Expression of prostaglandin endoperoxide H synthase-2 induced by nitric oxide in conditionally immortalized murine colonic epithelial cells

Therapeutic targeting of inflammation and tryptophan metabolism in colon and gastrointestinal cancer

Colorectal cancer (CRC) is the third most common cancer worldwide and the second leading cause of cancer death in the United States. Cytotoxic therapies cause significant adverse effects for most patients and do not offer cure in many advanced cases of CRC. Immunotherapy is a promising new approach to harness the body's own immune system and inflammatory response to attack and clear the cancer. Tryptophan metabolism along the kynurenine pathway (KP) is a particularly promising target for immunotherapy. Indoleamine 2,3-dioxygenase 1 (IDO1) is the most well studied of the enzymes that initiate this pathway and it is commonly overexpressed in CRC. Herein, we provide an in-depth review of how tryptophan metabolism and KP metabolites shape factors important to CRC pathogenesis including the host mucosal immune system, pivotal transcriptional pathways of neoplastic growth, and luminal microbiota. This pathway's role in other gastrointestinal (GI) malignancies such as gastric, pancreatic, esophageal, and GI stromal tumors is also discussed. Finally, we highlight how currently available small molecule inhibitors and emerging methods for therapeutic targeting of IDO1 might be applied to colon, rectal, and colitis-associated cancer.

iNOS-selective inhibitors for cancer prevention: promise and progress

Nitric oxide (NO) is involved in various physiological functions and its role in tumorigenesis has been well studied. A large majority of human and experimental tumors appear to progress owing to NO resulting from iNOS, further stimulated by proinflammatory cytokines. Conversely, in some cases, NO is associated with induction of apoptosis and tumor regression. This dichotomy of NO is largely explained by the complexity of signaling pathways in tumor cells, which respond to NO very differently depending on its concentration. In addition, NO alters many signaling pathways through chemical modifications, such as the addition of S-nitrosothiols and nitrosotyrosine to target proteins altering various biological pathways. Hence, iNOS inhibitors are designed and developed to inhibit various organ site cancers including the colon. Here, we review iNOS expression, generation of NO, involvement of NO in altering signaling pathways, and iNOS select inhibitors and their possible use for the prevention and treatment of various cancers.

n-Butyl benzyl phthalate promotes breast cancer progression by inducing expression of lymphoid enhancer factor 1

Environmental hormones play important roles in regulating the expression of genes involved in cell proliferation, drug resistance, and breast cancer risk; however, their precise role in human breast cancer cells during cancer progression remains unclear. To elucidate the effect of the most widely used industrial phthalate, n-butyl benzyl phthalate (BBP), on cancer progression, we evaluated the results of BBP treatment using a whole human genome cDNA microarray and MetaCore software and selected candidate genes whose expression was changed by more than ten-fold by BBP compared with controls to analyze the signaling pathways in human breast cancer initiating cells (R2d). A total of 473 genes were upregulated, and 468 were downregulated. Most of these genes are involved in proliferation, epithelial-mesenchymal transition, and angiogenesis signaling. BBP induced the viability, invasion and migration, and tube formation in vitro, and Matrigel plug angiogenesis in vivo of R2d and MCF-7. Furthermore, the viability and invasion and migration of these cell lines following BBP treatment was reduced by transfection with a small interfering RNA targeting the mRNA for lymphoid enhancer-binding factor 1; notably, the altered expression of this gene consistently differentiated tumors expressing genes involved in proliferation, epithelial-mesenchymal transition, and angiogenesis. These findings contribute to our understanding of the molecular impact of the environmental hormone BBP and suggest possible strategies for preventing and treating human breast cancer.

Chemoprevention of Colon Cancer by iNOS-Selective Inhibitors

Nitric oxide (NO) is a short-lived pleiotropic regulator and is required for numerous pathophysiological functions, including macrophage-mediated immunity and cancer. It is a highly reactive free radical produced from l-arginine by different isoforms of NO synthases (NOSs). Sustained induction of inducible NOS (iNOS) during chronic inflammatory conditions leads to the formation of reactive intermediates of NO, which are mutagenic and cause DNA damage or impairment of DNA repair, alter cell signaling, and promote proinflammatory and angiogenic properties of the cell, thus contributing to carcinogenesis. Besides its well-established role in inflammation, increased expression of iNOS has been observed in colorectal tumors and other cancers. NO-related signaling pathways involved in colon tumorigenesis seem to progress through stimulation of proinflammatory cytokines and via posttranslational protein modifications of important antiapoptotic molecules in the tumors. NO can stimulate and enhance tumor cell proliferation by promoting invasive, angiogenic, and migratory activities. In contrast, studies also suggest that high levels of NO may be protective against tumor growth by inducing tumor cell death. However, a number of in vitro studies and particularly experimental animal data support the notion that NO and its reactive metabolite peroxynitrite stimulate cyclooxygenase-2 activity, leading to generation of prostaglandins that enhance tumor growth. These prostaglandins further augment tumor promotion and invasive properties of tumor cells. Hence, selective inhibitors of iNOS and combination strategies to inhibit both iNOS and cyclooxygenase-2 may have a preventive role in colon cancer.

Toll-like receptor-4 inhibits enterocyte proliferation via impaired beta-catenin signaling in necrotizing enterocolitis

BACKGROUND & AIMS

Necrotizing enterocolitis (NEC), the leading cause of gastrointestinal death from gastrointestinal disease in preterm infants, is characterized by exaggerated TLR4 signaling and decreased enterocyte proliferation through unknown mechanisms. Given the importance of beta-catenin in regulating proliferation of many cell types, we hypothesize that TLR4 impairs enterocyte proliferation in NEC via impaired beta-catenin signaling.

METHODS

Enterocyte proliferation was detected in IEC-6 cells or in ileum or colon from wild-type, TLR4-mutant, or TLR4(-/-) mice after induction of NEC or endotoxemia. beta-Catenin signaling was assessed by cell fractionation or immunoconfocal microscopy to detect its nuclear translocation. Activation and inhibition of beta-catenin were achieved via cDNA or small interfering RNA, respectively. TLR4 in the intestinal mucosa was inhibited with adenoviruses expressing dominant-negative TLR4.

RESULTS

TLR4 activation significantly impaired enterocyte proliferation in the ileum but not colon in newborn but not adult mice and in IEC-6 enterocytes. beta-Catenin activation reversed these effects in vitro. To determine the mechanisms involved, TLR4 activation phosphorylated the upstream inhibitory kinase GSK3beta, causing beta-catenin degradation. NEC in both mouse and humans was associated with decreased beta-catenin and increased mucosal GSK3beta expression. Strikingly, the inhibition of enterocyte beta-catenin signaling in NEC could be reversed, and enterocyte proliferation restored, through adenoviral-mediated inhibition of TLR4 signaling in the small intestinal mucosa.

CONCLUSION

We now report a novel pathway linking TLR4 with inhibition of beta-catenin signaling via GSK3beta activation, leading to reduced enterocyte proliferation in vitro and in vivo. These data provide additional insights into the pathogenesis of diseases of intestinal inflammation such as NEC.

Convergence of nitric oxide and lipid signaling: anti-inflammatory nitro-fatty acids

The signaling mediators nitric oxide ( NO) and oxidized lipids, once viewed to transduce metabolic and inflammatory information via discrete and independent pathways, are now appreciated as interdependent regulators of immune response and metabolic homeostasis. The interactions between these two classes of mediators result in reciprocal control of mediator synthesis that is strongly influenced by the local chemical environment. The relationship between the two pathways extends beyond coregulation of NO and eicosanoid formation to converge via the nitration of unsaturated fatty acids to yield nitro derivatives (NO(2)-FA). These pluripotent signaling molecules are generated in vivo as an adaptive response to oxidative inflammatory conditions and manifest predominantly anti-inflammatory signaling reactions. These actions of NO(2)-FA are diverse, with these species serving as a potential chemical reserve of NO, reacting with cellular nucleophiles to posttranslationally modify protein structure, function, and localization. In this regard these species act as potent endogenous ligands for peroxisome proliferator-activated receptor gamma. Functional consequences of these signaling mechanisms have been shown in multiple model systems, including the inhibition of platelet and neutrophil functions, induction of heme oxygenase-1, inhibition of LPS-induced cytokine release in monocytes, increased insulin sensitivity and glucose uptake in adipocytes, and relaxation of preconstricted rat aortic segments. These observations have propelled further in vitro and in vivo studies of mechanisms of NO(2)-FA signaling and metabolism, highlighting the therapeutic potential of this class of molecules as anti-inflammatory drug candidates.

Novel mechanism for obesity-induced colon cancer progression

Adipose tissue secretes factors linked to colon cancer risk including leptin. A hallmark of cancer is sustained angiogenesis. While leptin promotes angiogenesis in adipose tissue, it is unknown whether leptin can induce epithelial cells to produce factors that may drive angiogenesis, vascular development and therefore cancer progression. The purpose of this study was to compare the effects of leptin-stimulated colon epithelial cells differing in adenomatous polyposis coli (Apc) genotype (gatekeeper tumor suppressor gene for colon cancer) on angiogenesis. We employed novel colonic epithelial cell lines derived from the Immorto mouse [young adult mouse colon (YAMC)] and the Immorto-Min mouse [Immorto-Min colonic epithelial cell (IMCE)], which carries the Apc Min mutation, to study the effects of leptin-stimulated colon epithelial cells on angiogenesis. We utilized ex vivo rat mesenteric capillary bioassay and human umbilical vein endothelial cell (HUVEC) models to study angiogenesis. IMCE cells stimulated with leptin produced significantly more vascular endothelial growth factor (VEGF) than YAMC (268 +/- 18 versus 124 +/- 8 pg/ml; P < 0.01) cells. Leptin treatment induced dose-dependent increases in VEGF only in IMCE cells. Conditioned media from leptin (50 ng/ml)-treated IMCE cells induced significant capillary formation compared with control, which was blocked by the addition of a neutralizing antibody against VEGF. Conditioned media from leptin-treated IMCE cells also induced HUVEC cell proliferation, chemotaxis, upregulation of adhesion proteins and cell-signaling activation resulting in nuclear factor kappa B nuclear translocation and DNA binding due to VEGF. This is the first study demonstrating that leptin can induce preneoplastic colon epithelial cells to orchestrate VEGF-driven angiogenesis and vascular development, thus providing a specific mechanism and potential target for obesity-associated cancer.

Protein Never in Mitosis Gene A Interacting-1 (PIN1) regulates degradation of inducible nitric oxide synthase in endothelial cells

The peptidyl-proline isomerase Protein Never in Mitosis Gene A Interacting-1 (PIN1) increases the level or activity of several transcription factors that can induce the inducible nitric oxide (NO) synthase (iNOS). PIN1 can also regulate mRNA and protein turnover. Here, the effect of depletion of PIN1 on induction of iNOS by Escherichia coli endotoxin (LPS) and interferon-gamma (IFNgamma) in murine aortic endothelial cells (MAEC) was determined. Suppression of PIN1 by 85% with small hairpin RNA enhanced the induction of NO and iNOS protein by LPS-IFNgamma. There was no effect on induction of iNOS mRNA, suggesting a posttranscriptional effect. The enhanced levels of iNOS protein were functionally significant since LPS-IFNgamma was cytotoxic to MAEC lacking PIN1 but not MAEC harboring an inactive control construct, and because cytotoxicity was blocked by the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester. Consistent with posttranscriptional action, knockdown of PIN1 increased the stability of iNOS protein in cycloheximide-treated cells. Furthermore, loss of iNOS was blocked by the calpain inhibitor carbobenzoxy-valinyl-phenylalaninal but not by the selective proteasome inhibitor epoxomicin. Immunoprecipitation indicated that PIN1 can interact with iNOS. Pull down of iNOS with a wild-type glutathione-S-transferase-PIN1 fusion protein, but not with a mutant of the amino terminal phospho-(serine/threonine)-proline binding WW domain of PIN1, indicated that this domain mediates interaction. The results suggest that PIN1 associates with iNOS and can limit its induction by facilitating calpain-mediated degradation in MAEC.

Intestinal epithelial cell up-regulation of LY6 molecules during colitis results in enhanced chemokine secretion

In the healthy colon, intestinal epithelial cells (IEC) form a physical barrier separating the myriad of gut Ags from the cells of the immune system. Simultaneously, IEC use several mechanisms to actively maintain immunologic tolerance to nonpathogenic Ags, including commensal bacteria. However, during inflammatory bowel disease (IBD), the line of defense provided by IEC is breached, resulting in uncontrolled immune responses. As IEC are a principal mediator of immune responses in the gut, we were interested in discerning the gene expression pattern of IEC during development and progression of IBD. Laser capture microdissection and microarray analysis were combined to identify the LY6 superfamily as strongly up-regulated genes in inflamed IEC of the colon in two models of murine colitis. Surface expression of LY6A and LY6C on IEC is induced by several cytokines present within the colitic gut, including IL-22 and IFN-gamma. Furthermore, cross-linking of LY6C results in production of a number of chemokines which are known to be involved in the immunopathogenesis of IBD. Increased chemokine production was cholesterol dependent, suggesting a role for lipid raft structures in the mechanism. As such, LY6 molecules represent novel targets to down-regulate chemokine expression in the colon and limit subsequent inflammation associated with IBD.

Microarray analysis reveals that leptin induces autocrine/paracrine cascades to promote survival and proliferation of colon epithelial cells in an Apc genotype-dependent fashion

The imbalance in systemic mediators of inflammation, such as leptin, is thought to be involved in obesity-associated cancers. In addition, systemic endocrine signals can influence the local autocrine/paracrine factors produced within this microenvironment to influence epithelial cell fate. We previously demonstrated that leptin preferentially promotes the survival and proliferation of colon epithelial cells possessing an Apc mutation (IMCE) but not model normal cells (YAMC). Therefore, the purpose of this study was to identify leptin-induced functional gene family changes which characterize the response of colon epithelial cells possessing an Apc mutation but not normal cells. Consistent with our knowledge of colon carcinogenesis, genes regulating the Wnt/beta-catenin-mediated pathway including Mdm2, Pik3r1, and Rb1 were upregulated by leptin. Importantly, leptin induced IGF-mediated pathway gene expression changes and their protein products in IMCE cells. In the IMCE cells IGFBP-6, IGF-1, and Crim1 expression was upregulated, while IGFBP-2, IGFBP-3, IGFBP-4, IGFBP-5, and Nov expression was downregulated by leptin treatment. These data establish a biologically plausible mechanistic link between the elevated levels of growth factors and the increased risk of colon cancer associated with obesity.

Inhibition of nitric oxide-induced apoptosis by nicotine in oral epithelial cells

Development of oral cancer is clearly linked to the usage of smokeless tobacco. The molecular mechanisms involved in this process are however not well understood. Toward this goal, we investigated the effect of smokeless tobacco exposure on apoptosis of oral epithelial cells. Exposure of oral epithelial cells to smokeless tobacco extract (STE) induces apoptosis in a dose-dependent manner, until a threshold level of nicotine is achieved upon which apoptosis is inhibited. 1 mM of nicotine is able to inhibit apoptosis significantly induced by STE in these oral cells. Exposure of cells to nicotine alone has no effect on apoptosis, but nicotine inhibits apoptosis induced by other agents present in STE. In this study we show that, the anti-apoptotic action of nicotine is specifically associated with down-regulation of nitric oxide (NO) production. Using specific inducers of NO, we have demonstrated that inhibition of apoptosis by nicotine is through down-regulation of NO production. Further, we observed that nicotine clearly acts as a sink of NO radicals, shown using peroxynitrite generator (SIN-1) in conjunction or absence of radical scavengers. Nicotine thus causes most damage in transformed epithelial cells as depicted by accumulation of nitrotyrosine in a 3-NT ELISA assay. Inhibition of apoptosis is a hallmark in tumor progression and propels development of cancer. It may further result in functional loss of apoptotic effector mechanisms in the transformed cells. Thus, our data clearly indicates that inhibition of NO-induced apoptosis by nicotine may lead to tobacco-induced oral carcinogenesis, and implies careful development of modalities in tobacco cessation programs.

Nitric oxide synthase inhibitors modulate nerve growth factor-mediated regulation of amyloid precursor protein expression in PC12 cells

Nerve growth factor (NGF) can regulate nitric oxide synthase (NOS) expression and nitric oxide (NO) can modulate NGF-mediated neurotrophic responses. In this study, the role of NO in NGF-stimulated amyloid precursor protein (APP) levels was studied. PC12 cells were treated with either the non-selective NOS inhibitor N(omega)-nitro-L-arginine methylester (L-NAME) or the inducible NOS selective inhibitor s-methylisothiourea (S-MIU), and the effect on NGF-mediated increases in APP expression was determined. NGF significantly increased total APP protein levels following 96 h of treatment and this increase was prevented in cells pre-treated with S-MIU. Pre-treatment of cells with actinomycin D also blocked this NGF-mediated induction of APP, indicating de novo protein synthesis is necessary. Treatment with NGF increased APP promoter activity; however, this increase was only partially inhibited by pre-treatment with S-MIU and was increased in the presence of L-NAME. This suggests that NO may be modulating other aspects of APP expression in addition to transcription. Inhibition of NGF signaling pathways was also investigated using inhibitors of mitogen-activated protein (MAP) kinase (U0126), Akt (LY294002) and protein kinase C (PKC; U73122 and bisindolylmaleimide 1 (BIS-1)) activation. Inhibition of each of these pathways prevented NGF-mediated increases in APP protein expression; however, only BIS-1 attenuated NGF-mediated increases in promoter activation. This study indicates that NO is involved in the NGF-mediated regulation of APP, in part at the level of APP transcription and could involve the modulation of NGF signal transduction pathways.

Inhibitory effects of asiatic acid on 7,12-dimethylbenz[a]anthracene and 12-O-tetradecanoylphorbol 13-acetate-induced tumor promotion in mice

Asiatic acid, a pentacyclic triterpene, has been reported to induce apoptosis of various human cancer cells. In the present study, we assessed the anti-tumor promoting effect of asiatic acid against 12-O-tetradecanoylphorbol 13-acetate (TPA)-mediated skin tumorigenesis in 7,12-dimethylbenz[a]anthracene (DMBA)-initiated ICR mice. Topical application of asiatic acid prior to each application of TPA resulted in a significant reduction in skin tumor formation. We also found that pre-application of asiatic acid alleviated TPA-induced [3H]thymidine incorporation, which is a conventional marker for skin tumor promotion. In addition, asiatic acid inhibited the TPA-induced generation of nitric oxide (NO) and expression of inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2), which are known to play important roles in tumor growth, especially in the promotion stage. In addition, topical application of aminoguanidine (AG), a selective iNOS inhibitor, and N(G)-nitro-L-arginine-methyl ester (NAME), another iNOS inhibitor, 30 min prior to TPA treatment significantly inhibited the TPA-induced COX-2 expression. These results suggest that asiatic acid may exert anti-tumorigenesis through inhibitory actions in NO and COX-2 signals.

Interleukin-6 production induced by leptin treatment promotes cell proliferation in an Apc (Min/+) colon epithelial cell line

Increased visceral adipose tissue results in elevated plasma leptin, which are associated with increased risk of a number of obesity-related cancers. However, research is contradictory regarding the role of elevated plasma leptin in colon cancer risk. Having established that leptin induced proliferation in a murine model of preneoplastic (Apc(Min/+); IMCE) colon epithelial cells but not normal (Apc(+/+); YAMC) cells, we hypothesized that the leptin-associated IMCE cell proliferation was a result of autocrine interleukin-6 (IL-6) production and ensuing IL-6 receptor (IL-6R) signaling. Here we show, for the first time, that leptin induces elevated IL-6 production in IMCE cells but not in YAMC cells. IL-6 treatment induced cell proliferation in IMCE cells, but not in YAMC cells, in a concentration-dependent manner from 0.1 to 100 ng/ml (P < 0.05). Interleukin-6-induced IMCE cell proliferation was blocked by the addition of a neutralizing anti-IL-6R antibody. In addition, leptin-induced IMCE cell proliferation was blocked by the addition of an anti-IL-6R neutralizing antibody. Further, we elucidate a novel mechanism by which leptin activates TACE/ADAM17-associated IL-6R shedding and trans-IL-6 signaling in IMCE by induction of IL-6 production. IL-6 treatment of IMCE cells was associated with STAT3, ERK, p38, MEK and JAK2 activation and associated STAT3 nuclear activation and translocation. These data implicate leptin-induced IL-6 production, signaling and subsequent STAT3 activation as early events promoting the survival/proliferation of colon epithelial preneoplastic cells. The elucidation of the leptin-initiated mechanism of preneoplastic cell proliferation establishes a biologically plausible link between the adipocyte-specific cytokine leptin and obesity-associated colon cancer.

Involvement of reactive nitrogen oxides for acquisition of metastatic properties of benign tumors in a model of inflammation-based tumor progression

The cells of a weakly tumorigenic and non-metastatic murine fibrosarcoma (QR-32) are converted into highly malignant tumors (acquiring metastatic potential) once they have grown in vivo after being co-implanted with gelatin sponge which induces inflammation. In the present study, we examined whether nitric oxide (NO) is involved in the inflammation-based tumor progression by administrating a specific inhibitor to inducible nitric oxide synthase, aminoguanidine (AG). First, we co-implanted 1 x 10(5) QR-32 cells with gelatin sponge (10 x 5 x 3 mm piece) into a subcutaneous space in C57BL6 mice. Administration of AG in drinking water (1%) had started 2 days before the tumor implantation and continued until the termination of the experiment. The incidence of tumor formation and the tumor growth did not differ between AG-treated group and -untreated group. On day 28, we excised the arising tumors to establish culture cell lines for evaluation of their acquisition of metastatic phenotype in other normal mice. Metastasis incidence and the number of metastatic colonies were significantly reduced in the tumor cell lines obtained from AG-treated mice compared to those from non-treated mice (p < 0.05). Immunohistochemical analysis demonstrated that inducible nitric oxide synthase and nitrotyrosine in the inflamed lesion were reduced in the AG-administered mice. However, intensity of 8-hydroxy-2-deoxyguanosine was not different between the groups. These results showed that nitric oxide and its reactive nitrogen oxide species cooperatively play a pivotal role in the progression of benign tumor cells in inflamed lesions.

Stage matters: choosing relevant model systems to address hypotheses in diet and cancer chemoprevention research

Clinical evidence reveals that the efficacy of dietary factors to prevent cancer is probably stage-dependent. The ability to demonstrate stage-specific effects of dietary compounds on normal, preneoplastic and malignant cell models may provide insights into puzzling clinical results from cancer chemoprevention trials. The relevance of these models to the field of cancer prevention is immense and will undoubtedly facilitate the ability to discover which dietary factors are most effective at preventing cancer and which, if any, specific steps in neoplastic transformation render cells refractory to the effects of dietary compounds. There are illustrative examples where exposure of high-risk individuals to dietary chemopreventive agents increases rather than decreases cancer risk. While geneticists and clinical oncologists acknowledge the morphological continuum along which tumors develop in specific tissues, tumor cells, rather than normal and preneoplastic cells, continue to be the primary in vitro reductionist tool employed to elucidate mechanisms underlying disease progression and to investigate the potential utility of dietary as well as other chemopreventive agents. Currently, there are few relevant model systems to study the progression of neoplastic transformation, especially in epithelial cells. We highlight examples of model systems isolated from prostate, breast, endometrial and intestinal tissue, with special emphasis on a specific set of non-tumorigenic, conditionally immortal cell lines derived from C57/BL6 mice [YAMC (Young Adult Mouse Colon cells; Apc+/+) cells and IMCE (Immorto-Min Colonic Epithelium cells; ApcMin/+) cells] that have yielded important information on early events in colorectal neoplasia development. These cell lines are an illustrative example of how researchers can examine stage-dependent effects of specific dietary components on carcinogenesis. The utilization of cell culture systems modeling early, middle and late stages of tumorigenesis will yield important insights into mechanisms by which dietary components impact cancer progression.

Leptin, insulin-like growth factor-1, and insulin-like growth factor-2 are mitogens in ApcMin/+ but not Apc+/+ colonic epithelial cell lines

The obese state is associated with elevated circulating levels of insulin, insulin-like growth factors (IGF), and leptin. Research is contradictory regarding the role of these elevated growth factors in colon cancer risk. We hypothesized that colonic epithelial cells that were Apc deficient (ApcMin/+) but not those expressing wild-type Apc (Apc+/+) would experience a hyperproliferative and antiapoptotic phenotype when exposed to these growth factors. This hypothesis was addressed using two nontumorigenic murine colonic epithelial cell lines with distinct Apc genotypes: Apc+/+ YAMC cells and ApcMin/+ IMCE cells. Cells were treated for 48 hours with various concentrations of leptin (0.001-50 ng/mL), IGF-1 (0.1-200 ng/mL), or IGF-2 (0.1-600 ng/mL). In YAMC cells, leptin caused a significant decrease in cell proliferation (P < 0.01) compared with controls due to induction of caspase activity and apoptosis. In contrast, in the IMCE cells, leptin induced a 75% increase in cell proliferation compared with controls (P < 0.0001). IGF-1 and IGF-2 also induced 50% greater proliferation in the IMCE cells (P < 0.001) compared with controls. Cotreatment of IMCE cells with leptin and either IGF-1 or IGF-2 induced greater proliferation than either growth factor alone (P < 0.0001). IMCE cell proliferation caused by leptin only treatment was associated with activation of p42/44 mitogen-activated protein kinase (MAPK), p38 MAPK, and nuclear factor-kappaB nuclear translocation but not with MAPK kinase or Janus-activated kinase/signal transducers and activators of transcription activation. These data provide the first evidence that leptin may interact with IGFs to promote survival and expansion of colonic epithelial cells that were Apc deficient (ApcMin/+) but not those expressing wild-type Apc (Apc+/+).

Beta-Catenin mutations in a mouse model of inflammation-related colon carcinogenesis induced by 1,2-dimethylhydrazine and dextran sodium sulfate

In a previous study, we developed a novel mouse model for colitis-related carcinogenesis, utilizing a single dose of azoxymethane (AOM) followed by dextran sodium sulfate (DSS) in drinking water. In the present study, we investigated whether colonic neoplasms can be developed in mice initiated with a single injection of another genotoxic colonic carcinogen 1,2-dimethylhydrazine (DMH), instead of AOM and followed by exposure of DSS in drinking water. Male crj: CD-1 (ICR) mice were given a single intraperitoneal administration (10, 20 or 40 mg/kg body weight) of DMH and 1-week oral exposure (2% in drinking water) of a non-genotoxic carcinogen, DSS. All animals were killed at week 20, histological alterations and immunohistochemical expression of beta-catenin, cyclooxygenase (COX-2) and inducible nitric oxide synthase (iNOS) were examined in induced colonic epithelial lesions (colonic dysplasias and neoplasms). Also, the beta-catenin gene mutations in paraffin-embedded colonic adenocarcinomas were analyzed by the single strand conformation polymorphism method, restriction enzyme fragment length polymorphism and direct sequencing. The incidences of colonic neoplasms with dysplastic lesions developed were 100% with 2.29+/-0.95 multiplicity, and 100% with 10.38+/-4.00 multiplicity in mice given DMH at doses of 10 mg/kg or 20 mg/kg and 2%DSS, respectively. Although approximately half of the mice given DMH at a dose of 40 mg/kg bodyweight were dead after 2-3 days after the injection, mice who received DMH 40 mg/kg and 2%DSS had 100% incidence of colonic neoplasms with 9.75+/-6.29 multiplicity. Immunohistochemical investigation revealed that adnocarcinomas, induced by DMH at all doses and 2%DSS, showed positive reactivities against beta-catenin, COX-2 and iNOS. In DMH/DSS-induced adenocarcinomas, 10 of 11 (90.9%) adenocacrcinomas had beta-catenin gene mutations. Half of the mutations were detected at codon 37 or 41, encoding serine and threonine that are direct targets for phosphorylation by glycogen synthase kinase-3beta. The present results suggests that, as in the previously reported model (AOM/DSS) our experimental protocol, DMH initiation followed by DSS, may provide a novel and useful mouse model for investigating inflammation-related colon carcinogenesis and for identifying xenobiotics with modifying effects.

Nitric oxide signaling in colon cancer chemoprevention

Nitric oxide (NO) is a pleiotrophic regulator, pivotal to numerous biological processes, including vasodilation, neurotransmission, and macrophage-mediated immunity. The highly reactive free radicals, produced by NO synthases (NOS) have been implicated in the modulation of carcinogenesis. Over-expression of inducible NOS (iNOS), a common phenomenon during chronic inflammatory conditions, generates sustainable amounts of NO, that its reactive intermediates are mutagenic, causing DNA damage or impairment of DNA repair, has been well established in carcinogenesis. Recent studies also implicate NO as having a key signaling molecule that regulates processes of tumorigenesis. Increased expression of iNOS has been observed in tumors of the colon, lung, oropharynx, reproductive organs, breast, and central nervous system besides its occurrence in chronic inflammatory diseases. Progression of a large majority of human and experimental colon tumors appears to progress by NO resulting from stimulation of proinflammatory cytokines, and inactivation (nitrosylation) of p53 mediated caspase activities in the tumors, whereas in some cases it associated with induction of apoptosis and tumor regression. This dichotomy is largely explained by the complexity of signaling pathways in tumor cells, that respond to NO very differently depending on its concentration. p53 mutation, functional loss, activation, and inactivation of apoptotic proteins all have been linked with NO resistance and dependence. Evidence from both in vitro and in vivo experiments support that NO and its reactive metabolite peroxynitrite stimulate COX-2 activity leading generation of tumor growth enhancing prostaglandins. Thus, NO mediated signaling can augment the tumor growth and metastasis by promoting invasive and angiogenic properties of tumor cells, which includes triggering and activation of COX-2. Thus, developing selective inhibitors of iNOS and NO-releasing agents may lead to important strategies for chemoprevention of colon cancer. Chemoprevention studies at preclinical level with several selective inhibitors of iNOS in both chemically and transgenic models of colon cancer are encouraging.

Inducible nitric oxide synthase upregulates cyclooxygenase-2 in mouse cholangiocytes promoting cell growth

Both inducible nitric oxide (NO) synthase (iNOS) and cyclooxygenase-2 (COX-2) have been implicated in the biliary tract carcinogenesis. However, it is not known whether these inflammatory mediators are induced by interdependent or parallel pathways. Because iNOS activity has been associated with diverse gene expression, the aim of this study was to determine whether iNOS induces COX-2. To address this objective, immortalized, but nonmalignant, murine cholangiocytes, 603B cells were employed for these studies. Both iNOS and COX-2 protein and mRNA were expressed in these cells. However, iNOS inhibition with either N-[3-(aminomethyl) benzyl]acetamidine or stable transfection with an iNOS antisense construct inhibited COX-2 mRNA and protein expression, an effect that was reversed by NO donors. COX-2 mRNA expression in 603B cells was reduced by pharmacological inhibitors of the p38 MAPK and JNK1/2 pathways. In contrast, neither inhibitors of the soluble guanylyl cyclase inhibitor/protein kinase G nor p42/44 MAPK pathways attenuated COX-2 mRNA expression. Finally, 603B cells grew at a rate threefold greater than 603B-iNOS antisense cells. The low growth rate of 603B-iNOS antisense cells could be restored to near that of the parent cell line with exogenous PGE(2.) In conclusion, iNOS induces COX-2 expression in cholangiocytes, which promotes cell growth. COX-2 induction may contribute to iNOS-associated carcinogenesis.

Suppression of intestinal polyposis in Apcmin/+ mice by targeting the nitric oxide or poly(ADP-ribose) pathways

Min mice have a germ-line nonsense mutation at codon 850 of the adenomatous polyposis coli (Apc) gene. These mice spontaneously develop multiple polyps in the small and large intestine at the age of 10-12 weeks. The aim of this study was to assess the role of reactive nitrogen species and poly(ADP-ribose) synthetase in tumorogenesis. Oxidative stress was found to be increased in the mucosa of the small intestine of Apc(min/+) mice with a concomitant increase in intestinal polyposis over control mice. Pharmacological inhibition of inducible nitric oxide synthase (NOS) with guanidinoethyldisulfide (GED) or stimulation of the breakdown of the nitrogen reactive species peroxynitrite using a potent decomposition catalyst, FP 15, reduced both the intestinal tumor load and the oxidative stress associated with intestinal polyposis in Apc(min/+) mice. Surprisingly, pharmacological inhibition of poly(ADP-ribose) synthetase by the phenanthridinone derivative PJ 34 also reduced the intestinal polyposis and oxidative stress in these mice, possibly through the inhibition of induction of nitric oxide synthase. These results suggest that reactive nitrogen species particularly peroxynitrite play a pivotal role in development of intestinal polyposis and that strategies to reduce both the oxidative stress and the formation of these radical species may be potential chemopreventive approaches for colorectal cancers.

Polyoma enhancer activator 3, an ets transcription factor, mediates the induction of cyclooxygenase-2 by nitric oxide in colorectal cancer cells

Abundant evidence supports the role of cyclooxygenase-2 (COX-2) in colorectal cancer. Nitric oxide (NO), a pro-inflammatory signaling factor, may regulate COX-2 expression and activity thereby linking hyper-inflammatory states to cancer susceptibility. Previously we showed that NO induced COX-2 expression. Although NO also activated the beta-catenin.T-cell factor/lymphocyte enhancing factor transcriptional pathway, a direct causal link between this pathway and COX-2 expression was not demonstrated. In this current study, we focused on NO-induced transcriptional activity and elucidated its role in COX-2 expression. NO donors stimulated the expression of peroxisome proliferator-activated receptor-delta and c-myc, both downstream genes of beta-catenin. They also induced the expression of polyoma enhancer activator 3 (PEA3) and increased its DNA-binding activity. To establish a role for PEA3 to beta-catenin-induced COX-2, we transfected RKO cells with beta-catenin and found that beta-catenin increased PEA3 expression. Also, there was higher PEA3 in immortal mouse colon epithelium cells (Apc(Min/)(+)) compared with young adult mouse colon cells (Apc(+/+)). Luciferase reporter assays revealed that, although several transcription factors/coactivator, acting alone or in synergistic combination, induced COX-2 promoter activity, PEA3 was one of the most potent. Interestingly, NO from NO donors or generated endogenously from transfected inducible nitric-oxide synthase, increased PEA3/p300-induced COX-2 promoter activity. We also found that an ETS site (-75/-72) and the NF-IL6 site were responsible for COX-2 activity induced by PEA3, PEA3/p300, and NO. Taken together, our results demonstrated that NO through beta-catenin signaling stimulated PEA3 to increase COX-2 activity. In addition, NO augmented the synergistic interaction between PEA3 and CBP/p300.

Chemical basis of inflammation-induced carcinogenesis

Chronic inflammation induced by biological, chemical, and physical factors has been associated with increased risk of human cancer at various sites. Inflammation activates a variety of inflammatory cells, which induce and activate several oxidant-generating enzymes such as NADPH oxidase, inducible nitric oxide synthase, myeloperoxidase, and eosinophil peroxidase. These enzymes produce high concentrations of diverse free radicals and oxidants including superoxide anion, nitric oxide, nitroxyl, nitrogen dioxide, hydrogen peroxide, hypochlorous acid, and hypobromous acid, which react with each other to generate other more potent reactive oxygen and nitrogen species such as peroxynitrite. These species can damage DNA, RNA, lipids, and proteins by nitration, oxidation, chlorination, and bromination reactions, leading to increased mutations and altered functions of enzymes and proteins (e.g., activation of oncogene products and/or inhibition of tumor-suppressor proteins) and thus contributing to the multistage carcinogenesis process. Appropriate treatment of inflammation should be explored further for chemoprevention of human cancers.

Genetic and epigenetic damage induced by reactive nitrogen species: implications in carcinogenesis

Chronic infection and inflammation are recognized risk factors for human cancer at various sites. Infection and inflammation can activate and induce a variety of oxidant-generating enzymes, including NADPH oxidase and inducible nitric oxide synthase. Reactive oxygen and nitrogen species produced by such enzymes react with each other to generate new and more potent reactive species. These oxidants not only can damage DNA and induce mutations, but also can activate oncogene products and/or inactivate tumor-suppressor proteins, thus contributing to most processes of carcinogenesis. Appropriate treatment of inflammation should be further explored for chemoprevention of human cancers, especially those associated with chronic inflammation.

Nitric oxide and prostaglandin E2 participate in lipopolysaccharide/interferon-gamma-induced heme oxygenase 1 and prevent RAW264.7 macrophages from UV-irradiation-induced cell death

Induction of heme oxygenase (HO)-1 during inflammation has been demonstrated in many cell types, but the contribution of inflammatory molecules nitric oxide (NO) and prostaglandin E(2) (PGE(2)) has remained unresolved. Here we show that NO donors including sodium nitroprusside (SNP) and spermine nonoate (SP-NO), and PGE(2) significantly stimulate HO-1 expression in RAW264.7 macrophages, associated with alternative induction on NO and PGE(2) in medium, respectively. NO donors also show the inductive effect on cyclo-oxygenase 2 protein and PGE(2) production. In the presence of lipopolysaccharide and interferon-gamma (LPS/IFN-gamma), HO-1 protein was induced slightly but significantly, and SNP, SP-NO, and PGE(2) enhanced HO-1 protein induced by LPS/IFN-gamma. L-Arginine analogs N-nitro-L-arginine methyl ester (L-NAME) and N-nitro-L-arginine (NLA) significantly block HO-1 protein induced by LPS/IFN-gamma associated with a decrease in NO (not PGE(2)) production. And, NSAIDs aspirin and diclofenase dose dependently inhibited LPS/IFN-gamma-induced HO-1 protein accompanied by suppression of PGE(2) (not NO) production. PD98059 (a specific inhibitor of MEKK), but not SB203580 (a specific inhibitor of p38 kinase), attenuated PGE(2) (not SP-NO) induced HO-1 protein. Under UVC (100 J/m(2)) and UVB (50 J/m(2)) irradiation, PGE(2) or SP-NO treatment prevents cells from UVC or UVB-induced cell death, and HO-1 inhibitor tin protoporphyrin (SnPP) reverses the preventive effects of PGE(2) and SP-NO. The protective activity induced by PGE(2) on UVC or UVB irradiation-induced cell death was blocked by MAPK inhibitor PD98059 (not SB203580). These results demonstrated that inflammatory molecules NO and PGE(2) were potent inducers of HO-1 gene, and protected cells from UV-irradiation-induced cell death through HO-1 induction.

Role of cyclooxygenase-2 and inducible nitric oxide synthase in pancreatic cancer

BACKGROUND AND AIM

Recently, it has been recognized that both cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) produce important endogenous factors of human tumor progression. However, the clinicopathological and biological significance of the expression of COX-2 and iNOS in pancreatic cancer remains unclear. The objective of this study is to find the possible roles and clinical significance of COX-2 and iNOS expression in pancreatic cancer.

METHODS

Seventy-two pancreatic adenocarcinoma tissue specimens were obtained through surgical resection. We investigated the immunohistochemical expression of COX-2 and iNOS in respect to variable clinicopathological characteristics, proliferation activity (by Ki-67 expression), apoptosis (by terminal deoxyribonucleotidyl transferase-mediated dUTP nick-end labeling stain), and microvessel density (by CD34 expression; angiogenesis).

RESULTS

Immunohistochemical investigations demonstrated immunolabeling of tumor cells with the primary antibodies, bovine anti-iNOS and anti-COX-2 antibodies. The COX-2 and iNOS positive rates were 41.7 and 66.7%, respectively. There was significant correlation between positive COX-2 and positive iNOS expression (P = 0.043). The proliferation index (Ki-67 labeling index) was higher in COX-2 positive specimens compared to COX-2 negative specimen (P = 0.015). The apoptotic index of positive iNOS expressions was significantly higher than negative expressions (P < 0.001). The expression of COX-2 and iNOS proteins did not correlate with age, sex, serum bilirubin, CA-19-9, location, size, American Joint Committee on Cancer stage, differentiation, distant metastasis, patient survival, or microvessel density.

CONCLUSIONS

Although the pattern of positive expression was similar in both enzymes, the effect on tumor progression differed; iNOS expression may play a role in apoptosis of tumor cell, while COX-2 expression may contribute to tumor proliferation. However, COX-2 and iNOS expression is not related to prognosis in patients with pancreatic cancer.

Enteroinvasive bacteria alter barrier and transport properties of human intestinal epithelium: role of iNOS and COX-2

BACKGROUND & AIMS

Various invasive pathogens cause diarrhea, but the mechanism(s) are poorly understood. We hypothesized that nitric oxide and prostaglandins might modulate chloride secretory and barrier properties of the infected intestinal epithelium and that diarrhea is caused, in part, by altered expression of inducible NO synthase (iNOS) and cyclooxygenase 2 (COX-2).

METHODS

Studies were conducted in human intestinal epithelial cell lines (HT29/cl.19A, Caco-2, and T84). Cells were infected with enteroinvasive Escherichia coli (EIEC 029:NM) or Salmonella dublin (SD), or nonpathogenic, noninvasive bacteria (Streptococcus thermophilus [ST] and Lactobacillus acidophilus [LA]). Infected cells and controls were tested for transepithelial resistance, chloride secretion, prostaglandin E2, guanosine 3',5'-cyclic monophosphate and adenosine 3',5'-cyclic monophosphate, and protein expression.

RESULTS

Cells infected with EIEC or SD, but not uninfected controls or ST/LA-exposed monolayers, showed a progressive reduction in transepithelial resistance starting at 6-12 hours. Infected HT29/cl.19A and Caco-2 cells, but not T84 cells, also showed an increase in total nitrite. Expression of iNOS, and consequently COX-2, was also increased, followed by increased production of prostaglandins and cyclic nucleotides. Furthermore, basal and stimulated chloride secretory responses to various agonists were enhanced in HT29/cl.19A and Caco-2 cells after infection with enteroinvasive bacteria, and this effect was reversed for some agonists by iNOS or COX-2 inhibitors. Increased expression of cystic fibrosis transmembrane conductance regulator and NKCC1 was also observed in EIEC or SD-infected cells vs. controls, secondary to NO synthase activity.

CONCLUSIONS

Up-regulation of iNOS and COX-2 by enteroinvasive bacteria can modulate chloride secretion and barrier function in intestinal epithelial cells. Thus, these enzymes represent possible therapeutic targets in infectious diarrhea.

Lack of inducible nitric oxide synthase promotes intestinal tumorigenesis in the Apc(Min/+) mouse

BACKGROUND & AIMS

The role of the inducible isoform of nitric oxide synthase (Nos2 or iNOS) in intestinal tumorigenesis is unclear. Conflicting data also exist regarding the ability of Nos2 to modulate expression and/or activity of cyclooxygenase 2 (Cox-2), which promotes intestinal tumorigenesis. Therefore, we determined the effect of a null Nos2 genotype on intestinal tumorigenesis and Cox-2 expression/activity in the Apc(Min/+) mouse model of familial adenomatous polyposis.

METHODS

Apc(Min/+)Nos2(-/-) mice were generated by successive crosses between C57BL/6-Apc(Min/+) and C57BL/6-Nos2(tm1Lau) mice. Adenoma characteristics of age-matched Apc(Min/+)Nos2(+/+) and Apc(Min/+)Nos2(-/-) mice were compared. The level and cellular localization of Nos2 messenger RNA (mRNA) expression in Apc(Min/+)Nos2(+/+) mouse intestine was determined. Cox-2 expression and activity were measured in both intestinal tissue and bone marrow-derived macrophages in vitro.

RESULTS

Apc(Min/+)Nos2(-/-) mice developed significantly more intestinal adenomas than Apc(Min/+)Nos2(+/+) littermates. Epithelial cell Nos2 mRNA expression was decreased in adenomas compared with histologically normal Apc(Min/+)Nos2(+/+) intestine. There was no significant difference in Cox-2 expression or activity in either intestine or bone marrow-derived macrophages from Apc(Min/+)Nos2(+/+) and Apc(Min/+)Nos2(-/-) animals.

CONCLUSIONS

Nos2 plays an antineoplastic role in the Apc(Min/+) mouse model of familial adenomatous polyposis. Nos2 does not modulate Cox-2 expression or activity in the Apc(Min/+) mouse.

n-6 and n-3 polyunsaturated fatty acids differentially modulate oncogenic Ras activation in colonocytes

Ras proteins are critical regulators of cell function, including growth, differentiation, and apoptosis, with membrane localization of the protein being a prerequisite for malignant transformation. We have recently demonstrated that feeding fish oil, compared with corn oil, decreases colonic Ras membrane localization and reduces tumor formation in rats injected with a colon carcinogen. Because the biological activity of Ras is regulated by posttranslational lipid attachment and its interaction with stimulatory lipids, we investigated whether docosahexaenoic acid (DHA), found in fish oil, compared with linoleic acid (LA), found in corn oil, alters Ras posttranslational processing, activation, and effector protein function in young adult mouse colon cells overexpressing H-ras (YAMC-ras). We show here that the major n-3 polyunsaturated fatty acid (PUFA) constituent of fish oil, DHA, compared with LA (an n-6 PUFA), reduces Ras localization to the plasma membrane without affecting posttranslational lipidation and lowers GTP binding and downstream p42/44(ERK)-dependent signaling. In view of the central role of oncogenic Ras in the development of colon cancer, the finding that n-3 and n-6 PUFA differentially modulate Ras activation may partly explain why dietary fish oil protects against colon cancer development.