CARD-Bcl10-Malt1 signalosomes: missing link to NF-kappaB

KLF5‑mediated expression of CARD11 promotes the progression of gastric cancer

Caspase recruitment domain-containing protein 11 (CARD11) has been reported as functioning in multiple types of cancers. In the present study, the role and mechanism of CARD11 in gastric cancer was investigated. First, CARD11 expression in gastric cancer tissues and the association of CARD11 with overall survival were analyzed by the encyclopedia of RNA interactomes database. CARD11 expression in gastric cancer cells was detected by western blotting and reverse transcription-quantitative PCR analyses. After CARD11 silencing, cell proliferation was evaluated by Cell Counting Kit-8 assay, 5-ethynyl-2'-deoxyuridine staining and flow cytometry analysis. Wound healing and Transwell assays were used to measure the capacities of cell migration and invasion. Additionally, the expression levels of epithelial-mesenchymal transition (EMT)-related proteins and mTOR-related proteins were detected by western blot analysis. HumanTFDB predicted the binding of the transcription factor Krüppel-like factor 5 (KLF5) to the CARD11 promoter, which was confirmed by dual luciferase reporter and chromatin immunoprecipitation assays. To explore the regulatory effects between KLF5 and CARD11, KLF5 was overexpressed to perform the rescue experiments in gastric cancer cells with CARD11 silencing. Results revealed that CARD11 was highly expressed in gastric cancer and was associated with poor prognosis. CARD11 interference inhibited the proliferation of gastric cancer cells and induced cell cycle arrest. Additionally, CARD11 silencing suppressed the migration, invasion and EMT of gastric cancer cells, accompanied by upregulated E-cadherin expression and downregulated N-cadherin and vimentin expression. Moreover, the transcription factor KLF5 positively regulated the transcription of CARD11 in gastric cancer. KLF5 overexpression reversed the effects of interference of CARD11 expression in gastric cancer cells to promote their proliferation, migration, invasion and EMT. KLF5 overexpression also led to a reduction in cell cycle arrest. Finally, interference of CARD11 expression suppressed the mTOR pathway, which was activated by KLF5. In conclusion, KLF5-mediated CARD11 promoted the proliferation, migration and invasion of gastric cancer cells.

The Gab2-MALT1 axis regulates thromboinflammation and deep vein thrombosis

Deep vein thrombosis (DVT) is the third most common cause of cardiovascular mortality. Several studies suggest that DVT occurs at the intersection of dysregulated inflammation and coagulation upon activation of inflammasome and secretion of interleukin 1β (IL-1β) in restricted venous flow conditions. Our recent studies showed a signaling adapter protein, Gab2 (Grb2-associated binder 2), plays a crucial role in propagating inflammatory signaling triggered by IL-1β and other inflammatory mediators in endothelial cells. The present study shows that Gab2 facilitates the assembly of the CBM (CARMA3 [CARD recruited membrane-associated guanylate kinase protein 3]-BCL-10 [B-cell lymphoma 10]-MALT1 [mucosa-associated lymphoid tissue lymphoma translocation protein 1]) signalosome, which mediates the activation of Rho and NF-κB in endothelial cells. Gene silencing of Gab2 or MALT1, the effector signaling molecule in the CBM signalosome, or pharmacological inhibition of MALT1 with a specific inhibitor, mepazine, significantly reduced IL-1β-induced Rho-dependent exocytosis of P-selectin and von Willebrand factor (VWF) and the subsequent adhesion of neutrophils to endothelial cells. MALT1 inhibition also reduced IL-1β-induced NF-κB-dependent expression of tissue factor and vascular cell adhesion molecule 1. Consistent with the in vitro data, Gab2 deficiency or pharmacological inhibition of MALT1 suppressed the accumulation of monocytes and neutrophils at the injury site and attenuated venous thrombosis induced by the inferior vena cava ligation-induced stenosis or stasis in mice. Overall, our data reveal a previously unrecognized role of the Gab2-MALT1 axis in thromboinflammation. Targeting the Gab2-MALT1 axis with MALT1 inhibitors may become an effective strategy to treat DVT by suppressing thromboinflammation without inducing bleeding complications.

MALT1 is a Targetable Driver of Epithelial-to-Mesenchymal Transition in Claudin-low, Triple-Negative Breast Cancer

MALT1 is the effector protein of the CARMA/Bcl10/MALT1 (CBM) signalosome, a multi-protein complex that drives pro-inflammatory signaling pathways downstream of a diverse set of receptors. While CBM activity is best known for its role in immune cells, emerging evidence suggests that it plays a key role in the pathogenesis of solid tumors, where it can be activated by selected G protein-coupled receptors (GPCRs). Here, we demonstrated that overexpression of GPCRs implicated in breast cancer pathogenesis, specifically the receptors for Angiotensin II and thrombin (AT1R and PAR1), drove a strong epithelial-to-mesenchymal transition (EMT) program in breast cancer cells that is characteristic of claudin-low, triple-negative breast cancer (TNBC). In concert, MALT1 was activated in these cells and contributed to the dramatic EMT phenotypic changes through regulation of master EMT transcription factors including Snail and ZEB1. Importantly, blocking MALT1 signaling, through either siRNA-mediated depletion of MALT1 protein or pharmacologic inhibition of its activity, was effective at partially reversing the molecular and phenotypic indicators of EMT. Treatment of mice with mepazine, a pharmacologic MALT1 inhibitor, reduced growth of PAR1+, MDA-MB-231 xenografts and had an even more dramatic effect in reducing the burden of metastatic disease. These findings highlight MALT1 as an attractive therapeutic target for claudin-low TNBCs harboring overexpression of one or more selected GPCRs. Implications: This study nominates a GPCR/MALT1 signaling axis as a pathway that can be pharmaceutically targeted to abrogate EMT and metastatic progression in TNBC, an aggressive form of breast cancer that currently lacks targeted therapies.

Cellular CARD11 Inhibits the Fusogenic Activity of Newcastle Disease Virus via CBM Signalosome-Mediated Furin Reduction in Chicken Fibroblasts

Newcastle disease virus (NDV) causes an infectious disease that poses a major threat to poultry health. Our previous study identified a chicken brain-specific caspase recruitment domain-containing protein 11 (CARD11) that was upregulated in chicken neurons and inhibited NDV replication. This raises the question of whether CARD11 plays a role in inhibiting viruses in non-neural cells. Here, chicken fibroblasts were used as a non-neural cell model to investigate the role. CARD11 expression was not significantly upregulated by either velogenic or lentogenic NDV infection in chicken fibroblasts. Viral replication was decreased in DF-1 cells stably overexpressing CARD11, while viral growth was significantly increased in the CARD11-knockdown DF-1 cell line. Moreover, CARD11 colocalized with the viral P protein and aggregated around the fibroblast nucleus, suggesting that an interaction existed between CARD11 and the viral P protein; this interaction was further examined by suppressing viral RNA polymerase activity by using a minigenome assay. Viral replication was inhibited by CARD11 in fibroblasts, and this result was consistent with our previous report in chicken neurons. Importantly, CARD11 was observed to reduce the syncytia induced by either velogenic virus infection or viral haemagglutinin-neuraminidase (HN) and F cotransfection in fibroblasts. We found that CARD11 inhibited the expression of the host protease furin, which is essential for cleavage of the viral F protein to trigger fusogenic activity. Furthermore, the CARD11-Bcl10-MALT1 (CBM) signalosome was found to suppress furin expression, which resulted in a reduction in the cleavage efficiency of the viral F protein to further inhibit viral syncytia. Taken together, our findings mainly demonstrated a novel CARD11 inhibitory mechanism for viral fusogenic activity in chicken fibroblasts, and this mechanism explains the antiviral roles of this molecule in NDV pathogenesis.

NF-κB Signaling Is Regulated by Fucosylation in Metastatic Breast Cancer Cells

A growing body of evidence indicates that the levels of fucosylation correlate with breast cancer progression and contribute to metastatic disease. However, very little is known about the signaling and functional outcomes that are driven by fucosylation. We performed a global proteomic analysis of 4T1 metastatic mammary tumor cells in the presence and absence of a fucosylation inhibitor, 2-fluorofucose (2FF). Of significant interest, pathway analysis based on our results revealed a reduction in the NF-κB and TNF signaling pathways, which regulate the inflammatory response. NF-κB is a transcription factor that is pro-tumorigenic and a prime target in human cancer. We validated our results, confirming that treatment of 4T1 cells with 2FF led to a decrease in NF-κB activity through increased IκBα. Based on these observations, we conclude that fucosylation is an important post-translational modification that governs breast cancer cell signaling.

B-cell lymphoma/leukaemia 10 and angiotensin II-induced kidney injury

AIMS

B-cell lymphoma/leukaemia 10 (Bcl10) is a member of the CARMA-Bcl10-MALT1 signalosome, linking angiotensin (Ang) II, and antigen-dependent immune-cell activation to nuclear factor kappa-B signalling. We showed earlier that Bcl10 plays a role in Ang II-induced cardiac fibrosis and remodelling, independent of blood pressure. We now investigated the role of Bcl10 in Ang II-induced renal damage.

METHODS AND RESULTS

Bcl10 knockout mice (Bcl10 KO) and wild-type (WT) controls were given 1% NaCl in the drinking water and Ang II (1.44 mg/kg/day) for 14 days. Additionally, Bcl10 KO or WT kidneys were transplanted onto WT mice that were challenged by the same protocol for 7 days. Kidneys of Ang II-treated Bcl10 KO mice developed less fibrosis and showed fewer infiltrating cells. Nevertheless, neutrophil gelatinase-associated lipocalin (Ngal) and kidney injury molecule (Kim)1 expression was higher in the kidneys of Ang II-treated Bcl10 KO mice, indicating exacerbated tubular damage. Furthermore, albuminuria was significantly higher in Ang II-treated Bcl10 KO mice accompanied by reduced glomerular nephrin expression and podocyte number. Ang II-treated WT mice transplanted with Bcl10 KO kidney showed more albuminuria and renal Ngal, compared to WT- > WT kidney-transplanted mice, as well as lower podocyte number but similar fibrosis and cell infiltration. Interestingly, mice lacking Bcl10 in the kidney exhibited less Ang II-induced cardiac hypertrophy than controls.

CONCLUSION

Bcl10 has multi-faceted actions in Ang II-induced renal damage. On the one hand, global Bcl10 deficiency ameliorates renal fibrosis and cell infiltration; on the other hand, lack of renal Bcl10 aggravates albuminuria and podocyte damage. These data suggest that Bcl10 maintains podocyte integrity and renal function.

Malt1 Protease Deficiency in Mice Disrupts Immune Homeostasis at Environmental Barriers and Drives Systemic T Cell-Mediated Autoimmunity

The paracaspase Malt1 is a key regulator of canonical NF-κB activation downstream of multiple receptors in both immune and nonimmune cells. Genetic disruption of Malt1 protease function in mice and MALT1 mutations in humans results in reduced regulatory T cells and a progressive multiorgan inflammatory pathology. In this study, we evaluated the altered immune homeostasis and autoimmune disease in Malt1 protease-deficient (Malt1PD) mice and the Ags driving disease manifestations. Our data indicate that B cell activation and IgG1/IgE production is triggered by microbial and dietary Ags preferentially in lymphoid organs draining mucosal barriers, likely as a result of dysregulated mucosal immune homeostasis. Conversely, the disease was driven by a polyclonal T cell population directed against self-antigens. Characterization of the Malt1PD T cell compartment revealed expansion of T effector memory cells and concomitant loss of a CD4⁺ T cell population that phenotypically resembles anergic T cells. Therefore, we propose that the compromised regulatory T cell compartment in Malt1PD animals prevents the efficient maintenance of anergy and supports the progressive expansion of pathogenic, IFN-γ-producing T cells. Overall, our data revealed a crucial role of the Malt1 protease for the maintenance of intestinal and systemic immune homeostasis, which might provide insights into the mechanisms underlying IPEX-related diseases associated with mutations in MALT1.

CARMA3 Mediates Allergic Lung Inflammation in Response to Alternaria alternata

The airway epithelial cell (AEC) response to allergens helps initiate and propagate allergic inflammation in asthma. CARMA3 is a scaffold protein that mediates G protein-coupled receptor-induced NF-κB activation in airway epithelium. In this study, we demonstrate that mice with CARMA3-deficient AECs have reduced airway inflammation, as well as reduced type 2 cytokine levels in response to Alternaria alternata. These mice also have reduced production of IL-33 and IL-25, and reduced numbers of innate lymphoid cells in the lung. We also show that CARMA3-deficient human AECs have decreased production of proasthmatic mediators in response to A. alternata. Finally, we show that CARMA3 interacts with inositol 1,4,5-trisphosphate receptors in AECs, and that inhibition of CARMA3 signaling reduces A. alternata-induced intracellular calcium release. In conclusion, we show that CARMA3 signaling in AECs helps mediate A. alternata-induced allergic airway inflammation, and that CARMA3 is an important signaling molecule for type 2 immune responses in the lung.

CARMA3: Scaffold Protein Involved in NF-κB Signaling

Scaffold proteins are defined as pivotal molecules that connect upstream receptors to specific effector molecules. Caspase recruitment domain protein 10 (CARD10) gene encodes a scaffold protein CARMA3, belongs to the family of CARD and membrane-associated guanylate kinase-like protein (CARMA). During the past decade, investigating the function of CARMA3 has revealed that it forms a complex with BCL10 and MALT1 to mediate different receptors-dependent signaling, including GPCR and EGFR, leading to activation of the transcription factor NF-κB. More recently, CARMA3 and its partners are also reported to be involved in antiviral innate immune response and DNA damage response. In this review, we summarize the biology of CARMA3 in multiple receptor-induced NF-κB signaling. Especially, we focus on discussing the function of CARMA3 in regulating NF-κB activation and antiviral IFN signaling in the context of recent progress in the field.

Autocleavage of the paracaspase MALT1 at Arg-781 attenuates NF-κB signaling and regulates the growth of activated B-cell like diffuse large B-cell lymphoma cells

MALT1 controls several receptors-mediated signaling to nuclear factor κB (NF-κB) through both its scaffold and protease function. MALT1 protease activity is shown to inactivate several negative regulators of NF-κB signaling and augment NF-κB activation ability. In this study, MALT1 was demonstrated to autoprocess itself in the presence of oligomerization-competent BCL10. Cleavage occurred after Arginine 781 located in the C-terminus of MALT1. Shortened MALT1 cleavage products showed attenuated binding ability with TRAF6. Its NF-κB activation ability was also weakened. Various MALT1 constructs including wild type, catalytically-inactive (MALT1_C464A), cleavage-defective (MALT1_R781L), or truncated (MALT1_1–781) form of MALT1 was introduced into MALT1-knocked-down-Jurkat T cells. Cleavage-defective MALT1_R781L retained its proteolytic and initial IκBα phosphorylation activity as MALT1. Truncated MALT1_1–781 mutant showed weakness in IκBα phosphorylation and the expression of NF-κB targets IL-2 and IFN-γ. Cleavage at R781 was detectable but marginal after activation with TPA/ionomycin or anti-CD3 antibody in lymphocytes. However, cleavage at R781 was evident in ABC-DLBCL cells such as OCI-Ly3, HBL-1. HBL-1 cells with induced expression of catalytically-inactive MALT1_C464A or cleavage-defective MALT1_R781L exhibited characteristic of retarded-growth. These findings suggested that cleavage at R781 of MALT1 played a role in the survival of ABC-DLBCL cells.

The CARMA3-Bcl10-MALT1 Signalosome Drives NFκB Activation and Promotes Aggressiveness in Angiotensin II Receptor-Positive Breast Cancer

The angiotensin II receptor AGTR1, which mediates vasoconstrictive and inflammatory signaling in vascular disease, is overexpressed aberrantly in some breast cancers. In this study, we established the significance of an AGTR1-responsive NFκB signaling pathway in this breast cancer subset. We documented that AGTR1 overexpression occurred in the luminal A and B subtypes of breast cancer, was mutually exclusive of HER2 expression, and correlated with aggressive features that include increased lymph node metastasis, reduced responsiveness to neoadjuvant therapy, and reduced overall survival. Mechanistically, AGTR1 overexpression directed both ligand-independent and ligand-dependent activation of NFκB, mediated by a signaling pathway that requires the triad of CARMA3, Bcl10, and MALT1 (CBM signalosome). Activation of this pathway drove cancer cell-intrinsic responses that include proliferation, migration, and invasion. In addition, CBM-dependent activation of NFκB elicited cancer cell-extrinsic effects, impacting endothelial cells of the tumor microenvironment to promote tumor angiogenesis. CBM/NFκB signaling in AGTR1⁺ breast cancer therefore conspires to promote aggressive behavior through pleiotropic effects. Overall, our results point to the prognostic and therapeutic value of identifying AGTR1 overexpression in a subset of HER2-negative breast cancers, and they provide a mechanistic rationale to explore the repurposing of drugs that target angiotensin II-dependent NFκB signaling pathways to improve the treatment of this breast cancer subset.Significance: These findings offer a mechanistic rationale to explore the repurposing of drugs that target angiotensin action to improve the treatment of AGTR1-expressing breast cancers. Cancer Res; 78(5); 1225-40. ©2017 AACR.

In vitro reconstitution of interactions in the CARD9 signalosome

The caspase-associated recruitment domain (CARD)-containing protein 9 (CARD9) signalosome is composed of CARD9, B-cell CLL/lymphoma 10 (BCL10) and mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1). The CARD9 signalosome has been reported to exert critical functions in the immunoreceptor tyrosine-based activation motif-coupled receptor-mediated activation of myeloid cells, through nuclear factor-κB pathways during innate immunity processes. During CARD9 signalosome assembly, BCL10 has been revealed to function as an adaptor protein and to interact with CARD9 via CARD-CARD interactions; BCL10 also interacts with MALT1 via its C-terminal Ser/Thr-rich region and the first immunoglobulin domain of MALT1. The CARD9 signalosome is implicated in critical biological processes; however, its structural and biochemical characteristics have yet to be elucidated. In the present study, CARD9 and BCL10 CARDs were successfully purified and characterized, and their biochemical properties were investigated. In addition, CARD9-BCL10 complexes were reconstituted in vitro under low salt and pH conditions. Furthermore, based on structural modeling data, a scheme was proposed to describe the interactions between CARD9 and BCL10. This provides a further understanding of the mechanism of how the CARD9 signalosome may be assembled.

Human IκBα Gain of Function: a Severe and Syndromic Immunodeficiency

Germline heterozygous gain-of-function (GOF) mutations of NFKBIA, encoding IκBα, cause an autosomal dominant (AD) form of anhidrotic ectodermal dysplasia with immunodeficiency (EDA-ID). Fourteen unrelated patients have been reported since the identification of the first case in 2003. All mutations enhanced the inhibitory activity of IκBα, by preventing its phosphorylation on serine 32 or 36 and its subsequent degradation. The mutation certainly or probably occurred de novo in 13 patients, whereas it was inherited from a parent with somatic mosaicism in one patient. Eleven mutations, belonging to two groups, were identified: (i) missense mutations affecting S32, S36, or neighboring residues (8 mutations, 11 patients) and (ii) nonsense mutations upstream from S32 associated with the reinitiation of translation downstream from S36 (3 mutations, 3 patients). Thirteen patients had developmental features of EDA, the severity and nature of which differed between cases. All patient cells tested displayed impaired NF-κB-mediated responses to the stimulation of various surface receptors involved in cell-intrinsic (fibroblasts), innate (monocytes), and adaptive (B and T cells) immunity, including TLRs, IL-1Rs, TNFRs, TCR, and BCR. All patients had profound B-cell deficiency. Specific immunological features, found in some, but not all patients, included a lack of peripheral lymph nodes, lymphocytosis, dysfunctional α/β T cells, and a lack of circulating γ/δ T cells. The patients had various pyogenic, mycobacterial, fungal, and viral severe infections. Patients with a missense mutation tended to display more severe phenotypes, probably due to higher levels of GOF proteins. In the absence of hematopoietic stem cell transplantation (HSCT), this condition cause death before the age of 1 year (one child). Two survivors have been on prophylaxis (at 9 and 22 years). Six children died after HSCT. Five survived, four of whom have been on prophylaxis (3 to 21 years post HSCT), whereas one has been well with no prophylaxis. Heterozygous GOF mutations in IκBα underlie a severe and syndromic immunodeficiency, the interindividual variability of which might partly be ascribed to the dichotomy of missense and nonsense mutations, and the hematopoietic component of which can be rescued by HSCT.

Effective Combination Therapies for B-cell Lymphoma Predicted by a Virtual Disease Model

The complexity of cancer signaling networks limits the efficacy of most single-agent treatments and brings about challenges in identifying effective combinatorial therapies. In this study, we used chronic active B-cell receptor (BCR) signaling in diffuse large B-cell lymphoma as a model system to establish a computational framework to optimize combinatorial therapy in silico We constructed a detailed kinetic model of the BCR signaling network, which captured the known complex cross-talk between the NFκB, ERK, and AKT pathways and multiple feedback loops. Combining this signaling model with a data-derived tumor growth model, we predicted viability responses of many single drug and drug combinations in agreement with experimental data. Under this framework, we exhaustively predicted and ranked the efficacy and synergism of all possible combinatorial inhibitions of eleven currently targetable kinases in the BCR signaling network. Ultimately, our work establishes a detailed kinetic model of the core BCR signaling network and provides the means to explore the large space of possible drug combinations. Cancer Res; 77(8); 1818-30. ©2017 AACR.

Moraxella catarrhalis induces CEACAM3-Syk-CARD9-dependent activation of human granulocytes

The human restricted pathogen Moraxella catarrhalis is an important causal agent for exacerbations in chronic obstructive lung disease in adults. In such patients, increased numbers of granulocytes are present in the airways, which correlate with bacteria-induced exacerbations and severity of the disease. Our study investigated whether the interaction of M. catarrhalis with the human granulocyte-specific carcinoembryonic antigen-related cell adhesion molecule (CEACAM)-3 is linked to NF-κB activation, resulting in chemokine production. Granulocytes from healthy donors and NB4 cells were infected with M. catarrhalis in the presence of different inhibitors, blocking antibodies and siRNA. The supernatants were analysed by enzyme-linked immunosorbent assay for chemokines. NF-κB activation was determined using a luciferase reporter gene assay and chromatin-immunoprecipitation. We found evidence that the specific engagement of CEACAM3 by M. catarrhalis ubiquitous surface protein A1 (UspA1) results in the activation of pro-inflammatory events, such as degranulation of neutrophils, ROS production and chemokine secretion. The interaction of UspA1 with CEACAM3 induced the activation of the NF-κB pathway via Syk and the CARD9 pathway and was dependent on the phosphorylation of the CEACAM3 ITAM-like motif. These findings suggest that the CEACAM3 signalling in neutrophils is able to specifically modulate airway inflammation caused by infection with M. catarrhalis.

Nanomolar Caffeic Acid Decreases Glucose Uptake and the Effects of High Glucose in Endothelial Cells

Epidemiological studies suggest that moderate and prolonged consumption of coffee is associated with a reduced risk of developing type 2 diabetes but the molecular mechanisms underlying this effect are not known. In this study, we report the effects of physiological concentrations of caffeic acid, easily achievable by normal dietary habits, in endothelial cells cultured in 25 mM of glucose (high glucose, HG). In HG, the presence of 10 nM caffeic acid was associated with a decrease of glucose uptake but not to changes of GLUT-1 membrane localization or mRNA levels. Moreover, caffeic acid countered HG-induced loss of barrier integrity, reducing actin rearrangement and FITC-dextran passage. The decreased flux of glucose associated to caffeic acid affected HG induced apoptosis by down-regulating the expression of initiator (caspase 8 and 9) and effector caspases (caspase 7 and 3) and by increasing the levels of phosphorylated Bcl-2. We also observed that caffeic acid in HG condition was associated to a reduction of p65 subunit nuclear levels with respect to HG alone. NF-κB activation has been shown to lead to apoptosis in HG treated cells and the analysis of the expression of a panel of about 90 genes related to NF-κB signaling pathway revealed that caffeic acid significantly influenced gene expression changes induced by HG. In conclusion, our results suggest that caffeic acid, decreasing the metabolic stress induced by HG, allows the activation of survival mechanisms mediated by a different modulation of NF-κB-related signaling pathways and to the activation of anti-apoptotic proteins.

NLRs: Nucleotide-Binding Domain and Leucine-Rich-Repeat-Containing Proteins

Eukaryotes have evolved strategies to detect microbial intrusion and instruct immune responses to limit damage from infection. Recognition of microbes and cellular damage relies on the detection of microbe-associated molecular patterns (MAMPs, also called PAMPS, or pathogen-associated molecular patterns) and so-called "danger signals" by various families of host pattern recognition receptors (PRRs). Members of the recently identified protein family of nucleotide-binding domain andleucine-rich-repeat-containing proteins (NLR), including Nod1, Nod2, NLRP3, and NLRC4, have been shown to detect specific microbial motifs and danger signals for regulating host inflammatory responses. Moreover, with the discovery that polymorphisms in NOD1, NOD2, NLRP1, and NLRP3 are associated with susceptibility to chronic inflammatory disorders, the view has emerged that NLRs act not only as sensors butalso can serve as signaling platforms for instructing and balancing host immune responses. In this chapter, we explore the functions of these intracellular innate immune receptors and examine their implication in inflammatory diseases.

Genetic errors of the human caspase recruitment domain-B-cell lymphoma 10-mucosa-associated lymphoid tissue lymphoma-translocation gene 1 (CBM) complex: Molecular, immunologic, and clinical heterogeneity

Three members of the caspase recruitment domain (CARD) family of adaptors (CARD9, CARD10, and CARD11) are known to form heterotrimers with B-cell lymphoma 10 (BCL10) and mucosa-associated lymphoid tissue lymphoma-translocation gene 1 (MALT1). These 3 CARD-BCL10-MALT1 (CBM) complexes activate nuclear factor κB in both the innate and adaptive arms of immunity. Human inherited defects of the 3 components of the CBM complex, including the 2 adaptors CARD9 and CARD11 and the 2 core components BCL10 and MALT1, have recently been reported. Biallelic loss-of-function mutant alleles underlie several different immunologic and clinical phenotypes, which can be assigned to 2 distinct categories. Isolated invasive fungal infections of unclear cellular basis are associated with CARD9 deficiency, whereas a broad range of clinical manifestations, including those characteristic of T- and B-lymphocyte defects, are associated with CARD11, MALT1, and BCL10 deficiencies. Interestingly, human subjects with these mutations have some features in common with the corresponding knockout mice, but other features are different between human subjects and mice. Moreover, germline and somatic gain-of-function mutations of MALT1, BCL10, and CARD11 have also been found in patients with other lymphoproliferative disorders. This broad range of germline and somatic CBM lesions, including loss-of-function and gain-of-function mutations, highlights the contribution of each of the components of the CBM complex to human immunity.

CARMA3 Is Critical for the Initiation of Allergic Airway Inflammation

Innate immune responses to allergens by airway epithelial cells (AECs) help initiate and propagate the adaptive immune response associated with allergic airway inflammation in asthma. Activation of the transcription factor NF-κB in AECs by allergens or secondary mediators via G protein-coupled receptors (GPCRs) is an important component of this multifaceted inflammatory cascade. Members of the caspase recruitment domain family of proteins display tissue-specific expression and help mediate NF-κB activity in response to numerous stimuli. We have previously shown that caspase recruitment domain-containing membrane-associated guanylate kinase protein (CARMA)3 is specifically expressed in AECs and mediates NF-κB activation in these cells in response to stimulation with the GPCR agonist lysophosphatidic acid. In this study, we demonstrate that reduced levels of CARMA3 in normal human bronchial epithelial cells decreases the production of proasthmatic mediators in response to a panel of asthma-relevant GPCR ligands such as lysophosphatidic acid, adenosine triphosphate, and allergens that activate GPCRs such as Alternaria alternata and house dust mite. We then show that genetically modified mice with CARMA3-deficient AECs have reduced airway eosinophilia and proinflammatory cytokine production in a murine model of allergic airway inflammation. Additionally, we demonstrate that these mice have impaired dendritic cell maturation in the lung and that dendritic cells from mice with CARMA3-deficient AECs have impaired Ag processing. In conclusion, we show that AEC CARMA3 helps mediate allergic airway inflammation, and that CARMA3 is a critical signaling molecule bridging the innate and adaptive immune responses in the lung.

Probes to monitor activity of the paracaspase MALT1

The human paracaspase mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) plays a central role in nuclear factor-κB (NF-κB) signaling as both a protease and scaffolding protein. Knocking out MALT1 leads to impaired NF-κB signaling and failure to mount an effective immune response. However, it is unclear to which degree it is the scaffolding function versus the proteolytic activity of MALT1 that is essential. Previous work involving a MALT1 inhibitor with low selectivity suggests that the enzymatic function plays an important role in different cell lines. To help elucidate this proteolytic role of MALT1, we have designed activity-based probes that inhibit its proteolytic activity. The probes selectively label active enzyme and can be used to inhibit MALT1 and trace its activity profile, helping to create a better picture of the significance of the proteolytic function of MALT1.

Inability to resolve specific infection generates innate immunodeficiency syndrome in Xiap-/- mice

Emerging evidence indicates that innate immunodeficiency syndromes are linked to mutations in innate receptors and to specific infections. X-linked lymphoproliferative syndrome type-2 (XLP-2) is associated with deficiency in X-linked inhibitor of apoptosis protein (XIAP), with poorly understood molecular mechanisms. Here we showed that XIAP deficiency selectively impaired B-cell chronic lymphocytic leukemia/lymphoma 10 (BCL10)-mediated innate responses to dectin-1 ligands but did not affect responses to various Toll-like receptor agonists. Consequently, Xiap(-/-) mice became highly vulnerable on Candida albicans infection. The compromised early innate responses led to the persistent presence of C albicans and inflammatory cytokines in Xiap(-/-) mice. Furthermore, priming of Xiap(-/-) mice with the dectin-1 ligand curdlan alone resulted in XLP-2-like syndromes. Restoration of dectin-1-induced Rac1 activation and phagocytosis by resolvin D1, but not up-regulation of nuclear factor-κB, rescued Xiap(-/-) mice from C albicans lethal infection. Therefore, development of XLP-2 in XIAP-deficient patients could be partly due to sustained inflammation as a consequence of defective BCL10-dependent innate immunity toward specific pathogens. Importantly, our results suggest the potential therapeutic value of resolvin D1 in the treatment of XLP-2 and innate immunodeficiency syndromes.

The adaptor CRADD/RAIDD controls activation of endothelial cells by proinflammatory stimuli

A hallmark of inflammation, increased vascular permeability, is induced in endothelial cells by multiple agonists through stimulus-coupled assembly of the CARMA3 signalosome, which contains the adaptor protein BCL10. Previously, we reported that BCL10 in immune cells is targeted by the "death" adaptor CRADD/RAIDD (CRADD), which negatively regulates nuclear factor κB (NFκB)-dependent cytokine and chemokine expression in T cells (Lin, Q., Liu, Y., Moore, D. J., Elizer, S. K., Veach, R. A., Hawiger, J., and Ruley, H. E. (2012) J. Immunol. 188, 2493-2497). This novel anti-inflammatory CRADD-BCL10 axis prompted us to analyze CRADD expression and its potential anti-inflammatory action in non-immune cells. We focused our study on microvascular endothelial cells because they play a key role in inflammation. We found that CRADD-deficient murine endothelial cells display heightened BCL10-mediated expression of the pleotropic proinflammatory cytokine IL-6 and chemokine monocyte chemoattractant protein-1 (MCP-1/CCL2) in response to LPS and thrombin. Moreover, these agonists also induce significantly increased permeability in cradd(-/-), as compared with cradd(+/+), primary murine endothelial cells. CRADD-deficient cells displayed more F-actin polymerization with concomitant disruption of adherens junctions. In turn, increasing intracellular CRADD by delivery of a novel recombinant cell-penetrating CRADD protein (CP-CRADD) restored endothelial barrier function and suppressed the induction of IL-6 and MCP-1 evoked by LPS and thrombin. Likewise, CP-CRADD enhanced barrier function in CRADD-sufficient endothelial cells. These results indicate that depletion of endogenous CRADD compromises endothelial barrier function in response to inflammatory signals. Thus, we define a novel function for CRADD in endothelial cells as an inducible suppressor of BCL10, a key mediator of responses to proinflammatory agonists.

The CBM signalosome: potential therapeutic target for aggressive lymphoma?

The CBM signalosome plays a pivotal role in mediating antigen-receptor induced NF-κB signaling to regulate lymphocyte functions. The CBM complex forms filamentous structure and recruits downstream signaling components to activate NF-κB. MALT1, the protease component in the CBM complex, cleaves key proteins in the feedback loop of the NF-κB signaling pathway and enhances NF-κB activation. The aberrant activity of the CBM complex has been linked to aggressive lymphoma. Recent years have witnessed dramatic progresses in understanding the assembly mechanism of the CBM complex, and advances in the development of targeted therapy for aggressive lymphoma. Here, we will highlight these progresses and give an outlook on the potential translation of this knowledge from bench to bedside for aggressive lymphoma patients.

Novel disulfide bond-mediated dimerization of the CARD domain was revealed by the crystal structure of CARMA1 CARD

CARMA1, BCL10 and MALT1 form a large molecular complex known as the CARMA1 signalosome during lymphocyte activation. Lymphocyte activation via the CARMA1 signalosome is critical to immune response and linked to many immune diseases. Despite the important role of the CARMA1 signalosome during lymphocyte activation and proliferation, limited structural information is available. Here, we report the dimeric structure of CARMA1 CARD at a resolution of 3.2 Å. Interestingly, although CARMA1 CARD has a canonical six helical-bundles structural fold similar to other CARDs, CARMA1 CARD shows the first homo-dimeric structure of CARD formed by a disulfide bond and reveals a possible biologically important homo-dimerization mechanism.

Analysis of immune-related loci identifies 48 new susceptibility variants for multiple sclerosis

Using the ImmunoChip custom genotyping array, we analyzed 14,498 subjects with multiple sclerosis and 24,091 healthy controls for 161,311 autosomal variants and identified 135 potentially associated regions (P < 1.0 × 10(-4)). In a replication phase, we combined these data with previous genome-wide association study (GWAS) data from an independent 14,802 subjects with multiple sclerosis and 26,703 healthy controls. In these 80,094 individuals of European ancestry, we identified 48 new susceptibility variants (P < 5.0 × 10(-8)), 3 of which we found after conditioning on previously identified variants. Thus, there are now 110 established multiple sclerosis risk variants at 103 discrete loci outside of the major histocompatibility complex. With high-resolution Bayesian fine mapping, we identified five regions where one variant accounted for more than 50% of the posterior probability of association. This study enhances the catalog of multiple sclerosis risk variants and illustrates the value of fine mapping in the resolution of GWAS signals.

Whole-exome sequencing and imaging genetics identify functional variants for rate of change in hippocampal volume in mild cognitive impairment

Whole-exome sequencing of individuals with mild cognitive impairment, combined with genotype imputation, was used to identify coding variants other than the apolipoprotein E (APOE) ε4 allele associated with rate of hippocampal volume loss using an extreme trait design. Matched unrelated APOE ε3 homozygous male Caucasian participants from the Alzheimer's Disease Neuroimaging Initiative (ADNI) were selected at the extremes of the 2-year longitudinal change distribution of hippocampal volume (eight subjects with rapid rates of atrophy and eight with slow/stable rates of atrophy). We identified 57 non-synonymous single nucleotide variants (SNVs) which were found exclusively in at least 4 of 8 subjects in the rapid atrophy group, but not in any of the 8 subjects in the slow atrophy group. Among these SNVs, the variants that accounted for the greatest group difference and were predicted in silico as 'probably damaging' missense variants were rs9610775 (CARD10) and rs1136410 (PARP1). To further investigate and extend the exome findings in a larger sample, we conducted quantitative trait analysis including whole-brain search in the remaining ADNI APOE ε3/ε3 group (N=315). Genetic variation within PARP1 and CARD10 was associated with rate of hippocampal neurodegeneration in APOE ε3/ε3. Meta-analysis across five independent cross sectional cohorts indicated that rs1136410 is also significantly associated with hippocampal volume in APOE ε3/ε3 individuals (N=923). Larger sequencing studies and longitudinal follow-up are needed for confirmation. The combination of next-generation sequencing and quantitative imaging phenotypes holds significant promise for discovery of variants involved in neurodegeneration.

An association study of TOLL and CARD with leprosy susceptibility in Chinese population

Previous genome-wide association studies (GWASs) identified multiple susceptibility loci that have highlighted the important role of TLR (Toll-like receptor) and CARD (caspase recruitment domain) genes in leprosy. A large three-stage candidate gene-based association study of 30 TLR and 47 CARD genes was performed in the leprosy samples of Chinese Han. Of 4363 SNPs investigated, eight SNPs showed suggestive association (P < 0.01) in our previously published GWAS datasets (Stage 1). Of the eight SNPs, rs2735591 and rs4889841 showed significant association (P < 0.001) in an independent series of 1504 cases and 1502 controls (Stage 2), but only rs2735591 (next to BCL10) showed significant association in the second independent series of 938 cases and 5827 controls (Stage 3). Rs2735591 showed consistent association across the three stages (P > 0.05 for heterogeneity test), significant association in the combined validation samples (P_corrected = 5.54 × 10⁻⁴ after correction for 4363 SNPs tested) and genome-wide significance in the whole GWAS and validation samples (P = 1.03 × 10⁻⁹, OR = 1.24). In addition, we demonstrated the lower expression of BCL10 in leprosy lesions than normal skins and a significant gene connection between BCL10 and the eight previously identified leprosy loci that are associated with NFκB, a major regulator of downstream inflammatory responses, which provides further biological evidence for the association. We have discovered a novel susceptibility locus on 1p22, which implicates BCL10 as a new susceptibility gene for leprosy. Our finding highlights the important role of both innate and adaptive immune responses in leprosy.

Bcl10 links saturated fat overnutrition with hepatocellular NF-kB activation and insulin resistance

Excess serum free fatty acids (FFAs) are fundamental to the pathogenesis of insulin resistance. With high-fat feeding, FFAs activate NF-kB in target tissues, initiating negative crosstalk with insulin signaling. However, the mechanisms underlying FFA-dependent NF-kB activation remain unclear. Here, we demonstrate that the saturated FA, palmitate, requires Bcl10 for NF-kB activation in hepatocytes. Uptake of palmitate, metabolism to diacylglycerol, and subsequent activation of protein kinase C (PKC) appear to mechanistically link palmitate with Bcl10, known as a central component of a signaling complex that, along with CARMA3 and MALT1, activates NF-kB downstream of selected cell surface receptors. Consequently, Bcl10-deficient mice are protected from hepatic NF-kB activation and insulin resistance following brief high-fat diet, suggesting that Bcl10 plays a major role in the metabolic consequences of acute overnutrition. Surprisingly, while CARMA3 also participates in the palmitate response, MALT1 is completely dispensable, thereby revealing an apparent nonclassical role for Bcl10 in NF-kB signaling.

Chronic activation of the kinase IKKβ impairs T cell function and survival

Activation of the transcription factor NF-κB is critical for cytokine production and T cell survival after TCR engagement. The effects of persistent NF-κB activity on T cell function and survival are poorly understood. In this study, using a murine model that expresses a constitutively active form of inhibitor of NF-κB kinase β (caIKKβ) in a T cell-specific manner, we demonstrate that chronic inhibitor of NF-κB kinase β signaling promotes T cell apoptosis, attenuates responsiveness to TCR-mediated stimulation in vitro, and impairs T cell responses to bacterial infection in vivo. caIKKβ T cells showed increased Fas ligand expression and caspase-8 activation, and blocking Fas/Fas ligand interactions enhanced cell survival. T cell unresponsiveness was associated with defects in TCR proximal signaling and elevated levels of B lymphocyte-induced maturation protein 1, a transcriptional repressor that promotes T cell exhaustion. caIKKβ T cells also showed a defect in IL-2 production, and addition of exogenous IL-2 enhanced their survival and proliferation. Conditional deletion of B lymphocyte-induced maturation protein 1 partially rescued the sensitivity of caIKKβ T cells to TCR triggering. Furthermore, adoptively transferred caIKKβ T cells showed diminished expansion and increased contraction in response to infection with Listeria monocytogenes expressing a cognate Ag. Despite their functional defects, caIKKβ T cells readily produced proinflammatory cytokines, and mice developed autoimmunity. In contrast to NF-κB's critical role in T cell activation and survival, our study demonstrates that persistent IKK-NF-κB signaling is sufficient to impair both T cell function and survival.

C-type lectin receptor-induced NF-κB activation in innate immune and inflammatory responses

The C-type lectin receptors (CLRs) belong to a large family of proteins that contain a carbohydrate recognition domain (CRD) and calcium binding sites on their extracellular domains. Recent studies indicate that many CLRs, such as Dectin-1, Dectin-2 and Mincle, function as pattern recognition receptors (PRRs) recognizing carbohydrate ligands from infected microorganisms. Upon ligand binding, these CLRs induce multiple signal transduction cascades through their own immunoreceptor tyrosine-based activation motifs (ITAMs) or interacting with ITAM-containing adaptor proteins such as FcRγ. Emerging evidence indicate that CLR-induced signaling cascades lead to the activation of nuclear factor kappaB (NF-κB) family of transcriptional factors through a Syk- and CARD9-dependent pathway(s). The activation of NF-κB plays a critical role in the induction of innate immune and inflammatory responses following microbial infection and tissue damages. In this review, we will summarize the recent progress on the signal transduction pathways induced by CLRs, and how these CLRs activate NF-κB and contribute to innate immune and inflammatory responses.

Crystal structure of the mucosa-associated lymphoid tissue lymphoma translocation 1 (MALT1) paracaspase region

The mucosa-associated lymphoid tissue lymphoma translocation 1 (MALT1) paracaspase, a key component of the Carma1/Bcl10/MALT1 signalosome, is critical for NF-κB signaling in multiple contexts. MALT1 is thought to function as a scaffold and protease to promote signaling; however, the biochemical and structural basis of paracaspase action remains largely unknown. Here we report the 1.75-Å resolution crystal structure of the MALT1 paracaspase region, which contains the paracaspase domain and an ensuing Ig-like domain. The paracaspase and the Ig domains appear as a single folding unit and interact with each other through extensive van der Waals contacts and hydrogen bonds. The paracaspase domain adopts a fold that is nearly identical to that of classic caspases and homodimerizes similarly to form an active protease. Unlike caspases, the active and mature form of the paracaspase domain remains a single uncleaved polypeptide and specifically recognizes the bound peptide inhibitor Val-Arg-Pro-Arg. In particular, the carboxyl-terminal amino acid Arg of the inhibitor is coordinated by three highly conserved acidic residues. This structure serves as an important framework for deciphering the function and mechanism of paracaspases exemplified by MALT1.

Specific effects of BCL10 Serine mutations on phosphorylations in canonical and noncanonical pathways of NF-κB activation following carrageenan

To determine the impact of B cell leukemia/lymphoma (BCL) 10 on the phosphorylation of crucial mediators in NF-κB-mediated inflammatory pathways, human colonic epithelial cells were exposed to carrageenan (CGN), a sulfated polysaccharide commonly used as a food additive and known to induce NF-κB nuclear translocation by both canonical and noncanonical pathways. Phosphorylations of intermediates in inflammatory cascades, including NF-κB-inducing kinase (NIK) at Thr(559), transforming growth factor-β-activating kinase (TAK) 1 at Thr(184), Thr(187), and Ser(192), and inhibitory factor κBα (IκBα) at Ser(32), were examined following mutation of BCL10 at Ser(138) and at Ser(218). Specific phosphoantibodies were used for detection by enzyme-linked immunosorbent assay, immunoblot, and confocal microscopy of differences in phosphorylation following transfection by mutated BCL10. Both mutations demonstrated dominant-negative effects, with inhibition of phospho(Ser(32))-IκBα to less than control levels. Both of the BCL10 mutations reduced the CGN-induced increases in nuclear RelA and p50, but only the Ser(138) mutation inhibited the CGN-induced increases in nuclear RelB and p52 and in NIK Thr(559) phosphorylation. Hence, the phosphorylation of BCL10 Ser(138), but not Ser(218), emerged as a critical event in activation of the noncanonical pathway of NF-κB activation. Either BCL10 Ser(138) or Ser(218) mutation inhibited the phosphorylation of TAK1 at Thr(184) and at Thr(187), but not at Ser(192). These findings indicate that BCL10 phosphorylations act upstream of phosphorylations of NIK, TAK1, and IκBα and differentially affect the canonical and noncanonical pathways of NF-κB activation.

NF-κB signaling pathways regulated by CARMA family of scaffold proteins

The NF-κB family of transcription factors plays a crucial role in cell activation, survival and proliferation. Its aberrant activity results in cancer, immunodeficiency or autoimmune disorders. Over the past two decades, tremendous progress has been made in our understanding of the signals that regulate NF-κB activation, especially how scaffold proteins link different receptors to the NF-κB-activating complex, the IκB kinase complex. The growing number of these scaffolds underscores the complexity of the signaling networks in different cell types. In this review, we discuss the role of scaffold molecules in signaling cascades induced by stimulation of antigen receptors, G-protein-coupled receptors and C-type Lectin receptors, resulting in NF-κB activation. Especially, we focus on the family of Caspase recruitment domain (CARD)-containing proteins known as CARMA and their function in activation of NF-κB, as well as the link of these scaffolds to the development of various neoplastic diseases through regulation of NF-κB.

Thrombin-dependent NF-{kappa}B activation and monocyte/endothelial adhesion are mediated by the CARMA3·Bcl10·MALT1 signalosome

Thrombin is a potent modulator of endothelial function and, through stimulation of NF-κB, induces endothelial expression of intracellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1). These cell surface adhesion molecules recruit inflammatory cells to the vessel wall and thereby participate in the development of atherosclerosis, which is increasingly recognized as an inflammatory condition. The principal receptor for thrombin on endothelial cells is protease-activated receptor-1 (PAR-1), a member of the G protein-coupled receptor superfamily. Although it is known that PAR-1 signaling to NF-κB depends on initial PKC activation, the subsequent steps leading to stimulation of the canonical NF-κB machinery have remained unclear. Here, we demonstrate that a complex of proteins containing CARMA3, Bcl10, and MALT1 links PAR-1 activation to stimulation of the IκB kinase complex. IκB kinase in turn phosphorylates IκB, leading to its degradation and the release of active NF-κB. Further, we find that although this CARMA3·Bcl10·MALT1 signalosome shares features with a CARMA1-containing signalosome found in lymphocytes, there are significant differences in how the signalosomes communicate with their cognate receptors. Specifically, whereas the CARMA1-containing lymphocyte complex relies on 3-phosphoinositide-dependent protein kinase 1 for assembly and activation, the CARMA3-containing endothelial signalosome functions completely independent of 3-phosphoinositide-dependent protein kinase 1 and instead relies on β-arrestin 2 for assembly. Finally, we show that thrombin-dependent adhesion of monocytes to endothelial cells requires an intact endothelial CARMA3·Bcl10·MALT1 signalosome, underscoring the importance of the signalosome in mediating one of the most significant pro-atherogenic effects of thrombin.

Tumor necrosis factor receptor-associated factor-6 and ribosomal S6 kinase intracellular pathways link the angiotensin II AT1 receptor to the phosphorylation and activation of the IkappaB kinase complex in vascular smooth muscle cells

Activation of NF-κB transcription factors by locally produced angiotensin II (Ang II) is proposed to be involved in chronic inflammatory reactions leading to atherosclerosis development. However, a clear understanding of the signaling cascades coupling the Ang II AT1 receptors to the activation of NF-κB transcription factors is still lacking. Using primary cultured aortic vascular smooth muscle cells, we show that activation of the IKK complex and NF-κB transcription factors by Ang II is regulated by phosphorylation of the catalytic subunit IKKβ on serine residues 177 and 181 in the activation T-loop. The use of pharmacological inhibitors against conventional protein kinases C (PKCs), mitogen-activated/extracellular signal-regulated kinase (MEK) 1/2, ribosomal S6 kinase (RSK), and silencing RNA technology targeting PKCα, IKKβ subunit, tumor growth factor β-activating kinase-1 (TAK1), the E3 ubiquitin ligase tumor necrosis factor receptor-associated factor-6 (TRAF6), and RSK isoforms, demonstrates the requirement of two distinct signaling pathway for the phosphorylation of IKKβ and the activation of the IKK complex by Ang II. Rapid phosphorylation of IKKβ requires a second messenger-dependent pathway composed of PKCα-TRAF6-TAK1, whereas sustained phosphorylation and activation of IKKβ requires the MEK1/2-ERK1/2-RSK pathway. Importantly, simultaneously targeting components of these two pathways completely blunts the phosphorylation of IKKβ and the proinflammatory effect of the octapeptide. This is the first report demonstrating activation of TAK1 by the AT1R. We propose a model whereby TRAF6-TAK1 and ERK-RSK intracellular pathways independently and sequentially converge to the T-loop phosphorylation for full activation of IKKβ, which is an essential step in the proinflammatory activity of Ang II.

Antigen receptor signaling to NF-kappaB via CARMA1, BCL10, and MALT1

The signaling pathway controlling antigen receptor-induced regulation of the transcription factor NF-kappaB plays a key role in lymphocyte activation and development and the generation of lymphomas. Work of the past decade has led to dramatic progress in the identification and characterization of new players in the pathway. Moreover, novel enzymatic activities relevant for this pathway have been discovered, which represent interesting drug targets for immuno-suppression or lymphoma treatment. Here, we summarize these findings and give an outlook on interesting open issues that need to be addressed in the future.

The CARMA3-Bcl10-MALT1 signalosome promotes angiotensin II-dependent vascular inflammation and atherogenesis

The CARMA1, Bcl10, and MALT1 proteins together constitute a signaling complex (CBM signalosome) that mediates antigen-dependent activation of NF-kappaB in lymphocytes, thereby representing a cornerstone of the adaptive immune response. Although CARMA1 is restricted to cells of the immune system, the analogous CARMA3 protein has a much wider expression pattern. Emerging evidence suggests that CARMA3 can substitute for CARMA1 in non-immune cells to assemble a CARMA3-Bcl10-MALT1 signalosome and mediate G protein-coupled receptor activation of NF-kappaB. Here we show that one G protein-coupled receptor, the type 1 receptor for angiotensin II, utilizes this mechanism for activation of NF-kappaB in endothelial and vascular smooth muscle cells, thereby inducing pro-inflammatory signals within the vasculature, a key factor in atherogenesis. Further, we demonstrate that Bcl10-deficient mice are protected from developing angiotensin-dependent atherosclerosis and aortic aneurysms. By uncovering a novel vascular role for the CBM signalosome, these findings illustrate that CBM-dependent signaling has functions outside the realm of adaptive immunity and impacts pathobiology more broadly than previously known.

L-CBM signaling in lymphocyte development and function

The nuclear factor-κB (NF-κB) plays a central role in the activation and survival of lymphocytes. NF-κB, therefore, is pivotal for acquired immunity, but the dysregulation of NF-κB signaling leads to inflammatory diseases and lymphomagenesis. Accumulating evidence has demonstrated that the mucosa-associated lymphoid tissue (MALT) lymphoma-related molecules, B-cell lymphoma 10 (BCL10) and MALT-lymphoma-translocation gene1 (MALT1), are essential signaling components for NF-κB and mitogen-activated protein kinase (MAPK) activation, mediated by the immunoreceptor tyrosine-based activation motif (ITAM)-coupled receptors involved in both innate and adaptive immunity. CARMA1 (also referred to as CARD11 and Bimp3) is a crucial regulator for ITAM-mediated signaling as it forms a complex with BCL10-MALT1 in lymphoid lineage cells such as T, B, natural killer (NK), and natural killer T (NKT) cells, known as the lymphoid CARMA1-BCL10-MALT1 (L-CBM) complex. In this review, recent understanding of the molecular and biological functions and the signal regulation mechanisms of the L-CBM complex are described and its role in disease development and potential as a therapeutic target is further discussed.

Platelet-activating factor-induced NF-kappaB activation and IL-8 production in intestinal epithelial cells are Bcl10-dependent

BACKGROUND

Platelet-activating factor (PAF), a potent proinflammatory phospholipid mediator, has been implicated in inducing intestinal inflammation in diseases such as inflammatory bowel disease (IBD) and necrotizing enterocolitis (NEC). However, its mechanisms of inducing inflammatory responses are not fully understood. Therefore, studies were designed to explore the mechanisms of PAF-induced inflammatory cascade in intestinal epithelial cells.

METHODS

Nuclear factor kappa B (NF-kappaB) activation was measured by luciferase assay and enzyme-linked immunosorbent assay (ELISA), and interleukin 8 (IL-8) production was determined by ELISA. B-cell lymphoma 10 (Bcl10), caspase recruitment domain-containing membrane-associated guanylate kinase protein 3 (CARMA3), and mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) mRNA and protein levels were assessed by real-time reverse-transcription polymerase chain reaction (RT-PCR) and Western blot, respectively. siRNA silencing of Bcl10 was used to examine its role in PAF-induced NF-kappaB activation and IL-8 production. The promoter region of the Bcl10 gene was cloned with the PCR method and promoter activity measured by luciferase assay.

RESULTS

The adaptor protein Bcl10 appeared to play an important role in the PAF-induced inflammatory pathway in human intestinal epithelial cells. Bcl10 was required for PAF-induced I kappaB alpha phosphorylation, NF-kappaB activation, and IL-8 production in NCM460, a cell line derived from normal human colon, and Caco-2, a transformed human intestinal cell line. PAF also stimulated Bcl10 interactions with CARMA3 and MALT1, and upregulated Bcl10 expression in these cells via transcriptional regulation.

CONCLUSIONS

These findings highlight a novel PAF-induced inflammatory pathway in intestinal epithelial cells, requiring Bcl10 as a critical mediator and involving CARMA3/Bcl10/MALT1 interactions. The proinflammatory effects of PAF play prominent roles in the pathogenesis of IBD and this pathway may present important targets for intervention in chronic inflammatory diseases of the intestine.

KiSS1 suppresses TNFalpha-induced breast cancer cell invasion via an inhibition of RhoA-mediated NF-kappaB activation

Tumor necrosis factor-alpha (TNFalpha) induces cancer development and metastasis, which is prominently achieved by nuclear factor-kappa B (NF-kappaB) activation. TNFalpha-induced NF-kappaB activation enhances cellular mechanisms including proliferation, migration, and invasion. KiSS1, a key regulator of puberty, was initially discovered as a tumor metastasis suppressor. The expression of KiSS1 was lost or down-regulated in different metastatic tumors. However, it is unclear whether KiSS1 regulates TNFalpha-induced NF-kappaB activation and further tumor cell migration. In this study, we demonstrate that KiSS1 suppresses the migration of breast cancer cells by inhibiting TNFalpha-induced NF-kappaB pathway and RhoA activation. Both KiSS1 overexpression and KP10 (kisspeptin-10) stimulation inhibited TNFalpha-induced NF-kappaB activity, suppressed TNFalpha-induced cell migration and cell attachment to fibronectin in breast cancer cells while KP10 has little effect on cancer cell proliferation. Furthermore, KP10 inhibited TNFalpha-induced cell migration and RhoA GTPase activation. Therefore, our data demonstrate that KiSS1 inhibits TNFalpha-induced NF-kappaB activation via downregulation of RhoA activation and suppression of breast cancer cell migration and invasion.

CARD9 versus CARMA1 in innate and adaptive immunity

Nuclear factor-kappaB (NF-kappaB) and mitogen-activated protein kinases (MAPKs) are activated upon engagement of a wide variety of immunoreceptors. Accumulating evidence has demonstrated that B-cell lymphoma 10 (BCL10) and mucosa-associated lymphoid tissue (MALT1) are essential signaling components for NF-kappaB and MAPK activation mediated by immunoreceptor tyrosine-based activation motif (ITAM)-coupled receptors in both adaptive and innate immunity. Recent studies have revealed that two caspase-recruitment domain (CARD) family adaptor molecules, CARD-containing MAGUK protein 1 (CARMA1) and CARD9, are crucial regulators of the ITAM-mediated signaling pathway by forming a complex with BCL10-MALT1 in lymphoid and myeloid cells, respectively. Here, we describe the immune responses and the cell-type-specific regulation mechanisms for NF-kappaB and MAPK activation controlled by CARMA1 and CARD9 through innate and adaptive immunoreceptors.

A P2X ion channel-triggered NF-kappaB pathway enhances TNF-alpha-induced IL-8 expression in airway epithelial cells

Extracellular ATP, acting at P2Y and P2X receptors, has recently been shown to contribute to airway inflammation. The aim of our study was to investigate the molecular mechanisms involved in the ATP-dependent regulation of IL-8 production by airway epithelial cells. Treatment of human normal tracheal (NT)-1 cells with ATP or its two analogs, alpha,beta-methylene ATP (alpha,beta-meATP) and 2'- and 3'-O-(4-benzoyl-benzoyl)-ATP (BzATP) activated NF-kappaB through the IkappaB kinase (IKK) complex, a process requiring Ca(2+), calmodulin (CaM), and Ca(2+)/CaM-dependent kinase (CaMK), but independent from phospholipase C. alpha,beta-meATP-induced IKK activation also occurred in the alveolar A549 cell line. Real-time RT-PCR revealed that NT-1 and A549 cells expressed P2X(4), P2X(5),and P2X(6) subtype mRNAs, whereas P2X(7) mRNAs were only detected in NT-1 cells. Polarized human primary nasal epithelial cells expressed all four P2X subtypes. Both alpha,beta-meATP and BzATP caused Ca(2+)-dependent binding of phosphorylated p65 (S536) NF-kappaB subunit to the endogenous IL-8 gene promoter in NT-1 cells. Although these agonists did not induce significant IL-8 gene expression by these cells, they markedly enhanced TNF-alpha-induced NF-kappaB activation, resulting in increased IL-8 expression and release. Application of alpha,beta-meATP or BzATP at the apical side of polarized human primary nasal epithelial cells sufficed to cause CaMK-dependent IL-8 release by these cells. Thus, ATP promotes TNF-alpha-elicited IL-8 expression through P2X ion channel-triggered Ca(2+) entry, leading to CaMK-dependent IKK activation and binding of active p65 to IL-8 gene promoter.

G protein-coupled receptor connectivity to NF-kappaB in inflammation and cancer

Complex intracellular network interactions regulate gene expression and cellular behavior. Whether at the site of inflammation or within a tumor, individual cells are exposed to a plethora of signals. The transcription factor nuclear factor-kappaB (NF-kappaB) regulates genes that control key cellular activities involved in inflammatory diseases and cancer. NF-kappaB is regulated by several distinct signaling pathways that may be activated individually or simultaneously. Multiple ligands and heterologous cell-cell interactions have an impact on NF-kappaB activity. The G protein-coupled receptor (GPCR) superfamily makes up the largest class of transmembrane receptors in the human genome and has multiple molecularly distinct natural ligands. GPCRs regulate proliferation, differentiation, and chemotaxis and play a major role in inflammatory diseases and cancer. Both GPCRs and NF-kappaB have been, and continue to be, major targets for drug discovery. A clear understanding of network interactions between GPCR signaling pathways and those that control NF-kB may be valuable for the development of better drugs and drug combinations.

IAP-targeted therapies for cancer

DNA damage, chromosomal abnormalities, oncogene activation, viral infection, substrate detachment and hypoxia can all trigger apoptosis in normal cells. However, cancer cells acquire mutations that allow them to survive these threats that are part and parcel of the transformation process or that may affect the growth and dissemination of the tumor. Eventually, cancer cells accumulate further mutations that make them resistant to apoptosis mediated by standard cytotoxic chemotherapy or radiotherapy. The inhibitor of apoptosis (IAP) family members, defined by the presence of a baculovirus IAP repeat (BIR) protein domain, are key regulators of cytokinesis, apoptosis and signal transduction. Specific IAPs regulate either cell division, caspase activity or survival pathways mediated through binding to their BIR domains, and/or through their ubiquitin-ligase RING domain activity. These protein-protein interactions and post-translational modifications are the subject of intense investigations that shed light on how these proteins contribute to oncogenesis and resistance to therapy. In the past several years, we have seen multiple approaches of IAP antagonism enter the clinic, and the rewards of such strategies are about to reap benefit. Significantly, small molecule pan-IAP antagonists that mimic an endogenous inhibitor of the IAPs, called Smac, have demonstrated an unexpected ability to sensitize cancer cells to tumor necrosis factor-alpha and to promote autocrine or paracrine production of this cytokine by the tumor cell and possibly, other cells too. This review will focus on these and other developmental therapeutics that target the IAPs in cancer.

A global transcriptional view of apoptosis in human T-cell activation

Background

T-cell activation is an essential step of immune response. The process of proper T-cell activation is strictly monitored and regulated by apoptosis signaling. Yet, regulation of apoptosis, an integral and crucial facet during the process of T-cell activation, is not well understood.

Methods

In this study, a Gene-Ontology driven global gene expression analysis coupled with protein abundance and activity assays identified genes and pathways associated with regulation of apoptosis in primary human CD3+ T cells and separately CD4+ and CD8+ T cells.

Results

We identified significantly regulated apoptotic genes in several protein families, such as BCL2 proteins, CASPASE proteins, and TNF receptors, and detailed their transcriptional kinetics during the T-cell activation process. Transcriptional patterns of a few select genes (BCL2A1, BBC3 and CASP3) were validated at the protein level. Many of these apoptotic genes are involved in NF-κB signaling pathway, including TNFRSF10A, TNFRSF10B, TRAF4, TRAF1, TRAF3, and TRAF6. Upregulation of NF-κB and IκB family genes (REL, RELA, and RELB, NFKBIA, NFKBIE and NFKB1) at 48 to 96 hours, supported by the increase of phosphorylated RELA (p65), suggests that the involvement of the NF-κB complex in the process of T-cell proliferation is not only regulated at the protein level but also at the transcriptional level. Examination of genes involved in MAP kinase signalling pathway, important in apoptosis, suggests an induction of p38 and ERK1 cascades in T-cell proliferation (at 48 to 96 hours), which was explored using phosphorylation assays for p38 (MAPK14) and ERK1 (MAPK3). An immediate and short-lived increase of AP-1 activity measured by DNA-binding activity suggests a rapid and transient activation of p38 and/or JNK cascades upon T-cell activation.

Conclusion

This comparative genome-scale, transcriptional analysis of T-cell activation in the CD4+ and CD8+ subsets and the mixed CD3+ population identified many apoptosis genes not previously identified in the context of T-cell activation. Furthermore, it provided a comprehensive temporal analysis of the transcriptional program of apoptosis associated with T-cell activation.

Multiple protein domains mediate interaction between Bcl10 and MALT1

Bcl10 and MALT1 are essential mediators of NF-kappaB activation in response to the triggering of a diverse array of transmembrane receptors, including antigen receptors. Additionally, both proteins are translocation targets in MALT lymphoma. Thus, a detailed understanding of the interaction between these mediators is of considerable biological importance. Previous studies have indicated that a 13-amino acid region downstream of the Bcl10 caspase recruitment domain (CARD) is responsible for interacting with the immunoglobulin-like domains of MALT1. We now provide evidence that the death domain of MALT1 and the CARD of Bcl10 also contribute to Bcl10-MALT1 interactions. Although a direct interaction between the MALT1 death domain and Bcl10 cannot be detected via immunoprecipitation, FRET data strongly suggest that the death domain of MALT1 contributes significantly to the association between Bcl10 and MALT1 in T cells in vivo. Furthermore, analysis of point mutants of conserved residues of Bcl10 shows that the Bcl10 CARD is essential for interaction with the MALT1 N terminus. Mutations that disrupt proper folding of the Bcl10 CARD strongly impair Bcl10-MALT1 interactions. Molecular modeling and functional analyses of Bcl10 point mutants suggest that residues Asp(80) and Glu(84) of helix 5 of the Bcl10 CARD directly contact MALT1. Together, these data demonstrate that the association between Bcl10 and MALT1 involves a complex interaction between multiple protein domains. Moreover, the Bcl10-MALT1 interaction is the second reported example of interactions between a CARD and a non-CARD protein region, which suggests that many signaling cascades may utilize CARD interactions with non-CARD domains.

Multifunctional roles for MALT1 in T-cell activation

The activation of T cells is vital to the successful elimination of pathogens, but can also have a deleterious role in autoimmunity and transplant rejection. Various signalling pathways are triggered by the T-cell receptor; these have key roles in the control of the T-cell response and represent interesting targets for therapeutic immunomodulation. Recent findings define MALT1 (mucosa-associated-lymphoid-tissue lymphoma-translocation gene 1) as a protein with proteolytic activity that controls T-cell activation by regulating key molecules in T-cell-receptor-induced signalling pathways.

Nod-like proteins in inflammation and disease

The field of innate immunity has undergone an enormous upheaval during the last decade. The discovery of different groups of proteins, called pattern recognition molecules (PRMs), which detect microbial components, so-called pathogen-associated molecular patterns (PAMPs) and trigger protective responses, had a huge impact on the understanding of innate immune responses. Among the PRMs, the intracellular Nod-like receptors (NLRs) have recently been identified as key mediators of inflammatory and immune responses. The NLR family is divided into subfamilies on the basis of their different signal transduction domains, and recent studies have highlighted the role of certain NLRs, including Nod1, Nod2, Nalp3, Ipaf and Naip5, in the detection of intracellular microbes and possibly 'danger signals'. In this review, we summarize the current knowledge on the function of these proteins in immunity and inflammation, with a focus on their participation in different disease pathologies.