Persistent induction of c-fos and c-jun expression by asbestos

Cellular defense mechanisms against asbestos fibers

Although inhalation of sufficient doses and dimensions of airborne asbestos dusts in an occupational setting can produce cancer in the lungs, pleura and peritoneum, tumors occur in <5-10% of exposed individuals, even among persons with considerable historical exposures. In this perspective, we review cell defense mechanisms that are involved in protective and adaptive responses to asbestos exposure. These adaptive responses are orchestrated through a multifaceted cellular program involving the concerted action of diverse stress response pathways, including antioxidant responses, DNA repair mechanisms, molecular mechanisms for intracellular signaling leading to proliferation, apoptosis, and inflammation, and cell cycle regulation. These cell defenses suggest that humans can adjust to moderate levels of stress or change without experiencing negative effects, implying the existence of a threshold dose. Likewise, reported no-observed adverse-effect levels (NOAELs) for various asbestos fiber types and asbestos-related cancers in experimental and epidemiological data further support the existence of a threshold dose and are discussed here.

Pleural mesothelioma (PMe): The evolving molecular knowledge of a rare and aggressive cancer

Mesothelioma is a type of late-onset cancer that develops in cells covering the outer surface of organs. Although it can affect the peritoneum, heart, or testicles, it mainly targets the lining of the lungs, making pleural mesothelioma (PMe) the most common and widely studied mesothelioma type. PMe is caused by exposure to fibres of asbestos, which when inhaled leads to inflammation and scarring of the pleura. Despite the ban on asbestos by most Western countries, the incidence of PMe is on the rise, also facilitated by a lack of specific symptomatology and diagnostic methods. Therapeutic options are also limited to mainly palliative care, making this disease untreatable. Here we present an overview of biological aspects underlying PMe by listing genetic and molecular mechanisms behind its onset, aggressive nature, and fast-paced progression. To this end, we report on the role of deubiquitinase BRCA1-associated protein-1 (BAP1), a tumour suppressor gene with a widely acknowledged role in the corrupted signalling and metabolism of PMe. This review aims to enhance our understanding of this devastating malignancy and propel efforts for its investigation.

Mechanisms and shapes of causal exposure-response functions for asbestos in mesotheliomas and lung cancers

This paper summarizes recent insights into causal biological mechanisms underlying the carcinogenicity of asbestos. It addresses their implications for the shapes of exposure-response curves and considers recent epidemiologic trends in malignant mesotheliomas (MMs) and lung fiber burden studies. Since the commercial amphiboles crocidolite and amosite pose the highest risk of MMs and contain high levels of iron, endogenous and exogenous pathways of iron injury and repair are discussed. Some practical implications of recent developments are that: (1) Asbestos-cancer exposure-response relationships should be expected to have non-zero background rates; (2) Evidence from inflammation biology and other sources suggests that there are exposure concentration thresholds below which exposures do not increase inflammasome-mediated inflammation or resulting inflammation-mediated cancer risks above background risk rates; and (3) The size of the suggested exposure concentration threshold depends on both the detailed time patterns of exposure on a time scale of hours to days and also on the composition of asbestos fibers in terms of their physiochemical properties. These conclusions are supported by complementary strands of evidence including biomathematical modeling, cell biology and biochemistry of asbestos-cell interactions in vitro and in vivo, lung fiber burden analyses and epidemiology showing trends in human exposures and MM rates.

Signaling of MK2 sustains robust AP1 activity for triple negative breast cancer tumorigenesis through direct phosphorylation of JAB1

Triple negative breast cancer (TNBC) cells are generally more invasive than estrogen receptor-positive (ER + ) breast cancer cells. Consistent with the importance of activator protein 1 (AP1) transcription factors in invasion, AP1 activity is much higher in TNBC lines than ER + lines. In TNBC cells, robust AP1 activity is facilitated by both ERK and p38^MAPK signaling pathways. While ERK signaling pathway regulates AP1 activity by controlling the abundance of AP1 transcription factors, p38^MAPK signaling pathway does it by enhancing AP1 binding to AP1 sites without altering their abundance. Here, we show that p38^MAPK regulation of AP1 activity involves both MAPKAPK2 (MK2) and JAB1, a known JUN-binding protein. MK2 not only interacts with JAB1 but also directly phosphorylates JAB1 at Ser177 in TNBC cells. Interestingly, Ser177 phosphorylation does not affect JAB1 and JUN interaction. Instead, interfering with p38^MAPK signaling pathway or introducing an S to A point mutation at Ser177 of JAB1 reduces JUN recruitment to the AP1 sites in cyclin D1, urokinase plasminogen activator (uPA) and uPA receptor promoters. Moreover, knockdown of JAB1 diminishes >60% of AP1 transcriptional activity in TNBC cells. Taken together, these results indicate that MK2-mediated phosphorylation of JAB1 facilitates JUN recruitment to AP1 sites, thus augmenting AP1 activity. In line with the role of JAB1 in AP1 activity, silencing JAB1 leads to dramatic reduction in TNBC cell growth, in vitro invasion and in vivo tumor outgrowth. This study suggests that the p38^MAPK-MK2 signaling pathway promotes TNBC tumorigenesis by sustaining robust AP1 activity.

Long-term instillation to four natural representative chrysotile of China induce the inactivation of P53 and P16 and the activation of C-JUN and C-FOS in the lung tissues of Wistar rats

Chrysotile is the only type of asbestos still widely exploited, and all kinds of asbestos including chrysotile was classified as a group I carcinogen by the IARC. There is a wealth of evidence that chrysotile can cause a range of cancers, including cancer of the lung, larynx, ovary, and mesothelioma. As the second largest chrysotile producer, China is at great risk of occupational exposure. Moreover, our previous experiment and some other studies have shown that the toxicity of mineral fibre from various mining areas may be different. To explore the oncogenic potential of chrysotile from different mining areas of China, Wistar rats were administered 0.5 mL chrysotile asbestos suspension of 2.0 mg/mL (from Akesai, Gansu; Mangnai, Qinghai; XinKang, Sichuan; and Shannan, Shaanxi) dissolved in saline by intratracheal instillation once-monthly and were sacrificed at 1 mo, 6 mo, and 12 mo. Our results found that chrysotile caused lung inflammation and lung tissue damage. Moreover, prolonged exposure of chrysotile can induce inactivation of the tumor suppressor gene P53 and P16 and activation of the protooncogene C-JUN and C-FOS both in the messenger RNA and protein level. In addition, chrysotile from Shannan and XinKang has a stronger effect which may link to cancer than that from Akesai and Mangnai.

Metabolic rewiring and redox alterations in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is a rare malignancy of mesothelial cells with increasing incidence, and in many cases, dismal prognosis due to its aggressiveness and lack of effective therapies. Environmental and occupational exposure to asbestos is considered the main aetiological factor for MPM. Inhaled asbestos fibres accumulate in the lungs and induce the generation of reactive oxygen species (ROS) due to the presence of iron associated with the fibrous silicates and to the activation of macrophages and inflammation. Chronic inflammation and a ROS-enriched microenvironment can foster the malignant transformation of mesothelial cells. In addition, MPM cells have a highly glycolytic metabolic profile and are positive in 18F-FDG PET analysis. Loss-of-function mutations of BRCA-associated protein 1 (BAP1) are a major contributor to the metabolic rewiring of MPM cells. A subset of MPM tumours show loss of the methyladenosine phosphorylase (MTAP) locus, resulting in profound alterations in polyamine metabolism, ATP and methionine salvage pathways, as well as changes in epigenetic control of gene expression. This review provides an overview of the perturbations in metabolism and ROS homoeostasis of MPM cells and the role of these alterations in malignant transformation and tumour progression.

Man-made mineral fiber effects on the expression of anti-oncogenes P53 and P16 and oncogenes C-JUN and C-FOS in the lung tissue of Wistar rats

Man-made mineral fibers (MMMFs) are substitutes for asbestos. MMMFs are widely used as insulation, but their molecular mechanisms underlying the tumorigenic effects in vivo have been poorly studied. For this reason, this work aimed to explore the properties and carcinogenic molecular mechanisms of MMMFs. The three MMMFs, rock wool (RW), glass fibers (GFs), and ceramic fibers (CFs), were prepared into respirable dust. Particle size, morphology, and chemical composition were analyzed by laser particle analyzer, scanning electron microscope, and X-ray fluorescence spectrometer, respectively. The Wistar rats were administered multiple intratracheal instillations of three MMMFs once a month. Then, several parameters (e.g. body mass, lung mass, and lung histology) were measured at 1, 3, and 6 months. After that, levels of P53, P16, C-JUN, and C-FOS mRNA and protein were measured by quantitative real-time reverse transcription polymerase chain reaction and Western blotting. This work found that exposure to MMMFs could influence the growth of body mass and increase lung mass. General conditions showed white nodules and irregular atrophy. In addition, MMMFs could lead to inactivation of anti-oncogene P16 and activation of proto-oncogenes (C-JUN and C-FOS) in the mRNA and protein levels, in which GF and CF were more obvious compared with RW. The effect of MMMFs was different, which may be related to the physical and chemical characteristics of different MMMFs. In conclusion, MMMFs (GF and CF) could induce an unbalanced expression of cancer-related genes in the lung tissues of rats. The understanding of the determinants of toxicity and carcinogenicity provides a scientific basis for developing and introducing new safer MMMF products, and the present study provides some useful insights into the carcinogenic mechanism of MMMFs.

Chrysotile effects on the expression of anti-oncogene P53 and P16 and oncogene C-jun and C-fos in Wistar rats' lung tissues

Chrysotile is the most widely used form of asbestos worldwide. China is the world's largest consumer and second largest producer of chrysotile. The carcinogenicity of chrysotile has been extensively documented, and accumulative evidence has shown that chrysotile is capable of causing lung cancer and other forms of cancer. However, molecular mechanisms underlying the tumorigenic effects of chrysotile remained poorly understood. To explore the carcinogenicity of chrysotile, Wistar rats were administered by intratracheal instillation (by an artificial route of administration) for 0, 0.5, 2, or 8 mg/ml of natural chrysotile (from Mangnai, Qinghai, China) dissolved in saline, repeated once a month for 6 months (a repeated high-dose exposure which may have little bearing on the effects following human exposure). The lung tissues were analyzed for viscera coefficients and histopathological alterations. Expression of P53, P16, C-JUN, and C-FOS was measured by western blotting and qRT-PCR. Our results found that chrysotile exposure leads the body weight to grow slowly and lung viscera coefficients to increase in a dose-dependent manner. General sample showed white nodules, punctiform asbestos spots, and irregular atrophy; moreover, HE staining revealed inflammatory infiltration, damage of alveolar structures, agglomerations, and pulmonary fibrosis. In addition, chrysotile can induce inactivation of the anti-oncogene P53 and P16 and activation of the proto-oncogenes C-JUN and C-FOS both in the messenger RNA and protein level. In conclusion, chrysotile induced an imbalanced expression of cancer-related genes in rats' lung tissue. These results contribute to our understanding of the carcinogenic mechanism of chrysotile.

Biological responses to asbestos inhalation and pathogenesis of asbestos-related benign and malignant disease

Asbestos comprises a group of fibrous minerals that are naturally occurring in the environment. Because of its natural properties, asbestos gained popularity for commercial applications in the late 19th century and was used throughout the majority of the 20th century, with predominant use in the construction, automotive, and shipbuilding industries. Asbestos has been linked to a spectrum of pulmonary diseases, such as pleural fibrosis and plaques, asbestosis, benign asbestos pleural effusion, small cell lung carcinoma, non-small cell lung carcinoma, and malignant mesothelioma. There are several mechanisms through which asbestos can lead to both benign and malignant disease, and they include alterations at the chromosomal level, activation of oncogenes, loss of tumor suppressor genes, alterations in cellular signal transduction pathways, generation of reactive oxygen and nitrogen species, and direct mechanical damage to cells from asbestos fibers. While known risk factors exist for the development of asbestos-related malignancies, there are currently no effective means to determine which asbestos-exposed patients will develop malignancy and which will not. There are also no established screening strategies to detect asbestos-related malignancies in patients who have a history of asbestos exposure. In this article, we present a case that highlights the different biological responses in human hosts to asbestos exposure.

Proteomic profiling change during the early development of silicosis disease

BACKGROUND

Silicosis is one of several severe occupational diseases for which effective diagnostic tools during early development are currently unavailable. In this study we focused on proteomic profiling during the early stages of silicosis to investigate the pathophysiology and identify the proteins involved.

METHODS

Two-dimensional (2D) gel electrophoresis and MALDI-TOF-MS were used to assess the proteomic differences between healthy individuals (HI), dust-exposed workers without silicosis (DEW) and silicosis patients (SP). Proteins abundances that differed by a factor of two-fold or greater were subjected to more detailed analysis, and enzyme linked to immunosorbent assay (ELISA) was employed to correlate with protein expression data.

RESULTS

Compared with HI, 42 proteins were more abundant and 8 were less abundant in DEW, and these were also differentially accumulated in SP. Closer inspection revealed that serine protease granzyme A, alpha-1-B-glycoprotein (A1BG) and the T4 surface glycoprotein precursor (TSGP) were among the up-regulated proteins in DEW and SP. Significant changes in serine proteases, glycoproteins and proto-oncogenes may be associated with the response to cytotoxicity and infectious pathogens by activation of T cells, positive regulation of extracellular matrix structural constituents and immune response, and fibroblast proliferation. Up-regulation of cytokines included TNFs, interferon beta precursor, interleukin 6, atypical chemokine receptor 2, TNFR13BV, and mutant IL-17F may be involved in the increased and persistent immune response and fibrosis that occurred during silicosis development.

CONCLUSIONS

Granzymes, glycoproteins, cytokines and immune factors were dramatically involved in the immune response, metabolism, signal regulation and fibrosis during the early development of silicosis. Proteomic profiling has expanded our understanding of the pathogenesis of silicosis, and identified a number of targets that may be potential biomarkers for early diagnosis of this debilitating disease.

Malignant mesothelioma as an oxidative stress-induced cancer: An update

Malignant mesothelioma (MM) is a relatively rare cancer that occurs almost exclusively following respiratory exposure to asbestos in humans. Its pathogenesis is closely associated with iron overload and oxidative stress in mesothelial cells. On fiber exposure, mesothelial cells accumulate fibers simultaneously with iron, which either performs physical scissor function or catalyzes free radical generation, leading to oxidative DNA damage such as strand breaks and base modifications, followed by activation of intracellular signaling pathways. Chrysotile, per se without iron, causes massive hemolysis and further adsorbs hemoglobin. Exposure to indigestible foreign materials also induces chronic inflammation, involving consistent generation of free radicals and subsequent activation of NALP3 inflammasomes in macrophages. All of these contribute to mesothelial carcinogenesis. Genomic alterations most frequently involve homozygous deletion of INK4A/4B, and other pathways such as Hippo and TGF-β pathways are also affected in MM. Recently, analyses of familial MM sorted out BAP1 as a novel responsible tumor suppressor gene, whose function is not fully elucidated. Five-year survival of mesothelioma is still ~8%, and this cancer is increasing worldwide. Connective tissue growth factor, a secretory protein creating a vicious cycle mediated by β-catenin, has been recognized as a hopeful target for therapy, especially in sarcomatoid subtype. Recent research outcomes related to microRNAs and cancer stem cells also offer additional novel targets for the treatment of MM. Iron reduction as chemoprevention of mesothelioma is helpful at least in an animal preclinical study. Integrated approaches to fiber-induced oxidative stress would be necessary to overcome this currently fatal disease.

Indications for distinct pathogenic mechanisms of asbestos and silica through gene expression profiling of the response of lung epithelial cells

Occupational and environmental exposures to airborne asbestos and silica are associated with the development of lung fibrosis in the forms of asbestosis and silicosis, respectively. However, both diseases display distinct pathologic presentations, likely associated with differences in gene expression induced by different mineral structures, composition and bio-persistent properties. We hypothesized that effects of mineral exposure in the airway epithelium may dictate deviating molecular events that may explain the different pathologies of asbestosis versus silicosis. Using robust gene expression-profiling in conjunction with in-depth pathway analysis, we assessed early (24 h) alterations in gene expression associated with crocidolite asbestos or cristobalite silica exposures in primary human bronchial epithelial cells (NHBEs). Observations were confirmed in an immortalized line (BEAS-2B) by QRT-PCR and protein assays. Utilization of overall gene expression, unsupervised hierarchical cluster analysis and integrated pathway analysis revealed gene alterations that were common to both minerals or unique to either mineral. Our findings reveal that both minerals had potent effects on genes governing cell adhesion/migration, inflammation, and cellular stress, key features of fibrosis. Asbestos exposure was most specifically associated with aberrant cell proliferation and carcinogenesis, whereas silica exposure was highly associated with additional inflammatory responses, as well as pattern recognition, and fibrogenesis. These findings illustrate the use of gene-profiling as a means to determine early molecular events that may dictate pathological processes induced by exogenous cellular insults. In addition, it is a useful approach for predicting the pathogenicity of potentially harmful materials.

Combined effects of asbestos and cigarette smoke on the development of lung adenocarcinoma: different carcinogens may cause different genomic changes

The carcinogens in cigarette smoke are distinct from asbestos. However, an understanding of their differential effects on lung adenocarcinoma development remains elusive. We investigated loss of heterozygosity (LOH) and the p53 mutation in 132 lung adenocarcinomas, for which asbestos body burden (AB; in numbers per gram of dry lung) was measured using adjacent normal lung. All cases were classified into 9 groups based on a matrix of cumulative smoking (CS in pack‑years; CS=0, 0<CS<25, ≥25 CS) and AB (AB=0, 0<AB<1,000, ≥1,000 AB). AB=0 indicates a lower level than the detection limit of ~100. LOH frequency increased only slightly with the elevation of CS in the AB=0 groups. In the AB>0 groups, LOH frequency increased as AB and/or CS was elevated and was significantly higher in the ≥1,000 AB, ≥25 CS group (p=0.032). p53 mutation frequency was the lowest in the AB=0, CS=0 group, increased as AB and/or CS rose, and was significantly higher in the ≥1,000 AB, ≥25 CS group (p=0.039). p53 mutations characteristic of smoking were frequently observed in the CS>0 groups contrary to non-specific mutations in the CS=0, AB>0 groups. Combined effects of asbestos and smoking were suggested by LOH and p53 analyses. Sole exposure to asbestos did not increase LOH frequency but increased non‑specific p53 mutations. These findings indicate that the major carcinogenic mechanism of asbestos may be tumor promotion, acting in an additive or synergistic manner, contributing to the genotoxic effect of smoking. Since this study was based on a general cancer center's experience, the limited sample size did not permit the consideration that the result was conclusive. Further investigation with a large sample size is needed to establish the mechanism of asbestos-induced lung carcinogenesis.

Differences in gene expression and cytokine production by crystalline vs. amorphous silica in human lung epithelial cells

Background

Exposure to respirable crystalline silica particles, as opposed to amorphous silica, is associated with lung inflammation, pulmonary fibrosis (silicosis), and potentially with lung cancer. We used Affymetrix/GeneSifter microarray analysis to determine whether gene expression profiles differed in a human bronchial epithelial cell line (BEAS 2B) exposed to cristobalite vs. amorphous silica particles at non-toxic and equal surface areas (75 and 150 × 10⁶μm²/cm²). Bio-Plex analysis was also used to determine profiles of secreted cytokines and chemokines in response to both particles. Finally, primary human bronchial epithelial cells (NHBE) were used to comparatively assess silica particle-induced alterations in gene expression.

Results

Microarray analysis at 24 hours in BEAS 2B revealed 333 and 631 significant alterations in gene expression induced by cristobalite at low (75) and high (150 × 10⁶μm²/cm²) amounts, respectively (p < 0.05/cut off ≥ 2.0-fold change). Exposure to amorphous silica micro-particles at high amounts (150 × 10⁶μm²/cm²) induced 108 significant gene changes. Bio-Plex analysis of 27 human cytokines and chemokines revealed 9 secreted mediators (p < 0.05) induced by crystalline silica, but none were induced by amorphous silica. QRT-PCR revealed that cristobalite selectively up-regulated stress-related genes and cytokines (FOS, ATF3, IL6 and IL8) early and over time (2, 4, 8, and 24 h). Patterns of gene expression in NHBE cells were similar overall to BEAS 2B cells. At 75 × 10⁶μm²/cm², there were 339 significant alterations in gene expression induced by cristobalite and 42 by amorphous silica. Comparison of genes in response to cristobalite (75 × 10⁶μm²/cm²) revealed 60 common, significant gene alterations in NHBE and BEAS 2B cells.

Conclusions

Cristobalite silica, as compared to synthetic amorphous silica particles at equal surface area concentrations, had comparable effects on the viability of human bronchial epithelial cells. However, effects on gene expression, as well as secretion of cytokines and chemokines, drastically differed, as the crystalline silica induced more intense responses. Our studies indicate that toxicological testing of particulates by surveying viability and/or metabolic activity is insufficient to predict their pathogenicity. Moreover, they show that acute responses of the lung epithelium, including up-regulation of genes linked to inflammation, oxidative stress, and proliferation, as well as secretion of inflammatory and proliferative mediators, can be indicative of pathologic potential using either immortalized lines (BEAS 2B) or primary cells (NHBE). Assessment of the degree and magnitude of these responses in vitro are suggested as predictive in determining the pathogenicity of potentially harmful particulates.

Carbon nanotubes and pleural damage: perspectives of nanosafety in the light of asbestos experience

Carbon nanotubes are molecular-scale one-dimensional manufactured materials which display several potential applications in engineering and materials science. Burgeoning evidence demonstrates that carbon nanotubes and asbestos share comparable physical properties. Therefore carbon nanotubes might display toxic effects and the extent of the toxicity is more specifically directed to lung and pleura. These effects are related to properties of carbon nanotubes, such as their structure, length, aspects ratio, surface area, degree of aggregation, extent of oxidation, bound functional group, method of manufacturing, concentration and dose. At the present there is no global agreement about the risk of carbon nanotubes on human health and in particular on their transformation capacity. Safety concerns regarding carbon nanotubes can be ameliorated. In this context, it is important to put the known hazards of carbon nanotubes into perspective. Here is presented an overview about toxicity issues in the application of carbon nanotubes to biological systems, taking into consideration the already known asbestos-induced mechanisms of biological damages.

Advances in the biology of malignant pleural mesothelioma

Malignant pleural mesothelioma is a highly aggressive cancer with a very poor prognosis. Although the mechanism of carcinogenesis is not fully understood, approximately 80% of malignant pleural mesothelioma can be attributed to asbestos fiber exposure. This disease is largely unresponsive to conventional chemotherapy or radiotherapy, and most patients die within 10-17 months of their first symptoms. Currently, malignant pleural mesothelioma therapy is guided by clinical stage and patient characteristics rather than by the histological or molecular features of the tumor. Several molecular pathways involved in malignant pleural mesothelioma have been identified; these include cell cycle regulation, apoptosis, growth factor pathways, and angiogenesis. Unfortunately, several agents targeting these processes, including erlotinib, gefitinib, and imatinib, have proven ineffective in clinical trials. A greater understanding of the molecular pathways involved in malignant pleural mesothelioma is needed to develop better diagnostics, therapeutics, and preventative measures. Moreover, understanding the biological basis of mesothelioma progression may facilitate personalized treatment approaches, and early identification of poor prognostic indicators may help reduce the heterogeneity of the clinical response. This paper reviews advances in the molecular biology of malignant pleural mesothelioma in terms of pathogenesis, the major molecular pathways and the associated therapeutic strategies, and the roles of biomarkers.

Pulmonary endpoints (lung carcinomas and asbestosis) following inhalation exposure to asbestos

Lung carcinomas and pulmonary fibrosis (asbestosis) occur in asbestos workers. Understanding the pathogenesis of these diseases is complicated because of potential confounding factors, such as smoking, which is not a risk factor in mesothelioma. The modes of action (MOA) of various types of asbestos in the development of lung cancers, asbestosis, and mesotheliomas appear to be different. Moreover, asbestos fibers may act differentially at various stages of these diseases, and have different potencies as compared to other naturally occurring and synthetic fibers. This literature review describes patterns of deposition and retention of various types of asbestos and other fibers after inhalation, methods of translocation within the lung, and dissolution of various fiber types in lung compartments and cells in vitro. Comprehensive dose-response studies at fiber concentrations inhaled by humans as well as bivariate size distributions (lengths and widths), types, and sources of fibers are rarely defined in published studies and are needed. Species-specific responses may occur. Mechanistic studies have some of these limitations, but have suggested that changes in gene expression (either fiber-catalyzed directly or by cell elaboration of oxidants), epigenetic changes, and receptor-mediated or other intracellular signaling cascades may play roles in various stages of the development of lung cancers or asbestosis.

Blocking of ERK1 and ERK2 sensitizes human mesothelioma cells to doxorubicin

BACKGROUND

Malignant mesotheliomas (MM) have a poor prognosis, largely because of their chemoresistance to anti-cancer drugs such as doxorubicin (Dox). Here we show using human MM lines that Dox activates extracellular signal-regulated kinases (ERK1 and 2), causally linked to increased expression of ABC transporter genes, decreased accumulation of Dox, and enhanced MM growth. Using the MEK1/2 inhibitor, U0126 and stably transfected shERK1 and shERK2 MM cell lines, we show that inhibition of both ERK1 and 2 sensitizes MM cells to Dox.

RESULTS

U0126 significantly modulated endogenous expression of several important drug resistance (BCL2, ABCB1, ABCC3), prosurvival (BCL2), DNA repair (BRCA1, BRCA2), hormone receptor (AR, ESR2, PPARγ) and drug metabolism (CYP3A4) genes newly identified in MM cells. In comparison to shControl lines, MM cell lines stably transfected with shERK1 or shERK2 exhibited significant increases in intracellular accumulation of Dox and decreases in cell viability. Affymetrix microarray analysis on stable shERK1 and shERK2 MM lines showed more than 2-fold inhibition (p ≤ 0.05) of expression of ATP binding cassette genes (ABCG1, ABCA5, ABCA2, MDR/TAP, ABCA1, ABCA8, ABCC2) in comparison to shControl lines. Moreover, injection of human MM lines into SCID mice showed that stable shERK1 or shERK2 lines had significantly slower tumor growth rates in comparison to shControl lines after Dox treatment.

CONCLUSIONS

These studies suggest that blocking ERK1 and 2, which play critical roles in multi-drug resistance and survival, may be beneficial in combination with chemotherapeutic drugs in the treatment of MMs and other tumors.

Asbestos, lung cancers, and mesotheliomas: from molecular approaches to targeting tumor survival pathways

Fifteen years have passed since we published findings in the AJRCMB demonstrating that induction of early response fos/jun proto-oncogenes in rodent tracheal and mesothelial cells correlates with fibrous geometry and pathogenicity of asbestos. Our study was the first to suggest that the aberrant induction of signaling responses by crocidolite asbestos and erionite, a fibrous zeolite mineral associated with the development of malignant mesotheliomas (MMs) in areas of Turkey, led to altered gene expression. New data questioned the widely held belief at that time that the carcinogenic effects of asbestos in the development of lung cancer and MM were due to genotoxic or mutagenic effects. Later studies by our group revealed that proto-oncogene expression and several of the signaling pathways activated by asbestos were redox dependent, explaining why antioxidants and antioxidant enzymes were elevated in lung and pleura after exposure to asbestos and how they alleviated many of the phenotypic and functional effects of asbestos in vitro or after inhalation. Since these original studies, our efforts have expanded to understand the interface between asbestos-induced redox-dependent signal transduction cascades, the relationship between these pathways and cell fate, and the role of asbestos and cell interactions in development of asbestos-associated diseases. Of considerable significance is the fact that the signal transduction pathways activated by asbestos are also important in survival and chemoresistance of MMs and lung cancers. An understanding of the pathogenic features of asbestos fibers and dysregulation of signaling pathways allows strategies for the prevention and therapy of asbestos-related diseases.

Emerging roles of ATF2 and the dynamic AP1 network in cancer

Cooperation among transcription factors is central for their ability to execute specific transcriptional programmes. The AP1 complex exemplifies a network of transcription factors that function in unison under normal circumstances and during the course of tumour development and progression. This Perspective summarizes our current understanding of the changes in members of the AP1 complex and the role of ATF2 as part of this complex in tumorigenesis.

Induction of epigenetic alterations by chronic inflammation and its significance on carcinogenesis

Chronic inflammation is deeply involved in development of human cancers, such as gastric and liver cancers. Induction of cell proliferation, production of reactive oxygen species, and direct stimulation of epithelial cells by inflammation-inducing factors have been considered as mechanisms involved. Inflammation-related cancers are known for their multiple occurrences, and aberrant DNA methylation is known to be present even in noncancerous tissues. Importantly, for some cancers, the degree of accumulation has been demonstrated to be correlated with risk of developing cancers. This indicates that inflammation induces aberrant epigenetic alterations in a tissue early in the process of carcinogenesis, and accumulation of such alterations forms "an epigenetic field for cancerization." This also suggests that inhibition of induction of epigenetic alterations and removal of the accumulated alterations are novel approaches to cancer prevention. Disturbances in cytokine and chemokine signals and induction of cell proliferations are important mechanisms of how inflammation induces aberrant DNA methylation. Aberrant DNA methylation is induced in specific genes, and gene expression levels, the presence of RNA polymerase II (active or stalled), and trimethylation of H3K4 are involved in the specificity. Expression of DNA methyltransferases (DNMTs) is not necessarily induced by inflammation, and local imbalance between DNMTs and factors that protect genes from DNA methylation seems to be important.

Genomic abnormalities and signal transduction dysregulation in malignant mesothelioma cells

Malignant mesothelioma (MM) is a tumor with poor prognosis associated with asbestos exposure. While it remains to be clarified how asbestos fibers confer genetic/epigenetic alterations and induce cellular transformation in normal mesothelial cells, the understanding of key molecular mechanisms of MM cell development, proliferation, and invasion has progressed. MM shows frequent genetic inactivation of tumor suppressor genes of p16(INK4a)/p14(ARF) and neurofibromatosis type 2 (NF2) which encodes Merlin, and epigenetic inactivation of RASSF1A. However, no frequent mutations of well-known oncogenes such as K-RAS and PIK3CA have been identified. Activation of multiple receptor tyrosine kinases including the epidermal growth factor receptor (EGFR) family and MET, and subsequent deregulations of mitogen-activated protein kinase (MAPK) and phosphatidylinositol-3-kinase (PI3K)-AKT signaling cascades are frequently observed in most MM cells. The tumor suppressive function of Merlin in MM cells is also being investigated by dissecting its possible downstream signaling cascade called the Hippo pathway. Further comprehensive delineation of dysregulated signaling cascades in MM cells will lead to identification of key addiction pathways for cell survival and proliferation of MM cells, which strongly promote establishment of a new molecular target therapy for MM.

Single- and multi-wall carbon nanotubes versus asbestos: are the carbon nanotubes a new health risk to humans?

Carbon nanotubes (CNT), since their discovery, have become one of the most promising nanomaterials in many industrial and biomedical applications. Due to their unique physicochemical properties, interest is growing in the manufacture of CNT-based products and their subsequent marketing. Since their discovery, the prospect of possible undesirable human health effects has been a focus of many scientific studies. Although CNT possess unique physical properties that include (1) nanoscale diameter, (2) a wide length distribution ranging from tens of nanometers to several micrometers, and (3) high aspect ratio, the fibrous-like shape and durability suggest that their toxic properties may be analogous to those observed with other fibrous particles, such as asbestos. The present study provides a summary of published findings on CNT bioactivity, such as the potential of CNT, especially of multi-wall carbon nanotubes (MWCNT), to activate signaling pathways modulating transcription factor activity, induce apoptosis, induce DNA damage, and initiate biological responses. Assessment of risks to human health and adoption of appropriate exposure controls is critical for the safe and successful introduction of CNT -based products for future applications.

Biopersistence and potential adverse health impacts of fibrous nanomaterials: what have we learned from asbestos?

Human diseases associated with exposure to asbestos fibers include pleural fibrosis and plaques, pulmonary fibrosis (asbestosis), lung cancer, and diffuse malignant mesothelioma. The critical determinants of fiber bioactivity and toxicity include not only fiber dimensions, but also shape, surface reactivity, crystallinity, chemical composition, and presence of transition metals. Depending on their size and dimensions, inhaled fibers can penetrate the respiratory tract to the distal airways and into the alveolar spaces. Fibers can be cleared by several mechanisms, including the mucociliary escalator, engulfment, and removal by macrophages, or through splitting and chemical modification. Biopersistence of long asbestos fibers can lead to inflammation, granuloma formation, fibrosis, and cancer. Exposure to synthetic carbon nanomaterials, including carbon nanofibers and carbon nanotubes (CNTs), is considered a potential health hazard because of their physical similarities with asbestos fibers. Respiratory exposure to CNTs can produce an inflammatory response, diffuse interstitial fibrosis, and formation of fibrotic granulomas similar to that observed in asbestos-exposed animals and humans. Given the known cytotoxic and carcinogenic properties of asbestos fibers, toxicity of fibrous nanomaterials is a topic of intense study. The mechanisms of nanomaterial toxicity remain to be fully elucidated, but recent evidence suggests points of similarity with asbestos fibers, including a role for generation of reactive oxygen species, oxidative stress, and genotoxicity. Considering the rapid increase in production and use of fibrous nanomaterials, it is imperative to gain a thorough understanding of their biologic activity to avoid the human health catastrophe that has resulted from widespread use of asbestos fibers.

ASBESTOS-INDUCED ACTIVATION OF CELL SIGNALING PATHWAYS IN HUMAN BRONCHIAL EPITHELIAL CELLS

Using respiratory epithelial cells transfected with either superoxide dismutase (SOD) or catalase, the authors tested the hypothesis that the activation of the epidermal growth factor (EGF) receptor signal pathway after asbestos exposure involves an oxidative stress. Western blotting using phospho-specific antibodies demonstrated that the EGF receptor kinase inhibitor PD153035 decreased both the phosphorylation of extracellular signal-regulated kinase (ERK)1/2 and its upstream signal pathway, including mitogen-activate protein kinase/ERK kinase (MEK)1/2. Similarly, the MEK1/2 kinase inhibitor PD98059 also demonstrated the ability to decrease phosphorylation of ERK1/2. Crocidolite-induced phosphorylation of EGF receptor, ERK1/2, and MEK1/2 was reduced by transfection of BEAS-2B cells with a catalase vector, supporting a participation of oxidative stress in this pathway. These results show that crocidolite can activate the phosphorylation of EGF receptor and its downstream cell signal pathway in BEAS-2B cells and this is associated with the oxidative stress presented by the fibers.

Placenta Growth Factor is a Survival Factor for Human Malignant Mesothelioma Cells

Placenta growth factor (PlGF) is a key regulator of pathological angiogenesis and its overexpression has been linked to neoplastic progression. To assess whether PlGF could have a role in malignant mesothelioma (MM), we analyzed the expression of PlGF, VEGF, and their cognate receptors (VEGF-R1 and VEGF-R2) and co-receptors (neuropilin-1 and neuropilin-2) in MM cell lines as well as in resected MM tissues, hyperplastic/reactive mesothelium and normal mesothelium. MM cell cultures expressed both ligands and the associated receptors to a variable extent and released different amounts of PlGF. As assessed by immunohistochemistry, PlGF expression was switched on in hyperplastic/reactive compared to normal mesothelium. Moreover, 74 and 94% of MM tissues overexpressed PlGF and VEGF-R1, respectively ( p<0.05 MM vs normal mesothelium). Administration of recombinant PlGF-2 did not elicit a significant stimulation of MM cell growth, while it was associated with a transient phosphorylation of Akt, suggesting that PlGF-2 could activate downstream effectors of proliferative and cytoprotective signals via VEGF-R1 in MM cells. Indeed, the administration of an anti-PlGF antibody was found to cause a significant reduction of MM cell survival. In conclusion, our data demonstrate that, by acting as a survival factor, PlGF can play a role which goes beyond the stimulation of angiogenesis in MM. This evidence could help the rational design of new therapeutic interventions for this aggressive tumor.

A protein kinase Cdelta-dependent protein kinase D pathway modulates ERK1/2 and JNK1/2 phosphorylation and Bim-associated apoptosis by asbestos

Inhalation of asbestos and oxidant-generating pollutants causes injury and compensatory proliferation of lung epithelium, but the signaling mechanisms that lead to these responses are unclear. We hypothesized that a protein kinase (PK)Cdelta-dependent PKD pathway was able to regulate downstream mitogen-activated protein kinases, affecting pro- and anti-apoptotic responses to asbestos. Elevated levels of phosphorylated PKD (p-PKD) were observed in distal bronchiolar epithelial cells of mice inhaling asbestos. In contrast, PKCdelta-/- mice showed significantly lower levels of p-PKD in lung homogenates and in situ after asbestos inhalation. In a murine lung epithelial cell line, asbestos caused significant increases in the phosphorylation of PKCdelta-dependent PKD, ERK1/2, and JNK1/2/c-Jun that occurred with decreases in the BH3-only pro-apoptotic protein, Bim. Silencing of PKCdelta, PKD, and use of small molecule inhibitors linked the ERK1/2 pathway to the prevention of Bim-associated apoptosis as well as the JNK1/2/c-Jun pathway to the induction of apoptosis. Our studies are the first to show that asbestos induces PKD phosphorylation in lung epithelial cells both in vivo and in vitro. PKCdelta-dependent PKD phosphorylation by asbestos is causally linked to a cellular pathway that involves the phosphorylation of both ERK1/2 and JNK1/2, which play opposing roles in the apoptotic response induced by asbestos.

Raw single-wall carbon nanotubes induce oxidative stress and activate MAPKs, AP-1, NF-kappaB, and Akt in normal and malignant human mesothelial cells

BACKGROUND

Single-wall carbon nanotubes (SWCNTs), with their unique physicochemical and mechanical properties, have many potential new applications in medicine and industry. There has been great concern subsequent to preliminary investigations of the toxicity, biopersistence, pathogenicity, and ability of SWCNTs to translocate to subpleural areas. These results compel studies of potential interactions of SWCNTs with mesothelial cells.

OBJECTIVE

Exposure to asbestos is the primary cause of malignant mesothelioma in 80-90% of individuals who develop the disease. Because the mesothelial cells are the primary target cells of asbestos-induced molecular changes mediated through an oxidant-linked mechanism, we used normal mesothelial and malignant mesothelial cells to investigate alterations in molecular signaling in response to a commercially manufactured SWCNT.

METHODS

In the present study, we exposed mesothelial cells to SWCNTs and investigated reactive oxygen species (ROS) generation, cell viability, DNA damage, histone H2AX phosphorylation, activation of poly(ADP-ribose) polymerase 1 (PARP-1), stimulation of extracellular signal-regulated kinase (ERKs), Jun N-terminal kinases (JNKs), protein p38, and activation of activator protein-1 (AP-1), nuclear factor kappaB (NF-kappaB), and protein serine-threonine kinase (Akt).

RESULTS

Exposure to SWCNTs induced ROS generation, increased cell death, enhanced DNA damage and H2AX phosphorylation, and activated PARP, AP-1, NF-kappaB, p38, and Akt in a dose-dependent manner. These events recapitulate some of the key molecular events involved in mesothelioma development associated with asbestos exposure.

CONCLUSIONS

The cellular and molecular findings reported here do suggest that SWCNTs can cause potentially adverse cellular responses in mesothelial cells through activation of molecular signaling associated with oxidative stress, which is of sufficient significance to warrant in vivo animal exposure studies.

YAP1 is involved in mesothelioma development and negatively regulated by Merlin through phosphorylation

We previously reported the results of bacterial artificial chromosome array comprehensive genomic hybridization of malignant pleural mesotheliomas (MPMs), including two cases with high-level amplification in the 11q22 locus. In this study, we found that the YAP1 gene encoding a transcriptional coactivator was localized in this amplified region and overexpressed in both cases, suggesting it as a candidate oncogene in this region. We analyzed the involvement of YAP1 in MPM proliferation, as well as its functional and physical interaction with Merlin encoded by the neurofibromatosis type 2 (NF2) tumor suppressor gene, which is frequently mutated in MPMs. YAP1-RNA interference suppressed growth of a mesothelioma cell line NCI-H290 with NF2 homozygous deletion, probably through cell-cycle arrest and apoptosis induction, whereas YAP1 transfection promoted the growth of MeT-5A, an immortalized mesothelial cell line. We also found that the introduction of NF2 into NCI-H290 induced phosphorylation at serine 127 of YAP1, which was accompanied by reduction of nuclear localization of YAP1, whereas nuclear localization of a YAP1 S 127A mutant was not affected. Furthermore, results of immunoprecipitation and in vitro pull-down assays indicated a physical interaction between Merlin and YAP1. These results suggest that YAP1 is involved in mesothelial cell growth and that the transcriptional coactivator activity of YAP1 is functionally inhibited by Merlin through the induction of phosphorylation and cytoplasmic retention of YAP1. This is the first report of negative regulatory signaling from Merlin to YAP1 in mammalian cells. Future studies of transcriptional targets of YAP1 in MPMs may shed light on the molecular mechanisms of MPM development and lead to new therapeutic strategies.

Molecular biology of malignant mesothelioma

Human malignancies develop via a multi-step that involves the accumulation of several key gene alterations with associated genetic and epigenetic events. Although malignant mesothelioma (MM) has been demonstrated to be clearly correlated with asbestos exposure, it remains poorly understood how asbestos fibers confer key gene alterations and induce cellular transformation in normal mesothelial cells, which results in the acquisition of malignant phenotypes, including deregulated cell proliferation and invasion. Malignant mesothelioma presents with the frequent inactivation of tumor suppressor genes of p16(INK4a)/p14(ARF) on chromosome 9p21 and neurofibromatosis type 2 (NF2) on chromosome 22q12, with the latter being responsible for the NF2 familial cancer syndrome. In contrast, MM shows infrequent mutation of the p53 gene, which is one of the most frequently mutated tumor suppressor genes in human malignancies. Genetic abnormalities of oncogenes have also been studied in MM, but no frequent mutations have been identified, including the epidermal growth factor receptor (EGFR) and K-RAS genes. Recent studies have suggested the activation of other receptor tyrosine kinases, including Met, and the deregulations of mitogen-activated protein kinase (MAPK) and phosphatidylinositol-3-kinase (PI3K)-AKT signaling cascades, although the alterations responsible for their activation are still not clear. Thus, further genome-wide studies of genetic and epigenetic alterations as well as detailed analyses of deregulated signaling cascades in MM are necessary to determine the molecular mechanisms of MM, which would also provide some clues for establishing a new molecular target therapy for MM.

HGF mediates cell proliferation of human mesothelioma cells through a PI3K/MEK5/Fra-1 pathway

The ligand hepatocyte growth factor/scatter factor (HGF) and its receptor tyrosine kinase, c-Met, are highly expressed in most human malignant mesotheliomas (MMs) and may contribute to their increased growth and viability. Based upon our observation that RNA silencing of fos-related antigen 1 (Fra-1) inhibited c-met expression in rat mesotheliomas (1), we hypothesized that Fra-1 was a key player in HGF-induced proliferation in human MMs. In three of seven human MM lines evaluated, HGF increased Fra-1 levels and phosphorylation of both extracellular signal-regulated kinase 5 (ERK5) and AKT that were inhibited by the phosphatidylinositol 3-kinase (PI3K) inhibitor, LY290042. HGF-dependent phosphorylation and Fra-1 expression were decreased after knockdown of Fra-1, whereas overexpression of Fra-1 blocked the expression of mitogen/extracellular signal-regulated kinase kinases (MEK)5 at the mRNA and protein levels. Stable MM cell lines using a dnMEK5 showed that basal Fra-1 levels were increased in comparison to empty vector control lines. HGF also caused increased MM cell viability and proliferating cell nuclear antigen (PCNA) expression that were abolished by knockdown of MEK5 or Fra-1. Data suggest that HGF-induced effects in some MM cells are mediated via activation of a novel PI3K/ERK5/Fra-1 feedback pathway that might explain tumor-specific effects of c-Met inhibitors on MM and other tumors.

Fra-1 governs cell migration via modulation of CD44 expression in human mesotheliomas

Silencing of Fra-1, a component of the dimeric transcription factor, activator protein-1 (AP-1), inhibits mRNA expression of c-met and cd44 in rat mesothelioma cells and is causally linked to maintenance of the transformed phenotype. However, the mechanisms of Fra-1 regulation and Fra-1 regulated gene expression in human malignant mesothelioma (MM) are unclear. We first show in a panel of human MM cells that Fra-1 mRNA expression in MM is complex and regulated by extracellular signal-regulated kinase (ERK1, ERK2), Src, and phosphatidyl-inositol-3-kinase (PI3K) pathways in a tumor-specific fashion. Cell lines with PI3K-dependent Fra-1 expression were SV40 positive and expressed the lowest basal Fra-1 levels. Levels of Fra-1 expression correlated with amounts of CD44 expression that were greater in simian virus 40 negative (SV40-) MM cells. Using dominant negative (dn), short hairpin (sh) and small interference (si) RNA constructs, we next demonstrate that expression of CD44, the principal hyaluronic receptor in MMs, correlates with Fra-expression in both simian virus 40 positive (SV40+) and SV40- MMs. Moreover, both Fra-1 and CD44 expression are linked to cell migration in SV40- MM cells. Lastly, in contrast to normal lung tissue, tissue microarrays revealed that Fra-1 was expressed in 33 of 34 human MMs, and that all CD44+ tumors were SV40-. These results suggest that Fra-1 is associated with cell migration in human MMs and that Fra-1 modulation of CD44 may govern migration of selected MMs.

Bacterial induction of early response genes and activation of proapoptotic factors in pleural mesothelial cells

In bacterial empyema the pleural mesothelium is constantly exposed to microorganisms. Staphylococcus aureus (S. aureus) is one of the most frequent pathogens associated with empyema. In an earlier study we demonstrated that S. aureus induced barrier dysfunction in pleural mesothelial cell monolayers. In the present study we report that S. aureus activates the early response genes c-fos and c-jun and activator protein-1 (AP-1), and induces proapoptosis genes Bad and Bak in primary mouse pleural mesothelial cells (PMCs). Our data indicate that in PMCs S. aureus induces apoptosis in a time- and multiplicity of infection (MOI)-dependent manner. Staphylococcus aureus induced Bcl (2), Bcl-X (L), c-fos, c-jun, and AP-1 expression in PMCs during the initial phase of infection. In S. aureus-infected PMCs, Bad and Bak gene expression was increased and correlated with DNA fragmentation and cytochrome-c release. Bcl (2) and Bcl-X (L) gene expression was significantly lower in S. aureus-infected PMCs than in uninfected PMCs 12 h postinfection. We conclude that at the initial stage of infection S. aureus modulates expression of early response genes c-fos and c-jun, and in the late phase of infection S. aureus induces expression of proapoptotic genes Bak and Bad in PMCs. Silencing AP-1 significantly inhibited S. aureus-induced Bak and Bad expression in PMCs. The upregulation of early response genes during the early phase of infection may contribute to the activation of proapoptotic genes Bak and Bad and release of cytochrome-c, caspase-3 thereby resulting in apoptosis in PMCs.

Update on the molecular biology of malignant mesothelioma

Malignant mesothelioma (MM) is a highly aggressive tumor with a very poor prognosis. The disease is largely unresponsive to conventional chemotherapy or radiotherapy, and most patients die within 10-17 months of the first symptoms. Novel, more effective therapeutic strategies are needed for this inexorably fatal disease. Improvement in our understanding of the molecular biology of MM has identified promising new candidates for targeted treatments. In this review the key molecular signaling pathways, including vascular endothelial growth factor (VEGF), epidermal growth factor (EGF), Wnt, and the cell cycle control genes p53, pRb, and bcl-2 that appear to play an important role in the pathogenesis of MM are explored.

Genomic profiling of malignant pleural mesothelioma with array-based comparative genomic hybridization shows frequent non-random chromosomal alteration regions including JUN amplification on 1p32

Genome-wide array-based comparative genomic hybridization analysis of malignant pleural mesotheliomas (MPM) was carried out to identify regions that display DNA copy number alterations. Seventeen primary tumors and nine cell lines derived from 22 individuals were studied, some of them originating from the same patients. Regions of genomic aberrations observed in >20% of individuals were 1q, 5p, 7p, 8q24 and 20p with gains, and 1p36.33, 1p36.1, 1p21.3, 3p21.3, 4q22, 4q34-qter, 6q25, 9p21.3, 10p, 13q33.2, 14q32.13, 18q and 22q with losses. Two regions at 1p32.1 and 11q22 showed a high copy gain. The 1p32.1 region contained a protooncogene, JUN, and we further demonstrated overexpression of JUN with real-time polymerase chain reaction analysis. As MPM cell lines did not overexpress JUN, our findings suggested that induction of JUN expression was involved in the development of MPM cells in vivo, which also might result in gene amplification in a subset of MPM. Meanwhile, the most frequent alteration was the 9p21.3 deletion, which includes the p16(INK4a)/p14(ARF) locus. With polymerase chain reaction analysis, we determined the extent of the homozygous deletion regions of the p16(INK4a)/p14(ARF) locus in MPM cell lines, which indicated that the deletion regions varied among cell lines. Our results with array comparative genomic hybridization analysis provide new insights into the genetic background of MPM, and also give some clues to develop a new molecular target therapy for MPM.

Gene expression profiles in asbestos-exposed epithelial and mesothelial lung cell lines

BACKGROUND

Asbestos has been shown to cause chromosomal damage and DNA aberrations. Exposure to asbestos causes many lung diseases e.g. asbestosis, malignant mesothelioma, and lung cancer, but the disease-related processes are still largely unknown. We exposed the human cell lines A549, Beas-2B and Met5A to crocidolite asbestos and determined time-dependent gene expression profiles by using Affymetrix arrays. The hybridization data was analyzed by using an algorithm specifically designed for clustering of short time series expression data. A canonical correlation analysis was applied to identify correlations between the cell lines, and a Gene Ontology analysis method for the identification of enriched, differentially expressed biological processes.

RESULTS

We recognized a large number of previously known as well as new potential asbestos-associated genes and biological processes, and identified chromosomal regions enriched with genes potentially contributing to common responses to asbestos in these cell lines. These include genes such as the thioredoxin domain containing gene (TXNDC) and the potential tumor suppressor, BCL2/adenovirus E1B 19kD-interacting protein gene (BNIP3L), GO-terms such as "positive regulation of I-kappaB kinase/NF-kappaB cascade" and "positive regulation of transcription, DNA-dependent", and chromosomal regions such as 2p22, 9p13, and 14q21. We present the complete data sets as Additional files.

CONCLUSION

This study identifies several interesting targets for further investigation in relation to asbestos-associated diseases.

Regulation of Exogenous Gene Expression by Superoxide

PURPOSE

Regulation of gene expression after gene introduction is a problematic aspect of gene therapy. Transcription regulates gene-specific transcriptional factors, which bind to regulatory regions in the promoter. The cytomegalovirus long terminal repeat (CMV-LTR) has a TPA response element (TRE) as a binding site for activator protein 1 (AP-1), which is induced by oxidative stress. The purpose of this study was to regulate exogenous gene expression in a vector with CMV-LTR using oxygen radicals.

METHODS

We used two plasmids (1) pQBI25 encoding CMV-LTR and red-shift green fluorescent protein (rsGFP) cDNA and (2) pRc/CMV-SOD encoding CMV-LTR and human Cu, Zn-superoxide dismutase (SOD) cDNA. FR cells were transfected with pQBI25 (FR-pQBI25 cells), and L2 cells were transfected with pRc/CMV-SOD (L2-pRc/CMV-SOD cells). Each type of cell was exposed to oxygen radicals using paraquat for 24 h. Levels of c-fos, c-jun and rsGFP mRNAs were determined using reverse transcription polymerase chain reaction (RT-PCR). Levels of rsGFP protein were measured by fluorometry. Total SOD activity was measured using the nitrite method.

RESULTS

Levels of c-fos, c-jun (AP-1 composition protein) and rsGFP mRNA were induced significantly by oxygen radical exposure in FR-pQBI25 cells. A positive correlation was observed between levels of c-fos mRNA and rsGFP mRNA and also between levels of c-jun mRNA and rsGFP mRNA. Levels of rsGFP protein were also induced significantly. Total SOD activity was induced significantly by oxygen radical exposure in L2-pRc/CMV-SOD cells.

CONCLUSIONS

This study suggests that gene expression driven by the CMV- LTR promoter may be regulated by oxygen radicals.

Cellular and molecular parameters of mesothelioma

Malignant mesotheliomas (MM) are neoplasms arising from mesothelial cells that line the body cavities, most commonly the pleural and peritoneal cavities. Although traditionally recognized as associated with occupational asbestos exposures, MMs can appear in individuals with no documented exposures to asbestos fibers, and emerging data suggest that genetic susceptibility and simian virus 40 (SV40) infections also facilitate the development of MMs. Both asbestos exposure and transfection of human mesothelial cells with SV40 large and small antigens (Tag, tag) cause genetic modifications and cell signaling events, most notably the induction of cell survival pathways and activation of receptors, and other proteins that favor the growth and establishment of MMs as well as their resistance to chemotherapy. Recent advances in high-throughput technologies documenting gene and protein expression in patients and animal models of MMs can now be validated in human MM tissue arrays. These have revealed expression profiles that allow more accurate diagnosis and prognosis of MMs. More importantly, serum proteomics has revealed two new candidates (osteopontin and serum mesothelin-related protein or SMRP) potentially useful in screening individuals for MMs. These mechanistic approaches offer new hope for early detection and treatment of these devastating tumors.

Oxidants and signaling by mitogen-activated protein kinases in lung epithelium

Oxidants in cigarette smoke and generated from asbestos fibers activate mitogen-activated protein kinase (MAPK) signaling cascades in lung epithelial cells in vitro and in vivo. These signaling pathways lead to the enhanced ability of Jun and Fos family members (i.e., components of the activator protein [AP]-1 transcription factor) to activate transcription of a number of AP-1-dependent target genes involved in cell proliferation or death, differentiation, and inflammation. Research by the Basbaum laboratory has been critical in showing that mucin transcription in response to cigarette smoke and gram-positive bacteria is mediated through activation of the epidermal growth factor receptor and MAPK cascades. Work from our laboratories supports the concept that MAPK signaling and AP-1 transactivation by cigarette smoke and asbestos may synergize in lung epithelial cell injury, compensatory proliferation of lung epithelial cells, and carcinogenesis, supporting a mechanistic framework for the striking increases in lung cancer incidence in asbestos workers who smoke. Targeting of MAPKs and inter-related signaling cascades may be critical to the prevention of lung cancers and control of mucin overproduction in a number of lung diseases including asthma, cystic fibrosis, chronic bronchitis, and chronic obstructive pulmonary disease.

Quantitative detection of asbestos fiber in gravelly sand using elastic body-exposure method

Chrysotile or crocidolite colloidal solution containing donor plasmid DNA and Escherichia coli cells was subjected to elastic body friction. These acicular clay minerals mediated E. coli antibiotic resistance plasmid transformation. Other clay minerals had no effect on E. coli transformation. The number of E. coli transformants was counted after elastic body exposure with various crocidolite concentrations. There was a correlation between the number of E. coli transformants and crocidolite concentration (between 40 and 1,000 ng/ml). A mixture consisting of sea sand and crocidolite was utilized as a model for quantitative detection of asbestos in gravelly sand. With sea sand containing 0.15-15 mg of crocidolite, a correlation between crocidolite concentration and the number of colonies derived from E. coli transformants was observed. This indicates that measurement of asbestos is possible even when the asbestos sample includes gravelly sand. Fluorescence microscopic observation of crocidolite colloidal solution indicated that crocidolite was present as spherical aggregates having diameters of 6-9 microm. Thus, the number of transformants correlated with that of 6-9 microm crocidolite aggregates.

Molecular biology of malignant mesothelioma: a review

Malignant mesothelioma (MM) is an uncommon tumor with high mortality and morbidity rates. It arises from mesothelial cells that line the pleural, pericardial, peritoneal, and testicular cavities. This is a disease with an indolent course because tumors arise 20 to 40 years after exposure to an inciting agent. Extensive research has shown that mesothelial cells are transformed into MM cells through various chromosomal and cellular pathway defects. These changes alter the normal cells' ability to survive, proliferate, and metastasize. This article discusses the alterations that occur in transforming normal mesothelial cells into MM. It also details some of the signal transduction pathways that seem to be important in MM with the potential for novel targeted therapeutics.