MEKK1 activates both IkappaB kinase alpha and IkappaB kinase beta

Tumoristatic effects of endostatin in prostate cancer is dependent on androgen receptor status

BACKGROUND

Although anti-angiogenic therapy is a promising new line of therapy for prostate cancer, we recently reported that stable expression of endostatin arrested the progression of prostate cancer to poorly differentiated state and distant metastasis in TRAMP mice. However, the same therapy failed to provide any benefit when given either during or after the onset of metastatic switch. The present study determined the possible mechanisms behind the selective advantage of endostatin therapy in early-stage disease.

METHODS

Angiogenesis-related gene expression analysis was performed to identify target genes and molecular pathways involved in the therapy effects. Based on the results from in vivo studies, and recapitulation of the in vivo data in vitro using tumorigenic and non-tumorigenic human prostate cancer cells that are either androgen-sensitive or androgen-independent, analyses of possible mechanisms of the selective advantage of early treatment were performed using assays for cell proliferation, apoptosis, migration, and cell signaling. The identified mechanisms were further confirmed in vivo.

RESULTS

Results indicated that cells with high androgen receptor (AR) expression were more sensitive to endostatin treatment than androgen-independent cells with low or no AR expression. Endostatin was found to significantly downregulate the expression of growth factors, receptor tyrosine kinases, proteases, and AR both in vitro and in vivo only when the cells express high-levels of AR. Cell proliferation was not influenced by endostatin treatment but migration was significantly affected only in androgen-sensitive cells. Targeted downregulation of AR prior to endostatin treatment in androgen-sensitive cells and overexpression of AR in androgen-independent cells indicated that the effect of endostatin via AR downregulation is mediated by a non-genotropic mechanism on Ras and RhoA pathways, and independently of AR on MAPK/ERK pathway.

CONCLUSIONS

These data indicate that systemically stable endostatin expression delays the onset of metastatic switch by acting on multiple pathways involving AR.

TNFR signaling: ubiquitin-conjugated TRAFfic signals control stop-and-go for MAPK signaling complexes

Nearly two decades after the initial cloning and identification of the founding father of the tumor necrosis factor receptor (TNFR) family, much has been learned about the mechanisms by which these receptors signal to critical transcription factors and other targets that regulate gene expression and cellular physiology. Mitogen-activated protein kinases (MAPKs) and inhibitor of nuclear factor (NF)-kappaB (I kappaB) kinases (IKKs) were identified early on as the upstream kinases responsible for activation of activator-protein 1 (AP-1) and NF-kappaB, respectively, and later on for their ability to control life-or-death decisions in TNF-stimulated cells. Both of these critical pathways are regulated at the level of MAPK kinase kinases (MAP3Ks), after which point they diverge. Recent work, however, illustrates that protein ubiquitination cascades play a critical initiating role in TNFR signaling and account for spatial and temporal separation of IKK and MAPK signaling cascades and thereby determine biological specificity and outcome. Cellular inhibitors of apoptosis (cIAPs) 1 and 2 are ubiquitin (Ub) ligases (E3s) that mediate canonical Lys48-linked ubiquitination of TNFR-associated factor 3 (TRAF3), marking it for subsequent degradation by the proteasome. TRAF3 degradation releases the brake on TRAF2/6:MAP3K signaling complexes responsible for MAPK activation, leading to their translocation from the cytoplasmic segment of the receptor to the cytosol where they initiate MAPK phosphorylation and activation. By contrast, IKK activation proceeds considerably faster than MAPK activation, takes place at the receptor, and is independent of cIAP1/2 activity and TRAF3 degradation. This arrangement may be important for ensuring the proper delivery of NF-kappaB-dependent survival signals and conversion of JNK-promoted death signals to proliferative ones.

Monocytic differentiation of leukemic HL-60 cells induced by co-treatment with TNF-alpha and MK886 requires activation of pro-apoptotic machinery

The block of hematopoietic differentiation program in acute myeloid leukemia cells can be overcome by differentiating agent like retinoic acid, but it has several side effects. A study of other differentiation signaling pathways is therefore useful to predict potential targets of anti-leukemic therapy. We demonstrated previously that the co-treatment of HL-60 cells with Tumor necrosis factor-alpha (TNF-alpha) (1 ng/mL) and inhibitor of 5-lipoxygenase MK886 (5 microm) potentiated both monocytic differentiation and apoptosis. In this study, we detected enhanced activation of three main types of mitogen-activated protein kinases (MAPKs) (p38, c-Jun amino-terminal kinase [JNK], extracellular signal-regulated kinase [ERK]), so we assessed their role in differentiation using appropriate pharmacologic inhibitors. The inhibition of pro-apoptotic MAPKs (p38 and JNK) suppressed the effect of MK886 + TNF-alpha co-treatment. On the other hand, down-regulation of pro-survival ERK pathway led to increased differentiation. Those effects were accompanied by increased activation of caspases in cells treated by MK886 + TNF-alpha. Pan-caspase inhibitor ZVAD-fmk significantly decreased both number of apoptotic and differentiated cells. The same effect was observed after inhibition of caspase 9, but not caspase 3 and 8. To conclude, we evidenced that the activation of apoptotic processes and pathways supporting apoptosis (p38 and JNK MAPKs) is required for the monocytic differentiation of HL-60 cells.

Ebola virus protein VP35 impairs the function of interferon regulatory factor-activating kinases IKKepsilon and TBK-1

The Ebola virus (EBOV) VP35 protein antagonizes the early antiviral alpha/beta interferon (IFN-alpha/beta) response. We previously demonstrated that VP35 inhibits the virus-induced activation of the IFN-beta promoter by blocking the phosphorylation of IFN-regulatory factor 3 (IRF-3), a transcription factor that is crucial for the induction of IFN-alpha/beta expression. Furthermore, VP35 blocks IFN-beta promoter activation induced by any of several components of the retinoic acid-inducible gene I (RIG-I)/melanoma differentiation-associated gene 5 (MDA-5)-activated signaling pathways including RIG-I, IFN-beta promoter stimulator 1 (IPS-1), TANK-binding kinase 1 (TBK-1), and IkappaB kinase epsilon (IKKepsilon). These results suggested that VP35 may target the IRF kinases TBK-1 and IKKepsilon. Coimmunoprecipitation experiments now demonstrate physical interactions of VP35 with IKKepsilon and TBK-1, and the use of an IKKepsilon deletion construct further demonstrates that the amino-terminal kinase domain of IKKepsilon is sufficient for interactions with either IRF-3 or VP35. In vitro, either IKKepsilon or TBK-1 phosphorylates not only IRF-3 but also VP35. Moreover, VP35 overexpression impairs IKKepsilon-IRF-3, IKKepsilon-IRF-7, and IKKepsilon-IPS-1 interactions. Finally, lysates from cells overexpressing IKKepsilon contain kinase activity that can phosphorylate IRF-3 in vitro. When VP35 is expressed in the IKKepsilon-expressing cells, this kinase activity is suppressed. These data suggest that VP35 exerts its IFN-antagonist function, at least in part, by blocking necessary interactions between the kinases IKKepsilon and TBK-1 and their normal interaction partners, including their substrates, IRF-3 and IRF-7.

Multi-targeted therapy of cancer by genistein

Soy isoflavones have been identified as dietary components having an important role in reducing the incidence of breast and prostate cancers in Asian countries. Genistein, the predominant isoflavone found in soy products, has been shown to inhibit the carcinogenesis in animal models. There is a growing body of experimental evidence showing that the inhibition of human cancer cell growth by genistein is mediated via the modulation of genes that are related to the control of cell cycle and apoptosis. It has been shown that genistein inhibits the activation of NF-kappaB and Akt signaling pathways, both of which are known to maintain a homeostatic balance between cell survival and apoptosis. Moreover, genistein antagonizes estrogen- and androgen-mediated signaling pathways in the processes of carcinogenesis. Furthermore, genistein has been found to have antioxidant properties, and shown to be a potent inhibitor of angiogenesis and metastasis. Taken together, both in vivo and in vitro studies have clearly shown that genistein, one of the major soy isoflavones is a promising agent for cancer chemoprevention and further suggest that it could be an adjunct to cancer therapy by virtue of its effects on reversing radioresistance and chemoresistance. In this review, we attempt to provide evidence for these preventive and therapeutic effects of genistein in a succinct manner highlighting comprehensive state-of-the-art knowledge regarding its multi-targeted biological and molecular effects in cancer cells.

Targeting nuclear factor-kappa B activation pathway by thymoquinone: role in suppression of antiapoptotic gene products and enhancement of apoptosis

Thymoquinone (TQ), derived from the medicinal plant Nigella sativa, exhibits antiinflammatory and anticancer activities through mechanism(s) that is not fully understood. Because numerous effects modulated by TQ can be linked to interference with the nuclear factor-kappaB (NF-kappa B) signaling, we investigated in detail the effect of this quinone on NF-kappa B pathway. As examined by DNA binding, we found that TQ suppressed tumor necrosis factor-induced NF-kappa B activation in a dose- and time-dependent manner and inhibited NF-kappaB activation induced by various carcinogens and inflammatory stimuli. The suppression of NF-kappaB activation correlated with sequential inhibition of the activation of I kappa B alpha kinase, I kappa B alpha phosphorylation, I kappa B alpha degradation, p65 phosphorylation, p65 nuclear translocation, and the NF-kappa B-dependent reporter gene expression. TQ specifically suppressed the direct binding of nuclear p65 and recombinant p65 to the DNA, and this binding was reversed by DTT. However, TQ did not inhibit p65 binding to DNA when cells were transfected with the p65 plasmid containing cysteine residue 38 mutated to serine. TQ also down-regulated the expression of NF-kappa B-regulated antiapoptotic (IAP1, IAP2, XIAP Bcl-2, Bcl-xL, and survivin), proliferative (cyclin D1, cyclooxygenase-2, and c-Myc), and angiogenic (matrix metalloproteinase-9 and vascular endothelial growth factor) gene products. This led to potentiation of apoptosis induced by tumor necrosis factor and chemotherapeutic agents. Overall, our results indicate that the anticancer and antiinflammatory activities previously assigned to TQ may be mediated in part through the suppression of the NF-kappa B activation pathway, as shown here, and thus may have potential in treatment of myeloid leukemia and other cancers.

Eicosanoids in tumor progression and metastasis

Eicosanoids and the enzymes responsible for their generation in living systems are involved in the mediation of multiple physiological and pathophysiological responses. These bioactive metabolites are part of complex cascades that initiate and perpetuate several disease processes such as atherosclerosis, arthritis, neurodegenerative conditions, and cancer. The intricate role played by each of these metabolites in the initiation, progression, and metastasis of solid tumors has been a subject of intense research in the scientific community. This review summarizes some of the key aspects of eicasonoids and the associated enzymes, and the pathways they mediate in promoting tumor progression and metastasis.

Manganese potentiates nuclear factor-kappaB-dependent expression of nitric oxide synthase 2 in astrocytes by activating soluble guanylate cyclase and extracellular responsive kinase signaling pathways

Inflammatory activation of glial cells is associated with neuronal injury in several degenerative movement disorders of the basal ganglia, including manganese neurotoxicity. Manganese (Mn) potentiates the effects of inflammatory cytokines on nuclear factor-kappaB (NF-kappaB)-dependent expression of nitric oxide synthase 2 (NOS2) in astrocytes, but the signaling mechanisms underlying this effect have remained elusive. It was postulated in the present studies that direct stimulation of cGMP synthesis and activation of mitogen-activated protein (MAP) kinase signaling pathways underlies the capacity of Mn to augment NF-kappaB-dependent gene expression in astrocytes. Exposure of primary cortical astrocytes to a low concentration of Mn (10 microM) potentiated expression of NOS2 mRNA and protein along with production of NO in response to interferon-gamma (IFNgamma) and tumor necrosis factor-alpha (TNFalpha), which was prevented by overexpression of dominant negative IkappaB alpha. Mn also potentiated IFNgamma- and TNFalpha-induced phosphorylation of extracellular response kinase (ERK), p38, and JNK, as well as cytokine-induced activation of a fluorescent NF-kappaB reporter construct in transgenic astrocytes. Activation of ERK preceded that of NF-kappaB and was required for maximal activation of NO synthesis. Independently of IFNgamma/TNFalpha, Mn-stimulated synthesis of cGMP in astrocytes and inhibition of soluble guanylate cyclase (sGC) abolished the potentiating effect of Mn on MAP kinase phosphorylation, NF-kappaB activation, and production of NO. These data indicate that near-physiological concentrations of Mn potentiate cytokine-induced expression of NOS2 and production of NO in astrocytes via activation of sGC, which promotes ERK-dependent enhancement of NF-kappaB signaling.

Molecular basis of parthenolide-dependent proapoptotic activity in cancer cells

This review outlines the molecular events that accompany the anti-tumor action of parthenolide (PN). Parthenolide (PN) is naturally derived compound, isolated from plant Tanacetum parthenium. PN has been previously shown to withdraw cells from cell cycle or to promote cell differentiation, and finally to induce programmed cell death. Recent advances in molecular biology indicate that this sesquiterpene lactone might evoke the above-mentioned effects by indirect action on genes. PN was shown to inhibit NF-kappaB- and STATs-mediated antiapoptotic gene transcription. On one hand, the proapoptotic activity of PN includes stimulation of intrinsic apoptotic pathway with the higher level of intracellular ROS and modifications of Bcl-2 family proteins (conformational changes of Bak and Bax, Bid cleavage). On the other hand, PN amplifies the apoptotic signal through the sensitization of cancer cells to extrinsic apoptosis, induced by TNF-alpha. These effects are specific to tumor cells. Unique properties of PN make this agent a promising metabolic inhibitor to retard tumorigenesis and to suppress tumor growth.

Death receptor-4 (DR4) expression is regulated by transcription factor NF-kappaB in response to etoposide treatment

Tumour necrosis factor related apoptosis inducing ligand (TRAIL) binds to death receptor 4 (DR4) activating the apoptotic signalling pathway. DNA damaging agents (genotoxins) such as etoposide increase DR4 expression and when combined with TRAIL induce a synergistic apoptotic response. The mechanism for up-regulation of DR4 expression following genotoxin treatment is not well understood. Herein, we determined that transcription factor NF-kappaB plays a role in genotoxin induced DR4 expression. Increased expression of DR4 following etoposide treatment is blocked by inhibition of the NF-kappaB pathway. Moreover, expression of the p65 subunit of NF-kappaB is sufficient to increase DR4 protein levels. Indeed, knockdown of p65 by RNA interference blocked etoposide up-regulation of DR4. We further identified a functional NF-kappaB binding site located in the DR4 promoter. Mutation of this site abrogates the induction of luciferase activity after p65 over-expression. Furthermore, electromobility shift assays and chromatin immunoprecipitaton suggest that NF-kappaB binds to this site upon etoposide treatment. MEK kinase 1 (MEKK1) is a serine threonine kinase that is activated following etoposide treatment and activates NF-kappaB. Expression of the kinase inactive MEKK1 (MEKK1-KM) abrogates the up-regulation of DR4 after etoposide treatment. Taken together, NF-kappaB plays a role in up-regulation of DR4 following etoposide treatment.

Ankyrin-rich membrane spanning protein plays a critical role in nuclear factor-kappa B signaling

Activation of nuclear factor-kappaB (NF-kappaB), a key feature of the neurotrophin signaling, has been shown to be critical for neuronal survival under pathologic settings. However, the precise mechanism by which neurotrophins activate NF-kappaB is not well understood. Here we report that the Ankyrin-rich Membrane Spanning (ARMS/Kidins220) protein, a novel transmembrane substrate of tropomyosin receptor kinase B (TrkB), plays an important role in NF-kappaB signaling elicited by brain-derived neurotrophic factor (BDNF). Accordingly, depletion of ARMS by specific RNA interference, or disruption of ARMS-TrkB interaction with expression of dominant-negative ARMS mutant, abolished BDNF-induced signaling to NF-kappaB. Our data further suggests that ARMS may promote NF-kappaB signaling via activation of mitogen-activated kinase (MAPK) and IkappaB kinase (IKK), thereby facilitating phosphorylation of RelA (major NF-kappaB subunit) at an IKK-sensitive site. The results shown here identify ARMS as a major factor that links neurotrophin signaling to NF-kappaB.

Atypical protein kinase C phosphorylates IKKalphabeta in transformed non-malignant and malignant prostate cell survival

Mechanistic pathways involving atypical protein kinase C-iota (aPKC-iota) have been targeted in various cancer cells such as lung cancer, brain and prostate due to PKCiota's antiapoptotic function, and role in cell proliferation and cell survival. In the current study, we examined the involvement of PKC-iota in the NF-kappaB pathway following treatment of prostate cells with the pro-inflammatory cytokine tumor necrosis factor alpha (TNFalpha). Results demonstrated that androgen-independent DU-145 prostate carcinoma is insensitive to TNFalpha while transformed non-tumorigenic prostate RWPE-1 cells showed a slight sensitivity to TNFalpha. However, androgen-dependent LNCaP prostate cells are more sensitive to TNFalpha treatment and undergo apoptosis. Results demonstrated that in DU-145 cells, TNFalpha-induced PKC-iota in phosphorylation of IKKalphabeta. In RWPE-1 cells, PKC-zeta phosphorylates IKKalphabeta. Degradation of IkappaBalpha was observed in all three cell lines, allowing NF-kappaB/p65 translocation to the nucleus. Although, IKKalpha is weakly activated in LNCaP cells, the upstream kinase phosphorylation of IKKalphabeta via aPKCs was not observed. Hence, aPKCs may play a role in activation of NFkappaB pathway in prostate cancer cells.

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.

Regulation of smooth muscle by inducible nitric oxide synthase and NADPH oxidase in vascular proliferative diseases

Inflammation plays a critical role in promoting smooth muscle migration and proliferation during vascular diseases such as postangioplasty restenosis and atherosclerosis. Another common feature of many vascular diseases is the contribution of reactive oxygen (ROS) and reactive nitrogen (RNS) species to vascular injury. Primary sources of ROS and RNS in smooth muscle are several isoforms of NADPH oxidase (Nox) and the cytokine-regulated inducible nitric oxide (NO) synthase (iNOS). One important example of the interaction between NO and ROS is the reaction of NO with superoxide to yield peroxynitrite, which may contribute to the pathogenesis of hypertension. In this review, we discuss the literature that supports an alternate possibility: Nox-derived ROS modulate NO bioavailability by altering the expression of iNOS. We highlight data showing coexpression of iNOS and Nox in vascular smooth muscle demonstrating the functional consequences of iNOS and Nox during vascular injury. We describe the relevant literature demonstrating that the mitogen-activated protein kinases are important modulators of proinflammatory cytokine-dependent expression of iNOS. A central hypothesis discussed is that ROS-dependent regulation of the serine/threonine kinase protein kinase Cdelta is essential to understanding how Nox may regulate signaling pathways leading to iNOS expression. Overall, the integration of nonphagocytic NADPH oxidase with cytokine signaling in general and in vascular smooth muscle in particular is poorly understood and merits further investigation.

Anacardic acid (6-nonadecyl salicylic acid), an inhibitor of histone acetyltransferase, suppresses expression of nuclear factor-kappaB-regulated gene products involved in cell survival, proliferation, invasion, and inflammation through inhibition of the inhibitory subunit of nuclear factor-kappaBalpha kinase, leading to potentiation of apoptosis

Anacardic acid (6-pentadecylsalicylic acid) is derived from traditional medicinal plants, such as cashew nuts, and has been linked to anticancer, anti-inflammatory, and radiosensitization activities through a mechanism that is not yet fully understood. Because of the role of nuclear factor-kappaB (NF-kappaB) activation in these cellular responses, we postulated that anacardic acid might interfere with this pathway. We found that this salicylic acid potentiated the apoptosis induced by cytokine and chemotherapeutic agents, which correlated with the down-regulation of various gene products that mediate proliferation (cyclin D1 and cyclooxygenase-2), survival (Bcl-2, Bcl-xL, cFLIP, cIAP-1, and survivin), invasion (matrix metalloproteinase-9 and intercellular adhesion molecule-1), and angiogenesis (vascular endothelial growth factor), all known to be regulated by the NF-kappaB. We found that anacardic acid inhibited both inducible and constitutive NF-kappaB activation; suppressed the activation of IkappaBalpha kinase that led to abrogation of phosphorylation and degradation of IkappaBalpha; inhibited acetylation and nuclear translocation of p65; and suppressed NF-kappaB-dependent reporter gene expression. Down-regulation of the p300 histone acetyltransferase gene by RNA interference abrogated the effect of anacardic acid on NF-kappaB suppression, suggesting the critical role of this enzyme. Overall, our results demonstrate a novel role for anacardic acid in potentially preventing or treating cancer through modulation of NF-kappaB signaling pathway.

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.

Human adenovirus type 19 infection of corneal cells induces p38 MAPK-dependent interleukin-8 expression

Background

Human adenovirus type 19 (HAdV-19) is a major cause of epidemic keratoconjunctivitis, the only ocular adenoviral infection associated with prolonged corneal inflammation. In this study, we investigated the role of p38 mitogen-activated protein kinase (MAPK) in HAdV-19 infection, with particular attention to the role of p38 MAPK in the transcriptional control of interleukin-8 (IL-8), a chemokine previously shown to be central to the initiation of adenovirus keratitis.

Results

We found that infection of corneal cells with HAdV-19 led to activation of p38 MAPK and its downstream targets, HSP-27 and ATF-2, within 15 to 30 minutes post-infection. Infection also induced phosphorylation of IκB and NFκB in a p38 MAPK-dependent fashion. Furthermore, HAdV-19 induced an interaction between p38 MAPK and NFκB-p65, followed by nuclear translocation of activated NFκB-p65 and its binding to the IL-8 promoter. The interaction between p38 MAPK and NFκB-p65 was inhibited in concentration-dependent fashion by SB203580, a chemical inhibitor of p38 MAPK, but not by SP600125, an inhibitor of JNK – another MAPK implicated in chemokine expression by HAdV-19 infected cells. IL-8 gene expression in HAdV-19 infection was significantly reduced in the presence of sequence-specific p38 MAPK siRNA but not control siRNA.

Conclusion

These results provide the first direct evidence for transcriptional regulation of IL-8 in HAdV-19 infected cells through the activation of the p38 MAPK signaling pathway. The p38 MAPK pathway may play a biologically important role in regulation of IL-8 gene expression in the adenovirus-infected cornea.

The interferon signaling network and transcription factor C/EBP-beta

Cytokines like interferons (IFNs) play a central role in regulating innate and specific immunities against the pathogens and neoplastic cells. A number of signaling pathways are induced in response to IFN in various cells. One classic mechanism employed by IFNs is the JAK-STAT signaling pathway for inducing cellular responses. Here we describe the non-STAT pathways that participate in IFN-induced responses. In particular, we will focus on the role played by transcription factor C/EBP-beta in mediating these responses.

Quercetin 3-O-β-(2″-galloyl)-glucopyranoside inhibits endotoxin LPS-induced IL-6 expression and NF-κB activation in macrophages

We previously isolated quercetin 3-O-beta-(2''-galloyl)-glucopyranoside (QG-32) from Persicaria lapathifolia (Polygonacease) as an inhibitor of superoxide production. In the present study, QG-32 was found to inhibit interleukin (IL)-6 production in endotoxin lipopolysaccharide (LPS)-stimulated macrophages RAW 264.7. The QG-32 attenuated LPS-induced synthesis of IL-6 transcript but also inhibited IL-6 promoter activity, indicating that the compound could down-regulate LPS-induced IL-6 expression at the transcription level. Since nuclear factor (NF)-kappaB has been evidenced to play a major mechanism in the LPS-induced IL-6 expression, an effect of QG-32 on NF-kappaB activating pathway was further analyzed. QG-32 inhibited nuclear import as well as DNA binding activity of NF-kappaB complex and subsequently suppressed NF-kappaB transcriptional activity in LPS-stimulated macrophages. However, QG-32 affected neither LPS-induced inhibitory kappaB (IkappaB) degradation nor IkappaB kinase (IKK) activation. In another experiment, QG-32 inhibited expression vector encoding NF-kappaB p65 or p50-elicited IL-6 promoter activity. Taken together, QG-32 could inhibit NF-kappaB-dependent IL-6 expression, targeting nuclear translocation of NF-kappaB complex downstream IkappaB degradation. This mechanism of action would be different from that of quercetin, an aglycone of QG-32, targeting IKK upstream IkappaB degradation. Finally, this study could provide a pharmacological potential of QG-32 in the inflammatory disorders.

A bioactive withanolide Tubocapsanolide A inhibits proliferation of human lung cancer cells via repressing Skp2 expression

Withanolides are generally defined as C(28) steroidal lactones built on an intact or rearranged ergostane skeleton and have been shown to exhibit antiproliferative activity on various types of cancer cells. In this study, we investigated the effect of a new withanolide Tubocapsanolide A isolated from Tubocapsicum anomalum and addressed its molecular action. Tubocapsanolide A inhibited proliferation of A549, H358, and H226 human lung cancer cells via induction of G(1) growth arrest. We found that Tubocapsanolide A treatment led to up-regulation of cyclin E, p21, and p27, whereas other cyclins and cyclin-dependent kinases were not affected in A549 cells. Conversely, Skp2, the F-box protein that is implicated in the mediation of degradation of p21 and p27, was significantly down-regulated. Chromatin immunoprecipitation assay suggested that Tubocapsanolide A suppressed Skp2 expression by inhibiting the binding of Rel A to the nuclear factor-kappaB site of Skp2 gene promoter. In addition, we showed that inhibition of Skp2 is a critical step for the suppression of cell proliferation by Tubocapsanolide A because ectoexpression of Skp2 effectively reversed Tubocapsanolide A-induced p27 up-regulation and growth inhibition in human lung cancer cells. Collectively, we have identified Skp2 as a molecular target for Tubocapsanolide A and suggest that this withanolide may be useful for the prevention or treatment of cancer cells with Skp2 overexpression.

Targeted Deletion of MKK4 Gene Potentiates TNF-Induced Apoptosis through the Down-Regulation of NF-κB Activation and NF-κB-Regulated Antiapoptotic Gene Products

MAPK kinase 4 (MKK4) is a dual-specificity kinase that activates both JNK and p38 MAPK. However, the mechanism by which MKK4 regulates TNF-induced apoptosis is not fully understood. Therefore, we used fibroblasts derived from MKK4 gene-deleted (MKK4-KO) mice to determine the role of this kinase in TNF signaling. We found that when compared with the wild-type cells, deletion of MKK4 gene enhanced TNF-induced apoptosis, and this correlated with down-regulation of TNF-induced cell-proliferative (COX-2 and cyclin D1) and antiapoptotic (survivin, IAP1, XIAP, Bcl-2, Bcl-x(L), and cFLIP) gene products, all regulated by NF-kappaB. Indeed we found that TNF-induced NF-kappaB activation was abrogated in MKK4 gene-deleted cells, as determined by DNA binding. Further investigation revealed that TNF-induced I kappaB alpha kinase activation, I kappaB alpha phosphorylation, I kappaB alpha degradation, and p65 nuclear translocation were all suppressed in MKK4-KO cells. NF-kappaB reporter assay revealed that NF-kappaB activation induced by TNF, TNFR1, TRADD, TRAF2, NIK, and I kappaB alpha kinase was modulated in gene-deleted cells. Overall, our results indicate that MKK4 plays a central role in TNF-induced apoptosis through the regulation of NF-kappaB-regulated gene products.

Fisetin, an inhibitor of cyclin-dependent kinase 6, down-regulates nuclear factor-kappaB-regulated cell proliferation, antiapoptotic and metastatic gene products through the suppression of TAK-1 and receptor-interacting protein-regulated IkappaBalpha kinase activation

Fisetin (3,7,3',4'-tetrahydroxyflavone) exhibits anti-inflammatory and antiproliferative effects through a mechanism that is poorly understood. Although fisetin has been cocrystalized with cyclin-dependent kinase 6 and inhibits its activity, this inhibition is not sufficient to explain various activities assigned to this flavonol. Because of the critical role of the NF-kappaB pathway in regulation of inflammation and proliferation of tumor cells, we postulated that fisetin modulates this pathway. To test this hypothesis, we examined the effect of fisetin on NF-kappaB and NF-kappaB-regulated gene products in vitro. We found that among nine different flavones tested, fisetin was potent in suppressing tumor necrosis factor (TNF)-induced NF-kappaB activation. Fisetin also suppressed the NF-kappaB activation induced by various inflammatory agents and carcinogens, and it blocked the phosphorylation and degradation of IkappaBalpha by inhibiting IkappaBalpha (IKK) activation, which in turn led to suppression of the phosphorylation and nuclear translocation of p65. NF-kappaB-dependent reporter gene expression was also suppressed by fisetin, as was NF-kappaB reporter activity induced by TNFR1, TRADD, TRAF2, NIK, and IKK but not that induced by p65 transfection. Fisetin also inhibited TNF-induced TAK1 and receptor-interacting protein activation, events that lie upstream of IKK activation. The expression of NF-kappaB-regulated gene products involved in antiapoptosis (cIAP-1/2, Bcl-2, Bcl-xL, XIAP, Survivin, and TRAF1), proliferation (cyclin D1, c-Myc, COX-2), invasion (ICAM-1 and MMP-9), and angiogenesis (vascular endothelial growth factor) were also down-regulated by fisetin. This correlated with potentiation of apoptosis induced by TNF, doxorubicin, and cisplatin. Thus, overall, our results indicate that fisetin mediates antitumor and anti-inflammatory effects through modulation of NF-kappaB pathways.

Celastrol, a novel triterpene, potentiates TNF-induced apoptosis and suppresses invasion of tumor cells by inhibiting NF-kappaB-regulated gene products and TAK1-mediated NF-kappaB activation

Celastrol, a quinone methide triterpene derived from the medicinal plant Tripterygium wilfordii, has been used to treat chronic inflammatory and autoimmune diseases, but its mechanism is not well understood. Therefore, we investigated the effects of celastrol on cellular responses activated by TNF, a potent proinflammatory cytokine. Celastrol potentiated the apoptosis induced by TNF and chemotherapeutic agents and inhibited invasion, both regulated by NF-kappaB activation. We found that TNF induced the expression of gene products involved in antiapoptosis (IAP1, IAP2, Bcl-2, Bcl-XL, c-FLIP, and survivin), proliferation (cyclin D1 and COX-2), invasion (MMP-9), and angiogenesis (VEGF) and that celastrol treatment suppressed their expression. Because these gene products are regulated by NF-kappaB, we postulated that celastrol mediates its effects by modulating the NF-kappaB pathway. We found that celastrol suppressed both inducible and constitutive NF-kappaB activation. Celastrol was found to inhibit the TNF-induced activation of IkappaBalpha kinase, IkappaBalpha phosphorylation, IkappaBalpha degradation, p65 nuclear translocation and phosphorylation, and NF-kappaB-mediated reporter gene expression. Recent studies indicate that TNF-induced IKK activation requires activation of TAK1, and we indeed found that celastrol inhibited the TAK1-induced NF-kappaB activation. Overall, our results suggest that celastrol potentiates TNF-induced apoptosis and inhibits invasion through suppression of the NF-kappaB pathway.

Morin (3,5,7,2',4'-Pentahydroxyflavone) abolishes nuclear factor-kappaB activation induced by various carcinogens and inflammatory stimuli, leading to suppression of nuclear factor-kappaB-regulated gene expression and up-regulation of apoptosis

PURPOSE

Morin is a flavone that exhibits antiproliferative, antitumor, and anti-inflammatory effects through a mechanism that is not well understood. Because of the role of transcription factor nuclear factor-kappaB (NF-kappaB) in the control of cell survival, proliferation, tumorigenesis, and inflammation, we postulated that morin mediates its effects by modulating NF-kappaB activation.

EXPERIMENTAL DESIGN

We investigated the effect of morin on NF-kappaB pathway activated by inflammatory agents, carcinogens, and tumor promoters. The effect of this flavone on expression of NF-kappaB-regulated gene products involved in cell survival, proliferation, and invasion was also examined.

RESULTS

We showed by DNA-binding assay that NF-kappaB activation induced by tumor necrosis factor (TNF), phorbol 12-myristate 13-acetate, lipopolysaccharide, ceramide, interleukin-1, and H(2)O(2) was suppressed by morin; the suppression was not cell type specific. The suppression of NF-kappaB by morin was mediated through inhibition of IkappaBalpha (inhibitory subunit of NF-kappaB) kinase, leading to suppression of phosphorylation and degradation of IkappaBalpha and consequent p65 nuclear translocation. Morin also inhibited the NF-kappaB-dependent reporter gene expression activated by TNF, TNF receptor (TNFR) 1, TNFR1-associated death domain, TNFR-associated factor 2, NF-kappaB-inducing kinase, IkappaB kinase, and the p65 subunit of NF-kappaB. NF-kappaB-regulated gene products involved in cell survival [inhibitor of apoptosis (IAP) 1, IAP2, X chromosome-linked IAP, Bcl-xL, and survivin], proliferation (cyclin D1 and cyclooxygenase-2), and invasion (matrix metalloproteinase-9) were down-regulated by morin. These effects correlated with enhancement of apoptosis induced by TNF and chemotherapeutic agents.

CONCLUSION

Overall, our results indicate that morin suppresses the activation of NF-kappaB and NF-kappaB-regulated gene expression, leading to enhancement of apoptosis. This may provide the molecular basis for the ability of morin to act as an anticancer and anti-inflammatory agent.

Simvastatin potentiates TNF-alpha-induced apoptosis through the down-regulation of NF-kappaB-dependent antiapoptotic gene products: role of IkappaBalpha kinase and TGF-beta-activated kinase-1

Numerous recent reports suggest that statins (hydroxy-3-methylglutaryl-CoA reductase inhibitors) exhibit potential to suppress tumorigenesis through a mechanism that is not fully understood. Therefore, in this article, we investigated the effects of simvastatin on TNF-alpha-induced cell signaling. We found that simvastatin potentiated the apoptosis induced by TNF-alpha as indicated by intracellular esterase activity, caspase activation, TUNEL, and annexin V staining. This effect of simvastatin correlated with down-regulation of various gene products that mediate cell proliferation (cyclin D1 and cyclooxygenase-2), cell survival (Bcl-2, Bcl-x(L), cellular FLIP, inhibitor of apoptosis protein 1, inhibitor of apoptosis protein 2, and survivin), invasion (matrix mellatoproteinase-9 and ICAM-1), and angiogenesis (vascular endothelial growth factor); all known to be regulated by the NF-kappaB. We found that simvastatin inhibited TNF-alpha-induced NF-kappaB activation, and l-mevalonate reversed the suppressive effect, indicating the role of hydroxy-3-methylglutaryl-CoA reductase. Simvastatin suppressed not only the inducible but also the constitutive NF-kappaB activation. Simvastatin inhibited TNF-alpha-induced IkappaBalpha kinase activation, which led to inhibition of IkappaBalpha phosphorylation and degradation, suppression of p65 phosphorylation, and translocation to the nucleus. NF-kappaB-dependent reporter gene expression induced by TNF-alpha, TNFR1, TNFR-associated death domain protein, TNFR-associated factor 2, TGF-beta-activated kinase 1, receptor-interacting protein, NF-kappaB-inducing kinase, and IkappaB kinase beta was abolished by simvastatin. Overall, our results provide novel insight into the role of simvastatin in potentially preventing and treating cancer through modulation of IkappaB kinase and NF-kappaB-regulated gene products.

Zn2+-induced NF-κB-dependent transcriptional activity involves site-specific p65/RelA phosphorylation

Zinc is an essential micronutrient, but is proinflammatory when inhaled into the lung. While it is recognized that zinc exposure of airway epithelial cells activates the transcription factor NF-kappaB and increases the expression of inflammatory cytokines to mediate this response, the underlying mechanism of NF-kappaB activation remains to be characterized. In this study, we investigated these Zn2+-induced signaling mechanisms in the BEAS-2B human airway epithelial cell line. Fifty micromolars Zn2+ induced NF-kappaB-dependent transcriptional activity. However, this occurred independently of IkappaBalpha degradation, an essential event in activation of the canonical NF-kappaB pathway, which is induced by physiological stimuli such as TNFalpha and IL-1beta. We also observed that 50 microM Zn2+ exposure caused p65/RelA phosphorylation on Ser 276, Ser 529, and Ser 536 in both cytoplasmic and nuclear cell fractions. Mutational analysis pointed to Ser 536 of p65/RelA as the determinant of Zn2+-induced NF-kappaB transactivation in BEAS-2B cells. Pharmacological inhibition of IKKalpha/beta activity reduced both Zn2+-induced p65/RelA phosphorylation at Ser 536 and NF-kappaB-dependent transcriptional activity, suggesting that IKKalpha/beta is necessary for these Zn2+-induced effects. Taken together, these data show that exposure to supraphysiological concentrations of Zn2+ induces NF-kappaB-dependent transcription through an alternate mechanism, suggesting a novel pathway for cellular responses to environmental stress.

IOP1, a novel hydrogenase-like protein that modulates hypoxia-inducible factor-1alpha activity

A central means by which mammalian cells respond to low oxygen tension is through the activation of the transcription factor HIF-1 (hypoxia-inducible factor-1). Under normoxic conditions, HIF-1alpha (the alpha subunit of HIF-1) is targeted for rapid degradation by the ubiquitin-proteasome pathway. Under hypoxic conditions, this degradation is inhibited, thereby leading to the stabilization and activation of HIF-1alpha. Here, we report the identification of IOP1 (iron-only hydrogenase-like protein 1), a protein homologous with enzymes present in anaerobic organisms that contain a distinctive iron-sulfur cluster. IOP1 is present in a broad range of cell types. Knockdown of IOP1 using siRNA (small interfering RNA) in mammalian cells increases protein levels of HIF-1alpha under both normoxic and hypoxic conditions, and augments hypoxia-induced HRE (hypoxia response element) reporter gene and endogenous HIF-1alpha target gene expressions. We find that IOP1 knockdown up-regulates HIF-1alpha mRNA levels, thereby providing a mechanism by which knockdown induces the observed effects. The results collectively provide evidence that IOP1 is a component of the protein network that regulates HIF-1alpha in mammalian cells.

Preadministration of high-dose salicylates, suppressors of NF-kappaB activation, may increase the chemosensitivity of many cancers: an example of proapoptotic signal modulation therapy

NF-kappaB activity is elevated in a high proportion of cancers, particularly advanced cancers that have been treated previously. Cytotoxic treatment selects for such up-regulation inasmuch as NF-kappaB promotes transcription of a large number of proteins that inhibit both the intrinsic and extrinsic pathways of apoptosis; NF-kappaB also boosts expression of mdr1, which expels many drugs from cells. Indeed, high NF-kappaB activity appears to be largely responsible for the chemo- and radioresistance of many cancers. Thus, agents that suppress NF-kappaB activity should be useful as adjuvants to cytotoxic cancer therapy. Of the compounds that are known to be NF-kappaB antagonists, the most practical for current use may be the nonsteroidal anti-inflammatory drugs aspirin, salicylic acid, and sulindac, each of which binds to and inhibits Ikappa kinase- beta, a central mediator of NF-kappa activation; the low millimolar plasma concentrations of salicylate required for effective inhibition of this kinase in vivo can be achieved with high-dose regimens traditionally used to manage rheumatic disorders. The gastrointestinal toxicity of such regimens could be minimized by using salsalate or enteric-coated sodium salicy-late or by administering misoprostol in conjunction with aspirin therapy. Presumably, best results would be seen if these agents were administered for several days prior to a course of chemo- or radiotherapy, continuing throughout the course. This concept should first be tested in nude mice bearing xenografts of chemoresistant human tumors known to have elevated NF-kappa activity. Ultimately, more complex adjuvant regimens can be envisioned in which salicylates are used in conjunction with other NF-kappa antagonists and/or agents that target other mediators of down-regulated apoptosis in cancer, such as Stat3; coadministration of salicylate and organic selenium may have intriguing potential in this regard. These strategies may also have potential as adjuvants to metronomic chemotherapy, which seeks to suppress angio-genesis by targeting cycling endothelial cells in tumors.

Withaferin a strongly elicits IkappaB kinase beta hyperphosphorylation concomitant with potent inhibition of its kinase activity

The transcription factor NFkappaB plays a critical role in normal and pathophysiological immune responses. Therefore, NFkappaB and the signaling pathways that regulate its activation have become a major focus of drug development programs. Withania somnifera (WS) is a medicinal plant that is widely used in Palestine for the treatment of various inflammatory disorders. In this study we show that the leave extract of WS, as well as its major constituent withaferin A (WA), potently inhibits NFkappaB activation by preventing the tumor necrosis factor-induced activation of IkappaB kinase beta via a thioalkylation-sensitive redox mechanism, whereas other WS-derived steroidal lactones, such as withanolide A and 12-deoxywithastramonolide, are far less effective. To our knowledge, this is the first communication of IkappaB kinase beta inhibition by a plant-derived inhibitor, coinciding with MEK1/ERK-dependent Ser-181 hyperphosphorylation. This prevents IkappaB phosphorylation and degradation, which subsequently blocks NFkappaB translocation, NFkappaB/DNA binding, and gene transcription. Taken together, our results indicate that pure WA or WA-enriched WS extracts can be considered as a novel class of NFkappaB inhibitors, which hold promise as novel anti-inflammatory agents for treatment of various inflammatory disorders and/or cancer.

Introduction to NF-kappaB: players, pathways, perspectives

This article serves as an introduction to the collection of reviews on nuclear factor-kappaB (NF-kappaB). It provides an overview of the discovery and current status of NF-kappaB as a research topic. Described are the structures, activities and regulation of the proteins in the NF-kappaB family of transcription factors. NF-kappaB signaling is primarily regulated by inhibitor kappaB (IkappaB) proteins and the IkappaB kinase complex through two major pathways: the canonical and non-canonical NF-kappaB pathways. The organization and focus of articles included in the following reviews are described, as well as likely future areas of research interest on NF-kappaB.

Spontaneous activation of the NF-κB signaling pathway in isolated normal glomeruli

In this report, we describe that NF-κB is spontaneously activated in isolated, normal glomeruli. Ex vivo incubation of isolated rat glomeruli triggered expression of a NF-κB-dependent gene, monocyte chemoattractant protein-1 (MCP-1), in parallel with downregulation of IκBα and IκBβ proteins and activation of the p65 NF-κB subunit. The induction of MCP-1 was also observed in mesangial cells coincubated with isolated glomeruli or exposed to media conditioned by isolated glomeruli (GCM), which was abrogated by inhibition of NF-κB. The activation of NF-κB by glomerulus-derived factors was confirmed using reporter mesangial cells that produce secreted alkaline phosphatase (SEAP) under the control of the κB enhancer element. When the reporter cells were adoptively transferred into normal glomeruli, expression of SEAP mRNA and activity of SEAP were also upregulated in the explanted glomeruli. The molecular weight of factors responsible for activation of NF-κB was >50 kDa, and TNF-α was identified as one of glomerulus-derived activators. To examine upstream events involved, we focused on MAP kinases that are spontaneously activated in explanted glomeruli. Selective suppression of ERK or p38 MAP kinase significantly attenuated activation of NF-κB in mesangial cells triggered by coculture with isolated glomeruli. Interestingly, the suppressive effects by MAP kinase inhibitors were not observed in mesangial cells treated with GCM. These data suggested that NF-κB was spontaneously activated in explanted glomeruli via autocrine/paracrine factors including TNF-α and that the production of NF-κB activators by glomeruli was, at least in part, through MAP kinase pathways.

Investigation of interleukin 1beta-mediated regulation of NF-kappaB activation in colonic cells reveals divergence between PKB and PDK-transduced events

Recent work has highlighted a role for PDK1 in adaptive immunity, however its contribution to innate immunity has not been addressed. We have investigated the role of PKB and PDK1 in IL-1beta-induced NF-kappaB activation. Over-expression of either in HCT 116 and HEK 293T cells, effected a reproducible NF-kappaB activation. This was validated in a one-hybrid assay utilizing Gal4-RelA and Gal4-luciferase assay. N-tosyl phenylalanyl chloromethyl ketone (TPCK), wortmannin and Ly294002 inhibited IL-1beta-induced NF-kappaB activation in both systems indicating involvement of the PI3K axis in this response. p65 (Rel A) Ser536 phosphorylation was not affected by the PI3K inhibitors but was dose-dependently attenuated by TPCK. Evaluation of IKK-associated activity using GST-p65 substrate phosphorylation in immune complex assays, revealed that whilst TPCK attenuated this, neither of the PI3K inhibitors had any effect. Furthermore whilst TPCK inhibited IL-1beta-induced p65 DNA binding, this was not apparent with either of wortmannin or Ly294002. Similarly, over-expression of PDK1 but not PKB resulted in promotion of p65 DNA binding. Using a p65-S536A reporter construct, we found inhibition of only PDK1 over-expression-induced, but not PKB over-expression-induced NF-kappaB activation. This was supported using biochemical analysis in which immunoprecipitated IKKgamma from IL-1beta-activated cells was unable to phosphorylate a p65-S536A substrate, confirming this as the dominant IKK-dependent site. In further support of a dissociated response, we observed an attenuation of the Ser177/181 IKK phosphorylation by TPCK but not in response to PI3K inhibition. Our data reveals for the first time that PDK1 and PKB may differentially activate NF-kappaB, and that TPCK may subserve a useful anti-inflammatory function by inhibiting IKKbeta.

Inhibition of NF-kappa B activation through targeting I kappa B kinase by celastrol, a quinone methide triterpenoid

Celastrol, a quinone methide triterpenoid, was isolated as an inhibitor of NF-kappaB from Celastrus orbiculatus. This compound dose-dependently inhibited a variety of stimuli-induced NF-kappa B-regulated gene expression and the DNA-binding of NF-kappa B in different cell lines without affecting DNA-binding activity of AP-1. Preincubation of celastrol completely blocked the LPS-, TNF-alpha-, or PMA-induced degradation and phosphorylation of I kappa B alpha. Importantly, celastrol inhibited IKK activity and the constitutively active IKK beta activity in a dose-dependent manner without either affecting the NF-kappa B activation induced by RelA over-expression or directly suppressing the DNA-binding of activated NF-kappa B. However, mutation of cysteine 179 in the activation loop of IKK beta abolished sensitivity towards to celastrol, suggesting that celastrol suppressed the NF-kappa B activation by targeting cysteine 179 in the IKK. To verify that celastrol is a NF-kappa B inhibitor, we investigated its effect on some NF-kappa B target genes expressions. Celastrol prevented not only LPS-induced mRNA expression of iNOS and TNF-alpha, but also TNF-alpha-induced Bfl-1/A1 expression, a prosurvival Bcl-2 homologue. Consistent with these results, celastrol significantly suppressed the production of NO and TNF-alpha in LPS-stimulated RAW264.7 cells, and increased the cytotoxicity of TNF-alpha in HT-1080 cells. We also demonstrated that celastrol showed anti-inflammatory and anti-tumor activities in animal models. Taken together, this study extends our understanding on the molecular mechanisms underlying the anti-inflammatory and anti-cancer activities of celastrol and celastrol-containing medicinal plant, which would be a valuable candidate for the intervention of NF-kappa B-dependent pathological conditions.

Redox-sensitive kinases of the nuclear factor-kappaB signaling pathway

NF-kappaB is an inducible transcription factor that plays a role in the expression of over one hundred genes involved in immunity, inflammation, proliferation, and in defense against apoptosis. NF-kappaB has been known to be redox regulated for some time and is a direct target for oxidation that can affect its ability to bind to DNA. Reactive oxygen species (ROS) have been identified as second messengers in cells, and play a role in receptor signaling and posttranslation modification of signaling molecules. These posttranslation modifications include oxidations of critical cysteines to sulfenic acids or mixed disulfides, which can affect the activity of proteins. Many kinases involved in direct or indirect activation of NF-kappaB are affected by oxidants and therefore, have the potential to alter NF-kappaB activity. This review will provide a summary of the NF-kappaB family, their activation and regulation, followed by a summary of cytoplasmic and nuclear kinases in this pathway whose activity is affected by oxidants. Additionally, recent investigations have revealed that the JNK signaling pathway, which is known to be redox regulated, and pro-apoptotic, is inhibited by NF-kappaB signaling. The crosstalk of NF-kappaB with other signaling pathways is therefore critical for cellular fate, notably survival or cell death under oxidative conditions, and will also be reviewed.

Essential role of tuberous sclerosis genes TSC1 and TSC2 in NF-kappaB activation and cell survival

The TSC1-TSC2 complex has recently been implicated in cell survival responses. We observed that NF-kappaB signaling is attenuated in TSC1- and TSC2-deficient MEFs concomitant with reduced survival following DNA damage or TNFalpha stimulation. Reconstitution of TSC2 expression in TSC2(-/-) MEFs rescued survival in an NF-kappaB activity-dependent manner. Furthermore, in TSC2(-/-) MEFs, the rapamycin-mediated inhibition of deregulated mTOR activity restored NF-kappaB activation and survival. This rapamycin-mediated effect was reversed by inhibition of NF-kappaB transcriptional activation or by inhibition of ERK1/2 MAP kinase or PI-3K pathways, which lie on signaling cascades that lead to NF-kappaB activation. These results provide evidence for a crosstalk between the TSC/Rheb/mTOR pathway and the NF-kappaB induction pathways and indicate that NF-kappaB functions as an important survival factor that regulates TSC2-dependent cell survival.

Molecular mediators of alphavbeta3-induced endothelial cell survival

The alphavbeta3 integrin interaction with the extracellular matrix (ECM) plays an essential role in inhibiting apoptosis in endothelial cells. We have recently shown that alphavbeta3 ligation on rat aortic endothelial cells (RAECs) specifically activates the transcription factor nuclear factor kappaB (NF-kappaB) and promotes cell survival. Inhibiting NF-kappaB nuclear translocation abolished the protective effect of alphavbeta3 ligands. Here, we report that ligation of alphavbeta3 by its ligand, osteopontin (OPN), induces the phosphorylation and activation of inhibitory kappa B kinase beta IKKbeta and promotes the specific degradation of inhibitory kappa Balpha (IkappaBalpha) in RAECs. Overexpression of a dominant negative (DN) IKKbeta protein prevents IkappaBalpha phosphorylation, NF-kappaB activation, and inhibits the protective effects of OPN. The NF-kappaB-inducing kinase (NIK) has been shown to be one of the upstream kinases involved in IKK activation. OPN-mediated NF-kappaB activity is increased upon NIK wild-type (WT) overexpression and blocked following NIK DN overexpression. In addition, NIK-/-mouse embryonic fibroblasts (MEFs) plated on OPN display reduced NF-kappaB activity and decreased IkappaBalpha phosphorylation compared to NIK+/+MEFs. Finally, functional inhibition of integrin beta3-dependent NF-kappaB signaling decreases OPN-induced IkappaBalpha, IKKbeta and NIK phosphorylation. These studies for the first time show that the alphavbeta3-NF-kappaB-dependent endothelial survival pathway is dependent on IkappaBalpha, IKKbeta, and NIK.

Indirubin enhances tumor necrosis factor-induced apoptosis through modulation of nuclear factor-kappa B signaling pathway

Although indirubin is known to exhibit anti-cancer and anti-inflammatory activities, very little is known about its mechanism of action. In this study, we investigated whether indirubin mediates its effects through interference with the NF-kappaB pathway. As examined by the DNA binding of NF-kappaB, we found that indirubin suppressed tumor necrosis factor (TNF)-induced NF-kappaB activation in a dose- and time-dependent manner. Indirubin also suppressed the NF-kappaB activation induced by various inflammatory agents and carcinogens. Further studies showed that indirubin blocked the phosphorylation and degradation of IkappaB alpha through the inhibition of activation of IkappaB alpha kinase and phosphorylation and nuclear translocation of p65. NF-kappaB reporter activity induced by TNFR1, TNF receptor-associated death domain, TRAF2, TAK1, NF-kappaB-inducing kinase, and IKKbeta was inhibited by indirubin but not that induced by p65 transfection. We also found that indirubin inhibited the expression of NF-kappaB-regulated gene products involved in antiapoptosis (IAP1, IAP2, Bcl-2, Bcl-xL, and TRAF1), proliferation (cyclin D1 and c-Myc), and invasion (COX-2 and MMP-9). This correlated with enhancement of the apoptosis induced by TNF and the chemotherapeutic agent taxol in human leukemic KBM-5 cells. Indirubin also suppressed cytokine-induced cellular invasion. Overall, our results indicate that anti-cancer and anti-inflammatory activities previously assigned to indirubin may be mediated in part through the suppression of the NF-kappaB activation pathway.

A novel beta-oxa polyunsaturated fatty acid downregulates the activation of the IkappaB kinase/nuclear factor kappaB pathway, inhibits expression of endothelial cell adhesion molecules, and depresses inflammation

Several novel polyunsaturated fatty acids (PUFAs) that contain either an oxygen or sulfur atom in the beta-position were found to exhibit more selective antiinflammatory properties than their natural PUFA counterparts. One of these, beta-oxa-23:4n-6, unlike natural PUFAs, lacked ability to stimulate oxygen radical production in neutrophils but caused marked inhibition of agonist-induced upregulation of leukocyte adhesion to cultured human umbilical vein endothelial cells (HUVEC) and E-selectin, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1 expression. In addition, beta-oxa-23:4n-6 inhibited acute and chronic inflammatory responses in mice as well as the upregulation of adhesion molecule expression in arterial endothelium. This action of beta-oxa-23:4n-6 required a functional 12- but not 5-lipoxygenase or cyclooxygenases, consistent with its metabolism via the 12-lipoxygenase pathway. Whereas beta-oxa-23:4n-6 did not affect the activation of mitogen-activated protein kinases by tumor necrosis factor, activation of the IkappaB kinase/nuclear factor kappaB pathway was selectively inhibited. These novel PUFAs could form the basis for a potential new class of pharmaceuticals for treating inflammatory diseases, including atherosclerosis.

A selective small molecule IkappaB Kinase beta inhibitor blocks nuclear factor kappaB-mediated inflammatory responses in human fibroblast-like synoviocytes, chondrocytes, and mast cells

IkappaB kinase (IKK) beta is essential for inflammatory cytokine-induced activation of nuclear factor kappaB (NF-kappaB). NF-kappaB plays a pivotal role in the function of major cell types that contribute to the pathophysiological process of rheumatoid arthritis (RA). Here, we report the mechanism and the effect of the IKKbeta inhibitor N-(6-chloro-7-methoxy-9H-beta-carbolin-8-yl)-2-methylnicotinamide (ML120B), a beta-carboline derivative, on NF-kappaB signaling and gene activation in RA-relevant cell systems. ML120B is a potent, selective, reversible, and ATP-competitive inhibitor of IKKbeta with an IC50 of 60 nM when evaluated in an IkappaBalpha kinase complex assay. ML120B does not inhibit other IKK isoforms or a panel of other kinases. ML120B concentration-dependently inhibits tumor necrosis factor alpha (TNFalpha)-stimulated NF-kappaB signaling via inhibition of IkappaBalpha phosphorylation, degradation, and NF-kappaB translocation into the nucleus. For the first time, we have demonstrated that in human fibroblast-like synoviocytes, TNFalpha- or interleukin (IL)-1beta-induced monocyte chemoattractant protein-1 regulated on activation, normal T cell expressed and secreted and production is IKKbeta-dependent. In addition, for the first time, we have demonstrated that lipopolysaccharide- or peptidoglycan-induced cytokine production in human cord blood-derived mast cells is IKKbeta-dependent. In addition, in human chondrocytes, ML120B inhibited IL-1beta-induced matrix metalloproteinase production with an IC50 of approximately 1 microM. ML120B also blocked IL-1beta-induced prostaglandin E2 production. In summary, ML120B blocked numerous NF-kappaB-regulated cell responses that are involved in inflammation and destructive processes in the RA joint. Our findings support the evaluation of IKKbeta inhibitors as anti-inflammatory agents for the treatment of RA.

Hepatitis C virus nonstructural 5B protein regulates tumor necrosis factor alpha signaling through effects on cellular IkappaB kinase

Hepatitis C virus (HCV) NS5B protein is a membrane-associated phosphoprotein that possesses an RNA-dependent RNA polymerase activity. We recently reported that NS5A protein interacts with TRAF2 and modulates tumor necrosis factor alpha (TNF-alpha)-induced NF-kappaB and Jun N-terminal protein kinase (JNK). Since NS5A and NS5B are the essential components of the HCV replication complex, we examined whether NS5B could modulate TNF-alpha-induced NF-kappaB and JNK activation. In this study, we have demonstrated that TNF-alpha-induced NF-kappaB activation is inhibited by NS5B protein in HEK293 and hepatic cells. Furthermore, NS5B protein inhibited both TRAF2- and IKK-induced NF-kappaB activation. Using coimmunoprecipitation assays, we show that NS5B interacts with IKKalpha. Most importantly, NS5B protein in HCV subgenomic replicon cells interacted with endogenous IKKalpha, and then TNF-alpha-mediated IKKalpha kinase activation was significantly decreased by NS5B. Using in vitro kinase assay, we have further found that NS5B protein synergistically activated TNF-alpha-mediated JNK activity in HEK293 and hepatic cells. These data suggest that NS5B protein modulates TNF-alpha signaling pathways and may contribute to HCV pathogenesis.

A novel NF-kappaB binding site controls human granzyme B gene transcription

Granzyme B expression is essential for eliciting NK cell cytotoxicity and T cell function. However, its transcriptional regulatory mechanism is not well understood. In this report, we demonstrate in human NK cells and T cells that the NF-kappaB-signaling pathway is involved in such control. Furthermore, a novel downstream human granzyme B gene sequence (GGAGATTCCC) was identified for NF-kappaB binding. EMSA, luciferase, and chromatin immunoprecipitation assays in vitro and in vivo indicated that this NF-kappaB binding site is functional in an NK cell line and its primary counterpart. Our data also demonstrate that this binding site is functional in Jurkat T cells. Taken together, we identified a novel NF-kappaB binding site, which plays a pivotal role in controlling human granzyme B gene transcription.

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.

Activation of MEKK1 by Rho GTPases

Mammalian MAP/ERK kinase kinase 1 (MEKK1) is MAP kinase kinase kinase (MAP3K) that is a crucial regulator of many cellular signaling cascades. One of the most important physiological functions of MEKK1 is its ability to regulate cell migration, because MEKK1 null mice are defective in eyelid closure. MEKK1 exhibits its signaling activity through interaction with a large array of cellular factors, including several proteins that are known to play central roles in controlling cell movement and motility. We have recently identified an interaction between MEKK1 and RhoA. This interaction occurs between the GTP-bound, active form of RhoA and the amino terminal region of MEKK1 that harbors a PHD domain with E3 ubiquitin ligase activity. RhoA-GTP activates MEKK1 in vitro and in cells. Here we describe in detail the assay methods for RhoA activation of MEKK1, including preparation of recombinant proteins and proteins immunoprecipitated from cells, pretreatment of proteins, and assay conditions. We also briefly explain the methods and conditions we use to identify the interaction between MEKK1 and RhoA in yeast and in mammalian cells.

Transactivation of CCL20 gene by Epstein-Barr virus latent membrane protein 1

CCL20 is expected to play a crucial role in the initiation of immune responses and tumour growth. However, expression of CCL20 in Epstein-Barr virus (EBV)-associated diseases has not been studied. We examined the contribution of EBV infection and EBV-encoded latent membrane protein (LMP)-1 to CCL20 expression. EBV infection and LMP-1 induced CCL20 mRNA expression in the EBV-negative Burkitt lymphoma (BL) cell lines and the embryonic kidney cell line. Histone deacetylase inhibitor-stimulated endogenous LMP-1 also induced CCL20 expression in an EBV-positive BL cell line. Analysis of the CCL20 promoter showed that it was activated by LMP-1 C-terminal activation region (CTAR)-1 and CTAR-2. Co-expression of IkappaB alpha, IkappaB beta, IkappaB kinase (IKK)alpha, IKKbeta, IKKgamma, nuclear factor (NF)-kappaB-inducing kinase and tumour necrosis factor receptor-associated factor 2 dominant-negative constructs with LMP-1 inhibited the activation of the CCL20 promoter by LMP-1, suggesting that LMP-1 induces CCL20 via NF-kappaB signalling. The requirement for the NF-kappaB-binding site in the CCL20 promoter in LMP-1 responsiveness was established. Our results indicate that activation of the NF-kappaB pathway by LMP-1 is required for the activation of CCL20 expression.

CCAAT/enhancer binding proteins and interferon signaling pathways

Interferons (IFNs) regulate a number of host responses, including innate and adaptive immunity against viruses, microbes, and neoplastic cells. These responses are dependent on the expression of IFN-stimulated genes (ISGs). Given the diversities in these responses and their kinetics, it is conceivable that a number of different factors are required for controlling them. Here, we describe one such pathway wherein transcription factor CAAAT/enhancer binding protein-beta (C/EBP-beta) is controlled via IFN-gamma-induced MAPK signaling pathways. At least two IFN-gamma-induced MAPK signals converge on to C/EBP-beta for inducing transcription. One of these, driven by extracellular signal-regulated kinases (ERKs), phosphorylates the C/EBP-beta protein in its regulatory domain. The second, driven by the mixed-lineage kinases (MLKs), induces a dephosphorylation leading to the recruitment of transcriptional coactivators.

Transactivation of the ICAM-1 gene by CD30 in Hodgkin's lymphoma

The ICAM-1/LFA-1 complex mediates cell-cell interaction. ICAM-1 is overexpressed in Hodgkin/Reed-Sternberg (H/RS) cells, and serum levels of its soluble form are higher in Hodgkin's lymphoma (HL) patients than in controls. There are no data, however, regarding the regulation of expression of ICAM-1 in H/RS cells. CD30 was identified in H/RS cells of HL and has attracted much interest as a molecular marker of HL. To analyze ICAM-1 expression in H/RS cells, we examined the expression of ICAM-1, LFA-1, CD30 and CD30L in HL-derived cell lines. All cell lines expressed ICAM-1 and CD30, but not LFA-1 or CD30L. CD30 induced ICAM-1 expression. Analysis of the ICAM-1 promoter showed the importance of NF-kappaB binding site for CD30-induced ICAM-1 gene expression. Coexpression of IkappaB, IKK, NIK and TRAF dominant-negative constructs with CD30 inhibited CD30-induced activation of ICAM-1 promoter, suggesting that CD30 induces ICAM-1 via NF-kappaB signalling. The ICAM-1 promoter was activated by the C-terminal region of CD30, which activated NF-kappaB signalling. A decoy CD30 lacking the cytoplasmic region inhibited ICAM-1 promoter activity in HL cell lines. Thus, in H/RS cells, ligand-independent activation of CD30 signalling activates NF-kappaB and this leads to constitutive ICAM-1 expression, suggesting a link between 2 well known phenotypic characteristics of HL, CD30 and ICAM-1 overexpression.

TAK1-mediated stress signaling pathways are essential for TNF-α-promoted pulmonary metastasis of murine colon cancer cells

We have recently established a TNF-alpha-promoted metastasis model, in which the ability to metastasize to the lung was enhanced by stimulation of cultured colon 26 cells with TNF-alpha before intravenous inoculation. To investigate intracellular events in metastatic cascades of TNF-alpha-treated cancer cells, we have focused on the stress signaling pathways to c-Jun N-terminal kinase (JNK) and p38. Treatment with a specific inhibitor, SP600125 or SB203580, in vitro suppressed TNF-alpha-induced migration and pulmonary metastasis. Activation of endogenous TAK1, a mitogen-activated protein kinase (MAP3K) regulating the JNK and p38 MAPK pathways, was induced rapidly by TNF-alpha, and co-transfection of TAK1 with its activator protein TAB1 stimulated activation of JNK and p38 MAPKs, which led to activation of the transcription factor AP-1. The activation of stress signaling pathways by TAK1 resulted in enhanced migration to fibronectin in vitro and metastasis to the lung in vivo without affecting cell proliferation in vitro and tumor growth in vivo. Moreover, knockdown of endogenous TAK1 using small interfering RNA (siRNA) suppressed the TNF-alpha-induced JNK/p38 activation, migration and pulmonary metastasis. These results indicate that TAK1-mediated stress signaling pathways in cancer cells are essential for TNF-alpha-promoted metastasis to the lung.

The PAK1 autoregulatory domain is required for interaction with NIK in Helicobacter pylori-induced NF-kappaB activation

Helicobacter pylori, the etiological agent of various human gastric diseases, induces the transcription factor nuclear factor kappaB (NF-kappaB) and proinflammatory cytokines/chemokines. We have characterised the direct interaction between p21-activated kinase 1 (PAK1) and NF-kappaB-inducing kinase (NIK) in H. pylori-infected epithelial cells. The dimerisation (DI) motif, which is part of the NH2-terminal autoregulatory domain of PAK1, is critical for this interaction, whereas NIK forms complexes with PAK1 through its carboxy-terminal IkappaB kinase alpha (IKKalpha) binding site. Since the identified interaction sites are also crucial for the binding of activator (Rac/Cdc42 in the case of PAK1) or effector molecules (IKKalpha in the case of NIK), sequential stepwise signalling is suggested. Furthermore, we show that mitogen-activated protein kinase kinase kinases (MAP3K), like TPL2 (tumour progression locus 2) and transforming growth factor beta-activated kinase 1 (TAK1), have no impact on H. pylori-induced activation of NF-kappaB. These results identify the roles of PAK1 and NIK in a unique pathway involved in H. pylori-induced NF-kappaB activation, which is crucial for the induction of the innate immune response.