Viral manipulation of STAT3: Evade, exploit, and injure

Germline STAT3 gain-of-function mutations in primary immunodeficiency: Impact on the cellular and clinical phenotype

Signal transducer and activator of transcription 3 (STAT3) is a key transcription factor involved in regulation of immune cell activation and differentiation. Recent discoveries highlight the role of germline activating STAT3 mutations in inborn errors of immunity characterized by early-onset multi-organ autoimmunity and lymphoproliferation. Much progress has been made in defining the clinical spectrum of STAT3 GOF disease and unraveling the molecular and cellular mechanisms underlying this disease. In this review, we summarize our current understanding of the disease and discuss the clinical phenotype, diagnostic approach, cellular and molecular effects of STAT3 GOF mutations and therapeutic concepts for these patients.

Viral growth factor- and STAT3 signaling-dependent elevation of the TCA cycle intermediate levels during vaccinia virus infection

Metabolism is a crucial frontier of host-virus interaction as viruses rely on their host cells to provide nutrients and energy for propagation. Vaccinia virus (VACV) is the prototype poxvirus. It makes intensive demands for energy and macromolecules in order to build hundreds and thousands of viral particles in a single cell within hours of infection. Our comprehensive metabolic profiling reveals profound reprogramming of cellular metabolism by VACV infection, including increased levels of the intermediates of the tri-carboxylic acid (TCA) cycle independent of glutaminolysis. By investigating the level of citrate, the first metabolite of the TCA cycle, we demonstrate that the elevation of citrate depends on VACV-encoded viral growth factor (VGF), a viral homolog of cellular epidermal growth factor. Further, the upregulation of citrate is dependent on STAT3 signaling, which is activated non-canonically at the serine727 upon VACV infection. The STAT3 activation is dependent on VGF, and VGF-dependent EGFR and MAPK signaling. Together, our study reveals a novel mechanism by which VACV manipulates cellular metabolism through a specific viral factor and by selectively activating a series of cellular signaling pathways.

Vaccinia virus (VACV) is a large DNA virus with an acute and increasing demand for energy and macromolecules to build hundreds and thousands of viral particles in a single cell within hours of infection. The demand postulates reprogramming of the TCA cycle, as it is the central metabolic hub of a cell that generates metabolites for energy production and macromolecule synthesis. We show that VACV infection reprograms cellular metabolism globally, elevating the TCA cycle intermediate levels and modulating related cell metabolism. The elevation of the TCA cycle intermediates depends on the virus-encoded growth factor that stimulates non-canonical STAT3 signaling during VACV infection. Our results provide the metabolic foundation of viral growth factor to boost VACV infection.

TSLP-Driven Chromatin Remodeling and Trained Systemic Immunity after Neonatal Respiratory Viral Infection

Our studies have previously shown a role for persistent TSLP production in the lungs of mice after early-life respiratory syncytial virus (RSV) infection that leads to an altered immune phenotype, including accumulation of "inflammatory" dendritic cells (DC). This study investigates the role of TSLP driving systemic trained immunity in DC in early-life RSV-infected mice. Bone marrow-derived DCs (BMDC) from early-life RSV-infected mice at 4 wk postinfection showed enhanced expression of costimulatory molecules and cytokines, including Tslp, that regulate immune cell function. The adoptive transfer of BMDC grown from early-life RSV-infected mice was sufficient to exacerbate allergic disease development. The addition of recombinant TSLP during differentiation of BMDC from naive mice induced a similar altered phenotype as BMDC grown from early-life RSV-infected mice, suggesting a role for TSLP in the phenotypic changes. To assess the role of TSLP in these changes, global transcriptomic characterization of TSLPR^-/- BMDC infected with RSV was performed and showed a higher upregulation of type 1 IFN genes and concomitant downregulation of inflammatory genes. Assay for transposase-accessible chromatin using sequencing analysis demonstrated that TSLPR^-/- BMDC had a parallel gain in physical chromatin accessibility near type 1 genes and loss in accessibility near genes related to RSV pathology, with IFN regulatory factor 4 (IRF4) and STAT3 predicted as top transcription factors binding within differentially accessible regions in wild-type. Importantly, these studies show that in the absence of TSLP signaling, BMDC are able to mount an appropriate type 1 IFN-associated antiviral response to RSV. In summary, RSV-induced TSLP alters chromatin structure in DC to drive trained innate immunity and activates pathogenic gene programs in mice.

Napabucasin Reduces Cancer Stem Cell Characteristics in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer. Cancer stem cells (CSCs) are a rare population with self-renewal and multipotent differentiation capacity, and reside among the more differentiated cancer cells. CSCs are associated with tumor recurrence, drug resistance and poor prognosis. The aim of this study was to determine the efficacy of napabucasin against HCC and elucidate the underlying molecular mechanisms. Napabucasin significantly decreased the viability of HCC cells in vitro by inducing apoptosis and cell cycle arrest. In addition, it suppressed CSC-related gene expression and spheroid formation in vitro, indicating depletion of CSCs. The anti-neoplastic effects of napabucasin was also evident in homograft tumor-bearing mouse models. Our findings provide the scientific basis of conducting clinical trials on napabucasin as a new therapeutic agent against HCC.

Inhibitors of the Transcription Factor STAT3 Decrease Growth and Induce Immune Response Genes in Models of Malignant Pleural Mesothelioma (MPM)

Simple Summary

Malignant pleural mesothelioma (MPM) is characterized by the lack of effective long-term treatments and highly prevalent drug resistance. The paucity of potential therapeutic targets has led to dismal prognosis. We have examined the functional role of the signal transducer and activator of transcription 3 (STAT3) transcription factor in MPM. Even though highly specific STAT3 inhibitors have not yet come to fruition, we performed experiments targeting STAT3 expression and subsequently supported these experiments with small molecule drugs that were previously validated to target STAT3-dependent activation mechanisms. These drugs are United States Food and Drug Administration (FDA)-approved and showed efficacy in preclinical models of MPM at concentrations that can safely be achieved in humans. We also identified genes that strongly support the essential role of STAT3 in cell growth and are consistent with a role of STAT3 in immune suppression. Overall, the results establish a central role for STAT3 in tumor growth and encourage further expedient development of STAT3 pathway inhibitors for clinical use.

Abstract

Malignant pleural mesothelioma (MPM) is an aggressive cancer defined by loss-of-function mutations with few therapeutic options. We examined the contribution of the transcription factor Signal transducer and activator of transcription 3 (STAT3) to cell growth and gene expression in preclinical models of MPM. STAT3 is activated in a variety of tumors and is thought to be required for the maintenance of cancer stem cells. Targeting STAT3 using specific small hairpin RNAs (shRNAs) or with the pharmacologic inhibitors atovaquone or pyrimethamine efficiently reduced cell growth in established cell lines and primary-derived lines while showing minimal effects in nontransformed LP9 mesothelial cells. Moreover, atovaquone significantly reduced viability and tumor growth in microfluidic cultures of primary MPM as well as in an in vivo xenotransplant model. Biological changes were linked to modulation of gene expression associated with STAT3 signaling, including cell cycle progression and altered p53 response. Reflecting the role of STAT3 in inducing localized immune suppression, using both atovaquone and pyrimethamine resulted in the modulation of immunoregulatory genes predicted to enhance an immune response, including upregulation of ICOSLG (Inducible T-Cell Costimulator Ligand or B7H2). Thus, our data strongly support a role for STAT3 inhibitors as anti-MPM therapeutics.

A Chemographic Audit of anti-Coronavirus Structure-activity Information from Public Databases (ChEMBL)

Discovery of drugs against newly emerged pathogenic agents like the SARS-CoV-2 coronavirus (CoV) must be based on previous research against related species. Scientists need to get acquainted with and develop a global oversight over so-far tested molecules. Chemography (herein used Generative Topographic Mapping, in particular) places structures on a human-readable 2D map (obtained by dimensionality reduction of the chemical space of molecular descriptors) and is thus well suited for such an audit. The goal is to map medicinal chemistry efforts so far targeted against CoVs. This includes comparing libraries tested against various virus species/genera, predicting their polypharmacological profiles and highlighting often encountered chemotypes. Maps are challenged to provide predictive activity landscapes against viral proteins. Definition of "anti-CoV" map zones led to selection of therein residing 380 potential anti-CoV agents, out of a vast pool of 800 M organic compounds.

The cross-talk between STAT1/STAT3 and ROS up-regulates PD-L1 and promotes the release of pro-inflammatory/immune suppressive cytokines in primary monocytes infected by HHV-6B

Programmed death ligand 1 (PD-L1) up-regulation on antigen presenting cells induces T cell dysfunction, strongly impairing immune response. Human Herpesviruses (HHV) 6B is a β-herpesvirus that, although displays a higher tropism for T cells, can infect other immune cells including monocytes and dendritic cells (DCs) and neuronal cells. We have previously shown that HHV-6B infection of primary monocytes reduced autophagy and induced Endoplasmic Reticulum (ER) stress/ Unfolded Protein Response (UPR), impairing their survival and differentiation into DCs. In this study, we found that PD-L1 expression was up-regulated by HHV-6B on the surface of infected monocytes and that its extracellular release also increased, effects known to lead to an impairment of anti-viral immune response. At molecular level, PD-L1 up-regulation correlated with the activation of a positive regulatory circuit between the increase of intracellular ROS and the activation of STAT1 and STAT3 induced by HHV-6B, accompanied by a high release of pro-inflammatory/immune suppressive cytokines. In conclusion, this study unveils new strategies put in place by HHV-6B to induce immune dysfunction and the underlying molecular pathways that could be targeted to counteract such immune suppressive effects.

Lymphotropic Viruses: Chronic Inflammation and Induction of Cancers

Inflammation induced by transcription factors, including Signal Transducers and Activators of Transcription (STATs) and NF-κB, in response to microbial pathogenic infections and ligand dependent receptors stimulation are critical for controlling infections. However, uncontrolled inflammation induced by these transcription factors could lead to immune dysfunction, persistent infection, inflammatory related diseases and the development of cancers. Although the induction of innate immunity and inflammation in response to viral infection is important to control virus replication, its effects can be modulated by lymphotropic viruses including human T-cell leukemia virus type 1 (HTLV-1), Κaposi's sarcoma herpesvirus (KSHV), and Epstein Barr virus (EBV) during de novo infection as well as latent infection. These lymphotropic viruses persistently activate JAK-STAT and NF-κB pathways. Long-term STAT and NF-κB activation by these viruses leads to the induction of chronic inflammation, which can support the persistence of these viruses and promote virus-mediated cancers. Here, we review how HTLV-1, KSHV and EBV hijack the function of host cell surface molecules (CSMs), which are involved in the regulation of chronic inflammation, innate and adaptive immune responses, cell death and the restoration of tissue homeostasis. Thus, better understanding of CSMs-mediated chronic activation of STATs and NF-κB pathways in lymphotropic virus-infected cells may pave the way for therapeutic intervention in malignancies caused by lymphotropic viruses.

The Dynamic Interface of Viruses with STATs

Viruses commonly antagonize the antiviral type I interferon response by targeting signal transducer and activator of transcription 1 (STAT1) and STAT2, key mediators of interferon signaling. Other STAT family members mediate signaling by diverse cytokines important to infection, but their relationship with viruses is more complex. Importantly, virus-STAT interaction can be antagonistic or stimulatory depending on diverse viral and cellular factors. While STAT antagonism can suppress immune pathways, many viruses promote activation of specific STATs to support viral gene expression and/or produce cellular conditions conducive to infection. It is also becoming increasingly clear that viruses can hijack noncanonical STAT functions to benefit infection. For a number of viruses, STAT function is dynamically modulated through infection as requirements for replication change. Given the critical role of STATs in infection by diverse viruses, the virus-STAT interface is an attractive target for the development of antivirals and live-attenuated viral vaccines. Here, we review current understanding of the complex and dynamic virus-STAT interface and discuss how this relationship might be harnessed for medical applications.

Role of the JAK/STAT Pathway in Cervical Cancer: Its Relationship with HPV E6/E7 Oncoproteins

The janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling pathway is associated with the regulation of essential cellular mechanisms, such as proliferation, invasion, survival, inflammation, and immunity. Aberrant JAK/STAT signaling contributes to cancer progression and metastatic development. STAT proteins play an essential role in the development of cervical cancer, and the inhibition of the JAK/STAT pathway may be essential for enhancing tumor cell death. Persistent activation of different STATs is present in a variety of cancers, including cervical cancer, and their overactivation may be associated with a poor prognosis and poor overall survival. The oncoproteins E6 and E7 play a critical role in the progression of cervical cancer and may mediate the activation of the JAK/STAT pathway. Inhibition of STAT proteins appears to show promise for establishing new targets in cancer treatment. The present review summarizes the knowledge about the participation of the different components of the JAK/STAT pathway and the participation of the human papillomavirus (HPV) associated with the process of cellular malignancy.

In Vitro and In Vivo Antiviral Activity of Gingerenone A on Influenza A Virus Is Mediated by Targeting Janus Kinase 2

Janus kinase (JAK) inhibitors have been developed as novel immunomodulatory drugs and primarily used for treating rheumatoid arthritis and other inflammatory diseases. Recent studies have suggested that this category of anti-inflammatory drugs could be potentially useful for the control of inflammation "storms" in respiratory virus infections. In addition to their role in regulating immune cell functions, JAK1 and JAK2 have been recently identified as crucial cellular factors involved in influenza A virus (IAV) replication and could be potentially targeted for antiviral therapy. Gingerenone A (Gin A) is a compound derived from ginger roots and a dual inhibitor of JAK2 and p70 S6 kinase (S6K1). Our present study aimed to determine the antiviral activity of Gin A on influenza A virus (IAV) and to understand its mechanisms of action. Here, we reported that Gin A suppressed the replication of three IAV subtypes (H1N1, H5N1, H9N2) in four cell lines. IAV replication was also inhibited by Ruxolitinib (Rux), a JAK inhibitor, but not by PF-4708671, an S6K1 inhibitor. JAK2 overexpression enhanced H5N1 virus replication and attenuated Gin A-mediated antiviral activity. In vivo experiments revealed that Gin A treatment suppressed IAV replication in the lungs of H5N1 virus-infected mice, alleviated their body weight loss, and prolonged their survival. Our study suggests that Gin A restricts IAV replication by inhibiting JAK2 activity; Gin A could be potentially useful for the control of influenza virus infections.

Lyssavirus P-protein selectively targets STAT3-STAT1 heterodimers to modulate cytokine signalling

Many viruses target signal transducer and activator of transcription (STAT) 1 to antagonise antiviral interferon signalling, but targeting of STAT3, a pleiotropic molecule that mediates signalling by diverse cytokines, is poorly understood. Here, using lyssavirus infection, quantitative live cell imaging, innate immune signalling and protein interaction assays, and complementation/depletion of STAT expression, we show that STAT3 antagonism is conserved among P-proteins of diverse pathogenic lyssaviruses and correlates with pathogenesis. Importantly, P-protein targeting of STAT3 involves a highly selective mechanism whereby P-protein antagonises cytokine-activated STAT3-STAT1 heterodimers, but not STAT3 homodimers. RT-qPCR and reporter gene assays indicate that this results in specific modulation of interleukin-6-dependent pathways, effecting differential antagonism of target genes. These data provide novel insights into mechanisms by which viruses can modulate cellular function to support infection through discriminatory targeting of immune signalling complexes. The findings also highlight the potential application of selective interferon-antagonists as tools to delineate signalling by particular STAT complexes, significant not only to pathogen-host interactions but also cell physiology, development and cancer.

HSV-1 Modulates IL-6 Receptor Expression on Human Dendritic Cells

Dendritic cells (DCs) are the guardians of the immune system since they are located in the majority of peripheral tissues. In addition, they are crucial for the induction of an effective immune response based on their unique capacity to stimulate naive T cells. During co-evolution, the human pathogen herpes simplex virus type 1 (HSV-1) has evolved several immune evasion mechanisms in order to subvert the host's immune system especially by targeting DC biology and function. Here we demonstrate that HSV-1 infection influences the IL-6 receptor (IL6R) expression both on protein and mRNA levels in/on human monocyte-derived mature DCs (mDCs). Surprisingly, reduced IL6R expression levels were also observed on uninfected bystander mDCs. Mechanistically, we clearly show that HSV-1-derived non-infectious light (L-) particles are sufficient to trigger IL6R regulation on uninfected bystander mDCs. These L-particles lack the viral DNA-loaded capsid and are predominantly produced during infection of mDCs. Our results show that the deletion of the HSV-1 tegument protein vhs partially rescued the reduced IL6R surface expression levels on/in bystander mDCs. Using a neutralizing antibody, which perturbs the transfer of L-particles to bystander mDCs, was sufficient to rescue the modulation of IL6R surface expression on uninfected bystander mDCs. This study provides evidence that L-particles transfer specific viral proteins to uninfected bystander mDCs, thereby negatively interfering with their IL6R expression levels, however, to a lesser extend compared to H-particles. Due to their immune-modulatory capacity, L-particles represent an elaborated approach of HSV-1-mediated immune evasion.

Luteolin ameliorates experimental colitis in mice through ERK-mediated suppression of inflammation, apoptosis and autophagy

Ulcerative colitis (UC) is a chronic inflammatory disease with increasing incidence and prevalence worldwide. Currently used treatments of UC are unsatisfactory, while natural bioactive compounds are considered to be emerging therapeutic agents. Luteolin (Lut) is a natural compound with beneficial effects in a variety of diseases, however, its effect in UC has been poorly studied. In this study we investigated the effect of Lut in posttreatment and cotreatment of dextran sulfate sodium (DSS)-induced experimental colitis in mice. In addition, the role of extracellular signal-regulated kinases 1/2 (ERK1/2) in the mechanism of action of Lut in experimental colitis was investigated using the ERK inhibitor PD0325901. Lut attenuated symptoms of DSS-induced colitis in mice, ameliorated colon tissue damage and reduced inflammation, apoptosis and autophagy. The effect was more pronounced if Lut was administered simultaneously with DSS. The administration of ERK inhibitor exacerbated DSS-induced colitis symptoms and prevented the protective effects of Lut. The results provide new mechanistic details underlying the anti-inflammatory, anti-apoptotic and anti-autophagic effects of Lut through the activation of the ERK signaling pathway. This suggested that Lut can be used as a novel therapeutic candidate in the treatment of UC or could be used as a supplement to existing therapy.

Inhibition of porcine epidemic diarrhea virus (PEDV) replication by A77 1726 through targeting JAK and Src tyrosine kinases

Porcine epidemic diarrhea (PED) virus (PEDV) is a coronavirus that primarily infects porcine intestinal epithelial cells and causes severe diarrhea and high fatality in piglets. A77 1726 is the active metabolite of leflunomide, a clinically approved anti-rheumatoid arthritis (RA) drug. A77 1726 inhibits the activity of protein tyrosine kinases (PTKs), p70 S6 kinase (S6K1), and dihydroorotate dehydrogenase (DHO-DHase). Whether A77 1726 can control coronavirus infections has not been investigated. Here we report that A77 1726 effectively restricted PEDV replication by inhibiting Janus kinases (JAKs) and Src kinase activities but not by inhibiting DHO-DHase and S6K1 activities. Overexpression of Src, JAK2 or its substrate STAT3 enhanced PEDV replication and attenuated the antiviral activity of A77 1726. Our study demonstrates for the first time the ability of A77 1726 to control coronavirus replication by inhibiting PTK activities. Leflunomide has potential therapeutic value for the control of PEDV and other coronavirus infections.

Silibinin and SARS-CoV-2: Dual Targeting of Host Cytokine Storm and Virus Replication Machinery for Clinical Management of COVID-19 Patients

COVID-19, the illness caused by infection with the novel coronavirus SARS-CoV-2, is a rapidly spreading global pandemic in urgent need of effective treatments. Here we present a comprehensive examination of the host- and virus-targeted functions of the flavonolignan silibinin, a potential drug candidate against COVID-19/SARS-CoV-2. As a direct inhibitor of STAT3—a master checkpoint regulator of inflammatory cytokine signaling and immune response—silibinin might be expected to phenotypically integrate the mechanisms of action of IL-6-targeted monoclonal antibodies and pan-JAK1/2 inhibitors to limit the cytokine storm and T-cell lymphopenia in the clinical setting of severe COVID-19. As a computationally predicted, remdesivir-like inhibitor of RNA-dependent RNA polymerase (RdRp)—the central component of the replication/transcription machinery of SARS-CoV-2—silibinin is expected to reduce viral load and impede delayed interferon responses. The dual ability of silibinin to target both the host cytokine storm and the virus replication machinery provides a strong rationale for the clinical testing of silibinin against the COVID-19 global public health emergency. A randomized, open-label, phase II multicentric clinical trial (SIL-COVID19) will evaluate the therapeutic efficacy of silibinin in the prevention of acute respiratory distress syndrome in moderate-to-severe COVID-19-positive onco-hematological patients at the Catalan Institute of Oncology in Catalonia, Spain.

Hepatitis C Virus and Hepatocellular Carcinoma: When the Host Loses Its Grip

Chronic infection with hepatitis C virus (HCV) is a major cause of hepatocellular carcinoma (HCC). Novel treatments with direct-acting antivirals achieve high rates of sustained virologic response; however, the HCC risk remains elevated in cured patients, especially those with advanced liver disease. Long-term HCV infection causes a persistent and accumulating damage of the liver due to a combination of direct and indirect pro-oncogenic mechanisms. This review describes the processes involved in virus-induced disease progression by viral proteins, derailed signaling, immunity, and persistent epigenetic deregulation, which may be instrumental to develop urgently needed prognostic biomarkers and as targets for novel chemopreventive therapies.

Regulation of Autophagy in Cells Infected With Oncogenic Human Viruses and Its Impact on Cancer Development

About 20% of total cancer cases are associated to infections. To date, seven human viruses have been directly linked to cancer development: high-risk human papillomaviruses (hrHPVs), Merkel cell polyomavirus (MCPyV), hepatitis B virus (HBV), hepatitis C virus (HCV), Epstein–Barr virus (EBV), Kaposi’s sarcoma-associated herpesvirus (KSHV), and human T-lymphotropic virus 1 (HTLV-1). These viruses impact on several molecular mechanisms in the host cells, often resulting in chronic inflammation, uncontrolled proliferation, and cell death inhibition, and mechanisms, which favor viral life cycle but may indirectly promote tumorigenesis. Recently, the ability of oncogenic viruses to alter autophagy, a catabolic process activated during the innate immune response to infections, is emerging as a key event for the onset of human cancers. Here, we summarize the current understanding of the molecular mechanisms by which human oncogenic viruses regulate autophagy and how this negative regulation impacts on cancer development. Finally, we highlight novel autophagy-related candidates for the treatment of virus-related cancers.

A Bartonella Effector Acts as Signaling Hub for Intrinsic STAT3 Activation to Trigger Anti-inflammatory Responses

Chronically infecting pathogens avoid clearance by the innate immune system by promoting premature transition from an initial pro-inflammatory response toward an anti-inflammatory tissue-repair response. STAT3, a central regulator of inflammation, controls this transition and thus is targeted by numerous chronic pathogens. Here, we show that BepD, an effector of the chronic bacterial pathogen Bartonella henselae targeted to infected host cells, establishes an exceptional pathway for canonical STAT3 activation, thereby impairing secretion of pro-inflammatory TNF-α and stimulating secretion of anti-inflammatory IL-10. Tyrosine phosphorylation of EPIYA-related motifs in BepD facilitates STAT3 binding and activation via c-Abl-dependent phosphorylation of Y₇₀₅. The tyrosine-phosphorylated scaffold of BepD thus represents a signaling hub for intrinsic STAT3 activation that is independent from canonical STAT3 activation via transmembrane receptor-associated Janus kinases. We anticipate that our findings on a molecular shortcut to STAT3 activation will inspire new treatment options for chronic infections and inflammatory diseases.

STAT3: A Potential Drug Target for Tumor and Inflammation

STAT (Signal Transducers and Activators of Transcription) is a cellular signal transcription factor involved in the regulation of many cellular activities, such as cell differentiation, proliferation, angiogenesis in normal cells. During the study of the STAT family, STAT3 was found to be involved in many diseases, such as high expression and sustained activation of STAT3 in tumor cells, promoting tumor growth and proliferation. In the study of inflammation, it was found that it plays an important role in the anti-inflammatory and repairing of damage tissues. Because of the important role of STAT3, a large number of studies have been obtained. At the same time, after more than 20 years of development, STAT3 has also been used as a target for drug therapy. And the discovery of small molecule inhibitors also promoted the study of STAT3. Since STAT3 has been extensively studied in inflammation and tumor regulation, this review presents the current state of research on STAT3.

STAT3 Regulates the Type I IFN-Mediated Antiviral Response by Interfering with the Nuclear Entry of STAT1

Signal transducer and activator of transcription 3 (STAT3) is a multifunctional factor that regulates inflammation and immunity. Knowledge of its regulatory mechanisms is very limited. Here, we showed that enterovirus 71 (EV71) infection induced the phosphorylation of STAT3 and the expression of its downstream inflammatory regulators. Knockdown of STAT3 with siRNAs significantly restricted viral RNA and protein levels, and also reduced viral titers. With further investigation, we found that importin α family member Karyopherin-α1 (KPNA1) was employed by both STAT1 and STAT3 for their nuclear import. The phosphorylated and un-phosphorylated STAT3 competed with STAT1 for binding to the decreased KPNA1 post infection and repressed downstream ISG expression. STAT3 knockdown alleviated the repressed type I IFN-mediated antiviral response upon infection and led to decreased viral replication. Taken together, our data suggested the role of STAT3 in maintaining the balance of inflammation and antiviral responses in the central nervous system (CNS) upon infection.

Chikungunya virus modulates the miRNA expression patterns in human synovial fibroblasts

Chikungunya virus (CHIKV) is an alphavirus transmitted by mosquitoes. CHIKV infection leads to polyarthritis and polyarthralgia among patients. The synovial fibroblasts are the primary target for CHIKV. The microRNAs (miRNAs) are the small endogenous noncoding RNAs which posttranscriptionally regulate the expression of genes by binding to their target messenger RNAs (mRNAs) through their 3'-untranslated regions. The miRNAs are the key regulators for various pathological processes including viral infection, cancer, cardiovascular disease, and neurodegeneration. This study was designed to dissect out the roles of miRNAs during CHIKV (Ross Strain E1: A226V) infection in primary human synovial fibroblasts. The miRNA microarray profiling was performed on the primary human synovial fibroblasts infected by CHIKV. The gene target prediction analysis, enrichment, and network analysis were performed by various bioinformatics analyses. The subset of 26 differentially expressed microRNAs (DEMs) were identified through microarray profiling and were further screened for gene predictions, Gene Ontology, pathway enrichment, and miRNA-mRNA network using various bioinformatics tools. The bioinformatics analysis indicates the role of DEMs by suppressing the immune response which may contribute to CHIKV persistence in human primary synovial fibroblasts. Our study provides the plausible roles of DEMs, miRNAs, and mRNA interactions and pathways involved in the molecular pathogenesis of CHIKV.

High expression of calreticulin indicates poor prognosis and modulates cell migration and invasion via activating Stat3 in nasopharyngeal carcinoma

Objective: Emerging evidence suggests that calreticulin (CALR) has great impacts on the tumor formation and progression of various cancers, but the role of CALR remains controversial. We investigated the expression and clinical significance of CALR in nasopharyngeal carcinoma (NPC). Methods: Immunohistochemistry was used to detect the expression of CALR in NPC tissues, and the correlation of CALR with clinicopathological characteristics and prognosis were analyzed. The cell functions of CALR in NPC cells were also performed in vitro. Results: Compared with non-tumor nasopharyngeal epithelium (NPE) tissues, CALR expression was markedly up-regulated in NPC tissues (P < 0.001), and the high expression of CALR was positively associated with advanced clinical stage (P=0.003) and metastasis (P=0.023). Compared to the patients with low expression of CALR, patients who displayed high expression of CALR may achieve a poorer progression-free survival (PFS) and overall survival (OS) (P < 0.001). Furthermore, multivariate analysis showed that high expression of CALR was an independent predictor of poor prognosis. In addition, we found that knockdown of CALR significantly inhibited the proliferation, migration and invasion of CNE2 and HONE1 cells in vitro, and the mechanism might be associated with inactivation of Stat3 signaling pathway. Conclusion: CALR may promote NPC progression and metastasis via involving Stat3 signaling pathway, and can be regarded as an effective potential predictor for progression and prognosis of NPC.

Pentagalloylglucose Inhibits the Replication of Rabies Virus via Mediation of the miR-455/SOCS3/STAT3/IL-6 Pathway

Our previous study showed that pentagalloylglucose (PGG), a naturally occurring hydrolyzable phenolic tannin, possesses significant anti-rabies virus (RABV) activity. In BHK-21 cells, RABV induced the overactivation of signal transducer and activator of transcription 3 (STAT3) by suppressing the expression of suppressor of cytokine signaling 3 (SOCS3). Inhibition of STAT3 by niclosamide, small interfering RNA, or exogenous expression of SOCS3 all significantly suppressed the replication of RABV. Additionally, RABV-induced upregulation of microRNA 455-5p (miR-455-5p) downregulated SOCS3 by directly binding to the 3' untranslated region (UTR) of SOCS3. Importantly, PGG effectively reversed the expression of miR-455-5p and its following SOCS3/STAT3 signaling pathway. Finally, activated STAT3 elicited the expression of interleukin-6 (IL-6), thereby contributing to RABV-associated encephalomyelitis; however, PGG restored the level of IL-6 in vitro and in vivo in a SOCS3/STAT3-dependent manner. Altogether, these data identify a new miR-455-5p/SOCS3/STAT3 signaling pathway that contributes to viral replication and IL-6 production in RABV-infected cells, with PGG exerting its antiviral effect by inhibiting the production of miR-455-5p and the activation of STAT3.IMPORTANCE Rabies virus causes lethal encephalitis in mammals and poses a serious public health threat in many parts of the world. Numerous strategies have been explored to combat rabies; however, their efficacy has always been unsatisfactory. We previously reported a new drug, PGG, which possesses a potent inhibitory activity on RABV replication. Herein, we describe the underlying mechanisms by which PGG exerts its anti-RABV activity. Our results show that RABV induces overactivation of STAT3 in BHK-21 cells, which facilitates viral replication. Importantly, PGG effectively inhibits the activity of STAT3 by disrupting the expression of miR-455-5p and increases the level of SOCS3 by directly targeting the 3' UTR of SOCS3. Furthermore, the downregulated STAT3 inhibits the production of IL-6, thereby contributing to a reduction in the inflammatory response in vivo Our study indicates that PGG effectively inhibits the replication of RABV by the miR-455-5p/SOCS3/STAT3/IL-6-dependent pathway.

Fine-Tuning of Type I Interferon Response by STAT3

Type I interferon (IFN-I) is induced during innate immune response and is required for initiating antiviral activity, growth inhibition, and immunomodulation. STAT1, STAT2, and STAT3 are activated in response to IFN-I stimulation. STAT1, STAT2, and IRF9 form ISGF3 complex which transactivates downstream IFN-stimulated genes and mediates antiviral response. However, the role of STAT3 remains to be characterized. Here, we review the multiple actions of STAT3 on suppressing IFN-I responses, including blocking IFN-I signaling, downregulating the expression of ISGF3 components, and antagonizing the transcriptional activity of ISGF3. Finally, we discuss the evolution of the suppressive activity of STAT3 and the therapeutic potential of STAT3 inhibitors in host defense against viral infections and IFN-I-associated diseases.

Autocrine STAT3 activation in HPV positive cervical cancer through a virus-driven Rac1-NFκB-IL-6 signalling axis

Persistent human papillomavirus (HPV) infection is the leading cause of cervical cancer. Although the fundamental link between HPV infection and oncogenesis is established, the specific mechanisms of virus-mediated transformation are not fully understood. We previously demonstrated that the HPV encoded E6 protein increases the activity of the proto-oncogenic transcription factor STAT3 in primary human keratinocytes; however, the molecular basis for STAT3 activation in cervical cancer remains unclear. Here, we show that STAT3 phosphorylation in HPV positive cervical cancer cells is mediated primarily via autocrine activation by the pro-inflammatory cytokine Interleukin 6 (IL-6). Antibody-mediated blockade of IL-6 signalling in HPV positive cells inhibits STAT3 phosphorylation, whereas both recombinant IL-6 and conditioned media from HPV positive cells leads to increased STAT3 phosphorylation within HPV negative cervical cancer cells. Interestingly, we demonstrate that activation of the transcription factor NFκB, involving the small GTPase Rac1, is required for IL-6 production and subsequent STAT3 activation. Our data provides new insights into the molecular re-wiring of cancer cells by HPV E6. We reveal that activation of an IL-6 signalling axis drives the autocrine and paracrine phosphorylation of STAT3 within HPV positive cervical cancers cells and that activation of this pathway is essential for cervical cancer cell proliferation and survival. Greater understanding of this pathway provides a potential opportunity for the use of existing clinically approved drugs for the treatment of HPV-mediated cervical cancer.

Zika Virus Infection Disrupts Astrocytic Proteins Involved in Synapse Control and Axon Guidance

The first human Zika virus (ZIKV) outbreak was reported in Micronesia in 2007, followed by one in Brazil in 2015. Recent studies have reported cases in Europe, Oceania and Latin America. In 2016, ZIKV transmission was also reported in the US and the World Health Organization declared it a Public Health Emergency of International Concern. Because various neurological conditions are associated with ZIKV, such as microcephaly, Guillain-Barré syndrome, and other disorders of both the central and peripheral nervous systems, including encephalopathy, (meningo)encephalitis and myelitis, and because of the lack of reliable patient diagnosis, numerous ongoing studies seek to understand molecular mechanisms underlying ZIKV pathogenesis. Astrocytes are one of the most abundant cells in the CNS. They control axonal guidance, synaptic signaling, neurotransmitter trafficking and maintenance of neurons, and are targeted by ZIKV. In this study, we used a newly developed multiplexed aptamer-based technique (SOMAScan) to examine > 1300 human astrocyte cell proteins. We identified almost 300 astrocyte proteins significantly dysregulated by ZIKV infection that span diverse functions and signaling pathways, including protein translation, synaptic control, cell migration and differentiation.

PLCε promotes urinary bladder cancer cells proliferation through STAT3/LDHA pathway‑mediated glycolysis

Phospholipase Cε (PLCε) and anaerobic glycolysis were determined to be involved in the development of human urinary bladder cancer (UBC), but the mechanisms remain unclear. In the present study, 64 bladder cancer specimens and 42 adjacent tissue specimens were obtained from 64 patients, and immunochemistry indicated that PLCε and lactate dehydrogenase (LDHA) are overexpressed in UBC. PLCε and LDHA were demonstrated to be positively correlated at transcription levels, indicating that one of these two genes may be regulated by another. To elucidate the mechanisms, PLCε was knocked down in T24 cells by short hairpin RNA, and then signal transducer and activator of transcription 3 (STAT3) phosphorylation and LDHA were determined to be downregulated, which indicated that PLCε may serve roles upstream of LDHA through STAT3 to regulate glycolysis in UBC. Furthermore, chromatin immunoprecipitation and luciferase reporter assays were performed to confirm that STAT3 could bind to the promoter of the LDHA gene to enhance its expression. A xenograft tumor mouse model also demonstrated similar results as the in vitro experiments, further confirming the role of PLCε in regulating bladder cell growth in vivo. Collectively, the present study demonstrated that PLCε may regulate glycolysis through the STAT3/LDHA pathway to take part in the development of human UBC.

Dissecting clinical outcome of porcine circovirus type 2 with in vivo derived transcriptomic signatures of host tissue responses

Background

Porcine Circovirus Type 2 (PCV2) is a pathogen that has the ability to cause often devastating disease manifestations in pig populations with major economic implications. How PCV2 establishes subclinical persistence and why certain individuals progress to lethal lymphoid depletion remain to be elucidated.

Results

Here we present PorSignDB, a gene signature database describing in vivo porcine tissue physiology that we generated from a large compendium of in vivo transcriptional profiles and that we subsequently leveraged for deciphering the distinct physiological states underlying PCV2-affected lymph nodes. This systems genomics approach indicated that subclinical PCV2 infections suppress a myeloid leukocyte mediated immune response. However, in contrast an inflammatory myeloid cell activation is promoted in PCV2 patients with clinical manifestations. Functional genomics further uncovered STAT3 as a druggable PCV2 host factor candidate. Moreover, IL-2 supplementation of primary lymphocytes enabled ex vivo study of PCV2 replication in its target cell, the lymphoblast.

Conclusion

Our systematic dissection of the mechanistic basis of PCV2 reveals that subclinical and clinical PCV2 display two diametrically opposed immunotranscriptomic recalibrations that represent distinct physiological states in vivo, which suggests a paradigm shift in this field. Finally, our PorSignDB signature database is publicly available as a community resource (http://www.vetvirology.ugent.be/PorSignDB/, included in Gene Sets from Community Contributors http://software.broadinstitute.org/gsea/msigdb/contributed_genesets.jsp) and provides systems biologists with a valuable tool for catalyzing studies of human and veterinary disease. Finally, a primary porcine lymphoblast cell culture system paves the way for unraveling the impact of host genetics on PCV2 replication.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5217-5) contains supplementary material, which is available to authorized users.

The eMERGE genotype set of 83,717 subjects imputed to ~40 million variants genome wide and association with the herpes zoster medical record phenotype

The Electronic Medical Records and Genomics (eMERGE) network is a network of medical centers with electronic medical records linked to existing biorepository samples for genomic discovery and genomic medicine research. The network sought to unify the genetic results from 78 Illumina and Affymetrix genotype array batches from 12 contributing medical centers for joint association analysis of 83,717 human participants. In this report, we describe the imputation of eMERGE results and methods to create the unified imputed merged set of genome‐wide variant genotype data. We imputed the data using the Michigan Imputation Server, which provides a missing single‐nucleotide variant genotype imputation service using the minimac3 imputation algorithm with the Haplotype Reference Consortium genotype reference set. We describe the quality control and filtering steps used in the generation of this data set and suggest generalizable quality thresholds for imputation and phenotype association studies. To test the merged imputed genotype set, we replicated a previously reported chromosome 6 HLA‐B herpes zoster (shingles) association and discovered a novel zoster‐associated loci in an epigenetic binding site near the terminus of chromosome 3 (3p29).

Oncogenic Signaling Induced by HCV Infection

The liver is frequently exposed to toxins, metabolites, and oxidative stress, which can challenge organ function and genomic stability. Liver regeneration is therefore a highly regulated process involving several sequential signaling events. It is thus not surprising that individual oncogenic mutations in hepatocytes do not necessarily lead to cancer and that the genetic profiles of hepatocellular carcinomas (HCCs) are highly heterogeneous. Long-term infection with hepatitis C virus (HCV) creates an oncogenic environment by a combination of viral protein expression, persistent liver inflammation, oxidative stress, and chronically deregulated signaling events that cumulate as a tipping point for genetic stability. Although novel direct-acting antivirals (DAA)-based treatments efficiently eradicate HCV, the associated HCC risk cannot be fully eliminated by viral cure in patients with advanced liver disease. This suggests that HCV may persistently deregulate signaling pathways beyond viral cure and thereby continue to perturb cancer-relevant gene function. In this review, we summarize the current knowledge about oncogenic signaling pathways derailed by chronic HCV infection. This will not only help to understand the mechanisms of hepatocarcinogenesis but will also highlight potential chemopreventive strategies to help patients with a high-risk profile of developing HCC.

Inactivation of Stat3 and crosstalk of miRNA155-5p and FOXO3a contribute to the induction of IGFBP1 expression by beta-elemene in human lung cancer

β-Elemene, an active component of natural plants, has been shown to exhibit anticancer properties. However, the detailed mechanism underlying these effects has yet to be determined. In this study, we show that β-elemene inhibits the growth of lung cancer cells. Mechanistically, we found that β-elemene decreased the phosphorylation of signal transducer and activator of transcription 3 (Stat3) and miRNA155-5p mRNA but induced the protein expression of human forkhead box class O (FOXO)3a; the latter two were abrogated in cells with overexpressed Stat3. Notably, miRNA155-5p mimics reduced FOXO3a luciferase reporter activity in the 3-UTR region and protein expression, whereas overexpressed FOXO3a countered the reduction of the miRNA155-5p levels by β-elemene. Moreover, β-elemene increased the mRNA and protein expression levels as well as promoter activity of insulin-like growth factor-binding protein 1 (IGFBP1); this finding was not observed in cells with a silenced FOXO3a gene and miRNA155-5p mimics. Finally, silencing of IGFBP1 blocked β-elemene-inhibited cell growth. Similar findings were observed in vivo. In summary, our results indicate that β-elemene increases IGFBP1 gene expression via inactivation of Stat3 followed by a reciprocal interaction between miRNA155-5p and FOXO3a. This effect leads to inhibition of human lung cancer cell growth. These findings reveal a novel molecular mechanism underlying the inhibitory effects of β-elemene on lung cancer cells.

A compound found in one Chinese medicinal herb inhibits the growth of lung cancer cells by indirectly activating a protein with anti-proliferative properties. Hann and colleagues from the Guangzhou University of Chinese Medicine, China, uncovered the molecular pathways by which β-elemene, a natural compound isolated from the Curcuma wenyujin plant, mediates the anti-cancer effects. They showed that β-elemene inactivates the two important regulatory molecules, one protein and another small RNA, while also inducing the expression of one protein that promotes in killing cancer cells. These changes lead to elevated levels of the protein that prevents cell invasion and spread. Collectively, this altered signaling inside the lung cancer cell lead to reduced growth, in both cell-based culture and mouse model. The findings help explain why β-elemene has potential as a therapeutic agent in lung cancer.