7,12-dimethylbenz(a)anthracene treatment of a c-rel mouse mammary tumor cell line induces epithelial to mesenchymal transition via activation of nuclear factor-kappaB

Prenatal airborne polycyclic aromatic hydrocarbon exposure, altered regulation of peroxisome proliferator-activated receptor gamma (Ppar)γ, and links with mammary cancer

Environmental exposure to polycyclic aromatic hydrocarbons (PAH) has been shown to be associated with chronic disease outcomes through multiple mechanisms including altered regulation of the transcription factor peroxisome proliferator-activated receptor gamma (Ppar) γ. Because PAH exposure and Pparγ each have been associated with mammary cancer, we asked whether PAH would induce altered regulation of Pparγ in mammary tissue, and whether this association may underlie the association between PAH and mammary cancer. Pregnant mice were exposed to aerosolized PAH at proportions that mimic equivalent human exposures in New York City air. We hypothesized that prenatal PAH exposure would alter Pparγ DNA methylation and gene expression and induce the epithelial to mesenchymal transition (EMT) in mammary tissue of offspring (F1) and grandoffspring (F2) mice. We also hypothesized that altered regulation of Pparγ in mammary tissue would associate with biomarkers of EMT, and examined associations with whole body weight. We found that prenatal PAH exposure lowered Pparγ mammary tissue methylation among grandoffspring mice at postnatal day (PND) 28. However, PAH exposure did not associate with altered Pparγ gene expression or consistently with biomarkers of EMT. Finally, lower Pparγ methylation, but not gene expression, was associated with higher body weight among offspring and grandoffspring mice at PND28 and PND60. Findings suggest additional evidence of multi-generational adverse epigenetic effects of prenatal PAH exposure among grandoffspring mice.

Environmental chemicals, breast cancer progression and drug resistance

Breast cancer (BC) is one of the most common causes of cancer in the world and the second leading cause of cancer deaths among women. Mortality is associated mainly with the development of metastases. Identification of the mechanisms involved in metastasis formation is, therefore, a major public health issue. Among the proposed risk factors, chemical environment and pollution are increasingly suggested to have an effect on the signaling pathways involved in metastatic tumor cells emergence and progression. The purpose of this article is to summarize current knowledge about the role of environmental chemicals in breast cancer progression, metastasis formation and resistance to chemotherapy. Through a scoping review, we highlight the effects of a wide variety of environmental toxicants, including persistent organic pollutants and endocrine disruptors, on invasion mechanisms and metastatic processes in BC. We identified the epithelial-to-mesenchymal transition and cancer-stemness (the stem cell-like phenotype in tumors), two mechanisms suspected of playing key roles in the development of metastases and linked to chemoresistance, as potential targets of contaminants. We discuss then the recently described pro-migratory and pro-invasive Ah receptor signaling pathway and conclude that his role in BC progression is still controversial. In conclusion, although several pertinent pathways for the effects of xenobiotics have been identified, the mechanisms of actions for multiple other molecules remain to be established. The integral role of xenobiotics in the exposome in BC needs to be further explored through additional relevant epidemiological studies that can be extended to molecular mechanisms.

(20S)G-Rh2 Inhibits NF-κB Regulated Epithelial-Mesenchymal Transition by Targeting Annexin A2

(1) Background: Epithelial-mesenchymal transition (EMT) is an essential step for cancer metastasis; targeting EMT is an important path for cancer treatment and drug development. NF-κB, an important transcription factor, has been shown to be responsible for cancer metastasis by enhancing the EMT process. Our previous studies showed that (20S)Ginsenoside Rh2 (G-Rh2) inhibits NF-κB activity by targeting Anxa2, but it is still not known whether this targeted inhibition of NF-κB can inhibit the EMT process. (2) Methods: In vivo (20S)G-Rh2-Anxa2 interaction was assessed by cellular thermal shift assay. Protein interaction was determined by immuno-precipitation analysis. NF-κB activity was determined by dual luciferase reporter assay. Gene expression was determined by RT-PCR and immuno-blot. EMT was evaluated by wound healing and Transwell assay and EMT regulating gene expression. (3) Results: Anxa2 interacted with the NF-κB p50 subunit, promoted NF-κB activation, then accelerated mesenchymal-like gene expression and enhanced cell motility; all these cellular processes were inhibited by (20S)G-Rh2. In contrast, these (20S)G-Rh2 effect were completely eliminated by overexpression of Anxa2-K301A, an (20S)G-Rh2-binding-deficient mutant of Anxa2. (4) Conclusion: (20S)G-Rh2 inhibited NF-κB activation and related EMT by targeting Anxa2 in MDA-MB-231 cells.

Targeting the Overexpressed YY1 in Cancer Inhibits EMT and Metastasis

There have been recent developments in the treatment of various cancers, in particular non-metastatic cancers. However, many of the responding patients often relapse initially through the development of spread micro and macro-metastases. Unfortunately, there are very few therapeutic modalities for the treatment of metastatic cancers. The development of cancer metastasis has been proposed to involve the epithelial-mesenchymal transition (EMT), in which the tumor cells with the EMT phenotype exhibit various phenotypic markers and molecular modifications that are manifested to resist most conventional therapies. YY1 is a target of the hyperactivated nuclear factor-kappa beta pathway in cancer and it was reported that YY1 also regulates cell survival and cell proliferation in addition to its role in EMT and resistance. The overexpression of YY1 in the majority of cancers has been correlated with poor prognosis. It is hypothesized that targeting YY1 may result in several anti-tumor activities, including inhibition of cell survival and cell proliferation, inhibition of EMT, and reversal of resistance. This review discusses the potential therapeutic targeting of an overexpressed transcription factor, Yin Yang 1 (YY1), which has been implicated in the development of EMT and drug resistance. Several examples targeting YY1 in experimental models are presented.

Towards Resolving the Pro- and Anti-Tumor Effects of the Aryl Hydrocarbon Receptor

We have postulated that the aryl hydrocarbon receptor (AHR) drives the later, more lethal stages of some cancers when chronically activated by endogenous ligands. However, other studies have suggested that, under some circumstances, the AHR can oppose tumor aggression. Resolving this apparent contradiction is critical to the design of AHR-targeted cancer therapeutics. Molecular (siRNA, shRNA, AHR repressor, CRISPR-Cas9) and pharmacological (AHR inhibitors) approaches were used to confirm the hypothesis that AHR inhibition reduces human cancer cell invasion (irregular colony growth in 3D Matrigel cultures and Boyden chambers), migration (scratch wound assay) and metastasis (human cancer cell xenografts in zebrafish). Furthermore, these assays were used for a head-to-head comparison between AHR antagonists and agonists. AHR inhibition or knockdown/knockout consistently reduced human ER⁻/PR⁻/Her2⁻ and inflammatory breast cancer cell invasion, migration, and metastasis. This was associated with a decrease in invasion-associated genes (e.g., Fibronectin, VCAM1, Thrombospondin, MMP1) and an increase in CDH1/E-cadherin, previously associated with decreased tumor aggression. Paradoxically, AHR agonists (2,3,7,8-tetrachlorodibenzo-p-dioxin and/or 3,3′-diindolylmethane) similarly inhibited irregular colony formation in Matrigel and blocked metastasis in vivo but accelerated migration. These data demonstrate the complexity of modulating AHR activity in cancer while suggesting that AHR inhibitors, and, under some circumstances, AHR agonists, may be useful as cancer therapeutics.

SDF-1 in Mammary Fibroblasts of Bovine with Mastitis Induces EMT and Inflammatory Response of Epithelial Cells

Fibroblasts constitute the majority of the stromal cells within bovine mammary gland, yet the functional contributions of these cells to mastitis and fibrosis and the mechanism are poorly understood. In this study, we demonstrate that inflammation-associated fibroblasts (INFs) extracted from bovine mammary glands with clinical mastitis had different expression pattern regarding to several extracellular matrix (ECM) proteins, chemokines and cytokines compared to normal fibroblasts (NFs) from dairy cows during lactation. The INFs induced epithelial-mesenchymal transition (EMT) and inflammatory responses of mammary epithelial cells in a vitro co-culture model. These functional contributions of INFs to normal epithelial cells were mediated through their ability to secrete stromal cell-derived factor 1 (SDF-1). SDF-1 was highly secreted/expressed by INFs, lipopolysaccharide (LPS) -treated NFs, lipoteichoic acid (LTA) -treated NFs, as well as mastitic tissue compared to their counterparts. Exogenous SDF-1 promoted EMT on epithelial cells through activating NF-κB pathway, induced inflammation response and inhibited proliferation of epithelial cells. In addition, SDF-1 was able to induce mastitis and slight fibrosis of mouse mammary gland, which was attenuated by a specific inhibitor of the receptor of SDF-1. Our findings indicate that stromal fibroblasts within mammary glands with mastitis contribute to EMT and inflammatory responses of epithelial cells through the secretion of SDF-1, which could result in the inflammation spread and fibrosis within mammary gland.

Anti-metastatic potential of resveratrol and its metabolites by the inhibition of epithelial-mesenchymal transition, migration, and invasion of malignant cancer cells

BACKGROUND

Increased epithelial-mesenchymal transition (EMT) and cell migration and invasion abilities of cancer cells play important roles in the metastatic process of cancer. Resveratrol is a stilbenoid, a type of natural polyphenol found in the skin of grapes, berries, and peanuts. A number of experiments have examined resveratrol's ability to target diverse pathways associated with carcinogenesis and cancer progression.

PURPOSE

This article aims to present updated overview of the knowledge that resveratrol and its metabolites or analogs have the potential to inhibit metastasis of cancer via affecting many signaling pathways related with EMT, cancer migration, and invasion in diverse organs of the body.

CHAPTERS

This article starts with a short introduction describing diverse beneficial effects of resveratrol including cancer prevention and the aim of the present study. To address the effects of resveratrol on cancer metastasis, mechanisms of EMT, migration, invasion, and their relevance with cancer metastasis, anti-metastatic effects of resveratrol through EMT-related signaling pathways and inhibitory effects of resveratrol on migration and invasion are highlighted. In addition, anti-metastatic potential of resveratrol metabolites and analogs is addressed.

CONCLUSION

Resveratrol was demonstrated to turn back the EMT process induced by diverse signaling pathways in several cellular and animal cancer models. In addition, resveratrol can exert chemopreventive efficacies on migration and invasion of cancer cells by inhibiting the related pathways and target molecules. Although these findings display the anti-metastatic potential of resveratrol, more patient-oriented clinical studies demonstrating the marked efficacies of resveratrol in humans are still needed.

Hypoxia inducible factor-1α-dependent epithelial to mesenchymal transition under hypoxic conditions in prostate cancer cells

Prostate cancer is the most commonly diagnosed cancer in men and the second leading cause of cancer death. Hypoxia is an environmental stimulus that plays an important role in the development and cancer progression especially for solid tumors. The key regulator under hypoxic conditions is stabilized hypoxia-inducible factor (HIF)-1α. In the present study, immune-fluorescent staining, siRNAs, qRT-PC, immunoblotting, cell migration and invasion assays were carried out to test typical epithelial to mesenchymal transition under hypoxia and the key regulators of this process in PC3, a human prostate cancer cell line. Our data demonstrated that hypoxia induces diverse molecular, phenotypic and functional changes in prostate cancer cells that are consistent with EMT. We also showed that a cell signal factor such as HIF-1α, which might be stabilized under hypoxic environment, is involved in EMT and cancer cell invasive potency. The induced hypoxia could be blocked by HIF-1α gene silencing and reoxygenation of EMT in prostate cancer cells, hypoxia partially reversed accompanied by a process of mesenchymal-epithelial reverting transition (MErT). EMT might be induced by activation of HIF-1α-dependent cell signaling in hypoxic prostate cancer cells.

Epithelial-mesenchymal transition: a new target in anticancer drug discovery

The conversion of cells with an epithelial phenotype into cells with a mesenchymal phenotype, referred to as epithelial-mesenchymal transition, is a critical process for embryonic development that also occurs in adult life, particularly during tumour progression. Tumour cells undergoing epithelial-mesenchymal transition acquire the capacity to disarm the body's antitumour defences, resist apoptosis and anticancer drugs, disseminate throughout the organism, and act as a reservoir that replenishes and expands the tumour cell population. Epithelial-mesenchymal transition is therefore becoming a target of prime interest for anticancer therapy. Here, we discuss the screening and classification of compounds that affect epithelial-mesenchymal transition, highlight some compounds of particular interest, and address issues related to their clinical application.

The impact of low-dose carcinogens and environmental disruptors on tissue invasion and metastasis

The purpose of this review is to stimulate new ideas regarding low-dose environmental mixtures and carcinogens and their potential to promote invasion and metastasis. Whereas a number of chapters in this review are devoted to the role of low-dose environmental mixtures and carcinogens in the promotion of invasion and metastasis in specific tumors such as breast and prostate, the overarching theme is the role of low-dose carcinogens in the progression of cancer stem cells. It is becoming clearer that cancer stem cells in a tumor are the ones that assume invasive properties and colonize distant organs. Therefore, low-dose contaminants that trigger epithelial-mesenchymal transition, for example, in these cells are of particular interest in this review. This we hope will lead to the collaboration between scientists who have dedicated their professional life to the study of carcinogens and those whose interests are exclusively in the arena of tissue invasion and metastasis.

Repeated sub-optimal photodynamic treatments with pheophorbide a induce an epithelial mesenchymal transition in prostate cancer cells via nitric oxide

Photodynamic therapy (PDT) is a clinically approved treatment that causes a selective cytotoxic effect in cancer cells. In addition to the production of singlet oxygen and reactive oxygen species, PDT can induce the release of nitric oxide (NO) by up-regulating nitric oxide synthases (NOS). Since non-optimal PDT often causes tumor recurrence, understanding the molecular pathways involved in the photoprocess is a challenging task for scientists. The present study has examined the response of the PC3 human metastatic prostate cancer cell line following repeated low-dose pheophorbide a treatments, mimicking non-optimal PDT treatment. The analysis was focused on the NF-kB/YY1/RKIP circuitry as it is (i) dysregulated in cancer cells, (ii) modulated by NO and (iii) correlated with the epithelial to mesenchymal transition (EMT). We hypothesized that a repeated treatment of non-optimal PDT induces low levels of NO that lead to cell growth and EMT via the regulation of the above circuitry. The expressions of gene products involved in the circuitry and in EMT were analyzed by western blot. The findings demonstrate the cytoprotective role of NO following non-optimal PDT treatments that was corroborated by the use of L-NAME, an inhibitor of NOS.

In silico identification of an aryl hydrocarbon receptor antagonist with biological activity in vitro and in vivo

The aryl hydrocarbon receptor (AHR) is critically involved in several physiologic processes, including cancer progression and multiple immune system activities. We, and others, have hypothesized that AHR modulators represent an important new class of targeted therapeutics. Here, ligand shape-based virtual modeling techniques were used to identify novel AHR ligands on the basis of previously identified chemotypes. Four structurally unique compounds were identified. One lead compound, 2-((2-(5-bromofuran-2-yl)-4-oxo-4H-chromen-3-yl)oxy)acetamide (CB7993113), was further tested for its ability to block three AHR-dependent biologic activities: triple-negative breast cancer cell invasion or migration in vitro and AHR ligand-induced bone marrow toxicity in vivo. CB7993113 directly bound both murine and human AHR and inhibited polycyclic aromatic hydrocarbon (PAH)- and TCDD-induced reporter activity by 75% and 90% respectively. A novel homology model, comprehensive agonist and inhibitor titration experiments, and AHR localization studies were consistent with competitive antagonism and blockade of nuclear translocation as the primary mechanism of action. CB7993113 (IC50 3.3 × 10(-7) M) effectively reduced invasion of human breast cancer cells in three-dimensional cultures and blocked tumor cell migration in two-dimensional cultures without significantly affecting cell viability or proliferation. Finally, CB7993113 effectively inhibited the bone marrow ablative effects of 7,12-dimethylbenz[a]anthracene in vivo, demonstrating drug absorption and tissue distribution leading to pharmacological efficacy. These experiments suggest that AHR antagonists such as CB7993113 may represent a new class of targeted therapeutics for immunomodulation and/or cancer therapy.

Effects of the HIF-1α and NF-κB loop on epithelial-mesenchymal transition and chemoresistance induced by hypoxia in pancreatic cancer cells

Hypoxia is a microenvironmental factor which plays a critical role in tumor development and chemoresistance. Epithelial-to-mesenchymal transition (EMT) induced by hypoxia is one of the critical causes of treatment failure and chemoresistance in different types of human cancers. Stabilization of the hypoxia-inducible factor-1α (HIF-1α) transcription complex, caused by intratumoral hypoxia, promotes tumor progression and chemoresistance. Previous evidence suggests that hypoxia can also activate nuclear factor-κB (NF-κB), a known mediator of EMT, which is accompanied by reduced expression of epithelial marker E-cadherin and enhanced expression of the mesenchymal markers Vimentin and N-cadherin as well as overexpression of various transcription factors of EMT, such as Snail and Twist. Based on this evidence, the present study aimed to investigate whether downregulation of the p65 subunit of NF-κB or HIF-1α by small interfering RNA (siRNA) may reverse the EMT phenotype and inhibit the proliferation and induce the apoptosis of pancreatic cancer cell lines (PANC-1, BxPC3) under hypoxic conditions in vitro and enhance the efficacy of gemcitabine in the treatment of pancreatic cancer. These results provide molecular evidence showing that the activation of the HIF-1α and NF-κB loop is mechanistically linked with the chemoresistance phenotype (EMT phenotype) of pancreatic cancer cells under hypoxic conditions, suggesting that the inactivation of HIF-1α and NF-κB signaling by novel strategies may be a potential targeted therapeutic approach for overcoming EMT and chemoresistance induced by hypoxia.

Effects of FAF1 overexpression on proliferation and apoptosis of gastric carcinoma HGC-27 cells

AIM: To investigate the influence of the overexpression of Fas-associated factor 1 (FAF1) on cell proliferation and apoptosis in human gastric cancer cell line HGC-27 to explore the relationship between FAF1 and gastric cancer.

METHODS: HGC-27 cells were divided into three groups: a negative control group, an empty vector transfection group (those transfected with empty vector particles 1.0 × 10⁸ TU/mL), and a FAF1 overexpression group (those transfected with recombinant FAF1 lentiviral particles 1.0 × 10⁸ TU/mL). Transfection efficiency was detected by laser scanning confocal microscopy. Protein expression level of FAF1 was detected by Western blot. Changes of cell ultrastructure were detected by transmission electron microscopy. Cell cycle distribution and apoptosis were observed by flow cytometry. Cell proliferation was detected by MTT assay.

RESULTS: The transfection efficiency was greater than 95% according to the green fluorescence. The expression of FAF1 protein was significantly higher in the FAF1 overexpression group than in the two control groups. The cell ultrastructure was normal in the two control groups; however, in the FAF1 overexpression group, cell nuclei split into pieces and apoptotic bodies and vacuoles formed. Overexpression of FAF1 inhibited HGC-27 cell growth, induced cell apoptosis, and changed the cell cycle progression. Compared to the negative control group and empty vector transfection group, cell doubling time was significantly extended, cell apoptosis was significantly increased (84.66% ± 5.92% vs 4.60% ± 3.80%, 7.32% ± 3.82%, both P < 0.05), the percentage of cells in G₀/G₁ phase was significantly decreased (46.43% ± 2.43% vs 54.93% ± 3.5%, 54% ± 0.3%, both P < 0.05), and the percentage of cells in G₂/M phase was significantly increased (29.78% ± 3.91% vs 19.33% ± 3.82%, 20.93% ± 2.46%, both P < 0.05) in the FAF1 overexpression group.

CONCLUSION: FAF1 overexpression could inhibit cell growth, induce cell apoptosis, and change cell cycle progression.

RAGE-binding S100A8/A9 promotes the migration and invasion of human breast cancer cells through actin polymerization and epithelial-mesenchymal transition

S100A8/A9 proteins are members of EF-hand calcium-binding proteins secreted by neutrophils and activated monocytes. S100A8/A9 has cell growth-promoting activity at low concentrations by binding to the receptor for advanced glycation end products (RAGE). In this study, we report for the first time that S100A8/A9 promoted the invasion of breast cancer cells depending on RAGE. In addition, RAGE binding to S100A8/A9 promoted the phosphorylation of LIN-11, Isl1, and MEC-3 protein domain kinase, as well as cofilin. This phosphorylation is a critical step in cofilin recycling and actin polymerization. Interestingly, RAGE binding to S100A8/A9 enhanced cell mesenchymal properties and induced epithelial-mesenchymal transition. Mechanistically, RAGE binding to S100A8/A9 stabilized Snail through the NF-κB signaling pathway. Based on these observations, RAGE expression in breast cancer cells was associated with lymph node and distant metastases in patients with invasive ductal carcinoma. Moreover, RAGE binding to S100A8/A9 promoted lung metastasis in vivo. In summary, our in vitro and in vivo results indicated that RAGE binding to S100A8/A9 played an important role in breast cancer invasion/metastasis. This study identified both RAGE and S100A8/A9 as potential anti-invasion targets for therapeutic intervention in breast cancer.

Restoration of miR-1228* expression suppresses epithelial-mesenchymal transition in gastric cancer

Dysregulated miRNAs play critical roles during carcinogenesis and cancer progression. In the present study, the function of miR-1228* in regulating cancer progression was investigated in gastric cancer. Decreased expression of miR-1228* was observed in human gastric cancer tissues comparing to normal tissues. Subsequently, the role of miR-1228* was evaluated in vivo using the tumor xenograft model. In this model, miR-1228* overexpression suppressed xenograft tumor formation. Furthermore, we demonstrated miR-1228* negatively regulated NF-κB activity in SGC-7901 gastric cancer cells and found that CK2A2 was a target of miR-1228*. Upregulation of miR-1228* decreased the expression of mesenchymal markers and increased the epithelial marker E-cadherin, suggesting its potential role in suppressing epithelial-mesenchymal transition. Collectively, these findings provide the first evidence that miR-1228* plays an important role in regulating gastric cancer growth and suggest that selective restoration of miR-1228* might be beneficial for gastric cancer therapy.

Vimentin and PSF act in concert to regulate IbeA+ E. coli K1 induced activation and nuclear translocation of NF-κB in human brain endothelial cells

BACKGROUND

IbeA-induced NF-κB signaling through its primary receptor vimentin as well as its co-receptor PSF is required for meningitic E. coli K1 penetration and leukocyte transmigration across the blood-brain barrier (BBB), which are the hallmarks of bacterial meningitis. However, it is unknown how vimentin and PSF cooperatively contribute to IbeA-induced cytoplasmic activation and nuclear translocation of NF-κB, which are required for bacteria-mediated pathogenicities.

METHODOLOGY/PRINCIPAL FINDINGS

IbeA-induced E. coli K1 invasion, polymorphonuclear leukocyte (PMN) transmigration and IKK/NF-κB activation are blocked by Caffeic acid phenethyl ester (CAPE), an inhibitor of NF-κB. IKKα/β phosphorylation is blocked by ERK inhibitors. Co-immunoprecipitation analysis shows that vimentin forms a complex with IκB, NF-κB and tubulins in the resting cells. A dissociation of this complex and a simultaneous association of PSF with NF-κB could be induced by IbeA in a time-dependent manner. The head domain of vimentin is required for the complex formation. Two cytoskeletal components, vimentin filaments and microtubules, contribute to the regulation of NF-κB. SiRNA-mediated knockdown studies demonstrate that IKKα/β phosphorylation is completely abolished in HBMECs lacking vimentin and PSF. Phosphorylation of ERK and nuclear translocation of NF-κB are entirely dependent on PSF. These findings suggest that vimentin and PSF cooperatively contribute to IbeA-induced cytoplasmic activation and nuclear translocation of NF-κB activation. PSF is essential for translocation of NF-κB and ERK to the nucleus.

CONCLUSION/SIGNIFICANCE

These findings reveal previously unappreciated facets of the IbeA-binding proteins. Cooperative contributions of vimentin and PSF to IbeA-induced cytoplasmic activation and nuclear translocation of NF-κB may represent a new paradigm in pathogen-induced signal transduction and lead to the development of novel strategies for the prevention and treatment of bacterial meningitis.

Inhibition of Epithelial-to-Mesenchymal Transition (EMT) in Cancer by Nitric Oxide: Pivotal Roles of Nitrosylation of NF-κB, YY1 and Snail

Treatment of cancer cell lines with high levels of nitric oxide (NO) via NO donors, such as DETANONOate, inhibits cell growth and survival pathways and sensitizes resistant tumor cells to apoptosis by chemoimmunotherapeutic drugs. In addition, we recently have reported that NO also inhibits the epithelial-to-mesenchymal transition (EMT) phenotype in metastatic cancer cell lines via dysregulation of the nuclear factor (NF)-κB/Snail/Yin Yang 1 (YY1)/Raf kinase inhibitor protein circuitry. The mechanism underlying NO-mediated dysregulation of this circuit was investigated, namely, NO-mediated inhibition of the activity of the transcription factors NF-κB, Snail, and YY1. We hypothesized that one mechanism of NO-mediated inhibition may invoke the NO-induced S-nitrosylation of these transcription factors. We demonstrate in metastatic and EMT⁺ human prostate carcinoma cell lines that treatment with NO results in the S-nitrosylation of NF-κB (p50), Snail, and YY1 and inhibits their activities, resulting in the reversal of the EMT phenotype into a mesenchymal-to-epithelial transition phenotype. These findings suggest that NO donors may be potential therapeutic agents in both the reversal of resistance and the inhibition of EMT and metastasis.

BI 5700, a Selective Chemical Inhibitor of IκB Kinase 2, Specifically Suppresses Epithelial-Mesenchymal Transition and Metastasis in Mouse Models of Tumor Progression

Increasing evidence suggests that processes termed epithelial-mesenchymal transitions (EMTs) play a key role in therapeutic resistance, tumor recurrence, and metastatic progression. NF-κB signaling has been previously identified as an important pathway in the regulation of EMT in a mouse model of tumor progression. However, it remains unclear whether there is a broad requirement for this pathway to govern EMT and what the relative contribution of IKK family members acting as upstream NF-κB activators is toward promoting EMT and metastasis. To address this question, we have used a novel, small-molecule inhibitor of IκB kinase 2 (IKK2/IKKβ), termed BI 5700. We investigated the role of IKK2 in a number of mouse models of EMT, including TGFβ-induced EMT in the mammary epithelial cell line EpRas, CT26 colon carcinoma cells, and 4T1 mammary carcinoma cells. The latter model was also used to evaluate in vivo activities of BI 5700.We found that BI 5700 inhibits IKK2 with an IC(50) of 9 nM and was highly selective as compared to other IKK family members (IKK1, IKKε, and TBK1) and other kinases. BI 5700 effectively blocks NF-κB activity in EpRas cells and prevents TGFβ-induced EMT. In addition, BI 5700 reverts EMT in mesenchymal CT26 cells and prevents EMT in the 4T1 model. Oral application of BI 5700 significantly interferes with metastasis after mammary fat-pad injection of 4T1 cells, yielding fewer, smaller, and more differentiated metastases as compared to vehicle-treated control animals. We conclude that IKK2 is a key regulator of both the induction and maintenance of EMT in a panel of mouse tumor progression models and that the IKK2 inhibitor BI 5700 constitutes a promising candidate for the treatment of metastatic cancers.

Nuclear factor-κB-dependent epithelial to mesenchymal transition induced by HIF-1α activation in pancreatic cancer cells under hypoxic conditions

BACKGROUND

Epithelial to mesenchymal transition (EMT) induced by hypoxia is one of the critical causes of treatment failure in different types of human cancers. NF-κB is closely involved in the progression of EMT. Compared with HIF-1α, the correlation between NF-κB and EMT during hypoxia has been less studied, and although the phenomenon was observed in the past, the molecular mechanisms involved remained unclear.

METHODOLOGY/PRINCIPAL FINDINGS

Here, we report that hypoxia or overexpression of hypoxia-inducible factor-1α (HIF-1α) promotes EMT in pancreatic cancer cells. On molecular or pharmacologic inhibition of NF-κB, hypoxic cells regained expression of E-cadherin, lost expression of N-cadherin, and attenuated their highly invasive and drug-resistant phenotype. Introducing a pcDNA3.0/HIF-1α into pancreatic cancer cells under normoxic conditions heightened NF-κB activity, phenocopying EMT effects produced by hypoxia. Conversely, inhibiting the heightened NF-κB activity in this setting attenuated the EMT phenotype.

CONCLUSIONS/SIGNIFICANCE

These results suggest that hypoxia or overexpression of HIF-1α induces the EMT that is largely dependent on NF-κB in pancreatic cancer cells.

Interaction of aryl hydrocarbon receptor and NF-κB subunit RelB in breast cancer is associated with interleukin-8 overexpression

The aryl hydrocarbon receptor (AhR) has been best known for its role in mediating the toxicity of dioxin. Here we show that AhR overexpression is found among estrogen receptor (ER)α-negative human breast tumors and that its overexpression is positively correlated to that of the NF-κB subunit RelB and Interleukin (IL)-8. Increased DNA binding activity of the AhR and RelB is coupled to IL-8 overexpression in primary breast cancer tissue, which was also supported by in situ hybridization. Activation of AhR in vitro by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induced IL-8 expression in MDA-MB 436 and MCF-7 cells in an AhR and RelB dependent manner. Consistently, downregulation of RelB or AhR by small interfering RNAs (siRNA) decreased the level of IL-8 but increased expression of ERα in vitro in MCF-7 cells. Our results strongly suggest that RelB and AhR have a critical role in the regulation of IL-8 and reveal a supportive role of RelB and AhR in the anti-apoptotic response in human breast cancer cells. AhR and RelB may present a novel therapeutic target for inflammatory driven breast carcinogenesis and tumor progression. Overexpression of pro-survival factors AhR and RelB may explain the process of the development of environmentally-induced type of breast cancers.

Suppression of WIF-1 through promoter hypermethylation causes accelerated proliferation of the aryl hydrocarbon receptor (AHR) overexpressing MCF10AT1 breast cancer cells

The cause for increased cell proliferation in AHR overexpressing breast cancer cells still remains unknown. Here we studied the molecular basis of aggressive cell proliferation of an AHR overexpressing and ERα functionally down-regulated MCF10AT1 cell line, designated as P20E, in comparison to a matched sub-line, P20C with normal AHR expression and ERα function. We found that a 4-day treatment of P20E cells with 5-aza-2'-deoxycytidine (AZ) caused a significant suppression of cell proliferation. Such an effect of AZ was accompanied with the significant recovery of ERα function. Among diagnostic markers of AZ-induced cellular changes we found conspicuous up-regulation of mRNA expression of Wnt inhibitory factor-1 (WIF-1), particularly in P20E. The possibility of AZ-induced demethylation on the promoter of WIF-1 gene was confirmed through methylation specific PCR assay. Such AZ-induced changes in P20E cells were also accompanied with the decrease in the binding of nuclear proteins to the (32)P labeled TRE (TCF response element) and the reduced accumulation of β-catenin protein in the cell nucleus, indicating the importance of Wnt/β-catenin pathway in maintaining the increased cell proliferation in P20E line over P20C line. The importance of WIF-1 in this regard has been validated by transfecting cells with siRNA against WIF-1, which caused an increase in cell proliferation. Moreover, artificial overexpression of ERα in both P20E as well as MDA-MB-231 cells increased the mRNA expression of WIF-1. Together these results support our main conclusion that the aggressive cell proliferation of this AHR-overexpressing sub-type of transformed mammary epithelial cells is assisted by the epigenetic suppression of WIF-1 gene, which is caused by the loss of ERα.

Mechanisms of nitric oxide-mediated inhibition of EMT in cancer: inhibition of the metastasis-inducer Snail and induction of the metastasis-suppressor RKIP

The role of nitric oxide (NO) in cancer has been controversial and is based on the levels of NO and the responsiveness of the tumor type. It remains unclear whether NO can inhibit the epithelial to mesenchymal transition (EMT) in cancer cells. EMT induction is mediated, in part, by the constitutive activation of the metastasis-inducer transcription factor, Snail and EMT can be inhibited by the metastasis-suppressor Raf-1 kinase inhibitor protein (RKIP) and E-cadherin. Snail is transcriptionally regulated by NF-κB and in turn, Snail represses RKIP transcription. Hence, we hypothesized that high levels of NO, that inhibit NF-κB activity, may also inhibit Snail and induce RKIP and leading to inhibition of EMT. We show that treatment of human prostate metastatic cell lines with the NO donor, DETANONOate, inhibits EMT and reverses both the mesenchymal phenotype and the cell invasive properties. Further, treatment with DETANONOate inhibits Snail expression and DNA-binding activity in parallel with the upregulation of RKIP and E-cadherin protein levels. The pivotal roles of Snail inhibition and RKIP induction in DETANONOate-mediated inhibition of EMT were corroborated by both Snail silencing by siRNA and by ectopic expression of RKIP. The in vitro findings were validated in vivo in mice bearing PC-3 xenografts and treated with DETANONOate. The present findings show, for the first time, the novel role of high subtoxic concentrations of NO in the inhibition of EMT. Thus, NO donors may exert therapeutic activities in the reversal of EMT and metastasis.

IKK(α) controls canonical TGF(ß)-SMAD signaling to regulate genes expressing SNAIL and SLUG during EMT in panc1 cells

The epithelial to mesenchymal transition (EMT) is a crucial step in tumor progression, and the TGFβ-SMAD signaling pathway is an inductor of EMT in many tumor types. One hallmark of EMT is downregulation of the adherens junction protein E-cadherin, a process mediated by transcription factors such as the zinc fingers SNAIL and SLUG. Here, we report that the catalytic IκB kinase (IKK) subunit IKKα is necessary for the silencing of E-cadherin in a Panc1 cell model of TGFβ-SMAD-mediated EMT, independently of NFκB. IKKα regulates canonical TGFβ-SMAD signaling by interacting with SMAD3 and controlling SMAD complex formation on DNA. Furthermore, we demonstrate that the TGFβ-IKKα-SMAD signaling pathway induces transcription of the genes encoding SNAIL and SLUG. In addition, we demonstrate that IKKα also modulates canonical TGFβ-SMAD signaling in human MDA-MB231 breast cancer cells, arguing for a more general impact of IKKα on the control of TGFβ-SMAD signaling. Taken together, these findings indicate that IKKα contributes to the tumor-promoting function of the TGFβ-SMAD signaling pathway in particular cancers.

Dual role of NO donors in the reversal of tumor cell resistance and EMT: Downregulation of the NF-κB/Snail/YY1/RKIP circuitry

Several studies have implicated the role of Nitric Oxide (NO) in the regulation of tumor cell behavior and have shown that NO either promotes or inhibits tumorigenesis. These conflicting findings have been resolved, in part, by the levels of NO used such that low levels promote tumor growth and high levels inhibit tumor growth. Our studies have focused on the use of high levels of NO provided primarily by the NO donor, DETANONOate. We have shown that treatment of resistant tumor cells with DETANONOate sensitizes them to apoptosis by both chemotherapeutic drugs and cytotoxic immunotherapeutic ligands. The underlying mechanisms by which NO sensitizes tumor cells to apoptosis were shown to be regulated, in part, by NO-mediated inhibition of the NF-κB survival/anti-apoptotic pathways and downstream of NF-κB by inhibition of the transcription factor Yin Yang 1 (YY1). In addition to NO-induced sensitization to apoptosis, we have also shown that NO induced the expression of the metastasis-suppressor/immunosurveillance cancer gene product, Raf-1 kinase inhibitor protein (RKIP). Overexpression of RKIP mimics NO in tumor cells-induced sensitization to apoptosis. The induction of RKIP by NO was the result of the inhibition of the RKIP repressor, Snail, downstream of NF-κB. These findings established the presence of a dysregulated NF-κB/Snail/YY1/ RKIP circuitry in resistance and that treatment with NO modifies this loop in tumor cells in favor of the inhibition of tumor cell survival and the response to cytotoxic drugs. Noteworthy, the NF-κB/Snail/YY1/RKIP loop consists of gene products that regulate the epithelial to mesenchymal transition (EMT) and, thus, tumor metastasis. Hence, we have found that treatment of metastatic cancer cell lines with DETANONOate inhibited the EMT phenotype, through both the inhibition of the metastasis-inducers, NF-κB and Snail and the induction of the metastasis-suppressor, RKIP. Altogether, the above findings establish, for the first time, the dual role of high levels of NO in the sensitization of tumor cells to apoptotic stimuli as well as inhibition of EMT. Hence, NO donors may be considered as novel potential therapeutic agents with dual roles in the treatment of patients with refractory cancer and in the prevention of the initiation of the metastatic cascade via EMT.

miR-218 inhibits the invasive ability of glioma cells by direct downregulation of IKK-β

Aberrant activation of nuclear factor-kappa B (NF-κB) pathway has been proven to play important roles in the development and progression of cancers. Activation of NF-κB via the classical pathway is modulated by IκBs kinase (IKK-β). However, the mechanism underlying the epigenetic regulation of IKK-β/NF-κB pathway remains largely unknown. In this study, we found that the expression level of miR-218 was markedly downregulated in glioma cell lines and in human primary glioma tissues. Upregulation of miR-218 dramatically reduced the migratory speed and invasive ability of glioma cells. Furthermore, we showed that ectopically expressing miR-218 in glioma cells resulted in downregulation of matrix metalloproteinase-9 (MMP-9) and reduction in NF-κB transactivity at a transcriptional level, but inhibition of miR-218 enhanced the expression of MMP-9 and transcriptional activity of NF-κB. Moreover, we showed that miR-218 inactivated the NF-κB pathway through downregulating IKK-β expression by directly targeting the 3'-untranslated region (3'-UTR) of IKK-β. Taken together, our results suggest that miR-218 plays an important role in preventing the invasiveness of glioma cells, and our results present a novel mechanism of miRNA-mediated direct suppression of IKK-β/NF-κB pathway in gliomas.

Dynamic expression of a LEF-EGFP Wnt reporter in mouse development and cancer

We have characterized a transgenic mouse line in which enhanced green fluorescent protein (EGFP) is expressed under the control of multimerized LEF-1 responsive elements. In embryos, EGFP was detected in known sites of Wnt activation, including the primitive streak, mesoderm, neural tube, somites, heart, limb buds, mammary placodes, and whisker follicles. In vitro cultured transgenic embryonic fibroblasts upregulated EGFP expression in response to activation of Wnt signaling by GSK3beta inhibition. Mammary tumor cell lines derived from female LEF-EGFP transgenic mice treated with the carcinogen 7, 12-dimethylbenz[a]anthracene (DMBA) also express EGFP. Thus, this transgenic line is useful for ex vivo and in vitro studies of Wnt signaling in development and cancer.

TAp63 is a transcriptional target of NF-kappaB

The p53 homologue p63 encodes multiple protein isoforms either with (TA) or without (DeltaN) the N-terminal transactivation domain. Accumulating evidence indicates that TAp63 plays an important role in various biological processes, including cell proliferation, differentiation, and apoptosis. However, how TAp63 is regulated remains largely unclear. In this study, we demonstrate that NF-kappaB induces TAp63 gene expression. The responsible elements for NF-kappaB-mediated TAp63 induction are located within the region from -784 to -296 bp in the TAp63 promoter, which contains two NF-kappaB binding sites. Ectopic expression of RelA stimulates TAp63 promoter-driven reporter activity and increases endogenous TAp63 mRNA levels. Inhibition of NF-kappaB by IkappaBalpha super-repressor or with a chemical inhibitor leads to down regulation of TAp63 mRNA expression and activity. In addition, mutations in the critical NF-kappaB-binding sites significantly abolish the effects of NF-kappaB on TAp63. Activation of NF-kappaB by TNFalpha enhances p50/RelA binding to the NF-kappaB binding sites. Furthermore, we show that an Sp1 site adjacent to the NF-kappaB sites plays a role in NF-kappaB-mediated upregulation of TAp63. Taken together, these data reveal that TAp63 is a transcriptional target of NF-kappaB, which may play a role in cell proliferation, differentiation and survival upon NF-kappaB activation by various stimuli.

NF-kappaB promotes epithelial-mesenchymal transition, migration and invasion of pancreatic carcinoma cells

The transcription factor NF-kappaB is constitutively active in pancreatic adenocarcinoma. Here we explore the contribution of NF-kappaB to the malignant phenotype of pancreatic cancer cells in addition to its anti-apoptotic role. Block of NF-kappaB signalling by non-destructible IkappaBalpha rendered cells resistant to TGF-beta-induced epithelial-mesenchymal transition (EMT). In contrast, NF-kappaB activation by TNF-alpha or expression of constitutively active IKK2 induced an EMT-phenotype with up-regulation of vimentin and ZEB1, and down-regulation of E-cadherin. EMT could also be induced in cells with defective TGF-beta signalling. Functional assays demonstrated reduced or strongly enhanced migration and invasion upon NF-kappaB inhibition or activation, respectively.

Over-expression of AEG-1 significantly associates with tumour aggressiveness and poor prognosis in human non-small cell lung cancer

Astrocyte elevated gene 1 (AEG-1), a novel oncoprotein, has been implicated in oncogenesis and cancer progression in various types of human cancers. The clinical significance and biological role of AEG-1 in non-small cell lung cancer (NSCLC), however, remain unclear. In the present study, we found that the expression of AEG-1 was markedly up-regulated in NSCLC cell lines and NSCLC tissues at the level of both transcription and translation. Ectopically expressed AEG-1 enhanced the migratory and invasive abilities of NSCLC cells, whereas knockdown of endogenous AEG-1 by specific shRNAs significantly inhibited these abilities. The function of AEG-1 on metastasis modulation was associated with the activation of the PI3K-Akt and NF-kappaB signalling pathways. Furthermore, we showed high expression of AEG-1 in 99/200 (49.5%) paraffin-embedded archival NSCLC specimens. Moreover, statistical analysis displayed a significant correlation in AEG-1 expression with the clinical stage (p < 0.001), T classification (p = 0.001), N classification (p = 0.015), distant metastasis (p = 0.004) and differentiation (p = 0.027). Patients with higher AEG-1 expression had an overall shorter survival time, whereas patients with lower expression of AEG-1 had a better survival time. Multivariate analysis suggested that AEG-1 expression might be an independent prognostic indicator for the survival of NSCLC patients. Taken together, our results suggest that elevated expression of AEG-1 plays an important role in the aggressiveness of NSCLC, leading to a poor clinical outcome.

MMTV mouse models and the diagnostic values of MMTV-like sequences in human breast cancer

Mouse mammary tumor virus (MMTV) long terminal repeat (LTR)-driven transgenic mice are excellent models for breast cancer as they allow for the targeted expression of various oncogenes and growth factors in neoplastic transformation of mammary glands. Numerous MMTV-LTR-driven transgenic mouse models of breast cancer have been created in the past three decades, including MMTV-neu/ErbB2, cyclin D1, cyclin E, Ras, Myc, int-1 and c-rel. These transgenic mice develop mammary tumors with different latency, histology and invasiveness, reflecting the oncogenic pathways activated by the transgene. Recently, homologous sequences of the env gene of MMTV have been identified in approximately 40% of human breast cancers, but not in normal breast or other types of cancers, suggesting possible involvement of mammary tumor virus in human breast carcinogenesis. Accumulating evidence demonstrates the association of MMTV provirus with progesterone receptor, p53 mutations and advanced-stage breast cancer. Thus, the detection of MMTV-like sequences may have diagnostic value to predict the clinical outcome of breast cancer patients.

Characterization of MCF mammary epithelial cells overexpressing the Arylhydrocarbon receptor (AhR)

Background

Recent reports indicate the existence of breast cancer cells expressing very high levels of the Arylhydrocarbon receptor (AhR), a ubiquitous intracellular receptor best known for mediating toxic action of dioxin and related pollutants. Positive correlation between the degree of AhR overexpression and states of increasing transformation of mammary epithelial cells appears to occur in the absence of any exogenous AhR ligands. These observations have raised many questions such as why and how AhR is overexpressed in breast cancer and its physiological roles in the progression to advanced carcinogenic transformation. To address those questions, we hypothesized that AhR overexpression occurs in cells experiencing deficiencies in normally required estrogen receptor (ER) signaling, and the basic role of AhR in such cases is to guide the affected cells to develop orchestrated cellular changes aimed at substituting the normal functions of ER. At the same time, the AhR serves as the mediator of the cell survival program in the absence of ER signaling.

Methods

We subjected two lines of Michigan Cancer Foundation (MCF) mammary epithelial cells to 3 different types ER interacting agents for a number of passages and followed the changes in the expression of AhR mRNA. The resulting sublines were analyzed for phenotypical changes and unique molecular characteristics.

Results

MCF10AT1 cells continuously exposed to 17-beta-estradiol (E2) developed sub-lines that show AhR overexpression with the characteristic phenotype of increased proliferation, and distinct resistance to apoptosis. When these chemically selected cell lines were treated with a specific AhR antagonist, 3-methoxy-4-nitroflavone (MNF), both of the above abnormal cellular characteristics disappeared, indicating the pivotal role of AhR in expressing those cellular phenotypes. The most prominent molecular characteristics of these AhR overexpressing MCF cells were found to be overexpression of ErbB2 and COX-2. Furthermore, we could demonstrate that suppression of AhR functions through anti-AhR siRNA or MNF causes the recovery of ERalpha functions.

Conclusion

One of the main causes for AhR overexpression in these MCF breast cancer cells appears to be the loss of ERalpha functions. This phenomenon is likely to be based on the mutually antagonistic relationship between ER and AhR.

Follistatin-like protein 1 promotes arthritis by up-regulating IFN-gamma

Follistatin-like protein-1 (FSTL-1) is a poorly characterized protein that is up-regulated in the early stage of collagen-induced arthritis and that exacerbates arthritis when delivered by gene transfer. The current study was designed to determine the mechanism by which FSTL-1 promotes arthritis. FSTL-1 was injected into mouse paws, resulting in severe paw swelling associated with up-regulation of IFN-gamma transcript and the IFN-gamma-induced chemokine, CXCL10. Mice depleted of T cells were protected. A central role for IFN-gamma was confirmed by the finding that mice deficient in IFN-gamma failed to exhibit paw swelling in response to injection of FSTL-1. Furthermore, IFN-gamma secretion from mouse spleen cells exposed to a weak TCR signal was increased 5-fold in the presence of FSTL-1. FSTL-1 could be induced by innate immune signals, including TLR4 agonists and the arthritogenic cytokine, IL-1beta, via an NFkappaB pathway. Finally, FSTL-1 was found to be overexpressed in human arthritis and its neutralization inhibited murine collagen-induced arthritis and suppressed IFN-gamma and CXCL10 production in arthritic joints. These findings demonstrate that FSTL-1 plays a critical role in arthritis by enhancing IFN-gamma signaling pathways and suggest a mechanism by which FSTL-1 bridges innate and adaptive immune responses.

E-cadherin controls beta-catenin and NF-kappaB transcriptional activity in mesenchymal gene expression

E-cadherin and its transcriptional repressor Snail1 (Snai1) are two factors that control epithelial phenotype. Expression of Snail1 promotes the conversion of epithelial cells to mesenchymal cells, and occurs concomitantly with the downregulation of E-cadherin and the upregulation of expression of mesenchymal genes such as those encoding fibronectin and LEF1. We studied the molecular mechanism controlling the expression of these genes in mesenchymal cells. Forced expression of E-cadherin strongly downregulated fibronectin and LEF1 RNA levels, indicating that E-cadherin-sensitive factors are involved in the transcription of these genes. E-cadherin overexpression decreased the transcriptional activity of the fibronectin promoter and reduced the interaction of beta-catenin and NF-kappaB with this promoter. Similar to beta-catenin, NF-kappaB was found, by co-immunoprecipitation and pull-down assays, to be associated with E-cadherin and other cell-adhesion components. Interaction of the NF-kappaB p65 subunit with E-cadherin or beta-catenin was reduced when adherens junctions were disrupted by K-ras overexpression or by E-cadherin depletion using siRNA. These conditions did not affect the association of p65 with the NF-kappaB inhibitor IkappaBalpha. The functional significance of these results was stressed by the stimulation of NF-kappaB transcriptional activity, both basal and TNF-alpha-stimulated, induced by an E-cadherin siRNA. Therefore, these results demonstrate that E-cadherin not only controls the transcriptional activity of beta-catenin but also that of NF-kappaB. They indicate too that binding of this latter factor to the adherens junctional complex prevents the transcription of mesenchymal genes.

Modification of cysteine residue in p65 subunit of nuclear factor-kappaB (NF-kappaB) by picroliv suppresses NF-kappaB-regulated gene products and potentiates apoptosis

Picroliv, an iridoid glycoside derived from the plant Picrorhiza kurroa, is used traditionally to treat fever, asthma, hepatitis, and other inflammatory conditions. However, the exact mechanism of its therapeutic action is still unknown. Because nuclear factor-kappaB (NF-kappaB) activation plays a major role in inflammation and carcinogenesis, we postulated that picroliv must interfere with this pathway by inhibiting the activation of NF-kappaB-mediated signal cascade. Electrophoretic mobility shift assay showed that pretreatment with picroliv abrogated tumor necrosis factor (TNF)-induced activation of NF-kappaB. The glycoside also inhibited NF-kappaB activated by carcinogenic and inflammatory agents, such as cigarette smoke condensate, phorbol 12-myristate 13-acetate, okadaic acid, hydrogen peroxide, lipopolysaccharide, and epidermal growth factor. When examined for the mechanism of action, we found that picroliv inhibited activation of IkappaBalpha kinase, leading to inhibition of phosphorylation and degradation of IkappaBalpha. It also inhibited phosphorylation and nuclear translocation of p65. Further studies revealed that picroliv directly inhibits the binding of p65 to DNA, which was reversed by the treatment with reducing agents, suggesting a role for a cysteine residue in interaction with picroliv. Mutation of Cys(38) in p65 to serine abolished this effect of picroliv. NF-kappaB inhibition by picroliv leads to suppression of NF-kappaB-regulated proteins, including those linked with cell survival (inhibitor of apoptosis protein 1, Bcl-2, Bcl-xL, survivin, and TNF receptor-associated factor 2), proliferation (cyclin D1 and cyclooxygenase-2), angiogenesis (vascular endothelial growth factor), and invasion (intercellular adhesion molecule-1 and matrix metalloproteinase-9). Suppression of these proteins enhanced apoptosis induced by TNF. Overall, our results show that picroliv inhibits the NF-kappaB activation pathway, which may explain its anti-inflammatory and anticarcinogenic effects.

NF-kappaB and epithelial to mesenchymal transition of cancer

During progression of an in situ to an invasive cancer, epithelial cells lose expression of proteins that promote cell-cell contact, and acquire mesenchymal markers, which promote cell migration and invasion. These events bear extensive similarities to the process of epithelial to mesenchymal transition (EMT), which has been recognized for several decades as critical feature of embryogenesis. The NF-kappaB family of transcription factors plays pivotal roles in both promoting and maintaining an invasive phenotype. After briefly describing the NF-kappaB family and its role in cancer, in this review we will first describe studies elucidating the functions of NF-kappaB in transcription of master regulator genes that repress an epithelial phenotype. In the second half, we discuss the roles of NF-kappaB in control of mesenchymal genes critical for promoting and maintaining an invasive phenotype. Overall, NF-kappaB is identified as a key target in prevention and in the treatment of invasive carcinomas.

Regulation of constitutive and inducible AHR signaling: complex interactions involving the AHR repressor

The AHR is well known for regulating responses to an array of environmental chemicals. A growing body of evidence supports the hypothesis that the AHR also plays perhaps an even more important role in modulating critical aspects of cell function including cell growth, death, and migration. As these and other important AHR activities continue to be elucidated, it becomes apparent that attention now must be directed towards the mechanisms through which the AHR itself is regulated. Here, we review what is known of and what biological outcomes have been attributed to the AHR repressor (AHRR), an evolutionarily conserved bHLH-PAS protein that inhibits both xenobiotic-induced and constitutively active AHR transcriptional activity in multiple species. We discuss the structure and evolution of the AHRR and the dominant paradigm of a xenobiotic-inducible negative feedback loop comprised of AHR-mediated transcriptional up-regulation of AHRR and the subsequent AHRR-mediated suppression of AHR activity. We highlight the role of the AHRR in limiting AHR activity in the absence of xenobiotic AHR ligands and the important contribution of constitutively repressive AHRR to cancer biology. In this context, we also suggest a new hypothesis proposing that, under some circumstances, constitutively active AHR may repress AHRR transcription, resulting in unbridled AHR activity. We also review the predominant hypotheses on the molecular mechanisms through which AHRR inhibits AHR as well as novel mechanisms through which the AHRR may exert AHR-independent effects. Collectively, this discussion emphasizes the importance of this understudied bHLH-PAS protein in tissue development, normal cell biology, xenobiotic responsiveness, and AHR-regulated malignancy.

The p53 homologue DeltaNp63alpha interacts with the nuclear factor-kappaB pathway to modulate epithelial cell growth

The p53 homologue DeltaNp63alpha is overexpressed and inhibits apoptosis in a subset of human squamous cell carcinomas (SCC). Here, we report that in normal keratinocytes overexpressing DeltaNp63alpha and in human squamous carcinoma cells, DeltaNp63alpha physically associates with phosphorylated, transcriptionally active nuclear c-Rel, a nuclear factor-kappaB family member, resulting in increased c-Rel nuclear accumulation. This accumulation and the associated enhanced proliferation driven by elevated DeltaNp63alpha are attenuated by c-Rel small interfering RNA or overexpression of mutant IkappaBalphaM, indicating that c-Rel-containing complex formation is critical to the ability of elevated DeltaNp63alpha to maintain proliferation in the presence of growth arresting signals. Consistent with a role in growth regulation, DeltaNp63alpha-c-Rel complexes bind a promoter motif and repress the cyclin-dependent kinase inhibitor p21WAF1 in both human squamous carcinoma cells and normal keratinocytes overexpressing DeltaNp63alpha. The relationship between DeltaNp63alpha and activated c-Rel is reflected in their strong nuclear staining in the proliferating compartment of primary head and neck SCC. This is the first report indicating that high levels of DeltaNp63alpha interact with activated c-Rel in keratinocytes and SCC, thereby promoting uncontrolled proliferation, a key alteration in the pathogenesis of cancers.

Green tea polyphenols reverse cooperation between c-Rel and CK2 that induces the aryl hydrocarbon receptor, slug, and an invasive phenotype

Exposure to and bioaccumulation of lipophilic environmental pollutants, such as polycyclic aromatic hydrocarbons (PAHs), has been implicated in breast cancer. Treatment of female rats with the prototypic xenobiotic PAH 7,12-dimethylbenz(a)anthracene (DMBA) induces mammary tumors with an invasive phenotype. Here, we show that green tea prevents or reverses loss of the epithelial marker E-cadherin on the surface of DMBA-induced in situ cancers. To investigate the mechanism(s) leading to a less invasive phenotype, the effects of the green tea polyphenol epigallocatechin-3 gallate (EGCG) on mammary tumor cells were assessed. EGCG reversed epithelial to mesenchymal transition (EMT) in DMBA-treated NF-kappaB c-Rel-driven mammary tumor cells and reduced levels of c-Rel and the protein kinase CK2. Ectopic coexpression of c-Rel and CK2alpha in untransformed mammary epithelial cells was sufficient to induce a mesenchymal gene profile. Mammary tumors and cell lines derived from MMTV-c-Rel x CK2alpha bitransgenic mice displayed a highly invasive phenotype. Coexpression of c-Rel and CK2, or DMBA exposure induced the aryl hydrocarbon receptor (AhR) and putative target gene product Slug, an EMT master regulator, which could be reversed by EGCG treatment. Thus, activation of c-Rel and CK2 and downstream targets AhR and Slug by DMBA induces EMT; EGCG can inhibit this signaling.

A role for the aryl hydrocarbon receptor in mammary gland tumorigenesis

The aryl hydrocarbon receptor (AhR) is an evolutionarily conserved transcription factor bound and activated by ubiquitous environmental pollutants. Historically, the AhR has been studied for its transcriptional regulation of genes encoding cytochrome P450 enzymes, which metabolize many of these chemicals into mutagenic and toxic intermediates. However, recent studies demonstrate that the AhR plays an important role in the biology of several cell types in the absence of environmental chemicals. Here, this paradigm shift is discussed in the context of a putative role for the AhR in mammary gland tumorigenesis. Data demonstrating high levels of constitutively active AhR in mammary tumors are summarized. Particular focus is placed on the likelihood that the AhR contributes to ongoing mammary tumor cell growth and on the possibility that the AhR inhibits apoptosis while promoting transition to an invasive, metastatic phenotype. A working model is proposed that may help explain the sometimes contradictory outcomes observed after AhR manipulation and that serves as a blueprint for the design of therapeutics which target the AhR in breast cancer. The theme that malignant cells reveal the functions for which the AhR has been evolutionarily conserved is presented throughout this discussion.

Oestrogen signalling inhibits invasive phenotype by repressing RelB and its target BCL2

Aberrant constitutive expression of c-Rel, p65 and p50 NF-kappaB subunits has been reported in over 90% of breast cancers. Recently, we characterized a de novo RelB NF-kappaB subunit synthesis pathway, induced by the cytomegalovirus (CMV) IE1 protein, in which binding of p50-p65 NF-kappaB and c-Jun-Fra-2 AP-1 complexes to the RELB promoter work in synergy to potently activate transcription. Although RelB complexes were observed in mouse mammary tumours induced by either ectopic c-Rel expression or carcinogen exposure, little is known about RelB in human breast disease. Here, we demonstrate constitutive de novo RelB synthesis is selectively active in invasive oestrogen receptor alpha (ERalpha)-negative breast cancer cells. ERalpha signalling reduced levels of functional NF-kappaB and Fra-2 AP-1 and inhibited de novo RelB synthesis, leading to an inverse correlation between RELB and ERalpha gene expression in human breast cancer tissues and cell lines. Induction of Bcl-2 by RelB promoted the more invasive phenotype of ERalpha-negative cancer cells. Thus, inhibition of de novo RelB synthesis represents a new mechanism whereby ERalpha controls epithelial to mesenchymal transition (EMT).

The Tumor Suppressor Activity of the Lysyl Oxidase Propeptide Reverses the Invasive Phenotype of Her-2/neu–Driven Breast Cancer

Expression of the lysyl oxidase gene (LOX) was found to inhibit the transforming activity of the ras oncogene in NIH 3T3 fibroblasts and was hence named the ras recision gene (rrg). Lysyl oxidase (LOX) is synthesized and secreted as a 50-kDa inactive proenzyme (Pro-LOX), which is processed by proteolytic cleavage to a functional 32-kDa enzyme and an 18-kDa propeptide (LOX-PP). Recently, the ras recision activity of the LOX gene in NIH 3T3 cells was mapped to its propeptide region. Here, we show for the first time that LOX-PP inhibits transformation of breast cancer cells driven by Her-2/neu, an upstream activator of Ras. LOX-PP expression in Her-2/neu-driven breast cancer cells in culture suppressed Akt, extracellular signal-regulated kinase, and nuclear factor-kappaB activation. Her-2/neu-induced epithelial to mesenchymal transition was reverted by LOX-PP, as judged by reduced levels of Snail and vimentin; up-regulation of E-cadherin, gamma-catenin, and estrogen receptor alpha; and decreased ability to migrate or to form branching colonies in Matrigel. Furthermore, LOX-PP inhibited Her-2/neu tumor formation in a nude mouse xenograft model. Thus, LOX-PP inhibits signaling cascades induced by Her-2/neu that promote a more invasive phenotype and may provide a novel avenue for treatment of Her-2/neu-driven breast carcinomas.

NF-kappaB represses E-cadherin expression and enhances epithelial to mesenchymal transition of mammary epithelial cells: potential involvement of ZEB-1 and ZEB-2

The transcription factor nuclear factor kappa B (NF-kappaB) is constitutively active in both cancer cells and stromal cells of breast cancer; however, the precise role of activated NF-kappaB in cancer progression is not known. Using parental MCF10A cells and a variant that expresses the myoepithelial marker p63 stably overexpressing the constitutively active p65 subunit of NF-kappaB (MCF10A/p65), we show that NF-kappaB suppresses the expression of epithelial specific genes E-cadherin and desmoplakin and induces the expression of the mesenchymal specific gene vimentin. P65 also suppressed the expression of p63 and the putative breast epithelial progenitor marker cytokeratin 5/6. MCF10A/p65 cells were phenotypically similar to cells undergoing epithelial to mesenchymal transition (EMT). MCF10A/p65 cells failed to form characteristic acini in three-dimensional Matrigel. Analysis of parental and MCF10A/p65 cells for genes previously shown to be involved in EMT revealed elevated expression of ZEB-1 and ZEB-2 in MCF10A/p65 cells compared to parental cells. In transient transfection assays, p65 increased ZEB-1 promoter activity. Furthermore, MCF10A cells overexpressing ZEB-1 showed reduced E-cadherin and p63 expression and displayed an EMT phenotype. The siRNA against ZEB-1 or ZEB-2 reduced the number of viable MCF10A/p65 but not parental cells, suggesting the dependence of MCF10A/p65 cells to ZEB-1 and ZEB-2 for cell cycle progression or survival. MCF10A cells chronically exposed to tumor necrosis factor alpha (TNFalpha), a potent NF-kappaB inducer, also exhibited the EMT-like phenotype and ZEB-1/ZEB-2 induction, both of which were reversed following TNFalpha withdrawal.