Activation of the heterodimeric IkappaB kinase alpha (IKKalpha)-IKKbeta complex is directional: IKKalpha regulates IKKbeta under both basal and stimulated conditions

Grass carp (Ctenopharyngodon idella) NIK up-regulates the expression of IL-8 by activating the NF-κB canonical pathway

NIK (NF-κB inducing kinase) belongs to the mitogen-activated protein kinase family, which activates NF-κB and plays a vital role in immunology, inflammation, apoptosis, and a series of pathological responses. In NF-κB noncanonical pathway, NIK and IKKα have been often studied in mammals and zebrafish. However, few have explored the relationship between NIK and other subunits of the IKK complex. As a classic kinase in the NF-κB canonical pathway, IKKβ has never been researched with NIK in fish. In this paper, the full-length cDNA sequence of grass carp (Ctenopharyngodon idella) NIK (CiNIK) was first cloned and identified. The expression level of CiNIK in grass carp cells was increased under GCRV stimuli. Under the stimulation of GCRV, poly (I:C), and LPS, the expression of NIK in various tissues of grass carp was also increased. This suggests that CiNIK responds to viral stimuli. To study the relationship between CiNIK and CiIKKβ, we co-transfected CiNIK-FLAG and CiIKKB-GFP into grass carp cells in coimmunoprecipitation and immunofluorescence experiments. The results revealed that CiNIK interacts with CiIKKβ. Besides, the degree of autophosphorylation of CiNIK was enhanced under poly (I:C) stimulation. CiIKKβ was phosphorylated by CiNIK and then activated the activity of p65. The activity change of p65 indicates that NF-κB downstream inflammatory genes will be functioning. CiNIK or CiIKKβ up-regulated the expression of IL-8. It got higher when CiNIK and CiIKKβ coexisted. This paper revealed that NF-κB canonical pathway and noncanonical pathway are not completely separated in generating benefits.

IKKα-Mediated Noncanonical NF-κB Signaling Is Required To Support Murine Gammaherpesvirus 68 Latency In Vivo

Noncanonical NF-κB signaling is activated in B cells via the tumor necrosis factor (TNF) receptor superfamily members CD40, lymphotoxin β receptor (LTβR), and B-cell-activating factor receptor (BAFF-R). The noncanonical pathway is required at multiple stages of B cell maturation and differentiation, including the germinal center reaction. However, the role of this pathway in gammaherpesvirus latency is not well understood. Murine gammaherpesvirus 68 (MHV68) is a genetically tractable system used to define pathogenic determinants. Mice lacking the BAFF-R exhibit defects in splenic follicle formation and are greatly reduced for MHV68 latency. We report a novel approach to disrupt noncanonical NF-κB signaling exclusively in cells infected with MHV68. We engineered a recombinant virus that expresses a dominant negative form of IκB kinase α (IKKα), named IKKα-SA, with S176A and S180A mutations that prevent phosphorylation by NF-κB-inducing kinase (NIK). We controlled for the transgene insertion by introducing two all-frame stop codons into the IKKα-SA gene. The IKKα-SA mutant but not the IKKα-SA.STOP control virus impaired LTβR-mediated activation of NF-κB p52 upon fibroblast infection. IKKα-SA expression did not impact replication in primary fibroblasts or in the lungs of mice following intranasal inoculation. However, the IKKα-SA mutant was severely defective in the colonization of the spleen and in the establishment of latency compared to the IKKα-SA.STOP control and wild-type (WT) MHV68 at 16 days postinfection (dpi). Reactivation was undetectable in splenocytes infected with the IKKα-SA mutant, but reactivation in peritoneal cells was not impacted by IKKα-SA. Taken together, the noncanonical NF-κB signaling pathway is essential for the establishment of latency in the secondary lymphoid organs of mice infected with the murine gammaherpesvirus pathogen MHV68. IMPORTANCE The latency programs of the human gammaherpesviruses Epstein-Barr virus (EBV) and Kaposi sarcoma-associated herpesvirus (KSHV) are associated with B cell lymphomas. It is critical to understand the signaling pathways that are used by gammaherpesviruses to establish and maintain latency in primary B cells. We used a novel approach to block noncanonical NF-κB signaling only in the infected cells of mice. We generated a recombinant virus that expresses a dominant negative mutant of IKKα that is nonresponsive to upstream activation. Latency was reduced in a route- and cell type-dependent manner in mice infected with this recombinant virus. These findings identify a significant role for the noncanonical NF-κB signaling pathway that might provide a novel target to prevent latent infection of B cells with oncogenic gammaherpesviruses.

B-cell maturation antigen targeting strategies in multiple myeloma treatment, advantages and disadvantages

B cell maturation antigen (BCMA), a transmembrane glycoprotein member of the tumor necrosis factor receptor superfamily 17 (TNFRSF17), highly expressed on the plasma cells of Multiple myeloma (MM) patients, as well as the normal population. BCMA is used as a biomarker for MM. Two members of the TNF superfamily proteins, including B-cell activating factor (BAFF) and A proliferation-inducing ligand (APRIL), are closely related to BCMA and play an important role in plasma cell survival and progression of MM. Despite the maximum specificity of the monoclonal antibody technologies, introducing the tumor-specific antigen(s) is not applicable for all malignancies, such as MM that there plenty of relatively specific antigens such as GPCR5D, MUC1, SLAMF7 and etc., but higher expression of BCMA on these cells in comparison with normal ones can be regarded as a relatively exclusive marker. Currently, different monoclonal antibody (mAb) technologies applied in anti-MM therapies such as daratuzumab, SAR650984, GSK2857916, and CAR-T cell therapies are some of these tools that are reviewed in the present manuscript. By the way, the structure, function, and signaling of the BCMA and related molecule(s) role in normal plasma cells and MM development, evaluated as well as the potential side effects of its targeting by different CAR-T cells generations. In conclusion, BCMA can be regarded as an ideal molecule to be targeted in immunotherapeutic methods, regarding lower potential systemic and local side effects.

NIK-IKK complex interaction controls NF-κB-dependent inflammatory activation of endothelium in response to LTβR ligation

NF-κB-inducing kinase (NIK; also known as MAP3K14) is a central regulator of non-canonical NF-κB signaling in response to stimulation of TNF receptor superfamily members, such as the lymphotoxin-β receptor (LTβR), and is implicated in pathological angiogenesis associated with chronic inflammation and cancer. Here, we identify a previously unrecognized role of the LTβR-NIK axis during inflammatory activation of human endothelial cells (ECs). Engagement of LTβR-triggered canonical and non-canonical NF-κB signaling promoted expression of inflammatory mediators and adhesion molecules, and increased immune cell adhesion to ECs. Sustained LTβR-induced inflammatory activation of ECs was NIK dependent, but independent of p100, indicating that the non-canonical arm of NF-κB is not involved. Instead, prolonged activation of canonical NF-κB signaling, through the interaction of NIK with IκB kinase α and β (also known as CHUK and IKBKB, respectively), was required for the inflammatory response. Endothelial inflammatory activation induced by synovial fluid from rheumatoid arthritis patients was significantly reduced by NIK knockdown, suggesting that NIK-mediated alternative activation of canonical NF-κB signaling is a key driver of pathological inflammatory activation of ECs. Targeting NIK could thus provide a novel approach for treating chronic inflammatory diseases.

NF-kappaΒ-inducing kinase regulates stem cell phenotype in breast cancer

Breast cancer stem cells (BCSCs) overexpress components of the Nuclear factor-kappa B (NF-κB) signaling cascade and consequently display high NF-κB activity levels. Breast cancer cell lines with high proportion of CSCs exhibit high NF-κB-inducing kinase (NIK) expression. The role of NIK in the phenotype of cancer stem cell regulation is poorly understood. Expression of NIK was analyzed by quantitative RT-PCR in BCSCs. NIK levels were manipulated through transfection of specific shRNAs or an expression vector. The effect of NIK in the cancer stem cell properties was assessed by mammosphere formation, mice xenografts and stem markers expression. BCSCs expressed higher levels of NIK and its inhibition through small hairpin (shRNA), reduced the expression of CSC markers and impaired clonogenicity and tumorigenesis. Genome-wide expression analyses suggested that NIK acts on ERK1/2 pathway to exert its activity. In addition, forced expression of NIK increased the BCSC population and enhanced breast cancer cell tumorigenicity. The in vivo relevance of these results is further supported by a tissue microarray of breast cancer samples in which we observed correlated expression of Aldehyde dehydrogenase (ALDH) and NIK protein. Our results support the essential involvement of NIK in BCSC phenotypic regulation via ERK1/2 and NF-κB.

Moderate activation of IKK2-NF-kB in unstressed adult mouse liver induces cytoprotective genes and lipogenesis without apparent signs of inflammation or fibrosis

Background

The NF-kB signaling, regulated by IKK1-p52/RelB and IKK2-p65, is activated by various stresses to protect or damage the liver, in context-specific manners. Two previous studies of liver-specific expression of constitutive active IKK2 (IKK2ca) showed that strong activation of IKK2-NF-kB in mouse livers caused inflammation, insulin resistance, and/or fibrosis. The purpose of this study was to understand how moderate activation of IKK2-NF-kB in adult mouse livers alters hepatic gene expression and pathophysiology.

Method

We generated mice with adult hepatocyte-specific activation of Ikk2 (Liv-Ikk2ca) using Alb-cre mice and Ikk2ca Rosa26 knockin mice in which a moderate expression of Ikk2ca transgene was driven by the endogenous Rosa26 promoter.

Results

Surprisingly, compared to wild-type mice, adult male Liv-Ikk2ca mice had higher hepatic mRNA expression of Ikk2 and classical NF-kB targets (e.g. Lcn2 and A20), as well as IKK1, NIK, and RelB, but no changes in markers of inflammation or fibrosis. Blood levels of IL-6 and MCP-1 remained unchanged, and histology analysis showed a lack of injury or infiltration of inflammatory cells in livers of Liv-Ikk2ca mice. Moreover, Liv-Ikk2ca mice had lower mRNA expression of prooxidative enzymes Cyp2e1 and Cyp4a14, higher expression of antioxidative enzymes Sod2, Gpx1, and Nqo1, without changes in key enzymes for fatty acid oxidation, glucose utilization, or gluconeogenesis. In parallel, Liv-Ikk2ca mice and wild-type mice had similar levels of hepatic reduced glutathione, endogenous reactive oxygen species, and lipid peroxidation. Additionally, Liv-Ikk2ca mice had higher Cyp3a11 without down-regulation of most drug processing genes. Regarding nuclear proteins of NF-kB subunits, Liv-Ikk2ca mice had moderately higher p65 and p50 but much higher RelB. Results of ChIP-qPCR showed that the binding of p50 to multiple NF-kB-target genes was markedly increased in Liv-Ikk2ca mice. Additionally, Liv-Ikk2ca mice had moderate increase in triglycerides in liver, which was associated with higher lipogenic factors Pparγ, Lxr, Fasn, Scd1, and CD36.

Conclusion

In summary, moderate activation of IKK2-NF-kB in unstressed adult mouse hepatocytes produces a cytoprotective gene expression profile and induces lipogenesis without apparent signs of inflammation or fibrosis, likely due to strong activation of the anti-inflammatory IKK1-RelB alternative NF-kB pathway as well as the Lxr.

Electronic supplementary material

The online version of this article (doi:10.1186/s12876-015-0325-z) contains supplementary material, which is available to authorized users.

An oncogenic role for alternative NF-κB signaling in DLBCL revealed upon deregulated BCL6 expression

Diffuse large B cell lymphoma (DLBCL) is a complex disease comprising diverse subtypes and genetic profiles. Possibly because of the prevalence of genetic alterations activating canonical NF-κB activity, a role for oncogenic lesions that activate the alternative NF-κB pathway in DLBCL has remained elusive. Here, we show that deletion/mutation of TRAF3, a negative regulator of the alternative NF-κB pathway, occurs in ∼15% of DLBCLs and that it often coexists with BCL6 translocation, which prevents terminal B cell differentiation. Accordingly, in a mouse model constitutive activation of the alternative NF-κB pathway cooperates with BCL6 deregulation in DLBCL development. This work demonstrates a key oncogenic role for the alternative NF-κB pathway in DLBCL development.

Receptor proximal kinases in NF-κB signaling as potential therapeutic targets in cancer and inflammation

Many signaling pathways leading to activation of transcription factors and gene expression are characterized by phosphorylation events mediated by specific kinases. The transcription factor NF-κB plays a key role in multiple cellular processes, including immune signaling, inflammation, development, proliferation and survival. Dysregulated NF-κB activation is associated with autoimmunity, chronic inflammation and cancer. Activation of NF-κB requires IκB kinase (IKK)α or β, the activity of which is regulated via phosphorylation by specific IKK kinases and by autophosphorylation. Receptor specificity is further obtained by the use of multiple upstream receptor proximal kinases. We review the identities of several IKK regulatory kinases as well as the proposed molecular mechanisms. In addition, we discuss the potential for therapeutic targeting of some of these kinases in the context of inflammatory diseases and cancer.

Priming IKKβ kinase for action

IKKβ (IκB kinase β) is a core component of signalling pathways that control the activation of NF-κB (nuclear factor κB) transcription factors, which regulate many physiological processes, including cell survival, immunity and DNA-damage responses. Like many kinases, activation of IKKβ requires phosphorylation of the activation loop of its kinase domain. Different upstream protein kinases, and IKKβ itself, have been reported to directly phosphorylate and activate IKKβ in vitro, but the exact molecular mechanism of IKKβ activation in cells has remained unclear. In a recent article in the Biochemical Journal, Zhang and co-workers showed that IKKβ is activated by two sequential phosphorylations of its activation loop in response to TNF (tumour necrosis factor), IL-1 (interleukin-1) and TLR (Toll-like receptor) ligands. Using a combination of biochemical and genetic approaches, they demonstrate that IKKβ is first phosphorylated by the upstream kinase TAK1 [TGFβ (transforming growth factor β)-activated kinase-1] at Ser177, which then serves as a priming signal for subsequent IKKβ autophosphorylation at Ser181. This study resolves two apparently conflicting earlier models of IKKβ activation into a single unified model, and suggests that the IKKβ activation loop may integrate distinct 'upsteam' signals to activate NF-κB.

The role of the IKK complex in viral infections

The NF‐κB signal transduction pathway is a critical regulator of multiple cellular functions that ultimately shift the balance between cell survival and death. The cascade is activated by many intrinsic and extrinsic stimuli, which is transduced via adaptor proteins to phosphorylate the IκB kinase (IKK) complex, which in turn phosphorylates the inhibitory IκBα protein to undergo proteasomal degradation and sets in motion nuclear events in response to the initial stimulus. Viruses are important modulators of the NF‐κB cascade and have evolved multiple mechanisms to activate or inhibit this pathway in a manner conducive to viral multiplication and establishment of a productive infectious cycle. This is a subject of extensive research by multiple laboratories whereby unraveling the interactions between specific viral components and members of the NF‐κB signal transduction cascade can shed unique perspectives on infection associated pathogenesis and novel therapeutic targets. In this review, we highlight the interactions between components of the IKK complex and multiple RNA and DNA viruses with the emphasis on mechanisms by which the interaction feeds the infection. Understanding these interactions will shed light on the exploitative capabilities of viruses to maintain an environment favorable for a productive infection.

Noncanonical Nuclear Factor Kappa B (NF-κB) Signaling and Potential for Therapeutics in Sepsis

NF-κB signaling plays a central role in the pathophysiology of severe sepsis and septic shock. Despite tremendous and missed efforts, novel therapeutics for severe sepsis and septic shock are still needed. Many drugs have been designed to target the canonical NF-κB signaling pathway with limited success, potentially due to the nonspecificity of the drugs for other kinases and the interaction of canonical signaling with other pathways. Here, we review the canonical and noncanonical signaling pathways of NF-κB, the cross talk and negative regulation of the two pathways, and the potential for therapeutics arising from the noncanonical NF-κB pathway in relation to the pathophysiology of septic shock.

cIAP2 represses IKKα/β-mediated activation of MDM2 to prevent p53 degradation

Cellular inhibitor of apoptosis proteins (cIAP1 and cIAP2) function to prevent apoptosis and are often overexpressed in various cancers. However, mutations in cIAP1/2 can activate the alternative NFκB pathway through IκBα-kinase-α (IKKα) and are associated with hematopoetic malignancies. In the current study, we found that knockdown of cIAP2 in human mammary epithelial cells resulted in activation of MDM2 through increased SUMOylation and profound reduction of the pool of MDM2 not phosphorylated at Ser166. cIAP2 siRNA markedly decreased p53 levels, which were rescued by addition of the MDM2 inhibitor, Nutlin3a. An IAP antagonist, which induces cIAP degradation, transiently increased MDM2 mRNA. Simultaneous transfection of siRNA for cIAP2 and IKKα reduced MDM2 protein, while expression of a kinase-dead IKKβ strongly increased non-Ser166 P-MDM2. Inhibition of either IKKα or -β partially rescued p53 levels, while concomitant IKKα/β inhibition fully rescued p53 after cIAP2 knockdown. Surprisingly, IKKα knockdown alone increased SUMO-MDM2, suggesting that in the absence of activation, IKKα can prevent MDM2 SUMOylation. cIAP2 knockdown disrupted the interaction between the MDM2 SUMO ligase, PIAS1 and IKKα. Partial knockdown of cIAP2 cooperated with (V12) H-ras-transfected mammary epithelial cells to enhance colony formation. In summary, our data identify a novel role for cIAP2 in maintaining wild-type p53 levels by preventing both an NFκB-mediated increase and IKKα/-β-dependent transcriptional and post-translational modifications of MDM2. Thus, mutations or reductions in cIAP2 could contribute to cancer promotion, in part, through downregulation of p53.

Distinct motifs in the intracellular domain of human CD30 differentially activate canonical and alternative transcription factor NF-κB signaling

The TNF-receptor superfamily member CD30 is expressed on normal and malignant lymphocytes, including anaplastic large cell lymphoma (ALCL) cells. CD30 transmits multiple effects, including activation of NF-κB signaling, cell proliferation, growth arrest and apoptosis. How CD30 generates these pleiotropic effects is currently unknown. Herein we describe ALCL cells expressing truncated forms of the CD30 intracellular domain that allowed us to identify the key regions responsible for transmitting its biological effects in lymphocytes. The first region (CD30_519–537) activated both the alternative and canonical NF-κB pathways as detected by p100 and IκBα degradation, IKKβ-dependent transcription of both IκBα and the cyclin-dependent kinase inhibitor p21^WAF1/CIP1 and induction of cell cycle arrest. In contrast, the second region of CD30 (CD30_538–595) induced some aspects of canonical NF-κB activation, including transcription of IκBα, but failed to activate the alternative NF-κB pathway or drive p21^WAF1/CIP1-mediated cell-cycle arrest. Direct comparison of canonical NF-κB activation by the two motifs revealed 4-fold greater p65 nuclear translocation following CD30_519–537 engagement. These data reveal that independent regions of the CD30 cytoplasmic tail regulate the magnitude and type of NF-κB activation and additionally identify a short motif necessary for CD30-driven growth arrest signals in ALCL cells.

Curcumin inhibits Rift Valley fever virus replication in human cells

Rift Valley fever virus (RVFV) is an arbovirus that is classified as a select agent, an emerging infectious virus, and an agricultural pathogen. Understanding RVFV-host interactions is imperative to the design of novel therapeutics. Here, we report that an infection by the MP-12 strain of RVFV induces phosphorylation of the p65 component of the NFκB cascade. We demonstrate that phosphorylation of p65 (serine 536) involves phosphorylation of IκBα and occurs through the classical NFκB cascade. A unique, low molecular weight complex of the IKK-β subunit can be observed in MP-12-infected cells, which we have labeled IKK-β2. The IKK-β2 complex retains kinase activity and phosphorylates an IκBα substrate. Inhibition of the IKK complex using inhibitors impairs viral replication, thus alluding to the requirement of an active IKK complex to the viral life cycle. Curcumin strongly down-regulates levels of extracellular infectious virus. Our data demonstrated that curcumin binds to and inhibits kinase activity of the IKK-β2 complex in infected cells. Curcumin partially exerts its inhibitory influence on RVFV replication by interfering with IKK-β2-mediated phosphorylation of the viral protein NSs and by altering the cell cycle of treated cells. Curcumin also demonstrated efficacy against ZH501, the fully virulent version of RVFV. Curcumin treatment down-regulated viral replication in the liver of infected animals. Our data point to the possibility that RVFV infection may result in the generation of novel versions of host components (such as IKK-β2) that, by virtue of altered protein interaction and function, qualify as unique therapeutic targets.

NF-κB directly regulates Fas transcription to modulate Fas-mediated apoptosis and tumor suppression

Fas is a member of the death receptor family. Stimulation of Fas leads to induction of apoptotic signals, such as caspase 8 activation, as well as "non-apoptotic" cellular responses, notably NF-κB activation. Convincing experimental data have identified NF-κB as a critical promoter of cancer development, creating a solid rationale for the development of antitumor therapy that suppresses NF-κB activity. On the other hand, compelling data have also shown that NF-κB activity enhances tumor cell sensitivity to apoptosis and senescence. Furthermore, although stimulation of Fas activates NF-κB, the function of NF-κB in the Fas-mediated apoptosis pathway remains largely undefined. In this study, we observed that deficiency of either Fas or FasL resulted in significantly increased incidence of 3-methylcholanthrene-induced spontaneous sarcoma development in mice. Furthermore, Fas-deficient mice also exhibited significantly greater incidence of azoxymethane and dextran sodium sulfate-induced colon carcinoma. In addition, human colorectal cancer patients with high Fas protein in their tumor cells had a longer time before recurrence occurred. Engagement of Fas with FasL triggered NF-κB activation. Interestingly, canonical NF-κB was found to directly bind to the FAS promoter. Blocking canonical NF-κB activation diminished Fas expression, whereas blocking alternate NF-κB increased Fas expression in human carcinoma cells. Moreover, although canonical NF-κB protected mouse embryo fibroblast (MEF) cells from TNFα-induced apoptosis, knocking out p65 diminished Fas expression in MEF cells, resulting in inhibition of FasL-induced caspase 8 activation and apoptosis. In contrast, knocking out p52 increased Fas expression in MEF cells. Our observations suggest that canonical NF-κB is a Fas transcription activator and alternate NF-κB is a Fas transcription repressor, and Fas functions as a suppressor of spontaneous sarcoma and colon carcinoma.

Kaposi's sarcoma associated herpesvirus encoded viral FLICE inhibitory protein K13 activates NF-κB pathway independent of TRAF6, TAK1 and LUBAC

BACKGROUND

Kaposi's sarcoma associated herpesvirus encoded viral FLICE inhibitory protein (vFLIP) K13 activates the NF-κB pathway by binding to the NEMO/IKKγ subunit of the IκB kinase (IKK) complex. However, it has remained enigmatic how K13-NEMO interaction results in the activation of the IKK complex. Recent studies have implicated TRAF6, TAK1 and linear ubiquitin chains assembled by a linear ubiquitin chain assembly complex (LUBAC) consisting of HOIL-1, HOIP and SHARPIN in IKK activation by proinflammatory cytokines.

METHODOLOGY/PRINCIPAL FINDINGS

Here we demonstrate that K13-induced NF-κB DNA binding and transcriptional activities are not impaired in cells derived from mice with targeted disruption of TRAF6, TAK1 and HOIL-1 genes and in cells derived from mice with chronic proliferative dermatitis (cpdm), which have mutation in the Sharpin gene (Sharpin(cpdm/cpdm)). Furthermore, reconstitution of NEMO-deficient murine embryonic fibroblast cells with NEMO mutants that are incapable of binding to linear ubiquitin chains supported K13-induced NF-κB activity. K13-induced NF-κB activity was not blocked by CYLD, a deubiquitylating enzyme that can cleave linear and Lys63-linked ubiquitin chains. On the other hand, NEMO was required for interaction of K13 with IKK1/IKKα and IKK2/IKKβ, which resulted in their activation by "T Loop" phosphorylation.

CONCLUSIONS/SIGNIFICANCE

Our results demonstrate that K13 activates the NF-κB pathway by binding to NEMO which results in the recruitment of IKK1/IKKα and IKK2/IKKβ and their subsequent activation by phosphorylation. Thus, K13 activates NF-κB via a mechanism distinct from that utilized by inflammatory cytokines. These results have important implications for the development of therapeutic agents targeting K13-induced NF-κB for the treatment of KSHV-associated malignancies.

Time-course analysis of injured skeletal muscle suggests a critical involvement of ERK1/2 signaling in the acute inflammatory response

INTRODUCTION

The coupling and timing of pro- and anti-inflammatory processes in skeletal muscle injury is poorly understood. We investigated the temporal response and regulated processes of extracellular signal-regulated kinases 1 and 2 (ERK1/2), p38, and IkappaB kinase (IKK) α/β signaling pathways after traumatic injury.

METHODS

Traumatic freeze injury was delivered to the tibialis anterior (TA) muscle in C57BL/6J mice, and injured and uninjured TA muscles were analyzed 3-72 h into the recovery period.

RESULTS

Significant increases in pro-inflammatory cytokine transcription accompanied IKKβ phosphorylation, robust ERK pathway activation, and reduced heat shock protein (Hsp) protein expression at 3-24 h. At 24 h, ERK activation was abolished concomitantly with a significant increase in mitogen-activated protein kinase phosphatase-1 (MKP-1). After 24 h, cytokine transcription along with ERK1/2 and IKKβ phosphorylation remained suppressed, whereas Hsp protein expression rose to significant levels by 72 h and associated with IKKβ.

CONCLUSIONS

Results indicate a bimodal regulation of ERK1/2 in acute inflammation in which it is supportive from 3 to 24 h, and suppressive from 24 to 72 h.

Doxorubicin-induced activation of NF-κB in melanoma cells is abrogated by inhibition of IKKβ, but not by a novel IKKα inhibitor

Drug resistance is arguably the most important challenge in cancer therapy. Here, doxorubicin induced profound of NF-κB activation in melanoma cells with a maximum (3.5-fold) at concentrations relevant in vivo. This was followed by transcriptional induction of several gene products involved in tumor progression. A novel IKKα inhibitor (BAY32-5915) was identified and characterized, and doxorubicin-induced NF-κB activation was assessed following inhibition of IKKα or IKKβ by small-molecular compounds. While the IKKα inhibitor did not affect doxorubicin-induced NF-κB activation, this process was completely abrogated when the IKKβ inhibitor, KINK-1, was used. Moreover, inhibition of IKKβ, but not IKKα, led to significantly increased apoptosis in response to doxorubicin. Our results indicate that the net outcome of chemotherapy is difficult to predict and may even involve mechanisms conferring chemoresistance. In case of doxorubicin-induced NF-κB activation, blocking IKKβ, but not IKKα, by small molecules can antagonize this activity and, thus, increase chemosensitivity.

Signaling by the tumor necrosis factor receptor superfamily in B-cell biology and disease

Members of the tumor necrosis factor receptor superfamily (TNFRSF) participate prominently in B-cell maturation and function. In particular, B-cell activating factor belonging to the TNF family receptor (BAFF-R), B-cell maturation antigen (BCMA), and transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI) play critical roles in promoting B-cell survival at distinct stages of development by engaging a proliferation-inducing ligand (APRIL) and/or BAFF. CD40 is also essential for directing the humoral response to T-cell-dependent antigens. Signaling by the TNFRSF is mediated primarily, albeit not exclusively, via the TNFR-associated factor (TRAF) proteins and activation of the canonical and/or non-canonical nuclear factor-κB (NF-κB) pathways. Dysregulated signaling by TNFRSF members can promote B-cell survival and proliferation, causing autoimmunity and neoplasia. In this review, we present a current understanding of the functions of and distinctions between APRIL/BAFF signaling by their respective receptors expressed on particular B-cell subsets. These findings are compared and contrasted with CD40 signaling, which employs similar signaling conduits to achieve distinct cellular outcomes in the context of the germinal center response. We also underscore how new findings and conceptual insights into TNFRSF signaling are facilitating the understanding of B-cell malignancies and autoimmune diseases.

Inhibitory kappa B Kinases as targets for pharmacological regulation

The inhibitory kappa B kinases (IKKs) are well recognized as key regulators of the nuclear factor kappa B (NF-κB) cascade and as such represent a point of convergence for many extracellular agents that activate this pathway. The IKKs generally serve to transduce pro-inflammatory and growth stimulating signals that contribute to major cellular processes but also play a key role in the pathogenesis of a number of human diseases. Therefore, the catalytic IKKs represent attractive targets for intervention with small molecule kinase inhibitors. IKK isoforms are assembled as variable multi-subunit IKK complexes that regulate not only NF-κB dimers, but also protein substrates out-with this cascade. Consequently, close consideration of how these individual complexes transduce extracellular signals and more importantly what impact small molecule inhibitors of the IKKs have on functional outcomes are demanded. A number of adenosine triphosphate (ATP)-competitive IKKβ-selective inhibitors have been developed but have demonstrated a lack of activity against IKKα. A number of these chemicals have also exhibited detrimental outcomes such as cellular toxicity and immuno-suppression. The impact of small molecule inhibitors of IKK catalytic activity will therefore be reappraised, examining the advantages and potential disadvantages to this type of intervention strategy in the treatment of diseases such as arthritis, intestinal inflammation and cancer. Furthermore, we will outline some emerging strategies, particularly the disruption of protein-protein interactions within the IKK complex, as an alternative route towards the development of novel pharmacological agents. Whether these alternatives may negate the limitations of ATP-competitive molecules and potentially avoid the issues of toxicity will be discussed.

NF-κB inducing kinase, NIK mediates cigarette smoke/TNFα-induced histone acetylation and inflammation through differential activation of IKKs

BACKGROUND

Nuclear factor (NF)-κB inducing kinase (NIK) is a central player in the non-canonical NF κB pathway, which phosphorylates IκB kinase α (IKKα) resulting in enhancement of target gene expression. We have recently shown that IKKα responds to a variety of stimuli including oxidants and cigarette smoke (CS) regulating the histone modification in addition to its role in NF-κB activation. However, the primary signaling mechanism linking CS-mediated oxidative stress and TNFα with histone acetylation and pro-inflammatory gene transcription is not well understood. We hypothesized that CS and TNFα increase NIK levels causing phosphorylation of IKKα, which leads to histone acetylation.

METHODOLOGY

To test this hypothesis, we investigated whether NIK mediates effects of CS and TNFα on histone acetylation in human lung epithelial cells in vitro and in lungs of mouse exposed to CS in vivo. CS increased the phosphorylation levels of IKKα/NIK in lung epithelial cells and mouse lungs. NIK is accumulated in the nuclear compartment, and is recruited to the promoters of pro-inflammatory genes, to induce posttranslational acetylation of histones in response to CS and TNFα. Cells in which NIK is knocked down using siRNA showed partial attenuation of CSE- and TNFα-induced acetylation of histone H3 on pro-inflammatory gene promoters. Additional study to determine the role of IKKβ/NF-κB pathway in CS-induced histone acetylation suggests that the canonical pathway does not play a role in histone acetylation particularly in response to CS in mouse lungs.

CONCLUSIONS

Overall, our findings provide a novel role for NIK in CS- and TNFα-induced histone acetylation, especially on histone H3K9.

A single nucleotide polymorphism in NF-κB inducing kinase is associated with mortality in septic shock

We tested the hypothesis that single nucleotide polymorphisms (SNPs) within genes of the NF-κB pathway are associated with altered clinical outcome of septic shock patients. We genotyped 59 SNPs in the NF-κB pathway in a discovery cohort of septic shock patients (St. Paul's Hospital [SPH], N = 589), which identified the C allele of rs7222094 T/C within MAP3K14 (NF-κB inducing kinase; NIK) associated with increased 28-d mortality (uncorrected p = 0.00024, Bonferroni corrected p = 0.014). This result was replicated in a second cohort of septic shock patients (Vasopressin and Septic Shock Trial [VASST; N = 616]) in which the CC genotype of rs7222094 was associated with increased 28-d mortality (Cox regression: SPH cohort hazard ratio [HR], 1.35; 95% confidence interval [CI], 1.12-1.64; p = 0.002 Caucasian only; and VASST cohort HR, 1.24; 95% CI, 1.00-1.52; p = 0.048 Caucasian only). Patients having the CC genotype of rs7222094 in SPH experienced more renal and hematological dysfunction (p = 0.003 and p = 0.011), while patients of the VASST cohort with the rs7222094 CC genotype showed the same trend toward more renal dysfunction. In lymphoblastoid cell lines, we found the rs7222094 genotype most strongly associated with mRNA expression of CXCL10, a chemokine regulated by NF-κB. Accordingly, we measured CXCL10 protein levels and found that the CC genotype of rs7222094 was associated with significantly lower levels than those of the TT genotype in lymphoblastoid cell lines (p < 0.05) and in septic shock patients (p = 0.017). This suggests that the CC genotype of NIK rs7222094 is associated with increased mortality and organ dysfunction in septic shock patients, perhaps due to altered regulation of NF-κB pathway genes, including CXCL10.

The kinase NIK as a therapeutic target in multiple myeloma

INTRODUCTION

Multiple myeloma (MM) is a neoplasm derived from B lymphocytes and often results in uncontrolled clonal expansion of antibody-secreting cells. While current treatments are able to prolong survival, MM remains incurable. Excessive NF-κB activity in MM contributes to tumor progression and survival.

AREAS COVERED

The contribution of NF-κB-inducing kinase (NIK) to alternative NF-κB signaling, where it is the key kinase, and classical NF-κB signaling. Modulation of NIK by natural and chemical factors and current and potential therapies for MM that target NIK.

EXPERT OPINION

Mutations affecting the activation of NIK have been identified in MM samples and cell lines, suggesting that NIK may be an important target for therapy of MM. NIK contributes to activation of both NF-κB pathways in MM, giving us the opportunity to limit two pathways contributing to oncogenic survival with a single therapeutic. Many of the mutations identified in MM cells result in the same outcome, hyperactive NIK, thus a single therapeutic may be effective in many patients even though they carry differing mutations. As NIK appears only to activate classical NF-κB when overexpressed, and in normal cells NIK levels are usually low, it is possible that therapeutics designed to limit the amount of NIK may not produce serious side effects in healthy cells.

TNFα cooperates with IFN-γ to repress Bcl-xL expression to sensitize metastatic colon carcinoma cells to TRAIL-mediated apoptosis

Background

TNF-related apoptosis-inducing ligand (TRAIL) is an immune effector molecule that functions as a selective anti-tumor agent. However, tumor cells, especially metastatic tumor cells often exhibit a TRAIL-resistant phenotype, which is currently a major impediment in TRAIL therapy. The aim of this study is to investigate the synergistic effect of TNFα and IFN-γ in sensitizing metastatic colon carcinoma cells to TRAIL-mediated apoptosis.

Methodology/Principal Findings

The efficacy and underlying molecular mechanism of cooperation between TNFα and IFN-γ in sensitizing metastatic colon carcinoma cells to TRAIL-mediated apoptosis were examined. The functional significance of TNFα- and IFN-γ-producing T lymphocyte immunotherapy in combination with TRAIL therapy in suppression of colon carcinoma metastasis was determined in an experimental metastasis mouse model. We observed that TNFα or IFN-γ alone exhibits minimal sensitization effects, but effectively sensitized metastatic colon carcinoma cells to TRAIL-induced apoptosis when used in combination. TNFα and IFN-γ cooperate to repress Bcl-xL expression, whereas TNFα represses Survivin expression in the metastatic colon carcinoma cells. Silencing Bcl-xL expression significantly increased the metastatic colon carcinoma cell sensitivity to TRAIL-induced apoptosis. Conversely, overexpression of Bcl-xL significantly decreased the tumor cell sensitivity to TRAIL-induced apoptosis. Furthermore, TNFα and IFN-γ also synergistically enhanced TRAIL-induced caspase-8 activation. TNFα and IFN-γ was up-regulated in activated primary and tumor-specific T cells. TRAIL was expressed in tumor-infiltrating immune cells in vivo, and in tumor-specific cytotoxic T lymphocytes (CTL) ex vivo. Consequently, TRAIL therapy in combination with TNFα/IFN-γ-producing CTL adoptive transfer immunotherapy effectively suppressed colon carcinoma metastasis in vivo.

Conclusions/Significance

TNFα and IFN-γ cooperate to overcome TRAIL resistance at least partially through enhancing caspase 8 activation and repressing Bcl-xL expression. Combined CTL immunotherapy and TRAIL therapy hold great promise for further development for the treatment of metastatic colorectal cancer.

Emerging complexity of protein ubiquitination in the NF-κB pathway

Members of the nuclear factor-κB (NF-κB) family of transcription factors play critical roles in regulating the expression of genes whose products are involved in inflammation, the immune response, cell proliferation, and the suppression of both death receptor- and stress-induced apoptosis. Abnormal NF-κB activation has been observed in various inflammatory diseases and many types of cancers. Gene knockout studies have clearly demonstrated that most of the physiologically relevant stimuli that activate NF-κB converge on inhibitor of κB kinase (IKK). Although the mechanism by which IKK activates NF-κB is well established, the upstream signaling mechanisms-those that underlie IKK activation by IKK kinases (IKK-Ks)-are not yet fully understood. The current belief is that members of the TNF receptor-associated factor (TRAF) family function as ubiquitin E3 ligases that catalyze non-canonical polyubiquitination of adaptor proteins, and that the ubiquitinated adaptor proteins in turn serve as platforms to recruit IKK and IKK-Ks, facilitating IKK activation through proximity-mediated phosphorylation. This review will focus on the most recent findings relating to the role of TRAFs-mediated protein ubiquitination in regulating IKK activation, and highlight the newly emerging complexity of protein ubiquitination in receptor-induced NF-κB activation.

NF-κB inducing kinase: a key regulator in the immune system and in cancer

NF-κB inducing kinase (NIK) is a kinase that activates the canonical and non-canonical NF-κB pathways to control transcriptional expression of certain proteins such as cytokines, chemokines and NF-κB signaling molecules. Many advances have been made in understanding the molecular mechanisms by which the stability of NIK is regulated to affect downstream signaling. Genetic mouse models suggest that NIK plays an essential role in the regulation of the immune system as well as in the bone microenvironment. Increasing evidence links NIK to the tumorigenesis of hematological cancers, such as multiple myeloma, and solid tumors, such as pancreatic carcinoma and melanoma. Understanding the mechanism by which NIK is de-regulated will potentially provide therapeutic options for certain diseases such as autoimmunity and cancer.

Oncogenic activation of NF-kappaB

Recent genetic evidence has established a pathogenetic role for NF-kappaB signaling in cancer. NF-kappaB signaling is engaged transiently when normal B lymphocytes respond to antigens, but lymphomas derived from these cells accumulate genetic lesions that constitutively activate NF-kappaB signaling. Many genetic aberrations in lymphomas alter CARD11, MALT1, or BCL10, which constitute a signaling complex that is intermediate between the B-cell receptor and IkappaB kinase. The activated B-cell-like subtype of diffuse large B-cell lymphoma activates NF-kappaB by a variety of mechanisms including oncogenic mutations in CARD11 and a chronic active form of B-cell receptor signaling. Normal plasma cells activate NF-kappaB in response to ligands in the bone marrow microenvironment, but their malignant counterpart, multiple myeloma, sustains a variety of genetic hits that stabilize the kinase NIK, leading to constitutive activation of the classical and alternative NF-kappaB pathways. Various oncogenic abnormalities in epithelial cancers, including mutant K-ras, engage unconventional IkappaB kinases to activate NF-kappaB. Inhibition of constitutive NF-kappaB signaling in each of these cancer types induces apoptosis, providing a rationale for the development of NF-kappaB pathway inhibitors for the treatment of cancer.

Negative feedback in noncanonical NF-kappaB signaling modulates NIK stability through IKKalpha-mediated phosphorylation

Canonical and noncanonical nuclear factor kappaB (NF-kappaB) signaling are the two basic pathways responsible for the release of NF-kappaB dimers from their inhibitors. Enhanced NF-kappaB signaling leads to inflammatory and proliferative diseases; thus, inhibitory pathways that limit its activity are critical. Whereas multiple negative feedback mechanisms control canonical NF-kappaB signaling, none has been identified for the noncanonical pathway. Here, we describe a mechanism of negative feedback control of noncanonical NF-kappaB signaling that attenuated the stabilization of NF-kappaB-inducing kinase (NIK), the central regulatory kinase of the noncanonical pathway, induced by B cell-activating factor receptor (BAFF-R) and lymphotoxin beta receptor (LTbetaR). Inhibitor of kappaB (IkappaB) kinase alpha (IKKalpha) was previously thought to lie downstream of NIK in the noncanonical NF-kappaB pathway; we showed that phosphorylation of NIK by IKKalpha destabilized NIK. In the absence of IKKalpha-mediated negative feedback, the abundance of NIK increased after receptor ligation. A form of NIK with mutations in the IKKalpha-targeted serine residues was more stable than wild-type NIK and resulted in increased noncanonical NF-kappaB signaling. Thus, in addition to the regulation of the basal abundance of NIK in unstimulated cells by a complex containing tumor necrosis factor receptor-associated factor (TRAF) and cellular inhibitor of apoptosis (cIAP) proteins, IKKalpha-dependent destabilization of NIK prevents the uncontrolled activity of the noncanonical NF-kappaB pathway after receptor ligation.

Classical and/or alternative NF-kappaB pathway activation in multiple myeloma

Mutations involving the nuclear factor-kappaB (NF-kappaB) pathway are present in at least 17% of multiple myeloma (MM) tumors and 40% of MM cell lines (MMCLs). These mutations, which are apparent progression events, enable MM tumors to become less dependent on bone marrow signals that activate NF-kappaB. Studies on a panel of 51 MMCLs provide some clarification of the mechanisms through which these mutations act and the significance of classical versus alternative activation of NF-kappaB. First, only one mutation (NFKB2) selectively activates the alternative pathway, whereas several mutations (CYLD, NFKB1, and TACI) selectively activate the classical pathway. However, most mutations affecting NF-kappaB-inducing kinase (NIK) levels (NIK, TRAF2, TRAF3, cIAP1&2, and CD40) activate the alternative but often both pathways. Second, we confirm the critical role of TRAF2 in regulating NIK degradation, whereas TRAF3 enhances but is not essential for cIAP1/2-mediated proteasomal degradation of NIK in MM. Third, using transfection to selectively activate the classical or alternative NF-kappaB pathways, we show virtually identical changes in gene expression in one MMCL, whereas the changes are similar albeit nonidentical in a second MMCL. Our results suggest that MM tumors can achieve increased autonomy from the bone marrow microenvironment by mutations that activate either NF-kappaB pathway.

IKKalpha and IKKbeta each function to regulate NF-kappaB activation in the TNF-induced/canonical pathway

Background

Activation of the transcription factor NF-κB by cytokines is rapid, mediated through the activation of the IKK complex with subsequent phosphorylation and degradation of the inhibitory IκB proteins. The IKK complex is comprised of two catalytic subunits, IKKα and IKKβ, and a regulatory protein known as NEMO. Using cells from mice that are genetically deficient in IKKβ or IKKα, or using a kinase inactive mutant of IKKβ, it has been proposed that IKKβ is critical for TNF-induced IκB phosphorylation/degradation through the canonical pathway while IKKα has been shown to be involved in the non-canonical pathway for NF-κB activation. These conclusions have led to a focus on development of IKKβ inhibitors for potential use in inflammatory disorders and cancer.

Methodology

Analysis of NF-κB activation in response to TNF in MEFs reveals that IKKβ is essential for efficient phosphorylation and subsequent degradation of IκBα, yet IKKα contributes to the NF-κB activation response in these cells as measured via DNA binding assays. In HeLa cells, both IKKα and IKKβ contribute to IκBα phosphorylation and NF-κB activation. A kinase inactive mutant of IKKβ, which has been used as evidence for the critical importance of IKKβ in TNF-induced signaling, blocks activation of NF-κB induced by IKKα, even in cells that are deficient in IKKβ.

Conclusions

These results demonstrate the importance of IKKα in canonical NF-κB activation, downstream of cytokine treatment of cells. The experiments suggest that IKKα will be a therapeutic target in inflammatory disorders.

Ursolic acid inhibits IL-1beta or TNF-alpha-induced C6 glioma invasion through suppressing the association ZIP/p62 with PKC-zeta and downregulating the MMP-9 expression

Ursolic acid (UA), a constant constituent of Rosmarinus officinalis extracts, is a triterpenoid compound which has been shown to have antioxidant and anticarcinogenic properties. In the present study, we found that UA was able to reduce interleukin-1 beta (IL-1beta) or tumor necrosis-alpha (TNF-alpha)-induced rat C6 glioma cell invasion, which was examined by a reconstituted basement membrane in a set of transwell chambers. However, the inhibitory effect of UA did not influence cell proliferation or cause cell cytotoxity. The results analyzed by zymography assay and Western blotting revealed that the activity and expression of matrix metalloproteinase-9 (MMP-9) was eliminated by UA in a dose-dependent manner. Because MMP-9 is the target gene of the transcription factor nuclear factor-kappaB (NF-kappaB), we further investigated the effect of UA on the activity of NF-kappaB. As expected, UA upregulated the levels of IkappaBalpha (IkappaBalpha) and attenuated the nuclear translocation of p65. Furthermore, UA suppressed the IL-1beta or TNF-alpha-induced activation of protein kinase C-zeta (PKC-zeta). Our data showed UA potently inhibited the association of ZIP/p62 and PKC-zeta. Taken together, we demonstrated that UA could efficiently inhibit the interaction of ZIP/p62 and PKC-zeta. It also further suppressed the activation of NF-kappaB and downregulation of the MMP-9 protein, which in turn contributed to its inhibitory effects on IL-1beta or TNF-alpha-induced C6 glioma cell invasion. These results all showcase the potential UA has in the chemoprevention and treatment of cancer metastasis and invasion.

Tumor necrosis factor-related weak inducer of apoptosis augments matrix metalloproteinase 9 (MMP-9) production in skeletal muscle through the activation of nuclear factor-kappaB-inducing kinase and p38 mitogen-activated protein kinase: a potential role of MMP-9 in myopathy

Destruction of skeletal muscle extracellular matrix is an important pathological consequence of many diseases involving muscle wasting. However, the underlying mechanisms leading to extracellular matrix breakdown in skeletal muscle tissues remain unknown. Using a microarray approach, we investigated the effect of tumor necrosis factor-related weak inducer of apoptosis (TWEAK), a recently identified muscle-wasting cytokine, on the expression of extracellular proteases in skeletal muscle. Among several other matrix metalloproteinases (MMPs), we found that the expression of MMP-9, a type IV collagenase, was drastically increased in myotubes in response to TWEAK. The level of MMP-9 was also higher in myofibers of TWEAK transgenic mice. TWEAK increased the activation of both classical and alternative nuclear factor-kappaB (NF-kappaB) signaling pathways. Inhibition of NF-kappaB activity blocked the TWEAK-induced production of MMP-9 in myotubes. TWEAK also increased the activation of AP-1, and its inhibition attenuated the TWEAK-induced MMP-9 production. Overexpression of a kinase-dead mutant of NF-kappaB-inducing kinase or IkappaB kinase-beta but not IkappaB kinase-alpha significantly inhibited the TWEAK-induced activation of MMP-9 promoter. The activation of MMP-9 also involved upstream recruitment of TRAF2 and cIAP2 proteins. TWEAK increased the activity of ERK1/2, JNK1, and p38 MAPK. However, the inhibition of only p38 MAPK blocked the TWEAK-induced expression of MMP-9 in myotubes. Furthermore the loss of body and skeletal muscle weights, inflammation, fiber necrosis, and degradation of basement membrane around muscle fibers were significantly attenuated in Mmp9 knock-out mice on chronic administration of TWEAK protein. The study unveils a novel mechanism of skeletal muscle tissue destruction in pathological conditions.

Phosphorylation and stabilization of TAp63gamma by IkappaB kinase-beta

Post-translational modification of the p53 family members is key to their regulation. Here we report the phosphorylation of TAp63gamma, but not DeltaNp63gamma, by IkappaB kinase beta (IKKbeta). Activation of IKKbeta by gamma radiation or tumor necrosis factor-alpha led to increased TAp63gamma protein levels in cells. IKKbeta, but not its kinase-defective mutant IKKbeta-K44A, led to this observed stabilization of TAp63gamma. This stabilization of TAp63gamma in response to gamma radiation was significantly decreased in the absence of IKKbeta. Phosphorylation of TAp63gamma blocks ubiquitylation and possible degradation of this protein. We postulate that phosphorylation of TAp63gamma by IKKbeta stabilizes the TAp63gamma protein by blocking ubiquitylation-dependent degradation of this protein.

Independent activation of Akt and NF-kappaB pathways and their role in resistance to TNF-alpha mediated cytotoxicity in gliomas

Tumor associated macrophages (TAMs) constitute a substantial mass in gliomas. The activated macrophages secrete various cytokines that affect diverse functions of tumors. The aim of this study was to elucidate the role of Akt and NF-kappaB pathways in resistance to TNF-alpha mediated cell death in human gliomas using monolayers and multicellular spheroids (MCS) as in vitro models. Akt and NF-kappaB are constitutively expressed and intimately involved in progression of gliomas. The activation of these pathways also renders the tumors resistant to conventional treatments including chemotherapy. While PI3K/Akt is shown to regulate the NF-kappaB activation in diverse systems, other studies place NF-kappaB upstream of Akt activation. Using a stable IkappaBalpha mutant LN-18 cell line and pharmacological inhibitors to PI3K/Akt (LY294002) and Akt (Akt2), we provide evidence that Akt and NF-kappaB are activated independently on stimulation with TNF-alpha and both the pathways contribute towards resistance to TNF-alpha mediated cell death. TNF-alpha-induced NF-kappaB activation independent of PI3K/Akt pathway was also confirmed in human glioma cell lines-LN-229 and U373MG. We also show that NF-kappaB and Akt are activated during spheroidogenesis and their expression is further enhanced on stimulation with TNF-alpha implicating their involvement in resistance to cell death. The findings thus underscore the relevance of spheroids as appropriate in vitro models for studying the signaling pathways in drug induced resistance.

Control of canonical NF-kappaB activation through the NIK-IKK complex pathway

Articles in recent years have described two separate and distinct NF-kappaB activation pathways that result in the differential activation of p50- or p52-containing NF-kappaB complexes. Studies examining tumor-necrosis factor receptor-associated factors (TRAFs) have identified positive roles for TRAF2, TRAF5, and TRAF6, but not TRAF3, in canonical (p50-dependent) NF-kappaB activation. Conversely, it recently was reported that TRAF3 functions as an essential negative regulator of the noncanonical (p52-dependent) NF-kappaB pathway. In this article, we provide evidence that TRAF3 potently suppresses canonical NF-kappaB activation and gene expression in vitro and in vivo. We also demonstrate that deregulation of the canonical NF-kappaB pathway in TRAF3-deficient cells results from accumulation of NF-kappaB-inducing kinase (NIK), the essential kinase mediating noncanonical NF-kappaB activation. Thus, our data demonstrate that inhibition of TRAF3 results in coordinated activation of both NF-kappaB activation pathways.

Signalling of toll-like receptors

Since Toll-like receptor (TLR) signaling was found crucial for the activation of innate and adaptive immunity, it has been the focus of immunological research. There are at least 13 identified mammalian TLRs, to date, that share similarities in their extracellular and intracellular domains. A vast number of ligands have been identified that are specifically recognized by different TLRs. As a response the TLRs dimerize and their signaling is initiated. The molecular basis of that signaling depends on the conserved part of their intracellular domain; namely the Toll/IL-1 receptor (TIR) domain. Upon TLR dimerization a TIR-TIR structure is formed that can recruit TIR-containing intracellular proteins that mediate their signaling. For this reason these proteins are named adapters. There are five adapters identified so far named myeloid differentiation primary response protein 88 (MyD88), MyD88-adapter like (Mal) or TIR domain-containing adapter (TIRAP), TIR domain-containing adapter inducing interferon-beta (IFN-beta) (TRIF) or TIR-containing adapter molecule-1 (TICAM-1), TRIF-related adapter molecule (TRAM) or TICAM-2, and sterile alpha and HEAT-Armadillo motifs (SARM). The first four play a fundamental role in TLR-signaling, defining which pathways will be activated, depending on which of these adapters will be recruited by each TLR. Among these adapter proteins MyD88 and TRIF are now considered as the signaling ones and hence the TLR pathways can be categorized as MyD88-dependent and TRIF-dependent.

Retroviral insertions in the VISION database identify molecular pathways in mouse lymphoid leukemia and lymphoma

AKXD recombinant inbred (RI) strains develop a variety of leukemias and lymphomas due to somatically acquired insertions of retroviral DNA into the genome of hematopoetic cells that can mutate cellular proto-oncogenes and tumor suppressor genes. We generated a new set of tumors from nine AKXD RI strains selected for their propensity to develop B-cell tumors, the most common type of human hematopoietic cancers. We employed a PCR technique called viral insertion site amplification (VISA) to rapidly isolate genomic sequence at the site of provirus insertion. Here we describe 550 VISA sequence tags (VSTs) that identify 74 common insertion sites (CISs), of which 21 have not been identified previously. Several suspected proto-oncogenes and tumor suppressor genes lie near CISs, providing supportive evidence for their roles in cancer. Furthermore, numerous previously uncharacterized genes lie near CISs, providing a pool of candidate disease genes for future research. Pathway analysis of candidate genes identified several signaling pathways as common and powerful routes to blood cancer, including Notch, E-protein, NFκB, and Ras signaling. Misregulation of several Notch signaling genes was confirmed by quantitative RT-PCR. Our data suggest that analyses of insertional mutagenesis on a single genetic background are biased toward the identification of cooperating mutations. This tumor collection represents the most comprehensive study of the genetics of B-cell leukemia and lymphoma development in mice. We have deposited the VST sequences, CISs in a genome viewer, histopathology, and molecular tumor typing data in a public web database called VISION (Viral Insertion Sites Identifying Oncogenes), which is located at http://www.mouse-genome.bcm.tmc.edu/vision.

Frequent engagement of the classical and alternative NF-kappaB pathways by diverse genetic abnormalities in multiple myeloma

Mechanisms of constitutive NF-kappaB signaling in multiple myeloma are unknown. An inhibitor of IkappaB kinase beta (IKKbeta) targeting the classical NF-kappaB pathway was lethal to many myeloma cell lines. Several cell lines had elevated expression of NIK due to genomic alterations or protein stabilization, while others had inactivating mutations of TRAF3; both kinds of abnormality triggered the classical and alternative NF-kappaB pathways. A majority of primary myeloma patient samples and cell lines had elevated NF-kappaB target gene expression, often associated with genetic or epigenetic alteration of NIK, TRAF3, CYLD, BIRC2/BIRC3, CD40, NFKB1, or NFKB2. These data demonstrate that addiction to the NF-kappaB pathway is frequent in myeloma and suggest that IKKbeta inhibitors hold promise for the treatment of this disease.

Recruitment and activation of RSK2 by HIV-1 Tat

The transcriptional activity of the integrated HIV provirus is dependent on the chromatin organization of the viral promoter and the transactivator Tat. Tat recruits the cellular pTEFb complex and interacts with several chromatin-modifying enzymes, including the histone acetyltransferases p300 and PCAF. Here, we examined the interaction of Tat with activation-dependent histone kinases, including the p90 ribosomal S6 kinase 2 (RSK2). Dominant-negative RSK2 and treatment with a small-molecule inhibitor of RSK2 kinase activity inhibited the transcriptional activity of Tat, indicating that RSK2 is important for Tat function. Reconstitution of RSK2 in cells from subjects with a genetic defect in RSK2 expression (Coffin-Lowry syndrome) enhanced Tat transactivation. Tat interacted with RSK2 and activated RSK2 kinase activity in cells. Both properties were lost in a mutant Tat protein (F38A) that is deficient in HIV transactivation. Our data identify a novel reciprocal regulation of Tat and RSK2 function, which might serve to induce early changes in the chromatin organization of the HIV LTR.

Low shear stress preferentially enhances IKK activity through selective sources of ROS for persistent activation of NF-kappaB in endothelial cells

NF-kappaB signaling pathway has been known to play a major role in the pathological process of atherogenesis. Unlike high shear stress, in which the NF-kappaB activity is transient, our earlier studies have demonstrated a persistent activation of NF-kappaB in response to low shear stress in human aortic endothelial cells. These findings partially explained why low shear regions that exist at bifurcations of arteries are prone to atherosclerosis, unlike the relatively atheroprotective high shear regions. In the present study, we further investigated 1) the role of NF-kappaB signaling kinases (IKKalpha and beta) that may be responsible for the sustained activation of NF-kappaB in low shear stress and 2) the regulation of these kinases by reactive oxygen species (ROS). Our results demonstrate that not only is a significant proportion of low shear-induced-kinase activity is contributed by IKKbeta, but it is also persistently induced for a prolonged time frame. The IKK activity (both alpha and beta) is blocked by apocynin (400 microM), a specific NADPH oxidase inhibitor, and diphenyleneiodonium chloride (DPI; 10 microM), an inhibitor of flavin-containing oxidases like NADPH oxidases. Determination of ROS also demonstrated an increased generation in low shear stress that could be blocked by DPI. These results suggest that the source of ROS generation in endothelial cells in response to low shear stress is NADPH oxidase. The DPI-inhibitable component of ROS is the primary regulator of specific upstream kinases that determine the persistent NF-kappaB activation selectively in low shear-induced endothelial cells.

IKKalpha and IKKbeta function in TNFalpha-stimulated adhesion molecule expression in human aortic smooth muscle cells

The role of NFkappaB and it's upstream kinases in regulating adhesion molecule expression in the smooth muscle of the vasculature remains controversial. We therefore examined the effect of blocking the NFkappaB pathway on TNFalpha-stimulated ICAM-1 and VCAM-1 expression in primary cultures of human aortic smooth muscle cells using an adenoviral wild-type IkappaB alpha construct (Ad.IkappaB alpha) and dominant-negative IKKalpha (Ad.IKKalpha+/-) and IKKbeta (Ad.IKKbeta+/-) constructs. Ad.IkappaB alpha treatment was found to block NFkappaB DNA-binding, and thereby completely prevent TNFalpha-stimulated ICAM-1 and VCAM-1 expression without influencing IKK activity. Ad.IKKbeta+/- treatment completely inhibited TNFalpha-stimulated IKK kinase activity, IkappaB alpha degradation and NFkappaB DNA-binding in addition to completely blocking TNFalpha-stimulated ICAM-1 and VCAM-1 expression. Ad.IKKalpha+/- treatment however had no detectable effect on NFkappaB DNA-binding or ICAM-1 and VCAM-1 expression. Our results demonstrate that TNFalpha-stimulated ICAM-1 and VCAM-1 expression in human aortic smooth muscle cells is NFkappaB-dependent, that IKKbeta is a suitable target for drug therapy and Ad.IKKbeta+/- an effective inhibitor of TNFalpha-stimulated ICAM-1 and VCAM-1 expression.

Peroxisome proliferator-activated receptor-γ inhibits cigarette smoke solution-induced mucin production in human airway epithelial (NCI-H292) cells

The main etiologic factor for chronic bronchitis is cigarette smoke. Exposure to cigarette smoke is reported to induce goblet cell hyperplasia and mucus production. Mucin synthesis in airways has been reported to be regulated by the EGFR system. Peroxisome proliferator-activated receptor-γ (PPAR-γ) is a member of the ligand-activated nuclear receptor superfamily. PPAR-γ is implicated in anti-inflammatory responses, but mechanisms underlying these varied roles remain ill-defined. Recently, reports have shown that upregulation of phosphatase and tensin homolog deleted on chromosome 10 (PTEN) might be one of the mechanisms through which PPAR-γ agonists exert their anti-inflammatory actions. However, no data are available on the role of PPAR-γ in smoke-induced mucin production. In this study, we investigated the effect of PPAR-γ agonist (rosiglitazone) on smoke-induced mucin production in NCI-H292 cells. Exposure to cigarette smoke causes a significant decrease in PTEN expression and increases dose-dependent EGFR-specific tyrosine phosphorylation, resulting in MUC5AC mucin production in NCI-H292 cells. PPAR-γ agonists or specific inhibitors of phosphoinositide 3-kinase exert inhibition of cigarette smoke-induced mucin production, with the upregulation of PTEN signaling and downregulation of Akt expression. This study demonstrates that PPAR-γ agonist functions as a regulator of epithelial cell inflammation that may result in reduction of mucin-producing cells in airway epithelium.

SAHA-sensitized prostate cancer cells to TNFalpha-related apoptosis-inducing ligand (TRAIL): mechanisms leading to synergistic apoptosis

Treatment of cancer cells with histone deacetylase inhibitors (HDACi) such as suberolylanilide hydroxamic acid (SAHA) activates genes that promote apoptosis. To enhance proapoptotic efficiency, SAHA has been used in combination with radiation, kinase inhibitors and cytotoxic drugs. Although several prostate cells respond to TNFalpha-Related Apoptosis-Inducing Ligand (TRAIL), LNCaP are resistant. This model system was utilized to examine the advantages of combined treatment with SAHA and TRAIL. In LNCaP cells, TRAIL induced synergistic apoptosis when combined even with the lowest dose of SAHA. Treatment with caspase inhibitor confirmed that SAHA-induced apoptosis was mediated through caspases. In addition to induction of apoptosis, SAHA and TRAIL decreased the levels of proapoptotic proteins IKKalpha, IKKbeta and IKKgamma, suggesting that SAHA treatment may reduce the activity of NFkappaB. However, assay for NFkappaB luciferase reporter activity showed highly significant increase in SAHA-treated cells, supporting earlier suggestions that HDACi promotes NFkappaB transcriptional activity. Further analyses to determine the mechanisms by which the combination of SAHA and TRAIL led to synergistic apoptosis indicated that the apoptotic response of LNCaP is due to a complex regulation of death receptor pathway and alterations of NFkappaB activity at several regulatory steps.

An alternative splice product of IkappaB kinase (IKKgamma), IKKgamma-delta, differentially mediates cytokine and human T-cell leukemia virus type 1 tax-induced NF-kappaB activation

NF-kappaB is an inducible transcription factor mediating innate immune responses whose activity is controlled by the multiprotein IkappaB kinase (IKK) "signalsome". The core IKK consists of two catalytic serine kinases, IKKalpha and IKKbeta, and a noncatalytic subunit, IKKgamma. IKKgamma is required for IKK activity by mediating kinase oligomerization and serving to couple the core catalytic subunits to upstream mitogen-activated protein 3-kinase cascades. We have discovered an alternatively spliced IKKgamma mRNA isoform, encoding an in-frame deletion of exon 5, termed IKKgamma-delta. Using a specific reverse transcription-PCR assay, we find that IKKgamma-delta is widely expressed in cultured human cells and normal human tissues. Because IKKgamma-Delta protein is lacking a critical coiled-coil domain important in protein-protein interactions, we sought to determine its signaling properties by examining its ability to self associate, couple to activators of the canonical pathway, and mediate human T-cell leukemia virus type 1 (HTLV-1) Tax-induced NF-kappaB activity. Coimmunoprecipitation and confocal colocalization assays indicate IKKgamma-delta has strong homo- and heterotypic association with wild-type (WT) IKKgamma and, like IKKgamma WT, associates with the IKKbeta kinase. Similarly, IKKgamma-delta mediates IKK kinase activity and downstream NF-kappaB-dependent transcription in response to tumor necrosis factor (TNF) and the NF-kappaB-inducing kinase-IKKalpha signaling pathway. Surprisingly, however, in contrast to IKKgamma WT, IKKgamma-delta is not able to mediate HTLV-1 Tax-induced NF-kappaB-dependent transcription, even though IKKgamma-delta binds and colocalizes with Tax. These observations suggest that IKKgamma-delta is a functionally distinct alternatively spliced mRNA product differentially mediating TNF-induced, but not Tax-induced, signals converging on the IKK signalsome. Differing levels of IKKgamma-delta expression, therefore, may affect signal transduction cascades coupling to IKK.

Akt regulates basal and induced processing of NF-kappaB2 (p100) to p52

NF-kappaB is a family of transcription factors important for innate and adaptive immunity. NF-kappaB is restricted to the cytoplasm by inhibitory proteins that are degraded when specifically phosphorylated, permitting NF-kappaB to enter the nucleus and activate target genes. Phosphorylation of the inhibitory proteins is mediated by an IkappaB kinase (IKK) complex, which can be composed of two subunits with enzymatic activity, IKKalpha and IKKbeta. The preferred substrate for IKKbeta is IkappaBalpha, degradation of which liberates p65 (RelA) to enter the nucleus where it induces genes important to innate immunity. IKKalpha activates a non-canonical NF-kappaB pathway in which p100 (NF-kappaB2) is processed to p52. Once produced, p52 can enter the nucleus and induce genes important to adaptive immunity. This study shows that Akt binds to and increases the activity of IKKalpha and thereby increases p52 production in cells. Constitutively active Akt augments non-canonical NF-kappaB activity, whereas kinase dead Akt or inhibition of phosphatidylinositol 3-kinase have the opposite effect. Basal and ligand-induced p52 production is reduced in mouse embryo fibroblasts deficient in Akt1 and Akt2 compared with parental cells. These observations show that Akt plays a role in activation of basal and induced non-canonical NF-kappaB activity.

Notch3 and pre-TCR interaction unveils distinct NF-kappaB pathways in T-cell development and leukemia

Notch signaling plays a critical role in T-cell differentiation and leukemogenesis. We previously demonstrated that, while pre-TCR is required for thymocytes proliferation and leukemogenesis, it is dispensable for thymocyte differentiation in Notch3-transgenic mice. Notch3-transgenic premalignant thymocytes and T lymphoma cells overexpress pTalpha/pre-TCR and display constitutive activation of NF-kappaB, providing survival signals for immature thymocytes. We provide genetic and biochemical evidence that Notch3 triggers multiple NF-kappaB activation pathways. A pre-TCR-dependent pathway preferentially activates NF-kappaB via IKKbeta/IKKalpha/NIK complex, resulting in p50/p65 heterodimer nuclear entry and recruitment onto promoters of Cyclin D1, Bcl2-A1 and IL7-receptor-alpha genes. In contrast, upon pTalpha deletion, Notch3 binds IKKalpha and maintains NF-kappaB activation through an alternative pathway, depending on an NIK-independent IKKalpha homodimer activity. The consequent NF-kappaB2/p100 processing allows nuclear translocation of p52/RelB heterodimers, which only trigger transcription from Bcl2-A1 and IL7-receptor-alpha genes. Our data suggest that a finely tuned interplay between Notch3 and pre-TCR pathways converges on regulation of NF-kappaB activity, leading to differential NF-kappaB subunit dimerization that regulates distinct gene clusters involved in either cell differentiation or proliferation/leukemogenesis.

Nuclear factor-kappaB-mediated cell survival involves transcriptional silencing of the mitochondrial death gene BNIP3 in ventricular myocytes

BACKGROUND

A survival role for the transcription factor nuclear factor-kappaB (NF-kappaB) in ventricular myocytes has been reported; however, the underlying mechanism is undefined. In this report we provide new mechanistic evidence that survival signals conferred by NF-kappaB impinge on the hypoxia-inducible death factor BNIP3.

METHODS AND RESULTS

Activation of the NF-kappaB signaling pathway by IKKbeta in ventricular myocytes suppressed mitochondrial permeability transition pore (PTP) opening and cell death provoked by BNIP3. Expression of IKKbeta or p65 NF-kappaB suppressed basal and hypoxia-inducible BNIP3 gene activity. Deletion analysis of the BNIP3 promoter revealed the NF-kappaB elements to be crucial for inhibiting basal and inducible BNIP3 gene activity. Cells derived from p65(-/-)-deficient mice or ventricular myocytes rendered defective for NF-kappaB signaling with a nonphosphorylative IkappaB exhibited increased basal BNIP3 gene expression, mitochondrial PTP, and cell death. Genetic or functional ablation of the BNIP3 gene in NF-kappaB-defective myocytes rescued them from mitochondrial defects and cell death.

CONCLUSIONS

The data provide new compelling evidence that NF-kappaB suppresses mitochondrial defects and cell death of ventricular myocytes through a mechanism that transcriptionally silences the death gene BNIP3. Collectively, our data provide new mechanistic insight into the mode by which NF-kappaB suppresses cell death and identify BNIP3 as a key transcriptional target for NF-kappaB-regulated expression in ventricular myocytes.