Translation initiation proteins, ubiquitin-proteasome system related proteins, and 14-3-3 proteins as response proteins in FL cells exposed to anti-benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide

Metabolomic analysis to define and compare the effects of PAHs and oxygenated PAHs in developing zebrafish

Polycyclic aromatic hydrocarbons (PAHs) and their oxygenated derivatives are ubiquitously present in diesel exhaust, atmospheric particulate matter and soils sampled in urban areas. Therefore, inhalation or non-dietary ingestion of both PAHs and oxy-PAHs are major routes of exposure for people; especially young children living in these localities. While there has been extensive research on the parent PAHs, limited studies exist on the biological effects of oxy-PAHs which have been shown to be more soluble and more mobile in the environment. Additionally, investigations comparing the metabolic responses resulting from parent PAHs and oxy-PAHs exposures have not been reported. To address these current gaps, an untargeted metabolomics approach was conducted to examine the in vivo metabolomic profiles of developing zebrafish (Danio rerio) exposed to 4 µM of benz[a]anthracene (BAA) or benz[a]anthracene-7,12-dione (BAQ). By integrating multivariate, univariate and pathway analyses, a total of 63 metabolites were significantly altered after 5 days of exposure. The marked perturbations revealed that both BAA and BAQ affect protein biosynthesis, mitochondrial function, neural development, vascular development and cardiac function. Our previous transcriptomic and genomic data were incorporated in this metabolomics study to provide a more comprehensive view of the relationship between PAH and oxy-PAH exposures on vertebrate development.

Pathway and time-resolved benzo[a]pyrene toxicity on Hepa1c1c7 cells at toxic and subtoxic exposure

Benzo[a]pyrene (B[a]P) is an environmental contaminant mainly studied for its toxic/carcinogenic effects. For a comprehensive and pathway orientated mechanistic understanding of the effects directly triggered by a toxic (5 μM) or a subtoxic (50 nM) concentration of B[a]P or indirectly by its metabolites, we conducted time series experiments for up to 24 h to study the effects in murine hepatocytes. These cells rapidly take up and actively metabolize B[a]P, which was followed by quantitative analysis of the concentration of intracellular B[a]P and seven representative degradation products. Exposure with 5 μM B[a]P led to a maximal intracellular concentration of 1604 pmol/5 × 10(4) cells, leveling at 55 pmol/5 × 10(4) cells by the end of the time course. Changes in the global proteome (>1000 protein profiles) and metabolome (163 metabolites) were assessed in combination with B[a]P degradation. Abundance profiles of 236 (both concentrations), 190 (only 5 μM), and 150 (only 50 nM) proteins were found to be regulated in response to B[a]P in a time-dependent manner. At the endogenous metabolite level amino acids, acylcarnitines and glycerophospholipids were particularly affected by B[a]P. The comprehensive chemical, proteome and metabolomic data enabled the identification of effects on the pathway level in a time-resolved manner. So in addition to known alterations, also protein synthesis, lipid metabolism, and membrane dysfunction were identified as B[a]P specific effects.

Identification of benzo[a]pyrene-induced cell cycle-associated alterations in MCF-7 cells using infrared spectroscopy with computational analysis

Chemical contaminants, such as benzo[a]pyrene (B[a]P), may modulate transcriptional responses in cells via the activation of aryl hydrocarbon receptor (AhR) or through responses to DNA damage following adduct formation. Attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy can be employed in a non-destructive fashion to interrogate the biochemical signature of cells via generation of infrared (IR) spectra. By applying to generated spectral datasets subsequent computational approaches such as principal component analysis plus linear discriminant analysis (PCA-LDA), derived data reduction is achieved to facilitate the visualization of wavenumber-related alterations in target cells. Discriminating spectral variables might be associated with lipid or glycogen content, conformational protein changes and phosphorylation, and structural alterations in DNA/RNA. Using this approach, we investigated the dose-related effects of B[a]P in MCF-7 cells concentrated in S- or G₀/G₁-phase. Our findings identified that in PCA-LDA scores plots a clear segregation of IR spectra was evident, with the major spectral alterations associated with DNA/RNA, secondary protein structure and lipid. Dose-related effects were observed and even with exposures as low as 10⁻⁹ M B[a]P, significant (P ≤ 0.001) separation of B[a]P-treated vs. vehicle control cells was noted. ATR-FTIR spectroscopy with computational analysis is a novel approach to identify the effects of environmental contaminants in target cells.

Nuclear proteome analysis of benzo(a)pyrene-treated HeLa cells

Previously, we employed a proteomics-based 2-D gel electrophoresis assay to show that exposure to 10μM benzo(a)pyrene (BaP) during a 24 h frame can lead to changes in nuclear protein expression and alternative splicing. To further expand our knowledge about the DNA damage response (DDR) induced by BaP, we investigated the nuclear protein expression profiles in HeLa cells treated with different concentrations of BaP (0.1, 1, and 10μM) using this proteomics-based 2-D gel electrophoresis assay. We found 125 differentially expressed proteins in BaP-treated cells compared to control cells. Among them, 79 (63.2%) were down-regulated, 46 (36.8%) were up-regulated; 8 showed changes in the 1μM and 10μM BaP-treated groups, 2 in the 0.1μM and 10μM BaP-treated groups, 4 in the 0.1μM and 1μM BaP-treated groups, and only one showed changes in all three groups. Fifty protein spots were chosen for liquid chromatography-tandem mass spectrometry (LC-MS/MS) identification, and of these, 39 were identified, including subunits of the 26S proteasome and Annexin A1. The functions of some identified proteins were further examined and the results showed that they might be involved in BaP-induced DDR. Taken together, these data indicate that proteomics is a valuable approach in the study of environmental chemical-host interactions, and the identified proteins could provide new leads for better understanding BaP-induced mutagenesis and carcinogenesis.

Role of poly(ADP-ribose) glycohydrolase in the regulation of cell fate in response to benzo(a)pyrene

Poly(ADP-ribosyl)ation is a crucial regulator of cell fate in response to genotoxic stress. Poly(ADP-ribosyl)ation plays important roles in multiple cellular processes, including DNA repair, chromosomal stability, chromatin function, apoptosis, and transcriptional regulation. Poly(ADP-ribose) (PAR) degradation is carried out mainly by poly(ADP-ribose) glycohydrolase (PARG) enzymes. Benzo(a)pyrene (BaP) is a known human carcinogen. Previous studies in our laboratory demonstrated that exposure to BaP caused a concentration-dependent DNA damage in human bronchial epithelial (16HBE) cells. The role of PARG in the regulation of DNA damage induced by BaP is still unclear. To gain insight into the function of PARG and PAR in response to BaP, we used lentiviral gene silencing to generate 16HBE cell lines with stably suppressed PARG, and determined parameters of cell death and cell cycle following BaP exposure. We found that PARG was partially dependent on PAR synthesis, PARG depletion led to PAR accumulation. BaP-induced cell death was regulated by PARG, the absence of which was beneficial for undamaged cells. Our results further suggested that PARG probably has influence on ATM/p53 pathway and metabolic activation of BaP. Experimental evidences provided from this study suggest significant preventive properties of PAR accumulation in the toxicity caused by BaP.

Phosphorylation of the α-subunit of the eukaryotic initiation factor-2 (eIF2α) alleviates benzo[a]pyrene-7,8-diol-9,10-epoxide induced cell cycle arrest and apoptosis in human cells

Benzo[a]pyrene-7,8-diol-9,10-epoxide (BPDE) is a carcinogen causing bulky-adduct DNA damage and inducing extensive cell responses regulating cell cycle, cell survival and apoptosis. However, the mechanism of cellular responses to BPDE exposure is not fully understood. In this study, we demonstrated the involvement of the phosphorylation of the α-subunit of the eukaryotic initiation factor-2 (eIF2α) in the cellular response to BPDE exposure and addressed the role of eIF2α phosphorylation in the regulation of the cellular stress. Phosphorylation of eIF2α was induced in a normal human FL amnion epithelial cell line, and the expression of ATF4, a conserved downstream transcriptional factor of eIF2α phosphorylation, was up-regulated after BPDE exposure; however, the four known primary kinases for eIF2α phosphorylation (GCN2, HRI, PKR, and PERK) were not found activated. While BPDE induced severe cell cycle arrest and apoptosis and decreased cell viability in FL cells, salubrinal, a selective inhibitor of eIF2α dephosphorylation, maintained the eIF2α phosphorylation and attenuated cell cycle arrest and apoptosis and promoted cell survival. The findings reveal that when BPDE causes cellular damages, it induces eIF2α phosphorylation as well, which produces a pro-survival and anti-apoptotic effect to alleviate the cellular damages. Thus, the present study proposes a new cellular defensive mechanism during the environmental mutagen and carcinogen attack.

DIGE-based protein expression analysis of B[a]P-exposed hepatoma cells reveals a complex stress response including alterations in oxidative stress, cell cycle control, and cytoskeleton motility at toxic and subacute concentrations

Although the effects of high concentrations of the carcinogen benzo[a]pyrene (B[a]P) have been studied extensively, little is known about its effects at subacute toxic concentrations, which are typical for environmental pollutants. We exposed murine Hepa1c1c7 cells to a toxic concentration (5 μM) and a subacute concentration (50 nM) of B[a]P over a period of 2-24 h to differentiate between acute and pseudochronic effects and conducted a time-course analysis of B[a]P-influenced protein expression by DIGE. In total, a set of 120 spots were found to be significantly altered due to B[a]P exposure of which 112 were subsequently identified by mass spectrometry. Clustering and principal component analysis were conducted to identify sets of proteins responding in a concerted manner to the exposure. Our results indicate an immediate response to the contaminant at the protein level and demonstrate that B[a]P exposure alters the cellular response by disturbing proteins involved in oxidative stress, cell cycle regulation, apoptosis, and cytoskeleton organization. Furthermore, network analysis of protein-protein interactions revealed a complex network of interacting, B[a]P-regulated proteins mostly belonging to the cytoskeleton organization and several signal transduction pathways.

Temporal gene expression changes induced by a low concentration of benzo[a]pyrene diol epoxide in a normal human cell line

(+ or -)-anti-Benzo[a]pyrene-7,8-diol-9,10-epoxide (BPDE), which causes bulky-adduct DNA damage, is well-characterized as the ultimate carcinogen of benzo[a]pyrene (BaP). In this study, we have employed Affymetrix HG-U133 Plus 2.0 microarray and quantitative real-time RT-PCR methods to investigate a temporal transcriptomic response triggered by a low concentration (0.05 microM) of BPDE at 1, 10, and 22 h after exposure in normal human cells. The differential gene expression profiles at the three time points varied greatly, and generally reflected a cellular responsive process from initiation to progression and to recovery after the BPDE-caused damage. The dynamic regulation of the genes related with cell cycle progression and cell fate exhibited a tendency from inhibition to survival, which was accordant with the cell cycle arrest and cytotoxicity data induced by the low-dose BPDE exposure. In silico comparison of the genomic data revealed that BPDE and ultraviolet induced a panel of common transcriptional responses, which might be related with a series of similar molecular processes elicited by these two DNA-damaging agents. In conclusion, this whole-genome time-course study has identified a dynamically regulated transcriptional signature after low-dose BPDE exposure, which may help to understand the complex mechanisms of mutagenesis and carcinogenesis induced by BPDE.