Regulation of Mitochondrial Antiviral Signaling Pathways

Mitochondrial antiviral immunity involves the detection of viral RNA by intracellular pattern-recognition receptors (PRRs) belonging to the RIG-I-like helicase family. The convergence of these and other signaling molecules to the outer mitochondrial membrane results in the rapid induction of antiviral cytokines including type-1 interferon. Here, we discuss recent studies describing new molecules implicated in the regulation of this antiviral response

How Mouse Macrophages Sense What Is Going On

Macrophages are central to both innate and adaptive immunity. With few exceptions, macrophages are the first cells that sense trouble and respond to disturbances in almost all tissues and organs. They sense their environment, inhibit or kill pathogens, take up apoptotic and necrotic cells, heal tissue damage, and present antigens to T cells. Although the origins (yolk sac versus monocyte-derived) and phenotypes (functions, gene expression profiles, surface markers) of macrophages vary between tissues, they have many receptors in common that are specific to one or a few molecular species. Here, we review the expression and function of almost 200 key macrophage receptors that help the macrophages sense what is going on, including pathogen-derived molecules, the state of the surrounding tissue cells, apoptotic and necrotic cell death, antibodies and immune complexes, altered self molecules, extracellular matrix components, and cytokines, including chemokines

Inhibition of IFN-γ Signaling by an Epstein-Barr Virus Immediate-Early Protein

AbstractViruses have evolved elaborate mechanisms to target many aspects of the host's immune response. The cytokine IFN-γ plays a central role in resistance of the host to infection via direct antiviral effects as well as modulation of the immune response. In this study, we demonstrate that the Epstein-Barr virus (EBV) immediate-early protein, BZLF1, inhibits the IFN-γ signaling pathway. BZLF1 decreases the ability of IFN-γ to activate a variety of important downstream target genes, such as IRF-1, p48, and CIITA, and prevents IFN-γ-induced class II MHC surface expression. Additionally, BZLF1 inhibits IFN-γ-induced STAT1 tyrosine phosphorylation and nuclear translocation. Finally, we demonstrate that BZLF1 decreases expression of the IFN-γ receptor, suggesting a mechanism by which EBV may escape antiviral immune responses during primary infection

NLR members NLRC4 and NLRP3 mediate sterile inflammasome activation in microglia and astrocytes

Inflammation in the brain accompanies several high-impact neurological diseases including multiple sclerosis (MS), stroke, and Alzheimer’s disease. Neuroinflammation is sterile, as damage-associated molecular patterns rather than microbial pathogens elicit the response. The inflammasome, which leads to caspase-1 activation, is implicated in neuroinflammation. In this study, we reveal that lysophosphatidylcholine (LPC), a molecule associated with neurodegeneration and demyelination, elicits NLRP3 and NLRC4 inflammasome activation in microglia and astrocytes, which are central players in neuroinflammation. LPC-activated inflammasome also requires ASC (apoptotic speck containing protein with a CARD), caspase-1, cathepsin-mediated degradation, calcium mobilization, and potassium efflux but not caspase-11. To study the physiological relevance, Nlrc4 −/− and Nlrp3 −/− mice are studied in the cuprizone model of neuroinflammation and demyelination. Mice lacking both genes show the most pronounced reduction in astrogliosis and microglial accumulation accompanied by decreased expression of the LPC receptor G2A, whereas MS patient samples show increased G2A. These results reveal that NLRC4 and NLRP3, which normally form distinct inflammasomes, activate an LPC-induced inflammasome and are important in astrogliosis and microgliosis

Mechanisms of NOD-like Receptor-Associated Inflammasome Activation

A major function of a subfamily of NLR (nucleotide-binding domain, leucine rich repeat containing or NOD-like receptor) proteins is in inflammasome activation, which has been implicated in a multitude of disease models and human diseases. This work will highlight key progress in understanding the mechanisms which activates the best studied NLRs (NLRP3, NLRC4, NAIP and NLRP1) and in uncovering new inflammasome NLRs

Inflammasomes and Metabolic Disorders: Old Genes in Modern Diseases

Modern medical and hygienic practices have greatly improved human health and longevity; however, increased human lifespan occurs concomitantly with the emergence of metabolic and age-related diseases. Studies over the past decade have strongly linked host inflammatory responses to the etiology of several metabolic diseases including atherosclerosis, type 2 diabetes (T2D), obesity and gout. A common immunological factor to these diseases is the activation of the inflammasome and release of pro-inflammatory cytokines that promote disease progression. Here we review the molecular mechanism(s) of inflammasome activation in response to metabolic damage associated molecular patterns (DAMPs) and discuss potential targets for therapeutic intervention

Structural constraints within a trimeric transcriptional regulatory region. Constitutive and interferon-gamma-inducible expression of the HLA-DRA gene.

Constitutive and inducible transcription of the major histocompatibility class II HLA-DRA gene involves the upstream S element and the conserved X and Y elements. In this report we have addressed the roles of spatial constraints and stereospecific alignment between the upstream S and X elements, and the X and Y elements, in both constitutive and interferon-gamma (gamma-IFN)-induced expression. Analysis of the constitutive expression in B cell lines (B-LCL) has previously shown that the X and Y elements must be stereoaligned. Further study reveals that any spacing changes between S and X, regardless of the helical alignment of these two elements, is not tolerated. These same restraints are involved in an inducible system, because the response to gamma-IFN treatment requires both stereo alignment between the X and Y elements and precise spacing between the S and X elements. Neither constitutive nor inducible expression can be restored by correcting the distance and spacing between only the S and Y elements with misalignment of X. These results reveal a common pathway for constitutive and inducible expression that may require either direct or indirect protein complex formation among proteins bound to three highly conserved regulatory elements. We have also evaluated the role of the A/T-rich sequence located immediately 5' of the Y element and show that it exerts little effect on constitutive and gamma-IFN induced DRA expression

MEK Inhibition Enhances Paclitaxel-induced Tumor Apoptosis

The anti-cancer drug paclitaxel (Taxol) alters microtubule assembly and activates pro-apoptotic signaling pathways. Previously, we and others found that paclitaxel activates endogenous JNK in tumor cells, and the activation of JNK contributes to tumor cell apoptosis. Here we find that paclitaxel activates the prosurvival MEK/ERK pathway, which conversely may compromise the efficacy of paclitaxel. Hence, a combination treatment of paclitaxel and MEK inhibitors was pursued to determine whether this treatment could lead to enhanced apoptosis. The inhibition of MEK/ERK with a pharmacologic inhibitor, U0126, together with paclitaxel resulted in a dramatic enhancement of apoptosis that is four times more than the additive value of the two drugs alone. Enhanced apoptosis was verified by the terminal transferase-mediated dUTP nick end labeling assay, by an enzyme-linked immunosorbent assay for histone-associated DNA fragments, and by flow cytometric analysis for DNA content. Specificity of the pharmacologic inhibitor was confirmed by the use of (a) a second MEK/ERK inhibitor and (b) a transdominant-negative MEK. Enhanced apoptosis was verified in breast, ovarian, and lung tumor cell lines, suggesting this effect is not cell type-specific. This is the first report of enhanced apoptosis detected in the presence of paclitaxel and MEK inhibition and suggests a new anticancer strategy

Mechanisms of NOD-like Receptor-Associated Inflammasome Activation

A major function of a subfamily of NLR (nucleotide-binding domain, leucine rich repeat containing or NOD-like receptor) proteins is in inflammasome activation, which has been implicated in a multitude of disease models and human diseases. This work will highlight key progress in understanding the mechanisms which activates the best studied NLRs (NLRP3, NLRC4, NAIP and NLRP1) and in uncovering new inflammasome NLRs

The Inflammasome NLRs in Immunity, Inflammation, and Associated Diseases

Inflammasome activation leads to caspase-1 activation, which causes the maturation cleavage of pro-IL-1β and pro-IL-18. A subgroup of the NLR (nucleotide-binding domain, leucine-rich repeat containing) proteins are key mediators of the inflammasome. Studies of gene-deficient mice and cells have implicated NLR inflammasomes in a host of responses to a wide range of microbial pathogens, inflammatory diseases, cancer, and metabolic and autoimmune disorders. Determining exactly how the inflammasome is activated in these diseases and disease models remains a challenge. This review presents and integrates recent progress in the field