Phosphorylation and ubiquitination of the IkappaB kinase complex by two distinct signaling pathways

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.

Novel molecule BBC0901 inhibits BRD4 and acts as a catabolic regulator in the pathogenesis of osteoarthritis

Osteoarthritis (OA) is induced by matrix degradation and inflammation mediated by bromo-domain-containing protein 4 (BRD4)-dependent catabolic factors. BRD4 acts as both a transcriptional regulator and an epigenetic reader. BBC0901 was identified as an inhibitor of BRD4 using a DNA-encoded library screening system. We aimed to demonstrate the effects of BBC0901 on OA pathogenesis by in vitro, ex vivo, and in vivo analyses. BBC0901 inhibited the expression of catabolic factors that degrade cartilage without significantly affecting the viability of mouse articular chondrocytes. Additionally, ex vivo experiments under conditions mimicking OA showed that BBC0901 suppressed extracellular matrix degradation. RNA sequencing analysis of gene expression patterns showed that BBC0901 inhibited the expression of catabolic factors, such as matrix metalloproteinases (MMPs) and cyclooxygenase (COX)2, along with reactive oxygen species (ROS) production. Furthermore, intra-articular (IA) injection of BBC0901 into the knee joint blocked osteoarthritic cartilage destruction by inhibition of MMP3, MMP13, COX2, interleukin (IL)6, and ROS production, thereby obstructing the nuclear factor kappa-light-chain-enhancer of activated B cell and mitogen activated protein kinase signaling. In conclusion, BBC0901-mediated BRD4 inhibition prevented OA development by attenuating catabolic signaling and hence, can be considered a promising IA therapeutic for OA.

Kv7.4 channel is a key regulator of vascular inflammation and remodeling in neointimal hyperplasia and abdominal aortic aneurysms

Inflammation has recently emerged as an important contributor for cardiovascular disease development and participates pivotally in the development of neointimal hyperplasia and abdominal aortic aneurysms (AAA) formation. Kv7.4/KCNQ4, a K⁺ channel, is one of the important regulators of vascular function but its role in vascular inflammation is unexplored. Here, we showed that the expression of Kv7.4 channel was elevated in the neointima and AAA tissues from mice and humans. Genetic deletion or pharmacological inhibition of Kv7.4 channel in mice alleviated neointimal hyperplasia and AAA formation via downregulation of a set of vascular inflammation-related genes, matrix metalloproteinases (MMP) 2/9, and intercellular adhesion molecule (ICAM-1). Furthermore, genetic deletion or inhibition of Kv7.4 channel suppressed the activation of tumor necrosis factor receptor 1 (TNFR1)-nuclear factor (NF)-κB signaling pathway via blockade of interaction between TNFR1 and TNFR1-associated death domain protein (TRADD) in vascular smooth muscle cells (VSMCs). Knockdown of Kv7.4 in vivo identified VSMC-expressed Kv7.4 as a major factor in vascular inflammation. Collectively, our findings suggest that Kv7.4 channel aggravates vascular inflammatory response, which promotes the neointimal hyperplasia and AAA formation. Inhibition of Kv7.4 channel may be a novel therapeutic strategy for vascular inflammatory diseases.

The Transcription Factor NF-κB Mediates Thyrotropin-Stimulated Expression of Thyroid Differentiation Markers

Background: The nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) transcription factor is a key regulator of cell survival, proliferation, and gene expression. Although activation of NF-κB signaling in thyroid follicular cells after thyrotropin (TSH) receptor (TSHR) engagement has been reported, the downstream signaling leading to NF-κB activation remains unexplored. Here, we sought to elucidate the mechanisms that regulate NF-κB signaling activation in response to TSH stimulation. Methods: Fisher rat-derived thyroid cell lines and primary cultures of NF-κB essential modulator (NEMO)-deficient mice thyrocytes were used as models. Signaling pathways leading to the activation of NF-κB were investigated by using chemical inhibitors and phospho-specific antibodies. Luciferase reporter gene assays and site-directed mutagenesis were used to monitor NF-κB-dependent gene transcriptional activity and the expression of thyroid differentiation markers was assessed by reverse transcription quantitative polymerase chain reaction and Western blot, respectively. Chromatin immunoprecipitation (ChIP) was carried out to investigate NF-κB subunit p65 DNA binding, and small interfering RNA (siRNA)-mediated gene knockdown approaches were used for studying gene function. Results: Using thyroid cell lines, we observed that TSH treatment leads to protein kinase C (PKC)-mediated canonical NF-κB p65 subunit nuclear expression. Moreover, TSH stimulation phosphorylated the kinase TAK-1, and its knockdown abolished TSH-induced NF-κB transcriptional activity. TSH induced the transcriptional activity of the NF-κB subunit p65 in a protein kinase A (PKA)-dependent phosphorylation at Ser-276. In addition, p65 phosphorylation at Ser-276 induced acetyl transferase p300 recruitment, leading to its acetylation on Lys-310 and thereby enhancing its transcriptional activity. Evaluation of the role played by NF-κB in thyroid physiology demonstrated that the canonical NF-κB inhibitor BAY 11-7082 reduced TSH-induced expression of thyroid differentiation markers. The involvement of NF-κB signaling in thyroid physiology was confirmed by assessing the TSH-induced gene expression in primary cultures of NEMO-deficient mice thyrocytes. ChIP and the knockdown experiments revealed that p65 is a nuclear effector of TSH actions, inducing the transcripcional expression of thyroid differentiation markers. Conclusions: Taken together, our results point to NF-κB being a pivotal mediator in the TSH-induced thyroid follicular cell differentiation, a relevant finding with potential physiological and pathophysiological implications.

CARD19, the protein formerly known as BinCARD, is a mitochondrial protein that does not regulate Bcl10-dependent NF-κB activation after TCR engagement

After T cell receptor (TCR) engagement, the CARD11-Bcl10-Malt1 (CBM) complex oligomerizes to transduce NF-κB activating signals. Bcl10 is then degraded to limit NF-κB activation. The cDNA AK057716 (BinCARD-1) was reported to encode a novel CARD protein that interacts with Bcl10 and modestly inhibits NF-κB activation. In a later study, a second isoform, BinCARD-2, was identified. Here, we report that the cDNA AK057716 (BinCARD-1) is an incompletely spliced derivative of the gene product of C9orf89, whereas CARD19 (BinCARD-2) represents the properly spliced isoform, with conservation across diverse species. Immunoblotting revealed expression of CARD19 in T cells, but no evidence of BinCARD-1 expression, and microscopy demonstrated that endogenous CARD19 localizes to mitochondria. Although we confirmed that both BinCARD-1 and CARD19 can inhibit NF-κB activation and promote Bcl10 degradation when transiently overexpressed in HEK293T cells, loss of endogenous CARD19 expression had little effect on Bcl10-dependent NF-κB activation, activation of Malt1 protease function, or Bcl10 degradation after TCR engagement in primary murine CD8 T cells. Together, these data indicate that the only detectable translated product of C9orf89 is the mitochondrial protein CARD19, which does not play a discernible role in TCR-dependent, Bcl10-mediated signal transduction to Malt1 or NF-κB.

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.

TAK1 lessens the activity of the paracaspase MALT1 during T cell receptor signaling

The CARMA1-BCL10-MALT1 (CBM) complex couples antigen receptors to the activation of Nuclear Factor κB (NF-κB) transcription factors in T/B lymphocytes. Within this signalosome, the MALT1 paracaspase serves dual roles: it is a crucial adaptor for signal transduction to NF-κB signaling, and a protease that shapes NF-κB activity and lymphocyte activation. Although a subtle choreography of ubiquitination and phosphorylation orchestrate the CBM, how precisely this complex and MALT1 enzyme are regulated continue to be elucidated. Here, we report that the chemical inhibition or the siRNA-based silencing of transforming growth factor beta-activated kinase 1 (TAK1), a known partner of the CBM complex required for NF-κB activation, enhanced the processing of MALT1 substrates. We further show that the assembly of the CBM as well as the ubiquitination of MALT1 was augmented when TAK1 was inhibited. Thus, TAK1 may initiate a negative feedback loop to finely tune the CBM complex activity.

Inflammatory osteolysis is regulated by site-specific ISGylation of the scaffold protein NEMO

Inflammatory osteolysis is governed by exacerbated osteoclastogenesis. Ample evidence points to central role of NF-κB in such pathologic responses, yet the precise mechanisms underpinning specificity of these responses remain unclear. We propose that motifs of the scaffold protein IKKγ/NEMO partly facilitate such functions. As proof-of-principle, we used site-specific mutagenesis to examine the role of NEMO in mediating RANKL-induced signaling in mouse bone marrow macrophages, known as osteoclast precursors. We identified lysine (K)270 as a target regulating RANKL signaling as K270A substitution results in exuberant osteoclastogenesis in vitro and murine inflammatory osteolysis in vivo. Mechanistically, we discovered that K270A mutation disrupts autophagy, stabilizes NEMO, and elevates inflammatory burden. Specifically, K270A directly or indirectly hinders binding of NEMO to ISG15, a ubiquitin-like protein, which we show targets the modified proteins to autophagy-mediated lysosomal degradation. Taken together, our findings suggest that NEMO serves as a toolkit to fine-tune specific signals in physiologic and pathologic conditions.

Ethanol Extract of Ligularia fischeri Inhibits the Lipopolysaccharide-Induced Inflammatory Response by Exerting Anti-Histone Acetyltransferase Activity to Negatively Regulate p65

Histone acetyltransferase (HAT) activity is well established to regulate inflammatory responses. In contrast, the mechanisms by which natural nutritional extracts influence epigenetic mechanisms to regulate inflammation have not yet been thoroughly investigated. Thus, in the present study, we observed that the anti-HAT activity exerted by an ethanol extract of Ligularia fischeri (ELF) inhibited inflammation. Specifically, we used a cell-free system to show that ELF attenuates HAT activity. We also demonstrated that ELF decreases lipopolysaccharide (LPS)-induced HAT mRNA and protein expression levels in Raw 264.7 cells, and thereby attenuates inflammation-induced patterns of hyperacetylation at nonhistone and histone-H4 proteins. Interestingly, we found that ELF blocked p65 translocation in LPS-stimulated Raw 264.7 cells by attenuating acetylation at lysine residue 310 of p65. Finally, we investigated whether ELF reduces the inflammatory cytokines, IL-6, IL-1β, and TNFα, using its HAT inhibitor activity. Taken together, these results suggest that ELF negatively regulates inflammatory responses by inhibiting HATs and HAT activity.

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.

Mechanisms of Regulated and Dysregulated CARD11 Signaling in Adaptive Immunity and Disease

CARD11 functions as a key signaling scaffold that controls antigen-induced lymphocyte activation during the adaptive immune response. Somatic mutations in CARD11 are frequently found in Non-Hodgkin lymphoma, and at least three classes of germline CARD11 mutations have been described as the basis for primary immunodeficiency. In this review, we summarize our current understanding of how CARD11 signals, how its activity is regulated, and how mutations bypass normal regulation to cause disease.

The CBM-opathies-A Rapidly Expanding Spectrum of Human Inborn Errors of Immunity Caused by Mutations in the CARD11-BCL10-MALT1 Complex

The caspase recruitment domain family member 11 (CARD11 or CARMA1)-B cell CLL/lymphoma 10 (BCL10)-MALT1 paracaspase (MALT1) [CBM] signalosome complex serves as a molecular bridge between cell surface antigen receptor signaling and the activation of the NF-κB, JNK, and mTORC1 signaling axes. This positions the CBM complex as a critical regulator of lymphocyte activation, proliferation, survival, and metabolism. Inborn errors in each of the CBM components have now been linked to a diverse group of human primary immunodeficiency diseases termed "CBM-opathies." Clinical manifestations range from severe combined immunodeficiency to selective B cell lymphocytosis, atopic disease, and specific humoral defects. This surprisingly broad spectrum of phenotypes underscores the importance of "tuning" CBM signaling to preserve immune homeostasis. Here, we review the distinct clinical and immunological phenotypes associated with human CBM complex mutations and introduce new avenues for targeted therapeutic intervention.

CARMA3 Is a Critical Mediator of G Protein-Coupled Receptor and Receptor Tyrosine Kinase-Driven Solid Tumor Pathogenesis

The CARMA–Bcl10–MALT1 (CBM) signalosome is an intracellular protein complex composed of a CARMA scaffolding protein, the Bcl10 linker protein, and the MALT1 protease. This complex was first recognized because the genes encoding its components are targeted by mutation and chromosomal translocation in lymphoid malignancy. We now know that the CBM signalosome plays a critical role in normal lymphocyte function by mediating antigen receptor-dependent activation of the pro-inflammatory, pro-survival NF-κB transcription factor, and that deregulation of this signaling complex promotes B-cell lymphomagenesis. More recently, we and others have demonstrated that a CBM signalosome also operates in cells outside of the immune system, including in several solid tumors. While CARMA1 (also referred to as CARD11) is expressed primarily within lymphoid tissues, the related scaffolding protein, CARMA3 (CARD10), is more widely expressed and participates in a CARMA3-containing CBM complex in a variety of cell types. The CARMA3-containing CBM complex operates downstream of specific G protein-coupled receptors (GPCRs) and/or growth factor receptor tyrosine kinases (RTKs). Since inappropriate expression and activation of GPCRs and/or RTKs underlies the pathogenesis of several solid tumors, there is now great interest in elucidating the contribution of CARMA3-mediated cellular signaling in these malignancies. Here, we summarize the key discoveries leading to our current understanding of the role of CARMA3 in solid tumor biology and highlight the current gaps in our knowledge.

TMEM43-S358L mutation enhances NF-κB-TGFβ signal cascade in arrhythmogenic right ventricular dysplasia/cardiomyopathy

Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is a genetic cardiac muscle disease that accounts for approximately 30% sudden cardiac death in young adults. The Ser358Leu mutation of transmembrane protein 43 (TMEM43) was commonly identified in the patients of highly lethal and fully penetrant ARVD subtype, ARVD5. Here, we generated TMEM43 S358L mouse to explore the underlying mechanism. This mouse strain showed the classic pathologies of ARVD patients, including structural abnormalities and cardiac fibrofatty. TMEM43 S358L mutation led to hyper-activated nuclear factor κB (NF-κB) activation in heart tissues and primary cardiomyocyte cells. Importantly, this hyper activation of NF-κB directly drove the expression of pro-fibrotic gene, transforming growth factor beta (TGFβ1), and enhanced downstream signal, indicating that TMEM43 S358L mutation up-regulates NF-κB-TGFβ signal cascade during ARVD cardiac fibrosis. Our study partially reveals the regulatory mechanism of ARVD development.

Bindarit reduces the incidence of acute aortic dissection complicated lung injury via modulating NF-κB pathway

The pathogenesis of acute aortic dissection (AAD) complicated acute lung injury (ALI) is not currently well defined. At present, no effective animal model has been established for AAD complicated ALI, which hinders research and development of an appropriate treatment regimen for the concurrent conditions. The aim of the present study was to evaluate the therapeutic effects of bindarit (Bnd), an indazolic derivative, on the production of monocyte chemoattractant protein (MCP)-1 in angiotensin II (AngII)-induced complicated ALI in rats. An AAD complicated ALI rat model was established using aminopropionitrile (BAPN) and AngII. The pathological features of AAD complicated ALI were assessed via biochemical and histopathological evaluations. AngII-stimulated human pulmonary microvascular endothelial cells (hPMVECs) were used to assess the effects of Bnd on MCP-1 expression. Western blot analysis was performed to analyze the expression of proteins that may be associated with the process. AAD complicated ALI was established following BAPN and AngII interference, and a massive accumulation of macrophages was observed in the lung tissues of the study rats. Bnd was able to significantly attenuate the incidence of AAD complicated ALI (P<0.05), and significantly inhibit the accumulation of macrophages (P<0.05). The overexpression of MCP-1 induced by AngII in hPMVECs was significantly inhibited by Bnd (P<0.05), which may be associated with downregulation of the classical nuclear factor-κB pathway. Bnd was able to attenuate the incidence of AAD complicated ALI, and inhibit the accumulation of macrophages in vivo. These findings provide a basis for future applications of Bnd as part of a therapeutic treatment schedule for aortic dissection complicated lung injury.

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.

Bupivacaine effectively relieves inflammation-induced pain by suppressing activation of the NF-κB signalling pathway and inhibiting the activation of spinal microglia and astrocytes

The pain induced by local acute inflammation results in mild to severe discomfort, in addition to the possibility of physiological dysfunction and psychiatric disorders, such as sleep disorders and depression. However, the pathogenesis of pain is yet to be fully elucidated. In the present study, the effects of bupivacaine were explored in rat models inflammatory pain in order to investigate the anti-pain mechanism of bupivacaine. Complete Freund's adjuvant (CFA) was injected into the right rear foot of the rats to establish a model of transient inflammation-induced pain. Rats were randomly divided into four groups (n=8): CFA, CFA plus bupivacaine, CFA plus saline and untreated. The mechanical withdrawal threshold (MWT) of the rats was detected prior to and following CFA injection, and the results demonstrated that the MWT in the right rear foot significantly decreased from the 1st day of CFA injection (P<0.01; n=8), as compared with the untreated controls. Bupivacaine treatment was demonstrated to significantly increase the MWT of rats treated with CFA stimulation, as compared with the CFA group (P<0.01). Rotarod testing was performed to assess the motor activity of the rats, and the results demonstrated no significant differences among the four groups (P>0.05). Furthermore, the respective body weights of the rats were determined every two days before and after CFA injection, and no significant differences were detected among the four groups (P>0.05). Western blot analysis was performed to analyze expression levels of IκB and nuclear factor (NF)-κB, and the results demonstrated that bupivacaine increased the expression of IκB and decreased the expression levels of NF-κB, as compared with the rats with CFA-induced inflammatory responses, suggesting that bupivacaine inhibited NF-κB activation in the dorsal horn of the lumbar spinal cord of the model rats. Furthermore, reverse transcription-quantitative polymerase chain reaction analysis was performed to analyze the expression levels of inflammatory cytokines, which demonstrated that bupivacaine significantly inhibited the expression of TNF-α, IL-1β and IL-6, as compared with the untreated group (P<0.01). Moreover, bupivacaine treatment significantly decreased the expression of spinal microglial marker OX42 and astrocyte marker-glial fibrillary acidic protein, as compared with the rats in the CFA group (P<0.01). The present findings demonstrated that treatment with bupivacaine significantly decreased the activation of microglia and astrocytes in rat models of inflammatory pain. Therefore, the present results may provide clarification of the pathogenesis and mechanism of inflammation-induced pain and may provide novel therapeutic strategies for the clinical treatment of pain.

TNF-α Modulation of Intestinal Tight Junction Permeability Is Mediated by NIK/IKK-α Axis Activation of the Canonical NF-κB Pathway

Tumor necrosis factor (TNF)-α, a key mediator of intestinal inflammation, causes an increase in intestinal epithelial tight junction (TJ) permeability by activating myosin light chain kinase (MLCK; official name MYLK3) gene. However, the precise signaling cascades that mediate the TNF-α-induced activation of MLCK gene and increase in TJ permeability remain unclear. Our aims were to delineate the upstream signaling mechanisms that regulate the TNF-α modulation of intestinal TJ barrier function with the use of in vitro and in vivo intestinal epithelial model systems. TNF-α caused a rapid activation of both canonical and noncanonical NF-κB pathway. NF-κB-inducing kinase (NIK) and mitogen-activated protein kinase kinase-1 (MEKK-1) were activated in response to TNF-α. NIK mediated the TNF-α activation of inhibitory κB kinase (IKK)-α, and MEKK1 mediated the activation of IKK complex, including IKK-β. NIK/IKK-α axis regulated the activation of both NF-κB p50/p65 and RelB/p52 pathways. Surprisingly, the siRNA induced knockdown of NIK, but not MEKK-1, prevented the TNF-α activation of both NF-κB p50/p65 and RelB/p52 and the increase in intestinal TJ permeability. Moreover, NIK/IKK-α/NF-κB p50/p65 axis mediated the TNF-α-induced MLCK gene activation and the subsequent MLCK increase in intestinal TJ permeability. In conclusion, our data show that NIK/IKK-α/regulates the activation of NF-κB p50/p65 and plays an integral role in the TNF-α-induced activation of MLCK gene and increase in intestinal TJ permeability.

Distinct Activation Mechanisms of NF-κB Regulator Inhibitor of NF-κB Kinase (IKK) by Isoforms of the Cell Death Regulator Cellular FLICE-like Inhibitory Protein (cFLIP)

The viral FLICE-like inhibitory protein (FLIP) protein from Kaposi sarcoma-associated herpesvirus activates the NF-κB pathway by forming a stable complex with a central region (amino acids 150-272) of the inhibitor of NF-κB kinase (IKK) γ subunits, thereby activating IKK. Cellular FLIP (cFLIP) forms are also known to activate the NF-κB pathway via IKK activation. Here we demonstrate that cFLIPL, cFLIPS, and their proteolytic product p22-FLIP all require the C-terminal region of NEMO/IKKγ (amino acids 272-419) and its ubiquitin binding function for activation of the IKK kinase (or kinase complex), but none form a stable complex with IKKγ. Our results further reveal that cFLIPLrequires the linear ubiquitin chain assembly complex and the kinase TAK1 for activation of the IKK kinase. Similarly, cFLIPSand p22-FLIP also require TAK1 but do not require LUBAC. In contrast, these isoforms are both components of complexes that incorporate Fas-associated death domain and RIP1, which appear essential for kinase activation. This conservation of IKK activation among the cFLIP family using different mechanisms suggests that the mechanism plays a critical role in their function.

MALT1 is required for EGFR-induced NF-κB activation and contributes to EGFR-driven lung cancer progression

The transcription factor nuclear factor kappa B (NF-κB) has been implicated in having a crucial role in the tumorigenesis of many types of human cancers. Although epidermal growth factor receptor (EGFR) can directly activate NF-κB, the mechanism by which EGFR induces NF-κB activation and the role of NF-κB in EGFR-associated tumor progression is still not fully defined. Herein, we found that mucosa-associated lymphoid tissue 1 (MALT1) is involved in EGFR-induced NF-κB activation in cancer cells, and that MALT1 deficiency impaired EGFR-induced NF-κB activation. MALT1 mainly functions as a scaffold protein by recruiting E3 ligase TRAF6 to IKK complex to activate NF-κB in response to EGF stimulation. Functionally, MALT1 inhibition shows significant defects in EGFR-associated tumor malignancy, including cell migration, metastasis and anchorage-independent growth. To further access a physiological role of MALT1-dependent NF-κB activation in EGFR-driven tumor progression, we generated triple-transgenic mouse model (tetO-EGFR(L858R); CCSP-rtTA; Malt1(-/-)), in which mutant EGFR-driven lung cancer was developed in the absence of MALT1 expression. MALT1-deficient mice show significantly less lung tumor burden when compared with its heterozygous controls, suggesting that MALT1 is required for the progression of EGFR-induced lung cancer. Mechanistically, MALT1 deficiency abolished both NF-κB and STAT3 activation in vivo, which is a result of a defect of interleukin-6 production. In comparison, MALT1 deficiency does not affect tumor progression in a mouse model (LSL-K-ras(G12D); CCSP-Cre; Malt1(-/-)) in which lung cancer is induced by expressing a K-ras mutant. Thus, our study has provided the cellular and genetic evidence that suggests MALT1-dependent NF-κB activation is important in EGFR-associated solid-tumor progression.

Identification of Critical Elements for Regulation of Inorganic Pyrophosphatase (PPA1) in MCF7 Breast Cancer Cells

Cytosolic inorganic pyrophosphatase plays an important role in the cellular metabolism by hydrolyzing inorganic pyrophosphate (PPi) formed as a by-product of various metabolic reactions. Inorganic pyrophosphatases are known to be associated with important functions related to the growth and development of various organisms. In humans, the expression of inorganic pyrophosphatase (PPA1) is deregulated in different types of cancer and is involved in the migration and invasion of gastric cancer cells and proliferation of ovarian cancer cells. However, the transcriptional regulation of the gene encoding PPA1 is poorly understood. To gain insights into PPA1 gene regulation, a 1217 bp of its 5'-flanking region was cloned and analyzed. The 5'-deletion analysis of the promoter revealed a 266 bp proximal promoter region exhibit most of the transcriptional activity and upon sequence analysis, three putative Sp1 binding sites were found to be present in this region. Binding of Sp1 to the PPA1 promoter was confirmed by Electrophoretic mobility shift assay (EMSA) and Chromatin immunoprecipitation (ChIP) assay. Importance of these binding sites was verified by site-directed mutagenesis and overexpression of Sp1 transactivates PPA1 promoter activity, upregulates protein expression and increases chromatin accessibility. p300 binds to the PPA1 promoter and stimulates Sp1 induced promoter activity. Trichostatin A (TSA), a histone deacetylase (HDAC) inhibitor induces PPA1 promoter activity and protein expression and HAT activity of p300 was important in regulation of PPA1 expression. These results demonstrated that PPA1 is positively regulated by Sp1 and p300 coactivates Sp1 induced PPA1 promoter activity and histone acetylation/deacetylation may contribute to a local chromatin remodeling across the PPA1 promoter. Further, knockdown of PPA1 decreased colony formation and viability of MCF7 cells.

The CO donor CORM-2 inhibits LPS-induced vascular cell adhesion molecule-1 expression and leukocyte adhesion in human rheumatoid synovial fibroblasts

BACKGROUND AND PURPOSE

Infection with Gram-negative bacteria has been recognized as an initiator of rheumatoid arthritis, which is characterized by chronic inflammation and infiltration of immune cells. Carbon monoxide (CO) exhibits anti-inflammatory properties. Here we have investigated the detailed mechanisms of vascular cell adhesion molecule-1 (VCAM-1) expression induced by LPS and if CO inhibited LPS-induced leukocyte adhesion to synovial fibroblasts by suppressing VCAM-1 expression.

EXPERIMENTAL APPROACH

Human rheumatoid arthritis synovial fibroblasts (RASFs) were incubated with LPS and/or the CO-releasing compound CORM-2. Effects of LPS on VCAM-1 levels were determined by analysing mRNA expression, promoter activity, protein expression, and immunohistochemical staining. The molecular mechanisms were investigated by determining the expression, activation, and binding activity of transcriptional factors using target signal antagonists.

KEY RESULTS

CORM-2 significantly inhibited inflammatory responses in LPS-treated RASFs by down-regulating the expression of adhesion molecule VCAM-1 and leukocyte infiltration. The down-regulation of LPS-induced VCAM-1 expression involved inhibition of the expression of phosphorylated-NF-κB p65 and AP-1 (p-c-Jun, c-Jun and c-Fos mRNA levels). These results were confirmed by chromatin immunoprecipitation assay to detect NF-κB and AP-1 DNA binding activity.

CONCLUSIONS AND IMPLICATIONS

LPS-mediated formation of the TLR4/MyD88/TRAF6/c-Src complex regulated NF-κB and MAPKs/AP-1 activation leading to VCAM-1 expression and leukocyte adhesion. CORM-2, which liberates CO to elicit direct biological activities, attenuated LPS-induced VCAM-1 expression by interfering with NF-κB and AP-1 activation, and significantly reduced LPS-induced immune cell infiltration of the synovium.

The endoplasmic reticulum adaptor protein ERAdP initiates NK cell activation via the Ubc13-mediated NF-κB pathway

NK cells play a pivotal role in innate immune responses against pathogenic infections. However, the underlying mechanisms driving defined NK functions remain largely elusive. In this study, we identified a novel endoplasmic reticulum (ER) membrane protein, ER adaptor protein (ERAdP), which is constitutively expressed in human and mouse NK cells. ERAdP is expressed at low levels in peripheral NK cells of hepatitis B virus-associated hepatocellular carcinoma patients. We show that ERAdP initiates NK cell activation through the NF-κB pathway. Notably, ERAdP interacts with ubiquitin-conjugating enzyme 13 (Ubc13) to potentiate its charging activity. Thus, ERAdP augments Ubc13-mediated NF-κB essential modulator ubiquitination to trigger the Ubc13-mediated NF-κB pathway, leading to NK cell activation. Finally, ERAdP transgenic mice display hyperactivated NK cells that are more resistant to pathogenic infections. Therefore, understanding the mechanism of ERAdP-mediated NK cell activation will provide strategies for treatment of infectious diseases.

The immunological synapse

The molecular interactions underlying regulation of the immune response take place in a nanoscale gap between T cells and antigen-presenting cells, termed the immunological synapse. If these interactions are regulated appropriately, the host is defended against a wide range of pathogens and deranged host cells. If these interactions are disregulated, the host is susceptible to pathogens or tumor escape at one extreme and autoimmunity at the other. Strategies targeting the synapse have helped to establish immunotherapy as a mainstream element in cancer treatment. This Masters' primer will cover the basics of the immunological synapse and some of the applications to tumor immunology.

Epithelial growth factor receptor-activated nuclear factor κB signaling and its role in epithelial growth factor receptor-associated tumors

Dysregulated epithelial growth factor receptor (EGFR) signaling is directly associated with a number of cancers, such as brain, lung, and breast cancer. The downstream signaling pathways activated by EGFR have been extensively studied, such as PI3K/AKT pathway, MAPK (mitogen-activated protein kinase) pathway, and STAT (signal transducer and activator of transcription) pathway. There are growing numbers of evidence suggesting that EGFR activates nuclear factor κB (NF-κB), which is a key transcription factor controlling a variety of cellular functions. However, relatively less is known about the signal transduction mechanism that links EGFR to NF-κB activation. Here, we discuss recent progress in EGFR-induced NF-κB pathways, including the identification of CARMA3-Bcl10-MALT1 complex and protein kinase C[Latin Small Letter Open E] as 2 essential signaling components linking EGFR to the activation of IκBα kinase. In addition, we discuss the multifunctional roles of NF-κB in EGFR-associated tumors, including proliferation, tumor invasiveness, metabolism, tumor-promoting microenvironment, and EGFR tyrosine kinase inhibitor resistance.

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.

T cell receptor signals to NF-κB are transmitted by a cytosolic p62-Bcl10-Malt1-IKK signalosome

Antigen-mediated stimulation of the T cell receptor (TCR) triggers activation of nuclear factor κB (NF-κB), a key transcriptional regulator of T cell proliferation and effector cell differentiation. TCR signaling to NF-κB requires both the Carma1-Bcl10-Malt1 (CBM) complex and the inhibitor of κB (IκB) kinase (IKK) complex; however, the molecular mechanisms connecting the CBM complex to activation of IKK are incompletely defined. We found that the active IKK complex is a component of a TCR-dependent cytosolic Bcl10-Malt1 signalosome containing the adaptor protein p62, which forms in effector T cells. Phosphorylated IκBα and NF-κB were transiently recruited to this signalosome before NF-κB translocated to the nucleus. Inhibiting the activity of the kinase TAK1 or IKK blocked the phosphorylation of IKK, but not the formation of p62-Bcl10-Malt1 clusters, suggesting that activation of IKK occurs after signalosome assembly. Furthermore, analysis of T cells from p62-deficient mice demonstrated that the p62-dependent clustering of signaling components stimulated activation of NF-κB in effector T cells. Thus, TCR-stimulated activation of NF-κB requires the assembly of cytosolic p62-Bcl10-Malt1-IKK signalosomes, which may ensure highly regulated activation of NF-κB in response to TCR engagement.

Nemo-like kinase (NLK) negatively regulates NF-kappa B activity through disrupting the interaction of TAK1 with IKKβ

Stringent negative regulation of the transcription factor NF-κB is essential for maintaining cellular stress responses and homeostasis. However, the tight regulation mechanisms of IKKβ are still not clear. Here, we reported that nemo-like kinase (NLK) is a suppressor of tumor necrosis factor (TNFα)-induced NF-κB signaling by inhibiting the phosphorylation of IKKβ. Overexpression of NLK largely blocked TNFα-induced NF-κB activation, p65 nuclear localization and IκBα degradation; whereas genetic inactivation of NLK showed opposing results. Mechanistically, we identified that NLK interacted with IκB kinase (IKK)-associated complex, which in turn inhibited the assembly of the TAK1/IKKβ and thereby, diminished the IκB kinase phosphorylation. Our results indicate that NLK functions as a pivotal negative regulator in TNFα-induced activation of NF-κB via disrupting the interaction of TAK1 with IKKβ.

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.

Ponatinib efficiently kills imatinib-resistant chronic eosinophilic leukemia cells harboring gatekeeper mutant T674I FIP1L1-PDGFRα: roles of Mcl-1 and β-catenin

BACKGROUND

T674I FIP1L1-PDGFRα in a subset of chronic eosinophilic leukemia (CEL) is a gatekeeper mutation that is resistant to many tyrosine kinase inhibitors (TKIs) (e.g., imatinib, nilotinib and dasatinib), similar to T315I Bcr-Abl. Therefore, novel TKIs effective against T674I FIP1L1-PDGFRα are needed. Ponatinib (AP24534) is a novel orally bioavailable TKI against T315I Bcr-Abl, but it is not clear whether ponatinib is effective against T674I FIP1L1-PDGFRα. The purpose of this study was to examine the effect of ponatinib on T674I FIP1L1-PDGFRα.

METHODS

Molecular docking analysis in silico was performed. The effects of ponatinib on PDGFRα signaling pathways, apoptosis and cell cycling were examined in EOL-1, BaF3 cells expressing either wild type (WT) or T674I FIP1L1-PDGFRα. The in vivo antitumor activity of ponatinib was evaluated with xenografted BaF3-T674I FIP1L1-PDGFRα cells in nude mice models.

RESULTS

Molecular docking analysis revealed that ponatinib could bind to the DFG (Asp-Phe-Gly)-out state of T674I PDGFRα. Ponatinib potently inhibited the phosphorylation of WT and T674I FIP1L1-PDGFRα and their downstream signaling molecules (e.g., Stat3, Stat5). Ponatinib strikingly inhibited the growth of both WT and T674I FIP1L1-PDGFRα-carrying CEL cells (IC50: 0.004-2.5 nM). It induced apoptosis in CEL cells with caspase-3-dependent cleavage of Mcl-1, and inhibited tyrosine phosphorylation of β-catenin to decrease its stability and pro-survival functions. In vivo, ponatinib abrogated the growth of xenografted BaF3-T674I FIP1L1-PDGFRα cells in nude mice.

CONCLUSIONS

Ponatinib is a pan-FIP1L1-PDGFRα inhibitor, and clinical trials are warranted to investigate its efficacy in imatinib-resistant CEL.

Dual-specificity phosphatase 14 (DUSP14/MKP6) negatively regulates TCR signaling by inhibiting TAB1 activation

T cell activation is dependent upon phosphorylation of MAPKs, which play a critical role in the regulation of immune responses. Dual-specificity phosphatase 14 (DUSP14; also known as MKP6) is classified as a MAPK phosphatase. The in vivo functions of DUSP14 remain unclear. Thus, we generated DUSP14-deficient mice and characterized the roles of DUSP14 in T cell activation and immune responses. DUSP14 deficiency in T cells resulted in enhanced T cell proliferation and increased cytokine production upon T cell activation. DUSP14 directly interacted with TGF-β-activated kinase 1 (TAK1)-binding protein 1 (TAB1) and dephosphorylated TAB1 at Ser(438), leading to TAB1-TAK1 complex inactivation in T cells. The phosphorylation levels of the TAB1-TAK1 complex and its downstream molecules, including JNK and IκB kinase, were enhanced in DUSP14-deficient T cells upon stimulation. The enhanced JNK and IκB kinase activation in DUSP14-deficient T cells was attenuated by TAB1 short hairpin RNA knockdown. Consistent with that, DUSP14-deficient mice exhibited enhanced immune responses and were more susceptible to experimental autoimmune encephalomyelitis induction. Thus, DUSP14 negatively regulates TCR signaling and immune responses by inhibiting TAB1 activation.

Combined immunodeficiencies with nonfunctional T lymphocytes

Immunodeficiencies with nonfunctional T cells comprise a heterogeneous group of conditions characterized by altered function of T lymphocytes in spite of largely preserved T cell development. Some of these forms are due to hypomorphic mutations in genes causing severe combined immunodeficiency. More recently, advances in human genome sequencing have facilitated the identification of novel genetic defects that do not affect T cell development, but alter T cell function and homeostasis. Along with increased susceptibility to infections, these conditions are characterized by autoimmunity and higher risk of malignancies. The study of these diseases, and of corresponding animal models, has provided fundamental insights on the mechanisms that govern immune homeostasis.

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.

USP18 inhibits NF-κB and NFAT activation during Th17 differentiation by deubiquitinating the TAK1-TAB1 complex

Reversible ubiquitin modification of cell signaling molecules has emerged as a critical mechanism by which cells respond to extracellular stimuli. Although ubiquitination of TGF-β-activated kinase 1 (TAK1) is critical for NF-κB activation in T cells, the regulation of its deubiquitination is unclear. We show that USP18, which was previously reported to be important in regulating type I interferon signaling in innate immunity, regulates T cell activation and T helper 17 (Th17) cell differentiation by deubiquitinating the TAK1-TAB1 complex. USP18-deficient T cells are defective in Th17 differentiation and Usp18(-/-) mice are resistant to experimental autoimmune encephalomyelitis (EAE). In response to T cell receptor engagement, USP18-deficient T cells exhibit hyperactivation of NF-κB and NFAT and produce increased levels of IL-2 compared with the wild-type controls. Importantly, USP18 is associated with and deubiquitinates the TAK1-TAB1 complex, thereby restricting expression of IL-2. Our findings thus demonstrate a previously uncharacterized negative regulation of TAK1 activity during Th17 differentiation, suggesting that USP18 may be targeted to treat autoimmune diseases.

A new look at T cell receptor signaling to nuclear factor-κB

Antigen stimulation of T cell receptor (TCR) signaling to nuclear factor (NF)-κB is required for T cell proliferation and differentiation of effector cells. The TCR-to-NF-κB pathway is generally viewed as a linear sequence of events in which TCR engagement triggers a cytoplasmic cascade of protein-protein interactions and post-translational modifications, ultimately culminating in the nuclear translocation of NF-κB. However, recent findings suggest a more complex picture in which distinct signalosomes, previously unrecognized proteins, and newly identified regulatory mechanisms play key roles in signal transmission. In this review, we evaluate recent data and suggest areas of future emphasis in the study of this important pathway.

A quantitative signaling screen identifies CARD11 mutations in the CARD and LATCH domains that induce Bcl10 ubiquitination and human lymphoma cell survival

Antigen receptor signaling to NF-κB, essential for normal lymphocyte activation, is dysregulated in several types of lymphoma. During normal signaling, the multidomain adapter CARD11 transitions from a closed, inactive state to an open, active scaffold that assembles a multiprotein complex, leading to NF-κB activation. The regulation of CARD11 scaffold function is bypassed by lymphoma-associated oncogenic CARD11 mutations that induce spontaneous signaling. We report an unbiased high-throughput quantitative signaling screen that identifies new CARD11 hyperactive variants and defines a LATCH domain that functions with the CARD to promote CARD11 autoinhibition. Gain-of-function mutations in the LATCH or CARD disrupt inhibitory domain binding, promote Bcl10 association, and induce Bcl10 ubiquitination, NF-κB activation, and human lymphoma cell survival. Our results identify CARD11 mutations with oncogenic potential, provide a mechanistic explanation for their signaling potency, and offer a straightforward method for the discovery of variants that promote the tumorigenesis of NF-κB-dependent lymphomas.

Tumor necrosis factor receptor-associated factor 6 (TRAF6) and TGFβ-activated kinase 1 (TAK1) play essential roles in the C-type lectin receptor signaling in response to Candida albicans infection

Tumor necrosis factor receptor-associated factor 6 (TRAF6) and TGFβ-activated kinase 1 (TAK1) are considered as key intermediates in Toll-like receptor (TLR) signaling. However, the role of TRAF6 and TAK1 in C-type lectin receptors (CLRs) in response to fungal infection has not been studied. In this study, we have utilized macrophages derived from TRAF6 knock-out mice and myeloid-specific TAK1-deficient mice and determined the role of TRAF6 and TAK1 in CLR-induced signal transduction events. We demonstrate that TRAF6 and TAK1 are required for NF-κB and JNK activation, and expression of proinflammatory cytokines in response to Candida albicans infection. Our results highlight TRAF6 and TAK1 as key components in the signaling cascade downstream of C-type lectin receptors and as critical mediators of the anti-fungal immune response. Therefore, our studies provide a mechanistic understanding of the host immune response to C. albicans, which has a significant impact for the development of anti-fungal therapeutics and in understanding risk-factors and determining susceptibility to C. albicans infection.

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.

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.

Hepatitis B virus X protein induces IKKα nuclear translocation via Akt-dependent phosphorylation to promote the motility of hepatocarcinoma cells

Hepatitis B virus (HBV) X protein (HBx) has been implicated in HBV-associated carcinogenesis through activation of IκB kinase (IKK)/nuclear factor kappa B (NF-κB) signaling pathway. Besides activating NF-κB in the cytoplasm, IKKα was found in the nucleus to regulate gene expression epigenetically in response to various stimuli. However, it is unknown whether nuclear IKKα plays a role in HBx-associated tumor progression. Moreover, the molecular mechanism underlying IKKα nuclear transport also remains to be elucidated. Here, we disclosed HBx as a new inducer of IKKα nuclear transport in hepatoma cells. HBx induced IKKα nuclear transport in an Akt-dependent manner. HBx-activated Akt promoted IKKα nuclear translocation via phosphorylating its threonine-23 (Thr23). In addition, IKKα ubiquitination enhanced by HBx and Akt also contributed to the IKKα accumulation in the nucleus, indicating the involvement of ubiquitination in Akt-increased IKKα nuclear transport in response to HBx. Furthermore, inhibition of IKKα nuclear translocation by mutation of its nuclear localization signal and Thr23 diminished IKKα-dependent cell migration. Taken together, our findings shed light on the molecular mechanism of IKKα nuclear translocation and provide a potential role of nuclear IKKα in HBx-mediated hepatocellular carcinoma (HCC) progression.

K63-linked ubiquitination in kinase activation and cancer

Ubiquitination has been demonstrated to play a pivotal role in multiple biological functions, which include cell growth, proliferation, apoptosis, DNA damage response, innate immune response, and neuronal degeneration. Although the role of ubiquitination in targeting proteins for proteasome-dependent degradation have been extensively studied and well-characterized, the critical non-proteolytic functions of ubiquitination, such as protein trafficking and kinase activation, involved in cell survival and cancer development, just start to emerge, In this review, we will summarize recent progresses in elucidating the non-proteolytic function of ubiquitination signaling in protein kinase activation and its implications in human cancers. The advancement in the understanding of the novel functions of ubiquitination in signal transduction pathways downstream of growth factor receptors may provide novel paradigms for the treatment of human cancers.

PKCθ synergizes with TLR-dependent TRAF6 signaling pathway to upregulate MUC5AC mucin via CARMA1

CARD-containing MAGUK protein 1 (CARMA1) plays a crucial role in regulating adaptive immune responses upon T-cell receptor (TCR) activation in T cells. Its role in regulating host mucosal innate immune response such as upregulation of mucin remains unknown. Here we show that CARMA1 acts as a key signaling mediator for synergistic upregulation of MUC5AC mucin by bacterium nontypeable Haemophilus influenzae (NTHi) and phorbol ester PMA in respiratory epithelial cells. NTHi-induced TLR-dependent TRAF6-MKK3-p38 MAPK signaling pathway synergizes with PKCθ-MEK-ERK signaling pathway. CARMA1 plays a crucial role in mediating this synergistic effect via TRAF6, thereby resulting in synergistic upregulation of MUC5AC mucin. Thus our study unveils a novel role for CARMA1 in mediating host mucosal innate immune response.

Regulation of NF-κB induction by TCR/CD28

NF-κB family transcription factors are a common downstream target for inducible transcription mediated by many different cell-surface receptors, especially those receptors involved in inflammation and adaptive immunity. It is now clear that different classes of receptors employ different proximal signaling strategies to activate the common NF-κB signaling components, such as the IKK complex. For antigen receptors expressed by T and B cells, this pathway requires a complex of proteins including the proteins Carma1, Bcl10, and Malt1. Here, we discuss some of what is known about regulation of these proteins downstream of TCR/CD3 and co-stimulatory CD28 signaling. We also discuss another unique aspect of TCR-mediated NF-κB activation, i.e., the spatial restriction imposed on signaling events by the formation of the immunological synapse between a T cell and antigen-presenting cell presenting specific peptide/MHC.

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.

Akt fine-tunes NF-κB-dependent gene expression during T cell activation

Activation of the NF-κB signaling pathway is critical for leukocyte activation and development. Although previous studies suggested a role for the Akt kinase in coupling the T cell antigen receptor and CD28 to NF-κB activation in T cells, the nature of the role of Akt in this pathway is still unclear. Using a targeted gene profiling approach, we found that a subset of NF-κB-dependent genes required Akt for optimal up-regulation during T cell activation. The selective effects of Akt were manifest at the level of mRNA transcription and p65/RelA binding to upstream promoters and appear to be due to altered formation of the Carma1-Bcl10 complex. The proinflammatory cytokine TNF-α was found to be particularly sensitive to Akt inhibition or knockdown, including in primary human blood T cells and a murine model of rheumatoid arthritis. Our findings are consistent with a hierarchy in the expression of NF-κB-dependent genes, controlled by the strength and/or duration of NF-κB signaling. More broadly, our results suggest that defining the more graded effects of signaling, such as those demonstrated here for Akt and the NF-κB pathway, is important to understanding how cells can fine-tune signaling responses for optimal sensitivity and specificity.

Mutual regulation between deubiquitinase CYLD and retroviral oncoprotein Tax

Background

Oncoprotein Tax, encoded by the human T-cell leukemia virus type 1 (HTLV1), persistently induces NF-κB activation, which contributes to HTLV1-mediated T-cell transformation. Recent studies suggest that the signaling function of Tax requires its ubiquitination, although how the Tax ubiquitination is regulated remains unclear.

Results

We show here that the deubiquitinase CYLD physically interacts with Tax and negatively regulates the ubiquitination of this viral protein. This function of CYLD is associated with inhibition of Tax-mediated activation of IKK although not that of Tak1. Interestingly, CYLD undergoes constitutive phosphorylation in HTLV1-transformed T cells, a mechanism known to inactivate the catalytic activity of CYLD. Consistently, a phospho-mimetic CYLD mutant fails to inhibit Tax ubiquitination.

Conclusion

These findings suggest that CYLD negatively regulates the signaling function of Tax through inhibition of Tax ubiquitination. Conversely, induction of CYLD phosphorylation may serve as a mechanism by which HTLV1 overrides the inhibitory function of CYLD, leading to the persistent activation of NF-κB.

Dephosphorylation of Bcl-10 by calcineurin is essential for canonical NF-κB activation in Th cells

Antigen-specific stimulation of T helper (Th) cells initiates signaling cascades that ultimately result in the activation of the transcription factors NF-κB, NFAT, and AP-1 which regulate, together with other factors, many T-cell functions such as cytokine production, proliferation, and differentiation. Ordered assembly and different phosphorylation events, along with subcellular translocation of the CARMA1/Bcl-10/MALT1 complex, determine NF-κB activation after T-cell receptor (TCR) triggering. We now provide evidence that inhibition of the Ser/Thr phosphatase calcineurin (CaN) prevents dephosphorylation of Bcl-10. CaN, in constant interaction with the Bcl-10/MALT1 complex, is able to dephosphorylate Bcl-10. The CaN inhibitor cyclosporine A (CsA) converts a transient phosphorylation of Bcl-10 Ser138 during the immediate early phase of T-cell activation into a persistent state. Thus, subsequent processes such as IKKβ phosphorylation, IκBα degradation, p65 nuclear translocation, and DNA binding are diminished. Consistently, CsA treatment does not affect the phosphorylation pattern of the upstream kinase PKCθ. Together, our findings demonstrate that CaN functions as a critical signaling molecule during Th cell activation, regulating Bcl-10 phosphorylation and thereby NF-κB activation.

The viral ankyrin repeat protein (ORF124L) from infectious spleen and kidney necrosis virus attenuates nuclear factor-κB activation and interacts with IκB kinase β

The ankyrin (ANK) repeat is one of the most common protein–protein interaction motifs, found predominantly in eukaryotes and bacteria, but the functions of the ANK repeat are rarely researched in animal viruses, with the exception of poxviruses. Infectious spleen and kidney necrosis virus (ISKNV) is a typical member of the genus Megalocytivirus in the family Iridoviridae and is a causative agent of epizootics in fish. The genome of ISKNV contains four putative viral ANK (vANK) repeat proteins and their functions remain largely unknown. In the present study, it was found that ORF124L, a vANK repeat protein in ISKNV, encodes a protein of 274 aa with three ANK repeats. Transcription of ORF124L was detected at 12 h post-infection (p.i.) and reached a peak at 40 h p.i. ORF124L was found to localize to both the nucleus and the cytoplasm in mandarin fish fry cells. ISKNV ORF124L interacted with the mandarin fish IκB kinase β protein (scIKKβ), and attenuated tumour necrosis factor alpha (TNF-α)- or phorbol myristate acetate (PMA)-induced activity of a nuclear factor κB (NF-κB)–luciferase reporter but did not interfere with the activity of an activator protein 1 (AP-1)–luciferase reporter. Phosphorylation of IκBα and nuclear translocation of NF-κB were also impaired by ISKNV ORF124L. In summary, ORF124L was identified as a vANK repeat protein and its role in inhibition of TNF-α-induced NF-κB signalling was investigated through interaction with the mandarin fish IKKβ. This work may help to improve our understanding of the function of fish iridovirus ANK repeat proteins.