IFN-γ elicits macrophage autophagy via the p38 MAPK signaling pathway

Autophagy is a major innate immune defense pathway in both plants and animals. In mammals, this cascade can be elicited by cytokines (IFN-γ) or pattern recognition receptors (TLRs and nucleotide-binding oligomerization domain-like receptors). Many signaling components in TLR- and nucleotide-binding oligomerization domain-like receptor-induced autophagy are now known; however, those involved in activating autophagy via IFN-γ remain to be elucidated. In this study, we engineered macrophages encoding a tandem fluorescently tagged LC3b (tfLC3) autophagosome reporter along with stably integrated short hairpin RNAs to demonstrate IFN-γ-induced autophagy required JAK 1/2, PI3K, and p38 MAPK but not STAT1. Moreover, the autophagy-related guanosine triphosphatase Irgm1 proved dispensable in both stable tfLC3-expressing RAW 264.7 and tfLC3-transduced Irgm1(-/-) primary macrophages, revealing a novel p38 MAPK-dependent, STAT1-independent autophagy pathway that bypasses Irgm1. These unexpected findings have implications for understanding how IFN-γ-induced autophagy is mobilized within macrophages for inflammation and host defense.     

Functional signaling of membrane-bound TL1A induces IFN-γ expression

TL1A, a TNF member implicated in autoimmune diseases, is a transmembrane protein that is processed to release soluble TL1A (TL1A-S). TL1A-S induces a Th1 response, although the functional significance of membrane-bound TL1A (TL1A-M) remains unknown. We generated TL1A-M expression in HEK-293 cells capable of binding DR3-Fc. Co-incubating IL-12/IL-18-primed CD4⁺ T cells with HEK-293 cells expressing TL1A-M induced 3-fold increase in IFN-γ that was blocked by anti-TL1A Ab. These results demonstrate that TL1A-M can bind death domain receptor 3 (DR3) through cell-cell contact to induce downstream IFN-γ secretion enhancement. Anti-TL1A antibodies designed to treat immune diseases should be verified to block both endogenous TL1A forms.     

Exercise-associated generation of PPARγ ligands activates PPARγ signaling events and upregulates genes related to lipid metabolism

The aim of the present study was to test the hypotheses that exercise is associated with generation of peroxisome proliferator-activated receptor-γ (PPARγ) ligands in the plasma and that this may activate PPARγ signaling within circulating monocytes, thus providing a mechanism to underpin the exercise-induced antiatherogenic benefits observed in previous studies. A cohort of healthy individuals undertook an 8-wk exercise-training program; samples were obtained before (Pre) and after (Post) standardized submaximal exercise bouts (45 min of cycling at 70% of maximal O(2) uptake, determined at baseline) at weeks 0, 4, and 8. Addition of plasma samples to PPARγ response element (PPRE)-luciferase reporter gene assays showed increased PPARγ activity following standardized exercise bouts (Post/Pre = 1.23 ± 0.10 at week 0, P < 0.05), suggesting that PPARγ ligands were generated during exercise. However, increases in PPARγ/PPRE-luciferase activity in response to the same standardized exercise bout were blunted during the training program (Post/Pre = 1.18 ± 0.14 and 1.10 ± 0.10 at weeks 4 and 8, respectively, P > 0.05 for both), suggesting that the relative intensity of the exercise may affect PPARγ ligand generation. In untrained individuals, specific transient increases in monocyte expression of PPARγ-regulated genes were observed within 1.5-3 h of exercise (1.7 ± 0.4, 2.6 ± 0.4, and 1.4 ± 0.1 fold for CD36, liver X receptor-α, and ATP-binding cassette subfamily A member 1, respectively, P < 0.05), with expression returning to basal levels within 24 h. In contrast, by the end of the exercise program, expression at the protein level of PPARγ target genes had undergone sustained increases that were not associated with an individual exercise bout (e.g., week 8 Pre/week 0 Pre = 2.79 ± 0.61 for CD36, P < 0.05). Exercise is known to upregulate PPARγ-controlled genes to induce beneficial effects in skeletal muscle (e.g., mitochondrial biogenesis and aerobic respiration). We suggest that parallel exercise-induced benefits may occur in monocytes, as monocyte PPARγ activation has been linked to beneficial antidiabetic effects (e.g., exercise-induced upregulation of monocytic PPARγ-controlled genes is associated with reverse cholesterol transport and anti-inflammatory effects). Thus, exercise-triggered monocyte PPARγ activation may constitute an additional rationale for prescribing exercise to type 2 diabetes patients.     

Involvement of PPAR-γ and p53 in DHA-induced apoptosis in Reh cells

Dendritic cells (DCs) are professional antigen-presenting cells and have come to be appreciated as critical controllers of the immune response, especially T cell responses. Apart from presenting antigens to T cells, DCs carry out many other functions in regulating immunity. DC-specific intercellular adhesion molecule (ICAM)-3 grabbing non-integrin (DC-SIGN) is a novel receptor that plays an important role in DC migration and adhesion, the inflammatory response, T cell activation, initiating the immune response, and immune escape of pathogens and tumors. DC-SIGN mediates DC binding to ICAM-3 on the T cell surface and ICAM-2 on the endothelial cell (EC) surface, and takes part in the initial interaction between DC and T cells or vascular ECs. The procedure of systematic evolution of ligands by exponential enrichment (SELEX) is a method in which single-stranded oligonucleotides are selected from a wide variety of sequences, based on their interaction with a target molecule. In this study, we selected DNA aptamers against DC-SIGN protein by SELEX, and measured their binding affinity for DC-SIGN. Finally, an appropriate aptamer with high affinity for DC-SIGN was obtained, and it blocked DC adhesion to ECs as effectively as anti-DC-SIGN monoclonal antibody.     

The association between IFN-γ and IL-4 genetic polymorphisms and childhood susceptibility to bronchial asthma

The present study aims to investigate the association between the genetic polymorphisms of interferon (IFN)-γ and interleukin (IL)-4 with childhood susceptibility to asthma and the levels of IFN-γ, IL-4, and immunoglobulin (Ig) E among asthmatic children. A total of 100 asthmatic children and 122 control children were enrolled in the present study. The genotypes of the IFN-γ gene at the − 179G/T locus and the IL-4 gene at the − 33C/T and − 589C/T loci were detected using polymerase chain reaction with restriction fragment length polymorphism. The IFN-γ gene at the + 874A/T locus and the IFN-γ CA repeats were tested using allele-specific and capillary electrophoresis, respectively, whereas the IFN-γ, IL-4, and total IgE levels were measured using enzyme-linked immunosorbent assays. The 100 asthmatic children and the 122 control children were all GG homozygous in the − 179 locus of the IFN-γ gene, which shows that the IFN-γ gene is not mutated at the − 179 locus. No significant differences were found in terms of genotypic and allelic frequency distribution in the IFN-γ gene or the CA repeat at the + 874A/T locus between the asthmatic children and the control (P > 0.05). An association was found between the polymorphism of the IFN-γ gene at + 874A/T and IFN-γ levels. IFN-γ expression was lower among patients with the AA genotype than those with the AT genotype (P < 0.05); the genotypic and allelic frequency distributions of the IL-4 gene at − 33C/T and − 589C/T were significantly different between the asthmatic children and the control (P < 0.05). The levels of IL-4 and IgE among children with TT genotype at the − 33 and − 589 loci were higher than those with the CT genotype, but only the polymorphism at − 33C/T was associated with IL-4 levels (P < 0.05). The polymorphisms of the IFN-γ gene at + 874A/T or the CA repeats are not correlated with susceptibility to asthma. Thus, the polymorphism at + 874A/T is correlated with IFN-γ level. The TT genotypes of the IL-4 gene at the − 33 and − 589 loci are associated with asthma susceptibility in children, and polymorphism at the − 33 locus may be associated with IL-4 level.     

Modeling oscillatory control in NF-κB, p53 and Wnt signaling

Oscillations are commonly observed in cellular behavior and span a wide range of timescales, from seconds in calcium signaling to 24 hours in circadian rhythms. In between lie oscillations with time periods of 1-5 hours seen in NF-κB, p53 and Wnt signaling, which play key roles in the immune system, cell growth/death and embryo development, respectively. In the first part of this article, we provide a brief overview of simple deterministic models of oscillations. In particular, we explain the mechanism of saturated degradation that has been used to model oscillations in the NF-κB, p53 and Wnt systems. The second part deals with the potential physiological role of oscillations. We use the simple models described earlier to explore whether oscillatory signals can encode more information than steady-state signals. We then discuss a few simple genetic circuits that could decode information stored in the average, amplitude or frequency of oscillations. The presence of frequency-detector circuit downstream of NF-κB or p53 would be a strong clue that oscillations are important for the physiological response of these signaling systems.     

PFT-α inhibits antibody-induced activation of p53 and pro-apoptotic signaling in 1-LN prostate cancer cells

Antibodies against the COOH-terminal domain of cell surface GRP78 induce apoptosis in cancer cell lines via activation of p53 signaling. We now have studied the effects of PFT-α, an inhibitor of p53-mediated apoptotic pathways, on anti-GRP78 antibody-induced activation of p53 and pro-apoptotic signaling in 1-LN prostate cancer cells. Pretreatment of 1-LN cancer cells with this agent significantly inhibited antibody or doxorubicin-induced upregulation of p53. Concomitantly, PFT-α treatment prevented down regulation of ERK1/2 activation by either antibody or doxorubicin. Likewise, PFT-α prevented increases in the pro-apoptotic proteins BAD, BAK, BAX, PUMA, and NOXA as well as activation of caspases-3, -7, and -9. We conclude that antibody-induced apoptosis in prostate cancer cells is mediated predominantly by p53 using the mitochondrial pathway of apoptosis.     

DNA vaccination of bison to brucellar antigens elicits elevated antibody and IFN-γ responses

Brucella abortus remains a threat to the health and well-being of livestock in states bordering the Greater Yellowstone Area. During the past several years, cohabitation of infected wildlife with cattle has jeopardized the brucellosis-free status of Idaho, USA; Wyoming, USA; and Montana, USA. Current livestock B. abortus vaccines have not proven to be efficacious in bison (Bison bison) or elk (Cervus elaphus nelsoni). One problem with the lack of vaccine efficacy may stem from the failure to understand wildlife immune responses to vaccines. In an attempt to understand their immune responses, bison were vaccinated with eukaryotic DNA expression vectors encoding the Brucella periplasmic protein, bp26, and the chaperone protein, trigger factor (TF). These DNA vaccines have previously been shown to be protective against Brucella infection in mice. Bison were immunized intramuscularly at weeks 0, 2, and 4 with bp26 and TF DNA vaccines plus CpG adjuvant or empty vector (control) plus CpG. Blood samples were collected before vaccination and at 8, 10, and 12 wk after primary vaccination. The results showed that bison immunized with bp26 and TF DNA vaccines developed enhanced antibody, proliferative T cell, and interferon-gamma (IFN-γ) responses upon in vitro restimulation with purified recombinant bp26 or TF antigens, unlike bison immunized with empty vector. Flow cytometric analysis revealed that the percentages of CD4(+) and CD8(+) T lymphocytes from the DNA-vaccinated groups were significantly greater than they were for those bison given empty vector. These data suggest that DNA vaccination of bison may elicit strong cellular immune responses and serve as an alternative for vaccination of bison for brucellosis.     

Does cytokine signaling link sphingolipid metabolism to host defense and immunity against virus infections?

Sphingosine 1-phosphate (S1P)-metabolizing enzymes regulate the level of bioactive sphingolipids that have curative potential. Recently, S1P-metabolizing enzymes such as sphingosine kinase 1 and S1P lyase were shown to regulate influenza virus replication and the virus-induced cytopathogenicity. The mechanism appeared to employ a JAK/STAT type I interferon signaling pathway that induces anti-viral status. Further, sphingosine analogs altered cytokine responses upon influenza virus infection. This article focuses on recent discoveries about the sphingolipid system that influences on host protection from viral virulence and the involvement of cytokine signaling in its underlying mechanisms. Deciphering the steps of this pathway could help us envision how the modulation of sphingolipid metabolism can be applied as a therapeutic approach to overcome infectious diseases.     

p53-mediated induction of Noxa and p53AIP1 requires NFκB

The intricate regulation of cell survival and cell death is critical for the existence of both normal and transformed cells. Two factors central to these processes are p53 and NFκB, with both factors having ascribed roles in both promoting and repressing cell death. Not surprisingly, a number of studies have previously reported interplay between p53 and NFκB. The mechanistic basis behind these observations, however, is currently incomplete. We report here further insights into this interplay using a system where blockade of NFκB inhibits cell death from p53, but at the same time sensitizes cells to death by TNFα. We found in agreement with a recent report showing that NFκB is required for the efficient activation of the BH3-only protein Noxa by the p53 family member p73, that p53’s ability to induce Noxa is also impeded by inhibition of NFκB. In contrast to the regulation by p73, however, blockade of NFκB downstream of p53 decreases Noxa protein levels without effects on Noxa mRNA. Our further analysis of the effects of NFκB inhibition on p53 target gene expression revealed that while most target genes analysed where unaffected by blockade of NFκB, the p53-mediated induction of the pro-apoptotic gene p53AIP1 was significantly dependent on NFκB. These studies therefore add further insight into the complex relationship of p53 and NFκB and since both Noxa and p53AIP1 have been shown to be important components of p53-mediated cell death responses, these findings may also indicate critical points where NFκB plays a pro-apoptotic role downstream of p53.     

Autocrine IFN-γ promotes naive CD8 T cell differentiation and synergizes with IFN-α to stimulate strong function

Autocrine IFN-γ signaling is important for CD4 differentiation to Th1 effector cells, but it has been unclear whether it contributes to CD8 T cell differentiation. We show in this paper that naive murine CD8 T cells rapidly and transiently produce low levels of IFN-γ upon stimulation with Ag and B7-1, with production peaking at ～8 h and declining by 24 h. The autocrine IFN-γ signals for upregulation of expression of T-bet and granzyme B and induces weak cytolytic activity and effector IFN-γ production. IFN-α acts synergistically with IFN-γ to support development of strong effector functions, whereas IL-12 induces high T-bet expression and strong function in the absence of IFN-γ signaling. Thus, IFN-γ is not only an important CD8 T cell effector cytokine, it is an autocrine/paracrine factor whose contributions to differentiation vary depending on whether the response is supported by IL-12 or type I IFN.     

Autophagy facilitates an IFN-γ response and signal transduction

Autophagy, that is directly triggered by invaded pathogens and indirectly triggered by IFN-γ, acts as a defense by mediating intracellular microbial recognition and clearance. In addition, autophagy contributes to inflammation by facilitating an IFN-γ response and signal transduction. For immune escape, downregulated autophagy may be a strategy used by microbes.     

IFN-γ upregulates survivin and Ifi202 expression to induce survival and proliferation of tumor-specific T cells

Background

A common procedure in human cytotoxic T lymphocyte (CTL) adoptive transfer immunotherapy is to expand tumor-specific CTLs ex vivo using CD3 mAb prior to transfer. One of the major obstacles of CTL adoptive immunotherapy is a lack of CTL persistence in the tumor-bearing host after transfer. The aim of this study is to elucidate the molecular mechanisms underlying the effects of stimulation conditions on proliferation and survival of tumor-specific CTLs.

Methodology/Principal Findings

Tumor-specific CTLs were stimulated with either CD3 mAb or cognate Ag and analyzed for their proliferation and survival ex vivo and persistence in tumor-bearing mice. Although both Ag and CD3 mAb effectively induced the cytotoxic effecter molecules of the CTLs, we observed that Ag stimulation is essential for sustained CTL proliferation and survival. Further analysis revealed that Ag stimulation leads to greater proliferation rates and less apoptosis than CD3 mAb stimulation. Re-stimulation of the CD3 mAb-stimulated CTLs with Ag resulted in restored CTL proliferative potential, suggesting that CD3 mAb-induced loss of proliferative potential is reversible. Using DNA microarray technology, we identified that survivin and ifi202, two genes with known functions in T cell apoptosis and proliferation, are differentially induced between Ag- and CD3 mAb-stimulated CTLs. Analysis of the IFN-γ signaling pathway activation revealed that Ag stimulation resulted in rapid phosphorylation of STAT1 (pSTAT1), whereas CD3 mAb stimulation failed to activate STAT1. Chromatin immunoprecipitation revealed that pSTAT1 is associated with the promoters of both survivin and ifi202 in T cells and electrophoresis mobility shift assay indicated that pSTAT1 directly binds to the gamma activation sequence element in the survivin and ifi202 promoters. Finally, silencing ifi202 expression significantly decreased T cell proliferation.

Conclusions/Significance

Our findings delineate a new role of the IFN-γ signaling pathway in regulating T cell proliferation and apoptosis through upregulating survivin and ifi202 expression.