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Oxidative stress and reactivation of long interspersed element-1 (LINE-1) are coincidently observed in bladder cancer (BlCa), but the mechanistic connection between these two oncogenic phenomena is unknown. Previously, we reported increases in oxidative stress and LINE-1 protein (ORF1p) expression in human BlCa tissues. In this study, we measured 5-methylcytosine (5mC), 8-hydroxydeoxyguanosine (8-OHdG), 8-oxoguanosine DNA glycosylase-1 (OGG1), H3K9me3 and HP1α in bladder tissues obtained from BlCa patients. Reactivation of LINE-1 by reactive oxygen species (ROS) through chromatin remodeling was investigated in seven BlCa cell lines. We found that 5mC was decreased, but 8-OHdG, H3K9me3 and HP1α levels were increased in BlCa tissues relative to the adjacent non-cancerous tissues. OGG1, H3K9me3 and HP1α expression in BlCa tissues were positively correlated with 8-OHdG levels. Following H2O2 treatment, LINE-1 transcript expression was increased in VM-CUB-1 and TCCSUP, whereas AluYa5 and AluYb8 transcripts were increased in BFTC905 cells. Basal expression of LINE-1 ORF1p varied among BlCa cell lines from none to very high. H2O2 treatment clearly increased expression of ORF1p in VM-CUB-1, TCCSUP and BFTC905. Chromatin immunoprecipitation experiments revealed that 5′-LINE-1 promoters became further enriched in H3K4me3 and H3K18ac in VM-CUB-1 and BFTC905 cells treated with H2O2. In contrast, 5′-LINE-1 promoters became more enriched in H3K9me3 and H3K27me3 in UM-UC-3 treated with H2O2. In summary, decreased 5mC, but increased 8-OHdG, H3K9me3 and HP1α expression were demonstrated in human BlCa tissues, indicating global DNA hypomethylation, increased oxidative stress and altered histone methylation in BlCa. Chromatin structures were profoundly changed in BlCa cells exposed to ROS, but expression of LINE-1 transcript and protein were at most modestly increased. ROS enhanced expression of full-length LINE-1 elements only in cell lines with pre-existing activation, which was paralleled by increased formation of active chromatin at LINE-1 promoter loci.

The histone demethylase UTX (gene: KDM6A) directs cell and tissue differentiation during development. Deleterious mutations in KDM6A occur in many human cancers, most frequently in urothelial carcinoma. The consequences of these mutations are poorly understood, plausibly, they may disturb urothelial differentiation. We therefore investigated the effects of UTX siRNA-mediated knockdown in two in vitro models of urothelial differentiation, namely, primary cultures of urothelial epithelial cells treated with troglitazone and PD153035 and the immortalized urothelial cell line HBLAK treated with high calcium and serum. In both models, efficient UTX knockdown did not block morphological and biochemical differentiation. An apparent delay was due to a cytotoxic effect on the cell cultures before the initiation of differentiation, which induced apoptosis partly in a p53-dependent manner. As a consequence, slowly cycling, smaller, KRT14high precursor cells in the HBLAK cell line were enriched at the expense of more differentiated, larger, proliferating KRT14low cells. UTX knockdown induced apoptosis and enriched KRT14high cells in the BFTC-905 papillary urothelial carcinoma cell line as well. Our findings suggest an explanation for the frequent occurrence of KDM6A mutations across all stages and molecular subtypes of urothelial carcinoma, whereby loss of UTX function does not primarily impede later stages of urothelial differentiation, but favors the expansion of precursor populations to provide a reservoir of potential tumor-initiating cells.

Background/aim Reactivation of long interspersed nuclear element-1 (LINE-1) and oxidative stress are suggested to have oncogenic potential to drive tumorigenesis and cancer progression. We previously demonstrated that reactive oxygen species (ROS) caused hypomethylation of LINE-1 elements in bladder cancer cells. In this study, we investigated the expression of LINE-1-encoded protein (ORF1p) and oxidative stress marker 4-hydroxynonenal (4-HNE) in human bladder cancer tissues, as well as induction of ORF1p expression by ROS in bladder cancer cell lines. Materials and methods Thirty-six cancerous and 15 non-cancerous adjacent tissues were immunohistochemically stained for ORF1p and 4-HNE. ORF1p expression and cell migration were determined in bladder cancer cells exposed to H2O2 Results: ORF1p and 4-HNE expression was higher in cancerous than non-cancerous tissues. Elevated ORF1p expression was associated with increased 4-HNE expression and with advanced tumors. H2O2 provoked oxidative stress and up-regulated ORF1p expression in VM-CUB-1 compared to the untreated control, and to a lesser degree in TCCSUP. H2O2 exposure enhanced cell migration in UM-UC-3, TCCSUP and VM-CUB-1. Conclusion Elevated ORF1p expression is associated with tumor progression. ROS experimentally induce ORF1p expression and promote migration in bladder cancer cells.

Oxidative stress contributes substantially to urothelial carcinogenesis. Its extent can be assessed by measurements of reactive species (mainly reactive oxygen species (ROS)), oxidatively modified damage products, and levels of various antioxidants. We presented herein the methods for the measurement of protein carbonyl content and intracellular production of ROS. Protein carbonyl is the most commonly used indicator of protein oxidation because it is early formed and relatively stable under oxidative stress. Determination of protein carbonyl relies on the derivatization of carbonyl groups (aldehydes: R-CHO and ketones: R-CO-R) with 2,4-dinitrophenylhydrazine (DNPH) under strongly acidic conditions to yield stable dinitrophenyl (DNP) hydrazones. Absorbance of the DNP hydrazones at 370-375 nm is proportional to the content of carbonyl groups. To report the protein carbonyl content, it is usually normalized by total proteins. Detection of intracellular ROS production is based on oxidation of 2',7'-dichlorofluorescein-diacetate (DCFH-DA) by ROS to produce the highly fluorescent 2',7'-dichlorofluorescein (DCF). Fluorescent intensity measured at 480 nm excitation and 535 nm emission is directly proportional to the amount of ROS generated.

Oxidative stress contributes substantially to urothelial carcinogenesis. Its extent can be assessed by measurements of reactive species (mainly reactive oxygen species (ROS)), oxidatively modified damage products, and levels of various antioxidants. We presented herein the methods for the measurement of protein carbonyl content and intracellular production of ROS. Protein carbonyl is the most commonly used indicator of protein oxidation because it is early formed and relatively stable under oxidative stress. Determination of protein carbonyl relies on the derivatization of carbonyl groups (aldehydes: R-CHO and ketones: R-CO-R) with 2,4-dinitrophenylhydrazine (DNPH) under strongly acidic conditions to yield stable dinitrophenyl (DNP) hydrazones. Absorbance of the DNP hydrazones at 370-375 nm is proportional to the content of carbonyl groups. To report the protein carbonyl content, it is usually normalized by total proteins. Detection of intracellular ROS production is based on oxidation of 2',7'-dichlorofluorescein-diacetate (DCFH-DA) by ROS to produce the highly fluorescent 2',7'-dichlorofluorescein (DCF). Fluorescent intensity measured at 480 nm excitation and 535 nm emission is directly proportional to the amount of ROS generated.

Reactive oxygen species (ROS) is excessively generated in tumors creating an oxidative stress in tumor microenvironment. We investigated hepatic expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and 8-hydroxydeoxyguanosine (8-OHdG) in hepatocellular carcinoma (HCC) patients, and asked if ROS epigenetically upregulated Nrf2 and enhanced aggressiveness in HCC cells. Expression of Nrf2 (n = 100) and 8-OHdG (n = 53) was remarkably increased in HCC tissues compared with the noncancerous hepatic tissues. Elevated expression of 8-OHdG was associated with poor survival in HCC patients. H2O2, as ROS representative, provoked oxidative stress in HepG2 cells, indicated by increased protein carbonyl content and decreased total antioxidant capacity. Nrf2 expression and 8-OHdG formation were markedly increased in the H2O2-treated cells compared with the untreated control. Co-treatment with antioxidants, tocopheryl acetate (TA) and S-adenosylmethionine (SAM) effectively attenuated expression of Nrf2 and 8-OHdG in H2O2-treated cells. HepG2 cells treated with H2O2 had significantly higher migration and invasion capabilities than the untreated control cells, and this aggressiveness was significantly inhibited by TA and SAM. Bisulfite sequencing revealed that CpG dinucleotides in Nrf2 promoter were unmethylated in the H2O2-treated cells similar to the untreated control. In conclusion, robust histological evidence of increased antioxidative response and oxidative DNA damage in human HCC tissues was demonstrated. Elevated oxidative DNA lesion 8-OHdG was associated with shorter survival. Experimentally, ROS enhanced Nrf2 expression, 8-OHdG formation and tumor progression in HCC cells. These effects were inhibited by antioxidants. Therefore, oxidative stress-reducing regimens might be beneficial to diminish the ROS-induced HCC progression.

Promoter hypermethylation of the runt-related transcription factor 3 (RUNX3) gene is associated with increased risk of hepatocellular carcinoma (HCC). Oxidative stress plays a vital role in both carcinogenesis and progression of HCC. However, whether oxidative stress and RUNX3 hypermethylation in HCC have a cause- and-effect relationship is not known. In this study, plasma protein carbonyl and total antioxidant capacity (TAC) in patients with hepatitis B virus (HBV)-associated HCC (n=60) and age-matched healthy subjects (n=80) was determined. RUNX3 methylation in peripheral blood mononuclear cells (PBMC) of subjects was measured by methylation-specific PCR. Effect of reactive oxygen species (ROS) on induction of RUNX3 hypermethylation in HCC cells was investigated. Plasma protein carbonyl content was significantly higher, whereas plasma TAC was significantly lower, in HCC patients than healthy controls. Based on logistic regression, increased plasma protein carbonyl and decreased plasma TAC were independently associated with increased risk for HCC. PBMC RUNX3 methylation in the patient group was significantly greater than in the healthy group. RUNX3 methylation in hydrogen peroxide (H2O2)-treated HepG2 cells was significantly higher than in untreated control cells. In conclusion, increase in oxidative stress in Thai patients with HBV-associated HCC was demonstrated. This oxidative increment was independently associated with an increased risk for HCC development. RUNX3 in PBMC was found to be hypermethylated in the HCC patients. In vitro, RUNX3 hypermethylation was experimentally induced by H2O2. Our findings suggest that oxidative stress is a cause of RUNX3 promoter hypermethylation in HCC cells.