Hypomethylation mediated by decreased DNMTs involves in the activation of proto-oncogene MPL in TK6 cells treated with hydroquinone

DNMT1 regulates hypermethylation and silences hsa_circ_401351 in hydroquinone-induced malignant TK6 cells

BACKGROUND

Benzene and its metabolite hydroquinone (HQ) are widely used in daily life, and long-term exposure to benzene or HQ can induce acute myeloid leukemia (AML). Circular RNAs (circRNAs) are mostly produced by reverse splicing of gene exon mRNA precursors. The modulation of circRNA expression is connected to leukemia progression; however, the molecular mechanism is still unknown.

MATERIALS AND METHODS

In this study, the cells were divided into four groups: PBS control group (PBS-TK6), TK6 malignantly transformed cells induced by 10.0 μmol/L HQ (HQ-TK6), and HQ-TK6 cells treated with 5 μmol/L 5-AzaC (DNA methyltransferase inhibitor) for 24 h (HQ + 5-AzaC). HQ-TK6 cells were treated with 200 nmol/L TSA (histone deacetylation inhibitor) for 24 h (HQ + TSA). qRT-PCR was used to identify the differential hsa_circ_401351 expression between the four groups. We further determined the hsa_circ_401351 promoter methylation level with methylation-specific PCR. DNMT1 and DNMT3b were knocked down by CRISPR/Cas9 to elucidate the specific molecular mechanism of hsa_circ_401351 in HQ-TK6 cells. CCK-8 and flow cytometry detected cell proliferation and apoptosis, respectively, after hsa_circ_401351 was overexpressed in HQ-TK6 cells.

RESULTS

Compared with the PBS-TK6 group, the expression of hsa_circ_401351 was found to be lower in the HQ-TK6 group. Nevertheless, treatment with 5-AzaC or TSA increased hsa_circ_401351 expression, with the upregulation being more pronounced in the TSA group. The expression of hsa_circ_401351 in the DNMT1 knockdown group was dramatically increased by 50% compared to that in the control group, and the DNA methylation level of the hsa_circ_401351 promoter region was decreased. When hsa_circ_401351 was overexpressed, HQ-TK6 cell proliferation was significantly slowed after 48 h compared with the control group. Flow cytometry showed that cells were mainly arrested in G1 phase, and apoptosis was significantly enhanced. Similarly, qRT-PCR and Western blot data showed significant reductions in Caspase-3 mRNA and protein production, and Bcl-2 mRNA levels were also elevated.

CONCLUSIONS

Overall, our research showed that elevated DNMT1 expression in HQ-TK6 cells increased methylation levels and decreased expression of the hsa_circ_401351 promoter region, limiting its ability to suppress HQ-TK6 cell growth and enhance apoptosis.

MiR-7-5p targeted Rb regulating cell cycle is involved in hydroquinone-induced malignant progression in human lymphoblastoid TK6 cells

MiR-7-5p has been demonstrated to inhibit tumorigenesis by limiting tumor cell proliferation, migration and invasion. However, its role in countering hydroquinone (HQ)-induced malignant phenotype of TK6 cells has remained unclear. The present study aimed to investigate whether miR-7-5p overexpression could restrain the malignant phenotype in TK6 cells exposed to HQ. The results displayed that HQ suppressed the expression of miR-7-5p and promoted cell cycle progression. Further investigations confirmed that miR-7-5p could decelerate the cell cycle progression by targeting Rb after acute HQ exposure. Through the regulation of the Rb/E2F1 signaling pathway, the overexpression of miR-7-5p mitigated HQ-induced malignant phenotype in TK6 cells by impeding cell cycle progression. In conclusion, miR-7-5p overexpression appears to be involved in HQ-induced malignant transformation by suppressing Rb/E2F1 signaling pathway, resulting in a deceleration of the cell cycle progression.

Aberrant DNA methylation-mediated NF-κB/fatty acid-binding protein 5 (FABP5) feed-forward loop promotes malignancy of colorectal cancer cells

Fatty acid-binding proteins (FABPs) are intracellular lipid-binding proteins that play roles in fatty acid transport and the regulation of gene expression. Dysregulated FABP expression and/or activity have been associated with cancer pathogenesis; in particular, epidermal-type FABP (FABP5) is upregulated in many types of cancer. However, the mechanisms regulating FABP5 expression and its involvement in cancer remain largely unknown. Here, we examined the regulation of FABP5 gene expression in non-metastatic and metastatic human colorectal cancer (CRC) cells. We found that FABP5 expression was upregulated in metastatic compared with non-metastatic CRC cells as well as in human CRC tissues compared with adjacent normal tissue. Analysis of the DNA methylation status of the FABP5 promoter showed that hypomethylation correlated with the malignant potential of the CRC cell lines. Moreover, FABP5 promoter hypomethylation also correlated with the expression pattern of splice variants of the DNA methyltransferase DNMT3B. ChIP assays and luciferase reporter assays demonstrated that the transcription factor nuclear factor-kappa B (NF-κB) was involved in regulating FABP5 expression. FABP5 expression could be upregulated in metastatic CRC cells by sequential promotion of DNA demethylation followed by activation of NF-κB. We also found that upregulated FABP5 in turn controlled NF-κB activity through IL-8 production. Collectively, these findings suggest the existence of a DNA methylation-dependent NF-κB /FABP5 positive feed-forward loop that may lead to constitutive activation of NF-κB signaling pathway and play a crucial role in CRC progression.

Hsa_circ_0001944 regulates apoptosis by regulating the binding of PARP1 and HuR in leukemia and malignant transformed cells induced by hydroquinone

Hydroquinone (HQ) is one of the major metabolites of benzene and can cause abnormal gene expression. It is a known carcinogen that alters cell cycle disruption and cell proliferation. However, its chemical mechanism remain a mystery. Circular RNAs (circRNAs) are a subtype of noncoding RNAs (ncRNAs) that play a variety of roles in biological processes. Hsa_circ_001944 expression was upregulated in 30 leukemia patients and HQ-induced malignant transformed TK6 cells. Hsa_circ_001944 silencing inhibited the growth of HQ-TK6 cells and halted the cell cycle. The silencing of hsa_circ_0001944 led to increased cell accumulation in G1 versus S phase, increased apoptosis in the sh1944 versus the shNC group, and increased levels of DNA damage (γ-H2AX), leading to cell cycle arrest. In summary, inhibition of hsa_circ_001944 restricted cell growth by inhibiting cell cycle arrest and induced growth of HQ-TK6 cells by modulating PARP1 expression. Hsa_circ_0001944 targeted HuR, which is a kind of RNA-binding protein, to control PARP1 expression via RNAinter, RBPmap, and RBPdb. Fluorescence in situ hybridization combined with immunofluorescent labeling and western blotting experiments showed that hsa_circ_001944 was able to dissociate HuR and PARP1 binding in HQ-TK6 cells, control PARP1 production, and ultimately alter the PARP1/H-Ras pathway.

PARP-1 modulates the expression of miR-223 through histone acetylation to involve in the hydroquinone-induced carcinogenesis of TK6 cells

The upstream regulators of microRNAs were rarely reported. Hydroquinone (HQ) is the main metabolite of benzene, one of the important environmental factors contributing to leukemia and lymphoma. In HQ-induced malignant transformed TK6 (TK6-HT) cells, the expression of PARP-1 and miR-223 were upregulated. When in PARP-1 silencing TK6-HT cells, miR-223 was downregulated and the apoptotic cell number correspondingly increased. In TK6 cells treated with HQ for different terms, the expression of miR-223 and PARP-1 were dynamically observed and found to be decreased and increased, respectively. Trichostatin A could increase the expression of miR-223, then the expression of HDAC1-2 and nuclear factor kappa B were found to be increased, but that of mH2A was decreased. PARP-1 silencing inhibited the protein expression of H3Ac, mH2A, and H3K27ac. By co-immunoprecipitation experiment, PARP-1 and HDAC2 were found to form a regulatory complex. In conclusion, we demonstrated that the upregulation of PARP-1 mediated activation of acetylation to promote the transcription of miR-223 possibly via coregulating with HDAC2, an epigenetic regulation mechanism involved in cell malignant transformation resulting from long-term exposure to HQ, in which course, H3K27ac might be a specific marker for the activation of histone H3, which also gives hints for benzene exposure research.

The DNMT1-associated lncRNA UCA1 was upregulated in TK6 cells transformed by long-term exposure to hydroquinone and benzene-exposed workers via DNA hypomethylation

Exposure to benzene or its metabolite hydroquinone (HQ) is a risk factor for a series of myeloid malignancies, and long noncoding RNAs play an important role in the process of pathogenesis. Urothelial cancer-associated 1 (UCA1) functions as an oncogene in the development of acute myeloid leukemia. However, the association between DNMT1 and UCA1 with benzene or HQ exposure has not been explored. We characterized UCA1 expression in cells briefly exposed to HQ (HQ-ST cells) and HQ-induced malignantly transformed (TK6-HT cells) treated with 5-aza-2'-deoxycytidine (5-AzaC) or trichostatin A (TSA). Compared to that in control cells, UCA1 expression was increased, whereas DNMT1 was decreased in HQ-ST cells and TK6-HT cells treated with 5-AzaC or TSA. Moreover, UCA1 expression was also upregulated and positively correlated with benzene exposure time in benzene-exposed workers. Furthermore, the expression of UCA1 was negatively associated with the DNA methylation level of its promoter in benzene-exposed workers. DNMT1 rather than DNMT3b knockout in TK6-HT cells activated the expression of UCA1 by inducing its promoter hypomethylation. These results suggest that benzene or HQ exposure leads to UCA1 upregulation via DNA hypomethylation in the UCA1 promoter, which is mediated by DNMT1.

PARP1-DNMT1-CTCF complex and the apoptotic-induced factor mRNA expressions in workers occupationally exposed to benzene

Exposure to benzene is a common occupational hazard as well as a hematopoietic system intoxicant, but the entire picture of its molecular pathogenesis is still hazy. Its leukemogenic effect could be attributed to DNA damage, decreased repair capacity, altered methylation patterns, and defective apoptosis. Poly ADP-ribose polymerase1, DNA methyltransferase1, and CCCTC-binding factor (PARP1-DNMT1-CTCF) complex play an essential role in methylation maintenance and DNA damage repair response. This study aimed to assess the expression of PARP1, PAR glycohydrolases (PARG), DNMT1, CTCF, and apoptosis-inducing factor (AIF) in subjects occupationally exposed to benzene. A total of 200 subjects were enrolled in this study: 100 workers occupationally exposed to benzene (painters and decorators) and 100 unexposed office workers. Occupational exposure data were obtained. The biochemical and hematological evaluations were done. Quantitative reverse transcription polymerase chain reaction (RT-PCR) was used to assess mRNA expression of PARP1, PARG, DNMT1, CTCF, and AIF. Both biochemical and hematological parameters were within normal limits; workplace benzene air concentration was significantly higher in exposed workers than the levels among controls (P < 0.001). Significant decrease in mRNA levels of PARP1, DNMT1, CTCF, and AIF was noticed among the exposed group (P = 0.01, P < 0.001, P = 0.004, P < 0.001, respectively) in comparison with the control group, while PARG showed non-significant difference (P = 0.16). There was a significant negative correlation between workplace benzene air concentration and expression levels of PARP1, DNMT1, and AIF. The reduced expression of PARP1, DNMT1, CTCF, and AIF observed in exposed workers may represent one of the first benzene-induced changes that might threaten erythropoiesis.

Regulatory loop between lncRNA FAS-AS1 and DNMT3b controls FAS expression in hydroquinone-treated TK6 cells and benzene-exposed workers

Hydroquinone (HQ), one of the main metabolites of benzene, is a well-known human leukemogen. However, the specific mechanism of how benzene or HQ contributes to the development of leukemia is unknown. In a previous study, we demonstrated the upregulation of DNA methyltransferase (DNMT) expression in HQ-induced malignant transformed TK6 (HQ-TK6) cells. Here, we investigated whether a regulatory loop between the long noncoding RNA FAS-AS1 and DNMT3b exists in HQ-TK6 cells and benzene-exposed workers. We found that the expression of FAS-AS1 was downregulated in HQ-TK6 cells and workers exposed to benzene longer than 1.5 years via histone acetylation, and FAS-AS1 expression was negatively correlated with the time of benzene exposure. Restoration of FAS-AS1 in HQ-TK6 cells promoted apoptosis and inhibited tumorigenicity in female nude mice. Interestingly, treatment with a DNMT inhibitor (5-aza-2-deoxycytidine), histone deacetylase inhibitor (trichostatin A), or DNMT3b knockout led to increased FAS-AS1 through increased H3K27ac protein expression in HQ-TK6 cells, and DNMT3b knockout decreased H3K27ac and DNMT3b enrichment to the FAS-AS1 promoter region, which suggested that DNMT3b and/or histone acetylation involve FAS-AS1 expression. Importantly, restoration of FAS-AS1 resulted in reduced expression of DNMT3b and SIRT1 and increased expression of FAS in both HQ-TK6 cells and xenograft tissues. Moreover, the average DNMT3b expression in 17 paired workers exposed to benzene within 1.5 years was decreased, but that of the remaining 103 paired workers with longer exposure times was increased. Conversely, DNMT3b was negatively correlated with FAS-AS1 expression. Both FAS-AS1 and DNMT3b influenced the enrichment of H3K27ac in the FAS promoter region by regulating the expression of SIRT1, consequently upregulating FAS expression. Taken together, these observations demonstrate crosstalk between FAS-AS1 and DNMT3b via a mutual inhibition loop and indicate a new mechanism by which FAS-AS1 regulates the expression of FAS in benzene-related carcinogenesis.

Avermectin inhibits neutrophil extracellular traps release by activating PTEN demethylation to negatively regulate the PI3K-ERK pathway and reducing respiratory burst in carp

Excessive residual avermectin (AVM) in the environment can have toxic effects on non-target organisms. AVM can exert immunotoxicity by inducing genomic demethylation, but its effect on neutrophil extracellular traps (NETs) release in carp is unclear. In this study, carp neutrophils were pretreated with 5 μg/L AVM or 4 μM DNA demethylation inhibitor (aurintricarboxylic acid, ATA), alone or in combination, and then treated with 4 μM phorbol 12-myristate 13-acetate (PMA) to stimulate NETs release. The results showed that exposure of carp neutrophils to AVM significantly suppressed NETs release and MPO expression, increased ROS production, and dramatically reduced PMA-induced cellular respiratory burst. In addition, AVM could bind to the MBD2 molecule, markedly upregulate MBD2 expression to cause demethylation, and clearly activate PTEN expression, thereby inhibiting the expression of PI3K, AKT, Raf, MEK, and ERK. However, these effects were alleviated by ATA. In conclusion, our study showed that AVM could inhibit NETs release in carp by inducing demethylation of PTEN to negatively regulate NETs synthesis pathways and reducing respiratory burst level. Our findings clarify the mechanism of AVM immunotoxicity to fish and are of great significance for efforts to protect the ecological environment and human health.

Up-regulation of DNMT3b contributes to HOTAIRM1 silencing via DNA hypermethylation in cells transformed by long-term exposure to hydroquinone and workers exposed to benzene

Benzene exposure is a risk factor of acute myeloid leukemia (AML), during such carcinogenesis long non-coding RNAs (lncRNAs) are important epigenetic regulators. HOTAIRM1 (HOXA transcript antisense RNA, myeloid-specific 1) plays an indispensable role in the development of AML. Hydroquinone (HQ) is one major metabolite of benzene and its ideal replacement in toxicology research. But the influence of benzene or HQ on HOTAIRM1 expression in AML associated pathway is still unclear. In the TK6 cells with short-term exposure to HQ (HQ-ST cells) or long term HQ exposure induced malignant transformed TK6 cells (HQ-MT cells), the relationship between DNMT3b and HOTAIRM1 was explored. Comparing to counterparts, HOTAIRM1 expression was increased firstly and then decreased in HQ-ST cells, and definitely decreased in HQ-MT cells; while the expression change tendency of DNMT3b was in contrast to that of HOTAIRM1. Moreover, the average HOTAIRM1 expression of 17 paired workers being exposed to benzene within 1.5 years was increased, but that of the remaining 92 paired workers with longer exposure time was decreased. Furthermore, in 5-AzaC (DNA methyltransferase inhibitor) or TSA (histone deacetylation inhibitor) treated HQ-MT cells, the expression of HOTAIRM1 was restored by reduced DNA promoter methylation levels. HQ-MT cells with DNMT3b knockout by CRISPR/Cas9 displayed the promoter hypomethylation and the increase of HOTAIRM1, also confirmed in benzene exposure workers. These suggest that long term exposure to HQ or benzene might induce the increase of DNMT3b expression and the promoter hypermethylation to silence the expression of HOTAIRM1, a possible tumor-suppressor in the AML associated carcinogenesis pathway.

E4F1 silencing inhibits the cell growth through cell-cycle arrest in malignant transformed cells induced by hydroquinone

Hydroquinone (HQ), one of the most significant metabolic activation products of benzene in an organism, can cause hematological toxicity, such as acute myeloid leukemia. It is a clear carcinogen that can cause changes in the disorder of cell cycle and cell growth. However, its molecular mechanisms remain unclear. E4 transcription factor 1 (E4F1), an important transcription factor, participating in the regulation of cell cycle may be related to the occurrence of tumor. Here, we examined the HQ-induced malignant transformed TK6 cells (TK6-HT) to illustrate the role of E4F1 in carcinogenesis. The present study showed that both the expressions of E4F1 messenger RNA and protein increased obviously in TK6-HT, preliminarily indicating that E4F1 is associated with HQ-induced carcinogenesis. To further explore the role of E4F1, we established E4F1 silencing TK6-HT (pLVX-shE4F1) and its control cells (pLVX-shNC) using lentiviral short hairpin RNA (shRNA) interference expression plasmid vector pLVX-shRNA. Flow cytometry and cell counting kit-8 assay were used to determine the effects of E4F1 silencing on cell cycle and cell growth, respectively. E4F1 silencing inhibited cell growth in TK6-HT. The results from flow cytometry indicated that the inhibitory effect on cell growth may be the results of the E4F1 silencing-induced accumulation in G2/M compared with TK6-HT-shNC. Meanwhile, levels of DNA damage (γ-H2AX), proteins of Rb and phosphorylated Rb, and reactive oxygen species were increased in TK6-HT-shRNA2 cells, which is the critical reason of cell-cycle arrest. In conclusion, E4F1 silencing inhibits the cell growth through cell-cycle arrest in malignant transformed cells induced by HQ.

The persistent organochlorine pesticide endosulfan modulates multiple epigenetic regulators with oncogenic potential in MCF-7 cells

Environmental cues and chemicals can potentially modulate the phenotypic expression of genome through alterations in the epigenetic mechanisms. Endosulfan is one of the extensively used organochlorine pesticides around the world which is known for its endocrine, neuro- and reproductive toxicity. This study was aimed to investigate the potential of α-endosulfan in modulation of multiple epigenetic enzymes in MCF-7 cells. The cells were treated with DMSO (control) or α-endosulfan (1 and 10μM) and the expression of various epigenetic enzymes was assayed by real-time PCR and immunoblotting, in addition to their activity assays. The results shows α-endosulfan, at 1 and 10μM concentration, significantly promoted viability of MCF-7 cells compared to untreated cells after 24h. The expression of DNA methyltransferases (DNMTs) was upregulated while the global DNA methylation status was initially affected, but later recovered. Total intracellular histone deacetylase (HDAC) activity was found to be significantly increased which was correlated with upregulation of class I HDACs (HDAC 1 and 3) while no significant alteration in the other HDAC classes was observed. The expression and activity of arginine and lysine methylation enzymes, protein arginine methyltransferase 5 (PRMT5) and Enhancer of Zeste homolog 2 (EZH2), respectively, were also found to be modulated by α-endosulfan. We found increased expression of histones H3 and H4, trimethylated H3K27 (product of EZH2), symmetric dimethylation of H4R3 (product of PRMT5) and five different (unidentified) proteins whose arginine residues are symmetrically dimethylated (by increased level of PRMT5) were enhanced in response to 10μM α-endosulfan after 24h exposure window. Moreover, overexpression of basal level of estrogen receptor alpha (ERα), suggests estrogenicity of α-endosulfan. In summary, our results shows modulatory impact of α-endosulfan on multiple cellular epigenetic regulators, known to possess oncogenic potential which might contribute to mechanistic insight of its action in future.

Do mutations in DNMT3A/3B affect global DNA hypomethylation among benzene-exposed workers in Southeast China?: Effects of mutations in DNMT3A/3B on global DNA hypomethylation

Global DNA hypomethylation is commonly observed in benzene-exposed workers, but the underlying mechanisms remain unclear. We sought to discover the relationships among reduced white blood cell (WBC) counts, micronuclear (MN) frequency, and global DNA methylation to determine whether there were associations with mutations in DNMT3A/3B. Therefore, we recruited 410 shoe factory workers and 102 controls from Wenzhou in Zhenjiang Province. A Methylated DNA Quantification Kit was used to quantify global DNA methylation, and single nucleotide polymorphisms (SNPs) in DNMT3A (rs36012910, rs1550117, and R882) and DNMT3B (rs1569686, rs2424909, and rs2424913) were identified using the restriction fragment length polymorphism method. A multilinear regression analysis demonstrated that the benzene-exposed workers experienced significant global DNA hypomethylation compared with the controls (β = -0.51, 95% CI: -0.69 to -0.32, P < 0.001). The DNMT3A R882 mutant allele (R882H and R882C) (β = -0.25, 95% CI: -0.54 to 0.04, P = 0.094) and the DNMT3B rs2424909 GG allele (β = -0.37, 95% CI: -0.70 to -0.03, P = 0.031) were significantly associated with global DNA hypomethylation compared with the wild-type genotype after adjusting for confounding factors. Furthermore, the MN frequency in the R882 mutant allele (R882H and R882C) (FR = 1.18, 95% CI: 0.99 to 1.40, P = 0.054) was higher than that of the wild-type. The results imply that hypomethylation occurs due to benzene exposure and that mutations in DNMTs are significantly associated with global DNA methylation, which might have influenced the induction of MN following exposure to benzene. Environ. Mol. Mutagen. 58:678-687, 2017. © 2017 Wiley Periodicals, Inc.

Differently expressed long noncoding RNAs and mRNAs in TK6 cells exposed to low dose hydroquinone

Previous studies have shown that long noncoding RNAs (lncRNAs) were related to human carcinogenesis and might be designated as diagnosis and prognosis biomarkers. Hydroquinone (HQ), as one of the metabolites of benzene, was closely relevant to occupational benzene poisoning and occupational leukemia. Using high-throughput sequencing technology, we investigated differences in lncRNA and mRNA expression profiles between experimental group (HQ 20 μmol/L) and control group (PBS). Compared to control group, a total of 65 lncRNAs and 186 mRNAs were previously identified to be aberrantly expressed more than two fold change in experimental group. To validate the sequencing results, we selected 10 lncRNAs and 10 mRNAs for quantitative real-time PCR (qRT-PCR). Through GO annotation and KEGG pathway analysis, we obtained 3 mainly signaling pathways, including P53 signaling pathway, which plays an important role in tumorigenesis and progression. After that, 25 lncRNAs and 32 mRNAs formed the lncRNA-mRNA co-expression network were implemented to play biological functions of the dysregulated lncRNAs transcripts by regulating gene expression. The lncRNAs target genes prediction provided a new idea for the study of lncRNAs. Finally, we have another important discovery, which is screened out 11 new lncRNAs without annotated. All these results uncovered that lncRNA and mRNA expression profiles in TK6 cells exposed to low dose HQ were different from control group, helping to further study the toxicity mechanisms of HQ and providing a new direction for the therapy of leukemia.

PARP‑1 may be involved in hydroquinone‑induced apoptosis by poly ADP‑ribosylation of ZO‑2

Hydroquinone (HQ), a major reactive metabolite of benzene, contributes to benzene-induced leukemia. The molecular mechanisms that underlie this activity remain to be elucidated. Poly ADP-ribosylation (PARylation) is a type of reversible posttranslational modification that is performed by enzymes in the PAR polymerase (PARP) family and mediates different biological processes, including apoptosis. Zona occludens 2 (ZO-2) is a tight junction scaffold protein, which is involved in cell proliferation and apoptosis. The present study investigated the activity and mechanisms regulated by PARP-1 during HQ-induced apoptosis using TK6 lymphoblastoid cells and PARP-1-silenced TK6 cells. The results revealed that exposure to 10 µM HQ for 72 h induced apoptosis in TK6 cells and that apoptosis was attenuated in PARP-1-silenced TK6 cells. In cells treated with HQ, inhibition of PARP-1 increased the expression of B cell leukemia/lymphoma 2 (Bcl-2), increased ATP production and reduced reactive oxygen species (ROS) production relative to the levels observed in cells treated with HQ alone. Co-localization of ZO-2 and PAR (or PARP-1 protein) was determined using immunofluorescence confocal microscopy. The findings of the present study revealed that ZO-2 was PARylated via an interaction with PARP-1, which was consistent with an analysis of protein expression that was performed using western blot analysis, which determined that ZO-2 protein expression was upregulated in HQ-treated control cells and downregulated in HQ-treated PARP-1-silenced TK6 cells. These findings indicated that prolonged exposure to a low dose of HQ induced TK6 cells to undergo apoptosis, whereas inhibiting PARP-1 attenuates cellular apoptosis by activating Bcl-2 and energy-saving processes and reducing ROS. The present study determined that PARP-1 was involved in HQ-induced apoptosis by PARylation of ZO-2.

Inhibition of autophagy enhances Hydroquinone-induced TK6 cell death

Hydroquinone (HQ), one of the metabolic products of benzene, is a carcinogen. It can induce apoptosis in lymphoma cells. However, whether HQ can induce autophagy and what roles autophagy plays in TK6 cells exposured to HQ remains unclear. In this study, we found that HQ could induce autophagy through techniques of qRT-PCR, Western blot, immunofluorescent assay of LC3 and transmission electron microscope. Furthermore, inhibiting autophagy using 3-methyladenine (3-MA) or chloroquine (CQ) significantly enhanced HQ-induced cell apoptosis, suggesting that autophagy may be a survival mechanism. Our study also showed that HQ activated PARP-1. Moreover, knockdown of PARP-1 strongly exhibited decreased autophagy related genes expression. In contrast, the absence of SIRT1 increased that. Altogether, our data provided evidence that HQ induced autophagy in TK6 cells and autophagy protected TK6 from HQ attack-induced injury in vitro, and the autophagy was partially mediated via activation of the PARP-1-SIRT1 signaling pathway.

Testicular Dnmt3 expression and global DNA methylation are down-regulated by gonadotropin releasing hormones in the ricefield eel Monopterus albus

In vertebrates, DNA methyltransferase 3 (Dnmt3) homologues are responsible for de novo DNA methylation and play important roles in germ cell development. In the present study, four dnmt3 genes, dnmt3aa, dnmt3ab, dnmt3ba and dnmt3bb.1, were identified in ricefield eels. Real-time quantitative PCR analysis showed that all four dnmt3 mRNAs were detected broadly in tissues examined, with testicular expression at relatively high levels. In the testis, immunostaining for all four Dnmt3 forms was mainly localized to spermatocytes, which also contained highly methylated DNA. All three forms of Gonadotropin-releasing hormone (Gnrh) in the ricefield eel were shown to decrease the expression of dnmt3 genes in the in vitro incubated testicular fragments through cAMP and IP₃/Ca²⁺ pathways. Moreover, in vivo treatment of male fish with three forms of Gnrh decreased significantly the testicular Dnmt3 expression at both mRNA and protein levels, and the global DNA methylation levels. These results suggest that the expression of Dnmt3 and global DNA methylation in the testis of ricefield eels are potentially down-regulated by Gnrh, and reveal a novel regulatory mechanism of testicular Dnmt3 expression in vertebrates.

Avermectin induced global DNA hypomethylation and over-expression of heat shock proteins in cardiac tissues of pigeon

Despite increasing evidences pointing to residues of avermectin (AVM) pose toxic effects on non-target organisms in environment, but the data in pigeon is insufficient. The alteration of global DNA methylation and response of heat shock proteins (Hsps) are important for assessing the AVM toxicity in cardiac tissues of pigeon (Columba livia). To investigate the effects of AVM exposure in cardiac tissues of pigeon, we detected the expression levels of DNA methyltransferases (Dnmts), methylated DNA-binding domain protein 2 (MBD2), and Hsp 60, 70 and 90. Pigeons were exposed to feed containing AVM (0, 20, 40 and 60mg/kg diet) for 30, 60, 90days respectively, and cardiac tissues were collected and analyzed. We found the transcriptional levels of Dnmt1, Dnmt3_a and Dnmt3_b mRNA were down-regulated, but the transcriptional levels of MBD2 mRNA were up-regulated by AVM exposure in cardiac tissues of pigeon. Necrocytosis, hemorrhage, infiltration of inflammatory cells and abundant vacuoles appeared in cardiac tissues after AVM exposure. Accompanying this phenotype, the mRNA transcriptional and/or protein levels of Hsp30, Hsp60, Hsp70 and Hsp90 increased. In conclusion, these results underscored AVM exposure caused DNA methylation machinery malfunctions, and induced over-expression of Hsps to improve the protective function against cardiac injury.

In vitro hydroquinone-induced instauration of histone bivalent mark on human retroelements (LINE-1) in HL60 cells

Benzene is extensively used in industry despite its leukemogenic activity, representing a significant occupational hazard. We investigated if long-term treatment with low-doses hydroquinone (HQ), a benzene metabolite, might be sufficient to alter in vitro the epigenetic signature underlining LINE-1 sequences, a poorly explored step in health risks associated with benzene exposure. In HL-60 cell line, exploring the epigenetic events occurring in chromatin, we found the transient instauration of the distinctive signature combining the repressive H3Lys27 tri-methylation mark and the activating H3Lys4 tri-methylation mark (H3K27me3/H3K4me3), indicating a tendency toward a poised chromatin conformation. These alterations are lost in time after short-term treatments, while the long-term setting, performed using a concentration within the levels of total HQ in peripheral blood of benzene-exposed workers, showed a gradual increase in H3K4me3. We observed the absence of statistically significant variations in DNA methylation and expression levels of LINE-1, despite a decrease in protein levels of UHRF1, DNA methyl-transferases and histone methyl-transferases. In conclusion, in vitro treatment with low-dose HQ determined the instauration of a reversible poised state of chromatin in LINE-1 sequences, suggesting that prolonged exposure could cause persistent epigenetic alterations.

Long-term exposure of K562 cells to benzene metabolites inhibited erythroid differentiation and elevated methylation in erythroid specific genes

Benzene is a common occupational hazard and a widespread environmental pollutant. Previous studies have revealed that 72 h exposure to benzene metabolites inhibited hemin-induced erythroid differentiation of K562 cells accompanied with elevated methylation in erythroid specific genes. However, little is known about the effects of long-term and low-dose benzene metabolite exposure. In this study, to elucidate the effects of long-term benzene metabolite exposure on erythroid differentiation, K562 cells were treated with low-concentration phenol, hydroquinone and 1,2,4-benzenetriol for at least 3 weeks. After exposure of K562 cells to benzene metabolites, hemin-induced hemoglobin synthesis declined in a concentration- and time-dependent manner, and the hemin-induced expressions of α-, β- and γ-globin genes and heme synthesis enzyme porphobilinogen deaminase were significantly suppressed. Furthermore, when K562 cells were continuously cultured without benzene metabolites for another 20 days after exposure to benzene metabolites for 4 weeks, the decreased erythroid differentiation capabilities still remained stable in hydroquinone- and 1,2,4-benzenetriol-exposed cells, but showed a slow increase in phenol-exposed K562 cells. In addition, methyltransferase inhibitor 5-aza-2'-deoxycytidine significantly blocked benzene metabolites inhibiting hemoglobin synthesis and expression of erythroid genes. Quantitative MassARRAY methylation analysis also confirmed that the exposure to benzene metabolites increased DNA methylation levels at several CpG sites in several erythroid-specific genes and their far-upstream regulatory elements. These results demonstrated that long-term and low-dose exposure to benzene metabolites inhibited the hemin-induced erythroid differentiation of K562 cells, in which DNA methylation played a role through the suppression of erythroid specific genes.

Applying a Weight-of-Evidence Approach to Evaluate Relevance of Molecular Landscapes in the Exposure-Disease Paradigm

Information on polymorphisms, mutations, and epigenetic events has become increasingly important in our understanding of molecular mechanisms associated with exposures-disease outcomes. Molecular landscapes can be developed to illustrate the molecular characteristics for environmental carcinogens as well as associated disease outcomes, although comparison of these molecular landscapes can often be difficult to navigate. We developed a method to organize these molecular data that uses a weight-of-evidence approach to rank overlapping molecular events by relative importance for susceptibility to an exposure-disease paradigm. To illustrate the usefulness of this approach, we discuss the example of benzene as an environmental carcinogen and myelodysplastic syndrome (MDS) as a causative disease endpoint. Using this weight-of-evidence method, we found overlapping polymorphisms in the genes for the metabolic enzymes GST and NQO1, both of which may infer risk of benzene-induced MDS. Polymorphisms in the tumor suppressor gene, TP53, and the inflammatory cytokine gene, TNF-α, were also noted, albeit inferring opposing outcomes. The alleles identified in the DNA repair gene RAD51 indicated an increased risk for MDS in MDS patients and low blood cell counts in benzene-exposed workers. We propose the weight-of-evidence approach as a tool to assist in organizing the sea of emerging molecular data in exposure-disease paradigms.

Poly(ADP-ribosyl)ation enhances H-RAS protein stability and causes abnormal cell cycle progression in human TK6 lymphoblastoid cells treated with hydroquinone

Hydroquinone (HQ), one of the most important benzene-derived metabolites, can induce aberrant cell cycle progression; however, the mechanism of this induction remains unclear. Poly(ADP-ribosyl)ation (PARylation), which is catalysed primarily by poly(ADP-ribose) polymerase-1 (PARP-1), participates in various biological processes, including cell cycle control. The results of the present study show an accumulation in G1 phase versus S phase of TK6 human lymphoblast cells treated with HQ for 48h compared with PBS-treated cells; after 72h of HQ treatment, the cells transitioned from G1 arrest to S phase arrest. We examined the expression of six genes related to the cell cycle or leukaemia to further explore the reason for this phenomenon. Among these genes, H-RAS was found to be associated with this phenomenon because its mRNA and protein expression decreased at 48h and increased at 72h. Experiments for PARP activity induction and inhibition revealed that the observed PARylation was positively associated with H-RAS expression. Moreover, in cells treated with HQ in conjunction with PARP-1 knockdown, expression of the H-RAS protein decreased and the number of cells in G1 phase increased. The degree of poly(ADP-ribosyl) modification of the H-RAS protein increased in cells treated with HQ for 72h, further supporting that changes in PARylation contributed to the rapid alteration of H-RAS protein expression, followed by abnormal progression of the cell cycle. Co-immunoprecipitation (co-IP) assays were employed to determine whether protein complexes were formed by PARP-1 and H-RAS proteins, and the direct interaction between these proteins indicated that PARylation regulated H-RAS expression. As detected by confocal microscopy, the H-RAS protein was found in the nucleus and cytoplasm. To our knowledge, this study is the first to reveal that H-RAS protein can be modified by PARylation.

Effects of atrazine and chlorpyrifos on DNA methylation in the brain and gonad of the common carp

DNA methylation is known to play an important role in the regulation of gene expression in animal. The purpose of the present study was to examine the effect of atrazine (ATR), chlorpyrifos (CPF) and combined ATR/CPF exposure on DNA methylation in the brain and gonad of common carp (Cyprinus carpio L.). The carp were sampled after a 40-d exposure to CPF and ATR, individually or in combination, followed by a 40-d recovery to measure the levels of global DNA methylation and the expression of methylation enzymes (DNA methyltransferases (DNMTs) and methylcytosine binding domain 2 (MBD2)) in the brain and gonad tissues. The results revealed that a significant global DNA hypomethylation in the common carp exposed to ATR, CPF and their mixture was observed compared to the control fish. The MBD2 mRNA expression was up-regulated in the brain and gonad of the common carp exposed to ATR, CPF and their mixture, in contrast, the DNMTs mRNA expression was down-regulated. The information regarding the effects of ATR and CPF on DNA methylation status generated in this study is important for pesticides toxicology evaluation. However, the effect of ATR and CPF on the methylation status of specific genes, as well as its detailed mechanism requires further investigation.

Effects of atrazine and chlorpyrifos on DNA methylation in the liver, kidney and gill of the common carp (Cyprinus carpio L.)

Pesticide exposure has repeatedly been associated with cancers, although the molecular mechanisms behind this association are largely undetermined. Abnormal DNA methylation plays a key role in the process of some disease. However, little was known about the effect of pesticides on DNA methylation in the common carp. In this study, we investigated the mRNA levels of DNA methyltransferases (DNMTs) and methyl-CpG-binding protein DNA-binding domain protein 2 (MBD2) as well as the DNA methylation levels in the liver, kidney and gill of the common carp (Cyprinus carpio L.) after 40-d exposure to atrazine (ATR) and chlorpyrifos (CPF) alone or in combination, and a 40-d recovery period. Juvenile common carp were exposed to various concentrations of ATR (at concentrations of 4.28, 42.8 and 428μg/L), CPF (1.16, 11.6 and 116μg/L), and an ATR/CPF mixture (at concentrations of 1.13, 11.3 and 113μg/L). The results revealed that the levels of genomic DNA methylation decreased in all tissues after 40d of exposure to ATR and CPF either individually or in combination. Moreover, the mRNA expression of DNMTs was down-regulated in all treatment groups. In contrast, the mRNA expression of MBD2 was up-regulated. These results demonstrated that long-term exposure to ATR, CPF and ATR/CPF mixtures could disrupt genomic DNA. It might imply that DNA methylation is involved in the toxicity caused by ATR and CPF in the common carp.

2,4-Dichlorophenol induces global DNA hypermethylation through the increase of S-adenosylmethionine and the upregulation of DNMTs mRNA in the liver of goldfish Carassius auratus

Altered DNA methylation is associated with changes in gene expression, signal transduction and stress response after exposure to a wide range of exogenous compounds, and abnormal methylation is a major toxic effect induced by chemicals such as benzene and phenols. 2,4-Dichlorophenol (2,4-DCP), a derivative of phenol, has been classified as a priority pollutant by the US EPA due to its toxic effects on aquatic organisms. However, the effect of 2,4-DCP on DNA methylation and its potential mechanism in fish are rarely understood. The present study aims to figure out whether 2,4-DCP could impact DNA methylation and explore its potential mechanisms by measuring the global DNA methylation levels, S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH) contents, the mRNA expression of DNA methyltransferase1 (DNMT1) and DNA methyltransferase3 (DNMT3) in the liver of goldfish Carassius auratus. DNA methylation levels were analyzed using high performance liquid chromatography (HPLC) and MspI/HpaII ethidium bromide assay, SAM and SAH contents were determined by HPLC, the mRNA expression of DNMT1 and DNMT3 was measured by quantitative-PCR (qPCR). The results showed that 2,4-DCP caused global DNA hypermethylation, elevated the methylation levels of CpG islands, increased the SAM and SAH contents, decreased the SAM/SAH ratio, and upregulated the mRNA expression of DNMT1 and DNMT3, while depletion of SAM with Na2SeO3 and inhibition of DNMTs activity with 5-aza-2'-deoxycytidine (5AdC) impaired 2,4-DCP-induced global DNA hypermethylation, suggesting that the increase of SAM contents and upregulation of the mRNA expression of DNMT1 and DNMT3 may play important roles in 2,4-DCP-induced global DNA hypermethylation process. Our report is the first one to show that short-term 2,4-DCP exposure caused the global DNA hypermethylation via altered SAM level and DNMTs expression in fish.

The promoter of miR-663 is hypermethylated in Chinese pediatric acute myeloid leukemia (AML)

BACKGROUND

There is growing evidence supporting a role for microRNAs (miRNA) as targets in aberrant mechanisms of DNA hypermethylation. Epigenetic silencing of tumor suppressor miRNAs, including miR-663, which has recently been reported to be inactivated by hypermethylation in several cancers, may play important roles in pediatric acute myeloid leukemia (AML). However, expression of miR-663 and its promoter methylation remain status unclear in childhood leukemia.

METHODS

Promoter methylation status of miR-663 was investigated by methylation specific PCR (MSP) and bisulfate genomic sequencing (BGS). Transcriptional expression of miR-663 was evaluated by semi-quantitative and real-time PCR, and the relationship between expression of miR-663 and promoter methylation was confirmed using 5-aza-2'-deoxycytidine (5-Aza) demethylation reagent.

RESULTS

MiR-663 was aberrantly methylated in 45.5% (5/11) leukemia cell lines; BGS showed that the promoter was significantly methylated in three AML cell lines; methylation of miR-663 was significantly higher in Chinese pediatric AML patients [41.4% (29/70)] compared to normal bone marrow (NBM) control samples [10.0% (3/30)]. These results were confirmed by both BGS and 5-Aza demethylation analysis. In addition, miR-663 transcript expression was significantly lower in AML patients, both with and without miR-663 methylation, compared to controls; however, there were no significant differences in clinical features or French-American-British (FAB) classification between patients with and without miR-663 methylation.

CONCLUSIONS

Expression of miR-663 was significantly lower in pediatric AML cells compared to NBM controls; furthermore, a high frequency of miR-663 promoter hypermethylation was observed in both AML cell lines and pediatric AML samples. Inactivation of miR-663 by promoter hypermethylation could be affected by 5-Aza demethylation. These findings suggest that hypermethylation of the miR-663 promoter may be an early event in the development of pediatric AML.

Specific inhibition of one DNMT1-including complex influences tumor initiation and progression

BACKGROUND

Reactivation of silenced tumor suppressor genes by DNMT inhibitors has provided an alternative approach to cancer therapy. However, DNMT inhibitors have also been shown to induce or enhance tumorigenesis via DNA hypomethylation-induced oncogene activation and chromosomal instability. To develop more specific DNMT inhibitors for efficient cancer therapy, we compared the effects of peptides designed to specifically disrupt the interaction of DNMT1 with different proteins.

FINDINGS

Our data indicated that the use of an unspecific DNMT inhibitor (5aza-2deoxycytidine), a DNMT1 inhibitor (procainamide) or peptides disrupting the DNMT1/PCNA, DNMT1/EZH2, DNMT1/HDAC1, DNMT1/DNMT3b and DNMT1/HP1 interactions promoted or enhanced in vivo tumorigenesis in a mouse glioma model. In contrast, a peptide disrupting the DNMT1/DMAP1 interaction, which per se did not affect tumor growth, sensitized cancer cells to chemotherapy/irradiation-induced cell death. Finally, our data indicated that the peptide disrupting the DNMT1/DMAP1 interaction increased the efficiency of temozolomide treatment.

CONCLUSION

Our data suggest that the DNMT1/DMAP1 interaction could be an effective anti-cancer target and opens a new avenue for the development of new strategies to design DNMT inhibitors.

DNA methylome alterations in chemical carcinogenesis

Carcinogenesis, a complex multifactorial process of the transformation of normal cells into malignant cells, is characterized by many biologically significant and interdependent alterations triggered by the mutational and/or non-mutational (i.e., epigenetic) events. One of these events, specific to all types of cancer, is alterations in DNA methylation. This review summarizes the current knowledge of the role of DNA methylation changes induced by various genotoxic chemicals (carcinogenic agents that interact with DNA) and non-genotoxic carcinogens (chemicals causing tumor by mechanisms other than directly damaging DNA) in the lung, colorectal, liver, and hematologic carcinogenesis. It also emphasizes the potential role for epigenetic changes to serve as markers for carcinogen exposure and carcinogen risk assessment.

De novo DNA methyltransferases: oncogenes, tumor suppressors, or both?

Aberrant promoter DNA hypermethylation of tumor suppressor genes is a hallmark of cancer. This alteration is largely dependent on the action of de novo DNA methyltransferases (DNMTs) early during tumor progression, which supports the oncogenic role for these enzymes. However, recent research has identified several inactivating mutations of de novo DNMTs in various types of tumor. In addition, it has been shown that loss of de novo DNA methylation activity at advanced tumor stages leads to the promoter DNA demethylation-dependent expression of specific oncogenes. These new data support the notion that de novo DNMTs also have an important role in the maintenance of DNA methylation and suggest that, in addition to acting as oncogenes, they also behave as tumor suppressors. This potential dual role might have clinical implications, as DNMTs are currently considered bona fide targets in cancer therapy.