Gene expression and mutation assessment provide clues of genetic and epigenetic mechanisms in liver tumors of oxazepam-exposed mice

MYCT-1 Gene Expression in Patients with Gastric Cancer: an Ex Vivo Study

Ploidy, p53, bcl-2, and c-myc genes are associated with gastric cancer. Myc target 1 (MYCT1) gene is an oncogenic gene and is associated with cancer progression through different signal transduction pathways identifying the corresponding genes The objective of the study was to evaluate the association between MYCT1 gene expression and gastric cancer. Real-time polymerase chain reaction (RT-PCR), western blot analysis, cell growth study, and TUNEL assay were performed for the human gastric cancer cell lines and human embryonic kidney cell line. β-Actin gene preferred as a control in RT-PCR. The ratio of MYCT1 gene expression to β-actin gene expression less than 0.5 was considered as downregulation. Using SDS-PAGE MYCT1 gene expression was measured in western blot analysis. Cells with and without the MYCT1 gene were incubated in 35 mm plates with 10% fetal bovine serum in the cell growth study. TUNEL assay was performed to detect the effect of the MYCT1 gene on the apoptosis of cells. The ratio of MYCT1 gene expression to β-actin gene expression was 0.47 ± 0.01 and 0.76 ± 0.01 for human gastric cancer cell lines and human embryonic kidney cell lines, respectively. MYCT1 gene expression was downregulated in the human gastric cancer cell lines than human embryonic kidney cell line (p < 0.001). MYCT1 gene decreased cell growth (p = 0.041) during 6 days of incubation study of cells. TUNEL assay showed only the fluorescence of PI in BGC823 cells without the MYCT1 gene. MYCT1 gene expression was downregulated in the human gastric cancer cell lines, and MYCT1 gene accelerates the apoptotic process.

Synthesis, X-ray crystal structure, DNA/protein binding and cytotoxicity studies of five α-aminophosphonate N-derivatives

Five new α-aminophosphonates are synthesized and characterized by EA, FT-IR, ¹H NMR, ¹³C NMR, ³¹P NMR, ESI-MS and X-ray crystallography. The X-ray analyses reveal that the crystal structures of 1-5 are monoclinic or triclinic system with the space group P 21/c, P-1, P-1, P2(1)/c and P-1, respectively. All P atoms of 1-5 have tetrahedral geometries involving two O-ethyl groups, one C_α atom, and a double bond O atom. The binding interaction of five new α-aminophosphonate N-derivatives (1-5) with calf thymus(CT)-DNA have been investigated by UV-visible and fluorescence emission spectrometry. The apparent binding constant (Kapp) values follows the order: 1 (3.38×10⁵M^-1)>2 (3.04×10⁵M^-1)>4 (2.52×10⁵M^-1)>5 (2.32×10⁵M^-1)>3 (2.10×10⁵M^-1), suggesting moderate intercalative binding mode between the compounds and DNA. In addition, fluorescence spectrometry of bovine serum albumin (BSA) with the compounds 1-5 showed that the quenching mechanism might be a static quenching procedure. For the compounds 1-5, the number of binding sites were about one for BSA and the binding constants follow the order: 1 (2.72×10⁴M^-1)>2 (2.27×10⁴M^-1)>4 (2.08×10⁴M^-1)>5 (1.79×10⁴M^-1)>3 (1.17×10⁴M^-1). Moreover, the DNA cleavage abilities of 1 exhibit remarkable changes and the in vitro cytotoxicity of 1 on tumor cells lines (MCF-7, HepG2 and HT29) have been examined by MTT and shown antitumor effect on the tested cells.

Epigenetic profiles as defined signatures of xenobiotic exposure

With the advent of high resolution sequencing technologies there has been increasing interest in the study of genome-wide epigenetic modification patterns that govern the underlying gene expression events of a particular cell or tissue type. There is now mounting evidence that perturbations to the epigenetic landscape occur during a host of cellular processes including normal proliferation/differentiation and aberrant outcomes such as carcinogenesis. Furthermore, epigenetic perturbations have been associated with exposure to a range of drugs and toxicants, including non-genotoxic carcinogens (NGCs). Although a variety of epigenetic modifications induced by NGCs have been studied previously, recent genome-wide integrated epigenomic and transcriptomic studies reveal for the first time the extent and dynamic nature of the epigenetic perturbations resulting from xenobiotic exposure. The interrogation and integration of one such epigenetic mark, the newly discovered 5-hydroxymethylcytosine (5hmC) modification, reveals that drug treatment associated perturbations of the epigenome can result in unique epigenetic signatures. This review focuses on how recent advances in the field of epigenetics can enhance our mechanistic understanding of xenobiotic exposure and provide novel safety biomarkers.

Dynamic changes in 5-hydroxymethylation signatures underpin early and late events in drug exposed liver

Aberrant DNA methylation is a common feature of neoplastic lesions, and early detection of such changes may provide powerful mechanistic insights and biomarkers for carcinogenesis. Here, we investigate dynamic changes in the mouse liver DNA methylome associated with short (1 day) and prolonged (7, 28 and 91 days) exposure to the rodent liver non-genotoxic carcinogen, phenobarbital (PB). We find that the distribution of 5mC/5hmC is highly consistent between untreated individuals of a similar age; yet, changes during liver maturation in a transcriptionally dependent manner. Following drug treatment, we identify and validate a series of differentially methylated or hydroxymethylated regions: exposure results in staged transcriptional responses with distinct kinetic profiles that strongly correlate with promoter proximal region 5hmC levels. Furthermore, reciprocal changes for both 5mC and 5hmC in response to PB suggest that active demethylation may be taking place at each set of these loci via a 5hmC intermediate. Finally, we identify potential early biomarkers for non-genotoxic carcinogenesis, including several genes aberrantly expressed in liver cancer. Our work suggests that 5hmC profiling can be used as an indicator of cell states during organ maturation and drug-induced responses and provides novel epigenetic signatures for non-genotoxic carcinogen exposure.

Haplotypes in the 5'-untranslated region of the CYP1A2 gene are inversely associated with lung cancer risk but do not correlate with caffeine metabolism

In this study, we analyzed the influence of CYP1A2 genetic variation and enzyme activity on lung cancer risk in a high-incidence area. A total of 95 lung cancer patients and 196 controls were genotyped for the -3860G/A, -3113A/G, -2467T/delT, -739T/G, and -163C/A polymorphisms in the 5'-untranslated region of the gene. In addition, a subset of 70 patients and 115 controls were phenotyped by high-performance liquid chromatography determination of the caffeine metabolic ratio (CMR). The -2467T/delT polymorphism and the CYP1A2*1V haplotype (-163C>A, -2467T>delT) were inversely associated with lung cancer risk (odds ratio [OR] = 0.47 [0.2-0.9]; P = 0.02 and OR = 0.13 [0.02-1.0]; P = 0.04; respectively). In addition, the CYP*1A/*1V and *1F (-163C>A)/*1D (-163C>A, -2467T>delT) diplotypes were absent in the patients group, whereas accounting for 7.1% (P = 0.017) and 5.6% (P = 0.037) of controls, respectively. Mean CMR was significantly higher in patients than in controls (10.50 ± 17.31 vs. 6.52 ± 6.26, P = 0.01) but regression analyses did not yield significant ORs for the association with lung cancer risk. Similarly, no significant correlations were found between any genetic variant and enzyme activity. Several CYP1A2 haplotypes and diplotypes containing the -2467delT variant were associated with lower lung cancer risk; however, they did not correlate with significant changes in CYP1A2 metabolic activity toward caffeine.

Environmental toxicants, epigenetics, and cancer

Tumorigenesis, a complex and multifactorial progressive process of transformation of normal cells into malignant cells, is characterized by the accumulation of multiple cancer-specific heritable phenotypes triggered by the mutational and/or non-mutational (i.e., epigenetic) events. Accumulating evidence suggests that environmental and occupational exposures to natural substances, as well as man-made chemical and physical agents, play a causative role in human cancer. In a broad sense, carcinogenesis may be induced through either genotoxic or non-genotoxic mechanisms; however, both genotoxic and non-genotoxic carcinogens also cause prominent epigenetic changes. This review presents current evidence of the epigenetic alterations induced by various chemical carcinogens, including arsenic, 1,3-butadine, and pharmaceutical and biological agents, and highlights the potential for epigenetic changes to serve as markers for carcinogen exposure and cancer risk assessment.

Non-genotoxic carcinogen exposure induces defined changes in the 5-hydroxymethylome

BACKGROUND

Induction and promotion of liver cancer by exposure to non-genotoxic carcinogens coincides with epigenetic perturbations, including specific changes in DNA methylation. Here we investigate the genome-wide dynamics of 5-hydroxymethylcytosine (5hmC) as a likely intermediate of 5-methylcytosine (5mC) demethylation in a DNA methylation reprogramming pathway. We use a rodent model of non-genotoxic carcinogen exposure using the drug phenobarbital.

RESULTS

Exposure to phenobarbital results in dynamic and reciprocal changes to the 5mC/5hmC patterns over the promoter regions of a cohort of genes that are transcriptionally upregulated. This reprogramming of 5mC/5hmC coincides with characteristic changes in the histone marks H3K4me2, H3K27me3 and H3K36me3. Quantitative analysis of phenobarbital-induced genes that are involved in xenobiotic metabolism reveals that both DNA modifications are lost at the transcription start site, while there is a reciprocal relationship between increasing levels of 5hmC and loss of 5mC at regions immediately adjacent to core promoters.

CONCLUSIONS

Collectively, these experiments support the hypothesis that 5hmC is a potential intermediate in a demethylation pathway and reveal precise perturbations of the mouse liver DNA methylome and hydroxymethylome upon exposure to a rodent hepatocarcinogen.

Promoter hypermethylation-induced transcriptional down-regulation of the gene MYCT1 in laryngeal squamous cell carcinoma

Background

MYCT1, previously named MTLC, is a novel candidate tumor suppressor gene. MYCT1 was cloned from laryngeal squamous cell cancer (LSCC) and has been found to be down-regulated in LSCC; however, the regulatory details have not been fully elucidated.

Methods

Here, we sought to investigate the methylation status of the CpG islands of MYCT1 and mRNA levels by bisulfite-specific PCR (BSP) based on sequencing restriction enzyme digestion, reverse transcription and real-time quantitative polymerase chain reaction (RQ-PCR). The function of specific sites in the proximal promoter of MYCT1 in LSCC was measured by transient transfection, luciferase assays, electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation assay (ChIP).

Results

The results suggested hypermethylation of 12 CpG sites of the promoter in both laryngeal cancer tissues and the laryngeal cancer line Hep-2 cell. The hypermethylation of the site CGCG (−695 to −692), which has been identified as the c-Myc binding site, was identified in laryngeal cancer tissues (59/73) compared to paired mucosa (13/73); in addition, statistical analysis revealed that the methylation status of this site significantly correlated with cancer cell differentiation(p < 0.01). The mRNA level of MYCT1 increased in Hep-2 cells treated with 5-aza-C (p < 0.01). The luciferase activity from mutant transfectants pGL3-MYCT1m (−852/+12, mut-695-C > A, mut-693-C > G) was significantly reduced compared with the wild type pGL3-MYCT1 (−852/+12), while the luciferase activity from wild transfectants pGL3-MYCT1 (−852/+12) rose after 5-aza treatment in Hep-2 cells. Finally, EMSA and ChIP confirmed that the methylation of the CGCG (−695 to −692) site prevented c-Myc from binding of the site and demethylation treatment of the 5′ flanking region of MYCT1 by 5-aza induced the increased occupation of the core promoter by c-Myc (p < 0.01).

Conclusion

In summary, this study concluded that hypermethylation contributed to the transcriptional down-regulation of MYCT1 and could inhibit cancer cell differentiation in LSCC. DNA methylation of the CGCG site (−695 to −692) of MYCT1 altered the promoter activity by interfering with its binding to c-Myc in LSCC. Epigenetic therapy of reactivating MYCT1 by 5-aza should be further evaluated in clinical trails of LSCC.

Global gene profiling of spontaneous hepatocellular carcinoma in B6C3F1 mice: similarities in the molecular landscape with human liver cancer

Hepatocellular carcinoma (HCC) is an important cause of morbidity and mortality worldwide. Although the risk factors of human HCC are well known, the molecular pathogenesis of this disease is complex, and in general, treatment options remain poor. The use of rodent models to study human cancer has been extensively pursued, both through genetically engineered rodents and rodent models used in carcinogenicity and toxicology studies. In particular, the B6C3F1 mouse used in the National Toxicology Program (NTP) two-year bioassay has been used to evaluate the carcinogenic effects of environmental and occupational chemicals, and other compounds. The high incidence of spontaneous HCC in the B6C3F1 mouse has challenged its use as a model for chemically induced HCC in terms of relevance to the human disease. Using global gene expression profiling, we identify the dysregulation of several mediators similarly altered in human HCC, including re-expression of fetal oncogenes, upregulation of protooncogenes, downregulation of tumor suppressor genes, and abnormal expression of cell cycle mediators, growth factors, apoptosis regulators, and angiogenesis and extracellular matrix remodeling factors. Although major differences in etiology and pathogenesis remain between human and mouse HCC, there are important similarities in global gene expression and molecular pathways dysregulated in mouse and human HCC. These data provide further support for the use of this model in hazard identification of compounds with potential human carcinogenicity risk, and may help in better understanding the mechanisms of tumorigenesis resulting from chemical exposure in the NTP two-year carcinogenicity bioassay.