C/EBP homologous protein (CHOP) up-regulates IL-6 transcription by trapping negative regulating NF-IL6 isoform

Direct and acute effects of advanced glycation end products on proteostasis in isolated mouse skeletal muscle

Advanced glycation end products (AGEs) have been implicated in several skeletal muscle dysfunctions. However, whether the adverse effects of AGEs on skeletal muscle are because of their direct action on the skeletal muscle tissue is unclear. Therefore, this study aimed to investigate the direct and acute effects of AGEs on skeletal muscle using an isolated mouse skeletal muscle to eliminate several confounders derived from other organs. The results showed that the incubation of isolated mouse skeletal muscle with AGEs (1 mg/mL) for 2-6 h suppressed protein synthesis and the mechanistic target of rapamycin signaling pathway. Furthermore, AGEs showed potential inhibitory effects on protein degradation pathways, including autophagy and the ubiquitin-proteasome system. Additionally, AGEs stimulated endoplasmic reticulum (ER) stress by modulating the activating transcription factor 6, PKR-like ER kinase, C/EBP homologous protein, and altered inflammatory cytokine expression. AGEs also stimulated receptor for AGEs (RAGE)-associated signaling molecules, including mitogen-activated protein kinases. These findings suggest that AGEs have direct and acute effect on skeletal muscle and disturb proteostasis by modulating intracellular pathways such as RAGE signaling, protein synthesis, proteolysis, ER stress, and inflammatory cytokines.

Signaling plasticity in the integrated stress response

The Integrated Stress Response (ISR) is an essential homeostatic signaling network that controls the cell's biosynthetic capacity. Four ISR sensor kinases detect multiple stressors and relay this information to downstream effectors by phosphorylating a common node: the alpha subunit of the eukaryotic initiation factor eIF2. As a result, general protein synthesis is repressed while select transcripts are preferentially translated, thus remodeling the proteome and transcriptome. Mounting evidence supports a view of the ISR as a dynamic signaling network with multiple modulators and feedback regulatory features that vary across cell and tissue types. Here, we discuss updated views on ISR sensor kinase mechanisms, how the subcellular localization of ISR components impacts signaling, and highlight ISR signaling differences across cells and tissues. Finally, we consider crosstalk between the ISR and other signaling pathways as a determinant of cell health.

Anticancer Activity of ST101, A Novel Antagonist of CCAAT/Enhancer Binding Protein β

CCAAT/enhancer binding protein β (C/EBPβ) is a basic leucine zipper (bZIP) family transcription factor, which is upregulated or overactivated in many cancers, resulting in a gene expression profile that drives oncogenesis. C/EBPβ dimerization regulates binding to DNA at the canonical TTGCGCAA motif and subsequent transcriptional activity, suggesting that disruption of dimerization represents a powerful approach to inhibit this previously "undruggable" oncogenic target. Here we describe the mechanism of action and antitumor activity of ST101, a novel and selective peptide antagonist of C/EBPβ that is currently in clinical evaluation in patients with advanced solid tumors. ST101 binds the leucine zipper domain of C/EBPβ, preventing its dimerization and enhancing ubiquitin-proteasome dependent C/EBPβ degradation. ST101 exposure attenuates transcription of C/EBPβ target genes, including a significant decrease in expression of survival, transcription factors, and cell-cycle-related proteins. The result of ST101 exposure is potent, tumor-specific in vitro cytotoxic activity in cancer cell lines including glioblastoma, breast, melanoma, prostate, and lung cancer, whereas normal human immune and epithelial cells are not impacted. Further, in mouse xenograft models ST101 exposure results in potent tumor growth inhibition or regression, both as a single agent and in combination studies. These data provide the First Disclosure of ST101, and support continued clinical development of ST101 as a novel strategy for targeting C/EBPβ-dependent cancers.

miR-21 and miR-146a: The microRNAs of inflammaging and age-related diseases

The first paper on "inflammaging" published in 2001 paved the way for a unifying theory on how and why aging turns out to be the main risk factor for the development of the most common age-related diseases (ARDs). The most exciting challenge on this topic was explaining how systemic inflammation steeps up with age and why it shows different rates among individuals of the same chronological age. The "epigenetic revolution" in the past twenty years conveyed that the assessment of the individual genetic make-up is not enough to depict the trajectories of age-related inflammation. Accordingly, others and we have been focusing on the role of non-coding RNA, i.e. microRNAs (miRNAs), in inflammaging. The results obtained in the latest 10 years underpinned the key role of a miRNA subset that we have called inflammamiRs, owing to their ability to master (NF-κB)-driven inflammatory pathways. In this review, we will focus on two inflammamiRs, i.e. miR-21-5p and miR-146a-5p, which target a variety of molecules belonging to the NF-κB/NLRP3 pathways. The interplay between miR-146a-5p and IL-6 in the context of aging and ARDs will also be highlighted. We will also provide the most relevant evidence suggesting that circulating inflammamiRs, along with IL-6, can measure the degree of inflammaging.

The long noncoding RNA of RMRP is downregulated by PERK, which induces apoptosis in hepatocellular carcinoma cells

Endoplasmic reticulum (ER) stress plays an important role in hepatocyte degeneration, especially in patients with chronic liver injury. Protein kinase R-like endoplasmic reticulum kinase (PERK) is a key molecule in ER stress. PERK may contribute to apoptotic cell death in HCC, however the details of the mechanism are not clear. In this study, we identified PERK-associated molecules using transcriptome analysis. We modulated PERK expression using a plasmid, tunicamycin and siRNA against PERK, and then confirmed the target gene expression with real-time PCR and Northern blotting. We further analyzed the apoptotic function. Transcriptome analysis revealed that expression of the RNA component of mitochondrial RNA processing endoribonuclease (RMRP), which is a long noncoding RNA, was strongly correlated with the function of PERK. The expression of RMRP was correlated with the expression of PERK in experiments with the siRNA and PERK plasmid in both HCC cell lines and human HCC tissue. Furthermore, RMRP downregulation induced apoptotic cell death. RMRP is downregulated by PERK, which induces apoptosis in HCC. RMRP could be a new therapeutic target to regulate HCC in patients with chronic liver diseases associated with ER stress.

Nogo-A Is Critical for Pro-Inflammatory Gene Regulation in Myocytes and Macrophages

Nogo-A (Rtn 4A), a member of the reticulon 4 (Rtn4) protein family, is a neurite outgrowth inhibitor protein that is primarily expressed in the central nervous system (CNS). However, previous studies revealed that Nogo-A was upregulated in skeletal muscles of Amyotrophic lateral sclerosis (ALS) patients. Additionally, experiments showed that endoplasmic reticulum (ER) stress marker, C/EBP homologous protein (CHOP), was upregulated in gastrocnemius muscle of a murine model of ALS. We therefore hypothesized that Nogo-A might relate to skeletal muscle diseases. According to our knocking down and overexpression results in muscle cell line (C2C12), we have found that upregulation of Nogo-A resulted in upregulation of CHOP, pro-inflammatory cytokines such as interleukin (IL)-6 and tumor necrosis factor (TNF)-α, while downregulation of Nogo-A led to downregulation of CHOP, IL-6 and TNF-α. Immunofluorescence results showed that Nogo-A and CHOP were expressed by myofibers as well as tissue macrophages. Since resident macrophages share similar functions as bone marrow-derived macrophages (BMDM), we therefore, isolated macrophages from bone marrow to study the role of Nogo-A in activation of these cells. Lipopolysaccharide (LPS)-stimulated BMDM in Nogo-KO mice showed low mRNA expression of CHOP, IL-6 and TNF-α compared to BMDM in wild type (WT) mice. Interestingly, Nogo knockout (KO) BMDM exhibited lower migratory activity and phagocytic ability compared with WT BMDM after LPS treatment. In addition, mice experiments data revealed that upregulation of Nogo-A in notexin- and tunicamycin-treated muscles was associated with upregulation of CHOP, IL-6 and TNF-α in WT group, while in Nogo-KO group resulted in low expression level of CHOP, IL-6 and TNF-α. Furthermore, upregulation of Nogo-A in dystrophin-deficient (mdx) murine model, myopathy and Duchenne muscle dystrophy (DMD) clinical biopsies was associated with upregulation of CHOP, IL-6 and TNF-α. To the best of our knowledge, this is the first study to demonstrate Nogo-A as a regulator of inflammation in diseased muscle and bone marrow macrophages and that deletion of Nogo-A alleviates muscle inflammation and it can be utilized as a therapeutic target for improving muscle diseases.

Iron Oxide Particles Alter Bacterial Uptake and the LPS-Induced Inflammatory Response in Macrophages

Exposure to geogenic (earth-derived) particulate matter (PM) is linked to severe bacterial infections in Australian Aboriginal communities. Experimental studies have shown that the concentration of iron in geogenic PM is associated with the magnitude of respiratory health effects, however, the mechanism is unclear. We investigated the effect of silica and iron oxide on the inflammatory response and bacterial phagocytosis in macrophages. THP-1 and peripheral blood mononuclear cell-derived macrophages were exposed to iron oxide (haematite or magnetite) or silica PM with or without exposure to lipopolysaccharide. Cytotoxicity and inflammation were assessed by LDH assay and ELISA respectively. The uptake of non-typeable Haemophilus influenzae by macrophages was quantified by flow cytometry. Iron oxide increased IL-8 production while silica also induced significant production of IL-1β. Both iron oxide and silica enhanced LPS-induced production of TNF-α, IL-1β, IL-6 and IL-8 in THP-1 cells with most of these responses replicated in PBMCs. While silica had no effect on NTHi phagocytosis, iron oxide significantly impaired this response. These data suggest that geogenic particles, particularly iron oxide PM, cause inflammatory cytokine production in macrophages and impair bacterial phagocytosis. These responses do not appear to be linked. This provides a possible mechanism for the link between exposure to these particles and severe bacterial infection.

The integrated stress response in pulmonary disease

The respiratory tract and its resident immune cells face daily exposure to stress, both from without and from within. Inhaled pathogens, including severe acute respiratory syndrome coronavirus 2, and toxins from pollution trigger a cellular defence system that reduces protein synthesis to minimise viral replication or the accumulation of misfolded proteins. Simultaneously, a gene expression programme enhances antioxidant and protein folding machineries in the lung. Four kinases (PERK, PKR, GCN2 and HRI) sense a diverse range of stresses to trigger this “integrated stress response”. Here we review recent advances identifying the integrated stress response as a critical pathway in the pathogenesis of pulmonary diseases, including pneumonias, thoracic malignancy, pulmonary fibrosis and pulmonary hypertension. Understanding the integrated stress response provides novel targets for the development of therapies.

The ageing lung under stress

Healthy ageing of the lung involves structural changes but also numerous cell-intrinsic and cell-extrinsic alterations. Among them are the age-related decline in central cellular quality control mechanisms such as redox and protein homeostasis. In this review, we would like to provide a conceptual framework of how impaired stress responses in the ageing lung, as exemplified by dysfunctional redox and protein homeostasis, may contribute to onset and progression of COPD and idiopathic pulmonary fibrosis (IPF). We propose that age-related imbalanced redox and protein homeostasis acts, amongst others (e.g.cellular senescence), as a “first hit” that challenges the adaptive stress-response pathways of the cell, increases the level of oxidative stress and renders the lung susceptible to subsequent injury and disease. In both COPD and IPF, additional environmental insults such as smoking, air pollution and/or infections then serve as “second hits” which contribute to persistently elevated oxidative stress that overwhelms the already weakened adaptive defence and repair pathways in the elderly towards non-adaptive, irremediable stress thereby promoting development and progression of respiratory diseases. COPD and IPF are thus distinct horns of the same devil, “lung ageing”.

Molecular Insight Into the IRE1α-Mediated Type I Interferon Response Induced by Proteasome Impairment in Myeloid Cells of the Brain

Proteostasis is critical for cells to maintain the balance between protein synthesis, quality control, and degradation. This is particularly important for myeloid cells of the central nervous system as their immunological function relies on proper intracellular protein turnover by the ubiquitin-proteasome system. Accordingly, disruption of proteasome activity due to, e.g., loss-of-function mutations within genes encoding proteasome subunits, results in systemic autoinflammation. On the molecular level, pharmacological inhibition of proteasome results in endoplasmic reticulum (ER) stress-activated unfolded protein response (UPR) as well as an induction of type I interferons (IFN). Nevertheless, our understanding as to whether and to which extent UPR signaling regulates type I IFN response is limited. To address this issue, we have tested the effects of proteasome dysfunction upon treatment with proteasome inhibitors in primary murine microglia and microglia-like cell line BV-2. Our data show that proteasome impairment by bortezomib is a stimulus that activates all three intracellular ER-stress transducers activation transcription factor 6, protein kinase R-like endoplasmic reticulum kinase and inositol-requiring protein 1 alpha (IRE1α), causing a full activation of the UPR. We further demonstrate that impaired proteasome activity in microglia cells triggers an induction of IFNβ1 in an IRE1-dependent manner. An inhibition of the IRE1 endoribonuclease activity significantly attenuates TANK-binding kinase 1-mediated activation of type I IFN. Moreover, interfering with TANK-binding kinase 1 activity also compromised the expression of C/EBP homologous protein 10, thereby emphasizing a multilayered interplay between UPR and type IFN response pathway. Interestingly, the induced protein kinase R-like endoplasmic reticulum kinase-activation transcription factor 4-C/EBP homologous protein 10 and IRE1-X-box-binding protein 1 axes caused a significant upregulation of proinflammatory cytokine interleukin 6 expression that exacerbates STAT1/STAT3 signaling in cells with dysfunctional proteasomes. Altogether, these findings indicate that proteasome impairment disrupts ER homeostasis and triggers a complex interchange between ER-stress sensors and type I IFN signaling, thus inducing in myeloid cells a state of chronic inflammation.

Inflammatory responses to a pathogenic West Nile virus strain

Background

West Nile virus (WNV) circulates across Australia and was referred to historically as Kunjin virus (WNV_KUN). WNV_KUN has been considered more benign than other WNV strains circulating globally. In 2011, a more virulent form of the virus emerged during an outbreak of equine arboviral disease in Australia.

Methods

To better understand the emergence of this virulent phenotype and the mechanism by which pathogenicity is manifested in its host, cells were infected with either the virulent strain (NSW2012), or less pathogenic historical isolates, and their innate immune responses compared by digital immune gene expression profiling. Two different cell systems were used: a neuroblastoma cell line (SK-N-SH cells) and neuronal cells derived from induced pluripotent stem cells (iPSCs).

Results

Significant innate immune gene induction was observed in both systems. The NSW2012 isolate induced higher gene expression of two genes (IL-8 and CCL2) when compared with cells infected with less pathogenic isolates. Pathway analysis of induced inflammation-associated genes also indicated generally higher activation in infected NSW2012 cells. However, this differential response was not paralleled in the neuronal cultures.

Conclusion

NSW2012 may have unique genetic characteristics which contributed to the outbreak. The data herein is consistent with the possibility that the virulence of NSW2012 is underpinned by increased induction of inflammatory genes.

Ac-SDKP ameliorates the progression of experimental autoimmune encephalomyelitis via inhibition of ER stress and oxidative stress in the hippocampus of C57BL/6 mice

Despite the attention given to the treatment of multiple sclerosis (MS), still no certain cure is available. The main purpose of MS drugs is acting against neuroinflammation which underlies the pathology of MS. Neuroinflammation is associated with endoplasmic reticulum (ER) stress that mediates neural apoptosis. In the present study, we hypothesized that the tetrapeptide N-acetyl-ser-asp-lys-pro (Ac-SDKP) with the previously described anti-fibrotic effects might have anti-inflammatory, anti-oxidative and anti-ER stress roles in the hippocampus. We used myelin oligodendrocyte glycoprotein (MOG) to induce experimental autoimmune encephalomyelitis (EAE), a widely-accepted animal model of MS, in C57BL/6 mice. The protein levels of ER stress-related molecules including caspase-12, C/EBP homologous protein (CHOP), and protein disulfide isomerase (PDI) in the hippocampus were examined by immunoblotting. Hence, reactive oxygen species (ROS) production, lipid peroxidation and antioxidant capacity of the hippocampus were studied. Moreover, hippocampal morphology changes, leukocytes infiltration, and the levels of IL-6 and IL-1β pro-inflammatory cytokines were evaluated. Our results displayed that Ac-SDKP down regulates caspase-12 and CHOP expression in the hippocampus-resident oligodendrocytes of EAE mice. Further, treatment with Ac-SDKP decreased oxidative stress markers and caspase-3 activation in the hippocampus of EAE mice. According to our findings, Ac-SDKP showed beneficial effects against ER stress and oxidative stress in addition to inflammation in the hippocampus of EAE mice. The present study provides the basis for further research on the therapeutic applications of Ac-SDKP to reduce ER stress and oxidative stress-induced apoptosis in neurodegenerative disorders.

Regulation and role of the ER stress transcription factor CHOP in alveolar epithelial type-II cells

Abstract

Idiopathic pulmonary fibrosis (IPF) is a fatal disease characterized by type-II alveolar epithelial cell (AECII) injury and fibroblast hyperproliferation. Severe AECII endoplasmic reticulum (ER) stress is thought to underlie IPF, but is yet incompletely understood. We studied the regulation of C/EBP homologous protein (CHOP), a proapoptotic ER-stress-related transcription factor (TF) in AECII-like cells. Interestingly, single or combined overexpression of the active ER stress transducers activating transcription factor-4 (Atf4) and activating transcription factor-6 (p50Atf6) or spliced x-box-binding protein-1 (sXbp1) in MLE12 cells did not result in a substantial Chop induction, as compared to the ER stress inducer thapsigargin. Employing reporter gene assays of distinct CHOP promoter fragments, we could identify that, next to the conventional amino acid (AARE) and ER stress response elements (ERSE) within the CHOP promoter, activator protein-1 (AP-1) and c-Ets-1 TF binding sites are necessary for CHOP induction. Serial deletion and mutation analyses revealed that both AP-1 and c-Ets-1 motifs act in concert to induce CHOP expression. In agreement, CHOP promoter activity was greatly enhanced upon combined versus single overexpression of AP-1 and c-Ets-1. Moreover, combined overexpression of AP-1 and c-Ets-1 in MLE12 cells alone in the absence of any other ER stress inducer was sufficient to induce Chop protein expression. Further, AP-1 and c-Ets-1 were upregulated in AECII under ER stress conditions and in human IPF. Finally, Chop overexpression in vitro resulted in AECII apoptosis, lung fibroblast proliferation, and collagen-I production. We propose that CHOP activation by AP-1 and c-Ets-1 plays a key role in AECII maladaptive ER stress responses and consecutive fibrosis, offering new therapeutic prospects in IPF.

Key messages

Overexpression of active ER stress sensors Atf4, Atf6, and Xbp1 does not induce Chop.

AP-1 and c-Ets-1 TFs are necessary for induction of the ER stress factor Chop.

AP-1 and c-Ets-1 alone induce Chop expression in the absence of any ER stress inducers.

AP-1 and c-Ets-1 are induced in AECII under ER stress conditions and in human IPF.

Chop expression alone triggers AECII apoptosis and consecutive profibrotic responses.

Electronic supplementary material

The online version of this article (10.1007/s00109-019-01787-9) contains supplementary material, which is available to authorized users.

ER stress-induced mediator C/EBP homologous protein thwarts effector T cell activity in tumors through T-bet repression

Understanding the intrinsic mediators that render CD8⁺ T cells dysfunctional in the tumor microenvironment is a requirement to develop more effective cancer immunotherapies. Here, we report that C/EBP homologous protein (Chop), a downstream sensor of severe endoplasmic reticulum (ER) stress, is a major negative regulator of the effector function of tumor-reactive CD8⁺ T cells. Chop expression is increased in tumor-infiltrating CD8⁺ T cells, which correlates with poor clinical outcome in ovarian cancer patients. Deletion of Chop in T cells improves spontaneous antitumor CD8⁺ T cell immunity and boosts the efficacy of T cell-based immunotherapy. Mechanistically, Chop in CD8⁺ T cells is elevated primarily through the ER stress-associated kinase Perk and a subsequent induction of Atf4; and directly represses the expression of T-bet, a master regulator of effector T cell function. These findings demonstrate the primary role of Chop in tumor-induced CD8⁺ T cell dysfunction and the therapeutic potential of blocking Chop or ER stress to unleash T cell-mediated antitumor immunity.

Physiological/pathological ramifications of transcription factors in the unfolded protein response

Numerous environmental, physiological, and pathological insults disrupt protein-folding homeostasis in the endoplasmic reticulum (ER), referred to as ER stress. Eukaryotic cells evolved a set of intracellular signaling pathways, collectively termed the unfolded protein response (UPR), to maintain a productive ER protein-folding environment through reprogramming gene transcription and mRNA translation. The UPR is largely dependent on transcription factors (TFs) that modulate expression of genes involved in many physiological and pathological conditions, including development, metabolism, inflammation, neurodegenerative diseases, and cancer. Here we summarize the current knowledge about these mechanisms, their impact on physiological/pathological processes, and potential therapeutic applications.

Subclinical cutaneous inflammation remained after permeability barrier disruption enhances UV sensitivity by altering ER stress responses and topical pseudoceramide prevents them

Stratum corneum forms the UV barrier. The effect of ultraviolet B (UVB) on normal skin was extensively studied; however, its effect on barrier perturbed skin remains undefined. Both barrier perturbation and UVB irradiation induce endoplasmic reticulum (ER) stress and unfolded protein response (UPR) in keratinocytes. Mild ER stress activates homeostatic UPR, while severe ER stress leads to abnormal UPR, promoting apoptosis and inflammation. Here, we investigated UV sensitivity and UVB-induced UPR in barrier-disrupted human skin and the effects of pseudoceramide-dominant emollient on UVB-induced skin responses. Tape-stripped skin of healthy volunteers showed enhanced susceptibility to erythema and augmented proinflammatory cytokines induction following suberythemal UVB irradiation. Suberythemal UVB activated XBP1 in normal skin, while increased CHOP transcription in barrier perturbed skin. After tape stripping, pseudoceramide-dominant emollient was applied for 3 days, and then, the areas were irradiated with suberythemal UVB. Pretreatment with topical pseudoceramide protected against UVB-induced upregulation of IL-1β, IL-6, and TNF-α transcription and reduced susceptibility to erythema following UVB. Topical pseudoceramide also suppressed suberythemal UVB-induced CHOP transcription in barrier-disrupted skin. Taken together, these data indicate that permeability barrier disruption increases UV sensitivity in human skin, partly via switch the UVB-induced UPR, from homeostatic signals to pro-apoptotic and proinflammatory signals. In addition, we conclude that pseudoceramide-dominant emollient suppresses excessive ER stress induction and CHOP activation following UVB in barrier damaged skin, providing evidence that pseudoceramide-dominant emollients can be promising strategies for photoprotection of the barrier damaged skin.

Hall of Fame among Pro-inflammatory Cytokines: Interleukin-6 Gene and Its Transcriptional Regulation Mechanisms

Pro-inflammatory cytokines that are generated by immune system cells and mediate many kinds of immune responses are kinds of endogenous polypeptides. They are also the effectors of the autoimmune system. It is generally accepted that interleukin (IL)-4, IL-6, IL-9, IL-17, and tumor necrosis factor-α are pro-inflammatory cytokines; however, IL-6 becomes a protagonist among them since it predominately induces pro-inflammatory signaling and regulates massive cellular processes. It has been ascertained that IL-6 is associated with a large number of diseases with inflammatory background, such as anemia of chronic diseases, angiogenesis acute-phase response, bone metabolism, cartilage metabolism, and multiple cancers. Despite great progress in the relative field, the targeted regulation of IL-6 response for therapeutic benefits remains incompletely to be understood. Therefore, it is conceivable that understanding mechanisms of IL-6 from the perspective of gene regulation can better facilitate to determine the pathogenesis of the disease, providing more solid scientific basis for clinical treatment translation. In this review, we summarize the candidate genes that have been implicated in clinical target therapy from the perspective of gene transcription regulation.

Causes and consequences of endoplasmic reticulum stress in rheumatic disease

Rheumatic diseases represent a heterogeneous group of inflammatory conditions, many of which involve chronic activation of both innate and adaptive immune responses by multiple genetic and environmental factors. These immune responses involve the secretion of excessive amounts of cytokines and other signalling mediators by activated immune cells. The endoplasmic reticulum (ER) is the cellular organelle that directs the folding, processing and trafficking of membrane-bound and secreted proteins, including many key components of the immune response. Maintaining homeostasis in the ER is critical to cell function and survival. Consequently, elaborate mechanisms have evolved to sense and respond to ER stress through three main signalling pathways that together comprise the unfolded protein response (UPR). Activation of the UPR can rapidly resolve the accumulation of misfolded proteins, direct permanent changes in the size and function of cells during differentiation, and critically influence the immune response and inflammation. Recognition of the importance of ER stress and UPR signalling pathways in normal and dysregulated immune responses has greatly increased in the past few years. This Review discusses several settings in which ER stress contributes to the pathogenesis of rheumatic diseases and considers some of the therapeutic opportunities that these discoveries provide.

cEBP Homologous Protein Expression in Macrophages Regulates the Magnitude and Duration of IL-6 Expression and Dextran Sodium Sulfate Colitis

Cellular stress enhances inflammatory cytokine gene expression by inducing cEBP homologous protein (CHOP). Engaging cell stress via thapsigargin induced CHOP and selectively prolonged lipopolysaccharide-stimulated interleukin-6 (IL-6) expression in bone marrow-derived macrophages from wild-type (WT) but not CHOP knockout (KO) mice. To determine the impact of this mechanism in vivo we employed dextran sodium sulfate (DSS)-induced colitis in irradiated mice reconstituted with bone marrow from WT or CHOP KO mice. WT recipients of CHOP KO bone marrow exhibited more rapid recovery from disease than did mice reconstituted with WT bone marrow as reflected in increased survival, reduced clinical scores, and colonic histopathology. No differences in mesenteric lymph node cell populations were observed between mice with WT or CHOP KO bone marrow during colitis. CD11b(+) macrophages infiltrating the lamina propria were, however, reduced in DSS-treated mice reconstituted with CHOP KO bone marrow. CHOP expression was observed within the infiltrating inflammatory CD11b(+) macrophages. Furthermore, IL-6 expression within the inflamed colon was significantly lower in mice with CHOP-deficient bone marrow. Our findings indicate that CHOP expression in myeloid cells plays an important role in determining the magnitude and duration of inflammatory response in vivo by modulating expression of proinflammatory cytokines such as IL-6 in infiltrating macrophages.

CCAAT/enhancer binding protein β in relation to ER stress, inflammation, and metabolic disturbances

The prevalence of the metabolic syndrome and underlying metabolic disturbances increase rapidly in developed countries. Various molecular targets are currently under investigation to unravel the molecular mechanisms that cause these disturbances. This is done in attempt to counter or prevent the negative health consequences of the metabolic disturbances. Here, we reviewed the current knowledge on the role of C/EBP-β in these metabolic disturbances. C/EBP-β deletion in mice resulted in downregulation of hepatic lipogenic genes and increased expression of β-oxidation genes in brown adipose tissue. Furthermore, C/EBP-β is important in the differentiation and maturation of adipocytes and is increased during ER stress and proinflammatory conditions. So far, studies were only conducted in animals and in cell systems. The results found that C/EBP-β is an important transcription factor within the metabolic disturbances of the metabolic system. Therefore, it is interesting to examine the potential role of C/EBP-β at molecular and physiological level in humans.

An activated unfolded protein response promotes retinal degeneration and triggers an inflammatory response in the mouse retina

Recent studies on the endoplasmic reticulum stress have shown that the unfolded protein response (UPR) is involved in the pathogenesis of inherited retinal degeneration caused by mutant rhodopsin. However, the main question of whether UPR activation actually triggers retinal degeneration remains to be addressed. Thus, in this study, we created a mouse model for retinal degeneration caused by a persistently activated UPR to assess the physiological and morphological parameters associated with this disease state and to highlight a potential mechanism by which the UPR can promote retinal degeneration. We performed an intraocular injection in C57BL6 mice with a known unfolded protein response (UPR) inducer, tunicamycin (Tn) and examined animals by electroretinography (ERG), spectral domain optical coherence tomography (SD-OCT) and histological analyses. We detected a significant loss of photoreceptor function (over 60%) and retinal structure (35%) 30 days post treatment. Analysis of retinal protein extracts demonstrated a significant upregulation of inflammatory markers including interleukin-1β (IL-1β), IL-6, tumor necrosis factor-α (TNF-α), monocyte chemoattractant protein-1 (MCP-1) and IBA1. Similarly, we detected a strong inflammatory response in mice expressing either Ter349Glu or T17M rhodopsin (RHO). These mutant rhodopsin species induce severe retinal degeneration and T17M rhodopsin elicits UPR activation when expressed in mice. RNA and protein analysis revealed a significant upregulation of pro- and anti-inflammatory markers such as IL-1β, IL-6, p65 nuclear factor kappa B (NF-kB) and MCP-1, as well as activation of F4/80 and IBA1 microglial markers in both the retinas expressing mutant rhodopsins. We then assessed if the Tn-induced inflammatory marker IL-1β was capable of inducing retinal degeneration by injecting C57BL6 mice with a recombinant IL-1β. We observed ~19% reduction in ERG a-wave amplitudes and a 29% loss of photoreceptor cells compared with control retinas, suggesting a potential link between pro-inflammatory cytokines and retinal pathophysiological effects. Our work demonstrates that in the context of an established animal model for ocular disease, the persistent activation of the UPR could be responsible for promoting retinal degeneration via the UPR-induced pro-inflammatory cytokine IL-1β.

The stress-response sensor chop regulates the function and accumulation of myeloid-derived suppressor cells in tumors

Adaptation of malignant cells to the hostile milieu present in tumors is an important determinant of their survival and growth. However, the interaction between tumor-linked stress and antitumor immunity remains poorly characterized. Here, we show the critical role of the cellular stress sensor C/EBP-homologous protein (Chop) in the accumulation and immune inhibitory activity of tumor-infiltrating myeloid-derived suppressor cells (MDSCs). MDSCs lacking Chop had decreased immune-regulatory functions and showed the ability to prime T cell function and induce antitumor responses. Chop expression in MDSCs was induced by tumor-linked reactive oxygen and nitrogen species and regulated by the activating-transcription factor-4. Chop-deficient MDSCs displayed reduced signaling through CCAAT/enhancer-binding protein-β, leading to a decreased production of interleukin-6 (IL-6) and low expression of phospho-STAT3. IL-6 overexpression restored immune-suppressive activity of Chop-deficient MDSCs. These findings suggest the role of Chop in tumor-induced tolerance and the therapeutic potential of targeting Chop in MDSCs for cancer immunotherapy.

Oroxylin A inhibits ATRA-induced IL-6 expression involved in retinoic acid syndrome by down-regulating CHOP

Production of IL-6 constituted the major cause of death in the ATRA trial called retinoic acid syndrome (RAS). LAP and LIP are active and inactive isoforms of C/EBPβ, respectively. Inactive LIP dimerized with LAP to eliminate its activity. Following treatment with ATRA, CHOP expression was increased and dimerized with LIP more preferentially than LAP to rescue function of LAP. Oroxylin A has been reported to activate CHOP, a key mediator of unfolded protein response (UPR) pathway, and resulted in apoptosis. Interestingly, we found that low concentration of oroxylin A (≦ 40 μM) showed no apoptosis effect on NB4 and HL-60 cells and decreased the CHOP protein level via promoting its degradation. MG132 was utilized to conform the effect of oroxylin A on degrading CHOP. Our results showed that oroxylin A decreased the level of IL-6 secretion of NB4 cells with or without ATRA treatment while the effect was eliminated by C/EBPβ siRNA. We conclude that oroxylin A possessed abilities of inhibiting the ATRA-induced IL-6 production via modulation of LAP/LIP/CHOP in leukemia cell lines, which could providing a therapeutic strategy for RAS.

Myostatin augments muscle-specific ring finger protein-1 expression through an NF-kB independent mechanism in SMAD3 null muscle

Smad (Sma and Mad-related protein) 2/3 are downstream signaling molecules for TGF-β and myostatin (Mstn). Recently, Mstn was shown to induce reactive oxygen species (ROS) in skeletal muscle via canonical Smad3, nuclear factor-κB, and TNF-α pathway. However, mice lacking Smad3 display skeletal muscle atrophy due to increased Mstn levels. Hence, our aims were first to investigate whether Mstn induced muscle atrophy in Smad3(-/-) mice by increasing ROS and second to delineate Smad3-independent signaling mechanism for Mstn-induced ROS. Herein we show that Smad3(-/-) mice have increased ROS levels in skeletal muscle, and inactivation of Mstn in these mice partially ablates the oxidative stress. Furthermore, ROS induction by Mstn in Smad3(-/-) muscle was not via nuclear factor-κB (p65) signaling but due to activated p38, ERK MAPK signaling and enhanced IL-6 levels. Consequently, TNF-α, nicotinamide adenine dinucleotide phosphate oxidase, and xanthine oxidase levels were up-regulated, which led to an increase in ROS production in Smad3(-/-) skeletal muscle. The exaggerated ROS in the Smad3(-/-) muscle potentiated binding of C/EBP homology protein transcription factor to MuRF1 promoter, resulting in enhanced MuRF1 levels leading to muscle atrophy.

Mycobacterial HBHA induces endoplasmic reticulum stress-mediated apoptosis through the generation of reactive oxygen species and cytosolic Ca2+ in murine macrophage RAW 264.7 cells

Mycobacterial heparin-binding haemagglutinin antigen (HBHA) is a virulence factor that induces apoptosis of macrophages. Endoplasmic reticulum (ER) stress-mediated apoptosis is an important regulatory response that can be utilised to study the pathogenesis of tuberculosis. In the present study, HBHA stimulation induced ER stress sensor molecules in a caspase-dependent manner. Pre-treatment of RAW 264.7 cells with an IκB kinase 2 inhibitor reduced not only C/EBP homology protein expression but also IL-6 and monocyte chemotactic protein-1 (MCP-1) production. BAPTA-AM reduced both ER stress responses and caspase activation and strongly suppressed HBHA-induced IL-6 and MCP-1 production in RAW 264.7 cells. Enhanced reactive oxygen species (ROS) production and elevated cytosolic [Ca(2+)]i levels were essential for HBHA-induced ER stress responses. Collectively, our data suggest that HBHA induces cytosolic [Ca(2+)]i, which influences the generation of ROS associated with the production of proinflammatory cytokines. These concerted and complex cellular responses induce ER stress-associated apoptosis during HBHA stimulation in macrophages. These results indicate that the ER stress pathway has an important role in the HBHA-induced apoptosis during mycobacterial infection.

GCN2-dependent metabolic stress is essential for endotoxemic cytokine induction and pathology

Activated inflammatory macrophages can express indoleamine 2,3-dioxygenase (IDO) and thus actively deplete their own tryptophan supply; however, it is not clear how amino acid depletion influences macrophage behavior in inflammatory environments. In this report, we demonstrate that the stress response kinase GCN2 promotes macrophage inflammation and mortality in a mouse model of septicemia. In vitro, enzymatic amino acid consumption enhanced sensitivity of macrophages to the Toll-like receptor 4 (TLR4) ligand lipopolysaccharide (LPS) with significantly increased interleukin 6 (IL-6) production. Tryptophan withdrawal induced the stress response proteins ATF4 and CHOP/GADD153; however, LPS stimulation rapidly enhanced expression of both proteins. Moreover, LPS-driven cytokine production under amino acid-deficient conditions was dependent on GCN2, as GCN2 knockout (GCN2KO) macrophages had a significant reduction of cytokine gene expression after LPS stimulation. To test the in vivo relevance of these findings, monocytic-lineage-specific GCN2KO mice were challenged with a lethal dose of LPS intraperitoneally (i.p.). The GCN2KO mice showed reduced inflammatory responses, with decreased IL-6 and IL-12 expression correlating with significant reduction in animal mortality. Thus, the data show that amino acid depletion stress signals (via GCN2) synergize with proinflammatory signals to potently increase innate immune responsiveness.

[Interluekin-1: from regulation of cell proliferation to chronic inflammatory diseases]

  Interleukin 1 (IL-1) was initially defined as a factor which is produced by macrophages and exhibits proliferative activity on thymocytes and fibroblasts, B cell activation and endogenous pyrogen activity. Now IL-1 is known to exhibit pleiotropic activities on various cell types and play important roles in the regulation of immune, nervous and endocrine systems, progression of tumor cells, hematopoietic cell proliferation/differentiation and especially in inflammatory diseases. In 1985 I found that IL-1 exhibits cytocidal activity against human melanoma cells. Since then I have been engaged in the research of various aspects of IL-1. This review summarizes current knowledge of IL-1, including our research and beneficial effect of IL-1 blocking on inflammatory diseases.

Amino acid catabolism: a pivotal regulator of innate and adaptive immunity

Enhanced amino acid catabolism is a common response to inflammation, but the immunologic significance of altered amino acid consumption remains unclear. The finding that tryptophan catabolism helped maintain fetal tolerance during pregnancy provided novel insights into the significance of amino acid metabolism in controlling immunity. Recent advances in identifying molecular pathways that enhance amino acid catabolism and downstream mechanisms that affect immune cells in response to inflammatory cues support the notion that amino acid catabolism regulates innate and adaptive immune cells in pathologic settings. Cells expressing enzymes that degrade amino acids modulate antigen-presenting cell and lymphocyte functions and reveal critical roles for amino acid- and catabolite-sensing pathways in controlling gene expression, functions, and survival of immune cells. Basal amino acid catabolism may contribute to immune homeostasis that prevents autoimmunity, whereas elevated amino acid catalytic activity may reinforce immune suppression to promote tumorigenesis and persistence of some pathogens that cause chronic infections. For these reasons, there is considerable interest in generating novel drugs that inhibit or induce amino acid consumption and target downstream molecular pathways that control immunity. In this review, we summarize recent developments and highlight novel concepts and key outstanding questions in this active research field.

[Progress of transcription factor CCAAT enhancer binding protein β]

CCAAT enhancer binding protein β (C/EBP β) belongs to CCAAT enhancer binding protein (C/EBP) family, which is a subfamily of basic leucine zipper (bZIP) protein family. C/EBP family plays important roles in many processes such as cell differentiation, metabolism, and development. In this paper, the structure, expression regulation, and function of C/EBP β were reviewed.

C/EBP homologous protein deficiency attenuates myocardial reperfusion injury by inhibiting myocardial apoptosis and inflammation

OBJECTIVE

To investigate whether and how the endoplasmic reticulum (ER) stress-induced, CCAAT/enhancer-binding protein-homologous protein (CHOP)-mediated pathway regulates myocardial ischemia/reperfusion injury.

METHODS AND RESULTS

Wild-type and chop-deficient mice underwent 50 minutes of left coronary artery occlusion followed by reperfusion. Expression of chop and spliced x-box binding protein-1 (sxbp1) mRNA was rapidly and significantly increased in reperfused myocardium of wild-type mice. chop-deficient mice exhibited markedly reduced injury size after reperfusion compared with wild-type mice, accompanied by a decreasing number of terminal deoxynucleotidyl transferase dUTP nick-end labeling-positive cardiomyocytes. Interestingly, myocardial inflammation, as assessed by expression of inflammatory cytokines and chemokines and numbers of infiltrated inflammatory cells, was also attenuated in chop-deficient mice. Moreover, expression of interleukin-6 mRNA in response to lipopolysaccharide was enhanced by simultaneous stimulation with thapsigargin, a potent ER stressor, in wild-type cardiomyocytes but not in chop-deficient cardiomyocytes. Finally, we found that superoxide was produced in reperfused myocardium and that intravenous administration of edaravone, a free radical scavenger, immediately before reperfusion significantly suppressed the superoxide overproduction and subsequent expression of sxbp1 and chop mRNA, followed by reduced injury size in wild-type mice.

CONCLUSIONS

The ER stress-induced, CHOP-mediated pathway, which is activated in part by superoxide overproduction after reperfusion, exacerbates myocardial ischemia/reperfusion injury by inducing cardiomyocyte apoptosis and myocardial inflammation.

Endoplasmic reticulum stress-induced transcription factor, CHOP, is crucial for dendritic cell IL-23 expression

The endoplasmic reticulum (ER) stress response detects malfunctions in cellular physiology, and microbial pattern recognition receptors recognize external threats posed by infectious agents. This study has investigated whether proinflammatory cytokine expression by monocyte-derived dendritic cells is affected by the induction of ER stress. Activation of ER stress, in combination with Toll-like receptor (TLR) agonists, markedly enhanced expression of mRNA of the unique p19 subunit of IL-23, and also significantly augmented secretion of IL-23 protein. These effects were not seen for IL-12 secretion. The IL-23 gene was found to be a target of the ER stress-induced transcription factor C/EBP homologous protein (CHOP), which exhibited enhanced binding in the context of both ER stress and TLR stimulation. Knockdown of CHOP in U937 cells significantly reduced the synergistic effects of TLR and ER stress on IL-23p19 expression, but did not affect expression of other LPS-responsive genes. The integration of ER stress signals and the requirement for CHOP in the induction of IL-23 responses was also investigated in a physiological setting: infection of myeloid cells with Chlamydia trachomatis resulted in the expression of CHOP mRNA and induced the binding of CHOP to the IL-23 promoter. Furthermore, knockdown of CHOP significantly reduced the expression of IL-23 in response to this intracellular bacterium. Therefore, the effects of pathogens and other environmental factors on ER stress can profoundly affect the nature of innate and adaptive immune responses.

Molecular symbiosis of CHOP and C/EBP beta isoform LIP contributes to endoplasmic reticulum stress-induced apoptosis

Induction of the transcription factor CHOP (CCAAT-binding homologous protein; GADD 153) is a critical cellular response for the transcriptional control of endoplasmic reticulum (ER) stress-induced apoptosis. Upon nuclear translocation, CHOP upregulates the transcription of proapoptotic factors and downregulates antiapoptotic genes. Transcriptional activation by CHOP involves heterodimerization with other members of the basic leucine zipper transcription factor (bZIP) family. We show that the bZIP protein C/EBP beta isoform LIP is required for nuclear translocation of CHOP during ER stress. In early ER stress, LIP undergoes proteasomal degradation in the cytoplasmic compartment. During later ER stress, LIP binds CHOP in both cytoplasmic and nuclear compartments and contributes to its nuclear import. By using CHOP-deficient cells and transfections of LIP-expressing vectors in C/EBP beta(-/-) mouse embryonic fibroblasts (MEFs), we show that the LIP-CHOP interaction has a stabilizing role for LIP. At the same time, CHOP uses LIP as a vehicle for nuclear import. LIP-expressing C/EBP beta(-/-) MEFs showed enhanced ER stress-induced apoptosis compared to C/EBP beta-null cells, a finding in agreement with the decreased levels of Bcl-2, a known transcriptional control target of CHOP. In view of the positive effect of CHOP-LIP interaction in mediating their proapoptotic functions, we propose this functional cooperativity as molecular symbiosis between proteins.

Platelet factor 4 regulation of monocyte KLF4 in experimental cerebral malaria

Cerebral malaria continues to be a difficult to treat complication of Plasmodium falciparum infection in children. We have shown that platelets can have major deleterious immune functions in experimental cerebral malaria (ECM). One of the platelet derived mediators we have identified as particularly important is platelet factor 4/CXCL4. Our prior work demonstrated that PF4(-/-) mice are protected from ECM, have reduced plasma cytokines, and have reduced T-cell trafficking to the brain. We now show that PF4 drives monocyte cytokine production in a Kruppel like factor 4 (KLF4) dependent manner. Monocyte depleted Plasmodium berghei infected mice have improved survival, and KLF4 is greatly increased in control, but not monocyte depleted mice. PF4(-/-) mice have less cerebral monocyte trafficking and no change in KLF4 expression. These data indicate that PF4 induction of monocyte KLF4 expression may be an important step in the pathogenesis of ECM.

Transcriptional regulation of the human growth hormone receptor (hGHR) gene V2 promoter by transcriptional activators and repressor

The V2 transcript is the major ubiquitously expressed human GH receptor (hGHR) mRNA in all tissues examined to date. In a previous investigation, we defined the V2 promoter as TATA-less and exhibiting many characteristics of a housekeeping gene promoter. We also demonstrated that its basal activity is determined by several different cis-regulatory regions within both the promoter and the V2 exon. In the present study, we used luciferase-reporter, site-directed mutagenesis, gel shift, chromatin immunoprecipitation, and quantitative RT-PCR assays to investigate the ability of certain transcription factors to regulate hGHR V2 transcription through these regions in mammalian cells, including human adipocytes. Ets1 was found to transactivate the V2 proximal promoter through specific Ets sites. Two CCAAT/enhancer-binding protein (C/EBP) family members [C/EBP-homologous protein (CHOP) and C/EBPbeta] enhanced V2 transcription via different pathways: indirectly, by association with a V2 exon region (CHOP), and directly, using a V2 proximal promoter noncanonical binding site (C/EBPbeta). The Notch signaling mediator, Hes1, potently suppressed V2 promoter activity through interaction with two Hes sites within the V2 exon. We propose that these transcriptional factors regulate hGHR V2 expression by acting as downstream nuclear effectors, linking specific signaling cascades (e.g. MAPK and Notch) triggered by different growth factor-, development-, and nutrition- as well as stress-related stimuli. Our data also suggest that these factors are likely to be important in the differentiation-induced increase in V2 mRNA expression in adipocytes, with Ets1 and CHOP functioning at the preadipocyte stage to prepare the cells for differentiation and increasing C/EBPs and decreasing Hes1 levels contributing during adipocyte maturation.

Regulation of interleukin-8 gene at a distinct site of its promoter by CCAAT enhancer-binding protein homologous protein in prostaglandin E2-treated human T cells

For a long period of time, the transcription factor CCAAT/enhancer-binding protein homologous protein (CHOP) has been thought to inhibit transcriptional activity for its ability to interact with CCAAT enhancer-binding protein family factors, thus preventing their binding to DNA. We have previously shown that in human T lymphocytes the CHOP phosphorylation induced by prostaglandin E(2) (PGE(2))-increased interleukin-8 (IL-8) gene expression. Given the CHOP positive role in the regulation of transcription, here we have investigated the molecular mechanism(s) by which CHOP increases IL-8 gene activity under PGE(2) stimulus. Transfection experiments with mutants showed both that the CHOP transactivation domain is essential for IL-8 transcription and that the IL-8/activator protein 1 (AP-1) promoter mutated in NF-kappaB and NF-IL-6, but not in the AP-1 site, harbors essential CHOP-responsive elements. CHOP silencing confirmed its role in the IL-8 transcriptional regulation and protein production, whereas c-Jun small interfering RNA experiments showed that the PGE(2)-induced activation of IL-8 promoter is mainly c-Jun-independent. Moreover, PGE(2) induced CHOP-DNA complexes only when the entire IL-8/AP-1 promoter or the wild type sequences encompassing the AP-1 upstream region were employed. Mutations introduced in these sequences prevented the DNA-CHOP complex formation. The IL-8/AP-1 mutant promoter lacking the sequence immediately upstream the AP-1 site is PGE(2)-unresponsive. Finally, chromatin immunoprecipitation data confirmed in vivo that PGE(2) induces CHOP binding to the IL-8 promoter. Taken together, our results suggest that the increased expression of CHOP in response to PGE(2) exerts a positive transcriptional regulation of the IL-8 promoter mediated by direct binding to a novel consensus site.

Critical and functional regulation of CHOP (C/EBP homologous protein) through the N-terminal portion

C/EBP homologous protein (CHOP) is an endoplasmic reticulum stress-inducible protein that plays a critical role in the regulation of programmed cell death; however, the regulation of its function has not been well characterized. We have previously demonstrated that CHOP is regulated by the ubiquitin-proteasome system. In this study, during the process of clarifying the mechanism of the degradation of CHOP, we identified a novel regulation domain of CHOP in its N-terminal portion that is involved in various regulations and functions. The CHOP N-terminal domain is necessary not only for protein degradation but also for its transactivity and interaction with p300. In addition, trichostatin A, a histone deacetylase inhibitor, repressed the degradation of CHOP protein via the N-terminal domain. TRB3, a mammalian tribbles homolog that functions as a repressor of CHOP, also interacted with CHOP via the N-terminal portion and significantly blocked the association of p300 with CHOP. These results suggest that the N-terminal portion of CHOP plays a crucial role in its functional regulation and enable us to identify a novel function of TRB3 as an intracellular antagonist of the p300-binding domain of CHOP.

Activation of the ATF3 gene through a co-ordinated amino acid-sensing response programme that controls transcriptional regulation of responsive genes following amino acid limitation

Expression of ATF3 (activating transcription factor 3) is induced by a variety of environmental stress conditions, including nutrient limitation. In the present study, we demonstrate that the increase in ATF3 mRNA content following amino acid limitation of human HepG2 hepatoma cells is dependent on transcriptional activation of the ATF3 gene, through a highly co-ordinated amino acid-responsive programme of transcription factor synthesis and action. Studies using transient over-expression and knockout fibroblasts showed that several ATF and C/EBP (CCAAT/enhancer-binding protein) family members contribute to ATF3 regulation. Promoter analysis showed that a C/EBP-ATF composite site at -23 to -15 bp relative to the transcription start site of the ATF3 gene functions as an AARE (amino acid response element). Chromatin immunoprecipitation demonstrated that amino acid limitation increased ATF4, ATF3, and C/EBPbeta binding to the ATF3 promoter, but the kinetics of each was markedly different. Immediately following histidine removal, there was a rapid increase in histone H3 acetylation prior to an enhancement in ATF4 binding and in histone H4 acetylation. These latter changes closely paralleled the initial increase in RNA pol II (RNA polymerase II) binding to the promoter and in the transcription rate from the ATF3 gene. The increase in ATF3 and C/EBPbeta binding was considerably slower and more closely correlated with a decline in transcription rate. A comparison of the recruitment patterns between ATF and C/EBP transcription factors and RNA polymerase II at the AARE of several amino acid-responsive genes revealed that a highly co-ordinated response programme controls the transcriptional activation of these genes following amino acid limitation.

IRAK-4 mutation (Q293X): rapid detection and characterization of defective post-transcriptional TLR/IL-1R responses in human myeloid and non-myeloid cells

Innate immunodeficiency has recently been reported as resulting from the Q293X IRAK-4 mutation with consequent defective TLR/IL-1R signaling. In this study we report a method for the rapid allele-specific detection of this mutation and demonstrate both cell type specificity and ligand specificity in defective IL-1R-associated kinase (IRAK)-4-deficient cellular responses, indicating differential roles for this protein in human PBMCs and primary dermal fibroblasts and in LPS, IL-1beta, and TNF-alpha signaling. We demonstrate transcriptional and post-transcriptional defects despite NF-kappaB signaling and intact MyD88-independent signaling and propose that dysfunctional complex 1 (IRAK1/TRAF6/TAK1) signaling, as a consequence of IRAK-4 deficiency, generates specific defects in MAPK activation that could underpin this patient's innate immunodeficiency. These studies demonstrate the importance of studying primary human cells bearing a clinically relevant mutation; they underscore the complexity of innate immune signaling and illuminate novel roles for IRAK-4 and the fundamental importance of accessory proinflammatory signaling to normal human innate immune responses and immunodeficiencies.

Myxoid liposarcoma FUS-DDIT3 fusion oncogene induces C/EBP beta-mediated interleukin 6 expression

The myxoid/round cell liposarcoma oncogene FUS-DDIT3 is the result of a translocation derived gene fusion between the splicing factor FUS and DDIT3. In order to investigate the downstream targets of DDIT3, and the transforming effects of the FUS-DDIT3 fusion protein, we have introduced DDIT3-GFP and FUS-DDIT3-GFP constructs into a human fibrosarcoma cell line. The gene expression profiles of stable transfectants were compared to the original fibrosarcoma cell line by microarray analysis. We here report that the NFkappaB and C/EBP beta controlled gene IL6 is upregulated in DDIT3- and FUS-DDIT3-expressing fibrosarcoma cell lines and in myxoid liposarcoma cell lines. Strong expression of the tumor associated multifunctional cytokine interleukin 6 was confirmed both at mRNA and protein level. Knockdown experiments using siRNA against CEBPB transcripts showed that the effect of FUS-DDIT3 on IL6 expression is C/EBP beta dependent. Chromatin immunoprecipitation revealed direct interaction between the IL6 promoter and the C/EBP beta protein. In addition, the effect of DDIT3 and FUS-DDIT3 on the expression of other acute phase genes was examined using real-time PCR. We demonstrate for the first time that DDIT3 and FUS-DDIT3 show opposite transcriptional regulation of IL8 and suggest that FUS-DDIT3 may affect the synergistic activation of promoters regulated by C/EBP beta and NFkappaB.

Cardioprotective stress response in the human fetal heart

OBJECTIVE

We propose that the fetal heart is highly resilient to hypoxic stress. Our objective was to elucidate the human fetal gene expression profile in response to simulated ischemia and reperfusion to identify molecular targets that account for the innate cardioprotection exhibited by the fetal phenotype.

METHODS

Primary cultures of human fetal cardiac myocytes (gestational age, 15-20 weeks) were exposed to simulated ischemia and reperfusion in vitro by using a simulated ischemic buffer under anoxic conditions. Total RNA from treated and baseline cells were isolated, reverse transcribed, and labeled with Cy3 or Cy5 and hybridized to a human cDNA microarray for expression analysis. This analysis revealed a highly significant (false discovery rate, <3%) suppression of interleukin 6 transcript levels during the reperfusion phase confirmed by means of quantitative polymerase chain reaction (0.25 +/- 0.11-fold). Interleukin 6 signaling during ischemia and reperfusion was assessed at the protein expression level by means of Western measurements of interleukin 6 receptor, the signaling subunit of the interleukin 6 receptor complex (gp130), and signal transducer of activated transcription 3. Posttranslational changes in the protein kinase B signaling pathway were determined on the basis of the phosphorylation status of protein kinase B, mitogen-activated protein kinase, and glycogen synthase kinase 3beta. The effect of suppression of a prohypertrophic kinase, integrin-linked kinase, with short-interfering RNA was determined in an ischemia and reperfusion-stressed neonatal rat cardiac myocyte model. Endogenous secretion of interleukin 6 protein in culture supernatants was measured by enzyme-linked immunosorbent assay.

RESULTS

Human fetal cardiac myocytes exhibited a significantly lower rate of apoptosis induction during ischemia and reperfusion and after exposure to staurosporine and recombinant interleukin 6 compared with that observed in neonatal rat cardiac myocytes ( P < .05 for all comparisons, analysis of variance). Exposure to exogenously added recombinant interleukin 6 increased the apoptotic rate in both rat and human fetal cardiac myocytes ( P < .05). Short-interfering RNA-mediated suppression of integrin-linked kinase, a prohypertrophy upstream kinase regulating protein kinase B and glycogen synthase kinase 3beta phosphorylation, was cytoprotective against ischemia and reperfusion-induced apoptosis in neonatal rat cardiac myocytes ( P < .05).

CONCLUSIONS

Human fetal cardiac myocytes exhibit a uniquely adaptive transcriptional response to ischemia and reperfusion that is associated with an apoptosis-resistant phenotype. The stress-inducible fetal cardiac myocyte gene repertoire is a useful platform for identification of targets relevant to the mitigation of cardiac ischemic injury and highlights a novel avenue involving interleukin 6 modulation for preventing the cardiac myocyte injury associated with ischemia and reperfusion.

Silencing of integrated human papillomavirus type 18 oncogene transcription in cells expressing SerpinB2

The serine protease inhibitor SerpinB2 (PAI-2), a major product of differentiating squamous epithelial cells, has recently been shown to bind and protect the retinoblastoma protein (Rb) from degradation. In human papillomavirus type 18 (HPV-18)-transformed epithelial cells the expression of the E6 and E7 oncoproteins is controlled by the HPV-18 upstream regulatory region (URR). Here we illustrate that PAI-2 expression in the HPV-18-transformed cervical carcinoma line HeLa resulted in the restoration of Rb expression, which led to the functional silencing of transcription from the HPV-18 URR. This caused loss of E7 protein expression and restoration of multiple E6- and E7-targeted host proteins, including p53, c-Myc, and c-Jun. Rb expression emerged as sufficient for the transcriptional repression of the URR, with repression mediated via the C/EBPbeta-YY1 binding site (URR 7709 to 7719). In contrast to HeLa cells, where the C/EBPbeta-YY1 dimer binds this site, in PAI-2- and/or Rb-expressing cells the site was occupied by the dominant-negative C/EBPbeta isoform liver-enriched transcriptional inhibitory protein (LIP). PAI-2 expression thus has a potent suppressive effect on HPV-18 oncogene transcription mediated by Rb and LIP, a finding with potential implications for prognosis and treatment of HPV-transformed lesions.

Tula hantavirus triggers pro-apoptotic signals of ER stress in Vero E6 cells

Tula virus is a member of the Hantavirus genus of the family Bunyaviridae. Viruses of this family have an unusual pattern of intracellular maturation at the ER–Golgi compartment. We recently found that Tula virus, similar to several other hantaviruses, is able to induce apoptosis in cultured cells [Li, X.D., Kukkonen, S., Vapalahti, O., Plyusnin, A., Lankinen, H., Vaheri, A., 2004. Tula hantavirus infection of Vero E6 cells induces apoptosis involving caspase 8 activation. J. Gen. Virol. 85, 3261–3268.]. However, the cellular mechanisms remain to be clarified. In this study, we demonstrate that the progressive replication of Tula virus in Vero E6 cells initiates several death programs that are intimately associated with ER stress: (1) early activation of ER-resident caspase-12; (2) phosphorylation of Jun NH₂-terminal kinase (JNK) and its downstream target transcriptional factor, c-jun; (3) induction of the pro-apoptotic transcriptional factor, growth arrest- and DNA damage-inducible gene 153, or C/EBP homologous protein (Gadd153/chop); and (4) changes in the ER-membrane protein BAP31 implying cross-talk with the mitochondrial apoptosis pathway. Furthermore, we confirmed that a sustained ER stress was induced marked by an increased expression of an ER chaperone Grp78/BiP. Taken together, we have identified involvement of ER stress-mediated death program in Tula virus-infected Vero E6 cells which provides a new approach to understand the mechanisms in hantavirus-induced apoptosis.

TRB3, a novel ER stress-inducible gene, is induced via ATF4-CHOP pathway and is involved in cell death

C/EBP homologous protein (CHOP) is a stress-inducible nuclear protein that is crucial for the development of programmed cell death and regeneration; however, the regulation of its function has not been well characterized. Slbo, a Drosophila homolog of C/EBP (CCAAT/enhancer binding protein), was shown to be unstabilized by tribbles. Here, we identified TRB3 as a tribbles ortholog in humans, which associated with CHOP to suppress the CHOP-dependent transactivation. TRB3 is induced by various forms endoplasmic reticulum (ER) stress later than CHOP. Tunicamycin treatment enhanced the TRB3 promoter activity, while dominant-negative forms of CHOP suppressed the tunicamycin-induced activation. In addition, the tunicamycin response region in the TRB3 promoter contains amino-acid response elements overlapping the CHOP-binding site, and CHOP and ATF4 cooperated to activate this promoter activity. Knockdown of endogenous ATF4 or CHOP expression dramatically repressed tunicamycin-induced TRB3 induction. Furthermore, knockdown of TRB3 expression decreased ER stress-dependent cell death. These results indicate that TRB3 is a novel target of CHOP/ATF4 and downregulates its own induction by repression of CHOP/ATF4 functions, and that it is involved in CHOP-dependent cell death during ER stress.

Prostaglandin E2 induces interleukin-8 gene transcription by activating C/EBP homologous protein in human T lymphocytes

The effect of prostaglandin E(2) (PGE(2)) in regulating the synthesis of the pro-inflammatory chemokine interleukin-8 (IL-8) in T lymphocytes is not yet defined, even though it may reduce or enhance IL-8 synthesis in other cell types. Here, we demonstrate that, in human T cells, PGE(2) induced IL-8 mRNA transcription through prostaglandin E(2) receptors 1- and 4-dependent signal transduction pathways leading to the activation of the transcription factor C/EBP homologous protein (CHOP), never before implicated in IL-8 transcription. Several kinases, including protein kinase C, Src family tyrosine kinases, phosphatidylinositol 3-kinase, and p38 MAPK, were involved in PGE(2)-induced CHOP activation and IL-8 production. The transactivation of the IL-8 promoter by CHOP was NF-kappaB-independent. Our data suggest that PGE(2) acts as a potent pro-inflammatory mediator by inducing IL-8 gene transcription in activated T cells through different signal transduction pathways leading to CHOP activation. These findings show the complexity with which PGE(2) regulates IL-8 synthesis by inhibiting or enhancing its production depending on the cell types and environmental conditions.

IL-6 as an intracrine growth factor for renal carcinoma cell lines

Interleukin-6 (IL-6) is produced at high levels by renal cell carcinoma cell lines. The molecular mechanisms involved in its possible role as an autocrine growth factor were investigated. IL-6 and IL-6 receptor expression was investigated in 8 renal cell carcinoma (RCC) cell lines. The modulation of RCC cell line proliferation by an anti-IL-6 Ab, an IL-6 antisense oligonucleotide (ASON) directed against the second exon of IL-6 and cytokines inhibiting IL-6 production (IL-4 and IL-13) was investigated. All 8 RCC cell lines expressed IL-6 mRNA, produced IL-6 and expressed the soluble and membrane-bound gp130 chain of IL-6 receptor. The gp80 chain of IL-6 receptor was undetectable at the surface of the 8 RCC cell lines tested, while the soluble form of gp80 was detectable in the supernatant of one of these cell lines. The addition of a blocking IL-6 Ab did not inhibit the proliferation of any of the 8 RCC cell lines. In contrast, IL-6 ASON inhibited specifically IL-6 production and the proliferation of all RCC cell lines. Exogenous IL-6 failed to restore RCC cell line proliferation blocked by ASON, indicating that IL-6 acts through an intracrine loop in RCC cell lines. IL-13 and IL-4 inhibited the proliferation of 7 of the 8 cell lines without interfering with IL-6 or IL-6 receptor expression. IL-6 ASON inhibited the proliferation of the 8 RCC cell lines tested additively with IL-4 or IL-13. IL-6 is an intracrine growth factor in renal cell carcinoma cell lines.