NF-kappaB and IKK as therapeutic targets in cancer

Identification of a ligand-induced transient refractory period in nuclear factor-kappaB signaling

In response to a variety of extracellular ligands, nuclear factor-kappaB (NF-kappaB) signaling regulates inflammation, cell proliferation, and apoptosis. It is likely that cells are not continuously exposed to stimulating ligands in vivo but rather experience transient pulses. To study the temporal regulation of NF-kappaB and its major regulator, inhibitor of NF-kappaBalpha (IkappaBalpha), in real time, we utilized a novel transcriptionally coupled IkappaBalpha-firefly luciferase fusion reporter and characterized the dynamics and responsiveness of IkappaBalpha processing upon a short 30-s pulse of tumor necrosis factor alpha (TNFalpha) or a continuous challenge of TNFalpha following a 30-s preconditioning pulse. Strikingly, a 30-s pulse of TNFalpha robustly activated inhibitor of NF-kappaB kinase (IKK), leading to IkappaBalpha degradation, NF-kappaB nuclear translocation, and strong transcriptional up-regulation of IkappaBalpha. Furthermore, we identified a transient refractory period (lasting up to 120 min) following preconditioning, during which the cells were not able to fully degrade IkappaBalpha upon a second TNFalpha challenge. Kinase assays of IKK activity revealed that regulation of IKK activity correlated in part with this transient refractory period. In contrast, experiments involving sequential exposure to TNFalpha and interleukin-1beta indicated that receptor dynamics could not explain this phenomenon. Utilizing a well accepted computational model of NF-kappaB dynamics, we further identified an additional layer of regulation, downstream of IKK, that may govern the temporal capacity of cells to respond to a second proinflammatory insult. Overall, the data suggested that nuclear export of NF-kappaB.IkappaBalpha complexes represented another rate-limiting step that may impact this refractory period, thereby providing an additional regulatory mechanism.

Targeting the nuclear factor-kappaB rescue pathway has promising future in human renal cell carcinoma therapy

Metastatic renal cell carcinoma (RCC) remains refractory to therapies. The nuclear factor-kappaB (NF-kappaB) transcription factor is involved in cell growth, cell motility, and vascularization. We evaluated whether targeting NF-kappaB could be of therapeutic and prognostic values in human RCC. The activation of the NF-kappaB pathway in human RCC cells and tumors was investigated by Western blot. In vitro, the effects of BAY 11-7085 and sulfasalazine, two NF-kappaB inhibitors, on tumor cell growth were investigated by cell counting, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide analysis, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling, and fluorescence-activated cell sorting. Their specificity toward NF-kappaB was analyzed by Western blot, confocal microscopy, NF-kappaB small interfering RNA, and NF-kappaB transcription assay. In vivo, the effects of BAY 11-7085 on the growth of human RCC tumors were investigated in nude mice. A tissue microarray (TMA) containing 241 cases of human RCC with 12 to 22 years of clinical follow-up and corresponding normal tissues was built up to assess prognostic significance of activated NF-kappaB. NF-kappaB is constitutively activated in cultured cells expressing or not the von Hippel-Lindau (VHL) tumor suppressor gene as a consequence of Akt kinase activation and in tumors. In vitro and in vivo NF-kappaB inhibition blocked tumor cell growth by inducing cell apoptosis. On the TMA, NF-kappaB activation was correlated with tumor dimension but was not found to be an independent prognostic factor for patient survival. This report provides strong evidence that the mechanisms responsible for the intrinsic resistance of RCC cells to apoptosis converge on NF-kappaB independently of VHL expression and that targeting this pathway has great anticancer potential.

Hepatocellular carcinoma and vitamin K

On the basis of reports of the antitumor effects of vitamin K on various cancers, we clinically investigated the suppressive effects of vitamin K2 on tumor recurrence after curative treatment for hepatocellular carcinoma (HCC). Our results showed that vitamin K2 administration significantly suppressed HCC recurrence. Our laboratory findings revealed that the inhibitory effect of vitamin K2 against HCC cell growth was generated by suppressing cyclin D1 expression through inhibition of NF-kappaB activation.

Neural stem cells, inflammation and NF-kappaB: basic principle of maintenance and repair or origin of brain tumours?

Several recent reports suggest that inflammatory signals play a decisive role in the self-renewal, migration and differentiation of multipotent neural stem cells (NSCs). NSCs are believed to be able to ameliorate the symptoms of several brain pathologies through proliferation, migration into the area of the lesion and either differentiation into the appropriate cell type or secretion of anti-inflammatory cytokines. Although NSCs have beneficial roles, current evidence indicates that brain tumours, such as astrogliomas or ependymomas are also caused by tumour-initiating cells with stem-like properties. However, little is known about the cellular and molecular processes potentially generating tumours from NSCs. Most pro-inflammatory conditions are considered to activate the transcription factor NF-kappaB in various cell types. Strong inductive effects of NF-kappaB on proliferation and migration of NSCs have been described. Moreover, NF-kappaB is constitutively active in most tumour cells described so far. Chronic inflammation is also known to initiate cancer. Thus, NF-kappaB might provide a novel mechanistic link between chronic inflammation, stem cells and cancer. This review discusses the apparently ambivalent role of NF-kappaB: physiological maintenance and repair of the brain via NSCs, and a potential role in tumour initiation. Furthermore, it reveals a possible mechanism of brain tumour formation based on inflammation and NF-kappaB activity in NSCs.

Inhibition of NF-kappaB activation with designed ankyrin-repeat proteins targeting the ubiquitin-binding/oligomerization domain of NEMO

The link between the NF-kappaB signal transduction pathway and cancer is now well established. Inhibiting this pathway is therefore a promising approach in the treatment of certain cancers through a pro-apoptotic effect in malignant cells. Owing to its central role in the pathway, the IkappaB kinase (IKK) complex is a privileged target for designing inhibitors. Previously, we showed that oligomerization of NEMO is necessary for IKK activation and defined a minimal oligomerization domain (CC2-LZ) for NEMO, and we developed NEMO peptides inhibiting NF-kappaB activation at the level of the IKK complex. To improve the low-affinity inhibitors, we used ribosome display to select small and stable proteins with high affinity against the individual CC2-LZ because the entire NEMO protein is poorly soluble. Several binders with affinities in the low nanomolar range were obtained. When expressed in human cells, some of the selected molecules, despite their partial degradation, inhibited TNF-alpha-mediated NF-kappaB activation while having no effect on the basal activity. Controls with a naive library member or null plasmid had no effect. Furthermore, we could show that this NF-kappaB inhibition occurs through a specific interaction between the binders and the endogenous NEMO, resulting in decreased IKK activation. These results indicate that in vitro selections with the NEMO subdomain alone as a target may be sufficient to lead to interesting compounds that are able to inhibit NF-kappaB activation.

A cell cycle regulatory network controlling NF-kappaB subunit activity and function

Aberrantly active NF-kappaB complexes can contribute to tumorigenesis by regulating genes that promote the growth and survival of cancer cells. We have investigated NF-kappaB during the cell cycle and find that its ability to regulate the G1-phase expression of key proto-oncogenes is subject to regulation by the integrated activity of IkappaB kinase (IKK)alpha, IKKbeta, Akt and Chk1. The coordinated binding of NF-kappaB subunits to the Cyclin D1, c-Myc and Skp2 promoters is dynamic with distinct changes in promoter occupancy and RelA(p65) phosphorylation occurring through G1, S and G2 phases, concomitant with a switch from coactivator to corepressor recruitment. Akt activity is required for IKK-dependent phosphorylation of NF-kappaB subunits in G1 and G2 phases, where Chk1 is inactive. However, in S-phase, Akt is inactivated, while Chk1 phosphorylates RelA and associates with IKKalpha, inhibiting the processing of the p100 (NF-kappaB2) subunit, which also plays a critical role in the regulation of these genes. These data reveal a complex regulatory network integrating NF-kappaB with the DNA-replication checkpoint and the expression of critical regulators of cell proliferation.

Protein kinase C-associated kinase is required for NF-kappaB signaling and survival in diffuse large B-cell lymphoma cells

Diffuse large B-cell lymphoma (DLBCL) is an aggressive and the most common type of non-Hodgkin lymphoma. Despite recent advances in treatment, less than 50% of the patients are cured with current multiagent chemotherapy. Abnormal NF-kappaB activity not only contributes to tumor development but also renders cancer cells resistant to chemotherapeutic agents. Identifying and targeting signaling molecules that control NF-kappaB activation in cancer cells may thus yield more effective therapy for DLBCL. Here, we show that while overexpression of protein kinase C-associated kinase (PKK) activates NF-kappaB signaling in DLBCL cells, suppression of PKK expression inhibits NF-kappaB activity in these cells. In addition, we show that NF-kappaB activation induced by B cell-activating factor of tumor necrosis factor family (BAFF) in DLBCL cells requires PKK. Importantly, we show that knockdown of PKK impairs the survival of DLBCL cells in vitro and inhibits tumor growth of xenografted DLBCL cells in mice. Suppression of PKK expression also sensitizes DLBCL cells to treatment with chemotherapeutic agents. Together, these results indicate that PKK plays a pivotal role in the survival of human DLBCL cells and represents a potential target for DLBCL therapy.

Anti-inflammatory interventions of NF-kappaB signaling: potential applications and risks

Signaling via NF-kappaB is a key process during inflammation and thus constitutes an attractive target for anti-inflammatory therapeutic interventions. Especially during initial hyperinflammatory states of an acute illness such as sepsis or in the course of chronic inflammation and autoimmune diseases inhibition of IKK-driven NF-kappaB activation provides a promising treatment strategy. Given its critical role in innate and adaptive immune responses, however, there is a certain amount of risk due to induced immunodeficiency that may follow inhibitory treatment. Moreover, its primary anti-apoptotic function suggests that blockade of NF-kappaB activation has dramatic effects on cell functions and survival and eventually worsens the course of an inflammatory disease. An overview of canonical and alternative NF-kappaB activation and its critical role in immune responses will be provided. A main topic focuses on recent animal studies and data derived from genetic studies in humans that provide an insight into potential effects of different therapeutic modulations of NF-kappaB inflammatory signaling. The pros and cons of NF-kappaB inhibition and treatment strategies will be critically reviewed.

The emerging roles of forkhead box (Fox) proteins in cancer

Forkhead box (Fox) proteins are a superfamily of evolutionarily conserved transcriptional regulators, which control a wide spectrum of biological processes. As a consequence, a loss or gain of Fox function can alter cell fate and promote tumorigenesis as well as cancer progression. Here we discuss the evidence that the deregulation of Fox family transcription factors has a crucial role in the development and progression of cancer, and evaluate the emerging role of Fox proteins as direct and indirect targets for therapeutic intervention, as well as biomarkers for predicting and monitoring treatment responses.

Constitutive and inducible nuclear factor-κB in immortalized normal human bronchial epithelial and non-small cell lung cancer cell lines

Constitutive activation of the proinflammatory nuclear factor kappaB (NF-kappaB) transcription factor p65(RelA)/p50 has been implicated in many cancers, including leukemias, lymphomas, and several solid tumors, including lung cancer. In many cases, constitutive NF-kappaB activation can be recapitulated in cell lines isolated from these cancers. To test whether this is the case with non-small cell lung cancer (NSCLC) cell lines, we investigated the basal levels of NF-kappaB proteins, their subcellular distribution, their DNA-binding activities, and the expression of NF-kappaB-responsive genes in 10 NSCLC cell lines. The immortalized human bronchial epithelial cell line BEAS-2B served as a normal control. We found little evidence of substantial constitutive NF-kappaB activation in NSCLC cell lines, although most all of the normal and NSCLC cells possessed inducible NF-kappaB. Our findings provide a resource for the use of particular NSCLC cell lines for the investigation of constitutive and inducible NF-kappaB activity in vitro.

LZAP, a putative tumor suppressor, selectively inhibits NF-kappaB

LZAP has been reported to inhibit cellular proliferation and clonogenic growth. Here, we report that decreased LZAP expression promoted cellular transformation, xenograft tumor growth, and xenograft tumor vascularity. Loss of LZAP also increased cellular invasion, and MMP-9 expression dependent on NF-kappaB. LZAP directly bound to RelA, impaired serine 536 phosphorylation of RelA, increased HDAC association with RelA, inhibited basal and stimulated NF-kappaB transcriptional activity, and was found at the promoter of selective NF-kappaB-responsive genes. LZAP protein levels were markedly decreased in 32% of primary HNSCCs (n = 28) and decreased LZAP levels in primary HNSCC correlated with increased expression of the NF-kappaB-regulated genes IL-8 and IkappaBalpha. In aggregate, these data support a role of LZAP in NF-kappaB regulation and tumor suppression.

Fructose and the metabolic syndrome: pathophysiology and molecular mechanisms

Emerging evidence suggests that increased dietary consumption of fructose in Western society may be a potentially important factor in the growing rates of obesity and the metabolic syndrome. This review will discuss fructose-induced perturbations in cell signaling and inflammatory cascades in insulin-sensitive tissues. In particular, the roles of cellular signaling molecules including nuclear factor kappa B (NFkB), tumor necrosis factor alpha (TNF-alpha), c-Jun amino terminal kinase 1 (JNK-1), protein tyrosine phosphatase 1B (PTP-1B), phosphatase and tensin homolog deleted on chromosome ten (PTEN), liver X receptor (LXR), farnesoid X receptor (FXR), and sterol regulatory element-binding protein-1c (SREBP-1c) will be addressed. Considering the prevalence and seriousness of the metabolic syndrome, further research on the underlying molecular mechanisms and preventative and curative strategies is warranted.

Regulation of mammalian target of rapamycin activity in PTEN-inactive prostate cancer cells by I kappa B kinase alpha

The mammalian target of rapamycin (mTOR) is a mediator of cell growth, survival, and energy metabolism at least partly through its ability to regulate mRNA translation. mTOR is activated downstream of growth factors, insulin, and Akt-dependent signaling associated with oncoprotein expression or loss of the tumor-suppressor PTEN. In this regard, mTOR activity is associated with cancer cell growth and survival. Here, we have explored an involvement of the I kappa B kinase (IKK) pathway, associated with nuclear factor-kappaB activation, in controlling mTOR activity. The experiments show that IKK alpha controls mTOR kinase activity in Akt-active, PTEN-null prostate cancer cells, with less involvement by IKK beta. In these cells, IKK alpha associates with mTOR, as part of the TORC1 complex, in an Akt-dependent manner. Additionally, IKKalpha is required for efficient induction of mTOR activity downstream of constitutively active Akt expression. The results indicate a novel role for IKK alpha in controlling mTOR function in cancer cells with constitutive Akt activity.

Many faces of NF-kappaB signaling induced by genotoxic stress

The nuclear factor-kappaB (NF-kappaB) family of dimeric transcription factors plays pivotal roles in physiologic and pathologic processes, including immune and inflammatory responses and development and progression of various human cancers. Inactive NF-kappaB dimers normally exist in the cytoplasm in association with inhibitor proteins belonging to the inhibitor of NF-kappaB (IkappaB) family of related proteins. Activation of NF-kappaB involves its release from IkappaB and subsequent nuclear translocation to induce expression of target genes. Intense research effort has revealed many distinct signaling pathways and mechanisms of NF-kappaB activation induced by immune and inflammatory stimuli. These aspects of NF-kappaB biology have been amply reviewed in the literature. However, those that involve DNA-damaging agents are less well understood, and multiple conflicting pathways and mechanisms have been described in the literature. In this review, we summarize the proposed mechanisms of NF-kappaB activation by various DNA-damaging agents, discuss the significance of such activation in the context of cancer treatment, and highlight some of the critical questions that remain to be addressed in future studies.

Insights into the structural basis of the GADD45beta-mediated inactivation of the JNK kinase, MKK7/JNKK2

NF-kappaB/Rel factors control programmed cell death (PCD), and this control is crucial to oncogenesis, cancer chemoresistance, and antagonism of tumor necrosis factor (TNF) alpha-induced killing. With TNFalpha, NF-kappaB-mediated protection involves suppression of the c-Jun-N-terminal kinase (JNK) cascade, and we have identified Gadd45beta, a member of the Gadd45 family, as a pivotal effector of this activity of NF-kappaB. Inhibition of TNFalpha-induced JNK signaling by Gadd45beta depends on direct targeting of the JNK kinase, MKK7/JNKK2. The mechanism by which Gadd45beta blunts MKK7, however, is unknown. Here we show that Gadd45beta is a structured protein with a predicted four-stranded beta-sheet core, five alpha-helices, and two acidic loops. Association of Gadd45beta with MKK7 involves a network of interactions mediated by its putative helices alpha3 and alpha4 and loops 1 and 2. Whereas alpha3 appears to primarily mediate docking to MKK7, loop 1 and alpha4-loop 2 seemingly afford kinase inactivation by engaging the ATP-binding site and causing conformational changes that impede catalytic function. These data provide a basis for Gadd45beta-mediated blockade of MKK7, and ultimately, TNFalpha-induced PCD. They also have important implications for treatment of widespread diseases.

Upregulation of Twist-1 by NF-kappaB blocks cytotoxicity induced by chemotherapeutic drugs

NF-kappaB/Rel transcription factors are central to controlling programmed cell death (PCD). Activation of NF-kappaB blocks PCD induced by numerous triggers, including ligand engagement of tumor necrosis factor receptor (TNF-R) family receptors. The protective activity of NF-kappaB is also crucial for oncogenesis and cancer chemoresistance. Downstream of TNF-Rs, this activity of NF-kappaB has been linked to the suppression of reactive oxygen species and the c-Jun-N-terminal-kinase (JNK) cascade. The mechanism by which NF-kappaB inhibits PCD triggered by chemotherapeutic drugs, however, remains poorly understood. To understand this mechanism, we sought to identify unrecognized protective genes that are regulated by NF-kappaB. Using an unbiased screen, we identified the basic-helix-loop-helix factor Twist-1 as a new mediator of the protective function of NF-kappaB. Twist-1 is an evolutionarily conserved target of NF-kappaB, blocks PCD induced by chemotherapeutic drugs and TNF-alpha in NF-kappaB-deficient cells, and is essential to counter this PCD in cancer cells. The protective activity of Twist-1 seemingly halts PCD independently of interference with cytotoxic JNK, p53, and p19(ARF) signaling, suggesting that it mediates a novel protective mechanism activated by NF-kappaB. Indeed, our data indicate that this activity involves a control of inhibitory Bcl-2 phosphorylation. The data also suggest that Twist-1 and -2 play an important role in NF-kappaB-dependent chemoresistance.

RbAp48 is a target of nuclear factor-kappaB activity in thyroid cancer

CONTEXT

We have recently shown that nuclear factor (NF)-kappaB activity is constitutively elevated in anaplastic human thyroid carcinomas. The inhibition of NF-kappaB in the anaplastic thyroid carcinoma cell line (FRO) leads to increased susceptibility to apoptosis induced by chemotherapeutic drugs and to the block of oncogenic activity.

OBJECTIVES

To understand better the molecular mechanisms played by NF-kappaB in thyroid oncogenesis, we performed a differential proteomic analysis between FRO transfected with a superrepressor form of inhibitor of kappaBalpha (IkappaBalphaM) and the parental counterpart (FRO Neo cells).

RESULTS

Differential proteomic analysis revealed that the retinoblastoma-associated protein 48 (RbAp48) is down-regulated in the absence of functional NF-kappaB. Immunohistochemical analysis of normal and pathological human thyroid specimens confirmed that RbAp48 is strongly overexpressed in primary human carcinomas. Reduction of RbAp48 expression using small interfering RNA determined the suppression of tumorigenicity, very likely due to the decrease of their growth rate rather than to an increased susceptibility to apoptosis. In addition, we showed that NF-kappaB, at least in part, transcriptionally controls RbAp 48. A functional NF-kappaB consensus sequence was located within the promoter region of RbAp48 human gene, and embryonic fibroblasts isolated from the p65 knockout mouse (murine embryonic fibroblasts p65-/-) showed decreased expression of RbAp48.

CONCLUSION

Our results show that RbAp48 is a NF-kappaB-regulated gene playing an important role in thyroid cancer cell autonomous proliferation.

Systemic targeting inhibitor of kappaB kinase inhibits melanoma tumor growth

Constitutive activation of nuclear factor-kappaB (NF-kappaB) has been directly implicated in tumorigenesis of various cancer types, including melanoma. Inhibitor of kappaB kinase (IKK) functions as a major mediator of NF-kappaB activation. Thus, development of an IKK-specific inhibitor has been a high priority, although it remains unclear whether systemic inhibition of IKK will provide therapeutic benefit. In this study, we show that inhibition of NF-kappaB activity in melanocytes that are persistently expressing an active H-Ras(V12) gene and are deficient in the tumor suppressors inhibitor A of cyclin-dependent kinase 4/alternative reading frame results in reduction of melanoma tumor growth in vivo. This effect is, at least in part, via regulation of NF-kappaB nuclear activation and RelA phosphorylation. Based on this result, we developed a double hammerhead ribozyme long-term expression system to silence either IKKalpha or IKKbeta. The ribozymes were placed in an EBV construct and delivered i.v. to nude mice bearing melanoma lesions, which developed after i.v. injection of H-Ras-transformed melanoma cells. Our in vivo data show that knockdown of endogenous IKKbeta significantly reduces the growth of the melanoma lesions and knockdown of either IKKalpha or IKKbeta prolongs the life span of immunocompetent mice.

NF-kappa B as a therapeutic target in neurodegenerative diseases

NF-kappaB is a transcription factor that regulates numerous physiological functions, and that is involved in the pathogenesis of various diseases. In the nervous system there is evidence supporting a dual role of NF-kappaB in neurodegenerative diseases; activation of NF-kappaB in neurons promotes their survival, whereas activation in glial and immune cells mediates pathological inflammatory processes. The reason for such a dichotomy lies in the complexity of the NF-kappaB system. Emerging research has begun to dissect the pathways leading to the activation of the different NF-kappaB proteins, and the gene targets of NF-kappaB, in cells of the nervous system. In this article the authors discuss recent findings concerning the roles of NF-kappaB in the pathogenesis of several neurodegenerative disorders, and its potential as a pharmaceutical target for these disorders.

NF-kappa B as a target for cancer therapy

NF-kappaB transcription factors and the signaling pathways that activate them play a critical role in cancer development, progression and therapy, and recently have become a focal point for intense drug discovery and development efforts. This article presents a critical review on the different types of inhibitors targeting the NF-kappaB pathway at several stages.

The human cytomegalovirus virion possesses an activated casein kinase II that allows for the rapid phosphorylation of the inhibitor of NF-kappaB, IkappaBalpha

We documented that the NF-kappaB signaling pathway was rapidly induced following human cytomegalovirus (HCMV) infection of human fibroblasts and that this induced NF-kappaB activity promoted efficient transactivation of the major immediate-early promoter (MIEP). Previously, we showed that the major HCMV envelope glycoproteins, gB and gH, initiated this NF-kappaB signaling event. However, we also hypothesized that there were additional mechanisms utilized by the virus to rapidly upregulate NF-kappaB. In this light, we specifically hypothesized that the HCMV virion contained IkappaBalpha kinase activity, allowing for direct phosphorylation of IkappaBalpha following virion entry into infected cells. In vitro kinase assays performed on purified HCMV virion extract identified bona fide IkappaBalpha kinase activity in the virion. The enzyme responsible for this kinase activity was identified as casein kinase II (CKII), a cellular serine-threonine protein kinase. CKII activity was necessary for efficient transactivation of the MIEP and IE gene expression. CKII is generally considered to be a constitutively active kinase. We suggest that this molecular characteristic of CKII represents the biologic rationale for the viral capture and utilization of this kinase early after infection. The packaging of CKII into the HCMV virion identifies that diverse molecular mechanisms are utilized by HCMV for rapid NF-kappaB activation. We propose that HCMV possesses multiple pathways to increase NF-kappaB activity to ensure that the correct temporal regulation of NF-kappaB occurs following infection and that sufficient threshold levels of NF-kappaB are reached in the diverse array of cells, including monocytes and endothelial cells, infected in vivo.

AS602868, a dual inhibitor of IKK2 and FLT3 to target AML cells

Acute myeloid leukemia (AML) cells carry molecular defects that promote their leukemic proliferation, resistance to apoptosis and defect in differentiation. Pharmacological targeting of the nuclear factor kappaB (NF-kappaB) pathway has been shown to promote apoptosis of primary AML cells and to sensitize blasts to neoplastic drugs (Frelin, Blood 2005, 105, 804). The Fms-like tyrosine kinase 3 (FLT3), which sustains proliferation of normal hematopoietic progenitors is frequently overexpressed or mutated in AML patients. Using Ba/F3 murine pre-B cells transfected with various mutants of FLT3 (ITD, D835V, D835Y) and the MV4-11 human AML line, we show that normal or oncogenic stimulation of FLT3 led to activation of NF-kappaB. Pharmacological inhibition of either FLT3 with AG1296 or NF-kappaB with the small molecule inhibitor of IkappaB kinase-2 AS602868 reduced viability and triggered cell death. Moreover, AS602868 was also found to interfere directly with FLT3 kinase activation. AS602868 thus appears to target two different kinases that play a crucial role in the pathogenesis of AML, making it particularly attractive as a new therapeutical approach for AML.

Cell death in NF-kappaB-dependent tumour cell lines as a result of NF-kappaB trapping by linker-modified hairpin decoy oligonucleotide

The transcription factor NF-kappaB is frequently activated in cancer, and is therefore a valuable target for cancer therapy. Decoy oligodeoxynucleotides (ODNs) inhibit NF-kappaB by preventing its binding to the promoter region of target genes. Few studies have used NF-kappaB-targeting with ODNs in cancer. Using a hairpin NF-kappaB-decoy ODN we found that it induced growth inhibition and cell death in NF-kappaB-dependent tumour cell lines. The ODN colocalized with the p50 subunit of NF-kappaB in cells and directly interacted with it in nuclear extracts. In TNFalpha-treated cells the ODN and the p50 subunit were found in the cytoplasm suggesting that the complex did not translocate to the nucleus. Transcriptional activity of NF-kappaB was efficiently inhibited by the ODN, whereas a scrambled ODN was without effect on transcription. Thus, ODN-mediated inhibition of NF-kappaB can efficiently promote cell death in cancer cells providing a potentially powerful approach to tumour growth inhibition.

Integrating cell-signalling pathways with NF-kappaB and IKK function

Nuclear factor (NF)-kappaB and inhibitor of NF-kappaB kinase (IKK) proteins regulate many physiological processes, including the innate- and adaptive-immune responses, cell death and inflammation. Disruption of NF-kappaB or IKK function contributes to many human diseases, including cancer. However, the NF-kappaB and IKK pathways do not exist in isolation and there are many mechanisms that integrate their activity with other cell-signalling networks. This crosstalk constitutes a decision-making process that determines the consequences of NF-kappaB and IKK activation and, ultimately, cell fate.

NF-kappaB as a potential molecular target for cancer therapy

Nuclear factor kappaB (NF-kappaB), a transcription factor, plays an important role in carcinogenesis as well as in the regulation of immune and inflammatory responses. NF-kappaB induces the expression of diverse target genes that promote cell proliferation, regulate apoptosis, facilitate angiogenesis and stimulate invasion and metastasis. Furthermore, many cancer cells show aberrant or constitutive NF-kappaB activation which mediates resistance to chemo- and radio-therapy. Therefore, the inhibition of NF-kappaB activation and its signaling pathway offers a potential cancer therapy strategy. In addition, recent studies have shown that NF-kappaB can also play a tumor suppressor role in certain settings. In this review, we focus on the role of NF-kappaB in carcinogenesis and the therapeutic potential of targeting NF-kappaB in cancer therapy.

Curcumin synergistically augments bcr/abl phosphorothioate antisense oligonucleotides to inhibit growth of chronic myelogenous leukemia cells

AIM

To investigate the growth inhibition effect of the combination of bcr/abl phosphorothioate antisense oligonucleotides (PS-ASODN) and curcumin (cur), and the possible mechanisms of cur on the chronic myelogenous leukemia cell line K562.

METHODS

The K562 cell line was used as a P210( bcr/abl )-positive cell model in vitro and was exposed to different concentrations of PS-ASODN (0-20 micromol/L), cur (0-20 micromol/L), or a combination of both. Growth inhibition and apoptosis of K562 cells were assessed by MTT assay and AO/EB fluorescent staining, respectively. The expression levels of P210( bcr/abl ), NF-kappaB and heat shock protein 90 (Hsp90) were assessed by Western blot.

RESULTS

Exposure to cur (5-20 micromol/L) and PSASODN (5-20 micromol/L) resulted in a synergistic inhibitory effect on cell growth. Growth inhibition was associated with the inhibition of the proliferation and induction of apoptosis. Western blot analysis showed that the drugs synergistically downregulated the level of P210( bcr/abl ) and NF-kappaB. Cur downregulated Hsp90, whereas no synergism was observed when cur was combined with PS-ASODN.

CONCLUSION

PS-ASODN and cur exhibited a synergistic inhibitory effect on the cell growth of K562. The synergistic growth inhibition was mediated through different mechanisms that involved the inhibition of P210( bcr/abl ).

Mutual cross-talk between reactive oxygen species and nuclear factor-kappa B: molecular basis and biological significance

Reactive oxygen species (ROS) are emerging as key effectors in signal transduction. This role of ROS is especially evident in the pathways leading to programmed cell death (PCD) elicited in response to certain stress stimuli and cytokines. In these pathways, cytotoxic ROS signaling appears to be mediated in part by activation of the c-Jun-N-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) cascade. Another pathway that is under ROS-mediated control in some systems is that leading to activation of transcription factor nuclear factor-kappa B (NF-kappaB), which is a central regulator of immunity, inflammation and cell survival. Remarkably, new evidence has unveiled the existence of a reciprocal, negative control that NF-kappaB exerts on ROS and JNK activities. This NF-kappaB-imposed restraint on ROS and JNK signaling is crucial for antagonism of PCD elicited by the proinflammatory cytokine tumor necrosis factor (TNF)alpha and likely other triggers. Effectors of this antagonistic cross-talk between NF-kappaB and ROS/JNK pathways have recently been identified. Because of the key roles that the prosurvival function of NF-kappaB plays in organismal physiology and disease, gaining a further mechanistic understanding of this cross-talk and NF-kappaB-dependent survival may be key to developing new therapies for the treatment of widespread human illnesses, such as cancer and chronic inflammatory conditions.

Nuclear factor-κB and inhibitor of κB kinase pathways in oncogenic initiation and progression

Abundant data support a key role for the transcription factor nuclear factor-kappaB (NF-kappaB) signaling pathway in controlling the initiation and progression of human cancer. NF-kappaB and associated regulatory proteins such as IkappaB kinase (IKK) are activated downstream of many oncoproteins and there is much evidence for the activation of NF-kappaB-dependent target genes in a variety of solid tumors and hematologic malignancies. This review focuses on the mechanisms by which the NF-kappaB pathway is activated in cancer and on the oncogenic functions controlled by activated NF-kappaB. Additionally, the effects of NF-kappaB activation in tumors relative to cancer therapy are also discussed.

Can NF-κB be a target for novel and efficient anti-cancer agents?

Since the discovery of the NF-kappaB transcription factor in 1986 and the cloning of the genes coding for NF-kappaB and IkappaB proteins, many studies demonstrated that this transcription factor can, in most cases, protect transformed cells from apoptosis and therefore participate in the onset or progression of many human cancers. Molecular studies demonstrated that ancient widely used drugs, known for their chemopreventive or therapeutic activities against human cancers, inhibit NF-kappaB, usually among other biological effects. It is therefore considered that the anti-cancer activities of NSAIDs (non-steroidal anti-inflammatory drugs) or glucocorticoids are probably partially related to the inhibition of NF-kappaB and new clinical trials are being initiated with old compounds such as sulfasalazine. In parallel, many companies have developed novel agents acting on the NF-kappaB pathway: some of these agents are supposed to be NF-kappaB specific (i.e. IKK inhibitors) while others have wide-range biological activities (i.e. proteasome inhibitors). Today, the most significant clinical data have been obtained with bortezomib, a proteasome inhibitor, for the treatment of multiple myeloma. This review discusses the preclinical and clinical data obtained with these various drugs and their putative future developments.

Theileria-induced constitutive IKK activation is independent of functional Hsp90

The intracellular parasite Theileria induces uncontrolled proliferation and host cell transformation. Parasite-induced transformation is accompanied by constitutive activation of IkappaB kinase (IKK), resulting in permanently high levels of activated nuclear factor (NF)-kappaB. IKK activation pathways normally require heat shock protein 90 (Hsp90), a chaperone that regulates the stability and activity of signalling molecules and can be blocked by the benzoquinone ansamycin compound geldanamycin (GA). In Theileria-transformed cells, IkappaBalpha and p65 phosphorylation, NF-kappaB nuclear translocation and DNA binding activity are largely resistant to GA and also NF-kappaB-dependent reporter gene expression is only partly affected. Our findings indicate that parasite-induced IKK activity does not require functional Hsp90.