A20 ubiquitin ligase-mediated polyubiquitination of RIP1 inhibits caspase-8 cleavage and TRAIL-induced apoptosis in glioblastoma

A20 in Kidney Transplantation and Autoimmunity

A20, the central inhibitor of NFκB, has multiple anti-inflammatory properties, making it an interesting target in kidney autoimmune disease and transplant biology. It has been shown to be able to inhibit inflammatory functions in macrophages, dendritic cells, T cells, and B cells in various ways, leading to less tissue damage and better graft outcomes. In this review, we will discuss the current literature regarding A20 in kidney transplantation and autoimmunity. Future investigations on animal models and in existing immunosuppressive therapies are needed to establish A20 as a therapeutic target in kidney transplantation and autoimmunity. Cell-based therapies, modified viruses or RNA-based therapies could provide a way for A20 to be utilized as a promising mediator of inflammation and tissue damage.

The SUMOylation and ubiquitination crosstalk in cancer

BACKGROUND

The cancer occurrence and progression are largely affected by the post-translational modifications (PTMs) of proteins. Currently, it has been shown that the relationship between ubiquitination and SUMOylation is highly complex and interactive. SUMOylation affects the process of ubiquitination and degradation of substrates. Contrarily, SUMOylation-related proteins are also regulated by the ubiquitination process thus altering their protein levels or activity. Emerging evidence suggests that the abnormal regulation between this crosstalk may lead to tumorigenesis.

PURPOSE

In this review, we have discussed the study of the relationship between ubiquitination and SUMOylation, as well as the possibility of a corresponding application in tumor therapy.

METHODS

The relevant literatures from PubMed have been reviewed for this article.

CONCLUSION

The interaction between ubiquitination and SUMOylation is crucial for the occurrence and development of cancer. A greater understanding of the crosstalk of SUMOylation and ubiquitination may be more conducive to the development of more selective and effective SUMOylation inhibitors, as well as a promotion of synergy with other tumor treatment strategies.

Regulation of apoptosis by ubiquitination in liver cancer

Apoptosis is a programmed cell death process critical to cell development and tissue homeostasis in multicellular organisms. Defective apoptosis is a crucial step in the malignant transformation of cells, including hepatocellular carcinoma (HCC), where the apoptosis rate is higher than in normal liver tissues. Ubiquitination, a post-translational modification process, plays a precise role in regulating the formation and function of different death-signaling complexes, including those involved in apoptosis. Aberrant expression of E3 ubiquitin ligases (E3s) in liver cancer (LC), such as cellular inhibitors of apoptosis proteins (cIAPs), X chromosome-linked IAP (XIAP), and linear ubiquitin chain assembly complex (LUBAC), can contribute to HCC development by promoting cell survival and inhibiting apoptosis. Therefore, the review introduces the main apoptosis pathways and the regulation of proteins in these pathways by E3s and deubiquitinating enzymes (DUBs). It summarizes the abnormal expression of these regulators in HCC and their effects on cancer inhibition or promotion. Understanding the role of ubiquitination in apoptosis and LC can provide insights into potential targets for therapeutic intervention.

SUMO1 degrader induces ER stress and ROS accumulation through deSUMOylation of TCF4 and inhibition of its transcription of StarD7 in colon cancer

Small molecule degraders of small ubiquitin-related modifier 1 (SUMO1) induce SUMO1 degradation in colon cancer cells and inhibits the cancer cell growth; however, it is unclear how SUMO1 degradation leads to the anticancer activity of the degraders. Genome-wide CRISPR-Cas9 knockout screen has identified StAR-related lipid transfer domain containing 7 (StarD7) as a critical gene for the degrader's anticancer activity. Here, we show that both StarD7 mRNA and protein are overexpressed in human colon cancer and its knockout significantly reduces colon cancer cell growth and xenograft progression. The treatment with the SUMO1 degrader lead compound HB007 reduces StarD7 mRNA and protein levels and increases endoplasmic reticulum (ER) stress and reactive oxygen species (ROS) production in colon cancer cells and three-dimensional (3D) organoids. The study further provides a novel mechanism of the compound anticancer activity that SUMO1 degrader-induced decrease of StarD7 occur through degradation of SUMO1, deSUMOylation and degradation of T cell-specific transcription 4 (TCF4) and thereby inhibition of its transcription of StarD7 in colon cancer cells, 3D organoids and patient-derived xenografts (PDX).

Modulation of the ubiquitin-proteasome system by phytochemicals: Therapeutic implications in malignancies with an emphasis on brain tumors

Regarding the multimechanistic nature of cancers, current chemo- or radiotherapies often fail to eradicate disease pathology, and frequent relapses or resistance to therapies occur. Brain malignancies, particularly glioblastomas, are difficult-to-treat cancers due to their highly malignant and multidimensional biology. Unfortunately, patients suffering from malignant tumors often experience poor prognoses and short survival periods. Thus far, significant efforts have been conducted to discover novel and more effective modalities. To that end, modulation of the ubiquitin-proteasome system (UPS) has attracted tremendous interest since it affects the homeostasis of proteins critically engaged in various cell functions, for example, cell metabolism, survival, proliferation, and differentiation. With their safe and multimodal actions, phytochemicals are among the promising therapeutic tools capable of turning the operation of various UPS elements. The present review, along with an updated outline of the role of UPS dysregulation in multiple cancers, provided a detailed discussion on the impact of phytochemicals on the UPS function in malignancies, especially brain tumors.

NF-κB/RelA controlled A20 limits TRAIL-induced apoptosis in pancreatic cancer

The emergence of resistance to systemic therapies in pancreatic ductal adenocarcinoma (PDAC) is still a major obstacle in clinical practice. Both, constitutive and inducible NF-κB activity are known as key players in this context. To identify differentially expressed and TRAIL resistance mediating NF-κB target genes, TRAIL sensitive and resistant PDAC cell lines were analyzed by transcriptome assays. In this context, A20 was identified as an NF-κB/RelA inducible target gene. Translational PDAC tissue analysis confirmed the correlation of elevated A20 protein expression with activated RelA expression in PDAC patients. In in vitro experiments, an elevated A20 expression is accompanied by a specific resistance toward TRAIL-mediated apoptosis but not to chemotherapeutic-induced cell death. This TRAIL resistance was attributed to A20´s E3-ligase activity-mediating Zink finger domain. Furthermore, the ubiquitin-binding scaffold protein p62 was identified as indispensable for the TRAIL-mediated apoptosis-inducing pathway affected by A20. The results of this study identify A20 as a possible therapeutic target to affect resistance to TRAIL-induced apoptosis in PDAC cells.

Research Progress for Targeting Deubiquitinases in Gastric Cancers

Gastric cancers (GCs) are malignant tumors with a high incidence that threaten global public health. Despite advances in GC diagnosis and treatment, the prognosis remains poor. Therefore, the mechanisms underlying GC progression need to be identified to develop prognostic biomarkers and therapeutic targets. Ubiquitination, a post-translational modification that regulates the stability, activity, localization, and interactions of target proteins, can be reversed by deubiquitinases (DUBs), which can remove ubiquitin monomers or polymers from modified proteins. The dysfunction of DUBs has been closely linked to tumorigenesis in various cancer types, and targeting certain DUBs may provide a potential option for cancer therapy. Multiple DUBs have been demonstrated to function as oncogenes or tumor suppressors in GC. In this review, we summarize the DUBs involved in GC and their associated upstream regulation and downstream mechanisms and present the benefits of targeting DUBs for GC treatment, which could provide new insights for GC diagnosis and therapy.

The resurrection of RIP kinase 1 as an early cell death checkpoint regulator-a potential target for therapy in the necroptosis era

Receptor-interacting serine threonine protein kinase 1 (RIPK1) has emerged as a central molecular switch in controlling the balance between cell survival and cell death. The pro-survival role of RIPK1 in maintaining cell survival is achieved via its ability to induce NF-κB-dependent expression of anti-apoptotic genes. However, recent advances have identified the pro-death function of RIPK1: posttranslational modifications of RIPK1 in the tumor necrosis factor receptor 1 (TNFR1)-associated complex-I, in the cytosolic complex-IIb or in necrosomes regulate the cytotoxic potential of RIPK1, forming an early cell death checkpoint. Since the kinase activity of RIPK1 is indispensable in RIPK3- and MLKL-mediated necroptosis induction, while it is dispensable in apoptosis, a better understanding of this early cell death checkpoint via RIPK1 might lead to new insights into the molecular mechanisms controlling both apoptotic and necroptotic modes of cell death and help develop novel therapeutic approaches for cancer. Here, we present an emerging view of the regulatory mechanisms for RIPK1 activity, especially with respect to the early cell death checkpoint. We also discuss the impact of dysregulated RIPK1 activity in pathophysiological settings and highlight its therapeutic potential in treating human diseases.

Improved understanding of the molecular mechanisms that allow a protein to control the balance between cell survival or early death could reveal new approaches to treating conditions including chronic inflammatory disease and cancer. Gang Min Hur and colleagues at Chungnam National University in Daejeon, South Korea, with Han-Ming Shen at the University of Macau in China, review emerging evidence about how the protein called receptor-interacting serine/threonine-protein kinase 1 (RIPK1) influences whether cells move towards death or survival at a key ‘checkpoint’ in cell development. Cells can undergo a natural process of programmed cell death called apoptosis, die abnormally in a disease process called necroptosis, or survive. RIPK1 appears able to influence which path is chosen depending on which genes it regulates and which proteins it interacts with. Many details are still unclear, and need further investigation.

Advances in the Study of the Ubiquitin-Editing Enzyme A20

Ubiquitin modification is a common post-translational protein modification and an important mechanism whereby the body regulates protein levels and functions. As a common enzyme associated with ubiquitin modification, the ubiquitin-editing enzyme A20 may be closely associated with the development of numerous pathological processes through its different structural domains. The aim of this paper is to provide an overview of the following: advances in ubiquitination research, the structure and function of A20, and the relationships between A20 and immune inflammatory response, apoptosis, necroptosis, pyroptosis, and autophagy.

Circ0008399 interaction with WTAP promotes assembly and activity of the m6A methyltransferase complex and promotes cisplatin resistance in bladder cancer

Cisplatin (CDDP)-based chemotherapy is the first-line treatment for muscle-invasive and metastatic bladder cancer (BC), yet most patients rapidly develop resistance. N6-methyladenosine (m6A) methylation is a pervasive RNA modification, and its specific role and potential mechanism in the regulation of CDDP chemosensitivity in BC remain unclear. Furthermore, studies have not yet fully elucidated whether circRNA can directly regulate m6A modification of mRNA. Here we report upregulation of a novel circRNA, hsa_circ_0008399 (circ0008399), by eukaryotic translation initiation factor 4A3 (EIF4A3) in BC tissues and cell lines. Functionally, circ0008399 inhibited apoptosis of BC cells. Mechanistically, circ0008399 bound Wilms' tumor 1-associating protein (WTAP) to promote formation of the WTAP/METTL3/METTL14 m6A methyltransferase complex. Circ0008399 increased expression of TNF alpha-induced protein 3 (TNFAIP3) by increasing its mRNA stability in an m6A-dependent manner. In BC patients, high expression of circ0008399 and WTAP was associated with poor outcomes. Importantly, activation of the circ0008399/WTAP/TNFAIP3 pathway decreased BC chemosensitivity to CDDP, and targeting the circ0008399/WTAP/TNFAIP3 axis enhanced the CDDP efficacy. Collectively, these findings give novel insights into circRNA-mediated regulation of m6A modifications and provide potential therapeutic targets for BC.

Tristetraprolin, a Potential Safeguard Against Carcinoma: Role in the Tumor Microenvironment

Tristetraprolin (TTP), a well-known RNA-binding protein, primarily affects the expression of inflammation-related proteins by binding to the targeted AU-rich element in the 3' untranslated region after transcription and subsequently mediates messenger RNA decay. Recent studies have focused on the role of TTP in tumors and their related microenvironments, most of which have referred to TTP as a potential tumor suppressor involved in regulating cell proliferation, apoptosis, and metastasis of various cancers, as well as tumor immunity, inflammation, and metabolism of the microenvironment. Elevated TTP expression levels could aid the diagnosis and treatment of different cancers, improving the prognosis of patients. The aim of this review is to describe the role of TTP as a potential safeguard against carcinoma.

The dual roles of A20 in cancer

A20 is a prototypical anti-inflammatory molecule that is linked to multiple human diseases, including cancers. The role of A20 as a tumor suppressor was first discovered in B cell lymphomas. Subsequent studies revealed the dual roles of A20 in solid cancers. This review focuses on the roles of A20 in different cancer types to demonstrate that the effects of A20 are cancer type-dependent. A20 plays antitumor roles in colorectal carcinomas and hepatocellular carcinomas, whereas A20 acts as an oncogene in breast cancers, gastric cancers and melanomas. Moreover, the roles of A20 in the setting of glioma therapy are context-dependent. The action mechanisms of A20 in different types of cancer are summarized. Additionally, the role of A20 in antitumor immunity is discussed. Furthermore, some open questions in this rapidly advancing field are proposed. Exploration of the actions and molecular mechanisms of A20 in cancer paves the way for the application of A20-targeting approaches in future cancer therapy.

Deubiquitinases: Modulators of Different Types of Regulated Cell Death

The mechanisms and physiological implications of regulated cell death (RCD) have been extensively studied. Among the regulatory mechanisms of RCD, ubiquitination and deubiquitination enable post-translational regulation of signaling by modulating substrate degradation and signal transduction. Deubiquitinases (DUBs) are involved in diverse molecular pathways of RCD. Some DUBs modulate multiple modalities of RCD by regulating various substrates and are powerful regulators of cell fate. However, the therapeutic targeting of DUB is limited, as the physiological consequences of modulating DUBs cannot be predicted. In this review, the mechanisms of DUBs that regulate multiple types of RCD are summarized. This comprehensive summary aims to improve our understanding of the complex DUB/RCD regulatory axis comprising various molecular mechanisms for diverse physiological processes. Additionally, this review will enable the understanding of the advantages of therapeutic targeting of DUBs and developing strategies to overcome the side effects associated with the therapeutic applications of DUB modulators.

Overcoming TRAIL Resistance for Glioblastoma Treatment

The tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) shows a promising therapeutic potential in cancer treatment as it exclusively causes apoptosis in a broad spectrum of cancer cells through triggering the extrinsic apoptosis pathway via binding to cognate death receptors, with negligible toxicity in normal cells. However, most cancers, including glioblastoma multiforme (GBM), display TRAIL resistance, hindering its application in clinical practice. Recent studies have unraveled novel mechanisms in regulating TRAIL-induced apoptosis in GBM and sought effective combinatorial modalities to sensitize GBM to TRAIL treatment, establishing pre-clinical foundations and the reasonable expectation that the TRAIL/TRAIL death receptor axis could be harnessed to treat GBM. In this review, we will revisit the status quo of the mechanisms of TRAIL resistance and emerging strategies for sensitizing GBM to TRAIL-induced apoptosis and also discuss opportunities of TRAIL-based combinatorial therapies in future clinical use for GBM treatment.

The role of E3 ubiquitin ligases in the development and progression of glioblastoma

Despite recent advances in our understanding of the disease, glioblastoma (GB) continues to have limited treatment options and carries a dismal prognosis for patients. Efforts to stratify this heterogeneous malignancy using molecular classifiers identified frequent alterations in targetable proteins belonging to several pathways including the receptor tyrosine kinase (RTK) and mitogen-activated protein kinase (MAPK) signalling pathways. However, these findings have failed to improve clinical outcomes for patients. In almost all cases, GB becomes refractory to standard-of-care therapy, and recent evidence suggests that disease recurrence may be associated with a subpopulation of cells known as glioma stem cells (GSCs). Therefore, there remains a significant unmet need for novel therapeutic strategies. E3 ubiquitin ligases are a family of >700 proteins that conjugate ubiquitin to target proteins, resulting in an array of cellular responses, including DNA repair, pro-survival signalling and protein degradation. Ubiquitin modifications on target proteins are diverse, ranging from mono-ubiquitination through to the formation of polyubiquitin chains and mixed chains. The specificity in substrate tagging and chain elongation is dictated by E3 ubiquitin ligases, which have essential regulatory roles in multiple aspects of brain cancer pathogenesis. In this review, we begin by briefly summarising the histological and molecular classification of GB. We comprehensively describe the roles of E3 ubiquitin ligases in RTK and MAPK, as well as other, commonly altered, oncogenic and tumour suppressive signalling pathways in GB. We also describe the role of E3 ligases in maintaining glioma stem cell populations and their function in promoting resistance to ionizing radiation (IR) and chemotherapy. Finally, we consider how our knowledge of E3 ligase biology may be used for future therapeutic interventions in GB, including the use of blood-brain barrier permeable proteolysis targeting chimeras (PROTACs).

TRAIL of Hope Meeting Resistance in Cancer

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) induces apoptosis selectively via its interaction with the death receptors TRAILR1/DR4 and TRAILR2/DR5 in a wide range of cancers, while sparing normal cells. Despite its tremendous potential for cancer therapeutics, the translation of TRAIL into the clinic has been confounded by TRAIL-resistant cancer populations. We discuss different molecular mechanisms underlying TRAIL-mediated apoptosis and resistance to TRAIL. We also discuss the successes and failures of recent preclinical and clinical studies of TRAIL-induced apoptosis, and current attempts to overcome TRAIL resistance, and we provide a perspective for improving the prospects of future clinical implementation.

Targeting the Ubiquitin System in Glioblastoma

Glioblastoma is the most common primary brain tumor in adults with poor overall outcome and 5-year survival of less than 5%. Treatment has not changed much in the last decade or so, with surgical resection and radio/chemotherapy being the main options. Glioblastoma is highly heterogeneous and frequently becomes treatment-resistant due to the ability of glioblastoma cells to adopt stem cell states facilitating tumor recurrence. Therefore, there is an urgent need for novel therapeutic strategies. The ubiquitin system, in particular E3 ubiquitin ligases and deubiquitinating enzymes, have emerged as a promising source of novel drug targets. In addition to conventional small molecule drug discovery approaches aimed at modulating enzyme activity, several new and exciting strategies are also being explored. Among these, PROteolysis TArgeting Chimeras (PROTACs) aim to harness the endogenous protein turnover machinery to direct therapeutically relevant targets, including previously considered "undruggable" ones, for proteasomal degradation. PROTAC and other strategies targeting the ubiquitin proteasome system offer new therapeutic avenues which will expand the drug development toolboxes for glioblastoma. This review will provide a comprehensive overview of E3 ubiquitin ligases and deubiquitinating enzymes in the context of glioblastoma and their involvement in core signaling pathways including EGFR, TGF-β, p53 and stemness-related pathways. Finally, we offer new insights into how these ubiquitin-dependent mechanisms could be exploited therapeutically for glioblastoma.

Preserving immune homeostasis with A20

A20/TNFAIP3 is a TNF induced gene that plays a profound role in preserving cellular and organismal homeostasis (Lee, et al., 2000; Opipari etal., 1990). This protein has been linked to multiple human diseases via genetic, epigenetic, and an emerging series of patients with mono-allelic coding mutations. Diverse cellular functions of this pleiotropically expressed protein include immune-suppressive, anti-inflammatory, and cell protective functions. The A20 protein regulates ubiquitin dependent cell signals; however, the biochemical mechanisms by which it performs these functions is surprisingly complex. Deciphering these cellular and biochemical facets of A20 dependent biology should greatly improve our understanding of murine and human disease pathophysiology as well as unveil new mechanisms of cell and tissue biology.

Regulation of NFκB Signalling by Ubiquitination: A Potential Therapeutic Target in Head and Neck Squamous Cell Carcinoma?

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer worldwide, with over 600,000 cases per year. The primary causes for HNSCC include smoking and alcohol consumption, with an increasing number of cases attributed to infection with Human Papillomavirus (HPV). The treatment options for HNSCC currently include surgery, radiotherapy, and/or platinum-based chemotherapeutics. Cetuximab (targeting EGFR) and Pembrolizumab (targeting PD-1) have been approved for advanced stage, recurrent, and/or metastatic HNSCC. Despite these advances, whilst HPV+ HNSCC has a 3-year overall survival (OS) rate of around 80%, the 3-year OS for HPV- HNSCC is still around 55%. Aberrant signal activation of transcription factor NFκB plays an important role in the pathogenesis and therapeutic resistance of HNSCC. As an important mediator of inflammatory signalling and the immune response to pathogens, the NFκB pathway is tightly regulated to prevent chronic inflammation, a key driver of tumorigenesis. Here, we discuss how NFκB signalling is regulated by the ubiquitin pathway and how this pathway is deregulated in HNSCC. Finally, we discuss the current strategies available to target the ubiquitin pathway and how this may offer a potential therapeutic benefit in HNSCC.

Esophageal cancer cells convert the death signal from TRAIL into a stimulus for survival during acid/bile exposure

BACKGROUND

TRAIL is best known for killing cancer cells selectively, however, some cancers resist TRAIL treatment for various reasons. Esophageal adenocarcinoma is such an example. Previously, we reported that the tumor cells interrupted TRAIL-mediated apoptosis by overexpressing the decoy receptors and survivin.

AIMS

To investigate TRAIL resistance in esophageal adenocarcinoma during GERD.

METHODS

We simulated GERD episodes in vitro by exposing cancer cells to the acid/bile conditions acutely as well as chronically. TRAIL and its receptors were examined for expression, interaction, and induction of cell death.

RESULTS

We found that acid/bile exposure drove the tumor cells to express TRAIL and TRAILR2 robustly, but did not lead to apoptosis, because the tumor cells overexpressed TRADD to replace FADD as the adaptor molecule to trigger NFκB activation instead of caspases, and thereby convert a death signal from TRAIL into a stimulus for survival. The tumor cells also overexpressed c-FLIP to keep caspases away from TRAILR2 in case FADD finds a way back to the death receptor.

CONCLUSION

Multiple reasons contribute to TRAIL resistance in esophageal adenocarcinoma, including overexpression of the decoy receptors to block the death receptors, using TRADD to replace FADD, and using c-FLIP to replace caspase-8.

Identification and Investigation of miRNAs From Gastrodia elata Blume and Their Potential Function

Gastrodia elata Blume (G. elata) is a valuable traditional Chinese medicine with neuroprotection, anti-inflammatory, and immune regulatory functions. MicroRNAs (miRNA) is a kind of endogenous noncoding small RNAs that plays distinctly important roles for gene regulation of organisms. So far, the research on G. elata is mainly focused on the pharmacological functions of the natural chemical ingredients, and the function of G. elata miRNA remains unknown. In this study, 5,718 known miRNAs and 38 novel miRNAs were identified by high-throughput sequencing from G. elata. Based on GO and KEGG analysis, we found that the human genes possibly regulated by G. elata miRNAs were related to the cell cycle, immune regulation, intercellular communication, etc. Furthermore, two novel miRNAs as Gas-miR01 and Gas-miR02 have stable and high expression in the medicinal tissues of G. elata. Further bioinformatics prediction showed that both Gas-miR01 and Gas-miR02 could target Homo sapiens A20 gene, furthermore, the dual-luciferase reporter gene assay and Western Blotting verified the interaction of Gas-miR01 or Gas-miR02 with A20. These evidences suggested that G. elata-unique miRNAs might be involved in certain physiological processes. The animal experiment showed that Gas-miR01 and Gas-miR02 could be detected in some tissues of mice by intragastric administration; meanwhile, the A20 expression in some tissues of mice was downregulated. These results supported for the functional study of G. elata miRNAs.

RIPK1 ubiquitination: Evidence, correlations and the undefined

Over the last two decades the mechanisms that underpin cell survival and cell death have been intensively studied. One molecule in particular, Receptor Interacting Protein Kinase 1 (RIPK1), has gained interest due to the ability to function upstream of both NF-κB signaling and caspase-dependent and -independent cell death. RIPK1 is critical in determining cell fate downstream of cytokine signaling receptors such as the Tumour Necrosis Factor Receptor Super Family (TNFRSF) and the innate immune Toll-like receptors. Various studies have attempted to untangle how ubiquitination of RIPK1 dictates signaling outcomes; however, due to the complex nature of ubiquitin signaling it has been difficult to prove that ubiquitination of RIPK1 does in fact influence signaling outcomes. Therefore, we ask the question: What do we really know about RIPK1 ubiquitination, and, to what extent can we conclude that ubiquitination of RIPK1 impacts RIPK1-mediated signaling events?

A20 promotes melanoma progression via the activation of Akt pathway

Melanoma is the most life-threatening skin cancer with increasing incidence around the world. Although recent advances in targeted therapy and immunotherapy have brought revolutionary progress of the treatment outcome, the survival of patients with advanced melanoma remains unoptimistic, and metastatic melanoma is still an incurable disease. Therefore, to further understand the mechanism underlying melanoma pathogenesis could be helpful for developing novel therapeutic strategy. A20 is a crucial ubiquitin-editing enzyme implicated immunity regulation, inflammatory responses and cancer pathogenesis. Herein, we report that A20 played an oncogenic role in melanoma. We first found that the expression of A20 was significantly up-regulated in melanoma cell lines. Then, we showed that knockdown of A20 suppressed melanoma cell proliferation in vitro and melanoma growth in vivo through the regulation of cell-cycle progression. Moreover, A20 could potentiate the invasive and migratory capacities of melanoma cell in vitro and melanoma metastasis in vivo by promoting epithelial–mesenchymal transition (EMT). Mechanistically, we found that Akt activation mediated the oncogenic effect of A20 on melanoma development, with the involvement of glycolysis. What’s more, the up-regulation of A20 conferred the acquired resistance to Vemurafenib in BRAF-mutant melanoma. Taken together, we demonstrated that up-regulated A20 promoted melanoma progression via the activation of Akt pathway, and that A20 could be exploited as a potential therapeutic target for melanoma treatment.

Transforming Growth Factor-β Promotes Homing and Therapeutic Efficacy of Human Mesenchymal Stem Cells to Glioblastoma

Human mesenchymal stem cell-based tumor therapeutic gene delivery is regarded as a promising strategy for the treatment of glioblastoma (GBM). However, the efficiency of these stem cells to home to the target sites limits their potential curative effect and clinical application. In this work, we provide a novel pretreatment approach for enhancing the homing capacity of human adipose-derived mesenchymal stem cells (hAMSCs) for stem cell-based tumor gene delivery for GBM therapy. Pre-exposure of these stem cells to TGF-β resulted in enhanced homing ability to GBM through increasing CXC chemokine receptor 4 (CXCR4) expression, as evidenced by a diminishing homing capacity when inhibition of the TGF-β receptor II and CXCR4 was applied. In addition, by pretreating hAMSCs expression of tumor necrosis factor-related apoptosis-inducing ligand with TGF-β, we achieved significant enhancements in the therapeutic efficacy as demonstrated by an increased number of migrated hAMSCs to target sites, decreased tumor volume, and prolonged survival time in a murine model of GBM. These findings highlight a straightforward method in which cell preconditioning methodology is utilized to promote therapeutic efficacy of a biological treatment for GBM.

A20 and Cell Death-driven Inflammation

A20 is a potent anti-inflammatory molecule, and mutations in TNFAIP3, the gene encoding A20, are associated with a wide panel of inflammatory pathologies, both in human and mouse. The anti-inflammatory properties of A20 are commonly attributed to its ability to suppress inflammatory NF-κB signaling by functioning as a ubiquitin-editing enzyme. However, A20 also protects cells from death, independently of NF-κB regulation, and recent work has demonstrated that cell death may drive some of the inflammatory conditions caused by A20 deficiency. Adding to the fact that the protective role of A20 does not primarily rely on its catalytic activities, these findings shed new light on A20 biology.

The SCFSkp2 ubiquitin ligase complex modulates TRAIL-R2-induced apoptosis by regulating FLIP(L)

TRAIL-R2 (DR5) is a clinically-relevant therapeutic target and a key target for immune effector cells. Herein, we identify a novel interaction between TRAIL-R2 and the Skp1-Cullin-1-F-box (SCF) Cullin-Ring E3 Ubiquitin Ligase complex containing Skp2 (SCF^Skp2). We find that SCF^Skp2 can interact with both TRAIL-R2’s pre-ligand association complex (PLAC) and ligand-activated death-inducing signalling complex (DISC). Moreover, Cullin-1 interacts with TRAIL-R2 in its active NEDDylated form. Inhibiting Cullin-1’s DISC recruitment using the NEDDylation inhibitor MLN4924 (Pevonedistat) or siRNA increased apoptosis induction in response to TRAIL. This correlated with enhanced levels of the caspase-8 regulator FLIP at the TRAIL-R2 DISC, particularly the long splice form, FLIP(L). We subsequently found that FLIP(L) (but not FLIP(S), caspase-8, nor the other core DISC component FADD) interacts with Cullin-1 and Skp2. Importantly, this interaction is enhanced when FLIP(L) is in its DISC-associated, C-terminally truncated p43-form. Prevention of FLIP(L) processing to its p43-form stabilises the protein, suggesting that by enhancing its interaction with SCF^Skp2, cleavage to the p43-form is a critical step in FLIP(L) turnover. In support of this, we found that silencing any of the components of the SCF^Skp2 complex inhibits FLIP ubiquitination, while overexpressing Cullin-1/Skp2 enhances its ubiquitination in a NEDDylation-dependent manner. DISC recruitment of TRAF2, previously identified as an E3 ligase for caspase-8 at the DISC, was also enhanced when Cullin-1’s recruitment was inhibited, although its interaction with Cullin-1 was found to be mediated indirectly via FLIP(L). Notably, the interaction of p43-FLIP(L) with Cullin-1 disrupts its ability to interact with FADD, caspase-8 and TRAF2. Collectively, our results suggest that processing of FLIP(L) to p43-FLIP(L) at the TRAIL-R2 DISC enhances its interaction with co-localised SCF^Skp2, leading to disruption of p43-FLIP(L)’s interactions with other DISC components and promoting its ubiquitination and degradation, thereby modulating TRAIL-R2-mediated apoptosis.

A20 targets PFKL and glycolysis to inhibit the progression of hepatocellular carcinoma

Abnormal expression of the E3 ubiquitin ligase A20 has been found in some malignant cancers, including hepatocellular carcinoma (HCC). Here, we discovered that A20 is an E3 ubiquitin ligase for phosphofructokinase, liver type (PFKL) in HCC A20 interacts with PFKL and promotes its degradation, therefore inhibiting glycolysis in HCC cell lines. Downregulation of A20 in HCC cells promotes proliferation, migration, and glycolysis, all of which can be inhibited by targeting PFKL with RNA interference. Importantly, A20 is downregulated in advanced HCC tissues and inversely correlated with PFKL expression. Thus, our findings establish A20 as a critical regulator of glycolysis and reveal a novel mechanism for A20 in tumor suppression and PFKL regulation. Given that an increased level of glycolysis is linked with HCC, this study also identifies potential therapeutic targets for HCC treatment.

The Skp2 Pathway: A Critical Target for Cancer Therapy

Strictly regulated protein degradation by ubiquitin-proteasome system (UPS) is essential for various cellular processes whose dysregulation is linked to serious diseases including cancer. Skp2, a well characterized component of Skp2-SCF E3 ligase complex, is able to conjugate both K48-linked ubiquitin chains and K63-linked ubiquitin chains on its diverse substrates, inducing proteasome mediated proteolysis or modulating the function of tagged substrates respectively. Overexpression of Skp2 is observed in various human cancers associated with poor survival and adverse therapeutic outcomes, which in turn suggests that Skp2 engages in tumorigenic activity. To that end, the oncogenic properties of Skp2 are demonstrated by various genetic mouse models, highlighting the potential of Skp2 as a target for tackling cancer. In this article, we will describe the downstream substrates of Skp2 as well as upstream regulators for Skp2-SCF complex activity. We will further summarize the comprehensive oncogenic functions of Skp2 while describing diverse strategies and therapeutic platforms currently available for developing Skp2 inhibitors.

Tumor necrosis factor related apoptosis inducing ligand (TRAIL) regulates deubiquitinase USP5 in tumor cells

The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) pathway has emerged as a cancer therapeutic target. However, clinical trials have proven that most human cancers are resistant to TRAIL. We show that exposure to recombinant TRAIL resulted in the accumulation of ubiquitinated proteins and free ubiquitin polymers, suggesting a link between TRAIL and the ubiquitin (Ub)-proteasome pathway. TRAIL treatment in cancer cells reduced the activity and cleavage of USP5, a deubiquitinase (DUB) previously shown to target unanchored Ub polymers and regulate p53-mediated transcription. TRAIL was effective in suppressing USP5 activity and cleavage in TRAIL-sensitive cells but not resistant cells. Knockdown of USP5 in TRAIL-resistant cells demonstrated that USP5 controls apoptotic responsiveness to TRAIL. USP5 cleavage and ubiquitination were blocked by caspase-8 specific inhibitors. A small-molecule USP5/9× inhibitor (G9) combined with TRAIL enhanced apoptosis and blocked colony growth in highly TRAIL-resistant cell lines. Finally, USP5 protein levels and activity were found to be frequently deregulated in TRAIL-resistant cells. Together, we conclude that activated TRAIL enhances USP5 activity and induces apoptosis in TRAIL-sensitive and -resistant cells. We also suggest that USP5 inhibition may be effective in inducing apoptotic thresholds to enhance responsiveness to TRAIL.

Expanding the spectrum of A20 haploinsufficiency in two Chinese families: cases report

Background

The association between mutations in the TNFAIP3 gene and a new autoinflammatory disease (called A20 haploinsufficiency, HA20) has recently been recognized. Here, we describe four patients with HA20 from two unrelated Chinese families.

Case presentation

A total of four patients from two families were included. The average age at onset was 5.9 years. All patients had no signs of eye or skin problems, such as uveitis, rash, folliculitis and dermal abscess. Prior to the recognition of HA20, P1 was diagnosed with SLE, liver fibrosis and hypothyroidism. She also had no oral, genital or perineal ulcers. P2 was diagnosed with Crohn’s disease and inflammatory bowel disease-related arthritis (IBD-RA). He had a perianal abscess but no oral or genital ulcers. P3, the father of P1 and P2, only had mild oral ulcers, arthralgia, and archosyrinx. P4 was diagnosed with polyarticular juvenile idiopathic arthritis (JIA), macrophage activation syndrome (MAS) and interstitial lung disease (ILD). Whole exome sequencing (WES) was performed in two families. WES revealed heterozygous c.559C > T in the TNFAIP3 gene in P1, P2 and P3, while the c.259C > T mutation in the TNFAIP3 gene was identified in P4. The c.259C > T mutations is novel.

Conclusion

HA20 had a different phenotype between families and even between family members with the same mutation. Liver fibrosis, hypothyroidism, ILD and MAS in the patients with HA20 were first reported in this study. Our results expanded the phenotype and genotype spectrum of A20 haploinsufficiency.

Electronic supplementary material

The online version of this article (10.1186/s12881-019-0856-1) contains supplementary material, which is available to authorized users.

Emerging role of zinc finger protein A20 as a suppressor of hepatocellular carcinoma

Hepatocellular carcinoma (HCC), the third leading cause of cancer-associated mortality worldwide, is a major public health problem. Zinc finger protein A20 (A20), an acute phase response gene, is a potent inhibitor of NF-κB signaling. A20 serves a critical role in liver protection, including limiting inflammation following hepatic injury, stimulating hepatocyte growth, and preventing hepatic ischemia-reperfusion injury. A20 is also involved in different processes, including tumorigenesis, progression, and metastasis through multiple mechanisms. Accumulated studies have reported the clinical implications and biological relevance of A20 in the development and progression of HCC. The underlying mechanisms of A20 in HCC include inhibition of epithelial-mesenchymal transition, protein tyrosine kinase 2 activation and Rac family GTPase 1 activity. Combining liver protection with tumor inhibition is a unique advantage of A20, which has the potential to be a novel treatment for promoting liver regeneration following liver resection in patients with HCC with liver cirrhosis. This review discusses the hepato-protective effect of A20 on hepatocytes and its potential role in cancer development, particularly its suppressor effect on HCC.

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.

Stimulations of the Culture Medium of Activated Microglia and TNF-Alpha on a Scrapie-Infected Cell Line Decrease the Cell Viability and Induce Marked Necroptosis That Also Occurs in the Brains from the Patients of Human Prion Diseases

Activation of microglia and increased expression of TNF-α are frequently observed in the brains of human and animal prion diseases. As an important cytokine, TNF-α participates in not only pro-inflammatory responses but also in cellular communication, cell differentiation, and cell death. However, the role of TNF-α in the pathogenesis of prion disease remains ambiguous. In this study, the activities of a scrapie-infected cell line SMB-S15 and its normal partner SMB-PS exposed to the supernatant of a LPS-activated microglia cell line BV2 were evaluated. After it was exposed to the LPS-stimulated supernatant of BV2 cells, the cell viability of SMB-S15 cells was markedly decreased, whereas that of the SMB-PS cells remained unchanged. The level of TNF-α was significantly increased in the LPS-stimulated supernatant of BV2 cells. Further, we found that the recombinant TNF-α alone induced the decreased cell viability of SMB-S15 and the neutralizing antibody for TNF-α completely antagonized the decreased cell viability caused by the LPS-stimulated supernatant of BV2 cells. Stimulation with TNF-α induced the remarkable increases of apoptosis-associated proteins in SMB-PS cells, such as cleaved caspase-3 and RIP1, whereas an obvious increase of necroptosis-associated protein in SMB-S15 cells, such as p-MLKL. Meanwhile, the upregulation of caspase-8 activity in SMB-PS cells was more significant than that of SMB-S15 cells. The decreased cell viability of SMB-S15 and the increased expression of p-MLKL induced by TNF-α were completely rescued by Necrostatin-1. Moreover, we verified that removal of PrP^Sc propagation in SMB-S15 cells by resveratrol partially rescues the cell tolerance to the stimulation of TNF-α. These data indicate that the prion-infected cell line SMB-S15 is more vulnerable to the stimulations of activated microglia and TNF-α, which is likely due to the outcome of necroptosis rather than apoptosis. Furthermore, significant upregulation of p-MLKL, MLKL, and RIP3 was detected in the post-mortem cortical brains of the patients of various types of human prion diseases, including sporadic Creutzfeldt-Jakob disease (sCJD), G114 V-genetic CJD (gCJD), and fatal familial insomnia (FFI).

Exploiting tumor-intrinsic signals to induce mesenchymal stem cell-mediated suicide gene therapy to fight malignant glioma

Background

Human mesenchymal stem cell (MSC)-based tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) gene delivery is regarded as an effective treatment for glioblastoma (GBM). However, adverse-free target site homing of the delivery vehicles to the tumor microsatellite nests is challenging, leading to erroneously sustained released of this suicide protein into the normal brain parenchyma; therefore, limiting off-target cytotoxicity and controlled expression of the suicide inductor is a prerequisite for the safe use of therapeutic stem cells.

Methods

Utilizing the intrinsic expression profile of GBM and its elevated expression of TGF-β relative to normal brain tissue, we sought to engineer human adipose-derived MSCs (hAMSC-SBE4-TRAIL) which augment the expression of TRAIL under the trigger of TGF-β signaling. We validated our therapeutic technology in a series of functional in vitro and in vivo assays using primary patient-derived GBM models.

Results

Our current findings show that these biologic delivery vehicles have high tumor tropism efficacy and expression TRAIL gene under the trigger of TGF-β-secreting GBMs, as well as avoid unspecific TRAIL secretion into normal brain tissue. hAMSC-SBE4-TRAIL inhibited the proliferation and induced apoptosis in experimental GBMs both in vitro and in vivo. In addition, our improved platform of engineered MSCs significantly decreased the tumor volume and prolonged survival time in a murine model of GBM.

Conclusions

Our results on the controlled release of suicide inductor TRAIL by exploiting an endogenous tumor signaling pathway demonstrate a significant improvement for the clinical utility of stem cell-mediated gene delivery to treat brain cancers. Harvesting immune-compatible MSCs from patients’ fat by minimally invasive procedures further highlights the clinical potential of this approach in the vision of applicability in a personalized manner. The hAMSC-SBE4-TRAIL exhibit great curative efficacy and are a promising cell-based treatment option for GBM to be validated in clinical exploration.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1194-0) contains supplementary material, which is available to authorized users.

MicroRNA regulation of TRAIL mediated signaling in different cancers: Control of micro steering wheels during the journey from bench-top to the bedside

Large-scale sequencing methodologies have helped us identify numerous genomic alterations and we have started to scratch the surface of many new targets for treatment of cancer and the associated predictive biomarkers. TRAIL (TNF-related apoptosis-inducing ligand) is a highly appreciated anti-cancer molecule because of its ability to selectively target cancer cells. However, confluence of information suggests that cancer cells develop resistance against TRAIL-based therapeutics. It is being realized that overexpression of anti-apoptotic proteins and inactivation of pro-apoptotic proteins significantly impairs TRAIL triggered apoptosis, particularly in clinical settings. Re-balancing of pro-and anti-apoptotic proteins and upregulation of death receptors with functionally active extrinsic and intrinsic apoptotic pathways are necessary to sensitize cancer cells to TRAIL based therapeutics. microRNAs (miRNAs) are involved in regulation of myriad of molecular processes and characterized into oncogenic and tumor suppressor miRNAs. Accumulating data has identified miRNAs which positively or negatively regulate TRAIL mediated signaling in cancer cells, helping us understand different steps at which TRAIL-mediated apoptotic signaling can be targeted. Here, we assess the status of our understanding of the mechanisms related to miRNA regulation of TRAIL mediated signaling, as well as the existing gaps therein, and discuss the challenges and opportunities that will help us get closer to personalized medicine.

PIM kinases mediate resistance of glioblastoma cells to TRAIL by a p62/SQSTM1-dependent mechanism

Glioblastoma (GBM) is the most common and aggressive brain tumor and is associated with poor prognosis. GBM cells are frequently resistant to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and finding new combinatorial therapies to sensitize glioma cells to TRAIL remains an important challenge. PIM kinases are serine/threonine kinases that promote cell survival and proliferation and are highly expressed in different tumors. In this work, we studied the role of PIM kinases as regulators of TRAIL sensitivity in GBM cells. Remarkably, PIM inhibition or knockdown facilitated activation by TRAIL of a TRAIL-R2/DR5-mediated and mitochondria-operated apoptotic pathway in TRAIL-resistant GBM cells. The sensitizing effect of PIM knockdown on TRAIL-induced apoptosis was mediated by enhanced caspase-8 recruitment to and activation at the death-inducing signaling complex (DISC). Interestingly, TRAIL-induced internalization of TRAIL-R2/DR5 was significantly reduced in PIM knockdown cells. Phospho-proteome profiling revealed a decreased phosphorylation of p62/SQSTM1 after PIM knockdown. Our results also showed an interaction between p62/SQSTM1 and the DISC that was reverted after PIM knockdown. In line with this, p62/SQSTM1 ablation increased TRAIL-R2/DR5 levels and facilitated TRAIL-induced caspase-8 activation, revealing an inhibitory role of p62/SQSTM1 in TRAIL-mediated apoptosis in GBM. Conversely, upregulation of TRAIL-R2/DR5 upon PIM inhibition and apoptosis induced by the combination of PIM inhibitor and TRAIL were abrogated by a constitutively phosphorylated p62/SQSTM1^S332E mutant. Globally, our data represent the first evidence that PIM kinases regulate TRAIL-induced apoptosis in GBM and identify a specific role of p62/SQSTM1^Ser332 phosphorylation in the regulation of the extrinsic apoptosis pathway activated by TRAIL.

E3 ubiquitin ligases and deubiquitinases as modulators of TRAIL-mediated extrinsic apoptotic signaling pathway

The tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) initiates the extrinsic apoptotic pathway through formation of the death-inducing signaling complex (DISC), followed by activation of effector caspases. TRAIL receptors are composed of death receptors (DR4 and DR5), decoy receptors (DcR1 and DcR2), and osteoprotegerin. Among them, only DRs activate apoptotic signaling by TRAIL. Since the levels of DR expressions are higher in cancer cells than in normal cells, TRAIL selectively activates apoptotic signaling pathway in cancer cells. However, multiple mechanisms, including down-regulation of DR expression and pro-apoptotic proteins, and up-regulation of anti-apoptotic proteins, make cancer cells TRAIL-resistant. Therefore, many researchers have investigated strategies to overcome TRAIL resistance. In this review, we focus on protein regulation in relation to extrinsic apoptotic signaling pathways via ubiquitination. The ubiquitin proteasome system (UPS) is an important process in control of protein degradation and stabilization, and regulates proliferation and apoptosis in cancer cells. The level of ubiquitination of proteins is determined by the balance of E3 ubiquitin ligases and deubiquitinases (DUBs), which determine protein stability. Regulation of the UPS may be an attractive target for enhancement of TRAIL-induced apoptosis. Our review provides insight to increasing sensitivity to TRAIL-mediated apoptosis through control of post-translational protein expression. [BMB Reports 2019; 52(2): 119-126].

The roles of ubiquitination in extrinsic cell death pathways and its implications for therapeutics

Regulation of cell survival and death, including apoptosis and necroptosis, is important for normal development and tissue homeostasis, and disruption of these processes can cause cancer, inflammatory diseases, and degenerative diseases. Ubiquitination is a cellular process that induces proteasomal degradation by covalently attaching ubiquitin to the substrate protein. In addition to proteolytic ubiquitination, nonproteolytic ubiquitination, such as M1-linked and K63-linked ubiquitination, has been shown to be important in recent studies, which have demonstrated its function in cell signaling pathways that regulate inflammation and cell death pathways. In this review, we summarize the TRAIL- and TNF-induced death receptor signaling pathways along with recent advances in this field and illustrate how different types of ubiquitination control cell death and survival. In particular, we provide an overview of the different types of ubiquitination, target residues, and modifying enzymes, including E3 ligases and deubiquitinating enzymes. Given the relevance of these regulatory pathways in human disease, we hope that a better understanding of the regulatory mechanisms of cell death pathways will provide insights into and therapeutic strategies for related diseases.

Emergence of Members of TRAF and DUB of Ubiquitin Proteasome System in the Regulation of Hypertrophic Cardiomyopathy

The ubiquitin proteasome system (UPS) plays an imperative role in many critical cellular processes, frequently by mediating the selective degradation of misfolded and damaged proteins and also by playing a non-degradative role especially important as in many signaling pathways. Over the last three decades, accumulated evidence indicated that UPS proteins are primal modulators of cell cycle progression, DNA replication, and repair, transcription, immune responses, and apoptosis. Comparatively, latest studies have demonstrated a substantial complexity by the UPS regulation in the heart. In addition, various UPS proteins especially ubiquitin ligases and proteasome have been identified to play a significant role in the cardiac development and dynamic physiology of cardiac pathologies such as ischemia/reperfusion injury, hypertrophy, and heart failure. However, our understanding of the contribution of UPS dysfunction in the plausible development of cardiac pathophysiology and the complete list of UPS proteins regulating these afflictions is still in infancy. The recent emergence of the roles of TNF receptor-associated factor (TRAFs) and deubiquitinating enzymes (DUBs) superfamily in hypertrophic cardiomyopathy has enhanced our knowledge. In this review, we have mainly compiled the TRAF superfamily of E3 ligases and few DUBs proteins with other well-documented E3 ligases such as MDM2, MuRF-1, Atrogin-I, and TRIM 32 that are specific to myocardial hypertrophy. In this review, we also aim to highlight their expression profile following physiological and pathological stimulation leading to the onset of hypertrophic phenotype in the heart that can serve as biomarkers and the opportunity for the development of novel therapies.

K6 linked polyubiquitylation of FADD by CHIP prevents death inducing signaling complex formation suppressing cell death

Fas-associated death domain (FADD) is an adaptor protein recruiting complexes of caspase 8 to death ligand receptors to induce extrinsic apoptotic cell death in response to a TNF superfamily member. Although, formation of the complex of FADD and caspase 8 upon death stimuli has been studied in detail, posttranslational modifications fine-tuning these processes have yet to be identified. Here we revealed that K6-linked polyubiquitylation of FADD on lysines 149 and 153 mediated by C terminus HSC70-interacting protein (CHIP) plays an important role in preventing formation of the death inducing signaling complex (DISC), thus leading to the suppression of cell death. Cells depleted of CHIP showed higher sensitivity toward death ligands such as FasL and TRAIL, leading to upregulation of DISC formation composed of a death receptor, FADD, and caspase 8. CHIP was able to bind to FADD, induce K6-linked polyubiquitylation of FADD, and suppress DISC formation. By mass spectrometry, lysines 149 and 153 of FADD were found to be responsible for CHIP-mediated FADD ubiquitylation. FADD mutated at these sites was capable of more potent cell death induction as compared with the wild type and was no longer suppressed by CHIP. On the other hand, CHIP deficient in E3 ligase activity was not capable of suppressing FADD function and of FADD ubiquitylation. CHIP depletion in ME-180 cells induced significant sensitization of these cells toward TRAIL in xenograft analyses. These results imply that K6-linked ubiquitylation of FADD by CHIP is a crucial checkpoint in cytokine-dependent extrinsic apoptosis.

Targeting CAND1 promotes caspase-8/RIP1-dependent apoptosis in liver cancer cells

Cullin-associated NEDD8-dissociated 1 (CAND1) plays a vital role in regulating the activity of Cullin-RING ubiquitin ligases (CRLs), which are frequently dysregulated in cancer. However, the role of CAND1 in hepatocellular carcinoma (HCC) remains unknown. Here, we found that CAND1 was overexpressed in HCC tissues compared to corresponding adjacent liver tissues (71.7% vs 16.7%); high expression of CAND1 was associated with poor overall survival (40.7 vs 57.3 months, P=0.0013); and CAND1 was an independent risk factor for the prognosis of HCC patients (N=138, P=0.018). Functional studies revealed that CAND1 knockdown efficiently suppressed the proliferation of liver cancer cells by activating caspase-8-dependent mitochondrial apoptosis. We also observed a mutual activation loop between caspase-8 and Receptor Interacting Protein 1 (RIP1), which amplified CAND1 knockdown-induced apoptotic signals in the cells. Furthermore, RIP1 inhibitor Necrostatin-1 eliminated the activation of caspase-8. In conclusion, our study pioneered in reporting high CAND1 expression as a predictor of poor prognosis for HCC patients. CAND1 silencing suppressed HCC cell proliferation by inducing caspase-8/RIP1-dependent apoptosis. These findings supported that CAND1 could be a new therapeutic target for liver cancer.

Transcriptome sequencing of neurologic diseases associated genes in HHV-6A infected human astrocyte

Human Herpesvirus 6 (HHV-6) has been involved in the development of several central nervous system (CNS) diseases, such as Alzheimer's disease, multiple sclerosis and glioma. In order to identify the pathogenic mechanism of HHV-6A infection, we carried out mRNA-seq study of human astrocyte HA1800 cell with HHV-6A GS infection. Using mRNA-seq analysis of HA1800-control cells with HA1800-HHV-6A GS cells, we identified 249 differentially expressed genes. After investigating these candidate genes, we found seven genes associated with two or more CNS diseases: CTSS, PTX3, CHI3L1, Mx1, CXCL16, BIRC3, and BST2. This is the first transcriptome sequencing study which showed the significant association of these genes between HHV-6A infection and neurologic diseases. We believe that our findings can provide a new perspective to understand the pathogenic mechanism of HHV-6A infection and neurologic diseases.

Molecular mechanisms of cell death: recommendations of the Nomenclature Committee on Cell Death 2018

Over the past decade, the Nomenclature Committee on Cell Death (NCCD) has formulated guidelines for the definition and interpretation of cell death from morphological, biochemical, and functional perspectives. Since the field continues to expand and novel mechanisms that orchestrate multiple cell death pathways are unveiled, we propose an updated classification of cell death subroutines focusing on mechanistic and essential (as opposed to correlative and dispensable) aspects of the process. As we provide molecularly oriented definitions of terms including intrinsic apoptosis, extrinsic apoptosis, mitochondrial permeability transition (MPT)-driven necrosis, necroptosis, ferroptosis, pyroptosis, parthanatos, entotic cell death, NETotic cell death, lysosome-dependent cell death, autophagy-dependent cell death, immunogenic cell death, cellular senescence, and mitotic catastrophe, we discuss the utility of neologisms that refer to highly specialized instances of these processes. The mission of the NCCD is to provide a widely accepted nomenclature on cell death in support of the continued development of the field.

Delineating Crosstalk Mechanisms of the Ubiquitin Proteasome System That Regulate Apoptosis

Regulatory functions of the ubiquitin-proteasome system (UPS) are exercised mainly by the ubiquitin ligases and deubiquitinating enzymes. Degradation of apoptotic proteins by UPS is central to the maintenance of cell health, and deregulation of this process is associated with several diseases including tumors, neurodegenerative disorders, diabetes, and inflammation. Therefore, it is the view that interrogating protein turnover in cells can offer a strategy for delineating disease-causing mechanistic perturbations and facilitate identification of drug targets. In this review, we are summarizing an overview to elucidate the updated knowledge on the molecular interplay between the apoptosis and UPS pathways. We have condensed around 100 enzymes of UPS machinery from the literature that ubiquitinates or deubiquitinates the apoptotic proteins and regulates the cell fate. We have also provided a detailed insight into how the UPS proteins are able to fine-tune the intrinsic, extrinsic, and p53-mediated apoptotic pathways to regulate cell survival or cell death. This review provides a comprehensive overview of the potential of UPS players as a drug target for cancer and other human disorders.

miR-200a enhances TRAIL-induced apoptosis in gastric cancer cells by targeting A20

Tumor necrosis factor-alpha-related apoptosis-inducing ligand (TRAIL) triggers apoptosis by inducing the death-inducing signaling complex (DISC) formation. Recently, TNFα-induced protein 3 (TNFAIP3, A20) was reported to prevent TRAIL-induced caspase 8 cleavage in the DISC by mediating ubiquitination of RIP1 in glioblastoma. However, whether A20 regulates caspase 8 cleavage in the DISC when TRAIL induces apoptosis in gastric cancer cells is unknown. In the present study, A20 interacted with RIP1 and DR4 in MGC803 and SGC7901 gastric cancer cells. Treatment with TRAIL promoted the A20-mediated polyubiquitination of RIP1, caspase 8 translocation into the DISC, and the interaction between caspase 8 and ubiquitinated RIP1. Inhibition of A20 expression prevented the polyubiquitination of RIP1 and promoted caspase 8 cleavage. Moreover, our data clarified that A20 is a target of miR-200a. Overexpression of miR-200a inhibited A20 expression and polyubiquitination of RIP1 and then promoted cleavage of caspase 8 and TRAIL-triggered apoptosis. Taken together, our results indicate that miR-200a enhanced TRAIL-triggered apoptosis in gastric cancer cells by targeting A20.

A20 inhibits the motility of HCC cells induced by TNF-α

Metastasis of hepatocellular carcinoma (HCC) can be facilitated by TNF-α, a prototypical inflammatory cytokine in the HCC microenvironment. A20 is a negative regulator of NF-κB signaling pathway. In the present study we ask whether A20 plays a role in HCC metastasis. We found that A20 expression was downregulated in the invasive cells of microvascular invasions (MVI) compared with the noninvasive cells in 89 tissue samples from patients with HCC by immunochemistry methods. Overexpression of A20 in HCC cell lines inhibited their motility induced by TNF-α. Furthermore, the overexpression of A20 inhibited epithelial-mesenchymal transition (EMT), FAK activation and RAC1 activity. By contrast, knockdown of A20 in one HCC cell line results in the converse. In addition, the overexpression of A20 restrained the formation of MVI in HCC xenograft in nude mice treated with TNF-α. All the results suggested that A20 functioned as a negative regulator in motility of HCC cells induced by TNF-α.

Loss of A20 in BM-MSCs regulates the Th17/Treg balance in Rheumatoid Arthritis

Mesenchymal stem cells (MSCs) are multi-potent cells that are self-renewable and possess the potential to differentiate into multiple lineages. Several studies demonstrated that MSCs could regulate a Th17/Treg balance and could be a potential therapeutic target for Rheumatoid Arthritis (RA). A20 is highly expressed in many cell types after the stimulation of TNF-α, where it may inhibit pro-inflammatory cytokine secretion. However, the expression of A20 in BM-MSCs in RA is not fully understood. In our study, we found that A20 was decreased in RA patients’ bone marrow MSCs (BM-MSCs), and with more IL-6 secretion, the balance of Th17/Treg was broken. In CIA mice, we found a moderate A20 decrease in mice MSCs as compared with those of control group in mRNA and protein levels. However, the IL-6 expression was increased. After umbilical cord MSCs treatment, A20 and IL-6 expressions were equal to the control group. Thus, our study indicates that loss of A20 in MSCs regulates the Th17/Treg balance in RA and the regulatory role of A20 in pro-inflammatory IL-6 production could be a potential target for the transfer of MSCs in RA adoptive therapy.

Paving TRAIL's Path with Ubiquitin

Despite its name, signalling induced by the tumour necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is versatile. Besides eliciting cell death by both apoptosis and necroptosis, TRAIL can also induce migration, proliferation, and cytokine production in cancerous and non-cancerous cells. Unravelling the mechanisms regulating the intricate balance between these different outputs could therefore facilitate our understanding of the role of TRAIL in tissue homeostasis, immunity, and cancer. Ubiquitination and its reversal, deubiquitination, are crucial modulators of immune receptor signalling. This review discusses recent progress on the orchestration of TRAIL signalling outcomes by ubiquitination of various components of the signalling complexes, our understanding of the molecular switches that decide between cell death and gene activation, and what remains to be discovered.