TNFR-associated factor-3 is associated with BAFF-R and negatively regulates BAFF-R-mediated NF-kappa B activation and IL-10 production

Absence of IκBβ/NFκB signaling does not attenuate acetaminophen-induced hepatic injury

Acetaminophen (N-acetyl-p-aminophenol [APAP]) toxicity is a common cause of acute liver failure. Innate immune signaling and specifically NFκB activation play a complex role in mediating the hepatic response to toxic APAP exposures. While inflammatory innate immune responses contribute to APAP-induced injury, these same pathways play a role in regeneration and repair. Previous studies have shown that attenuating IκBβ/NFκB signaling downstream of TLR4 activation can limit injury, but whether this pathway contributes to APAP-induced hepatic injury is unknown. We hypothesized that the absence of IκBβ/NFκB signaling in the setting of toxic APAP exposure would attenuate APAP-induced hepatic injury. To test this, we exposed adult male WT and IκBβ-/- mice to APAP (280 mg/kg, IP) and evaluated liver histology at early (2-24 hr) and late (48-72 hr) time points. Furthermore, we interrogated the hepatic expression of NFκB inflammatory (Cxcl1, Tnf, Il1b, Il6, Ptgs2, and Ccl2), anti-inflammatory (Il10, Tnfaip3, and Nfkbia), and Nrf2/antioxidant (Gclc, Hmox, and Nqo1) target genes previously demonstrated to play a role in APAP-induced injury. Conflicting with our hypothesis, we found that hepatic injury was similar in WT and IκBβ-/- mice. Acutely, the induced expression of some target genes was similar in WT and IκBβ-/- mice (Tnfaip3, Nfkbia, and Gclc), while others were either not induced (Cxcl1, Tnf, Ptgs2, and Il10) or significantly attenuated (Ccl2) in IκBβ-/- mice. At later time points, APAP-induced hepatic expression of Il1b, Il6, and Gclc was significantly attenuated in IκBβ-/- mice. Based on these findings, the therapeutic potential of targeting IκBβ/NFκB signaling to treat toxic APAP-induced hepatic injury is likely limited.

Past and present discovery of the BAFF/APRIL system - A bibliometric study from 1999 to 2023

Cytokines from the Tumour Necrosis Factor (TNF) family are important regulators of both physiological and pathological processes. The discovery of novel TNF ligands and receptors, BAFF and APRIL, have opened up new possibilities for scientists to explore the effect of these cytokines on the human immune system. The role of BAFF/APRIL system in B lymphocytes is particularly important for survival and maintenance of homeostasis. Aberrant expression of the system is associated with various immunological disorders. Hence, this study provides a comprehensive overview of the past and present BAFF/APRIL system research development in a bibliometric perspective. To our best knowledge, this is the first ever bibliometric analysis conducted focusing on the BAFF/APRIL system. A total of 1055 relevant documents were retrieved from WoSCC. Microsoft Excel, VOSviewer, and Biblioshiny of R studio were bibliometric tools used to analyse the scientific literature. From 1999, the annual publications showed an upward trend, with Journal of Immunology being the most productive journal. USA leads the race for BAFF/APRIL system research developments. Pascal Schneider, a senior researcher affiliated with University of Lausanne, Switzerland was recognised as the most productive author and institution in the BAFF/APRIL system research field. The research focus transitioned from focusing on the role of the system in B cell biology, to immunological disorders and finally to development of BAFF/APRIL targeting drugs. Despite several studies elucidating briefly the pathway mechanism of BAFF/APRIL system in B-cell selection, substantial research on the mechanism of action in disease models and T cell activation and development of immunomodulating drugs from natural origins remains largely unexplored. Therefore, future research focusing on these areas are crucial for the deeper understanding of the system in disease manifestations and progression allowing a better treatment management for various immunological disorders.

TRAF3 loss-of-function reveals the noncanonical NF-κB pathway as a therapeutic target in diffuse large B cell lymphoma

Here, we report recurrent focal deletions of the chr14q32.31-32 locus, including TRAF3, a negative regulator of NF-κB signaling, in de novo diffuse large B cell lymphoma (DLBCL) (24/324 cases). Integrative analysis revealed an association between TRAF3 copy number loss with accumulation of NIK, the central noncanonical (NC) NF-κB kinase, and increased NC NF-κB pathway activity. Accordingly, TRAF3 genetic ablation in isogenic DLBCL model systems caused upregulation of NIK and enhanced NC NF-κB downstream signaling. Knockdown or pharmacological inhibition of NIK in TRAF3-deficient cells differentially impaired their proliferation and survival, suggesting an acquired onco-addiction to NC NF-κB. TRAF3 ablation also led to exacerbated secretion of the immunosuppressive cytokine IL-10. Coculturing of TRAF3-deficient DLBCL cells with CD8+ T cells impaired the induction of Granzyme B and interferon (IFN) γ, which were restored following neutralization of IL-10. Our findings corroborate a direct relationship between TRAF3 genetic alterations and NC NF-κB activation, and highlight NIK as a potential therapeutic target in a defined subset of DLBCL.

CVID-Associated B Cell Activating Factor Receptor Variants Change Receptor Oligomerization, Ligand Binding, and Signaling Responses

PURPOSE

Binding of the B cell activating factor (BAFF) to its receptor (BAFFR) activates in mature B cells many essential pro-survival functions. Null mutations in the BAFFR gene result in complete BAFFR deficiency and cause a block in B cell development at the transition from immature to mature B cells leading therefore to B lymphopenia and hypogammaglobulinemia. In addition to complete BAFFR deficiency, single nucleotide variants encoding BAFFR missense mutations were found in patients suffering from common variable immunodeficiency (CVID), autoimmunity, or B cell lymphomas. As it remained unclear to which extent such variants disturb the activity of BAFFR, we performed genetic association studies and developed a cellular system that allows the unbiased analysis of BAFFR variants regarding oligomerization, signaling, and ectodomain shedding.

METHODS

In addition to genetic association studies, the BAFFR variants P21R, A52T, G64V, DUP92-95, P146S, and H159Y were expressed by lentiviral gene transfer in DG-75 Burkitt's lymphoma cells and analyzed for their impacts on BAFFR function.

RESULTS

Binding of BAFF to BAFFR was affected by P21R and A52T. Spontaneous oligomerization of BAFFR was disturbed by P21R, A52T, G64V, and P146S. BAFF-dependent activation of NF-κB2 was reduced by P21R and P146S, while interactions between BAFFR and the B cell antigen receptor component CD79B and AKT phosphorylation were impaired by P21R, A52T, G64V, and DUP92-95. P21R, G64V, and DUP92-95 interfered with phosphorylation of ERK1/2, while BAFF-induced shedding of the BAFFR ectodomain was only impaired by P21R.

CONCLUSION

Although all variants change BAFFR function and have the potential to contribute as modifiers to the development of primary antibody deficiencies, autoimmunity, and lymphoma, P21R is the only variant that was found to correlate positively with CVID.

Pooled screening of CAR T cells identifies diverse immune signaling domains for next-generation immunotherapies

Chimeric antigen receptors (CARs) repurpose natural signaling components to retarget T cells to refractory cancers but have shown limited efficacy in persistent, recurrent malignancies. Here, we introduce "CAR Pooling," a multiplexed approach to rapidly identify CAR designs with clinical potential. Forty CARs with signaling domains derived from a range of immune cell lineages were evaluated in pooled assays for their ability to stimulate critical T cell effector functions during repetitive stimulation that mimics long-term tumor antigen exposure. Several domains were identified from the tumor necrosis factor (TNF) receptor family that have been primarily associated with B cells. CD40 enhanced proliferation, whereas B cell-activating factor receptor (BAFF-R) and transmembrane activator and CAML interactor (TACI) promoted cytotoxicity. These functions were enhanced relative to clinical benchmarks after prolonged antigen stimulation, and CAR T cell signaling through these domains fell into distinct states of memory, cytotoxicity, and metabolism. BAFF-R CAR T cells were enriched for a highly cytotoxic transcriptional signature previously associated with positive clinical outcomes. We also observed that replacing the 4-1BB intracellular signaling domain with the BAFF-R signaling domain in a clinically validated B cell maturation antigen (BCMA)-specific CAR resulted in enhanced activity in a xenotransplant model of multiple myeloma. Together, these results show that CAR Pooling is a general approach for rapid exploration of CAR architecture and activity to improve the efficacy of CAR T cell therapies.

Advancing Biologic Therapy for Refractory Autoimmune Hepatitis

Biologic agents may satisfy an unmet clinical need for treatment of refractory autoimmune hepatitis. The goals of this review are to present the types and results of biologic therapy for refractory autoimmune hepatitis, indicate opportunities to improve and expand biologic treatment, and encourage comparative clinical trials. English abstracts were identified in PubMed by multiple search terms. Full-length articles were selected for review, and secondary and tertiary bibliographies were developed. Rituximab (monoclonal antibodies against CD20 on B cells), infliximab (monoclonal antibodies against tumor necrosis factor-alpha), low-dose recombinant interleukin 2 (regulatory T cell promoter), and belimumab (monoclonal antibodies against B cell activating factor) have induced laboratory improvement in small cohorts with refractory autoimmune hepatitis. Ianalumab (monoclonal antibodies against the receptor for B cell activating factor) is in clinical trial. These agents target critical pathogenic pathways, but they may also have serious side effects. Blockade of the B cell activating factor or its receptors may disrupt pivotal B and T cell responses, and recombinant interleukin 2 complexed with certain interleukin 2 antibodies may selectively expand the regulatory T cell population. A proliferation-inducing ligand that enhances T cell proliferation and survival is an unevaluated, potentially pivotal, therapeutic target. Fully human antibodies, expanded target options, improved targeting precision, more effective delivery systems, and biosimilar agents promise to improve efficacy, safety, and accessibility. In conclusion, biologic agents target key pathogenic pathways in autoimmune hepatitis, and early experiences in refractory disease encourage clarification of the preferred target, rigorous clinical trial, and comparative evaluations.

Review article: targeting the B cell activation system in autoimmune hepatitis

BACKGROUND

The B cell activation system, consisting of B cell activating factor and a proliferation-inducing ligand, may have pathogenic effects in autoimmune hepatitis.

AIMS

To describe the biological actions of the B cell activation system, indicate its possible role in autoimmune diseases, and evaluate its prospects as a therapeutic target in autoimmune hepatitis METHODS: English abstracts were identified in PubMed by multiple search terms. Full length articles were selected for review, and secondary and tertiary bibliographies were developed.

RESULTS

The B cell activating factor is crucial for the maturation and survival of B cells, and it can co-stimulate T cell activation, proliferation, and survival. It can also modulate the immune response by inducing interleukin 10 production by regulatory B cells. A proliferation-inducing ligand modulates and diversifies the antibody response by inducing class-switch recombination in B cells. It can also increase the proliferation, survival, and antigen activation of T cells. These immune stimulatory actions can be modulated by inducing proliferation of regulatory T cells. The B cell activation system has been implicated in diverse autoimmune diseases, and therapeutic blockade is a management strategy now being evaluated in autoimmune hepatitis.

CONCLUSIONS

The B cell activation system has profound effects on B and T cell function in autoimmune diseases. Blockade therapy is being actively evaluated in autoimmune hepatitis. Clarification of the critical pathogenic components of the B cell activation system will improve the targeting, efficacy, and safety of blockade therapy in this disease.

SMS2 deficiency impairs PKCδ-regulated B cell tolerance in the germinal center

B cell tolerance prevents autoimmunity by deleting or deactivating autoreactive B cells that otherwise may cause autoantibody-driven disorders, including systemic lupus erythematosus (lupus). Lupus is characterized by immunoglobulin Gs carrying a double-stranded (ds)-DNA autospecificity derived mainly from somatic hypermutation in the germinal center (GC), pointing to a checkpoint breach of GC B cell tolerance that leads to lupus. However, tolerance mechanisms in the GC remain poorly understood. Here, we show that upregulated sphingomyelin synthase 2 (SMS2) in anti-dsDNA GC B cells induces apoptosis by directly activating protein kinase C δ (PKCδ)'s pro-apoptotic activity. This tolerance mechanism prevents lupus autoimmunity in C57/BL6 mice and can be stimulated pharmacologically to inhibit lupus pathogenesis in lupus-prone NZBWF1 mice. Patients with lupus consistently have substantially reduced SMS2 expression in B cells and to an even greater extent in autoimmune-prone, age-associated B cells, suggesting that patients with lupus have insufficient SMS2-regulated B cell tolerance.

Receptor Oligomerization and Its Relevance for Signaling by Receptors of the Tumor Necrosis Factor Receptor Superfamily

With the exception of a few signaling incompetent decoy receptors, the receptors of the tumor necrosis factor receptor superfamily (TNFRSF) are signaling competent and engage in signaling pathways resulting in inflammation, proliferation, differentiation, and cell migration and also in cell death induction. TNFRSF receptors (TNFRs) become activated by ligands of the TNF superfamily (TNFSF). TNFSF ligands (TNFLs) occur as trimeric type II transmembrane proteins but often also as soluble ligand trimers released from the membrane-bound form by proteolysis. The signaling competent TNFRs are efficiently activated by the membrane-bound TNFLs. The latter recruit three TNFR molecules, but there is growing evidence that this is not sufficient to trigger all aspects of TNFR signaling; rather, the formed trimeric TNFL–TNFR complexes have to cluster secondarily in the cell-to-cell contact zone for full TNFR activation. With respect to their response to soluble ligand trimers, the signaling competent TNFRs can be subdivided into two groups. TNFRs of one group, designated as category I TNFRs, are robustly activated by soluble ligand trimers. The receptors of a second group (category II TNFRs), however, failed to become properly activated by soluble ligand trimers despite high affinity binding. The limited responsiveness of category II TNFRs to soluble TNFLs can be overcome by physical linkage of two or more soluble ligand trimers or, alternatively, by anchoring the soluble ligand molecules to the cell surface or extracellular matrix. This suggests that category II TNFRs have a limited ability to promote clustering of trimeric TNFL–TNFR complexes outside the context of cell–cell contacts. In this review, we will focus on three aspects on the relevance of receptor oligomerization for TNFR signaling: (i) the structural factors which promote clustering of free and liganded TNFRs, (ii) the signaling pathway specificity of the receptor oligomerization requirement, and (iii) the consequences for the design and development of TNFR agonists.

BAFF is involved in the pathogenesis of IgA nephropathy by activating the TRAF6/NF‑κB signaling pathway in glomerular mesangial cells

The aim of the present study was to investigate the involvement of B cell-activating factor (BAFF) in the pathogenesis of IgA nephropathy by activating the tumor necrosis factor receptor-associated factor 6 (TRAF6)/NF-κB signaling pathway in glomerular mesangial cells. For the clinical analysis, blood, urine and kidney tissue samples were collected from 58 patients diagnosed with primary IgA nephropathy by renal biopsy. For the in vitro study, glomerular mesangial cells were divided into five groups: Control (con)-short hairpin RNA (shRNA) (control group); con-shRNA + BAFF (20 ng/ml); con-shRNA + BAFF + BAFF-RFc chimera protein (500 µg/ml); TRAF6-shRNA; and TRAF6-shRNA + BAFF (20 ng/ml). For the in vivo experiments, 60 Sprague-Dawley rats were randomly divided into four groups: Con-small interfering RNA (siRNA) (control group); con-siRNA + IgA (IgA nephropathy group), BAFF-RFc chimera protein (2 µg/ml) + IgA, and TRAF6-siRNA (0.2 µM) + IgA. Reverse transcription-quantitative PCR was performed to evaluate the mRNA expression levels of TRAF6, connective tissue growth factor (CTGF), fibronectin (FN) and NF-κBP65. Western blot analysis was used to detect the protein expression levels of TRAF6, FN, CTGF and phosphorylated-NF-κBP65 in glomerular mesangial cells and kidney tissues. The results revealed that plasma BAFF levels were positively correlated with the severity of pathological damage in patients with IgA nephropathy. In vitro, BAFF induced the mRNA and protein expression of TRAF6, CTGF, FN and NF-κBP65 in glomerular mesangial cells. After the BAFF-RFc chimera protein was added to inhibit the binding of BAFF and BAFF-receptor (-R), this effect was reduced. In vivo, inhibition of the effects of BAFF via injection with the BAFF-R Fc chimera protein reduced kidney damage in rats suffering from IgA nephropathy. The effect on the expression of signaling pathway-associated proteins was also alleviated. In conclusion, BAFF enhanced the expression of fibroblast factors in the kidneys by activating the TRAF6/NF-κB signaling pathway.

Therapeutic effects of a novel BAFF blocker on arthritis

B-cell targeted therapy is effective for autoimmune diseases such as systemic lupus erythematosus and rheumatoid arthritis (RA), although there are setbacks in RA clinical trials. In this study, we designed a novel B-cell activating factor (BAFF) antagonist: BAFF-Trap, a recombinant glycoprotein with BAFF-binding domains of two BAFF receptors (TACI and Br3) linked to Fc domain of human IgG1. Unlike TACI-Fc, BAFF-Trap bound BAFF but not APRIL (a proliferation-inducing ligand), and significantly suppressed the development of collagen-induced arthritis and adjuvant-induced arthritis. Furthermore, BAFF-Trap inhibited proinflammatory cytokine expression, ameliorated joint damage and suppressed B- and T-cell activation. BAFF-Trap reduced dendritic cells in joints, and increased regulatory T cell, regulatory B-cell, and M2 macrophage. The function of BAFF-Trap was related to inhibition of canonical and noncanonical NF-κB activation. Thus, BAFF-Trap may be a valuable agent for the effective treatment of RA.

B-Cell Activating Factor Predicts Acute Rejection Risk in Kidney Transplant Recipients: A 6-Month Follow-Up Study

B cell activating factor (BAFF) belonging to TNF family is a cytokine that enhances B-cell proliferation and differentiation. Recently, It has been suggested that BAFF might be a potential therapeutic target for treating autoimmune disease. However, the relationship between BAFF and allograft rejection is controversial, and the clinical significance of BAFF in predicting allograft rejection need to be further explored. We conducted 6-month follow-up study to confirm the hypothesis that BAFF might be a risk factor for predicting acute rejection in kidney transplant recipients. At the end of the study, a total of 155 kidney transplant recipients were recruited from October 2015 to October 2017, and classified into acute rejection group (n = 34) and stable renal function group (n = 121) according to their clinical course. We demonstrate that the serum BAFF levels when acute rejection occurred was significantly higher than that in the stable renal function group (2426.19 ± 892.19 vs. 988.17 ± 485.63 pg/mL, P < 0.05). BAFF expression was significantly enhanced in the membrane and cytoplasm of renal tubule epithelial cells in the transplant kidney tissue with acute rejection, and a positive correlation between BAFF and C4d expression was also observed (r = 0.880, P = 0.001). ROC analyses highlight the superiority of serum BAFF level before transplant over those on other post-transplant days in prediction of acute rejection episodes. The sensitivity, specificity and AUC (area under curve) were 83.3, 89.5, and 0.886%, respectively. Kaplan-Meier survival analysis showed that recipients with higher pretransplant BAFF levels had higher acute rejection incidence (P = 0.003). In conclusion, we have identified that BAFF levels are associated with the acute rejection and could be a promising biomarker to predict kidney transplant rejection risks.

The role of BAFF and APRIL in rheumatoid arthritis

Development and activation of B cells quickly became clear after identifying new ligands and receptors in the tumor necrosis factor superfamily. B cell-activating factor (BAFF) and a proliferation-inducing ligand (APRIL) are the members of membrane proteins Type 2 family released by proteolytic cleavage of furin to form active, soluble homotrimers. Except for B cells, ligands are expressed by all such immune cells like T cells, dendritic cells, monocytes, and macrophages. BAFF and APRIL have two common receptors, namely TNFR homolog transmembrane activator and Ca2+ modulator and CAML interactor (TACI) and B cell-maturation antigen. BAFF alone can also be coupled with a third receptor called BAFFR (also called BR3 or BLyS Receptor). These receptors are often expressed by immune cells in the B-cell lineage. The binding of BAFF or APRIL to their receptors supports B cells differentiation and proliferation, immunoglobulin production and the upregulation of B cell-effector molecules expression. It is possible that the overexpression of BAFF and APRIL contributes to the pathogenesis of autoimmune diseases. In BAFF transgenic mice, there is a pseudo-autoimmune manifestation, which is associated with an increase in B-lymphocytes, hyperglobulinemia, anti-single stranded DNA, and anti-double-stranded DNA antibodies, and immune complexes in their peripheral blood. Furthermore, overexpressing BAFF augments the number of peripheral B220+ B cells with a normal proliferation rate, high levels of Bcl2, and prolonged survival and hyperactivity. Therefore, in this review article, we studied BAFF and APRIL as important mediators in B-cell and discussed their role in rheumatoid arthritis.

BAFF-R and TACI expression on CD3+ T cells: Interplay among BAFF, APRIL and T helper cytokines profile in systemic lupus erythematosus

BACKGROUND

Systemic lupus erythematosus (SLE) is the prototype of systemic autoimmune disease, characterized by loss of immune tolerance against self-antigens where autoantibody production is the hallmark of disease. B-cell-activating factor (BAFF) and A proliferation-inducing ligand (APRIL) are cytokines that promote autoreactive cell survival, immunoglobulin-class switching and autoantibody responses in human and mouse SLE models. BAFF and APRIL exert their functions through interactions with their receptors BAFF-R and TACI that are differentially expressed in B lymphocyte subsets, monocytes, dendritic cells and T lymphocytes. BAFF stimulation favors T lymphocyte activation and cytokine production through BAFF-R, which could contribute to the Th1, Th17 and/or Th2 response dysregulation observed in SLE patients.

OBJECTIVE

To evaluate the expression of the cytokines BAFF and APRIL and their association with the receptors BAFF-R and TACI on CD3+ T cells and to evaluate Th1/Th2/Th17 cytokine profile in patients with SLE.

METHODS

Fifteen healthy controls (HC) and 36 SLE patients were included, and their demographic and clinical data were assessed. The disease activity index (Mex-SLEDAI) and damage index (SLICC) were applied to the SLE patients. BAFF-R and TACI expression on CD3+ T cells were evaluated by flow cytometry. Serum BAFF and APRIL concentrations were measured by enzyme-linked immunosorbent assays (ELISA). Cytokine levels of Th1 (IL-12, IL-2, IFN-γ, TNF-α), Th2 (IL-4, IL-6, IL-10, IL-13) and Th17 (IL-1β e IL-17) were quantified with a multiplex assay (MAGPIX). Statistical analysis was performed using PASW Statistics v.20 and GraphPad Prism v.6 software.

RESULTS

No differences in BAFF-R or TACI expression on the CD3+ T cells of SLE and HC were observed. BAFF-R expression correlates inversely with disease activity (r = -0.538, p < 0.01), while TACI correlates with disease activity (r = 0.530, p < 0.05). Serum BAFF and APRIL levels were high in SLE patients and correlated with the disease activity index Mex-SLEDAI (r = 0.621, p < 0.01 and r = 0.416, p < 0.05). SLE patients were found to have significantly higher levels of IL-12, IFN-γ, TNF-α, IL-6, IL-10, IL-13, IL-1β and IL-17 compared to HC (p < 0.05). Cytokines IL-17 (r = 0.526) and TNF-α (r = 0.410) correlate with disease activity (p < 0.05), while APRIL (r = 0.477), IL-10 (r = 0.426) and IFN-γ (r = 0.440) levels were associated with organ damage (p < 0.01). Serum BAFF expression levels correlate with IL-4 (r = 0.424; p < 0.05), IL-6 (r = 0.420; p < 0.05) and IL-10 (r = 0.459; p < 0.01), whereas APRIL levels correlate with IL-2 (r = 0.666; p < 0.01), IL-12 (r = 0.611; p < 0.01) and TNF-α (r = 0.471; p < 0.05) cytokines. A subgroup of SLE patients with high serum BAFF levels (>2 ng/mL) also showed increased APRIL, IL-2, IL-6 and IL-10 levels (p < 0.05). Finally, BAFF, IL-4 and TNF-α serum levels were associated with high titers of antinuclear antibodies.

CONCLUSIONS

The study demonstrates an imbalance in the Th1/Th2 cytokine profile, with increased proinflammatory cytokines, as well as BAFF and APRIL serum levels. Associations of BAFF with Th2 profile cytokines and disease activity, as well as APRIL with Th1 profile cytokines and organ damage, suggest that BAFF and APRIL generated in the autoimmunity context could through still unknown mechanisms, modulate the microenvironment, and perpetuate the inflammatory response, autoantibody production and organ damage observed in SLE patients.

BAFF and BAFF-Receptor in B Cell Selection and Survival

The BAFF-receptor (BAFFR) is encoded by the TNFRSF13C gene and is one of the main pro-survival receptors in B cells. Its function is impressively documented in humans by a homozygous deletion within exon 2, which leads to an almost complete block of B cell development at the stage of immature/transitional B cells. The resulting immunodeficiency is characterized by B-lymphopenia, agammaglobulinemia, and impaired humoral immune responses. However, different from mutations affecting pathway components coupled to B cell antigen receptor (BCR) signaling, BAFFR-deficient B cells can still develop into IgA-secreting plasma cells. Therefore, BAFFR deficiency in humans is characterized by very few circulating B cells, very low IgM and IgG serum concentrations but normal or high IgA levels.

TRAF3 as a Multifaceted Regulator of B Lymphocyte Survival and Activation

The adaptor protein TNF receptor-associated factor 3 (TRAF3) serves as a powerful negative regulator in multiple aspects of B cell biology. Early in vitro studies in transformed cell lines suggested the potential of TRAF3 to inhibit signaling by its first identified binding receptor, CD40. However, because the canonical TRAF3 binding site on many receptors also mediates binding of other TRAFs, and whole-mouse TRAF3 deficiency is neonatally lethal, an accurate understanding of TRAF3's specific functions was delayed until conditional TRAF3-deficient mice were produced. Studies of B cell-specific TRAF3-deficient mice, complemented by investigations in normal and malignant mouse and human B cells, reveal that TRAF3 has powerful regulatory roles that are unique to this TRAF, as well as functions context-specific to the B cell. This review summarizes the current state of knowledge of these roles and functions. These include inhibition of signaling by plasma membrane receptors, negative regulation of intracellular receptors, and restraint of cytoplasmic NF- κB pathways. TRAF3 is also now known to function as a resident nuclear protein, and to impact B cell metabolism. Through these and additional mechanisms TRAF3 exerts powerful restraint upon B cell survival and activation. It is thus perhaps not surprising that TRAF3 has been revealed as an important tumor suppressor in B cells. The many and varied functions of TRAF3 in B cells, and new directions to pursue in future studies, are summarized and discussed here.

Regulation of T cell afferent lymphatic migration by targeting LTβR-mediated non-classical NFκB signaling

Lymphotoxin-beta receptor (LTβR) signaling in lymphatic endothelial cells (LEC) regulates leukocyte afferent lymphatic transendothelial migration (TEM). The function of individual signaling pathways for different leukocyte subsets is currently unknown. Here, we show that LTβR signals predominantly via the constitutive and ligand-driven non-classical NIK pathway. Targeting LTβR-NIK by an LTβR-derived decoy peptide (nciLT) suppresses the production of chemokines CCL21 and CXCL12, and enhances the expression of classical NFκB-driven VCAM-1 and integrin β4 to retain T cells on LEC and precludes T cell and dendritic cell TEM. nciLT inhibits contact hypersensitivity (CHS) at both the sensitization and elicitation stages, likely by inhibiting leukocyte migration. By contrast, targeting LTβR-classical NFκB signaling during the elicitation and resolution stages attenuates CHS, possibly by promoting leukocyte egress. These findings demonstrate the importance of LTβR signaling in leukocyte migration and LEC and lymphatic vessel function, and show that antagonist peptides may serve as lead compounds for therapeutic applications.

The oncogenic membrane protein LMP1 sequesters TRAF3 in B-cell lymphoma cells to produce functional TRAF3 deficiency

Loss-of-function mutations in genes encoding the signaling protein tumor necrosis factor receptor-associated factor 3 (TRAF3) are commonly found in human B-cell malignancies, especially multiple myeloma and B-cell lymphoma (BCL). B-cell TRAF3 deficiency results in enhanced cell survival, elevated activation receptor signaling, and increased activity of certain transcriptional pathways regulating expression of prosurvival proteins. A recent analysis of TRAF3 protein staining of ∼300 human BCL tissue samples revealed that a higher proportion of samples expressing the oncogenic Epstein-Barr virus-encoded protein latent membrane protein 1 (LMP1) showed low/negative TRAF3 staining than predicted. LMP1, a dysregulated mimic of the CD40 receptor, binds TRAF3 more effectively than CD40. We hypothesized that LMP1 may sequester TRAF3, reducing its availability to inhibit prosurvival signaling pathways in the B cell. This hypothesis was addressed via 2 complementary approaches: (1) comparison of TRAF3-regulated activation and survival-related events with relative LMP1 expression in human BCL lines and (2) analysis of the impact upon such events in matched pairs of mouse BCL lines, both parental cells and subclones transfected with inducible LMP1, either wild-type LMP1 or a mutant LMP1 with defective TRAF3 binding. Results from both approaches showed that LMP1-expressing B cells display a phenotype highly similar to that of B cells lacking TRAF3 genes, indicating that LMP1 can render B cells functionally TRAF3 deficient without TRAF3 gene mutations, a finding of significant relevance to selecting pathway-targeted therapies for B-cell malignancies.

Lipopolysaccharide Upregulated Intestinal Epithelial Cell Expression of Fn14 and Activation of Fn14 Signaling Amplify Intestinal TLR4-Mediated Inflammation

TLR4 in intestinal epithelial cells has been shown both inflammatory and homeostatic roles following binding of its cognate ligand lipopolysaccharide (LPS). TWEAK-Fn14 axis plays an important role in pathologies caused by excessive or abnormal inflammatory responses. This study aimed to evaluate potential cross-talk between TLR4 and TWEAK/Fn14 system in porcine small intestinal epithelial cells. Our in vivo results showed that, compared with the age-matched normal control piglets, increased expression of Fn14 in epithelium and decreased TWEAK expression in lamina propria were detected in the small intestinal of piglets stimulated with LPS. Consistent with this finding, treatment with LPS increased the expression of Fn14 and TLR4 while decreased TWEAK expression in porcine small intestinal epithelial cell lines SIEC02. Interestingly, modulating Fn14 activation using agonistic anti-Fn14 decreased TLR4-mediated TNF-α production by SIEC02. In addition, pretreatment of LPS-stimulated SIEC02 with recombinant TWEAK protein suppresses the expression of Fn14 and TNF-α and inhibits the negative impact of LPS on the tight junctional protein occludin expression. In conclusion, this study demonstrates that the TWEAK-independent Fn14 activation augments TLR4-mediated inflammatory responses in the intestine of piglets. Furthermore, the TWEAK-dependent suppression of Fn14 signaling may play a role in intestinal homeostasis.

B Cell-Activating Factor (BAFF)-Targeted B Cell Therapies in Inflammatory Bowel Diseases

Inflammatory bowel diseases (IBD) involve dysregulated immune responses to gut antigens in genetically predisposed individuals. While a better elucidation of IBD pathophysiology has considerably increased the number of treatment options, the need for more effective therapeutic strategies remains a pressing priority. Defects of both non-hematopoietic (epithelial and stromal) and hematopoietic (lymphoid and myeloid) cells have been described in patients with IBD. Within the lymphoid system, alterations of the T cell compartment are viewed as essential in the pathogenesis of IBD. However, growing evidence points to the additional perturbations of the B cell compartment. Indeed, the intestinal lamina propria from IBD patients shows an increased presence of antibody-secreting plasma cells, which correlates with enhanced pro-inflammatory immunoglobulin G production and changes in the quality of non-inflammatory IgA responses. These B cell abnormalities are compounded by the emergence of systemic antibody responses to various autologous and microbial antigens, which predates the clinical diagnosis of IBD and identifies patients with complicated disease. It is presently unclear whether such antibody responses play a pathogenetic role, as B cell depletion with the CD20-targeting monoclonal antibody rituximab did not ameliorate ulcerative colitis in a clinical trial. However, it must be noted that unresponsiveness to rituximab is also observed also in some patients with autoimmune disorders usually responsive to B cell-depleting therapies. In this review, we discussed mechanistic aspects of B cell-based therapies and their potential role in IBD with a special interest on BAFF and BAFF-targeting therapies buoyed by the success of anti-BAFF treatments in rheumatologic disorders.

TRAF3 as a powerful and multitalented regulator of lymphocyte functions

This review summarizes the current state of knowledge regarding the roles of the signaling adapter protein tumor necrosis factor receptor (TNFR)-associated factor 3 in regulating the functions of B and T lymphocytes. In B lymphocytes, TNFR-associated factor 3 inhibits signaling by TNFR superfamily receptors, Toll-like receptors, and interleukin-6R. In contrast, signaling to B cells by the virally encoded oncogenic protein latent membrane protein 1 is promoted by TNFR-associated factor 3. An important B cell-specific role for TNFR-associated factor 3 is the inhibition of homeostatic survival, directly relevant to the common occurrence of TNFR-associated factor 3 mutations in human B cell malignancies. TNFR-associated factor 3 was recently found to be a resident nuclear protein in B cells, where it interacts with and inhibits gene expression mediated by the cAMP response element-binding protein transcription complex, including expression of the prosurvival protein myeloid leukemia cell differentiation protein 1. In T lymphocytes, TNFR-associated factor 3 is required for normal signaling by the T cell antigen receptor, while inhibiting signaling by the interleukin-2 receptor. Cytoplasmic TNFR -associated factor 3 restrains nuclear factor-κB2 activation in both T and B cells. Clinical implications and future directions for the study of this context-dependent signaling regulator are discussed.

A therapeutic role for BLyS antagonists

B lymphocytestimulator (BLyS) is a vital B cell survivalfactor. Overexpressionof BLyS in mice may lead to systemic lupus erythematosus (SLE)-like disease, and treatment of bona fide SLE mice with BLyS antagonists ameliorates disease progression and enhances survival. BLyS overexpression is common in human SLE, and results from a phase I clinical trial with a BLyS antagonistin human SLE have shown the antagonist to be biologicallyactive and safe. These features collectivelypoint to BLyS as an attractive therapeutic target in human disease.

TRAF3, ubiquitination, and B-lymphocyte regulation

The signaling adapter protein tumor necrosis factor receptor (TNFR)-associated factor 3 (TRAF3) is both modified by and contributes to several types of ubiquitination events. TRAF3 plays a variety of context-dependent regulatory roles in all types of immune cells. In B lymphocytes, TRAF3 contributes to regulation of signaling by members of both the TNFR superfamily and innate immune receptors. TRAF3 also plays a unique cell type-specific and critical role in the restraint of B-cell homeostatic survival, a role with important implications for both B-cell differentiation and the pathogenesis of B-cell malignancies. This review focuses upon the relationship between ubiquitin and TRAF3, and how this contributes to multiple functions of TRAF3 in the regulation of signal transduction, transcriptional activation, and effector functions of B lymphocytes.

Serum elevation of B lymphocyte stimulator does not increase regulatory B cells in glioblastoma patients undergoing immunotherapy

Regulatory B cells that secrete IL-10 (IL-10(+) Bregs) represent a suppressive subset of the B cell compartment with prominent anti-inflammatory capacity, capable of suppressing cellular and humoral responses to cancer and vaccines. B lymphocyte stimulator (BLyS) is a key regulatory molecule in IL-10(+) Breg biology with tightly controlled serum levels. However, BLyS levels can be drastically altered upon chemotherapeutic intervention. We have previously shown that serum BLyS levels are elevated, and directly associated, with increased antigen-specific antibody titers in patients with glioblastoma (GBM) undergoing lymphodepletive temozolomide chemotherapy and vaccination. In this study, we examined corresponding IL-10(+) Breg responses within this patient population and demonstrate that the IL-10(+) Breg compartment remains constant before and after administration of the vaccine, despite elevated BLyS levels in circulation. IL-10(+) Breg frequencies were not associated with serum BLyS levels, and ex vivo stimulation with a physiologically relevant concentration of BLyS did not increase IL-10(+) Breg frequency. However, BLyS stimulation did increase the frequency of the overall B cell compartment and promoted B cell proliferation upon B cell receptor engagement. Therefore, using BLyS as an adjuvant with therapeutic peptide vaccination could promote humoral immunity with no increase in immunosuppressive IL-10(+) Bregs. These results have implications for modulating humoral responses in human peptide vaccine trials in patients with GBM.

NF-κB transcriptional activation by TNFα requires phospholipase C, extracellular signal-regulated kinase 2 and poly(ADP-ribose) polymerase-1

BACKGROUND

The nuclear enzyme poly(ADP-ribose) polymerase-1 (PARP-1) is required for pro-inflammatory effects of TNFα. Our previous studies demonstrated that PARP-1 mediates TNFα-induced NF-κB activation in glia. Here, we evaluated the mechanisms by which TNFα activates PARP-1 and PARP-1 mediates NF-κB activation.

METHODS

Primary cultures of mouse cortical astrocytes and microglia were treated with TNFα and suitable signaling pathway modulators (pharmacological and molecular). Outcome measures included calcium imaging, PARP-1 activation status, NF-κB transcriptional activity, DNA damage assesment and cytokine relesease profiling.

RESULTS

TNFα induces PARP-1 activation in the absence of detectable DNA strand breaks, as measured by the PANT assay. TNFα-induced transcriptional activation of NF-κB requires PARP-1 enzymatic activity. Enzymatic activation of PARP-1 by TNFα was blocked in Ca(2+)-free medium, by Ca(2+) chelation with BAPTA-AM, and by D609, an inhibitor of phoshatidyl choline-specific phospholipase C (PC-PLC), but not by thapsigargin or by U73112, an inhibitor of phosphatidyl inisitol-specific PLC (PI -PLC). A TNFR1 blocking antibody reduced Ca(2+) influx and PARP-1 activation. TNFα-induced PARP-1 activation was also blocked by siRNA downregulation of ERK2 and by PD98059, an inhibitor of the MEK / ERK protein kinase cascade. Moreover, TNFα-induced NF-κB (p65) transcriptional activation was absent in cells expressing PARP-1 that lacked ERK2 phosphorylation sites, while basal NF-κB transcriptional activation increased in cells expressing PARP-1 with a phosphomimetic substitution at an ERK2 phophorylation site.

CONCLUSIONS

These results suggest that TNFα induces PARP-1 activation through a signaling pathway involving TNFR1, Ca(2+) influx, activation of PC-PLC, and activation of the MEK1 / ERK2 protein kinase cascade. TNFα-induced PARP-1 activation is not associated with DNA damage, but ERK2 mediated phosphorylation of PARP-1.

The role of BAFF in the progression of rheumatoid arthritis

Rheumatoid arthritis (RA) is a common autoimmune disease that is marked by a systemic inflammatory reaction and joint erosions. Elevated levels of B cell activating factor (BAFF) have been detected in the serum and synovial fluid of RA patients. Moreover, the levels of BAFF increase in cases of autoimmune disease and are correlated with the level of disease activity. As an innate cytokine mediator, BAFF affects the immune response of the synovial microenvironment. In this review, we consider recent observations of BAFF and its receptors in RA progression, as well as the effects of BAFF on the cell-cell interactions network. We also summarize the clinical development of BAFF antagonists for the treatment of RA.

Synergistic induction of apoptosis by combination of BTK and dual mTORC1/2 inhibitors in diffuse large B cell lymphoma

Diffuse large B cell lymphoma is generally treated by chemotherapy and there is an unmet medical need for novel targeted therapies or combination therapies. Using in vitro screening, we have identified the combination of ibrutinib, an inhibitor of the tyrosine kinase BTK, and AZD2014, an mTOR catalytic inhibitor, as being highly synergistic in killing ABC-subtype DLBCL cell lines. Simultaneous inhibition of BTK and mTOR causes apoptosis both in vitro and in vivo and results in tumor regression in a xenograft model. We identify two parallel mechanisms that underlie apoptosis in this setting: cooperative inhibition of cap-dependent translation, and the inhibition of an NF-κB/IL10/STAT3 autocrine loop. Combined disruption of these pathways is required for apoptosis. These data represent a rational basis for the dual inhibition of BTK and mTOR as a potential treatment for ABC-subtype DLBCL.

Involvement of RNA Polymerase III in Immune Responses

Inflammation in the tumor microenvironment has many tumor-promoting effects. In particular, tumor-associated macrophages (TAMs) produce many cytokines which can support tumor growth by promoting survival of malignant cells, angiogenesis, and metastasis. Enhanced cytokine production by TAMs is tightly coupled with protein synthesis. In turn, translation of proteins depends on tRNAs, short abundant transcripts that are made by RNA polymerase III (Pol III). Here, we connect these facts by showing that stimulation of mouse macrophages with lipopolysaccharides (LPS) from the bacterial cell wall causes transcriptional upregulation of tRNA genes. The transcription factor NF-κB is a key transcription factor mediating inflammatory signals, and we report that LPS treatment causes an increased association of the NF-κB subunit p65 with tRNA genes. In addition, we show that p65 can directly associate with the Pol III transcription factor TFIIIB and that overexpression of p65 induces Pol III-dependent transcription. As a consequence of these effects, we show that inhibition of Pol III activity in macrophages restrains cytokine secretion and suppresses phagocytosis, two key functional characteristics of these cells. These findings therefore identify a radical new function for Pol III in the regulation of macrophage function which may be important for the immune responses associated with both normal and malignant cells.

Serum levels of B-cell activating factor in chronic hepatitis B virus infection: association with clinical diseases

B-lymphocyte activation is a common characteristic of chronic hepatitis B virus (HBV) infection. B cell-activating factor (BAFF) plays a crucial role in the development and activation of B lymphocytes. This study investigated serum BAFF levels in 232 patients with different clinical diseases of chronic HBV infection [33 chronic asymptomatic HBV carrier (ASC), 53 chronic hepatitis (CH), 72 liver cirrhosis (LC), and 74 hepatocellular carcinoma (HCC)] and 61 gender- and age-matched healthy controls. Serum BAFF levels in HBV patients were significantly elevated compared with healthy controls (P<0.001). HCC patients had significantly higher levels of serum BAFF than ASC, CH, and LC (all P<0.001). Serum levels of BAFF in LC were significantly higher than in ASC (P<0.001) and CH (P=0.002). Serum level of BAFF was an independent variable associated with the presence of HCC in comparison with other disease groups in multivariate analysis. The area under receiver-operating characteristic curve (AUC) value of BAFF levels was 0.914 for HCC versus ASC, 0.825 for HCC versus CH, and 0.607 for HCC versus LC, respectively. The AUC value of BAFF levels was 0.854 for LC versus ASC and 0.748 for LC versus CH, respectively. The AUC value of BAFF (0.888) for HCC was higher than that of alpha-fetoprotein (0.776). We first demonstrate that serum BAFF levels in chronic HBV infection are elevated, correlated with clinical diseases, and could be used as a biomarker for indicating disease mechanisms, activity, and diagnosis.

Regulatory roles of the tumor necrosis factor receptor BCMA

B cell maturation antigen (BCMA) is a tumor necrosis family receptor (TNFR) member that is predominantly expressed on terminally differentiated B cells and, upon binding to its ligands B cell activator of the TNF family (BAFF) and a proliferation inducing ligand (APRIL), delivers pro-survival cell signals. Thus, BCMA is mostly known for its functional activity in mediating the survival of plasma cells that maintain long-term humoral immunity. The expression of BCMA has also been linked to a number of cancers, autoimmune disorders, and infectious diseases that suggest additional roles for BCMA activity. Despite recent advances in our understanding of the roles for the related TNFR members BAFF-R and transmembrane activator and calcium-modulator and cyclophilin ligand interactor (TACI), the signaling pathway used by BCMA for mediating plasma cell survival as well as its putative function in certain disease states are not well understood. By examining the expression, regulation, and signaling targets of BCMA, we may gain further insight into this receptor and how it operates within cells in both health and disease. This information is important for identifying new therapeutic targets that may be relevant in treating diseases that involve the BAFF/APRIL cytokine network.

B-cell activating factor-receptor specific activation of tumor necrosis factor receptor associated factor 6 and the phosphatidyl inositol 3-kinase pathway in lymphoma B cells

B-cell activating factor-receptor (BAFF-R) is the primary BAFF receptor that is responsible for promoting B-cell development and survival. Malignant B-cells exploit the BAFF/BAFF-R system, and high serum BAFF levels or genetic alterations in BAFF receptors have been found in B-cell cancers. BAFF signaling impacts pro-survival pathways. However, other than nuclear factor-κB2 (NF-κB2), little is known about the specific pathways activated by individual BAFF receptors. Using a novel BAFF-R expression model we have demonstrated that activation of BAFF-R, independent of transmembrane activator and cytophilin ligand interactor (TACI) and B-cell maturation antigen (BCMA), can induce phosphorylation of Akt and glycogen synthase kinase 3β (GSK3β). Expression of an activated form of BAFF-R also enhanced a pro-survival gene expression pattern, including the novel BAFF-regulated gene Pin1, whose expression was phosphatidyl inositol 3-kinase (PI3K)-dependent. Additionally, we showed that TRAF6 is essential for mediating BAFF-R dependent activation of Akt. Together these data describe a novel role for TRAF6 in BAFF-R-specific activation of the PI3K pathway and provide evidence suggesting a new role for Pin1 in BAFF-R signaling.

Roles for TNF-receptor associated factor 3 (TRAF3) in lymphocyte functions

TRAF3 is an adapter protein that serves and regulates the functions of several types of receptors, located both inside the cell and at the plasma membrane. These include members of the TNF receptor superfamily (TNFR-SF), toll-like receptors (TLR), and cytokine receptors. It has become increasingly evident that the roles and functions of TRAF3 are highly context-dependent. TRAF3 can serve distinct roles for different receptors in the same cell, and also has highly cell-type-dependent functions. This review focuses upon the current state of knowledge regarding how TRAF3 regulates the biology and effector functions of B and T lymphocytes, two major cell types of the adaptive immune response in which TRAF3 has markedly distinct roles.

A Complex Relationship between TRAF3 and Non-Canonical NF-κB2 Activation in B Lymphocytes

The adaptor protein TRAF3 restrains B cell activating factor receptor (BAFFR) and CD40-mediated activation of the NF-κB2 pathway in B cells. Mice lacking TRAF3 specifically in B cells revealed the critical role of TRAF3 in restraining homeostatic B cell survival. Furthermore, loss-of-function mutations of the traf3 gene have been associated with human B cell malignancies, especially multiple myeloma (MM). It has been proposed that receptor-induced TRAF3 degradation leads to stabilization of the NF-κB inducing kinase (NIK), and subsequent NF-κB2 activation. However, it is unclear how receptor-mediated TRAF3 degradation or loss-of-function contributes to B cell-specific NF-κB2 activation. In the current study, we employed two complementary models to address this question. One utilized a mutant traf3 gene found in a human MM-derived cell line called LP1. The LP1 mutant TRAF3 protein lacks the TRAF-N and TRAF-C domains. Consistent with the paradigm described, expression of LP1 TRAF3 in B cells promoted higher basal levels of NF-κB2 activation compared to Wt TRAF3. However, LP1 did not associate with TRAF2, CD40, or BAFFR, and no LP1 degradation was observed following receptor engagement. Interestingly, LP1 showed enhanced NIK association. Thus, TRAF3 degradation becomes dispensable to activate NF-κB2 when it is unable to associate with TRAF2. In a second model, we examined several mutant forms of BAFFR that are unable to induce NF-κB2 activation in B cells. Signaling to B cells by each of these BAFFR mutants, however, induced levels of TRAF3 degradation similar to those induced by Wt BAFFR. Thus, in B cells, receptor-mediated TRAF3 degradation is not sufficient to promote NF-κB2 activation. We thus conclude that there is not a simple linear relationship in B lymphocytes between relative levels of cellular TRAF3, induced TRAF3 degradation, NIK activation, and NF-κB2 activation.

The Role of Ubiquitination in TWEAK-Stimulated Signaling

Tumor necrosis factor superfamily ligands and receptors are responsible for development, immunity, and homeostasis of metazoan organisms. Thus, it is not surprising that signals emanating from these receptors are tightly regulated. Binding of TNF-related weak inducer of apoptosis (TWEAK) to its cognate receptor, FN14, triggers the assembly of receptor-associated signaling complex, which allows the activation of canonical and non-canonical nuclear factor kappa B (NF-κB) as well as mitogen-activated protein kinase signaling pathways. Ubiquitin ligases cellular inhibitor of apoptosis 1 and 2 (c-IAP1 and 2) and adaptor proteins TNFR-associated factors 2 and 3 (TRAF2 and TRAF3) are crucial for the regulation of TWEAK signaling as they facilitate the recruitment of distal signaling components including IKK and linear ubiquitin chain assembly complex complexes. At the same time c-IAP1/2, together with TRAF2 and TRAF3, promote constitutive ubiquitination and proteasomal degradation of NF-κB inducing kinase (NIK) – a kinase with critical role in the activation of non-canonical NF-κB signaling. While c-IAP1/2 mediated ubiquitination allows the activation of TWEAK-stimulated canonical NF-κB signaling, these E3 ligases are negative regulators of non-canonical signaling. TWEAK stimulation prompts the recruitment of c-IAP1/2 as well as TRAF2 and TRAF3 to the FN14 signaling complex leading to c-IAP1/2 autoubiquitination and degradation, which stabilizes NIK and allows subsequent phosphorylation of IKKα and partial proteasomal processing of p100 to activate gene expression. Recent studies have revealed that the spatio-temporal pattern of TWEAK-stimulated ubiquitination is a carefully orchestrated process involving several substrates that are modified by different ubiquitin linkages. Understanding the significance of ubiquitination for TWEAK signaling is important for the overall understanding of TWEAK biology and for the design of therapeutics that can be used in the treatment of human pathologies that are driven by TWEAK/FN14 expression and activity.

Coregulation and modulation of NFκB-related genes in celiac disease: uncovered aspects of gut mucosal inflammation

It is known that the NFκB route is constitutively upregulated in celiac disease (CD), an immune-mediated disorder of the gut caused by intolerance to ingested gluten. Our aim was to scrutinize the expression patterns of several of the most biologically relevant components of the NFκB route in intestinal biopsies from active and treated patients and after in vitro gliadin challenge, and to assess normalization of the expression using an inhibitor of the MALT1 paracaspase. The expression of 93 NFκB genes was measured by RT-PCR in a set of uncultured active and treated CD and control biopsies, and in cultured biopsy series challenged with gliadin, the NFκB modulator, both compounds and none. Methylation of eight genes involved in NFκB signaling was analyzed by conventional pyrosequencing. Groups were compared and Pearson's correlation matrixes were constructed to check for coexpression and co-methylation. Our results confirm the upregulation of the NFκB pathway and show that constitutively altered genes usually belong to the core of the pathway and have central roles, whereas genes overexpressed only in active CD are more peripheral. Additionally, this is the first work to detect methylation level changes in celiac intestinal mucosa. Coexpression is very common in controls, whereas gliadin challenge and especially chronic inflammation present in untreated CD result in the disruption of the regulatory equilibrium. In contrast, co-methylation occurs more often in active CD. Importantly, NFκB modulation partially restores coregulation, opening the door to future therapeutic possibilities and targets.

Regulation of PI-3-Kinase and Akt Signaling in T Lymphocytes and Other Cells by TNFR Family Molecules

Activation of phosphoinositide 3-kinase (PI3K) and Akt (protein kinase B) is a common response triggered by a range of membrane-bound receptors on many cell types. In T lymphocytes, the PI3K-Akt pathway promotes clonal expansion, differentiation, and survival of effector cells and suppresses the generation of regulatory T cells. PI3K activation is tightly controlled by signals through the T cell receptor (TCR) and the co-stimulatory receptor CD28, however sustained and periodic signals from additional co-receptors are now being recognized as critical contributors to the activation of this pathway. Accumulating evidence suggests that many members of the Tumor Necrosis Factor receptor (TNFR) superfamily, TNFR2 (TNFRSF1B), OX40 (TNFRSF4), 4-1BB (TNFRSF9), HVEM (TNFRSF14), and DR3 (TNFRSF25), that are constitutive or inducible on T cells, can directly or indirectly promote activity in the PI3K-Akt pathway. We discuss recent data which suggests that ligation of one TNFR family molecule organizes a signalosome, via TNFR-associated factor (TRAF) adapter proteins in T cell membrane lipid microdomains, that results in the subsequent accumulation of highly concentrated depots of PI3K and Akt in close proximity to TCR signaling units. We propose this may be a generalizable mechanism applicable to other TNFR family molecules that will result in a quantitative contribution of these signalosomes to enhancing and sustaining PI3K and Akt activation triggered by the TCR. We also review data that other TNFR molecules, such as CD40 (TNFRSF5), RANK (TNFRSF11A), FN14 (TNFRSF12A), TACI (TNFRSF13B), BAFFR (TNFRSF13C), and NGFR (TNFRSF16), contribute to the activation of this pathway in diverse cell types through a similar ability to recruit PI3K or Akt into their signaling complexes.

Serum B-cell activating factor assessment in a population of Egyptian patients with systemic sclerosis

BACKGROUND

Systemic sclerosis (SSc) is a rare systemic connective tissue disease characterized by abnormal fibroblast proliferation and micro-vascular inflammatory changes.

AIM

To assess serum B-cell activating factor (BAFF) levels in patients with systemic sclerosis and to correlate this with disease features and disease severity.

METHODS

This is a case-control study in which patients with the established diagnosis of SSc were recruited. The diagnosis of SSc was established according to the American Rheumatology Association 1980 criteria for the classification of scleroderma. Patients' assessment included evaluation of skin involvement using the Modified Rodnan score and disease severity using the Medsger score. Twenty-five healthy matching controls were included. The sandwich enzyme-linked immunosorbent assay technique was used for direct assessment of serum BAFF in patients and controls.

RESULTS

The study included 60 patients (54 female and 6 male), with a mean age of 38.18 ± 12.06 years, with mean disease duration of 7.85 ± 4.075 years. Serum BAFF in patients ranged 98.2-5015 pg/mL with mean BAFF 1100 ± 835.4 pg/mL. In controls serum BAFF levels ranged 188.5-2314 pg/mL with mean BAFF 546.1 ± 471.1 pg/mL, showing a statistically significant elevation of serum BAFF levels in SSc patients (P = 0.0001) with insignificant correlation to skin disease or total Medsgar Score of the study population (P > 0.05). Serum BAFF levels showed significant correlation with episodes of pseudo-obstruction and methotrexate (MTX) use in the patients studied (P < 0.05).

CONCLUSION

Serum BAFF levels were significantly elevated in patients with SSc irrespective of disease subtype, disease duration or age of patients. This elevation in serum BAFF significantly related to gastrointestinal track involvement and MTX therapy.

Cellular inhibitors of apoptosis are global regulators of NF-κB and MAPK activation by members of the TNF family of receptors

Tumor necrosis factor (TNF) family members are essential for the development and proper functioning of the immune system. TNF receptor (TNFR) signaling is mediated through the assembly of protein signaling complexes that activate the nuclear factor κB (NF-κB) and mitogen-activated protein kinase (MAPK) pathways in a ubiquitin-dependent manner. The cellular inhibitor of apoptosis (c-IAP) proteins c-IAP1 and c-IAP2 are E3 ubiquitin ligases that are recruited to TNFR signaling complexes through their constitutive association with the adaptor protein TNFR-associated factor 2 (TRAF2). We demonstrated that c-IAP1 and c-IAP2 were required for canonical activation of NF-κB and MAPK by members of the TNFR family. c-IAPs were required for the recruitment of inhibitor of κB kinase β (IKKβ), the IKK regulatory subunit NF-κB essential modulator (NEMO), and RBCK1/Hoil1-interacting protein (HOIP) to TNFR signaling complexes and the induction of gene expression by TNF family members. In contrast, TNFRs that stimulated the noncanonical NF-κB pathway triggered translocation of c-IAPs, TRAF2, and TRAF3 from the cytosol to membrane fractions, which led to their proteasomal and lysosomal degradation. Finally, we established that signaling by B cell-activating factor receptor 3 induced the cytosolic depletion of TRAF3, which enabled noncanonical NF-κB activation. These results define c-IAP proteins as critical regulators of the activation of NF-κB and MAPK signaling pathways by members of the TNFR superfamily.

Roles of pro- and anti-inflammatory cytokines in the pathogenesis of SLE

SLE is an autoimmune inflammatory disease in which various pro- and anti-inflammatory cytokines, including TGF-β, IL-10, BAFF, IL-6, IFN-α, IFN-γ, IL-17, and IL-23, play crucial pathogenic roles. Virtually, all these cytokines can be generated by both innate and adaptive immune cells and exert different effects depending on specific local microenvironment. They can also interact with each other, forming a complex network to maintain delicate immune homeostasis. In this paper, we elaborate on the abnormal secretion and functions of these cytokines in SLE, analyze their potential pathogenic roles, and probe into the possibility of them being utilized as targets for therapy.

Signaling by the tumor necrosis factor receptor superfamily in B-cell biology and disease

Members of the tumor necrosis factor receptor superfamily (TNFRSF) participate prominently in B-cell maturation and function. In particular, B-cell activating factor belonging to the TNF family receptor (BAFF-R), B-cell maturation antigen (BCMA), and transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI) play critical roles in promoting B-cell survival at distinct stages of development by engaging a proliferation-inducing ligand (APRIL) and/or BAFF. CD40 is also essential for directing the humoral response to T-cell-dependent antigens. Signaling by the TNFRSF is mediated primarily, albeit not exclusively, via the TNFR-associated factor (TRAF) proteins and activation of the canonical and/or non-canonical nuclear factor-κB (NF-κB) pathways. Dysregulated signaling by TNFRSF members can promote B-cell survival and proliferation, causing autoimmunity and neoplasia. In this review, we present a current understanding of the functions of and distinctions between APRIL/BAFF signaling by their respective receptors expressed on particular B-cell subsets. These findings are compared and contrasted with CD40 signaling, which employs similar signaling conduits to achieve distinct cellular outcomes in the context of the germinal center response. We also underscore how new findings and conceptual insights into TNFRSF signaling are facilitating the understanding of B-cell malignancies and autoimmune diseases.

Roles of tumor necrosis factor receptor associated factor 3 (TRAF3) and TRAF5 in immune cell functions

A large and diverse group of receptors utilizes the family of cytoplasmic signaling proteins known as tumor necrosis factor receptor (TNFR)-associated factors (TRAFs). In recent years, there has been a resurgence of interest and exploration of the roles played by TRAF3 and TRAF5 in cellular regulation, particularly in cells of the immune system, the cell types of focus in this review. This work has revealed that TRAF3 and TRAF5 can play diverse roles for different receptors even in the same cell type, as well as distinct roles in different cell types. Evidence indicates that TRAF3 and TRAF5 play important roles beyond the TNFR-superfamily (SF) and viral mimics of its members, mediating certain innate immune receptor and cytokine receptor signals, and most recently, signals delivered by the T-cell receptor (TCR) signaling complex. Additionally, much research has demonstrated the importance of TRAF3-mediated cellular regulation via its cytoplasmic interactions with additional signaling proteins. In particular, we discuss below evidence for the participation by TRAF3 in a number of the regulatory post-translational modifications involving ubiquitin that are important in various signaling pathways.

Non-canonical NF-κB signaling activation and regulation: principles and perspectives

Nuclear-factor κB (NF-κB) transcription factors are activated by a wide variety of stimuli in diverse cell types and control key aspects of immune function and development. Receptor-mediated activation of NF-κB appears to occur through two distinct signaling pathways termed as the canonical and non-canonical NF-κB pathways. Although much work has demonstrated the physiological importance of non-canonical NF-κB signaling to immunity and its involvement in diverse pathologies, such as cancers and autoimmune disease, the architecture and regulation of the pathway is only beginning to be understood. The non-canonical pathway appears to be activated by a select set of receptors within the tumor necrosis factor superfamily, and we discuss the molecular mechanisms that connect ligation of these receptors to pathway activation. It has become increasingly clear that the key regulatory step of the pathway involves modulation of the post-translational degradation of NF-κB-inducing kinase (NIK), the central activating kinase of non-canonical NF-κB signaling. How NIK post-translational stability is controlled before and after receptor ligation is an important aspect of understanding non-canonical NF-κB signaling. Furthermore, how release of NF-κB dimers downstream of the pathway's activation is actually connected to its identified physiological and pathological roles is a key remaining question in the field.

Enhanced Toll-like receptor (TLR) responses of TNFR-associated factor 3 (TRAF3)-deficient B lymphocytes

The key role of TRAF6 in TLR signaling pathways is well known. More recent evidence has implicated TRAF3 as another TRAF family member important to certain TLR responses of myeloid cells. Previous studies demonstrate that TRAF3 functions are highly context-dependent, displaying receptor and cell-type specificity. We thus examined the TLR responses of TRAF3(-/-)mouse B lymphocytes to test the hypothesis that TRAF3 plays distinct roles in such responses, depending on cell type. TRAF3(-/-) DC are known to have a defect in type 1 IFN production and here, showed diminished production of TNF and IL-10 and unaltered IL-6. In marked contrast, TRAF3(-/-) B cells made elevated amounts of TNF and IL-6 protein, as well as IL-10 and IP-10 mRNA, in response to TLR ligands. Also, in contrast to TRAF3(-/-) DC, the type 1 IFN pathway was elevated in TRAF3(-/-) B cells. Increased early responses of TRAF3(-/-) B cells to TLR signals were independent of cell survival or proliferation but associated with elevated canonical NF-κB activation. Additionally, TRAF3(-/-) B cells displayed enhanced TLR-mediated expression of AID and Ig isotype switching. Thus, TRAF3 plays varied and cell type-specific, biological roles in TLR responses.

Aberrant expression of functional BAFF-system receptors by malignant B-cell precursors impacts leukemia cell survival

Despite exhibiting oncogenic events, patient's leukemia cells are responsive and dependent on signals from their malignant bone marrow (BM) microenvironment, which modulate their survival, cell cycle progression, trafficking and resistance to chemotherapy. Identification of the signaling pathways mediating this leukemia/microenvironment interplay is critical for the development of novel molecular targeted therapies.

We observed that primary leukemia B-cell precursors aberrantly express receptors of the BAFF-system, BAFF-R, BCMA, and TACI. These receptors are functional as their ligation triggers activation of NF-κB, MAPK/JNK, and Akt signaling. Leukemia cells express surface BAFF and APRIL ligands, and soluble BAFF is significantly higher in leukemia patients in comparison to age-matched controls. Interestingly, leukemia cells also express surface APRIL, which seems to be encoded by APRIL-δ, a novel isoform that lacks the furin convertase domain. Importantly, we observed BM microenvironmental cells express the ligands BAFF and APRIL, including surface and secreted BAFF by BM endothelial cells. Functional studies showed that signals through BAFF-system receptors impact the survival and basal proliferation of leukemia B-cell precursors, and support the involvement of both homotypic and heterotypic mechanisms.

This study shows an unforeseen role for the BAFF-system in the biology of precursor B-cell leukemia, and suggests that the target disruption of BAFF signals may constitute a valid strategy for the treatment of this cancer.

Innate control of B cell responses

Mature B cells generate protective immunity by undergoing immunoglobulin (Ig) class switching and somatic hypermutation, two Ig gene-diversifying processes that usually require cognate interactions with T cells that express CD40 ligand. This T cell-dependent pathway provides immunological memory but is relatively slow to occur. Thus, it must be integrated with a faster, T cell-independent pathway for B cell activation through CD40 ligand-like molecules that are released by innate immune cells in response to microbial products. Here, we discuss recent advances in our understanding of the interplay between the innate immune system and B cells, particularly at the mucosal interface. We also review the role of innate signals in the regulation of Ig diversification and production.

Deletion of cIAP1 and cIAP2 in murine B lymphocytes constitutively activates cell survival pathways and inactivates the germinal center response

B cells require signals delivered through B-cell activating factor of the TNF family receptor (BAFF-R) and CD40 to survive and produce antibody responses in vivo. In vitro data indicate that these signals are controlled by the homologous RING finger proteins cIAP1 and cIAP2, in collaboration with TRAF2 and TRAF3. There is also mounting evidence that all 4 of these signaling molecules can act as tumor suppressors in human B-lineage malignancies. However, it has not been possible to identify the roles of cIAP1 and cIAP2 in controlling B-cell physiology because of the absence of an appropriate in vivo model. Here we describe a unique genetically modified mouse in which the linked cIap1 and cIap2 genes can be independently inactivated. Deletion of cIAP1 plus cIAP2 (but not either protein alone) rendered primary B cells independent of BAFF-R for their survival and led to their uncontrolled accumulation in vivo. B cells deficient in cIAP1 and cIAP2 were also incapable of forming germinal centers, a key step in antibody-mediated immunity. These data define a fundamental role for cIAP1/cIAP2 in regulating B-cell survival and responsiveness, show this requires direct binding to TRAF2, and suggest how mutations of TRAF2, TRAF3, and cIAP1/cIAP2 contribute to B-lineage malignancies, such as multiple myeloma.

Constitutive BR3 receptor signaling in diffuse, large B-cell lymphomas stabilizes nuclear factor-κB-inducing kinase while activating both canonical and alternative nuclear factor-κB pathways

Aberrant nuclear factor κB (NF-κB) signaling has been found to be of particular importance in diffuse, large B-cell lymphoma (DLBCL) cell survival and proliferation. Although the canonical NF-κB signaling pathway has been studied in some detail, activation of the alternative NF-κB pathway in DLBCL is not well characterized. Important insights into the regulation of the alternative NF-κB pathway in B lymphocytes has recently revealed the regulatory importance of the survival kinase NIK (NF-κB-inducing kinase) in genetically engineered murine models. Our studies demonstrate that both the canonical and alternative NF-κB pathways are constitutively activated in DLBCL. We also demonstrate that NIK kinase aberrantly accumulates in DLBCL cells due to constitutive activation of B-cell activation factor (BAFF)-R (BR3) through interaction with autochthonous B-lymphocyte stimulator (BLyS) ligand in DLBCL cells. Activation of BR3 in DLBCL induces recruitment and degradation of tumor necrosis factor receptor-associated factor 3, which results in NIK kinase accumulation, IκBα phosphorylation, and NF-κB p100 processing, thereby resulting in continuous activation of both NF-κB pathways in DLBCL cells, leading to autonomous lymphoma cell growth and survival. These results further elucidate mechanisms involved in abnormal NF-κB activation in DLBCL, and should contribute to better future therapeutic approaches for patients with DLBCL.

In vivo control of B-cell survival and antigen-specific B-cell responses

Targeted modification of the mouse genome provides the capability to manipulate complex physiological processes in a precise and controlled manner. Investigation of B-lymphocyte biology has benefited not only from the targeted modification of genes controlling B-cell survival and responsiveness, but also from the manipulation of antigen specificity made possible by targeting endogenous immunoglobulin loci. In this review, we discuss recent results obtained from our laboratory using gene-targeted mouse models to investigate the in vivo regulation of B-cell survival and responsiveness. The control of BAFF-dependent survival signals by the TRAF2- and TRAF3-signaling proteins is discussed as is the potential involvement of these molecules in B-lineage malignancies. We also outline the development and use of the SW(HEL) model for analyzing antigen-specific B-cell responses in vivo. This includes insights into the control of early decision-making during T-dependent B-cell differentiation, the affinity maturation and plasma cell differentiation of germinal center B cells, and the identification of EBI2 as a key regulator of B-cell migration and differentiation.