Nitric oxide-mediated promotion of mammary tumour cell migration requires sequential activation of nitric oxide synthase, guanylate cyclase and mitogen-activated protein kinase

Involvement of VILIP-1 (visinin-like protein) and opposite roles of cyclic AMP and GMP signaling in in vitro cell migration of murine skin squamous cell carcinoma

VILIP-1 (visinin-like protein 1) is downregulated in various human squamous cell carcinoma (SCC). In a mouse skin SCC model VILIP-1 expression is reduced in aggressive tumor cells, accompanied by reduced cAMP levels. Overexpression of VILIP-1 in aggressive SCC cells led to enhanced cAMP production, in turn causing a reduction in invasive properties. Moreover, in primary neurons and neuronal tumor lines VILIP-1 enhanced cGMP signaling. Here, we set out to determine whether and how cAMP and cGMP signaling contribute to the VILIP-1 effect on enhanced SCC model cell migration, and thus most likely invasiveness in vivo. We found stronger increase in cGMP levels in aggressive, VILIP-1-negative SCC cells following stimulation of guanylyl cyclases NPR-A and -B with the natriuretic peptides ANP and CNP, respectively. Incubation with ANP or 8Br-cGMP to increase cGMP levels further enhanced the migration capacity of aggressive cells, whereas cell adhesion was unaffected. Increased cGMP was caused by elevated expression levels of NPR-A and -B. However, the expression level of VILIP-1 did not affect cGMP signaling and guanylyl cyclase expression in SCC. In contrast, VILIP-1 led to reduced migration of aggressive SCC cells depending on cAMP levels as shown by use of adenylyl cyclase (AC) inhibitor 2',3'-dideoxyadenosine. Involvement of cAMP-effectors PKA and EPAC play a role downstream of AC activation. VILIP-1-positive and -negative cells did not differ in mRNA expression of ACs, but an effect on enhanced protein expression and membrane localization of ACs was shown to underlie enhancement of cAMP production and, thus, reduction in cell migration by VILIP-1.

Reciprocal activation of macrophages and breast carcinoma cells by nitric oxide and colony-stimulating factor-1

Induction of inducible nitric oxide synthase (iNOS) gene expression, nitric oxide (NO) production and migration of RAW264.7 macrophages by coculture with breast cancer MDA-MB-231 cells or the addition of conditioned medium derived from MDA-MB-231 cells (MDA-CM) was identified. Increased iNOS/NO induction and migration of macrophages by MDA-CM were significantly blocked by adding the c-Jun-N-terminal protein kinase (JNK) inhibitor, SP600125, the nuclear factor-kappa B (NF-κB) inhibitor, BAY117082 and pyrrolidine dithiocarbamic acid and a dominant-negative JNK. The addition of an NO donor, Diethylenetriamine-NONOate, significantly activated expressions of MMP-9 and VEGF-A genes in breast carcinoma MDA-MD-231 cells and invasion of MDA-MB-231 cells in coculture with RAW264.7 macrophages as determined using Transwell systems, but that was inhibited by adding SP600125, BAY117082 and the nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester. Induction of heme oxygenase-1 in macrophages reduced MDA-CM-induced iNOS/NO, JNK and NF-κB activations in accordance with inhibiting VEGF-A and MMP-9 gene expressions by MDA-MB-231 cells via Transwell assays. Furthermore, VEGF, sRANKL, TNF-α, IL-1α, TGF-β, CSF-1 and MCP-1 were applied, and CSF-1 showed the most potent stimulation of iNOS/NO production and migration of macrophages. MCF-7 cells with lower CSF-1 expression than MDA-MB-231 cells showed a poor stimulatory effect on iNOS/NO production and migration of macrophages. Neutralization of CSF-1 in MDA-CM using CSF-1 antibody inhibited MDA-CM-induced iNOS protein expression and migration of macrophages, and CSF-1-induced iNOS protein and migration was blocked by adding JNK inhibitor SP and NF-κB inhibitor BAY. The reciprocal activation of breast cancer and macrophages via NO-CSF-1 is first elucidated herein.

NO to breast: when, why and why not?

Nitric oxide is a pleiotropic ancestral molecule, which elicits beneficial effect in many physiological settings but is also tenaciously expressed in numerous pathological conditions, particularly breast tumors. Nitric oxide is particularly harmful in adipogenic milieu of the breast, where it initiates and promotes tumorigenesis. Epidemiological studies have associated populations at a greater risk for developing breast cancer, predominantly estrogen receptor positive tumors, to express specific polymorphic forms of endothelial nitric oxide synthase, that produce sustained low levels of nitric oxide. Low sustained nitric oxide generates oxidative stress and inflammatory conditions at susceptible sites in the heterogeneous microenvironment of the breast, where it promotes cancer related events in specific cell types. Inflammatory conditions also stimulate inducible nitric oxide synthase expression, which dependent on the microenvironment, could promote or inhibit mammary tumors. In this review we re-examine the mechanisms by which nitric oxide promotes initiation and progression of breast cancer and address some of the controversies in the field.

Polyphenols and aging

Age-associated changes within an individual are inherently complex and occur at multiple levels of organismal function. The overall decline in function of various tissues is known to play a key role in both aging and the complex etiology of certain age-associated diseases such as Alzheimer's disease (AD) and cancer. Continuing research highlights the dynamic capacity of polyphenols to protect against age-associated disorders through a variety of important mechanisms. Numerous lines of evidence suggest that dietary polyphenols such as resveratrol, (-)-epigallocatechin-3-gallate (EGCG), and curcumin have the capacity to mitigate age-associated cellular damage induced via metabolic production of reactive oxygen species (ROS). However, recently acquired evidence also demonstrates a likely role for these polyphenols as anticancer agents capable of preventing formation of new vasculature in neoplastic tissues. Polyphenols have also been shown to possess other anticancer properties such as specific cell-signaling actions that may stimulate the activity of the regulatory protein SIRT1. Additionally, polyphenolic compounds have demonstrated their inhibitory effects against chronic vascular inflammation associated with atherosclerosis. These increasingly well-documented results have begun to provide a basis for considering the use of polyphenols in the development of novel therapies for certain human diseases. And while the mechanisms by which these effects occur are yet to be fully understood, it is evident that further investigation may yield a potential use for polyphenols as pharmacological interventions against specific age-associated diseases.

Nitric oxide-mediated invasion in Barrett's high-grade dysplasia and adenocarcinoma

Nitric oxide (NO) has been shown to induce double strand DNA breaks in Barrett's oesophagus (BO) and in other cancers has a role in invasion. The specific aims of this study were to investigate whether NO can induce invasion in cells representative of different stages of Barrett's progression and to determine possible underlying mechanisms. Physiological concentrations of NO that mimic luminal production of NO from dietary sources enhanced invasion in cell lines from high-grade dysplasia (GihTERT) and oesophageal adenocarcinoma (FLO) but not a non-dysplastic Barrett's cell line (QhTERT). Real-time reverse transcription-polymerase chain reaction revealed that NO induced expression of matrix metalloproteinase (MMP)-1, -3, -7, -9 and -10 and tissue inhibitor of metalloproteinase (TIMP)-1, -2 and -3 in these cell lines. Furthermore, ex vivo treatment of Barrett's biopsy samples with NO induced increases in MMP-1 and TIMP-1 expression, suggesting that NO enhances invasion through deregulating MMP and TIMP expression in epithelial cells. In keeping with these findings, microarray analysis and immunohistochemistry performed on biopsy samples showed enhanced expression of MMP-1, -3, -7 and -10 and TIMP-1 in the progression from non-dysplastic BO to adenocarcinoma, although this could not be directly attributed to the effect of NO. Thus, NO may play a role in Barrett's carcinogenesis through deregulating MMP and TIMP expression to enhance invasive potential.

Integrin alpha9beta1: Unique signaling pathways reveal diverse biological roles

Integrins are transmembrane heterodimeric receptors responsible for transducing and modulating signals between the extracellular matrix and cytoskeleton, ultimately influencing cell functions such as adhesion and migration. Integrin alpha9beta1 is classified within a two member sub-family of integrins highlighted in part by its specialized role in cell migration. The importance of this role is demonstrated by its regulation of numerous biological functions including lymphatic valve morphogenesis, lymphangiogenesis, angiogenesis and hematopoietic homeostasis. Compared to other integrins the signaling mechanisms that transduce alpha9beta1-induced cell migration are not well described. We have recently shown that Src tyrosine kinase plays a key proximal role to control alpha9beta1 signaling. Specifically it activates inducible nitric oxide synthase (iNOS) and in turn nitric oxide (NO) production as a means to transduce cell migration. Furthermore, we have also described a role for FAK, Erk and Rac1 in alpha9beta1 signal transduction. Here we provide an over view of known integrin alpha9beta1 signaling pathways and highlight its roles in diverse biological conditions.

Oxidative and nitrosative stress in the metastatic microenvironment

Metastases that are resistant to conventional therapies are the main cause of most cancer-related deaths in humans. Tumor cell heterogeneity, which associates with genomic and phenotypic instability, represents a major problem for cancer therapy. Additional factors, such as the attack of immune cells or organ-specific microenvironments, also influence metastatic cell behavior and the response to therapy. Interaction of cancer and endothelial cells in capillary beds, involving mechanical contact and transient adhesion, is a critical step in the initiation of metastasis. This interaction initiates a cascade of activation pathways that involves cytokines, growth factors, bioactive lipids and reactive oxygen and nitrogen species (ROS and RNS) produced by either the cancer cell or the endothelium. Vascular endothelium-derived NO and H₂O₂ are cytotoxic for the cancer cells, but also help to identify some critical molecular targets that appear essential for survival of invasive metastatic cell subsets. Surviving cancer cells that extravasate and start colonization of an organ or tissue can still be attacked by macrophages and be influenced by specific intraorgan microenvironment conditions. At all steps; from the primary tumor until colonization of a distant organ; metastatic cells undergo a dynamic process of constant adaptations that may lead to the survival of highly resistant malignant cell subsets. In this sequence of molecular events both ROS and RNS play key roles.

Fueling inflammation at tumor microenvironment: the role of multiligand/RAGE axis

The receptor for advanced glycation end products (RAGE), firstly described in 1992, is a single-transmembrane and multiligand member of the immunoglobulin protein family. RAGE engagement produces activation of multiple intracellular signaling mechanisms involved in several inflammation-associated clinical entities, such as diabetes, cancer, renal and heart failures, as well as neurodegenerative diseases. Although RAGE expression has been extensively reported in many cancer types, it is now emerging as a relevant element that can continuously fuel an inflammatory milieu at the tumor microenvironment, thus changing our perception of its contribution to cancer biology. In this review, we will discuss the role of multiligand/RAGE axis, particularly at the multicellular cross talk established in the inflammatory tumor microenvironment. A better understanding of its contribution may provide new targets for tumor management and risk assessment.

Targeting nitric oxide for cancer therapy

A blueprint for the ideal anticancer molecule would include most of the properties of nitric oxide (NO•), but the ability to exploit these characteristics in a therapeutic setting requires a detailed understanding of the biology and biochemistry of the molecule. These properties include the ability of NO• to affect tumour angiogenesis, metastasis, blood flow and immuno surveillance. Furthermore NO• also has the potential to enhance both radio- and chemotherapy. However, all of these strategies are dependent on achieving appropriate levels of NO•, since endogenous levels of NO• appear to have a clear role in tumour progression. This review aims to summarize the role of NO• in cancer with particular emphasis on how the properties of NO• can be exploited for therapy.

Nitric oxide synthase variants and disease-free survival among treated and untreated breast cancer patients in a Southwest Oncology Group clinical trial

PURPOSE

Numerous chemotherapeutic agents are cytotoxic through generation of reactive species, and variability in genes related to oxidative stress may influence disease-free survival (DFS). We examined relationships between DFS and variants in NOS3, as well as NQO1, NQO2, and CBR3, among treated and untreated breast cancer patients in a Southwest Oncology Group clinical trial (S8897).

EXPERIMENTAL DESIGN

In the parent trial, women were assigned according to prognostic features; the high-risk group was randomized to cyclophosphamide, i.v. methotrexate, and 5-fluorouracil or to cyclophosphamide, i.v. doxorubicin, and 5-fluorouracil +/- tamoxifen, and the low-risk group did not receive adjuvant therapy. We extracted DNA from normal lymph node tissue and examined functional polymorphisms in NOS3, NQO1, NQO2, and CBR3, in relation to DFS, using Cox proportional hazard model.

RESULTS

There were significant interactions between DFS, adjuvant therapy, and NOS3 Glu298Asp and -786 polymorphisms, alone and in combination (P for interaction = 0.008). When NOS3 genotypes were combined, women with genotypes encoding for lower nitric oxide who received chemotherapy had a >2-fold increase in hazard of progression (hazard ratio, 2.32; 95% confidence interval, 1.26-4.25), whereas there was reduced risk for those who did not receive adjuvant therapy (hazard ratio, 0.42; 95% confidence interval, 0.19-0.95). There were no associations between the other genotypes and DFS in either group.

CONCLUSION

Variants encoding lower activity of NOS3 may affect outcomes in breast cancer patients, with the direction of risk differing depending on chemotherapy status. These results may mirror the known dual functions of nitric oxide and nitric oxide synthase, depending on oxidative environment.

Integrin alpha9beta1 mediates enhanced cell migration through nitric oxide synthase activity regulated by Src tyrosine kinase

Integrins are important mediators of cell adhesion and migration, which in turn are essential for diverse biological functions, including wound healing and cancer metastasis. The integrin alpha9beta1 is expressed on numerous mammalian tissues and can mediate accelerated cell migration. As the molecular signaling mechanisms that transduce this effect are poorly defined, we investigated the pathways by which activated integrin alpha9beta1 signals migration. We found for the first time that specific ligation of integrin alpha9beta1 rapidly activates Src tyrosine kinase, with concomitant tyrosine phosphorylation of p130Cas and activation of Rac-1. Furthermore, activation of integrin alpha9beta1 also enhanced NO production through activation of inducible nitric oxide synthase (iNOS). Inhibition of Src tyrosine kinase or NOS decreased integrin-alpha9beta1-dependent cell migration. Src appeared to function most proximal in the signaling cascade, in a FAK-independent manner to facilitate iNOS activation and NO-dependent cell migration. The cytoplasmic domain of integrin alpha9 was crucial for integrin-alpha9beta1-induced Src activation, subsequent signaling events and cell migration. When taken together, our results describe a novel and unique mechanism of coordinated interactions of the integrin alpha9 cytoplasmic domain, Src tyrosine kinase and iNOS to transduce integrin-alpha9beta1-mediated cell migration.

Molecular mechanisms of nitric oxide-dependent inhibition of TPA-induced matrix metalloproteinase-9 (MMP-9) in MCF-7 cells

Matrix metalloproteinase-9 (MMP-9) is implicated in the invasion and metastasis of breast cancer cells. We investigated the modulatory effects of nitric oxide (NO) on the 12-O-tetradecanoylphorbol 13-acetate (TPA)-induced MMP-9 expression in MCF-7 cells. Different chemical NO donors inhibited the extracellular content of TPA-induced MMP-9 protein and MMP-9 activity as assessed by gelatin-zymography and ELISA, respectively. Concomitant with the reduction in the extracellular MMP-9 content NO strongly decreased the steady-state levels of MMP-9 mRNA which in turn leads to a lower recruitment of MMP-9 transcripts to polysomes and to a diminished MMP-9 translation. Reporter gene assays revealed that the inhibition in MMP-9 expression by NO is mainly attributed to a 0.67 kb fragment of the 5'-promoter region of the MMP-9 gene but independent of the 3'untranslated region thus indicating that MMP-9 suppression by NO mainly results from transcriptional events. Electrophoretic mobility shift assays (EMSA), showed that NO specifically interferes with the TPA-induced DNA binding affinity of c-Jun and c-Fos without affecting the TPA-induced increase in the levels of the transcription factors. Using pharmacological inhibitors and small interfering (si)RNA we found that PKCdelta is indispensably involved in the TPA-triggered MMP-9 expression. Concomitantly, the TPA-evoked increase in total PKC activity was strongly attenuated in the lysates from NO-treated MCF-7 cells, thus suggesting that NO attenuates TPA-triggered MMP-9 mainly through a direct inhibition of PKCdelta. Modulation of MMP-9 by NO highlights the complex roles of NO in the regulation of MMP-9 in breast cancer cells.

An intron 4 VNTR polymorphism of the endothelial nitric oxide synthase gene is associated with early-onset colorectal cancer

Endothelial-derived nitric oxide, which is produced by endothelial nitric oxide synthase (eNOS), may play an important role in colorectal carcinogenesis. However, the putative contribution of common eNOS genetic polymorphisms to colorectal cancer risk remains unknown. We genotyped 3 polymorphisms of eNOS (T-786C, G894T, and intron4b/a) in 727 colorectal adenocarcinoma cases and 736 age- and sex-matched healthy controls in Taiwan. Genotypes of the T-786C and G894T polymorphisms were determined by fluorescence polarization assays and the 27-bp variable number of tandem repeat (VNTR) polymorphism in intron 4 (intron4b/a) was analyzed by PCR. Logistic regression was used to calculate odds ratios (ORs) and 95% confidence intervals (CIs). Among younger participants (< or =60 yrs), the intron4a variant genotype was associated with a significantly increased risk of colorectal cancer, compared with the intron4bb genotype (OR = 1.60, 95% CI = 1.04-2.46). In addition, those young individuals bearing a greater number of high-risk genotypes (OR > 1, i.e., CT+TT for T-786C, ba+aa for intron4b/a, and GG for G894T) of eNOS had a higher colorectal cancer risk (p(trend) = 0.039). Compared with younger individuals without any putative high-risk genotypes, those with 3 high-risk genotypes had a significantly greater cancer risk (OR = 1.89, 95% CI = 1.04-3.43). Our results suggest that the eNOS intron4b/a polymorphism may contribute to early-onset colorectal cancer risk in the Taiwanese population.

Reactive nitrogen species: molecular mechanisms and potential significance in health and disease

Reactive nitrogen species (RNS) are various nitric oxide-derived compounds, including nitroxyl anion, nitrosonium cation, higher oxides of nitrogen, S-nitrosothiols, and dinitrosyl iron complexes. RNS have been recognized as playing a crucial role in the physiologic regulation of many, if not all, living cells, such as smooth muscle cells, cardiomyocytes, platelets, and nervous and juxtaglomerular cells. They possess pleiotropic properties on cellular targets after both posttranslational modifications and interactions with reactive oxygen species. Elevated levels of RNS have been implicated in cell injury and death by inducing nitrosative stress. The aim of this comprehensive review is to address the mechanisms of formation and removal of RNS, highlighting their potential cellular targets: lipids, DNA, and proteins. The specific importance of RNS and their paradoxic effects, depending on their local concentration under physiologic conditions, is underscored. An increasing number of compounds that modulate RNS processing or targets are being identified. Such compounds are now undergoing preclinical and clinical evaluations in the treatment of pathologies associated with RNS-induced cellular damage. Future research should help to elucidate the involvement of RNS in the therapeutic effect of drugs used to treat neurodegenerative, cardiovascular, metabolic, and inflammatory diseases and cancer.

Induced nitric oxide synthase as a major player in the oncogenic transformation of inflamed tissue

Nitric oxide (NO) is a free radical that is involved in the inflammatory process and carcinogenesis. There are four nitric oxide synthase enzymes involved in NO production: induced nitric oxide synthase (iNOS), endothelial NO synthase (eNOS), neural NO synthase (nNOS), and mitochondrial NOS. iNOS is an inducible and key enzyme in the inflamed tissue. Recent literatures indicate that NO as well as iNOS and eNOS can modulate cancer-related events including nitro-oxidative stress, apoptosis, cell cycle, angio-genesis, invasion, and metastasis. This chapter focuses on linking NO/iNOS/eNOS to inflammation and carcinogenesis from experimental evidence to potential targets on cancer prevention and treatment.

Nitric oxide and airway epithelial barrier function: regulation of tight junction proteins and epithelial permeability

Acute airway inflammation is associated with enhanced production of nitric oxide (NO(.)) and altered airway epithelial barrier function, suggesting a role of NO(.) or its metabolites in epithelial permeability. While high concentrations of S-nitrosothiols disrupted transepithelial resistance (TER) and increased permeability in 16HBE14o- cells, no significant barrier disruption was observed by NONOates, in spite of altered distribution and expression of some TJ proteins. Barrier disruption of mouse tracheal epithelial (MTE) cell monolayers in response to inflammatory cytokines was independent of NOS2, based on similar effects in MTE cells from NOS2-/- mice and a lack of effect of the NOS2-inhibitor 1400W. Cell pre-incubation with LPS protected MTE cells from TER loss and increased permeability by H2O2, which was independent of NOS2. However, NOS2 was found to contribute to epithelial wound repair and TER recovery after mechanical injury. Overall, our results demonstrate that epithelial NOS2 is not responsible for epithelial barrier dysfunction during inflammation, but may contribute to restoration of epithelial integrity.

Tumor-host interactions: the role of inflammation

It is well established that interactions between tumor cells and the host tissue stroma play a key role in determining whether and how any given solid malignancy will develop. In most cases, tumor cells hijack stromal cell functions for their own benefit and ultimately dictate the rules of engagement to the host tissue microenvironment. However, the contribution of the different stromal cell components to tumor growth remains to be clarified. Because most solid tumors are accompanied by a local inflammatory response, it has long been thought that inflammation and carcinogenesis are related. If formal proof that cancer can be initiated by inflammation in the absence of exogenous carcinogens is still lacking, there is abundant evidence that the inflammatory response can play a central role in modulating tumor growth and progression. This review will discuss some of the mechanisms whereby inflammation can both enhance and inhibit tumor growth.

Activation of estrogen receptor-alpha by the anion nitrite

In this study, the ability of nitrite and nitrate to mimic the effects of estradiol on growth and gene expression was measured in the human breast cancer cell line MCF-7. Similar to estradiol, treatment of MCF-7 cells with either 1 mumol/L nitrite or 1 mumol/L nitrate resulted in approximately 4-fold increase in cell growth and 2.3-fold to 3-fold increase in progesterone receptor (PgR), pS2, and cathepsin D mRNAs that were blocked by the antiestrogen ICI 182,780. The anions also recruited estrogen receptor-alpha (ERalpha) to the pS2 promoter and activated exogenously expressed ERalpha when tested in transient cotransfection assays. To determine whether nitrite or nitrate was the active anion, diphenyleneiodonium was used to inhibit oxidation/reduction reactions in the cell. The ability of diphenyleneiodonium to block the effects of nitrate, but not nitrite, on the induction of PgR mRNA and the activation of exogenously expressed ERalpha suggests that nitrite is the active anion. Concentrations of nitrite, as low as 100 nmol/L, induced a significant increase in PgR mRNA, suggesting that physiologically and environmentally relevant doses of the anion activate ERalpha. Nitrite activated the chimeric receptor Gal-ER containing the DNA-binding domain of GAL-4 and the ligand-binding domain of ERalpha and blocked the binding of estradiol to the receptor, suggesting that the anion activates ERalpha through the ligand-binding domain. Mutational analysis identified the amino acids Cys381, His516, Lys520, Lys529, Asn532, and His547 as important for nitrite activation of the receptor.

Inducible nitric oxide synthase: correlation with extracapsular spread and enhancement of tumor cell invasion in head and neck squamous cell carcinoma

BACKGROUND

Extracapsular nodal spread is a major prognostic indicator in head and neck cancer. Nitric oxide (NO), primarily produced by the enzyme inducible NO synthase (iNOS), has a large number of actions in cancer biology, but no studies have investigated its possible role in extracapsular spread or tumor invasion.

METHODS

Immunochemistry was used to study iNOS expression in 48 patients with either extracapsular or encapsulated metastasis. In vitro invasion assays were performed using H357 (an oral squamous cell carcinoma cell line) using the iNOS inhibitor drug, 1400 W.

RESULTS

iNOS expression was significantly associated with extracapsular spread, with 22/27 cases showing positive iNOS expression compared with 8/21 cases in the encapsulated group (p = .01). Invasion of H357 cells was inhibited by 1400 W at concentrations of 100 microM and 1 mM (p = .002, p = .003).

CONCLUSION

iNOS protein seems to be associated with extracapsular spread and invasion in head and neck cancer. Further studies are required to understand this role more fully.

Nitric oxide-induced resistance or sensitization to death in tumor cells

This report summarizes the present state of our knowledge pertaining to the NO-induced resistance or sensitization of tumor cell death. The effects of NO and its synergy with members of the TNF family, with cytotoxic drugs, and with ionizing radiations have been investigated. The dual effect of NO-induced resistance or sensitization and the underlying molecular mechanisms are discussed.

EP2 prostanoid receptor promotes squamous cell carcinoma growth through epidermal growth factor receptor transactivation and iNOS and ERK1/2 pathways

In squamous cell carcinoma, the levels of nitric oxide (NO) derived from inducible NO synthase (iNOS) and prostaglandin E2 (PGE2) derived from cyclooxygenase-2 (COX-2) originated from tumor cells or tumor-associated inflammatory cells have been reported to correlate with tumor growth, metastasis, and angiogenesis. The present study examined the role of the iNOS signaling pathway in PGE2-mediated tumor invasiveness and proliferation in squamous cell carcinoma, A431, and SCC-9 cells. Cell invasion and proliferation promoted by PGE2 were blocked by iNOS silencing RNA or iNOS/guanylate cyclase (GC) pharmacological inhibition. Consistently, iNOS-GC pathway inhibitors blocked mitogen-activated protein kinase-ERK1/2 phosphorylation, which was required to mediate PGE2 functions. In vivo, in A431 cells implanted in nude mice, GC inhibition also decreased the tumor proliferation index and ERK1/2 activation. PGE2 effects were confined to the selective stimulation of the EP2 receptor subtype, leading to epidermal growth factor receptor (EGFR) transactivation via protein kinase A (PKA) and c-Src activation. EP2-mediated ERK1/2 activation and cell functions were abolished by inhibitors of PKA, c-Src, and EGFR, as well as by inhibiting iNOS pathway. Silencing of iNOS also impaired EGFR-induced ERK1/2 phosphorylation. These results indicate that iNOS/GC signaling is a downstream player in the control of EP2/EGFR-mediated tumor cell proliferation and invasion.

Neuronal nitric oxide synthase protects neuroblastoma cells from oxidative stress mediated by garlic derivatives

In this study, we further examined the effects of diallyl disulfide (DADS), one of the major components of oil-soluble garlic extracts (GE) and of raw water GE on SH-SY5Y and NSC34 neuronal cell lines. Both treatments with DADS and GE were able to induce growth arrest and apoptosis, and we observed an increased flux of reactive oxygen and nitrogen species as early signs of cytotoxicity. We demonstrated that the content of neuronal nitric oxide synthase (nNOS) increased as early as 1 h of treatment demonstrating to be a very early sensor of DADS and GE cytotoxicity. Treatments with L-nitropropyl-arginine, an inhibitor of nNOS, increased the rate of apoptosis whereas the overexpression of nNOS significantly reduced cell death by inhibiting DNA damage, protein oxidation, and the activation of the JNK/c-Jun apoptotic signaling cascade. Overall these results demonstrate that garlic derivatives may modulate nNOS and suggest an important contribution of nitric oxide in counteracting their reactive oxygen species-mediated cytotoxicity.

Nitric oxide in physiologic concentrations targets the translational machinery to increase the proliferation of human breast cancer cells: involvement of mammalian target of rapamycin/eIF4E pathway

Nitric oxide (NO) in nanomolar (nmol/L) concentrations is consistently detected in tumor microenvironment and has been found to promote tumorigenesis. The mechanism by which NO enhances tumor progression is largely unknown. In this study, we investigated the possible mechanisms and identified cellular targets by which NO increases proliferation of human breast cancer cell lines MDA-MB-231 and MCF-7. DETA-NONOate, a long acting NO donor, with a half-life of 20 h, was used. We found that NO (nmol/L) dramatically increased total protein synthesis in MDA-MB-231 and MCF-7 and also increased cell proliferation. NO specifically increased the translation of cyclin D1 and ornithine decarboxylase (ODC) without altering their mRNA levels or half-lives. Critical components in the translational machinery, such as phosphorylated mammalian target of rapamycin (mTOR) and its downstream targets, phosphorylated eukaryotic translation initiation factor and p70 S6 kinase, were up-regulated following NO treatment, and inhibition of mTOR with rapamycin attenuated NO induced increase of cyclin D1 and ODC. Activation of translational machinery was mediated by NO-induced up-regulation of the Raf/mitogen-activated protein/extracellular signal-regulated kinase (ERK) kinase/ERK (Raf/MEK/ERK) and phosphatidylinositol 3-kinase (PI-3 kinase)/Akt signaling pathways. Up-regulation of the Raf/MEK/ERK and PI-3 kinase/Akt pathways by NO was found to be mediated by activation of Ras, which was cyclic guanosine 3',5'-monophosphate independent. Furthermore, inactivation of Ras by farnesyl transferase inhibitor or K-Ras small interfering RNA attenuated NO-induced increase in proliferation signaling and cyclin D1 and ODC translation, further confirming the involvement of Ras activation during NO-induced cell proliferation.

Genetic polymorphisms of NOS3 are associated with the risk of invasive breast cancer with lymph node involvement

Endothelial nitric oxide synthase (NOS3) produces nitric oxide which is a mediator of cytotoxic effects potentially associated with breast cancer. We evaluated the role of genetic polymorphisms of NOS3 in breast cancer etiology, in a case-control study conducted in Korea. We recruited 1,385 eligible patients with histologically confirmed incident breast cancer cases and 968 hospital-based controls. Two potentially functional NOS3 polymorphisms in the promoter region (-786T > C) and exon 7 (894G > T, Glu298Asp) were genotyped and individual haplotypes were estimated. Odds ratios (ORs) and 95% confidential intervals (95% CIs) were calculated by unconditional logistic regression, adjusting for age, body mass index, education, family history of breast cancer in first and second degree relatives, age at first full-term pregnancy and parity. There was no overall association between the -786T > C or 894G > T genotype and breast cancer risk. However, the -786C allele was marginally associated with decreased risk for invasive breast cancer with lymph node involvement (OR = 0.76, 95% CI = 0.56-1.04). And, compared to TG-TG carriers, all other haplotype pairs were significantly associated with invasive breast cancer with lymph node involvement (OR = 0.77, 95% CI = 0.59-0.99). Our results suggest that genetic polymorphisms in NOS3 modify individual susceptibility to invasive breast cancer with lymph node involvement in Korean women.

Nitric oxide and peroxynitrite in health and disease

The discovery that mammalian cells have the ability to synthesize the free radical nitric oxide (NO) has stimulated an extraordinary impetus for scientific research in all the fields of biology and medicine. Since its early description as an endothelial-derived relaxing factor, NO has emerged as a fundamental signaling device regulating virtually every critical cellular function, as well as a potent mediator of cellular damage in a wide range of conditions. Recent evidence indicates that most of the cytotoxicity attributed to NO is rather due to peroxynitrite, produced from the diffusion-controlled reaction between NO and another free radical, the superoxide anion. Peroxynitrite interacts with lipids, DNA, and proteins via direct oxidative reactions or via indirect, radical-mediated mechanisms. These reactions trigger cellular responses ranging from subtle modulations of cell signaling to overwhelming oxidative injury, committing cells to necrosis or apoptosis. In vivo, peroxynitrite generation represents a crucial pathogenic mechanism in conditions such as stroke, myocardial infarction, chronic heart failure, diabetes, circulatory shock, chronic inflammatory diseases, cancer, and neurodegenerative disorders. Hence, novel pharmacological strategies aimed at removing peroxynitrite might represent powerful therapeutic tools in the future. Evidence supporting these novel roles of NO and peroxynitrite is presented in detail in this review.

Nitric oxide, a double edged sword in cancer biology: Searching for therapeutic opportunities

Nitric oxide (NO) is a pleiotropic molecule critical to a number of physiological and pathological processes. The last decade has witnessed major advances in dissecting NO biology and its role in cancer pathogenesis. However, the complexity of the interactions between different levels of NO and several aspects of tumor development/progression has led to apparently conflicting findings. Furthermore, both anti-NO and NO-based anticancer strategies appear effective in several preclinical models. This paradoxical dichotomy is leaving investigators with a double challenge: to determine the net impact of NO on cancer behavior and to define the therapeutic role of NO-centered anticancer strategies. Only a comprehensive and dynamic view of the cascade of molecular and cellular events underlying tumor biology and affected by NO will allow investigators to exploit the potential antitumor properties of drugs interfering with NO metabolism. Available data suggest that NO should be considered neither a universal target nor a magic bullet, but rather a signal transducer to be modulated according to the molecular makeup of each individual cancer and the interplay with conventional antineoplastic agents.

WP760, a melanoma selective drug

PURPOSE

Our goal was to perform studies on the specificity and antimelanoma mechanism of a novel bis-anthracycline, WP760. WP760 initially identified in the NCI 160 screen as anti-melanoma.

METHODS

The methyl thiazolyl tetrazolium reduction (MTT) assay was used to test tumor cell growth inhibition; confocal microscopy to view WP760 intracellular distribution; flow cytometry for cell-cycle arrest and apoptosis; and Western blotting was employed to identify and compare quantities and kinetics of cell growth related molecule levels.

RESULTS

WP760 induced G(2)/M-phase cell-cycle arrest and apoptosis in melanoma cell lines and short-term melanoma explants established from clinical specimens in a time and concentration dependent manner at nM concentrations. In contrast, effects on fibroblasts and A549 lung cancer cells required higher concentrations, suggesting that WP760 possesses selectivity for melanoma. Molecular studies indicated that WP760 induced p53 stabilization, checkpoint kinase 2 and p27(Kip1) protein upregulation, and activation of caspase-3. Endogenous nitric oxide (NO) production has been implicated in the chemoresistance of melanoma; WP760 caused inhibition of the inducible nitric oxide synthase (iNOS) protein as well as inhibition of phosphorylation of ERK, known to drive the iNOS pathway. Based on WP760 localization into mitochondria, and caspase-3 inhibitor block the killing of WP760, the intrinsic pathway of apoptosis appears to have been activated.

CONCLUSIONS

Our results indicate that WP760 affects a critical and unique set of growth regulatory effects in melanoma, and is a promising candidate for further preclinical studies.

Promoter polymorphism (-786t>C) in the endothelial nitric oxide synthase gene is associated with risk of sporadic breast cancer in non-Hispanic white women age younger than 55 years

BACKGROUND

Nitric oxide (NO) is constitutively synthesized in the endothelium by endothelial nitric oxide synthase (eNOS) and acts as a pleiotropic regulator involved in carcinogenesis. Most breast cancers develop from mammary epithelial cells; therefore, NO may play a role in their development. It was hypothesized that eNOS polymorphisms are associated with risk of breast cancer.

METHODS

In the current hospital-based case-control study of 421 non-Hispanic white women with sporadic breast cancer and 423 frequency-matched control subjects, we genotyped 3 polymorphisms of eNOS (i.e., -786T>C, the 27-base pair [bp] variable number of tandem repeats [VNTR] in intron 4, and 894G>T [Glu298Asp]) and assessed their associations with risk of breast cancer.

RESULTS

It was found that, compared with -786TT, the -786C variant genotypes were associated with a significantly increased risk of breast cancer in an allele dose-dependent manner (adjusted odds ratio [OR], 1.33 [95% confidence interval (95% CI)], 0.99-1.77 for -786TC; and OR, 1.79 [95% CI, 1.11-2.87] for -786CC; P(trend) = .007), but 27-bp VNTR and 894G>T genotypes were not. Stratification analysis demonstrated that the risk associated with -786C variant genotypes (-786TC/CC) was more pronounced in smokers and in those 50 years or older (OR, 1.82 [95% CI, 1.19-2.80] and OR, 2.08 [95% CI, 1.25-3.45], respectively), and in the estrogen and progesterone receptor-negative cases (OR, 1.70 [95% CI, 1.10-2.62] and OR, 1.57 [95% CI, 1.07-2.32], respectively). Furthermore, the C4G haplotype derived from the observed genotypes was also associated with a significantly increased risk of breast cancer (OR, 2.16; 95% CI, 1.07-4.36).

CONCLUSIONS

The results suggest that eNOS polymorphisms (especially -786T>C) may play a role in the development of sporadic breast cancer.

Nitric oxide promotes airway epithelial wound repair through enhanced activation of MMP-9

The airway epithelium provides a protective barrier against inhaled environmental toxins and microorganisms, and epithelial injury initiates a number of processes to restore its barrier integrity, including activation of matrix metalloproteinases such as MMP-9 (92-kD gelatinase B). Airway epithelial cells continuously produce nitric oxide (NO), which has been linked to cell migration and MMP-9 regulation in several cell types, but the importance of epithelial NO in mediating airway epithelial repair or MMP-9 activation is unknown. Using primary or immortalized human bronchial epithelial cells, we demonstrate that low concentrations of NO promote epithelial cell migration and wound repair in an in vitro wound assay, which was associated with increased localized expression and activation of MMP-9. In addition, in HBE1 cells that were stably transfected with inducible NOS (NOS2), to mimic constitutive epithelial NOS2 expression in vivo, NOS inhibition decreased epithelial wound repair and MMP-9 expression. The stimulatory effects of NO on epithelial wound repair and MMP-9 expression were dependent on cGMP-mediated pathways and were inhibited by 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ), an inhibitor of soluble guanylyl cyclase. Inhibition of cGMP-dependent protein kinase (PKG) attenuated NO-mediated epithelial wound closure, but did not affect MMP-9 expression. However, pharmacologic MMP inhibition and siRNA knockdown of MMP-9 expression demonstrated the contribution of MMP-9 to NO-mediated wound closure. Overall, our results demonstrate that NOS2-derived NO contributes to airway epithelial repair by both PKG-dependent and -independent mechanisms, and involves NO-dependent expression and activation of MMP-9.

uPAR expression under hypoxic conditions depends on iNOS modulated ERK phosphorylation in the MDA-MB-231 breast carcinoma cell line

Urokinase plasminogen activator receptor (uPAR) plays a major role in cancer invasion and metastasis and uPAR expression is correlated with a poor prognosis in various cancer types. Moreover, the expression of uPAR is increased under hypoxic conditions. Nitric oxide (NO) and its metabolites produced by inducible nitric oxide synthase (iNOS) are important products of hypoxic stress, and NO may activate or modulate extracellular signal regulated kinase (ERK). Here, we evaluated uPA, uPAR, and activated ERK levels under hypoxic conditions, and the modulatory effects of iNOS and NO in the MDA-MB-231 human breast cancer cell line. Cells were incubated in a hypoxic or normoxic incubator and treated with PD98059 (a MEK 1/2 inhibitor, which abrogates ERK phosphorylation) and aminoguanidine (a selective iNOS inhibitor). uPAR expression, ERK phosphorylation, and uPA activity were found to be increased under hypoxic conditions. Moreover, when cells were treated with PD98059 under hypoxic conditions, uPAR was downregulated, whereas aminoguanidine markedly increased ERK phosphorylation in a dose dependent manner. Furthermore, aminoguanidine increased uPAR expression and prevented the inhibition of uPAR expression by PD98059. These results demonstrated that uPAR is induced by hypoxia and that increased uPAR expression is mediated by ERK phosphorylation, which in turn is modulated by iNOS/NO in MDA-MB-231 cells. We conclude that iNOS/NO downregulates the expression of uPAR under hypoxic conditions via ERK pathway modulation.

Genetic polymorphisms of eNOS, hormone receptor status, and survival of breast cancer

The endothelial cell-specific form of nitric oxide synthase (eNOS) may play an important role in tumor progression via angiogenesis or apoptosis. We studied eNOS -786T > C and 894G > T (Glu298Asp), two functionally significant SNPs, in relation to hazard of breast cancer recurrence or death in 873 women with incident, non-metastatic breast cancer, recruited from two teaching hospitals in Seoul, Korea, 1995-2002. Hazards were estimated by Cox proportional hazard models, in relation to genotype, adjusting for hormone receptor status, lymph node involvement, and tumor size. Women carriers of the eNOS -786C allele had significantly increased hazards of breast cancer recurrence or death, compared with women having the TT genotype (HR = 2.1, 95% CI = 1.03-4.33); risks increased up to 3-fold in ER positive cases (HR = 3.2, 95% CI = 0.95-10.50). The hazard was also increased in eNOS 894T carriers, however, it did not reach statistical significance (HR = 1.8, 95% CI = 0.85-3.93). The combined genotypes containing -786C or 894T was associated with a 2.5-fold risk, compared to the TT-GG genotypes, the most dominant genotype combination (95% CI = 1.29-4.68), with the greatest risks in ER positive cases (HR = 4.9, 95% CI = 1.31-18.36). These results indicate that the eNOS -786C polymorphism, and possibly the 894T polymorphism, are associated with breast cancer recurrence and death, particularly in women with ER positive tumors.

The role of nitric oxide in tumour progression

Nitric oxide (NO) and nitric oxide synthases are ubiquitous in malignant tumours and are known to exert both pro- and anti-tumour effects. We summarize our current understanding of the role of NO in tumour progression, especially in relation to angiogenesis and vascular functions. We also discuss potential strategies for cancer treatment that modulate NO production and/or its downstream signalling pathways.

The biphasic nature of nitric oxide responses in tumor biology

The dual or biphasic responses of cancer to nitric oxide (NO) arise from its concentration dependent ability to regulate tumor growth, migration, invasion, survival, angiogenesis, and metastasis. The outcome of these various NO-dependent processes is dictated by several factors including NO flux, the chemical redox environment, and the duration of NO exposure. Further, it was recently discovered that an NO-induced redox flux in vascular endothelial cells hypersensitizes these cells to the antiangiogenic effects of thrombospondin-1. This suggests a novel treatment paradigm for targeting tumor-driven angiogenesis that combines redox modulation with mimetic derivatives of thrombospondin-1. This article discusses the biphasic nature of NO in cancer biology and the implications of NO-driven redox flux for modulation of tumor-stimulated angiogenesis, growth, and metastasis.

Nitric oxide and hormones in breast cancer: allies or enemies?

Unlike other types of cancer, tumors of the breast are greatly influenced by steroid hormones. The effect of estrogen and progesterone depends on the presence of their specific receptors and these constitute important parameters in determining the aggressiveness of the tumor, the feasibility of certain therapies and the prediction of relapse. The molecular mechanisms of steroid hormone action have not been fully elucidated but recent findings implicate the nitric oxide (NO) pathway in some of these effects. Both hormones can regulate the nitric oxide synthases (NOS) and, in turn, the NO produced has profound consequences on tumor cell homeostasis. On one hand, estrogen increases the activity of endothelial NOS (eNOS or NOSIII), while progesterone activates inducible NOS (iNOS or NOSII) expression. The data presented suggest that the low levels of NO produced by NOSIII mediate the proliferative effect of estrogen. On the other hand, the increase in apoptosis in response to progesterone could implicate the high levels of NO produced by induction of NOSII expression. Understanding of the mechanisms and interactions of steroid hormones with the NO pathway could lead to the development of new approaches and strategies for the effective treatment of breast cancer.

Regulation of p53 and suppression of apoptosis by the soluble guanylyl cyclase/cGMP pathway in human ovarian cancer cells

Dysregulated apoptosis plays a critical role in the development of a number of aberrant cellular processes, including tumorigenesis and chemoresistance. However, the mechanisms that govern the normal apoptotic program are not completely understood. Soluble guanylyl cyclase (sGC) and cyclic guanosine monophosphate (cGMP) promote mammalian cell viability via an unknown mechanism and p53 status is a key determinant of cell fate in human ovarian cancer cells. Whether an interaction exists between these two determinants of cell fate is unknown. We hypothesized that basal sGC activity reduces p53 content and attenuates p53-dependent apoptosis in human ovarian cancer cells. Suppression of sGC activity with the specific inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) lowered cGMP content, and increased p53 protein content and induced apoptosis in three ovarian cancer cell lines, effects which were attenuated by the cGMP analog 8-Br-cGMP and by Atrial Natriuretic Factor, an activator of particulate guanylyl cyclase, which circumvent the inhibition of sGC. ODQ prolonged p53 half-life, induced phosphorylation of p53 on Ser15, and upregulated the p53-dependent gene products p21, murine double minute-2, and the proapoptotic, p53-responsive gene product Bax. ODQ activated caspase-3, and ODQ-induced apoptosis was inhibited by overexpression of X-linked inhibitor of apoptosis Protein. Pretreatment with the specific p53 inhibitor pifithrin or downregulation of p53 using a specific small inhibitory RNA significantly attenuated ODQ-induced apoptosis. Moreover, ODQ-induced upregulation of p21 and Bax and ODQ-induced apoptosis were significantly reduced in a p53 mutant cell line relative to the wild-type parental cell line. Thus, the current study establishes that basal sGC/cGMP activity regulates p53 protein stability, content, and function, possibly by altering p53 phosphorylation and stabilization, and promotes cell survival in part through regulation of caspase-3 and p53.

Polymorphisms of the endothelial nitric oxide synthase gene in breast cancer

Nitric oxide (NO) is known to be critically involved in breast carcinogenesis. Genetic polymorphisms of the gene encoding for endothelial nitric oxide synthase (Nos3), the enzyme catalyzing the production of the NO, are known to predispose to malignant disease. Whether these polymorphisms also influence breast cancer risk is unknown. In the present case-control study, we ascertained 2 polymorphisms of the Nos3 gene cluster (Nos3 exon 7 Glu298Asp and a 27-base pair repeat in intron 4 of Nos3) in 269 Caucasian patients with breast cancer and 244 healthy controls using pyrosequencing and PCR, respectively. Presence of the exon 7 Nos3 polymorphism predisposed women to breast cancer (p=0.03, Odds ratio [95% Confidence Intervals]=1.9 [1.1-3.6]), but was not associated with any clinico-pathological parameters. No significant associations were ascertained with respect to the intron 4 Nos3 polymorphism. In our series, presence of the mutant exon7 Nos3 polymorphism was associated with an increased risk for breast cancer in Caucasian women.

Endothelial nitric oxide synthase is segregated from caveolin-1 and localizes to the leading edge of migrating cells

The enzyme endothelial Nitric Oxide Synthase (eNOS) is involved in key physiological and pathological processes, including cell motility and apoptosis. It is widely believed that at the cell surface eNOS is localized in caveolae, where caveolin-1 negatively regulates its activity, however, there are still uncertainties on its intracellular distribution. Here, we applied high resolution confocal microscopy to investigate the surface distribution of eNOS in transfected HeLa cells and in human umbilical vein endothelial cells (HUVEC) endogenously expressing the enzyme. In confluent and non-confluent HUVEC and HeLa cells, we failed to detect substantial colocalization between eNOS and caveolin-1 at the cell surface. Instead, in non-confluent cells, eNOS was concentrated in ruffles and at the leading edge of migrating cells, colocalizing with actin filaments and with the raft marker ganglioside G(M1), and well segregated from caveolin-1, which was restricted to the posterior region of the cells. Treatments that disrupted microfilaments caused loss of eNOS from the cell surface and decreased Ca(2+)-stimulated activity, suggesting a role of the cytoskeleton in the localization and function of the enzyme. Our results provide a morphological correlate for the role of eNOS in cell migration and raise questions on the site of interaction between eNOS and caveolin-1.

Nitric oxide and metastatic cell behaviour

Nitric oxide (NO) is a pleiotropic signalling molecule that subserves a wide variety of basic cellular functions and also manifests itself pathophysiologically. As regards cancer and its progression, however, the reported role of NO appears surprisingly inconsistent. In this review, we focus on metastasis, the process of cancer cell spread and secondary tumour formation. In a 'reductionist' approach, we consider the metastatic cascade to be made up of a series of basic cellular behaviours (such as proliferation, apoptosis, adhesion, secretion migration, invasion and angiogenesis). We evaluate how NO controls such behaviours, in comparison with normal cells. The available information suggests strongly that NO signalling would be expected to regulate these behaviours both positively and negatively and this probably leads to the observed apparent variability in the NO status of cancer cells and tissues. Thus, the role of NO in cancer is more complex than previously thought. A number of suggestions are made, including consideration of novel mechanisms, such as ion channels, in order to achieve a more consistent and integrated understanding of NO signalling in cancer and to realise its clinical potential.

Nitrative and oxidative DNA damage in intrahepatic cholangiocarcinoma patients in relation to tumor invasion

AIM: Nitrative and oxidative DNA damage such as 8-nitroguanine and 8-oxo-7,8-dihydro-2’-deoxyguanosine (8-oxodG) formation has been implicated in initiation and/ or promotion of inflammation-mediated carcinogenesis. The aim of this study is to clarify whether these DNA lesions participate in the progression of intrahepatic cholangiocarcinoma.

METHODS: We investigated the relation of the formation of 8-nitroguanine and 8-oxodG and the expression of hypoxia-inducible factor-1α (HIF-1α) with tumor invasion in 37 patients with intra-hepatic cholangiocarcinoma.

RESULTS: Immunohistochemical analyses revealed that 8-nitroguanine and 8-oxodG formation occurred to a much greater extent in cancerous tissues than in non-cancerous tissues. HIF-1α could be detected in cancerous tissues in all patients, suggesting low oxygen tension in the tumors. HIF-1α expression was correlated with inducible nitric oxide synthase (iNOS) expression (r = 0.369 and P = 0.025) and 8-oxodG formation (r = 0.398 and P = 0.015). Double immunofluorescence study revealed that iNOS and HIF-1α co-localized in cancerous tissues. Notably, the formation of 8-oxodG was correlated significantly with lymphatic invasion (r = 0.386 and P = 0.018). Moreover, 8-nitroguanine and 8-oxodG in non-cancerous tissues were associated significantly with neural invasion (P = 0.042 and P = 0.026, respectively). These results suggest that reciprocal activation between HIF-1α and iNOS mediates persistent DNA damage, which induces tumor invasiveness via mutations, resulting in poor prognosis.

CONCLUSION: The formation of 8-nitroguanine and 8-oxodG plays an important role in multiple steps of genetic changes leading to tumor progression, including invasiveness.

Arginine and cancer

Arginine is a dibasic, cationic, semiessential amino acid with numerous roles in cellular metabolism. It serves as an intermediate in the urea cycle and as a precursor for protein, polyamine, creatine and nitric oxide (NO) biosynthesis. Arginine is conditionally essential since it becomes necessary under periods of growth and after recovery after injury. Arginine also promotes wound healing and functions as a secretagogue stimulating the release of growth hormone, insulin-like growth factor 1, insulin, and prolactin. Furthermore, arginine has several immunomodulatory effects such as stimulating T- and natural killer cell activity and influencing pro-inflammatory cytokine levels. The discover that l-arginine is the sole precursor for the multifunctional messenger molecule nitric oxide (NO) led to investigation into the role of arginine in numerous physiologic and pathophysiologic phenomena including cancer. Although NO was first identified in endothelial cells, it is now recognized to be generated by a variety of cell types, including several tumor cell lines and solid human tumors. Unfortunately, the precise role of NO in cancer is poorly understood but it may influence tumor initiation, promotion, and progression, tumor-cell adhesion, apoptosis angiogenesis, differentiation, chemosensitivity, radiosensitivity, and tumor-induced immunosuppression. The biological effects of NO are complex and dependent upon numerous regulatory factors. Further research is necessary to enhance our understanding of the complex mechanisms that regulate NO's role in tumor biology. A better understanding of the role of arginine-derived NO in cancer may lead to novel antineoplastic and chemopreventative strategies.

Hypoxic inducible factor 1alpha, extracellular signal-regulated kinase, and p53 are regulated by distinct threshold concentrations of nitric oxide

NO produced in tumors can either positively or negatively regulate growth. To examine this dichotomy, effects of NO concentration and duration on the posttranslational regulation of several key proteins were examined in human breast MCF7 cells under aerobic conditions. We found that different concentration thresholds of NO appear to elicit a discrete set of signal transduction pathways. At low steady-state concentrations of NO (<50 nM), extracellular signal-regulated kinase (ERK) phosphorylation was induced via a guanylate cyclase-dependent mechanism. Hypoxic inducible factor 1alpha (HIF-1alpha) accumulation was associated with an intermediate amount of NO (>100 nM), whereas p53 serine 15 phosphorylation occurred at considerably higher levels (>300 nM). ERK phosphorylation was transient during NO exposure. HIF-1alpha stabilization paralleled the presence of NO, whereas p53 serine 15 phosphorylation was detected during, and persisted after, NO exposure. The dose-dependent effects of synthetic NO donors were mimicked by activated macrophages cocultured with MCF7 cells at varying ratios. ERK and HIF-1alpha activation was similar in breast cancer cell lines either mutant (MB231) or null (MB157) in p53. The stabilization of HIF-1alpha by NO was not observed with increased MCF7 cell density, demonstrating the interrelationship between NO and O(2) consumption. The findings show that concentration and duration of NO exposure are critical determinants in the regulation of tumor-related proteins.