Lysine 63-linked polyubiquitination of TAK1 at lysine 158 is required for tumor necrosis factor alpha- and interleukin-1beta-induced IKK/NF-kappaB and JNK/AP-1 activation

Inflammation and cancer cell survival: TRAF2 as a key player

TNF receptor-associated factor 2 (TRAF2) plays a crucial role in both physiological and pathological processes. It takes part in the regulation of cell survival and death, tissue regeneration, development, endoplasmic reticulum stress response, autophagy, homeostasis of the epithelial barrier and regulation of adaptive and innate immunity. Initially identified for its interaction with TNF receptor 2 (TNFR2), TRAF2 contains a TRAF domain that enables homo- and hetero-oligomerization, allowing it to interact with multiple receptors and signaling molecules. While best known for mediating TNFR1 and TNFR2 signaling, TRAF2 also modulates other receptor pathways, including MAPK, NF-κB, and Wnt/β-catenin cascades. By regulating NF-κB-inducing kinase (NIK), TRAF2 is a key activator of the alternative NF-κB pathway, linking it to inflammatory diseases, immune dysfunction, and tumorigenesis. In the innate immune system, TRAF2 influences macrophage differentiation, activation, and survival and stimulates natural killer cell cytotoxicity. In the adaptive immune system, it represses effector B- and T-cell activity while sustaining regulatory T-cell function, thus promoting immune suppression. The lack of fine-tuning of TRAF2 activity leads to excessive NF-kB activation, driving chronic inflammation and autoimmunity. Although TRAF2 can act as a tumor suppressor, it is predominantly described as a tumor promoter, as its expression has been correlated with increased metastatic potential and poorer prognosis in several types of cancer. Targeting TRAF2 or TRAF2-dependent signaling pathways might represent a promising anti-cancer therapeutic strategy.

Ubiquitin-specific protease: an emerging key player in cardiomyopathy

Protein quality control (PQC) plays a vital role in maintaining normal heart function, as cardiomyocytes are relatively sensitive to misfolded or damaged proteins, which tend to accumulate under pathological conditions. Ubiquitin-specific protease (USP) is the largest deubiquitinating enzyme family and a key component of the ubiquitin proteasome system (UPS), which is a non-lysosomal protein degradation machinery to mediate PQC in cells. USPs regulate the stability or activity of the target proteins that involve intracellular signaling, transcriptional control of inflammation, antioxidation, and cell growth. Recent studies demonstrate that the USPs can regulate fibrosis, lipid metabolism, glucose homeostasis, hypertrophic response, post-ischemic recovery and cell death such as apoptosis and ferroptosis in cardiomyocytes. Since myocardial cell loss is an important component of cardiomyopathy, therefore, these findings suggest that the UPSs play emerging roles in cardiomyopathy. This review briefly summarizes recent literature on the regulatory roles of USPs in the occurrence and development of cardiomyopathy, giving us new insights into the molecular mechanisms of USPs in different cardiomyopathy and potential preventive strategies for cardiomyopathy.

RGMb drives macrophage infiltration to aggravate kidney disease

The importance of macrophages in kidney diseases has been well established; however, the mechanisms underlying the infiltration of macrophages into injured kidneys are not well understood. RGMb is a member of the repulsive guidance molecule (RGM) family. RGMb can be expressed on the cell surface but a large portion of RGMb is localized intracellularly. Among various immune cell types, macrophages express the highest levels of RGMb, but the biological functions of RGMb in macrophages remain largely unknown. We find that RGMb promoted macrophage migration in vitro and that in vivo, RGMb enhanced infiltration of macrophages into injured kidneys and aggravated kidney inflammation and injury in mice. Mechanistically, RGMb bound to TAB1 inside the cell and facilitated the interaction between TRAF6 ubiquitin ligase and TAB1, thereby promoting TRAF6-mediated K63-linked polyubiquitination and phosphorylation of TAK1, followed by increased αTAT1 phosphorylation and α-tubulin acetylation. The resulting changes in the cytoskeleton promoted macrophage migration in vitro and in vivo. Deletion of Rgmb in macrophages markedly reduced TAK1 phosphorylation, αTAT1 phosphorylation, and α-tubulin acetylation and attenuated macrophage infiltration, renal inflammation, tubular injury, and interstitial fibrosis during kidney injury. Our results suggest that macrophage RGMb promotes kidney disease by increasing macrophage infiltration via the TRAF6-TAB1-TAK1/αTAT1/α-tubulin cascade.

TAK1 at the crossroads of multiple regulated cell death pathways: from molecular mechanisms to human diseases

Regulated cell death (RCD), the form of cell death that can be genetically controlled by multiple signaling pathways, plays an important role in organogenesis, tissue remodeling, and maintenance of organism homeostasis and is closely associated with various human diseases. Transforming growth factor‐beta‐activated kinase 1 (TAK1) is a member of the serine/threonine protein kinase family, which can respond to different internal and external stimuli and participate in inflammatory and immune responses. Emerging evidence suggests that TAK1 is an important regulator at the crossroad of multiple RCD pathways, including apoptosis, necroptosis, pyroptosis, and PANoptosis. The regulation of TAK1 affects disease progression through multiple signaling pathways, and therapeutic strategies targeting TAK1 have been proposed for inflammatory diseases, central nervous system diseases, and cancers. In this review, we provide an overview of the downstream signaling pathways regulated by TAK1 and its binding proteins. Their critical regulatory roles in different forms of cell death are also summarized. In addition, we discuss the potential of targeting TAK1 in the treatment of human diseases, with a specific focus on neurological disorders and cancer.

Targeting TAK1: Evolution of inhibitors, challenges, and future directions

The increasing incidence of inflammatory and malignant diseases signifies the need to develop first-in-class drugs with novel mechanisms of action. In this respect, the transforming growth factor (TGF)-β-activated kinase 1 (TAK1), an essential part of several signaling pathways, is considered relevant and promising. This manuscript provides a brief overview of the signal transduction orchestrated by TAK1 within these pathways, followed by an in-depth and thorough analysis of the chemical matter demonstrated to inhibit this kinase. Special attention is given to the selectivity profiling of inhibitors, as well as to the outcomes of their biological characterization. Because published TAK1 inhibitors differ significantly in their kinome selectivity, active-site binding, and biological activity, we hope that this review will allow a judicial estimation of their quality and usefulness for TAK1-addressing assays. Our thoughts on the perspectives and possible developments of the field are also provided to assist scientists who are involved in the design and development of TAK1-targeting modulators.

Modulation of extrinsic apoptotic pathway by intracellular glycosylation

The importance of post-translational modifications (PTMs), particularly O-GlcNAcylation, of cytoplasmic proteins in apoptosis has been neglected for quite a while. Modification of cytoplasmic proteins by a single N-acetylglucosamine sugar is a dynamic and reversible PTM exhibiting properties more like phosphorylation than classical O- and N-linked glycosylation. Due to the sparse information existing, we have only limited understanding of how GlcNAcylation affects cell death. Deciphering the role of GlcNAcylation in cell fate may provide further understanding of cell fate decisions. This review focus on the modulation of extrinsic apoptotic pathway via GlcNAcylation carried out by O-GlcNAc transferase (OGT) or by other bacterial effector proteins.

Mechanisms of oxidative stress in interstitial cystitis/bladder pain syndrome

Interstitial cystitis/bladder pain syndrome (IC/BPS) is characterized by bladder and/or pelvic pain, increased urinary urgency and frequency and nocturia. The pathophysiology of IC/BPS is poorly understood, and theories include chronic inflammation, autoimmune dysregulation, bacterial cystitis, urothelial dysfunction, deficiency of the glycosaminoglycan (GAG) barrier and urine cytotoxicity. Multiple treatment options exist, including behavioural interventions, oral medications, intravesical instillations and procedures such as hydrodistension; however, many clinical trials fail, and patients experience an unsatisfactory treatment response, likely owing to IC/BPS phenotype heterogeneity and the use of non-targeted interventions. Oxidative stress is implicated in the pathogenesis of IC/BPS as reactive oxygen species impair bladder function via their involvement in multiple molecular mechanisms. Kinase signalling pathways, nociceptive receptors, mast-cell activation, urothelial dysregulation and circadian rhythm disturbance have all been linked to reactive oxygen species and IC/BPS. However, further research is necessary to fully uncover the role of oxidative stress in the pathways driving IC/BPS pathogenesis. The development of new models in which these pathways can be manipulated will aid this research and enable further investigation of promising therapeutic targets.

RIPK3 signaling and its role in regulated cell death and diseases

Receptor-interacting protein kinase 3 (RIPK3), a member of the receptor-interacting protein kinase (RIPK) family with serine/threonine protein kinase activity, interacts with RIPK1 to generate necrosomes, which trigger caspase-independent programmed necrosis. As a vital component of necrosomes, RIPK3 plays an indispensable role in necroptosis, which is crucial for human life and health. In addition, RIPK3 participates in the pathological process of several infections, aseptic inflammatory diseases, and tumors (including tumor-promoting and -suppressive activities) by regulating autophagy, cell proliferation, and the metabolism and production of chemokines/cytokines. This review summarizes the recent research progress of the regulators of the RIPK3 signaling pathway and discusses the potential role of RIPK3/necroptosis in the aetiopathogenesis of various diseases. An in-depth understanding of the mechanisms and functions of RIPK3 may facilitate the development of novel therapeutic strategies.

Saikosaponin F ameliorates depression-associated dry eye disease by inhibiting TRIM8-induced TAK1 ubiquitination

AIMS

Saikosaponin F (SsF) is one of the major active ingredients of Radix Bupleuri, an herb widely used in the treatment of depression. Studies have shown that dry eye disease often occurs together with depression. The aim of this study is to investigate whether SsF can improve depression-associated dry eye disease and explore the underlying mechanism.

METHODS

Behavioral test was used to verify the effect of SsF on CUMS-induced depression-like behaviors in mice. Corneal fluorescein staining, phenol red cotton thread test and periodic acid-Schiff (PAS) staining were used to observe the effect of SsF on depression-associated dry eye disease. Western blot (WB) was performed to observe the expression of TAK1 protein and key proteins of NF-κB and MAPK (P38) inflammatory pathways in the hippocampus and cornea. Immunohistochemical staining was used to observe the expression of microglia, and immunoprecipitation was used to observe K63-linked TAK1 ubiquitination. Subsequently, we constructed a viral vector sh-TAK1 to silence TAK1 protein to verify whether SsF exerted its therapeutic effect based on TAK1. The expression of inflammatory factors such as IL-1β, TNF-α and IL-18 in hippocampus and cornea were detected by ELISA. Overexpression of TRIM8 (OE-TRIM8) by viral vector was used to verify whether SsF improved depression-associated dry eye disease based on TRIM8.

RESULTS

SsF treatment significantly improved the depression-like behavior, increased tear production and restored corneal injury in depression-related dry eye model mice. SsF treatment downregulated TAK1 expression and TRIM8-induced K63-linked TAK1 polyubiquitination, while inhibiting the activation of NF-κB and MAPK (P38) inflammatory pathways and microglial expression. In addition, selective inhibition of TAK1 expression ameliorated depression-associated dry eye disease, while overexpression of TRIM8 attenuated the therapeutic effect of SsF on depression-associated dry eye disease.

CONCLUSION

SsF inhibited the polyubiquitination of TAK1 by acting on TRIM8, resulting in the downregulation of TAK1 expression, inhibition of inflammatory response, and improvement of CUMS-induced depression-associated dry eye disease.

Changes in Cells Associated with Insulin Resistance

Insulin is a polypeptide hormone synthesized and secreted by pancreatic β-cells. It plays an important role as a metabolic hormone. Insulin influences the metabolism of glucose, regulating plasma glucose levels and stimulating glucose storage in organs such as the liver, muscles and adipose tissue. It is involved in fat metabolism, increasing the storage of triglycerides and decreasing lipolysis. Ketone body metabolism also depends on insulin action, as insulin reduces ketone body concentrations and influences protein metabolism. It increases nitrogen retention, facilitates the transport of amino acids into cells and increases the synthesis of proteins. Insulin also inhibits protein breakdown and is involved in cellular growth and proliferation. On the other hand, defects in the intracellular signaling pathways of insulin may cause several disturbances in human metabolism, resulting in several chronic diseases. Insulin resistance, also known as impaired insulin sensitivity, is due to the decreased reaction of insulin signaling for glucose levels, seen when glucose use in response to an adequate concentration of insulin is impaired. Insulin resistance may cause, for example, increased plasma insulin levels. That state, called hyperinsulinemia, impairs metabolic processes and is observed in patients with type 2 diabetes mellitus and obesity. Hyperinsulinemia may increase the risk of initiation, progression and metastasis of several cancers and may cause poor cancer outcomes. Insulin resistance is a health problem worldwide; therefore, mechanisms of insulin resistance, causes and types of insulin resistance and strategies against insulin resistance are described in this review. Attention is also paid to factors that are associated with the development of insulin resistance, the main and characteristic symptoms of particular syndromes, plus other aspects of severe insulin resistance. This review mainly focuses on the description and analysis of changes in cells due to insulin resistance.

Role of the ubiquitin-proteasome system on macrophages in the tumor microenvironment

Tumor-associated macrophages (TAMs) are key components of the tumor microenvironment, and their different polarization states play multiple roles in tumors by secreting cytokines, chemokines, and so on, which are closely related to tumor development. In addition, the enrichment of TAMs is often associated with poor prognosis of tumors. Thus, targeting TAMs is a potential tumor treatment strategy, in which therapeutic approaches such as reducing TAMs numbers, remodeling TAMs phenotypes, and altering their functions are being extensively investigated. Meanwhile, the ubiquitin-proteasome system (UPS), an important mechanism of protein hydrolysis in eukaryotic cells, participates in cellular processes by regulating the activity and stability of key proteins. Interestingly, UPS plays a dual role in the process of tumor development, and its role in TAMs deserve to be investigated in depth. This review builds on this foundation to further explore the multiple roles of UPS on TAMs and identifies a promising approach to treat tumors by targeting TAMs with UPS.

Classical swine fever virus NS5A protein antagonizes innate immune response by inhibiting the NF-κB signaling

The NS5A non-structural protein of classical swine fever virus (CSFV) is a multifunctional protein involved in viral genomic replication, protein translation, assembly of infectious virus particles, and regulation of cellular signaling pathways. Previous report showed that NS5A inhibited nuclear factor kappa B (NF-κB) signaling induced by poly(I:C); however, the mechanism involved has not been elucidated. Here, we reported that NS5A directly interacted with NF-κB essential modulator (NEMO), a regulatory subunit of the IκB kinase (IKK) complex, to inhibit the NF-κB signaling pathway. Further investigations showed that the zinc finger domain of NEMO and the aa 126-250 segment of NS5A are essential for the interaction between NEMO and NS5A. Mechanistic analysis revealed that NS5A mediated the proteasomal degradation of NEMO. Ubiquitination assay showed that NS5A induced the K27-linked but not the K48-linked polyubiquitination of NEMO for proteasomal degradation. In addition, NS5A blocked the K63-linked polyubiquitination of NEMO, thus inhibiting IKK phosphorylation, IκBα degradation, and NF-κB activation. These findings revealed a novel mechanism by which CSFV inhibits host innate immunity, which might guide the drug design against CSFV in the future.

TAK1 is an essential kinase for STING trafficking

The translocation of stimulator of interferon genes (STING) from the endoplasmic reticulum (ER) to the ER-Golgi intermediate compartment (ERGIC) enables its activation. However, the mechanism underlying the regulation of STING exit from the ER remains elusive. Here, we found that STING induces the activation of transforming growth factor beta-activated kinase 1 (TAK1) prior to STING trafficking in a TAK1 binding protein 1 (TAB1)-dependent manner. Intriguingly, activated TAK1 directly mediates STING phosphorylation on serine 355, which facilitates its interaction with STING ER exit protein (STEEP) and thereby promotes its oligomerization and translocation to the ERGIC for subsequent activation. Importantly, activation of TAK1 by monophosphoryl lipid A, a TLR4 agonist, boosts cGAMP-induced antitumor immunity dependent on STING phosphorylation in a mouse allograft tumor model. Taken together, TAK1 was identified as a checkpoint for STING activation by promoting its trafficking, providing a basis for combinatory tumor immunotherapy and intervention in STING-related diseases.

Small molecule activators of TAK1 promotes its activity-dependent ubiquitination and TRAIL-mediated tumor cell death

TAK1 is a key modulator of both NF-κB signaling and RIPK1. In TNF signaling pathway, activation of TAK1 directly mediates the phosphorylation of IKK complex and RIPK1. In a search for small molecule activators of RIPK1-mediated necroptosis, we found R406/R788, two small molecule analogs that could promote sustained activation of TAK1. Treatment with R406 sensitized cells to TNF-mediated necroptosis and RIPK1-dependent apoptosis by promoting sustained RIPK1 activation. Using click chemistry and multiple biochemical binding assays, we showed that treatment with R406 promotes the activation of TAK1 by directly binding to TAK1, independent of its original target Syk kinase. Treatment with R406 promoted the ubiquitination of TAK1 and the interaction of activated TAK1 with ubiquitinated RIPK1. Finally, we showed that R406/R788 could promote the cancer-killing activities of TRAIL in vitro and in mouse models. Our studies demonstrate the possibility of developing small molecule TAK1 activators to potentiate the effect of TRAIL as anticancer therapies.

CD137 (4-1BB) requires physically associated cIAPs for signal transduction and antitumor effects

CD137 (4-1BB) is a member of the TNFR family that mediates potent T cell costimulatory signals upon ligation by CD137L or agonist monoclonal antibodies (mAbs). CD137 agonists attain immunotherapeutic antitumor effects in cancer mouse models, and multiple agents of this kind are undergoing clinical trials. We show that cIAP1 and cIAP2 are physically associated with the CD137 signaling complex. Moreover, cIAPs are required for CD137 signaling toward the NF-κB and MAPK pathways and for costimulation of human and mouse T lymphocytes. Functional evidence was substantiated with SMAC mimetics that trigger cIAP degradation and by transfecting cIAP dominant-negative variants. Antitumor effects of agonist anti-CD137 mAbs are critically dependent on the integrity of cIAPs in cancer mouse models, and cIAPs are also required for signaling from CARs encompassing CD137's cytoplasmic tail.

Insulin signaling and its application

The discovery of insulin in 1921 introduced a new branch of research into insulin activity and insulin resistance. Many discoveries in this field have been applied to diagnosing and treating diseases related to insulin resistance. In this mini-review, the authors attempt to synthesize the updated discoveries to unravel the related mechanisms and inform the development of novel applications. Firstly, we depict the insulin signaling pathway to explain the physiology of insulin action starting at the receptor sites of insulin and downstream the signaling of the insulin signaling pathway. Based on this, the next part will analyze the mechanisms of insulin resistance with two major provenances: the defects caused by receptors and the defects due to extra-receptor causes, but in this study, we focus on post-receptor causes. Finally, we discuss the recent applications including the diseases related to insulin resistance (obesity, cardiovascular disease, Alzheimer's disease, and cancer) and the potential treatment of those based on insulin resistance mechanisms.

Tripartite Motif Protein Family in Central Nervous System Diseases

Tripartite motif (TRIM) protein superfamily is a group of E3 ubiquitin ligases characterized by the conserved RING domain, the B-box domain, and the coiled-coil domain (RBCC). It is widely involved in various physiological and pathological processes, such as intracellular signal transduction, cell cycle regulation, oncogenesis, and innate immune response. Central nervous system (CNS) diseases are composed of encephalopathy and spinal cord diseases, which have a high disability and mortality rate. Patients are often unable to take care of themselves and their life quality can be seriously declined. Initially, the function research of TRIM proteins mainly focused on cancer. However, in recent years, accumulating attention is paid to the roles they play in CNS diseases. In this review, we integrate the reported roles of TRIM proteins in the pathological process of CNS diseases and related signaling pathways, hoping to provide theoretical bases for further research in treating CNS diseases targeting TRIM proteins. TRIM proteins participated in CNS diseases. TRIM protein family is characterized by a highly conserved RBCC domain, referring to the RING domain, the B-box domain, and the coiled-coil domain. Recent research has discovered the relations between TRIM proteins and various CNS diseases, especially Alzheimer's disease, Parkinson's disease, and ischemic stroke.

Emerging role of TAK1 in the regulation of skeletal muscle mass

Maintenance of skeletal muscle mass and strength throughout life is crucial for heathy living and longevity. Several signaling pathways have been implicated in the regulation of skeletal muscle mass in adults. TGF-β-activated kinase 1 (TAK1) is a key protein, which coordinates the activation of multiple signaling pathways. Recently, it was discovered that TAK1 is essential for the maintenance of skeletal muscle mass and myofiber hypertrophy following mechanical overload. Forced activation of TAK1 in skeletal muscle causes hypertrophy and attenuates denervation-induced muscle atrophy. TAK1-mediated signaling in skeletal muscle promotes protein synthesis, redox homeostasis, mitochondrial health, and integrity of neuromuscular junctions. In this article, we have reviewed the role and potential mechanisms through which TAK1 regulates skeletal muscle mass and growth. We have also proposed future areas of research that could be instrumental in exploring TAK1 as therapeutic target for improving muscle mass in various catabolic conditions and diseases.

Type I Cystatin Derived from Fasciola gigantica Suppresses Macrophage-Mediated Inflammatory Responses

There is an inverse relationship between the high incidence of helminth infection and the low incidence of inflammatory disease. Hence, it may be that helminth molecules have anti-inflammatory effects. Helminth cystatins are being extensively studied for anti-inflammatory potential. Therefore, in this study, the recombinant type I cystatin (stefin-1) of Fasciola gigantica (rFgCyst) was verified to have LPS-activated anti-inflammatory potential, including in human THP-1-derived macrophages and RAW 264.7 murine macrophages. The results from the MTT assay suggest that rFgCyst did not alter cell viability; moreover, it exerted anti-inflammatory activity by decreasing the production of proinflammatory cytokines and mediators, including IL-1β, IL-6, IL-8, TNF-α, iNOS, and COX-2 at the gene transcription and protein expression levels, as determined by qRT-PCR and Western blot analysis, respectively. Further, the secretion levels of IL-1β, IL-6, and TNF-α determined by ELISA and the NO production level determined by the Griess test were decreased. Furthermore, in Western blot analysis, the anti-inflammatory effects involved the downregulation of pIKKα/β, pIκBα, and pNF-κB in the NF-κB signaling pathway, hence reducing the translocation from the cytosol into the nucleus of pNF-κB, which subsequently turned on the gene of proinflammatory molecules. Therefore, cystatin type 1 of F. gigantica is a potential candidate for inflammatory disease treatment.

Anti-Inflammatory Effect of Garcinol Extracted from Garcinia dulcis via Modulating NF-κB Signaling Pathway

Garcinia is a significant medicinal plant with many beneficial phytoconstituents, including garcinol. This study investigated the anti-inflammatory effect of garcinol isolated from Garcinia dulcis fruit in LPS-activated THP-1 and Raw 264.7 macrophages. The results demonstrated that the low concentration of garcinol did not alter cell viability. Furthermore, co-incubation of garcinol with LPS inhibited the production of pro-inflammatory cytokines, including TNF-α, IL-8, IL-6, IL-1β, and pro-inflammatory mediators, including iNOS and COX-2 at the mRNA and protein expression levels. Garcinol also decreased the secretion of TNF-α, IL-6, IL-1β, PGE2, and NO. Moreover, the anti-inflammatory effects involved an alteration in the NF-κB signaling pathway. Downregulation of pIKKα/β, pIκBα, and pNF-κB was observed, hence reducing the translocation of pNF-κB from the cytosol into the nucleus, which subsequently decreased the production of pro-inflammatory molecules. Therefore, garcinol isolated from Garcinia dulcis is a potential candidate as an anti-inflammatory agent for inflammation-related disease treatment.

Rainbow trout USP4 downregulates LPS-induced inflammation by removing the K63-linked ubiquitin chain on TAK1

Ubiquitin-specific protease 4 (USP4) is pivotal in negatively regulating the Toll-like receptor (TLR) signaling-mediated innate immune response. Although USP4 has been well studied in mammals, its role in TLR signaling pathways in fish remains largely unknown. In this study, we investigated the role of USP4 (OmUSP4) in regulating TLR response in rainbow trout Oncorhynchus mykiss. OmUSP4 contained the characteristic domains conserved in other USP4s: domain in USP (DUSP), ubiquitin-like (UBL), and the bi-part catalytic domain known as USP. OmUSP4 expression was increased in RTH-149 cells by stimulation with fish-pathogenic bacteria and bacterial ligands. Gain- and loss-of-function experiments revealed that OmUSP4 mitigated the activation of MAPKs and NF-κB, as well as the expression of pro-inflammatory cytokines in LPS-stimulated cells. OmUSP4 interacted with TAK1, a critical mediator in TLR-mediated NF-κB signaling pathways. LPS stimulation increased the K63-linked polyubiquitination of TAK1, which was significantly suppressed when OmUSP4 was compelled to be overexpressed. These results imply that OmUSP4 might function like mammals to downregulate LPS-induced inflammation in rainbow trout by removing the K63-linked ubiquitin chain on TAK1.

Integration of O-GlcNAc into Stress Response Pathways

The modification of nuclear, mitochondrial, and cytosolic proteins by O-linked βN-acetylglucosamine (O-GlcNAc) has emerged as a dynamic and essential post-translational modification of mammalian proteins. O-GlcNAc is cycled on and off over 5000 proteins in response to diverse stimuli impacting protein function and, in turn, epigenetics and transcription, translation and proteostasis, metabolism, cell structure, and signal transduction. Environmental and physiological injury lead to complex changes in O-GlcNAcylation that impact cell and tissue survival in models of heat shock, osmotic stress, oxidative stress, and hypoxia/reoxygenation injury, as well as ischemic reperfusion injury. Numerous mechanisms that appear to underpin O-GlcNAc-mediated survival include changes in chaperone levels, impacts on the unfolded protein response and integrated stress response, improvements in mitochondrial function, and reduced protein aggregation. Here, we discuss the points at which O-GlcNAc is integrated into the cellular stress response, focusing on the roles it plays in the cardiovascular system and in neurodegeneration.

The Gab2-MALT1 axis regulates thromboinflammation and deep vein thrombosis

Deep vein thrombosis (DVT) is the third most common cause of cardiovascular mortality. Several studies suggest that DVT occurs at the intersection of dysregulated inflammation and coagulation upon activation of inflammasome and secretion of interleukin 1β (IL-1β) in restricted venous flow conditions. Our recent studies showed a signaling adapter protein, Gab2 (Grb2-associated binder 2), plays a crucial role in propagating inflammatory signaling triggered by IL-1β and other inflammatory mediators in endothelial cells. The present study shows that Gab2 facilitates the assembly of the CBM (CARMA3 [CARD recruited membrane-associated guanylate kinase protein 3]-BCL-10 [B-cell lymphoma 10]-MALT1 [mucosa-associated lymphoid tissue lymphoma translocation protein 1]) signalosome, which mediates the activation of Rho and NF-κB in endothelial cells. Gene silencing of Gab2 or MALT1, the effector signaling molecule in the CBM signalosome, or pharmacological inhibition of MALT1 with a specific inhibitor, mepazine, significantly reduced IL-1β-induced Rho-dependent exocytosis of P-selectin and von Willebrand factor (VWF) and the subsequent adhesion of neutrophils to endothelial cells. MALT1 inhibition also reduced IL-1β-induced NF-κB-dependent expression of tissue factor and vascular cell adhesion molecule 1. Consistent with the in vitro data, Gab2 deficiency or pharmacological inhibition of MALT1 suppressed the accumulation of monocytes and neutrophils at the injury site and attenuated venous thrombosis induced by the inferior vena cava ligation-induced stenosis or stasis in mice. Overall, our data reveal a previously unrecognized role of the Gab2-MALT1 axis in thromboinflammation. Targeting the Gab2-MALT1 axis with MALT1 inhibitors may become an effective strategy to treat DVT by suppressing thromboinflammation without inducing bleeding complications.

Spata2L Suppresses TLR4 Signaling by Promoting CYLD-Mediated Deubiquitination of TRAF6 and TAK1

Toll-like receptor 4 (TLR4) is a key pattern recognition receptor that can be activated by bacterial lipopolysaccharide to elicit inflammatory response. Proper activation of TLR4 is critical for the host defense against microbial infections. Since overactivation of TLR4 causes deleterious effects and inflammatory diseases, its activation needs to be tightly controlled by negative regulatory mechanisms, among which the most pivotal could be deubiquitination of key signaling molecules mediated by deubiquitinating enzymes (DUBs). CYLD is a member of the USP family of DUBs that acts as a critical negative regulator of TLR4-depedent inflammatory responses by deconjugating polyubiquitin chains from signaling molecules, such as TRAF6 and TAK1. Dysregulation of CYLD is implicated in inflammatory diseases. However, how the function of CYLD is regulated during inflammatory response remains largely unclear. Recently, we and other authors have shown that Spata2 functions as an important CYLD partner to regulate enzymatic activity of CYLD and substrate binding by this protein. Here, we show that a Spata2-like protein, Spata2L, can also form a complex with CYLD to inhibit the TLR4-dependent inflammatory response. We found that Spata2L constitutively interacts with CYLD and that the deficiency of Spata2L enhances the LPS-induced NF-κB activation and proinflammatory cytokine gene expression. Mechanistically, Spata2L potentiated CYLD-mediated deubiquitination of TRAF6 and TAK1 likely by promoting CYLD enzymatic activity. These findings identify Spata2L as a novel CYLD regulator, provide new insights into regulatory mechanisms underlying CYLD role in TLR4 signaling, and suggest potential targets for modulating TLR4-induced inflammation.

TRIM38 protects H9c2 cells from hypoxia/reoxygenation injury via the TRAF6/TAK1/NF-κB signalling pathway

Tripartite motif (TRIM) 38 is a ubiquitin E3 protein ligase that is involved in various intracellular physiological processes. However, the role of TRIM38 in myocardial ischaemia/reperfusion (I/R) injury remains to be elucidated. We aimed to establish an in vitro cellular hypoxia/reperfusion (H/R) model to explore the role and potential mechanisms of TRIM38 in H9c2, a rat cardiomyoblast cell line. Recombinant adenoviruses for silencing or overexpressing TRIM38 were constructed and transfected into H9c2 cells. Western blotanalysisshowed that TRIM38 expression was significantly decreased after H/R injury. Functionally, TRIM38 expression relieved inflammatory responses and oxidative stress, and inhibited H/R-induced apoptosis in H9c2 cells. Mechanistically, TRIM38 overexpression inhibited H/R-induced transforming growth factor beta-activated kinase 1 (TAK1)/nuclear factor-kappa B (NF-κB) pathway activity in H9c2 cells. The opposite results were observed after TRIM38 knockdown. Furthermore, H/R-induced injury aggravated by TRIM38 deficiency in H9c2 cells was reversed upon treatment with 5Z-7-oxozeaenol, a TAK1 inhibitor. Therefore, TRIM38 reduction attenuated the anti-apoptotic capacity and anti-inflammatory potential of H/R-stimulated H9c2 cells by activating the TAK1/NF-κB signalling pathway. Specifically, TRIM38 alleviated H/R-induced H9c2 cell injury by promoting TNF receptor-associated factor 6 degradation, which led to the inactivation of the TAK1/NF-κB signalling pathway. Thus, our study provides new insights into the molecular mechanisms underlying H/R-induced myocardial injuries.

Necroptosis in heart disease: Molecular mechanisms and therapeutic implications

Cell death is a crucial event underlying cardiac ischemic injury, pathological remodeling, and heart failure. Unlike apoptosis, necrosis had long been regarded as a passive and unregulated process. However, recent studies demonstrate that a significant subset of necrotic cell death is actively mediated through regulated pathways - a process known as "regulated necrosis". As a form of regulated necrosis, necroptosis is mediated by death receptors and executed through the activation of receptor interacting protein kinase 3 (RIPK3) and its downstream substrate mixed lineage kinase-like domain (MLKL). Recent studies have provided compelling evidence that necroptosis plays an important role in myocardial homeostasis, ischemic injury, pathological remodeling, and heart failure. Moreover, it has been shown that genetic and pharmacological manipulations of the necroptosis signaling pathway elicit cardioprotective effects. Important progress has also been made regarding the molecular mechanisms that regulate necroptotic cell death in vitro and in vivo. In this review, we discuss molecular and cellular mechanisms of necroptosis, potential crosstalk between necroptosis and other cell death pathways, functional implications of necroptosis in heart disease, and new therapeutic strategies that target necroptosis signaling.

The E3 ubiquitin ligase TRIM31 plays a critical role in hypertensive nephropathy by promoting proteasomal degradation of MAP3K7 in the TGF-β1 signaling pathway

Renal fibrosis and inflammation are critical for the initiation and progression of hypertensive renal disease (HRD). However, the signaling mechanisms underlying their induction are poorly understood, and the role of tripartite motif-containing protein 31 (TRIM31), an E3 ubiquitin ligase, in HRD remains unclear. This study aimed to elucidate the role of TRIM31 in the pathogenesis of HRD, discover targets of TRIM31, and explore the underlying mechanisms. Pathological specimens of human HRD kidney were collected and an angiotensin II (AngII)-induced HRD mouse model was developed. We found that TRIM31 was markedly reduced in both human and mouse HRD renal tissues. A TRIM31^-/- mice was thus constructed and showed significantly aggravated hypertension-induced renal dysfunction, fibrosis, and inflammation, following chronic AngII infusion compared with TRIM31^+/+ mice. In contrast, overexpression of TRIM31 by injecting adeno-associated virus (AAV) 9 into C57BL/6J mice markedly ameliorated renal dysfunction, fibrotic and inflammatory response in AngII-induced HRD relative to AAV-control mice. Mechanistically, TRIM31 interacted with and catalyzed the K48-linked polyubiquitination of lysine 72 on Mitogen-activated protein kinase kinase kinase 7 (MAP3K7), followed by the proteasomal degradation of MAP3K7, which further negatively regulated TGF-β1-mediated Smad and MAPK/NF-κB signaling pathways. In conclusion, this study has demonstrated for the first time that TRIM31 serves as an important regulator in AngII-induced HRD by promoting MAP3K7 K48-linked polyubiquitination and inhibiting the TGF-β1 signaling pathway.

Usp8 promotes tumor cell migration through activating the JNK pathway

Tumor metastasis is the most cause of high mortality for cancer patients. Identification of novel factors that modulate tumor cell migration is of great significance for therapeutic strategies. Here, we find that the ubiquitin-specific protease 8 (Usp8) promotes tumor cell migration through activating the c-Jun N-terminal kinase (JNK) pathway. Genetic epistasis analyses uncover Usp8 acts upstream of Tak1 to control the JNK pathway. Consistently, biochemical results reveal that Usp8 binds Tak1 to remove ubiquitin modification from Tak1, leading to its stabilization. In addition, human USP8 also triggers tumor cell migration and activates the JNK pathway. Finally, we show that knockdown of USP8 in human breast cancer cells suppresses cell migration. Taken together, our findings demonstrate that a conserved Usp8-Tak1-JNK axis promotes tumor cell migration, and providing USP8 as a potential therapeutic target for cancer treatment.

FAM177A1 Inhibits IL-1β-Induced Signaling by Impairing TRAF6-Ubc13 Association

The proinflammatory cytokine IL-1β is a crucial mediator of inflammatory responses. IL-1β-induced signaling is finely regulated by various mechanisms, and its imbalance is involved in a variety of diseases. In this study, we identified FAM177A1, a protein of unknown function, as a negative regulator of IL-1β-induced signaling in human cells. Overexpression of FAM177A1 inhibited IL-1β-triggered activation of NF-κB and transcription of inflammatory genes, whereas knockdown of FAM177A1 showed the opposite effects. Mechanistically, FAM177A1 competitively bound to the E3 ubiquitin ligase TRAF6 and impaired its interaction with the E2-conjugating enzyme Ubc13; therefore, it inhibited TRAF6-mediated polyubiquitination and recruitment of downstream signaling molecules. These findings reveal a function of FAM177A1 and promote our understanding of the regulatory mechanisms of IL-1β-induced inflammatory responses.

TNF-α-induced E3 ligase, TRIM15 inhibits TNF-α-regulated NF-κB pathway by promoting turnover of K63 linked ubiquitination of TAK1

Ubiquitin E3-ligases are recruited at different steps of TNF-α-induced NF-κB activation; however, their role in temporal regulation of the pathway remains elusive. The study systematically identified TRIMs as potential feedback regulators of the TNF-α-induced NF-κB pathway. We further observed that TRIM15 is "late" response TNF-α-induced gene and inhibits the TNF-α-induced NF-κB pathway in several human cell lines. TRIM15 promotes turnover of K63-linked ubiquitin chains in a PRY/SPRY domain-dependent manner. TRIM15 interacts with TAK1 and inhibits its K63-linked ubiquitination, thus NF-κB activity. Further, TRIM15 interacts with TRIM8 and inhibits cytosolic translocation to antagonize TRIM8 modualted NF-κB. TRIM8 and TRIM15 also show functionally inverse correlation in psoriasis condition. In conclusion, TRIM15 is TNF-α-induced late response gene and inhibits TNF-α induced NF-κB pathway hence a feedback modulator to keep the proinflammatory NF-κB pathway under control.

RIPK3 signaling and its role in the pathogenesis of cancers

RIPK3 (receptor-interacting protein kinase 3) is a serine/threonine-protein kinase. As a key component of necrosomes, RIPK3 is an essential mediator of inflammatory factors (such as TNFα-tumor necrosis factor α) and infection-induced necroptosis, a programmed necrosis. In addition, RIPK3 signaling is also involved in the regulation of apoptosis, cytokine/chemokine production, mitochondrial metabolism, autophagy, and cell proliferation by interacting with and/or phosphorylating the critical regulators of the corresponding signaling pathways. Similar to apoptosis, RIPK3-signaling-mediated necroptosis is inactivated in most types of cancers, suggesting RIPK3 might play a critical suppressive role in the pathogenesis of cancers. However, in some inflammatory types of cancers, such as pancreatic cancers and colorectal cancers, RIPK3 signaling might promote cancer development by stimulating proliferation signaling in tumor cells and inducing an immunosuppressive response in the tumor environment. In this review, we summarize recent research progress in the regulators of RIPK3 signaling, and discuss the function of this pathway in the regulation of mixed lineage kinase domain-like (MLKL)-mediated necroptosis and MLKL-independent cellular behaviors. In addition, we deliberate the potential roles of RIPK3 signaling in the pathogenesis of different types of cancers and discuss the potential strategies for targeting this pathway in cancer therapy.

TRIM26 positively regulates the inflammatory immune response through K11-linked ubiquitination of TAB1

Protein ubiquitination plays an important role in the regulation of TGF-β-activated kinase 1 (TAK1)-mediated NF-κB activation. It is well established that TAK1 activation is tightly regulated with its binding partners, TAK1-binding proteins (TAB1-3). However, the tight regulation of TAK1 activation remains elusive. Here, using Trim26-knockout mice and Trim26-transgenic mice, we found that TRIM26 acts as a positive regulator of TAK1 activation by ubiquitinating its binding partner TAB1. Knockout of Trim26 inhibited TAK1 activation and downstream kinases activation, thus decreasing the induction of proinflammatory cytokines following LPS, TNF-α, and IL-1β stimulation. Mechanistically, TRIM26 catalyzes the K11-linked polyubiquitination of TAB1 at Lys294, Lys319, and Lys335 to enhance the activation of TAK1 and subsequent NF-κB and MAPK signaling. Consequently, Trim26 deficiency protects mice from LPS-induced septic shock in vivo. Moreover, Trim26 deficiency attenuates the severity of dextran sodium sulfate (DSS)-induced colitis. Thus, these finding provides a novel insight into how TAK1 activation is regulated through TRIM26-mediated ubiquitination of TAB1 and reveals the new function of TRIM26 in the regulation of the inflammatory innate immune response.

Regulation of Mitogen-Activated Protein Kinase Signaling Pathways by the Ubiquitin-Proteasome System and Its Pharmacological Potential

Mitogen-activated protein kinase (MAPK) cascades are evolutionarily conserved signaling pathways that play essential roles in transducing extracellular environmental signals into diverse cellular responses to maintain homeostasis. These pathways are classically organized into an architecture of three sequentially acting protein kinases: a MAPK kinase kinase that phosphorylates and activates a MAPK kinase, which in turn phosphorylates and activates the effector MAPK. The activity of MAPKs is tightly regulated by phosphorylation of their activation loop, which can be modulated by positive and negative feedback mechanisms to control the amplitude and duration of the signal. The signaling outcomes of MAPK pathways are further regulated by interactions of MAPKs with scaffolding and regulatory proteins. Accumulating evidence indicates that, in addition to these mechanisms, MAPK signaling is commonly regulated by ubiquitin-proteasome system (UPS)-mediated control of the stability and abundance of MAPK pathway components. Notably, the biologic activity of some MAPKs appears to be regulated mainly at the level of protein turnover. Recent studies have started to explore the potential of targeted protein degradation as a powerful strategy to investigate the biologic functions of individual MAPK pathway components and as a new therapeutic approach to overcome resistance to current small-molecule kinase inhibitors. Here, we comprehensively review the mechanisms, physiologic importance, and pharmacological potential of UPS-mediated protein degradation in the control of MAPK signaling. SIGNIFICANCE STATEMENT: Accumulating evidence highlights the importance of targeted protein degradation by the ubiquitin-proteasome system in regulating and fine-tuning the signaling output of mitogen-activated protein kinase (MAPK) pathways. Manipulating protein levels of MAPK cascade components may provide a novel approach for the development of selective pharmacological tools and therapeutics.

TRIMs: selective recruitment at different steps of the NF-κB pathway-determinant of activation or resolution of inflammation

TNF-α-induced NF-κB pathway is an essential component of innate and adaptive immune pathway, and it is tightly regulated by various post-translational modifications including ubiquitination. Oscillations in NF-κB activation and temporal gene expression are emerging as critical determinants of inflammatory response, however, the regulators of unique outcomes in different patho-physiological conditions are not well understood. Tripartite Motif-containing proteins (TRIMs) are RING domain-containing E3 ligases involved in the regulation of cellular homeostasis, metabolism, cell death, inflammation, and host defence. Emerging reports suggest that TRIMs are recruited at different steps of TNF-α-induced NF-κB pathway and modulate via their E3 ligase activity. TRIMs show synergy and antagonism in the regulation of the NF-κB pathway and also regulate it in a feedback manner. TRIMs also regulate pattern recognition receptors (PRRs) mediated inflammatory pathways and may have evolved to directly regulate a specific arm of immune signalling. The review emphasizes TRIM-mediated ubiquitination and modulation of TNF-α-regulated temporal and NF-κB signaling and its possible impact on unique transcriptional and functional outcomes.

TRIM47 activates NF-κB signaling via PKC-ε/PKD3 stabilization and contributes to endocrine therapy resistance in breast cancer

Increasing attention has been paid to roles of tripartite motif-containing (TRIM) family proteins in cancer biology, often functioning as E3 ubiquitin ligases. In the present study, we focus on a contribution of TRIM47 to breast cancer biology, particularly to endocrine therapy resistance, which is a major clinical problem in breast cancer treatment. We performed immunohistochemical analysis of TRIM47 protein expression in 116 clinical samples of breast cancer patients with postoperative endocrine therapy using tamoxifen. Our clinicopathological study showed that higher immunoreactivity scores of TRIM47 were significantly associated with higher relapse rate of breast cancer patients (P = 0.012). As functional analyses, we manipulated TRIM47 expression in estrogen receptor-positive breast cancer cells MCF-7 and its 4-hydroxytamoxifen (OHT)-resistant derivative OHTR, which was established in a long-term culture with OHT. TRIM47 promoted both MCF-7 and OHTR cell proliferation. MCF-7 cells acquired tamoxifen resistance by overexpressing exogenous TRIM47. We found that TRIM47 enhances nuclear factor kappa-B (NF-κB) signaling, which further up-regulates TRIM47. We showed that protein kinase C epsilon (PKC-ε) and protein kinase D3 (PKD3), known as NF-κB-activating protein kinases, are directly associated with TRIM47 and stabilized in the presence of TRIM47. As an underlying mechanism, we showed TRIM47-dependent lysine 27-linked polyubiquitination of PKC-ε. These results indicate that TRIM47 facilitates breast cancer proliferation and endocrine therapy resistance by forming a ternary complex with PKC-ε and PKD3. TRIM47 and its associated kinases can be a potential diagnostic and therapeutic target for breast cancer refractory to endocrine therapy.

USP18 negatively regulates and inhibits lipopolysaccharides-induced sepsis by targeting TAK1 activity

Sepsis is an inflammatory disease with exacerbated inflammation at early stage. Inflammatory cytokines play critical roles in the pathophysiology of sepsis. Ubiquitin specific peptidase 18 (USP18), a deubiquitinating enzyme, has been shown to modulate transforming growth factor-β-activated kinase 1 (TAK1) activity. However, it is not clear about the precise role of USP18 in sepsis. Here we investigated the potential effect of USP18 on inflammation in sepsis. We generated mice with USP18 or/and TAK1 deficiency in macrophages (USP18 MKO mice, TAK1 MKO mice and USP18 MKO TAK1 MKO mice) and established lipopolysaccharides (LPS)-induced septic mice model. Bone marrow derived macrophages were isolated from wild type (WT), USP18 MKO or TAK1 MKO mice and treated with LPS or CpG, the expressions of cytokines including IL-6, IL-10, IL-1β, and TNF-α were measured. The activation of NF-κB, ERK, p38 signaling pathways and ubiquitination of TAK1 were detected. We induced sepsis in WT, USP18 MKO, TAK1 MKO or USP18 MKO TAK1 MKO mice and evaluated the survival rate, lung pathology and inflammation cytokine level in serum. Macrophages deficient in USP18 produced significantly increased IL-6, IL-1β and TNF-α post LPS or CpG stimulation. Macrophages deficient in USP18 had promoted activation of NF-κB, p38 and ERK, and increased ubiquitination of TAK1. Mice with TAK1 deficiency in macrophages had increased survival rates, decreased immune cell infiltration in lung, and decreased pro-inflammatory cytokines in serum. In contrast, mice with USP18 deficiency in macrophages had decreased survival rates, increased cell infiltration in lung and increased pro-inflammatory cytokines in serum. USP18 alleviated LPS-induced sepsis by inhibiting TAK1 activity.

Gab2 (Grb2-Associated Binder2) Plays a Crucial Role in Inflammatory Signaling and Endothelial Dysfunction

[Figure: see text].

Positive regulation of TNFR1 signaling via SH3 recognition motif

TNF is a pleiotropic cytokine and shows its biological function by binding to its receptors called TNFR1 and TNFR2. While TNFR1 induces apoptosis by activation of caspase-8 via the “death domain”, it also activates IKKα/β, MKK3/6, MKK4/7 by activation of TAK1. Although the TNFR1 signaling pathway is known by in large, it is not known how AKT and MAPKs p38, ERK1/2, and JNK1/2 are activated. The presence of a proline-rich PPAP region, (P448PAP451, a binding site for the SH3 domain-containing proteins) very close to the C-terminus promoted us to determine whether this region has any role in the TNFR1 signal transduction. To test this, the codons of P448 and P451 were changed to that of Alanin, GCG, via site-directed mutagenesis, and this plasmid was named as TNFR1-SH3-P/A. Subsequently, ectopically expressed the wild type TNFR1 and TNFR1-SH3-P/A in 293T cells and determined the levels of TNF-α-mediated phosphorylations of ERK, p38, JNK and AKT, NF-kB, and caspase-8 activation. While ectopic expression of our mutant diminished TNFα-mediated phosphorylations of p38, JNK, ERK and AKT, it increased NF-kB, and caspase-8 activations. In conclusion, TNFα-mediated ERK, AKT, JNK, p38 activations are affected by TNFR1 SH3 domain modifications.

Deficiency of Lipin2 Results in Enhanced NF-κB Signaling and Osteoclast Formation in RAW-D Murine Macrophages

Lipin2 is a phosphatidate phosphatase that plays critical roles in fat homeostasis. Alterations in Lpin2, which encodes lipin2, cause the autoinflammatory bone disorder Majeed syndrome. Lipin2 limits lipopolysaccharide (LPS)-induced inflammatory responses in macrophages. However, little is known about the precise molecular mechanisms underlying its anti-inflammatory function. In this study, we attempted to elucidate the molecular link between the loss of lipin2 function and autoinflammatory bone disorder. Using a Lpin2 knockout murine macrophage cell line, we showed that lipin2 deficiency enhances innate immune responses to LPS stimulation through excessive activation of the NF-κB signaling pathway, partly because of TAK1 signaling upregulation. Lipin2 depletion also enhanced RANKL-mediated osteoclastogenesis and osteoclastic resorption activity accompanied by NFATc1 dephosphorylation and increased nuclear accumulation. These results suggest that lipin2 suppresses the development of autoinflammatory bone disorder by fine-tuning proinflammatory responses and osteoclastogenesis in macrophages. Therefore, this study provides insights into the molecular pathogenesis of monogenic autoinflammatory bone disorders and presents a potential therapeutic intervention.

Spotlight on USP4: Structure, Function, and Regulation

The deubiquitinating enzyme (DUB)–mediated cleavage of ubiquitin plays a critical role in balancing protein synthesis and degradation. Ubiquitin-specific protease 4 (USP4), a member of the largest subfamily of cysteine protease DUBs, removes monoubiquitinated and polyubiquitinated chains from its target proteins. USP4 contains a DUSP (domain in USP)–UBL (ubiquitin-like) domain and a UBL-insert catalytic domain, sharing a common domain organization with its paralogs USP11 and USP15. USP4 plays a critical role in multiple cellular and biological processes and is tightly regulated under normal physiological conditions. When its expression or activity is aberrant, USP4 is implicated in the progression of a wide range of pathologies, especially cancers. In this review, we comprehensively summarize the current knowledge of USP4 structure, biological functions, pathological roles, and cellular regulation, highlighting the importance of exploring effective therapeutic interventions to target USP4.

TAK1-TABs Complex: A Central Signalosome in Inflammatory Responses

Transforming growth factor-β (TGF-β)-activated kinase 1 (TAK1) is a member of the MAPK kinase kinase (MAPKKK) family and has been implicated in the regulation of a wide range of physiological and pathological processes. TAK1 functions through assembling with its binding partners TAK1-binding proteins (TAB1, TAB2, and TAB3) and can be activated by a variety of stimuli such as tumor necrosis factor α (TNFα), interleukin-1β (IL-1β), and toll-like receptor ligands, and they play essential roles in the activation of NF-κB and MAPKs. Numerous studies have demonstrated that post-translational modifications play important roles in properly controlling the activity, stability, and assembly of TAK1-TABs complex according to the indicated cellular environment. This review focuses on the recent advances in TAK1-TABs-mediated signaling and the regulations of TAK1-TABs complex by post-translational modifications.

Deciphering the Role of Innate Immune NF-ĸB Pathway in Pancreatic Cancer

Simple Summary

Chronic inflammation is a major mechanism that underlies the aggressive nature and treatment resistance of pancreatic cancer. In many ways, the molecular mechanisms that drive chronic inflammation in pancreatic cancer are very similar to our body’s normal innate immune response to injury or invading microorganisms. Therefore, during cancer development, pancreatic cancer cells hijack the innate immune pathway to foster a chronically inflamed tumor environment that helps shield them from immune attack and therapeutics. While blocking the innate immune pathway is theoretically reasonable, untoward side effects must also be addressed. In this review, we comprehensively summarize the literature that describe the role of innate immune signaling in pancreatic cancer, emphasizing the specific role of this pathway in different cell types. We review the interaction of the innate immune pathway and cancer-driving signaling in pancreatic cancer and provide an updated overview of novel therapeutic opportunities against this mechanism.

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers with no effective treatment option. A predominant hallmark of PDAC is the intense fibro-inflammatory stroma which not only physically collapses vasculature but also functionally suppresses anti-tumor immunity. Constitutive and induced activation of the NF-κB transcription factors is a major mechanism that drives inflammation in PDAC. While targeting this pathway is widely supported as a promising therapeutic strategy, clinical success is elusive due to a lack of safe and effective anti-NF-κB pathway therapeutics. Furthermore, the cell type-specific contribution of this pathway, specifically in neoplastic cells, stromal fibroblasts, and immune cells, has not been critically appraised. In this article, we highlighted seminal and recent literature on molecular mechanisms that drive NF-κB activity in each of these major cell types in PDAC, focusing specifically on the innate immune Toll-like/IL-1 receptor pathway. We reviewed recent evidence on the signaling interplay between the NF-κB and oncogenic KRAS signaling pathways in PDAC cells and their collective contribution to cancer inflammation. Lastly, we reviewed clinical trials on agents that target the NF-κB pathway and novel therapeutic strategies that have been proposed in preclinical studies.

Regeneration of Damaged Tendon-Bone Junctions (Entheses)-TAK1 as a Potential Node Factor

Musculoskeletal dysfunctions are highly prevalent due to increasing life expectancy. Consequently, novel solutions to optimize treatment of patients are required. The current major research focus is to develop innovative concepts for single tissues. However, interest is also emerging to generate applications for tissue transitions where highly divergent properties need to work together, as in bone-cartilage or bone-tendon transitions. Finding medical solutions for dysfunctions of such tissue transitions presents an added challenge, both in research and in clinics. This review aims to provide an overview of the anatomical structure of healthy adult entheses and their development during embryogenesis. Subsequently, important scientific progress in restoration of damaged entheses is presented. With respect to enthesis dysfunction, the review further focuses on inflammation. Although molecular, cellular and tissue mechanisms during inflammation are well understood, tissue regeneration in context of inflammation still presents an unmet clinical need and goes along with unresolved biological questions. Furthermore, this review gives particular attention to the potential role of a signaling mediator protein, transforming growth factor beta-activated kinase-1 (TAK1), which is at the node of regenerative and inflammatory signaling and is one example for a less regarded aspect and potential important link between tissue regeneration and inflammation.

Inhibition of TGFβ-activated protein kinase 1 ameliorates myocardial ischaemia/reperfusion injury via endoplasmic reticulum stress suppression

Transforming growth factor β-activated protein kinase 1 (TAK1) involves in various biological responses and is a key regulator of cell death. However, the role of TAK1 on acute myocardial ischaemia/reperfusion (MI/R) injury is unknown. We observed that TAK1 activation increased significantly after MI/R and hypoxia/reoxygenation (H/R), and we hypothesized that TAK1 has an important role in MI/R injury. Mice (TAK1 inhibiting by 5Z-7-oxozeaenol or silencing by AAV9 vector) were exposed to MI/R injury. Primary cardiomyocytes (TAK1 silencing by siRNA; and overexpressing TAK1 by adenovirus vector) were used to induce H/R injury model in vitro. Inhibition of TAK1 significantly decreased MI/R-induced myocardial infarction area, reduced cell death and improved cardiac function. Mechanistically, TAK1 silencing suppressed MI/R-induced myocardial oxidative stress and attenuated endoplasmic reticulum (ER) stress both in vitro and in vivo. In addition, the inhibition of ROS by NAC partially reversed the damage of TAK1 in vitro. Our study presents the first direct evidence that inhibition of TAK1 mitigated MI/R injury, and TAK1 mediated ROS/ER stress/apoptosis signal pathway is important for the pathogenesis of MI/R injury.

MiR-146a-5p promotes IL-1β-induced chondrocyte apoptosis through the TRAF6-mediated NF-kB pathway

OBJECTIVE

This study aimed to explore the role of the miR-146a-5p/TRAF6/NF-KB axis in chondrocyte apoptosis.

METHODS

Transcriptome sequencing for microRNA expression in control and osteoarthritic cartilage was performed. Bioinformatic analysis was performed to identify the target genes of miR-146a-5p, and subsequently, Gene Ontology (GO) terms and KEGG pathways were identified. Furthermore, protein-protein interactions were analyzed to identify the hub regulatory gene of miR-146a-5p. MiR-146a-5p mimic, inhibitor and the corresponding negative control were constructed, and the apoptosis rates were measured in the transfected groups by flow cytometry, TUNEL staining and Western blot. Potential miRNA-target interactions were identified by dual-luciferase reporter assay.

RESULTS

The microRNA array demonstrated that miR-146a-5p was significantly upregulated in osteoarthritic tissues, which was further confirmed by PCR analysis. Compared with the control group, IL-1β significantly decreased the viability of chondrocytes, while coculture with miR-146a-5p inhibitor rescued the IL-1β-induced inhibition of chondrocyte viability. Western blot results also identified the proapoptotic effects of miR-146a-5p. Bioinformatic analysis results revealed that miR-146a-5p targeted 159 potential genes, and TRAF6 was the hub gene among the 159 genes. The relative expression of TRAF6 was significantly decreased in the IL-1β-induced group. When siTRAF6 was added, apoptosis was significantly increased. Luciferase reporter assays showed that luciferase activity of the TRAF6 3'-UTR reporter was decreased in chondrocytes after transfection with the miR-146a-5p mimic.

CONCLUSIONS

This work showed that miR-146 induces chondrocyte apoptosis by targeting the TRAF6-mediated NF-KB signaling pathway, and miR-146 may be a potential target for OA treatment.

TAK1 mediates convergence of cellular signals for death and survival

TGF-β activated kinase 1, a MAPK kinase kinase family serine threonine kinase has been implicated in regulating diverse range of cellular processes that include embryonic development, differentiation, autophagy, apoptosis and cell survival. TAK1 along with its binding partners TAB1, TAB2 and TAB3 displays a complex pattern of regulation that includes serious crosstalk with major signaling pathways including the C-Jun N-terminal kinase (JNK), p38 MAPK, and I-kappa B kinase complex (IKK) involved in establishing cellular commitments for death and survival. This review also highlights how TAK1 orchestrates regulation of energy homeostasis via AMPK and its emerging role in influencing mTORC1 pathway to regulate death or survival in tandem.

CALML6 Controls TAK1 Ubiquitination and Confers Protection against Acute Inflammation

Proper regulation of innate immune response is important for individual health. The NF-κB signaling pathway plays crucial roles in innate immunity and inflammation, and its aberrant activation is implicated in diverse diseases and disorders. In this study, we report that calmodulin-like 6 (CALML6), a member of the EF-hand protein family, is a negative regulator of the NF-κB signaling pathway. CALML6 attenuated TNF-stimulated phosphorylation of proteins downstream of TGF-β-activated kinase 1 (TAK1) and inhibited TAK1-induced NF-κB activation. Further studies showed that CALML6 interacted with TAK1 and recruited the deubiquitylating enzyme cylindromatosis to repress the K63-linked polyubiquitination of TAK1. CALML6 transgenic mice had higher tolerances to lethal LPS treatment in vivo. These findings suggest that CALML6 is a negative regulator of the NF-κB signaling pathway, which is important for maintaining the balance of the innate immune response.

Coupling Conjugation and Deconjugation Activities to Achieve Cellular Ubiquitin Dynamics

In eukaryotic cells, proteome remodeling is mediated by the ubiquitin-proteasome system, which regulates protein degradation, trafficking, and signaling events in the cell. Interplay between the cellular proteome and ubiquitin is complex and dynamic and many regulatory features that support this system have only recently come into focus. An unexpected recurring feature in this system is the physical interaction between E3 ubiquitin ligases and deubiquitylases (DUBs). Recent studies have reported on the regulatory significance of DUB-E3 interactions and it is becoming clear that they play important but complicated roles in the regulation of diverse cellular processes. Here, we summarize the current understanding of interactions between ubiquitin conjugation and deconjugation machineries and we examine the regulatory logic of these enigmatic complexes.