Functional roles in cell signaling of adaptor protein TRADD from a structural perspective

Deciphering the Role of Epstein-Barr Virus Latent Membrane Protein 1 in Immune Modulation: A Multifaced Signalling Perspective

The disruption of antiviral sensors and the evasion of immune defences by various tactics are hallmarks of EBV infection. One of the EBV latent gene products, LMP1, was shown to induce the activation of signalling pathways, such as NF-κB, MAPK (JNK, ERK1/2, p38), JAK/STAT and PI3K/Akt, via three subdomains of its C-terminal domain, regulating the expression of several cytokines responsible for modulation of the immune response and therefore promoting viral persistence. The aim of this review is to summarise the current knowledge on the EBV-mediated induction of immunomodulatory molecules by the activation of signal transduction pathways with a particular focus on LMP1-mediated mechanisms. A more detailed understanding of the cytokine biology molecular landscape in EBV infections could contribute to the more complete understanding of diseases associated with this virus.

The ever-expanding role of cytokine receptor DR3 in T cells

Death Receptor 3 (DR3) is a cytokine receptor of the Tumor Necrosis Factor receptor superfamily that plays a multifaceted role in both innate and adaptive immunity. Based on the death domain motif in its cytosolic tail, DR3 had been proposed and functionally affirmed as a trigger of apoptosis. Further studies, however, also revealed roles of DR3 in other cellular pathways, including inflammation, survival, and proliferation. DR3 is expressed in various cell types, including T cells, B cells, innate lymphocytes, myeloid cells, fibroblasts, and even outside the immune system. Because DR3 is mainly expressed on T cells, DR3-mediated immune perturbations leading to autoimmunity and other diseases were mostly attributed to DR3 activation of T cells. However, which T cell subset and what T effector functions are controlled by DR3 to drive these processes remain incompletely understood. DR3 engagement was previously found to alter CD4 T helper subset differentiation, expand the Foxp3+ Treg cell pool, and maintain intraepithelial γδ T cells in the gut. Recent studies further unveiled a previously unacknowledged aspect of DR3 in regulating innate-like invariant NKT (iNKT) cell activation, expanding the scope of DR3-mediated immunity in T lineage cells. Importantly, in the context of iNKT cells, DR3 ligation exerted costimulatory effects in agonistic TCR signaling, unveiling a new regulatory framework in T cell activation and proliferation. The current review is aimed at summarizing such recent findings on the role of DR3 on conventional T cells and innate-like T cells and discussing them in the context of immunopathogenesis.

Downregulation of BIRC2 hinders the progression of rheumatoid arthritis through regulating TRADD

AIM

Rheumatoid arthritis (RA) is a chronic inflammation mediated by an autoimmune response. Baculoviral IAP repeat-containing 2 (BIRC2) and tumor necrosis factor receptor 1-associated death domain protein (TRADD) have been reported to be highly expressed in RA, while their specific roles during RA progression remain unclear. This study aims to explore the specific regulation of BIRC2/TRADD during the progression of RA.

METHODS

C28/I2 cells were stimulated by lipopolysaccharide (LPS) to establish an in vitro RA cellular model. The expression level of BIRC2 and TRADD was examined by quantitative real-time polymerase chain reaction and western blot. Cell Counting Kit-8 and flow cytometry assays were performed to examine cell viability and necroptosis, respectively. The oxidative stress markers were detected using commercial kits, and the pro-inflammatory cytokines were measured by ELISA assay. The interaction between BIRC2 and TRADD was verified by co-immunoprecipitation assay.

RESULTS

BIRC2 and TRADD were discovered to be highly expressed in LPS-mediated C28/I2 cells. BIRC2 knockdown was demonstrated to inhibit LPS-induced cell viability loss, necroptosis, oxidative stress, and inflammation in C28/I2 cells. BIRC2 could interact with TRADD and positively regulate TRADD expression. In addition, the protective role of BIRC2 knockdown against LPS-mediated injuries in C28/I2 cells was partly weakened by TRADD overexpression.

CONCLUSION

In summary, BIRC2 knockdown alleviated necroptosis, oxidative stress, and inflammation in LPS-mediated C28/I2 cells, which might correlate to the regulatory role of TRADD, indicating a novel target for the treatment of RA.

Molecular cloning, functional characterization of duck TRADD and its effect on infection with duck Tembusu virus

Tumor necrosis factor receptor 1 (TNFR1) associated death domain protein (TRADD) is a pivotal adaptor in TNF signaling pathway and plays an important role in apoptosis and immune regulation. The function of TRADD has been investigated extensively in mammals, however, the role of TRADD in ducks remains obscure. To reveal the function of duck TRADD (duTRADD) in the apoptosis and innate immune response, the TRADD homologue of mallard (Anas platyrhynchos) has been cloned and the function of duTRADD is investigated in this study. We conducted sequence analysis of the duTRADD, the open reading frame (ORF) region of duTRADD gene was 1065 bp, encoding 354 amino acids (aa), which shares similar functional domain to its mammalian counterpart. Tissue distribution profile of duTRADD in 7-day-old ducklings showed that the expression level of the gene was the highest in heart, followed by liver and brain. Accordingly, duck Tembusu virus (DTMUV) has been shown to decrease duTRADD expression, while overexpression of duTRADD inhibited DTMUV replication in a dose-dependent manner. Furthermore, duTRADD activated the transcriptional activity of caspase-3/8/9, the flow cytometry showed that duTRADD significantly induced apoptosis. However, duTRADD showed hardly any effect on the transcriptional activity of IFN-α/β and its downstream interferon-stimulated genes (ISGs). The current data support the conclusion that duTRADD is a novel pro-apoptotic protein with a critical role in defense against DTMUV invasion. These results lay the theoretical foundation for the development of new anti-DTMUV strategies.

Downregulation of TNFR2 decreases survival gene expression, promotes apoptosis and affects the cell cycle of gastric cancer cells

BACKGROUND

Chronic inflammation due to Helicobacter pylori (H. pylori) infection promotes gastric carcinogenesis. Tumour necrosis factor-α (TNF-α), a key mediator of inflammation, induces cell survival or apoptosis by binding to two receptors (TNFR1 and TNFR2). TNFR1 can induce both survival and apoptosis, while TNFR2 results only in cell survival. The dysregulation of these processes may contribute to carcinogenesis.

AIM

To evaluate the effects of TNFR1 and TNFR2 downregulation in AGS cells treated with H. pylori extract on the TNF-α pathway.

METHODS

AGS cell lines containing TNFR1 and TNFR2 receptors downregulated by specific shRNAs and nonsilenced AGS cells were treated with H. pylori extract for 6 h. Subsequently, quantitative polymerase chain reaction with TaqMan^® assays was used for the relative quantification of the mRNAs (TNFA, TNFR1, TNFR2, TRADD, TRAF2, CFLIP, NFKB1, NFKB2, CASP8, CASP3) and miRNAs (miR-19a, miR-34a, miR-103a, miR-130a, miR-181c) related to the TNF-α signalling pathway. Flow cytometry was employed for cell cycle analysis and apoptosis assays.

RESULTS

In nonsilenced AGS cells, H. pylori extract treatment increased the expression of genes involved in cell survival and inhibited both apoptosis (NFKB1, NFKB2 and CFLIP) and the TNFR1 receptor. TNFR1 downregulation significantly decreased the expression of the TRADD and CFLIP genes, although no change was observed in the cellular process or miRNA expression. In contrast, TNFR2 downregulation decreased the expression of the TRADD and TRAF2 genes, which are both important downstream mediators of the TNFR1-mediated pathway, as well as that of the NFKB1 and CFLIP genes, while upregulating the expression of miR-19a and miR-34a. Consequently, a reduction in the number of cells in the G0/G1 phase and an increase in the number of cells in the S phase were observed, as well as the promotion of early apoptosis.

CONCLUSION

Our findings mainly highlight the important role of TNFR2 in the TNF-α pathway in gastric cancer, indicating that silencing it can reduce the expression of survival and anti-apoptotic genes.

Glycosylation-Dependent Induction of Programmed Cell Death in Murine Adenocarcinoma Cells

Altered surface glycosylation is a major hallmark of tumor cells associated with aggressive phenotype and poor prognosis. By recognizing specific carbohydrate motifs, lectins can be applied to distinguish tumor from healthy cells based on the expression of glycosylation-dependent markers. Through their ability to bind to specific carbohydrates, lectins induce cell agglutination and cross-link surface glycoproteins, thereby mediating mitogenic and death-inducing effects in various cell types. The carbohydrate-selective cytotoxic effect of lectins also enables their possible application in therapies targeting cancer cells. To clarify the intracellular pathways mediating cell death induced by a group of plant and fungal lectins, we investigated mouse adenocarcinoma MC-38 cells harboring inactive genes involved in apoptosis, necroptosis and pyroptosis. Treatment of MC-38 cells with wheat germ agglutinin, Maackia amurensis lectin I, and Aleuria aurantia lectin induced multiple cell death pathways through reactions that relied on the autophagy machinery without depending on caspase activation. Furthermore, inhibition of de novo protein synthesis by cycloheximide strongly decreased the cytotoxic response, indicating that the lectins investigated induced cell death via effector molecules that are not expressed under normal circumstances and supporting the non-apoptotic nature of cell death. The broad cytotoxic response to lectins can be beneficial for the development of combination therapies targeting tumor cells. Given that tumors acquire resistance to various cytotoxic treatments because of mutations in cell death pathways, compounds inducing broad cytotoxic responses, such as lectins, represent potent sensitizers to promote tumor cell killing.

A Structural and Functional Perspective of Death Receptor 6

As a member of the tumor necrosis factor receptor superfamily (TNFRSF), death receptor 6 (DR6) has a similar structural architecture to other family members. The extracellular region of DR6 contains four cysteine-rich domains, followed by a single-pass transmembrane domain and an intracellular region. Since its discovery, DR6 has become an orphan receptor ubiquitously expressed to transduce unique signaling pathways. Although the free ectodomains of β-amyloid precursor protein (APP) can bind to DR6 to induce apoptotic signals, the natural ligands of DR6 still remain largely unknown. In this review, we focus on recent research progress of structural and functional studies on DR6 for better understanding DR6-mediated signaling and the treatment of DR6-related diseases.

Natural Peptides Inducing Cancer Cell Death: Mechanisms and Properties of Specific Candidates for Cancer Therapeutics

Nowadays, cancer has become the second highest leading cause of death, and it is expected to continue to affect the population in forthcoming years. Additionally, treatment options will become less accessible to the public as cases continue to grow and disease mechanisms expand. Hence, specific candidates with confirmed anticancer effects are required to develop new drugs. Among the novel therapeutic options, proteins are considered a relevant source, given that they have bioactive peptides encrypted within their sequences. These bioactive peptides, which are molecules consisting of 2–50 amino acids, have specific activities when administered, producing anticancer effects. Current databases report the effects of peptides. However, uncertainty is found when their molecular mechanisms are investigated. Furthermore, analyses addressing their interaction networks or their directly implicated mechanisms are needed to elucidate their effects on cancer cells entirely. Therefore, relevant peptides considered as candidates for cancer therapeutics with specific sequences and known anticancer mechanisms were accurately reviewed. Likewise, those features which turn certain peptides into candidates and the mechanisms by which peptides mediate tumor cell death were highlighted. This information will make robust the knowledge of these candidate peptides with recognized mechanisms and enhance their non-toxic capacity in relation to healthy cells and further avoid cell resistance.

Natural Peptides Inducing Cancer Cell Death: Mechanisms and Properties of Specific Candidates for Cancer Therapeutics

Nowadays, cancer has become the second highest leading cause of death, and it is expected to continue to affect the population in forthcoming years. Additionally, treatment options will become less accessible to the public as cases continue to grow and disease mechanisms expand. Hence, specific candidates with confirmed anticancer effects are required to develop new drugs. Among the novel therapeutic options, proteins are considered a relevant source, given that they have bioactive peptides encrypted within their sequences. These bioactive peptides, which are molecules consisting of 2–50 amino acids, have specific activities when administered, producing anticancer effects. Current databases report the effects of peptides. However, uncertainty is found when their molecular mechanisms are investigated. Furthermore, analyses addressing their interaction networks or their directly implicated mechanisms are needed to elucidate their effects on cancer cells entirely. Therefore, relevant peptides considered as candidates for cancer therapeutics with specific sequences and known anticancer mechanisms were accurately reviewed. Likewise, those features which turn certain peptides into candidates and the mechanisms by which peptides mediate tumor cell death were highlighted. This information will make robust the knowledge of these candidate peptides with recognized mechanisms and enhance their non-toxic capacity in relation to healthy cells and further avoid cell resistance.

Molecular Evidence of the Inhibitory Potential of Melatonin against NaAsO2-Induced Aging in Male Rats

Arsenic (As) poisoning is widespread due to exposure to pollution. The toxic level of (As) causes oxidative stress-induced aging and tissue damage. Since melatonin (MLT) has anti-oxidant and anti-aging properties, we aimed to evaluate the protective effect of MLT against the toxicity of sodium arsenite (NaAsO₂). Healthy male NMRI mice were divided into eight different groups. The control group received a standard regular diet. Other groups were treated with varying diets, including MLT alone, NaAsO₂, and NaAsO₂ plus MLT. After one month of treatment, biochemical and pathological tests were performed on blood, heart, and lung tissue samples. NaAsO₂ increased the levels of TNF-α, 8-hydroxy-2-deoxy guanosine (8OHdG), malondialdehyde (MDA), reactive oxygen species (ROS), and high mobility group box 1 (HMGB1), increased the expression of TNF receptor type 1-associated death domain (TRADD) mRNA and telomerase reverse transcriptase, and decreased the expression of Klotho (KL) mRNA in both plasma and tissues. In contrast, MLT reduced MDA, ROS, HMGB1, lactate, and TNF-α enhanced the mRNA expression of KL, and suppressed the mRNA expression of the TERT and TRADD genes. Thus, MLT confers potent protection against NaAsO₂- induced tissue injury and oxidative stress.

The Great Escape: The Power of Cancer Stem Cells to Evade Programmed Cell Death

Cancer is one of the primary causes of death worldwide. Tumour malignancy is related to tumor heterogeneity, which has been suggested to be due to a small subpopulation of tumor cells named cancer stem cells (CSCs). CSCs exert a key role in metastasis development, tumor recurrence, and also epithelial-mesenchymal transition, apoptotic resistance, self-renewal, tumorigenesis, differentiation, and drug resistance. Several current therapies fail to eradicate tumors due to the ability of CSCs to escape different programmed cell deaths. Thus, developing CSC-selective and programmed death-inducing therapeutic approaches appears to be of primary importance. In this review, we discuss the main programmed cell death occurring in cancer and the promising CSC-targeting agents developed in recent years. Even if the reported studies are encouraging, further investigations are necessary to establish a combination of agents able to eradicate CSCs or inhibit their growth and proliferation.