NF-kappaB is a negative regulator of IL-1beta secretion as revealed by genetic and pharmacological inhibition of IKKbeta

Nuclear factor-kappaB and tumor-associated macrophages

Tumor-associated macrophages (TAM) have been linked with the progression of cancer by favoring tumor angiogenesis, growth, and metastasis. The precise mechanisms that maintain the protumor phenotype of TAM are poorly understood, but recent research has highlighted a number of signaling pathways that are important in TAM phenotype and function. Nuclear factor-kappaB (NF-kappaB) is considered the master regulator of inflammatory and immune responses. Recently several genetic studies have indicated NF-kappaB is an important pathway in TAM for the integration of signals from the tumor microenvironment that promote carcinogenesis. This review will focus on the role of NF-kappaB in TAM and the potential of targeting this pathway as a novel therapeutic strategy against cancer.

IKK regulation and human genetics

The IKK kinase complex is the core element of the NF-κB cascade. It is essentially made of two kinases (IKKα and IKKβ) and a regulatory subunit, NEMO/IKKγ. Additional components may exist, transiently or permanently, but their characterization is still uncertain. In this review, we will focus on the NEMO molecule, and describe the results which have been obtained, and the hypotheses which have been proposed, to explain how NEMO controls the activation of the IKK complex. NEMO is one of the very few non-redundant components of the NF-κB cascade, and the localization of the gene that encodes it on the X chromosome suggests it is likely to be the target of mutations leading to pathologies: this is indeed the case, and we will also present the current status of our knowledge regarding NEMO-associated pathologies.

Macrophages and NF-κB in cancer

Macrophages are tissue resident phagocytes with important roles in development, wound healing, and inflammation. There is enormous heterogeneity in macrophage phenotype, from 'classically' activated macrophages that have important roles in inflammation and innate immunity, to 'alternative' macrophage activation that is associated with wound healing, angiogenesis, and immune-suppression. Most, if not all, solid tumors have a significant macrophage population, clinical and experimental evidence suggests tumor-associated macrophages (TAM) are linked with tumor progression. The trophic functions of TAM are associated with increased angiogenesis, malignant cell invasion, and metastasis. NF-κB is s central regulator of inflammation and NF-κB activation particularly in TAM is linked with promotion of carcinogenesis in various experimental models of inflammation-associated cancer. NF-κB activation in TAM has, therefore, been suggested to represent a molecular link between inflammation and cancer. However, TAM frequently display an anti-inflammatory phenotype linked with immune-suppression that is not easily reconciled with a pro-inflammatory function for NF-κB in TAM. Here, I review the form and function of TAM and discuss the role of NF-κB activation in TAM in carcinogenesis.

Molecular mechanisms of the physiological functions of the aryl hydrocarbon (dioxin) receptor, a multifunctional regulator that senses and responds to environmental stimuli

The aryl hydrocarbon receptor (AhR) was originally identified as a ligand-activated transcription factor that is involved in the induction of xenobiotic-metabolizing Cytochrome P4501A1 (CYP1A1). For several decades, AhR has been studied in relation to toxicology and pharmacology. With recent discoveries on novel AhR functions, AhR research has expanded into multiple aspects of physiology, such as reproduction, innate immunity and tumor suppression. In this review, we summarize and discuss recent progress in mechanistic and functional studies on AhR with particular emphasis on physiological processes.

IKK- and NF-κB-mediated functions in carcinogenesis

Since the initial cloning of RelA and its close relationship to c-Rel, the cellular homolog of the viral oncoprotein v-Rel, the nuclear factor κB (NF-κB) signaling pathway and its upstream activating kinase complex (IκB-kinase) have been suspected to play a major role in tumorigenesis. This was further corroborated by the discovery of oncogenic mutations in NF-κB proteins in certain lymphoid malignancies and the notion that NF-κB is persistently activated in a large variety of solid tumors. With the advent of conditional knockout mice allowing tissue-specific targeting of the various components of the NF-κB signaling pathway, it was possible to genetically test the cell autonomous and non-autonomous functions of NF-κB in inflammation-associated cancer as well as sporadic cancers. Here, we review molecular evidence that demonstrates the various functions of NF-κB during different tumor stages and that supports the rationale to target NF-κB in cancer prevention and therapy.

The resolution of inflammation and cancer

Inflammation has long been thought to contribute to the development of cancer; however there is also clear evidence that the immune system can recognize and eliminate cancer cells. Current research suggests that cancer-associated inflammation has a dual role in tumor progression; inflammatory mediators promote the malignant activity of cancer cells by acting as growth factors and also stimulate angiogenesis, however, cancer-associated inflammation is also linked with immune-suppression that allows cancer cells to evade detection by the immune system. In this review we will discuss the dual role of inflammation in cancer and how endogenous anti-inflammatory mechanisms may equally be important in carcinogenesis.

Dangerous liaisons: STAT3 and NF-kappaB collaboration and crosstalk in cancer

Transcriptional factors of the NF-kappaB family and STAT3 are ubiquitously expressed and control numerous physiological processes including development, differentiation, immunity, metabolism and cancer. Both NF-kappaB and STAT3 are rapidly activated in response to various stimuli including stresses and cytokines, although they are regulated by entirely different signaling mechanisms. Once activated, NF-kappaB and STAT3 control the expression of anti-apoptotic, pro-proliferative and immune response genes. Some of these genes overlap and require transcriptional cooperation between the two factors. The activation of and interaction between STAT3 and NF-kappaB plays a key role in controlling the dialog between the malignant cell and its microenvironment, especially with inflammatory/immune cells that infiltrate tumors. Quite often, cytokines whose expression is induced in response to NF-kappaB in immune cells of the tumor microenvironment lead to STAT3 activation in both malignant and immune cells. While within malignant and pre-malignant cells STAT3 exerts important oncogenic functions, within inflammatory cells it may also suppress tumor promotion through its anti-inflammatory effects. Other interactions and forms of crosstalk between NF-kappaB and STAT3 include physical interaction between the two, cooperation of these factors at gene promoters/enhancers, the NF-kappaB dependent expression of inhibitors of STAT3 activation and the participation of STAT3 in inflammatory cells in the negative regulation NF-kappaB. Despite these versatile and occasionally antagonistic interactions, NF-kappaB and STAT3 cooperate to promote the development and progression of colon, gastric and liver cancers. In addition to explaining the molecular pathogenesis of cancer, these interactions also offer opportunities for the design of new therapeutic interventions.

Inflammatory arthritis in caspase 1 gene-deficient mice: contribution of proteinase 3 to caspase 1-independent production of bioactive interleukin-1beta

OBJECTIVE

Caspase 1, a known cysteine protease, is a critical component of the inflammasome. Both caspase 1 and neutrophil serine proteases such as proteinase 3 (PR3) can process pro-interleukin-1beta (proIL-1beta), a crucial cytokine linked to the pathogenesis of rheumatoid arthritis. This study was undertaken to establish the relative importance of caspase 1 and serine proteases in mouse models of acute and chronic inflammatory arthritis.

METHODS

Acute and chronic arthritis were induced in caspase 1-/- mice, and the lack of caspase 1 was investigated for its effects on joint swelling, cartilage metabolism, and histopathologic features. In addition, caspase 1 activity was inhibited in mice lacking active cysteine proteases, and the effects of dual blockade of caspase 1 and serine proteases on arthritis severity and histopathologic features were evaluated.

RESULTS

Surprisingly, caspase 1-/- mice, in a model of acute (neutrophil-dominated) arthritis, developed joint swelling to an extent similar to that in wild-type control mice. Joint fluid concentrations of bioactive IL-1beta were comparable in caspase 1-/- mice and controls. In contrast, induction of chronic arthritis (characterized by minimal numbers of neutrophils) in caspase 1-/- mice led to reduced joint inflammation and less cartilage damage, implying a caspase 1-dependent role in this process. In mice lacking neutrophil serine PR3, inhibition of caspase 1 activity resulted in decreased bioactive IL-1beta concentrations in the synovial tissue and less suppression of chondrocyte anabolic function. In addition, dual blockade of both PR3 and caspase 1 led to protection against cartilage and bone destruction.

CONCLUSION

Caspase 1 deficiency does not affect neutrophil-dominated joint inflammation, whereas in chronic arthritis, the lack of caspase 1 results in reduced joint inflammation and cartilage destruction. These findings suggest that inhibitors of caspase 1 are not able to interfere with the whole spectrum of IL-1beta production, and therefore such inhibitors may be of therapeutic value only in inflammatory conditions in which limited numbers of neutrophils are present.

Caspase 1-independent activation of interleukin-1beta in neutrophil-predominant inflammation

OBJECTIVE

Interleukin-1beta (IL-1beta) is a key cytokine linked to the pathogenesis of acute arthritis. Caspase 1, neutrophil elastase, and chymase all process proIL-1beta to its biologically active form. This study was undertaken to examine the potential contributions of each of these proteases in experimental models of inflammatory arthritis.

METHODS

Caspase 1-deficient (Casp1-/-) and wild-type (WT) mice were tested for their response to arthritogenic K/BxN serum transfer for induction of arthritis or injection of monosodium urate monohydrate (MSU) crystals for induction of peritonitis. All mice were prophylactically treated with inhibitors of neutrophil elastase or chymase. Arthritic paws were tested for the presence of IL-1beta protein by enzyme-linked immunosorbent assay and Western blotting. Neutrophils and mast cells from WT and mutant mice were tested for their ability to secrete IL-1beta after in vitro stimulation, in the presence of protease inhibitors.

RESULTS

Casp1-/- and WT mice developed paw swelling to the same extent in the K/BxN serum transfer-induced arthritis model. MSU crystal injection into Casp1-/- mice also resulted in neutrophil influx and production of measurable peritoneal IL-1beta protein. Both of these responses were attenuated with neutrophil elastase inhibitors. K/BxN serum transfer-induced arthritis was also reduced by treatment with a chymase inhibitor. Casp1-/- neutrophils and mast cells, when exposed to MSU crystals, secreted similar amounts of IL-1beta protein upon in vitro stimulation with lipopolysaccharide, albeit at lower levels than that secreted by WT cells. Elastase and chymase inhibitors reduced the amount of IL-1beta released by these cells.

CONCLUSION

The production of IL-1beta by neutrophils and mast cells is not exclusively dependent on caspase 1, and other proteases can compensate for the loss of caspase 1 in vivo. These pathways might therefore compromise the caspase 1-targeted therapies in neutrophil-predominant arthritis.

Gene expression profiling in mouse liver infected with Clonorchis sinensis metacercariae

Clonorchis sinensis, the parasite that causes clonorchiasis, is endemic in many Asian countries, and infection with the organism drives changes in the liver tissues of the host. However, information regarding the molecular events in clonorchiasis remains limited, and little is currently known about host-pathogen interactions in clonorchiasis. In this study, we assessed the gene expression profiles in mice livers via DNA microarray analysis 1, 2, 4, and 6 weeks after induced metacercariae infection. Functional clustering of the gene expression profile showed that the immunity-involved genes were induced in the livers of the mice at the early stage of metacercariae infection, whereas immune responses were reduced in the 6-week liver tissues after infection in which the metacercariae became adult flukes. Many genes involved in fatty acid metabolism, including Peci, Cyp4a10, Acat1, Ehhadh, Gcdh, and Cyp2 family were downregulated in the infected livers. On the other hand, the liver tissues infected with the parasite expressed Wnt signaling molecules such as Wnt7b, Fzd6, and Pdgfrb and cell cycle-regulating genes including cyclin-D1, Cdca3, and Bcl3. These investigations constitute an excellent starting point for increased understanding of the molecular mechanisms underlying host-pathogen interaction during the development of C. sinensis in the host liver.

IKK/NF-kappaB and STAT3 pathways: central signalling hubs in inflammation-mediated tumour promotion and metastasis

Our understanding of the molecular mechanisms that link inflammation and cancer has significantly increased in recent years. Here, we analyse genetic evidence indicating that the transcription factors nuclear factor-kappaB (NF-kappaB) and signal transducer and activator of transcription 3 (STAT3) have a central role in this context by regulating distinct functions in cancer cells and surrounding non-tumorigenic cells. In immune cells, NF-kappaB induces the transcription of genes that encode pro-inflammatory cytokines, which can act in a paracrine manner on initiated cells. By contrast, in tumorigenic cells, both NF-kappaB and STAT3 control apoptosis, and STAT3 can also enhance proliferation. Consequently, inflammation should be considered as a valuable target for cancer prevention and therapy.

Hypersensitivity of aryl hydrocarbon receptor-deficient mice to lipopolysaccharide-induced septic shock

Aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, is known to mediate a wide variety of pharmacological and toxicological effects caused by polycyclic aromatic hydrocarbons. Recent studies have revealed that AhR is involved in the normal development and homeostasis of many organs. Here, we demonstrate that AhR knockout (AhR KO) mice are hypersensitive to lipopolysaccharide (LPS)-induced septic shock, mainly due to the dysfunction of their macrophages. In response to LPS, bone marrow-derived macrophages (BMDM) of AhR KO mice secreted an enhanced amount of interleukin-1beta (IL-1beta). Since the enhanced IL-1beta secretion was suppressed by supplementing Plasminogen activator inhibitor-2 (Pai-2) expression through transduction with Pai-2-expressing adenoviruses, reduced Pai-2 expression could be a cause of the increased IL-1beta secretion by AhR KO mouse BMDM. Analysis of gene expression revealed that AhR directly regulates the expression of Pai-2 through a mechanism involving NF-kappaB but not AhR nuclear translocator (Arnt), in an LPS-dependent manner. Together with the result that administration of the AhR ligand 3-methylcholanthrene partially protected mice with wild-type AhR from endotoxin-induced death, these results raise the possibility that an appropriate AhR ligand may be useful for treating patients with inflammatory disorders.

The nuclear factor NF-kappaB pathway in inflammation

The nuclear factor NF-kappaB pathway has long been considered a prototypical proinflammatory signaling pathway, largely based on the role of NF-kappaB in the expression of proinflammatory genes including cytokines, chemokines, and adhesion molecules. In this article, we describe how genetic evidence in mice has revealed complex roles for the NF-kappaB in inflammation that suggest both pro- and anti-inflammatory roles for this pathway. NF-kappaB has long been considered the "holy grail" as a target for new anti-inflammatory drugs; however, these recent studies suggest this pathway may prove a difficult target in the treatment of chronic disease. In this article, we discuss the role of NF-kappaB in inflammation in light of these recent studies.

Critical role for interleukin-1beta (IL-1beta) during Chlamydia muridarum genital infection and bacterial replication-independent secretion of IL-1beta in mouse macrophages

Recent findings have implicated interleukin-1beta (IL-1beta) as an important mediator of the inflammatory response in the female genital tract during chlamydial infection. But how IL-1beta is produced and its specific role in infection and pathology are unclear. Therefore, our goal was to determine the functional consequences and cellular sources of IL-1beta expression during a chlamydial genital infection. In the present study, IL-1beta(-/-) mice exhibited delayed chlamydial clearance and decreased frequency of hydrosalpinx compared to wild-type (WT) mice, implying an important role for IL-1beta both in the clearance of infection and in the mediation of oviduct pathology. At the peak of IL-1beta secretion in WT mice, the major producers of IL-1beta in vivo are F4/80(+) macrophages and GR-1(+) neutrophils, but not CD45(-) epithelial cells. Although elicited mouse macrophages infected with Chlamydia muridarum in vitro secrete minimal IL-1beta, in vitro prestimulation of macrophages by Toll-like receptor (TLR) ligands such as lipopolysaccharide (LPS) purified from Escherichia coli or C. trachomatis L2 prior to infection greatly enhanced secretion of IL-1beta from these cells. By using LPS-primed macrophages as a model system, it was determined that IL-1beta secretion was dependent on caspase-1, potassium efflux, and the activity of serine proteases. Significantly, chlamydia-induced IL-1beta secretion in macrophages required bacterial viability but not growth. Our findings demonstrate that IL-1beta secreted by macrophages and neutrophils has important effects in vivo during chlamydial infection. Additionally, prestimulation of macrophages by chlamydial TLR ligands may account for the elevated levels of pro-IL-1beta mRNA observed in vivo in this cell type.

VX-166: a novel potent small molecule caspase inhibitor as a potential therapy for sepsis

Introduction

Prevention of lymphocyte apoptosis by caspase inhibition has been proposed as a novel treatment approach in sepsis. However, it has not been clearly demonstrated that caspase inhibitors improve survival in sepsis models when dosed post-insult. Also, there are concerns that caspase inhibitors might suppress the immune response. Here we characterize VX-166, a broad caspase inhibitor, as a novel potential treatment for sepsis.

Methods

VX-166 was studied in a number of enzymatic and cellular assays. The compound was then tested in a murine model of endotoxic shock (lipopolysaccharide (LPS), 20 mg/kg IV) and a 10 d rat model of polymicrobial sepsis by caecal ligation and puncture (CLP).

Results

VX-166 showed potent anti-apoptotic activity in vitro and inhibited the release of interleukin (IL)-1beta and IL-18. In the LPS model, VX-166 administered 0, 4, 8 and 12 h post-LPS significantly improved survival in a dose-dependent fashion (P < 0.0028). In the CLP model, VX-166 continuously administered by mini-osmotic pump significantly improved survival when dosed 3 h after insult, (40% to 92%, P = 0.009). When dosed 8 h post-CLP, VX-166 improved survival from 40% to 66% (P = 0.19). Mode of action studies in the CLP model confirmed that VX-166 significantly inhibited thymic atrophy and lymphocyte apoptosis as determined by flow cytometry (P < 0.01). VX-166 reduced plasma endotoxin levels (P < 0.05), suggesting an improved clearance of bacteria from the bloodstream. Release of IL-1beta in vivo or T-cell activation in vitro were moderately affected.

Conclusions

Our studies enhance the case for the use of caspase inhibitors in sepsis. VX-166 itself has promise as a therapy for the treatment of sepsis in man.

Disordered macrophage cytokine secretion underlies impaired acute inflammation and bacterial clearance in Crohn's disease

The cause of Crohn's disease (CD) remains poorly understood. Counterintuitively, these patients possess an impaired acute inflammatory response, which could result in delayed clearance of bacteria penetrating the lining of the bowel and predispose to granuloma formation and chronicity. We tested this hypothesis in human subjects by monitoring responses to killed Escherichia coli injected subcutaneously into the forearm. Accumulation of (111)In-labeled neutrophils at these sites and clearance of (32)P-labeled bacteria from them were markedly impaired in CD. Locally increased blood flow and bacterial clearance were dependent on the numbers of bacteria injected. Secretion of proinflammatory cytokines by CD macrophages was grossly impaired in response to E. coli or specific Toll-like receptor agonists. Despite normal levels and stability of cytokine messenger RNA, intracellular levels of tumor necrosis factor (TNF) were abnormally low in CD macrophages. Coupled with reduced secretion, these findings indicate accelerated intracellular breakdown. Differential transcription profiles identified disease-specific genes, notably including those encoding proteins involved in vesicle trafficking. Intracellular destruction of TNF was decreased by inhibitors of lysosomal function. Together, our findings suggest that in CD macrophages, an abnormal proportion of cytokines are routed to lysosomes and degraded rather than being released through the normal secretory pathway.

Elevated levels of IL-1beta in Fanconi anaemia group A patients due to a constitutively active phosphoinositide 3-kinase-Akt pathway are capable of promoting tumour cell proliferation

FA (Fanconi anaemia) is a hereditary disease characterized by congenital malformations, progressive bone marrow failure and an extraordinary elevated predisposition to develop cancer. In the present manuscript we describe an anomalous high level of the proinflammatory cytokine IL-1beta (interleukin-1beta) present in the serum of FA patients. The elevated levels of IL-1beta were completely reverted by transduction of a wild-type copy of the FancA cDNA into FA-A (FA group A) lymphocytes. Although the transcription factor NF-kappaB (nuclear factor-kappaB) is a well established regulator of IL-1beta expression, our experiments did not show any proof of elevated NF-kappaB activity in FA-A cells. However, we found that the overexpression of IL-1beta in FA-A cells is related to a constitutively activated PI3K (phosphoinositide 3-kinase)-Akt pathway in these cells. We provide evidence that the effect of Akt on IL-1beta activation is mediated by the inhibition of GSK3beta (glycogen synthase kinase 3beta). Finally, our data indicate that the levels of IL-1beta produced by FA-A lymphoblasts are enough to promote an activation of the cell cycle in primary glioblastoma progenitor cells. Together, these results demonstrate that the constitutive activation of the PI3K-Akt pathway in FA cells upregulates the expression of IL-1beta through an NF-kappaB-independent mechanism and that this overproduction activates the proliferation of tumour cells.

The caspase-cleaved form of LYN mediates a psoriasis-like inflammatory syndrome in mice

We showed previously that Lyn is a substrate for caspases, a family of cysteine proteases, involved in the regulation of apoptosis and inflammation. Here, we report that expression of the caspase-cleaved form of Lyn (LynDeltaN), in mice, mediates a chronic inflammatory syndrome resembling human psoriasis. Genetic ablation of TNF receptor 1 in a LynDeltaN background rescues a normal phenotype, indicating that LynDeltaN mice phenotype is TNF-alpha-dependent. The predominant role of T cells in the disease occurring in LynDeltaN mice was highlighted by the distinct improvement of LynDeltaN mice phenotype in a Rag1-deficient background. Using pan-genomic profiling, we also established that LynDeltaN mice show an increased expression of STAT-3 and inhibitory members of the NFkappaB pathway. Accordingly, LynDeltaN alters NFkappaB activity underlying a link between inhibition of NFkappaB and LynDeltaN mice phenotype. Finally, analysis of Lyn expression in human skin biopsies of psoriatic patients led to the detection of Lyn cleavage product whose expression correlates with the activation of caspase 1. Our data identify a new role for Lyn as a regulator of psoriasis through its cleavage by caspases.

NF-kappaB regulation: the nuclear response

Nuclear factor κB (NF-κB) is an inducible transcription factor that tightly regulates the expression of a large cohort of genes. As a key component of the cellular machinery NF-κB is involved in a wide range of biological processes including innate and adaptive immunity, inflammation, cellular stress responses, cell adhesion, apoptosis and proliferation. Appropriate regulation of NF-κB is critical for the proper function and survival of the cell. Aberrant NF-κB activity has now been implicated in the pathogenesis of several diseases ranging from inflammatory bowel disease to autoimmune conditions such as rheumatoid arthritis. Systems governing NF-κB activity are complex and there is an increased understanding of the importance of nuclear events in regulating NF-κB's activities as a transcription factor. A number of novel nuclear regulators of NF-κB such as IκB-ζ and PDZ and LIM domain 2 (PDLIM2) have now been identified, adding another layer to the mechanics of NF-κB regulation. Further insight into the functions of these molecules raises the prospect for better understanding and rational design of therapeutics for several important diseases.

Targeting innate immunity protein kinase signalling in inflammation

Inflammation is an evolutionarily conserved host reaction that is initiated in response to trauma, tissue damage and infection. It leads to changes in tissue homeostasis and blood flow, immune-cell activation and migration, and secretion of cytokines and mediators in a spatio-temporally coordinated manner. Progress in understanding of the mechanisms of the inflammatory response has identified various protein kinases that act as essential signalling components and therefore represent potential therapeutic targets. This article summarizes advances in the identification and validation of such targets, and discusses key issues for the development of small-molecule kinase inhibitors as a new generation of oral anti-inflammatory drugs, including feedback loops, inhibitor specificity and combination therapy.

NLR-mediated control of inflammasome assembly in the host response against bacterial pathogens

The host response against diverse bacterial pathogens involves activation of specialized immune cells and elaboration of pro-inflammatory cytokines that help to coordinate appropriate host defense. Members of the interleukin-1 (IL-1) cytokine family, IL-1beta and IL-18, are central players in this process. Extracellular release of the mature, active form of these cytokines requires their processing by the cysteine protease caspase-1, which therefore serves as a key regulator of the inflammatory response. In addition to its role in secretion of pro-inflammatory cytokines, caspase-1 is also required for a form of cell death, recently termed pyroptosis, that occurs in macrophages infected by certain bacterial pathogens. Caspase-1 itself is synthesized as a pro-enzyme, which must first be activated by autocatalytic cleavage. This activation requires recruitment of caspase-1 into multiprotein complexes known as inflammasomes. The Nod-like receptor (NLR) family of cytosolic proteins play an important role in detecting inflammatory stimuli and subsequently mediate inflammasome assembly. A common feature of NLR proteins that trigger inflammasome assembly in response to bacterial infection is that they appear to sense membrane perturbation or delivery of bacterial components into the cytosol through bacterial pore-forming toxins or bacterial secretion systems. This review will discuss the recent developments regarding caspase-1 activation in response to bacterial infection, cross-talk between caspase-1 and other pathways involved in regulating cell death, and recent findings that a number of bacterial pathogens possess mechanisms to inhibit caspase-1 activation.

The inflammasomes: guardians of the body

The innate immune system relies on its capacity to rapidly detect invading pathogenic microbes as foreign and to eliminate them. The discovery of Toll-like receptors (TLRs) provided a class of membrane receptors that sense extracellular microbes and trigger antipathogen signaling cascades. More recently, intracellular microbial sensors have been identified, including NOD-like receptors (NLRs). Some of the NLRs also sense nonmicrobial danger signals and form large cytoplasmic complexes called inflammasomes that link the sensing of microbial products and metabolic stress to the proteolytic activation of the proinflammatory cytokines IL-1beta and IL-18. The NALP3 inflammasome has been associated with several autoinflammatory conditions including gout. Likewise, the NALP3 inflammasome is a crucial element in the adjuvant effect of aluminum and can direct a humoral adaptive immune response. In this review, we discuss the role of NLRs, and in particular the inflammasomes, in the recognition of microbial and danger components and the role they play in health and disease.

Immunological and inflammatory functions of the interleukin-1 family

More than any other cytokine family, the interleukin (IL)-1 family is closely linked to the innate immune response. This linkage became evident upon the discovery that the cytoplasmic domain of the IL-1 receptor type I is highly homologous to the cytoplasmic domains of all Toll-like receptors (TLRs). Thus, fundamental inflammatory responses such as the induction of cyclooxygenase type 2, increased expression of adhesion molecules, or synthesis of nitric oxide are indistinguishable responses of both IL-1 and TLR ligands. Both families nonspecifically affect antigen recognition and lymphocyte function. IL-1beta is the most studied member of the IL-1 family because of its role in mediating autoinflammatory diseases. Although the TLR and IL-1 families evolved to assist in host defense against infection, unlike the TLR family, the IL-1 family also includes members that suppress inflammation, both specifically within the IL-1 family but also nonspecifically for TLR ligands and the innate immune response.

Regulation and function of NF-kappaB transcription factors in the immune system

The mammalian Rel/NF-kappaB family of transcription factors, including RelA, c-Rel, RelB, NF-kappaB1 (p50 and its precursor p105), and NF-kappaB2 (p52 and its precursor p100), plays a central role in the immune system by regulating several processes ranging from the development and survival of lymphocytes and lymphoid organs to the control of immune responses and malignant transformation. The five members of the NF-kappaB family are normally kept inactive in the cytoplasm by interaction with inhibitors called IkappaBs or the unprocessed forms of NF-kappaB1 and NF-kappaB2. A wide variety of signals emanating from antigen receptors, pattern-recognition receptors, receptors for the members of TNF and IL-1 cytokine families, and others induce differential activation of NF-kappaB heterodimers. Although work over the past two decades has shed significant light on the regulation of NF-kappaB transcription factors and their functions, much progress has been made in the past two years revealing new insights into the regulation and functions of NF-kappaB. This recent progress is covered in this review.

Hypoxia-inducible factors 1 and 2 are important transcriptional effectors in primary macrophages experiencing hypoxia

Ischemia exists in many diseased tissues, including arthritic joints, atherosclerotic plaques, and malignant tumors. Macrophages accumulate in these sites and up-regulate hypoxia-inducible transcription factors (HIFs) 1 and 2 in response to the hypoxia present. Here we show that the gene expression profile in primary human and murine macrophages changes markedly when they are exposed to hypoxia for 18 hours. For example, they were seen to up-regulate the cell surface receptors, CXCR4 and GLUT1, and the potent, tumor-promoting cytokines, vascular endothelial growth factor A, interleukin (IL)-1beta and IL-8, adrenomedullin, CXCR4, and angiopoietin-2. Hypoxia also stimulated their expression and/or phosphorylation of various proteins in the nuclear factor-kappaB (NF-kappaB) signaling pathway. We then used both genetic and pharmacologic methods to manipulate the levels of HIFs-1alpha and 2alpha or NF-kappaB in primary macrophages to elucidate their role in the hypoxic induction of many of these key genes. These studies showed that both HIF-1 and -2, but not NF-kappaB, are important transcriptional effectors regulating the responses of macrophages to such a period of hypoxia. Further studies using experimental mouse models are now warranted to investigate the role of such macrophage responses in the progression of various diseased tissues, such as malignant tumors.

Induction and termination of inflammatory signaling in group B streptococcal sepsis

SUMMARY

Group B streptococcus (GBS) is part of the normal genital and gastrointestinal flora in healthy humans. However, GBS is a major cause of sepsis and meningitis in newborn infants in the Western world and an important pathogen in many developing countries. The dissection of the host response to GBS may increase the general understanding of innate immunity in sepsis, because newborn infants lack a sufficient adaptive response. Inflammatory signal induction in macrophages by GBS seems largely preserved in newborn infants, as shown both in vitro and in vivo. The engagement of Toll-like receptor 2 (TLR2) by lipoproteins and a myeloid differentiation factor 88 (MyD88)--dependent pathway induced by GBS cell wall are both important in this context. TLR2 activation of microglia by GBS induces neuronal damage, which might account for the high morbidity of GBS meningitis. At the same time, TLR2 mediates activation-induced cell death (AICD), a process involved in the containment of inflammation. In newborn infants, AICD and anti-bacterial polymorphonuclear leukocyte activity appears to be compromised. Accordingly, neonatal aberrations in the pathogen-specific negative control of inflammatory signaling are likely to contribute to excessive inflammation and neurological sequelae in GBS sepsis and meningitis.

Secreted interleukin-1alpha induces a metastatic phenotype in pancreatic cancer by sustaining a constitutive activation of nuclear factor-kappaB

Transcription factor nuclear factor-kappaB (NF-kappaB) is constitutively activated in most pancreatic cancer tissues and cell lines but not in normal pancreas nor in immortalized/nontumorigenic human pancreatic ductal epithelial cells. Inhibition of constitutive NF-kappaB activation in pancreatic cancer cell lines suppresses tumorigenesis and tumor metastasis. Recently, we identified autocrine secretion of proinflammatory cytokine interleukin (IL)-1alpha as the mechanism of constitutive NF-kappaB activation in metastatic pancreatic cancer cell lines. However, the role of IL-1alpha in determining the metastatic potential of pancreatic tumor remains to be further investigated. In the current study, we stably expressed IL-1alpha in the nonmetastatic, IL-1alpha-negative MiaPaCa-2 cell lines. Our results showed that the secretion of IL-1alpha in MiaPaCa-2 cells constitutively activated NF-kappaB and increased the expression of NF-kappaB downstream genes involved in the different steps of the metastatic cascade, such as urokinase-type plasminogen activator, vascular endothelial growth factor, and IL-8. MiaPaCa-2/IL-1alpha cells showed an enhanced cell invasion in vitro compared with parental MiaPaCa-2 cells and induced liver metastasis in an orthotopic mouse model. The metastatic phenotype induced by IL-1alpha was inhibited by the expression of phosphorylation-defective IkappaB (IkappaB S32, 36A), which blocked NF-kappaB activation. Consistently, silencing the expression of IL-1alpha by short hairpin RNA in the highly metastatic L3.6pl pancreatic cancer cells completely suppressed their metastatic spread. In summary, these findings showed that IL-1alpha plays key roles in pancreatic cancer metastatic behavior through the constitutive activation of NF-kappaB. Our findings further support the possible link between inflammation and cancer and suggest that IL-1alpha may be a potential therapeutic target for treating pancreatic adenocarcinoma.

Persistent systemic inflammation and atypical enterocolitis in patients with NEMO syndrome

The NEMO syndrome is a primary immunodeficiency with immune and non-immune manifestations. The immune deficiency is heterogeneous showing defects in humoral, innate, and cell-mediated immunity. While the clinical aspects of the immunodeficiency are increasingly well understood, little is known about autoimmune manifestations in NEMO patients. We therefore sought to examine serologic markers of systemic inflammation and intestinal pathology in a kindred of patients with the NEMO syndrome. We observed persistent elevation of erythrocyte sedimentation rates in five patients, and two were symptomatic, with a chronic but atypical enterocolitis. Though pathologic lesions in these two patients were consistent with acute inflammation, sustained clinical improvement was only achieved with systemic and/or topical glucocorticoid therapy. Our data suggest that some patients with the NEMO syndrome exhibit persistent elevation of inflammatory markers similar to systemic autoimmune diseases and may subsequently develop an atypical enterocolitis.

The Inflammasomes: Guardians of the Body

The innate immune system relies on its capacity to rapidly detect invading pathogenic microbes as foreign and to eliminate them. The discovery of Toll-like receptors (TLRs) provided a class of membrane receptors that sense extracellular microbes and trigger antipathogen signaling cascades. More recently, intracellular microbial sensors have been identified, including NOD-like receptors (NLRs). Some of the NLRs also sense nonmicrobial danger signals and form large cytoplasmic complexes called inflammasomes that link the sensing of microbial products and metabolic stress to the proteolytic activation of the proinflammatory cytokines IL-1β and IL-18. The NALP3 inflammasome has been associated with several autoinflammatory conditions including gout. Likewise, the NALP3 inflammasome is a crucial element in the adjuvant effect of aluminum and can direct a humoral adaptive immune response. In this review, we discuss the role of NLRs, and in particular the inflammasomes, in the recognition of microbial and danger components and the role they play in health and disease.

The Inflammasomes: Guardians of the Body

The innate immune system relies on its capacity to rapidly detect invading pathogenic microbes as foreign and to eliminate them. The discovery of Toll-like receptors (TLRs) provided a class of membrane receptors that sense extracellular microbes and trigger antipathogen signaling cascades. More recently, intracellular microbial sensors have been identified, including NOD-like receptors (NLRs). Some of the NLRs also sense nonmicrobial danger signals and form large cytoplasmic complexes called inflammasomes that link the sensing of microbial products and metabolic stress to the proteolytic activation of the proinflammatory cytokines IL-1β and IL-18. The NALP3 inflammasome has been associated with several autoinflammatory conditions including gout. Likewise, the NALP3 inflammasome is a crucial element in the adjuvant effect of aluminum and can direct a humoral adaptive immune response. In this review, we discuss the role of NLRs, and in particular the inflammasomes, in the recognition of microbial and danger components and the role they play in health and disease.

The Inflammasomes: Guardians of the Body

The innate immune system relies on its capacity to rapidly detect invading pathogenic microbes as foreign and to eliminate them. The discovery of Toll-like receptors (TLRs) provided a class of membrane receptors that sense extracellular microbes and trigger antipathogen signaling cascades. More recently, intracellular microbial sensors have been identified, including NOD-like receptors (NLRs). Some of the NLRs also sense nonmicrobial danger signals and form large cytoplasmic complexes called inflammasomes that link the sensing of microbial products and metabolic stress to the proteolytic activation of the proinflammatory cytokines IL-1β and IL-18. The NALP3 inflammasome has been associated with several autoinflammatory conditions including gout. Likewise, the NALP3 inflammasome is a crucial element in the adjuvant effect of aluminum and can direct a humoral adaptive immune response. In this review, we discuss the role of NLRs, and in particular the inflammasomes, in the recognition of microbial and danger components and the role they play in health and disease.

The Inflammasomes: Guardians of the Body

The innate immune system relies on its capacity to rapidly detect invading pathogenic microbes as foreign and to eliminate them. The discovery of Toll-like receptors (TLRs) provided a class of membrane receptors that sense extracellular microbes and trigger antipathogen signaling cascades. More recently, intracellular microbial sensors have been identified, including NOD-like receptors (NLRs). Some of the NLRs also sense nonmicrobial danger signals and form large cytoplasmic complexes called inflammasomes that link the sensing of microbial products and metabolic stress to the proteolytic activation of the proinflammatory cytokines IL-1β and IL-18. The NALP3 inflammasome has been associated with several autoinflammatory conditions including gout. Likewise, the NALP3 inflammasome is a crucial element in the adjuvant effect of aluminum and can direct a humoral adaptive immune response. In this review, we discuss the role of NLRs, and in particular the inflammasomes, in the recognition of microbial and danger components and the role they play in health and disease.

Kinetic of RelA activation controls magnitude of TLR-mediated IL-12p40 induction

IL-12 is a crucial cytokine for dendritic cell-mediated induction of Th 1 cell differentiation. TLR ligands induce IL-12 to differing extents. Stimulation of dendritic cells allowed for the differentiation of three groups of TLRs; potency to induce IL-12 decreased in the order of TLR7/9, TLR3/4, and TLR1/2/6 stimulation. The MAPK, PI3K, and IRF (IFN regulatory factor) signaling pathways could be ruled out to be the cause for the differences in IL-12p40 induction. However, we observed that stimulation of dendritic cells with different TLR ligands resulted in striking differences in the kinetics of NF-kappaB activation. LPS induced a rapid but short-lived activation of RelA, whereas CpG-DNA stimulation resulted in prolonged RelA activity at the IL-12p40 promoter. Only TLR2 and TLR4 ligands were capable of inducing S536 phosphorylation of RelA, which has been proposed to be responsible for early termination of NF-kappaB activation. It is suggested that differences in the kinetics of a common TLR signaling module affect the biological response patterns of various TLRs, with IL-12p40 being a gene that needs prolonged NF-kappaB activation.

Is NF-kappaB a good target for cancer therapy? Hopes and pitfalls

Nuclear factor kappaB (NF-kappaB) transcription factors have a key role in many physiological processes such as innate and adaptive immune responses, cell proliferation, cell death, and inflammation. It has become clear that aberrant regulation of NF-kappaB and the signalling pathways that control its activity are involved in cancer development and progression, as well as in resistance to chemotherapy and radiotherapy. This article discusses recent evidence from cancer genetics and cancer genome studies that support the involvement of NF-kappaB in human cancer, particularly in multiple myeloma. The therapeutic potential and benefit of targeting NF-kappaB in cancer, and the possible complications and pitfalls of such an approach, are explored.

Mammalian target of rapamycin (mTOR) orchestrates the defense program of innate immune cells

The mammalian target of rapamycin (mTOR) can be viewed as cellular master complex scoring cellular vitality and stress. Whether mTOR controls also innate immune-defenses is currently unknown. Here we demonstrate that TLR activate mTOR via phosphoinositide 3-kinase/Akt. mTOR physically associates with the MyD88 scaffold protein to allow activation of interferon regulatory factor-5 and interferon regulatory factor-7, known as master transcription factors for pro-inflammatory cytokine- and type I IFN-genes. Unexpectedly, inactivation of mTOR did not prevent but increased lethality of endotoxin-mediated shock, which correlated with increased levels of IL-1beta. Mechanistically, mTOR suppresses caspase-1 activation, thus inhibits release of bioactive IL-1beta. We have identified mTOR as indispensable component of PRR signal pathways, which orchestrates the defense program of innate immune cells.

Cell Defence and Survival

Central to immune defence mechanisms is the role of transcription factor nuclear factor kappa B (NF-kB). This is a complex biochemical topic with ever more controls revealed. NF-kB determines the production of proinflammatory cytokines and chemokines. Pharmacologists step in with possible means of control. Other systems involved in defence include the cyclooxygenase 2 (Cox-2) enzyme and perioxisome proliferator-activated receptors. Insulin receptor activation needs to be seen in context. The mTOR system directs uptake of nutrients by cells. mTOR is suppressed by rapamycin, whose usage is now quite considerable in the control of transplant rejection.

Compensatory IKKalpha activation of classical NF-kappaB signaling during IKKbeta inhibition identified by an RNA interference sensitization screen

A subtype of diffuse large B-cell lymphoma (DLBCL), termed activated B-cell-like (ABC) DLBCL, depends on constitutive nuclear factor-kappaB (NF-kappaB) signaling for survival. Small molecule inhibitors of IkappaB kinase beta (IKKbeta), a key regulator of the NF-kappaB pathway, kill ABC DLBCL cells and hold promise for the treatment of this lymphoma type. We conducted an RNA interference genetic screen to investigate potential mechanisms of resistance of ABC DLBCL cells to IKKbeta inhibitors. We screened a library of small hairpin RNAs (shRNAs) targeting 500 protein kinases for shRNAs that would increase the killing of an ABC DLBCL cell line in the presence of a small molecule IKKbeta inhibitor. Two independent shRNAs targeting IKKalpha synergized with the IKKbeta inhibitor to kill three different ABC DLBCL cell lines but were not toxic by themselves. Surprisingly, IKKalpha shRNAs blocked the classical rather than the alternative NF-kappaB pathway in ABC DLBCL cells, as judged by inhibition of IkappaBalpha phosphorylation. IKKalpha shRNA toxicity was reversed by coexpression of wild-type but not kinase inactive forms of IKKalpha, suggesting that IKKalpha may directly phosphorylate IkappaBalpha under conditions of IKKbeta inhibition. In models of physiologic NF-kappaB pathway activation by CARD11 or tumor necrosis factor-alpha, compensatory IKKalpha activity was also observed with IKKbeta inhibition. These results suggest that therapy for ABC DLBCL may be improved by targeting both IKKalpha and IKKbeta, possibly through CARD11 inhibition.

Myeloid cells control termination of lung inflammation through the NF-kappaB pathway

Although acute lung inflammation in response to local or systemic infection involves myeloid and nonmyeloid cells, the interplay between different cell types remains poorly defined. Since NF-kappaB is a key transcription factor for innate immunity, we investigated whether dysregulated NF-kappaB activation in myeloid cells impacts inflammatory signaling in nonmyeloid cells and generation of neutrophilic lung inflammation in response to systemic endotoxemia. We generated bone marrow chimeras by fetal liver transplantation of cells deficient in IkappaBalpha or p50 into lethally irradiated NF-kappaB reporter transgenic mice. No differences were apparent between bone marrow chimeras in the absence of an inflammatory stimulus; however, following intraperitoneal injection of Escherichia coli lipopolysaccharide (LPS), IkappaBalpha- or p50-deficient bone marrow chimeras showed increased NF-kappaB activation in nonhematopoietic cells, exaggerated neutrophilic inflammation, and higher mortality compared with untransplanted reporter mice and wild-type bone marrow chimeras. Primary bone marrow-derived macrophages (BMDM) from IkappaBalpha(-/-) or p50(-/-) exhibited increased NF-kappaB activation and macrophage inflammatory protein-2 production after LPS treatment compared with wild-type cells, and coculture of BMDM with lung epithelial (A549) cells resulted in increased NF-kappaB activation in A549 cells and excess IL-8 production by these epithelial cells. These studies indicate an important role for inhibitory members of the NF-kappaB family acting specifically within myeloid cells to limit inflammatory responses in the lungs.

Alendronate augments interleukin-1beta release from macrophages infected with periodontal pathogenic bacteria through activation of caspase-1

Nitrogen-containing bisphosphonates (NBPs) are anti-bone-resorptive drugs with inflammatory side effects that include osteomyelitis and osteonecrosis of the jaw. Oral bacteria have been considered to be a trigger for these NBP-associated jaw bone diseases. The present study examined the effects of alendronate (a typical NBP) and clodronate (a non-NBP) on the production of proinflammatory cytokines by macrophages infected with Porphyromonas gingivalis and Tannerella forsythia, which are important pathogens of periodontal diseases. Pretreatment with alendronate augmented IL-1beta, but not TNFalpha, production by macrophages infected with P. gingivalis or T. forsythia. This augmentation of IL-1beta production was inhibited by clodronate. Furthermore, caspase-1, a promoter of IL-1beta production, was activated by treatment with alendronate, and caspase-1 inhibitor reduced the production of IL-1beta induced by alendronate and P. gingivalis. These results suggest that NBPs augment periodontal pathogenic bacteria-induced IL-1beta release via caspase-1 activation, and this phenomenon may contribute to the development of NBP-associated inflammatory side effects including jaw osteomyelitis. Co-treatment with clodronate may prevent and/or reduce these inflammatory effects induced by NBPs.

NF-kappaB signaling, liver disease and hepatoprotective agents

The NF-kappaB signaling pathway has particular relevance to several liver diseases including hepatitis (liver infection by Helicobacter, viral hepatitis induced by HBV and HCV), liver fibrosis and cirrhosis and hepatocellular carcinoma. Furthermore, the NF-kappaB signaling pathway is a potential target for development of hepatoprotective agents. Several types of drugs including: selective estrogen receptor modulators (SERMs), antioxidants, proteasome inhibitors, IKK inhibitors and nucleic acid-based decoys have been shown to interfere with NF-kappaB activity at different levels and may be useful for the treatment of liver diseases. However, NF-kappaB also plays an important hepatoprotective function that needs to be taken into consideration during development of new therapeutic regimens.

Cell penetrating peptide inhibitors of nuclear factor-kappa B

The nuclear factor kappa B (NF-kappaB) transcription factors are activated by a range of stimuli including pro-inflammatory cytokines. Active NF-kappaB regulates the expression of genes involved in inflammation and cell survival and aberrant NF-kappaB activity plays pathological roles in certain types of cancer and diseases characterized by chronic inflammation. NF-kappaB signaling is an attractive target for the development of novel anti-inflammatory or anti-cancer drugs and we discuss here how the method of peptide transduction has been used to specifically target NF-kappaB. Peptide transduction relies on the ability of certain small cell-penetrating peptides (CPPs) to enter cells, and a panel of CPP-linked inhibitors (CPP-Is) has been developed to directly inhibit NF-kappaB signaling. Remarkably, several of these NF-kappaB-targeting CPP-Is are effective in vivo and therefore offer exciting potential in the clinical setting.

The kinase p38 alpha serves cell type-specific inflammatory functions in skin injury and coordinates pro- and anti-inflammatory gene expression

The mitogen-activated protein kinase p38 mediates cellular responses to injurious stress and immune signaling. Among the many p38 isoforms, p38 alpha is the most widely expressed in adult tissues and can be targeted by various pharmacological inhibitors. Here we investigated how p38 alpha activation is linked to cell type-specific outputs in mouse models of cutaneous inflammation. We found that both myeloid and epithelial p38 elicit inflammatory responses, yet p38 alpha signaling in each cell type served distinct inflammatory functions and varied depending on the mode of skin irritation. In addition, myeloid p38 alpha limited acute inflammation via activation of anti-inflammatory gene expression dependent on mitogen- and stress-activated kinases. Our results suggest a dual function for p38 alpha in the regulation of inflammation and show mixed potential for its inhibition as a therapeutic strategy.

Relationship between the gingival sulcus depth and interleukin-1 isoform concentrations within the adjacent gingival tissue

BACKGROUND AND OBJECTIVE

While there is substantial information concerning the concentrations of interleukin-1 isoforms within gingival crevicular fluid, there is little information concerning their concentrations within either normal or diseased gingival tissues. Therefore, the aim of this study was to evaluate the relationship between the concentrations of gingival interleukin-1 isoforms and the adjacent sulcular depth.

MATERIAL AND METHODS

Interdental gingival papillae were excised and grouped based on adjacent pocket depth and the presence of bleeding on probing. Gingiva adjacent to a sulcus of < or = 3 mm without bleeding on probing were classified as 'normal'; gingiva adjacent to a 3-mm sulcus with bleeding on probing were classified as 'diseased-slight'; gingiva adjacent to a 4-6-mm sulcus featuring bleeding on probing were classified as 'diseased-moderate'; and gingiva adjacent to a sulcus of > 6 mm featuring bleeding on probing were classified as 'diseased-severe'. Tissues were solublized and the concentrations of interleukin-1beta, interleukin-1alpha, interleukin-1 receptor antagonist and interleukin-6 were assessed by enzyme-linked immunosorbent assay. Data were compared by factorial analysis of variance, the post-hoc Tukey test and the Pearson's correlation test.

RESULTS

Gingival concentrations of interleukin-6, interleukin-1 receptor antagonist, interleukin-1alpha- and interleukin-1beta were significantly greater at diseased-severe sites than at normal, diseased-slight, or diseased-moderate sites (p < 0.05); the gingival concentrations of interleukin-1 receptor antagonist and interleukin-1alpha were significantly greater at diseased-severe than at diseased-moderate sites (p < 0.05). Interleukin-1 receptor antagonist concentrations were significantly correlated with both interleukin-1alpha and interleukin-1beta concentrations. The ratios of concentrations of the interleukin-1 isoforms were different at the various stages of inflammation.

CONCLUSION

Our data indicated a progressive increase in gingival concentrations of interleukin-1 isoforms with increased adjacent sulcular depth. However, within 'diseased' tissues, the proportional concentrations of interleukin-1alpha and -beta to interleukin-1 receptor antagonist were lowest within diseased-severe tissues.

Loss of the autophagy protein Atg16L1 enhances endotoxin-induced IL-1beta production

Systems for protein degradation are essential for tight control of the inflammatory immune response. Autophagy, a bulk degradation system that delivers cytoplasmic constituents into autolysosomes, controls degradation of long-lived proteins, insoluble protein aggregates and invading microbes, and is suggested to be involved in the regulation of inflammation. However, the mechanism underlying the regulation of inflammatory response by autophagy is poorly understood. Here we show that Atg16L1 (autophagy-related 16-like 1), which is implicated in Crohn's disease, regulates endotoxin-induced inflammasome activation in mice. Atg16L1-deficiency disrupts the recruitment of the Atg12-Atg5 conjugate to the isolation membrane, resulting in a loss of microtubule-associated protein 1 light chain 3 (LC3) conjugation to phosphatidylethanolamine. Consequently, both autophagosome formation and degradation of long-lived proteins are severely impaired in Atg16L1-deficient cells. Following stimulation with lipopolysaccharide, a ligand for Toll-like receptor 4 (refs 8, 9), Atg16L1-deficient macrophages produce high amounts of the inflammatory cytokines IL-1beta and IL-18. In lipopolysaccharide-stimulated macrophages, Atg16L1-deficiency causes Toll/IL-1 receptor domain-containing adaptor inducing IFN-beta (TRIF)-dependent activation of caspase-1, leading to increased production of IL-1beta. Mice lacking Atg16L1 in haematopoietic cells are highly susceptible to dextran sulphate sodium-induced acute colitis, which is alleviated by injection of anti-IL-1beta and IL-18 antibodies, indicating the importance of Atg16L1 in the suppression of intestinal inflammation. These results demonstrate that Atg16L1 is an essential component of the autophagic machinery responsible for control of the endotoxin-induced inflammatory immune response.