NF-kappaB and IKK as therapeutic targets in cancer

Neutrophil apoptosis: relevance to the innate immune response and inflammatory disease

Neutrophils are the most abundant cell type involved in the innate immune response. They are rapidly recruited to sites of injury or infection where they engulf and kill invading microorganisms. Neutrophil apoptosis, the process of programmed cell death that prevents the release of neutrophil histotoxic contents, is tightly regulated and limits the destructive capacity of neutrophil products to surrounding tissue. The subsequent recognition and phagocytosis of apoptotic cells by phagocytic cells such as macrophages is central to the successful resolution of an inflammatory response and it is increasingly apparent that the dying neutrophil itself exerts an anti-inflammatory effect through modulation of surrounding cell responses, particularly macrophage inflammatory cytokine release. Apoptosis may be delayed, induced or enhanced by micro-organisms dependent on their immune evasion strategies and the health of the host they encounter. There is now an established field of research aimed at understanding the regulation of apoptosis and its potential as a target for therapeutic intervention in inflammatory and infective diseases. This review focuses on the physiological regulation of neutrophil apoptosis with respect to the innate immune system and highlights recent advances in mechanistic understanding of apoptotic pathways and their therapeutic manipulation in appropriate and excessive innate immune responses.

High expression levels of IKKalpha and IKKbeta are necessary for the malignant properties of liver cancer

IKK-NF-kappaB signaling is regarded as an important factor in hepatocarcinogenesis and a potential target for liver cancer therapy. Therefore, in this study, we analyzed the expression of mRNAs encoding components and targets of NF-kappaB signaling including IKKalpha, IKKbeta, RANK, RANKL, OPG, CyclinD3, mammary serine protease inhibitor (Maspin), CyclinD1, c-FLIP, Bcl-xl, Stat3, Cip1 and Cip2 by real-time PCR in 40 patients with liver cancer. After statistical analysis, 7 indices including IKKalpha, IKKbeta, RANK, Maspin, c-FLIP, Cip2 and cyclinD1 were found to show significant differences between tumor tissue and its corresponding adjacent tissue. When IKKalpha and IKKbeta were downregulated in the hepatocellular carcinoma (HCC) cell lines of MHCC-97L and MHCC-97H in vitro, the numbers of BrdU positive cells were decreased in both IKKalpha and IKKbeta knockdown cells. Levels of apoptosis were also investigated in IKKalpha and IKKbeta knockdown cells. The growth of HCC was inhibited in the subcutaneous implantation model, and lung metastatogenesis was also significantly inhibited in the kidney capsule transplantation model. Downregulation of IKKalpha and IKKbeta in HCC cultured in vitro revealed that increased Maspin, OPG and RANKL expression was associated with metastasis of HCC. These findings were associated with downregulation of Bcl-XL and c-FLIP, which may be the reason for increased apoptosis. The therapeutic effect of IKKalpha and IKKbeta downregulation depends on extent of NF-kappaB inhibition and the malignant nature of the HCC. We anticipate that IKK-targeted gene therapy can be used in the treatment of HCC, a cancer that is notoriously resistant to radiation and chemotherapy.

NF-kappaB inhibition through proteasome inhibition or IKKbeta blockade increases the susceptibility of melanoma cells to cytostatic treatment through distinct pathways

Metastasized melanoma is almost universally resistant to chemotherapy. Given that constitutive or drug-induced upregulation of NF-kappaB activity is associated with this chemoresistance, NF-kappaB inhibition may increase the susceptibility to antitumoral therapy. On the cellular level, two principles of NF-kappaB inhibition, proteasome inhibition by bortezomib and IkappaB kinase-beta (IKKbeta) inhibition by the kinase inhibitor of NF-kappaB-1 (KINK-1), significantly increased the antitumoral efficacy of camptothecin. When combined with camptothecin, either of the two NF-kappaB-inhibiting principles synergistically influenced progression-related in vitro functions, including cell growth, apoptosis, and invasion through an artificial basement membrane. In addition, when C57BL/6 mice were intravenously injected with B16F10 melanoma cells, the combination of cytostatic treatment with either of the NF-kappaB-inhibiting compounds revealed significantly reduced pulmonary metastasis compared to either treatment alone. However, on the molecular level, nuclear translocation of p65, cell cycle analysis, and expression of NF-kappaB-dependent gene products disclosed distinctly different molecular mechanisms, resulting in the same functional effect. That proteasome inhibition and IKKbeta inhibition affect distinct molecular pathways downstream of NF-kappaB, both leading to increased chemosensitivity, is previously unreported. Thus, it is conceivable that switching the two principles of NF-kappaB inhibition, once resistance to one of the agents occurs, will improve future treatment regimens.

Aurora-A down-regulates IkappaBalpha via Akt activation and interacts with insulin-like growth factor-1 induced phosphatidylinositol 3-kinase pathway for cancer cell survival

Background

The mitotic Aurora-A kinase exerts crucial functions in maintaining mitotic fidelity. As a bona fide oncoprotein, Aurora-A aberrant overexpression leads to oncogenic transformation. Yet, the mechanisms by which Aurora-A enhances cancer cell survival remain to be elucidated.

Results

Here, we found that Aurora-A overexpression was closely correlated with clinic stage and lymph node metastasis in tongue carcinoma. Aurora-A inhibitory VX-680 suppressed proliferation, induced apoptosis and markedly reduced migration in cancer cells. We further showed that insulin-like growth factor-1, a PI3K physiological activator, reversed VX-680-decreased cell survival and motility. Conversely, wortmannin, a PI3K inhibitor, combined with VX-680 showed a synergistic effect on inducing apoptosis and suppressing migration. In addition, Aurora-A inhibition suppressed Akt activation, and VX-680-induced apoptosis was attenuated by Myr-Akt overexpression, revealing a cross-talk between Aurora-A and PI3K pathway interacting at Akt activation. Significantly, we showed that suppression of Aurora-A decreased phosphorylated Akt and was associated with increased IkappaBα expression. By contrast, Aurora-A overexpression upregulated Akt activity and downregulated IkappaBα, these changes were accompanied by nuclear translocation of nuclear factor-κB and increased expression of its target gene Bcl-xL. Lastly, Aurora-A overexpression induced IkappaBα reduction was abrogated by suppression of Akt either chemically or genetically.

Conclusion

Taken together, our data established that Aurora-A, via activating Akt, stimulated nuclear factor-κB signaling pathway to promote cancer cell survival, and promised a novel combined chemotherapy targeting both Aurora-A and PI3K in cancer treatment.

Chemosensitization in non-small cell lung cancer cells by IKK inhibitor occurs via NF-kappaB and mitochondrial cytochrome c cascade

In this study, we demonstrated with mechanistic evidence that parthenolide, a sesquiterpene lactone, could antagonize paclitaxel-mediated NF-kappaB nuclear translocation and activation by selectively targeting I-kappaB kinase (IKK) activity. We also found that parthenolide could target IKK activity and then inhibit NF-kappaB; this promoted cytochrome c release and activation of caspases 3 and 9. Inhibition of caspase activity blocked the activation of caspase cascade, implying that the observed synergy was related to caspases 3 and 9 activation of parthenolide. In contrast, paclitaxel individually induced apoptosis via a pathway independent of the mitochondrial cytochrome c cascade. Finally, exposure to parthenolide resulted in the inhibition of several NF-kappaB transcript anti-apoptotic proteins such as c-IAP1 and Bcl-xl. These data strengthen the rationale for using parthenolide to decrease the apoptotic threshold via caspase-dependent processes for treatment of non-small cell lung cancer with paclitaxel chemoresistance.

Biscoclaurine alkaloid cepharanthine inhibits the growth of primary effusion lymphoma in vitro and in vivo and induces apoptosis via suppression of the NF-kappaB pathway

Primary effusion lymphoma (PEL) is a unique and recently identified non-Hodgkin's lymphoma that was originally identified in patients with AIDS. PEL is caused by the Kaposi sarcoma-associated herpes virus (KSHV/HHV-8) and shows a peculiar presentation involving liquid growth in the serous body cavity and a poor prognosis. As the nuclear factor (NF)-kappaB pathway is activated in PEL and plays a central role in oncogenesis, we examined the effect of a biscoclaurine alkaloid, cepharanthine (CEP) on PEL derived cell lines (BCBL-1, TY-1 and RM-P1), in vitro and in vivo. An methylthiotetrazole assay revealed that the cell proliferation of PEL cell lines was significantly suppressed by the addition of CEP (1-10 microg/ml). CEP also inhibited NF-kappaB activation and induced apoptotic cell death in PEL cell lines. We established a PEL animal model by intraperitoneal injection of BCBL-1, which led to the development of ascites and diffuse infiltration of organs, without obvious solid lymphoma formation, which resembles the diffuse nature of human PEL. Intraperitoneal administration of CEP inhibited ascites formation and diffuse infiltration of BCBL-1 without significant systemic toxicity in this model. These results indicate that NF-kappaB could be an ideal molecular target for treating PEL and that CEP is quite useful as a unique therapeutic agent for PEL.

Addressing reported pro-apoptotic functions of NF-kappaB: targeted inhibition of canonical NF-kappaB enhances the apoptotic effects of doxorubicin

The ability of the transcription factor NF-κB to upregulate anti-apoptotic proteins has been linked to the chemoresistance of solid tumors to standard chemotherapy. In contrast, recent studies have proposed that, in response to doxorubicin, NF-κB can be pro-apoptotic through repression of anti-apoptotic target genes. However, there is little evidence analyzing the outcome of NF-κB inhibition on the cytotoxicity of doxorubicin in studies describing pro-apoptotic NF-κB activity. In this study, we further characterize the activation of NF-κB in response to doxorubicin and evaluate its role in chemotherapy-induced cell death in sarcoma cells where NF-κB is reported to be pro-apoptotic. Doxorubicin treatment in U2OS cells induced canonical NF-κB activity as evidenced by increased nuclear accumulation of phosphorylated p65 at serine 536 and increased DNA–binding activity. Co-treatment with a small molecule IKKβ inhibitor, Compound A, abrogated this response. RT–PCR evaluation of anti-apoptotic gene expression revealed that doxorubicin-induced transcription of cIAP2 was inhibited by Compound A, while doxorubicin-induced repression of other anti-apoptotic genes was unaffected by Compound A or siRNA to p65. Furthermore, the combination of doxorubicin and canonical NF-κB inhibition with Compound A or siRNA to p65 resulted in decreased cell viability measured by trypan blue staining and MTS assay and increased apoptosis measured by cleaved poly (ADP-ribose) polymerase and cleaved caspase 3 when compared to doxorubicin alone. Our results demonstrate that doxorubicin-induced canonical NF-κB activity associated with phosphorylated p65 is anti-apoptotic in its function and that doxorubicin-induced repression of anti-apoptotic genes occurs independent of p65. Therefore, combination therapies incorporating NF-κB inhibitors together with standard chemotherapies remains a viable method to improve the clinical outcomes in patients with advanced stage malignancies.

MEKK3 expression correlates with nuclear factor kappa B activity and with expression of antiapoptotic genes in serous ovarian carcinoma

BACKGROUND

Constitutively activated nuclear factor kappa B (NFkappaB) contributes to the development of cancer by regulating the expression of genes involved in cell survival, metastasis, and angiogenesis. The authors have demonstrated that MEKK3 plays a critical role in cytokine-mediated NFkappaB activation, and that stable expression of MEKK3 in cultured cells leads to increased NFkappaB activity.

METHODS

MEKK3 expression in ovarian cancer cells or tumors was assessed by Western blotting and real-time polymerase chain reaction. NFkappaB activities were analyzed by electrophoretic mobility shift assay and luciferase reporter assays. Western blot analysis for the survival factors were also performed and correlated with MEKK3 and NFkappaB activities. Cell survival assays were used to determine the sensitivity of ovarian cancer cells to various chemotherapeutic agents.

RESULTS

The authors found that 63% of the ovarian cancers had higher MEKK3 expression than the normal ovarian epithelial cells. Ovarian cancers with high MEKK3 showed correspondingly high IkappaB kinase and NFkappaB activity. Moreover, MEKK3 coimmunoprecipitated with Akt and cooperated with Akt to synergistically activate NFkappaB. Consistent with increased MEKK3 and NFkappaB activity in ovarian cancers, Bcl-2, Bcl-xL, survivin, and X-linked inhibitor of apoptosis levels were increased, which correlated with increased resistance to chemotherapeutic agents. Knockdown of MEKK3 with small interfering RNA significantly increased cancer cell sensitivity to paclitaxel.

CONCLUSIONS

MEKK3 may be aberrantly expressed in ovarian cancers and plays an important role in tumors with constitutively activated NFkappaB.

PKR activity is required for acute leukemic cell maintenance and growth: a role for PKR-mediated phosphatase activity to regulate GSK-3 phosphorylation

Recent reports demonstrate that PKR is constitutively active in a variety of tumors and is required for tumor maintenance and growth. Here we report acute leukemia cell lines contain elevated levels of p-T451 PKR and PKR activity as compared to normal controls. Inhibition of PKR with a specific inhibitor, as well as overexpression of a dominant-negative PKR, inhibited cell proliferation and induced cell death. Interestingly, PKR inhibition using the specific inhibitor resulted in a time-dependent augmentation of AKT S473 and GSK-3alpha S21 phosphorylation, which was confirmed in patient samples. Increased phosphorylation of AKT and GSK-3alpha was not dependent on PI3K activity. PKR inhibition augmented levels of p-S473 AKT and p-S21/9 GSK-3alpha/beta in the presence of the PI3K inhibitor, LY294002, but was unable to augment GSK-3alpha or beta phosphorylation in the presence of the AKT inhibitor, A443654. Pre-treatment with the PKR inhibitor blocked the ability of A443654 and LY294002 to promote phosphorylation of eIF2alpha, indicating the mechanism leading to AKT phosphorylation and activation did not require eIF2alpha phosphorylation. The effects of PKR inhibition on AKT and GSK-3 phosphorylation were found to be, in part, PP2A-dependent. These data indicate that, in acute leukemia cell lines, constitutive basal activity of PKR is required for leukemic cell homeostasis and growth and functions as a negative regulator of AKT, thereby increasing the pool of potentially active GSK-3.

Loss of inhibitor of growth (ING-4) is implicated in the pathogenesis and progression of human astrocytomas

Inhibitor of growth 4 (ING-4) is a tumor suppressor gene that interacts with nuclear factor-kappaB (NF-kappaB) and represses its transcriptional activity. Several lines of evidence suggest that the tumor suppressor gene ING-4, the transcription factor NF-kappaB and its target genes matrix metalloproteases MMP-2, MMP-9 and urokinase plasminogen activator (u-PA) are critically involved in tumor invasion. The aim of the present study was to investigate immunohistochemically the expression pattern of ING-4, NF-kappaB and the NF-kappaB downstream targets MMP-2, MMP-9 and u-PA in human astrocytomas from 101 patients. We found that ING-4 expression was significantly decreased in astrocytomas, and ING-4 loss was associated with tumor grade progression. Expression of p65, a NF-kappaB subunit, was significantly higher in grade IV than in grade III and grade I/II tumors, and a statistical significant negative correlation between expression of ING-4 and expression of nuclear p65 was noticed. MMP-9, MMP-2 and u-PA were overexpressed in human astrocytomas. Of note, astrocytomas of advanced histologic grades (grade III, IV) displayed significantly higher expression levels of these proteins compared to tumors of lower grades (grade I, II). Collectively, our data suggest an essential role for ING-4 in human astrocytoma development and progression possibly through regulation of the NF-kappaB-dependent expression of genes involved in tumor invasion.

Constitutive non-canonical NFkappaB signaling in pancreatic cancer cells

Constitutive classical NFkappaB activation has been implicated in the development of pancreatic cancer, and inhibition of classical NFkappaB signaling sensitizes pancreatic cancer cells to apoptosis. However, the role of the more recently described non-canonical NFkappaB pathway has not been specifically addressed in pancreatic cancer. The non-canonical pathway requires stabilization of NIK and IKKalpha-dependent phosphorylation and processing of NFkappaB2/p100 to p52. This leads to the activation of p52-RelB heterodimers that regulate genes encoding lymphoid-specific chemokines and cytokines. We performed qRT-PCR to detect gene expression in a panel of pancreatic ductal adenocarcinoma cell lines (BxPC-3, PCA-2, PANC-1, Capan-1, Hs-766T, AsPC-1, MiaPACA-2) and found only modest elevation of classical NFkappaB-dependent genes. In contrast, each of the tumor cell lines displayed dramatically elevated levels of subsets of the non-canonical NFkappaB target genes CCL19, CCL21, CXCL12, CXCL13 and BAFF. Consistent with activation of the non-canonical pathway, p52 and RelB co-localized in adenocarcinoma cells in sections of pancreatic tumor tissue, and each of the tumor cell lines displayed elevated p52 levels. Furthermore, p52 and RelB co-immunoprecipitated from pancreatic cancer cells and immunoblotting revealed that NIK was stabilized and p100 was constitutively phosphorylated in a subset of the cell lines. Finally, stable overexpression of dominant negative IKKalpha significantly inhibited non-canonical target gene expression in BxPC-3 cells. These findings therefore demonstrate that the non-canonical NFkappaB pathway is constitutively active and functional in pancreatic cancer cells.

Increases in nuclear p65 activation in dystrophic skeletal muscle are secondary to increases in the cellular expression of p65 and are not solely produced by increases in IkappaB-alpha kinase activity

Dystrophin-deficient muscle exhibits substantial increases in nuclear NF-kappaB activation. To examine potential mechanisms for this enhanced activation, the present study employs conventional Western blot techniques to provide the first determination of the relative expression of NF-kappaB signaling molecules in adult nondystrophic and dystrophic (mdx) skeletal muscle. The results indicate that dystrophic muscle is characterized by increases in the whole cell expression of IkappaB-alpha, p65, p50, RelB, p100, p52, IKK, and TRAF-3. The proportion of phosphorylated IkappaB-alpha, p65, NIK, and IKKbeta, and the level of cytosolic IkappaB-alpha, were also increased in the mdx diaphragm. Proteasomal inhibition using MG-132 increased the proportion of phosphorylated IkappaB-alpha in nondystrophic diaphragm, but did not significantly increase this proportion in the mdx diaphragm. This result suggests that phosphorylated IkappaB-alpha accumulates in dystrophic cytosol because the rate of IkappaB-alpha degradation is lower than the effective rate of IkappaB-alpha synthesis and phosphorylation. Dystrophic increases in SUMO-1 (small ubiquitin modifier-1) protein and in Akt activation were also observed. The results indicate that increases in nuclear p65 activation in dystrophic muscle are not produced solely by increases in the activity of IkappaB-alpha kinase (IKK), but are due primarily to increases in the expression of p65 and other NF-kappaB signaling components.

Suppression of NF-kappaB activity by parthenolide induces X-ray sensitivity through inhibition of split-dose repair in TP53 null prostate cancer cells

We have shown that parthenolide, a sesquiterpene lactone, is a radiation sensitizer for human CGL1 hybrid cells that have constitutively activated NF-kappaB and wild-type p53. Since many malignant cells have nonfunctional p53, we investigated whether parthenolide could alter the X-ray sensitivity of PC-3 prostate cancer cells, a p53 null cell line with constitutively activated NF-kappaB. The addition of 5 microM parthenolide induced non-apoptotic cell death, inhibited PC-3 proliferation, and increased the population doubling time from 23+/-1 h to 49+/-4 h. Parthenolide also inhibited constitutive and radiation-induced NF-kappaB binding activity and enhanced the X-ray sensitivity of these p53 null PC-3 cells by a dose modification factor of 1.7. Cell cycle analysis of PC-3 cells treated with parthenolide showed only small alterations in G1 and G2/M cells, and these appeared to be insufficient to explain the observed radiosensitization. Split-dose studies using clinically relevant 2- and 4-Gy fractions demonstrated that parthenolide completely inhibited split-dose repair in PC-3 cells. We hypothesized that inhibition of NF-kappaB activity by parthenolide was responsible for the observed X-ray sensitization and inhibition of split-dose repair. To test this hypothesis, we knocked down the expression of NF-kappaB p65 protein, an active component of NF-kappaB in both PC-3 and CGL1 cells, by siRNA. Inhibition of NF-kappaB activity by knockdown of p65 increased radiation sensitivity and completely inhibited split-dose repair in both cell lines in a nearly identical manner as parthenolide treatment alone. Treating p65-depleted PC-3 cells with 5 microM parthenolide did not further increase their radiation sensitivity or the inhibition of split-dose repair. We propose that the suppression of radiation-induced NF-kappaB activity by parthenolide leads to X-ray sensitization through inhibition of split-dose repair in p53 null PC-3 prostate cancer cells.

Potential pharmacological control of the NF-κB pathway

Nuclear factor (NF)-kappaB governs the expression of numerous genes that are important for various cellular responses. Its activation is induced by a wide variety of stimuli including stress, cigarette smoke, viral and bacterial products, cytokines, free radicals, carcinogens and tumor promoters to name a few. Deregulation of the NF-kappaB pathway has been observed in and attributed to the development of a variety of human ailments including cancers, autoimmune disorders, pulmonary, cardiovascular, neurodegenerative and skin diseases. Efforts to develop modulators of NF-kappaB have yielded several candidates, some of which are currently in Phase I/II of clinical trials. In addition, it is now becoming apparent that several of the approved drugs being currently used also work, in part, owing to their ability to influence the NF-kappaB pathway. In this article, we focus on the druggable components of the NF-kappaB signaling system and on the recent development of novel therapeutics that target NF-kappaB in various diseases.

Roles of NF-kappaB in health and disease: mechanisms and therapeutic potential

The NF-kappaB (nuclear factor kappaB) family of transcription factors are involved in a myriad of activities, including the regulation of immune responses, maturation of immune cells, development of secondary lymphoid organs and osteoclastogenesis. Fine tuning by positive and negative regulators keeps the NF-kappaB signalling pathway in check. Microbial products and genetic alterations in NF-kappaB and other signalling pathway components can lead to deregulation of NF-kappaB signalling in several human diseases, including cancers and chronic inflammatory disorders. NF-kappaB-pathway-specific therapies are being actively investigated, and these hold promises as interventions of NF-kappaB-related ailments.

Comprehensive evaluation of a novel nuclear factor-kappaB inhibitor, quinoclamine, by transcriptomic analysis

BACKGROUND AND PURPOSE

The transcription factor nuclear factor-kappaB (NF-kappaB) has been linked to the cell growth, apoptosis and cell cycle progression. NF-kappaB blockade induces apoptosis of cancer cells. Therefore, NF-kappaB is suggested as a potential therapeutic target for cancer. Here, we have evaluated the anti-cancer potential of a novel NF-kappaB inhibitor, quinoclamine (2-amino-3-chloro-1,4-naphthoquinone).

EXPERIMENTAL APPROACH

In a large-scale screening test, we found that quinoclamine was a novel NF-kappaB inhibitor. The global transcriptional profiling of quinoclamine in HepG2 cells was therefore analysed by transcriptomic tools in this study.

KEY RESULTS

Quinoclamine suppressed endogenous NF-kappaB activity in HepG2 cells through the inhibition of IkappaB-alpha phosphorylation and p65 translocation. Quinoclamine also inhibited induced NF-kappaB activities in lung and breast cancer cell lines. Quinoclamine-regulated genes interacted with NF-kappaB or its downstream genes by network analysis. Quinoclamine affected the expression levels of genes involved in cell cycle or apoptosis, suggesting that quinoclamine exhibited anti-cancer potential. Furthermore, quinoclamine down-regulated the expressions of UDP glucuronosyltransferase genes involved in phase II drug metabolism, suggesting that quinoclamine might interfere with drug metabolism by slowing down the excretion of drugs.

CONCLUSION AND IMPLICATIONS

This study provides a comprehensive evaluation of quinoclamine by transcriptomic analysis. Our findings suggest that quinoclamine is a novel NF-kappaB inhibitor with anti-cancer potential.

NFkappaB signaling in carcinogenesis and as a potential molecular target for cancer therapy

It has become increasingly clear that deregulation of the NFkappaB signaling cascade is a common underlying feature of many human ailments including cancers. The past two decades of intensive research on NFkappaB has identified the basic mechanisms that govern the functioning of this pathway but uncovering the details of why this pathway works differently in different cellular contexts or how it interacts with other signaling pathways remains a challenge. A thorough understanding of these processes is needed to design better and more efficient therapeutic approaches to treat complex diseases like cancer. In this review, we summarize the literature documenting the involvement of NFkappaB in cancer, and then focus on the approaches that are being undertaken to develop NFkappaB inhibitors towards treatment of human cancers.

Phenanthrene-based tylophorine-1 (PBT-1) inhibits lung cancer cell growth through the Akt and NF-kappaB pathways

Tylophorine and related natural compounds exhibit potent antitumor activities. We previously showed that PBT-1, a synthetic C9-substituted phenanthrene-based tylophorine (PBT) derivative, significantly inhibits growth of various cancer cells. In this study, we further explored the mechanisms and potential of PBT-1 as an anticancer agent. PBT-1 dose-dependently suppressed colony formation and induced cell cycle G2/M arrest and apoptosis. DNA microarray and pathway analysis showed that PBT-1 activated the apoptosis pathway and mitogen-activated protein kinase signaling. In contrast, PBT-1 suppressed the nuclear factor kappaB (NF-kappaB) pathway and focal adhesion. We further confirmed that PBT-1 suppressed Akt activation accelerated RelA degradation via IkappaB kinase-alpha and down-regulated NF-kappaB target gene expression. The reciprocal recruitment of RelA and RelB on COX-2 promoter region led to down-regulation of transcriptional activity. We conclude that PBT-1 induces cell cycle G2/M arrest and apoptosis by inactivating Akt and by inhibiting the NF-kappaB signaling pathway. PBT-1 may be a good drug candidate for anticancer chemotherapy.

Natural and synthetic α,β-unsaturated carbonyls for NF-κB inhibition

BACKGROUND

The nuclear transcription factor NF-κB has gained considerable importance due to its major involvement in inflammation and constitutive activity in malignant cells. It is induced by a variety of stimuli and controls the expression of several proteins involved in biological processes. Numerous natural products and synthesized organic molecules have been reported to inhibit NF-κB and have played an integral role in identifying implicated pathways. Prominent among them are the sesquiterpene lactones, polyphenolic enones and other α,β-unsaturated carbonyl-containing molecules, particularly α-methylene-γ-butyrolactones.

DISCUSSION

This mini-review provides an introductory overview of some of the associated pathways involving NF-κB in cancer and discusses the structures and mode of action of natural α,β-unsaturated carbonyl-containing inhibitors and their synthetic counterparts. A review of the recent methods for the synthesis of α-alkylidene-γ-butyrolactones is also provided, with the aim of arousing the interest of synthetic chemists for the design and development of novel NF-κB inhibitors.

CONCLUSIONS

Modulating damaging effects without harming the inflammatory and immune responses are crucial parameters for developing NF-κB inhibitors. Examination of novel α,β-unsaturated carbonyls and the further discovery of simple methods to prepare such molecules should lead to the identification of site-specific inhibitors.

Arenamides A-C, cytotoxic NFkappaB inhibitors from the marine actinomycete Salinispora arenicola

Three new cyclohexadepsipeptides, arenamides A-C (1-3), were isolated from the fermentation broth of a marine bacterial strain identified as Salinispora arenicola. The planar structures of these compounds were assigned by detailed interpretation of NMR and MS/MS spectroscopic data. The absolute configurations of the amino acids, and those of the chiral centers on the side chain, were established by application of the Marfey and modified Mosher methods. The effect of arenamides A and B on NFkappaB activity was studied with stably transfected 293/NFkappaB-Luc human embryonic kidney cells induced by treatment with tumor necrosis factor (TNF). Arenamides A (1) and B (2) blocked TNF-induced activation in a dose- and time-dependent manner with IC(50) values of 3.7 and 1.7 microM, respectively. In addition, the compounds inhibited nitric oxide (NO) and prostaglandin E(2) (PGE(2)) production with lipopolysaccharide (LPS)-induced RAW 264.7 macrophages. Moderate cytotoxicity was observed with the human colon carcinoma cell line HCT-116, but no cytotoxic effect was noted with cultured RAW cells. Taken together, these data suggest that the chemoprevention and anti-inflammatory characteristics of arenamides A and B warrant further investigation.

Biologic sequelae of I{kappa}B kinase (IKK) inhibition in multiple myeloma: therapeutic implications

Nuclear factor-kappaB (NF-kappaB) has an important role in multiple myeloma (MM) cell pathogenesis in the context of the bone marrow (BM) microenvironment. In NF-kappaB signaling cascades, IkappaB kinase alpha (IKKalpha) and IKKbeta are key molecules that predominantly mediate noncanonical and canonical pathways, respectively. In this study, we examined the biologic sequelae of the inhibition of IKKalpha versus IKKbeta in MM cell lines. All MM cell lines have constitutive canonical NF-kappaB activity, and a subset of MM cell lines shows noncanonical NF-kappaB activity. Adhesion to BM stromal cells further activates both canonical and noncanonical NF-kappaB activity. IKKbeta inhibitor MLN120B blocks canonical pathway and growth of MM cell lines but does not inhibit the noncanonical NF-kappaB pathway. Although IKKalpha knockdown induces significant growth inhibition in the cell lines with both canonical and noncanonical pathways, it does not inhibit NF-kappaB activation. Importantly, IKKalpha down-regulation decreases expression of beta-catenin and aurora-A, which are known to mediate MM cell growth and survival. Finally, IKKbeta inhibitor enhances the growth inhibition triggered by IKKalpha down-regulation in MM cells with both canonical and noncanonical NF-kappaB activity. Combination therapy targeting these kinases therefore represents a promising treatment strategy in MM.

Suppression of N-Ras by shRNA-expressing plasmid increases sensitivity of HepG2 cells to vincristine-induced growth inhibition

Oncogenic ras genes relate to the development of human cancers. In this study, we used a plasmid-mediated short-hairpin RNA (shRNA) targeting N-ras gene to combine with clinical drug vincristine (VCR) for the treatment of human hepatoma cells. Our results showed that anti-N-Ras shRNA expression vector (pCSH1-shNR) knocked down the target mRNA and protein. Higher efficacy on growth inhibition was observed when pCSH1-shNR was combined with VCR. This synergistic effect was associated with abrogation of VCR-induced overexpressions of P-glycoprotein and multidrug resistance-associated protein 1 by pCSH1-shNR through downregulations of N-Ras and total Ras. Western blot analysis showed that pCSH1-shNR-induced downregulations of N-Ras and total Ras were potentiated by VCR. Following Ras downregulation, phosphorylations of ERK1/2 and Akt were dramatically inhibited by combinatory treatment. The data showed that pCSH1-shNR-induced inhibition of nuclear factor-kappaB was enhanced by VCR. In addition, the combination of pCSH1-shNR and VCR synergistically inhibited the growth of human hepatoma HepG2 in vivo. Our findings suggested that combination of gene-specific therapeutics and appropriate chemotherapeutic agents might be a promising approach for the treatment of human hepatocellular carcinoma.

The vital link between the ubiquitin-proteasome pathway and DNA repair: impact on cancer therapy

Proteasome-dependent protein degradation is involved in a variety of biological processes, including cell-cycle regulation, apoptosis, and stress-responses. Growing evidence from translational research and clinical trials proved the effectiveness of proteasome inhibitors (PIs) in treating several types of hematological malignancies. Although various key molecules in ubiquitin-dependent cellular processes have been proposed as relevant targets of therapeutic proteasome inhibition, our current understanding is far from complete. Recent rapid progress in DNA repair research has unveiled a crucial role of the ubiquitin-proteasome pathway (UPP) in regulating DNA repair. These findings thus bring up the idea that DNA repair pathways could be effective targets of PIs in mediating their cytotoxicity and enhancing the effect of radiotherapy and some DNA-damaging chemotherapeutic agents, such as cisplatin and camptothecin. In this review, we present the current perspective on the UPP-dependent regulatory mechanisms of DNA repair and discuss their therapeutic potential in the application of PIs to a broad spectrum of human cancers.

IkappaB kinase-alpha regulates endothelial cell motility and tumor angiogenesis

The transcription factor nuclear factor-kappaB (NF-kappaB) is constitutively activated in many types of cancers and has been implicated in gene expression important for angiogenesis, tumor growth, progression, and metastasis. Here, we show that the NF-kappaB activator, IkappaB kinase-alpha (IKKalpha), but not IKKbeta, promotes endothelial cell motility and tumor angiogenesis. IKKalpha is elevated in tumor vasculature compared with normal endothelium. Overexpression of IKKalpha in endothelial cells promoted cell motility and vascular tubule formation in a three-dimensional culture assay, and conversely, knockdown of IKKalpha in endothelial cells inhibited cell motility, compared with controls. Interestingly, blocking NF-kappaB activation totally abolished IKKalpha-induced angiogenic function. Furthermore, using a tumor and endothelial cell cotransplantation model, we show that overexpression of IKKalpha in endothelial cells significantly increased tumor vascular formation compared with controls, which contributed to increased tumor growth and tumor cell proliferation, and decreased tumor cell apoptosis. Collectively, these findings have identified a new function for IKKalpha through the canonical NF-kappaB pathway in tumor angiogenesis.

The NF-kappaB transcription factor pathway as a therapeutic target in cancer: methods for detection of NF-kappaB activity

NF-kappaB transcription factors marshal innate and adaptive immunity and inflammation. NF-kappaB also counters programmed cell death (PCD) induced by the proinflammatory cytokine tumor necrosis factor (TNF)alpha, and this activity of NF-kappaB is crucial for organismal physiology, chronic inflammation, and tumorigenesis. Indeed, whereas NF-kappaB contributes to many aspects of oncogenesis, it is now clear that its suppressive action on PCD is central to this process. Notably, recent studies indicate that NF-kappaB represents a crucial link in the well-established association between inflammation and carcinogenesis. In this link, NF-kappaB promotes synthesis of inflammatory mediators (e.g. TNFalpha) that stimulate growth of cancer cells, and upregulates genes that protect these cells against PCD induced by inflammatory signals. Elevated NF-kappaB activity also hampers tumor-cell killing inflicted by radiation and chemotherapeutic drugs, and in so doing, promotes resistance to anticancer therapy. Accordingly, NF-kappaB-targeting drugs are increasingly being used for treatment of human malignancies. Owing to the ubiquitous nature of the NF-kappaB pathway, however, these drugs have serious side effects, which limit their clinical use. Thus, a preferable approach would be to block, rather than NF-kappaB itself, its critical downstream targets that mediate discrete functions in cancer, such as prosurvival functions. Recent discoveries unraveling tissue specificity in the NF-kappaB-inducible mechanism(s) for control of PCD and identifying putative effectors of this control clearly validate this therapeutic approach. Given the emerging role of TNFkappa-induced signals of NF-kappaB activation in cancer and the potential of these signals for yielding new anticancer therapies, we focus herein on the methods most commonly used for analysis of the molecular steps leading from the triggering of TNF-Receptor (TNF-R)1 - the primary receptor of TNFalpha - to the induction of NF-kappaB. Specifically, we review the methods used for analysis of TNF-R1 trafficking, assembly of so-called TNF-R1 complex I, formation and activation of the IkappaB kinase (IKK) complex, phosphorylation and proteolysis of inhibitory IkappaB proteins, post-translational modifications and nuclear translocation of NF-kappaB dimers, induction of NF-kappaB transcriptional activity and binding to specific promoters, and upregulation of NF-kappaB target genes. The analysis of these events in cancerous cells may not only provide a better understanding of the basis for the role of NF-kappaB in carcinogenesis, but also potential new targets for selective anticancer therapy.

Tumor suppressor SMAR1 represses IkappaBalpha expression and inhibits p65 transactivation through matrix attachment regions

Aberrant NF-kappaB activity promotes tumorigenesis. However, NF-kappaB also inhibits tumor growth where tumor suppressor pathways remain unaltered. Thus, its role in tumorigenesis depends upon the function of other cellular factors. Tumor suppressor SMAR1 down-modulated in high grade breast cancers is regulated by p53 and is reported to interact and stabilize p53. Because both SMAR1 and NF-kappaB are involved in tumorigenesis, we investigated the effect of SMAR1 upon NF-kappaB activity. We show that SMAR1 induction by doxorubicin or overexpression produces functional NF-kappaB complexes that are competent for binding to NF-kappaB consensus sequence. However, SMAR1 induced p65-p50 complex is phosphorylation- and transactivation-deficient. Induction of functional NF-kappaB complexes stems from down-regulation of IkappaBalpha transcription through direct binding of SMAR1 to the matrix attachment region site present in IkappaBalpha promoter and recruitment of corepressor complex. Real time PCR array for NF-kappaB target genes revealed that SMAR1 down-regulates a subset of NF-kappaB target genes that are involved in tumorigenesis. We also show that SMAR1 inhibits tumor necrosis factor alpha-induced induction of NF-kappaB suggesting that activation of NF-kappaB by SMAR1 is independent and different from classical pathway. Thus, for the first time we report that a tumor suppressor protein SMAR1 can modulate NF-kappaB transactivation and inhibit tumorigenesis by regulating NF-kappaB target genes.

CAPERalpha is a novel Rel-TAD-interacting factor that inhibits lymphocyte transformation by the potent Rel/NF-kappaB oncoprotein v-Rel

The Rel/NF-kappaB transcription factors are constitutively activated in many human cancers. The Rel proteins in this family are implicated in leukemia/lymphomagenesis, but the mechanism is not completely understood. Previous studies showed that the transcription activation domains (TADs) of the viral oncoprotein v-Rel and its cellular Rel/NF-kappaB homologues c-Rel and RelA are key determinants of their different transforming activities in primary lymphocytes. Substitution of a Rel TAD for that of RelA conferred a strong transforming phenotype upon RelA, which otherwise failed to transform cells. To gain insights into protein interactions that influence cell transformation by the Rel TADs, we identified factors that interact with the TAD of v-Rel, the most oncogenic member of the Rel/NF-kappaB family. We report that the coactivator for transcription factors AP-1 and estrogen receptors, CAPERalpha, interacts with the v-Rel TAD and potently synergizes v-Rel-mediated transactivation. Importantly, coexpression of CAPERalpha markedly reduced and delayed v-Rel's transforming activity in primary lymphocytes, whereas a dominant-negative mutant enhanced the kinetics of v-Rel-mediated transformation. Furthermore, small interfering RNA-mediated knockdown of CAPERalpha in v-Rel-transformed lymphocytes significantly enhanced colony formation in soft agar. Since the potency of Rel-mediated transactivation is an important determinant of lymphocyte transformation, as is Rel's ability to induce transcriptional repression, these data suggest that CAPERalpha's interaction with the Rel TAD could modulate Rel/NF-kappaB's transforming activity by facilitating expression or dampening repression of specific gene subsets important for oncogenesis. Overall, this study identifies CAPERalpha as a new transcriptional coregulator for v-Rel and reveals an important role in modulating Rel's oncogenic activity.

Imatinib resistance in multidrug-resistant K562 human leukemic cells

The multidrug resistance phenotype (MDR) is one of the major causes of failure in cancer chemotherapy and it is associated with the over-expression of P-glycoprotein (P-gp or MDR1) in tumor cell membranes. A constitutive NF-kappaB activity has been observed in several haematological malignancies and this is associated with its anti-apoptotic role. In the present work, the relationship between NF-kappaB and MDR phenotype was evaluated in wild type K562 human leukemic cells (K562-WT) and in its vincristine-resistant counterpart, K562-Vinc cells. These data showed that K562-Vinc cells, which express an active P-gp, exhibited MDR phenotype. The resistant indexes (IC(50)(K562-Vinc)/IC(50)(K562-WT)) for structurally unrelated drugs like imatinib, doxorubicin and colchicine were 8.0+/-0.3, 2.8+/-0.4 and 44.8+/-8.8, respectively. The imatinib resistance was reversed by P-gp blockade suggesting the involvement of P-gp in imatinib transport. We observed that NF-kappaB was constitutively activated in both cell lines but in a lesser extent in K562-Vinc. The inhibition of NF-kappaB with BAY 11-7082 increased the cytotoxicity of imatinib in K562-Vinc cells but not in K562-WT. Further, the co-administration of imatinib and BAY 11-7082 sensitized multidrug-resistant K562 cells to cell death as detected by increased percentage of annexin V positive cells. The induced cell death in K562-Vinc cells was associated with activation of caspases 9 and 3. Finally, we provide data showing that BAY 11-7082 down-regulates the expression of P-gp suggesting that the activity of NF-kappaB could be functionally associated to this protein in K562 cells. Our results indicate that the vincristine-resistant K562 cells which developed MDR phenotype, exhibited resistance to imatinib associated with a functional P-gp over-expression. This resistance could be partially overcome by the inhibition of NF-kappaB pathway.

Enhancement of apoptotic damage of squamous cell carcinoma cells by inhibition of the mitochondrial DNA repairing system

Mitochondrial DNA (mtDNA) repair systems are thought to be associated with the susceptibility of cancer cells to anticancer agents. The present study investigated the relationship between the susceptibility to gamma-rays and the mtDNA repair ability of oral squamous cell carcinoma (OSC) cell lines. The levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG) and mtDNA common deletion in both nuclear and mitochondrial DNA of OSC-2, OSC-3 and OSC-6 cells (radio-sensitive cell lines) after gamma-ray-irradiation were higher than those of OSC-1, OSC-4 and OSC-5 cells (radio-resistant cell lines). Compared with OSC-2, OSC-3 and OSC-6 cells, OSC-1, OSC-4 and OSC-5 cells had higher levels of activity of phosphoinositide-3 kinase (PI-3K)/Akt and more strongly expressed 8-hydroxyguanine DNA glycosylase (OGG1), DNA polymerase gamma (POLG) and mitochondrial transcription factor A (Tfam). Down-regulation of these mtDNA-repair-associated molecules by the RNA interference technique enhanced the susceptibility of OSC-2 and OSC-5 cells to gamma-rays, and the expression of Tfam and POLG was down-regulated by inhibitors of PI-3K/Akt signaling. These results indicate that the inhibition of mtDNA repair capacity by PI-3K/Akt signal inhibitors and OGG1 down-regulator in cancer cells may be a useful strategy for cancer treatment when combined with ionizing irradiation and chemotherapeutic drugs.

Regulation of the RelA (p65) transactivation domain

The RelA (p65) NF-kappaB (nuclear factor kappaB) subunit contains an extremely active C-terminal transcriptional activation domain, required for its cellular function. In the present article, we review our knowledge of this domain, its modifications and its known interacting proteins. Moreover, we discuss how analysis of its evolutionary conservation reveals distinct subdomains and conserved residues that might give insights into its regulation and function.

Origin and pathogenesis of nodular lymphocyte-predominant Hodgkin lymphoma as revealed by global gene expression analysis

The pathogenesis of nodular lymphocyte–predominant Hodgkin lymphoma (NLPHL) and its relationship to other lymphomas are largely unknown. This is partly because of the technical challenge of analyzing its rare neoplastic lymphocytic and histiocytic (L&H) cells, which are dispersed in an abundant nonneoplastic cellular microenvironment. We performed a genome-wide expression study of microdissected L&H lymphoma cells in comparison to normal and other malignant B cells that indicated a relationship of L&H cells to and/or that they originate from germinal center B cells at the transition to memory B cells. L&H cells show a surprisingly high similarity to the tumor cells of T cell–rich B cell lymphoma and classical Hodgkin lymphoma, a partial loss of their B cell phenotype, and deregulation of many apoptosis regulators and putative oncogenes. Importantly, L&H cells are characterized by constitutive nuclear factor κB activity and aberrant extracellular signal-regulated kinase signaling. Thus, these findings shed new light on the nature of L&H cells, reveal several novel pathogenetic mechanisms in NLPHL, and may help in differential diagnosis and lead to novel therapeutic strategies.

Relation between menin expression and NF-kappaB activity in an intestinal cell line

In a previous study, we demonstrated that the Men1 gene is mainly expressed in the proliferative crypt compartment of the small intestine and that a reduction of menin expression in the crypt-like IEC-17 cell line induces an increase in proliferation rate concomitant with an increase in cyclin D1 expression. The aim of the present study was to test the hypothesis that the NF-kappaB pathway may be involved in cyclin D1 overexpression. Transcriptional activity of the cyclin D1 gene promoter was increased upon reduction of menin expression. Blockade of the NF-kappaB pathway restored proliferation, cell cycle, cyclin D1 gene transcription and cyclin D1 expression levels to those observed in the presence of menin. These data support a correlation between cyclin D1 expression, NF-kappaB activity and menin expression in this epithelial cell line and are relevant to the physiological function of menin in regulating proliferation in the intestinal epithelium.

17-Acetoxyjolkinolide B irreversibly inhibits IkappaB kinase and induces apoptosis of tumor cells

Nuclear factor-kappaB (NF-kappaB) is critically important for tumor cell survival, growth, angiogenesis, and metastasis. One of the key events in the NF-kappaB signaling is the activation of inhibitor of NF-kappaB kinase (IKK) in response to stimuli of various cytokines. We have identified 17-acetoxyjolkinolide B (17-AJB) from a traditional Chinese medicinal herb Euphorbia fischeriana Steud as a novel small-molecule inhibitor of IKK. 17-AJB effectively inhibited tumor necrosis factor-alpha-induced NF-kappaB activation and induced apoptosis of tumor cells. 17-AJB had no effect on binding of tumor necrosis factor-alpha to its receptor or on binding of NF-kappaB to DNA. It inhibited NF-kappaB nuclear translocation. Detailed analysis revealed that the direct target of 17-AJB was IKK. 17-AJB kept IKK in its phosphorylated form irreversibly. This irreversible modification of IKK inactivated its kinase activity, leading to its failure to activate NF-kappaB. The effect of 17-AJB on IKK was specific. It had no effect on other kinases such as p38, p44/42, and JNK. In addition, 17-AJB induced apoptosis in tumor cells. The effects of 17-AJB on apoptosis correlated with inhibition of expression of the NF-kappaB-regulated genes. Taken together, our data suggest that 17-AJB is a novel type NF-kappaB pathway inhibitor. Its unique interaction mechanism with IKK may render it a strong apoptosis inducer of tumor cells and a novel type anticancer drug candidate.

Human cytomegalovirus modulation of signal transduction

An upregulation of cellular signaling pathways is observed in multiple cell types upon human cytomegalovirus (HCMV) infection, suggesting that a global feature of HCMV infection is the activation of the host cell. HCMV initiates and maintains cellular signaling through a multitiered process that is dependent on a series of events: (1) the viral glycoprotein ligand interacts with its cognate receptor, (2) cellular enzymes and viral tegument proteins present in the incoming virion are released and (3) a variety of viral gene products are expressed. Viral-mediated cellular modification has differential outcomes depending on the cell type infected. In permissive cell types, such as diploid fibroblasts, the upregulation of cellular signaling pathways following infection can initiate the viral gene cascade and promote the efficient transcription of multiple viral gene classes. In other cell types, such as endothelial cells and monocytes/macrophages, the upregulation of cellular pathways initiates functional host changes that allow viral spread to multiple organ systems. Together, the modification of signaling processes appears to be part of a thematic strategy deployed by the virus to direct the required functional changes in target cells that ultimately promote viral survival and persistence in the host.

Differential involvement of IkappaB kinases alpha and beta in cytokine- and insulin-induced mammalian target of rapamycin activation determined by Akt

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 such as insulin, cytokines such as TNF, and Akt-dependent signaling associated with oncoprotein expression. mTOR is negatively controlled by the tuberous sclerosis complex 1/2 (TSC1/2), and activation of Akt induces phosphorylation of TSC2, which blocks the repressive TSC1/2 activity. Previously, we showed that activation of mTOR in PTEN-deficient cancer cells involves IkappaB kinase (IKK) alpha, a catalytic subunit of the IKK complex that controls NF-kappaB activation. Recently, a distinct IKK subunit, IKKbeta, was shown to phosphorylate TSC1 to promote mTOR activation in an Akt-independent manner in certain cells stimulated with TNF and in some cancer cells. In this study, we have explored the involvement of both IKKalpha and IKKbeta in insulin- and TNF-induced mTOR activation. Insulin activation of mTOR requires Akt in a manner that involves IKKalpha, preferentially to IKKbeta, and TSC2 phosphorylation. TNF, in most cells examined, activates Akt to use IKKalpha to control mTOR activation. In MCF7 cells, TNF does not activate Akt and requires IKKbeta to activate mTOR. The results show that Akt-dependent signaling, induced by cytokines or insulin, alters the IKK subunit-dependent control of mTOR.

Active roles for inhibitory kappaB kinases alpha and beta in nuclear factor-kappaB-mediated chemoresistance to doxorubicin

Chemotherapy agents have been shown to induce the transcription factor nuclear factor-kappaB (NF-kappaB) and subsequent chemoresistance in fibrosarcomas and other cancers. The mechanism of NF-kappaB-mediated chemoresistance remains unclear, with a previous report suggesting that doxorubicin induces this response independent of the inhibitory kappaB kinases (IKK). Other studies have indicated that IKKbeta, but not IKKalpha, is required. Mouse embryo fibroblasts devoid of IKKalpha, IKKbeta, or both subunits (double knockout) were treated with doxorubicin. The absence of either IKKalpha or IKKbeta or both kinases resulted in impaired induction of NF-kappaB DNA-binding activity in response to doxorubicin. To provide a valid clinical correlate, HT1080 human fibrosarcoma cells were transfected with small interference RNA specific for IKKalpha or IKKbeta and then subsequently treated with doxorubicin. Knockdown of IKKalpha severely impaired the ability of doxorubicin to initiate NF-kappaB DNA-binding activity. However, a decrease in either IKKalpha or IKKbeta resulted in decreased phosphorylation of p65 in response to doxorubicin. The inhibition of doxorubicin-induced NF-kappaB activation by the knockdown of either catalytic subunit resulted in increased cleaved caspase-3 and cleaved poly(ADP-ribose) polymerase and increased apoptosis when compared with doxorubicin alone. The results of this study validate current approaches aimed at NF-kappaB inhibition to improve clinical therapies. Moreover, we show that IKKalpha plays a critical role in NF-kappaB-mediated chemoresistance in response to doxorubicin and may serve as a potential target in combinational strategies to improve chemotherapeutic response.

Prevalence of bortezomib-resistant constitutive NF-kappaB activity in mantle cell lymphoma

BACKGROUND

The proteasome inhibitor bortezomib can inhibit activation of the transcription factor NF-kappaB, a mechanism implicated in its anti-neoplastic effects observed in mantle cell lymphoma (MCL). However, NF-kappaB can be activated through many distinct mechanisms, including proteasome independent pathways. While MCL cells have been shown to harbor constitutive NF-kappaB activity, what fraction of this activity in primary MCL samples is sensitive or resistant to inhibition by bortezomib remains unclear.

RESULTS

Proteasome activity in the EBV-negative MCL cell lines Jeko-1 and Rec-1 is inhibited by greater than 80% after exposure to 20 nM bortezomib for 4 hours. This treatment decreased NF-kappaB activity in Jeko-1 cells, but failed to do so in Rec-1 cells when assessed by electrophoretic mobility shift assay (EMSA). Concurrently, Rec-1 cells were more resistant to the cytotoxic effects of bortezomib than Jeko-1 cells. Consistent with a proteasome inhibitor resistant pathway of activation described in mouse B-lymphoma cells (WEHI231) and a breast carcinoma cell line (MDA-MB-468), the bortezomib-resistant NF-kappaB activity in Rec-1 cells is inhibited by calcium chelators, calmodulin inhibitors, and perillyl alcohol, a monoterpene capable of blocking L-type calcium channels. Importantly, the combination of perillyl alcohol and bortezomib is synergistic in eliciting Rec-1 cell cytotoxicity. The relevance of these results is illuminated by the additional finding that a considerable fraction of primary MCL samples (8 out of 10) displayed bortezomib-resistant constitutive NF-kappaB activity.

CONCLUSION

Our findings show that bortezomib-resistant NF-kappaB activity is frequently observed in MCL samples and suggest that this activity may be relevant to MCL biology as well as serve as a potential therapeutic target.

Regulation of programmed cell death by NF-kappaB and its role in tumorigenesis and therapy

The Rel/NF-kappaB transcription factors are key regulators of programmed cell death (PCD). Their activity has significant physiological relevance for normal development and homeostasis in various tissues and important pathological consequences are associated with aberrant NF-kappaB activity, including hepatocyte apoptosis, neurodegeneration, and cancer. While NF-kappaB is best characterized for its protective activity in response to proapoptotic stimuli, its role in suppressing programmed necrosis has come to light more recently. NF-kappaB most commonly antagonizes PCD by activating the expression of antiapoptotic proteins and antioxidant molecules, but it can also promote PCD under certain conditions and in certain cell types. It is therefore important to understand the pathways that control NF-kappaB activation in different settings and the mechanisms that regulate its anti- vs pro-death activities. Here, we review the role of NF-kappaB in apoptotic and necrotic PCD, the mechanisms involved, and how its activity in the cell death response impacts cancer development, progression, and therapy. Given the role that NF-kappaB plays both in tumor cells and in the tumor microenvironment, recent findings underscore the NF-kappaB signaling pathway as a promising target for cancer prevention and treatment.

Systems biology-defined NF-kappaB regulons, interacting signal pathways and networks are implicated in the malignant phenotype of head and neck cancer cell lines differing in p53 status

BACKGROUND

Aberrant activation of the nuclear factor kappaB (NF-kappaB) pathway has been previously implicated as a crucial signal promoting tumorigenesis. However, how NF-kappaB acts as a key regulatory node to modulate global gene expression, and contributes to the malignant heterogeneity of head and neck cancer, is not well understood.

RESULTS

To address this question, we used a newly developed computational strategy, COGRIM (Clustering Of Gene Regulons using Integrated Modeling), to identify NF-kappaB regulons (a set of genes under regulation of the same transcription factor) for 1,265 genes differentially expressed by head and neck cancer cell lines differing in p53 status. There were 748 NF-kappaB targets predicted and individually annotated for RELA, NFkappaB1 or cREL regulation, and a prevalence of RELA related genes was observed in over-expressed clusters in a tumor subset. Using Ingenuity Pathway Analysis, the NF-kappaB targets were reverse-engineered into annotated signature networks and pathways, revealing relationships broadly altered in cancer lines (activated proinflammatory and down-regulated Wnt/beta-catenin and transforming growth factor-beta pathways), or specifically defective in cancer subsets (growth factors, cytokines, integrins, receptors and intermediate kinases). Representatives of predicted NF-kappaB target genes were experimentally validated through modulation by tumor necrosis factor-alpha or small interfering RNA for RELA or NFkappaB1.

CONCLUSION

NF-kappaB globally regulates diverse gene programs that are organized in signal networks and pathways differing in cancer subsets with distinct p53 status. The concerted alterations in gene expression patterns reflect cross-talk among NF-kappaB and other pathways, which may provide a basis for molecular classifications and targeted therapeutics for heterogeneous subsets of head and neck or other cancers.

IkappaB kinase beta (IKKbeta/IKK2/IKBKB)--a key molecule in signaling to the transcription factor NF-kappaB

IKKbeta/IKBKB (IkappaB kinase beta), also designated as IKK2, was named after its function of phosphorylating IkappaB molecules, the inhibitors of NF-kappaB transcription factors. The kinase activity of IKKbeta targets two adjacent serine residues of IkappaB leading to ubiquitination and proteasomal degradation of the inhibitor, followed by release and activation of NF-kappaB. Many signaling pathways that activate NF-kappaB converge at the level of IKKbeta. Examples of stimuli leading to IKKbeta and subsequent NF-kappaB activation include inflammatory cytokines (IL-1, TNFalpha), endotoxins (lipopolysaccharide), viral infection and double strand RNA as well as physical signals such as UV-irradiation. Transcription factors of the NF-kappaB protein family have a great variety of functions in regulating the immune system, cellular differentiation, survival and proliferation. NF-kappaB is an essential factor in acute as well as chronic inflammation, a pathological state which is either cause or co-factor in a great variety of diseases. Moreover, recent data suggest that many variants of cancer are characterized by elevated constitutive activity of NF-kappaB, which can act as a survival factor for malignant cells by its predominantly anti-apoptotic function. Given the tight regulation of NF-kappaB by IkappaB molecules and the central role of IKKbeta in phosphorylation and degradation of the inhibitor, IKKbeta is a very promising target for pharmaceutical substances aiming at interfering with NF-kappaB activation.

Parthenolide sensitizes cells to X-ray-induced cell killing through inhibition of NF-kappaB and split-dose repair

Human cancers have multiple alterations in cell signaling pathways that promote resistance to cytotoxic therapy such as X rays. Parthenolide is a sesquiterpene lactone that has been shown to inhibit several pro-survival cell signaling pathways, induce apoptosis, and enhance chemotherapy-induced cell killing. We investigated whether parthenolide would enhance X-ray-induced cell killing in radiation resistant, NF-kappaB-activated CGL1 cells. Treatment with 5 microM parthenolide for 48 to 72 h inhibited constitutive NF-kappaB binding and cell growth, reduced plating efficiency, and induced apoptosis through stabilization of p53 (TP53), induction of the pro-apoptosis protein BAX, and phosphorylation of BID. Parthenolide also enhanced radiation-induced cell killing, increasing the X-ray sensitivity of CGL1 cells by a dose modification factor of 1.6. Flow cytometry revealed that parthenolide reduced the percentage of X-ray-resistant S-phase cells due to induction of p21 waf1/cip1 (CDKN1A) and the onset of G1/S and G2/M blocks, but depletion of radioresistant S-phase cells does not explain the observed X-ray sensitization. Further studies demonstrated that the enhancement of X-ray-induced cell killing by parthenolide is due to inhibition of split-dose repair.

Prolonged exposure to IL-1beta and IFNgamma induces necrosis of L929 tumor cells via a p38MAPK/NF-kappaB/NO-dependent mechanism

Interleukin-1beta (IL-1beta) is a cytokine that shares with tumor necrosis factor (TNF) the ability to initiate largely similar signaling pathways, leading to proinflammatory gene expression. In contrast to TNF, however, IL-1beta is not believed to induce tumor cell death. Here we demonstrate that prolonged treatment with IL-1beta, in combination with interferon-gamma (IFNgamma), is cytotoxic for L929 tumor cells. IL-1beta/IFNgamma-induced cytotoxicity requires only minimal amounts of IL-1beta and shows morphological features of necrosis. Although TNF induces a similar response, we could exclude a contribution of endogenous TNF production in the effect of IL-1beta/IFNgamma. Cell death in response to IL-1beta/IFNgamma is independent of caspases, but requires the IL-1beta/IFNgamma-induced production of inducible nitric oxide synthase (iNOS) and NO. Moreover, necrosis and iNOS/NO production could be prevented by treatment of the cells with a p38 mitogen activated protein kinase (p38MAPK) or IkappaB kinase beta inhibitor. Altogether, these findings demonstrate that prolonged exposure to IL-1beta plus IFNgamma induces L929 tumor cell necrosis, via a p38MAPK and nuclear factor-kappaB (NF-kappaB)-dependent signaling pathway, leading to the expression of iNOS and the production of toxic NO levels.