Interferon-gamma stimulates the expression of the inducible cAMP early repressor in macrophages through the activation of casein kinase 2. A potentially novel pathway for interferon-gamma-mediated inhibition of gene transcription

Lactate and lactylation in macrophage metabolic reprogramming: current progress and outstanding issues

It is commonly known that different macrophage phenotypes play specific roles in different pathophysiological processes. In recent years, many studies have linked the phenotypes of macrophages to their characteristics in different metabolic pathways, suggesting that macrophages can perform different functions through metabolic reprogramming. It is now gradually recognized that lactate, previously overlooked as a byproduct of glycolytic metabolism, acts as a signaling molecule in regulating multiple biological processes, including immunological responses and metabolism. Recently, lactate has been found to mediate epigenetic changes in macrophages through a newfound lactylation modification, thereby regulating their phenotypic transformation. This novel finding highlights the significant role of lactate metabolism in macrophage function. In this review, we summarize the features of relevant metabolic reprogramming in macrophages and the role of lactate metabolism therein. We also review the progress of research on the regulation of macrophage metabolic reprogramming by lactylation through epigenetic mechanisms.

Emerging functions and therapeutic targets of IL-38 in central nervous system diseases

Interleukin (IL)-38 is a newly discovered cytokine of the IL-1 family, which binds various receptors (i.e., IL-36R, IL-1 receptor accessory protein-like 1, and IL-1R1) in the central nervous system (CNS). The hallmark physiological function of IL-38 is competitive binding to IL-36R, as does the IL-36R antagonist. Emerging research has shown that IL-38 is abnormally expressed in the serum and brain tissue of patients with ischemic stroke (IS) and autism spectrum disorder (ASD), suggesting that IL-38 may play an important role in neurological diseases. Important advances include that IL-38 alleviates neuromyelitis optica disorder (NMOD) by inhibiting Th17 expression, improves IS by protecting against atherosclerosis via regulating immune cells and inflammation, and reduces IL-1β and CXCL8 release through inhibiting human microglial activity post-ASD. In contrast, IL-38 mRNA is markedly increased and is mainly expressed in phagocytes in spinal cord injury (SCI). IL-38 ablation attenuated SCI by reducing immune cell infiltration. However, the effect and underlying mechanism of IL-38 in CNS diseases remain inadequately characterized. In this review, we summarize the biological characteristics, pathophysiological role, and potential mechanisms of IL-38 in CNS diseases (e.g., NMOD, Alzheimer's disease, ASD, IS, TBI, and SCI), aiming to explore the therapeutic potential of IL-38 in the prevention and treatment of CNS diseases.

Unveiling the veil of lactate in tumor-associated macrophages: a successful strategy for immunometabolic therapy

Lactate, traditionally regarded as a metabolic waste product at the terminal of the glycolysis process, has recently been found to have multifaceted functional roles in metabolism and beyond. A metabolic reprogramming phenomenon commonly seen in tumor cells, known as the "Warburg effect," sees high levels of aerobic glycolysis result in an excessive production of lactate. This lactate serves as a substrate that sustains not only the survival of cancer cells but also immune cells. However, it also inhibits the function of tumor-associated macrophages (TAMs), a group of innate immune cells ubiquitously present in solid tumors, thereby facilitating the immune evasion of malignant tumor cells. Characterized by their high plasticity, TAMs are generally divided into the pro-inflammatory M1 phenotype and the pro-tumour M2 phenotype. Through a process of 'education' by lactate, TAMs tend to adopt an immunosuppressive phenotype and collaborate with tumor cells to promote angiogenesis. Additionally, there is growing evidence linking metabolic reprogramming with epigenetic modifications, suggesting the participation of histone modification in diverse cellular events within the tumor microenvironment (TME). In this review, we delve into recent discoveries concerning lactate metabolism in tumors, with a particular focus on the impact of lactate on the function of TAMs. We aim to consolidate the molecular mechanisms underlying lactate-induced TAM polarization and angiogenesis and explore the lactate-mediated crosstalk between TAMs and tumor cells. Finally, we also touch upon the latest progress in immunometabolic therapies and drug delivery strategies targeting glycolysis and lactate production, offering new perspectives for future therapeutic approaches.

Comparative Analysis of Differentially Expressed Circular RNAs in Polarized Macrophages

Macrophage polarization is a process that macrophages exert different functions according to surrounding micro-environment. Macrophages commonly exist in two distinct subsets: classically activated M1 macrophages and alternatively activated M2 macrophages. Circular RNAs (circRNAs) are a novel class of non-coding RNAs generated by back-splicing. Thousands of circRNAs were identified in different cells and tissues. Recent studies have revealed that circRNAs play a crucial role in regulating transcriptional and post-transcriptional gene expression. However, the effects and roles of circRNAs in macrophage polarization have not been well elucidated. Here, circRNAs expression profiles were determined in human THP-1 macrophages incubated in conditions causing activation toward M1 (interferon-γ + LPS) or M2 (interleukin-4) phenotypes. Overall, 9,720 circular RNA were detected from RNA sequencing data. Compared with M2 macrophages, a total of 140 circRNAs were aberrantly expressed in M1 macrophages, including 71 up-regulated circRNAs and 69 down-regulated circRNAs. Quantitative real-time PCR (qRT-PCR) results were generally consistent with the selected differentially expressed circRNAs. Gene Ontology (GO) and KEGG pathway analyses were used to predict biological functions and potential mechanisms of the host linear transcripts of these up-regulated and down-regulated circRNAs. Furthermore, we found that the expression level of circRNA-RNF19B (circRNF19B) in M1 macrophages was significantly higher than that in THP-1 macrophages and M2 macrophages. circRNF19B expression was increased when M2 converted to M1 whereas decreased when M1 converted to M2. Knockdown of circRNF19B following the activation of THP-1 cells using interferon-γ + LPS diminished the expression of M1 macrophages markers and elevated the expression of M2 macrophages markers. In conclusion, these data suggest the involvement of altered circRNAs expression patterns in macrophages exposure to different activating conditions. Circular RNAs may play important roles in regulating macrophage polarization.

Pro-atherogenic actions of signal transducer and activator of transcription 1 serine 727 phosphorylation in LDL receptor deficient mice via modulation of plaque inflammation

Atherosclerosis is a chronic inflammatory disorder of the vasculature regulated by cytokines. We have previously shown that extracellular signal-regulated kinase-1/2 (ERK1/2) plays an important role in serine 727 phosphorylation of signal transducer and activator of transcription-1 (STAT1) transactivation domain, which is required for maximal interferon-γ signaling, and the regulation of modified LDL uptake by macrophages in vitro. Unfortunately, the roles of ERK1/2 and STAT1 serine 727 phosphorylation in atherosclerosis are poorly understood and were investigated using ERK1 deficient mice (ERK2 knockout mice die in utero) and STAT1 knock-in mice (serine 727 replaced by alanine; STAT1 S727A). Mouse Atherosclerosis RT² Profiler PCR Array analysis showed that ERK1 deficiency and STAT1 S727A modification produced significant changes in the expression of 18 and 49 genes, respectively, in bone marrow-derived macrophages, with 17 common regulated genes that included those that play key roles in inflammation and cell migration. Indeed, ERK1 deficiency and STAT1 S727A modification attenuated chemokine-driven migration of macrophages with the former also impacting proliferation and the latter phagocytosis. In LDL receptor deficient mice fed a high fat diet, both ERK1 deficiency and STAT1 S727A modification produced significant reduction in plaque lipid content, albeit at different time points. The STAT1 S727A modification additionally caused a significant reduction in plaque content of macrophages and CD3 T cells and diet-induced cardiac hypertrophy index. In addition, there was a significant increase in plasma IL-2 levels and a trend toward increase in plasma IL-5 levels. These studies demonstrate important roles of STAT1 S727 phosphorylation in particular in the regulation of atherosclerosis-associated macrophage processes in vitro together with plaque lipid content and inflammation in vivo, and support further assessment of its therapeutical potential.

How can a traffic light properly work if it is always green? The paradox of CK2 signaling

CK2 is a constitutively active protein kinase that assuring a constant level of phosphorylation to its numerous substrates supports many of the most important biological functions. Nevertheless, its activity has to be controlled and adjusted in order to cope with the varying needs of a cell, and several examples of a fine-tune regulation of its activity have been described. More importantly, aberrant regulation of this enzyme may have pathological consequences, e.g. in cancer, chronic inflammation, neurodegeneration, and viral infection. Our review aims at summarizing our current knowledge about CK2 regulation. In the first part, we have considered the most important stimuli shown to affect protein kinase CK2 activity/expression. In the second part, we focus on the molecular mechanisms by which CK2 can be regulated, discussing controversial aspects and future perspectives.

Oncometabolites lactate and succinate drive pro-angiogenic macrophage response in tumors

Macrophages are innate phagocytic leukocytes that are highly present in solid tumors, where they are referred to as tumor-associated macrophages (TAMs). In solid tumors, the microenvironment is often immunosuppressive and hypoxic regions are prevalent. These hypoxic conditions impose tumor cells to reprogram their metabolism, shifting from oxidative phosphorylation to anaerobic glycolysis. This so-called glycolytic switch enables hypoxic tumor cells to survive, proliferate, and eventually to outcompete untransformed cells. The hypoxia-induced change in tumor cell metabolism leads to the production of oncometabolites, among which are the glycolytic end-metabolite lactate and the tricarboxylic acid cycle intermediate succinate. TAMs can react to these oncometabolites, resulting in an altered maturation and the adoption of pro-angiogenic features. These angiogenesis-promoting TAMs have been reported to cooperate with tumor cells in the formation of new vessels, and even have been considered an important cause of resistance against anti-angiogenic therapies. For a long time, the mechanisms by which lactate and succinate activated pro-angiogenic TAMs were not understood. Researchers now start to unravel and understand some of the underlying mechanisms. Here, the importance of microenvironmental cues in inducing different macrophage activation states is discussed, as well as the role of hypoxia in the recruitment and activation of pro-angiogenic macrophages. In addition, the latest findings on the oncometabolites lactate and succinate in the activation of angiogenesis supporting macrophages are reviewed. Finally, various oncometabolite-targeting therapeutic strategies are proposed that could improve the response to anti-angiogenic therapies. SIGNIFICANCE STATEMENT: Tumor-associated macrophages (TAMs) are known promotors of tumor neovascularization, and significantly contribute to the emergence of resistance to anti-angiogenic therapies. Recent evidence suggests that the angiogenesis promoting phenotype of TAMs can be activated by hypoxic tumor cell-derived oncometabolites, including lactate and succinate. Here, the latest findings into the lactate- and succinate-mediated mechanistic activation of pro-angiogenic TAMs are reviewed, and therapeutic strategies that interfere with this mechanism and may delay or even prevent acquired resistance to anti-angiogenic agents are discussed.

Tumor immunoevasion via acidosis-dependent induction of regulatory tumor-associated macrophages

Many tumors evolve sophisticated strategies to evade the immune system, and these represent major obstacles for efficient antitumor immune responses. Here we explored a molecular mechanism of metabolic communication deployed by highly glycolytic tumors for immunoevasion. In contrast to colon adenocarcinomas, melanomas showed comparatively high glycolytic activity, which resulted in high acidification of the tumor microenvironment. This tumor acidosis induced Gprotein-coupled receptor-dependent expression of the transcriptional repressor ICER in tumor-associated macrophages that led to their functional polarization toward a non-inflammatory phenotype and promoted tumor growth. Collectively, our findings identify a molecular mechanism of metabolic communication between non-lymphoid tissue and the immune system that was exploited by high-glycolytic-rate tumors for evasion of the immune system.

IL-38 has an anti-inflammatory action in psoriasis and its expression correlates with disease severity and therapeutic response to anti-IL-17A treatment

IL-36 cytokines, a subgroup of IL-1 family, comprise IL-36α, IL-36β, and IL-36γ agonists, abundantly expressed in psoriatic skin, and IL-36RA and IL-38 antagonists. In psoriatic skin, IL-36 cytokines interfere with keratinocyte cornification programs and induce the release of antimicrobial peptides and chemokines active on neutrophils and Th17 lymphocytes. To date, the role of IL-38 antagonist in psoriasis remains to be defined. Here, we demonstrate that skin and circulating IL-38 levels are reduced in psoriatic patients and in other skin diseases characterized by neutrophilic infiltrate. In psoriasis, the balance of IL-36γ agonist/IL-38 antagonist serum levels is in favor of agonists and is closely associated with disease severity. Interestingly, IL-38 is upregulated by anti-IL-17A biological treatment and positively correlates with the therapeutic efficacy of secukinumab in psoriatic patients. The downregulation of IL-38 expression is strictly related to keratinocyte de-differentiation triggered by the inflammatory cytokines IL-36γ, IL-17, and IL-22. Finally, we demonstrate that administration of recombinant full-length IL-38 counteracts in vitro the biological processes induced by IL-36γ in human keratinocytes and endothelial cells and attenuates in vivo the severity of the psoriasiform phenotype induced by IMQ in mice. Such effects are achieved by restoring the physiological programs of keratinocyte proliferation and differentiation, and reducing the immune cell infiltrates.

CD38 Is Robustly Induced in Human Macrophages and Monocytes in Inflammatory Conditions

Macrophages and their monocyte precursors mediate innate immune responses and can promote a spectrum of phenotypes from pro-inflammatory to pro-resolving. Currently, there are few markers that allow for robust dissection of macrophage phenotype. We recently identified CD38 as a marker of inflammatory macrophages in murine in vitro and in vivo models. However, it is unknown whether CD38 plays a similar marker and/or functional role in human macrophages and inflammatory diseases. Here, we establish that CD38 transcript and protein are robustly induced in human macrophages exposed to LPS (±IFN-γ) inflammatory stimuli, but not with the alternative stimulus, IL-4. Pharmacologic and/or genetic CD38 loss-of-function significantly reduced the secretion of inflammatory cytokines IL-6 and IL-12p40 and glycolytic activity in human primary macrophages. Finally, monocyte analyses in systemic lupus erythematosus patients revealed that, while all monocytes express CD38, high CD38 expression in the non-classical monocyte subpopulation is associated with disease. These data are consistent with an inflammatory marker role for CD38 in human macrophages and monocytes.

Mapping macrophage polarization over the myocardial infarction time continuum

In response to myocardial infarction (MI), cardiac macrophages regulate inflammation and scar formation. We hypothesized that macrophages undergo polarization state changes over the MI time course and assessed macrophage polarization transcriptomic signatures over the first week of MI. C57BL/6 J male mice (3–6 months old) were subjected to permanent coronary artery ligation to induce MI, and macrophages were isolated from the infarct region at days 1, 3, and 7 post-MI. Day 0, no MI resident cardiac macrophages served as the negative MI control. Whole transcriptome analysis was performed using RNA-sequencing on n = 4 pooled sets for each time. Day 1 macrophages displayed a unique pro-inflammatory, extracellular matrix (ECM)-degrading signature. By flow cytometry, day 0 macrophages were largely F4/80^highLy6C^low resident macrophages, whereas day 1 macrophages were largely F4/80^lowLy6C^high infiltrating monocytes. Day 3 macrophages exhibited increased proliferation and phagocytosis, and expression of genes related to mitochondrial function and oxidative phosphorylation, indicative of metabolic reprogramming. Day 7 macrophages displayed a pro-reparative signature enriched for genes involved in ECM remodeling and scar formation. By triple in situ hybridization, day 7 infarct macrophages in vivo expressed collagen I and periostin mRNA. Our results indicate macrophages show distinct gene expression profiles over the first week of MI, with metabolic reprogramming important for polarization. In addition to serving as indirect mediators of ECM remodeling, macrophages are a direct source of ECM components. Our study is the first to report the detailed changes in the macrophage transcriptome over the first week of MI.

CK2 induced RIG-I drives metabolic adaptations in IFNγ-treated glioma cells

Given the known anti-tumorigenic properties of IFNγ, its effect on glioma cell survival was investigated. Though IFNγ had no effect on glioma cell viability, it induced cell cycle arrest. This was accompanied by increased expression of p53 and retinoic acid inducible gene (RIG-I). While RIG-I had no effect on glioma cell survival, it increased expression of p53 and its downstream target TP53 induced glycolysis and apoptosis regulator (TIGAR). IFNγ induced mitochondrial co-localization of RIG-I was concomitant with its ability to regulate ROS generation, oxidative phosphorylation (OXPHOS) and key enzymes involved in glycolysis and pentose phosphate pathway. Importantly, metabolic gene profiling indicated a suppressed glycolytic pathway in glioma cells upon IFNγ treatment. In addition, IFNγ mediated increase in casein kinase 2 (CK2) expression positively regulated RIG-I expression. These findings demonstrate how IFNγ induced CK2 regulates RIG-I to drive a complex program of metabolic adaptation and redox homeostasis, crucial for determining glioma cell fate.

Prostaglandin D2 is a novel repressor of IFNγ induced indoleamine-2,3-dioxygenase via the DP1 receptor and cAMP pathway

Expression of elevated levels of Indoleamine 2,3-dioxygenase (IDO) is well established as a mechanism of cancer induced immunosuppression. Pharmacological inhibition of IDO activity is thus a promising alternative in the treatment of cancer. Previously we demonstrated that cyclooxygenase derived metabolites of arachidonic acid inhibited the interferon-gamma mediated induction of IDO in both THP-1 cells and human monocytes. Here we identified that of the five primary prostanoids produced by COX-1/COX-2, only PGD2 displayed significant repressor activity. PGD2 inhibited IDO activity with an IC50 of 7.2µM in THP-1 cells and 5.2µM in monocytes. PGD2 caused a significant decrease in both IDO mRNA and protein. Using receptor specific agonists, PGD2 was found to act via the DP1 receptor, while the CRTH2 receptor was not involved. A DP1 antagonist significantly reduced the activity of PGD2, while CRTH2 agonists were ineffective. PGD2 increased intracellular cAMP levels and exogenous N(6)-cAMP was also found to be highly inhibitory. The effects of PGD2 via cAMP were blocked by Rp-cAMP indicating involvement of PKA. PGD2 also stimulated CREB phosphorylation, a PKA dependent transcription factor. This is the first report demonstrating that PGD2, a prostanoid typically associated with allergy, can inhibit IDO activity via the DP1/cAMP/PKA/CREB pathway. Our findings suggest that PGD2 and its derivatives may form the basis of novel repressors of IFNγ-mediated IDO expression.

Increased occurrence of protein kinase CK2 in astrocytes in Alzheimer's disease pathology

BACKGROUND

Alzheimer's disease (AD) is the most common neurodegenerative disease. In addition to the occurrence of amyloid deposits and widespread tau pathology, AD is associated with a neuroinflammatory response characterized by the activation of microglia and astrocytes. Protein kinase 2 (CK2, former casein kinase II) is involved in a wide variety of cellular processes. Previous studies on CK2 in AD showed controversial results, and the involvement of CK2 in neuroinflammation in AD remains elusive.

METHODS

In this study, we used immunohistochemical and immunofluorescent staining methods to investigate the localization of CK2 in the hippocampus and temporal cortex of patients with AD and non-demented controls. We compared protein levels with Western blotting analysis, and we investigated CK2 activity in human U373 astrocytoma cells and human primary adult astrocytes stimulated with IL-1β or TNF-α.

RESULTS

We report increased levels of CK2 in the hippocampus and temporal cortex of AD patients compared to non-demented controls. Immunohistochemical analysis shows CK2 immunoreactivity in astrocytes in AD and control cases. In AD, the presence of CK2 immunoreactive astrocytes is increased. CK2 immunopositive astrocytes are associated with amyloid deposits, suggesting an involvement of CK2 in the neuroinflammatory response. In U373 cells and human primary astrocytes, the selective CK2 inhibitor CX-4945 shows a dose-dependent reduction of the IL-1β or TNF-α induced MCP-1 and IL-6 secretion.

CONCLUSIONS

This data suggests that CK2 in astrocytes is involved in the neuroinflammatory response in AD. The reduction in pro-inflammatory cytokine secretion by human astrocytes using the selective CK2 inhibitor CX-4945 indicates that CK2 could be a potential target to modulate neuroinflammation in AD.

Protein kinase CK2 in breast cancer: the CK2β regulatory subunit takes center stage in epithelial plasticity

Structurally, protein kinase CK2 consists of two catalytic subunits (α and α') and two regulatory subunits (β), which play a critical role in targeting specific CK2 substrates. Compelling evidence shows the complexity of the CK2 cellular signaling network and supports the view that this enzyme is a key component of regulatory protein kinase networks that are involved in several aspects of cancer. CK2 both activates and suppresses the expression of a number of essential oncogenes and tumor suppressors, and its expression and activity are upregulated in blood tumors and virtually all solid tumors. The prognostic significance of CK2α expression in association with various clinicopathological parameters highlighted this kinase as an adverse prognostic marker in breast cancer. In addition, several recent studies reported its implication in the regulation of the epithelial-to-mesenchymal transition (EMT), an early step in cancer invasion and metastasis. In this review, we briefly overview the contribution of CK2 to several aspects of cancer and discuss how in mammary epithelial cells, the expression of its CK2β regulatory subunit plays a critical role in maintaining an epithelial phenotype through CK2-mediated control of key EMT-related transcription factors. Importantly, decreased CK2β expression in breast tumors is correlated with inefficient phosphorylation and nuclear translocation of Snail1 and Foxc2, ultimately leading to EMT induction. This review highlights the pivotal role played by CK2β in the mammary epithelial phenotype and discusses how a modest alteration in its expression may be sufficient to induce dramatic effects facilitating the early steps in tumor cell dissemination through the coordinated regulation of two key transcription factors.

Protein kinase CK2 is a critical regulator of epithelial homeostasis in chronic intestinal inflammation

The molecular mechanisms that restore intestinal epithelial homeostasis during colitis are incompletely understood. Here, we report that during intestinal inflammation, multiple inflammatory cytokines promote the activity of a master regulator of cell proliferation and apoptosis, serine/threonine kinase CK2. Enhanced mucosal CK2 protein expression and activity were observed in animal models of chronic colitis, particularly within intestinal epithelial cells (IECs). The in vitro treatment of intestinal epithelial cell lines with cytokines resulted in increased CK2 expression and nuclear translocation of its catalytic α subunit. Similarly, nuclear translocation of CK2α was a prominent feature observed in colonic crypts from individuals with ulcerative colitis and Crohn's disease. Further in vitro studies revealed that CK2 activity promotes epithelial restitution, and protects normal IECs from cytokine-induced apoptosis. These observations identify CK2 as a key regulator of homeostatic properties of the intestinal epithelium that serves to promote wound healing, in part through inhibition of apoptosis under conditions of inflammation.

Pathogen recognition and mechanisms in Atlantic cod (Gadus morhua) head kidney cells: bacteria (LPS) and virus (poly I:C) signals through different pathways and affect distinct genes

Understanding pathogen recognition and mechanisms in Atlantic cod are of significant importance for both basic research on wild populations and health management in aquaculture. A microarray approach was utilized to search for effects of viral (polyinosinic acid:polycytidylic acid), bacterial (lipopolysaccharide) and polyclonal activator (phytohaemoagglutinin) stress in Atlantic cod head kidney cells. LPS cell activation increased mRNA expression of interleukin 8; interleukin-1β; cyclooxygenase 2; leukocyte derived chemotaxin 2; carboxyl-esterase 2 and environmental biomarker cytochrome P450 1A. Mitogen activated protein kinase p38 and cathepsin F were down regulated by LPS. The antiviral responses induced by double stranded RNA clearly increased transcription of Toll like receptor 3 and interferon stimulating gene 15. The phytohaemoagglutinin response seemed to be more non-specific. Special for the phytohaemoagglutinin induction was the increase in major histocompatibility complex class I. CC chemokine type 2 mRNA expression was increased by phytohaemoagglutinin, lipopolysaccharide and polyinosinic acid:polycytidylic acid, while mitogen activated protein kinase p38 and leukocyte derived chemotaxin 2 were down regulated by phytohaemoagglutinin. Oxidative stress related genes like catalase and glutaredoxin and the anti-apoptotic gene Bcl-2 showed no transcriptional changes compared to control in any of the treatments. Eicosanoids like prostaglandin 2, leukotriene B4 and B5 were constitutively produced by cod head kidney cells in vitro. The most remarkable feature of eicosanoid secretion is the higher production of leukotrienes against prostaglandins, indicating that the lipooxygenase pathway is preferred over the cyclooxygenase pathway. Although there were no significant differences in eicosanoid secretion between the groups, polyinosinic acid:polycytidylic acid showed a clear tendency to increase the levels of leukotriene B4 and B5. This study reveals distinct signatures of bacteria and virus transcriptional responses in cod head kidney cells. In addition, the novel finding that cytochrome P450 1A was upregulated during the antibacterial response indicates a connection between immunity and aryl hydrocarbon receptor activation in Atlantic cod.

Phosphorylation of RIG-I by casein kinase II inhibits its antiviral response

RIG-I is an intracellular RNA virus sensor that mediates a signaling pathway that triggers the alpha/beta interferon (IFN-α/β) immune defenses. However, the mechanism for regulation of RIG-I activity remains largely unknown. Here we show that RIG-I activity is regulated by phosphorylation and dephosphorylation in its repressor domain (RD). Threonine at amino acid (aa) 770 and serine at aa 854 to 855 of RIG-I are phosphorylated by casein kinase II (CK2) in the resting state of the cell and dephosphorylated when cells are infected by RNA virus. Mutation at aa position 770 or 854 to 855 of RIG-I renders it constitutively active. Pharmacological inhibition of CK2 enhances virus-induced expression of IFN-β and suppresses virus proliferation, while inhibition of phosphatase reduces virus-induced expression of IFN-β. Overexpression of CK2 suppresses RIG-I-mediated signaling, while silencing of CK2 results in the increased suppression of virus proliferation. Our results reveal a novel mechanism of the regulation of RIG-I activity during RNA virus infection.

The impact of PTEN regulation by CK2 on PI3K-dependent signaling and leukemia cell survival

Gene alterations affecting elements of PI3K signaling pathway do not appear to be sufficient to explain the extremely high frequency of PI3K signaling hyperactivation in leukemia. It has been known for long that PTEN phosphorylation at the C-terminal tail, in particular by CK2, contributes to the stabilization and simultaneous inhibition of this critical tumor suppressor. However, direct evidence of the involvement of this mechanism in cancer has been gathered only recently. It is now known that CK2-mediated posttranslational, non-deleting, inactivation of PTEN occurs in T-ALL, CLL and probably other leukemias and solid tumors. To explore this knowledge for therapeutic purposes remains one of the challenges ahead.

Interferon-gamma elevates nicotinamide N-methyltransferase activity and nicotinamide level in human glioma cells

Nicotinamide N-methyltransferase (NNMT) catalyzes the N-methylation of nicotinamide. NNMT is strongly expressed in tumor cells and an increase in NNMT activity may reduce cellular nicotinamide level and thereby promote cell survival in the cells. However, there has been no report of a relationship between NNMT activity and nicotinamide level in tumor cells. We report herein that human glioma cells produce relatively large amounts of NNMT and that when these cells are cultured in the presence of interferon-gamma (IFN-gamma) their 1-methylnicotinamide levels increase. To clarify the mechanisms by which IFN-gamma increases 1-methylnicotinamide levels in these cells, we measured NNMT activity and the levels of NNMT expression, nicotinamide and nicotinamide adenine dinucleotide (NAD(+)) in the presence and absence of IFN-gamma. We also examined whether addition of exogenous 1-methylnicotinamide directly affects cell viability and/or the cellular levels of 1-methylnicotinamide, nicotinamide and NAD(+). While addition of 1-methylnicotinamide increased the total amount of cellular 1-methylnicotinamide present, it did not affect nicotinamide or NAD(+) levels, or cell viability. Conversely, IFN-gamma significantly increased NNMT activity and the nicotinamide cellular concentration, while leaving NNMT expression and the NAD(+) cellular concentration unchanged. Therefore, the increase in the 1-methylnicotinamide level found when IFN-gamma is present in culture may be a consequence of increases in both the nicotinamide concentration and NNMT activity, whereas, 1-methylnicotinamide did not influence nicotinamide levels, NAD(+) levels, or cell viability per se. These results suggest that an increase in NNMT activity does not always reduce cellular nicotinamide concentration in tumor cells.

The neuropeptide calcitonin gene-related peptide causes repression of tumor necrosis factor-alpha transcription and suppression of ATF-2 promoter recruitment in Toll-like receptor-stimulated dendritic cells

Sensory nerves may dampen inflammatory processes through the release of the neuropeptide calcitonin gene-related peptide (CGRP). CGRP mediates immunosuppressive activities through up-regulation of interleukin-10 or, alternatively, through an interleukin-10-independent pathway that is associated with rapid induction of the transcriptional inducible cAMP early repressor (ICER). In this work, we further investigated the molecular mechanisms of immune modulation by CGRP. Using TLR2-stimulated dendritic cells, we show that inhibition of tumor necrosis factor-alpha production by CGRP is dependent on up-regulation of endogenous ICER. Dendritic cell expression of ICER was selectively induced by CGRP and elevation of cellular cAMP levels but not by numerous pro- and anti-inflammatory cytokines. Treatment of dendritic cells with CGRP did not interfere with the induction of Tnfa gene expression but caused premature repression of TLR2-induced transcriptional activity. ATF-2 was rapidly phosphorylated and recruited to the Tnfa promoter following ligation of TLR2. Concomitant administration of CGRP completely prevented binding of ATF-2 to the Tnfa promoter, whereas recruitment of ICER was markedly elevated. In contrast, CGRP did not influence TLR2-stimulated binding of NF-kappaB p65. Together, these results are consistent with a model suggesting that CGRP causes rapid up-regulation of ICER, which in turn competes with ATF-2 for binding to the Tnfa promoter, leading to repression of gene expression.

Requirement for nuclear factor kappa B signalling in the interleukin-1-induced expression of the CCAAT/enhancer binding protein-delta gene in hepatocytes

Elevated circulating levels of acute phase proteins (APP) are associated with inflammation and inflammatory disorders such as cardiovascular disease. APP are mainly synthesised by hepatocytes and their transcription is induced by pro-inflammatory cytokines such as interleukin-1 (IL-1). The molecular mechanisms underlying the IL-1-induced expression of key transcription factors implicated in the regulation of APP are poorly understood. We have investigated this aspect using the CCAAT/enhancer binding protein-delta (C/EBPdelta) as a model gene. IL-1 induced the expression of C/EBPdelta mRNA and protein in the human hepatoma Hep3B cell line, a widely employed model system for studies on cytokine signalling in relation to the expression of APP. The IL-1-mediated induction of C/EBPdelta expression was attenuated in the presence of pharmacological inhibitors against c-Jun N-terminal kinase (JNK) (curcumin and SP600125), casein kinase 2 (CK2) (apigenin) and nuclear factor-kappaB (NF-kappaB) (NF-kappaB activation inhibitor). RNA interference assays showed significant attenuation of the IL-1-induced expression of C/EBPdelta following knockdown of the p50 and p65 subunits of NF-kappaB. IL-1 induced NF-kappaB DNA binding and activation by this transcription factor and this was attenuated by curcumin and apigenin. Taken together, these results suggest a potentially crucial role for NF-kappaB in the IL-1-induced expression of C/EBPdelta, and thereby downstream APP genes regulated by this transcription factor.

The interferon-gamma-mediated inhibition of lipoprotein lipase gene transcription in macrophages involves casein kinase 2- and phosphoinositide-3-kinase-mediated regulation of transcription factors Sp1 and Sp3

The mechanisms underlying transcriptional inhibition by interferon-gamma (IFN-gamma) are poorly understood despite the existence of a large number of genes that are regulated in this manner and the key role of this cytokine in inflammatory disorders such as atherosclerosis. We have previously identified a novel mechanism for transcriptional inhibition by IFN-gamma that involves a reduction in the binding of transcription factors Sp1 and Sp3 to regulatory sequences in the lipoprotein lipase (LPL) gene. In the present study, we have investigated the signalling pathways that impact on the IFN-gamma-mediated regulation of Sp1/Sp3 binding and LPL gene transcription in macrophages. The IFN-gamma-mediated inhibition of LPL promoter activity was prevented by expression of dominant negative forms of casein kinase 2 (CK2) and protein kinase B (PKB), a key downstream component of the phosphoinositide-3-kinase (PI3K) pathway. IFN-gamma activated both the catalytic subunits of CK2 without affecting their expression. CK2 interacted with both Sp1 and Sp3 and this association was increased by IFN-gamma. Electrophoretic mobility shift assays showed that a CK2-mediated phosphorylation of either cellular extracts or recombinant Sp1 reduced binding to the regulatory region in the LPL gene. The action of PKB was potentially mediated through mammalian target for rapamycin proteins. Taken together, these results suggest a key role for CK2 and PI3K signalling pathways in the IFN-gamma-mediated inhibition of macrophage LPL gene transcription through the regulation of Sp1/Sp3 binding.

Interferon gamma: a master regulator of atherosclerosis

Atherosclerosis is a chronic inflammatory disease that is characterized by the development of fibrotic plaques in the arterial wall. The disease exhibits a complex aetiology and its progression is influenced by a number of environmental and genetic risk factors. The cytokine interferon-gamma (IFN-gamma), a key regulator of immune function, is highly expressed in atherosclerotic lesions and has emerged as a significant factor in atherogenesis. Evidence from both mouse models of atherosclerosis and in vitro cell culture has suggested that the role of IFN-gamma is complex since both pro- and anti-atherogenic actions have been affiliated to it. This review will focus on evaluating the contribution of IFN-gamma to atherosclerosis and, in particular, how it regulates immune responses to the disease.

In cardiac myocytes, cAMP elevation triggers the down-regulation of transcripts and promoter activity for cyclic AMP phosphodiesterase-4A10 (PDE4A10)

Transcripts for the PDE4A10 cyclic AMP phosphodiesterase isoform are present in a wide variety of rat tissues including the heart. Sequence comparisons between the putative human and mouse promoters revealed a number of conserved regions including both an Sp1 and a CREB-binding site. The putative mouse PDE4A10 promoter was amplified from genomic DNA and sub-cloned into a luciferase reporter vector for investigation of activity in neonatal cardiac myocytes. Transfection with this construct identified a high level of luciferase expression in neonatal cardiac myocytes. Surprisingly, this activity was down-regulated by elevation of intracellular cAMP through a process involving PKA, but not EPAC, signalling. Such inhibition of the rodent PDE4A10 promoter activity in response to elevated cAMP levels is in contrast to the PDE4 promoters so far described. Site-directed mutagenesis revealed that the Sp1 binding site at promoter position -348 to -336 is responsible for the basal constitutive expression of murine PDE4A10. The conserved CREB-binding motif at position -370 to -363 also contributes to basal promoter activity but does not in itself confer cAMP inhibition upon the PDE4A10 promoter. EMSA analysis confirmed the authenticity of CREB and Sp1 binding sites. The transcriptional start site was identified to be an adenine residue at position -55 in the mouse PDE4A10 promoter. We present evidence that this novel down-regulation of PDE4A10 is mediated by the transcription factor ICER in a PKA dependent manner. The pool of cAMP in cardiac myocytes that down-regulates PDE4A10 is regulated by beta-adrenoceptor coupled adenylyl cyclase activity and via hydrolysis determined predominantly by the action of PDE4 (cAMP phosphodiesterase-4) and not PDE3 (cAMP phosphodiesterase-3). We suggest that increased cAMP may remodel cAMP-mediated signalling events by not only increasing the expression of specific PDE4 cAMP phosphodiesterases but also by down-regulating specific isoforms, such as is shown here for PDE4A10 in cardiac myocytes.

Protein kinase CK2, an important regulator of the inflammatory response?

Casein kinase 2 (CK2) is a highly conserved serine-threonine kinase that uses both adenosine triphosphate and guanosine triphosphate as phosphate donors. This constitutively active and ubiquitously expressed enzyme is often present as a tetrameric holoenzyme complex of two catalytic subunits (alpha and/or alpha') and two regulatory beta subunits. The enzyme is known to phosphorylate more than 300 substrates and controls a wide range of processes, including the regulation of cell cycle, apoptosis, transformation, and circadian rhythm. Several lines of recent evidence also suggest a potentially important role for CK2 in the control of the inflammatory response. This review will give an overview of CK2 and its regulation and describe the evidence implicating its role in inflammation.

Major histocompatibility class II transactivator expression in smooth muscle cells from A2b adenosine receptor knock-out mice: cross-talk between the adenosine and interferon-gamma signaling

Atherosclerosis characterized by sustained inflammation and aberrant extracellular matrix alterations. Our previous investigation has defined major histocompatibility class II transactivator (CIITA) as a key factor in mediating these two processes in smooth muscle cells. Here, we demonstrate that CIITA and major histocompatibility class II expression are elevated in interferon-gamma (IFN-gamma)-treated smooth muscle cells from A2b adenosine receptor (A2bAR(-/-)) knock-out mice, as compared with wild type cells. An A2-type adenosine receptor agonist suppresses these effects of IFN-gamma in wild type cells, which can be blocked by an A2bAR-specific antagonist. We further identify that increased cellular cAMP levels are responsible for the down-regulation of CIITA expression and, hence, reduced IFN-gamma response as evidenced by the following data: 1) direct activation of adenylyl cyclase activity is both necessary and sufficient to suppress the IFN-gamma response; 2) inhibition of phosphodiesterase activity attenuates IFN-gamma induced transcription events; and 3) direct treatment with cAMP analog abrogates CIITA activation and IFN-gamma response. Therefore, our data establish possible cross-talk between the adenosine signaling through cAMP and IFN-gamma during regulation of CIITA expression.

Gene expression analysis of zebrafish retinal ganglion cells during optic nerve regeneration identifies KLF6a and KLF7a as important regulators of axon regeneration

Unlike mammals, teleost fish are able to mount an efficient and robust regenerative response following optic nerve injury. Although it is clear that changes in gene expression accompany axonal regeneration, the extent of this genomic response is not known. To identify genes involved in successful nerve regeneration, we analyzed gene expression in zebrafish retinal ganglion cells (RGCs) regenerating their axons following optic nerve injury. Microarray analysis of RNA isolated by laser capture microdissection from uninjured and 3-day post-optic nerve injured RGCs identified 347 up-regulated and 29 down-regulated genes. Quantitative RT-PCR and in situ hybridization were used to verify the change in expression of 19 genes in this set. Gene ontological analysis of the data set suggests regenerating neurons up-regulate genes associated with RGC development. However, not all regeneration-associated genes are expressed in differentiating RGCs indicating the regeneration is not simply a recapitulation of development. Knockdown of six highly induced regeneration-associated genes identified two, KLF6a and KLF7a, that together were necessary for robust RGC axon re-growth. These results implicate KLF6a and KLF7a as important mediators of optic nerve regeneration and suggest that not all induced genes are essential to mount a regenerative response.

The role of protein kinase CK2 in intestinal epithelial cell inflammatory signaling

BACKGROUND

The transcription factor NF-kappaB is believed to play a key pathophysiological role in chronic intestinal inflammation. Further characterization of its mechanism of regulation, predominantly through cell signaling pathways, may provide clues as to the means of its intervention. One such potential signaling candidate is the protein kinase CK2. Despite its known ability to influence NF-kappaB activation, it has received no attention in this particular setting.

AIM

To characterize the aspects of its activation in response to IL-1beta in the colonic cell lines Caco2 and HCT116.

MATERIALS AND METHODS

A biochemical analysis of kinase activation was performed using phospho-specific antibodies as well as immune complex kinase assays; transcription factor activity was measured by transient transfection and luciferase-based NF-kappaB reporter assays; pro-inflammatory molecule expression was determined using RT-PCR.

RESULTS

In this report, we show an enhanced activation of CK2 bound to IKKgamma or the p65 subunit of the NF-kappaB in response to IL-1beta stimulation of intestinal epithelial cells. Using two established NF-kappaB reporters, we demonstrate that CK2 is involved in NF-kappaB regulation through the p65 serine 529 site. Using co-immunoprecipitation studies, we also show that p65 is bound to CK2 predominantly in the nucleus. From a functional perspective, two CK2 specific inhibitors were then shown to attenuate IL-8 reporter activation. Finally, the expression of a series of pro-inflammatory molecules including IL-8, GRO-alpha, MCP-1, TNFalpha and iNOS were variably affected in response to CK2 inhibition.

CONCLUSION

CK2 plays an active role in NF-kappaB signaling in intestinal epithelial cell lines and may represent a possible target for intervention.

Transforming growth factor-beta-regulated expression of genes in macrophages implicated in the control of cholesterol homoeostasis

The regulation of macrophage cholesterol homoeostasis is of crucial importance in the pathogenesis of atherosclerosis, an underlying cause of heart attack and stroke. Several recent studies have revealed a critical role for the cytokine TGF-beta (transforming growth factor-beta), a key regulator of the immune and inflammatory responses, in atherogenesis. We discuss here the TGF-beta signalling pathway and its role in this disease along with the outcome of our recent studies on the action of the cytokine on the expression of key genes implicated in the uptake or efflux of cholesterol by macrophages and the molecular mechanisms underlying such regulation.

Critical role for casein kinase 2 and phosphoinositide-3-kinase in the interferon-gamma-induced expression of monocyte chemoattractant protein-1 and other key genes implicated in atherosclerosis

OBJECTIVE

The interferon-gamma (IFN-gamma)-mediated regulation of macrophage gene expression is of crucial importance in the pathogenesis of atherosclerosis. The mechanisms underlying the actions of IFN-gamma signaling in macrophages were investigated using monocyte chemoattractant protein (MCP)-1 as a model gene.

METHODS AND RESULTS

The IFN-gamma-induced expression of MCP-1 in macrophages was attenuated by inhibitors of phosphoinositide-3-kinase (PI3K), casein kinase 2 (CK2), and Janus kinase (JAK)-2. AKT was the downstream target for PI3K action. Electrophoretic mobility shift assays and chromatin immunoprecipitation showed that signal transducer and activator of transcription (STAT)-1 interacted with IFN-gamma responsive elements in the MCP-1 gene promoter. The IFN-gamma-induced activity of the MCP-1 gene promoter and an artificial promoter containing STAT1 responsive elements was inhibited by expression of dominant negative forms of JAK-1 and -2, STAT1, CK2, and AKT. The action of CK2 and AKT on STAT1 activation was mediated, at least in part, through the regulation of serine 727 phosphorylation. Analysis of a number of other genes regulated by this cytokine and implicated in atherosclerosis revealed a gene-specific action for PI3K/AKT in IFN-gamma signaling.

CONCLUSIONS

These studies provide novel insights into the role of PI3K/AKT and CK2 in IFN-gamma signaling relevant to changes in macrophage gene expression during atherosclerosis.

Tumor necrosis factor-alpha activates transcription of inducible repressor form of 3',5'-cyclic adenosine 5'-monophosphate-responsive element binding modulator and represses P450 aromatase and inhibin alpha-subunit expression in rat ovarian granulosa cells by a p44/42 mitogen-activated protein kinase-dependent mechanism

The proinflammatory cytokine TNFalpha has important actions at the level of the ovary, including inhibition of P450 aromatase (P450AROM) activity and the secretion of inhibin, two proteins that are markers of the granulosa cell's differentiated status. Because the transcription of both P450AROM and inhibin alpha-subunit can be suppressed in the ovary by the inducible repressor isoform of cAMP-responsive element binding modulator (ICER), we have investigated whether TNFalpha and its intracellular messenger ceramide can induce ICER expression and the mechanisms whereby the induction is accomplished. ICER mRNA levels were assessed by RT-PCR in granulosa cells treated with TNFalpha, the ceramide-mobilizing enzyme sphingomyelinase (SMase), or C6-cer, a cell-permeant ceramide analog. Rapid (3 h) yet transient increases in the four isoforms of ICER were observed in response to all treatments. Likewise, ICER protein measured by immunoprecipitation with a specific antibody increases after TNFalpha, SMase, or C6-cer treatment. The mandatory phosphorylation of cAMP-responsive element binding was also observed in response to TNFalpha, SMase, or C6-cer and shown to be prevented by the p44/42 MAPK-specific inhibitor PD098059 but no other kinase blockers. Activation of p44/42 MAPK by the cytokine and its messenger was subsequently demonstrated as well as the inhibition of ICER expression by PD098059. Finally, the blocking of p44/42 MAPK activation prevented TNFalpha inhibition of FSH-dependent increases in P450AROM and inhibin alpha-subunit mRNA levels, thus indicating that p44/42 MAPK-mediated ICER expression may be accountable for the effects of TNFalpha on the expression of both proteins.

Interferon-γ dose-dependently inhibits prostaglandin E2-mediated dendritic-cell-migration towards secondary lymphoid organ chemokines

Monocyte-derived human dendritic cells (MoDCs) are increasingly applied as cellular vaccines for cancer patients. Important features for their efficacy include high migratory responsiveness to lymph node-chemokines and most likely their ability to produce bioactive IL-12 p70 upon subsequent contact with CD40 ligand-expressing T-cells. The current standard DC-maturation cocktail for clinical trials is inflammatory cytokines (TNF-alpha, IL-1beta and IL-6) combined with prostaglandin E(2) (PGE(2)), inducing phenotypically mature MoDCs with high migratory responsiveness to CCR7 ligands. This cocktail does not, however, induce or prime for production of IL-12 p70. Addition of IFN-gamma to PGE(2)-containing maturation cocktails has been shown to prime for substantial production of IL-12 p70 by subsequent CD40 ligation, but the impact of IFN-gamma on phenotypic maturation and migratory responsiveness induced by PGE(2)-containing inflammatory stimuli still remains elusive. Here, we demonstrate that addition of IFN-gamma to the standard maturation cocktail decreased CCR7 mRNA and down-regulated CCR7 expression on MoDCs in a dose-dependent manner. Moreover, addition of IFN-gamma was found to suppress MoDC-migration towards the CCR7-ligands CCL19 and CCL21. These novel findings indicate that addition of IFN-gamma to DC-maturation stimuli may have no beneficial impact on MoDC-vaccine efficiency and further implicate IFN-gamma as a negative feedback factor in DC migration towards draining lymph nodes when full-blown Th1-type responses are established. Such mechanism may restrict an uncontrolled and potentially harmful amplification of the adaptive Th1 response.

Transforming growth factor-beta-induced expression of the apolipoprotein E gene requires c-Jun N-terminal kinase, p38 kinase, and casein kinase 2

OBJECTIVE

The cytokine transforming growth factor-beta (TGF-beta) and apolipoprotein E (apoE) play potent antiatherogenic roles. Despite such importance, the mechanisms underlying the regulation of apoE expression by TGF-beta have not been characterized and were therefore investigated.

METHODS AND RESULTS

Using THP-1 cell line as a model system, with key findings confirmed in primary cultures, we show that TGF-beta induces the expression of apoE, and this is prevented by pharmacological inhibitors of c-Jun N-terminal kinase (JNK), p38 kinase, and casein kinase 2 (CK2). In support for an important role for these pathways, TGF-beta activates JNK, p38 kinase, and CK2, and dominant-negative (DN) forms of these proteins inhibit the cytokine-induced apoE expression. TGF-beta also increases the phosphorylation and expression of c-Jun, a downstream target for JNK action and a component of activator protein-1 (AP-1), and DN c-Jun inhibits the induction of apoE expression in response to the cytokine. AP-1 DNA binding was also induced by TGF-beta, and the action of p38 kinase, JNK, and CK2 converged on the activation of c-Jun/AP-1.

CONCLUSIONS

These studies reveal a novel role for JNK, p38 kinase, CK2, and c-Jun/AP-1 in the TGF-beta-induced expression of apoE.

Regulation of gene expression in RAW 264.7 macrophage cell line by interferon-γ

Macrophages play an important role in immune responses and in inflammatory disease states such as atherosclerosis. Interferon-gamma (IFN-gamma) is a major cytokine involved in the activation of macrophages. To elucidate the primary response of various genes and biological pathways regulated by IFN-gamma in macrophage, we analyzed the gene expression profile in RAW 264.7 macrophage cells treated with IFN-gamma for 4h. Microarray analysis revealed that about 400 genes were differentially expressed, of which about 250 genes were up-regulated and 150 were down-regulated. Functional organization of the transcriptome revealed that induced genes are involved in antimicrobial and antiviral responses, antigen presentation, chemokine and cytokine signaling, and inhibition of cell growth. We also found that expression of genes involved in cell-cycle control, DNA repair, and lipid metabolism was suppressed by IFN-gamma. We also identified induction of multiple transcription factors by IFN-gamma in RAW 264.7 cells. Functional annotation of genes regulated by IFN-gamma in RAW 264.7 cells may provide novel insights into the role of macrophages in immunity and in inflammatory disease.

Lipoprotein lipase is expressed by glomerular mesangial cells

Lipoprotein lipase expressed by the vasculature plays a key role in atherogenesis by enhancing the binding and uptake of lipoproteins and, thereby, leading to the formation of lipid-loaded foam cells. Hyperlipidemia also accelerates the progression of glomerular diseases and addition of exogenous lipoprotein lipase to mesangial cells has been shown to lead to an enhanced binding of lipoproteins to these cells. Despite such potential importance, the expression of endogenous lipoprotein lipase by cells of the glomeruli has, as yet, not been investigated. We show here for the first time that mesangial cells, but not epithelial cells, express lipoprotein lipase. The minimal lipoprotein lipase gene promoter was active in mesangial cells and inhibited by interferon-gamma, which is known to suppress its expression.

Effects of forskolin on Kupffer cell production of interleukin-10 and tumor necrosis factor alpha differ from those of endogenous adenylyl cyclase activators: possible role for adenylyl cyclase 9

Proinflammatory cytokines like tumor necrosis factor alpha (TNF-alpha) that are released from Kupffer cells may trigger liver inflammation and damage. Hence, endogenous mechanisms for limiting TNF-alpha expression are crucial for avoiding the development of sepsis. Such mechanisms include the anti-inflammatory actions of interleukin-10 (IL-10) as well as signaling induced by the intracellular second messenger cyclic AMP (cAMP). Kupffer cells express several receptors that activate cAMP synthesis, including E-prostanoid receptors and beta-adrenergic receptors. The expression and role of specific adenylyl cyclases in the inhibition of Kupffer cell activation have so far not been subject to study. Pretreatment of rat Kupffer cell cultures with cAMP analogues [8-(4-chlorophenyl)-thio-cAMP], adenylyl cyclase activator (forskolin), or ligands for G-coupled receptors (isoproterenol or prostaglandin E2) 30 min before the addition of lipopolysaccharide (LPS) (1 microg/ml) caused attenuated TNF-alpha levels in culture medium (forskolin/isoproterenol, P < or = 0.05; prostaglandin E2, P < or = 0.01). Forskolin also reduced IL-10 mRNA and protein (P < or = 0.05), which was not observed with the other cAMP-inducing agents. Furthermore, we found that rat Kupffer cells express high levels of the forskolin-insensitive adenylyl cyclase 9 compared to whole liver and that this expression is down-regulated by LPS (P < or = 0.05). We conclude that regulation of TNF-alpha and IL-10 in Kupffer cells depends on the mechanism by which cAMP is elevated. Forskolin and prostaglandin E2 differ in their effects, which suggests a possible role of forskolin-insensitive adenylyl cyclases like adenylyl cyclase 9.

Stat1-independent induction of SOCS-3 by interferon-gamma is mediated by sustained activation of Stat3 in mouse embryonic fibroblasts

Using microarray technology, we previously demonstrated that IFN-gamma induces suppressor of cytokine signaling-3 (SOCS-3) in Stat1-/- mouse embryonic fibroblasts and bone marrow-derived macrophages. In this study, we have investigated the mechanism by which SOCS-3 is induced by Stat1-independent signal transduction pathway. Tyrosine kinases Jak1 and Jak2 are required for SOCS-3 induction by IFN-gamma in mouse embryonic fibroblasts. IFN-gamma stimulated strong and sustained activation of Stat1 whereas Stat3 activation was weak and transient in wild-type fibroblasts. In contrast, Stat3 is activated strongly and in a sustained manner in Stat1-/- fibroblasts. The Src kinase inhibitor SU6656 suppressed IFN-gamma activation of Stat3 in both wild-type and Stat1-/- fibroblasts. However, SU6656 inhibited IFN-gamma induction of SOCS-3 completely in Stat1-/- but not in wild-type fibroblasts. Knock down of Stat3 by short interfering RNA abrogated Stat3 activation and SOCS-3 induction by IFN-gamma in Stat1-/- fibroblasts. In human fibrosarcoma cell line 2fTGH, IFN-gamma activated Stat1 but not Stat3. SOCS-3 induction by IFN-gamma is strictly Stat1-dependent. The Stat1 docking site is required for SOCS-3 induction by IFN-gamma in human lung adenocarcinoma cells. We propose a model in which sustained activation of Stat1 or Stat3 mediates SOCS-3 induction by IFN-gamma in wild-type and Stat1-/- mouse embryonic fibroblasts, respectively.

IFN-gamma activates cAMP/PKA/CREB signaling pathway in murine peritoneal macrophages

Interferon-gamma (IFN-gamma) is a macrophage-activating cytokine that serves critical functions in innate and adaptive immunity and is thought to be mediated by the Jak-Stat signaling pathway. The present study establishes for the first time that cyclic adenosine monophosphate, protein kinase A, and cAMP response element-binding protein (cAMP/PKA/CREB) are coregulators of the IFN-gamma signaling pathway. Experimental data indicate that exogenous IFN-gamma stimulated cAMP accumulation and PKA activation in time-dependent and dose-dependent manners in murine peritoneal macrophages. Moreover, IFN-gamma stimulated CREB phosphorylation and CREB DNA binding, which could be significantly attenuated by PKA inhibition with H89. It appears that a novel cAMP/PKA/CREB signaling pathway is activated by IFN-gamma in macrophages, suggesting that an alternate signaling pathway exists in macrophages in response to IFN-gamma.

A critical role for the Sp1-binding sites in the transforming growth factor-beta-mediated inhibition of lipoprotein lipase gene expression in macrophages

Increasing evidence suggests that the cytokine transforming growth factor-β (TGF-β) inhibits the development of atherosclerosis. The lipoprotein lipase (LPL) enzyme expressed by macrophages has been implicated in the pathogenesis of atherosclerosis by stimulating the uptake of lipoprotein particles. Unfortunately, the action of TGF-β on the expression of LPL in macrophages remains largely unclear. We show that TGF-β inhibits LPL gene expression at the transcriptional level. Transient transfection assays reveal that the −31/+187 sequence contains the minimal TGF-β-responsive elements. Electrophoretic mobility shift assays show that Sp1 and Sp3 interact with two regions in the −31/+187 sequence. Mutations of these Sp1/Sp3 sites abolish the TGF-β-mediated suppression whereas multimers of the sequence impart the response to a heterologous promoter. TGF-β has no effect on the binding or steady-state polypeptide levels of Sp1 and Sp3. These results, therefore, suggest a novel mechanism for the TGF-β-mediated repression of LPL gene transcription that involves regulation of the action of Sp1 and Sp3.

A Central Role for the Hsp90·Cdc37 Molecular Chaperone Module in Interleukin-1 Receptor-associated-kinase-dependent Signaling by Toll-like Receptors

Toll-like receptors (TLRs) serve crucial roles in innate immunity by mediating the activation of macrophages by microbial pathogens. The protein kinase interleukin-1 receptor associated kinase (IRAK-1) is a key component of TLR signaling pathways via its interaction with TRAF6, which subsequently leads to the activation of MAP kinases and various transcription factors. IRAK-1 is degraded following TLR activation, and this has been proposed to contribute to tolerance in macrophages by limiting further TLR-mediated signaling. Using a mass spectrometric-based approach, we have identified a cohort of chaperones and co-chaperones including Hsp90 and Cdc37, which bind to IRAK-1 but not IRAK-4 in 293T cells. Pharmacologic inhibition of Hsp90 led to a rapid decline in the expression level of IRAK-1, whereas overexpression of Cdc37 enhanced the activation and oligomerization of IRAK-1 in 293T cells. Significantly, the inhibition of Hsp90 in macrophages resulted in the destabilization and degradation of IRAK-1 but not IRAK-4. Concomitant with the loss of IRAK-1 expression was a reduction in the activation of p38 MAP kinase and Erk1/2 following stimulation with the bacterially derived TLR ligands, lipopolysaccharide and CpG DNA. Moreover, TLR ligand-induced expression of proinflammatory cytokines was also reduced. Thus we conclude that the level of on-going support provided to IRAK-1 by the Hsp90-Cdc37 chaperone module directly influences the magnitude of TLR-mediated macrophage activation. In addition, because further TLR signaling depends on the synthesis of new IRAK-1, the Hsp90-Cdc37 chaperone module could also contribute to tolerance in macrophages by controlling the rate at which nascent IRAK-1 is folded into a functional conformation.

Subtype-specific regulation of equilibrative nucleoside transporters by protein kinase CK2

Two subtypes of equilibrative transporters, es (equilibrative inhibitor-sensitive) and ei (equilibrative inhibitor-insensitive), are responsible for the majority of nucleoside flux across mammalian cell membranes. Sequence analyses of the representative genes, ENT1 {equilibrative nucleoside transporter 1; also known as SLC29A1 [solute carrier family 29 (nucleoside transporters), member 1]} and ENT2 (SLC29A2), suggest that protein kinase CK2-mediated phosphorylation may be involved in the regulation of es- and ei-mediated nucleoside transport. We used human osteosarcoma cells transfected with catalytically active or inactive alpha' and alpha subunits of CK2 to assess the effects of CK2 manipulation on nucleoside transport activity. Expression of inactive CK2alpha' (decreased CK2alpha' activity) increased the number of binding sites (approximately 1.5-fold) for the es-specific probe [3H]NBMPR ([3H]nitrobenzylthioinosine), and increased (approximately 1.8-fold) the V(max) for 2-chloro[3H]adenosine of the NBMPR-sensitive (es) nucleoside transporter. There was a concomitant decrease in the V(max) of the NBMPR-resistant (ei-mediated) uptake of 2-chloro[3H]adenosine. This inhibition of CK2alpha' activity had no effect, however, on either the K(D) of [3H]NBMPR binding or the K(m) of 2-chloro[3H]adenosine uptake. Quantitative PCR showed a transient decrease in the expression of both hENT1 (human ENT1) and hENT2 mRNAs within 4-12 h of induction of the inactive CK2alpha' subunit, but both transcripts had returned to control levels by 24 h. These data suggest that inhibition of CK2alpha' reduced ei activity by attenuation of hENT2 transcription, while the increase in es/hENT1 activity was mediated by post-translational action of CK2. The observed modification in es activity was probably due to a CK2alpha'-mediated change in the phosphorylation state of the ENT1 protein, or an interacting protein, effecting an increase in the plasma membrane lifetime of the transport proteins.

Adenine nucleotides inhibit cytokine generation by human mast cells through a Gs-coupled receptor

ATP and ADP activate functionally distinct G protein-coupled purinergic (P2Y) receptors. We determined the expression and function of adenine nucleotide-specific P2Y receptors on cord blood-derived human mast cells (hMCs). Human MCs expressed mRNA encoding the ADP-specific P2Y1, P2Y12, and P2Y13 receptors; the ATP/UTP-specific P2Y2 receptor; and the ATP-selective P2Y11 receptor. ADP (0.05-50 muM) induced calcium flux that was completely blocked by a P2Y1 receptor-selective antagonist and was not cross-desensitized by ATP. Low doses of ADP induced strong phosphorylation of ERK and p38 MAPKs; higher doses stimulated eicosanoid production and exocytosis. Although MAPK phosphorylation was blocked by a combination of P2Y1- and P2Y12-selective antagonists, neither interfered with secretion responses. Unexpectedly, both ADP and ATP inhibited the generation of TNF-alpha in response to the TLR2 ligand, peptidoglycan, and blocked the production of TNF-alpha, IL-8, and MIP-1beta in response to leukotriene D(4). These effects were mimicked by two ATP analogues, adenosine 5'-O-(3-thiotriphosphate) and 2',3'-O-(4-benzoyl-benzoyl) adenosine 5'-triphosphate (BzATP), but not by adenosine. ADP, ATP, adenosine 5'-O-(3-thiotriphosphate), and 2',3'-O-(4-benzoyl-benzoyl) adenosine 5'-triphosphate each induced cAMP accumulation, stimulated the phosphorylation of CREB, and up-regulated the expression of inducible cAMP early repressor, a CREB-dependent inhibitor of cytokine transcription. Human MCs thus express several ADP-selective P2Y receptors and at least one G(s)-coupled ADP/ATP receptor. Nucleotides could therefore contribute to MC-dependent microvascular leakage in atherosclerosis, tissue injury, and innate immunity while simultaneously limiting the extent of subsequent inflammation by attenuating the generation of inducible cytokines by MCs.

Trafficking of TRPP2 by PACS proteins represents a novel mechanism of ion channel regulation

The trafficking of ion channels to the plasma membrane is tightly controlled to ensure the proper regulation of intracellular ion homeostasis and signal transduction. Mutations of polycystin-2, a member of the TRP family of cation channels, cause autosomal dominant polycystic kidney disease, a disorder characterized by renal cysts and progressive renal failure. Polycystin-2 functions as a calcium-permeable nonselective cation channel; however, it is disputed whether polycystin-2 resides and acts at the plasma membrane or endoplasmic reticulum (ER). We show that the subcellular localization and function of polycystin-2 are directed by phosphofurin acidic cluster sorting protein (PACS)-1 and PACS-2, two adaptor proteins that recognize an acidic cluster in the carboxy-terminal domain of polycystin-2. Binding to these adaptor proteins is regulated by the phosphorylation of polycystin-2 by the protein kinase casein kinase 2, required for the routing of polycystin-2 between ER, Golgi and plasma membrane compartments. Our paradigm that polycystin-2 is sorted to and active at both ER and plasma membrane reconciles the previously incongruent views of its localization and function. Furthermore, PACS proteins may represent a novel molecular mechanism for ion channel trafficking, directing acidic cluster-containing ion channels to distinct subcellular compartments.

Differential regulation of DAP12 and molecules associated with DAP12 during host responses to mycobacterial infection

DAP12 and its associating molecules MDL-1, TREM-1, and TREM-2 are the recently identified immune regulatory molecules, expressed primarily on myeloid cells including monocytes/macrophages, dendritic cells, NK cells, and neutrophils. However, little is known about the regulation of their expression during host antimicrobial responses. We have investigated the effect of pulmonary mycobacterial infection and type 1 cytokines on the expression of these molecules both in vivo and in vitro. While DAP12 was constitutively expressed at high levels in the lungs, the MDL-1, TREM-1, and TREM-2 molecules were inducible during mycobacterial infection. Their kinetic expression was correlated with that of the type 1 cytokines tumor necrosis factor alpha (TNF-alpha) and gamma interferon (IFN-gamma). In primary lung macrophage cultures, high constitutive levels of DAP12 and TREM-2 were not modulated by mycobacterial or type 1 cytokine exposure. In contrast, expression of both MDL-1 and TREM-1 was markedly induced by mycobacterial infection and such induction was inhibited by concurrent exposure to IFN-gamma. On mycobacterial infection of TNF-alpha(-/-) and IFN-gamma(-/-) mice in vivo or their lung macrophages in vitro, TNF-alpha was found to be critical for mycobacterially induced MDL-1, but not TREM-1, expression whereas IFN-gamma negatively regulated mycobacterially induced MDL-1 and TREM-1 expression. Our findings thus suggest that DAP12 and its associating molecules are differentially regulated by mycobacterial infection and type 1 cytokines and that MDL-1- and TREM-1-triggered DAP12 signaling may play an important role in antimicrobial type 1 immunity.

Pulmonary surfactant protein A augments the phagocytosis of Streptococcus pneumoniae by alveolar macrophages through a casein kinase 2-dependent increase of cell surface localization of scavenger receptor A

Pulmonary surfactant proteins A (SP-A) and D (SP-D), members of the collectin family, play important roles in the innate immune system of the lung. Here, we show that SP-A but not SP-D augmented phagocytosis of Streptococcus pneumoniae by alveolar macrophages, independent of its binding to the bacteria. Analysis of the SP-A/SP-D chimeras, in which progressively longer carboxyl-terminal regions of SP-A were replaced with the corresponding SP-D regions, has revealed that the SP-D region Gly(346)-Phe(355) can be substituted for the SP-A region Leu(219)-Phe(228) without altering the SP-A activity of enhancing the phagocytosis and that the SP-A region Cys(204)-Cys(218) is required for the SP-A-mediated phagocytosis. Acetylated low density lipoprotein significantly reduced the SP-A-stimulated uptake of the bacteria. SP-A failed to enhance the phagocytosis of S. pneumoniae by alveolar macrophages derived from scavenger receptor A (SR-A)-deficient mice, demonstrating that SP-A augments SRA-mediated phagocytosis. Preincubation of macrophages with SP-A at 37 degrees C but not at 4 degrees C stimulated the phagocytosis. The SP-A-mediated enhanced phagocytosis was not inhibited by the presence of cycloheximide. SP-A increased cell surface localization of SR-A that was inhibitable by apigenin, a casein kinase 2 (CK2) inhibitor. SP-A-treated macrophages exhibited significantly greater binding of acetylated low density lipoprotein than nontreated cells. The SP-A-stimulated phagocytosis was also abolished by apigenin. In addition, SP-A stimulated CK2 activity. These results demonstrate that SP-A enhances the phagocytosis of S. pneumoniae by alveolar macrophages through a CK2-dependent increase of cell surface SR-A localization. This study reveals a novel mechanism of bacterial clearance by alveolar macrophages.

Interleukin-6 represses the transcription of the CCAAT/enhancer binding protein-alpha gene in hepatoma cells by inhibiting its ability to autoactivate the proximal promoter region

The cytokine interleukin-6 (IL-6) plays key roles in the immune and inflammatory responses, acute-phase reaction and hematopoiesis. Such biological actions of IL-6 are characterised by both the activation and the inhibition of gene transcription. Unfortunately, in contrast to gene activation, the mechanism by which IL-6 suppresses transcription remains largely unclear. We have, therefore, investigated this aspect using the Xenopus laevis CCAAT/enhancer binding protein-alpha (C/EBPalpha) gene promoter as a model. We show by transient transfection assays of various promoter-luciferase DNA constructs into hepatoma cells that a C/EBP recognition sequence in the proximal promoter region is essential for the IL-6-mediated repression. Electrophoretic mobility shift assays showed that C/EBPalpha was the major protein that bound to this site and, consistent with its expression pattern, the binding was reduced when the cells were exposed to IL-6. Co-transfection assays revealed for the first time that the ability of C/EBPalpha, but not C/EBPbeta or Sp1, to transactivate the promoter was decreased dramatically when the cells were incubated with IL-6. These studies, therefore, identify a novel mechanism for IL-6-mediated repression of gene transcription that involves a reduction in C/EBPalpha-mediated activation.

Inducible cAMP early repressor (ICER) in the nervous system - a transcriptional regulator of neuronal plasticity and programmed cell death

The acronym ICER (inducible cAMP early repressor) refers to a group of four proteins produced from the CREM/ICER gene due to use of an internal promoter (P2) placed in an intron of the CREM (cAMP responsive element modulator) gene. The ICER proteins contain DNA binding/leucine zipper domains that make them endogenous inhibitors of transcription driven by CREB (cAMP responsive element binding protein) and its cognates, CREM and ATF-1 (activating transcription factor-1). ICER expression is inducible in the brain and in neuronal culture by a variety of stimuli. As a CREB antagonist, ICER appears to be of pivotal importance in neuronal plasticity and programmed cell death.

Interferon-gamma interferes with transforming growth factor-beta signaling through direct interaction of YB-1 with Smad3

Transforming growth factor-beta (TGF-beta) and interferon-gamma (IFN-gamma) exert antagonistic effects on collagen synthesis in human dermal fibroblasts. We have recently shown that Y box-binding protein YB-1 mediates the inhibitory effects of IFN-gamma on alpha2(I) procollagen gene (COL1A2) transcription through the IFN-gamma response element located between -161 and -150. Here we report that YB-1 counter-represses TGF-beta-stimulated COL1A2 transcription by interfering with Smad3 bound to the upstream sequence around -265 and subsequently by interrupting the Smad3-p300 interaction. Western blot and immunofluorescence analyses using inhibitors for Janus kinases or casein kinase II suggested that the casein kinase II-dependent signaling pathway mediates IFN-gamma-induced nuclear translocation of YB-1. Down-regulation of endogenous YB-1 expression by double-stranded YB-1-specific RNA abrogated the transcriptional repression of COL1A2 by IFN-gamma in the absence and presence of TGF-beta. In transient transfection assays, overexpression of YB-1 in human dermal fibroblasts exhibited antagonistic actions against TGF-beta and Smad3. Physical interaction between Smad3 and YB-1 was demonstrated by immunoprecipitation-Western blot analyses, and electrophoretic mobility shift assays using the recombinant Smad3 and YB-1 proteins indicated that YB-1 forms a complex with Smad3 bound to the Smad-binding element. Glutathione S-transferase pull-down assays showed that YB-1 binds to the MH1 domain of Smad3, whereas the central and carboxyl-terminal regions of YB-1 were required for its interaction with Smad3. YB-1 also interferes with the Smad3-p300 interaction by its preferential binding to p300. Altogether, the results provide a novel insight into the mechanism by which IFN-gamma/YB-1 counteracts TGF-beta/Smad3. They also indicate that IFN-gamma/YB-1 inhibits COL1A2 transcription by dual actions: via the IFN-gamma response element and through a cross-talk with the TGF-beta/Smad signaling pathway.