In oesophageal squamous cells, nitric oxide causes S-nitrosylation of Akt and blocks SOX2 (sex determining region Y-box 2) expression

Etiologic factors for Barrett's esophagus: toward countermeasures in Asia

INTRODUCTION

Over the past several decades, Europe and the United States have experienced a rapid increase in esophageal adenocarcinoma. Research and countermeasures against Barrett's esophagus, its precancerous lesion, are progressing. Because esophageal adenocarcinoma has an extremely poor prognosis when diagnosed in an advanced stage, recommendations for early cancer detection have been made based on the various proven etiological factors of Barrett's esophagus and the actual cancer risk of Barrett's esophagus. In recent years, there have been indications of an increase in esophageal adenocarcinoma in Japan, and a similar trend of cancer will occur shortly in other Asian countries. Consequently, Asian countries must implement similar countermeasures against Barrett's esophagus and esophageal adenocarcinoma, referencing the knowledge gained thus far in Europe and the United States.

AREAS COVERED

This review summarizes the latest findings on the etiologic factors of Barrett's esophagus and discusses the differences between Westerners and Asians. The current status of Barrett's esophagus in Japan and other Asian countries is also summarized.

EXPERT OPINION

The etiological factors and cancer incidence of Barrett's esophagus in Asia diverge somewhat from those observed in Europe and America. Therefore, it is imperative to implement measures that are tailored to the actual circumstances of Asian people.

Promises and Limitations of Current Models for Understanding Barrett's Esophagus and Esophageal Adenocarcinoma

BACKGROUND & AIMS

This review was developed to provide a thorough and effective update on models relevant to esophageal metaplasia, dysplasia, and carcinogenesis, focusing on the advantages and limitations of different models of Barrett's esophagus (BE) and esophageal adenocarcinoma (EAC).

METHODS

This expert review was written on the basis of a thorough review of the literature combined with expert interpretation of the state of the field. We emphasized advances over the years 2012-2023 and provided detailed information related to the characterization of established human esophageal cell lines.

RESULTS

New insights have been gained into the pathogenesis of BE and EAC using patient-derived samples and single-cell approaches. Relevant animal models include genetic as well as surgical mouse models and emphasize the development of lesions at the squamocolumnar junction in the mouse stomach. Rat models are generated using surgical approaches that directly connect the small intestine and esophagus. Large animal models have the advantage of including features in human esophagus such as esophageal submucosal glands. Alternatively, cell culture approaches remain important in the field and allow for personalized approaches, and scientific rigor can be ensured by authentication of cell lines.

CONCLUSIONS

Research in BE and EAC remains highly relevant given the morbidity and mortality associated with cancers of the tubular esophagus and gastroesophageal junction. Careful selection of models and inclusion of human samples whenever possible will ensure relevance to human health and disease.

Mechanisms and pathophysiology of Barrett oesophagus

Barrett oesophagus, in which a metaplastic columnar mucosa that can predispose individuals to cancer development lines a portion of the distal oesophagus, is the only known precursor of oesophageal adenocarcinoma, the incidence of which has increased profoundly over the past several decades. Most evidence suggests that Barrett oesophagus develops from progenitor cells at the oesophagogastric junction that proliferate and undergo epithelial-mesenchymal transition as part of a wound-healing process that replaces oesophageal squamous epithelium damaged by gastroesophageal reflux disease (GERD). GERD also seems to induce reprogramming of key transcription factors in the progenitor cells, resulting in the development of the specialized intestinal metaplasia that is characteristic of Barrett oesophagus, probably through an intermediate step of metaplasia to cardiac mucosa. Genome-wide association studies suggest that patients with GERD who develop Barrett oesophagus might have an inherited predisposition to oesophageal metaplasia and that there is a shared genetic susceptibility to Barrett oesophagus and to several of its risk factors (such as GERD, obesity and cigarette smoking). In this Review, we discuss the mechanisms, pathophysiology, genetic predisposition and cells of origin of Barrett oesophagus, and opine on the clinical implications and future research directions.

Kyoto international consensus report on anatomy, pathophysiology and clinical significance of the gastro-oesophageal junction

OBJECTIVE

An international meeting was organised to develop consensus on (1) the landmarks to define the gastro-oesophageal junction (GOJ), (2) the occurrence and pathophysiological significance of the cardiac gland, (3) the definition of the gastro-oesophageal junctional zone (GOJZ) and (4) the causes of inflammation, metaplasia and neoplasia occurring in the GOJZ.

DESIGN

Clinical questions relevant to the afore-mentioned major issues were drafted for which expert panels formulated relevant statements and textural explanations.A Delphi method using an anonymous system was employed to develop the consensus, the level of which was predefined as ≥80% of agreement. Two rounds of voting and amendments were completed before the meeting at which clinical questions and consensus were finalised.

RESULTS

Twenty eight clinical questions and statements were finalised after extensive amendments. Critical consensus was achieved: (1) definition for the GOJ, (2) definition of the GOJZ spanning 1 cm proximal and distal to the GOJ as defined by the end of palisade vessels was accepted based on the anatomical distribution of cardiac type gland, (3) chemical and bacterial (Helicobacter pylori) factors as the primary causes of inflammation, metaplasia and neoplasia occurring in the GOJZ, (4) a new definition of Barrett's oesophagus (BO).

CONCLUSIONS

This international consensus on the new definitions of BO, GOJ and the GOJZ will be instrumental in future studies aiming to resolve many issues on this important anatomic area and hopefully will lead to better classification and management of the diseases surrounding the GOJ.

The Immune Underpinnings of Barrett's-Associated Adenocarcinogenesis: a Retrial of Nefarious Immunologic Co-Conspirators

There is no doubt that chronic gastroesophageal reflux disease increases the risk of esophageal adenocarcinoma (EAC) by several fold (odds ratio, 6.4; 95% CI, 4.6-9.1), and some relationships between reflux disease-mediated inflammation and oncogenic processes have been explored; however, the precise interconnections between the immune response and genomic instabilities underlying these pathologic processes only now are emerging. Furthermore, the precise cell of origin of the precancerous stages associated with EAC development, Barrett's esophagus, be it cardia resident or embryonic remnant, may shape our interpretation of the likely immune drivers. This review integrates the current collective knowledge of the immunology underlying EAC development and outlines a framework connecting proinflammatory pathways, such as those mediated by interleukin 1β, tumor necrosis factor α, leukemia inhibitory factor, interleukin 6, signal transduction and activator of transcription 3, nuclear factor-κB, cyclooxygenase-2, and transforming growth factor β, with oncogenic pathways in the gastroesophageal reflux disease-Barrett's esophagus-EAC cancer sequence. Further defining these immune and molecular railroads may show a map of the routes taken by gastroesophageal cells on their journey toward EAC tumor phylogeny. The selective pressures applied by this immune-induced journey likely impact the phenotype and genotype of the resulting oncogenic destination and further exploration of lesser-defined immune drivers may be useful in future individualized therapies or enhanced selective application of recent immune-driven therapeutics.

Nitric oxide could promote development of Barrett's esophagus by S-nitrosylation-induced inhibition of Rho-ROCK signaling in esophageal fibroblasts

Barrett's esophagus arises in the process of wound healing in distal esophageal epithelium damaged by gastroesophageal reflux disease. Differentiation of fibroblast into myofibroblasts, a smooth muscle cell-like phenotype and tissue contraction are crucial processes in wound healing. No study has evaluated mechanism by which luminal esophageal nitric oxide (NO) affect Rho-associated coiled coil-forming protein kinase (Rho-ROCK) signaling pathway, a key factor of tissue contraction, in stromal fibroblasts to develop Barrett's esophagus. Using esophageal fibroblasts, we performed collagen-based cell contraction assays and evaluated influence of Rho-ROCK signaling in the exposure to acidic bile salts and NOC-9, which is an NO donor. We found that enhanced cell contraction induced by acidic bile salts was inhibited by NO, accompanied by decrease in phosphorylated myosin light chain expression and stress fiber formation. NO directly S-nitrosylated GTP-RhoA and consequently blocked Rho-ROCK signaling. Moreover, exposure to NO and Y27632, a Rho-ROCK signaling inhibitor, decreased α-SMA expression and increased bone morphogenetic protein-4 (BMP4) expression and secretion. These findings could account for the increased expression of BMP4 in the columnar epithelial cells and stromal fibroblasts in human Barrett's esophagus. NO could impair wound contraction by blocking the Rho-ROCK signaling pathway and promote the development of Barrett's esophagus.NEW & NOTEWORTHY Barrett's esophagus is the condition where esophageal epithelium damaged by gastroesophageal reflux disease (GERD) is abnormally healed via replacing of metaplastic columnar epithelium, but very few studies have conducted focusing wound healing in the development of Barrett's esophagus. Esophageal luminal nitric oxide inhibits Rho-ROCK signaling pathway in esophageal fibroblasts, which leads to delay tissue contraction, a pivotal step in proper wound healing. Moreover, this inhibition increases tissue BMP4 expression. Impaired wound healing could be related to Barrett's esophagus.

Pillars and Gaps of S-Nitrosylation-Dependent Epigenetic Regulation in Physiology and Cancer

Nitric oxide (NO) is a diffusible signaling molecule produced by three isoforms of nitric oxide synthase, which release NO during the metabolism of the amino acid arginine. NO participates in pathophysiological responses of many different tissues, inducing concentration-dependent effect. Indeed, while low NO levels generally have protective effects, higher NO concentrations induce cytotoxic/cytostatic actions. In recent years, evidences have been accumulated unveiling S-nitrosylation as a major NO-dependent post-translational mechanism ruling gene expression. S-nitrosylation is a reversible, highly regulated phenomenon in which NO reacts with one or few specific cysteine residues of target proteins generating S-nitrosothiols. By inducing this chemical modification, NO might exert epigenetic regulation through direct effects on both DNA and histones as well as through indirect actions affecting the functions of transcription factors and transcriptional co-regulators. In this light, S-nitrosylation may also impact on cancer cell gene expression programs. Indeed, it affects different cell pathways and functions ranging from the impairment of DNA damage repair to the modulation of the activity of signal transduction molecules, oncogenes, tumor suppressors, and chromatin remodelers. Nitrosylation is therefore a versatile tool by which NO might control gene expression programs in health and disease.

Resolvin D1 attenuates acid-induced DNA damage in esophageal epithelial cells and rat models of acid reflux

The role of resolvin D1 (RvD1) in gastroesophageal reflux disease (GERD) remains largely unknown. Here, we investigated the potential role of RvD1 in acid-induced DNA damage in esophageal epithelial cells, patients with refractory GERD and a rat model of acid reflux. Weak acid exposure induced longer comet tails, reactive oxygen species (ROS) generation, oxidative DNA damage and DNA double-strand breaks (DSBs) in cells and RvD1 (0.1 μM) blocked all these effects. Mechanistic analyses showed that apart from ROS-reducing effects, RvD1 possessed a strong capacity to promote DNA damage repair, augmenting cell cycle checkpoint activity and DSB repair by modulating phosphatase and tensin homolog (PTEN) in cells. We also detected the surface expression of formyl peptide receptor 2 (FPR2), a receptor for RvD1, in the esophageal epithelial cells, and inhibition of FPR2 abrogated the protective effects of RvD1 on cells. Furthermore, a positive correlation between RvD1 and PTEN was observed predominantly in the esophageal epithelium from patients with refractory GERD (r = 0.67, P < 0.05). Additionally, RvD1 administration upregulated PTEN, suppressed DNA DSBs and alleviated microscopic damage in the rat model of gastric reflux. FPR2 gene silencing abolished the therapeutic effects of RvD1 on the rat model. Taken together, RvD1 binding to FPR2 protects the esophageal epithelium from acid reflux-induced DNA damage via a mechanism involving the inhibition of ROS production and facilitation of DSB repair. These findings support RvD1 as a promising approach that may be valuable for the treatment of GERD.

GATA4 blocks squamous epithelial cell gene expression in human esophageal squamous cells

GATA4 promotes columnar epithelial cell fate during gastric development. When ectopically expressed in the developing mouse forestomach, the tissue emerges as columnar-like rather than stratified squamous with gene expression changes that parallel those observed in the pre-malignant squamous to columnar metaplasia known as Barrett's esophagus (BE). GATA4 mRNA up-regulation and gene amplification occur in BE and its associated cancer, esophageal adenocarcinoma (EAC), and GATA4 gene amplification correlates with poor patient outcomes. Here, we explored the effect of ectopic expression of GATA4 in mature human esophageal squamous epithelial cells. We found that GATA4 expression in esophageal squamous epithelial cells compromised squamous cell marker gene expression and up-regulated expression of the canonical columnar cell cytokeratin KRT8. We observed GATA4 occupancy in the p63, KRT5, and KRT15 promoters, suggesting that GATA4 directly represses expression of squamous epithelial cell marker genes. Finally, we verified GATA4 protein expression in BE and EAC and found that exposure of esophageal squamous epithelial cells to acid and bile, known BE risk factors, induced GATA4 mRNA expression. We conclude that GATA4 suppresses expression of genes marking the stratified squamous epithelial cell lineage and that this repressive action by GATA4 may have implications in BE and EAC.

Recent insights into the biology of Barrett's esophagus

Barrett's esophagus (BE) is the only known precursor to esophageal adenocarcinoma (EAC), an aggressive cancer with a poor prognosis. Our understanding of the pathogenesis and Barrett's metaplasia is incomplete, and this has limited the development of new therapeutic targets and agents, risk stratification ability, and management strategies. This review outlines current insights into the biology of BE and addresses controversies surrounding cell of origin, cellular reprogramming theories, updates on esophageal epithelial barrier function, and the significance of goblet cell metaplasia and its association with malignant change. Further research into the basic biology of BE is vital as it will underpin novel therapies and improve our ability to predict malignant progression and help identify the minority of patients who will develop EAC.

SOX2 protein biochemistry in stemness, reprogramming, and cancer: the PI3K/AKT/SOX2 axis and beyond

Research of the past view years expanded our understanding of the various physiological functions the cell-fate determining transcription factor SOX2 exerts in ontogenesis, reprogramming, and cancer. However, while scientific reports featuring novel and exciting aspects of SOX2-driven biology are published in near weekly routine, investigations in the underlying protein-biochemical processes that transiently tailor SOX2 activity to situational demand are underrepresented and have not yet been comprehensively summarized. Largely unrecognizable to modern array or sequencing-based technology, various protein secondary modifications and concomitant function modulations have been reported for SOX2. The chemical modifications imposed onto SOX2 are inherently heterogeneous, comprising singular or clustered events of phosphorylation, methylation, acetylation, ubiquitination, SUMOylation, PARPylation, and O-glycosylation that reciprocally affect each other and critically impact SOX2 functionality, often in a tissue and species-specific manner. One recurring regulatory principle though is the canonical PI3K/AKT signaling axis to which SOX2 relates in various entangled, albeit not exclusive ways. Here we provide a comprehensive review of the current knowledge on SOX2 protein modifications, their proposed relationship to the PI3K/AKT pathway, and regulatory influence on SOX2 with regards to stemness, reprogramming, and cancer.

Short-term aromatase inhibition induces prostatic alterations in adult wistar rat: A biochemical, histopathological and immunohistochemical study

PURPOSE

This study aimed to evaluate the effects of estrogen reduction on amyloid deposition, some lipid metabolism and oxidative stress markers, PSA-like production and p63 expression in the prostate of the adult rat.

METHODS

Aromatase inhibitor: Formestane (4-OHA), was administrated to male rats, at a dose of 0.1 mg/kg b.w./day, for 10 days. The control group (CONT) received the same volume of placebo injection (NaCl 0.9%).

RESULTS

4-OHA treatment induced a significant accumulation of intraprostatic cholesterol (138.90 ± 17.64 vs 85.12 ± 2.87, p = 0.01); against an insignificant diminution of malondialdehyde (412.6 ± 54.35 vs 842.70 ± 336.50, p > 0.05) and glutathione (2.40 ± 0.23 vs 3.65 ± 0.88, p > 0.05). This was associated with a significant decrease of nitric oxide (31.76 ± 7.07 vs 179.40 ± 58.35, p = 0.024). Additionally, 4-OHA significantly increased the intraprostatic production of PSA-like (11.12 ± 2.78 vs 3.91 ± 0.43, p = 0.043). The prostatic histology revealed an amyloid deposition, in all prostatic lobes and a smooth muscle layer growth (p < 0.05); especially significant in the dorsal and lateral lobes. Theses lobes manifested a basal cells proliferation, with a 3-fold increase of p63 expression (p < 0.001). The ventral lobe presented epithelial atrophy (37.80 ± 16.20 vs 167.60 ± 5.16, p < 0.05); with occasional and significant proliferative foci (247.00 ± 9.573 vs 167.60 ± 5.16 p < 0.05).

DISCUSSION AND CONCLUSION

Aromatase inhibition, in the adult male rat, alters the prostatic function by reducing nitric oxide availability and inducing amyloid deposition along with limiting the differentiation of basal cells, through a lobe-specific p63-overexpression.

Pathogenesis and Cells of Origin of Barrett's Esophagus

In patients with Barrett's esophagus (BE), metaplastic columnar mucosa containing epithelial cells with gastric and intestinal features replaces esophageal squamous mucosa damaged by gastroesophageal reflux disease. This condition is estimated to affect 5.6% of adults in the United States, and is a major risk factor for esophageal adenocarcinoma. Despite the prevalence and importance of BE, its pathogenesis is incompletely understood and there are disagreements over the cells of origin. We review mechanisms of BE pathogenesis, including transdifferentiation and transcommitment, and discuss potential cells of origin, including basal cells of the squamous epithelium, cells of esophageal submucosal glands and their ducts, cells of the proximal stomach, and specialized populations of cells at the esophagogastric junction (residual embryonic cells and transitional basal cells). We discuss the concept of metaplasia as a wound-healing response, and how cardiac mucosa might be the precursor of the intestinal metaplasia of BE. Finally, we discuss shortcomings in current diagnostic criteria for BE that have important clinical implications.

Guts and Gall: Bile Acids in Regulation of Intestinal Epithelial Function in Health and Disease

Epithelial cells line the entire surface of the gastrointestinal tract and its accessory organs where they primarily function in transporting digestive enzymes, nutrients, electrolytes, and fluid to and from the luminal contents. At the same time, epithelial cells are responsible for forming a physical and biochemical barrier that prevents the entry into the body of harmful agents, such as bacteria and their toxins. Dysregulation of epithelial transport and barrier function is associated with the pathogenesis of a number of conditions throughout the intestine, such as inflammatory bowel disease, chronic diarrhea, pancreatitis, reflux esophagitis, and cancer. Driven by discovery of specific receptors on intestinal epithelial cells, new insights into mechanisms that control their synthesis and enterohepatic circulation, and a growing appreciation of their roles as bioactive bacterial metabolites, bile acids are currently receiving a great deal of interest as critical regulators of epithelial function in health and disease. This review aims to summarize recent advances in this field and to highlight how bile acids are now emerging as exciting new targets for disease intervention.

GSNOR modulates hyperhomocysteinemia-induced T cell activation and atherosclerosis by switching Akt S-nitrosylation to phosphorylation

The adaptive immune system plays a critical role in hyperhomocysteinemia (HHcy)-accelerated atherosclerosis. Recent studies suggest that HHcy aggravates atherosclerosis with elevated oxidative stress and reduced S-nitrosylation level of redox-sensitive protein residues in the vasculature. However, whether and how S-nitrosylation contributes to T-cell-driven atherosclerosis remain unclear. In the present study, we report that HHcy reduced the level of protein S-nitrosylation in T cells by inducing S-nitrosoglutathione reductase (GSNOR), the key denitrosylase that catalyzes S-nitrosoglutathione (GSNO), which is the main restored form of nitric oxide in vivo. Consequently, secretion of inflammatory cytokines [interferon-γ (IFN-γ) and interleukin-2] and proliferation of T cells were increased. GSNOR knockout or GSNO stimulation rectified HHcy-induced inflammatory cytokine secretion and T-cell proliferation. Site-directed mutagenesis of Akt at Cys224 revealed that S-nitrosylation at this site was pivotal for the reduced phosphorylation at Akt Ser473, which led to impaired Akt signaling. Furthermore, on HHcy challenge, as compared with GSNOR^+/+ApoE^-/- littermate controls, GSNOR^-/-ApoE^-/- double knockout mice showed reduced T-cell activation with concurrent reduction of atherosclerosis. Adoptive transfer of GSNOR^-/- T cells to ApoE^-/- mice fed homocysteine (Hcy) decreased atherosclerosis, with fewer infiltrated T cells and macrophages in plaques. In patients with HHcy and coronary artery disease, the level of plasma Hcy was positively correlated with Gsnor expression in peripheral blood mononuclear cells and IFN-γ⁺ T cells but inversely correlated with the S-nitrosylation level in T cells. These data reveal that T cells are activated, in part via GSNOR-dependent Akt denitrosylation during HHcy-induced atherosclerosis. Thus, suppression of GSNOR in T cells may reduce the risk of atherosclerosis.

Aspirin prevents NF-κB activation and CDX2 expression stimulated by acid and bile salts in oesophageal squamous cells of patients with Barrett's oesophagus

OBJECTIVE

In previous studies using oesophageal squamous cells from patients with Barrett's oesophagus (normal oesophageal squamous (NES)-B cells) and from patients without Barrett's oesophagus (NES-G cells), we showed that acid and bile salts induced caudal-related homeobox transcription factor 2 (CDX2) expression only in NES-B cells. CDX2, a transcription factor required to form intestinal epithelium, is a target of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signalling, which can be inhibited by aspirin. We explored mechanisms underlying differences between NES-B and NES-G cells in CDX2 expression and effects of aspirin on that CDX2 expression.

DESIGN

We exposed NES-B and NES-G cells to acid and bile salts, with and without aspirin, and evaluated effects on IκB-NF-κB-PKAc complex activation, p65 NF-κB subunit function, and CDX2 expression.

RESULTS

In both NES-B and NES-G cells, acid and bile salts activated nicotinamide adenine dinucleotide phosphate oxidase to generate H₂O₂, which activated the IκB-NF-κB-PKAc complex. NES-B cells exhibited higher levels of phosphorylated IκB and p65 and greater NF-κB transcriptional activity than NES-G cells, indicating greater IκB-NF-κB-PKAc complex activation by acid and bile salts in NES-B cells, and p65 siRNA prevented their increased expression of CDX2. Aspirin blocked IκB phosphorylation, p65 nuclear translocation, CDX2 promoter activation and CDX2 expression induced by acid and bile salts in NES-B cells.

CONCLUSIONS

Differences between NES-B and NES-G cells in NF-κB activation by acid and bile salts can account for their differences in CDX2 expression, and their CDX2 expression can be blocked by aspirin. These findings might explain why some patients with GORD develop Barrett's oesophagus while others do not, and why aspirin might protect against development of Barrett's oesophagus.

Reflux esophagitis and its role in the pathogenesis of Barrett's metaplasia

Reflux esophagitis damages the squamous epithelium that normally lines the esophagus, and promotes replacement of the damaged squamous lining by the intestinal metaplasia of Barrett's esophagus, the precursor of esophageal adenocarcinoma. Therefore, to prevent the development of Barrett's metaplasia and esophageal adenocarcinoma, the pathogenesis of reflux esophagitis must be understood. We have reported that reflux esophagitis, both in a rat model and in humans, develops as a cytokine-mediated inflammatory injury (i.e., cytokine sizzle), not as a caustic chemical injury (i.e., acid burn), as traditionally has been assumed. Moreover, reflux induces activation of hypoxia inducible factor (HIF)-2α, which enhances the transcriptional activity of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) causing increases in pro-inflammatory cytokines and in migration of T lymphocytes, an underlying molecular mechanism for this cytokine-mediated injury. In some individuals, reflux esophagitis heals with Barrett's metaplasia. A number of possibilities exist for the origin of the progenitor cells that give rise to this intestinal metaplasia including those of the esophagus, the proximal stomach, or the bone marrow. However, intestinal cells are not normally found in the esophagus, the stomach, or the bone marrow. Thus, the development of Barrett's intestinal metaplasia must involve some molecular reprogramming of key developmental transcription factors within the progenitor cell, a process termed transcommitment, which may be initiated by the noxious components of the gastric refluxate. This review will highlight recent studies on the pathogenesis of reflux esophagitis and on reflux-related molecular reprogramming of esophageal squamous epithelial cells in the pathogenesis of Barrett's metaplasia.

[NO and cancer: itinerary of a double agent]

Protein S-nitrosylation is now recognized as a ubiquitous regulatory mechanism. Like any post-translational modifications, S-nitrosylation is critical for the control of numerous cellular processes. It is now clear that S-nitrosylation is playing a double game, enhancing or inhibiting the tumor growth or the induction of cell death. Thanks to research aimed at demonstrating NO cytotoxic effects, new therapeutic strategies based on NO donor drugs have emerged. Although therapeutic NO donors can target a large number of proteins, the cellular mechanism is still not fully understood. This review reflects the current state of knowledge on S-nitrosylated proteins that take part of the oncogenic and apoptotic signaling, putting forward proteins with potential interest in cancer therapy.

From Reflux Esophagitis to Esophageal Adenocarcinoma

Reflux esophagitis causes Barrett's metaplasia, an abnormal esophageal mucosa predisposed to adenocarcinoma. Medical therapy for reflux esophagitis focuses on decreasing gastric acid production with proton pump inhibitors. We have reported that reflux esophagitis in a rat model develops from a cytokine-mediated inflammatory injury, not from a caustic chemical (acid) injury. In this model, refluxed acid and bile stimulate the release of inflammatory cytokines from esophageal squamous cells, recruiting lymphocytes first to the submucosa and later to the luminal surface. Emerging studies on acute reflux esophagitis in humans support this new concept, suggesting that reflux-induced cytokine release may be a future target for medical therapies. Sometimes, reflux esophagitis heals with Barrett's metaplasia, a process facilitated by reflux-related nitric oxide (NO) production and Sonic Hedgehog (Hh) secretion by squamous cells. We have shown that NO reduces expression of genes that promote a squamous cell phenotype, while Hh signaling induces genes that mediate the development of the columnar cell phenotypes of Barrett's metaplasia. Agents targeting esophageal NO production or Hh signaling conceivably could prevent the development of Barrett's esophagus. Persistent reflux promotes cancer in Barrett's metaplasia. We have reported that acid and bile salts induce DNA damage in Barrett's cells. Bile salts also cause NF-x03BA;B activation in Barrett's cells, enabling them to resist apoptosis in the setting of DNA damage and likely contributing to carcinogenesis. Oral treatment with ursodeoxycholic acid prevents the esophageal DNA damage and NF-x03BA;B activation induced by toxic bile acids. Altering bile acid composition might be another approach to cancer prevention.

Nitric oxide as a regulator of B. anthracis pathogenicity

Nitric oxide (NO) is a key physiological regulator in eukaryotic and prokaryotic organisms. It can cause a variety of biological effects by reacting with its targets or/and indirectly inducing oxidative stress. NO can also be produced by bacteria including the pathogenic Bacillus anthracis; however, its role in the infectious process only begins to emerge. NO incapacitates macrophages by S-nitrosylating the intracellular proteins and protects B. anthracis from oxidative stress. It is also implicated in the formation of toxic peroxynitrite. In this study we further assessed the effects of B. anthracis NO produced by the NO synthase (bNOS) on bacterial metabolism and host cells in experiments with the bNOS knockout Sterne strain. The mutation abrogated accumulation of nitrite and nitrate as tracer products of NO in the culture medium and markedly attenuated growth in both aerobic and microaerobic conditions. The regulatory role of NO was also suggested by the abnormally high rate of nitrate denitrification by the mutant in the presence of oxygen. Anaerobic regulation mediated by NO was reflected in reduced fermentation of glucose by the mutant correlating with the reduced toxicity of bacteria toward host cells in culture. The toxic effect of NO required permeabilization of the target cells as well as the activity of fermentation-derived metabolite in the conditions of reduced pH. The host cells demonstrated increased phosphorylation of major survivor protein kinase AKT correlating with reduced toxicity of the mutant in comparison with Sterne. Our global proteomic analysis of lymph from the lymph nodes of infected mice harboring bacteria revealed numerous changes in the pattern and levels of proteins associated with the activity of bNOS influencing key cell physiological processes relevant to energy metabolism, growth, signal transduction, stress response, septic shock, and homeostasis. This is the first in vivo observation of the bacterial NO effect on the lymphatic system.