Macrophages facilitate coal tar pitch extract-induced tumorigenic transformation of human bronchial epithelial cells mediated by NF-κB

The Carcinogenic Properties of Overlooked yet Prevalent Polycyclic Aromatic Hydrocarbons in Human Lung Epithelial Cells

The WHO classified air pollution as a human lung carcinogen and polycyclic aromatic hydrocarbons (PAHs) are components of both indoor (e.g., tobacco smoke and cookstoves) and outdoor (e.g., wildfires and industrial and vehicle emissions) air pollution, thus a human health concern. However, few studies have evaluated the adverse effects of low molecular weight (LMW) PAHs, the most abundant PAHs in the environment. We hypothesized that LMW PAHs combined with the carcinogenic PAH benzo[a]pyrene (B[a]P) act as co-carcinogens in human lung epithelial cell lines (BEAS-2B and A549). Therefore, in this paper, we evaluate several endpoints, such as micronuclei, gap junctional intercellular communication (GJIC) activity, cell cycle analysis, anti-BPDE-DNA adduct formation, and cytotoxicity after mixed exposures of LMW PAHs with B[a]P. The individual PAH doses used for each endpoint did not elicit cytotoxicity nor cell death and were relevant to human exposures. The addition of a binary mixture of LMW PAHs (fluoranthene and 1-methylanthracene) to B[a]P treated cells resulted in significant increases in micronuclei formation, dysregulation of GJIC, and changes in cell cycle as compared to cells treated with either B[a]P or the binary mixture alone. In addition, anti-BPDE-DNA adducts were significantly increased in human lung cells treated with B[a]P combined with the binary mixture of LMW PAHs as compared to cells treated with B[a]P alone, further supporting the increased co-carcinogenic potential by LMW PAHs. Collectively, these novel studies using LMW PAHs provide evidence of adverse pulmonary effects that should warrant further investigation.

LncRNA-ENST00000556926 regulates the proliferation, apoptosis and mRNA transcriptome of malignant-transformed BEAS-2B cells induced by coal tar pitch

As a byproduct of coal tar distillation, coal tar pitch (CTP) has been proven to be carcinogenic to human. However, the mechanisms of lung cancer induced by CTP are still unclear. It has been shown that long non-coding RNAs (LncRNAs) play an important role in the development of human cancers. This study aims to investigate the effect of LncRNA-ENST00000556926 on malignant-transformed human bronchial epithelial (BAES-2B) cells induced by coal tar pitch extracts (CTPE). In this study, BEAS-2B cells were treated with 2.4 μg/ml of CTPE for 72 h and then passaged; and the cells were treated 4 times in the same procedure, then passaged until passage 30 (CTPE30). Cell counting kit-8 (CCK-8) assay was used to detect cell viability, then cell cycle and apoptosis were analyzed by flow cytometry, and transcriptome sequencing analysis was used to detect differentially expressed mRNAs after interference of ENST00000556926. The results indicated that the expression of ENST00000556926 in CTPE30 group was significantly higher compared with control group. Furthermore, after interfering the expression of ENST00000556926, cell viability was inhibited, and cell cycle was arrested while apoptosis of malignant-transformed BEAS-2B cells was promoted. Moreover, a total of 159 differentially expressed mRNAs were screened out after interference of ENST00000556926, including 62 up-regulated mRNAs and 97 down-regulated mRNAs. In addition, knockdown of ENST00000556926 decreased the expression of thioredoxin domain containing 5 (TXNDC5) and FOXD1. In conclusion, LncRNA-ENST00000556926 could regulate the proliferation, apoptosis and mRNA transcriptome of malignant-transformed BEAS-2B cells induced by CTP, which may provide a novel treatment strategy for lung cancer.

Escherichia coli infection activates the production of IFN-α and IFN-β via the JAK1/STAT1/2 signaling pathway in lung cells

Escherichia coli infections can result in lung injury, which may be closely linked to the induction of interferon secretion. The Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway is one of most important pathways that regulate interferon production. Thus, the present study aimed to dissect whether E. coli infections can regulate interferon production and the underlying mechanisms. For this aim, two lung cell lines, a human bronchial epithelial cell line transformed with Ad12-SV40 2B (BEAS-2b) and a human fetal lung fibroblast (HFL1) cell line, were used. The effects of E. coli infections on interferon production were studied using qRT-PCR, Western blot, and siRNA knockdown assays. E. coli infections remarkably promoted the expression levels of IFN-α, IFN-β, and ISGs. Major components of the JAK/STAT pathway, including JAK1, STAT1, and STAT2, were demonstrated to be regulated by E. coli infections. Importantly, knockdown of JAK1, STAT1, and STAT2 abolished the induction of IFN-α, IFN-β, and ISGs by E. coli. Therefore, experiments in the present study demonstrated that E. coli infections remarkably promoted interferon production in lung cells, which was closely regulated by the JAK/STAT signaling pathway. The findings in the present study are useful for further understanding the pathogenesis of E. coli infections in the lung and finding novel therapies to treat E. coli-induced lung injury.

Epigenetic-Based Biomarkers in the Malignant Transformation of BEAS-2B Cells Induced by Coal Tar Pitch Extract

Background and Objectives: The carcinogenicity of coal tar pitch (CTP) to occupational workers has been confirmed by the International Agency for Research on Cancer, especially for lung cancer. Herein, we explored the dynamic changes of epigenetic modifications in the malignant transformation process of CTP-induced BEAS-2B cells and also provided clues for screening early biomarkers of CTP-associated occupational lung cancer. Material and Methods: BEAS-2B cells treated with 3.0 μg/mL CTP extract (CTPE) were cultured to the 30th passage to set up a malignant transformation model, which was confirmed by platelet clone formation assay and xenograft assay. DNA methylation levels were determined by ultraviolet-high performance liquid chromatography. mRNA levels in cells and protein levels in supernatants were respectively detected by Real-Time PCR and enzyme-linked immunosorbent assay. Results: The number of clones and the ability of tumor formation in nude mice of CTPE-exposed BEAS-2B cells at 30th passage were significantly increased compared to vehicle control. Moreover, genomic DNA methylation level was down-regulated. The mRNA levels of DNMT1, DNMT3a and HDAC1 as well as the expression of DNMT1 protein were up-regulated since the 10th passage. From the 20th passage, the transcriptional levels of DNMT3b, let-7a and the expression of DNMT3a, DNMT3b, and HDAC1 proteins were detected to be higher than vehicle control, while the level of miR-21 increased only at the 30th passage. Conclusion: Data in this study indicated that the changes of epigenetic molecules including DNMT1, DNMT3a, DNMT3b, HDAC1, and let-7a occurred at the early stages of BEAS-2B cell malignant transformation after CTPE exposure, which provided critical information for screening early biomarkers of CTP-associated occupational lung cancer.

LncRNA-ENST00000501520 promotes the proliferation of malignant-transformed BEAS-2B cells induced with coal tar pitch mediated by target genes

As a human carcinogen, coal tar pitch (CTP) can significantly increase the risk of lung cancer. However, the mechanism underlying CTP-induced lung carcinogenesis has not been well understood. This study aims to explore the role of the LncRNA-ENST00000501520 in the proliferation of malignant-transformed human bronchial epithelial cells (BAES-2B) induced by CTP extract for the first time. BEAS-2B cells were stimulated with 2.4 μg/mL CTP extract, and then passaged for three times, which were named passage 1 and then passaged until passage 30 (named as CTP group). The ENST000001520 of cells in CTP group was interfered using siRNA. The results showed that ENST000001520 located in cell nucleus (>80%) had no or weak ability of protein encoding. After interference of ENST000001520, the migration and proliferation of cells in CTP group were inhibited, and the cell cycle was arrested in the G0/G1 phase; however, the apoptosis of cells in CTP group was promoted. The target genes (SKB1, CLTB, TAP2, PIPK2, and SOCS3) of ENST000001520 were screened out, and the mRNA and protein expression of SBK1 and SOCS3 was significantly decreased after ENST000001520 interference. SBK1 and SOCS3 may play a promoting role in occurrence and development of cancers. The study suggests that LncRNA-ENST00000501520 could promote the proliferation in malignant-transformed BEAS-2B cells induced with CTP extract which may be mediated by target genes. This study may provide a new target for prevention and treatment of lung cancer.

NLRP3 inflammasome activation involved in LPS and coal tar pitch extract-induced malignant transformation of human bronchial epithelial cells

Inflammatory microenvironment has been found as a new characteristic of cancer; however, the mechanisms of inflammation-related lung cancer remain unclear. To explore the role of NLRP3 inflammsome activation in inflammation-related lung carcinogenesis, a cell model was set up. Human bronchial epithelial cells (BEAS-2B) were stimulated with 1 μg/mL lipopolysaccharide (LPS) for 24 hours, and then treated with 2.4 μg/mL coal tar pitch extract (CTPE) for 24 hours, after removal of LPS and CTPE, the cells were numbered passage 1 and were passaged and treated in this way until passage 30, which was called LPS + CTPE group. DMSO and Saline were used as vehicle controls. Malignant transformation of cells in passage 30 was evaluated by morphological change, platelet clone formation assay, and tumor formation in nude mice. The mRNA levels of NLRP3 and IL-1β were detected by real time-PCR. The combination of NLRP3 and caspase-1 were determined using immunofluorescence and confocal. The protein expression of NLRP3, cleaved caspase-1(p10), and cleaved IL-1β was detected using Western blot. It was shown that CTPE, LPS + CTPE-stimulated BEAS-2B cells of passage 30 changed a lot morphologically. The clone formation rates, the rates of positive cells of NLRP3 and caspase-1 combination, the mRNA levels of NLRP3 and IL-1β, the protein expression of NLRP3, cleaved caspase-1(p10) and cleaved IL-1β of cells exposed with CTPE and LPS + CTPE at passage 30 were significantly increased compared to vehicle controls. Furthermore, the ability of tumor formation in nude mice, the rates of clone formation and positive cells, mRNA and protein levels of NLRP3 inflammasome activation-related factors in LPS + CTPE-induced cells were all higher than those in cells stimulated with CTPE alone. In conclusion, the cell model of inflammation-related lung cancer is set up successfully, and NLRP3 inflammasome activation may be involved in the malignant transformation of BEAS-2B cells which induced by CTPE alone or LPS combined with CTPE.

NF-E2-related factor 2 serves a key function in resistance to malignant transformation of BEAS-2B cells induced by coal tar pitch

Coal tar pitch (CTP) is a key factor in the development of occupational lung cancer. In order to investigate the function of the anti-oxidative signaling pathway regulated by NF-E2-related factor 2 (Nrf2) during cancer development, BEAS-2B cells were cultured with CTP extract for 30 passages. It was revealed that malignant transformation occurred in cells between the 20 and 30th passage. The expression levels of Nrf2 and NAD(P)H:quinone oxidoreductase 1 (NQO1) were promoted throughout the CTP exposure culture, and there was a positive linear correlation between the expression levels of Nrf2 and NQO1. Following knockdown of Nrf2 expression, the level of NQO1 decreased markedly and malignant transformation was more likely to occur. It was hypothesized that CTP may be toxic to BEAS-2B cells, which may lead to malignant transformation. Nrf2 was a quick response factor: Counteracting cytotoxicity by promoting the expression of anti-oxidative genes. Thus, Nrf2 was associated with the malignant transformation of BEAS-2B cells exposed to CTP and may be a potential therapeutic target.

Coal tar pitch extract could induce chromosomal instability of human bronchial epithelial cells mediated by spindle checkpoint-related proteins

Coal tar pitch (CTP) is a byproduct of coal tar distillation. The workers working with coal tar or in aluminum smelters, potrooms and carbon plants have the opportunities of exposing to coal tar pitch volatiles. Coal tar pitches from which polycyclic aromatic hydrocarbons (PAHs) originate have been shown to exhibit lung carcinogenicity in humans. Chromosomal instability (CIN) is a mechanism in carcinogenesis, however, whether CIN is involved in coal tar pitch-induced lung cancer remains elusive. In this present study, human bronchial epithelial cells (BEAS-2B) were first exposed to coal tar pitch extracts (CTPE) to induce a malignant transformation model. Then, the occurrence of severe chromosomal changes detected using G band, R band and multiplex fluorescence in situ hybridization (M-FISH) staining were examined. It was shown that more clones of transformed BEAS-2B cells at passage 30 following stimulation with CTPE were formed in the soft agar compared with the vehicle control. Moreover, the expression of the spindle checkpoint-related proteins, mitotic arrest defective 2 (Mad2), budding uninhibited in benzimidazole 1 (Bub1), and anaphase-promoting complex (APC), indicators of abnormal chromosomes and carcinogenesis, reduced in CTPE-treated BEAS-2B cells at Passage 30 compared with the vehicle control using real-time PCR and immunohistochemistry. In summary, exposure of BEAS-2B cells to CTPE may induce chromosomal instability through spindle checkpoint-related proteins.

Inflammatory stimuli promote growth and invasion of pancreatic cancer cells through NF-κB pathway dependent repression of PP2Ac

Previous studies have indicated that inflammatory stimulation represses protein phosphatase 2A (PP2A), a well-known tumor suppressor. However, whether PP2A repression participates in pancreatic cancer progression has not been verified. We used lipopolysaccharide (LPS) and macrophage-conditioned medium (MCM) to establish in vitro inflammation models, and investigated whether inflammatory stimuli affect pancreatic cancer cell growth and invasion PP2A catalytic subunit (PP2Ac)-dependently. Via nude mouse models of orthotopic tumor xenografts and dibutyltin dichloride (DBTC)-induced chronic pancreatitis, we evaluated the effect of an inflammatory microenvironment on PP2Ac expression in vivo. We cloned the PP2Acα and PP2Acβ isoform promoters to investigate the PP2Ac transcriptional regulation mechanisms. MCM accelerated pancreatic cancer cell growth; MCM and LPS promoted cell invasion. DBTC promoted xenograft growth and metastasis, induced tumor-associated macrophage infiltration, promoted angiogenesis, activated the nuclear factor-κB (NF-κB) pathway, and repressed PP2Ac expression. In vitro, LPS and MCM downregulated PP2Ac mRNA and protein. PP2Acα overexpression attenuated JNK, ERK, PKC, and IKK phosphorylation, and impaired LPS/MCM-stimulated cell invasion and MCM-promoted cell growth. LPS and MCM activated the NF-κB pathway in vitro. LPS and MCM induced IKK and IκB phosphorylation, leading to p65/RelA nuclear translocation and transcriptional activation. Overexpression of the dominant negative forms of IKKα attenuated LPS and MCM downregulation of PP2Ac, suggesting inflammatory stimuli repress PP2Ac expression NF-κB pathway-dependently. Luciferase reporter gene assay verified that LPS and MCM downregulated PP2Ac transcription through an NF-κB-dependent pathway. Our study presents a new mechanism in inflammation-driven cancer progression through NF-κB pathway-dependent PP2Ac repression.

Long-term exposures to low doses of silver nanoparticles enhanced in vitro malignant cell transformation in non-tumorigenic BEAS-2B cells

To predict carcinogenic potential of AgNPs on the respiratory system, BEAS-2B cells (human bronchial epithelial cells) were chronically exposed to low- and non-cytotoxic dose (0.13 and 1.33μg/ml) of AgNPs for 4months (#40 passages). To assess malignant cell transformation of chronic exposure to AgNPs, several bioassays including anchorage independent agar colony formation, cell migration/invasion assay, and epithelial-mesenchymal transition (EMT) were performed in BEAS-2B cells. Chronic exposure to AgNPs showed a significant increase of anchorage independent agar colony formation and cell migration/invasion. EMT, which is the loss of epithelial markers (E-Cadherin and Keratin) and the gain of mesenchymal marker (N-cadherin and Vimentin), was induced by chronic exposure to AgNPs. These responses indicated that chronic exposure to AgNPs could acquire characteristics of tumorigenic cells from normal BEAS-2B cells. In addition, caspase-3, p-p53, p-p38, and p-JNK were significantly decreased, while p-ERK1/2 was significantly increased. MMP-9 related to cell migration/invasion was upregulated, while a MMP-9 inhibitor, TIMP-1 was down-regulated. These results indicated that BEAS-2B cells exposed to AgNPs could induce anti-apoptotic response/anoikis resistance, and cell migration/invasion by complex regulation of MAPK kinase (p38, JNK, and ERK) and p53 signaling pathways. Therefore, we suggested that long-term exposure to low-dose of AgNPs could enhance malignant cell transformation in non-tumorigenic BEAS-2B cells. Our findings provide useful information needed to assess the carcinogenic potential of AgNPs.

Changes in telomere length and telomerase activity in human bronchial epithelial cells induced by coal tar pitch extract

Coal tar pitch is a confirmed human carcinogen and is composed mainly of polycyclic aromatic hydrocarbons.

Macrophages promote coal tar pitch extract-induced tumorigenesis of BEAS-2B cells and tumor metastasis in nude mice mediated by AP-1

BACKGROUND

We sought to evaluate the role of tumor associated macrophages (TAMs) on the promotion of coal tar pitch extract (CTPE)-induced tumorigenesis of human bronchial epithelial cells (BEAS-2B) and tumor metastasis in nude mice, and related mechanisms.

MATERIALS AND METHODS

BEAS-2B cells were first treated with 2.4 mg/mL CTPE for 72 hours. After removal of CTPE, the cells were continuously cultured and passaged using trypsin-EDTA. THP-1 cells were used as macrophage-like cells. BEAS-2B cells under different conditions (n=6/ group) were injected into the back necks of nude mice, and alterations of tumor xenograft growth, indicative of tumorigenicity, and tumor metastasis were determined. Pathological changes (tumor nests and microvascular lesions) of HE-stained tumor tissues were also evaluated. The expression of AP-1(c-Jun) in xenografts and metastatic tumors was determined using immunohistochemistry.

RESULTS

Tumor size and weight in nude mice transplanted with the mixture of CTPE-induced passage 30 BEAS-2B and THP-1 cells (2:1) were increased compared to those from the CTPE-treated BEAS-2B cells at passage 30 alone at different observation time points. Tumor metastasis to lymph nodes and liver was only detected after transplantation of a mixture the two kinds of cells. The numbers of tumor nests and microvascular lesions, and the expression levels of AP-1 (c-Jun) in tumors from the mixture of two kinds of cells were increased apparently in contrast to those in tumor from the CTPE-treated BEAS-2B cells of passage 30 alone. In addition, there was positive correlation between AP-1 (c-Jun) expression level and the number of microvascular lesions, or between AP-1 (c-Jun) expression level and tumor metastasis in these two groups.

CONCLUSIONS

TAMs not only facilitate tumorigenesis transformation of CTPE-induced BEAS-2B cells, but also promote tumor growth, angiogenesis and metastasis in nude mice in vivo, which may be mediated by AP-1.

Spontaneous mesotheliomas in F344/N rats are characterized by dysregulation of cellular growth and immune function pathways

Aged male Fischer 344/N rats are prone to developing spontaneous peritoneal mesotheliomas that arise predominantly from the tunica vaginalis of the testes. A definitive cause for the predominance of this neoplasm in F344/N rats is unknown. Investigation of the molecular alterations that occur in spontaneous rat mesotheliomas may provide insight into their pathogenesis as well enable a better understanding regarding the mechanisms underlying chemically induced mesothelioma in rodents. Mesothelial cell function represents a complex interplay of pathways related to host defense mechanisms and maintenance of cellular homeostasis. Global gene expression profiles of spontaneous mesotheliomas from vehicle control male F344/N rats from 2-year National Toxicology Program carcinogenicity bioassays were analyzed to determine the molecular features of these tumors and elucidate tumor-specific gene expression profiles. The resulting gene expression pattern showed that spontaneous mesotheliomas are associated with upregulation of various growth factors, oncogenes, cytokines, pattern recognition response receptors, and pathogen-associated molecular patterns receptors, and the production of reactive oxygen and nitrogen species, as well as downregulation of apoptosis pathways. Alterations in these pathways in turn trigger molecular responses that stimulate cell proliferation and promote tumor survival and progression.

Polycyclic aromatic hydrocarbon-induced signaling events relevant to inflammation and tumorigenesis in lung cells are dependent on molecular structure

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental and occupational toxicants, which are a major human health concern in the U.S. and abroad. Previous research has focused on the genotoxic events caused by high molecular weight PAHs, but not on non-genotoxic events elicited by low molecular weight PAHs. We used an isomeric pair of low molecular weight PAHs, namely 1-Methylanthracene (1-MeA) and 2-Methylanthracene (2-MeA), in which only 1-MeA possessed a bay-like region, and hypothesized that 1-MeA, but not 2-MeA, would affect non-genotoxic endpoints relevant to tumor promotion in murine C10 lung cells, a non-tumorigenic type II alveolar pneumocyte and progenitor cell type of lung adenocarcinoma. The non-genotoxic endpoints assessed were dysregulation of gap junction intercellular communication function and changes in the major pulmonary connexin protein, connexin 43, using fluorescent redistribution and immunoblots, activation of mitogen activated protein kinases (MAPK) using phosphospecific MAPK antibodies for immunoblots, and induction of inflammatory genes using quantitative RT-PCR. 2-MeA had no effect on any of the endpoints, but 1-MeA dysregulated gap junctional communication in a dose and time dependent manner, reduced connexin 43 protein expression, and altered membrane localization. 1-MeA also activated ERK1/2 and p38 MAP kinases. Inflammatory genes, such as cyclooxygenase 2, and chemokine ligand 2 (macrophage chemoattractant 2), were also upregulated in response to 1-MeA only. These results indicate a possible structure-activity relationship of these low molecular weight PAHs relevant to non-genotoxic endpoints of the promoting aspects of cancer. Therefore, our novel findings may improve the ability to predict outcomes for future studies with additional toxicants and mixtures, identify novel targets for biomarkers and chemotherapeutics, and have possible implications for future risk assessment for these PAHs.