Identification of a human NF-kappaB-activating protein, TAB3

The ubiquitin-like protein FAT10 in hepatocellular carcinoma cells limits the efficacy of anti-VEGF therapy

INTRODUCTION

The efficacy of anti-vascular endothelial growth factor (VEGF) therapy is limited. However, the key factors involved in limiting the efficacy of anti-VEGF therapy and the underlying mechanisms remain unclear.

OBJECTIVES

To investigate the effects and mechanisms of human leukocyte antigen F locus-adjacent transcript 10 (FAT10), a ubiquitin-like protein, in limiting the efficacy of anti-VEGF therapy in hepatocellular carcinoma (HCC) cells.

METHODS

FAT10 was knocked out in HCC cells using the clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein 9 technology. Bevacizumab (BV), an anti-VEGF monoclonal antibody, was used to evaluate the efficacy of anti-VEGF therapy in vivo. Mechanisms of FAT10 action were assessed by RNA sequencing, glutathione S-transferase pulldown assays and in vivo ubiquitination assays.

RESULTS

FAT10 accelerated VEGF-independent angiogenesis in HCC cells which limited BV efficacy and BV-aggravated hypoxia and inflammation promoted FAT10 expression. FAT10 overexpression increased levels of proteins involved in several signaling pathways in HCC cells, resulting in upregulation of VEGF and multiple non-VEGF proangiogenic factors. Upregulation of multiple FAT10-mediated non-VEGF signals compensated for the inhibition of VEGF signaling by BV, enhancing VEGF-independent angiogenesis and promoting HCC growth.

CONCLUSIONS

Our preclinical findings identify FAT10 in HCC cells as a key factor limiting the efficacy of anti-VEGF therapy and elucidate its underlying mechanisms. This study provides new mechanistic insights into the development of antiangiogenic therapies.

TGFβ1-driven SMAD2/3 phosphorylation and myofibroblast emergence are fully dependent on the TGFβ1 pre-activation of MAPKs and controlled by maternal leucine zipper kinase

Following wounding, endogenously secreted TGFβs drive resident and bone marrow-derived cells to convert into α-smooth actin (SMA)-rich, contractile myofibroblasts. The TGFβ effect is initiated by the phosphorylation of SMADs 2 and 3 (SMAD2/3). This event has been referred to as the canonical response to TGFβ. TGFβ also elicits other responses viewed as parallel events not directly connected to the SMAD activation, and thus referred to as noncanonical. A recognized response is the phosphorylation of the -activated kinase (TAK1/MAP3K), an upstream component of the mitogen-activated protein kinase (MAPK) cascade. We have now examined the relationship between these two effects of TGFβ1 at their earliest stages. The bulk of the studies were carried out with primary fibroblasts derived from the human cornea. The results' widespread relevance was confirmed in critical experiments with dermal-, and Tenon's capsule-derived fibroblasts. Cells were treated with kinase inhibitors or targeting siRNAs followed by induction by 2 ng/ml TGFβ1, and/or 10 ng/ml TNF-α. Cells were collected after 1 to 30 min for Western blot analysis and assayed for the accumulation of phosphorylated TAK1, ASK1, JNK1/2, p38, HPS27, MELK, SMAD2/3, and GAPDH. The effect of the kinase inhibitors on α-SMA expression and α-SMA stress fiber organization was also tested. For the immediate response to TGFβ1 we found that a) activation of the MAPK pathway was completed within 1 min after the addition of TGFβ1; b) phosphorylation of JNK1/2 was fully dependent on TAK1 and ASK1 activity, c) phosphorylation of MELK was fully dependent on JNK1/2 activity; d) phosphorylation of ASK1 depends on MELK activity, indicating the existence of an ASK1-MELK positive activation feedback loop; e) phosphorylation of SMAD2/3 started only after a 5 min period and reached a nadir after 10-15 min, f) the latter phosphorylation was fully blocked by inhibition of TAK1, ASK1, JNK1/2, and MELK, and siRNA-driven MELK downregulation; g) the inhibitors equally blocked the α-SMA protein expression, stress fiber development, and cell morphology changes at 72 h. These results demonstrate that the activation of the canonical pathway is fully subordinate to the activity of the MAPK pathway, challenging the concept of canonical and noncanonical TGFβ pathways and that SMAD2/3 activation is mediated by MELK, a kinase not previously associated with rapid pharmacological responses.

Autophagy suppression facilitates macrophage M2 polarization via increased instability of NF-κB pathway in hepatocellular carcinoma

The tumor microenvironment is a highly heterogeneous circumstance composed of multiple components, while tumor-associated macrophages (TAMs) are major innate immune cells with highly plastic and are always educated by tumor cells to structure an advantageous pro-tumor immune microenvironment. Despite emerging evidence focalizing the role of autophagy in other immune cells, the regulatory mechanism of autophagy in macrophage polarization remains poorly understood. Herein, we demonstrated that hepatocellular carcinoma (HCC) cells educated macrophages toward M2-like phenotype polarization under the condition of coculture. Moreover, we observed that inhibition of macrophage autophagy promoted M2-like macrophage polarization, while the tendency was impeded when autophagy was motivated. Mechanistically, macrophage autophagy inhibition inactivates the NF-κB pathway by increasing the instability of TAB3 via ubiquitination degradation, which leads to the M2-like phenotype polarization of macrophages. Both immunohistochemistry staining using human HCC tissues and experiment in vivo verified autophagy inhibition is correlated with M2 macrophage polarization. Altogether, we illustrated that macrophage autophagy was involved in the process of HCC cells domesticating M2 macrophage polarization via the NF-κB pathway. These results provide a new target to interfere with the polarization of macrophages to M2-like phenotype during HCC progression.

Macrophages-derived exosomes modulates wear particle-induced osteolysis via miR-3470b targeting TAB3/NF-κB signaling

Image 1.

miR‑27a‑3p upregulation by p65 facilitates cervical tumorigenesis by increasing TAB3 expression and is involved in the positive feedback loop of NF‑κB signaling

An altered microRNA (miRNA/miR)‑27a‑3p expression has been identified in cervical cancer, while the exact regulatory mechanisms responsible for the dysregulation of miR‑27a‑3p remain to be fully elucidated. In the present study, a NF‑κB/p65 binding site was identified upstream of the miR‑23a/27a/24‑2 cluster and p65 binding enhanced the transcription of pri‑miR‑23a/27a/24‑2, as well as the expression levels of mature miRNAs, including miR‑27a‑3p in HeLa cells. Mechanistically, using bioinformatics analyses and experimental validation, TGF‑β activated kinase 1 binding protein 3 (TAB3) was identified as a direct target of miR‑27a‑3p. By binding to the 3'UTR of TAB3, miR‑27a‑3p significantly enhanced TAB3 expression. Functionally, it was found that the overexpression of miR‑27a‑3p and TAB3 promoted the malignant potential of cervical cancer cells, as evaluated using cell growth, migration and invasion assays, and specific cell marker determinations in the epithelial mesenchymal transition progression, and vice versa. Further rescue experiments revealed that the enhanced malignant effects induced by miR‑27a‑3p were mediated via its upregulation of TAB3 expression. Moreover, miR‑27a‑3p and TAB3 also activated the NF‑κB signaling pathway and formed a positive feedback regulatory loop composing of p65/miR‑27a‑3p/TAB3/NF‑κB. On the whole, the findings presented herein may provide novel insight into the underlying cervical tumorigenesis and novel biomarker identification for clinical applications.

A Novel Look at Dosage-Sensitive Sex Locus Xp21.2 in a Case of 46,XY Partial Gonadal Dysgenesis without NR0B1 Duplication

A region of 160 kb at Xp21.2 has been defined as dosage-sensitive sex reversal (DSS) and includes the NR0B1 gene, considered to be the candidate gene involved in XY gonadal dysgenesis if overexpressed. We describe a girl with 46,XY partial gonadal dysgenesis carrying a 297 kb duplication at Xp21.2 upstream of NR0B1 initially detected by chromosomal microarray analysis. Fine mapping of the breakpoints by whole-genome sequencing showed a tandem duplication of TASL (CXorf21), GK and partially TAB3, upstream of NR0B1. This is the first description of an Xp21.2 duplication upstream of NR0B1 associated with 46,XY partial gonadal dysgenesis.

Hsa-microRNA-27b-3p inhibits hepatocellular carcinoma progression by inactivating transforming growth factor-activated kinase-binding protein 3/nuclear factor kappa B signalling

Background

MicroRNAs (miRNAs) play crucial roles in the development of hepatocellular carcinoma (HCC). Hsa-microRNA-27b-3p (hsa-miR-27b) is involved in the formation and progression of various cancers, but its role and clinical value in HCC remain unclear.

Methods

The expression of hsa-miR-27b in HCC was examined by quantitative real-time PCR (qRT-PCR) and in situ hybridization (ISH) assays of clinical samples. Cell Counting Kit-8 assays (CCK-8), 5-ethynyl-2′-deoxyuridine (EdU) incorporation assays, Transwell assays, filamentous actin (F-actin) staining and western blot analyses were used to determine the effects of hsa-miR-27b on HCC cells in vitro. Subcutaneous xenograft and lung metastatic animal experiments were conducted to verify the role of hsa-miR-27b in HCC in vivo. In silico prediction, qRT-PCR, western blot, anti-Argonaute 2 (AGO2) RNA immunoprecipitation (RIP) and dual luciferase reporter assays were applied to identify the target genes of hsa-miR-27b. To detect the impacts of hsa-miR-27b on nuclear factor kappa B (NF-кB) signalling cascades mediated by transforming growth factor-activated kinase-binding protein 3 (TAB3), we performed qRT-PCR, western blot assays, immunofluorescence staining, immunohistochemistry (IHC) and dual-luciferase reporter assays. Recombinant oncolytic adenovirus (Onco^Ad) overexpressing hsa-miR-27b was constructed to detect their therapeutic value in HCC.

Results

The expression of hsa-miR-27b was lower in HCC than in adjacent non-tumourous tissues (ANTs), and the reduced expression of hsa-miR-27b was associated with worse outcomes in patients with HCC. Hsa-miR-27b significantly inhibited the proliferation, migration, invasion, subcutaneous tumour growth and lung metastasis of HCC cells. The suppression of hsa-miR-27b promoted the nuclear translocation of NF-κB by upregulating TAB3 expression. TAB3 was highly expressed in HCC compared with ANTs and was negatively correlated with the expression of hsa-miR-27b. The impaired cell proliferation, migration and invasion by hsa-miR-27b overexpression were recovered by ectopic expression of TAB3. Recombinant Onco^Ad with overexpression of hsa-miR-27b induced anti-tumour activity compared with that induced by negative control (NC) Onco^Ad in vivo and in vitro.

Conclusions

By targeting TAB3, hsa-miR-27b acted as a tumour suppressor by inactivating the NF-кB pathway in HCC in vitro and in vivo, indicating its therapeutic value against HCC.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s11658-022-00370-4.

Recent advances in applying G-quadruplex for SARS-CoV-2 targeting and diagnosis: A review

The coronavirus SARS-CoV-2 has caused a health care crisis all over the world since the end of 2019. Although vaccines and neutralizing antibodies have been developed, rapidly emerging variants usually display stronger immune escape ability and can better surpass vaccine protection. Therefore, it is still vital to find proper treatment strategies. To date, antiviral drugs against SARS-CoV-2 have mainly focused on proteases or polymerases. Notably, noncanonical nucleic acid structures called G-quadruplexes (G4s) have been identified in many viruses in recent years, and numerous G4 ligands have been developed. During this pandemic, literature on SARS-CoV-2 G4s is rapidly accumulating. Here, we first summarize the recent progress in the identification of SARS-CoV-2 G4s and their intervention by ligands. We then introduce the potential interacting proteins of SARS-CoV-2 G4s from both the virus and the host that may regulate G4 functions. The innovative strategy to use G4s as a diagnostic tool in SARS-CoV-2 detection is also reviewed. Finally, we discuss some key questions to be addressed in the future.

Alternative splicing of apoptosis genes promotes human T cell survival

Alternative splicing occurs in the vast majority of human genes, giving rise to distinct mRNA and protein isoforms. We, and others, have previously identified hundreds of genes that change their isoform expression upon T cell activation via alternative splicing; however, how these changes link activation input with functional output remains largely unknown. Here, we investigate how costimulation of T cells through the CD28 receptor impacts alternative splicing in T cells activated through the T cell receptor (TCR, CD3) and find that while CD28 signaling alone has minimal impact on splicing, it enhances the extent of change for up to 20% of TCR-induced alternative splicing events. Interestingly, a set of CD28-enhanced splicing events occur within genes encoding key components of the apoptotic signaling pathway; namely caspase-9, Bax, and Bim. Using both CRISPR-edited cells and antisense oligos to force expression of specific isoforms, we show for all three of these genes that the isoform induced by CD3/CD28 costimulation promotes resistance to apoptosis, and that changes in all three genes together function combinatorially to further promote cell viability. Finally, we show that the JNK signaling pathway, induced downstream of CD3/CD28 costimulation, is required for each of these splicing events, further highlighting their co-regulation. Together, these findings demonstrate that alternative splicing is a key mechanism by which costimulation of CD28 promotes viability of activated T cells.

LncRNA PCIR Is an Oncogenic Driver via Strengthen the Binding of TAB3 and PABPC4 in Triple Negative Breast Cancer

Long non-coding RNAs (LncRNA) as the key regulators in all stages of tumorigenesis and metastasis. However, the underlying mechanisms are largely unknown. Here, we report a lncRNA RP11-214F16.8, which renamed Lnc-PCIR, is upregulated and higher RNA level of Lnc-PCIR was positively correlated to the poor survival of patients with triple negative breast cancer (TNBC) tissues. Lnc-PCIR overexpression significantly promoted cell proliferation, migration, and invasion in vitro and in vivo. RNA pulldown, RNA immunoprecipitation (RIP) and RNA transcriptome sequencing technology (RNA-seq) was performed to identify the associated proteins and related signaling pathways. Mechanistically, higher Lnc-PCIR level of blocks PABPC4 proteasome-dependent ubiquitination degradation; stable and highly expressed PABPC4 can further increase the stability of TAB3 mRNA, meanwhile, overexpression of Lnc-PCIR can disrupt the binding status of TAB3 and TAB2 which lead to activate the TNF-α/NF-κB pathway in TNBC cells. Our findings suggest that Lnc-PCIR promotes tumor growth and metastasis via up-regulating the mRNA/protein level of TAB3 and PABPC4, activating TNF-α/NF-κB signaling pathway in TNBC.

Apolipoprotein E Signals via TLR4 to Induce CXCL5 Secretion by Asthmatic Airway Epithelial Cells

The primary function of APOE (apolipoprotein E) is to mediate the transport of cholesterol- and lipid-containing lipoprotein particles into cells by receptor-mediated endocytosis. APOE also has pro- and antiinflammatory effects, which are both context and concentration dependent. For example, Apoe^-/- mice exhibit enhanced airway remodeling and hyperreactivity in experimental asthma, whereas increased APOE levels in lung epithelial lining fluid induce IL-1β secretion from human asthmatic alveolar macrophages. However, APOE-mediated airway epithelial cell inflammatory responses and signaling pathways have not been defined. Here, RNA sequencing of human asthmatic bronchial brushing cells stimulated with APOE identified increased expression of mRNA transcripts encoding multiple proinflammatory genes, including CXCL5 (C-X-C motif chemokine ligand 5), an epithelial-derived chemokine that promotes neutrophil activation and chemotaxis. We subsequently characterized the APOE signaling pathway that induces CXCL5 secretion by human asthmatic small airway epithelial cells (SAECs). Neutralizing antibodies directed against TLR4 (Toll-like receptor 4), but not TLR2, attenuated APOE-mediated CXCL5 secretion by human asthmatic SAECs. Inhibition of TAK1 (transforming growth factor-β-activated kinase 1), IκKβ (inhibitor of nuclear factor κ B kinase subunit β), TPL2 (tumor progression locus 2), and JNK (c-Jun N-terminal kinase), but not p38 MAPK (mitogen-activated protein kinase) or MEK1/2 (MAPK kinase 1/2), attenuated APOE-mediated CXCL5 secretion. The roles of TAK1, IκKβ, TPL2, and JNK in APOE-mediated CXCL5 secretion were verified by RNA interference. Furthermore, RNA interference showed that after APOE stimulation, both NF-κB p65 and TPL2 were downstream of TAK1 and IκKβ, whereas JNK was downstream of TPL2. In summary, elevated levels of APOE in the airway may activate a TLR4/TAK1/IκKβ/NF-κB/TPL2/JNK signaling pathway that induces CXCL5 secretion by human asthmatic SAECs. These findings identify new roles for TLR4 and TPL2 in APOE-mediated proinflammatory responses in asthma.

Role of RNA Guanine Quadruplexes in Favoring the Dimerization of SARS Unique Domain in Coronaviruses

Coronaviruses may produce severe acute respiratory syndrome (SARS). As a matter of fact, a new SARS-type virus, SARS-CoV-2, is responsible for the global pandemic in 2020 with unprecedented sanitary and economic consequences for most countries. In the present contribution we study, by all-atom equilibrium and enhanced sampling molecular dynamics simulations, the interaction between the SARS Unique Domain and RNA guanine quadruplexes, a process involved in eluding the defensive response of the host thus favoring viral infection of human cells. Our results evidence two stable binding modes involving an interaction site spanning either the protein dimer interface or only one monomer. The free energy profile unequivocally points to the dimer mode as the thermodynamically favored one. The effect of these binding modes in stabilizing the protein dimer was also assessed, being related to its biological role in assisting the SARS viruses to bypass the host protective response. This work also constitutes a first step in the possible rational design of efficient therapeutic agents aiming at perturbing the interaction between SARS Unique Domain and guanine quadruplexes, hence enhancing the host defenses against the virus.

TAB3 upregulates PIM1 expression by directly activating the TAK1-STAT3 complex to promote colorectal cancer growth

Transforming growth factor-β-activated kinase 1 (TAK1)-binding protein 3 (TAB3) and the proviral integration site for Moloney murine leukaemia virus 1 (PIM1) are implicated in cancer development. In this study, we investigated the relationship between TAB3 and PIM1 in colorectal cancer (CRC) and determined the potential role and molecular mechanism of TAB3 in PIM1-mediated CRC growth. We found that TAB3 and PIM1 expression levels were positively correlated in CRC tissues. The knockdown of TAB3 significantly decreased PIM1 expression and inhibited CRC proliferation in vitro and in vivo. The upregulation of PIM1 rescued the decreased cell proliferation induced by TAB3 knockdown, whereas PIM1 knockdown decreased TAB3-enhanced CRC proliferation. Additionally, TAB3 regulates PIM1 expression through the STAT3 signalling pathway and confirmed a positive correlation between TAB3 and phosphorylated-STAT3 expression in CRC tissues. Patients with high expression of TAB3 and phosphorylated-STAT3 had the worst prognosis. Mechanistically, TAB3 regulates PIM1 expression by promoting STAT3 phosphorylation and activation through the formation of the TAB3-TAK1-STAT3 complex. Overall, a novel CRC regulatory circuit involving the TAB3-TAK1-STAT3 complex and PIM1 was identified, the dysfunction of which may contribute to CRC tumorigenesis.

USP15 potentiates NF-κB activation by differentially stabilizing TAB2 and TAB3

Tumor necrosis factor α (TNFα)- and interleukin 1β (IL-1β)-induced nuclear factor-κB (NF-κB) activation play key roles in inflammation, immunity, and cancer development. Here, we identified one of the deubiquitinating enzymes (DUBs), ubiquitin-specific protease 15 (USP15), as a positive regulator in both TNFα- and IL-1β-induced NF-κB activation. Overexpression of USP15 potentiated TNFα- or IL-1β-triggered NF-κB activation and downstream gene transcription, whereas knockdown of USP15 had opposite effects. Mechanistically, upon TNFα stimulation, USP15 showed an enhanced interaction with transforming growth factor-β activated kinase-1 (TAK1)-TAK1 binding protein (TAB) complex to inhibit the proteolysis of TAB2/3 by different pathways. Apart from deubiquitination dependently inducing cleavage of lysine 48-linked TAB2 ubiquitination, USP15 also DUB independently inhibited lysosome-associated TAB2 degradation, thus enhanced TAB2 stabilization. For TAB3, USP15 inhibited NBR1-mediated selective autophagic TAB3 degradation independent of its deubiquitinating activity. Together, our results reveal a novel USP15-mediated mechanism through which efficient NF-κB activation is achieved by differentially maintaining the TAB2/3 stability.

miR-204-5p Represses Bone Metastasis via Inactivating NF-κB Signaling in Prostate Cancer

The prime issue derived from prostate cancer (PCa) is its high prevalence to metastasize to bone. MicroRNA-204-5p (miR-204-5p) has been reported to be involved in the development and metastasis in a variety of cancers. However, the clinical significance and biological functions of miR-204-5p in bone metastasis of PCa are still not reported yet. In this study, we find that miR-204-5p expression is reduced in PCa tissues and serum sample with bone metastasis compared with that in PCa tissues and serum sample without bone metastasis, which is associated with advanced clinicopathological characteristics and poor bone metastasis-free survival in PCa patients. Moreover, upregulation of miR-204-5p inhibits the migration and invasion of PCa cells in vitro, and importantly, upregulating miR-204-5p represses bone metastasis of PCa cells in vivo. Our results further demonstrated that miR-204-5p suppresses invasion, migration, and bone metastasis of PCa cells via inactivating nuclear factor κB (NF-κB) signaling by simultaneously targeting TRAF1, TAB3, and MAP3K3. In clinical PCa samples, miR-204-5p expression negatively correlates with TRAF1, TAB3, and MAP3K3 expression and NF-κB signaling activity. Therefore, our findings reveal a new mechanism underpinning the bone metastasis of PCa, as well as provide evidence that miR-204-5p might serve as a novel serum biomarker in bone metastasis of PCa.

This study identifies a novel functional role of miR-204-5p in bone metastasis of prostate cancer and supports the potential clinical value of miR-204-5p as a serum biomarker in bone metastasis of PCa.

Metastatic group 3 medulloblastoma is driven by PRUNE1 targeting NME1-TGF-β-OTX2-SNAIL via PTEN inhibition

Genetic modifications during development of paediatric groups 3 and 4 medulloblastoma are responsible for their highly metastatic properties and poor patient survival rates. PRUNE1 is highly expressed in metastatic medulloblastoma group 3, which is characterized by TGF-β signalling activation, c-MYC amplification, and OTX2 expression. We describe the process of activation of the PRUNE1 signalling pathway that includes its binding to NME1, TGF-β activation, OTX2 upregulation, SNAIL (SNAI1) upregulation, and PTEN inhibition. The newly identified small molecule pyrimido-pyrimidine derivative AA7.1 enhances PRUNE1 degradation, inhibits this activation network, and augments PTEN expression. Both AA7.1 and a competitive permeable peptide that impairs PRUNE1/NME1 complex formation, impair tumour growth and metastatic dissemination in orthotopic xenograft models with a metastatic medulloblastoma group 3 cell line (D425-Med cells). Using whole exome sequencing technology in metastatic medulloblastoma primary tumour cells, we also define 23 common 'non-synonymous homozygous' deleterious gene variants as part of the protein molecular network of relevance for metastatic processes. This PRUNE1/TGF-β/OTX2/PTEN axis, together with the medulloblastoma-driver mutations, is of relevance for future rational and targeted therapies for metastatic medulloblastoma group 3.10.1093/brain/awy039_video1awy039media15742053534001.

Evidence for a Role of TGF-β-Activated Kinase 1 and MAP3K7 Binding Protein 3 in Peanut-Specific T-Cell Responses

Peanut allergy is considered to be the most common cause for food-induced anaphylaxis. Currently, no approved treatment is available. Avoidance is the only measure to prevent anaphylactic reactions to peanuts. T-helper cells are of special importance for the sensitization process and the maintenance of allergic inflammation. Identifying markers of allergen-specific T-cell responses may help to develop novel treatment approaches. Therefore, we aimed to define new T-cell target genes in Ara h 2-specific T cells and to investigate the possibility of using them as biomarkers of peanut allergy in peripheral blood mononuclear cells (PBMCs). We performed whole mRNA array analysis (whole human genome oligo microarray) of in vitro expanded Ara h 2-specific T cells (CFSElowCD3+CD4+) from 5 peanut-allergic (PA) and 5 non-peanut-sensitized individuals. Expression of selected genes as a result of a two-step bioinformatic approach was confirmed in a second cohort by quantitative PCR. TGF-β- activated kinase 1 and MAP3K7 binding protein 3 (TAB3), calcium/calmodulin-dependent protein kinase type IV (CAMK4) and HemK methyltransferase family member 1 (HEMK1) were significantly upregulated in Ara h 2-specific T cells of PA patients. In addition, the expression of these genes was also assessed in unstimulated PBMCs from a cohort (n = 43) of PA, atopic non-PA, and nonatopic controls. Interestingly, in unstimulated PBMCs, TAB3 expression was significantly downregulated in PA patients compared to atopic non-PA individuals. Thus, TAB3 may play a significant role at the level of T-cell activation and may also be a candidate biomarker for PA.

Identification of therapeutic targets for inflammation in sickle cell disease (SCD) among Indian patients using gene expression data analysis

Sickle cell disease (SCD) is life-threatening hemoglobinopathy prevalent in India, Sub-Saharan Africa and Middle East. Inflammation plays a pivotal role in disease process and involves intricate interaction among leukocytes, platelets, sickle erythrocytes and vascular endothelium. Available disease modifying therapies are hydroxyl-urea and blood transfusion. Therefore, it is of interest to develop improved pharmacological agents for SCD. We report up-regulated genes in steady state and vaso-occlusive crisis using analysis of gene expression data obtained by microarray experiment for SCD as potential targets. The association of these targets with inflammation in pathway analysis is also documented.

TAB3 O-GlcNAcylation promotes metastasis of triple negative breast cancer

O-GlcNAcylation is a post-translational modification that regulates a broad range of nuclear and cytoplasmic proteins and is emerging as a key regulator of various biological processes. Although previous studies have shown that increased levels of global O-GlcNAcylation and O-GlcNActransferase are linked to the incidence of metastasis in triple negative breast cancer (TNBC) patients, the molecular basis behind this is not fully understood. In this study, we have determined that the TAK1 binding protein 3 (TAB3) was O-GlcNAcylated at Ser408 by OGT in the TNBC, which was required for its Thr404 phosphorylation, TAK1 activation and downstream nuclear factor kappa B (NF-κB) activation in TNBC. O-GlcNAcylation of TAB3 was induced by p38 MAPK and it in turn enhances the TAK1 mediated p38MAPK activation, which forms the positive feedback loop in TAB3mediated NF-κB activation. In TNBC, TAB3O-GlcNAcylationmediated cell migration and invasion by activating its downstream NF-κB. The expression of TAB3 O-GlcNAcylation increased in TNBC patients, and it was significantly correlated with poor prognoses of the patients. Our study provides insights into the mechanism of TAB3 regulating activity and suggests its important implications in TNBC metastasis.

Human papillomavirus oncogenic E6 protein regulates human β-defensin 3 (hBD3) expression via the tumor suppressor protein p53

Human β-defensin-3 (hBD3) is an epithelial cell-derived innate immune regulatory molecule overexpressed in oral dysplastic lesions and fosters a tumor-promoting microenvironment. Expression of hBD3 is induced by the epidermal growth factor receptor signaling pathway. Here we describe a novel pathway through which the high-risk human papillomavirus type-16 (HPV-16) oncoprotein E6 induces hBD3 expression in mucosal keratinocytes. Ablation of E6 by siRNA induces the tumor suppressor p53 and diminishes hBD3 in HPV-16 positive CaSki cervical cancer cells and UM-SCC-104 head and neck cancer cells. Malignant cells in HPV-16-associated oropharyngeal cancer overexpress hBD3. HPV-16 E6 induces hBD3 mRNA expression, peptide production and gene promoter activity in mucosal keratinocytes. Reduction of cellular levels of p53 stimulates hBD3 expression, while activation of p53 by doxorubicin inhibits its expression in primary oral keratinocytes and CaSki cells, suggesting that p53 represses hBD3 expression. A p53 binding site in the hBD3 gene promoter has been identified by using electrophoretic mobility shift assays and chromatin immunoprecipitation (ChIP). In addition, the p63 protein isoform ΔNp63α, but not TAp63, stimulated transactivation of the hBD3 gene and was co-expressed with hBD3 in head and neck cancer specimens. Therefore, high-risk HPV E6 oncoproteins may stimulate hBD3 expression in tumor cells to facilitate tumorigenesis of HPV-associated head and neck cancer.

TAB3 upregulates Survivin expression to promote colorectal cancer invasion and metastasis by binding to the TAK1-TRAF6 complex

Transforming growth factor-β-activated kinase 1 (TAK1)-binding protein 3 (TAB3) is involved in cancer proliferation and metastasis, but its role in colorectal cancer remains unclear. In this study, we demonstrated that TAB3 is upregulated in colorectal cancer tissues and that high TAB3 levels correlated with tumor metastasis and a poor prognosis in colorectal cancer. In addition, TAB3 knockdown decreased Survivin expression and suppressed colorectal cancer cell migration and invasion in vitro, and reduced liver metastasis in vivo. Importantly, we found that TAB3 regulated Survivin expression by activating the NF-κB pathway through the formation of the TAK1-TAB3-TRAF6 complex. These findings suggest TAB3 may be a useful prognostic biomarker in colorectal cancer and a target for treatment of metastatic colorectal cancer.

Up-Regulation of TAB3 Is Involved in Neuronal Apoptosis After Intracerebral Hemorrhage

Human transforming growth factor β-activated kinase (TAK1)-binding protein 3 (TAB3) is a regulator of NF-κB which has been mainly found in a variety of cancers. While TAB3 is highly expressed in brain tissue, little is known about the function of TAB3 in central nervous system. Our group established an animal ICH model with autologous whole blood injected into brain, and also a cell ICH model with hemin stimulation. Our Western blot result showed up-regulation of TAB3 during neuronal apoptosis in the model of intracerebral hemorrhage (ICH), which was also approved by immunofluorescence and immunohistochemistry result. Besides, increasing TAB3 level was accompanied by the increased expression of active-caspase-3, active-caspase-8, and decreased expression of Bcl-2. Furthermore, in in vitro study, the level of neuronal apoptosis was decreased by applying TAB3- RNA interference in PC12 cells. All the results above suggested that TAB3 probably participates in the process of neuronal apoptosis following ICH.

miR-892b Silencing Activates NF-κB and Promotes Aggressiveness in Breast Cancer

The strength and duration of NF-κB signaling is tightly controlled at multiple levels under physiologic conditions, but the mechanism underlying constitutive activation of the NF-κB pathway in cancer remains unclear. In this study, we investigated miRNA-mediated regulation of the NF-κB cascade in breast cancer. We report that miR-892b expression was significantly downregulated in human breast cancer specimens and correlated with poor patient survival. Overexpression of miR-892b in breast cancer cells significantly decreased tumor growth, metastatic capacity, and the ability to induce angiogenesis, whereas miR-892b depletion enhanced these properties, in vitro and in vivo. Furthermore, we demonstrate that miR-892b attenuated NF-κB signaling by directly targeting and suppressing multiple mediators of NF-κB, including TRAF2, TAK1, and TAB3, and thus, miR-892b silencing in breast cancer cells sustains NF-κB activity. Moreover, miR-892b downregulation was attributed to aberrant hypermethylation of its promoter. Taken together, our results provide insight into a new mechanism by which NF-κB signaling becomes constitutively activated in breast cancer and suggest a tumor-suppressive role for miR-829b, prompting further investigation into miRNA mimics for cancer therapy.

Human MicroRNA miR-532-5p Exhibits Antiviral Activity against West Nile Virus via Suppression of Host Genes SESTD1 and TAB3 Required for Virus Replication

West Nile virus (WNV) is a mosquito-transmitted flavivirus that naturally circulates between mosquitos and birds but can also infect humans, causing severe neurological disease. The early host response to WNV infection in vertebrates primarily relies on the type I interferon pathway; however, recent studies suggest that microRNAs (miRNAs) may also play a notable role. In this study, we assessed the role of host miRNAs in response to WNV infection in human cells. We employed small RNA sequencing (RNA-seq) analysis to determine changes in the expression of host miRNAs in HEK293 cells infected with an Australian strain of WNV, Kunjin (WNVKUN), and identified a number of host miRNAs differentially expressed in response to infection. Three of these miRNAs were confirmed to be significantly upregulated in infected cells by quantitative reverse transcription (qRT)-PCR and Northern blot analyses, and one of them, miR-532-5p, exhibited a significant antiviral effect against WNVKUN infection. We have demonstrated that miR-532-5p targets and downregulates expression of the host genes SESTD1 and TAB3 in human cells. Small interfering RNA (siRNA) depletion studies showed that both SESTD1 and TAB3 were required for efficient WNVKUN replication. We also demonstrated upregulation of mir-532-5p expression and a corresponding decrease in the expression of its targets, SESTD1 and TAB3, in the brains of WNVKUN -infected mice. Our results show that upregulation of miR-532-5p and subsequent suppression of the SESTD1 and TAB3 genes represent a host antiviral response aimed at limiting WNVKUN infection and highlight the important role of miRNAs in controlling RNA virus infections in mammalian hosts.

IMPORTANCE

West Nile virus (WNV) is a significant viral pathogen that poses a considerable threat to human health across the globe. There is no specific treatment or licensed vaccine available for WNV, and deeper insight into how the virus interacts with the host is required to facilitate their development. In this study, we addressed the role of host microRNAs (miRNAs) in antiviral response to WNV in human cells. We identified miR-532-5p as a novel antiviral miRNA and showed that it is upregulated in response to WNV infection and suppresses the expression of the host genes TAB3 and SESTD1 required for WNV replication. Our results show that upregulation of miR-532-5p and subsequent suppression of the SESTD1 and TAB3 genes represent an antiviral response aimed at limiting WNV infection and highlight the important role of miRNAs in controlling virus infections in mammalian hosts.

Research Resource: Androgen Receptor Activity Is Regulated Through the Mobilization of Cell Surface Receptor Networks

The aberrant expression of androgen receptor (AR)-dependent transcriptional programs is a defining pathology of the development and progression of prostate cancers. Transcriptional cofactors that bind AR are critical determinants of prostate tumorigenesis. To gain a deeper understanding of the proteins linked to AR-dependent gene transcription, we performed a DNA-affinity chromatography-based proteomic screen designed to identify proteins involved in AR-mediated gene transcription in prostate tumor cells. Functional experiments validated the coregulator roles of known AR-binding proteins in AR-mediated transcription in prostate tumor cells. More importantly, novel coregulatory functions were detected in components of well-established cell surface receptor-dependent signal transduction pathways. Further experimentation demonstrated that components of the TNF, TGF-β, IL receptor, and epidermal growth factor signaling pathways modulated AR-dependent gene transcription and androgen-dependent proliferation in prostate tumor cells. Collectively, our proteomic dataset demonstrates that the cell surface receptor- and AR-dependent pathways are highly integrated, and provides a molecular framework for understanding how disparate signal-transduction pathways can influence AR-dependent transcriptional programs linked to the development and progression of human prostate cancers.

Macro advances in microRNAs and myocardial regeneration

PURPOSE OF REVIEW

Myocardial injury and disease often result in heart failure, a major cause of death worldwide. To achieve myocardial regeneration and foster development of efficient therapeutics for cardiac injury, it is essential to uncover molecular mechanisms that will promote myocardial regeneration. In this review, we examine the latest progress made in elucidation of the roles of small non-coding RNAs called microRNAs (miRs) in myocardial regeneration.

RECENT FINDINGS

Promising progress has been made in studying cardiac regeneration. Several miRs, which include miR-590, miR-199a, miR-17-92 cluster, miR-199a-214 cluster, miR-34a, and miR-15 family, have been recently shown to play an essential role in myocardial regeneration by regulating different processes during cardiac repair, including cell death, proliferation, and metabolism. For example, miR-590 promotes cardiac regeneration through activating cardiomyocyte proliferation, whereas miR-34a inhibits cardiac repair through inducing apoptosis.

SUMMARY

These recent findings shed new light on our understanding of myocardial regeneration and suggest potential novel therapeutic targets to treat cardiac disease.

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.

MicroRNA-26b suppresses the NF-κB signaling and enhances the chemosensitivity of hepatocellular carcinoma cells by targeting TAK1 and TAB3

Background

Abnormal activation of the NF-κB pathway is closely related to tumorigenesis and chemoresistance. Therefore, microRNAs that possess the NF-κB inhibitory activity may provide novel targets for anti-cancer therapy. miR-26 family members have been shown to be frequently downregulated in hepatocellular carcinoma (HCC) and correlated with the poor survival of HCC patients. To date, there is no report disclosing the regulatory role of miR-26 on the NF-κB pathway and its biological significance.

Methods

The effects of miR-26b on the NF-κB signaling pathway and the chemosensitivity of cancer cells were examined in two HCC cell lines, QGY-7703 and MHCC-97H, using both gain- and loss-of-function studies. The correlation between miR-26b level and apoptosis rate was further investigated in clinical HCC specimens.

Results

Both TNFα and doxorubicin treatment activated the NF-κB signaling pathway in HCC cells. However, the restoration of miR-26b expression significantly inhibited the phosphorylation of IκBα and p65, blocked the nuclear translocation of NF-κB, reduced the NF-κB reporter activity, and consequently abrogated the expression of NF-κB target genes in TNFα or doxorubicin-treated HCC cells. Furthermore, the ectopic expression of miR-26b dramatically sensitized HCC cells to the doxorubicin-induced apoptosis, whereas the antagonism of miR-26b attenuated cell apoptosis. Consistently, the miR-26b level was positively correlated with the apoptosis rate in HCC tissues. Subsequent investigations revealed that miR-26b inhibited the expression of TAK1 and TAB3, two positive regulators of NF-κB pathway, by binding to their 3’-untranslated region. Moreover, knockdown of TAK1 or TAB3 phenocopied the effects of miR-26b overexpression.

Conclusions

These data suggest that miR-26b suppresses NF-κB signaling and thereby sensitized HCC cells to the doxorubicin-induced apoptosis by inhibiting the expression of TAK1 and TAB3. Our findings highlight miR-26b as a potent inhibitor of the NF-κB pathway and an attractive target for cancer treatment.

Genome-wide screening reveals that miR-195 targets the TNF-α/NF-κB pathway by down-regulating IκB kinase alpha and TAB3 in hepatocellular carcinoma

Nuclear factor kappa B (NF-κB) is an important factor linking inflammation and tumorigenesis. In this study we experimentally demonstrated through a high-throughput luciferase reporter screen that NF-κB signaling can be directly targeted by nearly 29 microRNAs (miRNAs). Many of these miRNAs can directly target NF-κB signaling nodes by binding to their 3' untranslated region (UTR). miR-195, a member of the miR-15 family, is frequently down-regulated in gastrointestinal cancers, especially in hepatocellular carcinoma (HCC). The expression level of miR-195 is inversely correlated with HCC tumor size. We further show that miR-195 suppresses cancer cell proliferation and migration in vitro and reduces tumorigenicity and metastasis in vivo. Additionally, miR-195 may exert its tumor suppressive function by decreasing the expression of multiple NF-κB downstream effectors by way of the direct targeting of IKKα and TAB3.

CONCLUSION

Multiple miRNAs are involved in the NF-κB signaling pathway and miR-195 plays important inhibitory roles in cancer progression and may be a potential therapeutic target.

TAK1 (MAP3K7) signaling regulates hematopoietic stem cells through TNF-dependent and -independent mechanisms

A cytokine/stress signaling kinase Tak1 (Map3k7) deficiency is known to impair hematopoietic progenitor cells. However, the role of TAK1 signaling in the stem cell function of the hematopoietic system is not yet well defined. Here we characterized hematopoietic stem cells (HSCs) harboring deletion of Tak1 and its activators, Tak1 binding proteins 1 and 2 (Tab1 and Tab2) using a competitive transplantation assay in a mouse model. Tak1 single or Tab1/Tab2 double deletions completely eliminated the reconstitution activity of HSCs, whereas Tab1 or Tab2 single deletion did not cause any abnormality. Tak1 single or Tab1/Tab2 double deficient lineage-negative, Sca-1⁺, c-Kit⁺ (LSK) cells did not proliferate and underwent cell death. We found that Tnfr1 deficiency restored the reconstitution activity of Tak1 deficient bone marrow cells for 6–18 weeks. However, the reconstitution activity of Tak1- and Tnfr1-double deficient bone marrow cells declined over the long term, and the number of phenotypically identified long-term hematopoietic stem cells were diminished. Our results indicate that TAB1- or TAB2-dependent activation of TAK1 is required for maintenance of the hematopoietic system through two mechanisms: one is prevention of TNF-dependent cell death and the other is TNF-independent maintenance of long-term HSC.

β-TrCP-mediated IRAK1 degradation releases TAK1-TRAF6 from the membrane to the cytosol for TAK1-dependent NF-κB activation

Interleukin-1 (IL-1) receptor-associated kinase (IRAK1) is phosphorylated, ubiquitinated, and degraded upon IL-1 stimulation. IRAK1 can be ubiquitinated through both K48- and K63-linked polyubiquitin chains upon IL-1 stimulation. While the Pellino proteins have been shown to meditate K63-linked polyubiquitination on IRAK1, the E3 ligase for K48-linked ubiquitination of IRAK1 has not been identified. In this study, we report that the SCF (Skp1-Cullin1-F-box)-β-TrCP complex functions as the K48-linked ubiquitination E3 ligase for IRAK1. IL-1 stimulation induced the interaction of IRAK1 with Cullin1 and β-TrCP. Knockdown of β-TrCP1 and β-TrCP2 attenuated the K48-linked ubiquitination and degradation of IRAK1. Importantly, β-TrCP deficiency abolished the translocation TAK1-TRAF6 complex from the membrane to the cytosol, resulting in a diminishment of the IL-1-induced TAK1-dependent pathway. Taken together, these results implicate a positive role of β-TrCP-mediated IRAK1 degradation in IL-1-induced TAK1 activation.

Mammalian MAPK signal transduction pathways activated by stress and inflammation: a 10-year update

The mammalian stress-activated families of mitogen-activated protein kinases (MAPKs) were first elucidated in 1994, and by 2001, substantial progress had been made in identifying the architecture of the pathways upstream of these kinases as well as in cataloguing candidate substrates. This information remains largely sound. Nevertheless, an informed understanding of the physiological and pathophysiological roles of these kinases remained to be accomplished. In the past decade, there has been an explosion of new work using RNAi in cells, as well as transgenic, knockout and conditional knockout technology in mice that has provided valuable insight into the functions of stress-activated MAPK pathways. These findings have important implications in our understanding of organ development, innate and acquired immunity, and diseases such as atherosclerosis, tumorigenesis, and type 2 diabetes. These new developments bring us within striking distance of the development and validation of novel treatment strategies. Herein we first summarize the molecular components of the mammalian stress-regulated MAPK pathways and their regulation as described thus far. We then review some of the in vivo functions of these pathways.

Epithelial transforming growth factor β-activated kinase 1 (TAK1) is activated through two independent mechanisms and regulates reactive oxygen species

Dysregulation in cellular redox systems results in accumulation of reactive oxygen species (ROS), which are causally associated with a number of disease conditions. Transforming growth factor β-activated kinase 1 (TAK1) is a signaling intermediate of innate immune signaling pathways and is critically involved in the redox regulation in vivo. Ablation of TAK1 causes accumulation of ROS, resulting in epithelial cell death and inflammation. Here we determine the mechanism by which TAK1 kinase is activated in epithelial tissues. TAB1 and TAB2 are structurally unrelated TAK1 binding protein partners. TAB2 is known to mediate polyubiquitin chain-dependent TAK1 activation in innate immune signaling pathways, whereas the role of TAB1 is not defined. We found that epithelial-specific TAB1 and TAB2 double- but not TAB1 or TAB2 single-knockout mice phenocopied epithelial-specific TAK1 knockout mice. We demonstrate that phosphorylation-dependent basal activity of TAK1 is dependent on TAB1. Ablation of both TAB1 and TAB2 diminished the activity of TAK1 in vivo and causes accumulation of ROS in the epithelial tissues. These results demonstrate that epithelial TAK1 activity is regulated through two unique, TAB1-dependent basal and TAB2-mediated stimuli-dependent mechanisms.

The effects of TLR activation on T-cell development and differentiation

Invading pathogens have unique molecular signatures that are recognized by Toll-like receptors (TLRs) resulting in either activation of antigen-presenting cells (APCs) and/or costimulation of T cells inducing both innate and adaptive immunity. TLRs are also involved in T-cell development and can reprogram Treg cells to become helper cells. T cells consist of various subsets, that is, Th1, Th2, Th17, T follicular helper (Tfh), cytotoxic T lymphocytes (CTLs), regulatory T cells (Treg) and these originate from thymic progenitor thymocytes. T-cell receptor (TCR) activation in distinct T-cell subsets with different TLRs results in differing outcomes, for example, activation of TLR4 expressed in T cells promotes suppressive function of regulatory T cells (Treg), while activation of TLR6 expressed in T cells abrogates Treg function. The current state of knowledge of regarding TLR-mediated T-cell development and differentiation is reviewed.

Identification and functional characterization of novel phosphorylation sites in TAK1-binding protein (TAB) 1

TAB1 was defined as a regulatory subunit of the protein kinase TAK1, which functions upstream in the pathways activated by interleukin (IL)-1, tumor necrosis factor (TNF), toll-like receptors (TLRs) and stressors. However, TAB1 also functions in the p38 MAPK pathway downstream of TAK1. We identified amino acids (aa) 452/453 and 456/457 of TAB1 as novel sites phosphorylated by TAK1 as well as by p38 MAPK in intact cells as well as in vitro. Serines 452/453 and 456/457 were phosphorylated upon phosphatase blockade by calyculin A, or in response to IL-1 or translational stressors such as anisomycin and sorbitol. Deletion or phospho-mimetic mutations of aa 452–457 of TAB1 retain TAB1 and p38 MAPK in the cytoplasm. The TAB1 mutant lacking aa 452–457 decreases TAB1-dependent phosphorylation of p38 MAPK. It also enhances TAB1-dependent CCL5 secretion in response to IL-1 and increases activity of a post-transcriptional reporter gene, which contains the CCL5 3′ untranslated region. These data suggest a complex role of aa 452–457 of TAB1 in controlling p38 MAPK activity and subcellular localization and implicate these residues in TAK1- or p38 MAPK-dependent post-transcriptional control of gene expression.

Cysteine methylation disrupts ubiquitin-chain sensing in NF-κB activation

NF-κB is crucial for innate immune defence against microbial infection. Inhibition of NF-κB signalling has been observed with various bacterial infections. The NF-κB pathway critically requires multiple ubiquitin-chain signals of different natures. The question of whether ubiquitin-chain signalling and its specificity in NF-κB activation are regulated during infection, and how this regulation takes place, has not been explored. Here we show that human TAB2 and TAB3, ubiquitin-chain sensory proteins involved in NF-κB signalling, are directly inactivated by enteropathogenic Escherichia coli NleE, a conserved bacterial type-III-secreted effector responsible for blocking host NF-κB signalling. NleE harboured an unprecedented S-adenosyl-l-methionine-dependent methyltransferase activity that specifically modified a zinc-coordinating cysteine in the Npl4 zinc finger (NZF) domains in TAB2 and TAB3. Cysteine-methylated TAB2-NZF and TAB3-NZF (truncated proteins only comprising the NZF domain) lost the zinc ion as well as the ubiquitin-chain binding activity. Ectopically expressed or type-III-secretion-system-delivered NleE methylated TAB2 and TAB3 in host cells and diminished their ubiquitin-chain binding activity. Replacement of the NZF domain of TAB3 with the NleE methylation-insensitive Npl4 NZF domain resulted in NleE-resistant NF-κB activation. Given the prevalence of zinc-finger motifs and activation of cysteine thiol by zinc binding, methylation of zinc-finger cysteine might regulate other eukaryotic pathways in addition to NF-κB signalling.

Inhibition of autophagy by TAB2 and TAB3

Autophagic responses are coupled to the activation of the inhibitor of NF-κB kinase (IKK). Here, we report that the essential autophagy mediator Beclin 1 and TGFβ-activated kinase 1 (TAK1)-binding proteins 2 and 3 (TAB2 and TAB3), two upstream activators of the TAK1-IKK signalling axis, constitutively interact with each other via their coiled-coil domains (CCDs). Upon autophagy induction, TAB2 and TAB3 dissociate from Beclin 1 and bind TAK1. Moreover, overexpression of TAB2 and TAB3 suppresses, while their depletion triggers, autophagy. The expression of the C-terminal domain of TAB2 or TAB3 or that of the CCD of Beclin 1 competitively disrupts the interaction between endogenous Beclin 1, TAB2 and TAB3, hence stimulating autophagy through a pathway that requires endogenous Beclin 1, TAK1 and IKK to be optimally efficient. These results point to the existence of an autophagy-stimulatory 'switch' whereby TAB2 and TAB3 abandon inhibitory interactions with Beclin 1 to engage in a stimulatory liaison with TAK1.

Comprehending the complex connection between PKCbeta, TAK1, and IKK in BCR signaling

The transcription factor nuclear factor-kappaB (NF-kappaB) contributes to many events in the immune system. Characterization of NF-kappaB has facilitated our understanding of immune cell differentiation, survival, proliferation, and effector functions. Intense research continues to elucidate the role of NF-kappaB, which is shared in several receptor signaling pathways, such as Toll-like receptors, the tumor necrosis factor receptor, and antigen receptors. The specificity of cellular responses emanating from stimulation of these receptors is determined by post-translational modification, or 'fine tuning', which regulates spatiotemporal dynamics of downstream signaling. Understanding the fine tuning mechanisms of NF-kappaB activation is crucial for insights into biological regulation and for understanding how cellular signaling pathways are tightly regulated to guide different cell fates. In this review, we focus on recent advances that illuminate the fine tuning mechanisms of NF-kappaB activation by BCR signaling and have increased our comprehension of complex signal systems.

TAB2 scaffolds TAK1 and NLK in repressing canonical Wnt signaling

The TAK1-NLK cascade is a mitogen-activated protein kinase-related pathway that plays an inhibitory role in canonical Wnt/beta-catenin signaling through regulating the LEF1/TCF family transcriptional factors. TAB2 (TAK1-binding protein 2) is a putative TAK1 interacting protein that is involved in the regulation of TAK1. Here, we found that TAB2 could directly interact with NLK and function as a scaffold protein to facilitate the interaction between TAK1 and NLK. Knocking down TAB2 using small interfering RNA abolished the interaction of TAK1 with NLK in mammalian cells. The intermediate region (residues 292-417) of TAB2 was mapped for its binding to NLK. TAB2-DeltaM, a TAB2 mutant lacking this region, showed a lower affinity for NLK and became defective in its scaffolding function. In addition, TAB2, but not TAB2-DeltaM, mediated TAK1-dependent activation of NLK and LEF1 polyubiquitylation, resulting in the inhibition of canonical Wnt signaling. Moreover, Wnt3a stimulation led to an increase in the interaction of TAB2 with NLK and the formation of a TAK1.TAB2.NLK complex, suggesting that this TAK1-TAB2-NLK pathway may constitute a negative feedback mechanism for canonical Wnt signaling.

Use of forward genetics to discover novel regulators of NF-kappaB

Forward and reverse genetic experiments have both played important roles in revealing critical aspects of mammalian signal transduction pathways in cell culture experiments. Only recently have we begun to comprehend the depth, breadth, and complexity of these pathways and of their interrelationships. Here, we summarize successful examples in which different forward genetic approaches have led to novel discoveries in NF-kappaB signaling. We believe that forward genetics will continue to play an irreplaceable role in advancing our understanding of the complexities of the pathways that regulate the functions of this key transcription factor.

WDR34 is a novel TAK1-associated suppressor of the IL-1R/TLR3/TLR4-induced NF-kappaB activation pathway

Toll-like receptors (TLRs) act as sensors of microbial components and elicit innate immune responses. All TLR signaling pathways activate the nuclear factor-kappaB (NF-kappaB), which controls the expression of inflammatory cytokine genes. Transforming growth factor-beta-activated kinase 1 (TAK1) is a serine/threonine protein kinase that is critically involved in the activation of NF-kappaB by tumor necrosis factor (TNFalpha), interleukin-1beta (IL-1beta) and TLR ligands. In this study, we identified a novel protein, WD40 domain repeat protein 34 (WDR34) as a TAK1-interacting protein in yeast two-hybrid screens. WDR34 interacted with TAK1, TAK1-binding protein 2 (TAB2), TAK1-binding protein 3 (TAB3) and tumor necrosis factor receptor-associated factor 6 (TRAF6) in overexpression and under physiological conditions. Overexpression of WDR34 inhibited IL-1beta-, polyI:C- and lipopolysaccharide (LPS)-induced but not TNFalpha-induced NF-kappaB activation, whereas knockdown of WDR34 by a RNA-interference construct potentiated NF-kappaB activation by these ligands. Our findings suggest that WDR34 is a TAK1-associated inhibitor of the IL-1R/TLR3/TLR4-induced NF-kappaB activation pathway.

Transforming growth factor-beta (TGF-beta1) activates TAK1 via TAB1-mediated autophosphorylation, independent of TGF-beta receptor kinase activity in mesangial cells

Transforming growth factor-beta1 (TGF-beta1) is a multifunctional cytokine that signals through the interaction of type I (TbetaRI) and type II (TbetaRII) receptors to activate distinct intracellular pathways. TAK1 is a serine/threonine kinase that is rapidly activated by TGF-beta1. However, the molecular mechanism of TAK1 activation is incompletely understood. Here, we propose a mechanism whereby TAK1 is activated by TGF-beta1 in primary mouse mesangial cells. Under unstimulated conditions, endogenous TAK1 is stably associated with TbetaRI. TGF-beta1 stimulation causes rapid dissociation from the receptor and induces TAK1 phosphorylation. Deletion mutant analysis indicates that the juxtamembrane region including the GS domain of TbetaRI is crucial for its interaction with TAK1. Both TbetaRI-mediated TAK1 phosphorylation and TGF-beta1-induced TAK1 phosphorylation do not require kinase activity of TbetaRI. Moreover, TbetaRI-mediated TAK1 phosphorylation correlates with the degree of its association with TbetaRI and requires kinase activity of TAK1. TAB1 does not interact with TGF-beta receptors, but TAB1 is indispensable for TGF-beta1-induced TAK1 activation. We also show that TRAF6 and TAB2 are required for the interaction of TAK1 with TbetaRI and TGF-beta1-induced TAK1 activation in mouse mesangial cells. Taken together, our data indicate that TGF-beta1-induced interaction of TbetaRI and TbetaRII triggers dissociation of TAK1 from TbetaRI, and subsequently TAK1 is phosphorylated through TAB1-mediated autophosphorylation and not by the receptor kinase activity of TbetaRI.

The SARS-unique domain (SUD) of SARS coronavirus contains two macrodomains that bind G-quadruplexes

Since the outbreak of severe acute respiratory syndrome (SARS) in 2003, the three-dimensional structures of several of the replicase/transcriptase components of SARS coronavirus (SARS-CoV), the non-structural proteins (Nsps), have been determined. However, within the large Nsp3 (1922 amino-acid residues), the structure and function of the so-called SARS-unique domain (SUD) have remained elusive. SUD occurs only in SARS-CoV and the highly related viruses found in certain bats, but is absent from all other coronaviruses. Therefore, it has been speculated that it may be involved in the extreme pathogenicity of SARS-CoV, compared to other coronaviruses, most of which cause only mild infections in humans. In order to help elucidate the function of the SUD, we have determined crystal structures of fragment 389-652 ("SUD(core)") of Nsp3, which comprises 264 of the 338 residues of the domain. Both the monoclinic and triclinic crystal forms (2.2 and 2.8 A resolution, respectively) revealed that SUD(core) forms a homodimer. Each monomer consists of two subdomains, SUD-N and SUD-M, with a macrodomain fold similar to the SARS-CoV X-domain. However, in contrast to the latter, SUD fails to bind ADP-ribose, as determined by zone-interference gel electrophoresis. Instead, the entire SUD(core) as well as its individual subdomains interact with oligonucleotides known to form G-quadruplexes. This includes oligodeoxy- as well as oligoribonucleotides. Mutations of selected lysine residues on the surface of the SUD-N subdomain lead to reduction of G-quadruplex binding, whereas mutations in the SUD-M subdomain abolish it. As there is no evidence for Nsp3 entering the nucleus of the host cell, the SARS-CoV genomic RNA or host-cell mRNA containing long G-stretches may be targets of SUD. The SARS-CoV genome is devoid of G-stretches longer than 5-6 nucleotides, but more extended G-stretches are found in the 3'-nontranslated regions of mRNAs coding for certain host-cell proteins involved in apoptosis or signal transduction, and have been shown to bind to SUD in vitro. Therefore, SUD may be involved in controlling the host cell's response to the viral infection. Possible interference with poly(ADP-ribose) polymerase-like domains is also discussed.

MicroRNAs 15a and 16 regulate tumor proliferation in multiple myeloma

Detailed genomic studies have shown that cytogenetic abnormalities contribute to multiple myeloma (MM) pathogenesis and disease progression. Nevertheless, little is known about the characteristics of MM at the epigenetic level and specifically how microRNAs regulate MM progression in the context of the bone marrow milieu. Therefore, we performed microRNA expression profiling of bone marrow derived CD138(+) MM cells versus their normal cellular counterparts and validated data by qRT-PCR. We identified a MM-specific microRNA signature characterized by down-expression of microRNA-15a/-16 and overexpression of microRNA-222/-221/-382/-181a/-181b (P < .01). We investigated the functional role of microRNA-15a and -16 and showed that they regulate proliferation and growth of MM cells in vitro and in vivo by inhibiting AKT serine/threonine-protein-kinase (AKT3), ribosomal-protein-S6, MAP-kinases, and NF-kappaB-activator MAP3KIP3. Moreover, miRNA-15a and -16 exerted their anti-MM activity even in the context of the bone marrow milieu in vitro and in vivo. These data indicate that microRNAs play a pivotal role in the biology of MM and represent important targets for novel therapies in MM.

HSP90 is required for TAK1 stability but not for its activation in the pro-inflammatory signaling pathway

The protein kinase transforming-growth-factor-beta-activated kinase-1 (TAK1) is a key regulator in the pro-inflammatory signaling pathway and is activated by tumor necrosis factor-alpha, interleukin-1 (IL-1) and lipopolysaccharide (LPS). We describe the identification of TAK1 as a client protein of the 90 kDa heat-shock protein (Hsp90)/cell division cycle protein 37 (Cdc37) chaperones. However, Hsp90 is not required for the activation of TAK1 as short exposure to the Hsp90 inhibitor, 17-(allylamino)-17-demethoxygeldanamycin (17-AAG) did not affect its activation by LPS or IL-1. Prolonged treatment of cells with 17-AAG inhibits Hsp90 and downregulates TAK1. Our results suggest that Hsp90 is required for the folding and stability of TAK1 but is displaced and no longer required when TAK1 is complexed to TAK1-binding protein-1 (TAB1).

Pellino 3b negatively regulates interleukin-1-induced TAK1-dependent NF kappaB activation

IL-1 receptor-associated kinase (IRAK) is phosphorylated, ubiquitinated, and degraded upon interleukin-1 (IL-1) stimulation. In this study, we showed that IRAK can be ubiquitinated through both Lys-48- and Lys-63-linked polyubiquitin chains upon IL-1 induction. Pellino 3b is the RING-like motif ubiquitin protein ligase that promotes the Lys-63-linked polyubiquitination on IRAK. Pellino 3b-mediated Lys-63-linked IRAK polyubiquitination competed with Lys-48-linked IRAK polyubiquitination for the same ubiquitination site, Lys-134 of IRAK, thereby blocking IL-1-induced IRAK degradation. Importantly, the negative impact of Pellino 3b on IL-1-induced IRAK degradation correlated with the inhibitory effect of Pellino 3b on the IL-1-induced TAK1-dependent pathway, suggesting that a positive role of IRAK degradation in IL-1 induced TAK1 activation. Taken together, our results suggest that Pellino 3b acts as a negative regulator for IL-1 signaling by regulating IRAK degradation through its ubiquitin protein ligase activity.

Protein phosphatase 2A is a negative regulator of transforming growth factor-beta1-induced TAK1 activation in mesangial cells

TAK1 (transforming growth factor (TGF)-beta-activated kinase 1) is a serine/threonine kinase that is rapidly activated by TGF-beta1 and plays a vital function in its signal transduction. Once TAK1 is activated, efficient down-regulation of TAK1 activity is important to prevent excessive TGF-beta1 responses. The regulatory mechanism of TAK1 inactivation following TGF-beta1 stimulation has not been elucidated. Here we demonstrate that protein phosphatase 2A (PP2A) plays a pivotal role as a negative regulator of TAK1 activation in response to TGF-beta1 in mesangial cells. Treatment with okadaic acid (OA) induces autophosphorylation of Thr-187 in the activation loop of TAK1. In vitro dephosphorylation assay suggests that Thr-187 in TAK1 is a major dephosphorylation target of PP2A. TGF-beta1 stimulation rapidly activates TAK1 in a biphasic manner, indicating that TGF-beta1-induced TAK1 activation is tightly regulated. The association of PP2A(C) with TAK1 is enhanced in response to TGF-beta1 stimulation and closely parallels TGF-beta1-induced TAK1 activity. Attenuation of PP2A activity by OA treatment or targeted knockdown of PP2A(C) with small interfering RNA enhances TGF-beta1-induced phosphorylation of TAK1 at Thr-187 and MKK3 (MAPK kinase 3). Endogenous TAK1 co-precipitates with PP2A(C) but not PP6(C), another OA-sensitive protein phosphatase, and knockdown of PP6(C) by small interfering RNA does not affect TGF-beta1-induced phosphorylation of TAK1 at Thr-187 and MKK3. Moreover, ectopic expression of phosphatase-deficient PP2A(C) enhances TAK1-mediated MKK3 phosphorylation by TGF-beta1 stimulation, whereas the expression of wild-type PP2A(C) suppresses the MKK3 phosphorylation. Taken together, our data indicate that PP2A functions as a negative regulator in TGF-beta1-induced TAK1 activation.

Molecular basis for the unique deubiquitinating activity of the NF-kappaB inhibitor A20

Nuclear factor kappaB (NF-kappaB) activation in tumor necrosis factor, interleukin-1, and Toll-like receptor pathways requires Lys63-linked nondegradative polyubiquitination. A20 is a specific feedback inhibitor of NF-kappaB activation in these pathways that possesses dual ubiquitin-editing functions. While the N-terminal domain of A20 is a deubiquitinating enzyme (DUB) for Lys63-linked polyubiquitinated signaling mediators such as TRAF6 and RIP, its C-terminal domain is a ubiquitin ligase (E3) for Lys48-linked degradative polyubiquitination of the same substrates. To elucidate the molecular basis for the DUB activity of A20, we determined its crystal structure and performed a series of biochemical and cell biological studies. The structure reveals the potential catalytic mechanism of A20, which may be significantly different from papain-like cysteine proteases. Ubiquitin can be docked onto a conserved A20 surface; this interaction exhibits charge complementarity and no steric clash. Surprisingly, A20 does not have specificity for Lys63-linked polyubiquitin chains. Instead, it effectively removes Lys63-linked polyubiquitin chains from TRAF6 without dissembling the chains themselves. Our studies suggest that A20 does not act as a general DUB but has the specificity for particular polyubiquitinated substrates to assure its fidelity in regulating NF-kappaB activation in the tumor necrosis factor, interleukin-1, and Toll-like receptor pathways.