The immunotoxicity mechanism of hemocytes in Chlamys farreri incubated with noradrenaline and benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide alone or in combination.

Benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE) is the active intermediate metabolite of benzo[a]pyrene (B[a]P) and is considered the ultimate immunotoxicant. The neuroendocrine immunoregulatory network of bivalves is affected under pollutant stress. Besides, bivalves are frequently affected by pollutants in marine environments, yet the combined effects of neuroendocrine factors and detoxification metabolites on bivalves under pollutant stress and the signal pathways that mediate this immunoregulation are not well understood. Therefore, we incubated the hemocytes of Chlamys farreri with the neuroendocrine factor noradrenaline (NA) and the B[a]P detoxification metabolite BPDE, alone or in combination, to examine the immunotoxic effects of NA and BPDE on the hemocytes in C. farreri. Furthermore, the effects of NA and BPDE on the hemocyte signal transduction pathway were investigated by assessing potential downstream targets. The results revealed that NA and BPDE, alone or in combination, resulted in a significant decrease in phagocytic activity, bacteriolytic activity and the total hemocyte count. In addition, the immunotoxicity induced by BPDE was further exacerbated by co-treatment with NA, and the two showed synergistic effects. Analysis of signaling pathway factors showed that NA activated G proteins by binding to α-AR, which transmitted information to the Ca2+-NF-κB signaling pathway to regulate the expression of phagocytosis-associated proteins and regulated cytokinesis through the cAMP signaling pathway. BPDE could activate PTK and affect phagocytosis and cytotoxicity proteins through Ca2+-NF-κB signal pathway, also affect the regulation of phagocytosis and cytotoxicity by inhibiting the AC-cAMP-PKA pathway to down-regulate the expression of NF-κB and CREB. In addition, BPDE and NA may affect the immunity of hemocytes by down-regulating phagocytosis-related proteins through inhibition of the lectin pathway, while regulating the expression of cytotoxicity-related proteins through the C-type lectin. In summary, immune parameters were suppressed through Ca2+ and cAMP dependent pathways exposed to BPDE and the immunosuppressive effects were enhanced by the neuroendocrine factor NA.

BaP/BPDE suppressed endothelial cell angiogenesis to induce miscarriage by promoting MARCHF1/GPX4-mediated ferroptosis.

Environmental benzo(a)pyrene (BaP) and its ultimate metabolite BPDE (benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide) are universal and inevitable persistent organic pollutants and endocrine disrupting chemicals. Angiogenesis in placental decidua plays a pivotal role in healthy pregnancy. Ferroptosis is a newly identified and iron-dependent cell death mode. However, till now, BaP/BPDE exposure, ferroptosis, defective angiogenesis, and miscarriage have never been correlated; and their regulatory mechanisms have been rarely explored. In this study, we used assays with BPDE-exposed HUVECs (human umbilical vein endothelial cells), decidual tissues and serum samples collected from unexplained recurrent miscarriage and their matched healthy control groups, and placental tissues of BaP-exposed mouse miscarriage model. We found that BaP/BPDE exposure caused ferroptosis and then directly suppressed angiogenesis and eventually induced miscarriage. In mechanism, BaP/BPDE exposure up-regulated free Fe2+ level and promoted lipid peroxidation and also up-regulated MARCHF1 (a novel E3 ligase of GPX4) level to promote the ubiquitination degradation of GPX4, both of which resulted in HUVEC ferroptosis. Furthermore, we also found that GPX4 protein down-regulated the protein levels of VEGFA and ANG-1, two key proteins function for angiogenesis, and thus suppressed HUVEC angiogenesis. In turn, supplement with GPX4 could suppress ferroptosis, recover angiogenesis, and alleviate miscarriage. Moreover, the levels of free Fe2+ and VEGFA in serum might predict the risk of miscarriage. Overall, this study uncovered the crosstalk among BaP/BPDE exposure, ferroptosis, angiogenesis, and miscarriage, discovering novel toxicological effects of BaP/BPDE on human reproductive health. This study also warned the public to avoid exposure to polycyclic aromatic hydrocarbons during pregnancy to effectively prevent adverse pregnancy outcomes.

Potential pathway and mechanisms underlining the immunotoxicity of benzo[a]pyrene to Chlamys farreri.

The long-distance migration of polycyclic aromatic hydrocarbons (PAHs) promotes their release into the marine environment, posing a serious threat to marine life. Studies have shown that PAHs have significant immunotoxicity effects on bivalves, but the exact mechanism of immunotoxicity remains unclear. This paper aims to investigate the effects of exposure to 0.4, 2, and 10 µg/L of benzo(a)pyrene (B[a]P) on the immunity of Chlamys farreri under environmental conditions, as well as the potential molecular mechanism. Multiple biomarkers, including phagocytosis rate, metabolites, neurotoxicity, oxidative stress, DNA damage, and apoptosis, were adopted to assess these effects. After exposure to 0.4, 2, and 10 µg/L B[a]P, obvious concentration-dependent immunotoxicity was observed, indicated by a decrease in the hemocyte index (total hemocyte count, phagocytosis rate, antibacterial and bacteriolytic activity). Analysis of the detoxification metabolic system in C. farreri revealed that B[a]P produced B[a]P-7,8-diol-9,10-epoxide (BPDE) through metabolism, which led to an increase in the expression of protein tyrosine kinase (PTK). In addition, the increased content of neurotransmitters (including acetylcholine, γ -aminobutyric acid, enkephalin, norepinephrine, dopamine, and serotonin) and related receptors implied that B[a]P might affect immunity through neuroendocrine system. The changes in signal pathway factors involved in immune regulation indicated that B[a]P interfered with Ca2+ and cAMP signal transduction via the BPDE-PTK pathway or neuroendocrine pathway, resulting in immunosuppression. Additionally, B[a]P induced the increase in reactive oxygen species (ROS) content and DNA damage, as well as an upregulation of key genes in the mitochondrial pathway and death receptor pathway, leading to the increase of apoptosis rate. Taken together, this study comprehensively investigated the detoxification metabolic system, neuroendocrine system, and cell apoptosis to explore the toxic mechanism of bivalves under B[a]P stress.

Potential molecular mechanism underlying the harmed haemopoiesis upon Benzo[a]pyrene exposure in Chlamys farreri.

Benzo[a]pyrene (B[a]P), a ubiquitous contamination in the marine environments, has the potential to impact the immune response of bivalves by affecting the hemocyte parameters, especially total hemocyte count (THC). THC is mainly determined by haematopoietic mechanisms and apoptosis of hemocytes. Many studies have found that B[a]P can influence the proliferation and differentiation of hemocytes. However, the link between the toxic mechanisms of haematopoietic and environmental pollutants is not explicitly stated. This study is to investigate the toxic effects of B[a]P on haematopoietic mechanisms in C. farreri. Through the tissue expression distribution experiment and EDU assay, gill is identified as a potential haematopoietic tissue in C. farreri. Subsequently, the scallops were exposed to B[a]P (0.05, 0.5, 5 µg/L) for 1d, 3d, 6d, 10d and 15d. Then BPDE content, DNA damage, gene expression of haematopoietic factors and haematopoietic related pathways were determined in gill and hemocytes. The results showed that the expression of CDK2 was significantly decreased under B[a]P exposure through three pathways: RYR/IP3-calcium, BPDE-CHK1 and Notch pathway, resulting in cell cycle arrest. In addition, B[a]P also significantly reduced the number of proliferating hemocytes by affecting the Wnt pathway. Meanwhile, B[a]P can significantly increase the content of ROS, causing a downregulation of FOXO gene expression. The gene expression of Notch pathway and ERK pathway was also detected. The present study suggested that B[a]P disturbed differentiation by multiple pathways. Furthermore, the expression of SOX11 and CD9 were significantly decreased, which directly indicated that differentiation of hemocytes was disturbed. In addition, phagocytosis, phenoloxidase activity and THC were also significant decreased. In summary, the impairment of haematopoietic activity in C. farreri further causes immunotoxicity under B[a]P exposure. This study will improve our understanding of the immunotoxicity mechanism of bivalve under B[a]P exposure.

Crystalline silica-exposed human lung epithelial cells presented enhanced anchorage-independent growth with upregulated expression of BRD4 and EZH2 in autocrine and paracrine manners.

Crystalline silica-induced inflammation possibly facilitates carcinogenesis. Here, we investigated its effect on lung epithelium damage. We prepared conditioned media of immortalized human bronchial epithelial cell lines (hereinafter bronchial cell lines) NL20, BEAS-2B, and 16HBE14o- pre-exposed to crystalline silica (autocrine crystalline silica conditioned medium), a phorbol myristate acetate-differentiated THP-1 macrophage line, and VA13 fibroblast line pre-exposed to crystalline silica (paracrine crystalline silica conditioned medium). As cigarette smoking imposes a combined effect on crystalline silica-induced carcinogenesis, a conditioned medium was also prepared using the tobacco carcinogen benzo[a]pyrene diol epoxide. Crystalline silica-exposed and growth-suppressed bronchial cell lines exhibited enhanced anchorage-independent growth in autocrine crystalline silica and benzo[a]pyrene diol epoxide conditioned medium compared with that in unexposed control conditioned medium. Crystalline silica-exposed nonadherent bronchial cell lines in autocrine crystalline silica and benzo[a]pyrene diol epoxide conditioned medium showed increased expression of cyclin A2, cdc2, and c-Myc, and of epigenetic regulators and enhancers, BRD4 and EZH2. Paracrine crystalline silica and benzo[a]pyrene diol epoxide conditioned medium also accelerated the growth of crystalline silica-exposed nonadherent bronchial cell lines. Culture supernatants of nonadherent NL20 and BEAS-2B in crystalline silica and benzo[a]pyrene diol epoxide conditioned medium had higher EGF concentrations, whereas those of nonadherent 16HBE14o- had higher TNF-α levels. Recombinant human EGF and TNF-α promoted anchorage-independent growth in all lines. Treatment with EGF and TNF-α neutralizing antibodies inhibited cell growth in crystalline silica conditioned medium. Recombinant human TNF-α induced BRD4 and EZH2 expression in nonadherent 16HBE14o-. The expression of γH2AX occasionally increased despite PARP1 upregulation in crystalline silica-exposed nonadherent lines with crystalline silica and benzo[a]pyrene diol epoxide conditioned medium. Collectively, crystalline silica- and benzo[a]pyrene diol epoxide-induced inflammatory microenvironments comprising upregulated EGF or TNF-α expression may promote crystalline silica-damaged nonadherent bronchial cell proliferation and oncogenic protein expression despite occasional γH2AX upregulation. Thus, carcinogenesis may be cooperatively aggravated by crystalline silica-induced inflammation and genotoxicity.

BPDE, the Migration and Invasion of Human Trophoblast Cells, and Occurrence of Miscarriage in Humans: Roles of a Novel lncRNA-HZ09.

BACKGROUND: Recurrent miscarriage (RM) affects 1%-3% of pregnancies. However, in almost 50% of cases, the cause is unknown. Increasing evidence have shown that benzo(a)pyrene [B(a)P], a representative of polycyclic aromatic hydrocarbons (PAHs), is correlated with miscarriage. However, the underlying mechanisms of B(a)P/benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE)-induced trophoblast cell dysfunctions and miscarriage remain largely unknown. OBJECTIVE: The objective was to discover the role(s) of a novel lncRNA, lnc-HZ09, in the regulation of BPDE-inhibited migration and invasion of trophoblast cells and the occurrence of miscarriage. METHOD: Human trophoblast cells were treated with 0, 0.25, 0.5, 1.0, or 1.5µM BPDE with or without corresponding lnc-HZ09 silencing or overexpression. Using these cells, we evaluated cell migration and invasion, the mRNA and protein levels of members of the PLD1/RAC1/CDC42 pathway, the regulatory roles of lnc-HZ09 in PLD1 transcription and mRNA stability, and lnc-HZ09 transcription and stability. Human villous tissues were collected from RM (n=15) group and their matched healthy control (HC, n=15) group. We evaluated the levels of BPDE-DNA adducts, lnc-HZ09, and the mRNA and protein expression of members of the PLD1/RAC1/CDC42 pathway, and correlated their relative expression levels. We further constructed 0, 0.05 or 0.2mg/kg B(a)P-induced mouse miscarriage model (each n=6), in which the mRNA and protein expression of members of the Pld1/Rac1/Cdc42 pathway were measured. RESULTS: We identified a novel lnc-HZ09. Human trophoblast cells treated with lnc-HZ09 exhibited less cell migration and invasion. In addition, the levels of this lncRNA were higher in villous tissues from women with recurrent miscarriage than those from healthy individuals. SP1-mediated PLD1 mRNA levels were lower, and HuR-mediated PLD1 mRNA stability was less in trophoblast cells overexpressing lnc-HZ09. However, trophoblast cells treated with MSX1 had higher levels of lnc-HZ09, and METTL3-mediated m6A methylation on lnc-HZ09 resulted in greater lnc-HZ09 RNA stability. In BPDE-treated human trophoblast cells and in RM villous tissues, MSX1-mediated lnc-HZ09 transcription and METTL3-mediated lnc-HZ09 stability were both greater. In our mouse miscarriage model, B(a)P-treated mice had lower mRNA and protein levels of members of the Pld1/Rac1/Cdc42 pathway. DISCUSSION: These results suggest that in human trophoblast cells, BPDE exposure up-regulated lnc-HZ09 level, suppressed PLD1/RAC1/CDC42 pathway, and inhibited migration and invasion, providing new insights in understanding the causes and mechanisms of unexplained miscarriage. https://doi.org/10.1289/EHP10477.

Acute cytotoxicity test of PM2.5, NNK and BPDE in human normal bronchial epithelial cells: A comparison of a co-culture model containing macrophages and a mono-culture model.

BACKGROUND: Based on extensive research on cytotoxicity of exogenous compounds in vitro, it is essential to develop a cell model that better mimics environment in vivo to explore cytotoxic mechanisms of exogenous compounds. METHODS: A co-culture system was established using a transwell system with Beas-2B and U937 cells. Cells were treated with fine particulate matter (PM2.5; 25, 50 and 100 µg/mL), nicotine-derived nitrosamine ketone (NNK; 50, 100 and 200 µg/mL) and benzo(a)pyrene diol epoxide (BPDE; 0.5, 2 and 8 µM) for 24 h. Cell proliferation, apoptosis and cell cycle, DNA damage were detected by CCK-8 and EdU, flow cytometry, and comet assay, respectively. Differentially expressed transcript and cytokine concentrations were determined by transcriptome sequencing and Cytokine Array, respectively. RESULTS: Compared with mono-culture, cell proliferation increased, apoptosis decreased, and DNA damage decreased in a dose-response relationship in co-culture. Gene expression profile was significantly different in co-culture, with significantly increased expression levels of 48 cytokines in co-culture. CONCLUSION: Cytotoxic damage to Beas-2B cells induced by exogenous carcinogens, including PM2.5, NNK and BPDE, was significantly reduced in a co-culture system compared with a mono-culture system. The mechanism may be related to changes in expression of cytokines, such as LIF, and activation of related pathways, such as TNF signaling pathway. Cytotoxic damage to Beas-2B induced by PM2.5, NNK and BPDE, was significantly reduced in co-culture. The mechanism may be related to changes in expression of cytokines and activation of related pathways. These findings provide new insights into cytotoxicity and experimental basis for safety evaluations of exogenous carcinogens.

Exposure to Benzo(a)pyrene damages mitochondrial function via suppressing mitochondrial melatonin receptors in ovarian corpus luteum during early pregnancy.

Benzo(a)pyrene (BaP) is a well-known environmental endocrine pollutant, which has ovarian toxicity in mammals. Ovarian corpus luteum (CL), as the main source of progesterone synthesis in early pregnant female, requires a large number of mitochondria for energy supply. We previously demonstrated that BaP and its metabolite benzo(a)pyren-7, 8-dihydrodiol-9, 10-epoxide (BPDE) inhibited the ovarian melatonin receptors (MTRs) expression and decreased the levels of estrogen and progesterone during early pregnancy in mice. Emerging researches show that MTRs also exist on mitochondrial membrane and participate in the regulation of mitochondrial function. However, the relationship between BaP, MTRs on mitochondrial membrane and mitochondrial function remains unknown. Consequently, this study focuses on the effect and potential mechanism of BaP on ovarian luteal mitochondrial function during early pregnancy. We found that BaP and its metabolite BPDE decreased MTRs in early pregnant CL and luteinized KGN cells, especially in mitochondria. Furthermore, BaP or BPDE up-regulated the expression of SIRT3, Mfn2 and Drp-1, damaged mitochondrial morphology and decreased the MMP and the ATP levels, thereby causing mitochondrial dysfunction. Notably, activation of the MTRs on mitochondrial membrane by MTRs agonist ramelteon partially alleviated BPDE-induced up-regulation of SIRT3, Mfn2 and Drp-1, reduced mitochondrial fragmentation and enhanced the MMP and the ATP levels, thus restoring the expression of steroid rate-limiting enzymes. Together, these findings firstly proved that BaP and BPDE down-regulate MTRs on mitochondrial membrane, and further injure mitochondrial function in early pregnant rats' CL, which provides a new insight for understanding the exact mechanism of the BaP-induced ovarian toxicity.

Immunotoxicity pathway and mechanism of benzo[a]pyrene on hemocytes of Chlamys farreri in vitro.

Benzo[a]pyrene (B[a]P), a typical PAHs widely existing in the marine environment, has been extensively studied for its immunotoxicity due to its persistence and high toxicity. Nevertheless, the immunotoxicity mechanism remain incompletely understood. In this study, isolated hemocytes of Chlamys farreri were exposed at three concentrations of B[a]P (5, 10 and 15 µg/mL), and the effects of B[a]P on detoxification metabolism, signal transduction, humoral immune factors, exocytosis and phagocytosis relevant proteins and immune function at 0, 6, 12, 24 h were studied. Results illustrated the AhR, ARNT and CYP1A1 were significantly induced by B[a]P at 12 h. Additionally, the content of B[a]P metabolite BPDE increased in a dose-dependent manner with pollutants. Under B[a]P stimulation, the expressions of PTK (Src, Fyn) and PLC-Ca2+-PKC pathway gene increased significantly, while the transcription level of AC-cAMP-PKA pathway gene decreased remarkably. Additionally, the expressions of nuclear transcription factors (CREB, NF-κB), complement system genes and C-type lectin genes up-regulated obviously. The gene expressions of phagocytosis and exocytosis related proteins were also notably affected. 5 µg/mL B[a]P could promote phagocytosis in a transitory time, but with the increase of exposure time and concentration of B[a]P, the phagocytosis, antibacterial and bacteriolytic activities gradually decreased. These results indicated that similar to vertebrates, BPDE, the metabolite of B[a]P, mediated downstream signal transduction via PTK in bivalves. The declined of the immune defense ability of hemocytes might be closely related to the inhibition of AC-cAMP-PKA pathway and the imbalance of intracellular Ca2+ pathway. In addition, the results manifested that complement and lectin systems play a significant role in regulating immune response. In this study, the direct relationship between detoxification metabolism and immune signal transduction in bivalves under B[a]P stress was demonstrated for the first time, which provided important information for the potential molecular mechanism of B[a]P-induced immune system disorder in bivalves.

Lnc-HZ08 regulates BPDE-induced trophoblast cell dysfunctions by promoting PI3K ubiquitin degradation and is associated with miscarriage.

Increasing evidences have shown that pregnant women might miscarry after exposure with environmental BaP (benzo(a)pyrene). Additionally, BPDE (benzo(a)pyren-7,8-dihydrodiol-9,10-epoxide), the ultimate metabolite of BaP, could induce dysfunctions of human trophoblast cells. However, it is rarely correlated between miscarriage and trophoblast dysfunctions. Moreover, their underlying mechanisms are still largely unidentified. In this study, a novel lncRNA (long non-coding RNA), lnc-HZ08, was identified to be highly expressed in human recurrent miscarriage (RM) tissues and in BPDE-treated human trophoblast cells. Lnc-HZ08 acts as a RNA scaffold to interact with both PI3K and its ubiquitin ligase CBL (Cbl proto-oncogene), enhances their protein interactions, and promotes PI3K ubiquitin degradation. In RM tissues and BPDE-treated trophoblast cells, DNA methylation level in lnc-HZ08 promoter region was reduced, which promotes estrogen receptor 1 (ER)-mediated lnc-HZ08 transcription. Subsequently, this upregulated lnc-HZ08 downregulated PI3K level, suppressed PI3K/p-AKT/p-P21/CDK2 pathway, and thus weakened proliferation, migration, and invasion of human trophoblast cells, which further induces miscarriage. These results may provide novel scientific and clinical insights in the occurrence of unexplained miscarriage. A novel lncRNA (lnc-HZ08) regulates the functions of human trophoblast cells and affects miscarriage. Lnc-HZ08 promotes PI3K ubiquitin degradation by enhancing CBL and PI3K interactions, downregulates PI3K/p-AKT/p-P21/CDK2 pathway, and weakens proliferation, migration, and invasion of trophoblast cells. BPDE exposure reduces the DNA methylation level in lnc-HZ08 promoter region and promotes estrogen receptor 1 (ER)-mediated lnc-HZ08 transcription. The suppressed PI3K/p-AKT/p-P21/CDK2 pathway regulated by increased lnc-HZ08 is associated with miscarriage. These results provide novel insights in the occurrence of unexplained miscarriage. Graphical Headlights • Lnc-HZ08 downregulates PI3K/p-AKT/p-P21/CDK2 pathway to suppress proliferation, migration, and invasion of human trophoblast cells, and affects miscarriage. • Lnc-HZ08 acts as a RNA scaffold to enhance the protein interaction of PI3K and its ubiquitin ligase CBL, which increases PI3K ubiquitination and degradation. • Lnc-HZ08 transcription is associated with DNA methylation on its promoter region and transcription factor ER.

Novel lncRNA-HZ04 promotes BPDE-induced human trophoblast cell apoptosis and miscarriage by upregulating IP3 R1 /CaMKII/SGCB pathway by competitively binding with miR-hz04.

Normal pregnancy is essential for human reproduction. However, BaP (benzo(a)pyrene) and its metabolite BPDE (benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide) could cause dysfunctions of human trophoblast cells and might further induce miscarriage. Yet, the underlying mechanisms remain largely unknown. Herein, we identified a novel upregulated lnc-HZ04 and a novel downregulated miR-hz04 in villous tissues of unexplained recurrent miscarriage (RM) relative to those in healthy control tissues and also in BPDE-treated human trophoblast cells. Lnc-HZ04 directly and specifically bound with miR-hz04, diminished the reduction effects of miR-hz04 on IP3 R1 mRNA expression level and on IP3 R1 mRNA stability, and then activated the Ca2+ -mediated IP3 R1 /p-CaMKII/SGCB pathway, which further promoted trophoblast cell apoptosis. The miR-hz04 target site on lnc-HZ04 played crucial roles in these regulations. In normal trophoblast, relatively less lnc-HZ04 and more miR-hz04 suppressed this apoptosis pathway and gave normal pregnancy. After exposure to BPDE or in RM tissues, p53 was upregulated, which might promote p53-mediated lnc-HZ04 transcription. Relatively more lnc-HZ04 and less miR-hz04 activated this apoptosis pathway and might further induce miscarriage. BaP could also induce mice miscarriage by upregulating its corresponding murine apoptosis pathway. Therefore, BPDE-induced apoptosis of human trophoblast cells was associated with the occurrence of miscarriage. This work discovered the regulation roles of lnc-HZ04 and miR-hz04 and provided scientific and clinical understanding of the occurrence of unexplained miscarriage.

Toxicological Effects of BPDE on Dysfunctions of Female Trophoblast Cells.

Polycyclic aromatic hydrocarbons (PAHs) are widely spread persistent environmental toxicants. Its typical representative benzo[a]pyrene (BaP) is a human carcinogen. BaP can pass through the placental barrier and is finally metabolized into benzo[a]pyren-7, 8-dihydrodiol-9, 10-epoxide (BPDE). BPDE can form DNA adducts, which directly affect the female reproductive health. Based on the special physiological functions of trophoblast cells and its important effect on normal pregnancy, this chapter describes the toxicity and molecular mechanism of BPDE-induced dysfunctions of trophoblast cells. By affecting the invasion, migration, apoptosis, proliferation, inflammation, and hormone secretion of trophoblast cells, BPDE causes diseases such as choriocarcinoma, intrauterine growth restriction, eclampsia, and abortion. In the end, it is expected to provide a scientific basis and prevention approach for women's reproductive health and decision-making basis for the formulation of environmental health standards.

Adaptive upregulation of DNA repair genes following benzo(a)pyrene diol epoxide protects against cell death at the expense of mutations.

A coordinated and faithful DNA damage response is of central importance for maintaining genomic integrity and survival. Here, we show that exposure of human cells to benzo(a)pyrene 9,10-diol-7,8-epoxide (BPDE), the active metabolite of benzo(a)pyrene (B(a)P), which represents a most important carcinogen formed during food preparation at high temperature, smoking and by incomplete combustion processes, causes a prompt and sustained upregulation of the DNA repair genes DDB2, XPC, XPF, XPG and POLH. Induction of these repair factors on RNA and protein level enhanced the removal of BPDE adducts from DNA and protected cells against subsequent BPDE exposure. However, through the induction of POLH the mutation frequency in the surviving cells was enhanced. Activation of these adaptive DNA repair genes was also observed upon B(a)P treatment of MCF7 cells and in buccal cells of human volunteers after cigarette smoking. Our data provide a rational basis for an adaptive response to polycyclic aromatic hydrocarbons, which occurs however at the expense of mutations that may drive cancer formation.

Ubiquitin Protein Ligase Ring2 Is Involved in S-phase Checkpoint and DNA Damage in Cells Exposed to Benzo[a]pyrene.

Previous studies in our laboratory demonstrated that Ring2 may affect DNA damage and repair through pathways other than through regulating the expression of the nucleotide excision repair protein. In a series of experiments using wild-type cell (16HBE and WI38) and small interfering RNA (siRNA) Ring2 cells exposed to benzo[a]pyrene (BaP), we evaluated the cell cycle and DNA damage. The benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE-DNA) adduct assay demonstrated that in vitro exposure to BaP increased DNA damage in a time- and dose-dependent manner in wild-type and siRNA Ring2 cells. Analysis of covariance showed that a decrease of Ring2 caused DNA hypersensitivity to BaP. Flow cytometry results and proliferating cell nuclear antigen levels indicated that inhibition of Ring2 attenuated the effect of BaP on S-phase arrest. Taken together, these data implied that the lower proportion of cells in the S phase induced by inhibition of Ring2 may play an important role in DNA hypersensitivity to BaP.

The shifting perception on antioxidants: the case of vitamin E and ß-carotene.

Antioxidants are vital for aerobic life, and for decades the expectations of antioxidants as health promoting agents were very high. However, relatively recent meta-analyses of clinical studies show that supplementation of antioxidants does not result in the presumed health benefit, but is associated with increased mortality. The dilemma that still needs to be solved is: what are antioxidants in the end, healthy or toxic? We have evaluated this dilemma by examining the presumed health effects of two individual antioxidants with opposite images i.e. the "poisonous" ß-carotene and the "wholesome" vitamin E and focused on one aspect, namely their role in inducing BPDE-DNA adducts. It appears that both antioxidants promote DNA adduct formation indirectly by inhibition of the protective enzyme glutathione-S-transferase π (GST π). Despite their opposite image, both antioxidants display a similar type of toxicity. It is concluded that, in the appreciation of antioxidants, first their benefits should be identified and substantiated by elucidating their molecular mechanism. Subsequently, the risks should be identified including the molecular mechanism. The optimal benefit-risk ratio has to be determined for each antioxidant and each individual separately, also considering the dose.

Benzo[a]pyrene-7,8-diol-9,10-epoxide inhibits gap junction intercellular communication via phosphorylation of tumor progression locus 2 in WB-F344 rat liver epithelial cells.

Benzo[a]pyrene-7,8-diol-9,10-epoxide (B[a]PDE), a major metabolite of benzo[a]pyrene, has been reported to function as a human carcinogen. However, the molecular mechanism of how B[a]PDE regulates signaling pathways during tumor promotion remains unclear. In this study, we investigated the effects of B[a]PDE on the regulation of gap junction intercellular communication (GJIC), one of the major carcinogenic processes, and its main regulatory signaling pathways using WB-F344 rat liver epithelial (WB-F344 RLE) cells. Treatment of benzo[a]pyrene or B[a]PDE resulted in GJIC inhibition, and B[a]PDE was more active at lower concentrations than benzo[a]pyrene in the suppression of GJIC. This suggests that B[a]PDE is a stronger GJIC inhibitor. B[a]PDE at 1 µM reversibly inhibited GJIC in WB-F344 RLE cells, which was attributable to hyperphosphorylation of connexin43 (Cx43) via phosphorylation of mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK) and extracellular signal-regulated kinase (ERK). We found that B[a]PDE induced phosphorylation of tumor progression locus 2 (Tpl2), a direct upstream regulator of MEK. Tpl2 inhibitor recovered B[a]PDE-induced GJIC inhibition and attenuated B[a]PDE-induced MEK/ERK phosphorylation in WB-F344 RLE cells. Collectively, our results suggest that B[a]PDE suppresses GJIC by activating Tpl2 and subsequently the MEK/ERK pathway and Cx43 phosphorylation in WB-F344 RLE cells. These results outline the potential importance of Tpl2 as a novel therapeutic target for B[a]PDE-induced GJIC inhibition during cancer promotion.

Oncogenic role of long noncoding RNA AF118081 in anti-benzo[a]pyrene-trans-7,8-dihydrodiol-9,10-epoxide-transformed 16HBE cells.

Lung cancer is the leading cause of cancer deaths and remains an important public health problem worldwide. Long noncoding RNAs (lncRNAs) are newly identified regulators of tumorigenesis and tumor progression. However, the role of lncRNAs in lung cancer induced by environmental carcinogens remains largely unknown. In this study, an lncRNA microarray was used to compare the expression profiles of malignantly transformed 16HBE cells (16HBE-T) induced with anti-benzo[a]pyrene-trans-7,8-diol-9,10-epoxide (anti-BPDE) and normal 16HBE cells (16HBE-N). Using quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR), lncRNA AF118081 was identified as the most significantly overexpressed lncRNA in 16HBE-T cells, lung cancer cells, and patient samples. Cell proliferation, colony formation, apoptosis, migration, and invasion were assayed in 16HBE-T cells following the knockdown of lncRNA AF118081 with small interfering RNA. AF118081 knockdown inhibited cell growth and tumor invasion. An in vivo (nude mouse) model was then used to assay tumor growth, and the downregulation of AF118081 clearly suppressed tumor growth, consistent with the results of the in vitro assays. Together, these findings identify a new oncogenic lncRNA, lncRNA AF118081, in malignantly transformed 16HBE cells. This enhances our understanding of lncRNAs as important regulatory elements in chemical carcinogenesis and potential targets of lung cancer therapies.

Variants of mouse DNA polymerase κ reveal a mechanism of efficient and accurate translesion synthesis past a benzo[a]pyrene dG adduct.

DNA polymerase κ (Polκ) is the only known Y-family DNA polymerase that bypasses the 10S (+)-trans-anti-benzo[a]pyrene diol epoxide (BPDE)-N(2)-deoxyguanine adducts efficiently and accurately. The unique features of Polκ, a large structure gap between the catalytic core and little finger domain and a 90-residue addition at the N terminus known as the N-clasp, may give rise to its special translesion capability. We designed and constructed two mouse Polκ variants, which have reduced gap size on both sides [Polκ Gap Mutant (PGM) 1] or one side flanking the template base (PGM2). These Polκ variants are nearly as efficient as WT in normal DNA synthesis, albeit with reduced accuracy. However, PGM1 is strongly blocked by the 10S (+)-trans-anti-BPDE-N(2)-dG lesion. Steady-state kinetic measurements reveal a significant reduction in efficiency of dCTP incorporation opposite the lesion by PGM1 and a moderate reduction by PGM2. Consistently, Polκ-deficient cells stably complemented with PGM1 GFP-Polκ remained hypersensitive to BPDE treatment, and complementation with WT or PGM2 GFP-Polκ restored BPDE resistance. Furthermore, deletion of the first 51 residues of the N-clasp in mouse Polκ (mPolκ(52-516)) leads to reduced polymerization activity, and the mutant PGM2(52-516) but not PGM1(52-516) can partially compensate the N-terminal deletion and restore the catalytic activity on normal DNA. However, neither WT nor PGM2 mPolκ(52-516) retains BPDE bypass activity. We conclude that the structural gap physically accommodates the bulky aromatic adduct and the N-clasp is essential for the structural integrity and flexibility of Polκ during translesion synthesis.

DNA synthesis inhibition in response to benzo[a]pyrene dihydrodiol epoxide is associated with attenuation of p(34)cdc2: Role of p53.

Our previous findings demonstrated that DNA damage by polynuclear aromatic hydrocarbons (PAHs) triggers a cellular protective response of growth inhibition (G1-S cell cycle arrest and inhibition of DNA synthesis) in human fibroblasts associated with accumulation of p53 protein, a growth-inhibitory transcription factor. Here, we report that BPDE (the ultimate carcinogenic metabolite of the PAH benzo[a]pyrene) treatment triggers a variable extent of inhibition of DNA synthesis/cell growth, which does not correspond to the extent of increased p53 accumulation. BPDE treatment of cells significantly attenuates expression of p(34)cdc2, a cell cycle activating protein. Although the role of cdc2 down-regulation in inhibition of cell cycle progression is well known, cdc2 down-regulation in response to cellular insult by PAHs has not been reported. Unlike p53 accumulation, there is a correspondence between DNA synthesis/cell growth inhibition and cdc2 down-regulation by BPDE. BPDE-induced cdc2 down-regulation is p53 dependent, although there is no correspondence between p53 accumulation and cdc2 down-regulation. BPDE-induced cdc2 down-regulation corresponded with accumulation of the cell cycle inhibitor protein p21 (transactivation product of p53). DNA synthesis/cell growth inhibition in response to DNA-damaging PAHs may involve down-regulation of cdc2 protein mediated by p53 activation (transactivation ability), and the extent of p53 accumulation is not the sole determining factor in this regard.

ERCC1 and ERCC2 haplotype modulates induced BPDE-DNA adducts in primary cultured lymphocytes.

BACKGROUND: Benzo[a]pyrene(B[a]P), and its ultimate metabolite Benzo[a]pyrene 7,8-diol 9,10-epoxide (BPDE), are classic DNA damaging carcinogens. DNA damage caused by BPDE is normally repaired by Nucleotide Excision Repair (NER), of which ERCC1 and ERCC2/XPD exert an indispensable role. Genetic variations in ERCC1 and ERCC2 have been related to DNA repair efficiency. In this study we used lymphocytes from healthy individuals to show that polymorphisms in ERCC1 and ERCC2 are directly associated with decreased DNA repair efficiency. METHODS: ERCC1 (rs3212986 and rs11615) and ERCC2 (rs13181, rs1799793 and rs238406) were genotyped in 818 healthy Han individuals from the northeast of China. BPDE induced DNA adducts in lymphocytes were assessed by high performance liquid chromatography (HPLC) in 282 randomly selected participants. The effect of ERCC1 rs3212986 and ERCC2 rs238406 on DNA damage caused by B[a]P was assessed with a modified comet assay. RESULTS: We found that the variant genotypes of ERCC1 rs3212986 and ERCC2 rs238406 were associated with the high levels of BPDE-DNA adducts. Especially ERCC1 rs3212986 A-allele variant was significantly associated with the high BPDE-DNA adducts. Haplotype analysis showed that the ERCC1 haplotype AC (OR = 2.36, 95% CI = 1.84-2.97), ERCC2 haplotype AGA (OR = 1.51, 95% CI = 1.06-2.15) and haplotype block AGAAC (OR = 5.28, 95% CI = 2.95-9.43), AGCAC (OR = 1.35 95% CI = 1.13-1.60) were linked with high BPDE-DNA adducts. In addition, we found that the combined minor alleles of ERCC1 rs3212986 and ERCC2 rs238406 were associated with a reduced DNA repair capacity. CONCLUSIONS: Our results suggest that the variant genotypes of ERCC1 rs3212986 and ERCC2 rs238406 are associated with decreased repair efficiency of BPDE induced DNA damage, and may be predictive for an individual's DNA repair capacity in response to environmental carcinogens.