TAK1 ubiquitination regulates doxorubicin-induced NF-κB activation

PARVB deficiency alleviates cisplatin-induced tubular injury by inhibiting TAK1 signaling

Cisplatin-induced renal tubular injury largely restricts the wide-spread usage of cisplatin in the treatment of malignancies. Identifying the key signaling pathways that regulate cisplatin-induced renal tubular injury is thus clinically important. PARVB, a focal adhesion protein, plays a crucial role in tumorigenesis. However, the function of PARVB in kidney disease is largely unknown. To investigate whether and how PARVB contributes to cisplatin-induced renal tubular injury, a mouse model (PARVB cKO) was generated in which PARVB gene was specifically deleted from proximal tubular epithelial cells using the Cre-LoxP system. In this study, we found depletion of PARVB in proximal tubular epithelial cells significantly attenuates cisplatin-induced renal tubular injury, including tubular cell death and inflammation. Mechanistically, PARVB associates with transforming growth factor-β-activated kinase 1 (TAK1), a central regulator of cell survival and inflammation that is critically involved in mediating cisplatin-induced renal tubular injury. Depletion of PARVB promotes cisplatin-induced TAK1 degradation, inhibits TAK1 downstream signaling, and ultimately alleviates cisplatin-induced tubular cell damage. Restoration of PARVB or TAK1 in PARVB-deficient cells aggravates cisplatin-induced tubular cell injury. Finally, we demonstrated that PARVB regulates TAK1 protein expression through an E3 ligase ITCH-dependent pathway. PARVB prevents ITCH association with TAK1 to block its ubiquitination. Our study reveals that PARVB deficiency protects against cisplatin-induced tubular injury through regulation of TAK1 signaling and indicates targeting this pathway may provide a novel therapeutic strategy to alleviate cisplatin-induced kidney damage.

Dual-specificity phosphatase 26 protects against kidney injury caused by ischaemia-reperfusion through restraint of TAK1-JNK/p38-mediated apoptosis and inflammation of renal tubular epithelial cells

Dual-specificity phosphatase 26 (DUSP26) acts as a pivotal player in the transduction of signalling cascades with its dephosphorylating activity. Currently, DUSP26 attracts extensive attention due to its particular function in several pathological conditions. However, whether DUSP26 plays a role in kidney ischaemia-reperfusion (IR) injury is unknown. Aims of the current work were to explore the relevance of DUSP26 in kidney IR damage. DUSP26 levels were found to be decreased in renal tubular epithelial cells following hypoxia-reoxygenation (HR) and kidney samples subjected to IR treatments. DUSP26-overexpressed renal tubular epithelial cells exhibited protection against HR-caused apoptosis and inflammation, while DUSP26-depleted renal tubular epithelial cells were more sensitive to HR damage. Upregulation of DUSP26 in rat kidneys by infecting adenovirus expressing DUSP26 markedly ameliorated kidney injury caused by IR, while also effectively reducing apoptosis and inflammation. The mechanistic studies showed that the activation of transforming growth factor-β-activated kinase 1 (TAK1)-JNK/p38 MAPK, contributing to kidney injury under HR or IR conditions, was restrained by increasing DUSP26 expression. Pharmacological restraint of TAK1 markedly diminished DUSP26-depletion-exacebated effects on JNK/p38 activation and HR injury of renal tubular cells. The work reported a renal-protective function of DUSP26, which protects against IR-related kidney damage via the intervention effects on the TAK1-JNK/p38 axis. The findings laid a foundation for understanding the molecular pathogenesis of kidney IR injury and provide a prospective target for treating this condition.

Upregulation of TRIM16 mitigates doxorubicin-induced cardiotoxicity by modulating TAK1 and YAP/Nrf2 pathways in mice

The clinic application of doxorubicin (DOX) is severely limited by its severe cardiotoxicity. Tripartite motif-containing protein 16 (TRIM16) has E3 ubiquitin ligase activity and is upregulated in cardiomyocytes under pathological stress, yet its role in DOX-induced cardiotoxicity remains elusive. This study aims to investigate the role and mechanism of TRIM16 in DOX cardiotoxicity. Following TRIM16 overexpression in hearts with AAV9-TRIM16, mice were intravenously administered DOX at a dose of 4 mg/kg/week for 4 weeks to assess the impact of TRIM16 on doxorubicin-induced cardiotoxicity. Transfection of OE-TRIM16 plasmids and siRNA-TRIM16 was performed in neonatal rat cardiomyocytes (NRCMs). Our results revealed that DOX challenge elicited a significant upregulation of TRIM16 proteins in cardiomyocytes. TRIM16 overexpression efficiently ameliorated cardiac function while suppressing inflammation, ROS generation, apoptosis and fibrosis provoked by DOX in the myocardium. TRIM16 knockdown exacerbated these alterations caused by DOX in NRCMs. Mechanistically, OE-TRIM16 augmented the ubiquitination and degradation of p-TAK1, thereby arresting JNK and p38MAPK activation evoked by DOX in cardiomyocytes. Furthermore, DOX enhanced the interaction between p-TAK1 and YAP1 proteins, resulting in a reduction in YAP and Nrf2 proteins in cardiomyocytes. OE-TRIM16 elevated YAP levels and facilitated its nuclear translocation, thereby promoting Nrf2 expression and mitigating oxidative stress and inflammation. This effect was nullified by siTRIM16 or TAK1 inhibitor Takinib. Collectively, the current study elaborates that upregulating TRIM16 mitigates DOX-induced cardiotoxicity through anti-inflammation and anti-oxidative stress by modulating TAK1-mediated p38 and JNK as well as YAP/Nrf2 pathways, and targeting TRIM16 may provide a novel strategy to treat DOX-induced cardiotoxicity.

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.

Ubiquitin-specific peptidases: Players in bone metabolism

Osteoporosis is an ageing-related disease, that has become a major public health problem and its pathogenesis has not yet been fully elucidated. Substantial evidence suggests a strong link between overall age-related disease progression and epigenetic modifications throughout the life cycle. As an important epigenetic modification, ubiquitination is extensively involved in various physiological processes, and its role in bone metabolism has attracted increasing attention. Ubiquitination can be reversed by deubiquitinases, which counteract protein ubiquitination degradation. As the largest and most structurally diverse cysteinase family of deubiquitinating enzymes, ubiquitin-specific proteases (USPs), comprising the largest and most structurally diverse cysteine kinase family of deubiquitinating enzymes, have been found to be important players in maintaining the balance between bone formation and resorption. The aim of this review is to explore recent findings highlighting the regulatory functions of USPs in bone metabolism and provide insight into the molecular mechanisms governing their actions during bone loss. An in-deep understanding of USPs-mediated regulation of bone formation and bone resorption will provide a scientific rationale for the discovery and development of novel USP-targeted therapeutic strategies for osteoporosis.

Emerging Roles of Non-proteolytic Ubiquitination in Tumorigenesis

Ubiquitination is a critical type of protein post-translational modification playing an essential role in many cellular processes. To date, more than eight types of ubiquitination exist, all of which are involved in distinct cellular processes based on their structural differences. Studies have indicated that activation of the ubiquitination pathway is tightly connected with inflammation-related diseases as well as cancer, especially in the non-proteolytic canonical pathway, highlighting the vital roles of ubiquitination in metabolic programming. Studies relating degradable ubiquitination through lys48 or lys11-linked pathways to cellular signaling have been well-characterized. However, emerging evidence shows that non-degradable ubiquitination (linked to lys6, lys27, lys29, lys33, lys63, and Met1) remains to be defined. In this review, we summarize the non-proteolytic ubiquitination involved in tumorigenesis and related signaling pathways, with the aim of providing a reference for future exploration of ubiquitination and the potential targets for cancer therapies.

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.

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.

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.

GRAMD4 inhibits tumour metastasis by recruiting the E3 ligase ITCH to target TAK1 for degradation in hepatocellular carcinoma

BACKGROUND

Aberrant TAK1 (transforming growth factor β-activated kinase 1) activity is known to be involved in a variety of malignancies, but the regulatory mechanisms of TAK1 remain poorly understood. GRAMD4 (glucosyltransferase Rab-like GTPase activator and myotubularin domain containing 4) is a newly discovered p53-independent proapoptotic protein with an unclear role in HCC (hepatocellular carcinoma).

RESULTS

In this research, we found that GRAMD4 expression was lower in HCC samples, and its downregulation predicted worse prognosis for patients after surgical resection. Functionally, GRAMD4 inhibited HCC migration, invasion and metastasis. Mechanistically, GRAMD4 interacted with TAK1 to promote its protein degradation, thus, resulting in the inactivation of MAPK (Mitogen-activated protein kinase) and NF-κB pathways. Furthermore, GRAMD4 was proved to recruit ITCH (itchy E3 ubiquitin protein ligase) to promote the ubiquitination of TAK1. Moreover, high expression of TAK1 was correlated with low expression of GRAMD4 in HCC patients.

CONCLUSIONS

GRAMD4 inhibits the migration and metastasis of HCC, mainly by recruiting ITCH to promote the degradation of TAK1, which leads to the inactivation of MAPK and NF-κB signalling pathways.

Silencing of METTL3 effectively hinders invasion and metastasis of prostate cancer cells

Background: Since primary prostate cancer (PCa) can advance to the life-threatening metastatic PCa, exploring the molecular mechanisms underlying PCa metastasis is crucial for developing the novel targeted preventive strategies for decreasing the mortality of PCa. RNA N⁶-methyladenosine (m⁶A) is an emerging regulatory mechanism for gene expression and its specific roles in PCa progression remains elusive. Methods: Western blotting, quantitative real-time PCR and immunohistochemical analyses were used to detect target gene expression in PCa cells in vitro and prostate tissues from patients. RNA immunoprecipitation was conducted to analyze the specific binding of mRNA to the target protein. Migration and invasion assays were used to assess the migratory capacities of cancer cells. The correlation between target gene expression and survival rate of PCa patients was analyzed based the TCGA database. Results: We found that total RNA N⁶-methyladenosine (m⁶A) modification levels were markedly upregulated in human PCa tissues due to increased expression of methyltransferase like 3 (METTL3). Further studies revealed that the migratory and invasive capacities of PCa cells were markedly suppressed upon METTL3 knockdown. Mechanistically, METTL3 mediates m⁶A modification of USP4 mRNA at A2696, and m⁶A reader protein YTHDF2 binds to and induces degradation of USP4 mRNA by recruiting RNA-binding protein HNRNPD to the mRNA. Decrease of USP4 fails to remove the ubiquitin group from ELAVL1 protein, resulting in a reduction of ELAVL1 protein. Lastly, downregulation of ELAVL1 in turn increases ARHGDIA expression, promoting migration and invasion of PCa cells. Conclusions: Our findings highlight the role of METTL3 in modulating invasion and metastasis of PCa cells, providing insight into promising therapeutic strategies for hindering PCa progressing to deadly metastases.

Negative Regulation of the Innate Immune Response through Proteasomal Degradation and Deubiquitination

The rapid and dynamic activation of the innate immune system is achieved through complex signaling networks regulated by post-translational modifications modulating the subcellular localization, activity, and abundance of signaling molecules. Many constitutively expressed signaling molecules are present in the cell in inactive forms, and become functionally activated once they are modified with ubiquitin, and, in turn, inactivated by removal of the same post-translational mark. Moreover, upon infection resolution a rapid remodeling of the proteome needs to occur, ensuring the removal of induced response proteins to prevent hyperactivation. This review discusses the current knowledge on the negative regulation of innate immune signaling pathways by deubiquitinating enzymes, and through degradative ubiquitination. It focusses on spatiotemporal regulation of deubiquitinase and E3 ligase activities, mechanisms for re-establishing proteostasis, and degradation through immune-specific feedback mechanisms vs. general protein quality control pathways.

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 Inhibitor Enhances the Therapeutic Treatment for Glioblastoma

Glioblastoma (GBM) is a brain tumor characterized by poor therapeutic response and overall survival. Despite relevant progress in conventional treatments represented by the clinical use of temozolomide (TMZ), a combination of approaches might be a possible future direction for treating GBM. Transforming growth factor-beta-activated kinase-1 (TAK1) is an essential component in genotoxic stresses-induced NF-κB-activation and mitogen-activated protein kinase (MAPK)-pathways; however, the role of TAK1 in GBM-chemoresistance remains unknown. This study aimed to verify, in GBM human cell lines, in an in vivo U87-xenograft model and in TMZ-treated-patients, the effect of TAK1 inhibition on the sensitivity of GBM cells to chemotherapy. In vitro model, using GBM cell lines, showed that 5Z-7-oxozeaenol augmented the cytotoxic effects of TMZ, blocking TMZ-induced NF-κB-activation, reducing DNA-damage and enhancing TMZ-induced apoptosis in GMB cell lines. We showed a reduction in tumor burden as well as tumor volume in the xenograft model following the treatment with 5Z-7-oxozaenol associated with TMZ. Our results showed a significant up-regulation in TAK1, p-p38, p-JNK and NF-κB in glioblastoma TMZ-treated-patients and denoted the role of 5Z-7-oxozeaenol in increasing the sensitivity of GBM cells to chemotherapy, proving to be an effective coadjuvant to current GBM chemotherapeutic regimens, suggesting a new option for therapeutic treatment of GBM.

The BTB-TAZ protein MdBT2 negatively regulates the drought stress response by interacting with the transcription factor MdNAC143 in apple

Drought stress is a severe source of abiotic stress that can affect apple yield and quality, yet the underlying molecular mechanism of the drought stress response and the role of MdBT2 in the process remain unclear. Here, we find that MdBT2 negatively regulates the drought stress response. Both in vivo and in vitro assays indicated that MdBT2 interacted physically with and ubiquitinated MdNAC143, a member of the NAC TF family that is a positive regulator under drought stress. In addition, MdBT2 promotes the degradation of MdNAC143 via the 26S proteasome system. A series of transgenic assays in apple calli and Arabidopsis verify that MdBT2 confers susceptibility to drought stress at least in part by the regulation of MdNAC143. Overall, our findings provide new insight into the mechanism of MdBT2, which functions antagonistically to MdNAC143 in regulating drought stress by regulating the potential downstream target protein MdNAC143 for proteasomal degradation in apple.

Blockade of p38 kinase impedes the mobilization of protumorigenic myeloid populations to impact breast cancer metastasis

Patients with metastatic breast cancer (MBC) have limited therapeutic options and novel treatments are critically needed. Prior research implicates tumor-induced mobilization of myeloid cell populations in metastatic progression, as well as being an unfavorable outcome in MBC; however, the underlying mechanisms for these relationships remain unknown. Here, we provide evidence for a novel mechanism by which p38 promotes metastasis. Using triple-negative breast cancer models, we showed that a selective inhibitor of p38 (p38i) significantly reduced tumor growth, angiogenesis, and lung metastasis. Importantly, p38i decreased the accumulation of myeloid populations, namely, myeloid-derived suppressor cells (MDSCs) and CD163+ tumor-associated macrophages (TAMs). p38 controlled the expression of tumor-derived chemokines/cytokines that facilitated the recruitment of protumor myeloid populations. Depletion of MDSCs was accompanied by reduced TAM infiltration and phenocopied the antimetastatic effects of p38i. Reciprocally, p38i increased tumor infiltration by cytotoxic CD8+ T cells. Furthermore, the CD163+ /CD8+ expression ratio inversely correlated with metastasis-free survival in breast cancer, suggesting that targeting p38 may improve clinical outcomes. Overall, our study highlights a previously unknown p38-driven pathway as a therapeutic target in MBC.

USP4 function and multifaceted roles in cancer: a possible and potential therapeutic target

Cancer remains one of the major culprits causing disease-related deaths and leads to a high morbidity and similar mortality. Insidious onset, difficult early detection and a lack of broad-spectrum and effective multi-cancer therapeutic targets have limited the prolongation of cancer patients’ survival for decades. Therefore, a versatile therapeutic target which is involved in various cancer-related signaling pathways and different cancers may be more effective for cancer targeted therapy. USP4, one of the DUBs members which participates in deubiquitination, an inverse process of ubiquitination, can regulate various classical cancer-related signaling pathways, and thereby plays a vital role in some pathological and physiological processes including tumor initiation and progression. Recently, USP4 has been found to exert versatile influences on cells proliferation, migration and invasion, also apoptosis of various tumors. Moreover, USP4 can also act as a prognostic biomarker in several cancers. This review will give a comprehensive introduction of USP4 about its regulatory mechanisms, related signaling pathways, pathophysiological functions and the roles in various cancers which may help us better understand its biological functions and improve future studies to construct suitable USP4-targeted cancer therapy system.

The p38-interacting protein p38IP suppresses TCR and LPS signaling by targeting TAK1

Negative regulation of immunoreceptor signaling is required for preventing hyperimmune activation and maintaining immune homeostasis. The roles of p38IP in immunoreceptor signaling remain unclear. Here, we show that p38IP suppresses T-cell receptor (TCR)/LPS-activated NF-κB and p38 by targeting TAK1 kinase and that p38IP protein levels are downregulated in human PBMCs from rheumatoid arthritis (RA) patients, inversely correlating with the enhanced activity of NF-κB and p38. Mechanistically, p38IP interacts with TAK1 to disassemble the TAK1-TAB (TAK1-binding protein) complex. p38IP overexpression decreases TCR-induced binding of K63-linked polyubiquitin (polyUb) chains to TAK1 but increases that to TAB2, and p38IP knockdown shows the opposite effects, indicating unanchored K63-linked polyUb chain transfer from TAB2 to TAK1. p38IP dynamically interacts with TAK1 upon stimulation, because of the polyUb chain transfer and the higher binding affinity of TAK1 and p38IP for polyUb-bound TAB2 and TAK1, respectively. Moreover, p38IP scaffolds the deubiquitinase USP4 to deubiquitinate TAK1 once TAK1 is activated. These findings reveal a novel role and the mechanisms of p38IP in controlling TCR/LPS signaling and suggest that p38IP might participate in RA pathogenesis.

TAK1 signaling regulates p53 through a mechanism involving ribosomal stress

Triple-negative breast cancer (TNBC) is among the most aggressive forms of breast cancer with limited therapeutic options. TAK1 is implicated in aggressive behavior of TNBC, while means are not fully understood. Here, we report that pharmacological blockade of TAK1 signaling hampered ribosome biogenesis (RBG) by reducing expression of RBG regulators such as RRS1, while not changing expression of ribosomal core proteins. Notably, TAK1 blockade upregulated expression of p53 target genes in cell lines carrying wild type (wt) TP53 but not in p53-mutant cells, suggesting involvement of ribosomal stress in the response. Accordingly, p53 activation by blockade of TAK1 was prevented by depletion of ribosomal protein RPL11. Further, siRNA-mediated depletion of TAK1 or RELA resulted in RPL11-dependent activation of p53 signaling. Knockdown of RRS1 was sufficient to disrupt nucleolar structures and resulted in activation of p53. TCGA data showed that TNBCs express high levels of RBG regulators, and elevated RRS1 levels correlate with unfavorable prognosis. Cytotoxicity data showed that TNBC cell lines are more sensitive to TAK1 inhibitor compared to luminal and HER2+ cell lines. These results show that TAK1 regulates p53 activation by controlling RBG factors, and the TAK1-ribosome axis is a potential therapeutic target in TNBC.

miR-34b/c regulates doxorubicin-induced myocardial cell injury through ITCH

Objective: To determine the underlying mechanism of miR-34b/c in regulating doxorubicin (Dox)-induced myocardial cell injury.Methods: The viability of mouse myocardial cells HL-1 was detected by MTT assay. The apoptosis of HL-1 cells was detected by TUNEL assay. mRNA expressions of ITCH, TNF-α and IL-6 were measured by qRT-PCR. Protein levels of ITCH, NF-κB, TNF-α and IL-6 were measured by western blot. Dual luciferase assay was performed to detect the regulation of miR-34b/c on ITCH. Mouse model of cardiomyopathy was induced by intraperitoneal injection of Dox.Results: Dox reduced HL-1 cell viability and activated NF-κB pathway in HL-1 cells. miR-34b/c expressions were gradually up-regulated and ITCH expression was gradually down-regulated in Dox-treated HL-1 cells. miR-34b/c expression had negative correlation with the mRNA expression of ITCH. Besides, ITCH was a target of miR-34b/c. miR-34b/c mimic reduced cell viability, suppressed ITCH expression, increased TNF-α and IL-6 level, and promoted NF-κB expression in nucleus and cytoplasm of HL-1 cells. Whereas silencing miR-34 protected HL-1 cells through regulating ITCH. Finally, we demonstrated miR-34 antagomir-protected myocardial cells in mouse model of cardiomyopathy.Conclusion: miR-34b/c decreased HL-1 cell viability and promoted the secretion of proinflammatory cytokines in Dox-induced myocardial cells through ITCH/NF-κB pathway.

Synthesis of Isosteviol analogues as potential protective agents against Doxorubicin-induced cardiomyopathy in zebrafish embryos

Doxorubicin (DOX) is a powerful anthracycline antibiotic agent which is widely used to treat various types of cancers. Despite efficacy, it displays severe cardiotoxic side effects. Discovery of novel and effective protective agents against DOX-induced cardiotoxicity has been a subject of great interest. Herein, we report the synthesis of two series of analogues of Isosteviol (ISV) 1 with modifications at C-16, C-19 positions as the first series and at C-15, C-16 positions as the other series. Interestingly second series analogues have shown a potential protective effect against DOX-induced cardiotoxicity in zebrafish embryos in vivo. Further, we have demonstrated that the synthesized new analogues of ISV, prevented the morphological distortions caused due to DOX cardiotoxicity in zebrafish heart and the associated cardiac impairments.

Suppression of the Ubiquitin Pathway by Small Molecule Binding to Ubiquitin Enhances Doxorubicin Sensitivity of the Cancer Cells

Development of inhibitors for ubiquitin pathway has been suggested as a promising strategy to treat several types of cancers, which has been showcased by recent success of a series of novel anticancer drugs based on inhibition of ubiquitin pathways. Although the druggability of enzymes in ubiquitin pathways has been demonstrated, ubiquitin itself, the main agent of the pathway, has not been targeted. Whereas conventional enzyme inhibitors are used to silence the ubiquitination or reverse it, they cannot disrupt the binding activity of ubiquitin. Herein, we report that the scaffolds of sulfonated aryl diazo compounds, particularly Congo red, could disrupt the binding activity of ubiquitin, resulting in the activity equivalent to inhibition of ubiquitination. NMR mapping assay demonstrated that the chemical directly binds to the recognition site for ubiquitin processing enzymes on the surface of ubiquitin, and thereby blocks the binding of ubiquitin to its cognate receptors. As a proof of concept for the druggability of the ubiquitin molecule, we demonstrated that Congo red acted as an intracellular inhibitor of ubiquitin recognition and binding, which led to inhibition of ubiquitination, and thereby, could be used as a sensitizer for conventional anticancer drugs, doxorubicin.

USP4 deficiency exacerbates hepatic ischaemia/reperfusion injury via TAK1 signalling

Ubiquitin-specific peptidase 4 (USP4) protein is a type of deubiquitination enzyme that is correlated with many important biological processes. However, the function of USP4 in hepatic ischaemia/reperfusion (I/R) injury remains unknown. The aim of the present study was to explore the role of USP4 in hepatic I/R injury. USP4 gene knockout mice and primary hepatocytes were used to construct hepatic I/R models. The effect of USP4 on hepatic I/R injury was examined via pathological and molecular analyses. Our results indicated that USP4 was significantly up-regulated in liver of mice subjected to hepatic I/R injury. USP4 knockout mice exhibited exacerbated hepatic I/R injury, as evidenced by enhanced liver inflammation via the nuclear factor κB (NF-κB) signalling pathway and increased hepatocyte apoptosis. Additionally, USP4 overexpression inhibited hepatocyte inflammation and apoptosis on hepatic I/R stimulation. Mechanistically, our study demonstrates that USP4 deficiency exerts its detrimental effects on hepatic I/R injury by inducing activation of the transforming growth factor β-activated kinase 1 (TAK1)/JNK signalling pathways. TAK1 was required for USP4 function in hepatic I/R injury as TAK1 inhibition abolished USP4 function in vitro In conclusion, our study demonstrates that USP4 deficiency plays a detrimental role in hepatic I/R injury by promoting activation of the TAK1/JNK signalling pathways. Modulation of this axis may be a novel strategy to alleviate the pathological process of hepatic I/R injury.

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.

Evidence for the Involvement of the Master Transcription Factor NF-κB in Cancer Initiation and Progression

Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) is responsible for the regulation of a large number of genes that are involved in important physiological processes, including survival, inflammation, and immune responses. At the same time, this transcription factor can control the expression of a plethora of genes that promote tumor cell proliferation, survival, metastasis, inflammation, invasion, and angiogenesis. The aberrant activation of this transcription factor has been observed in several types of cancer and is known to contribute to aggressive tumor growth and resistance to therapeutic treatment. Although NF-κB has been identified to be a major contributor to cancer initiation and development, there is evidence revealing its role in tumor suppression. This review briefly highlights the major mechanisms of NF-κB activation, the role of NF-κB in tumor promotion and suppression, as well as a few important pharmacological strategies that have been developed to modulate NF-κB function.

Next-generation proteasome inhibitor oprozomib enhances sensitivity to doxorubicin in triple-negative breast cancer cells

Doxorubicin (DOX) is the most common chemotherapeutic drug for treatment of breast cancer but intrinsic and acquired resistance frequently occurs and severe side effects occur at high doses. DOX might induce activation of NF-κB causing this resistance, in which case proteasome inhibitors could inhibit activation of NF-κB by blocking inhibitory factor κB-alpha degradation. Triple-negative breast cancer (TNBC) is highly progressive and there are no established therapeutic targets against TNBC. Although some proteasome inhibitors have been shown to have antitumor effects in breast cancer, the effect of orally bioavailable proteasome inhibitor oprozomib on TNBC proliferation remains unclear. In the present study, we investigated the role of oprozomib in two TNBC lines, MDA-MB-231 and BT-549. Oprozomib had cytotoxic effects on TNBC cells and increased DOX-induced cytotoxic effects and apoptosis by enhancing DOX-induced JNK/p38 MAPK phosphorylation and inhibiting DOX-induced inhibitory factor êB alpha degradation. These results suggest that oprozomib has potent antitumor effects on TNBC in vitro and can sensitize TNBC cells to DOX treatment. The combination of DOX and oprozomib may be an effective and feasible therapeutic option for TNBC.

Inhibitor of Tec kinase, LFM-A13, decreases pro-inflammatory mediators production in LPS-stimulated RAW264.7 macrophages via NF-κB pathway

Tec kinase, a prototypical member of the Tec tyrosine kinases family, was shown to mainly govern lymphocyte proliferation. In the present study, we investigated the role of Tec kinase in acute inflammatory response in lipopolysaccharide (LPS) challenge. First, we demonstrate that Tec kinase activity was observed in RAW264.7 macrophages exposed to LPS. Tec and phosphorylated Tec expression were upregulated in a dose- and time-dependent manner after LPS stimulation. LPS increased monocyte chemotactic protein (MCP)-1 secretion and intercellular adhesion molecule (ICAM)-1 expression, and increasing mRNA expression was consistently observed. LPS also induced IκBα phoshporylaytion and its degradation, increased NF-κB p65 phoshporylaytion and translocation to nuclei in RAW264.7 cells. Pretreatment with LFM-A13 decreased LPS-induced cytokines and chemokines production and mRNA levels, blocked NF-κB transactivation. These effects of LPS were also prevented by Tec-siRNA. Additionally, LFM-A13 or Tec-siRNA obviously inhibited LPS-induced TGFβ-activated kinase 1(TAK1) phosphorylation. Taken together, our results suggest that Tec kinase involves in acute inflammation process in LPS-stimulated RAW264.7 cells, at least mediated by activating TAK1/ NF-κB signal pathway.

TAK1 inhibitor 5Z-7-oxozeaenol sensitizes cervical cancer to doxorubicin-induced apoptosis

Aberrant activation of nuclear factor-κB (NF-κB) allows cancer cells to escape chemotherapy-induced cell death and acts as one of the major mechanisms of acquired chemoresistance in cervical cancer. TAK1, a crucial mediator that upregulates NF-κB activation in response to cellular genotoxic stress, is required for tumor cell viability and survival. Herein, we examined whether TAK1 inhibition is a potential therapeutic strategy for treating cervical cancer. We found that TAK1 inhibitor 5Z-7-oxozeaenol significantly augmented the cytotoxic effects of Dox in a panel of cervical cancer cell lines. Treatment with 5Z-7-oxozeaenol hindered Dox-induced NF-κB activation and promoted Dox-induced apoptosis in cervical cancer cells. Moreover, 5Z-7-oxozeaenol showed similar effects in both positive and negative human papillomavirus-infected cervical cancer cells. Taken together, our results provide evidence that TAK1 inhibition significantly sensitizes cervical cancer cells to chemotherapy-induced cell death and supports the use of TAK1 inhibitor with current chemotherapies in the clinic for patients with refractory cervical cancer.

Second-generation proteasome inhibitor carfilzomib enhances doxorubicin-induced cytotoxicity and apoptosis in breast cancer cells

Proteasome inhibition is an attractive approach for anticancer therapy. Doxorubicin (DOX) is widely used for treatment in a number of cancers including breast cancer; however, the development of DOX resistance largely limits its clinical application. One of the possible mechanisms of DOX-resistance is that DOX might induce the activation of NF-κB. In this case, proteasome inhibitors could inhibit the activation of NF-κB by blocking inhibitory factor κB (IκB) degradation. Carfilzomib, a second-generation proteasome inhibitor, overcomes bortezomib resistance and lessens its side-effects. Currently, the effect of carfilzomib on breast cancer cell proliferation remains unclear. In this study, we exploited the role of carfilzomib in seven breast cancer cell lines, MCF7, T-47D, MDA-MB-361, HCC1954, MDA-MB-468, MDA-MB-231, and BT-549, representing all major molecular subtypes of breast cancer. We found that carfilzomib alone had cytotoxic effects on the breast cancer cells and it increased DOX-induced cytotoxic effects and apoptosis in combination by enhancing DOX-induced JNK phosphorylation and inhibiting DOX-induced IκBα degradation. The results suggest that carfilzomib has potent antitumor effects on breast cancer in vitro and can sensitize breast cancer cells to DOX treatment. DOX in combination with carfilzomib may be an effective and feasible therapeutic option in the clinical trials for treating breast cancer.

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.

Inhibition of transforming growth factor β-activated kinase 1 prevents inflammation-related cartilage degradation in osteoarthritis

Osteoarthritis (OA) is a common debilitating joint disorder, there’s still no available disease-modifying drug for OA currently. This study aims to explore the role of TAK1 in OA pathogenesis and therapeutic efficiency of TAK1 inhibition for OA. The contribution of TAK1 to OA pathogenesis was investigated by intra-articular injection of TAK1-encoding adenovirus in rats. TAK1 inhibitor 5Z-7-induced expression changes of extracellular matrix (ECM)-related genes were detected by real-time PCR. The protective effect of 5Z-7 against OA progression was evaluated in a post-traumatic OA rat model. Our results showed that intra-articular injection of Ad-Tak1 induced cartilage destruction and OA-related cytokine secretion in rat joints. TAK1 inhibition by 5Z-7 efficiently blocked NF-κB, JNK and p38 pathways activation in OA chondrocytes and synoviocytes, Meanwhile, 5Z-7 significantly decreased the expression of matrix-degrading enzymes and pro-inflammatory cytokine, while increased ECM protein expression, which are all crucial components in OA. 5Z-7 also ameliorated ECM loss in OA cartilage explants. More importantly, 5Z-7 significantly protected against cartilage destruction in a rat model of OA. In conclusion, our findings provide the first in vivo evidence that TAK1 contributes to OA by disrupting cartilage homeostasis, thus represents an ideal target for OA treatment, with 5Z-7 as a candidate therapeutic.

The E3 ligase Itch in immune regulation and beyond

Itch or itchy E3 ubiquitin ligase was initially discovered by genetic studies on the mouse coat color changes, and its deletion results in an itchy phenotype with constant skin scratching and multi-organ inflammation. It is a member of the homologous to E6-associated protein C-terminus (HECT)-type family of E3 ligases, with the protein-interacting WW-domains for the recruitment of substrate and the HECT domain for the transfer of ubiquitin to the substrate. Since its discovery, numerous studies have demonstrated that Itch is involved in the control of many aspects of immune responses including T-cell activation and tolerance and T-helper cell differentiation. Itch is also implicated in other biological contexts such as tumorigenesis, development, and stress responses. Many signaling pathways are regulated by Itch-promoted ubiquitylation of diverse target proteins. Itch is also involved in human diseases. Here, we discuss the major progress in understanding the biological significance of Itch-promoted protein ubiquitylation in the immune and other systems and in Itch-mediated regulation of signal transduction.

Next-generation proteasome inhibitor MLN9708 sensitizes breast cancer cells to doxorubicin-induced apoptosis

Doxorubicin (Dox), one of the most effective chemotherapy drug for cancer treatment, is limited by its severe side effects and chemoresistance. Dox induces DNA damage and leads to significant proteomic changes in the cancer cells, which makes the ubiquitin-proteasome system a potential target to enhance the efficacy of Dox therapy. The unsuccessful clinical trials of proteasome inhibitor PS-341 (bortezomib) in solid tumors led to the invention of MLN9708 (ixazomib), an orally bioavailable next-generation proteasome inhibitor with improved pharmacokinetic and pharmacodynamic features. In this preclinical study, we used eight human breast cancer cell lines, which represent the major molecular subtypes of breast cancer, to validate the cytotoxic effects of MLN9708, alone and in combination with Dox. We found that MLN9708 had cytotoxic effects, induced autophagy and MKP-1 expression, and enhanced Dox-induced apoptosis in these cell lines. MLN9708 also enhanced Dox-induced JNK and p38 phosphorylation and inhibited Dox-induced IκBα degradation. Our in vitro results suggest that MLN9708 has antitumor effects in breast cancer and can sensitize breast cancer cells to Dox treatment. This promising combination may be an effective and feasible therapeutic option for treating breast cancer and warrants clinical validation.

Novel Lys63-linked ubiquitination of IKKβ induces STAT3 signaling

NFκB signaling plays a significant role in human disease, including breast and ovarian carcinoma, insulin resistance, embryonic lethality and liver degeneration, rheumatoid arthritis, aging and Multiple Myeloma (MM). Inhibitor of κB (IκB) kinase β (IKKβ) regulates canonical Nuclear Factor κB (NFκB) signaling in response to inflammation and cellular stresses. NFκB activation requires Lys63-linked (K63-linked) ubiquitination of upstream proteins such as NEMO or TAK1, forming molecular complexes with membrane-bound receptors. We demonstrate that IKKβ itself undergoes K63-linked ubiquitination. Mutations in IKKβ at Lys171, identified in Multiple Myeloma and other cancers, lead to a dramatic increase in kinase activation and K63-linked ubiquitination. These mutations also result in persistent activation of STAT3 signaling. Liquid chromatography (LC)-high mass accuracy tandem mass spectrometry (MS/MS) analysis identified Lys147, Lys418, Lys555 and Lys703 as predominant ubiquitination sites in IKKβ. Specific inhibition of the UBC13-UEV1A complex responsible for K63-linked ubiquitination establishes Lys147 as the predominant site of K63-ubiquitin conjugation and responsible for STAT3 activation. Thus, IKKβ activation leads to ubiquitination within the kinase domain and assemblage of a K63-ubiquitin conjugated signaling platform. These results are discussed with respect to the importance of upregulated NFκB signaling known to occur frequently in MM and other cancers.

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.

TAK1 inhibitor 5Z-7-oxozeaenol sensitizes neuroblastoma to chemotherapy

Treatment failure in high risk neuroblastoma is largely due to development of chemoresistance. NF-κB activation is one of the resistance mechanisms for cancer cells to escape from chemotherapy-induced cell-death. TAK1 is an essential component in genotoxic stresses-induced NF-κB activation; however, the role of TAK1 in the development of chemoresistance in neuroblastoma remains unknown. Using a panel of neuroblastoma cell lines, we found that TAK1 inhibitor 5Z-7-oxozeaenol significantly augmented the cytotoxic effects of doxorubicin (Dox) and etoposide (VP-16) on neuroblastoma cell lines. TAK1 inhibition also enhanced the inhibitory effect of Dox and VP-16 on anchorage-independent growth. Treatment of neuroblastoma cells with 5Z-7-oxozeaenol blocked Dox- and VP16-induced NF-κB activation and enhanced Dox- and VP16-induced apoptosis. Moreover, 5Z-7-oxozeaenol was able to overcome the established chemoresistance in LA-N-6 neuroblastoma cells. Using an orthotopic neuroblastoma mouse model, we found that 5Z-7-oxozeaenol significantly enhanced chemotherapeutic efficacy in vivo. Together, our results provide a proof-of-concept that TAK1 inhibition significantly increases the sensitivity of neuroblastoma cells to chemotherapy-induced cell-death and can serve as an effective adjunct to current chemotherapeutic regimens for high risk diseases.

Deubiquitylating enzymes and DNA damage response pathways

Covalent post-translational modification of proteins by ubiquitin and ubiquitin-like factors has emerged as a general mechanism to regulate myriad intra-cellular processes. The addition and removal of ubiquitin or ubiquitin-like proteins from factors has recently been demonstrated as a key mechanism to modulate DNA damage response (DDR) pathways. It is thus, timely to evaluate the potential for ubiquitin pathway enzymes as DDR drug targets for therapeutic intervention. The synthetic lethal approach provides exciting opportunities for the development of targeted therapies to treat cancer: most tumours have lost critical DDR pathways, and thus rely more heavily on the remaining pathways, while normal tissues are still equipped with all DDR pathways. Here, we review key deubiquitylating enzymes (DUBs) involved in DDR pathways, and describe how targeting DUBs may lead to selective therapies to treat cancer patients.

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.

Taraxerol inhibits LPS-induced inflammatory responses through suppression of TAK1 and Akt activation

Taraxerol, a triterpenoid compound, has potent anti-inflammatory effects. However, the molecular mechanisms are not clear. In the study, taraxerol concentration dependently inhibited nitric-oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) at the protein and mRNA levels and these inhibitions decreased the production of nitric oxide (NO), prostaglandin 2 (PGE2), tumor necrosis factor-α (TNF-α), interleukin (IL)-6, and IL-1β induced by LPS. Furthermore, we found that taraxerol suppressed translocation of nuclear factor-κB (NF-κB), phosphorylation of IκBα, blocked the IκBα degradation as well as IKK and mitogen-activated protein kinase (MAPK) activation by inactivation of TGF-β-activated kinase-1 (TAK1) and Akt. In addition, taraxerol significantly inhibited the formation of TAK1/TAK-binding protein1 (TAB1), which was accompanied by inducing degradation of TAK1, decreasing LPS-induced polyubiquitination of TAK1 as well as TAK1 phosphorylation. Taken together, our data suggest that taraxerol downregulates the expression of proinflammatory mediators in macrophages by interfering with the activation of TAK1 and Akt, thus preventing NF-κB activation.