TANK potentiates tumor necrosis factor receptor-associated factor-mediated c-Jun N-terminal kinase/stress-activated protein kinase activation through the germinal center kinase pathway

Toll-like receptors in sepsis-associated cytokine storm and their endogenous negative regulators as future immunomodulatory targets

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Sepsis infects more than 48.9 million people world-wide, with 19.7 million deaths.

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Cytokine storm plays a significant role in sepsis, along with severe COVID-19.

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TLR signaling pathways plays a crucial role in generating the cytokine storm.

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Endogenous negative regulators of TLR signaling are crucial to regulate cytokine storm.

Cytokine storm generates during various systemic acute infections, including sepsis and current pandemic called COVID-19 (severe) causing devastating inflammatory conditions, which include multi-organ failure or multi-organ dysfunction syndrome (MODS) and death of the patient. Toll-like receptors (TLRs) are one of the major pattern recognition receptors (PRRs) expressed by immune cells as well as non-immune cells, including neurons, which play a crucial role in generating cytokine storm. They recognize microbial-associated molecular patterns (MAMPs, expressed by pathogens) and damage or death-associate molecular patterns (DAMPs; released and/expressed by damaged/killed host cells). Upon recognition of MAMPs and DAMPs, TLRs activate downstream signaling pathways releasing several pro-inflammatory mediators [cytokines, chemokines, interferons, and reactive oxygen and nitrogen species (ROS or RNS)], which cause acute inflammation meant to control the pathogen and repair the damage. Induction of an exaggerated response due to genetic makeup of the host and/or persistence of the pathogen due to its evasion mechanisms may lead to severe systemic inflammatory condition called sepsis in response to the generation of cytokine storm and organ dysfunction. The activation of TLR-induced inflammatory response is hardwired to the induction of several negative feedback mechanisms that come into play to conclude the response and maintain immune homeostasis. This state-of-the-art review describes the importance of TLR signaling in the onset of the sepsis-associated cytokine storm and discusses various host-derived endogenous negative regulators of TLR signaling pathways. The subject is very important as there is a vast array of genes and processes implicated in these negative feedback mechanisms. These molecules and mechanisms can be targeted for developing novel therapeutic drugs for cytokine storm-associated diseases, including sepsis, severe COVID-19, and other inflammatory diseases, where TLR-signaling plays a significant role.

The roles of grouper TANK in innate immune defense against iridovirus and nodavirus infections

The TRAF family member-associated nuclear factor (NF)-κB activator (TANK) was first identified as a TRAF-binding protein with both stimulatory and inhibitory properties in host innate immune activation. To elucidate the roles of TANK in teleosts, we cloned and characterized the TANK homologue of orange-spotted grouper (Epinephelus coioides). The open reading frame (ORF) of EcTANK consists of 1026 nucleotides encoding a 342 amino acid protein with a predicted molecular mass of 38.24 kDa. EcTANK shares 89.47% and 88.89% identity with Larimichthys crocea TANK and Lates calcarifer TANK, respectively. EcTANK was distributed in all 11 examined tissues. The expression of EcTANK in the spleen increased after infection with Singapore grouper iridovirus (SGIV) and red-spotted grouper nervous necrosis virus (RGNNV). EcTANK was mainly located in the cytoplasm of grouper spleen cells. EcTANK enhanced SGIV and RGNNV replication during viral infection in vitro. Overexpression EcTANK decreased the expression levels of interferon-associated cytokines and pro-inflammatory factors, and enhanced activation of NF-κB. Taken together, these results suggest that EcTANK may play an important role in antiviral innate immune activation in grouper.

Genotyping of immune-related loci associated with delayed HBeAg seroconversion in immune-active chronic hepatitis B patients

The progression of chronic hepatitis B (CHB) is associated with single-nucleotide polymorphisms (SNPs). In this study, we demonstrated the association between immune-related SNPs and delayed spontaneous HBeAg seroconversion in immune-active CHB patients. In addition, we investigated the impact of delayed spontaneous HBeAg seroconversion-related SNPs on HBeAg seroconversion within 3 years during antiviral treatment. We enrolled 332 CHB patients and genotyped 124 SNPs associated with HBV-infected clinical outcomes, including 32 interleukin-related genes, 62 HLA genes, 9 CD marker genes, 7 NK cell receptor genes, and 14 other genes, using ABI OpenArray as a platform. Comparing the immune-active CHB patients with delayed spontaneous HBeAg seroconversion (persistent HBeAg seropositivity, older than 40 years) to those with early inefficient HBeAg seroconversion (HBeAg seroconversion with high viremia, younger than 40 years), logistic analysis revealed that rs3820998 (TANK), rs2621377 (HLA-DOB), rs3130215 (HLA-DPB2), rs2255336 (KLRK1), and rs11614913 (MIR-196A2) were significantly associated with delayed spontaneous HBeAg seroconversion. Using multivariate analysis, we determined that high serum HBV DNA levels (OR = 1.66, 95% CI = 1.33-2.08), rs3820998 (CA, OR = 3.37, 95% CI = 1.24-9.12), rs2621377 (TC, OR = 4.96, 95% CI = 1.85-13.3), rs2255336 (TT, OR = 0.09, 95% CI = 0.01-0.86), and rs11614913 (TT, OR = 2.53, 95% CI = 1.05-6.11) were five independent risk factors for delayed spontaneous HBeAg seroconversion. After patients received nucleos(t)ide analogue treatment, rs3820998 heterozygous CA variant conversely became the only independent favorable factor for treatment-induced HBeAg seroconversion within 3 years (OR = 0.21, 95% CI = 0.06-0.78). These results indicate that distinct immune-related SNPs play a vital role in regulating HBeAg status in immune-active CHB patients with or without antiviral treatment.

Transcriptome and DNA Methylome Analysis in a Mouse Model of Diet-Induced Obesity Predicts Increased Risk of Colorectal Cancer

Colorectal cancer (CRC) tends to occur at older age; however, CRC incidence rates have been rising sharply among young age groups. The increasing prevalence of obesity is recognized as a major risk, yet the mechanistic underpinnings remain poorly understood. Using a diet-induced obesity mouse model, we identified obesity-associated molecular changes in the colonic epithelium of young and aged mice, and we further investigated whether the changes were reversed after weight loss. Transcriptome analysis indicated that obesity-related colonic cellular metabolic switch favoring long-chain fatty acid oxidation happened in young mice, while obesity-associated downregulation of negative feedback regulators of pro-proliferative signaling pathways occurred in older mice. Strikingly, colonic DNA methylome was pre-programmed by obesity at young age, priming for a tumor-prone gene signature after aging. Furthermore, obesity-related changes were substantially preserved after short-term weight loss, but they were largely reversed after long-term weight loss. We provided mechanistic insights into increased CRC risk in obesity.

Molecular cloning and characterization of TANK of black carp Mylopharyngodon piceus

The TRAF family member-associated NF-κB activator (TANK) is linked to the regulation of the transcription of NF-κB in mammals; however, its role in interferon induction is unclear. To elucidate the roles of TANK in teleost, the TANK homologue of black carp (Mylopharyngodon piceus) has been cloned and characterized in this paper. The open reading frame (ORF) of black carp TANK (bcTANK) comprises 1050 nucleotides and the predicted bcTANK protein contains 350 amino acids. The transcription of bcTANK in host cells increased in response to the stimulation of LPS, poly (I:C), SVCV and GCRV. bcTANK migrated around 50 KDa in immunoblot assay and was identified as a cytosolic protein by immunofluorescent staining in both EPC and HeLa cells. bcTANK could not induce the activity of IFN promoter in luciferase reporter assay in EPC cells; however, the IFN-activation ability of bcTANK was obviously enhanced when the cells were treated with LPS, poly (I:C) or virus. Both CPE ratio and virus titer in the media of EPC cells expressing bcTANK were obviously lower than those of the control cells, which were examined by violet crystal staining and plaque assay separately. Taken together, our data support the conclusion that bcTANK plays an important role in the antiviral innate immune activation of black carp.

TRAF family member-associated NF-kappa B activator (TANK) expression increases in injured sensory neurons and is transcriptionally regulated by Sox11

Peripheral nerve injury evokes rapid and complex changes in gene transcription and cellular signaling pathways. Understanding how these changes are functionally related is essential for developing new approaches that accelerate and improve nerve regeneration. Toward this goal we found that nerve injury induces a rapid and significant up-regulation of the transcription factor Sox11 in dorsal root ganglia (DRG) neurons. Gain and loss of function studies have shown this increase is essential for normal axon regeneration. To determine how Sox11 impacts neuronal gene expression, DRG neurons were treated with Sox11 siRNA to identify potential transcriptional targets. One gene significantly reduced by Sox11 knockdown was TRAF (tumor necrosis factor (TNF) receptor-associated factor)-associated NF-κB activator (TANK). Here we show that TANK is expressed in DRG neurons, that TANK expression is increased in response to peripheral nerve injury and that Sox11 overexpression in vitro increases TANK expression. Injury and in vitro overexpression were also found to preferentially increase TANK transcript variant 3 and a larger TANK protein isoform. To determine if Sox11 regulates TANK transcription bioinformatic analysis was used to identify potential Sox-binding motifs within 5kbp of the TANK 5' untranslated region (UTR) across several mammalian genomes. Two sites in the mouse TANK gene were examined. Luciferase expression assays coupled with site-directed mutagenesis showed each site contributes to enhanced TANK promoter activity. In addition, chromatin immunoprecipitation assays showed direct Sox11 binding in regions containing the two identified Sox motifs in the mouse TANK 5'-UTR. These studies are the first to show that TANK is expressed in DRG neurons, that TANK is increased by peripheral nerve injury and that the regulation of TANK expression is, at least in part, controlled by the injury-associated transcription factor Sox11.

TRAF1 phosphorylation on Serine 139 modulates NF-κB activity downstream of 4-1BB in T cells

The Tumour Necrosis Factor (TNF) Receptor-associated factor-1 (TRAF1) adaptor protein is a key component in initiating intracellular signalling pathways downstream of TNF receptors (TNFR). More importantly, TRAF1 has a pattern of expression restricted primarily to lymphoid cells and plays an important role in lymphocyte survival. TRAF1 has been shown to be phosphorylated on Serine 139, consequently inhibiting NF-κB activation downstream of TNFR2 when expressed in HeLa cells. We have previously demonstrated that TRAF1 cooperates with the TNFR family member 4-1BB to mediate signalling in T cells. However, the impact of TRAF1 phosphorylation on events downstream of 4-1BB in T cells remained to be defined. Using a proteomics approach we demonstrate that TANK-binding kinase 1 (TBK1) preferentially associates with the TRAF1 Serine 139 to Alanine (S139A) mutant. TBK1 is a kinase that functions upstream of NIK and IKK in the activation of the NF-κB pathway. When TRAF1-deficient CD8 T cells were reconstituted with the TRAF1 S139A mutant, we observed more sustained levels of IκBα degradation in response to 4-1BB stimulation in contrast to cells expressing either TRAF1 wild-type or TRAF1 S139D phospho-mimetic mutant. Together, these findings define the importance of the basal phosphorylation state of the TRAF1 Serine 139 residue in coordinating signalling events downstream of 4-1BB in primary T cells.

TRAF family member-associated NF-κB activator (TANK) induced by RANKL negatively regulates osteoclasts survival and function

Osteoclasts are the principle bone-resorbing cells. Precise control of balanced osteoclast activity is indispensable for bone homeostasis. Osteoclast activation mediated by RANK-TRAF6 axis has been clearly identified. However, a negative regulation-machinery in osteoclast remains unclear. TRAF family member-associated NF-κB activator (TANK) is induced by about 10 folds during osteoclastogenesis, according to a genome-wide analysis of gene expression before and after osteoclast maturation, and confirmed by western blot and quantitative RT-PCR. Bone marrow macrophages (BMMs) transduced with lentivirus carrying tank-shRNA were induced to form osteoclast in the presence of RANKL and M-CSF. Tank expression was downregulated by 90% by Tank-shRNA, which is confirmed by western blot. Compared with wild-type (WT) cells, osteoclastogenesis of Tank-silenced BMMs was increased, according to tartrate-resistant acid phosphatase (TRAP) stain on day 5 and day 7. Number of bone resorption pits by Tank-silenced osteoclasts was increased by 176% compared with WT cells, as shown by wheat germ agglutinin (WGA) stain and scanning electronic microscope (SEM) analysis. Survival rate of Tank-silenced mature osteoclast is also increased. However, acid production of Tank-knockdown cells was not changed compared with control cells. IκBα phosphorylation is increased in tank-silenced cells, indicating that TANK may negatively regulate NF-κB activity in osteoclast. In conclusion, Tank, whose expression is increased during osteoclastogenesis, inhibits osteoclast formation, activity and survival, by regulating NF-κB activity and c-FLIP expression. Tank enrolls itself in a negative feedback loop in bone resorption. These results may provide means for therapeutic intervention in diseases of excessive bone resorption.

TRAF family member-associated NF-κB activator (TANK) is a negative regulator of osteoclastogenesis and bone formation

The differentiation of bone-resorbing osteoclasts is induced by RANKL signaling, and leads to the activation of NF-κB via TRAF6 activation. TRAF family member-associated NF-κB activator (TANK) acts as a negative regulator of Toll-like receptors (TLRs) and B-cell receptor (BCR) signaling by inhibiting TRAF6 activation. Tank(-/-) mice spontaneously develop autoimmune glomerular nephritis in an IL-6-dependent manner. Despite its importance in the TCRs and BCR-activated TRAF6 inhibition, the involvement of TANK in RANKL signaling is poorly understood. Here, we report that TANK is a negative regulator of osteoclast differentiation. The expression levels of TANK mRNA and protein were up-regulated during RANKL-induced osteoclastogenesis, and overexpression of TANK in vitro led to a decrease in osteoclast formation. The in vitro osteoclastogenesis of Tank(-/-) cells was significantly increased, accompanied by increased ubiquitination of TRAF6 and enhanced canonical NF-κB activation in response to RANKL stimulation. Tank(-/-) mice showed severe trabecular bone loss, but increased cortical bone mineral density, because of enhanced bone erosion and formation. TANK mRNA expression was induced during osteoblast differentiation and Tank(-/-) osteoblasts exhibited enhaced NF-κB activation, IL-11 expression, and bone nodule formation than wild-type control cells. Finally, wild-type mice transplanted with bone marrow cells from Tank(-/-) mice showed trabecular bone loss analogous to that in Tank(-/-) mice. These findings demonstrate that TANK is critical for osteoclastogenesis by regulating NF-κB, and is also important for proper bone remodeling.

Regulation of the PKCθ-NF-κB Axis in T Lymphocytes by the Tumor Necrosis Factor Receptor Family Member OX40

Antigen primed T lymphocytes need to expand and persist to promote adaptive immunity. The growth and survival signals that control this are in large part provided by the NF-κB pathway in activated or effector/memory T cells. Although several membrane receptors impact NF-κB activation, signaling from OX40 (CD134, TNFRSF4), a member of the tumor necrosis factor receptor (TNFR) superfamily, has proven to be important for T cell immunity and a strong contributor to NF-κB activity. PKCθ directs the T cell receptor (TCR) and CD28-dependent assembly of a CBM complex (CARMA1, BCL10, and MALT1) for efficient activation of NF-κB, raising the question of whether other membrane bound receptors that activate NF-κB also require this PKCθ-CBM axis to control TCR-independent T cell activity. We discuss here our recent data demonstrating that after ligation by OX40L (CD252, TNFSF4) expressed on antigen-presenting cells, OX40 translocates into detergent-insoluble membrane lipid microdomains (DIM or lipid rafts) in T cells irrespective of TCR signals, and assembles into a signaling complex containing PKCθ, together with TRAF2, RIP1, the CBM complex, and the IKKα/β/Γ complex. PKCθ is required for optimal NF-κB activation mediated by OX40 and thus works as an essential component of this OX40 signalosome. We also discuss the likelihood that other TNFR superfamily molecules might complex with PKCθ in T cells, and whether PKC isoforms may be critical to the function of TNFR molecules in general.

Programming the magnitude and persistence of antibody responses with innate immunity

Many successful vaccines induce persistent antibody responses that can last a lifetime. The mechanisms by which they do so remain unclear, but emerging evidence indicates that they activate dendritic cells via Toll-like receptors (TLRs). For example, the yellow fever vaccine YF-17D, one of the most successful empiric vaccines ever developed, activates dendritic cells via multiple TLRs to stimulate proinflammatory cytokines. Triggering specific combinations of TLRs in dendritic cells can induce synergistic production of cytokines, which results in enhanced T-cell responses, but its impact on antibody responses remain unknown. Learning the critical parameters of innate immunity that program such antibody responses remains a major challenge in vaccinology. Here we demonstrate that immunization of mice with synthetic nanoparticles containing antigens plus ligands that signal through TLR4 and TLR7 induces synergistic increases in antigen-specific, neutralizing antibodies compared to immunization with nanoparticles containing antigens plus a single TLR ligand. Consistent with this there was enhanced persistence of germinal centres and of plasma-cell responses, which persisted in the lymph nodes for >1.5 years. Surprisingly, there was no enhancement of the early short-lived plasma-cell response relative to that observed with single TLR ligands. Molecular profiling of activated B cells, isolated 7 days after immunization, indicated that there was early programming towards B-cell memory. Antibody responses were dependent on direct triggering of both TLRs on B cells and dendritic cells, as well as on T-cell help. Immunization protected completely against lethal avian and swine influenza virus strains in mice, and induced robust immunity against pandemic H1N1 influenza in rhesus macaques.

Differential B-lymphocyte regulation by CD40 and its viral mimic, latent membrane protein 1

CD40 plays a vital role in humoral immunity, via its potent and multifaceted function as an activating receptor of various immune cells, most notably B lymphocytes. The Epstein-Barr virus-encoded transforming protein latent membrane protein 1 (LMP1) serves as a functional mimic of CD40 signals to B cells but lacks key regulatory controls that restrain CD40 signaling. This allows LMP1 to activate B cells in an abnormal manner that can contribute to the pathogenesis of human B-cell lymphoma and autoimmune disease. This review focuses upon a comparative analysis of CD40 versus LMP1 functions and mechanisms of action in B lymphocytes, discussing how this comparison can provide valuable information on both how CD40 signaling is normally regulated and how LMP1 disrupts the normal CD40 pathways, which can provide information of value to therapeutic design.

Inhibiting TRAF2-mediated activation of NF-kappaB facilitates induction of AP-1

The compound 5-(4-methoxyarylimino)-2-N-(3,4-dichlorophenyl)-3-oxo-1,2,4-thiadiazolidine (P(3)-25) is known to possess anti-bacterial, anti-fungal, and anti-tubercular activities. In this report, we provide evidence that P(3)-25 inhibits NF-kappaB, known to induce inflammatory and tumorigenic responses. It activates AP-1, another transcription factor. It inhibits TRAF2-mediated NF-kappaB activation but not TRAF6-mediated NF-kappaB DNA binding by preventing its association with TANK (TRAF for NF-kappaB). It facilitates binding of MEKK1 with TRAF2 and thereby activates JNK and AP-1. We provide evidence, for the first time, that suggests that the interaction of P(3)-25 with TRAF2 leads to inhibition of the NF-kappaB pathway and activation of AP-1 pathway. These results suggest novel approaches to design of P(3)-25 as an anti-cancer/inflammatory drug for therapy through regulation of the TRAF2 pathway.

TANK is a negative regulator of Toll-like receptor signaling and is critical for the prevention of autoimmune nephritis

The intensity and duration of immune responses are controlled by multiple proteins that modulate Toll-like receptor (TLR) signaling. TRAF family member-associated NF-κB activator (TANK) has been implicated in positive regulation of interferon-regulatory factor-3 as well as NF-κB. Here we demonstrate that TANK is not involved in interferon responses, and is a negative regulator of proinflammatory cytokine production induced by TLR signaling. TLR-induced polyubiquitination of TRAF6 was upregulated in Tank^−/−macrophages. Notably, Tank^−/− mice spontaneously developed fatal glomerulonephritis owing to deposition of immune complexes. Autoantibody production in Tank^−/− mice was rescued by antibiotic treatment or the absence of interleukin (IL)-6 or MyD88. These results demonstrate that constitutive TLR signaling by intestinal commensal microflora is suppressed by TANK.

FOXO3a Turns the Tumor Necrosis Factor Receptor Signaling Towards Apoptosis Through Reciprocal Regulation of c-Jun N-Terminal Kinase and NF-κB

Objective— We evaluated the full range effects of FOXO3a in endothelial cells (ECs) by microarray analysis and investigated the role of FOXO3a regulating TNF receptor signaling pathway.

Methods and Results— Human umbilical vein endothelial cells (HUVECs) were transfected with adenoviral vectors expressing constitutively active FOXO3a (Ad-TM-FOXO3a). Ad-TM-FOXO3a transfection caused remarkable apoptosis, which were accompanied with upregulation of genes related with TNF receptor signaling, such as TNF-α, TANK (TRAF-associated NF-κB activator), and TTRAP (TRAF and TNF receptor-associated protein). Furthermore, κB-Ras1 (IκB-interacting Ras-like protein-1) which is known to block IκB degradation was found increased, and intranuclear translocation of NF-κB was inhibited. GADD45β and XIAP, negative regulators of c-Jun N-terminal kinase (JNK), were suppressed and JNK activity was increased. Attenuation of TNF signaling pathway either by blocking antibody for TNF receptor or by blocking JNK with DMAP (6-dimethylaminopurine) or Ad-TAM67 (dominant negative c-Jun) cotransfection, significantly reduced FOXO3a-induced apoptosis. Finally, treatment of vasculature with heat shock, an activator of endogenous FOXO3a, resulted in EC apoptosis, which was completely rescued by Ad-TAM67.

Conclusion— FOXO3a promotes apoptosis of ECs, through activation of JNK and suppression of NF-κB. These data identify a novel role of FOXO3a to turn TNF receptor signaling to a proapoptotic JNK-dependent pathway.

Modulation of the interferon antiviral response by the TBK1/IKKi adaptor protein TANK

Induction of type I interferons can be triggered by viral components through Toll-like receptors or intracellular viral receptors such as retinoic acid-inducible gene I. Here, we demonstrate that the TRAF (tumor necrosis factor receptor-associated factor) family member-associated NF-kappaB activator (TANK) plays an important role in interferon induction through both retinoic acid-inducible gene I- and Toll-like receptor-dependent pathways. TANK forms complexes with both upstream signal mediators, such as Cardif/MAVS/IPS-1/VISA, TRIF (Toll-interleukin-1 receptor domain-containing adaptor inducing interferon-beta), and TRAF3 and downstream mediators TANK-binding kinase 1, inducible IkappaB kinase, and interferon regulatory factor 3. In addition, it synergizes with these signaling components in interferon induction. Specific knockdown of TANK results in reduced type I interferon production, increased viral titers, and enhanced cell sensitivity to viral infection. Thus, TANK may be a critical adaptor that regulates the assembly of the TANK-binding kinase 1-inducible IkappaB kinase complex with upstream signaling molecules in multiple antiviral pathways.

The mitogen-activated protein kinase kinase kinase kinase GCKR positively regulates canonical and noncanonical Wnt signaling in B lymphocytes

Wnt ligands bind receptors of the Frizzled (Fz) family to control cell fate, proliferation, and polarity. Canonical Wnt/Fz signaling stabilizes beta-catenin by inactivating GSK3beta, leading to the translocation of beta-catenin to the nucleus and the activation of Wnt target genes. Noncanonical Wnt/Fz signaling activates RhoA and Rac, and the latter triggers the activation of c-Jun N-terminal kinase (JNK). Here, we show that exposure of B-lymphocytes to Wnt3a-conditioned media activates JNK and raises cytosolic beta-catenin levels. Both the Rac guanine nucleotide exchange factor Asef and the mitogen-activated protein kinase kinase kinase kinase germinal center kinase-related enzyme (GCKR) are required for Wnt-mediated JNK activation in B cells. In addition, we show that GCKR positively affects the beta-catenin pathway in B cells. Reduction of GCKR expression inhibits Wnt3a-induced phosphorylation of GSK3beta at serine 9 and decreases the accumulation of cytosolic beta-catenin. Furthermore, Wnt signaling induces an interaction between GCKR and GSK3beta. Our findings demonstrate that GCKR facilitates both canonical and noncanonical Wnt signaling in B lymphocytes.

TNFalpha- and IKKbeta-mediated TANK/I-TRAF phosphorylation: implications for interaction with NEMO/IKKgamma and NF-kappaB activation

Pro-inflammatory cytokines trigger signalling cascades leading to NF-kappaB (nuclear factor-kappaB)-dependent gene expression through IKK [IkappaB (inhibitory kappaB) kinase]-dependent phosphorylation and subsequent degradation of the IkappaB proteins and via induced phosphorylation of p65. These signalling pathways rely on sequentially activated kinases which are assembled by essential and non-enzymatic scaffold proteins into functional complexes. Here, we show that the pro-inflammatory cytokine TNFalpha (tumour necrosis factor alpha) promotes TANK [TRAF (TNF receptor-associated factor) family member associated NF-kappaB activator] recruitment to the IKK complex via a newly characterized C-terminal zinc finger. Moreover, we show that TANK is phosphorylated by IKKbeta upon TNFalpha stimulation and that this modification negatively regulates TANK binding to NEMO (NF-kappaB essential modulator). Interestingly, reduced TANK expression by RNA interference attenuates TNFalpha-mediated induction of a subset of NF-kappaB target genes through decreased p65 transactivation potential. Therefore the scaffold protein TANK is required for the cellular response to TNFalpha by connecting upstream signalling molecules to the IKKs and p65, and its subsequent IKKbeta-mediated phosphorylation may be a mechanism to terminate the TANK-dependent wave of NF-kappaB activation.

Protein kinase clk/STY is differentially regulated during erythroleukemia cell differentiation: a bias toward the skipped splice variant characterizes postcommitment stages

Clk/STY is a LAMMER protein kinase capable to phosphorylate serine/arginine-rich (SR) proteins that modulate pre-mRNA splicing. Clk/STY alternative splicing generates transcripts encoding a full-length kinase and a truncated catalytically inactive protein. Here we showed that clk/STY, as well as other members of the family (e.g. clk2, clk3 and clk4), are up-regulated during HMBA-induced erythroleukemia cell differentiation. mRNAs coding for the full-length and the truncated forms were responsible for the overall increased expression. In clk/STY, however, a switch was observed for the ratio of the two alternative spliced products. In undifferentiated cells the full-length transcript was more abundant whereas the transcript encoding for the truncated form predominated at latter stages of differentiation. Surprisingly, overexpression of clk/STY did not alter the splicing switch upon differentiation in MEL cells. These results suggest that clk/STY might contribute to control erythroid differentiation by a mechanism that implicates a balance between these two isoforms.

Gene expression signatures in neutrophils exposed to glucocorticoids: A new paradigm to help explain “neutrophil dysfunction” in parturient dairy cows

Neutrophils are the first line of immunity against most pathogens that infect cattle. These normally short-lived white blood cells develop from myeloid-lineage cells in bone marrow. Upon maturation, bone marrow neutrophils are released into the circulation where they marginate on inflamed blood vessel endothelial cells and migrate through them into the area of infection. Once migrated, neutrophils do not reenter the circulation, but rather, perform their bactericidal functions and die by apoptosis in the tissue. The cytokine and hormonal milieu of the blood and extracellular tissue fluid can influence neutrophil development and immunity-related activities, but the molecular basis of these phenotypic changes and physiological benefits or drawbacks of them are poorly understood. In the current paper, we review new gene expression information that resulted from two of our functional genomics studies designed to evaluate effects of glucocorticoid hormones on bovine neutrophils. This work provides one model to describe complex changes that occur in neutrophils as the cells respond to glucocorticoids, which might act to alter the cells' functional priorities and tip the delicate balance between health and disease during stress, including at parturition. A bovine immunobiology microarray and real time RT-PCR were used to study blood neutrophils collected during the natural surge of endogenous glucocorticoid (cortisol) in parturient dairy cows and bone marrow neutrophils collected from glucocorticoid (dexamethasone)-treated dairy steers. The gene expression signatures we observed led us to perform additional phenotyping of the neutrophils and correlation analyses, which together painted a picture suggesting that glucocorticoids have key roles in modulating neutrophil development, life span, and tissue defense functions during parturition and hormone therapy. Based on these observations, we postulate that glucocorticoids orchestrate adaptive changes in the entire neutrophil system that support increased cell numbers and longevity in blood and heightened remodeling activity in tissues, while at the same time decreasing some important antimicrobial defense activities of the cells. Thus, our functional genomics studies have enabled us to elucidate multiple consequences of neutrophil exposure to glucocorticoids, highlighting a probable role for this interaction in the induction of parturition and partly explaining why some parturient dairy cows may experience heightened incidence and severity of inflammatory diseases like mastitis.

The multifaceted roles of TRAFs in the regulation of B-cell function

Tumour-necrosis factor receptor (TNFR)-associated factors (TRAFs) are cytoplasmic adaptor proteins that are important in lymphocyte activation and apoptosis. Many studies of TRAFs have used models of exogenous overexpression by non-lymphoid cells. However, the actions of TRAFs present at normal levels in lymphoid cells often differ considerably from those that have been established in non-lymphocyte overexpression models. As I discuss here, information obtained from studying these molecules in physiological settings in B cells reveals that they have several roles, which are both unique and overlapping. These include activation of kinases and transcription factors, and interactions with other signalling proteins, culminating in the induction or inhibition of biological functions.

The signaling adaptors and pathways activated by TNF superfamily

Members of the TNF receptor superfamily play pivotal roles in numerous biological events in metazoan organisms. Ligand-mediated trimerization by corresponding homo- or heterotrimeric ligands, the TNF family ligands, causes recruitment of several intracellular adaptors, which activate multiple signal transduction pathways. While recruitment of death domain (DD) containing adaptors such as Fas associated death domain (FADD) and TNFR associated DD (TRADD) can lead to the activation of a signal transduction pathway that induces apoptosis, recruitment of TRAF family proteins can lead to the activation of transcription factors such as, NF-kappaB and JNK thereby promoting cell survival and differentiation as well as immune and inflammatory responses. Individual TNF receptors are expressed in different cell types and have a range of affinities for various intracellular adaptors, which provide tremendous signaling and biological specificities. In addition, numerous signaling modulators are involved in regulating activities of signal transduction pathways downstream of receptors in this superfamily. Most of the TNF receptor superfamily members as well as many of their signaling mediators, have been uncovered in the last two decades. However, much remains unknown about how individual signal transduction pathways are regulated upon activation by any particular TNF receptor, under physiological conditions.

Morphological and immune response alterations in the intestinal mucosa of the mouse after short periods on a low-magnesium diet

The importance of Mg for the immune function is well recognized; however, there is no information available about the effect of Mg intake on the modulation of local immune response in the intestine. Thus, in the present study the hypothesis that short periods of Mg deprivation can affect intestinal mucosa and local immune response was tested. For this purpose, OF1 female mice were fed a semipurified diet (1000 mg Mg/kg diet). For 3 d before immunization and 1 d after, half of the animals were fed a Mg-deficient diet (30 mg Mg/kg diet), three immunizations per os were performed every 3 weeks with Escherichia coli producing the CS31A capsule-like protein (1010 or bacteria per animal). Mice were killed 10 d after the last immunization. The level of specific anti CS31A immunoglobulin (Ig) G and IgA in the serum and secretory IgA in the intestinal secretions and faeces were measured by ELISA. The results indicated that administration of a high dose of immunogen with a low-Mg diet led to lower specific IgA levels in the intestinal mucus and serum. Administration of a low dose of immunogen with a low-Mg diet led to lower IgA and IgG levels in the serum and secretory IgA coproantibodies. To assess alterations of intestinal mucosa caused by a low-Mg diet for a short period, histological and scanning electron microscopy analyses were performed on samples from mice (not submitted to the vaccination protocol) after 3 d on the Mg-deficient diet. These analyses showed several alterations, suggesting perturbations in the growth of the intestinal mucosa. These changes were accompanied by modifications in the expression of several genes involved in cell growth and stress response. From this present work, it may be concluded that short periods of Mg deprivation can affect the intestinal mucosa and local immune response of the intestine.

CD40-mediated p38 mitogen-activated protein kinase activation is required for immunoglobulin class switch recombination to IgE

BACKGROUND

Signaling through CD40 activates multiple kinases and signal pathways that drive diverse CD40-mediated biologic functions. The specific pathways activated by CD40 signaling involving CD40-dependent Ig class switch recombination (CSR) have not been defined.

OBJECTIVE

We sought to dissect CD40-activated signaling required for CD40-mediated Ig CSR by using the specific signal pathway inhibitors, with the emphasis on CD40-activated p38 mitogen-activated protein kinase (p38 MAPK) signaling in CD40-mediated CSR to IgE.

METHODS

Human B cells were costimulated with IL-4 plus anti-CD40 in the presence or absence of specific signal pathway inhibitors. Ig production, kinase phosphorylation, IgH epsilon germline transcripts and Smu-Sepsilon recombination were examined, and their relationships were analyzed.

RESULTS

CD40-dependent IgE induction was inhibited by the specific p38 MAPK inhibitor SB203580 but not by the extracellular signal-regulated protein kinase-specific inhibitor PD98059 or the phosphatidylinositol 3-kinase-specific inhibitor LY294002. CD40 activation of p38 MAPK correlated with CD40-dependent IgE production, and IgE suppression by SB203580 correlated with the inhibition of CD40-activated p38 MAPK phosphorylation. Suppression of IgE production by SB203580 was not due to inhibition of cell proliferation because SB203580 did not suppress IL-4 plus alpha-CD40-induced cell proliferation. SB203580, but neither PD98059 nor LY294002, inhibited CD40-dependent Smu-Sepsilon recombination, as determined by using a digestion circularization PCR assay. The inhibitory effects of SB203580 on IgE production and Smu-Sepsilon recombination were directly related to its ability to suppress production of Ig epsilon germline transcripts.

CONCLUSION

These results demonstrate that p38 MAPK is required for CD40-mediated class switching to IgE.

T lymphocyte activation--an inside overview

Activated T lymphocytes play an important role in autoimmune disease. The process of T-cell activation is therefore of significant importance in understanding the pathogenesis of many rheumatic diseases. This process can be observed from outside the lymphocyte, but we have also gained increased understanding of many of the intracellular events of T-cell activation. This review tries to draw out the most important receptors, pathways, and transcription factors involved in the process.

Downstream regulator TANK binds to the CD40 recognition site on TRAF3

TRAFs (tumor necrosis factor receptor [TNFR]-associated factors) bind to the cytoplasmic portion of liganded TNFRs and stimulate activation of NF-kappaB or JNK pathways. A modulator of TRAF signaling, TANK, serves as either an enhancer or an inhibitor of TRAF-mediated signaling pathways. The crystal structure of a region of TANK bound to TRAF3 has been determined and compared to a similar CD40/TRAF3 complex. TANK and CD40 bind to the same crevice on TRAF3. The recognition motif PxQxT is presented in a boomerang-like structure in TANK that is markedly different from the hairpin loop that forms in CD40 upon binding to TRAF3. Critical TANK contact residues were confirmed by mutagenesis to be required for binding to TRAF3 or TRAF2. Binding affinity, measured by isothermal titration calorimetry and competition assays, demonstrated that TANK competes with CD40 for the TRAF binding site.

Expression and function of TRAF-3 splice-variant isoforms in human lymphoma cell lines

TRAF-3 gene products are signaling adaptor molecules required for lymphocytes to mediate T-dependent antibody responses in vivo. Previous work identified 8 splice-variant TRAF-3 mRNA species by RT-PCR that have the potential to encode novel isoforms, seven of which induce NF-kappaB activation when over-expressed in 293 cells. Here, their expression was characterized by RNAse protection assay, which showed the T cell line Jurkat D1.1 and the B cell lines BJAB, Daudi, and Raji each expressed mRNA encoding TRAF-3 splice-variants in approximately the same rank order (from highest to lowest); TRAF-3 Delta103aa, Delta83aa, full-length, Delta25aa, Delta52aa, Delta56aa, Delta27aa, and Delta221aa mRNA. The TRAF-3 Delta130aa mRNA was not detectable in any of the cell lines examined. The functional effect of over-expressing each TRAF-3 splice-variant on NF-kappaB activation was studied in the TRAF-5-responsive B cell line, BJAB. Of the seven TRAF-3 splice-variant isoforms that induce NF-kappaB activation in 293 cells, only TRAF-3 Delta27aa, Delta103aa, or Delta130aa induce NF-kappaB activation in BJAB cells. Together, these data indicate that a number of TRAF-3 splice-variant mRNAs are expressed and function in B and T lymphoma lines, which suggests that certain TRAF-3 splice-variant isoforms may participate in mediating the known functions of the TRAF-3 gene in lymphocytes.

The TNF-receptor-associated factor family: scaffold molecules for cytokine receptors, kinases and their regulators

The TNF-receptor-associated factor (TRAF) family is a phylogenetically conserved group of scaffold proteins that link receptors of the IL-1R/Toll and TNF receptor family to signalling cascades, leading to the activation of NF-kappaB and mitogen-activated protein kinases. Furthermore, TRAF proteins serve as a docking platform for a variety of regulators of these signalling pathways and are themselves often regulated at the transcriptional and posttranslational level. In this review, we address the structural and molecular basis of TRAF protein functions and highlight their role in cytokine signalling.

Mammalian mitogen-activated protein kinase signal transduction pathways activated by stress and inflammation

The molecular details of mammalian stress-activated signal transduction pathways have only begun to be dissected. This, despite the fact that the impact of these pathways on the pathology of chronic inflammation, heart disease, stroke, the debilitating effects of diabetes mellitus, and the side effects of cancer therapy, not to mention embryonic development, innate and acquired immunity, is profound. Cardiovascular disease and diabetes alone represent the most significant health care problems in the developed world. Thus it is not surprising that understanding these pathways has attracted wide interest, and in the past 10 years, dramatic progress has been made. Accordingly, it is now becoming possible to envisage the transition of these findings to the development of novel treatment strategies. This review focuses on the biochemical components and regulation of mammalian stress-regulated mitogen-activated protein kinase (MAPK) pathways. The nuclear factor-kappa B pathway, a second stress signaling paradigm, has been the subject of several excellent recent reviews (258, 260).

Tumor necrosis factor receptor-associated factor (TRAF) 2 and its role in TNF signaling

Tumor necrosis factor (TNF) is the prototypic member of the TNF ligand family and has a key role in the regulation of inflammatory processes. TNF exerts its functions by interaction with the death domain-containing TNF-receptor 1 (TNF-R1) and the non-death domain-containing TNF-receptor 2 (TNF-R2), both members of a receptor family complementary to the TNF ligand family. Due to the prototypic features of the TNF receptors and their importance for the regulation of inflammation, the signal transduction mechanisms utilized by these receptors have been extensively studied. Several proteins that interact directly or indirectly with the cytoplasmic domains of TNF-R1 and TNF-R2 have been identified in the recent years giving ideas how these receptors are connected to the apoptotic pathway and the signaling cascades leading to activation of NF-kappaB and JNK. Of special interest are TNF receptor-associated factor (TRAF) 1 and 2, which defines a novel group of adaptor proteins involved in signal transduction by most members of the TNF receptor family, of IL-1 receptor and IL-17 receptor as well as some members of the TOLL-like receptor family. TRAF 2 is currently the best-characterized TRAF family member, having a key role in mediating TNF-R1-induced activation of NF-kappaB and JNK. Moreover, recent studies suggest that TRAF 2 represents an integration point for pro- and antiapoptotic signals. This review focuses on the molecular mechanisms that underlay signal initiation by TNF-R1 and TNF-R2, with particular consideration of the role of TRAF 2, and highlights the importance of this molecule for the integration of such antagonizing pathways as death induction and NF-kappaB-mediated surviving signals.

Activation of the Ikappa B kinases by RIP via IKKgamma /NEMO-mediated oligomerization

To understand the mechanism of activation of the IkappaB kinase (IKK) complex in the tumor necrosis factor (TNF) receptor 1 pathway, we examined the possibility that oligomerization of the IKK complex triggered by ligand-induced trimerization of the TNF receptor 1 complex is responsible for activation of the IKKs. Gel filtration analysis of the IKK complex revealed that TNFalpha stimulation induces a large increase in the size of this complex, suggesting oligomerization. Substitution of the C-terminal region of IKKgamma, which interacts with RIP, with a truncated DR4 lacking its cytoplasmic death domain, produced a molecule that could induce IKK and NF-kappaB activation in cells in response to TRAIL. Enforced oligomerization of the N terminus of IKKgamma or truncated IKKalpha or IKKbeta lacking their serine-cluster domains can also induce IKK and NF-kappaB activation. These data suggest that IKKgamma functions as a signaling adaptor between the upstream regulators such as RIP and the IKKs and that oligomerization of the IKK complex by upstream regulators is a critical step in activation of this complex.

Tumour necrosis factors receptor associated signalling molecules and their role in activation of apoptosis, JNK and NF-kappaB

Tumour necrosis factor (TNF) is a pleiotropic cytokine that mediates apoptosis, cell proliferation, immunomodulation, inflammation, viral replication, allergy, arthritis, septic shock, insulin resistance, autoimmune diseases, and other pathological conditions. TNF transduces these cellular responses through two distinct receptors: type I, which are expressed on all cell types, and type II, which are expressed only on cells of the immune system and endothelial cells. At the cellular level, these receptors activate the pathways leading to the activation of transcription factors NF-kappaB and AP-1, apoptosis and proliferation, and mitogen activated protein kinases. None of these receptors exhibit any enzymatic activity but the signals are transmitted through the recruitment of more than a dozen different signalling proteins, which together form signalling cascades. Inhibitors of TNF signalling have therapeutic value as indicated by the approval of the soluble TNF receptors and anti-TNF antibodies for rheumatoid arthritis and for inflammatory bowl disease.

Membrane localization of TRAF 3 enables JNK activation

Members of the tumor necrosis factor receptor family as well as other receptors achieve their diverse biological effects through the activation of intracellular signals including the c-Jun N-terminal kinase (JNK) pathway. Such signals are believed to be delivered through mediators known as TNF receptor-associated factors (TRAFs). Although the N-terminal zinc finger region of TRAFs has been shown to be essential for downstream signaling, there is no indication yet as to the nature of its role or of the factors that distinguish the N terminus of TRAF 3, which does not activate JNK in the systems examined thus far, from those of other TRAFs, which do activate this pathway. In the present study, it is shown that, among the known TRAFs, localization to the insoluble cell pellet fraction consistently correlates with JNK activation and that both characteristics map to the TRAF N terminus. Furthermore, it is demonstrated that forced localization of TRAF 3 to the cell membrane is sufficient to convert this molecule into an activator of JNK. This suggests that one of the roles of the TRAF N terminus may be to participate in interactions that promote the recruitment of TRAFs to the membrane and that this localization effect plays an important role in TRAF-mediated JNK activation.