TAK1 Lys-158 but not Lys-209 is required for IL-1β-induced Lys63-linked TAK1 polyubiquitination and IKK/NF-κB activation

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.

MicroRNA‑143‑3p levels are reduced in the peripheral blood of patients with gestational diabetes mellitus and influences pancreatic β‑cell function and viability

Pancreatic β-cell dysfunction has been demonstrated to mediate key roles in the pathogenesis of gestational diabetes mellitus (GDM). Accumulating evidence has supported the functional involvement of microRNAs (miRNAs) in various types of diabetes, including GDM. However, the detailed biological effect of miRNAs in pancreatic β-cell dysfunction remains poorly understood. In the present study, microarray data of miRNAs in the blood plasma of patients with GDM were retrieved from the Gene Expression Omnibus dataset under the accession number GSE98043. Reverse transcription-quantitative PCR (RT-qPCR) was performed to measure the expression levels of miR-143-3p in the blood plasma isolated from 30 female patients with GDM women and 30 healthy female individuals. Subsequently, murine pancreatic β-cell line, MIN6 cells were treated with high glucose (HG) to construct in vitro cell models of GDM. miR-143-3p in HG-treated MIN6 cells was overexpressed or knocked down using miR-143-3p mimics and miR-143-3p inhibitor. Cell viability, insulin secretion and proinflammatory cytokine production were examined using CCK-8 and ELISA, respectively Cell apoptosis was measured by flow cytometry assay. The protein expression levels of proteins involved in the TAK1/NF-κB pathway were also assessed using western blot. The levels of miR-143-3p were found to be markedly lower in samples from patients with GDM, which were in turn negatively correlated with blood glucose levels. Overexpression of miR-143-3p in MIN6 cells significantly reversed HG-induced cell apoptosis and impairments in cell viability and insulin secretion. In addition, miR-143-3p overexpression attenuated HG-induced proinflammatory cytokine production by MIN6 cells. Subsequently, TGFβ-activated kinase 1 (TAK1), an upstream regulator of the NF-κB pathway, was found to be a direct target of miR-143-3p in pancreatic β cells through luciferase assays and western blot. Overexpression of TAK1 was revealed to abolish the curative effects of miR-143-3p on insulin secretion, cell viability and inflammatory response in HG-treated MIN6 cells. In addition, miR-143-3p could inactivate the NF-κB pathway by inhibiting TAK1 expression. Collectively, these results suggest that miR-143-3p levels are downregulated in the peripheral blood of patients with GDM. Therefore, miR-143-3p overexpression may serve as a method for preventing pancreatic β cell dysfunction by inhibiting the TAK1/NF-κB pathway.

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.

LncRNA linc00152/NF-κB feedback loop promotes fibroblast-like synovial cells inflammation in rheumatoid arthritis via regulating miR-103a/TAK1 axis and YY1 expression

INTRODUCTION

Overexpressed inflammatory cytokines are the main factors causing rheumatoid arthritis (RA) tissue damage and pathological deterioration, and lncRNAs has found to beinvolved in some autoinflammatory diseases.

METHODS

We designed this study to investigate the effect of lncRNA linc00152 on rheumatoid arthritis inflammation and explore its molecular mechanism.

RESULT

We found that linc00152 was not only up-regulated in rheumatoid arthritis fibroblast-like synoviocytes (RAFLS), but also stimulated by TNF-α/IL-1β in adose- and time-dependent manner in RAFLS and this expression depends on the NF-κB signaling pathway. Conversely, linc00152 promoted TNF-α/IL-1β expression in RAFLS induced by TNF-α/IL-1β. In addition, we found that linc00152 promoted TAK1 expression by targeting inhibition of miR-103a and activated TAK1-mediated NF-κB pathway. NF-kB indirectly promotes linc00152 expression by promoting the transcription activity of YY1, and YY1 directly promotes linc00152 expression by binding the promoter of linc00152.

CONCLUSION

Our data suggested that the linc00152/NF-κB feedback loop promotes RAFLS inflammation via regulating miR-103a/TAK1 axis and YY1 expression. Thus, linc00152 acts as a switch to control this regulatory circuit and may serve as a diagnostic and therapeutic target for RA treatment.

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.

Tripartite Motif-Containing 27 Attenuates Liver Ischemia/Reperfusion Injury by Suppressing Transforming Growth Factor β-Activated Kinase 1 (TAK1) by TAK1 Binding Protein 2/3 Degradation

BACKGROUND AND AIMS

Hepatic ischemia-reperfusion (I/R) injury, which mainly involves inflammatory responses and apoptosis, is a common cause of organ dysfunction in liver transplantation (LT). As a critical mediator of inflammation and apoptosis in various cell types, the role of tripartite motif-containing (TRIM) 27 in hepatic I/R injury remains worthy of study.

APPROACH AND RESULTS

This study systemically evaluated the putative role of TRIM27/transforming growth factor β-activated kinase 1 (TAK1)/JNK (c-Jun N-terminal kinase)/p38 signaling in hepatic I/R injury. TRIM27 expression was significantly down-regulated in liver tissue from LT patients, mice subjected to hepatic I/R surgery, and hepatocytes challenged by hypoxia/reoxygenation (H/R) treatment. Subsequently, using global Trim27 knockout mice (Trim27-KO mice) and hepatocyte-specific Trim27 transgenic mice (Trim27-HTG mice), TRIM27 functions to ameliorate liver damage, reduce the inflammatory response, and prevent cell apoptosis. In parallel in vitro studies, activating TRIM27 also prevented H/R-induced hepatocyte inflammation and apoptosis. Mechanistically, TRIM27 constitutively interacted with the critical components, TAK1 and TAK1 binding protein 2/3 (TAB2/3), and promoted the degradation of TAB2/3, leading to inactivation of TAK1 and the subsequent suppression of downstream JNK/p38 signaling.

CONCLUSIONS

TRIM27 is a key regulator of hepatic I/R injury by mediating the degradation of TAB2/3 and suppression of downstream TAK1-JNK/p38 signaling. TRIM27 may be a promising approach to protect the liver against I/R-mediated hepatocellular damage in transplant recipients.

TRAF6 and TAK1 Contribute to SAMHD1-Mediated Negative Regulation of NF-κB Signaling

Sterile alpha motif and HD domain-containing protein 1 (SAMHD1) restricts HIV-1 replication by limiting the intracellular deoxynucleoside triphosphate (dNTP) pool. SAMHD1 also suppresses the activation of NF-κB in response to viral infections and inflammatory stimuli. However, the mechanisms by which SAMHD1 negatively regulates this pathway remain unclear. Here, we show that SAMHD1-mediated suppression of NF-κB activation is modulated by two key mediators of NF-κB signaling, tumor necrosis factor (TNF) receptor-associated factor 6 (TRAF6) and transforming growth factor β-activated kinase 1 (TAK1). We compared NF-κB activation stimulated by interleukin (IL)-1β in monocytic THP-1 control and SAMHD1 knockout (KO) cells with and without partial TRAF6 knockdown (KD), or in cells treated with TAK1 inhibitors. Relative to control cells, IL-1β-treated SAMHD1 KO cells showed increased phosphorylation of the inhibitor of NF-κB (IκBα), an indication of pathway activation, and elevated levels of TNF-α mRNA. Moreover, SAMHD1 KO combined with TRAF6 KD or pharmacological TAK1 inhibition reduced IκBα phosphorylation and TNF-α mRNA to the level of control cells. SAMHD1 KO cells infected with single-cycle HIV-1 showed elevated infection and TNF-α mRNA levels compared to control cells, and the effects were significantly reduced by TRAF6 KD or TAK1 inhibition. We further demonstrated that overexpressed SAMHD1 inhibited TRAF6-stimulated NF-κB reporter activity in HEK293T cells in a dose-dependent manner. SAMHD1 contains a nuclear localization signal (NLS), but an NLS-defective SAMHD1 exhibited a suppressive effect similar to the wild-type protein. Our data suggest that the TRAF6-TAK1 axis contributes to SAMHD1-mediated suppression of NF-κB activation and HIV-1 infection.IMPORTANCE Cells respond to pathogen infection by activating a complex innate immune signaling pathway, which culminates in the activation of transcription factors and secretion of a family of functionally and genetically related cytokines. However, excessive immune activation may cause tissue damage and detrimental effects on the host. Therefore, in order to maintain host homeostasis, the innate immune response is tightly regulated during viral infection. We have reported SAMHD1 as a novel negative regulator of the innate immune response. Here, we provide new insights into SAMHD1-mediated negative regulation of the NF-κB pathway at the TRAF6-TAK1 checkpoint. We show that SAMHD1 inhibits TAK1 activation and TRAF6 signaling in response to proinflammatory stimuli. Interestingly, TRAF6 knockdown in SAMHD1-deficient cells significantly inhibited HIV-1 infection and activation of NF-κB induced by virus infection. Our research reveals a new negative regulatory mechanism by which SAMHD1 participates in the maintenance of cellular homeostasis during HIV-1 infection and inflammation.

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.

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.

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.

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.

Silencing of Long Noncoding RNA Nespas Aggravates Microglial Cell Death and Neuroinflammation in Ischemic Stroke

Background and Purpose- Ischemic stroke is one of the leading causes of morbidity and mortality worldwide and a major cause of long-term disability. Recently, long noncoding RNAs have been revealed, which are tightly associated with several human diseases. However, the functions of long noncoding RNAs in ischemic stroke still remain largely unknown. In the current study, for the first time, we investigated the role of long noncoding RNA Nespas in ischemic stroke. Methods- We used in vivo models of middle cerebral artery occlusion and in vitro models of oxygen-glucose deprivation to illustrate the effect of long noncoding RNA Nespas on ischemic stroke. Results- We found expression of Nespas was significantly increased in ischemic cerebral tissues and oxygen-glucose deprivation-treated BV2 cells in a time-dependent manner. Silencing of Nespas aggravated middle cerebral artery occlusion operation-induced IR injury and cell death. In addition, proinflammatory cytokine production and NF-κB (nuclear factor-κB) signaling activation were inhibited by Nespas overexpression. TAK1 (transforming growth factor-β-activated kinase 1) was found to directly interact with Nespas, and TAK1 activation was significantly suppressed by Nespas. At last, we found Nespas-inhibited TRIM8 (tripartite motif 8)-induced K63-linked polyubiquitination of TAK1. Conclusions- We showed that Nespas played anti-inflammatory and antiapoptotic roles in cultured microglial cells after oxygen-glucose deprivation stimulation and in mice after ischemic stroke by inhibiting TRIM8-related K63-linked polyubiquitination of TAK1.

TAK1 is a druggable kinase for diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL) is the most common form of lymphoma, and up to 30% DLBCL patients eventually died by using first-line chemotherapy regimens. Currently, Bruton tyrosine kinase (BTK) inhibitor (ibrutinib) is one of the most promising medicine in clinical trials for DLBCL, to which about 25% of patients with relapsed or refractory DLBCL are responsive. Thus, it is urgent to discover new druggable targets for DLBCL, especially for patients who are unresponsive to first-line chemotherapy and ibrutinib. Here, we found that MAP 3K7 (TAK1) is required for DLBCL survival. Inhibition of TAK1 by small molecule 5Z7 or genetic silence could massively induce deaths of DLBCL cells. Mechanistically, TAK1 inhibition could dramatically reduce the nuclear factor kappa B (NF-κB) activity. Notably, ibrutinib-resistant DLBCL cells also respond to TAK1 inhibition. Database analysis showed that high expression of TAK1 in patients with DLBCL shows poor survival. A subtype of DLBCL patients showed that high expression of both TAK1 and BTK1 is poorly responsive to the current chemotherapy. Moreover, DLBCL cell line with high expression of both TAK1 and BTK1 is resistant to Dox. Simultaneously targeting TAK1 and BTK not only increases cellular toxicity of individual drug but also enhances the sensitivity to Dox. Taken together, we provide convincing evidence to show that kinase TAK1 is a druggable target in DLBCL. SIGNIFICANCE OF THE STUDY: Currently, there is still a significant portion of patients with DLBCL who are unresponsive to first-line chemotherapy. Thus, identification of novel druggable targets such as kinase is critical important. Here, we found that TAK1 inhibition promotes death of DLBCL cells through inhibition of chronic NF-κB signalling. Importantly, TAK1 inhibition overcomes ibrutinib resistance in DLBCL cells. Finally, DLBCL patients with high expression of both TAK1 and BTK showed extremely poor survival. In summary, we provide convincing results to demonstrate a potential important druggable kinase in DLBCL.

Oncogenic mutations in IKKβ function through global changes induced by K63-linked ubiquitination and result in autocrine stimulation

Mutations at position K171 in the kinase activation loop of Inhibitor of κB kinase beta (IKKβ) occur in multiple myeloma, spleen marginal zone lymphoma and mantle cell lymphoma. Previously, we demonstrated that these result in constitutive kinase activation and stimulate Signal Transducer and Activator of Transcription 3 (STAT3). This work also identified K147 as a site of K63-linked regulatory ubiquitination required for activation of signaling pathways. We now present a more detailed analysis of ubiquitination sites together with a comprehensive examination of the signaling pathways activated by IKKβ K171E mutants. Downstream activation of STAT3 is dependent upon the activity of: UBE2N, the E2 ubiquitin ligase involved in K63-linked ubiquitination; TAK1 (MAP3K7), or TGFβ Activated Kinase, which forms a complex required for NFκB activation; JAK kinases, involved proximally in the phosphorylation of STAT transcription factors in response to inflammatory cytokines; and gp130, or IL-6 Receptor Subunit Beta which, upon binding IL-6 or other specific cytokines, undergoes homodimerization leading to activation of associated JAKs, resulting in STAT activation. We further demonstrate, using an IL-6-responsive cell line, that IKKβ K171E mutants stimulate the release of IL-6 activity into conditioned media. These results show that IKKβ K171E mutants trigger an autocrine loop in which IL-6 is secreted and binds to the IL-6 receptor complex gp130, resulting in JAK activation. Lastly, by examining the differential abundance of proteins associated with K63-only-ubiquitinated IKKβ K171E, proteomic analysis demonstrates the global activation of proliferative responses. As cancers harboring K171-mutated IKKβ are likely to also exhibit activated STAT3 and p44/42 MAPK (Erk1/2), this suggests the possibility of using MAPK (Erk1/2) and JAK inhibitors, or specific ubiquitination inhibitors. K63-linked ubiquitination occurs in other kinases at sites homologous to K147 in IKKβ, including K578 in BRAF V600E, which serves as an oncogenic driver in melanoma and other cancers.

MPB, a novel berberine derivative, enhances lysosomal and bactericidal properties via TGF-β-activated kinase 1-dependent activation of the transcription factor EB

Lysosome has a crucial role in clearance of endocytosed pathogens from the cell. Small molecules that can boost lysosome function and bactericidal ability to cope with subsequent infection are urgently needed. Here, we report that MPB, a novel berberine derivative, induced lysosome-based degradation and clearance of methicillin-resistant Staphylococcus aureus and enteroinvasive Escherichia coli in macrophages. MPB caused nuclear translocation of transcription factor EB (TFEB), which boosted expression of lysosome genes. TFEB silencing repressed the MPB-mediated enhancements in degradation and bacterial eradication. MPB switched on TFEB nuclear translocation by coupling 2 parallel signaling pathways. MPB-triggered JNK activation led to 14-3-3δ being released from TFEB, which, in turn, caused TFEB nuclear translocation. In addition, MPB induced AMPK activation and subsequent inhibition of mechanistic target of rapamycin activity, which also contributed to TFEB nuclear translocation. Importantly, genetical or pharmaceutical inhibition of TGF-β-activated kinase 1 (TAK1) reduced MPB action remarkably. MPB acted through TAK1 at lysine 158 to activate JNK and AMPK and, thus, induced TFEB-dependent bactericidal activity in macrophages. Therefore, our study reveals a novel mechanism by which MPB controls JNK and AMPK phosphorylation cascades to activate lysosomal function and bactericidal activity via TAK1 K158-dependent manner, which may offer insight into novel therapeutic strategies to control bacterial infection.-Liu, X., Zhang, N., Liu, Y., Liu, L., Zeng, Q., Yin, M., Wang, Y., Song, D., Deng, H. MPB, a novel berberine derivative, enhances lysosomal and bactericidal properties via TGF-β-activated kinase 1-dependent activation of the transcription factor EB.

The Us2 Gene Product of Herpes Simplex Virus 2 modulates NF-κB activation by targeting TAK1

HSV-2 is one of the most common sexually transmitted pathogens worldwide and HSV-2 infection triggers cytokine and chemokine production. However, little is known about which HSV-2 genes engage in the regulation of NF-κB signaling and what mechanisms are involved. In a screen of the unique short (Us) regions of HSV-2, we observed that HSV-2 Us2 activates NF-κB signaling. We additionally indicated that deficiencies of Us2 decrease HSV-2 WT mediated NF-κB activation and cytokine and chemokine production, and overexpression of Us2 showed opposite effects. Co-immunoprecipitations indicated that Us2 interacted with TGF-β activated kinase 1 (TAK1), a serine/threonine kinase essential for NF-κB activation, and Us2 has the ability to regulate the TAK1-mediated pathway and induces TAK1 downstream signaling. Further studies verified that Us2 induced the phosphorylation of TAK1, resulting in the activation of TAK1 mediated downstream signaling. The role of Us2 in HSV-2 induced NF-κB pathways was also confirmed in the Us2-deficient mutant and HSV-2 WT infected mice. Our results indicate that HSV-2 Us2 gene product binds to TAK1 to positively regulate NF-κB signaling and, for the first time, provide insights into the molecular mechanism.

Rapid Activation of Transforming Growth Factor β-Activated Kinase 1 in Chondrocytes by Phosphorylation and K63 -Linked Polyubiquitination Upon Injury to Animal Articular Cartilage

Objective

Mechanical injury to cartilage predisposes to osteoarthritis (OA). Wounding of the articular cartilage surface causes rapid activation of MAP kinases and NF‐κB, mimicking the response to inflammatory cytokines. This study was undertaken to identify the upstream signaling mechanisms involved.

Methods

Cartilage was injured by dissecting it from the articular surface of porcine metacarpophalangeal (MCP) joints or by avulsing murine proximal femoral epiphyses. Protein phosphorylation was assayed by Western blotting of cartilage lysates. Immunolocalization of phosphorylated activating transcription factor 2 (ATF‐2) and NF‐κB/p65 was detected by confocal microscopy. Messenger RNA (mRNA) was measured by quantitative reverse transcriptase–polymerase chain reaction (qRT‐PCR). Receptor associated protein 80 (RAP‐80) ubiquitin interacting motif agarose was used in a pull‐down assay to obtain K⁶³‐polyubiquitinated proteins. Ubiquitin linkages on immunoprecipitated transforming growth factor β–activated kinase 1 (TAK‐1) were analyzed with deubiquitinases.

Results

Sharp injury to porcine cartilage caused rapid activation of JNK and NF‐κB pathways and the upstream kinases MKK‐4, IKK, and TAK‐1. Pharmacologic inhibition of TAK‐1 in porcine cartilage abolished JNK and NF‐κB activation and reduced the injury‐dependent inflammatory gene response. High molecular weight species of phosphorylated TAK‐1 were induced by injury, indicating its ubiquitination. An overall increase in K⁶³‐linked polyubiquitination was detected upon injury, and TAK‐1 was specifically linked to K⁶³‐ but not K⁴⁸‐polyubiquitin chains. In mice, avulsion of wild‐type femoral epiphyses caused similar intracellular signaling that was reduced in cartilage‐specific TAK‐1–null mice. Epiphyseal cartilage of MyD88‐null and TRAF‐6–null mice responded to injury, suggesting the involvement of a ubiquitin E3 ligase other than TRAF‐6.

Conclusion

Activation of TAK‐1 by phosphorylation and K⁶³‐linked polyubiquitination by injury indicates its role in driving cell activation. Further studies are needed to identify the upstream ubiquitination mechanisms, including the E3 ligase involved.

Post-Translational Modifications of the TAK1-TAB Complex

Transforming growth factor-β (TGF-β)-activated kinase 1 (TAK1) is a member of the mitogen-activated protein kinase kinase kinase (MAPKKK) family that is activated by growth factors and cytokines such as TGF-β, IL-1β, and TNF-α, and mediates a wide range of biological processes through activation of the nuclear factor-κB (NF-κB) and the mitogen-activated protein (MAP) kinase signaling pathways. It is well established that activation status of TAK1 is tightly regulated by forming a complex with its binding partners, TAK1-binding proteins (TAB1, TAB2, and TAB3). Interestingly, recent evidence indicates the importance of post-translational modifications (PTMs) of TAK1 and TABs in the regulation of TAK1 activation. To date, a number of PTMs of TAK1 and TABs have been revealed, and these PTMs appear to fine-tune and coordinate TAK1 activities depending on the cellular context. This review therefore focuses on recent advances in the understanding of the PTMs of the TAK1-TAB complex.

Anti-Inflammatory Effects of TRAF-Interacting Protein in Rheumatoid Arthritis Fibroblast-Like Synoviocytes

Rheumatoid arthritis (RA) is a chronic systemic inflammatory disease characterized by inflammatory cell infiltration, synovial inflammation, and cartilage destruction. Proliferative fibroblast-like synoviocytes (FLS) play crucial roles in both propagation of inflammation and joint damage because of their production of great amount of proinflammatory cytokines and proteolytic enzymes. In this study, we investigate the role of TRAF-interacting protein (TRIP) in regulating inflammatory process in RA-FLS. TRIP expression was attenuated in RA-FLS compared with osteoarthritis- (OA-) FLS. Overexpression of TRIP significantly inhibited the activation of NF-κB signaling and decreased the production of proinflammatory cytokines and matrix metalloproteinases (MMPs) in TNFα-stimulated RA-FLS. Furthermore, TRIP was found to interact with transforming growth factor β-activated kinase 1 (TAK1) and promoting K48-linked polyubiquitination of TAK1 in RA-FLS. Our results demonstrate that TRIP has anti-inflammatory effects on RA-FLS and suggest TRIP as a potential therapeutic target for human RA.

JNK Signaling: Regulation and Functions Based on Complex Protein-Protein Partnerships

The c-Jun N-terminal kinases (JNKs), as members of the mitogen-activated protein kinase (MAPK) family, mediate eukaryotic cell responses to a wide range of abiotic and biotic stress insults. JNKs also regulate important physiological processes, including neuronal functions, immunological actions, and embryonic development, via their impact on gene expression, cytoskeletal protein dynamics, and cell death/survival pathways. Although the JNK pathway has been under study for >20 years, its complexity is still perplexing, with multiple protein partners of JNKs underlying the diversity of actions. Here we review the current knowledge of JNK structure and isoforms as well as the partnerships of JNKs with a range of intracellular proteins. Many of these proteins are direct substrates of the JNKs. We analyzed almost 100 of these target proteins in detail within a framework of their classification based on their regulation by JNKs. Examples of these JNK substrates include a diverse assortment of nuclear transcription factors (Jun, ATF2, Myc, Elk1), cytoplasmic proteins involved in cytoskeleton regulation (DCX, Tau, WDR62) or vesicular transport (JIP1, JIP3), cell membrane receptors (BMPR2), and mitochondrial proteins (Mcl1, Bim). In addition, because upstream signaling components impact JNK activity, we critically assessed the involvement of signaling scaffolds and the roles of feedback mechanisms in the JNK pathway. Despite a clarification of many regulatory events in JNK-dependent signaling during the past decade, many other structural and mechanistic insights are just beginning to be revealed. These advances open new opportunities to understand the role of JNK signaling in diverse physiological and pathophysiological states.

The ubiquitin E3 ligase TRAF6 exacerbates pathological cardiac hypertrophy via TAK1-dependent signalling

Tumour necrosis factor receptor-associated factor 6 (TRAF6) is a ubiquitin E3 ligase that regulates important biological processes. However, the role of TRAF6 in cardiac hypertrophy remains unknown. Here, we show that TRAF6 levels are increased in human and murine hypertrophied hearts, which is regulated by reactive oxygen species (ROS) production. Cardiac-specific Traf6 overexpression exacerbates cardiac hypertrophy in response to pressure overload or angiotensin II (Ang II) challenge, whereas Traf6 deficiency causes an alleviated hypertrophic phenotype in mice. Mechanistically, we show that ROS, generated during hypertrophic progression, triggers TRAF6 auto-ubiquitination that facilitates recruitment of TAB2 and its binding to transforming growth factor beta-activated kinase 1 (TAK1), which, in turn, enables the direct TRAF6-TAK1 interaction and promotes TAK1 ubiquitination. The binding of TRAF6 to TAK1 and the induction of TAK1 ubiquitination and activation are indispensable for TRAF6-regulated cardiac remodelling. Taken together, we define TRAF6 as an essential molecular switch leading to cardiac hypertrophy in a TAK1-dependent manner.

Hepatocyte TRAF3 promotes liver steatosis and systemic insulin resistance through targeting TAK1-dependent signalling

Non-alcoholic fatty liver disease (NAFLD) is characterized by hepatic steatosis, insulin resistance and a systemic pro-inflammatory response. Here we show that tumour necrosis factor receptor-associated factor 3 (TRAF3) is upregulated in mouse and human livers with hepatic steatosis. After 24 weeks on a high-fat diet (HFD), obesity, insulin resistance, hepatic steatosis and inflammatory responses are significantly ameliorated in liver-specific TRAF3-knockout mice, but exacerbated in transgenic mice overexpressing TRAF3 in hepatocytes. The detrimental effects of TRAF3 on hepatic steatosis and related pathologies are confirmed in ob/ob mice. We further show that in response to HFD, hepatocyte TRAF3 binds to TGF-β-activated kinase 1 (TAK1) to induce TAK1 ubiquitination and subsequent autophosphorylation, thereby enhancing the activation of downstream IKKβ-NF-κB and MKK-JNK-IRS1(307) signalling cascades, while disrupting AKT-GSK3β/FOXO1 signalling. The TRAF3-TAK1 interaction and TAK1 ubiquitination are indispensable for TRAF3-regulated hepatic steatosis. In conclusion, hepatocyte TRAF3 promotes HFD-induced or genetic hepatic steatosis in a TAK1-dependent manner.

TAK1 modulates satellite stem cell homeostasis and skeletal muscle repair

Satellite cells are resident adult stem cells that are required for regeneration of skeletal muscle. However, signalling mechanisms that regulate satellite cell function are less understood. Here we demonstrate that transforming growth factor-β-activated kinase 1 (TAK1) is important in satellite stem cell homeostasis and function. Inactivation of TAK1 in satellite cells inhibits muscle regeneration in adult mice. TAK1 is essential for satellite cell proliferation and its inactivation causes precocious differentiation. Moreover, TAK1-deficient satellite cells exhibit increased oxidative stress and undergo spontaneous cell death, primarily through necroptosis. TAK1 is required for the activation of NF-κB and JNK in satellite cells. Forced activation of NF-κB improves survival and proliferation of TAK1-deficient satellite cells. Furthermore, TAK1-mediated activation of JNK is essential to prevent oxidative stress and precocious differentiation of satellite cells. Collectively, our study suggests that TAK1 is required for maintaining the pool of satellite stem cells and for regenerative myogenesis.

Polyubiquitination of Transforming Growth Factor β-activated Kinase 1 (TAK1) at Lysine 562 Residue Regulates TLR4-mediated JNK and p38 MAPK Activation

Toll-like receptor 4 (TLR4) plays an important role in innate immunity by eliciting inflammation. Upon receptor engagement, transforming growth factor β-activated kinase 1 (TAK1) is an essential mediator that transmits a signal from the receptor to downstream effectors, IκB kinase (IKK) and the mitogen-activated protein kinases (MAPKs), which control the production of inflammatory cytokines. However, the association between phosphorylation and ubiquitination of TAK1 is not yet clear. Here, we examined the crosstalk between phosphorylation and polyubiquitination of TAK1 and further investigated the mechanism of distinct activation of MAPKs and IKK. Inhibition of TAK1 phosphorylation enhanced Lys63-linked polyubiquitination of TAK1. Conversely, ubiquitin modification was counteracted by phospho-mimic TAK1 mutant, T(184,187)D. Moreover, using LC-MS analysis, Lys562 of TAK1 was identified as a novel Lys63-linked ubiquitination site and as the key residue in the feedback regulation. Mutation of Lys562 of TAK1 leads to a decrease in TAK1 phosphorylation and specific inhibition of the MAPK pathway, but has no effect on formation of the TAK1-containing complex. Our findings demonstrate a feedback loop for phosphorylation and ubiquitination of TAK1, indicating a dynamic regulation between TAK1 polyubiquitiantion and phosphorylated activation, and the molecular mechanism by which IKK and MAPKs are differentially activated in the TLR4 pathway.

Ndfip1 regulates itch ligase activity and airway inflammation via UbcH7

The ubiquitin-ligating enzyme (E3) Itch plays a crucial role in the regulation of inflammation, and Itch deficiency leads to severe airway inflammation. However, the molecular mechanisms by which Itch function is regulated remain elusive. In this study, we found that nontypeable Haemophilus influenzae induces the association of Itch with Ndfip1. Both Itch(-/-) and Ndfip1(-/-) mice exhibited severe airway inflammation in response to nontypeable Haemophilus influenza, which was associated with elevated expression of proinflammatory cytokines. Ndfip1 enhanced Itch ligase activity and facilitated Itch-mediated Tak1 ubiquitination. Mechanistically, Ndfip1 facilitated recruitment of ubiquitin-conjugating enzyme (E2) UbcH7 to Itch. The N-terminal region of Ndfip1 binds to UbcH7, whereas the PY motif binds to Itch. Hence, Ndfip1 acts as an adaptor for UbcH7 and Itch. Reconstitution of full-length Ndfip1 but not the mutants that fail to interact with either UbcH7 or Itch, restored the defect in Tak1 ubiquitination and inhibited elevated proinflammatory cytokine expression by Ndfip1(-/-) cells. These results provide new mechanistic insights into how Itch function is regulated during inflammatory signaling, which could be exploited therapeutically in inflammatory diseases.

HIV-1 Vpr stimulates NF-κB and AP-1 signaling by activating TAK1

BACKGROUND

The Vpr protein of human immunodeficiency virus type 1 (HIV-1) plays an important role in viral replication. It has been reported that Vpr stimulates the nuclear factor-κB (NF-κB) and activator protein 1 (AP-1) signaling pathways, and thereby regulates viral and host cell gene expression. However, the molecular mechanism behind this function of Vpr is not fully understood.

RESULTS

Here, we have identified transforming growth factor-β-activated kinase 1 (TAK1) as the important upstream signaling molecule that Vpr associates with in order to activate NF-κB and AP-1 signaling. HIV-1 virion-associated Vpr is able to stimulate phosphorylation of TAK1. This activity of Vpr depends on its association with TAK1, since the S79A Vpr mutant lost interaction with TAK1 and was unable to activate TAK1. This association allows Vpr to promote the interaction of TAB3 with TAK1 and increase the polyubiquitination of TAK1, which renders TAK1 phosphorylation. In further support of the key role of TAK1 in this function of Vpr, knockdown of endogenous TAK1 significantly attenuated the ability of Vpr to activate NF-κB and AP-1 as well as the ability to stimulate HIV-1 LTR promoter.

CONCLUSIONS

HIV-1 Vpr enhances the phosphorylation and polyubiquitination of TAK1, and as a result, activates NF-κB and AP-1 signaling pathways and stimulates HIV-1 LTR promoter.

Helicobacter pylori activates NF-κB by inducing Ubc13-mediated ubiquitination of lysine 158 of TAK1

The Helicobacter pylori virulence factor CagA targets a variety of host proteins to alter different cellular responses, including the induction of pro-inflammatory cytokines. We have previously shown that CagA-facilitated lysine 63-linked ubiquitination of TAK1 is essential for the H. pylori-induced NF-κB activation and the expression of proinflammatory cytokines. However, the molecular mechanism for TAK1 ubiquitination and activation in H. pylori-mediated NF-κB activation remains elusive. Here, we identify lysine 158 of TAK1 as the key residue undergoing lysine 63-linked ubiquitination in response to H. pylori infection. Mutation of lysine 158 to arginine prevents the ubiquitination of TAK1 and impairs H. pylori-induced TAK1 and NF-κB activation. Moreover, we demonstrate that E2 ubiquitin conjugating enzyme Ubc13 is involved in H. pylori-mediated TAK1 ubiquitination. Suppressing the activity of Ubc13 by a dominant-negative mutant or siRNA abolishes CagA-facilitated and H. pylori-induced TAK1 and NF-κB activation. These findings further underscore the importance of lysine 63-linked ubiquitination of TAK1 in H. pylori-induced NF-κB activation and NF-κB-mediated inflammatory response.

NF-kappaB-dependent microRNA-425 upregulation promotes gastric cancer cell growth by targeting PTEN upon IL-1β induction

Overexpression of the proinflammatory cytokine IL-1β is associated with diverse diseases, including cancer. Alteration of microRNAs has been observed in cancer cells exposed to proinflammatory cytokines, yet their function in inflammation stress remains elusive. Here, we show that IL-1β induces the upregulation of miR-425, which negatively regulates phosphatase and tensin homolog expression by targeting its 3’ UTR. An increase in miR-425 depends on IL-1β-induced NF-kappaB activation, which enhances miR-425 gene transcription upon IL-1β induction. Consequently, repression of phosphatase and tensin homolog by miR-425 promotes gastric cancer cell proliferation, which is required to protect cells from cisplatin-induced apoptosis. Taken together, our data support a critical role for NF-kappaB-dependent upregulation of miR-425, which represents a new pathway for the repression of phosphatase and tensin homolog activation and the promotion of cell survival upon IL-1β induction.

Loss of Trabid, a new negative regulator of the drosophila immune-deficiency pathway at the level of TAK1, reduces life span

A relatively unexplored nexus in Drosophila Immune deficiency (IMD) pathway is TGF-beta Activating Kinase 1 (TAK1), which triggers both immunity and apoptosis. In a cell culture screen, we identified that Lysine at position 142 was a K63-linked Ubiquitin acceptor site for TAK1, required for signalling. Moreover, Lysine at position 156 functioned as a K48-linked Ubiquitin acceptor site, also necessary for TAK1 activity. The deubiquitinase Trabid interacted with TAK1, reducing immune signalling output and K63-linked ubiquitination. The three tandem Npl4 Zinc Fingers and the catalytic Cysteine at position 518 were required for Trabid activity. Flies deficient for Trabid had a reduced life span due to chronic activation of IMD both systemically as well as in their gut where homeostasis was disrupted. The TAK1-associated Binding Protein 2 (TAB2) was linked with the TAK1-Trabid interaction through its Zinc finger domain that pacified the TAK1 signal. These results indicate an elaborate and multi-tiered mechanism for regulating TAK1 activity and modulating its immune signal.

Chronic activation of immune responses results in health problems including gastrointestinal infections, metabolic imbalances and inflammatory bowel diseases that may lead to colorectal cancer. Central to this, is the balance of activation/restriction of nuclear factor-κB (NF-κB) during innate immune responses. To study signaling through NF-κB, we use the fruit fly Drosophila melanogaster as a genetically tractable model system that reflects human biology (due to the evolutionary conservation between innate immunity in flies and mammals), while reducing the complexity of the human disease of interest. We have found a new negative regulator of the Drosophila NF-κB pathway named Trabid. Its loss released the pathway and resulted in constitutive immune activation both in the gut as well as in the whole fly. This spontaneous immune activation reduced life span in the absence of infection, especially when it was combined with loss of another known negative regulator of the same pathway, a protein named Pirk. Stem cell activity in the gut in a pirk;trabid double mutant was found to be significantly increased, as the gut was trying to balance enterocyte loss. Trabid was acting at the level of TGF-beta Activating Kinase 1 (TAK1), which triggers both immunity and cell death.

Regulation of NF-κB signalling by the mono-ADP-ribosyltransferase ARTD10

Adenosine diphosphate-ribosylation is a post-translational modification mediated by intracellular and membrane-associated extracellular enzymes and many bacterial toxins. The intracellular enzymes modify their substrates either by poly-ADP-ribosylation, exemplified by ARTD1/PARP1, or by mono-ADP-ribosylation. The latter has been discovered only recently, and little is known about its physiological relevance. The founding member of mono-ADP-ribosyltransferases is ARTD10/PARP10. It possesses two ubiquitin-interaction motifs, a unique feature among ARTD/PARP enzymes. Here, we find that the ARTD10 ubiquitin-interaction motifs bind to K63-linked poly-ubiquitin, a modification that is essential for NF-κB signalling. We therefore studied the role of ARTD10 in this pathway. ARTD10 inhibits the activation of NF-κB and downstream target genes in response to interleukin-1β and tumour necrosis factor-α, dependent on catalytic activity and poly-ubiquitin binding of ARTD10. Mechanistically ARTD10 interferes with poly-ubiquitination of NEMO, which interacts with and is a substrate of ARTD10. Our findings identify a novel regulator of NF-κB signalling and provide evidence for cross-talk between K63-linked poly-ubiquitination and mono-ADP-ribosylation.

Activation of TAK1 by Sef-S induces apoptosis in 293T cells

Sef (similar expression to fgf genes, also named IL-17RD) was identified as a negative regulator of fibroblast growth factor signaling. Sef-S, an alternative splice isoform of Sef, inhibits FGF-induced NIH3T3 cell proliferation. Here we report that Sef-S physically interacts with TAK1, induces Lys63-linked TAK1 polyubiquitination on lysine 209 and TAK1-mediated JNK and p38 activation. Co-overexpression of TAK1 WT, K34R, K150R, K158R mutants with Sef-S induces Lys63-linked TAK1 polyubiquitination whereas TAK1 K63R and K209R mutants fail. Furthermore, co-overexpression of Sef-S and TAK1 induce 293T cells apoptosis. These results reveal Sef-S actives Lys63-linked TAK1 polyubiquitination on lysine 209, induces TAK1-mediated JNK and p38 activation and also results apoptosis in 293T cells.

Cell type-specific function of TAK1 in innate immune signaling

Transforming growth factor β-activated kinase 1 (TAK1 or MAP3K7) is a key signaling component of nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways. Activation of TAK1 is tightly regulated through its binding partners and protein modifications. Although TAK1 functions as an essential and positive regulator of innate immune signaling and apoptosis in mouse embryonic fibroblasts (MEFs), T cells, and other cells, it negatively regulates cell development and activation of proinflammatory signaling pathways in neutrophils. However, the molecular mechanisms responsible for the opposite roles of TAK1 in different cell types remain to be addressed. In this article, we discuss the latest progresses in our understanding of TAK1 regulation, function, and mechanisms in a cell-type specific manner.

Lysine 63-linked ubiquitination modulates mixed lineage kinase-3 interaction with JIP1 scaffold protein in cytokine-induced pancreatic β cell death

The mixed lineage kinase MLK3 plays a crucial role in compromising mitochondrial integrity and functions as a proapoptotic competence factor in the early stages of cytokine-induced pancreatic β cell death. In an effort to identify mechanisms that regulate MLK3 activity in β cells, we discovered that IL-1β stimulates Lys-63-linked ubiquitination of MLK3 via a conserved, TRAF6-binding peptapeptide motif in the catalytic domain of the kinase. TRAF6-mediated ubiquitination was required for dissociation of inactive monomeric MLK3 from the scaffold protein IB1/JIP1, facilitating the subsequent dimerization, autophosphorylation, and catalytic activation of MLK3. Inability to ubiquitinate MLK3, or the presence of A20, an upstream Lys-63-linked deubiquitinase, strongly curtailed the ability of MLK3 to affect the proapoptotic translocation of BAX in cytokine-stimulated pancreatic β cells, an early step in the progression toward β cell death. These studies suggest a novel mechanism for MLK3 activation and provide new clues for therapeutic intervention in promoting β cell survival.

Deletion of TAK1 in the myeloid lineage results in the spontaneous development of myelomonocytic leukemia in mice

Previous studies of the conditional ablation of TGF-β activated kinase 1 (TAK1) in mice indicate that TAK1 has an obligatory role in the survival and/or development of hematopoietic stem cells, B cells, T cells, hepatocytes, intestinal epithelial cells, keratinocytes, and various tissues, primarily because of these cells’ increased apoptotic sensitivity, and have implicated TAK1 as a critical regulator of the NF-κB and stress kinase pathways and thus a key intermediary in cellular survival. Contrary to this understanding of TAK1’s role, we report a mouse model in which TAK1 deletion in the myeloid compartment that evoked a clonal myelomonocytic cell expansion, splenomegaly, multi-organ infiltration, genomic instability, and aggressive, fatal myelomonocytic leukemia. Unlike in previous reports, simultaneous deletion of TNF receptor 1 (TNFR1) failed to rescue this severe phenotype. We found that the features of the disease in our mouse model resemble those of human chronic myelomonocytic leukemia (CMML) in its transformation to acute myeloid leukemia (AML). Consequently, we found TAK1 deletion in 13 of 30 AML patients (43%), thus providing direct genetic evidence of TAK1’s role in leukemogenesis.

TAK1 ubiquitination regulates doxorubicin-induced NF-κB activation

Chemotherapeutic agents- and radiation therapy-induced NF-κB activation in cancer cells contributes to aggressive tumor growth and resistance to chemotherapy and ionizing radiation during cancer treatment. TAK1 has been shown to be required for genotoxic stress-induced NF-κB activation. However, whether TAK1 ubiquitination is involved in genotoxic stress-induced NF-κB activation remains unknown. Herein, we demonstrate that TAK1 ubiquitination plays an important role in the positive and negative regulation of doxorubicin (Dox)-induced NF-κB activation. We found that TAK1 was required for Dox-induced NF-κB activation. At the early stage of Dox treatment, Dox induced Lys63-linked TAK1 polyubiquitination at lysine 158 residue. USP4 inhibited Dox-induced TAK1 Lys63-linked polyubiquitination and knockdown of USP4 enhanced Dox-induced NF-κB activation. At the late stage of Dox treatment, Dox induced Lys48-linked TAK1 polyubiquitination to promote TAK1 degradation. ITCH inhibited Dox-induced NF-κB activation by promoting Lys48-linked TAK1 polyubiquitination and its subsequent degradation. Our study indicates that TAK1 ubiquitination plays critical roles in the regulation of Dox-induced NF-κB activation. Thus, intervention of TAK1 kinase activity or TAK1 Lys63-linked polyubiquitination pathways might greatly enhance the therapeutic efficacy of Dox.

Lys48-linked TAK1 polyubiquitination at lysine-72 downregulates TNFα-induced NF-κB activation via mediating TAK1 degradation

Protein kinases are important regulators of intracellular signal transduction pathways and play critical roles in diverse cellular processes. TAK1, a member of the MAPKKK family, is essential for TNFα-induced NF-κB activation. Phosphorylation and Lys(63)-linked polyubiquitination (polyUb) of TAK1 are critical for its activation. However, whether TAK1 is regulated by polyubiquitination-mediated protein degradation after its activation remains unknown. Here we report that TNFα induces TAK1 Lys(48) linked polyubiquitination and degradation at the later time course. Furthermore, we provide direct evidence that TAK1 is modified by Lys(48)-linked polyubiquitination at lysine-72 by mass spectrometry. A K72R point mutation on TAK1 abolishes TAK1 Lys(48)-linked polyubiquitination and enhances TAK1/TAB1 co-overexpression-induced NF-κB activation. As expected, TAK1 K72R mutation inhibits TNFα-induced Lys(48)-linked TAK1 polyubiquitination and degradation. TAK1 K72R mutant prolongs TNFα-induced NF-κB activation and enhances TNFα-induced IL-6 gene expression. Our findings demonstrate that TNFα induces Lys(48)-linked polyubiquitination of TAK1 at lysine-72 and this polyubiquitination-mediated TAK1 degradation plays a critical role in the downregulation of TNFα-induced NF-κB activation.

TGF-β-activated kinase-1: New insights into the mechanism of TGF-β signaling and kidney disease

Transforming growth factor-β (TGF-β) is a multifunctional cytokine that regulates a wide variety of cellular functions, including cell growth, cellular differentiation, apoptosis, and wound healing. TGF-β1, the prototype member of the TGF-β superfamily, is well established as a central mediator of renal fibrosis. In chronic kidney disease, dysregulation of expression and activation of TGF-β1 results in the relentless synthesis and accumulation of extracellular matrix proteins that lead to the development of glomerulosclerosis and tubulointerstitial fibrosis, and ultimately to end-stage renal disease. Therefore, specific targeting of the TGF-β signaling pathway is seemingly an attractive molecular therapeutic strategy in chronic kidney disease. Accumulating evidence demonstrates that the multifunctionality of TGF-β1 is connected with the complexity of its cell signaling networks. TGF-β1 signals through the interaction of type I and type II receptors to activate distinct intracellular pathways. Although the Smad signaling pathway is known as a canonical pathway induced by TGF-β1, and has been the focus of many previous reviews, importantly TGF-β1 also induces various Smad-independent signaling pathways. In this review, we describe evidence that supports current insights into the mechanism and function of TGF-β-activated kinase 1 (TAK1), which has emerged as a critical signaling molecule in TGF-β-induced Smad-independent signaling pathways. We also discuss the functional role of TAK1 in mediating the profibrotic effects of TGF-β1.

Tripartite motif 8 (TRIM8) modulates TNFα- and IL-1β-triggered NF-κB activation by targeting TAK1 for K63-linked polyubiquitination

The tripartite motif (TRIM)-containing proteins are a family of proteins that have been known to be involved in divergent biological processes, including important roles in immune responses through regulating various signaling pathways. In this study, we identified a member of the TRIM family, TRIM8, as a positive regulator of tumor necrosis factor-α (TNFα) and interleukin-1β (IL-1β)-triggered NF-κB activation. Overexpression of TRIM8 activated NF-κB and potentiated TNFα- and IL-1β-induced activation of NF-κB, whereas knockdown of TRIM8 had opposite effects. Coimmunoprecipitations indicated that TRIM8 interacted with TGFβ activated kinase 1 (TAK1), a serine/threonine kinase essential for TNFα- and IL-β-induced NF-κB activation. Furthermore, we found that TRIM8 mediated K63-linked polyubiquitination of TAK1 triggered by TNFα and IL-1β. Our findings demonstrate that TRIM8 serves as a critical regulator of TNFα- and IL-1β-induced NF-κB activation by mediating K63-linked polyubiquitination of TAK1.

USP4 targets TAK1 to downregulate TNFα-induced NF-κB activation

Lys63-linked polyubiquitination of transforming growth factor-β-activated kinase 1 (TAK1) has an important role in tumor necrosis factor-α (TNFα)-induced NF-κB activation. Using a functional genomic approach, we have identified ubiquitin-specific peptidase 4 (USP4) as a deubiquitinase for TAK1. USP4 deubiquitinates TAK1 in vitro and in vivo. TNFα induces association of USP4 with TAK1 to deubiquitinate TAK1 and downregulate TAK1-mediated NF-κB activation. Overexpression of USP4 wild type, but not deuibiquitinase-deficient C311A mutant, inhibits both TNFα- and TAK1/TAB1 co-overexpression-induced TAK1 polyubiquitination and NF-κB activation. Notably, knockdown of USP4 in HeLa cells enhances TNFα-induced TAK1 polyubiquitination, IκB kinase phosphorylation, IκBα phosphorylation and ubiquitination, as well as NF-κB-dependent gene expression. Moreover, USP4 negatively regulates IL-1β-, LPS- and TGFβ-induced NF-κB activation. Together, our results demonstrate that USP4 serves as a critical control to downregulate TNFα-induced NF-κB activation through deubiquitinating TAK1.