Death domain complex of the TNFR-1, TRADD, and RIP1 proteins for death-inducing signaling

Regulated Cell Death of Retinal Ganglion Cells in Glaucoma: Molecular Insights and Therapeutic Potentials

Glaucoma is a group of diseases characterized by the degeneration of retinal ganglion cells (RGCs) and progressive, irreversible vision loss. High intraocular pressure (IOP) heightens the likelihood of glaucoma and correlates with RGC loss. While the current glaucoma therapy prioritizes lower the IOP; however, RGC, and visual loss may persist even when the IOP is well-controlled. As such, discovering and creating IOP-independent neuroprotective strategies for safeguard RGCs is crucial for glaucoma management. Investigating and clarifying the mechanism behind RGC death to counteract its effects is a promising direction for glaucoma control. Empirical studies of glaucoma reveal the role of multiple regulated cell death (RCD) pathways in RGC death. This review delineates the RCD of RGCs following IOP elevation and optic nerve damage and discusses the substantial benefits of mitigating RCD in RGCs in preserving visual function.

Alleviation of temporomandibular joint osteoarthritis by targeting RIPK1-mediated inflammatory signalling

Temporomandibular joint osteoarthritis (TMJOA), prevalent in adolescents and the elderly, has serious physical and psychological consequences. TMJOA is a degenerative disease of the cartilage and bone, mostly driven by inflammation, and synoviocytes are the first and most important inflammatory factor releasers. Receptor-interacting serine/threonine-protein kinase (RIPK1) promotes inflammatory response and cell death during an array of illnesses. This research aimed to explore the impacts of RIPK1 inhibitor therapy in TMJOA and the mechanism of RIPK1 in inducing inflammation during TMJOA. Herein, inhibition of RIPK1 suppressed the elevated levels of inflammatory factors, nuclear factor kappa B (NF-κB), along with markers of apoptosis and necroptosis after tumour necrosis factor (TNF)-α/cycloheximide (CHX) treatment in synoviocytes. Moreover, inflammation models were constructed in vivo through complete Freund's adjuvant (CFA) induction and disc perforation, and the findings supported that RIPK1 inhibition protected TMJ articular cartilage against progressive degradation. RIPK1 regulates NF-κB activation via cellular inhibitor of apoptosis proteins (cIAP), apoptosis via caspase-8, and necroptosis via RIPK3/mixed lineage kinase domain-like (MLKL) in synoviocytes, which in turn facilitates TMJOA inflammation progression.

Progress in Research on TLR4-Mediated Inflammatory Response Mechanisms in Brain Injury after Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) is one of the common clinical neurological emergencies. Its incidence accounts for about 5-9% of cerebral stroke patients. Even surviving patients often suffer from severe adverse prognoses such as hemiplegia, aphasia, cognitive dysfunction and even death. Inflammatory response plays an important role during early nerve injury in SAH. Toll-like receptors (TLRs), pattern recognition receptors, are important components of the body's innate immune system, and they are usually activated by damage-associated molecular pattern molecules. Studies have shown that with TLR 4 as an essential member of the TLRs family, the inflammatory transduction pathway mediated by it plays a vital role in brain injury after SAH. After SAH occurrence, large amounts of blood enter the subarachnoid space. This can produce massive damage-associated molecular pattern molecules that bind to TLR4, which activates inflammatory response and causes early brain injury, thus resulting in serious adverse prognoses. In this paper, the process in research on TLR4-mediated inflammatory response mechanism in brain injury after SAH was reviewed to provide a new thought for clinical treatment.

DED Interaction of FADD and Caspase-8 in the Induction of Apoptotic Cell Death

Fas-associated death domain (FADD) is an adapter molecule that bridges the interaction between receptor-interacting protein 1 (RIP1) and aspartate-specific cysteine protease-8 (caspase-8). As the primary mediator of apoptotic cell death, caspase-8 has two N-terminal death-effector domains (DEDs) and it interacts with other proteins in the DED subfamily through several conserved residues. In the tumor necrosis receptor-1 (TNFR-1)-dependent signaling pathway, apoptosis is triggered by the caspase-8/FADD complex by stimulating receptor internalization. However, the molecular mechanism of complex formation by the DED proteins remains poorly understood. Here, we found that direct DED-DED interaction between FADD and caspase-8 and the structure-based mutations (Y8D/I128A, E12A/I128A, E12R/I128A, K39A/I128A, K39D/I128A, F122A/I128A, and L123A/I128A) of caspase-8 disrupted formation of the stable DED complex with FADD. Moreover, the monomeric crystal structure of the caspase-8 DEDs (F122A/I128A) was solved at 1.7 Å. This study will provide new insight into the interaction mechanism and structural characteristics between FADD and caspase-8 DED subfamily proteins.

Alternatively Spliced Isoforms of the P2X7 Receptor: Structure, Function and Disease Associations

The P2X7 receptor (P2X7R) is an ATP-gated membrane ion channel that is expressed by multiple cell types. Following activation by extracellular ATP, the P2X7R mediates a broad range of cellular responses including cytokine and chemokine release, cell survival and differentiation, the activation of transcription factors, and apoptosis. The P2X7R is made up of three P2X7 subunits that contain specific domains essential for the receptor’s varied functions. Alternative splicing produces P2X7 isoforms that exclude one or more of these domains and assemble in combinations that alter P2X7R function. The modification of the structure and function of the P2X7R may adversely affect cellular responses to carcinogens and pathogens, and alternatively spliced (AS) P2X7 isoforms have been associated with several cancers. This review summarizes recent advances in understanding the structure and function of AS P2X7 isoforms and their associations with cancer and potential role in modulating the inflammatory response.

The Role of Necroptosis: Biological Relevance and Its Involvement in Cancer

Simple Summary

A new form of programmed necrosis called necroptosis has emerged. This new and well-documented type of programmed cell death is involved in several human diseases, including cancer. RIPK1, the main mediator of necroptosis, in response to different stimuli, activates several molecular pathways leading to inflammation, cell survival, or cell death. Targeting necroptosis could be a new strategy for advanced therapies. In this review, we focus on the biological relevance of this type of programmed cell death and its main executor RIPK1 in pathogenesis to find novel potential clinical intervention strategies.

Abstract

Regulated cell death mechanisms are essential for the maintenance of cellular homeostasis. Evasion of cell death is one of the most important hallmarks of cancer. Necroptosis is a caspase independent form of regulated cell death, investigated as a novel therapeutic strategy to eradicate apoptosis resistant cancer cells. The process can be triggered by a variety of stimuli and is controlled by the activation of RIP kinases family as well as MLKL. The well-studied executor, RIPK1, is able to modulate key cellular events through the interaction with several proteins, acting as strategic crossroads of several molecular pathways. Little evidence is reported about its involvement in tumorigenesis. In this review, we summarize current studies on the biological relevance of necroptosis, its contradictory role in cancer and its function in cell fate control. Targeting necroptosis might be a novel therapeutic intervention strategy in anticancer therapies as a pharmacologically controllable event.

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

TRADD participates in various receptor signaling pathways and plays vital roles in many biological activities, including cell survival and apoptosis, in different cellular contexts. TRADD has two distinct functional domains, a TRAF-binding domain at the N-terminus and a death domain (DD) at the C-terminus. The TRAF binding domain of TRADD folds into an α-β plait topology and is mainly responsible for binding TRAF2, while the TRADD-DD can interact with a variety of DD-containing proteins, including receptors and intracellular signaling molecules. After activation of specific receptors such as TNFR1 and DR3, TRADD can bind to the receptor through DD-DD interaction, creating a membrane-proximal platform for the recruitment of downstream molecules to propagate cellular signals. In this review, we highlight recent advances in the studies of the structural mechanism of TRADD adaptor functions for NF-κB activation and apoptosis induction. We also provide suggestions for future structure research related to TRADD-mediated signaling pathways.

The role of IL-1β and TNF-α in intervertebral disc degeneration

Low back pain (LBP), a prevalent and costly disease around the world, is predominantly caused by intervertebral disc (IVD) degeneration (IDD). LBP also presents a substantial burden to public health and the economy. IDD is mainly caused by aging, trauma, genetic susceptibility, and other factors. It is closely associated with changes in tissue structure and function, including progressive destruction of the extracellular matrix (ECM), enhanced senescence, disc cell death, and impairment of tissue biomechanical function. The inflammatory process, exacerbated by cytokines interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), are considered to be the key mediators of IDD and LBP. IL-1β and TNF-α are the most important proinflammatory cytokines, as they have powerful proinflammatory activities and can promote the secretion of a variety of proinflammatory mediators. They are also upregulated in the degenerative IVDs, and they are closely related to various pathological IDD processes, including inflammatory response, matrix destruction, cellular senescence, autophagy, apoptosis, pyroptosis, and proliferation. Therefore, anti-IL-1β and anti-TNF-α therapies may have the potential to alleviate disc degeneration and LBP. In this paper, we reviewed the expression pattern and signal transduction pathways of IL-1β and TNF-α, and we primarily focused on their similar and different roles in IDD. Because IL-1β and TNF-α inhibition have the potential to alleviate IDD, an in-depth understanding of the role of IL-1β and TNF-α in IDD will benefit the development of new treatment methods for disc degeneration with IL-1β and TNF-α at the core.

RIPK1: A rising star in inflammatory and neoplastic skin diseases

Skin diseases bring great psychological and physical impacts on patients, however, a considerable number of skin diseases still lack effective treatments, such as psoriasis, systemic lupus erythematosus, melanoma and so on. Receptor-interacting serine threonine kinase 1 (RIPK1) plays an important role in cell death, especially necroptosis, associated with inflammation and tumor. As many molecules modulate the ubiquitination of RIPK1, disruption of this checkpoint can lead to skin diseases, which can be ameliorated by RIPK1 inhibitors. This review will focus on the molecular mechanism of RIPK1 activation in inflammation as well as the current knowledges on the contribution of RIPK1 in skin diseases.

Heterogeneous responses to low level death receptor activation are explained by random molecular assembly of the Caspase-8 activation platform

Ligand binding to death receptors activates apoptosis in cancer cells. Stimulation of death receptors results in the formation of intracellular multiprotein platforms that either activate the apoptotic initiator Caspase-8 to trigger cell death, or signal through kinases to initiate inflammatory and cell survival signalling. Two of these platforms, the Death-Inducing Signalling Complex (DISC) and the RIPoptosome, also initiate necroptosis by building filamentous scaffolds that lead to the activation of mixed lineage kinase domain-like pseudokinase. To explain cell decision making downstream of death receptor activation, we developed a semi-stochastic model of DISC/RIPoptosome formation. The model is a hybrid of a direct Gillespie stochastic simulation algorithm for slow assembly of the RIPoptosome and a deterministic model of downstream caspase activation. The model explains how alterations in the level of death receptor-ligand complexes, their clustering properties and intrinsic molecular fluctuations in RIPoptosome assembly drive heterogeneous dynamics of Caspase-8 activation. The model highlights how kinetic proofreading leads to heterogeneous cell responses and results in fractional cell killing at low levels of receptor stimulation. It reveals that the noise in Caspase-8 activation-exclusively caused by the stochastic molecular assembly of the DISC/RIPoptosome platform-has a key function in extrinsic apoptotic stimuli recognition.

Herbs-partitioned moxibustion alleviates aberrant intestinal epithelial cell apoptosis by upregulating A20 expression in a mouse model of Crohn’s disease

BACKGROUND

A20 inhibits intestinal epithelial cell apoptosis in Crohn’s disease, and herbs-partitioned moxibustion (HPM) has been demonstrated to be an effective treatment for Crohn’s disease. However, the mechanism by which HPM reduces intestinal epithelial cell apoptosis in Crohn’s disease has not been thoroughly elucidated to date.

AIM

To elucidate whether HPM exerts its effects by upregulating A20 to affect intestinal epithelial cell apoptosis in a Crohn’s disease mouse model.

METHODS

In this study, mice with A20 deletion in intestinal epithelial cells (A20^IEC-KO) were utilized to establish a Crohn’s disease mouse model with 2,4,6-trinitrobenzene sulfonic acid (TNBS) administration, as well as wild-type mice. Mice were randomly divided into normal control (NC), model control (MC), mesalazine (MESA), and HPM groups. The morphology of the colonic mucosa was observed by hematoxylin-eosin staining, and serum endotoxin and apoptosis of epithelial cells were evaluated by enzyme-linked immunosorbent assay and terminal dUTP nick-end labeling assay accordingly. The protein expression levels of A20 and tumor necrosis factor receptor 1 (TNFR1)-related signaling molecules were evaluated by Western blot, and co-expression of A20 and TNFR1-associated death domain (TRADD) and co-expression of A20 and receptor-interacting protein 1 (RIP1) were observed by double immunofluorescence staining.

RESULTS

The intestinal epithelial barrier was noted to have an improvement in the HPM group of wild-type (WT) mice compared with that in A20^IEC-KO mice. Compared with A20 ^IEC-KO HPM mice, serum endotoxin levels and apoptosis percentages were decreased (P < 0.01), A20 expression levels were increased (P < 0.01), and expression of TNFR1, TRADDD, and RIP1 was decreased in the HPM group of WT mice (P_TNFR1 < 0.05, P_TRADD < 0.01, P_RIP1 < 0.01). Both of the co-expression of A20/TRADD and A20/RIP1 showed a predominantly yellow fluorescence in the HPM group of WT mice, while a predominantly red fluorescence was noted in the HPM group of A20^IEC-KO mice.

CONCLUSION

Our findings suggest that HPM in treating Crohn’s disease functions possibly via upregulation of the A20 expression level, resulting in downregulation of TNFR1, TRADD, and RIP1 to alleviate increased cell apoptosis in the intestinal epithelial barrier in Crohn's disease.

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.

Death domain of p75 neurotrophin receptor: a structural perspective on an intracellular signalling hub

The death domain (DD) is a globular protein motif with a signature feature of an all-helical Greek-key motif. It is a primary mediator of a variety of biological activities, including apoptosis, cell survival and cytoskeletal changes, which are related to many neurodegenerative diseases, neurotrauma, and cancers. DDs exist in a wide range of signalling proteins including p75 neurotrophin receptor (p75^NTR ), a member of the tumour necrosis factor receptor superfamily. The specific signalling mediated by p75^NTR in a given cell depends on the type of ligand engaging the extracellular domain and the recruitment of cytosolic interactors to the intracellular domain, especially the DD, of the receptor. In solution, the p75^NTR -DDs mainly form a symmetric non-covalent homodimer. In response to extracellular signals, conformational changes in the p75^NTR extracellular domain (ECD) propagate to the p75^NTR -DD through the disulfide-bonded transmembrane domain (TMD) and destabilize the p75^NTR -DD homodimer, leading to protomer separation and exposure of binding sites on the DD surface. In this review, we focus on recent advances in the study of the structural mechanism of p75^NTR -DD signalling through recruitment of diverse intracellular interactors for the regulation and control of diverse functional outputs.

Progress in studies of necroptosis and its relationship to disease processes

This review briefly introduces the mechanism and detection methods of necroptosis in recent years. The most significant points of this review focus on the involvement of necroptotic proteins in disease progression. The following aspects are summarized: 1) RIPs, MLKL, and the upstream and downstream molecules that mediate necroptosis; 2) The development of detection methods for necroptosis; 3) The involvement of related necroptotic proteins in diverse diseases etiology; and 4) The application of necroptotic proteins in disease diagnosis.

MicroRNA expression in serum samples of sulfur mustard veterans as a diagnostic gateway to improve care

Sulfur mustard is a vesicant chemical warfare agent, which has been used during Iraq-Iran-war. Many veterans and civilians still suffer from long-term complications of sulfur mustard exposure, especially in their lung. Although the lung lesions of these patients are similar to Chronic Obstructive Pulmonary Disease (COPD), there are some differences due to different etiology and clinical care. Less is known on the molecular mechanism of sulfur mustard patients and specific treatment options. microRNAs are master regulators of many biological pathways and proofed to be stable surrogate markers in body fluids. Based on that microRNA expression for serum samples of sulfur mustard patients were examined, to establish specific microRNA patterns as a basis for diagnostic use and insight into affected molecular pathways. Patients were categorized based on their long-term complications into three groups and microRNA serum levels were measured. The differentially regulated microRNAs and their corresponding gene targets were identified. Cell cycle arrest, ageing and TGF-beta signaling pathways showed up to be the most deregulated pathways. The candidate microRNA miR-143-3p could be validated on all individual patients. In a ROC analysis miR-143-3p turned out to be a suitable diagnostic biomarker in the mild and severe categories of patients. Further microRNAs which might own a link to the biology of the sulfur mustard patients are miR-365a-3p, miR-200a-3p, miR-663a. miR-148a-3p, which showed up only in a validation study, might be linked to the airway complications of the sulfur mustard patients. All the other candidate microRNAs do not directly link to COPD phenotype or lung complications. In summary the microRNA screening study characterizes several molecular differences in-between the clinical categories of the sulfur mustard exposure groups and established some useful microRNA biomarkers. qPCR raw data is available via the Gene Expression Omnibus https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE110797.

TRADD mediates the tumor necrosis factor-induced apoptosis of L929 cells in the absence of RIP3

Receptor-interacting protein kinase 3 (RIP3) is a critical initiator in mediating necroptosis induced by tumor necrosis factor alpha (TNFα) in L929 cells, so knockdown of RIP3 inhibits TNFα-induced L929 cell necroptosis. However, RIP3 knockdown was shown to switch TNFα-induced necroptosis to apoptosis in L929 cells in other studies. Therefore, whether RIP3 knockdown blocks the TNFα-induced death of L929 cells is controversial. In this study, TNFα activated caspase pathway and induced cell death in RIP3 knockdown L929 cells, and the RIP3-independent cell death had been blocked by Z-VAD-FMK (pan-caspase inhibitor) or caspase 8 knockdown, demonstrating that RIP3 knockdown switched TNFα-induced necroptosis to caspase-dependent apoptosis. Although both TNF receptor type 1-associated death domain protein (TRADD) and RIP1 have been reported to mediate TNFα-induced apoptosis, the knockdown of TRADD, but not RIP1, suppressed TNFα-induced activation of the caspase pathway and subsequent apoptosis in RIP3 knockdown L929 cells. In addition, TRADD bound and activated caspase 8 during the RIP3-independent apoptosis process, indicating that TRADD initiates RIP3-independent apoptosis by activating the caspase pathway. Collectively, we identified the target and mechanism underlying RIP3-independent apoptosis and elucidated the coordinated roles of RIP3 and TRADD in mediating the programmed cell death of L929 cells following TNFα stimulation.

10H-3,6-Diazaphenothiazine induces G2/M phase cell cycle arrest and caspase-dependent apoptosis and inhibits cell invasion of A2780 ovarian carcinoma cells through the regulation of NF-κB and (BIRC6-XIAP) complexes

The asymptomatic properties and high treatment resistance of ovarian cancer result in poor treatment outcomes and high mortality rates. Although the fundamental chemotherapy provides promising anticancer activities, it is associated with severe side effects. The derivative of phenothiazine, namely, 10H-3,6-diazaphenothiazine (PTZ), was synthesized and reported with ideal anticancer effects in a previous paper. In this study, detailed anticancer properties of PTZ was examined on A2780 ovarian cancer cells by investigating the cytotoxicity profiles, mechanism of apoptosis, and cell invasion. Research outcomes revealed PTZ-induced dose-dependent inhibition on A2780 cancer cells (IC₅₀ =0.62 µM), with significant less cytotoxicity toward HEK293 normal kidney cells and H9C2 normal heart cells. Generation of reactive oxygen species (ROS) and polarization of mitochondrial membrane potential (ΔΨm) suggests PTZ-induced cell death through oxidative damage. The RT² Profiler PCR Array on apoptosis pathway demonstrated PTZ-induced apoptosis via intrinsic (mitochondria-dependent) and extrinsic (cell death receptor-dependent) pathway. Inhibition of NF-κB and subsequent inhibition of (BIRC6-XIAP) complex activities reduced the invasion rate of A2780 cancer cells penetrating through the Matrigel™ Invasion Chamber. Lastly, the cell cycle analysis hypothesizes that the compound is cytostatic and significantly arrests cell proliferation at G₂/M phase. Hence, the exploration of the underlying anticancer mechanism of PTZ suggested its usage as promising chemotherapeutic agent.

Pathogenicity-associated protein domains: The fiercely-conserved evolutionary signatures

Proteins have highly conserved domains that determine their functionality. Out of the thousands of domains discovered so far across all living forms, some of the predominant clinically-relevant domains include IENR1, HNHc, HELICc, Pro-kuma_activ, Tryp_SPc, Lactamase_B, PbH1, ChtBD3, CBM49, acidPPc, G3P_acyltransf, RPOL8c, KbaA, HAMP, HisKA, Hr1, Dak2, APC2, Citrate_ly_lig, DALR, VKc, YARHG, WR1, PWI, ZnF_BED, TUDOR, MHC_II_beta, Integrin_B_tail, Excalibur, DISIN, Cadherin, ACTIN, PROF, Robl_LC7, MIT, Kelch, GAS2, B41, Cyclin_C, Connexin_CCC, OmpH, Bac_rhodopsin, AAA, Knot1, NH, Galanin, IB, Elicitin, ACTH, Cache_2, CHASE, AgrB, PRP, IGR, and Antimicrobial21. These domains are distributed in nucleases/helicases, proteases, esterases, lipases, glycosylase, GTPases, phosphatases, methyltransferases, acyltransferase, acetyltransferase, polymerase, kinase, ligase, synthetase, oxidoreductase, protease inhibitors, nucleic acid binding proteins, adhesion and immunity-related proteins, cytoskeletal component-manipulating proteins, lipid biosynthesis and metabolism proteins, membrane-associated proteins, hormone-like and signaling proteins, etc. These domains are ubiquitous stretches or folds of the proteins in pathogens and allergens. Pathogenesis alleviation efforts can benefit enormously if the characteristics of these domains are known. Hence, this review catalogs and discusses the role of such pivotal domains, suggesting hypotheses for better understanding of pathogenesis at molecular level.

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Proteins have highly conserved regions or domains across pathogens and allergens.

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Knowledge on these critical domains can facilitate our understanding of pathogenesis mechanisms.

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Such immune manipulation-related domains include IENR1, HNHc, HELICc, ACTIN, PROF, Robl_LC7, OmpH etc.

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These domains are presnt in enzyme, transcription regulators, adhesion proteins, and hormones.

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This review discusses and hypothesizes on these domains.

Structural insights of homotypic interaction domains in the ligand-receptor signal transduction of tumor necrosis factor (TNF)

Several members of tumor necrosis factor receptor (TNFR) superfamily that these members activate caspase-8 from death-inducing signaling complex (DISC) in TNF ligand-receptor signal transduction have been identified. In the extrinsic pathway, apoptotic signal transduction is induced in death domain (DD) superfamily; it consists of a hexahelical bundle that contains 80 amino acids. The DD superfamily includes about 100 members that belong to four subfamilies: death domain (DD), caspase recruitment domain (CARD), pyrin domain (PYD), and death effector domain (DED). This superfamily contains key building blocks: with these blocks, multimeric complexes are formed through homotypic interactions. Furthermore, each DD-binding event occurs exclusively. The DD superfamily regulates the balance between death and survival of cells. In this study, the structures, functions, and unique features of DD superfamily members are compared with their complexes. By elucidating structural insights of DD superfamily members, we investigate the interaction mechanisms of DD domains; these domains are involved in TNF ligand-receptor signaling. These DD superfamily members play a pivotal role in the development of more specific treatments of cancer. [BMB Reports 2016; 49(3): 159-166]

Tumor necrosis factor-α: a key contributor to intervertebral disc degeneration

Intervertebral disc (IVD) degeneration (IDD) is the most common cause leading to low back pain (LBP), which is a highly prevalent, costly, and crippling condition worldwide. Current treatments for IDD are limited to treat the symptoms and do not target the pathophysiology. Tumor necrosis factor-α (TNF-α) is one of the most potent pro-inflammatory cytokines and signals through its receptors TNFR1 and TNFR2. TNF-α is highly expressed in degenerative IVD tissues, and it is deeply involved in multiple pathological processes of disc degeneration, including matrix destruction, inflammatory responses, apoptosis, autophagy, and cell proliferation. Importantly, anti-TNF-α therapy has shown promise for mitigating disc degeneration and relieving LBP. In this review, following a brief description of TNF-α signal transduction, we mainly focus on the expression pattern and roles of TNF-α in IDD, and summarize the emerging progress regarding its inhibition as a promising biological therapeutic approach to disc degeneration and associated LBP. A better understanding will help to develop novel TNF-α-centered therapeutic interventions for degenerative disc disease.

Sublytic C5b-9 Induces Glomerular Mesangial Cell Apoptosis through the Cascade Pathway of MEKK2-p38 MAPK-IRF-1-TRADD-Caspase 8 in Rat Thy-1 Nephritis

The apoptosis of glomerular mesangial cells (GMCs) in the early phase of rat Thy-1 nephritis (Thy-1N), a model of human mesangioproliferative glomerulonephritis (MsPGN), is primarily triggered by sublytic C5b-9. However, the mechanism of GMC apoptosis induced by sublytic C5b-9 remains unclear. In this study, we demonstrate that expressions of TNFR1-associated death domain-containing protein (TRADD) and IFN regulatory factor-1 (IRF-1) were simultaneously upregulated in the renal tissue of Thy-1N rats (in vivo) and in GMCs under sublytic C5b-9 stimulation (in vitro). In vitro, TRADD was confirmed to be a downstream gene of IRF-1, because IRF-1 could bind to TRADD gene promoter to promote its transcription, leading to caspase 8 activation and GMC apoptosis. Increased phosphorylation of p38 MAPK was verified to contribute to IRF-1 and TRADD production and caspase 8 activation, as well as to GMC apoptosis induced by sublytic C5b-9. Furthermore, phosphorylation of MEK kinase 2 (MEKK2) mediated p38 MAPK activation. More importantly, three sites (Ser^153/164/239) of MEKK2 phosphorylation were identified and demonstrated to be necessary for p38 MAPK activation. In addition, silencing of renal MEKK2, IRF-1, and TRADD genes or inhibition of p38 MAPK activation in vivo had obvious inhibitory effects on GMC apoptosis, secondary proliferation, and urinary protein secretion in rats with Thy-1N. Collectively, these findings indicate that the cascade axis of MEKK2-p38 MAPK-IRF-1-TRADD-caspase 8 may play an important role in GMC apoptosis following exposure to sublytic C5b-9 in rat Thy-1N.

Analysis of esophageal cancer cell lines exposed to X-ray based on radiosensitivity influence by tumor necrosis factor-α

Assess the effects of tumor necrosis factor-α (TNF-α) in enhancing the radiosensitivity of esophageal cancer cell line in vitro. Three esophageal cancer cell line cells were exposed to X-ray with or without TNF-α treatment. MTT assay was used to evaluate the cell growth curve, and flow cytometry was performed to assess the cell apoptosis. The radiosensitizing effects of TNF-α were detected by cell colony formation assay. Western blotting was applied to observe the expression of NF-κB and caspase-3 protein in the exposed cells. Our results indicated that cellular inhibition rate increased over time, the strongest is combined group (P < 0.05). Western blotting showed that the decline expression of NF-κB protein was stated between only rhTNF-α and only X-ray radiation group and the maximum degree was manifested in combined group. Caspase-3 protein content expression just works opposite. Three kinds of cells in the NF-κB protein were similar without rhTNF-α. Then SEG1 NF-κB protein content was reduced more than other two kinds. We concluded that the cells treated with TNF-α showed significantly suppressed cell proliferation, increasing the cell apoptosis, and caspase-3 protein expression after X-ray exposure. TNF-α can enhance the radiosensitivity of esophageal cancer to enhancing the effect of the former.

Hydrogen sulfide protects against TNF-α induced neuronal cell apoptosis through miR-485-5p/TRADD signaling

BACKGROUND AND OBJECTIVE

Increasing studies suggest that miRNAs are served as responders and regulators for pathological change in human. miR-485-5p is such a miRNA that has been proved to be affected by spinal cord I/R injury. This study was to investigate the functional involvement and mechanism of miR-485-5p in sulfuretted hydrogen (H2S) protecting neural cell from injury.

METHODS

In this study, serum tumor necrosis factor (TNF-α) and miR-485-5p were detected in 20 patients with spinal cord ischemia/reperfusion (I/R) injury and in 20 healthy control. H2S was administered by GYY4137 treatment. Two TNF-α-stimulated neural human cell lines, AGE1.HN and SY-SH-5Y, were used for in vitro I/R experiments. Quantitative RT-PCR was performed to determine miR-485-5p expression. QRT-PCR and western blot were respectively performed to evaluate expression of tumor necrosis factor receptor type 1-associated DEATH domain protein (TRADD).

RESULTS

The result showed that serum TNF-α was significantly reduced in patients compared with healthy control. In vitro TNF-α treatment dose dependently caused GE1.HN and SY-SH-5Y apoptosis, whereas this promotion action was reversed by CYY4137. Moreover, we found that H2S protected neuronal cell against apoptosis via TRADD dependent. By luciferase reporting gene assay, western blot and qRT-PCR, we confirmed that TRADD expression was regulated by miR-485-5p. Such miR-485-5p/TRADD axis was proved to be involved in GE1.HN and SY-SH-5Y neural cell-protective process of H2S.

CONCLUSION

In summary, our data for the first time identifies miR-485-5p/TRADD axis in hydrogen sulfide protecting against TNF-α-induced neuronal cell apoptosis.