Protein kinase R-dependent regulation of interleukin-10 in response to double-stranded RNA

The immune response to RNA suppresses nucleic acid synthesis by limiting ribose 5-phosphate

During infection viruses hijack host cell metabolism to promote their replication. Here, analysis of metabolite alterations in macrophages exposed to poly I:C recognises that the antiviral effector Protein Kinase RNA-activated (PKR) suppresses glucose breakdown within the pentose phosphate pathway (PPP). This pathway runs parallel to central glycolysis and is critical to producing NADPH and pentose precursors for nucleotides. Changes in metabolite levels between wild-type and PKR-ablated macrophages show that PKR controls the generation of ribose 5-phosphate, in a manner distinct from its established function in gene expression but dependent on its kinase activity. PKR phosphorylates and inhibits the Ribose 5-Phosphate Isomerase A (RPIA), thereby preventing interconversion of ribulose- to ribose 5-phosphate. This activity preserves redox control but decreases production of ribose 5-phosphate for nucleotide biosynthesis. Accordingly, the PKR-mediated immune response to RNA suppresses nucleic acid production. In line, pharmacological targeting of the PPP during infection decreases the replication of the Herpes simplex virus. These results identify an immune response-mediated control of host cell metabolism and suggest targeting the RPIA as a potential innovative antiviral treatment.

PKR induces TGF-β and limits oncolytic immune therapy

BACKGROUND

Mammalian cells have developed multiple intracellular mechanisms to defend against viral infections. These include RNA-activated protein kinase (PKR), cyclic GMP-AMP synthase and stimulation of interferon genes (cGAS-STING) and toll-like receptor-myeloid differentiation primary response 88 (TLR-MyD88). Among these, we identified that PKR presents the most formidable barrier to oncolytic herpes simplex virus (oHSV) replication in vitro.

METHODS

To elucidate the impact of PKR on host responses to oncolytic therapy, we generated a novel oncolytic virus (oHSV-shPKR) which disables tumor intrinsic PKR signaling in infected tumor cells.

RESULTS

As anticipated, oHSV-shPKR resulted in suppression of innate antiviral immunity and improves virus spread and tumor cell lysis both in vitro and in vivo. Single cell RNA sequencing combined with cell-cell communication analysis uncovered a strong correlation between PKR activation and transforming growth factor beta (TGF-ß) immune suppressive signaling in both human and preclinical models. Using a murine PKR targeting oHSV, we found that in immune-competent mice this virus could rewire the tumor immune microenvironment to increase the activation of antigen presentation and enhance tumor antigen-specific CD8 T cell expansion and activity. Further, a single intratumoral injection of oHSV-shPKR significantly improved the survival of mice bearing orthotopic glioblastoma. To our knowledge, this is the first report to identify dual and opposing roles of PKR wherein PKR activates antivirus innate immunity and induces TGF-ß signaling to inhibit antitumor adaptive immune responses.

CONCLUSIONS

Thus, PKR represents the Achilles heel of oHSV therapy, restricting both viral replication and antitumor immunity, and an oncolytic virus that can target this pathway significantly improves response to virotherapy.

Antinociceptive and anti-inflammatory activities of Copaifera pubiflora Benth oleoresin and its major metabolite ent-hardwickiic acid

ETHNOPHARMACOLOGICAL RELEVANCE

Copaifera species folkloric names are "copaíbas, copaibeiras, copaívas or oil stick", which are widely used in Brazilian folk medicine. Among all ethnopharmacological applications described for Copaifera spp oleoresins, their anti-inflammatory effect stands out. However, the knowledge of anti-inflammatory and antinociceptive properties of Copaifera pubiflora Benth is scarce.

AIM OF THE STUDY

To investigate the cytotoxic, anti-inflammatory, and antinociceptive activities of C. pubiflora oleoresin (CPO), and its major compound ent-hardwickiic acid (HA).

MATERIAL AND METHODS

The phosphatase assay was used to evaluate the cytotoxicity of CPO and HA in three different cell lines. CPO and HA doses of 1, 3, and 10 mg/kg were employed in the biological assays. The assessment of motor activity was performed using open-field and rotarod tests. Anti-inflammatory activity of CPO and HA was assessed through luciferase assay, measurement of INF-γ, IL-1β, IL-6, IL-10, and TNF-α in a multi-spot system with the immortalized cell line THP-1, zymosan-induced arthritis, and carrageenan-induced paw edema. Acetic acid-induced abdominal writhing and formalin tests were undertaken to evaluate the antinociceptive potential of CPO and HA. In addition, the evaluation using carrageenan was performed to investigate the effect of CPO in pain intensity to a mechanical stimulus (mechanical hyperalgesia), using the von Frey filaments. A tail-flick test was used to evaluate possible central CPO and HA actions.

RESULTS

In the cytotoxicity evaluation, CPO and HA were not cytotoxic to the cell lines tested. CPO and HA (10 mg/kg) did not affect animals' locomotor capacity in both open-field and rotarod tests. In the luciferase assay, CPO and HA significantly reduced luciferase activity (p < 0.05). This reduction indicates a decrease in NF-κB activity. HA and CPO decreased INF-γ, IL-1β, IL-6, IL-10, and TNF-α at 24 and 72 h in the multi-spot system. In zymosan-induced arthritis, CPO and HA decreased the number of neutrophils in the joint of arthritic mice and the number of total leukocytes (p < 0.05). In experimental arthritis HA significantly decreased joint swelling (p < 0.05). CPO and HA also increased the mechanical threshold during experimental arthritis. HA and CPO significantly inhibited the carrageenan-induced paw edema, being the doses of 10 mg/kg the most effective, registering maximum inhibitions of 58 ± 8% and 76 ± 6% respectively, p < 0.05. CPO and HA reduced the nociceptive behavior in both phases of formalin at all tested doses. The highest doses tested displayed inhibitions of 87 ± 1% and 72 ± 4%, respectively, p < 0.001, in the first phase, and 87 ± 1% and 81 ± 2%, respectively, p < 0.001, in the second phase. Oral treatment of CPO and HA (1, 3, 10 mg/kg) significantly reduced the nociceptive response in acetic acid-induced abdominal writhings, and the 10 mg/kg dose was the most effective with maximum inhibitions of 86 ± 2% and 82 ± 1%, respectively, p < 0.001. Both HA and CPO significantly decreased the intensity of mechanical inflammatory hyper-nociception on carrageenan-induced hyperalgesia at all tested doses, and 10 mg/kg was the most effective dose with maximum inhibitions of 73 ± 5% and 74 ± 7%, respectively, p < 0.05.CPO increased the tail-flick latencies in mice, and concomitant administration of naloxone partially reduced its effect.

CONCLUSIONS

CPO and HA may inhibit the production of inflammatory cytokines by suppressing the NF-κB signaling pathway, resulting in anti-inflammatory and antinociceptive activities.

Biology and therapeutic potential of interleukin-10

The authors review the molecular mechanisms regulating IL-10 production and response and describe classic and novel functions of IL-10 in immune and non-immune cells. They further discuss the therapeutic potential of IL-10 in different diseases and the outstanding questions underlying an effective application of IL-10 in clinical settings.

The cytokine IL-10 is a key anti-inflammatory mediator ensuring protection of a host from over-exuberant responses to pathogens and microbiota, while playing important roles in other settings as sterile wound healing, autoimmunity, cancer, and homeostasis. Here we discuss our current understanding of the regulation of IL-10 production and of the molecular pathways associated with IL-10 responses. In addition to IL-10’s classic inhibitory effects on myeloid cells, we also describe the nonclassic roles attributed to this pleiotropic cytokine, including how IL-10 regulates basic processes of neural and adipose cells and how it promotes CD8 T cell activation, as well as epithelial repair. We further discuss its therapeutic potential in the context of different diseases and the outstanding questions that may help develop an effective application of IL-10 in diverse clinical settings.

Regulation of Interleukin-10 Expression

Interleukin (IL)-10 is an essential anti-inflammatory cytokine that plays important roles as a negative regulator of immune responses to microbial antigens. Loss of IL-10 results in the spontaneous development of inflammatory bowel disease as a consequence of an excessive immune response to the gut microbiota. IL-10 also functions to prevent excessive inflammation during the course of infection. IL-10 can be produced in response to pro-inflammatory signals by virtually all immune cells, including T cells, B cells, macrophages, and dendritic cells. Given its function in maintaining the delicate balance between effective immunity and tissue protection, it is evident that IL-10 expression is highly dynamic and needs to be tightly regulated. The transcriptional regulation of IL-10 production in myeloid cells and T cells is the topic of this review. Drivers of IL-10 expression as well as their downstream signaling pathways and transcription factors will be discussed. We will examine in more detail how various signals in CD4⁺ T cells converge on common transcriptional circuits, which fine-tune IL-10 expression in a context-dependent manner.

PKR: A Kinase to Remember

Aging is a major risk factor for many diseases including metabolic syndrome, cancer, inflammation, and neurodegeneration. Identifying mechanistic common denominators underlying the impact of aging is essential for our fundamental understanding of age-related diseases and the possibility to propose new ways to fight them. One can define aging biochemically as prolonged metabolic stress, the innate cellular and molecular programs responding to it, and the new stable or unstable state of equilibrium between the two. A candidate to play a role in the process is protein kinase R (PKR), first identified as a cellular protector against viral infection and today known as a major regulator of central cellular processes including mRNA translation, transcriptional control, regulation of apoptosis, and cell proliferation. Prolonged imbalance in PKR activation is both affected by biochemical and metabolic parameters and affects them in turn to create a feedforward loop. Here, we portray the central role of PKR in transferring metabolic information and regulating cellular function with a focus on cancer, inflammation, and brain function. Later, we integrate information from open data sources and discuss current knowledge and gaps in the literature about the signaling cascades upstream and downstream of PKR in different cell types and function. Finally, we summarize current major points and biological means to manipulate PKR expression and/or activation and propose PKR as a therapeutic target to shift age/metabolic-dependent undesired steady states.

Evidence for dispensability of protein kinase R in host control of tuberculosis

Genetic deficiency of protein kinase R (PKR) in mice was reported to enhance macrophage activation in vitro in response to interferon-γ (IFNγ) and to reduce the burden of Mycobacterium tuberculosis (Mtb) in vivo (Wu et al. PloS One. 2012 7:e30512). Consistent with this, treatment of wild-type (WT) macrophages in vitro with a novel PKR inhibitor (Bryk et al., Bioorg. Med. Chem. Lett. 2011 21:4108-4114) also enhanced IFN-γ-dependent macrophage activation (Wu et al. PloS One. 2012 7:e30512). Here we show that co-treatment with IFN-γ and a new PKR inhibitor identified herein to be highly but not completely selective likewise induced macrophages to produce more reactive nitrogen intermediates (RNI) and tumor necrosis factor alpha (TNF-α) and less interleukin 10 (IL-10) than seen with IFN-γ alone. Unexpectedly, however, this new PKR inhibitor had a comparable effect on PKR-deficient macrophages. Retrospective investigation revealed that the PKR-deficient mice in (Wu et al. PloS One. 2012 7:e30512) had not been backcrossed. On comparing genetically matched PKR-deficient and WT mice, we saw no impact of PKR deficiency on macrophage activation in vitro or during the course of Mtb infection in vivo. In addition, although 129S1/SvImJ macrophage responses to IFN-γ were greater than those of C57BL/6J macrophages, PKR was not required to mediate the IFN-γ-dependent production of IL-10, RNI or TNF-α in either strain. Together the data cast doubt on PKR as a potential therapeutic target for tuberculosis.

IL-10-mediated signals act as a switch for lymphoproliferation in Human T-cell leukemia virus type-1 infection by activating the STAT3 and IRF4 pathways

Human T-cell leukemia virus type-1 (HTLV-1) causes two distinct diseases, adult T-cell leukemia/lymphoma (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Since there are no disease-specific differences among HTLV-1 strains, the etiological mechanisms separating these respective lymphoproliferative and inflammatory diseases are not well understood. In this study, by using IL-2-dependent HTLV-1-infected T-cell lines (ILTs) established from patients with ATL and HAM/TSP, we demonstrate that the anti-inflammatory cytokine IL-10 and its downstream signals potentially act as a switch for proliferation in HTLV-1-infected cells. Among six ILTs used, ILTs derived from all three ATL patients grew much faster than those from three HAM/TSP patients. Although most of the ILTs tested produced IFN-γ and IL-6, the production of IL-10 was preferentially observed in the rapid-growing ILTs. Interestingly, treatment with exogenous IL-10 markedly enhanced proliferation of the slow-growing HAM/TSP-derived ILTs. The IL-10-mediated proliferation of these ILTs was associated with phosphorylation of STAT3 and induction of survivin and IRF4, all of which are characteristics of ATL cells. Knockdown of STAT3 reduced expression of IL-10, implying a positive-feedback regulation between STAT3 and IL-10. STAT3 knockdown also reduced survivin and IRF4 in the IL-10- producing or IL-10- treated ILTs. IRF4 knockdown further suppressed survivin expression and the cell growth in these ILTs. These findings indicate that the IL-10-mediated signals promote cell proliferation in HTLV-1-infected cells through the STAT3 and IRF4 pathways. Our results imply that, although HTLV-1 infection alone may not be sufficient for cell proliferation, IL-10 and its signaling pathways within the infected cell itself and/or its surrounding microenvironment may play a critical role in pushing HTLV-1-infected cells towards proliferation at the early stages of HTLV-1 leukemogenesis. This study provides useful information for understanding of disease mechanisms and disease-prophylactic strategies in HTLV-1 infection.

A Novel Agonist of the TRIF Pathway Induces a Cellular State Refractory to Replication of Zika, Chikungunya, and Dengue Viruses

The ongoing concurrent outbreaks of Zika, Chikungunya, and dengue viruses in Latin America and the Caribbean highlight the need for development of broad-spectrum antiviral treatments. The type I interferon (IFN) system has evolved in vertebrates to generate tissue responses that actively block replication of multiple known and potentially zoonotic viruses. As such, its control and activation through pharmacological agents may represent a novel therapeutic strategy for simultaneously impairing growth of multiple virus types and rendering host populations resistant to virus spread. In light of this strategy's potential, we undertook a screen to identify novel interferon-activating small molecules. Here, we describe 1-(2-fluorophenyl)-2-(5-isopropyl-1,3,4-thiadiazol-2-yl)-1,2-dihydrochromeno[2,3-c]pyrrole-3,9-dione, which we termed AV-C. Treatment of human cells with AV-C activates innate and interferon-associated responses that strongly inhibit replication of Zika, Chikungunya, and dengue viruses. By utilizing genome editing, we investigated the host proteins essential to AV-C-induced cellular states. This showed that the compound requires a TRIF-dependent signaling cascade that culminates in IFN regulatory factor 3 (IRF3)-dependent expression and secretion of type I interferon to elicit antiviral responses. The other canonical IRF3-terminal adaptor proteins STING and IPS-1/MAVS were dispensable for AV-C-induced phenotypes. However, our work revealed an important inhibitory role for IPS-1/MAVS, but not TRIF, in flavivirus replication, implying that TRIF-directed viral evasion may not occur. Additionally, we show that in response to AV-C, primary human peripheral blood mononuclear cells secrete proinflammatory cytokines that are linked with establishment of adaptive immunity to viral pathogens. Ultimately, synthetic innate immune activators such as AV-C may serve multiple therapeutic purposes, including direct antimicrobial responses and facilitation of pathogen-directed adaptive immunity.IMPORTANCE The type I interferon system is part of the innate immune response that has evolved in vertebrates as a first line of broad-spectrum immunological defense against an unknowable diversity of microbial, especially viral, pathogens. Here, we characterize a novel small molecule that artificially activates this response and in so doing generates a cellular state antagonistic to growth of currently emerging viruses: Zika virus, Chikungunya virus, and dengue virus. We also show that this molecule is capable of eliciting cellular responses that are predictive of establishment of adaptive immunity. As such, this agent may represent a powerful and multipronged therapeutic tool to combat emerging and other viral diseases.

Zinc Oxide Nanoparticle-Poly I:C RNA Complexes: Implication as Therapeutics against Experimental Melanoma

There is current interest in harnessing the combined anticancer and immunological effect of nanoparticles (NPs) and RNA. Here, we evaluate the bioactivity of poly I:C (pIC) RNA, bound to anticancer zinc oxide NP (ZnO-NP) against melanoma. Direct RNA association to unfunctionalized ZnO-NP is shown by observing change in size, zeta potential, and absorption/fluorescence spectra upon complexation. RNA corona was visualized by transmission electron microscopy (TEM) for the first time. Binding constant (K_b = 1.6-2.8 g^-1 L) was determined by modified Stern-Volmer, absorption, and biological surface activity index analysis. The pIC-ZnO-NP complex increased cell death for both human (A375) and mouse (B16F10) cell lines and suppressed tumor cell growth in BALB/C-B16F10 mouse melanoma model. Ex vivo tumor analysis indicated significant molecular activity such as changes in the level of phosphoproteins JNK, Akt, and inflammation markers IL-6 and IFN-γ. High throughput proteomics analysis revealed zinc oxide and poly I:C-specific and combinational patterns that suggested possible utility as an anticancer and immunotherapeutic strategy against melanoma.

The atypical IκB protein IκB(NS) is important for Toll-like receptor-induced interleukin-10 production in B cells

Although a major function of B cells is to mediate humoral immunity by producing antigen-specific antibodies, a specific subset of B cells is important for immune suppression, which is mainly mediated by the secretion of the anti-inflammatory cytokine interleukin-10 (IL-10). However, the mechanism by which IL-10 is induced in B cells has not been fully elucidated. Here, we report that IκBNS , an inducible nuclear IκB protein, is important for Toll-like receptor (TLR)-mediated IL-10 production in B cells. Studies using IκB(NS) knockout mice revealed that the number of IL-10-producing B cells is reduced in IκB(NS)(-/-) spleens and that the TLR-mediated induction of cytoplasmic IL-10-positive cells and IL-10 secretion in B cells are impaired in the absence of IκB(NS). The impairment of IL-10 production by a lack of IκB(NS) was not observed in TLR-triggered macrophages or T-cell-receptor-stimulated CD4(+) CD25(+) T cells. In addition, IκB(NS)-deficient B cells showed reduced expression of Prdm1 and Irf4 and failed to generate IL-10(+) CD138(+) plasmablasts. These results suggest that IκB(NS) is selectively required for IL-10 production in B cells responding to TLR signals, so defining an additional role for IκB(NS) in the control of the B-cell-mediated immune responses.

Microarray Analysis of Antigen-Dependent B-Cell Activation Gene Expression in Bitches with Pyometra

Canine pyometra is defined as a complex disease associated with activation and proliferation of immune specific cells, B and T cells, as well as synthesis and activation of immune and pro-inflammatory molecules. Although all of these mechanisms are well recognized in several human immune diseases and cancers, the possible role or dysfunction of these molecules in dogs with pyometra still requires investigation. This study was aimed to examine antigen-dependent B-cell activation gene expression (CD4, CD28, CD40, CD80, Fas, HLA-DRB1 and IL10) in a total of 24 mixed-breed bitch uteri with pyometra and 20 healthy controls. Using canine RNA microarray assays (Affymetrix) altogether 17,138 different transcripts were analyzed. A significant increase was found of CD28, CD40, HLA-DRB1 (P<0.001), and CD4, CD80, Fas and IL10 (P<0.01) in the group of bitches with pyometra, as compared to controls. In the affected group an increased share of CD4, CD28, CD40, CD80, Fas, HLA-DRB1 and IL10, (13.6-, 2.8-, 2.9-, 5.6-, 3.3-, 4.4-, and 6.5-fold increase, respectively) was also detected. It is suggested that an increased expression of B cell-specific immune response molecules may be associated with recruitment of immunologically specific cells in bitches with pyometra as well as with activation of pro-inflammatory proteins as a consequence of exposure to foreign antigens due to bacterial infection.

Identification of 10 cowpox virus proteins that are necessary for induction of hemorrhagic lesions (red pocks) on chorioallantoic membranes

Cowpox viruses (CPXV) cause hemorrhagic lesions ("red pocks") on infected chorioallantoic membranes (CAM) of embryonated chicken eggs, while most other members of the genus Orthopoxvirus produce nonhemorrhagic lesions ("white pocks"). Cytokine response modifier A (CrmA) of CPXV strain Brighton Red (BR) is necessary but not sufficient for the induction of red pocks. To identify additional viral proteins involved in the induction of hemorrhagic lesions, a library of single-gene CPXV knockout mutants was screened. We identified 10 proteins that are required for the formation of hemorrhagic lesions, which are encoded by CPXV060, CPXV064, CPXV068, CPXV069, CPXV074, CPXV136, CPXV168, CPXV169, CPXV172, and CPXV199. The genes are the homologues of F12L, F15L, E2L, E3L, E8R, A4L, A33R, A34R, A36R, and B5R of vaccinia virus (VACV). Mutants with deletions in CPXV060, CPXV168, CPXV169, CPXV172, or CPXV199 induced white pocks with a comet-like shape on the CAM. The homologues of these five genes in VACV encode proteins that are involved in the production of extracellular enveloped viruses (EEV) and the repulsion of superinfecting virions by actin tails. The homologue of CPXV068 in VACV is also involved in EEV production but is not related to actin tail induction. The other genes encode immunomodulatory proteins (CPXV069 and crmA) and viral core proteins (CPXV074 and CPXV136), and the function of the product of CPXV064 is unknown.

IMPORTANCE

It has been known for a long time that cowpox virus induces hemorrhagic lesions on chicken CAM, while most of the other orthopoxviruses produce nonhemorrhagic lesions. Although cowpox virus CrmA has been proved to be responsible for the hemorrhagic phenotype, other proteins causing this phenotype remain unknown. Recently, we generated a complete single-gene knockout bacterial artificial chromosome (BAC) library of cowpox virus Brighton strain. Out of 183 knockout BAC clones, 109 knockout viruses were reconstituted. The knockout library makes possible high-throughput screening for studying poxvirus replication and pathogenesis. In this study, we screened all 109 single-gene knockout viruses and identified 10 proteins necessary for inducing hemorrhagic lesions. The identification of these genes gives a new perspective for studying the hemorrhagic phenotype and may give a better understanding of poxvirus virulence.

PKR mediated regulation of inflammation and IL-10 during viral encephalomyelitis

Double-stranded RNA-dependent protein kinase (PKR) regulates antiviral activity, immune responses, apoptosis and neurotoxicity. Gliatropic coronavirus infection induced PKR activation in infected as well uninfected cells within the central nervous system (CNS). However, PKR deficiency only modestly increased viral replication and did not affect IFN-α/β or IL-1β expression. Despite reduced Il-6, Ccl5, and Cxcl10 mRNA, protein levels remained unaltered. Furthermore, PKR deficiency selectively reduced IL-10 production in CD4, but not CD8 T cells, without affecting CNS pathology. The results demonstrate the ability of PKR to balance neuroinflammation by selectively modulating key cytokines and chemokines in CNS resident and CD4 T cells.

Cell-type-specific effects of RNase L on viral induction of beta interferon

The interferon (IFN)-inducible antiviral state is mediated in part by the 2′,5′-oligoadenylate (2-5A) synthetase (OAS)/RNase L system. 2-5A, produced from ATP by OAS proteins in response to viral double-stranded RNA, binds to and activates RNase L. RNase L restricts viral infections by degrading viral and cellular RNA, inducing autophagy and apoptosis, and producing RNA degradation products that amplify production of type I interferons (IFNs) through RIG-I-like receptors. However, the effects of the OAS/RNase L pathway on IFN induction in different cell types that vary in basal levels of these proteins have not been previously reported. Here we report higher basal expression of both RNase L and OAS in mouse macrophages in comparison to mouse embryonic fibroblasts (MEFs). In MEFs, RNase L gene knockout decreased induction of IFN-β by encephalomyocarditis virus infection or poly(rI):poly(rC) (pIC) transfection. In contrast, in macrophages, RNase L deletion increased (rather than decreased) induction of IFN-β by virus or pIC. RNA damage from RNase L in virus-infected macrophages is likely responsible for reducing IFN-β production. Similarly, direct activation of RNase L by transfection with 2-5A induced IFN-β in MEFs but not in macrophages. Also, viral infection or pIC transfection caused RNase L-dependent apoptosis of macrophages but not of MEFs. Our results suggest that cell-type-specific differences in basal levels of OAS and RNase L are determinants of IFN-β induction that could affect tissue protection and survival during viral infections.

Type I interferons (IFNs) such as IFN-β are essential antiviral cytokines that are often required for animal survival following infections by highly pathogenic viruses. Therefore, host factors that regulate type I IFN production are critically important for animal and human health. Previously we reported that the OAS/RNase L pathway amplifies antiviral innate immunity by enhancing IFN-β production in mouse embryonic fibroblasts and in virus-infected mice. Here we report that high basal levels of OAS/RNase L in macrophages reduce, rather than increase, virus induction of IFN-β. RNA damage and apoptosis caused by RNase L were the likely reasons for the decreased IFN-β production in virus-infected macrophages. Our studies suggest that during viral infections, the OAS/RNase L pathway can either enhance or suppress IFN production, depending on the cell type. IFN regulation by RNase L is suggested to contribute to tissue protection and survival during viral infections.

The regulation of IL-10 expression

Interleukin (IL)-10 is an important immunoregulatory cytokine and an understanding of how IL-10 expression is controlled is critical in the design of immune intervention strategies. IL-10 is produced by almost all cell types within the innate (including macrophages, monocytes, dendritic cells (DCs), mast cells, neutrophils, eosinophils and natural killer cells) and adaptive (including CD4(+) T cells, CD8(+) T cells and B cells) immune systems. The mechanisms of IL-10 regulation operate at several stages including chromatin remodelling at the Il10 locus, transcriptional regulation of Il10 expression and post-transcriptional regulation of Il10 mRNA. In addition, whereas some aspects of Il10 gene regulation are conserved between different immune cell types, several are cell type- or stimulus-specific. Here, we outline the complexity of IL-10 production by discussing what is known about its regulation in macrophages, monocytes, DCs and CD4(+) T helper cells.

Epigenomic elements enriched in the promoters of autoimmunity susceptibility genes

Genome-wide association studies have identified a number of autoimmune disease-susceptibility genes. Whether or not these loci share any regulatory or functional elements, however, is an open question. Finding such common regulators is of considerable research interest in order to define systemic therapeutic targets. The growing amount of experimental genomic annotations, particularly those from the ENCODE project, provide a wealth of opportunities to search for such commonalities. We hypothesized that regulatory commonalities might not only delineate a regulatory landscape predisposing to autoimmune diseases, but also define functional elements distinguishing specific diseases. We further investigated if, and how, disease-specific epigenomic elements can identify novel genes yet to be associated with the diseases. We evaluated transcription factors, histone modifications, and chromatin state data obtained from the ENCODE project for statistically significant over- or under-representation in the promoters of genes associated with Systemic Lupus Erythematosus (SLE), Rheumatoid Arthritis (RA), and Systemic Sclerosis (SSc). We identified BATF, BCL11A, IRF4, NFkB, PAX5, and PU.1 as transcription factors over-represented in SLE- and RA-susceptibility gene promoters. H3K4me1 and H3K4me2 epigenomic marks were associated with SLE susceptibility genes, and H3K9me3 was common to both SLE and RA. In contrast to a transcriptionally active signature in SLE and RA, SSc-susceptibility genes were depleted in activating epigenomic elements. Using epigenomic elements enriched in SLE and RA, we identified additional immune and B cell signaling-related genes with the same elements in their promoters. Our analysis suggests common and disease-specific epigenomic elements that may define novel therapeutic targets for controlling aberrant activation of autoimmune susceptibility genes.

The protein kinase double-stranded RNA-dependent (PKR) enhances protection against disease cause by a non-viral pathogen

PKR is well characterized for its function in antiviral immunity. Using Toxoplasma gondii, we examined if PKR promotes resistance to disease caused by a non-viral pathogen. PKR(-/-) mice infected with T. gondii exhibited higher parasite load and worsened histopathology in the eye and brain compared to wild-type controls. Susceptibility to toxoplasmosis was not due to defective expression of IFN-γ, TNF-α, NOS2 or IL-6 in the retina and brain, differences in IL-10 expression in these organs or to impaired induction of T. gondii-reactive T cells. While macrophages/microglia with defective PKR signaling exhibited unimpaired anti-T. gondii activity in response to IFN-γ/TNF-α, these cells were unable to kill the parasite in response to CD40 stimulation. The TRAF6 binding site of CD40, but not the TRAF2,3 binding sites, was required for PKR phosphorylation in response to CD40 ligation in macrophages. TRAF6 co-immunoprecipitated with PKR upon CD40 ligation. TRAF6-PKR interaction appeared to be indirect, since TRAF6 co-immunoprecipitated with TRAF2 and TRAF2 co-immunoprecipitated with PKR, and deficiency of TRAF2 inhibited TRAF6-PKR co-immunoprecipitation as well as PKR phosphorylation induced by CD40 ligation. PKR was required for stimulation of autophagy, accumulation the autophagy molecule LC3 around the parasite, vacuole-lysosomal fusion and killing of T. gondii in CD40-activated macrophages and microglia. Thus, our findings identified PKR as a mediator of anti-microbial activity and promoter of protection against disease caused by a non-viral pathogen, revealed that PKR is activated by CD40 via TRAF6 and TRAF2, and positioned PKR as a link between CD40-TRAF signaling and stimulation of the autophagy pathway.

Estradiol modulates tumor necrosis factor-induced endothelial inflammation: role of tumor necrosis factor receptor 2

The sex hormone estradiol (E(2)) appears to mediate both anti-atherogenic and pro-inflammatory effects in premenopausal women, suggesting a complex immunomodulatory role. Tumor necrosis factor (TNF) is a key pro-inflammatory cytokine involved in the pathogenesis of atherosclerosis and other inflammatory diseases. Alterations at the TNF receptors (TNFRs) and their downstream signaling/transcriptional pathways can affect inflammatory responses. Given this background, we hypothesized that chronic E(2) exposure would alter endothelial inflammatory response involving modulation at the levels of TNFRs and signaling pathways. HUVECs were used as the model system. Pre-treatment with E(2) did not significantly alter TNF-induced upregulation of pro-inflammatory molecules ICAM-1 (3-6 times) and VCAM-1 (5-7 times). However, pharmacological inhibition of transcriptional pathways suggested a partial shift from NF-ĸB (from 97 to 64%) towards the JNK/AP-1 pathway in ICAM-1 upregulation on E(2) treatment. In contrast, VCAM-1 expression remained NF-ĸB dependent in both control (∼96%) and E(2) treated (∼85%) cells. The pro-inflammatory TNF effects were mediated by TNFR1. Interestingly, E(2) pre-treatment increased TNFR2 levels in these cells. Concomitant TNFR2 activation (but not TNFR1 activation alone) led to the shift towards JNK/AP-1-mediated ICAM-1 upregulation in E(2)-treated cells, suggesting the effects of chronic E(2) to be dependent on TNFR2 signaling.

Inhibition of JAKs in macrophages increases lipopolysaccharide-induced cytokine production by blocking IL-10-mediated feedback

Macrophages are an important source of cytokines following infection. Stimulation of macrophages with TLR agonists results in the secretion of TNF-α, IL-6, and IL-12, and the production of these cytokines is controlled by multiple feedback pathways. Macrophages also produce IL-10, which acts to inhibit proinflammatory cytokine production by macrophages via a JAK/STAT3-dependent pathway. We show in this paper that, Ruxolitinib, a recently described selective inhibitor of JAKs, increases TNF, IL-6, and IL-12 secretion in mouse bone marrow-derived macrophages stimulated with LPS. This effect is largely due to its ability to block IL-10-mediated feedback inhibition on cytokine transcription in macrophages. Similar results were also obtained with a second structurally unrelated Jak inhibitor, Tofacitinib. In addition, LPS induced the production of IFN-β, which was then able to activate JAKs in macrophages, resulting in the stimulation of STAT1 phosphorylation. The initial induction of IL-10 was independent of JAK signaling; however, inhibition of JAKs did reduce IL-10 secretion at later time points. This reflected a requirement for the IFN-β feedback loop to sustain IL-10 transcription following LPS stimulation. In addition to IL-10, IFN-β also helped sustain IL-6 and IL-12 transcription. Overall, these results suggest that inhibition of JAKs may increase the inflammatory potential of macrophages stimulated with TLR4 agonists.

Regulation of double-stranded RNA dependent protein kinase expression and attenuation of protein synthesis induced by bacterial toll-like receptors agonists in the absence of interferon

Double-stranded RNA dependent protein kinase (PKR) is a host defense enzyme whose expression is up-regulated in response to interferons (IFNs) and during viral infections. Increased levels of PKR can result in its activation, which, in turn, inhibits global cellular protein synthesis. Despite growing evidence suggesting the involvement of PKR in bacterial infections, little is known about its expression, regulation and cellular role in nonviral infections. The aim of this work was to determine the expression and regulation of PKR in response to stimulation of human THP-1 monocytes with bacterial agonists of TLR2/4. Treatment of cells with Pam3CSK4 or lipopolyssacharide (LPS) resulted in an increase in PKR mRNA and protein levels. Robust PKR expression at later times correlated with a decrease in global protein synthesis. PKR was also required to regulate the inhibition of protein synthesis triggered by LPS in mouse splenocytes. Surprisingly, no increase of IFN-β or IFN-α mRNA levels was detected after treatment of THP-1 cells with toll-like receptor (TLR) agonists. In accordance with this, the supernatants from LPS or Pam3CSK4-treated cells lacked the ability to activate the PKR and ISG56 promoters in gene reporter assays carried out in HEK293T cells. The expression of PKR induced by TLRs agonists was dramatically impaired when cells were treated in the presence of tosyl-phenylalanyl chloromethylketone or Mithramycin, suggesting that NF-κB and Sp1 transcription factors, but not those activated by IFNs, regulate the expression of PKR in human monocytes.

Role of interleukin 10 transcriptional regulation in inflammation and autoimmune disease

Interleukin 10 (IL-10) is a cytokine with potent anti-inflammatory properties that plays a central role in limiting host immune response to pathogens, thereby preventing damage to the host and maintaining normal tissue homeostasis. Dysregulation of IL-10 is associated with enhanced immunopathology in response to infection as well as increased risk for development of many autoimmune diseases. Thus a fundamental understanding of IL-10 gene expression is critical for our comprehension of disease progression and resolution of host inflammatory response. In this review, we discuss modes of regulation of IL-10 gene expression in immune effector cell types, including signal transduction, epigenetics, promoter architecture, and post-transcriptional regulation, and how aberrant regulation contributes to immunopathology and disease progression.

Improved control of tuberculosis and activation of macrophages in mice lacking protein kinase R

Host factors that microbial pathogens exploit for their propagation are potential targets for therapeuic countermeasures. No host enzyme has been identified whose genetic absence benefits the intact mammalian host in vivo during infection with Mycobacterium tuberculosis (Mtb), the leading cause of death from bacterial infection. Here, we report that the dsRNA-dependent protein kinase (PKR) is such an enzyme. PKR-deficient mice contained fewer viable Mtb and showed less pulmonary pathology than wild type mice. We identified two potential mechanisms for the protective effect of PKR deficiency: increased apoptosis of macrophages in response to Mtb and enhanced activation of macrophages in response to IFN-gamma. The restraining effect of PKR on macrophage activation was explained by its mediation of a previously unrecognized ability of IFN-gamma to induce low levels of the macrophage deactivating factor interleukin 10 (IL10). These observations suggest that PKR inhibitors may prove useful as an adjunctive treatment for tuberculosis.

Double-stranded RNA-dependent protein kinase links pathogen sensing with stress and metabolic homeostasis

As chronic inflammation is a hallmark of obesity, pathways that integrate nutrient- and pathogen sensing pathways are of great interest in understanding the mechanisms of insulin resistance, type 2 diabetes, and other chronic metabolic pathologies. Here, we provide evidence that double-stranded RNA-dependent protein kinase (PKR) can respond to nutrient signals as well as endoplasmic reticulum (ER) stress and coordinate the activity of other critical inflammatory kinases such as the c-Jun N-terminal kinase (JNK) to regulate insulin action and metabolism. PKR also directly targets and modifies insulin receptor substrate and hence integrates nutrients and insulin action with a defined pathogen response system. Dietary and genetic obesity features marked activation of PKR in adipose and liver tissues and absence of PKR alleviates metabolic deterioration due to nutrient or energy excess in mice. These findings demonstrate PKR as a critical component of an inflammatory complex that responds to nutrients and organelle dysfunction.

The regulation of IL-10 production by immune cells

Interleukin-10 (IL-10), a cytokine with anti-inflammatory properties, has a central role in infection by limiting the immune response to pathogens and thereby preventing damage to the host. Recently, an increasing interest in how IL10 expression is regulated in different immune cells has revealed some of the molecular mechanisms involved at the levels of signal transduction, epigenetics, transcription factor binding and gene activation. Understanding the specific molecular events that regulate the production of IL-10 will help to answer the remaining questions that are important for the design of new strategies of immune intervention.

Vaccinia virus E3 suppresses expression of diverse cytokines through inhibition of the PKR, NF-kappaB, and IRF3 pathways

The vaccinia virus double-stranded RNA binding protein E3 has been demonstrated to inhibit the expression of cytokines, including beta interferon (IFN-beta) and tumor necrosis factor alpha (TNF-alpha). However, few details regarding the molecular mechanisms of this inhibition have been described. Using real-time PCR arrays, we found that E3 suppressed the induction of a diverse array of cytokines representing members of the IFN, interleukin (IL), TNF, and transforming growth factor cytokine families. We discovered that the factor(s) responsible for the induction of IL-6, TNF-alpha, and inhibin beta A (INHBA) was associated with the early and late phases of virus infection. In contrast, the factor(s) which regulates IFN-beta induction was associated with the late phase of replication. We have found that expression of these cytokines can be induced by transfection of cells with RNA isolated from vaccinia virus-infected cells. Moreover, we provide evidence that E3 antagonizes both PKR-dependent and PKR-independent pathways to regulate cytokine expression. PKR-dependent activation of p38 and NF-kappaB was required for vaccinia virus-induced INHBA expression, whereas induction of TNF-alpha required only PKR-dependent NF-kappaB activation. In contrast, induction of IL-6 and IFN-beta was largely PKR independent. IL-6 induction is regulated by NF-kappaB, while IFN-beta induction is mediated by IFN-beta promoter stimulator 1 and IFN regulatory factor 3/NF-kappaB. Collectively, these results indicate that E3 suppresses distinct but interlinked host signaling pathways to inhibit the expression of a diverse array of cytokines.

Activation of host antiviral RNA-sensing factors necessary for herpes simplex virus type 1-activated transcription of host cell fucosyltransferase genes FUT3, FUT5, and FUT6 and subsequent expression of sLe(x) in virus-infected cells

Herpes simplex virus type 1 (HSV-1) induces expression of a selectin receptor, the carbohydrate epitope sialyl Lewis X (sLe(x)), at the surface of infected cells. The molecular background to this phenomenon is that a viral immediate early RNA interacts with as yet unidentified host factors, eventually resulting in transcription of three dormant host fucosyltransferase genes (FUT3, FUT5, and FUT6), whose gene products are rate-limiting for synthesis of sLe(x). The aim of the present study was to define the immediate targets for the viral RNA in this process. We found that the Protein Kinase R (PKR) inhibitors 2-aminopurine (2-AP) and C16 inhibited FUT3, FUT5, and FUT6 expression as well as HSV-1-induced expression of sLe(x), indicating a primary role of PKR as a viral RNA target. The PKR-dependent activation of the FUT genes seemed neither to involve PKR effects on translation nor to involve NF-kappaB- or JNK-dependent activation. IMD-0354, known as an inhibitor of the NF-kappaB-activating factor IKK-2, induced FUT transcription via a novel IKK-2-independent mechanism, irrespective of whether the cells were virus-infected or not. Altogether, the results suggested that PKR is the primary target for HSV-1 early RNA during induction of FUT3, FUT5, and FUT6, and that the subsequent steps in the transcriptional activation of these host genes involve a hitherto unknown IMD-0354, yet IKK-2-independent, pathway.

Interleukin-10: new perspectives on an old cytokine

Interleukin-10 (IL-10) has long been recognized to have potent and broad-spectrum anti-inflammatory activity, which has been unequivocally established in various models of infection, inflammation, and even in cancer. However, because of the marginal successes of the initial clinical trials using recombinant IL-10, some of the interest in this cytokine as an anti-inflammatory therapeutic has diminished. New work showing IL-10 production from regulatory T cells and even T-helper 1 T cells has reinvigorated the field and revealed the power of this cytokine to influence immune responses. Furthermore, new preclinical studies suggest that combination therapies, using antibodies to IL-10 along with chemotherapy, can be effective in treating bacterial, viral, or neoplastic diseases. Studies to understand IL-10 gene expression in the various cell types may lead to new therapeutics to enhance or inhibit IL-10 production. In this review, we summarize what is known about the regulation of IL-10 gene expression by various immune cells. We speculate on the promise that this cytokine holds to influence immune responses and mitigate immune pathologies.