CARMA1 coiled-coil domain is involved in the oligomerization and subcellular localization of CARMA1 and is required for T cell receptor-induced NF-kappaB activation

Dominant interfering CARD11 variants disrupt JNK signaling to promote GATA3 expression in T cells

Several "primary atopic disorders" are linked to monogenic defects that attenuate TCR signaling, favoring T helper type 2 (TH2) cell differentiation. Patients with CARD11-associated atopy with dominant interference of NF-κB signaling (CADINS) disease suffer from severe atopy, caused by germline loss-of-function/dominant interfering (LOF/DI) CARD11 variants. The CARD11 scaffold enables TCR-induced activation of NF-κB, mTORC1, and JNK signaling, yet the function of CARD11-dependent JNK signaling in T cells remains nebulous. Here we show that CARD11 is critical for TCR-induced activation of JNK1 and JNK2, as well as canonical JUN/FOS AP-1 family members. Patient-derived CARD11 DI variants attenuated WT CARD11 JNK signaling, mirroring effects on NF-κB. Transcriptome profiling revealed JNK inhibition upregulated TCR-induced expression of GATA3 and NFATC1, key transcription factors for TH2 cell development. Further, impaired CARD11-JNK signaling was linked to enhanced GATA3 expression in CADINS patient T cells. Our findings reveal a novel intrinsic mechanism connecting impaired CARD11-dependent JNK signaling to enhanced GATA3/NFAT2 induction and TH2 cell differentiation in CADINS patients.

Chimeric and mutant CARD9 constructs enable analyses of conserved and diverged autoinhibition mechanisms in the CARD-CC protein family

Caspase recruitment domain-containing protein (CARD)9, CARD10, CARD11, and CARD14 all belong to the CARD-coiled coil (CC) protein family and originated from a single common ancestral protein early in vertebrate evolution. All four proteins form CARD-CC/BCL10/MALT1 (CBM) complexes leading to nuclear factor-kappa-B (NF-κB) activation after upstream phosphorylation by various protein kinase C (PKC) isoforms. CBM complex signaling is critical for innate and adaptive immunity, but aberrant activation can cause autoimmune or autoinflammatory diseases, or be oncogenic. CARD9 shows a superior auto-inhibition compared with other CARD-CC family proteins, with very low spontaneous activity when overexpressed in HEK293T cells. In contrast, the poor auto-inhibition of other CARD-CC family proteins, especially CARD10 (CARMA3) and CARD14 (CARMA2), is hampering characterization of upstream activators or activating mutations in overexpression studies. We grafted different domains from CARD10, 11, and 14 on CARD9 to generate chimeric CARD9 backbones for functional characterization of activating mutants using NF-κB reporter gene activation in HEK293T cells as readout. CARD11 (CARMA1) activity was not further reduced by grafting on CARD9 backbones. The chimeric CARD9 approach was subsequently validated by using several known disease-associated mutations in CARD10 and CARD14, and additional screening allowed us to identify several previously unknown activating natural variants in human CARD9 and CARD10. Using Genebass as a resource of exome-based disease association statistics, we found that activated alleles of CARD9 correlate with irritable bowel syndrome (IBS), constipation, osteoarthritis, fibromyalgia, insomnia, anxiety, and depression, which can occur as comorbidities.

CARMA3: A potential therapeutic target in non-cancer diseases

Caspase recruitment domain and membrane-associated guanylate kinase-like protein 3 (CARMA3) is a scaffold protein widely expressed in non-hematopoietic cells. It is encoded by the caspase recruitment domain protein 10 (CARD10) gene. CARMA3 can form a CARMA3-BCL10-MALT1 complex by recruiting B cell lymphoma 10 (BCL10) and mucosa-​associated lymphoid tissue lymphoma translocation protein 1 (MALT1), thereby activating nuclear factor-​κB (NF-κB), a key transcription factor that involves in various biological responses. CARMA3 mediates different receptors-dependent signaling pathways, including G protein-coupled receptors (GPCRs) and receptor tyrosine kinases (RTKs). Inappropriate expression and activation of GPCRs and/or RTKs/CARMA3 signaling lead to the pathogenesis of human diseases. Emerging studies have reported that CARMA3 mediates the development of various types of cancers. Moreover, CARMA3 and its partners participate in human non-cancer diseases, including atherogenesis, abdominal aortic aneurysm, asthma, pulmonary fibrosis, liver fibrosis, insulin resistance, inflammatory bowel disease, and psoriasis. Here we provide a review on its structure, regulation, and molecular function, and further highlight recent findings in human non-cancerous diseases, which will provide a novel therapeutic target.

Mechanistic impact of oligomer poisoning by dominant-negative CARD11 variants

The CARD11 scaffold controls antigen receptor signaling to NF-κB, JNK, and mTOR. Three classes of germline mutations in CARD11 cause Primary Immunodeficiency, including homozygous loss-of-function (LOF) mutations in CARD11 deficiency, heterozygous gain-of-function (GOF) mutations in BENTA disease, and heterozygous dominant-negative LOF mutations in CADINS. Here, we characterize LOF CARD11 mutants with a range of dominant-negative activities to identify the mechanistic properties that cause these variants to exert dominant effects when heterozygous. We find that strong dominant negatives can poison signaling from mixed wild-type:mutant oligomers at two steps in the CARD11 signaling cycle, at the Opening Step and at the Cofactor Association Step. Our findings provide evidence that CARD11 oligomer subunits cooperate in at least two steps during antigen receptor signaling and reveal how different LOF mutations in the same oligomeric signaling hub may cause disease with different inheritance patterns.

CCDC167 as a potential therapeutic target and regulator of cell cycle-related networks in breast cancer

According to cancer statistics reported in 2020, breast cancer constitutes 30% of new cancer cases diagnosed in American women. Histological markers of breast cancer are expressions of the estrogen receptor (ER), the progesterone receptor (PR), and human epidermal growth factor receptor (HER)-2. Up to 80% of breast cancers are grouped as ER-positive, which implies a crucial role for estrogen in breast cancer development. Therefore, identifying potential therapeutic targets and investigating their downstream pathways and networks are extremely important for drug development in these patients. Through high-throughput technology and bioinformatics screening, we revealed that coiled-coil domain-containing protein 167 (CCDC167) was upregulated in different types of tumors; however, the role of CCDC167 in the development of breast cancer still remains unclear. Integrating many kinds of databases including ONCOMINE, MetaCore, IPA, and Kaplan-Meier Plotter, we found that high expression levels of CCDC167 predicted poor prognoses of breast cancer patients. Knockdown of CCDC167 attenuated aggressive breast cancer growth and proliferation. We also demonstrated that treatment with fluorouracil, carboplatin, paclitaxel, and doxorubicin resulted in decreased expression of CCDC167 and suppressed growth of MCF-7 cells. Collectively, these findings suggest that CCDC167 has high potential as a therapeutic target for breast cancer.

Critical protein-protein interactions within the CARMA1-BCL10-MALT1 complex: Take-home points for the cell biologist

The CBM complex, which is composed of the proteins CARMA1, BCL10, and MALT1, serves multiple pivotal roles as a mediator of T-cell receptor and B-cell receptor-dependent NF-κB induction and lymphocyte activation. CARMA1, BCL10, and MALT1 are each proto-oncoproteins and dysregulation of CBM signaling, as a result of somatic gain-of-function mutation or chromosomal translocation, is a hallmark of multiple lymphoid malignancies including Activated B-cell Diffuse Large B-cell Lymphoma. Moreover, loss-of-function as well as gain-of-function germline mutations in CBM complex proteins have been associated with a range of immune dysregulation syndromes. A wealth of detailed structural information has become available over the past decade through meticulous interrogation of the interactions between CBM components. Here, we review key findings regarding the biochemical nature of these protein-protein interactions which have ultimately led the field to a sophisticated understanding of how these proteins assemble into high-order filamentous CBM complexes. To date, approaches to therapeutic inhibition of the CBM complex for the treatment of lymphoid malignancy and/or auto-immunity have focused on blocking MALT1 protease function. We also review key studies relating to the structural impact of MALT1 protease inhibitors on key protein-protein interactions.

Gain-of-function mutations in CARD11 promote enhanced aggregation and idiosyncratic signalosome assembly

BENTA (B cell Expansion with NF-κB and T cell Anergy) is a novel lymphoproliferative disorder caused by germline, gain-of-function (GOF) mutations in the lymphocyte-restricted scaffolding protein CARD11. Similar somatic CARD11 mutations are found in lymphoid malignancies such as diffuse large B cell lymphoma (DLBCL). Normally, antigen receptor (AgR) engagement converts CARD11 into an active conformation that nucleates a signalosome required for IκB kinase (IKK) activation and NF-κB nuclear translocation. However, GOF CARD11 mutants drive constitutive NF-κB activity without AgR stimulation. Here we show that unlike wild-type CARD11, GOF CARD11 mutants can form large, peculiar cytosolic protein aggregates we term mCADS (mutant CARD11 dependent shells). MALT1 and phospho-IKK are reliably colocalized with mCADS, indicative of active signaling. Moreover, endogenous mCADS are detectable in ABC-DLBCL lines harboring similar GOF CARD11 mutations. The unique aggregation potential of GOF CARD11 mutants may represent a novel therapeutic target for treating BENTA or DLBCL.

Hypomorphic caspase activation and recruitment domain 11 (CARD11) mutations associated with diverse immunologic phenotypes with or without atopic disease

BACKGROUND

Caspase activation and recruitment domain 11 (CARD11) encodes a scaffold protein in lymphocytes that links antigen receptor engagement with downstream signaling to nuclear factor κB, c-Jun N-terminal kinase, and mechanistic target of rapamycin complex 1. Germline CARD11 mutations cause several distinct primary immune disorders in human subjects, including severe combined immune deficiency (biallelic null mutations), B-cell expansion with nuclear factor κB and T-cell anergy (heterozygous, gain-of-function mutations), and severe atopic disease (loss-of-function, heterozygous, dominant interfering mutations), which has focused attention on CARD11 mutations discovered by using whole-exome sequencing.

OBJECTIVES

We sought to determine the molecular actions of an extended allelic series of CARD11 and to characterize the expanding range of clinical phenotypes associated with heterozygous CARD11 loss-of-function alleles.

METHODS

Cell transfections and primary T-cell assays were used to evaluate signaling and function of CARD11 variants.

RESULTS

Here we report on an expanded cohort of patients harboring novel heterozygous CARD11 mutations that extend beyond atopy to include other immunologic phenotypes not previously associated with CARD11 mutations. In addition to (and sometimes excluding) severe atopy, heterozygous missense and indel mutations in CARD11 presented with immunologic phenotypes similar to those observed in signal transducer and activator of transcription 3 loss of function, dedicator of cytokinesis 8 deficiency, common variable immunodeficiency, neutropenia, and immune dysregulation, polyendocrinopathy, enteropathy, X-linked-like syndrome. Pathogenic variants exhibited dominant negative activity and were largely confined to the CARD or coiled-coil domains of the CARD11 protein.

CONCLUSION

These results illuminate a broader phenotypic spectrum associated with CARD11 mutations in human subjects and underscore the need for functional studies to demonstrate that rare gene variants encountered in expected and unexpected phenotypes must nonetheless be validated for pathogenic activity.

A Unique Heterozygous CARD11 Mutation Combines Pathogenic Features of Both Gain- and Loss-of-Function Patients in a Four-Generation Family

CARD11 is a lymphocyte-specific scaffold molecule required for proper activation of B- and T-cells in response to antigen. Germline gain-of-function (GOF) mutations in the CARD11 gene cause a unique B cell lymphoproliferative disorder known as B cell Expansion with NF-κB and T cell Anergy (BENTA). In contrast, patients carrying loss-of-function (LOF), dominant negative (DN) CARD11 mutations present with severe atopic disease. Interestingly, both GOF and DN CARD11 variants cause primary immunodeficiency, with recurrent bacterial and viral infections, likely resulting from impaired adaptive immune responses. This report describes a unique four-generation family harboring a novel heterozygous germline indel mutation in CARD11 (c.701-713delinsT), leading to one altered amino acid and a deletion of 4 others (p.His234_Lys238delinsLeu). Strikingly, affected members exhibit both moderate B cell lymphocytosis and atopic dermatitis/allergies. Ectopic expression of this CARD11 variant stimulated constitutive NF-κB activity in T cell lines, similar to other BENTA patient mutations. However, unlike other GOF mutants, this variant significantly impeded the ability of wild-type CARD11 to induce NF-κB activation following antigen receptor ligation. Patient lymphocytes display marked intrinsic defects in B cell differentiation and reduced T cell responsiveness in vitro. Collectively, these data imply that a single heterozygous CARD11 mutation can convey both GOF and DN signaling effects, manifesting in a blended BENTA phenotype with atopic features. Our findings further emphasize the importance of balanced CARD11 signaling for normal immune responses.

Ubiquitination and phosphorylation of the CARD11-BCL10-MALT1 signalosome in T cells

Antigen receptor-induced signaling plays an important role in inflammation and immunity. Formation of a CARD11-BCL10-MALT1 (CBM) signaling complex is a key event in T- and B cell receptor-induced gene expression by regulating NF-κB activation and mRNA stability. Deregulated CARD11, BCL10 or MALT1 expression or CBM signaling have been associated with immunodeficiency, autoimmunity and cancer, indicating that CBM formation and function have to be tightly regulated. Over the past years great progress has been made in deciphering the molecular mechanisms of assembly and disassembly of the CBM complex. In this context, several posttranslational modifications play an indispensable role in regulating CBM function and downstream signal transduction. In this review we summarize how the different CBM components as well as their interplay are regulated by protein ubiquitination and phosphorylation in the context of T cell receptor signaling.

Loss-of-function mutations in caspase recruitment domain-containing protein 14 (CARD14) are associated with a severe variant of atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is a highly prevalent chronic inflammatory skin disease that is known to be, at least in part, genetically determined. Mutations in caspase recruitment domain-containing protein 14 (CARD14) have been shown to result in various forms of psoriasis and related disorders.

OBJECTIVE

We aimed to identify rare DNA variants conferring a significant risk for AD through genetic and functional studies in a cohort of patients affected with severe AD.

METHODS

Whole-exome and direct gene sequencing, immunohistochemistry, real-time PCR, ELISA, and functional assays in human keratinocytes were used.

RESULTS

In a cohort of patients referred with severe AD, DNA sequencing revealed in 4 patients 2 rare heterozygous missense mutations in the gene encoding CARD14, a major regulator of nuclear factor κB (NF-κB). A dual luciferase reporter assay demonstrated that both mutations exert a dominant loss-of-function effect and result in decreased NF-κB signaling. Accordingly, immunohistochemistry staining showed decreased expression of CARD14 in patients' skin, as well as decreased levels of activated p65, a surrogate marker for NF-κB activity. CARD14-deficient or mutant-expressing keratinocytes displayed abnormal secretion of key mediators of innate immunity.

CONCLUSIONS

Although dominant gain-of-function mutations in CARD14 are associated with psoriasis and related diseases, loss-of-function mutations in the same gene are associated with a severe variant of AD.

Holding All the CARDs: How MALT1 Controls CARMA/CARD-Dependent Signaling

The scaffold proteins CARMA1-3 (encoded by the genes CARD11, -14 and -10) and CARD9 play major roles in signaling downstream of receptors with immunoreceptor tyrosine activation motifs (ITAMs), G-protein coupled receptors (GPCR) and receptor tyrosine kinases (RTK). These receptors trigger the formation of oligomeric CARMA/CARD-BCL10-MALT1 (CBM) complexes via kinases of the PKC family. The CBM in turn regulates gene expression by the activation of NF-κB and AP-1 transcription factors and controls transcript stability. The paracaspase MALT1 is the only CBM component having an enzymatic (proteolytic) activity and has therefore recently gained attention as a potential drug target. Here we review recent advances in the understanding of the molecular function of the protease MALT1 and summarize how MALT1 scaffold and protease function contribute to the transmission of CBM signals. Finally, we will highlight how dysregulation of MALT1 function can cause pathologies such as immunodeficiency, autoimmunity, psoriasis, and cancer.

NF-κB Activation in Lymphoid Malignancies: Genetics, Signaling, and Targeted Therapy

The NF-κB transcription factor family plays a crucial role in lymphocyte proliferation and survival. Consequently, aberrant NF-κB activation has been described in a variety of lymphoid malignancies, including diffuse large B-cell lymphoma, Hodgkin lymphoma, and adult T-cell leukemia. Several factors, such as persistent infections (e.g., with Helicobacter pylori), the pro-inflammatory microenvironment of the cancer, self-reactive immune receptors as well as genetic lesions altering the function of key signaling effectors, contribute to constitutive NF-κB activity in these malignancies. In this review, we will discuss the molecular consequences of recurrent genetic lesions affecting key regulators of NF-κB signaling. We will particularly focus on the oncogenic mechanisms by which these alterations drive deregulated NF-κB activity and thus promote the growth and survival of the malignant cells. As the concept of a targeted therapy based on the mutational status of the malignancy has been supported by several recent preclinical and clinical studies, further insight in the function of NF-κB modulators and in the molecular mechanisms governing aberrant NF-κB activation observed in lymphoid malignancies might lead to the development of additional treatment strategies and thus improve lymphoma therapy.

Lymphocyte signaling and activation by the CARMA1-BCL10-MALT1 signalosome

The CARMA1-BCL10-MALT1 (CBM) signalosome triggers canonical NF-κB signaling and lymphocyte activation upon antigen-receptor stimulation. Genetic studies in mice and the analysis of human immune pathologies unveiled a critical role of the CBM complex in adaptive immune responses. Great progress has been made in elucidating the fundamental mechanisms that dictate CBM assembly and disassembly. By bridging proximal antigen-receptor signaling to downstream signaling pathways, the CBM complex exerts a crucial scaffolding function. Moreover, the MALT1 subunit confers a unique proteolytic activity that is key for lymphocyte activation. Deregulated 'chronic' CBM signaling drives constitutive NF-κB signaling and MALT1 activation, which contribute to the development of autoimmune and inflammatory diseases as well as lymphomagenesis. Thus, the processes that govern CBM activation and function are promising targets for the treatment of immune disorders. Here, we summarize the current knowledge on the functions and mechanisms of CBM signaling in lymphocytes and how CBM deregulations contribute to aberrant signaling in malignant lymphomas.

Baculovirus FP25K Localization: Role of the Coiled-Coil Domain

Two types of viruses are produced during the baculovirus life cycle: budded virus (BV) and occlusion-derived virus (ODV). A particular baculovirus protein, FP25K, is involved in the switch from BV to ODV production. Previously, FP25K from the model alphabaculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV) was shown to traffic ODV envelope proteins. However, FP25K localization and the domains involved are inconclusive. Here we used a quantitative approach to study FP25K subcellular localization during infection using an AcMNPV bacmid virus that produces a functional AcMNPV FP25K-green fluorescent protein (GFP) fusion protein. During cell infection, FP25K-GFP localized primarily to the cytoplasm, particularly amorphous structures, with a small fraction being localized in the nucleus. To investigate the sequences involved in FP25K localization, an alignment of baculovirus FP25K sequences revealed that the N-terminal putative coiled-coil domain is present in all alphabaculoviruses but absent in betabaculoviruses. Structural prediction indicated a strong relatedness of AcMNPV FP25K to long interspersed element 1 (LINE-1) open reading frame 1 protein (ORF1p), which contains an N-terminal coiled-coil domain responsible for cytoplasmic retention. Point mutations and deletions of this domain lead to a change in AcMNPV FP25K localization from cytoplasmic to nuclear. The coiled-coil and C-terminal deletion viruses increased BV production. Furthermore, a betabaculovirus FP25K protein lacking this N-terminal coiled-coil domain localized predominantly to the nucleus and exhibited increased BV production. These data suggest that the acquisition of this N-terminal coiled-coil domain in FP25K is important for the evolution of alphabaculoviruses. Moreover, with the divergence of preocclusion nuclear membrane breakdown in betabaculoviruses and membrane integrity in alphabaculoviruses, this domain represents an alphabaculovirus adaptation for nuclear trafficking of occlusion-associated proteins.

IMPORTANCE

Baculovirus infection produces two forms of viruses: BV and ODV. Manufacturing of ODV involves trafficking of envelope proteins to the inner nuclear membrane, mediated partly through the FP25K protein. Since FP25K is present in alpha-, beta-, and gammabaculoviruses, it is uncertain if this trafficking function is conserved. In this study, we looked at alpha- and betabaculovirus FP25K trafficking by its localization. Alphabaculovirus FP25K localized primarily to the cytoplasm, whereas betabaculovirus FP25K localized to the nucleus. We found that an N-terminal coiled-coil domain present in all alphabaculovirus FP25K proteins, but absent in betabaculovirus FP25K, was critical for alphabaculovirus FP25K cytoplasmic localization. We believe that this represents an evolutionary process that partly led to the gain of function of this N-terminal coiled-coil domain in alphabaculovirus FP25K to aid in nuclear trafficking of occlusion-associated proteins. Due to betabaculovirus breakdown of the nuclear membrane before occlusion, this function is not needed, and the domain was lost or never acquired.

Phosphatidylinositol 4-Phosphate 5-Kinases in the Regulation of T Cell Activation

Phosphatidylinositol 4,5-biphosphate kinases (PIP5Ks) are critical regulators of T cell activation being the main enzymes involved in the synthesis of phosphatidylinositol 4,5-biphosphate (PIP2). PIP2 is indeed a pivotal regulator of the actin cytoskeleton, thus controlling T cell polarization and migration, stable adhesion to antigen-presenting cells, spatial organization of the immunological synapse, and co-stimulation. Moreover, PIP2 also serves as a precursor for the second messengers inositol triphosphate, diacylglycerol, and phosphatidylinositol 3,4,5-triphosphate, which are essential for the activation of signaling pathways regulating cytokine production, cell cycle progression, survival, metabolism, and differentiation. Here, we discuss the impact of PIP5Ks on several T lymphocyte functions with a specific focus on the role of CD28 co-stimulation in PIP5K compartimentalization and activation.

CD28 costimulatory signals in T lymphocyte activation: Emerging functions beyond a qualitative and quantitative support to TCR signalling

CD28 is one of the most important co-stimulatory receptors necessary for full T lymphocyte activation. By binding its cognate ligands, B7.1/CD80 or B7.2/CD86, expressed on the surface of professional antigen presenting cells (APC), CD28 initiates several signalling cascades, which qualitatively and quantitatively support T cell receptor (TCR) signalling. More recent data evidenced that human CD28 can also act as a TCR-independent signalling unit, by delivering specific signals, which regulate the expression of pro-inflammatory cytokine/chemokines. Despite the enormous progresses made in identifying the mechanisms and molecules involved in CD28 signalling properties, much remains to be elucidated, especially in the light of the functional differences observed between human and mouse CD28. In this review we provide an overview of the current mechanisms and molecules through which CD28 support TCR signalling and highlight recent findings on the specific signalling motifs that regulate the unique pro-inflammatory activity of human CD28.

Clustering of CARMA1 through SH3-GUK domain interactions is required for its activation of NF-κB signalling

CARMA1-mediated NF-κB activation controls lymphocyte activation through antigen receptors and survival of some malignant lymphomas. CARMA1 clusters are formed on physiological receptor-mediated activation or by its oncogenic mutation in activated B-cell-diffuse large B-cell lymphomas (ABC-DLBCLs) with constitutive NF-κB activation. However, regulatory mechanisms and relevance of CARMA1 clusters in the NF-κB pathway are unclear. Here we show that SH3 and GUK domain interactions of CARMA1 link CARMA1 clustering to signal activation. SH3 and GUK domains of CARMA1 interact by either intra- or intermolecular mechanisms, which are required for activation-induced assembly of CARMA1. Disruption of these interactions abolishes the formation of CARMA1 microclusters at the immunological synapse, CARMA-regulated signal activation following antigen receptor stimulation as well as spontaneous CARMA1 clustering and NF-κB activation by the oncogenic CARMA1 mutation in ABC-DLBCLs. Thus, the SH3-GUK interactions that regulate CARMA1 cluster formations are promising therapeutic targets for ABC-DLBCLs.

The three CARMA sisters: so different, so similar: a portrait of the three CARMA proteins and their involvement in human disorders

Initially identified by their ability to modulate the functional activity of BCL10, the three CARMA proteins, CARMA1, -2, and -3, have recently themselves taken a leading role on the stage of molecular medicine. Although considered for some time as simple ancillary proteins, increasingly accumulating recent data evidently indicate a role of primary importance for these three proteins in the pathophysiology of several human tumors and inflammatory disorders. In fact, recent scientific literature clearly establishes that CARMA1 is one of the most mutated genes in a subtype of B-cell lymphoma and, at the same time, responsible for some rare human immunodeficiency conditions. On the other hand, mutations in CARMA2 are responsible for the hereditary transmission of some inflammatory disorders of the skin, including familial psoriasis and ptiriasis; whereas expression of CARMA3 appears to be deregulated in different human tumors. Here we describe and summarize the mutations found in the genes coding for the three CARMA proteins in these different human pathological conditions, and offer an interpretation of the molecular mechanisms from which arise the biological outcomes in which these proteins are involved.

The role of CARMA1 in T cells

Caspase recruitment domain-containing membrane-associated guanylate kinase protein-1 (CARMA1), a member of the membrane associated guanylate kinase (MAGUK) family of kinases, is essential for T lymphocyte activation and proliferation via T-cell receptor (TCR) mediated NF-κB activation. Recent studies suggest a broader role for CARMA1 regulating other T-cell functions as well as a role in non-TCR-mediated signaling pathways important for lymphocyte development and functions. In addition, CARMA1 has been shown to be an important component in the pathogenesis of several human diseases. Thus, comprehensively defining its mechanisms of action and regulation could reveal novel therapeutic targets for T-cell-mediated diseases and lymphoproliferative disorders.

A model of an integrated immune system pathway in Homo sapiens and its interaction with superantigen producing expression regulatory pathway in Staphylococcus aureus: comparing behavior of pathogen perturbed and unperturbed pathway

Response of an immune system to a pathogen attack depends on the balance between the host immune defense and the virulence of the pathogen. Investigation of molecular interactions between the proteins of a host and a pathogen helps in identifying the pathogenic proteins. It is necessary to understand the dynamics of a normally behaved host system to evaluate the capacity of its immune system upon pathogen attack. In this study, we have compared the behavior of an unperturbed and pathogen perturbed host system. Moreover, we have developed a formalism under Flux Balance Analysis (FBA) for the optimization of conflicting objective functions. We have constructed an integrated pathway system, which includes Staphylococcal Superantigen (SAg) expression regulatory pathway and TCR signaling pathway of Homo sapiens. We have implemented the method on this pathway system and observed the behavior of host signaling molecules upon pathogen attack. The entire study has been divided into six different cases, based on the perturbed/unperturbed conditions. In other words, we have investigated unperturbed and pathogen perturbed human TCR signaling pathway, with different combinations of optimization of concentrations of regulatory and signaling molecules. One of these cases has aimed at finding out whether minimization of the toxin production in a pathogen leads to the change in the concentration levels of the proteins coded by TCR signaling pathway genes in the infected host. Based on the computed results, we have hypothesized that the balance between TCR signaling inhibitory and stimulatory molecules can keep TCR signaling system into resting/stimulating state, depending upon the perturbation. The proposed integrated host-pathogen interaction pathway model has accurately reflected the experimental evidences, which we have used for validation purpose. The significance of this kind of investigation lies in revealing the susceptible interaction points that can take back the Staphylococcal Enterotoxin (SE)-challenged system within the range of normal behavior.

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.

The MORC family: new epigenetic regulators of transcription and DNA damage response

Microrchidia (MORC) is a highly conserved nuclear protein superfamily with widespread domain architectures that intimately link MORCs with signaling-dependent chromatin remodeling and epigenetic regulation. Accumulating structural and biochemical evidence has shed new light on the mechanistic action and emerging role of MORCs as epigenetic regulators in diverse nuclear processes. In this Point of View, we focus on discussing recent advances in our understanding of the unique domain architectures of MORC family of chromatin remodelers and their potential contribution to epigenetic control of DNA template-dependent processes such as transcription and DNA damage response. Given that the deregulation of MORCs has been linked with human cancer and other diseases, further efforts to uncover the structure and function of MORCs may ultimately lead to the development of new approaches to intersect with the functionality of MORC family of chromatin remodeling proteins to correct associated pathogenesis.

Structural insights into the assembly of CARMA1 and BCL10

The CBM complex (CARMA1, BCL10 and MALT1) plays a crucial role in B and T lymphocyte activation. CARMA1 serves as a scaffold for BCL10, MALT1 and other effector proteins and regulates various signaling pathways related to the immune response. The assembly of CARMA1 and BCL10 is mediated through a CARD-CARD interaction. Here, we report the crystal structure of the CARD domain of CARMA1 at a resolution of 1.75 Å. The structure consists of six helices, as previously determined for CARD domains. Structural and computational analysis identified the binding interface between CARMA1-CARD and BCL10-CARD, which consists of a basic patch in CARMA1 and an acidic patch in BCL10. Site-directed mutagenesis, co-immunoprecipitation and an NF-κB activation assay confirmed that the interface is necessary for association and downstream signaling. Our studies provide molecular insight into the assembly of CARMA1 and BCL10.

Pathogenetic importance and therapeutic implications of NF-κB in lymphoid malignancies

Derangement of the nuclear factor κB (NF-κB) pathway initiates and/or sustains many types of human cancer. B-cell malignancies are particularly affected by oncogenic mutations, translocations, and copy number alterations affecting key components the NF-κB pathway, most likely owing to the pervasive role of this pathway in normal B cells. These genetic aberrations cause tumors to be 'addicted' to NF-κB, which can be exploited therapeutically. Since each subtype of lymphoid cancer utilizes different mechanisms to activate NF-κB, several different therapeutic strategies are needed to address this pathogenetic heterogeneity. Fortunately, a number of drugs that block signaling cascades leading to NF-κB are in early phase clinical trials, several of which are already showing activity in lymphoid malignancies.

Regulation of NF-κB by the CARD proteins

Scaffold proteins play pivotal roles in the regulation of signal transduction pathways by connecting upstream receptors to downstream effector molecules. During the last decade, many scaffold proteins that contain caspase-recruitment domains (CARD) have been identified. Investigating the roles of CARD proteins has revealed that many of them play crucial roles in signaling cascades leading to activation of nuclear factor-κB (NF-κB). In this review, we discuss the contributions of CARD proteins to NF-κB activation in various signaling cascades. In particular, we share some of our personal experiences during the initial investigation of the functions of the CARMA family of CARD proteins and then summarize the roles of these proteins in signaling pathways induced by antigen receptors, G protein-coupled receptors, receptor tyrosine kinase, and C-type lectin receptors in the context of recent progress in these field.

A novel association between filamin A and NF-κB inducing kinase couples CD28 to inhibitor of NF-κB kinase α and NF-κB activation

CD28 costimulatory molecule plays a critical role in the activation of NF-κB. Indeed, while stimulation of T cells with either professional APCs or anti-TCR plus anti-CD28 antibodies efficiently activates NF-κB, TCR alone fails to do that. Moreover, CD28 stimulation by B7 in the absence of TCR may activate IκB kinase α (IKKα) and a non-canonical NF-κB2-like pathway, in human primary CD4(+) T cells. Despite its functional relevance in NF-κB activation, the molecules connecting autonomous CD28-mediated signals to IKKα and NF-κB activation remain still unknown. In searching for specific upstream activators linking CD28 to the IKKα/NF-κB cascade, we identify a novel constitutive association between filamin A (FLNa) and the NF-κB inducing kinase (NIK), in both Jurkat and human primary T cells. Following CD28 engagement by B7, in the absence of TCR, FLNa-associated NIK is activated and induces IKKα kinase activity. Both proline (P(208)YAP(211)P(212)) and tyrosine residues (Y(206)QPY(209)APP) within the C-terminal proline-rich motif of CD28 are involved in the recruitment of FLNa/NIK complexes to the membrane as well as in the activation of NIK and IKKα.

The dynamic distribution of CARD11 at the immunological synapse is regulated by the inhibitory kinesin GAKIN

T cell receptor (TCR) signaling to NF-κB is required for antigen-induced T cell activation. We conducted an expression-cloning screen for modifiers of CARD11, a critical adaptor in antigen receptor signaling, and identified the kinesin-3 family member GAKIN as a CARD11 inhibitor. GAKIN negatively regulates TCR signaling to NF-κB, associates with CARD11 in a signal-dependent manner and can compete with the required signaling protein, Bcl10, for association. In addition, GAKIN dynamically localizes to the immunological synapse and regulates the redistribution of CARD11 from the central region of the synapse to a distal region. We propose that CARD11 scaffold function and occupancy at the center of the synapse are negatively regulated by GAKIN to tune the output of antigen-receptor signaling.

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.

CARMA3: A novel scaffold protein in regulation of NF-κB activation and diseases

CARD recruited membrane associated protein 3 (CARMA3) is a novel scaffold protein. It belongs to the CARMA protein family, and is known to activate nuclear factor (NF)-κB. However, it is still unknown which receptor functions upstream of CARMA3 to trigger NF-κB activation. Recently, several studies have demonstrated that CARMA3 serves as an indispensable adaptor protein in NF-κB signaling under some G protein-coupled receptors (GPCRs), such as lysophosphatidic acid (LPA) receptor and angiotensin (Ang) II receptor. Mechanistically, CARMA3 recruits its essential downstream molecules Bcl10 and MALT1 to form the CBM (CARMA3-Bcl10-MALT1) signalosome whereby it triggers NF-κB activation. GPCRs and NF-κB play pivotal roles in the regulation of various cellular functions, therefore, aberrant regulation of the GPCR/NF-κB signaling axis leads to the development of many types of diseases, such as cancer and atherogenesis. Recently, the GPCR/CARMA3/NF-κB signaling axis has been confirmed in these specific diseases and it plays crucial roles in the pathogenesis of disease progression. In ovarian cancer cell lines, knockdown of CARMA3 abolishes LPA receptor-induced NF-κB activation, and reduces LPA-induced ovarian cancer invasion. In vascular smooth cells, downregulation of CARMA3 substantially impairs Ang-II-receptor-induced NF-κB activation, and in vivo studies have confirmed that Bcl10-deficient mice are protected from developing Ang-II-receptor-induced atherosclerosis and aortic aneurysms. In this review, we summarize the biology of CARMA3, describe the role of the GPCR/CARMA3/NF-κB signaling axis in ovarian cancer and atherogenesis, and speculate about the potential roles of this signaling axis in other types of cancer and diseases. With a significant increase in the identification of LPA- and Ang-II-like ligands, such as endothelin-1, which also activates NF-κB via CARMA3 and contributes to the development of many diseases, CARMA3 is emerging as a novel therapeutic target for various types of cancer and other diseases.

Dephosphorylation of Carma1 by PP2A negatively regulates T-cell activation

The Carma1-Bcl10-Malt1 (CBM) complex bridges T-cell receptor (TCR) signalling to the canonical IκB kinase (IKK)/NF-κB pathway. NF-κB activation is triggered by PKCθ-dependent phosphorylation of Carma1 after TCR/CD28 co-stimulation. PKCθ-phosphorylated Carma1 was suggested to function as a molecular scaffold that recruits preassembled Bcl10-Malt1 complexes to the membrane. We have identified the serine-threonine protein phosphatase PP2A regulatory subunit Aα (PPP2R1A) as a novel interaction partner of Carma1. PPP2R1A is associated with Carma1 in resting as well as activated T cells in the context of the active CBM complex. By siRNA-mediated knockdown and in vitro dephosphorylation, we demonstrate that PP2A removes PKCθ-dependent phosphorylation of Ser645 in Carma1, and show that maintenance of this phosphorylation is correlated with increased T-cell activation. As a result of PP2A inactivation, we find that enhanced Carma1 S645 phosphorylation augments CBM complex formation, NF-κB activation and IL-2 or IFN-γ production after stimulation of Jurkat T cells or murine Th1 cells. Thus, our data define PP2A-mediated dephosphorylation of Carma1 as a critical step to limit T-cell activation and effector cytokine production.

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.

An enigmatic tail of CD28 signaling

CD28 costimulation regulates a wide range of cellular processes, from proliferation and survival to promoting the differentiation of specialized T-cell subsets. Since first being identified over 20 years ago, CD28 has remained a subject of intense study because of its profound consequences on T cell function and its potential for therapeutic manipulation. In this review we highlight the signaling cascades initiated by the major signaling motifs in CD28, focusing on PI-3 kinase-dependent and -independent pathways and how these are linked to specific cellular outcomes. Recent studies using gene targeted knockin mice have clarified the relative importance of these motifs on in vivo immune responses; however, much remains to be elucidated. Understanding the mechanism behind costimulation holds great potential for development of new clinically relevant reagents, a fact beginning to be realized with the advent of drugs that prevent CD28 ligation and signaling.

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.

Oncogenic activation of NF-kappaB

Recent genetic evidence has established a pathogenetic role for NF-kappaB signaling in cancer. NF-kappaB signaling is engaged transiently when normal B lymphocytes respond to antigens, but lymphomas derived from these cells accumulate genetic lesions that constitutively activate NF-kappaB signaling. Many genetic aberrations in lymphomas alter CARD11, MALT1, or BCL10, which constitute a signaling complex that is intermediate between the B-cell receptor and IkappaB kinase. The activated B-cell-like subtype of diffuse large B-cell lymphoma activates NF-kappaB by a variety of mechanisms including oncogenic mutations in CARD11 and a chronic active form of B-cell receptor signaling. Normal plasma cells activate NF-kappaB in response to ligands in the bone marrow microenvironment, but their malignant counterpart, multiple myeloma, sustains a variety of genetic hits that stabilize the kinase NIK, leading to constitutive activation of the classical and alternative NF-kappaB pathways. Various oncogenic abnormalities in epithelial cancers, including mutant K-ras, engage unconventional IkappaB kinases to activate NF-kappaB. Inhibition of constitutive NF-kappaB signaling in each of these cancer types induces apoptosis, providing a rationale for the development of NF-kappaB pathway inhibitors for the treatment of cancer.

Serine 649 phosphorylation within the protein kinase C-regulated domain down-regulates CARMA1 activity in lymphocytes

Phosphorylation of CARMA1 is a crucial event initiating the assembly of IkappaB kinase and JNK signaling complexes downstream of activated Ag receptors. We previously mapped three protein kinase C (PKC) target sites in murine CARMA1 in vitro, and demonstrated that mutation of two of these serines (S564 and S657) resulted in reduced NF-kappaB activation, whereas mutation of the third serine (S649) had no clear effect. In this study, we report that when low concentrations of Ag receptor activators are used, loss of S649 (by mutation to alanine) promotes enhanced IkappaB kinase and JNK activation in both B and T cell lines. Reconstitution of CARMA1(-/-) DT40 B cells with CARMA1 S649A leads to increased cell death and reduced cell growth in comparison to wild-type CARMA1, likely a result of enhanced JNK activation. To directly determine whether S649 is modified in vivo, we generated phospho-specific Abs recognizing phospho-S649, and phospho-S657 as a positive control. Although phospho-S657 peaked and declined rapidly after Ag receptor stimulation, phospho-S649 occurred later and was maintained for a significantly longer period poststimulation in both B and T cells. Interestingly, phospho-S657 was completely abolished in PKCbeta-deficient B cells, whereas delayed phosphorylation at S649 was partially intact and depended, in part, upon novel PKC activity. Thus, distinct PKC-mediated CARMA1 phosphorylation events exert opposing effects on the activation status of CARMA1. We propose that early phosphorylation events at S657 and S564 promote the initial assembly of the CARMA1 signalosome, whereas later phosphorylation at S649 triggers CARMA1 down-regulation.

CD28 and CTLA-4 coreceptor expression and signal transduction

SUMMARY

T-cell activation is mediated by antigen-specific signals from the TCRzeta/CD3 and CD4-CD8-p56lck complexes in combination with additional co-signals provided by coreceptors such as CD28, inducible costimulator (ICOS), cytotoxic T-lymphocyte antigen-4 (CTLA-4), programmed death (PD-1), and others. CD28 and ICOS provide positive signals that promote and sustain T-cell responses, while CTLA-4 and PD-1 limit responses. The balance between stimulatory and inhibitory co-signals determines the ultimate nature of T-cell responses where response to foreign pathogen is achieved without excess inflammation and autoimmunity. In this review, we outline the current knowledge of the CD28 and CTLA-4 signaling mechanisms [involving phosphatidylinositol 3 kinase (PI3K), growth factor receptor-bound protein 2 (Grb2), Filamin A, protein kinase C theta (PKCtheta), and phosphatases] that control T-cell immunity. We also present recent findings on T-cell receptor-interacting molecule (TRIM) regulation of CTLA-4 surface expression, and a signaling pathway involving CTLA-4 activation of PI3K and protein kinase B (PKB)/AKT by which cell survival is ensured under conditions of anergy induction.

CARMA1-mediated NF-kappaB and JNK activation in lymphocytes

Activation of transcription factor nuclear factor-kappaB (NF-kappaB) and Jun N-terminal kinase (JNK) play the pivotal roles in regulation of lymphocyte activation and proliferation. Deregulation of these signaling pathways leads to inappropriate immune response and contributes to the development of leukemia/lymphoma. The scaffold protein CARMA1 [caspase-recruitment domain (CARD) membrane-associated guanylate kinase (MAGUK) protein 1] has a central role in regulation of NF-kappaB and the JNK2/c-Jun complex in both B and T lymphocytes. During last several years, tremendous work has been done to reveal the mechanism by which CARMA1 and its signaling partners, B cell CLL-lymphoma 10 and mucosa-associated lymphoid tissue 1, are activated and mediate NF-kappaB and JNK activation. In this review, we summarize our findings in revealing the roles of CARMA1 in the NF-kappaB and JNK signaling pathways in the context of recent advances in this field.

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.

n-3 polyunsaturated fatty acids suppress the localization and activation of signaling proteins at the immunological synapse in murine CD4+ T cells by affecting lipid raft formation

The molecular properties of immunosuppressive n-3 polyunsaturated fatty acids (PUFA) have not been fully elucidated. Using CD4(+) T cells from wild-type control and fat-1 transgenic mice (enriched in n-3 PUFA), we show that membrane raft accumulation assessed by Laurdan (6-dodecanoyl-2-dimethyl aminonaphthalene) labeling was enhanced in fat-1 cells following immunological synapse (IS) formation by CD3-specific Ab expressing hybridoma cells. However, the localization of protein kinase Ctheta, phospholipase Cgamma-1, and F-actin into the IS was suppressed. In addition, both the phosphorylation status of phospholipase Cgamma-1 at the IS and cell proliferation as assessed by CFSE labeling and [(3)H]thymidine incorporation were suppressed in fat-1 cells. These data imply that lipid rafts may be targets for the development of dietary agents for the treatment of autoimmune and chronic inflammatory diseases.

The protein kinase C-responsive inhibitory domain of CARD11 functions in NF-kappaB activation to regulate the association of multiple signaling cofactors that differentially depend on Bcl10 and MALT1 for association

The activation of NF-kappaB by T-cell receptor (TCR) signaling is critical for T-cell activation during the adaptive immune response. CARD11 is a multidomain adapter that is required for TCR signaling to the IkappaB kinase (IKK) complex. During TCR signaling, the region in CARD11 between the coiled-coil and PDZ domains is phosphorylated by protein kinase Ctheta (PKCtheta) in a required step in NF-kappaB activation. In this report, we demonstrate that this region functions as an inhibitory domain (ID) that controls the association of CARD11 with multiple signaling cofactors, including Bcl10, TRAF6, TAK1, IKKgamma, and caspase-8, through an interaction that requires both the caspase recruitment domain (CARD) and the coiled-coil domain. Consistent with the ID-mediated control of their association, we demonstrate that TRAF6 and caspase-8 associate with CARD11 in T cells in a signal-inducible manner. Using an RNA interference rescue assay, we demonstrate that the CARD, linker 1, coiled-coil, linker 3, SH3, linker 4, and GUK domains are each required for TCR signaling to NF-kappaB downstream of ID neutralization. Requirements for the CARD, linker 1, and coiled-coil domains in signaling are consistent with their roles in the association of CARD11 with Bcl10, TRAF6, TAK1, caspase-8, and IKKgamma. Using Bcl10- and MALT1-deficient cells, we show that CARD11 can recruit signaling cofactors independently of one another in a signal-inducible manner.

Oncogenic CARD11 mutations in human diffuse large B cell lymphoma

Diffuse large B cell lymphoma (DLBCL) is the most common form of non-Hodgkin's lymphoma. In the least curable (ABC) subtype of DLBCL, survival of the malignant cells is dependent on constitutive activation of the nuclear factor-kappaB (NF-kappaB) signaling pathway. In normal B cells, antigen receptor-induced NF-kappaB activation requires CARD11, a cytoplasmic scaffolding protein. To determine whether CARD11 contributes to tumorigenesis, we sequenced the CARD11 gene in human DLBCL tumors. We detected missense mutations in 7 of 73 ABC DLBCL biopsies (9.6%), all within exons encoding the coiled-coil domain. Experimental introduction of CARD11 coiled-coil domain mutants into lymphoma cell lines resulted in constitutive NF-kappaB activation and enhanced NF-kappaB activity upon antigen receptor stimulation. These results demonstrate that CARD11 is a bona fide oncogenein DLBCL, providing a genetic rationale for the development of pharmacological inhibitors of the CARD11 pathway for DLBCL therapy.

Cutting edge: identification of a pre-ligand assembly domain (PLAD) and ligand binding site in the IL-17 receptor

IL-17 is the hallmark cytokine of the newly described "Th17" lymphocyte population. The composition, subunit dynamics, and ligand contacts of the IL-17 receptor are poorly defined. We previously demonstrated that the IL-17RA subunit oligomerizes in the membrane without a ligand. In this study, computational modeling identified two fibronectin-III-like (FN) domains in IL-17RA connected by a nonstructured linker, which we predicted to mediate homotypic interactions. In yeast two-hybrid, the membrane-proximal FN domain (FN2), but not the membrane-distal domain (FN1), formed homomeric interactions. The ability of FN2 to drive ligand-independent multimerization was verified by coimmunoprecipitation and fluorescence resonance energy transfer microscopy. Thus, FN2 constitutes a "pre-ligand assembly domain" (PLAD). Further studies indicated that the FN2 linker domain contains the IL-17 binding site, which was never mapped. However, the FN1 domain is also required for high affinity interactions with IL-17. Therefore, although the PLAD is located entirely within FN2, effective ligand binding also involves contributions from the linker and FN1.