Induction of PUMA-α and down-regulation of PUMA-β expression is associated with benzo(a)pyrene-induced apoptosis in MCF-7 cells

Leaching of metals from red mud and toxicity in human cells in vitro

Toxicity of red mud, a waste from alumina production, was studied using human breast cancer MCF-7 cells. Culture medium was prepared by mixing water for 3 days with the red mud and removing solid particles afterwards (red mud water). Culture for 48 h of the cells in this medium in neutral pH decreased the cell viability, as analyzed by the MTT-test, and increased the formation of reactive oxygen species. Thus, neutralization does not eliminate the toxicity of red mud. In preliminary experiments, a combined effect of five metals (Cr, Li, V, Al, As) increased the formation of ROS (reactive oxygen species) statistically significantly. Each element separately did not have a similar effect. In environmental applications, red mud is likely to be used after activation. In this work, the red mud was activated using hydrochloric acid to study the physical and chemical properties before and after the treatment. Activation increased the specific surface area of red mud from 16 m2 g-1 to 148 m2 g-1, which is beneficial in many environmental applications such as in the adsorptive removal of pollutants. After activation, leaching of some elements from the red mud decreased (e.g. Al from 38.0 to 0.56 mg L-1, As from 21.0 to 2.1 μg L-1, V from 172.0 to 29.8 μg L-1) while some increased (e.g. Li from 0.04 to 2.81 mg L-1, Cr from 0.35 to 3.23 mg L-1).

Toxicity of diuron metabolites in human cells

Diuron, a highly used herbicide worldwide, is metabolized into several toxic metabolites. DCA (3,4-dichloroaniline), DCPU [3-(3, 4-dichlorophenyl)urea] and DCPMU [3-(3,4-dichlorophenyl)-1-methyl urea] reduced viability of human placental choriocarcinoma BeWo, human breast adenocarcinoma MCF-7 and human colon adenocarcinoma Caco-2 cells as judged by the MTT assay, where color formation is dependent on functional mitochondria in viable cells. Based on the IC₅₀ values in BeWo cells the order of cytotoxicity was DCA > DCPU > diuron > DCPMU, and in Caco-2 cells DCPMU > DCPU > DCA, diuron. In MCF-7 cells, only DCPU had an IC₅₀ within the range of the concentrations used. In the PI-digitonin viability assay, only the highest concentration (200 μM) of DCPU caused a statistically significant decrease in viability in any cell line. There was no correlation between cytotoxicity and ROS production. This indicates that diuron metabolites are toxic in cells of human origin with mitochondria as the target, but ROS not the likely mechanism.

Effects of novel brominated flame retardant TBBPA on human airway epithelial cell (A549) in vitro and proteome profiling

The cellular toxicity response of human airway epithelial cells (A549) to tetrabromobisphenol (TBBPA) was assessed in vitro. Cell viability, levels of intracellular reactive oxygen species (ROS), lipid peroxidation (MDA), and caspase-3 activity were determined after A549 treated with varying concentrations of TBBPA. A comparative proteomic analysis was performed in cells treated with different concentrations of TBBPA (0, 10, and 40 μg/mL). Two-way anova analysis showed that cell viability was significantly decreased after treatment by TBBPA with a concentration of 16 μg/mL for 48 hr, however, the caspase-3 activities, ROS generation, and MDA content increased. Ultrastructural observation revealed that the cell was morphological damaged after exposure to 64 μg/mL TBBPA, with mitochondria seriously injured and the smooth endoplasmic reticulum dilated. There was a good correlation between ROS generation and mitochondrial dysfunction. Seventeen differentially expressed proteins involved in various biological processes were identified. These findings provide a basis for understanding the mechanisms of cell dysfunction and perturbation of antioxidant status induced by additive flame retardant on airway epithelial cells.

Targeted inhibition of histone H3K27 demethylation is effective in high-risk neuroblastoma

High-risk neuroblastoma is often distinguished by amplification of MYCN and loss of differentiation potential. We performed high-throughput drug screening of epigenetic-targeted therapies across a large and diverse tumor cell line panel and uncovered the hypersensitivity of neuroblastoma cells to GSK-J4, a small-molecule dual inhibitor of lysine 27 of histone 3 (H3K27) demethylases ubiquitously transcribed tetratricopeptide repeat, X chromosome (UTX), and histone demethylase Jumonji D3 (JMJD3). Mechanistically, GSK-J4 induced neuroblastoma differentiation and endoplasmic reticulum (ER) stress, with accompanying up-regulation of p53 up-regulated modulator of apoptosis (PUMA) and induction of cell death. Retinoic acid (RA)-resistant neuroblastoma cells were sensitive to GSK-J4. In addition, GSK-J4 was effective at blocking the growth of chemorefractory and patient-derived xenograft models of high-risk neuroblastoma in vivo. Furthermore, GSK-J4 and RA combination increased differentiation and ER stress over GSK-J4 effects and limited the growth of neuroblastomas resistant to either drug alone. In MYCN-amplified neuroblastoma, PUMA induction by GSK-J4 sensitized tumors to the B cell lymphoma 2 (BCL-2) inhibitor venetoclax, demonstrating that epigenetic-targeted therapies and BCL-2 homology domain 3 mimetics can be rationally combined to treat this high-risk subset of neuroblastoma. Therefore, H3K27 demethylation inhibition is a promising therapeutic target to treat high-risk neuroblastoma, and H3K27 demethylation can be part of rational combination therapies to induce robust antineuroblastoma activity.

Benzo(a)pyrene inhibits migration and invasion of extravillous trophoblast HTR-8/SVneo cells via activation of the ERK and JNK pathway

Benzo(a)pyrene (BaP) is a persistent organic pollutant (POP) that is a serious threat to human health. Numerous studies have shown that BaP causes adverse effects in pregnancy, but the mechanism remains unclear. The moderate invasion of trophoblast cells into the endometrium is an important factor during successful embryo implantation. The aim of this study was to investigate the effect and mechanism of BaP on the invasion and migration of trophoblast cells. HTR-8/SVneo cells were treated with different concentrations (1, 5, 10, 25, 50 and 100 μM) of BaP. The invasion and migration of HTR-8/SVneo cells were observed after BaP treatment. The protein levels related to migration and invasion was detected by Western blot. The results confirmed that BaP inhibits the migration and invasion of extravillous trophoblast HTR-8/SVneo cells. Further investigations indicated that the protein levels of MMP-2, MMP-9 and E-cadherin in HTR-8/SVneo cells were changed by BaP treatment. Moreover, the data demonstrated that BaP activated the MAPK signaling pathway. Pretreatment with specific inhibitors of MAPK rescued BaP-induced change in the migration and invasion of HTR-8/SVneo cells. Taken together, our results indicated that BaP inhibits invasion and the migration of HTR-8/SVneo cells, which might cause a failure in early pregnancy. Copyright © 2015 John Wiley & Sons, Ltd.

Synthesis and characterisation of morin reduced gold nanoparticles and its cytotoxicity in MCF-7 cells

There is significant interest in investigating the therapeutic potential of phytochemical reduced and bound gold nanoparticles (AuNPs) as it bridges the gap between nanotechnology and therapy. In the present study, AuNPs prepared using the flavonoid morin (mAuNPs) are characterised and have been studied for their anti-cancer effects. The -OH groups of morin reduce Au(3+) and stabilize Au(0) to form spherical and crystalline mAuNPs. These mAuNPs are biocompatible towards normal human blood cells and breast epithelial cells. Through TEM analysis, we report that they are readily taken up by breast cancer cells (MCF-7) to induce cell death. Apoptosis has also been assessed by other morphological observations and cell viability studies. Flow cytometric studies reveal that the cells undergo a transient phase of apoptosis progressing towards secondary necrosis as the dose and time of mAuNPs treatment increases. The ability of mAuNPs to induce cell death in MCF-7 cells indicates its potential as an anti-cancer agent.

Chloropicrin-induced toxic responses in human lung epithelial cells

Chloropicrin is a slowly evaporating toxic irritant that is known to cause damage in the respiratory system. Here we used a lung epithelial cell line (A549) to study the molecular responses underlying chloropicrin toxicity. Glutathione (GSH), synthetic peptide and 2'-deoxyguanosine were used as in vitro trapping agents to identify early markers of chloropicrin toxicity. Microscopy of the cells revealed massive vacuolization by chloropicrin exposure (80-100μM). The number of apoptotic cells increased with the chloropicrin concentration as assessed by flow cytometry. Immunoblotting analysis revealed increases in the amount of four proteins (p53, p21, p27 and phospho-Erk1/2) that are involved in DNA-damage, cell cycle regulation and apoptosis. Chloropicrin evoked a dose-dependent increase in levels of reactive oxygen species within one hour of exposure. The treatment triggered also the formation of disulphide bonds between the model thiol-containing peptides as analysed by LC/MS. Chloropicrin did not form stable adducts with the model peptides or 2'-deoxyguanosine. N-acetyl-cysteine (1mM NAC) fully prevented the vacuoles and chloropicrin-induced cytotoxicity. The results suggest that an oxidative insult, particularly modification of free sulfhydryl groups in proteins is involved in the acute toxicity evoked by chloropicrin in airway epithelial cells. The protective effect of NAC as a potential antidote in chloropicrin intoxication will require further investigation.

Silencing prion protein in MDA-MB-435 breast cancer cells leads to pleiotropic cellular responses to cytotoxic stimuli

Prion protein (PrP) is well studied for its pathogenic role in prion disease, but its potential contribution to other pathological processes is less understood. PrP is expressed in a variety of cancers and at least in pancreatic and breast cancers, its expression appears to be associated with poor prognosis. To understand the role of PrP in breast cancer cells, we knocked down PrP expression in MDA-MB-435 breast cancer cells with small interfering RNA and subjected these cells to a series of analyses. We found that PrP knockdown in these cells does not affect cell proliferation or colony formation, but significantly influences the cellular response to cytotoxic stimuli. Compared to control cells, PrP knockdown cells exhibited an increased susceptibility to serum deprivation induced apoptosis, no change to staurosporine- or paclitaxel-induced cell deaths, and a reduced susceptibility to chemotherapy drug doxorubicin-induced cell death. To understand the mechanism of unexpected role of PrP in exacerbating doxorubicin-induced cytotoxicity, we analyzed cell death related Bcl-2 family proteins. We found that PrP knockdown alters the expression of several Bcl-2 family proteins, correlating with increased resistance to doxorubicin-induced cytotoxicity. Moreover, the enhanced doxorubicin resistance is independent of DNA damage related p53 pathway, but at least partially through the ERK1/2 pathway. Together, our study revealed that silencing PrP in MDA-MB-435 breast cancer cells results in very different responses to various cytotoxic stimuli and ERK1/2 signaling pathway is involved in PrP silencing caused resistance to doxorubicin.

The attenuation of early benzo(a)pyrene-induced carcinogenic insults by diallyl disulfide (DADS) in MCF-10A cells

Diallyl disulfide (DADS), a garlic organosulfur compound, has been researched as a cancer prevention agent; however, the role of DADS in the suppression of cancer initiation in nonneoplastic cells has not been elucidated. To evaluate DADS inhibition of early carcinogenic events, MCF-10A cells were pretreated (PreTx) with DADS followed by the ubiquitous carcinogen benzo(a)pyrene (BaP), or cotreated (CoTx) with DADS and BaP for up to 24 h. The cells were evaluated for changes in cell viability/proliferation, cell cycle, induction of peroxide formation, and DNA damage. BaP induced a statistically significant increase in cell proliferation at 6 h, which was attenuated with DADS CoTx. PreTx with 6 and 60 μM of DADS inhibited BaP-induced G2/M arrest by 68% and 78%, respectively. DADS, regardless of concentration or method, inhibited BaP-induced extracellular aqueous peroxide formation within 24 h. DADS attenuated BaP-induced DNA single-strand breaks at all time points through both DADS Pre- and CoTx, with significant inhibition for all treatments sustained after 6 h. DADS was effective in inhibiting BaP-induced cell proliferation, cell cycle transitions, reactive oxygen species, and DNA damage in a normal cell line, and thus may inhibit environmentally induced breast cancer initiation.

Diallyl trisulfide as an inhibitor of benzo(a)pyrene-induced precancerous carcinogenesis in MCF-10A cells

Diallyl trisulfide (DATS) is a garlic organosulfide that is toxic to cancer cells, however, little is known about its effect in the initiation phase of carcinogenesis. We sought to determine whether DATS could inhibit the carcinogen, benzo(a)pyrene (BaP), from inducing precancerous activity, in vitro. MCF-10A cells were either pre-treated (PreTx) or concurrently treated (CoTx) with 1 μM BaP, and 6 or 60 μM DATS for up to 24h. The DATS 6 and 60 μM CoTx inhibited BaP-induced cell proliferation by an average of 71.1% and 120.8%, respectively, at 6h. The 60 μM DATS pretreatment decreased BaP-induced G2/M cell cycle transition by 127%, and reduced the increase in cells in the S-phase by 42%; whereas 60 μM DATS CoTx induced a 177% increase in cells in G1. DATS effectively inhibited (P<0.001) BaP-induced peroxide formation by at least 54%, which may have prevented the formation of BaP-induced DNA strand breaks. In this study, we reveal mechanisms involved in DATS inhibition of BaP-induced carcinogenesis, including inhibition of cell proliferation, regulation of cell cycle, attenuation of ROS formation, and inhibition of DNA damage. At the doses evaluated, DATS appears to be an effective attenuator of BaP-induced breast carcinogenesis, in vitro.

Benzo(a)pyrene-induced mitochondrial dysfunction and cell death in p53-null Hep3B cells

Benzo(a)pyrene (BaP) has been shown to induce apoptosis and necrosis in various cell types. However, the effect of BaP on mitochondria function and p73, and their possible roles in BaP-induced cell death have not been well studied. This study focused on mitochondria-mediated cell death and the occurrence of p73 protein accumulation in BaP-treated human hepatoma Hep3B (p53-null) cells. We found that BaP (8, 16, 32 and 64μM) induced early necrosis at 12h and delayed apoptosis at 24h. BaP dramatically induced ethoxyresorufin-O-deethylase activity and led to significant increase in oxidative stress at early time points (6 and 12h). Necrotic cell death was concurrent with loss of mitochondrial membrane potential, decrease in the ATP level and activities of Na(+)/K(+)-ATPase and Ca(2+)/Mg(2+)-ATPase. However, these changes were reversed in the process of apoptosis. In addition, after BaP treatment, c-Jun N-terminal kinase (JNK) and Bax were activated during apoptosis and no change in p73 protein level was observed. These results revealed that the cells with mitochondria dysfunction and ATP depletion underwent necrosis at early time point and apoptosis afterward when they recovered from mitochondrial dysfunction and ATP depletion. Activation of JNK and Bax possibly contributed to BaP-induced apoptosis.

DNA damage and DNA damage response in human bronchial epithelial BEAS-2B cells following exposure to 2-nitrobenzanthrone and 3-nitrobenzanthrone: role in apoptosis

Nitro-polycyclic aromatic hydrocarbons (nitro-PAHs) are mutagenic and carcinogenic environmental pollutants found in diesel exhaust and on urban air pollution particles. In the present study, human bronchial epithelial BEAS-2B cells were exposed to 2-nitrobenzanthrone (2-NBA) and 3-nitrobenzanthrone (3-NBA). DNA damage responses were compared to those observed after exposure to 1-nitropyrene (1-NP) and benzo[a]pyrene (B[a]P). Examination by microscopy revealed that 3-NBA was the most potent toxic compound while weaker responses were observed with 1-NP and B[a]P. Most interestingly, 2-NBA did not induce cell death or any other stress-related responses. 3-NBA induced a typical apoptotic cell death judged by nuclear condensation and little plasma membrane damage as well as cleavage of caspase 3 and poly-(ADP-ribose) polymerase (PARP). Exposure to 3-NBA resulted in an accumulation of cells in S-phase, and further analysis by Western blotting, immunocytochemistry and flow cytometry revealed that 3-NBA induced a DNA damage response characterized by phosphorylation of ATM (ataxia-telangiectasia mutated), checkpoint kinase (Chk) 2/Chk1, H2AX and p53. The p53 inhibitor pifithrin-α inhibited 3-NBA-induced apoptosis while small effects were seen using pifithrin-μ, suggesting that 3-NBA-induced cell death is a result of transcriptional activation of p53. In conclusion, 3-NBA is a potent inducer of apoptosis, which seemed to be triggered by the DNA damage response. Furthermore, a change of the nitro-group to the second position (i.e. 2-NBA) dramatically changed the cellular reactivity of the compound.

Mitochondrial dysfunction and transactivation of p53-dependent apoptotic genes in BaP-treated human fetal lung fibroblasts

Benzo(a)pyrene (BaP) has been shown to be an inducer of apoptosis. However, mechanisms involved in BaP-induced mitochondrial dysfunction are not well-known. In this study, human fetal lung fibroblasts cells were treated with BaP (8, 16, 32, 64 and 128 μM) for 4 and 12 h. Cell viability, intracellular level of reactive oxygen species (ROS), total antioxidant capacity (T-AOC), mitochondrial membrane potential (Δ Ψm) and cytochrome c release were determined. Changes in transcriptional levels of p53-dependent apoptotic genes ( p53, APAF1, CASPASE3, CASPASE9, NOXA and PUMA) were measured. At time point of 4 h, BaP induced the intracellular ROS generation in 64 ( p < .05) and 128 μM BaP groups ( p < .01) but decreased the T-AOC activities in 32, 64 ( p < .05 for both) and 128 μM BaP groups ( p < .01). At time point of 12 h, Δ Ψm significantly decreased in ≥32 μM BaP groups ( p < .05 for all). Amount of mitochondrial cytochrome c significantly increased in 128 μM BaP group ( p < .01). Transcriptional levels of CASPASE3, CASPASE9, APAF1 and PUMA were up-regulated in all BaP groups ( p < .05 for all) and in ≥32 μM groups for NOXA ( p < .05). But only in 16 μM BaP group a relatively little expression of p53 mRNA was observed ( p < .05). The results indicate that in the earlier period BaP promoted the generation of excessive ROS and subsequently the mitochondrial depolarization, whereas transactivations of the p53-dependent apoptotic genes were significantly induced at the later period.

Gene-specific repression of the p53 target gene PUMA via intragenic CTCF-Cohesin binding

The p53 transcriptional program orchestrates alternative responses to stress, including cell cycle arrest and apoptosis, but the mechanism of cell fate choice upon p53 activation is not fully understood. Here we report that PUMA (p53 up-regulated modulator of apoptosis), a key mediator of p53-dependent cell death, is regulated by a noncanonical, gene-specific mechanism. Using chromatin immunoprecipitation assays, we found that the first half of the PUMA locus (approximately 6 kb) is constitutively occupied by RNA polymerase II and general transcription factors regardless of p53 activity. Using various RNA analyses, we found that this region is constitutively transcribed to generate a long unprocessed RNA with no known coding capacity. This permissive intragenic domain is constrained by sharp chromatin boundaries, as illustrated by histone marks of active transcription (histone H3 Lys9 trimethylation [H3K4me3] and H3K9 acetylation [H3K9Ac]) that precipitously transition into repressive marks (H3K9me3). Interestingly, the insulator protein CTCF (CCCTC-binding factor) and the Cohesin complex occupy these intragenic chromatin boundaries. CTCF knockdown leads to increased basal expression of PUMA concomitant with a reduction in chromatin boundary signatures. Importantly, derepression of PUMA upon CTCF depletion occurs without p53 activation or activation of other p53 target genes. Therefore, CTCF plays a pivotal role in dampening the p53 apoptotic response by acting as a gene-specific repressor.