Inhibition of RelA phosphorylation sensitizes apoptosis in constitutive NF-kappaB-expressing and chemoresistant cells

Actin-binding protein alpha-actinin 4 (ACTN4) is a transcriptional co-activator of RelA/p65 sub-unit of NF-kB

ACTN4 is an actin-binding protein that participates in cytoskeleton organisation. It resides both in the cytoplasm and nucleus and physically associates with various transcription factors. Here, we describe an effect of ACTN4 expression on transcriptional activity of the RelA/p65 subunit of NF-kB. We demonstrate that ACTN4 enhances RelA/p65-dependant expression of c-fos, MMP-3 and MMP-1 genes, but it does not affect TNC, ICAM1 and FN1 expression. Importantly, actin-binding domains of ACTN4 are not critical for the nuclear translocation and co-activation of RelA/p65-dependent transcription. Collectively, our data suggest that in the nucleus, ACTN4 functions as a selective transcriptional co-activator of RelA/p65.

Protein kinase CK2 enhances Mcl-1 gene expression through the serum response factor-mediated pathway in the rat hippocampus

The protein kinase CK2 (casein kinase 2) is a ubiquitous serine/threonine protein kinase that suppresses apoptosis. CK2 is composed of catalytic and regulatory subunits, and CK2-dependent phosphorylation is a global mechanism in the inhibition of caspase signaling pathways. The serum response factor (SRF) is an important regulator of cell growth and differentiation. Although CK2 has been shown to phosphorylate SRF in vitro, the biological relevance of this interaction remains largely unclear. We observed increased SRF phosphorylation and increased Mcl-1 gene expression in hippocampal CA1 neurons following transfection with a plasmid expressing the wild-type CK2α (CK2αWT) protein, whereas transfection with a plasmid expressing a catalytically inactive mutant of CK2α (CK2α156A) reduced Mcl-1 gene expression. Cotransfection with a plasmid expressing the inactive SRF99A mutant inhibited the CK2αWT-induced upregulation of Mcl-1 gene expression. The expression of either the CK2α156A or the SRF99A mutant also inhibited the glutamate-induced upregulation of Mcl-1 protein expression in PC12 cells. Our results suggest that CK2-mediated signaling represents a cellular mechanism that may aid in the development of alternative therapeutic strategies to attenuate apoptosis in hippocampal neurons.

Beta-D-glucoside protects against advanced glycation end products (AGEs)-mediated diabetic responses by suppressing ERK and inducing PPAR gamma DNA binding

Accumulation of advanced glycation end products (AGEs), due to excessive amounts of 3- or 4-carbon sugars derived from glucose; cause multiple consequences in diabetic patients and older persons. The transcription factor, peroxisome proliferator-activated receptor gamma (PPARγ), is down regulated in the diabetic condition. Drugs targeting PPARγ were developed for diabetes therapy. We found that AGE inhibited PPARγ activity in different cell types induced by PPARγ activators, like troglitazone, rosiglitazone, oleamide, and anandamide. AGE induced translocation of PPARγ from nucleus to cytoplasm, increased on activation of ERK in cells. Antioxidants that inhibit AGE-induced NF-κB activation by preventing ROI generation were unable to protect AGE-mediated decrease in PPARγ activity. Only mangiferin, a β-D-glucoside, prevented AGE-mediated decrease in PPARγ activity and inhibited phosphorylation of ERK and cytoplasmic translocation of PPARγ. Mangiferin interacts with PPARγ and enhanced its DNA binding activity as predicted by in silico and shown by in vitro DNA-binding activity. Overall, the data suggest that (i) mangiferin inhibited AGE-induced ERK activation thereby inhibited PPARγ phosphorylation and cytoplasmic translocation; (ii) mangiferin interacts with PPARγ and enhances its DNA-binding ability. With these dual effects, mangiferin can be a likely candidate for developing therapeutic drug against diabetes.

Preclinical pharmacology of AZD5363, an inhibitor of AKT: pharmacodynamics, antitumor activity, and correlation of monotherapy activity with genetic background

AKT is a key node in the most frequently deregulated signaling network in human cancer. AZD5363, a novel pyrrolopyrimidine-derived compound, inhibited all AKT isoforms with a potency of 10 nmol/L or less and inhibited phosphorylation of AKT substrates in cells with a potency of approximately 0.3 to 0.8 μmol/L. AZD5363 monotherapy inhibited the proliferation of 41 of 182 solid and hematologic tumor cell lines with a potency of 3 μmol/L or less. Cell lines derived from breast cancers showed the highest frequency of sensitivity. There was a significant relationship between the presence of PIK3CA and/or PTEN mutations and sensitivity to AZD5363 and between RAS mutations and resistance. Oral dosing of AZD5363 to nude mice caused dose- and time-dependent reduction of PRAS40, GSK3β, and S6 phosphorylation in BT474c xenografts (PRAS40 phosphorylation EC(50) ~ 0.1 μmol/L total plasma exposure), reversible increases in blood glucose concentrations, and dose-dependent decreases in 2[18F]fluoro-2-deoxy-D-glucose ((18)F-FDG) uptake in U87-MG xenografts. Chronic oral dosing of AZD5363 caused dose-dependent growth inhibition of xenografts derived from various tumor types, including HER2(+) breast cancer models that are resistant to trastuzumab. AZD5363 also significantly enhanced the antitumor activity of docetaxel, lapatinib, and trastuzumab in breast cancer xenografts. It is concluded that AZD5363 is a potent inhibitor of AKT with pharmacodynamic activity in vivo, has potential to treat a range of solid and hematologic tumors as monotherapy or a combinatorial agent, and has potential for personalized medicine based on the genetic status of PIK3CA, PTEN, and RAS. AZD5363 is currently in phase I clinical trials.

The diverse and complex roles of NF-κB subunits in cancer

It is only recently that the full importance of nuclear factor-κB (NF-κB) signalling to cancer development has been understood. Although much attention has focused on the upstream pathways leading to NF-κB activation, it is now becoming clear that the inhibitor of NF-κB kinases (IKKs), which regulate NF-κB activation, have many independent functions in tissue homeostasis and normal immune function that could compromise the clinical utility of IKK inhibitors. Therefore, if the NF-κB pathway is to be properly exploited as a target for both anticancer and anti-inflammatory drugs, it is appropriate to reconsider the complex roles of the individual NF-κB subunits.

Advanced glycation end products (AGEs) induce apoptosis via a novel pathway: involvement of Ca2+ mediated by interleukin-8 protein

Advanced glycation end products (AGEs) accumulate in diabetic patients due to high blood glucose levels and cause multiple deleterious effects. In this study, we provide evidence that the AGE increased cell death, one such deleterious effect. Methyl glyoxal-coupled human serum albumin (AGE-HSA) induced transcription factors such as NF-κB, NF-AT, and AP-1. AGE acts through its cell surface receptor, RAGE, and degranulates vesicular contents including interleukin-8 (IL-8). The number of RAGEs, as well as the amount of NF-κB activation, is low, but the cell death is higher in neuronal cells upon AGE treatment. Degranulated IL-8 acts through its receptors, IL-8Rs, and induces sequential events in cells: increase in intracellular Ca(2+), activation of calcineurin, dephosphorylation of cytoplasmic NF-AT, nuclear translocation of NF-AT, and expression of FasL. Expressed FasL increases activity of caspases and induces cell death. Although AGE increases the amount of reactive oxygen intermediate, accompanying cell death is not dependent upon reactive oxygen intermediate. AGE induces autophagy, which partially protects cells from cell death. A novel mechanism of AGE-mediated cell death in different cell types, especially in neuronal cells where it is an early event, is provided here. Thus, this study may be important in several age-related neuronal diseases where AGE-induced apoptosis is observed because of high amounts of AGE.

Cyclooxygenase 2-dependent and independent activation of Akt through casein kinase 2α contributes to human bladder cancer cell survival

Background

Survival rate for patients presenting muscle invasive bladder cancer is very low, and useful therapeutic target has not been identified yet. In the present study, new COX2 downstream signals involved in urothelial carcinoma cell survival were investigated in vitro and in vivo.

Methods

COX2 gene was silenced by siRNA transfection. Orthotopic implantation animal model and transurethral instillation of siRNA with atelocollagen was constructed to examine the effects of COX2 knockdown in vivo. Cell cycle was examined by flowcytoketry. Surgical specimens derived from patients with urinary bladder cancer (all were initially diagnosed cases) were used for immunohistochemical analysis of the indicated protein expression in urothelial carcinoma cells.

Results

Treatment with the COX2 inhibitor or knockdown of COX2 reduced expression of casein kinase (CK) 2 α, a phophorylated Akt and urokinase type plasminogen activator (uPA), resulting in p27 induction, cell cycle arrest at G1 phase and cell growth suppression in human urothelial carcinoma cell lines expressing COX2. Silencing of CK2α exhibited the similar effects. Even in UMUC3 cells lacking the COX2 gene, COX2 inhibition also inhibited cell growth through down-regulation of the CK2α-Akt/uPA axis. The mouse orthotropic bladder cancer model demonstrated that the COX2 inhibitor, meloxicam significantly reduced CK2α, phosphorylated Akt and uPA expression, whereas induced p27 by which growth and invasiveness of bladder cancer cells were strongly inhibited. Immunohistochemically, high expression of COX2, CK2α and phosphorylated form of Akt was found in high-grade, invasive carcinomas as well as carcinoma in situ, but not in low-grade and noninvasive phenotypes.

Conclusions

COX2-dependent and independent activation of CK2α-Akt/uPA signal is mainly involved in urothelial carcinoma cell survival, moreover, not only COX2 but also CK2α could be direct targets of COX2 inhibitors.

Brain-derived neurotrophic factor enhances Bcl-xL expression through protein kinase casein kinase 2-activated and nuclear factor kappa B-mediated pathway in rat hippocampus

Brain-derived neurotrophic factor (BDNF) was shown to produce its neuroprotective effect through extracellular signal-regulated kinase 1/2 (ERK1/2) and phosphatidylinositol-3 kinase (PI3-K) signaling. But whether other pathways also mediate the neuroprotective effect of BDNF is less known. In this study, we found that direct administration of BDNF to rat hippocampal CA1 area dose-dependently increased the mRNA and protein levels of Bcl-xL. BDNF also increased protein kinase casein kinase II (CK2) activity and NF-κB phosphorylation at Ser529 dose-dependently. Further, transfection of the wild-type CK2α DNA to CA1 neurons increased nuclear factor kappa B (NF-κB) phosphorylation and Bcl-xL mRNA expression, whereas transfection of CK2α156A, the catalytically inactive mutant of CK2α, decreased these measures. Moreover, transfection of CK2α small interfering RNA (siRNA) blocked the enhancing effect of BDNF on NF-κB phosphorylation and Bcl-xL expression. These results were further confirmed by treatment of 4,5,6,7-tetrabromobenzotriazole (TBB), a specific CK2 inhibitor. Transfection of NF-κBS529A, the dominant negative mutant of NF-κB, prevented the enhancing effect of BDNF on Bcl-xL expression. More importantly, BDNF activation of CK2 is not affected by co-administration of the ERK1/2 inhibitor, PD98059, and the PI3-K inhibitor, LY294002. These results demonstrate a novel BDNF signaling pathway and provide an alternative therapeutic strategy for the protective effect of BDNF on hippocampal neurons in vivo.

Azadirachtin interacts with retinoic acid receptors and inhibits retinoic acid-mediated biological responses

Considering the role of retinoids in regulation of more than 500 genes involved in cell cycle and growth arrest, a detailed understanding of the mechanism and its regulation is useful for therapy. The extract of the medicinal plant Neem (Azadirachta indica) is used against several ailments especially for anti-inflammatory, anti-itching, spermicidal, anticancer, and insecticidal activities. In this report we prove the detailed mechanism on the regulation of retinoic acid-mediated cell signaling by azadirachtin, active components of neem extract. Azadirachtin repressed all trans-retinoic acid (ATRA)-mediated nuclear transcription factor κB (NF-κB) activation, not the DNA binding but the NF-κB-dependent gene expression. It did not inhibit IκBα degradation, IκBα kinase activity, or p65 phosphorylation and its nuclear translocation but inhibited NF-κB-dependent reporter gene expression. Azadirachtin inhibited TRAF6-mediated, but not TRAF2-mediated NF-κB activation. It inhibited ATRA-induced Sp1 and CREB (cAMP-response element-binding protein) DNA binding. Azadirachtin inhibited ATRA binding with retinoid receptors, which is supported by biochemical and in silico evidences. Azadirachtin showed strong interaction with retinoid receptors. It suppressed ATRA-mediated removal of retinoid receptors, bound with DNA by inhibiting ATRA binding to its receptors. Overall, our data suggest that azadirachtin interacts with retinoic acid receptors and suppresses ATRA binding, inhibits falling off the receptors, and activates transcription factors like CREB, Sp1, NF-κB, etc. Thus, azadirachtin exerts anti-inflammatory and anti-metastatic responses by a novel pathway that would be beneficial for further anti-inflammatory and anti-cancer therapies.

Ras puts the brake on doxorubicin-mediated cell death in p53-expressing cells

Doxorubicin is one of the most effective molecules used in the treatment of various tumors. Contradictory reports often open windows to understand the role of p53 tumor suppressor in doxorubicin-mediated cell death. In this report, we provide evidences that doxorubicin induced more cell death in p53-negative tumor cells. Several cells, having p53 basal expression, showed increase in p53 DNA binding upon doxorubicin treatment. Doxorubicin induced cell death in p53-positive cells through expression of p53-dependent genes and activation of caspases and caspase-mediated cleavage of cellular proteins. Surprisingly, in p53-negative cells, doxorubicin-mediated cell death was more aggressive (faster and intense). Doxorubicin increased the amount of Fas ligand (FasL) by enhancing activator protein (AP) 1 DNA binding in both p53-positive and p53-negative cells, but the basal expression of Fas was higher in p53-negative cells. Anti-FasL antibody considerably protected doxorubicin-mediated cell death in both types of cells. Activation of caspases was faster in p53-negative cells upon doxorubicin treatment. In contrast, the basal expression of Ras oncoprotein was higher in p53-positive cells, which might increase the basal expression of Fas in these cells. Overexpression of Ras decreased the amount of Fas in p53-negative cells, thereby decreasing doxorubicin-mediated aggressive cell death. Overall, this study will help to understand the much studied chemotherapeutic drug, doxorubicin-mediated cell signaling cascade, that leads to cell death in p53-positive and -negative cells. High basal expression of Fas might be an important determinant in doxorubicin-mediated cell death in p53-negative cells.

Novel derivative of benzofuran induces cell death mostly by G2/M cell cycle arrest through p53-dependent pathway but partially by inhibition of NF-kappaB

The Dracaena resin is widely used in traditional medicine as an anticancer agent, and benzofuran lignan is the active component. In this report, we provide evidence that the synthetic derivative of benzofuran lignan (Benfur) showed antitumor activities. It induced apoptosis in p53-positive cells. Though it inhibited endotoxin-induced nuclear factor kappaB (NF-kappaB) activation in both p53-positive and -negative cells, the activation of caspase 3 was observed in p53-positive cells. It showed partial cell death effect in both p53-positive and -negative cells through inhibition of NF-kappaB. Cell cycle analysis using flow cytometry showed that treatment with this novel benozofuran lignan derivative to Jurkat T-cells, but not U-937 cells, resulted in a G2/M arrest in a dose- and time-dependent manner. It increased amounts of p21, p27, and cyclin B, but not phospho-Rb through p53 nuclear translocation in Jurkat T-cells, but not in U-937 cells. It inhibited amounts of MDM2 (murine double minute 2) by repressing the transcription factor Sp1, which was also proved in silico. It induced cell death in tumor cells, but not in primary T-cells. Overall, our data suggest that Benfur-mediated cell death is partially dependent upon NF-kappaB, but predominantly dependent on p53. Thus, this novel benzofuran lignan derivative can be effective chemopreventive or chemotherapeutic agent against malignant T-cells.

Posttranslational modifications of NF-kappaB: another layer of regulation for NF-kappaB signaling pathway

The eukaryotic transcription factor NF-kappaB regulates a wide range of host genes that control the inflammatory and immune responses, programmed cell death, cell proliferation and differentiation. The activation of NF-kappaB is tightly controlled both in the cytoplasm and in the nucleus. While the upstream cytoplasmic regulatory events for the activation of NF-kappaB are well studied, much less is known about the nuclear regulation of NF-kappaB. Emerging evidence suggests that NF-kappaB undergoes a variety of posttranslational modifications, and that these modifications play a key role in determining the duration and strength of NF-kappaB nuclear activity as well as its transcriptional output. Here we summarize the recent advances in our understanding of the posttranslational modifications of NF-kappaB, the interplay between the various modifications, and the physiological relevance of these modifications.

Inhibiting TRAF2-mediated activation of NF-kappaB facilitates induction of AP-1

The compound 5-(4-methoxyarylimino)-2-N-(3,4-dichlorophenyl)-3-oxo-1,2,4-thiadiazolidine (P(3)-25) is known to possess anti-bacterial, anti-fungal, and anti-tubercular activities. In this report, we provide evidence that P(3)-25 inhibits NF-kappaB, known to induce inflammatory and tumorigenic responses. It activates AP-1, another transcription factor. It inhibits TRAF2-mediated NF-kappaB activation but not TRAF6-mediated NF-kappaB DNA binding by preventing its association with TANK (TRAF for NF-kappaB). It facilitates binding of MEKK1 with TRAF2 and thereby activates JNK and AP-1. We provide evidence, for the first time, that suggests that the interaction of P(3)-25 with TRAF2 leads to inhibition of the NF-kappaB pathway and activation of AP-1 pathway. These results suggest novel approaches to design of P(3)-25 as an anti-cancer/inflammatory drug for therapy through regulation of the TRAF2 pathway.

Azadirachtin interacts with the tumor necrosis factor (TNF) binding domain of its receptors and inhibits TNF-induced biological responses

The role of azadirachtin, an active component of a medicinal plant Neem (Azadirachta indica), on TNF-induced cell signaling in human cell lines was investigated. Azadirachtin blocks TNF-induced activation of nuclear factor kappaB (NF-kappaB) and also expression of NF-kappaB-dependent genes such as adhesion molecules and cyclooxygenase 2. Azadirachtin inhibits the inhibitory subunit of NF-kappaB (IkappaB alpha) phosphorylation and thereby its degradation and RelA (p65) nuclear translocation. It blocks IkappaB alpha kinase (IKK) activity ex vivo, but not in vitro. Surprisingly, azadirachtin blocks NF-kappaB DNA binding activity in transfected cells with TNF receptor-associated factor (TRAF)2, TNF receptor-associated death domain (TRADD), IKK, or p65, but not with TNFR, suggesting its effect is at the TNFR level. Azadirachtin blocks binding of TNF, but not IL-1, IL-4, IL-8, or TNF-related apoptosis-inducing ligand (TRAIL) with its respective receptors. Anti-TNFR antibody or TNF protects azadirachtin-mediated down-regulation of TNFRs. Further, in silico data suggest that azadirachtin strongly binds in the TNF binding site of TNFR. Overall, our data suggest that azadirachtin modulates cell surface TNFRs thereby decreasing TNF-induced biological responses. Thus, azadirachtin exerts an anti-inflammatory response by a novel pathway, which may be beneficial for anti-inflammatory therapy.

Nuclear NF-kappaB p65 phosphorylation at serine 276 by protein kinase A contributes to the malignant phenotype of head and neck cancer

PURPOSE

Aberrant nuclear activation and phosphorylation of the canonical NF-kappaB subunit RELA/p65 at Serine-536 by inhibitor kappaB kinase is prevalent in head and neck squamous cell carcinoma (HNSCC), but the role of other kinases in NF-kappaB activation has not been well defined. Here, we investigated the prevalence and function of p65-Ser276 phosphorylation by protein kinase A (PKA) in the malignant phenotype and gene transactivation, and studied p65-Ser276 as a potential target for therapy.

EXPERIMENTAL DESIGN

Phospho and total p65 protein expression and localization were determined in HNSCC tissue array and in cell lines. The effects of the PKA inhibitor H-89 on NF-kappaB activation, downstream gene expression, cell proliferation and cell cycle were examined. Knockdown of PKA by specific siRNA confirmed the specificity.

RESULTS

NF-kappaB p65 phosphorylated at Ser276 was prevalent in HNSCC and adjacent dysplastic mucosa, but localized to the cytoplasm in normal mucosa. In HNSCC lines, tumor necrosis factor-alpha (TNF-alpha) significantly increased, whereas H-89 inhibited constitutive and TNF-alpha-induced nuclear p65 (Ser276) phosphorylation, and significantly suppressed NF-kappaB and target gene IL-8 reporter activity. Knockdown of PKA by small interfering RNA inhibited NF-kappaB, IL-8, and BCL-XL reporter gene activities. H-89 suppressed cell proliferation, induced cell death, and blocked the cell cycle in G(1)-S phase. Consistent with its biological effects, H-89 down-modulated expression of NF-kappaB-related genes Cyclin D1, BCL2, BCL-XL, COX2, IL-8, and VEGF, as well as induced cell cycle inhibitor p21(CIP1/WAF1), while suppressing proliferative marker Ki67.

CONCLUSIONS

NF-kappaB p65 (Ser276) phosphorylation by PKA promotes the malignant phenotype and holds potential as a therapeutic target in HNSCC.

Late phase activation of nuclear transcription factor kappaB by doxorubicin is mediated by interleukin-8 and induction of apoptosis via FasL

Doxorubicin is one of the most effective molecules used in the treatment of various tumors. Contradictory reports often open windows to understand the doxorubicin-mediated signaling to exert its apoptosis effect. In this report, we provide evidences that doxorubicin induced biphasic induction of nuclear factor kappaB (NF-kappaB) of immediate activation followed by decrease in the amount of RelA (p65) subunit possibly by inducing the activity of proteasome, but not proteases. Further induction of NF-kappaB was observed through interleukin 8 (IL-8), expressed by doxorubicin treatment. Increased amount of IL-8 induced apoptosis via increase in the releases of intracellular Ca(2+), activation of calcineurin, nuclear translocation of nuclear factor activated T cell (NF-AT), and NF-AT-dependent FasL expression. Anti-IL-8 or -FasL antibody, dominant negative TRAF6 (TRAF6-DN), or TRAF6 binding peptide (TRAF6-BP) inhibited doxorubicin-mediated late phase induction of NF-kappaB and diminished cell death. Thus, our study clearly demonstrated that doxorubicin-mediated cell death is obtained through expression of IL-8. IL-8-mediated calcification is required for enhancement of doxorubicin-mediated cell death. Overall, this study will help to understand the much studied chemotherapeutic drug, doxorubicin-mediated cell signaling cascade to exert its effect during chemotherapy.

A dihydrobenzofuran lignan induces cell death by modulating mitochondrial pathway and G2/M cell cycle arrest

A dihydrobenzofuran lignan, the dimerization product of caffeic acid methyl ester, has shown pronounced antileishmanial and antiplasmodial activities. The present study showed the effect of this compound on cell cycle and apoptosis. Flow cytometric analysis revealed that the cells were arrested in the G2/M phase. Activation of caspase 3, but not caspase 8, generation of ROS, upstream of caspase-3, release of cytochrome c,increase in Bax level, and decrease in Bcl-2 level suggested the involvement of mitochondrial damage. Loss of mitochondrial transmembrane potential independent of caspase activation further suggested the mode of apoptosis. Dihydrobenzofuran-mediated cell death was absent in Bcl-xL-overexpressed cells. Overall, our results justify the role of dihydrobenzofuran lignan as potential antitumor agent, causing G2/M arrest and apoptosis involving the mitochondrial controlled pathway. These findings open promising insights as to how this specific dihydrobenzofuran lignan mediates cytotoxicity and may prove a molecular rationale for future therapeutic interventions in carcinogenesis.

Inhibition of constitutive activity of nuclear transcription factor kappaB sensitizes doxorubicin-resistant cells to apoptosis

Doxorubicin is one of the most effective agents used in the treatment of various tumors. Its use is restricted by the development of resistance to apoptosis, the mechanism of which is not fully understood. Nuclear transcription factor kappaB (NF-kappaB) has been shown both to block apoptosis and to promote cell proliferation, and hence has been considered as an important target for anticancer drug development. We found that in wild type and Dox-revertant MCF-7 cells, Doxorubicin induced NF-kappaB was transient and Dox-resistant cells showed high basal activity of NF-kappaB and expression of genes dependent on it. Moreover, in resistant cells Doxorubicin was unable to induce apoptosis as detected by assays for reactive oxygen intermediates generation, lipid peroxidation, cytotoxicity, PARP degradation and Bcl-2 expression. High basal expressions of multi-drug resistant protein and transglutaminase were found in Dox-resistant cells and inhibition of NF-kappaB decreased those amounts and also sensitized these cells by Doxorubicin. These observations collectively suggest that high NF-kappaB activity confers resistance to Doxorubicin and its inhibition potentiates apoptosis. This study indicates that NF-kappaB plays an important role in chemoresistance and establishes the fact that inhibition of NF-kappaB will be a novel approach in chemotherapy.

A plant flavonoid fisetin induces apoptosis in colon cancer cells by inhibition of COX2 and Wnt/EGFR/NF-kappaB-signaling pathways

Overexpression of cyclooxygenase 2 (COX2) and uncontrolled wingless and Int (Wnt)-signaling pathway have long been suggested to play crucial roles in colorectal cancer. Studies show that selective COX2 inhibitors possess great potential as chemopreventive agents for colon cancer. Recent studies suggest that targeting COX2 and epidermal growth factor receptor (EGFR) may provide better therapeutic strategy than inhibiting either single target and that this may alleviate the problem of COX2 inhibitor-associated side effects. Therefore, there have been intensive efforts to develop novel dietary substances that target COX2 and EGFR activation. Fisetin is a naturally occurring flavonoid commonly found in various vegetables and fruits. We found that the treatment of COX2-overexpressing HT29 human colon cancer cells with fisetin (30-120 microM) resulted in induction of apoptosis, downregulation of COX2 protein expression without affecting COX1 and inhibited the secretion of prostaglandin E2. Treatment of cells with fisetin also inhibited Wnt-signaling activity through downregulation of beta-catenin and T cell factor 4 and decreased the expression of target genes such as cyclin D1 and matrix metalloproteinase 7. Fisetin treatment of cells also inhibited the activation of EGFR and nuclear factor-kappa B (NF-kappaB). Finally, the formation of colonies in soft agar was suppressed by fisetin treatment. Taken together, we provide evidence that the plant flavonoid fisetin can induce apoptosis and suppress the growth of colon cancer cells by inhibition of COX2- and Wnt/EGFR/NF-kappaB-signaling pathways. We suggest that fisetin could be a useful agent for prevention and treatment of colon cancer.