Tyrosine phosphorylation regulates H2O2 production in lung fibroblasts stimulated by transforming growth factor beta1

Integration of inflammation, fibrosis, and cancer induced by carbon nanotubes

Carbon nanotubes (CNTs) are nanomaterials with unique physicochemical properties that are targets of great interest for industrial and commercial applications. Notwithstanding, some characteristics of CNTs are associated with adverse outcomes from exposure to pathogenic particulates, raising concerns over health risks in exposed workers and consumers. Indeed, certain forms of CNTs induce a range of harmful effects in laboratory animals, among which inflammation, fibrosis, and cancer are consistently observed for some CNTs. Inflammation, fibrosis, and malignancy are complex pathological processes that, in summation, underlie a major portion of human disease. Moreover, the functional interrelationship among them in disease pathogenesis has been increasingly recognized. The CNT-induced adverse effects resemble certain human disease conditions, such as pneumoconiosis, idiopathic pulmonary fibrosis (IPF), and mesothelioma, to some extent. Progress has been made in understanding CNT-induced pathologic conditions in recent years, demonstrating a close interconnection among inflammation, fibrosis, and cancer. Mechanistically, a number of mediators, signaling pathways, and cellular processes are identified as major mechanisms that underlie the interplay among inflammation, fibrosis, and malignancy, and serve as pathogenic bases for these disease conditions in CNT-exposed animals. These studies indicate that CNT-induced pathological effects, in particular, inflammation, fibrosis, and cancer, are mechanistically, and in some cases, causatively, interrelated. These findings generate new insights into CNT adverse effects and pathogenesis and provide new targets for exposure monitoring and drug development against inflammation, fibrosis, and cancer caused by inhaled nanomaterials.

Relevance of Non-Targeted Effects for Radiotherapy and Diagnostic Radiology; A Historical and Conceptual Analysis of Key Players

Non-targeted effects (NTE) such as bystander effects or genomic instability have been known for many years but their significance for radiotherapy or medical diagnostic radiology are far from clear. Central to the issue are reported differences in the response of normal and tumour tissues to signals from directly irradiated cells. This review will discuss possible mechanisms and implications of these different responses and will then discuss possible new therapeutic avenues suggested by the analysis. Finally, the importance of NTE for diagnostic radiology and nuclear medicine which stems from the dominance of NTE in the low-dose region of the dose–response curve will be presented. Areas such as second cancer induction and microenvironment plasticity will be discussed.

4-O-Methylhonokiol Protects HaCaT Cells from TGF-β1-Induced Cell Cycle Arrest by Regulating Canonical and Non-Canonical Pathways of TGF-β Signaling

4-O-methylhonokiol, a neolignan compound from Magnolia Officinalis, has been reported to have various biological activities including hair growth promoting effect. However, although transforming growth factor-β (TGF-β) signal pathway has an essential role in the regression induction of hair growth, the effect of 4-O-methylhonokiol on the TGF-β signal pathway has not yet been elucidated. We thus examined the effect of 4-O-methylhonokiol on TGF-β-induced canonical and noncanonical pathways in HaCaT human keratinocytes. When HaCaT cells were pretreated with 4-O-methylhonokiol, TGF-β1-induced G1/G0 phase arrest and TGF-β1-induced p21 expression were decreased. Moreover, 4-O-methylhonokiol inhibited nuclear translocation of Smad2/3, Smad4 and Sp1 in TGF-β1-induced canonical pathway. We observed that ERK phosphorylation by TGF-β1 was significantly attenuated by treatment with 4-O-methylhonokiol. 4-O-methylhonokiol inhibited TGF-β1-induced reactive oxygen species (ROS) production and reduced the increase of NADPH oxidase 4 (NOX4) mRNA level in TGF-β1-induced noncanonical pathway. These results indicate that 4-O-methylhonokiol could inhibit TGF-β1-induced cell cycle arrest through inhibition of canonical and noncanonical pathways in human keratinocyte HaCaT cell and that 4-O-methylhonokiol might have protective action on TGF-β1-induced cell cycle arrest.

Focal adhesion kinase signaling determines the fate of lung epithelial cells in response to TGF-β

Alveolar epithelial cell (AEC) injury and apoptosis are prominent pathological features of idiopathic pulmonary fibrosis (IPF). There is evidence of AEC plasticity in lung injury repair response and in IPF. In this report, we explore the role of focal adhesion kinase (FAK) signaling in determining the fate of lung epithelial cells in response to transforming growth factor-β1 (TGF-β1). Rat type II alveolar epithelial cells (RLE-6TN) were treated with or without TGF-β1, and the expressions of mesenchymal markers, phenotype, and function were analyzed. Pharmacological protein kinase inhibitors were utilized to screen for SMAD-dependent and -independent pathways. SMAD and FAK signaling was analyzed using siRNA knockdown, inhibitors, and expression of a mutant construct of FAK. Apoptosis was measured using cleaved caspase-3 and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining. TGF-β1 induced the acquisition of mesenchymal markers, including α-smooth muscle actin, in RLE-6TN cells and enhanced the contraction of three-dimensional collagen gels. This phenotypical transition or plasticity, epithelial-myofibroblast plasticity (EMP), is dependent on SMAD3 and FAK signaling. FAK activation was found to be dependent on ALK5/SMAD3 signaling. We observed that TGF-β1 induces both EMP and apoptosis in the same cell culture system but not in the same cell. While blockade of SMAD signaling inhibited EMP, it had a minimal effect on apoptosis; in contrast, inhibition of FAK signaling markedly shifted to an apoptotic fate. The data support that FAK activation determines whether AECs undergo EMP vs. apoptosis in response to TGF-β1 stimulation. TGF-β1-induced EMP is FAK- dependent, whereas TGF-β1-induced apoptosis is favored when FAK signaling is inhibited.

Adventitial Fibroblast Nox4 Expression and ROS Signaling in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease arising from remodeling and narrowing of pulmonary arteries (PA) resulting in high pulmonary arterial blood pressure and ultimately right ventricular failure. Elevated production of reactive oxygen species (ROS) by NADPH oxidase 4 (Nox4), a constitutively active enzyme, has been associated with oxygen sensing, vasomotor control, cellular proliferation, differentiation, migration, apoptosis, senescence, fibrosis, and angiogenesis. Further, elevated expression of Nox4 has been reported in a number of cardiovascular diseases, including atherosclerosis, hypertension, cardiac failure, ischemic stroke, and PAH. However, the cellular location of Nox4 and its contribution to aberrant vascular remodeling in PAH remains poorly understood. The goal of this review is to summarize the recent literature on the enzymatic regulation of Nox4 in the production of ROS in PAH. In the vascular wall, Nox4 is present in fibroblasts, a primary cell of the adventitia, and matches the adventitial location of ROS production in PAH. Further, in adventitial fibroblasts, Nox4 overexpression stimulates migration and proliferation as well as matrix gene expression. Collectively, reports indicate that Nox4 contributes to altered fibroblast behavior, ROS production leading to hypertensive vascular remodeling and the development of PAH. Finally, we address the functional significance of Nox4 in fibroblasts, and also suggest an "outside in" (adventitial) process of vascular remodeling that is mediated by Nox4, which although has physiological roles in the intimal layer (i.e., endothelium), may also have pathologic importance in the adventitial layer of the vascular wall through signaling in fibroblasts.

Myofibroblasts and lung fibrosis induced by carbon nanotube exposure

Carbon nanotubes (CNTs) are newly developed materials with unique properties and a range of industrial and commercial applications. A rapid expansion in the production of CNT materials may increase the risk of human exposure to CNTs. Studies in rodents have shown that certain forms of CNTs are potent fibrogenic inducers in the lungs to cause interstitial, bronchial, and pleural fibrosis characterized by the excessive deposition of collagen fibers and the scarring of involved tissues. The cellular and molecular basis underlying the fibrotic response to CNT exposure remains poorly understood. Myofibroblasts are a major type of effector cells in organ fibrosis that secrete copious amounts of extracellular matrix proteins and signaling molecules to drive fibrosis. Myofibroblasts also mediate the mechano-regulation of fibrotic matrix remodeling via contraction of their stress fibers. Recent studies reveal that exposure to CNTs induces the differentiation of myofibroblasts from fibroblasts in vitro and stimulates pulmonary accumulation and activation of myofibroblasts in vivo. Moreover, mechanistic analyses provide insights into the molecular underpinnings of myofibroblast differentiation and function induced by CNTs in the lungs.

In view of the apparent fibrogenic activity of CNTs and the emerging role of myofibroblasts in the development of organ fibrosis, we discuss recent findings on CNT-induced lung fibrosis with emphasis on the role of myofibroblasts in the pathologic development of lung fibrosis. Particular attention is given to the formation and activation of myofibroblasts upon CNT exposure and the possible mechanisms by which CNTs regulate the function and dynamics of myofibroblasts in the lungs. It is evident that a fundamental understanding of the myofibroblast and its function and regulation in lung fibrosis will have a major influence on the future research on the pulmonary response to nano exposure, particle and fiber-induced pneumoconiosis, and other human lung fibrosing diseases.

Oxidative Modifications of Protein Tyrosyl Residues Are Increased in Plasma of Human Subjects with Interstitial Lung Disease

RATIONALE

Interstitial lung diseases (ILDs) are associated with oxidative stress. Plasma biomarkers that are directly linked to oxidative stress responses in this disease have not been identified. Stable oxidation products of tyrosine residues in proteins may reflect the oxidative microenvironment in the lung or a systemic inflammatory state.

OBJECTIVES

To determine if levels of protein tyrosine oxidation are elevated in plasma of patients with ILD compared with an age- and sex-matched healthy control cohort.

METHODS

Three tyrosine oxidation products (3-chlorotyrosine, 3-nitrotyrosine, and o,o'-dityrosine) were quantified by tandem mass spectrometry in cellular models, a mouse model of injury-induced fibrosis, and in plasma of healthy control subjects and patients with ILD (n = 42 in each group).

MEASUREMENTS AND MAIN RESULTS

Plasma levels of 3-chlorotyrosine, 3-nitrotyrosine, and o,o'-dityrosine were markedly elevated in patients with ILD compared with control subjects with receiver operating characteristic curves separating these groups of 0.872, 0.893, and 0.997, respectively. In a murine model of lung fibrosis, levels of all three oxidative tyrosine modifications were increased in plasma and lung tissue. Cellular models support a critical role for a heme peroxidase and enzymatic sources of reactive oxygen species in the generation of these oxidized products.

CONCLUSIONS

We demonstrate an increase in oxidized tyrosine moieties within proteins in the circulating plasma of patients with ILD. These data support the potential for development of oxidative stress-related biomarkers in early diagnosis, prognostication, and/or in evaluating responsiveness to emerging therapies for ILD.

NADPH oxidase-2 is a key regulator of human dermal fibroblasts: a potential therapeutic strategy for the treatment of skin fibrosis

The proliferation of human skin dermal fibroblasts (HDFs) is a critical step in skin fibrosis, and transforming growth factor-beta1 (TGF-β1) exerts pro-oxidant and fibrogenic effects on HDFs. In addition, the oxidative stress system has been implicated in the pathogenesis of skin disease. However, the role of NADPH oxidase as a mediator of TGF-β1-induced effects in HDFs remains unknown. Thus, our aim was to investigate the role of NADPH in human skin dermal fibroblasts. Primary fibroblasts were cultured and pretreated with various stimulants. Real-time Q-PCR and Western blotting analyses were used for mRNA and protein detection. In addition, siRNA technology was applied for gene knock-down analysis. Hydrogen peroxide production and 2',7'-dichlorofluorescein diacetate (DCFDA) measurement assay were performed. Here, our findings demonstrated that HDFs express key components of non-phagocytic NADPH oxidase mRNA. TGF-β1 induced NOX2 and reactive oxygen species formation via NADPH oxidase activity. In contrast, NOX3 was barely detectable, and other NOXs did not display significant changes. In addition, TGF-β1 phosphorylated MAPKs and increased activator protein-1 (AP-1) in a redox-sensitive manner, and NOX2 suppression inhibited baseline and TGF-β1-mediated stimulation of Smad2 phosphorylation. Moreover, TGF-β1 stimulated cell proliferation, migration, collagen I and fibronectin expression, and bFGF and PAI-1 secretion: these effects were attenuated by diphenylene iodonium (DPI), an NADPH oxidase inhibitor, and NOX2 siRNA. Importantly, NOX2 siRNA suppresses collagen production in primary keloid dermal fibroblasts. These findings provide the proof of concept for NADPH oxidase as a potential target for the treatment of skin fibrosis.

Calcium Homeostasis and Ionic Mechanisms in Pulmonary Fibroblasts

Fibroblasts are key cellular mediators of many chronic interstitial lung diseases, including idiopathic pulmonary fibrosis, scleroderma, sarcoidosis, drug-induced interstitial lung disease, and interstitial lung disease in connective tissue disease. A great deal of effort has been expended to understand the signaling mechanisms underlying the various cellular functions of fibroblasts. Recently, it has been shown that Ca(2+) oscillations play a central role in the regulation of gene expression in human pulmonary fibroblasts. However, the mechanisms whereby cytosolic [Ca(2+)] are regulated and [Ca(2+)] oscillations transduced are both poorly understood. In this review, we present the general concepts of [Ca(2+)] homeostasis, of ionic mechanisms responsible for various Ca(2+) fluxes, and of regulation of gene expression by [Ca(2+)]. In each case, we then also summarize the original findings that pertain specifically to pulmonary fibroblasts. From these data, we propose an overall signaling cascade by which excitation of the fibroblasts triggers pulsatile release of internally sequestered Ca(2+), which, in turn, activates membrane conductances, including voltage-dependent Ca(2+) influx pathways. Collectively, these events produce recurring Ca(2+) oscillations, the frequency of which is transduced by Ca(2+)-dependent transcription factors, which, in turn, orchestrate a variety of cellular events, including proliferation, synthesis/secretion of extracellular matrix proteins, autoactivation (production of transforming growth factor-β), and transformation into myofibroblasts. That unifying hypothesis, in turn, allows us to highlight several specific cellular targets and therapeutic intervention strategies aimed at controlling unwanted pulmonary fibrosis. The relationships between Ca(2+) signaling events and the unfolded protein response and apoptosis are also explored.

NADPH oxidases in lung health and disease

SIGNIFICANCE

The evolution of the lungs and circulatory systems in vertebrates ensured the availability of molecular oxygen (O2; dioxygen) for aerobic cellular metabolism of internal organs in large animals. O2 serves as the physiologic terminal acceptor of mitochondrial electron transfer and of the NADPH oxidase (Nox) family of oxidoreductases to generate primarily water and reactive oxygen species (ROS), respectively.

RECENT ADVANCES

The purposeful generation of ROS by Nox family enzymes suggests important roles in normal physiology and adaptation, most notably in host defense against invading pathogens and in cellular signaling.

CRITICAL ISSUES

However, there is emerging evidence that, in the context of chronic stress and/or aging, Nox enzymes contribute to the pathogenesis of a number of lung diseases.

FUTURE DIRECTIONS

Here, we review evolving functions of Nox enzymes in normal lung physiology and emerging pathophysiologic roles in lung disease.

Fibroblast-to-myofibroblast switch is mediated by NAD(P)H oxidase generated reactive oxygen species

Tumour–stroma interaction is a prerequisite for tumour progression in skin cancer. Hereby, a critical step in stromal function is the transition of tumour-associated fibroblasts to MFs (myofibroblasts) by growth factors, for example TGFβ (transforming growth factor beta(). In this study, the question was addressed of whether fibroblast-associated NAD(P)H oxidase (NADH/NADPH oxidase), known to be activated by TGFβ1, is involved in the fibroblast-to-MF switch. The up-regulation of αSMA (alpha smooth muscle actin), a biomarker for MFs, is mediated by a TGFβ1-dependent increase in the intracellular level of ROS (reactive oxygen species). This report demonstrates two novel aspects of the TGFβ1 signalling cascade, namely the generation of ROS due to a biphasic NAD(P)H oxidase activity and a ROS-dependent downstream activation of p38 leading to a transition of dermal fibroblasts to MFs that can be inhibited by the selective NAD(P)H oxidase inhibitor apocynin. These data suggest that inhibition of NAD(P)H oxidase activity prevents the fibroblast-to-MF switch and may be important for chemoprevention in context of a ‘stromal therapy’ which was described earlier.

Downregulation of tumor growth and invasion by redox-active nanoparticles

AIMS

Melanoma is the most aggressive type of malignant skin cancer derived from uncontrolled proliferation of melanocytes. Melanoma cells possess a high potential to metastasize, and the prognosis for advanced melanoma is rather poor due to its strong resistance to conventional chemotherapeutics. Nanomaterials are at the cutting edge of the rapidly developing area of nanomedicine. The potential of nanoparticles for use as carrier in cancer drug delivery is infinite with novel applications constantly being tested. The noncarrier use of cerium oxide nanoparticles (CNPs) is a novel and promising approach, as those particles per se show an anticancer activity via their oxygen vacancy-mediated chemical reactivity.

RESULTS

In this study, the question was addressed of whether the use of CNPs might be a valuable tool to counteract the invasive capacity and metastasis of melanoma cells in the future. Therefore, the effect of those nanoparticles on human melanoma cells was investigated in vitro and in vivo. Concentrations of polymer-coated CNPs being nontoxic for stromal cells showed a cytotoxic, proapoptotic, and anti-invasive capacity on melanoma cells. In vivo xenograft studies with immunodeficient nude mice showed a decrease of tumor weight and volume after treatment with CNPs.

INNOVATION

In summary, the redox-active CNPs have selective pro-oxidative and antioxidative properties, and this study is the first to show that CNPs prevent tumor growth in vivo.

CONCLUSION

The application of redox-active CNPs may form the basis of new paradigms in the treatment and prevention of cancers.

Secreted protein acidic and rich in cysteine (SPARC) is upregulated by transforming growth factor (TGF)-β and is required for TGF-β-induced hydrogen peroxide production in fibroblasts

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a poorly understood progressive disease characterized by the recurrent damage of alveolar epithelial cells as well as inappropriate expansion and activation of fibroblasts resulting in pronounced extracellular matrix (ECM) deposition. Although recent studies have indicated the involvement of secreted protein acidic and rich in cysteine (SPARC), a matricellular protein regulating ECM deposition, in the pathogenesis of fibrosis, factors regulating SPARC expression or roles of SPARC in fibrosis have not been fully elucidated.

RESULTS

Among the profibrotic factors examined in cultured fibroblasts, we showed that SPARC expression was upregulated mainly by transforming growth factor (TGF)-β. We also showed that expression of SPARC in the lung was upregulated in the murine bleomycin-induced pulmonary fibrosis model, which was inhibited by TGF-β receptor I inhibitor. Knockdown of SPARC in fibroblasts using siRNA or treatment with the antioxidant N-acetylcysteine attenuated epithelial cell injury induced by TGF-β-activated fibroblasts in a coculture system. We also demonstrated that SPARC was required for hydrogen peroxide (H2O2) production in fibroblasts treated with TGF-β. Furthermore, TGF-β activated integrin-linked kinase (ILK), which was inhibited by SPARC siRNA. Knockdown of ILK attenuated extracellular H2O2 generation in TGF-β-stimulated fibroblasts. Our results indicated that SPARC is upregulated by TGF-β and is required for TGF-β-induced H2O2 production via activation of ILK, and this H2O2 production from fibroblasts is capable of causing epithelial cell injury.

CONCLUSIONS

The results presented in this study suggest that SPARC plays a role in epithelial damage in the IPF lung via enhanced H2O2 production from fibroblasts activated by TGF-β. Therefore, SPARC inhibition may prevent epithelial injury in IPF lung and represent a potential therapeutic approach for IPF.

Characterization of primary cultures of cholesteatoma-associated fibroblasts

OBJECTIVES

The aim of this study was to characterize primary cultured fibroblasts derived from cholesteatoma (CHO) tissue to get evidence of their possible role for determining the different biological behavior of this aural pathology.

MATERIALS AND METHODS

Primary cultures of human fibroblasts were obtained from middle ear CHO specimens and from controls of normal human skin collected during surgical procedures. Cells were incubated with anti-vimentin monoclonal antibody, anti-cytokeratins monoclonal antibody and anti-α-smooth muscle actin monoclonal antibody. For reactive oxygen species detection, fibroblasts were incubated with 2',7'-dichlorofluorescein diacetate. Immunofluorescence, flow cytometry, confocal, and transmission electron microscopy were carried out.

RESULTS

Cholesteatoma-associated fibroblasts (CHO-AFs) were characterized by a higher degree of cytoplasmic complexity, by the expression of α-smooth muscle actin and by a greater basal production of reactive oxygen species in comparison with controls, reflecting a more differentiated phenotype consistent with myofibroblasts.

CONCLUSION

It is possible to suggest that the differentiated phenotype of CHO-AFs might be coupled with a more or less aggressive clinical behavior, and hence, these cultures might represent powerful tools for investigating biology and clinical evolution of this disease.

Crosstalk between platelet-derived growth factor-induced Nox4 activation and MUC8 gene overexpression in human airway epithelial cells

Reactive oxygen species (ROS) contribute to chronic airway inflammation, and NADPH oxidase (Nox) is an important source of ROS. However, little is known of the role that ROS play in chronic upper respiratory tract inflammation. We investigated the mechanism of ROS generation and its association with mucin gene overexpression in the nasal epithelium. The level of platelet-derived growth factor (PDGF) expression was increased in sinusitis mucosa, and high-level PDGF expression induced intracellular ROS, followed by MUC8 gene overexpression in normal human nasal epithelial cells. Knockdown of Nox4 expression with Nox4 siRNA decreased PDGF-induced intracellular ROS and MUC8 expression. Infection with an adenovirus containing Nox4 cDNA resulted in Nox4 overexpression and increased intracellular levels of ROS and MUC8 expression. PDGF and Nox4 overexpression are essential components of intracellular ROS generation and may contribute to chronic inflammation in the nasal epithelium through induction of MUC8 overexpression.

Mitochondrial translocation of oxidized cofilin induces caspase-independent necrotic-like programmed cell death of T cells

Oxidative stress leads to T-cell hyporesponsiveness or death. The actin-binding protein cofilin is oxidized during oxidative stress, which provokes a stiff actin cytoskeleton and T-cell hyporesponsiveness. Here, we show that long-term oxidative stress leads to translocation of cofilin into the mitochondria and necrotic-like programmed cell death (PCD) in human T cells. Notably, cofilin mutants that functionally mimic oxidation by a single mutation at oxidation-sensitive cysteins (Cys-39 or Cys-80) predominately localize within the mitochondria. The expression of these mutants alone ultimately leads to necrotic-like PCD in T cells. Accordingly, cofilin knockdown partially protects T cells from the fatal effects of long-term oxidative stress. Thus, we introduce the oxidation and mitochondrial localization of cofilin as the checkpoint for necrotic-like PCD upon oxidative stress as it occurs, for example, in tumor environments.

IPF: new insight on pathogenesis and treatment

Recent years have seen a robust influx of exciting new observations regarding the mechanisms that regulate the initiation and progression of pulmonary fibrosis but the pathogenesis remains poorly understood. The search for an alternative hypothesis to unremitting, chronic inflammation as the primary explanation for the pathophysiology of idiopathic pulmonary fibrosis (IPF) derives, in part, from the lack of therapeutic efficacy of high-dose immunosuppressive therapy in patients with IPF. The inflammatory hypothesis of IPF has since been challenged by the epithelial injury hypothesis, in which fibrosis is believed to result from epithelial injury, activation, and/or apoptosis with abnormal wound healing. This hypothesis suggests that recurrent unknown injury to distal pulmonary parenchyma causes repeated epithelial injury and apoptosis. The resultant loss of alveolar epithelium exposes the underlying basement membrane to oxidative damage and degradation. Emerging concepts suggest that IPF is the result of epithelial-mesenchymal interaction. The initiation of this fibrotic response may depend upon genetic factors and environmental triggers; the role of Th1 or Th2 cell-derived cytokines may also be important. This process appears to be unique to usual interstitial pneumonia/IPF. It is clear that IPF is a heterogeneous disease with variations in pathology, high-resolution computed tomography findings, and patterns of progression. Idiopathic pulmonary fibrosis is a complex disorder, and no unifying hypothesis has been identified at present that explains all the abnormalities.

Telomeric DNA induces p53-dependent reactive oxygen species and protects against oxidative damage

BACKGROUND

Reactive oxygen species (ROS) are generated by cellular metabolism as well as by exogenous agents. While ROS can promote cellular senescence, they can also act as signaling molecules for processes that do not lead to senescence. Telomere homolog oligonucleotides (T-oligos) induce adaptive DNA damage responses including increased DNA repair capacity and these effects are mediated, at least in part, through p53.

OBJECTIVE

Studies were undertaken to determine whether such p53-mediated protective responses include enhanced antioxidant defenses.

METHODS

Normal human fibroblasts as well as R2F fibroblasts expressing wild type or dominant negative p53 were treated with an 11-base T-oligo, a complementary control oligo or diluents alone and then examined by western blot analysis, immunofluorescence microscopy and various biochemical assays.

RESULTS

We now report that T-oligo increases the level of the antioxidant enzymes superoxide dismutase 1 and 2 and protects cells from oxidative damage; and that telomere-based gammaH2AX (DNA damage) foci that form in response to T-oligos contain phosphorylated ATM and Chk2, proteins known to activate p53 and to mediate cell cycle arrest in response to oxidative stress. Further, T-oligo increases cellular ROS levels via a p53-dependent pathway, and these increases are abrogated by the NAD(P)H oxidase inhibitor diphenyliodonium chloride.

CONCLUSION

These results suggest the existence of innate telomere-based protective responses that act to reduce oxidative damage to cells. T-oligo treatment induces the same responses and offers a new model for studying intracellular ROS signaling and the relationships between DNA damage, ROS, oxidative stress, and cellular defense mechanisms.

Cellular senescence: molecular mechanisms, in vivo significance, and redox considerations

Cellular senescence is recognized as a critical cellular response to prolonged rounds of replication and environmental stresses. Its defining characteristics are arrested cell-cycle progression and the development of aberrant gene expression with proinflammatory behavior. Whereas the mechanistic events associated with senescence are generally well understood at the molecular level, the impact of senescence in vivo remains to be fully determined. In addition to the role of senescence as an antitumor mechanism, this review examines cellular senescence as a factor in organismal aging and age-related diseases, with particular emphasis on aberrant gene expression and abnormal paracrine signaling. Senescence as an emerging factor in tissue remodeling, wound repair, and infection is considered. In addition, the role of oxidative stress as a major mediator of senescence and the role of NAD(P)H oxidases and changes to intracellular GSH/GSSG status are reviewed. Recent findings indicate that senescence and the behavior of senescent cells are amenable to therapeutic intervention. As the in vivo significance of senescence becomes clearer, the challenge will be to modulate the adverse effects of senescence without increasing the risks of other diseases, such as cancer. The uncoupled relation between cell-cycle arrest and the senescent phenotype suggests that this is an achievable outcome.

Effects of thioredoxin reductase-1 deletion on embryogenesis and transcriptome

Thioredoxin reductases (Txnrd) maintain intracellular redox homeostasis in most organisms. Metazoan Txnrds also participate in signal transduction. Mouse embryos homozygous for a targeted null mutation of the txnrd1 gene, encoding the cytosolic thioredoxin reductase, were viable at embryonic day 8.5 (E8.5) but not at E9.5. Histology revealed that txnrd1-/- cells were capable of proliferation and differentiation; however, mutant embryos were smaller than wild-type littermates and failed to gastrulate. In situ marker gene analyses indicated that primitive streak mesoderm did not form. Microarray analyses on E7.5 txnrd-/- and txnrd+/+ littermates showed similar mRNA levels for peroxiredoxins, glutathione reductases, mitochondrial Txnrd2, and most markers of cell proliferation. Conversely, mRNAs encoding sulfiredoxin, IGF-binding protein 1, carbonyl reductase 3, glutamate cysteine ligase, glutathione S-transferases, and metallothioneins were more abundant in mutants. Many gene expression responses mirrored those in thioredoxin reductase 1-null yeast; however, mice exhibited a novel response within the peroxiredoxin catalytic cycle. Thus, whereas yeast induce peroxiredoxin mRNAs in response to thioredoxin reductase disruption, mice induced sulfiredoxin mRNA. In summary, Txnrd1 was required for correct patterning of the early embryo and progression to later development. Conserved responses to Txnrd1 disruption likely allowed proliferation and limited differentiation of the mutant embryo cells.

Transforming growth factor-beta1 effects on endothelial monolayer permeability involve focal adhesion kinase/Src

Transforming growth factor (TGF)-beta1 activity has been shown to increase vascular endothelial barrier permeability, which is believed to precede several pathologic conditions, including pulmonary edema and vessel inflammation. In endothelial monolayers, TGF-beta1 increases permeability, and a number of studies have demonstrated the alteration of cell-cell contacts by TGF-beta1. We hypothesized that focal adhesion complexes also likely contribute to alterations in endothelial permeability. We examined early signal transduction events associated with rapid changes in monolayer permeability and the focal adhesion complex of bovine pulmonary artery endothelial cells. Western blotting revealed rapid tyrosine phosphorylation of focal adhesion kinase (FAK) and Src kinase in response to TGF-beta1; inhibition of both of these kinases using pp2 (4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine), ameliorates TGF-beta1-induced monolayer permeability. Activation of FAK/Src requires activation of the epidermal growth factor receptor downstream of the TGF-beta receptors, and is blocked by the epidermal growth factor receptor inhibitor AG1478. Immunohistochemistry showed that actin and the focal adhesion proteins paxillin, vinculin, and hydrogen peroxide-inducible clone-5 (Hic-5) are rearranged in response to TGF-beta1; these proteins are released from focal adhesion complexes. Rearrangement of paxillin and vinculin by TGF-beta1 is not blocked by the FAK/Src inhibitor, pp2, or by SB431542 inhibition of the TGF-beta type I receptor, anaplastic lymphoma kinase 5; however, pp1 (4-Amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine), which inhibits both type I and type II TGF-beta receptors, does block paxillin and vinculin rearrangement. Hic-5 protein rearrangement requires FAK/Src activity. Together, these results suggest that TGF-beta1-induced monolayer permeability involves focal adhesion and cytoskeletal rearrangement through both FAK/Src-dependent and -independent pathways.

Epithelial-mesenchymal interactions in pulmonary fibrosis

Pulmonary fibrosis represents the sequelae of a variety of acute and chronic lung injuries of known and unknown etiologies. Tissue specimens obtained from patients with pulmonary fibrosis, regardless of the etiology, consistently show evidence of an ongoing wound-repair response. Epithelial-mesenchymal interactions have critical roles in normal lung development, tissue repair processes, and fibrosis. Current hypotheses propose that dysregulated function of, and impaired communication between, epithelial and mesenchymal cells prevent resolution of the wound-repair response and contribute to the pathobiology of pulmonary fibrosis. This hypothesis is supported by abundant evidence from patients, animal models, and cell-culture studies demonstrating abnormalities in epithelial cell and mesenchymal cell activities including proliferation, differentiation, and survival. This article reviews the aberrant epithelial and mesenchymal cellular phenotypes found in the context of pulmonary fibrosis and discusses the mechanisms that perpetuate these cellular phenotypes.

Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, and usually fatal pulmonary disease for which there are no proven drug therapies. Anti-inflammatory and immunosuppressive agents have been largely ineffective. The precise relationship of IPF to other idiopathic interstitial pneumonias (IIPs) is not known, despite the observation that different histopathologic patterns of IIP may coexist in the same patient. We propose that these different histopathologic 'reaction' patterns may be determined by complex interactions between host and environmental factors that alter the local alveolar milieu. Recent paradigms in IPF pathogenesis have focused on dysregulated epithelial-mesenchymal interactions, an imbalance in T(H)1/T(H)2 cytokine profile and potential roles for aberrant angiogenesis. In this review, we discuss these evolving concepts in disease pathogenesis and emerging therapies designed to target pro-fibrogenic pathways in IPF.

Transforming growth factor-beta1 induces Nox4 NAD(P)H oxidase and reactive oxygen species-dependent proliferation in human pulmonary artery smooth muscle cells

Transforming growth factor-beta1 (TGF-beta1) is abundantly expressed in pulmonary hypertension, but its effect on the pulmonary circulation remains unsettled. We studied the consequences of TGF-beta1 stimulation on freshly isolated human pulmonary artery smooth muscle cells (HPASMC). TGF-beta1 initially promoted differentiation, with upregulated expression of smooth muscle contractile proteins. TGF-beta1 also induced expression of Nox4, the only NAD(P)H oxidase membrane homolog found in HPASMC, through a signaling pathway involving Smad 2/3 but not mitogen-activated protein (MAP) kinases. TGF-beta1 likewise increased production of reactive oxygen species (ROS), an effect significantly reduced by the NAD(P)H oxidase flavoprotein inhibitor diphenylene iodonium (DPI) and by Nox4 siRNAs. In the absence of TGF-beta1, Nox4 was present in freshly cultured cells but progressively lost with each passage in culture, paralleling a decrease in ROS production by HPASMC over time. At a later time point (72 h), TGF-beta1 promoted HPASMC proliferation in a manner partially inhibited by Nox4 small interfering RNA and dominant negative Smad 2/3, indicating that TGF-beta1 stimulates HPASMC growth in part by a redox-dependent mechanism mediated through induction of Nox4. HPASMC activation of the MAP kinases ERK1/2 was reduced by the NAD(P)H oxidase inhibitors DPI and 4-(2-aminoethyl)benzenesulfonyl fluoride, suggesting that TGF-beta1 may facilitate proliferation by upregulating Nox4 and ROS production, with transient oxidative inactivation of phosphatases and augmentation of growth signaling cascades. These findings suggest that Nox4 is the relevant Nox homolog in HPASMC. This is the first observation that TGF-beta1 regulates Nox4, with important implications for mechanisms of pulmonary vascular remodeling.

Hypoxia-induced post-translational changes in red blood cell protein map of newborns

Tyrosine (Tyr) phosphorylation is implicated in the modification of several erythrocyte functions, such as metabolic pathways and membrane transport, as well as in signal transduction systems. Here we describe the map of Tyr-phosphorylated soluble proteins of newborn red blood cells (RBC) using an in vitro model simulating RBC reoxygenation at birth after an intrauterine hypoxic event. We tested the hypothesis that a hypoxic environment and subsequent reoxygenation promote post-translational changes in the RBC protein map of newborns, in addition to desferrioxamine (DFO)-chelatable iron (DCI) release and methemoglobin (MetHb) formation. Umbilical cord blood RBC were incubated under hypoxic conditions for 16 h at 37 degrees C, and subsequently for 8 h under aerobic conditions. Control erythrocytes were incubated under aerobic conditions at 37 degrees C for the period of the experiment, i.e. for 24 h. Tyr-phosphorylation proteins were assessed using advanced high-resolution two-dimensional electrophoresis, 2-D immunoblot analysis with anti-phosphotyrosine (anti-pTyr) antibodies, and computer-aided electrophoretogram analysis. Higher DCI release and MetHb formation were observed in newborn RBC incubated under hypoxic conditions than in those incubated aerobically. Different immunoreactivity patterns with anti-pTyr antibodies were also observed between newborn RBC incubated under hypoxic conditions and controls. A hypoxic environment is a factor promoting DCI release, a well-known condition of oxidative stress. This is the first map of Tyr-phosphorylated soluble proteins of newborn RBC obtained using an in vitro model simulating RBC reoxygenation at birth after an intrauterine hypoxic event. Our results suggest that hypoxia increases Tyr-phosphorylation of antioxidant proteins, protecting RBC against oxidative stress.

Cyclic stretch increases VEGF expression in pulmonary arterial smooth muscle cells via TGF-β1 and reactive oxygen species: a requirement for NAD(P)H oxidase

Our previous studies have indicated that transforming growth factor (TGF)-β1 and VEGF expression are increased in the smooth muscle cell (SMC) layer of the pulmonary vessels of lambs with pulmonary hypertension secondary to increased pulmonary blood flow. Furthermore, we found that TGF-β1 expression increased before VEGF. Because of the increased blood flow in the shunt lambs, the SMC in the pulmonary vessels are exposed to increased levels of the mechanical force, cyclic stretch. Thus, in this study, using primary cultures of pulmonary arterial SMC isolated from pulmonary arteries of 4-wk-old lambs, we investigated the role of cyclic stretch in the apparent coordinated regulation of TGF-β1 and VEGF. Our results demonstrated that cyclic stretch induced a significant increase in VEGF expression both at the mRNA and protein levels ( P < 0.05). The increased VEGF mRNA was preceded by both an increased expression and secretion of TGF-β1 and an increase in reactive oxygen species (ROS) generation. In addition, a neutralizing antibody against TGF-β1 abolished the cyclic stretch-dependent increases in both superoxide generation and VEGF expression. Our data also demonstrated that cyclic stretch activated an NAD(P)H oxidase that was TGF-β1 dependent and that NAD(P)H oxidase inhibitors abolished the cyclic stretch-dependent increase in VEGF expression. Therefore, our results indicate that cyclic stretch upregulates VEGF expression via the TGF-β1-dependent activation of NAD(P)H oxidase and increased generation of ROS.

Idiopathic pulmonary fibrosis: emerging concepts on pharmacotherapy

Idiopathic pulmonary fibrosis (IPF) is a progressive, fibrosing disease of the distal air spaces of the lung of unknown aetiology. IPF is usually fatal with a median survival of < 3 years. There are currently no effective pharmacotherapeutic agents for the treatment of IPF. In this review, unifying concepts on the pathogenesis of IPF based on understanding of host responses to tissue injury are presented. These host responses involve tightly regulated and contextually orchestrated inflammatory and repair processes. Dysregulation of either of these processes can lead to pathological outcomes. Fibrosis results from an exaggerated or dysregulated repair process that proceeds 'uncontrolled' even after inflammatory responses have subsided. Disease heterogeneity may arise when inflammation and repair are in different (dys)regulatory phases, thus accounting for regional disparity. Usual interstitial pneumonia (UIP), the histopathological correlate of clinical IPF, represents a more fibrotic tissue reaction pattern and for which anti-inflammatory agents are ineffective. Emerging 'antifibrotic' drugs and strategies for UIP/IPF are discussed. The importance of accurately phenotyping a highly heterogeneous disease process that may require individualised and 'combined' therapies is emphasised.

The Death-Inducing Effect and Genomic Instability

Exposure to ionizing radiation can induce a heritable change in the unirradiated progeny of irradiated cells. This non-targeted effect of ionizing radiation manifests as genomic instability, and although there is some debate as to the role of genomic instability in the carcinogenic process, it is thought by some to be an early step in radiation carcinogenesis. Although the mechanism of induction of genomic instability is not clearly understood, evidence suggests that secreted factors from irradiated cells may be involved. We have previously identified another non-targeted effect of ionizing radiation, the death-inducing effect. Exposure of unirradiated GM10115 cells to medium from chromosomally unstable clones was generally found to be cytotoxic. However, occasionally cells will survive in medium from unstable clones and can be clonally expanded. The absolute yield of survivors is independent of the initial number of cells plated when cell densities reached 5,000 or more cells/dish. After cytogenetic analysis of the surviving colonies, we found chromosomal instability in three of 40 clones analyzed, while some clones exhibited increased micronucleus frequency and HPRT mutation frequency. These data suggest that our chromosomally unstable GM10115 cells secrete factors that are cytotoxic to the majority of stable, parental cells but are also capable of inducing a heritable change in some of the survivors that can manifest as delayed genomic instability. These results suggest a mechanism whereby instability can be perpetuated through the influences of potentially cytotoxic factors produced by genomically unstable clones.

Hydrogen peroxide is a diffusible paracrine signal for the induction of epithelial cell death by activated myofibroblasts

Cell-cell signaling roles for reactive oxygen species (ROS) generated in response to growth factors/cytokines in nonphagocytic cells are not well defined. In this study, we show that fibroblasts isolated from lungs of patients with idiopathic pulmonary fibrosis (IPF) generate extracellular hydrogen peroxide (H2O2) in response to the multifunctional cytokine, transforming growth factor-beta1 (TGF-beta1). In contrast, TGF-beta1 stimulation of small airway epithelial cells (SAECs) does not result in detectable levels of extracellular H2O2. IPF fibroblasts independently stimulated with TGF-beta1 induce loss of viability and death of overlying SAECs when cocultured in a compartmentalized Transwell system. These effects on SAECs are inhibited by the addition of catalase to the coculture system or by the selective enzymatic blockade of H2O2 production by IPF fibroblasts. IPF fibroblasts heterogeneously express alpha-smooth muscle actin stress fibers, a marker of myofibroblast differentiation. Cellular localization of H2O2 by a fluorescent-labeling strategy demonstrated that extracellular secretion of H2O2 is specific to the myofibroblast phenotype. Thus, myofibroblast secretion of H2O2 functions as a diffusible death signal for lung epithelial cells. This novel mechanism for intercellular ROS signaling may be important in physiological/pathophysiological processes characterized by regenerating epithelial cells and activated myofibroblasts.

c-Src and hydrogen peroxide mediate transforming growth factor-beta1-induced smooth muscle cell-gene expression in 10T1/2 cells

OBJECTIVE

Transforming growth factor-beta1 (TGF-beta1) controls the expression of numerous genes, including smooth muscle cell (SMC)-specific genes and extracellular matrix protein genes. Here we investigated whether c-Src plays a role in TGF-beta1 signaling in mouse embryonic fibroblast C3H10T1/2 cells.

METHODS AND RESULTS

TGF-beta1 induction of the SMC contractile protein SM22alpha gene expression was inhibited by PP1 (an inhibitor of Src family kinases) or by C-terminal Src kinase (a negative regulator of c-Src). Induction of SM22alpha by TGF-beta1 was markedly attenuated in SYF cells (c-Src(-), Yes(-), and Fyn(-)) compared with Src(++) cells (c-Src(++), Yes(-), and Fyn(-)). PP1 also inhibited the TGF-beta1-induced expression of serum response factor (SRF), a transcription factor regulating the SMC marker gene expression. Confocal immunofluorescence analysis showed that TGF-beta1 stimulates production of hydrogen peroxide. Antioxidants such as catalase or NAD(P)H oxidase inhibitors such as apocynin inhibited the TGF-beta1-induced expression of SM22alpha. Furthermore, we demonstrate that TGF-beta1 induction of the plasminogen activator inhibitor-1 (PAI-1) gene, which is known to be dependent on Smad but not on SRF, is inhibited by PP1 and apocynin.

CONCLUSIONS

Our results suggest that TGF-beta1 activates c-Src and generates hydrogen peroxide through NAD(P)H oxidase, and these signaling pathways lead to the activation of specific sets of genes, including SM22alpha and PAI-1. TGF-beta1 controls the expression of numerous genes, including SM22alpha and PAI-1. We investigated whether c-Src plays a role in TGF-beta1 signaling. TGF-beta1 induction of such genes was significantly reduced in Src family tyrosine kinase-deficient cells, and Csk and pharmacological inhibitors for Src family kinases or antioxidants inhibit the effects of TGF-beta1. These results indicate that c-Src and hydrogen peroxide are required for TGF-beta1 signaling.

Role of oxidative modifications in atherosclerosis

This review focuses on the role of oxidative processes in atherosclerosis and its resultant cardiovascular events. There is now a consensus that atherosclerosis represents a state of heightened oxidative stress characterized by lipid and protein oxidation in the vascular wall. The oxidative modification hypothesis of atherosclerosis predicts that low-density lipoprotein (LDL) oxidation is an early event in atherosclerosis and that oxidized LDL contributes to atherogenesis. In support of this hypothesis, oxidized LDL can support foam cell formation in vitro, the lipid in human lesions is substantially oxidized, there is evidence for the presence of oxidized LDL in vivo, oxidized LDL has a number of potentially proatherogenic activities, and several structurally unrelated antioxidants inhibit atherosclerosis in animals. An emerging consensus also underscores the importance in vascular disease of oxidative events in addition to LDL oxidation. These include the production of reactive oxygen and nitrogen species by vascular cells, as well as oxidative modifications contributing to important clinical manifestations of coronary artery disease such as endothelial dysfunction and plaque disruption. Despite these abundant data however, fundamental problems remain with implicating oxidative modification as a (requisite) pathophysiologically important cause for atherosclerosis. These include the poor performance of antioxidant strategies in limiting either atherosclerosis or cardiovascular events from atherosclerosis, and observations in animals that suggest dissociation between atherosclerosis and lipoprotein oxidation. Indeed, it remains to be established that oxidative events are a cause rather than an injurious response to atherogenesis. In this context, inflammation needs to be considered as a primary process of atherosclerosis, and oxidative stress as a secondary event. To address this issue, we have proposed an "oxidative response to inflammation" model as a means of reconciling the response-to-injury and oxidative modification hypotheses of atherosclerosis.

Platelet derived growth factor (PDGF)-induced reactive oxygen species in the lens epithelial cells: the redox signaling

Low level of reactive oxygen species (ROS) has been shown to play an important role in host defense and mediating mitogen-stimulated cell signaling in several cell types. This study is to identify the mitogen-induced endogenous ROS generation and the range of exogenous H(2)O(2) that initiate redox signaling and cell proliferation in human lens epithelial cells (HLE B3), using platelet-derived growth factor (PDGF) as a model. To detect ROS generation, serum starved HLE cells (1.6 million) were loaded with fluorescent dye, 2',7'-dichlorofluorescin diacetate (DCFH-DA), before exposing to PDGF (1 ng ml(-1)). The fluorescence generated from the oxidant-sensitive DCFH, the intracellular product of DCFH-DA hydrolysate, was immediately measured in live cells by confocal laser light microscopy (lambda(Ex)=488 nm, lambda(Em)=522 nm, laser power=10%). PDGF-stimulated cells showed strong transient fluorescence during the 60 min while no fluorescence could be seen in the unstimulated cells. The PDGF-induced fluorescence could be suppressed with cells preloaded with N-acetyl-L-cysteine (NAC, 30 mm), catalase (1 mg ml(-1)), or D-mannitol (100mm). The ability of catalase to penetrate and function in HLE cells was confirmed by western blot, enzyme activity and immunofluorescence microscopic analyses. PDGF induced DNA synthesis within one hour as measured by (3)H-thymidine incorporation, and transiently activated the mitogen-activated protein kinases (MAPKs) of ERK1/2 and JNK. PDGF-stimulated DNA synthesis and MAPK activation were eliminated in the presence of catalase or mannitol. Low levels of H(2)O(2) (10-20 microm) mimicked PDGF in both MAPK stimulation and cell proliferation. In conclusion, the mitogenic stimulus function of PDGF in HLE cells appears to be mediated via ROS to activate MAPKs and cell proliferation, which can be mimicked by low levels of H(2)O(2). It is proposed that the physiological function of ROS, the redox signaling, is present in the HLE cells and may play an important role in the development and maintenance of the lens.

Paracrine effect of TGF-β1 on downregulation of gap junctional intercellular communication between human dermal fibroblasts

Disruption of gap junctional intercellular communication (GJIC) is associated with tumor progression during multistage carcinogenesis. A coordinated interaction of epithelial tumor cells with the stromal environment via growth factors is a prerequisite for tumor invasion. Here, the involvement of growth factors in downregulation of homologous GJIC of dermal fibroblasts, used as model for stromal cells, was examined. Tumor cell derived transforming growth factor-beta1 (TGF-beta1), having oncogenic activities at late stages of carcinogenesis, was identified as being responsible for downregulation of GJIC via an increase in the level of reactive oxygen species in stromal fibroblasts. Lowering the level of reactive oxygen species by antioxidants, such as the cell-permeable N-acetyl-L-cysteine, prevented TGF-beta1-mediated downregulation of intercellular communication between confluent fibroblasts.

Mechanisms of pulmonary fibrosis

Tissue injury evokes highly conserved, tightly regulated inflammatory responses and less well-understood host repair responses. Both inflammation and repair involve the recruitment, activation, apoptosis, and eventual clearance of key effector cells. In this review, we propose the concept of pulmonary fibrosis as a dysregulated repair process that is perpetually "turned on" even though classical inflammatory pathways may be dampened or "switched off." Significant regional heterogeneity, with varied histopathological patterns of inflammation and fibrosis, has been observed in individual patients with idiopathic pulmonary fibrosis. We discuss environmental factors and host response factors, such as genetic susceptibility and age, that may influence these varied manifestations. Better understanding of the mechanisms of lung repair, which include alveolar reepithelialization, myofibroblast differentiation/activation, and apoptosis, should offer more effective therapeutic options for progressive pulmonary fibrosis.

Early single cell bifurcation of pro- and antiapoptotic states during oxidative stress

In a population of cells undergoing oxidative stress, an individual cell either succumbs to apoptotic cell death or maintains homeostasis and survives. Exposure of PC-12-D(2)R cells to 200 microm hydrogen peroxide (H(2)O(2)) induces apoptosis in about half of cells after 24 h. After 1-h exposure to 200 microm H(2)O(2), both antiapoptotic extracellular regulated kinase (ERK) phosphorylation and pro-apoptotic Ser-15-p53 phosphorylation are observed. Microarray and real-time PCR assays of gene expression after H(2)O(2) exposure identified several transcripts, including egr1, that are rapidly induced downstream of ERK. Single cell analysis of egr1 induction and of phospho-ERK and phospho-p53 formation revealed the presence of two distinct cellular programs. Whereas the proportion of cells activating ERK versus p53 at 1 h depended on H(2)O(2) concentration, individual cells showed exclusively either phospho-p53 formation or activation of ERK and egr1 induction. Exposure to H(2)O(2) for 1 h also elicited these two non-overlapping cellular responses in both dopaminergic SN4741 cells and differentiated postmitotic PC-12-D(2)R cells. Repressing p53 with pifithrin-alpha or small interfering RNA increased ERK phosphorylation by H(2)O(2), indicating that p53-dependent suppression of ERK activity may contribute to the bi-stable single cell responses observed. By 24 h, the subset of cells in which ERK activity was suppressed exhibit caspase 3 activation and the nuclear condensation characteristic of apoptosis. These studies suggest that the individual cell rapidly and stochastically processes the oxidative stress stimulus, leading to an all-or-none cytoprotective or pro-apoptotic signaling response.

Deactivation of murine alveolar macrophages by peroxisome proliferator-activated receptor-γ ligands

Peroxisome proliferator-activated receptor-γ (PPAR-γ), a member of the nuclear hormone receptor family of ligand-dependent transcription factors, is a critical regulator of adipocyte differentiation and glucose metabolism. The expression, regulation, and functional significance of PPAR-γ in alveolar macrophages (AMs), the predominant resident immune effector cell within the alveolus, have not been previously examined. In this study, we show that, in contrast to peritoneal macrophages, resident murine AMs constitutively express high levels of PPAR-γ. Expression was primarily located in the nucleus by immunofluorescence staining. Quantitative real-time RT-PCR demonstrated that the predominant isoform was PPAR-γ2. Expression of PPAR-γ was induced by the anti-inflammatory cytokine IL-4. Treatment of murine AMs with PPAR-γ ligands suppresses PMA-stimulated oxidative burst activity and LPS + IFN-γ-mediated expression of inducible nitric oxide synthase. In addition, LPS-induced IL-12 mRNA and protein expression was inhibited by PPAR-γ ligands. These results support an important immunomodulatory role for PPAR-γ in AM responses.

Involvement of calcineurin in transforming growth factor-beta-mediated regulation of extracellular matrix accumulation

Calcineurin is a calcium-dependent, serine/threonine phosphatase that functions as a signaling intermediate. In this study, we investigated the role of calcineurin in transforming growth factor-beta (TGF-beta)-mediated cellular effects and examined the signaling pathway involved in activation of calcineurin. Calcineurin is activated by TGF-beta in a time- and dose-dependent manner. Consistent with increased phosphatase activity, the calcineurin substrate, NFATc1, is dephosphorylated and transported to the nucleus. Inhibition of calcineurin prior to the addition of TGF-beta revealed that calcineurin is required for TGF-beta-mediated accumulation of extracellular matrix (ECM) proteins but not cell hypertrophy. Conversely, overexpression of constitutively active calcineurin was sufficient to induce ECM protein expression. The mechanism of calcineurin activation by TGF-beta was found to be induction of a low, sustained increase of intracellular calcium. Chelation of extracellular calcium blocked both TGF-beta-mediated calcium influx and calcineurin activity. Finally, calcium entry was found to be dependent upon generation of reactive oxygen species (ROS) including superoxide anion and hydrogen peroxide. Accordingly, inhibition of ROS generation also blocked TGF-beta-mediated calcineurin phosphatase activity and decreased ECM accumulation. In conclusion, this study describes a new pathway for TGF-beta-mediated regulation of ECM via generation of ROS, calcium influx, and activation of calcineurin.

Activation of the pro-survival phosphatidylinositol 3-kinase/AKT pathway by transforming growth factor-beta1 in mesenchymal cells is mediated by p38 MAPK-dependent induction of an autocrine growth factor

Transforming growth factor-beta1 (TGF-beta1) is a multifunctional cytokine involved in differentiation, growth, and survival of mesenchymal cells while inhibiting growth/survival of most other cell types. The mechanism(s) of pro-survival signaling by TGF-beta1 in mesenchymal cells is unclear. In this report, we demonstrate that TGF-beta1 protects against serum deprivation-induced apoptosis of mesenchymal cells isolated from patients with acute lung injury and of normal human fetal lung fibroblasts (IMR-90). TGF-beta receptor(s)-activated signaling in these cells involves rapid activation of the Smad and p38 MAPK pathways within minutes of TGF-beta1 treatment followed by a more delayed activation of the pro-survival phosphatidylinositol 3-kinase-protein kinase B (PKB)/Akt pathway. Pharmacological inhibition of p38 MAPK with SB203580 or expression of a p38 kinase-deficient mutant protein inhibits TGF-beta1-induced PKB/Akt phosphorylation. Conditioned medium from TGF-beta1-treated cells rapidly induces PKB/Akt activation in an SB203580- and suramin-sensitive manner, suggesting p38 MAPK-dependent production of a secreted growth factor that activates this pro-survival pathway by an autocrine/paracrine mechanism. Inhibition of the phosphatidylinositol 3-kinase-PKB/Akt pathway blocks TGF-beta1-induced resistance to apoptosis. These results demonstrate the activation of a novel TGF-beta1-activated pro-survival/anti-apoptotic signaling pathway in mesenchymal cells/fibroblasts that may explain cell-specific actions of TGF-beta1 and provide mechanistic insights into its pro-fibrotic and tumor-promoting effects.

Myofibroblast differentiation by transforming growth factor-beta1 is dependent on cell adhesion and integrin signaling via focal adhesion kinase

Myofibroblast differentiation and activation by transforming growth factor-beta1 (TGF-beta1) is a critical event in the pathogenesis of human fibrotic diseases, but regulatory mechanisms for this effect are unclear. In this report, we demonstrate that stable expression of the myofibroblast phenotype requires both TGF-beta1 and adhesion-dependent signals. TGF-beta1-induced myofibroblast differentiation of lung fibroblasts is blocked in non-adherent cells despite the preservation of TGF-beta receptor(s)-mediated signaling of Smad2 phosphorylation. TGF-beta1 induces tyrosine phosphorylation of focal adhesion kinase (FAK) including that of its autophosphorylation site, Tyr-397, an effect that is dependent on cell adhesion and is delayed relative to early Smad signaling. Pharmacologic inhibition of FAK or expression of kinase-deficient FAK, mutated by substituting Tyr-397 with Phe, inhibit TGF-beta1-induced alpha-smooth muscle actin expression, stress fiber formation, and cellular hypertrophy. Basal expression of alpha-smooth muscle actin is elevated in cells grown on fibronectin-coated dishes but is decreased on laminin and poly-d-lysine, a non-integrin binding polypeptide. TGF-beta1 up-regulates expression of integrins and fibronectin, an effect that is associated with autophosphorylation/activation of FAK. Thus, a safer and more effective therapeutic strategy for fibrotic diseases characterized by persistent myofibroblast activation may be to target this integrin/FAK pathway while not interfering with tumor-suppressive functions of TGF-beta1/Smad signaling.

[Regulation of gene expression by active oxygen species]

Reactive oxygen species (ROS) are generated from cells stimulated by various cytokines, hormones, and stresses, and regulate cellular functions such as gene expression and cell growth. They affect activities of many types of molecular targets, including signaling molecules and transcription factors. Early-response genes (c-fos, egr-I and JE) that encode transcription factors are induced by ROS, and activities of their products are modulated by ROS through redox-based mechanisms. We isolated a novel gene, hic-5, that was induced by hydrogen peroxide and encodes a focal adhesion protein. hic-5 was found to translocate to the nucleus in cells treated with ROS and regulates several cellular genes. We propose that hic-5 is a key element in the transduction of signals from the cell surface to the nucleus under oxidative stress.

Bystander effects in radiation-induced genomic instability

Exposure of GM10115 hamster-human hybrid cells to X-rays can result in the induction of chromosomal instability in the progeny of surviving cells. This instability manifests as the dynamic production of novel sub-populations of cells with unique cytogenetic rearrangements involving the "marker" human chromosome. We have used the comet assay to investigate whether there was an elevated level of endogenous DNA breaks in chromosomally unstable clones that could provide a source for the chromosomal rearrangements and thus account for the persistent instability observed. Our results indicate no significant difference in comet tail measurement between non-irradiated and radiation-induced chromosomally unstable clones. Using two-color fluorescence in situ hybridization we also investigated whether recombinational events involving the interstitial telomere repeat-like sequences in GM10115 cells were involved at frequencies higher than random processes would otherwise predict. Nine of 11 clones demonstrated a significantly higher than expected involvement of these interstitial telomere repeat-like sequences at the recombination junction between the human and hamster chromosomes. Since elevated levels of endogenous breaks were not detected in unstable clones we propose that epigenetic or bystander effects (BSEs) lead to the activation of recombinational pathways that perpetuate the unstable phenotype. Specifically, we expand upon the hypothesis that radiation induces conditions and/or factors that stimulate the production of reactive oxygen species (ROS). These reactive intermediates then contribute to a chronic pro-oxidant environment that cycles over multiple generations, promoting chromosomal recombination and other phenotypes associated with genomic instability.

Molecular mechanism of transforming growth factor (TGF)-beta1-induced glutathione depletion in alveolar epithelial cells. Involvement of AP-1/ARE and Fra-1

Glutathione (GSH) is a ubiquitous antioxidant in lung epithelial cells and lung lining fluid. Transforming growth factor beta1 (TGF-beta1) is a pleiotropic cytokine involved in cellular proliferation and differentiation. The level of TGF-beta1 is elevated in many chronic inflammatory lung disorders associated with oxidant/antioxidant imbalance. In this study, we show that TGF-beta1 depletes GSH by down-regulating expression of the enzyme responsible for its formation, gamma-glutamylcysteine synthetase (gamma-GCS) and induces reactive oxygen species production in type II alveolar epithelial cells (A549). To investigate the molecular mechanisms of inhibition of glutathione synthesis, we employed reporters containing fragments from the promoter region of the gamma-GCS heavy subunit (h), the gene that encodes the catalytic subunit of gamma-GCS. We found that TGF-beta1 reduced the expression of the long gamma-GCSh construct (-3802/GCSh-5'-Luc), suggesting that an antioxidant response element (ARE) may be responsible for mediating the TGF-beta1 effect. Interestingly, the electrophoretic mobility shift assay revealed that the DNA binding activity of both activator protein-1 (AP-1) and ARE was increased in TGF-beta1-treated epithelial cells. The gamma-GCSh ARE contains a perfect AP-1 site embedded within it, and mutation of this internal AP-1 sequence, but not the surrounding ARE, prevented DNA binding. Further studies revealed that c-Jun and Fra-1 dimers, members of the AP-1 family previously shown to exert a negative effect on phase II gene expression, bound to the ARE sequence. We propose a novel mechanism of gamma-GCSh down-regulation by TGF-beta1 that involves the binding of c-Jun and Fra-1 dimers to the distal promoter. The findings of this study provide important information, which may be used for the modulation of glutathione biosynthesis in inflammation.

Reactive oxygen species differentially affect T cell receptor-signaling pathways

Oxidative stress plays an important role in the induction of T lymphocyte hyporesponsiveness observed in several human pathologies including cancer, rheumatoid arthritis, leprosy, and AIDS. To investigate the molecular basis of oxidative stress-induced T cell hyporesponsiveness, we have developed an in vitro system in which T lymphocytes are rendered hyporesponsive by co-culture with oxygen radical-producing activated neutrophils. We have observed a direct correlation between the level of T cell hyporesponsiveness induced and the concentration of reactive oxygen species produced. Moreover, induction of T cell hyporesponsiveness is blocked by addition of N-acetyl cysteine, Mn(III)tetrakis(4-benzoic acid)porphyrin chloride, and catalase, confirming the critical role of oxidative stress in this system. The pattern of tyrosine-phosphorylated proteins was profoundly altered in hyporesponsive as compared with normal T cells. In hyporesponsive T cells, T cell receptor (TCR) ligation no longer induced phospholipase C-gamma1 activation and caused reduced Ca(2+) flux. In contrast, despite increased levels of ERK1/2 phosphorylation, TCR-dependent activation of mitogen-activated protein kinase ERK1/2 was unaltered in hyporesponsive T lymphocytes. A late TCR-signaling event such as caspase 3 activation was as well unaffected in hyporesponsive T lymphocytes. Our data indicate that TCR-signaling pathways are differentially affected by physiological levels of oxidative stress and would suggest that although "hyporesponsive" T cells have lost certain effector functions, they may have maintained or gained others.

Peplomycin, a bleomycin derivative, induces myofibroblasts in pulmonary fibrosis

To analyse the mechanism by which a bleomycin derivative, peplomycin (PLM) induces pulmonary fibrosis, we investigated differentiation of rat pulmonary fibroblasts to myofibroblasts (MF). In intraperitoneally PLM (5 mg/kg/day)-injected rats, the peripheries of lungs adjacent to the pleura revealed advanced fibrosis with a small number of alpha-smooth muscle actin (alpha-SMA)-positive MF, which ultrastructurally possessed abundant microfilaments and cellular organelles. In the fibrotic tissue, the expression of alpha-SMA-mRNA was detected by in situ reverse transcription-polymerase (RT-PCR). The message was strong just after a 2-week administration of PLM then decreased thereafter, although fibrosis advanced. When pulmonary fibroblasts were separated from saline-injected rats (N-Fib) and cultivated for 7 days in the presence of 5 mg/mL PLM, alpha-SMA protein was weakly expressed, while the majority of pulmonary fibroblasts separated from PLM-injected rats (P-Fib) became positive for alpha-SMA in 7-day cultivation and the expression of alpha-SMA in P-Fib was strongly increased by cultivation in the presence of PLM and transforming growth factor-beta (TGF-beta), but not basic fibroblast growth factor (bFGF) or platelet-derived growth factor (PDGF), although the cell proliferation was most strongly enhanced by bFGF and only slightly by PLM and TGF-beta. The alpha-SMA-positive cells expressed vimentin, but only weakly expressed desmin. Additionally, P-Fib generated larger amounts of TGF-beta and bFGF than were generated by N-Fib. These results indicate that PLM induces pulmonary fibrosis by differentiating fibroblasts to alpha-SMA-positive MF, and that bFGF and TGF-beta play each critical role in the different phases of PLM-induced pulmonary fibrosis by inducing fibroblast proliferation and transformation, respectively.

Oxidative protein cross-linking reactions involving L-tyrosine in transforming growth factor-beta1-stimulated fibroblasts

The mechanisms by which ligand-stimulated generation of reactive oxygen species in nonphagocytic cells mediate biologic effects are largely unknown. The profibrotic cytokine, transforming growth factor-beta1 (TGF-beta1), generates extracellular hydrogen peroxide (H2O2) in contrast to intracellular reactive oxygen species production by certain mitogenic growth factors in human lung fibroblasts. To determine whether tyrosine residues in fibroblast-derived extracellular matrix (ECM) proteins may be targets of H2O2-mediated dityrosine-dependent cross-linking reactions in response to TGF-beta1, we utilized fluorophore-labeled tyramide, a structurally related phenolic compound that forms dimers with tyrosine, as a probe to detect such reactions under dynamic cell culture conditions. With this approach, a distinct pattern of fluorescent labeling that seems to target ECM proteins preferentially was observed in TGF-beta1-treated cells but not in control cells. This reaction required the presence of a heme peroxidase and was inhibited by catalase or diphenyliodonium (a flavoenzyme inhibitor), similar to the effect on TGF-beta1-induced dityrosine formation. Exogenous addition of H2O2 to control cells that do not release extracellular H2O2 produced a similar fluorescent labeling reaction. These results support the concept that, in the presence of heme peroxidases in vivo, TGF-beta1-induced H2O2 production by fibroblasts may mediate oxidative dityrosine-dependent cross-linking of ECM protein(s). This effect may be important in the pathogenesis of human fibrotic diseases characterized by overexpression/activation of TGF-beta1.

Elevated superoxide production by active H-ras enhances human lung WI-38VA-13 cell proliferation, migration and resistance to TNF-alpha

Accumulating evidence has suggested that cellular production of superoxide acts as an intracellular messenger to regulate gene expression and modulate cellular activities. In this report, we set out to investigate the role of active H-ras-mediated superoxide production on tumor cell malignancy in a SV-40 transformed human lung WI-38 VA-13 cell line. Stable transfection and expression of constitutively active mutant V12-H-ras (V12-H-ras) dramatically increased intracellular production of superoxide. The expression of V12-H-ras significantly enhanced cell proliferation, migration and resistance to TNF-alpha treatment compared to that of parental and vector control cells, while expression of wild type H-ras (WT-H-ras) only had modest effects. Upon scavenging by superoxide dismutase and other molecules that decrease the intracellular level of active H-ras mediated superoxide production, cell proliferation, migration and resistance to TNF-alpha were significantly reduced. Furthermore, we demonstrated that the activation of membrane NADPH oxidase activity by expression of active H-ras contributed to the intracellular superoxide production. The causal relationship between membrane superoxide production and increased cell proliferation, migration, and resistance to TNF-alpha by the expression of active H-ras, has provided direct evidence to demonstrate that superoxide acts as an intracellular messenger to cascade ras oncogenic signal relay and to modulate tumor malignant activity.