The TNFR2-TRAF signaling complex contains two novel proteins related to baculoviral inhibitor of apoptosis proteins

Molecular characterization and functional analysis of tumor necrosis factor receptor-associated factor 2/7 and tumor necrosis factor receptor 1-associated death domain protein from Larimichthys crocea

In the present study, we characterized tumor necrosis factor receptor-associated factor 2/7 (lcTRAF2/7) and TNFR1-associated death domain protein (lcTRADD) in Larimichthys crocea (L. crocea) and examined their expression profiles in tissues of Vibrio-challenged and unchallenged fish. The coding sequences of lcTRAF2, lcTRAF7, and lcTRADD were 1488, 2454, and 744 nucleotides, and they encoded proteins of 495, 344, and 248 amino acids, respectively. The results of phylogenetic analysis revealed that lcTRAF2, lcTRAF7, and lcTRADD were closest to Oplegnathus fasciatus (85%), Xiphophorus maculatus (97%), and Acanthochromis polyacanthus (65%), respectively. Multiple sequence alignment showed that lcTRAF2 and lcTRAF7 were highly conserved with other vertebrate TRAFs in their functional domains; however, lcTRADD was poorly conserved. The results of quantitative real-time polymerase chain reaction analysis indicated that lcTRAF2, lcTRAF7, and lcTRADD were constitutively expressed in the spleen, liver, kidney, heart, brain, gill, bladder, skin, fin, eye, and muscle. After challenging fish with Vibrio parahaemolyticus, the mRNA expression levels of lcTRAF2, lcTRAF7, and lcTRADD were upregulated in liver, spleen, and kidney. Immunofluorescence staining revealed that lcTRAF2 and lcTRADD were cytoplasmic in localization, whereas lcTRAF7 targeted both the cytoplasm and nucleus. In addition, the NF-κB protein level was upregulated after lipopolysaccharide stimulation in lcTRAF2, lcTRAF7, or lcTRADD overexpressing cells. Taken collectively, these results have improved our understanding of the functions of TRAF2, TRAF7, and TRADD in pathogenic infections in teleosts.

Fish TRAF2 promotes innate immune response to RGNNV infection

Tumour necrosis factor receptor-associated factors (TRAFs) are key regulatory proteins in the NF-κB signaling pathways. TRAF2 participates in the activation of both canonical and non-canonical NF-κB pathways, which are crucial for cell inflammation and cell survival. To elucidate its function in teleost fish, TRAF2 homologues of yellow grouper (Epinephelus awoara) and golden pompano (Trachinotus ovatus) have been cloned and characterized in this study. The open reading frame (ORF) of grouper TRAF2 (EaTRAF2) consists of 1563 nucleotides encoding a 521 amino acid protein with a predicted molecular mass of 58.70 kDa. The ORF of golden pompano TRAF2 (ToTRAF2) consists of 1563 nucleotides encoding a 521 amino acid protein with a predicted molecular mass of 58.66 kDa EaTRAF2 and ToTRAF2 share 99.23% and 99.42% identity with orange-spotted grouper (Epinephelus coioides) TRAF2 (EcTRAF2), respectively. Quantitative real-time PCR analysis indicated that the expression of EaTRAF2 was increased in grouper spleen (GS) cells after Red-spotted grouper nervous necrosis virus (RGNNV) infection; while the expression of ToTRAF2 was decreased in golden pompano brain (TOGB) cells after RGNNV infection. Both EaTRAF2 and ToTRAF2 were identified as a cytosolic protein and suggested to be associated with vesicles scattering in the cytoplasm. Both EaTRAF2 and ToTRAF2 enhanced RGNNV replication during viral infection in vitro. Further studies showed that EaTRAF2 and ToTRAF2 overexpression decreased the expression levels of interferon associated cytokines and pro-inflammatory factors. Taken together, these results are important for better understanding of the function of TRAF2 in fish and reveal its involvement in host response to immune challenges in RGNNV.

The Multiple Roles of the IAP Super-family in cancer

The Inhibitor of Apoptosis proteins (IAPs) are a family of proteins that are mainly known for their anti-apoptotic activity and ability to directly bind and inhibit caspases. Recent research has however revealed that they have extensive roles in governing numerous other cellular processes. IAPs are known to modulate ubiquitin (Ub)-dependent signaling pathways through their E3 ligase activity and influence activation of nuclear factor κB (NF-κB). In this review, we discuss the involvement of IAPs in individual hallmarks of cancer and the current status of therapies targeting these critical proteins.

Pathophysiological landscape of osteoarthritis

A sharp rise in osteoarthritis (OA) incidence is expected as over 25% of world population ages in the coming decade. Although OA is considered a degenerative disease, mounting evidence suggests a strong connection with chronic metabolic conditions and low-grade inflammation. OA pathology is increasingly understood as a complex interplay of multiple pathological events including oxidative stress, synovitis and immune responses revealing its intricate nature. Cellular, biochemical and molecular aspects of these pathological events along with major outcomes of the relevant research studies in this area are discussed in the present review. With reference to their published and unpublished work, the authors strongly propose synovitis as a central OA pathology and the key OA pathological events are described in connection with it. Recent research outcomes also have succeeded to establish a linkage between metabolic syndrome and OA, which has been precisely included in the present review. Impact of aging process cannot be neglected in OA. Cell senescence is an important mechanism of aging through which it facilitates development of OA like other degenerative disorders, also discussed within a frame of OA. Conclusively, the reviewers urge low-grade inflammation linked to aging and derailed immune function as a pathological platform for OA development and progression. Thus, interventions targeted to prevent inflammaging hold a promising potential in effective OA management and efforts should be invested in this direction.

Selective Targeting of TNF Receptors as a Novel Therapeutic Approach

Tumor necrosis factor (TNF) is a central regulator of immunity. Due to its dominant pro-inflammatory effects, drugs that neutralize TNF were developed and are clinically used to treat inflammatory and autoimmune diseases, such as rheumatoid arthritis, inflammatory bowel disease and psoriasis. However, despite their clinical success the use of anti-TNF drugs is limited, in part due to unwanted, severe side effects and in some diseases its use even is contraindicative. With gaining knowledge about the signaling mechanisms of TNF and the differential role of the two TNF receptors (TNFR), alternative therapeutic concepts based on receptor selective intervention have led to the development of novel protein therapeutics targeting TNFR1 with antagonists and TNFR2 with agonists. These antibodies and bio-engineered ligands are currently in preclinical and early clinical stages of development. Preclinical data obtained in different disease models show that selective targeting of TNFRs has therapeutic potential and may be superior to global TNF blockade in several disease indications.

IAP-Mediated Protein Ubiquitination in Regulating Cell Signaling

Over the last decade, the E3-ubiquitine ligases from IAP (Inhibitor of Apoptosis) family have emerged as potent regulators of immune response. In immune cells, they control signaling pathways driving differentiation and inflammation in response to stimulation of tumor necrosis factor receptor (TNFR) family, pattern-recognition receptors (PRRs), and some cytokine receptors. They are able to control the activity, the cellular fate, or the stability of actors of signaling pathways, acting at different levels from components of receptor-associated multiprotein complexes to signaling effectors and transcription factors, as well as cytoskeleton regulators. Much less is known about ubiquitination substrates involved in non-immune signaling pathways. This review aimed to present IAP ubiquitination substrates and the role of IAP-mediated ubiquitination in regulating signaling pathways.

Targeting triple-negative breast cancers with the Smac-mimetic birinapant

Smac mimetics target inhibitor of apoptosis (IAP) proteins, thereby suppressing their function to facilitate tumor cell death. Here we have evaluated the efficacy of the preclinical Smac-mimetic compound A and the clinical lead birinapant on breast cancer cells. Both exhibited potent in vitro activity in triple-negative breast cancer (TNBC) cells, including those from patient-derived xenograft (PDX) models. Birinapant was further studied using in vivo PDX models of TNBC and estrogen receptor-positive (ER⁺) breast cancer. Birinapant exhibited single agent activity in all TNBC PDX models and augmented response to docetaxel, the latter through induction of TNF. Transcriptomic analysis of TCGA datasets revealed that genes encoding mediators of Smac-mimetic-induced cell death were expressed at higher levels in TNBC compared with ER⁺ breast cancer, resulting in a molecular signature associated with responsiveness to Smac mimetics. In addition, the cell death complex was preferentially formed in TNBCs versus ER⁺ cells in response to Smac mimetics. Taken together, our findings provide a rationale for prospectively selecting patients whose breast tumors contain a competent death receptor signaling pathway for the further evaluation of birinapant in the clinic.

Association of the Polymorphism rs13259960 in SLEAR With Predisposition to Systemic Lupus Erythematosus

OBJECTIVE

Genome-wide association studies have identified many susceptibility loci for systemic lupus erythematosus (SLE). However, most of these loci are located in noncoding regions of the genome. Long noncoding RNAs (lncRNAs) are pervasively expressed and have been reported to be involved in various diseases. This study aimed to explore the genetic significance of lncRNAs in SLE.

METHODS

A genome-wide survey of SLE risk variants in lncRNA gene loci was performed in Han Chinese subjects (4,556 with SLE and 9,451 healthy controls). The functional relevance of an SLE risk variant in one of the lncRNA genes was explored using biochemical and molecular cell biology analyses. In vitro loss-of-function and gain-of-function strategies were used to clarify the functional and phenotypic relevance of this SLE susceptibility lncRNA. Moreover, correlation of this lncRNA with the degree of apoptosis in the peripheral blood of SLE patients was evaluated.

RESULTS

A novel SLE susceptibility locus in a lncRNA gene, designated SLEAR (for SLE-associated RNA), was identified at the single-nucleotide polymorphism rs13259960 (odds ratio 1.35, P_combined = 1.03 × 10^-11 ). The A>G variation at rs13259960, located in an intronic enhancer, was found to impair STAT1 recruitment to the enhancer that loops to the SLEAR promoter, resulting in decreased SLEAR production in peripheral blood mononuclear cells from patients with SLE (3 with the G/G genotype, 22 with A/G, and 103 with A/A at rs13259960; P = 0.0241). Moreover, SLEAR interacted with the RNA binding proteins interleukin enhancer binding factor 2, heterogeneous nuclear RNP F, and TATA-binding protein-associated factor 15, to form a complex for transcriptional activation of the downstream antiapoptotic genes. In addition, SLEAR regulated apoptosis of Jurkat cells in vitro, and its expression level was correlated with the degree of cell death in the peripheral blood of patients with SLE (r = 0.824, P = 2.15 × 10^-8 ; n = 30).

CONCLUSION

These findings suggest a mechanism by which the risk variant at rs13259960 modulates SLEAR expression and confers a predisposition to SLE. Taken together, these results may give insights into the etiology of SLE.

Molecular and Functional Characterization of Inhibitor of Apoptosis Proteins (IAP, BIRP) in Echinococcus granulosus

The larval stage of Echinococcus granulosus sensu lato, resulting in cystic echinococcosis, a parasitic zoonosis, causes huge economic losses to the livestock industry and poses a threat to public health. Inhibitor of apoptosis proteins (IAPs) is a class of endogenous anti-apoptotic family, which plays a significant functional role in the regulation of organism’s development. Herein, to explore potential functions of IAPs in E. granulosus, two members of IAPs from E. granulosus (Eg-IAP and Eg-BIRP) were cloned, expressed, and molecularly characterized. Eg-IAP and Eg-BIRP encoded putative 331 and 168 residue proteins, respectively. Bioinformatic analysis showed that both proteins contained a type II BIR domain-the essential functional domain of IAPs. Fluorescence immunohistochemistry revealed that both proteins were ubiquitously localized in all life-cycle stages of E. granulosus. Our fluorescent quantitative PCR (RT-qPCR) results revealed relatively higher transcription levels of two Eg-IAPs in protoscoleces (PSCs) compared to the 18-day strobilated worms. We further used different concentrations of LCL161, a Smac-mimetic pan-IAPs inhibitor, to induce the apoptosis in PSCs in vitro, and revealed that the survival rate of PSCs and transcription levels of both genes were negatively correlated with the concentration of LCL161. While the results of light microscopy, transmission electron microscopy (TEM), and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay also showed a higher apoptotic rate in PSCs with the increasing concentrations of LCL161. Taken together, our findings provide the reasonable evidence that both Eg-IAP and Eg-BIRP have potential implication in critical anti-apoptotic roles during the development of E. granulosus.

Negative Regulation of TNFR1 Signaling Via PKA-Mediated Phosphorylation of TNFR1

Tumor necrosis factor alpha (TNF-α) plays a paramount role in homeostasis by inducing tumor cytotoxicity and activating immune system. The signaling complexes formed by TNFR1 to activate JNK, p38, and nuclear factor-kappa B pathways and to subsequently induce apoptosis and necroptosis are well known. However, this "canonical TNF-α signaling" does not explain how ERK, AKT, and STAT3 can be activated by TNF-α. In addition, little to nothing is known about negative regulation of TNFR1 signaling. Because cyclic AMP-activated kinase (PKA) shows anti-TNF and anti-inflammatory activities, we postulated that PKA might affect TNF-α signaling by directly phosphorylating TNFR1. In line with this, we identified 2 putative PKA-phosphorylation motifs RRRT₄₁₁ and REAT₄₁₇ within the death domain of TNFR1, and investigated whether "canonical" and "noncanonical" TNFR1 signaling is regulated by modifications of T411 and T417. In this study, we demonstrate for the first time that PKA directly binds to and phosphorylates TNFR1 after TNF-α stimulation. To further support our hypothesis, we generated alanine and phosphomimetic (aspartic acid) mutants of TNFR1 at positions T411 and T417, ectopically expressed these mutants, and determined their influence on TNF-α-induced activations of ERKs, AKT, STAT3, p38α, and JNK1/2. Our results clearly showed that phosphomimetic mutants significantly suppressed and alanine mutants augmented TNF-α-induced phosphorylations of ERKs, AKT, Stat3, p38α, and JNKs. These findings strongly suggest that PKA-mediated phosphorylation of T411 and T417 of TNFR1 interferes with both "canonical" and "noncanonical" TNF-α signaling. [Figure: see text].

Targeting XIAP for Promoting Cancer Cell Death-The Story of ARTS and SMAC

Inhibitors of apoptosis (IAPs) are a family of proteins that regulate cell death and inflammation. XIAP (X-linked IAP) is the only family member that suppresses apoptosis by directly binding to and inhibiting caspases. On the other hand, cIAPs suppress the activation of the extrinsic apoptotic pathway by preventing the formation of pro-apoptotic signaling complexes. IAPs are negatively regulated by IAP-antagonist proteins such as Smac/Diablo and ARTS. ARTS can promote apoptosis by binding and degrading XIAP via the ubiquitin proteasome-system (UPS). Smac can induce the degradation of cIAPs but not XIAP. Many types of cancer overexpress IAPs, thus enabling tumor cells to evade apoptosis. Therefore, IAPs, and in particular XIAP, have become attractive targets for cancer therapy. In this review, we describe the differences in the mechanisms of action between Smac and ARTS, and we summarize efforts to develop cancer therapies based on mimicking Smac and ARTS. Several Smac-mimetic small molecules are currently under evaluation in clinical trials. Initial efforts to develop ARTS-mimetics resulted in a novel class of compounds, which bind and degrade XIAP but not cIAPs. Smac-mimetics can target tumors with high levels of cIAPs, whereas ARTS-mimetics are expected to be effective for cancers with high levels of XIAP.

Necroptosis, ADAM proteases and intestinal (dys)function

Recently, an unexpected connection between necroptosis and members of the a disintegrin and metalloproteinase (ADAM) protease family has been reported. Necroptosis represents an important cell death routine which helps to protect from viral, bacterial, fungal and parasitic infections, maintains adult T cell homeostasis and contributes to the elimination of potentially defective organisms before parturition. Equally important for organismal homeostasis, ADAM proteases control cellular processes such as development and differentiation, immune responses or tissue regeneration. Notably, necroptosis as well as ADAM proteases have been implicated in the control of inflammatory responses in the intestine. In this review, we therefore provide an overview of the physiology and pathophysiology of necroptosis, ADAM proteases and intestinal (dys)function, discuss the contribution of necroptosis and ADAMs to intestinal (dys)function, and review the current knowledge on the role of ADAMs in necroptotic signaling.

Distinct modes of TNF signaling through its two receptors in health and disease

TNF is a key proinflammatory and immunoregulatory cytokine whose deregulation is associated with the development of autoimmune diseases and other pathologies. Recent studies suggest that distinct functions of TNF may be associated with differential engagement of its two receptors: TNFR1 or TNFR2. In this review, we discuss the relative contributions of these receptors to pathogenesis of several diseases, with the focus on autoimmunity and neuroinflammation. In particular, we discuss the role of TNFRs in the development of regulatory T cells during neuroinflammation and recent findings concerning targeting TNFR2 with agonistic and antagonistic reagents in various murine models of autoimmune and neuroinflammatory disorders and cancer.

Targeting apoptotic caspases in cancer

Members of the caspase family of proteases play essential roles in the initiation and execution of apoptosis. These caspases are divided into two groups: the initiator caspases (caspase-2, -8, -9 and -10), which are the first to be activated in response to a signal, and the executioner caspases (caspase-3, -6, and -7) that carry out the demolition phase of apoptosis. Many conventional cancer therapies induce apoptosis to remove the cancer cell by engaging these caspases indirectly. Newer therapeutic applications have been designed, including those that specifically activate individual caspases using gene therapy approaches and small molecules that repress natural inhibitors of caspases already present in the cell. For such approaches to have maximal clinical efficacy, emerging insights into non-apoptotic roles of these caspases need to be considered. This review will discuss the roles of caspases as safeguards against cancer in the context of the advantages and potential limitations of targeting apoptotic caspases for the treatment of cancer.

Infantile Epithelioid Sarcoma with Genomic Segmental Amplification of BIRC3/YAP1 as Double Minutes Plus Trisomy 2: A Case Report

Introduction: Epithelioid sarcoma is a malignant mesenchymal tumor exhibiting epithelioid cytomorphology and epithelial phenotype. Its histogenesis is unknown, but its tumorigenesis may relate to inactivation of hSNF5/SMARCB1/INI1 tumor suppressor gene. This tumor typically affects young adults and older children, but it is uncommon in infants. Case Report: We describe a unique neoplasm in a 15-month-old infant presenting with a heel mass. The tumor was remarkable for retention of SMARCB1/INI1 expression. Conventional cytogenetic analysis revealed trisomy 2 and double minutes, and SNP array analysis confirmed the trisomy 2 and identified segmental amplification of chromosome 11 containing YAP1 and BIRC3; FISH testing proved that the double minutes consisted of BIRC3 and YAP1, potent oncogenes related to tumorigenesis of several types of tumors but not described in epithelioid sarcoma. Conclusion: Our findings expand the spectrum of cytogenetic alterations in this neoplasm, help in better understanding its tumorigenesis, and suggest potential therapeutic targets.

Reverse engineering gene networks using global-local shrinkage rules

Inferring gene regulatory networks from high-throughput 'omics' data has proven to be a computationally demanding task of critical importance. Frequently, the classical methods break down owing to the curse of dimensionality, and popular strategies to overcome this are typically based on regularized versions of the classical methods. However, these approaches rely on loss functions that may not be robust and usually do not allow for the incorporation of prior information in a straightforward way. Fully Bayesian methods are equipped to handle both of these shortcomings quite naturally, and they offer the potential for improvements in network structure learning. We propose a Bayesian hierarchical model to reconstruct gene regulatory networks from time-series gene expression data, such as those common in perturbation experiments of biological systems. The proposed methodology uses global-local shrinkage priors for posterior selection of regulatory edges and relaxes the common normal likelihood assumption in order to allow for heavy-tailed data, which were shown in several of the cited references to severely impact network inference. We provide a sufficient condition for posterior propriety and derive an efficient Markov chain Monte Carlo via Gibbs sampling in the electronic supplementary material. We describe a novel way to detect multiple scales based on the corresponding posterior quantities. Finally, we demonstrate the performance of our approach in a simulation study and compare it with existing methods on real data from a T-cell activation study.

The first cloned echinoderm tumor necrosis factor receptor from Holothuria leucospilota: Molecular characterization and functional analysis

In this study, an echinoderm tumor necrosis factor receptor named HLTNFR-16 was first cloned from the tropical sea cucumber Holothuria leucospilota. The full-length cDNA of HLTNFR-16 is 3675 bp in size, containing a 415 bp 5'-untranslated region (UTR), a 2024 bp 3'-UTR and a 1236 bp open reading frame (ORF) encoding a protein of 411 amino acids with a deduced molecular weight of 45.63 kDa. The HLTNFR-16 protein contains a signal peptide, four TNFR domains (the last three were identified as extracellular cysteine-rich domains), a transmembrane region and a death domain. Phylogenetic analysis showed that HLTNFR-16 was clustered into a clade with TNFR-16s in other species, indicating that this echinoderm TNFR may be a new member of the TNFR-16 subfamily. The results of TUNEL assay showed that the over expression of HLTNFR-16 could induce apoptosis in HEK293T cells. When HLTNFR-16 was silenced by siRNA, the apoptosis of sea cucumber coelomocytes induced by inactivated Vibrio harveyi was suppressed significantly, indicating that HLTNFR-16 is important for apoptosis induction. Additionally, luciferase reporter assay exhibited that the over-expressed HLTNFR-16 in HEK293T cells could activate the transcription factors nuclear factor-κB (NF-κB) and activator protein-1 (AP-1). Moreover, the secretion of proinflammatory cytokines interleukin (IL)-1β, IL-6 and IL-18 in HEK293T cells was increased by the over-expression of HLTNFR-16. This study provides evidences for the potential roles of sea cucumber TNFR in the innate immunity.

Genetically engineered T cells for cancer immunotherapy

T cells in the immune system protect the human body from infection by pathogens and clear mutant cells through specific recognition by T cell receptors (TCRs). Cancer immunotherapy, by relying on this basic recognition method, boosts the antitumor efficacy of T cells by unleashing the inhibition of immune checkpoints and expands adaptive immunity by facilitating the adoptive transfer of genetically engineered T cells. T cells genetically equipped with chimeric antigen receptors (CARs) or TCRs have shown remarkable effectiveness in treating some hematological malignancies, although the efficacy of engineered T cells in treating solid tumors is far from satisfactory. In this review, we summarize the development of genetically engineered T cells, outline the most recent studies investigating genetically engineered T cells for cancer immunotherapy, and discuss strategies for improving the performance of these T cells in fighting cancers.

TNFR2 induced priming of the inflammasome leads to a RIPK1-dependent cell death in the absence of XIAP

The pediatric immune deficiency X-linked proliferative disease-2 (XLP-2) is a unique disease, with patients presenting with either hemophagocytic lymphohistiocytosis (HLH) or intestinal bowel disease (IBD). Interestingly, XLP-2 patients display high levels of IL-18 in the serum even while in stable condition, presumably through spontaneous inflammasome activation. Recent data suggests that LPS stimulation can trigger inflammasome activation through a TNFR2/TNF/TNFR1 mediated loop in xiap^−/− macrophages. Yet, the direct role TNFR2-specific activation plays in the absence of XIAP is unknown. We found TNFR2-specific activation leads to cell death in xiap^−/− myeloid cells, particularly in the absence of the RING domain. RIPK1 kinase activity downstream of TNFR2 resulted in a TNF/TNFR1 cell death, independent of necroptosis. TNFR2-specific activation leads to a similar inflammatory NF-kB driven transcriptional profile as TNFR1 activation with the exception of upregulation of NLRP3 and caspase-11. Activation and upregulation of the canonical inflammasome upon loss of XIAP was mediated by RIPK1 kinase activity and ROS production. While both the inhibition of RIPK1 kinase activity and ROS production reduced cell death, as well as release of IL-1β, the release of IL-18 was not reduced to basal levels. This study supports targeting TNFR2 specifically to reduce IL-18 release in XLP-2 patients and to reduce priming of the inflammasome components.

TRAF2 Controls Death Receptor-Induced Caspase-8 Processing and Facilitates Proinflammatory Signaling

Tumor necrosis factor (TNF) receptor associated factor-2 (TRAF2) knockout (KO) cells were generated to investigate the role of TRAF2 in signaling by TNFR1 and the CD95-type death receptors (DRs) TRAILR1/2 and CD95. To prevent negative selection effects arising from the increased cell death sensitivity of TRAF2-deficient cells, cell lines were used for the generation of the TRAF2 KO variants that were protected from DR-induced apoptosis downstream of caspase-8 activation. As already described in the literature, TRAF2 KO cells displayed enhanced constitutive alternative NFκB signaling and reduced TNFR1-induced activation of the classical NFκB pathway. There was furthermore a significant but only partial reduction in CD95-type DR-induced upregulation of the proinflammatory NFκB-regulated cytokine interleukin-8 (IL8), which could be reversed by reexpression of TRAF2. In contrast, expression of the TRAF2-related TRAF1 protein failed to functionally restore TRAF2 deficiency. TRAF2 deficiency resulted furthermore in enhanced procaspase-8 processing by DRs, but this surprisingly came along with a reduction in net caspase-8 activity. In sum, our data argue for (i) a non-obligate promoting function of TRAF2 in proinflammatory DR signaling and (ii) a yet unrecognized stabilizing effect of TRAF2 on caspase-8 activity.

Targeting Regulatory T Cells by Addressing Tumor Necrosis Factor and Its Receptors in Allogeneic Hematopoietic Cell Transplantation and Cancer

An intricate network of molecular and cellular actors orchestrates the delicate balance between effector immune responses and immune tolerance. The pleiotropic cytokine tumor necrosis factor-alpha (TNF) proves as a pivotal protagonist promoting but also suppressing immune responses. These opposite actions are accomplished through specialist cell types responding to TNF via TNF receptors TNFR1 and TNFR2. Recent findings highlight the importance of TNFR2 as a key regulator of activated natural FoxP3⁺ regulatory T cells (Tregs) in inflammatory conditions, such as acute graft-vs.-host disease (GvHD) and the tumor microenvironment. Here we review recent advances in our understanding of TNFR2 signaling in T cells and discuss how these can reconcile seemingly conflicting observations when manipulating TNF and TNFRs. As TNFR2 emerges as a new and attractive target we furthermore pinpoint strategies and potential pitfalls for therapeutic targeting of TNFR2 for cancer treatment and immune tolerance after allogeneic hematopoietic cell transplantation.

CD95/Fas and metastatic disease: What does not kill you makes you stronger

CD95 (also known as Fas) is the prototype of death receptors; however, evidence suggests that this receptor mainly implements non-apoptotic signaling pathways such as NF-κB, MAPK, and PI3K that are involved in cell migration, differentiation, survival, and cytokine secretion. At least two different forms of CD95 L exist. The multi-aggregated transmembrane ligand (m-CD95 L) is cleaved by metalloproteases to release a homotrimeric soluble ligand (s-CD95 L). Unlike m-CD95 L, the interaction between s-CD95 L and its receptor CD95 fails to trigger apoptosis, but instead promotes calcium-dependent cell migration, which contributes to the accumulation of inflammatory Th17 cells in damaged organs of lupus patients and favors cancer cell invasiveness. Novel inhibitors targeting the pro-inflammatory roles of CD95/CD95 L may provide attractive therapeutic options for patients with chronic inflammatory disorders or cancer. This review discusses the roles of the CD95/CD95 L pair in cell migration and metastasis.

Up-regulation of tumor necrosis factor-α pathway survival genes and of the receptor TNFR2 in gastric cancer

BACKGROUND

Gastric carcinogenesis can be induced by chronic inflammation triggered by Helicobacter pylori (H. pylori) infection. Tumor necrosis factor (TNF)-α and its receptors (TNFR1 and TNFR2) regulate important cellular processes, such as apoptosis and cell survival, and the disruption of which can lead to cancer. This signaling pathway is also modulated by microRNAs (miRNAs), altering gene expression.

AIM

To evaluate the mRNA and miRNAs expression involved in the TNF-α signaling pathway in gastric cancer (GC) tissues and its relationship.

METHODS

Quantitative polymerase chain reaction (qPCR) by TaqMan^® assay was used to quantify the RNA transcript levels of TNF-α signaling pathway (TNF, TNFR1, TNFR2, TRADD, TRAF2, CFLIP, NFKB1, NFKB2, CASP8, CASP3) and miRNAs that targets genes from this pathway (miR-19a, miR-34a, miR-103a, miR-130a, miR-181c) in 30 GC fresh tissue samples. Molecular diagnosis of H. pylori was performed by nested PCR for gene HSP60. A miRNA:mRNA interaction network was construct using Cytoscape v3.1.1 from the in silico analysis performed using public databases.

RESULTS

Up-regulation of cellular survival genes as TNF, TNFR2, TRADD, TRAF2, CFLIP, and NFKB2, besides CASP8 and miR-34a was observed in GC tissues, whereas mediators of apoptosis such as TNFR1 and CASP3 were down-regulated. When the samples were stratified by histological type, the expression of miR-103a and miR-130a was significantly increased in the diffuse-type of GC compared to the intestinal-type. However, no influence of H. pylori infection was observed on the expression levels of mRNA and miRNAs analyzed. Moreover, the miRNA:mRNA interaction network showed several interrelations between the miRNAs and their target genes, highlighting miR-19a and miR-103a, which has as predicted or validated target a large number of genes in the TNF-α pathway, including TNF, TNFR1, TNFR2, CFLIP, TRADD, CASP3 and CASP8.

CONCLUSION

Our findings show that cell survival genes mediated by TNF/TNFR2 binding is up-regulated in GC favoring its pro-tumoral effect, while pro-apoptotic genes as CASP3 and TNFR1 are down-regulated, indicating disbalance between apoptosis and cell proliferation processes in this neoplasm. This process can also be influenced by an intricate regulatory network of miRNA:mRNA.

The regulation of circadian clock by tumor necrosis factor alpha

All organisms display circadian rhythms which are under the control of the circadian clock located in the hypothalamus at the suprachiasmatic nucleus, (SCN). The circadian rhythms allow individuals to adjust their physiological activities and daily behavior for the diurnal changes in the living environment. To achieve these, all metabolic processes are aligned with the sleep/wake and fasting/feeding cycles. Subtle changes of daily behavior or food intake can result in misalignment of circadian rhythms. This can cause development of variety of metabolic diseases and even cancer. Although light plays a pivotal role for the activation of the master clock in SCN, the peripheral secondary clocks (or non-SCN), such as melatonin, growth hormone (GH), insulin, adiponectin and Ghrelin also are important in maintaining the circadian rhythms in the brain and peripheral organs. In recent years, growing body of evidence strongly suggest that CA²⁺ signaling, tumor necrosis factor alpha (TNFα) and transforming growth factor beta (TGFβ) also play very important roles in the regulation of circadian rhythms by regulating the transcription of the clock genes.

Telbivudine Reduces Parvovirus B19-Induced Apoptosis in Circulating Angiogenic Cells

Aims: Human parvovirus B19 (B19V) infection directly induces apoptosis and modulates CXCR4 expression of infected marrow-derived circulating angiogenic cells (CACs). This leads to dysfunctional endogenous vascular repair. Treatment for B19V-associated disease is restricted to symptomatic treatment. Telbivudine, a thymidine analogue, established in antiviral treatment for chronic hepatitis B, modulates pathways that might influence induction of apoptosis. Therefore, we tested the hypothesis of whether telbivudine influences B19V-induced apoptosis of CAC. Methods and Results: Pretreatment of two CAC-lines, early outgrowth endothelial progenitor cells (eo-EPC) and endothelial colony-forming cells (ECFC) with telbivudine before in vitro infection with B19V significantly reduced active caspase-3 protein expression (−39% and −40%, both p < 0.005). Expression of Baculoviral Inhibitor of apoptosis Repeat-Containing protein 3 (BIRC3) was significantly downregulated by in vitro B19V infection in ECFC measured by qRT-PCR. BIRC3 downregulation was abrogated with telbivudine pretreatment (p < 0.001). This was confirmed by single gene PCR (p = 0.017) and Western blot analysis. In contrast, the missing effect of B19V on angiogenic gene expression postulates a post-transcriptional modulation of CXCR4. Conclusions: We for the first time show a treatment approach to reduce B19V-induced apoptosis. Telbivudine reverses B19V-induced dysregulation of BIRC3, thus, intervening in the apoptosis pathway and protecting susceptible cells from cell death. This approach could lead to an effective B19V treatment to reduce B19V-related disease.

Targeting TNFR2 as a Novel Therapeutic Strategy for Alzheimer's Disease

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder and the most common cause of dementia. Accumulating experimental evidence shows the important linkage between tumor necrosis factor-α (TNF) and AD, but the exact role of TNF in AD is still not completely understood. Although TNF-inhibitors are successfully used for treating several diseases, total inhibition of TNF can cause side effects, particularly in neurological diseases. This is attributed to the opposing roles of the two TNF receptors. TNF receptor 1 (TNFR1) predominantly mediates inflammatory and pro-apoptotic signaling pathways, whereas TNF receptor 2 (TNFR2) is neuroprotective and promotes tissue regeneration. Therefore, the specific activation of TNFR2 signaling, either by directly targeting TNFR2 via TNFR2 agonists or by blocking TNFR1 signaling with TNFR1-selective antagonists, seems a promising strategy for AD therapy. This mini-review discusses the involvement of TNFR2 and its signaling pathway in AD and outlines its potential application as therapeutic target. A better understanding of the function of TNFR2 may lead to the development of a treatment for AD.

Targeting the BIR Domains of Inhibitor of Apoptosis (IAP) Proteins in Cancer Treatment

Inhibitor of apoptosis (IAP) proteins are characterized by the presence of the conserved baculoviral IAP repeat (BIR) domain that is involved in protein-protein interactions. IAPs were initially thought to be mainly responsible for caspase inhibition, acting as negative regulators of apoptosis, but later works have shown that IAPs also control a plethora of other different cellular pathways. As X-linked IAP (XIAP), and other IAP, levels are often deregulated in cancer cells and have been shown to correlate with patients' prognosis, several approaches have been pursued to inhibit their activity in order to restore apoptosis. Many small molecules have been designed to target the BIR domains, the vast majority being inspired by the N-terminal tetrapeptide of Second Mitochondria-derived Activator of Caspases/Direct IAp Binding with Low pI (Smac/Diablo), which is the natural XIAP antagonist. These compounds are therefore usually referred to as Smac mimetics (SMs). Despite the fact that SMs were intended to specifically target XIAP, it has been shown that they also interact with cellular IAP-1 (cIAP1) and cIAP2, promoting their proteasome-dependent degradation. SMs have been tested in combination with several cytotoxic compounds and are now considered promising immune modulators which can be exploited in cancer therapy, especially in combination with immune checkpoint inhibitors. In this review, we give an overview of the structural hot-spots of BIRs, focusing on their fold and on the peculiar structural patches which characterize the diverse BIRs. These structures are exploited/exploitable for the development of specific and active IAP inhibitors.

Linear ubiquitination at a glance

Ubiquitination (also known as ubiquitylation) is a post-translational modification that creates versatility in cell signalling and regulates a multitude of cellular processes. Its versatility lies in the capacity to form eight different inter-ubiquitin linkages through the seven lysine residues of ubiquitin and through its N-terminal methionine (M1). The latter, referred to as linear or M1 linkage, is created by the linear ubiquitin chain assembly complex (LUBAC), the only E3 ligase known to date that is capable of forming linear ubiquitin chains de novo Linear ubiquitin chains are crucial modulators of innate and adaptive immune responses, and act by regulating inflammatory and cell death signalling. In this Cell Science at a Glance article and the accompanying poster, we review the current knowledge on the role of LUBAC and linear ubiquitination in immune signalling and human physiology. We specifically focus on the role for LUBAC in signalling that is induced by the cytokine tumour necrosis factor (TNF) and its role in inflammation, gene activation and cell death. Furthermore, we highlight the roles of deubiquitinases (DUBs) that cleave M1 linkages and add an additional layer in the control of LUBAC-mediated immune signalling.

Oligonol, a Low Molecular Weight Polyphenol, Enhances Apoptotic Cell Death in Ovarian Cancer Cells via Suppressing NF-κB Activation

BACKGROUND

Oligonol, a low molecular weight polyphenol derived from lychee fruit, not only has anti-inflammatory effects in various disease conditions but also has antitumor-promoting effects. We evaluate the nuclear factor-kappa B (NF-κB)-related anticancer effect of oligonol in ovarian cancer using SKOV-3 cells.

METHODS

Cell viability was examined after oligonol treatment using MTT assay and reactive oxygen species (ROS) production measurement. Subsequently, apoptotic cell death was visualized by the TdT-mediated dUTP nick-end labeling (TUNEL) method. The effect of oligonol on the NF-κB signaling pathway was evaluated using western blot analysis and luciferase activity measurement of p65, an NF-κB subunit.

RESULTS

Cell viability significantly decreased after oligonol treatment of 72 h. Apoptosis-related markers were highly expressed in oligonol-treated cells, and increased apoptosis after oligonol treatment was also confirmed using the TUNEL assay. Western blotting results showed the expression of NF-κB signaling pathway factors, p-ERK, TRAF2, and p-IκBα, increased following treatment with oligonol, whereas p65 and COX-2 expression decreased. Immunofluorescence imaging results showed p65 luciferase activity in the nucleus as well as a shift to cytoplasmic expression.

CONCLUSION

Oligonol treatment significantly enhances apoptotic cell death in SKOV-3 cells, with the suppression of NF-κB activation, which plays an essential role in this anticancer effect.

Signal Transduction Via Co-stimulatory and Co-inhibitory Receptors

T-cell receptor (TCR)-mediated antigen-specific stimulation is essential for initiating T-cell activation. However, signaling through the TCR alone is not sufficient for inducing an effective response. In addition to TCR-mediated signaling, signaling through antigen-independent co-stimulatory or co-inhibitory receptors is critically important not only for the full activation and functional differentiation of T cells but also for the termination and suppression of T-cell responses. Many studies have investigated the signaling pathways underlying the function of each molecular component. Co-stimulatory and co-inhibitory receptors have no kinase activity, but their cytoplasmic region contains unique functional motifs and potential phosphorylation sites. Engagement of co-stimulatory receptors leads to recruitment of specific binding partners, such as adaptor molecules, kinases, and phosphatases, via recognition of a specific motif. Consequently, each co-stimulatory receptor transduces a unique pattern of signaling pathways. This review focuses on our current understanding of the intracellular signaling pathways provided by co-stimulatory and co-inhibitory molecules, including B7:CD28 family members, immunoglobulin, and members of the tumor necrosis factor receptor superfamily.

Recent advances in understanding inhibitor of apoptosis proteins

The inhibitor of apoptosis proteins (IAPs) are a family of proteins that were chiefly known for their ability to inhibit apoptosis by blocking caspase activation or activity. Recent research has shown that cellular IAP1 (cIAP1), cIAP2, and X-linked IAP (XIAP) also regulate signaling by receptors of the innate immune system by ubiquitylating their substrates. These IAPs thereby act at the intersection of pathways leading to cell death and inflammation. Mutation of IAP genes can impair tissue homeostasis and is linked to several human diseases. Small-molecule IAP antagonists have been developed to treat certain malignant, infectious, and inflammatory diseases. Here, we will discuss recent advances in our understanding of the functions of cIAP1, cIAP2, and XIAP; the consequences of their mutation or dysregulation; and the therapeutic potential of IAP antagonist drugs.

Tumor Necrosis Factor Receptor-Associated Factor Regulation of Nuclear Factor κB and Mitogen-Activated Protein Kinase Pathways

Tumor necrosis factor receptor (TNFR)-associated factors (TRAFs) are a family of structurally related proteins that transduces signals from members of TNFR superfamily and various other immune receptors. Major downstream signaling events mediated by the TRAF molecules include activation of the transcription factor nuclear factor κB (NF-κB) and the mitogen-activated protein kinases (MAPKs). In addition, some TRAF family members, particularly TRAF2 and TRAF3, serve as negative regulators of specific signaling pathways, such as the noncanonical NF-κB and proinflammatory toll-like receptor pathways. Thus, TRAFs possess important and complex signaling functions in the immune system and play an important role in regulating immune and inflammatory responses. This review will focus on the role of TRAF proteins in the regulation of NF-κB and MAPK signaling pathways.

A novel caspase-associated recruitment domain (CARD) containing protein (CgCARDCP-1) involved in LPS recognition and NF-κB activation in oyster (Crassostrea gigas)

Caspase-associated recruitment domain (CARD) containing proteins play critical roles in molecular interaction and regulation of various signaling pathways, such as the activation of caspase and NF-κB singling pathway in the process of apoptosis or inflammation. In the present study, a novel CARD containing protein (designed CgCARDCP-1) was identified and characterized from oyster Crassostrea gigas. Molecular feature analysis revealed that, the open reading frame (ORF) of CgCARDCP-1 gene was 759 bp encoding a polypeptide of 253 amino acids with a conserved N-terminal CARD domain and two transcriptional coactivator p15 (PC4) domains in C-terminus. Homologous alignment showed that the amino acid sequence of CgCARDCP-1 shared 30%-46% identity with that of caspase-2. By RT-PCR detection, the mRNA transcripts of CgCARDCP-1 were found to be widely distributed in various tissues of oyster with the highest expression level in hemocytes and mantle. And CgCARDCP-1 protein was mostly distributed in the cytoplasm of oyster hemocytes as shown by immunohistochemistry. Moreover, the CgCARDCP-1 mRNA expression level in hemocytes was significantly up-regulated after lipopolysaccharide (LPS) and Vibrio splendidus stimulations. The recombinant CgCARDCP-1 displayed strong binding activity with LPS in vitro. In addition, after transfected into the HEK-293T cell with luciferase reporter system, CgCARDCP-1 could significantly promote the NF-κB activation (1.29-fold, p < 0.05) compared to that in the control group. These results collectively demonstrated that the CgCARDCP-1 might serve as a recognition molecule for LPS and a regulator of NF-κB activation in the immune response of oyster.

α-lipoic acid reduces postreperfusion syndrome in human liver transplantation - a pilot study

A double-blind randomized controlled trial was performed to compare the safety and efficacy of α-lipoic acid (ALA) in liver transplantation (LT). The grafts were randomized to receive ALA or placebo before the cold ischemia time. Furthermore, patients transplanted with the ALA-perfused graft received 600 mg of intravenous ALA, while patients with the nonperfused graft received the placebo just before graft reperfusion. Hepatic biopsy was performed 2 h postreperfusion. Blood samples were collected before, during and 1 and 2 days after reperfusion. Quantitative polymerase chain reaction (qPCR) analysis was performed on biopsies to assess genes involved in the response to hypoxia, apoptosis, cell growth, survival and proliferation, cytokine production and tissue damage protection. Nine of 40 patients developed postreperfusion syndrome (PRS), but seven of them belonged to the control group. There was a decrease in PHD2 and an increase in alpha subunit of hypoxia-inducible factor-1 (HIF-1α) and baculoviral IAP repeat containing 2 (Birc2) transcript levels in the biopsies from the ALA-treated versus the control group of patients. Additionally, plasma levels of alarmins were lower in ALA-treated patients than control patients, which suggests that ALA-treated grafts are less inflammatory than untreated grafts. These results showed that ALA is safe for use in LT, induces gene changes that protect against hypoxia and oxidative stress and reduces the appearance of PRS.

Inhibitors of apoptosis: clinical implications in cancer

Inhibitor of apoptosis (IAP) family comprises a group of endogenous proteins that function as main regulators of caspase activity and cell death. They are considered the main culprits in evasion of apoptosis, which is a fundamental hallmark of carcinogenesis. Overexpression of IAP proteins has been documented in various solid and hematological malignancies, rendering them resistant to standard chemotherapeutics and radiation therapy and conferring poor prognosis. This observation has urged their exploitation as therapeutic targets in cancer with promising pre-clinical outcomes. This review describes the structural and functional features of IAP proteins to elucidate the mechanism of their anti-apoptotic activity. We also provide an update on patterns of IAP expression in different tumors, their impact on treatment response and prognosis, as well as the emerging investigational drugs targeting them. This aims at shedding the light on the advances in IAP targeting achieved to date, and encourage further development of clinically applicable therapeutic approaches.

Regulation of innate and adaptive antitumor immunity by IAP antagonists

Inhibition of the T-cell co-inhibitory checkpoint receptors or their ligands CTLA-4, PD-1 and PD-L1 using monoclonal antibodies has proven to be highly effective against many cancers. Yet many cancers remain resistant to checkpoint blockade, and durable remissions occur in only a minority of patients. Novel approaches to enhancing antitumor responses are thus necessary in order to expand the reach of these treatments. The inhibitor of apoptosis (IAP) protein family comprises a diverse group of proteins, many of which have immunoregulatory roles. Small molecule IAP antagonists have been developed and are undergoing early phase clinical testing. These drugs were initially developed to promote tumor cell apoptosis; however, a considerable body of work now indicates that IAP antagonists induce antitumor activity through modulation of innate and adaptive immunity. Primarily through inhibition of cellular (c)-IAP1 and c-IAP2, IAP antagonists can activate alternative NF-κB signaling, promoting B-cell survival, activation of dendritic cells and delivering a broad co-stimulatory signal to T cells. At the same time, IAP antagonists can promote tumor cell intrinsic sensitization to innate immune signals, and enhance tumor cell killing by inflammatory cytokines and phagocytic macrophages. These drugs thus represent an attractive investigational approach to immunotherapy, providing a positive signaling counterpart to the relief of signal inhibition conferred by checkpoint blockade.

TRAF1 Is Critical for Regulating the BRAF/MEK/ERK Pathway in Non-Small Cell Lung Carcinogenesis

Tumor necrosis factor receptor (TNFR)-associated factor 1 (TRAF1) is a unique TRAF protein that can interact directly or indirectly with multiple TNFR family members, regulatory proteins, kinases, and adaptors that contribute to its diverse functions in specific tissues. However, the role of TRAF1 in non-small cell lung cancer (NSCLC) remains unknown. In this study, we report that TRAF1 is overexpressed in human lung cancer cells and tissues. TRAF1 expression level inversely correlated with patient survival probability. Loss of TRAF1 decelerated tumor invasion in a urethane-induced lung carcinogenesis mouse model. Furthermore, TRAF1 expression affected TRAF2-mediated BRAF Lys48-linked ubiquitination, which was followed by the inhibition of growth and differentiation, and the induction of death in lung cancer cells. Overall, our work suggests that TRAF1 plays a novel role in the regulation of the BRAF/MEK/ERK signaling pathway in NSCLC and offers a candidate molecular target for lung cancer prevention and therapy.Significance: These findings identify TRAF1 as a new therapeutic target for NSCLC. Cancer Res; 78(14); 3982-94. ©2018 AACR.

XIAP Loss Triggers RIPK3- and Caspase-8-Driven IL-1β Activation and Cell Death as a Consequence of TLR-MyD88-Induced cIAP1-TRAF2 Degradation

X-linked Inhibitor of Apoptosis (XIAP) deficiency predisposes people to pathogen-associated hyperinflammation. Upon XIAP loss, Toll-like receptor (TLR) ligation triggers RIPK3-caspase-8-mediated IL-1β activation and death in myeloid cells. How XIAP suppresses these events remains unclear. Here, we show that TLR-MyD88 causes the proteasomal degradation of the related IAP, cIAP1, and its adaptor, TRAF2, by inducing TNF and TNF Receptor 2 (TNFR2) signaling. Genetically, we define that myeloid-specific cIAP1 loss promotes TLR-induced RIPK3-caspase-8 and IL-1β activity in the absence of XIAP. Importantly, deletion of TNFR2 in XIAP-deficient cells limited TLR-MyD88-induced cIAP1-TRAF2 degradation, cell death, and IL-1β activation. In contrast to TLR-MyD88, TLR-TRIF-induced interferon (IFN)β inhibited cIAP1 loss and consequent cell death. These data reveal how, upon XIAP deficiency, a TLR-TNF-TNFR2 axis drives cIAP1-TRAF2 degradation to allow TLR or TNFR1 activation of RIPK3-caspase-8 and IL-1β. This mechanism may explain why XIAP-deficient patients can exhibit symptoms reminiscent of patients with activating inflammasome mutations.

The Significance of Tumor Necrosis Factor Receptor Type II in CD8+ Regulatory T Cells and CD8+ Effector T Cells

Tumor necrosis factor (TNF) is a pleiotropic cytokine that has both pro-inflammatory and anti-inflammatory functions. The biological functions of TNF are mediated by two receptors, TNF receptor type I (TNFR1) and TNF receptor type II (TNFR2). TNFR1 is expressed universally on almost all cell types and has been extensively studied, whereas TNFR2 is mainly restricted to immune cells and some tumor cells and its role is far from clarified. Studies have shown that TNFR2 mediates the stimulatory activity of TNF on CD4⁺Foxp3⁺ regulatory T cells (Tregs) and CD8⁺Foxp3⁺ Tregs, and is involved in the phenotypic stability, proliferation, activation, and suppressive activity of Tregs. TNFR2 can also be expressed on CD8⁺ effector T cells (Teffs), which delivers an activation signal and cytotoxic ability to CD8⁺ Teffs during the early immune response, as well as an apoptosis signal to terminate the immune response. TNFR2-induced abolition of TNF receptor-associated factor 2 (TRAF2) degradation may play an important role in these processes. Consequently, due to the distribution of TNFR2 and its pleiotropic effects, TNFR2 appears to be critical to keeping the balance between Tregs and Teffs, and may be an efficient therapeutic target for tumor and autoimmune diseases. In this review, we summarize the biological functions of TNFR2 expressed on CD8⁺Foxp3⁺ Tregs and CD8⁺ Teffs, and highlight how TNF uses TNFR2 to coordinate the complex events that ultimately lead to efficient CD8⁺ T cell-mediated immune responses.

Caspase-8 function, and phosphorylation, in cell migration

Caspase-8 is involved in a number of cellular functions, with the most well established being the control of cell death. Yet caspase-8 is unique among the caspases in that it acts as an environmental sensor, transducing a range of signals to cells, modulating responses that extend far beyond simple survival. Ranging from the control of apoptosis and necroptosis and gene regulation to cell adhesion and migration, caspase-8 uses proteolytic and non-proteolytic functions to alter cell behavior. Novel interacting partners provide mechanisms for caspase-8 to position itself at signaling nodes that affect a variety of signaling pathways. Here, we examine the catalytic and noncatalytic modes of action by which caspase-8 influences cell adhesion and migration. The mechanisms vary from post-cleavage remodeling of the cytoskeleton to signaling elements that control focal adhesion turnover. This is facilitated by caspase-8 interaction with a host of cell proteins ranging from the proteases caspase-3 and calpain-2 to adaptor proteins such as p85 and Crk, to the Src family of tyrosine kinases.

The E3 ubiquitin ligases HOIP and cIAP1 are recruited to the TNFR2 signaling complex and mediate TNFR2-induced canonical NF-κB signaling

Tumor Necrosis Factor (TNF) is a proinflammatory cytokine that elicits its action by binding to two cell surface TNF receptors (TNFR), TNFR1 and TNFR2, which are expressed by many different cell types. Stimulation of TNFR1 activates canonical NF-κB signaling, leading to the NF-κB dependent expression of a large number of genes. Canonical NF-κB signaling requires the assembly of a TNFR1 signaling complex at the cell membrane, whose formation is regulated by different protein ubiquitination events. In this context, recruitment of the Linear Ubiquitin Chain Assembly Complex (LUBAC) to TNFR1 plays an important role by mediating M1-linked polyubiquitination of specific NF-κB signaling proteins. In contrast to TNFR1, much less is known about the role of ubiquitination in TNFR2 signaling. Here we demonstrate that specific TNFR2 stimulation rapidly triggers M1- and K63-linked polyubiquitination at the TNFR2 signaling complex. In agreement, TNFR2 stimulation induces the recruitment of HOIP, a LUBAC component and the only known E3 ubiquitin ligase for M1-polyubiquitination, to the TNFR2 signaling complex. Also cIAP1, a E3 ubiquitin ligase able to modify proteins with K63-polyubiquitin chains, was recruited to the TNFR2 signaling complex. Treatment of cells with a cIAP antagonist inhibited the recruitment of HOIP and prevented HOIP-mediated M1-ubiquitination of the TNFR2 signaling complex, indicating that HOIP recruitment to the TNFR2 relies on cIAPs. Finally, we show that both HOIP and cIAP1 are required for TNFR2-induced canonical NF-κB activation. Together, our findings demonstrate an important role for M1- and K63-linked polyubiquitination in TNFR2 signaling.

Therapeutic opportunities based on caspase modulation

Caspases are a family of proteolytic enzymes that play a critical role in the regulation of programmed cell death via apoptosis. Activation of caspases is frequently impaired in human cancers, contributing to cancer formation, progression and therapy resistance. A better understanding of the molecular mechanisms regulating caspase activation in cancer cells is therefore highly important. Thus, targeted modulation of caspase activation and apoptosis represents a promising approach for the development of new therapeutic options to elucidate cancer cell death.

Checkpoints in TNF-Induced Cell Death: Implications in Inflammation and Cancer

Tumor necrosis factor (TNF) is a proinflammatory cytokine that coordinates tissue homeostasis by regulating cytokine production, cell survival, and cell death. However, how life and death decisions are made in response to TNF is poorly understood. Many inflammatory pathologies are now recognized to be driven by aberrant TNF-induced cell death, which, in most circumstances, depends on the kinase Receptor-interacting serine/threonine-protein kinase 1 (RIPK1). Recent advances have identified ubiquitin (Ub)-mediated phosphorylation of RIPK1 as belonging to crucial checkpoints for cell fate in inflammation and infection. A better understanding of these checkpoints might lead to new approaches for the treatment of chronic inflammatory diseases fueled by aberrant RIPK1-induced cell death, and/or reveal novel strategies for anticancer immunotherapies, harnessing the ability of RIPK1 to trigger immunogenic cell death.

TRAF2 of black carp upregulates MAVS-mediated antiviral signaling during innate immune response

Tumor necrosis factor receptor-associated factor 2 (TRAF2) is a crucial component of the tumor necrosis factor (TNF) mediated signaling of higher vertebrates. To elucidate its function in teleost fish, TRAF2 homologue of black carp (Mylopharyngodon piceus) has been cloned and characterized in this study. The open reading frame (ORF) of black carp TRAF2 (bcTRAF2) consists of 1611 nucleotides and bcTRAF2 contains 536 amino acids. bcTRAF2 protein migrated around 65 KDa in immunoblot analysis of both EPC and HEK293T cells. bcTRAF2 was identified as a cytosolic protein and suggested to be associated with vesicles scattering in the cytoplasm. NF-κB transcription instead of IFN transcription was activated by bcTRAF2 in reporter assay. It was interesting that bcMAVS-mediated IFN production was up-regulated by bcTRAF2 in a dose dependent manner in reporter assay. Accordingly, EPC cells transfected with both bcMAVS and bcTRAF2 showed enhanced antiviral activity comparing EPC cells only expressing bcMAVS. When co-expressed with bcMAVS, bcTRAF2 was redistributed in the cytoplasm and its subcellular location overlapped with the subcellular location of bcMAVS, which suggested the association between these two molecules. Taken together, the data generated in this paper supported the conclusion that bcTRAF2 was recruited into host innate immune response and positively regulated bcMAVS-mediated antiviral signaling.

Modulation of apoptotic response by LAR family phosphatases-cIAP1 signaling during urinary tract morphogenesis

The elimination of unwanted cells by apoptosis is necessary for tissue morphogenesis. However, the cellular control of morphogenetic apoptosis is poorly understood, notably the modulation of cell sensitivity to apoptotic stimuli. Ureter maturation, the process by which the ureter is displaced to the bladder wall, represents an exquisite example of morphogenetic apoptosis, requiring the receptor protein tyrosine phosphatases (RPTPs): LAR and RPTPσ. Here we show that LAR-RPTPs act through cellular inhibitor of apoptosis protein 1 (cIAP1) to modulate caspase 3,7-mediated ureter maturation. Pharmacologic or genetic inactivation of cIAP1 reverts the apoptotic deficit of LAR-RPTP-deficient embryos. Moreover, Birc2 (cIAP1) inactivation generates excessive apoptosis leading to vesicoureteral reflux in newborns, which underscores the importance of apoptotic modulation during urinary tract morphogenesis. We finally demonstrate that LAR-RPTP deficiency increases cIAP1 stability during apoptotic cell death. Together these results identify a mode of cIAP1 regulation playing a critical role in the cellular response to apoptotic pathway activation in the embryo.