosis, a genetic disease associated with chronic infection and inflammation and ultimately respiratory failure. The most common CF-causing mutation is F508del and CFTR modulators (correctors and potentiators) are being developed to rescue its trafficking and activity defects. However, there are currently no modulators that stabilize the rescued membrane F508del-CFTR which is endocytosed and quickly degraded resulting in a shorter half-life than wild-type (WT). We previously reported that the extracellular signal-regulated kinase (ERK) MAPK pathway is involved in CFTR degradation upon cigarette smoke exposure. Interestingly, we found that ERK phosphorylation was increased in CF human bronchial epithelial (HBE) cells (CF-HBE41o- and primary CF-HBE) compared to non-CF controls, and this was likely due to signaling by the epidermal growth factor receptor (EGFR). EGFR can be activated by several ligands, and we provide evidence that amphiregulin (AREG) is important for activating this signaling axis in CF. The natural osmolyte ectoine stabilizes membrane macromolecules. We show that ectoine decreases ERK phosphorylation, increases the half-life of rescued CFTR, and increases CFTR-mediated chloride transport in combination with the CFTR corrector VX-661. Additionally, ectoine reduces production of AREG and interleukin-8 by CF primary bronchial epithelial cells. In conclusion, EGFR-ERK signaling negatively regulates CFTR and is hyperactive in CF, and targeting this axis with ectoine may prove beneficial for CF patients.

Flaviviruses: Innate Immunity, Inflammasome Activation, Inflammatory Cell Death, and Cytokines

The innate immune system is the host’s first line of defense against the invasion of pathogens including flavivirus. The programmed cell death controlled by genes plays an irreplaceable role in resisting pathogen invasion and preventing pathogen infection. However, the inflammatory cell death, which can trigger the overflow of a large number of pro-inflammatory cytokines and cell contents, will initiate a severe inflammatory response. In this review, we summarized the current understanding of the innate immune response, inflammatory cell death pathway and cytokine secretion regulation during Dengue virus, West Nile virus, Zika virus, Japanese encephalitis virus and other flavivirus infections. We also discussed the impact of these flavivirus and viral proteins on these biological processes. This not only provides a scientific basis for elucidating the pathogenesis of flavivirus, but also lays the foundation for the development of effective antiviral therapies.

Type I interferon receptor (IFNAR2) deficiency reveals Zika virus cytopathicity in human macrophages and microglia

Macrophages are key target cells of Zika virus (ZIKV) infection, implicated as a viral reservoir seeding sanctuary sites such as the central nervous system and testes. This rests on the apparent ability of macrophages to sustain ZIKV replication without experiencing cytopathic effects. ZIKV infection of macrophages triggers an innate immune response involving type I interferons (IFN-I), key antiviral cytokines that play a complex role in ZIKV pathogenesis in animal models. To investigate the functional role of the IFN-I response we generated human induced pluripotent stem cell (iPSC)-derived macrophages from a patient with complete deficiency of IFNAR2, the high affinity IFN-I receptor subunit. Accompanying the profound defect of IFN-I signalling in IFNAR2 deficient iPS-macrophages we observed significantly enhanced ZIKV replication and cell death, revealing the inherent cytopathicity of ZIKV towards macrophages. These observations were recapitulated by genetic and pharmacological ablation of IFN-I signalling in control iPS-macrophages and extended to a model of iPS-microglia. Thus, the capacity of macrophages to support noncytolytic ZIKV replication depends on an equilibrium set by IFN-I, suggesting that innate antiviral responses might counterintuitively promote ZIKV persistence via the maintenance of tissue viral reservoirs relevant to pathogenesis.

Activation of interferon regulatory factor 3 by replication-competent vaccinia viruses improves antitumor efficacy mediated by T cell responses

Recently, oncolytic vaccinia viruses (VACVs) have shown their potential to provide for clinically effective cancer treatments. The reason for this clinical usefulness is not only the direct destruction of infected cancer cells but also activation of immune responses directed against tumor antigens. For eliciting a robust antitumor immunity, a dominant T helper 1 (Th1) cell differentiation of the response is preferred, and such polarization can be achieved by activating the Toll-like receptor 3 (TLR3)-interferon regulatory factor 3 (IRF3) signaling pathway. However, current VACVs used as oncolytic viruses to date still encode several immune evasion proteins involved in the inhibition of this signaling pathway. By inactivating genes of selected regulatory virus proteins, we aimed for a candidate virus with increased potency to activate cellular antitumor immunity but at the same time with a fully maintained replicative capacity in cancer cells. The removal of up to three key genes (C10L, N2L, and C6L) from VACV did not reduce the strength of viral replication, both in vitro and in vivo, but resulted in the rescue of IRF3 phosphorylation upon infection of cancer cells. In syngeneic mouse tumor models, this activation translated to enhanced cytotoxic T lymphocyte (CTL) responses directed against tumor-associated antigens and neo-epitopes and improved antitumor activity.

Organoid modeling of Zika and herpes simplex virus 1 infections reveals virus-specific responses leading to microcephaly

Viral infection in early pregnancy is a major cause of microcephaly. However, how distinct viruses impair human brain development remains poorly understood. Here we use human brain organoids to study the mechanisms underlying microcephaly caused by Zika virus (ZIKV) and herpes simplex virus (HSV-1). We find that both viruses efficiently replicate in brain organoids and attenuate their growth by causing cell death. However, transcriptional profiling reveals that ZIKV and HSV-1 elicit distinct cellular responses and that HSV-1 uniquely impairs neuroepithelial identity. Furthermore, we demonstrate that, although both viruses fail to potently induce the type I interferon system, the organoid defects caused by their infection can be rescued by distinct type I interferons. These phenotypes are not seen in 2D cultures, highlighting the superiority of brain organoids in modeling viral infections. These results uncover virus-specific mechanisms and complex cellular immune defenses associated with virus-induced microcephaly.

IFITM proteins that restrict the early stages of respiratory virus infection do not influence late-stage replication

Interferon-induced transmembrane (IFITM) proteins inhibit a broad range of enveloped viruses by blocking entry into host cells. We used an inducible overexpression system to investigate if IFITM1, IFITM2 and IFITM3 could modulate early and/or late stages of influenza A virus (IAV) or parainfluenza virus (PIV)-3 infection in human A549 airway epithelial cells. IAV and PIV-3 represent respiratory viruses which utilise distinct cellular entry pathways. We verify entry by endocytosis for IAV, whereas PIV-3 infection was consistent with fusion at the plasma membrane. Following induction prior to infection, all three IFITM proteins restricted the percentage of IAV-infected cells at 8 hours post-infection. In contrast, prior induction of IFITM1 and IFITM2 did not inhibit PIV-3 infection, although a modest reduction was observed with IFITM3. siRNA-mediated knockdown of endogenous IFITM1, IFITM2 and IFITM3 expression, in the presence or absence of pre-treatment with type I interferon, resulted in increased IAV, but not PIV-3, infection. This suggests that while all three IFITMs display antiviral activity against IAV, they do not restrict the early stages of PIV-3 infection. IAV and PIV-3 infection culminates in viral egress through budding at the plasma membrane. Inducible expression of IFITM1, IFITM2 or IFITM3 immediately after infection did not impact titres of infectious virus released from IAV or PIV-3 infected cells. Our findings show that IFITM proteins differentially restrict the early stages of infection of two respiratory viruses with distinct cellular entry pathways, but do not influence the late stages of replication for either virus. IMPORTANCE Interferon-induced transmembrane (IFITM) proteins restrict the initial stages of infection for several respiratory viruses, however their potential to modulate the later stages of virus replication has not been explored. In this study we highlight the utility of an inducible overexpression system to assess the impact of IFITM proteins on either early or late stage replication of two respiratory viruses. We demonstrate antiviral activity by IFITM1, IFITM2 and IFITM3 against influenza A virus (IAV) but not parainfluenza virus (PIV)-3 during the early stages of cellular infection. Furthermore, IFITM induction following IAV or PIV-3 infection does not restrict the late stages of replication of either virus. Our findings show that IFITM proteins can differentially restrict the early stages of infection of two viruses with distinct cellular entry pathways, yet do not influence the late stages of replication for either virus.

Novel Nucleoside Analogues as Effective Antiviral Agents for Zika Virus Infections

Previously considered a neglected flavivirus, Zika virus has recently emerged as a public health concern due to its ability to spread rapidly and cause severe neurological disorders, such as microcephaly in newborn babies from infected mothers, and Guillain-Barré syndrome in adults. Despite extensive efforts towards the identification of effective therapies, specific antivirals are still not available. As part of ongoing medicinal chemistry studies to identify new antiviral agents, we screened against Zika virus replication in vitro in a targeted internal library of small-molecule agents, comprising both nucleoside and non-nucleoside agents. Among the compounds evaluated, novel aryloxyphosphoramidate prodrugs of the nucleosides 2′-C-methyl-adenosine, 2-CMA, and 7-deaza-2′C-methyl-adenosine, 7-DMA, were found to significantly inhibit the virus-induced cytopathic effect in multiple relevant cell lines. In addition, one of these prodrugs exhibits a synergistic antiviral effect against Zika virus when applied in combination with an indirect antiviral agent, a l-dideoxy bicyclic pyrimidine nucleoside analogue, which potently inhibits vaccinia and measles viruses in vitro by targeting a host pathway. Our findings provide a solid basis for further development of an antiviral therapy for Zika virus infections, possibly exploiting a dual approach combining two different agents, one targeting the viral polymerase (direct-acting antiviral), the second targeting a host-directed autophagy mechanism.

OIP5-AS1 modulates epigenetic regulator HDAC7 to enhance non-small cell lung cancer metastasis via miR-140-5p

Long non-coding RNAs have been reported to be involved in non-small cell lung cancer (NSCLC) progression. However, whether Opa-interacting protein 5 antisense RNA 1 (OIP5-AS1) serves a role in NSCLC remains unclear. Bioinformatics analysis of The Cancer Genome Atlas datasets showed clinical significance and relevance of OIP5-AS1 in NSCLC. Western blotting and reverse transcription-quantitative PCR revealed protein and RNA expression levels of the genes [including OIP5-AS1, microRNA (miR)-140-5p, histone deacetylase 7 (HDAC7) and vascular endothelial growth factor A (VEGFA)]. Direct associations between the genes (miR-140-5p and OIP5-AS1, or miR-140-5p and HDAC7) were confirmed using a dual-luciferase reporter assay. Lymphatic vessel formation and invasion ability were detected using a lymphatic vessel formation assay and Transwell invasion assay. OIP5-AS1 knockdown attenuated lymphatic vessel length and invasion. The role of OIP5-AS1 was reverted by miR-140-5p. HDAC7 and VEGFA are downstream effectors of miR-140-5p-mediated NSCLC metastasis. OIP5-AS1, miR-140-5p, HDAC7 and VEGFA were all dysregulated in human clinical NSCLC tumor tissues. In conclusion, the present results demonstrated a novel mechanism for OIP5-AS1-induced metastatic phenotypes of NSCLC via the miR-140-5p/HDAC7/VEGFA axis.