ABSTRACT
Epigenetic alteration by oxidative stress is vitally involved in carcinogenesis and cancer progression. Previously, we demonstrated that oxidative stress was increased in hepatocellular carcinoma (HCC) patients and associated with tumor aggressiveness. Herein, we immunohistochemically investigated whether histone methylation, specifically H4K20me3, was upregulated in human hepatic tissues obtained from HCC patients (n = 100). Also, we experimentally explored if the H4K20me3 was upregulated by reactive oxygen species (ROS) and contributed to tumor progression in HCC cell lines. We found that H4K20me3 level was increased in HCC tissues compared with the adjacent noncancerous liver tissues. H3K9me3 and H3K4me3 levels were also increased in HCC tissues. Cox regression analysis revealed that the elevated H4K20me3 level was associated with tumor recurrence and short survival in HCC patients. Experimentally, H2O2 provoked oxidative stress and induced H4K20me3 formation in HepG2 and Huh7 cells. Transcript expression of histone methyltransferase Suv420h2 (for H4K20me3), Suv39h1 (for H3K9me3), and Smyd3 (for H3K4me3) were upregulated in H2O2-treated HCC cells. H2O2 also induced epithelial-mesenchymal transition (EMT) in HCC cells, indicated by decreased E-cadherin but increased α-SMA and MMP-9 mRNA expression. Migration, invasion, and colony formation in HCC cells were markedly increased following the H2O2 exposure. Inhibition of H4K20me3 formation by A196 (a selective inhibitor of Suv420h2) attenuated EMT and reduced tumor migration in H2O2-treated HCC cells. In conclusion, we demonstrated for the first time that H4K20me3 level was increased in human HCC tissues, and it was independently associated with poor prognosis in HCC patients. ROS upregulated H4K20me3 formation, induced mRNA expression of EMT markers, and promoted tumor progression in human HCC cells. Inhibition of H4K20me3 formation reduced EMT and tumor aggressive phenotypes in ROS-treated HCC cells. Possibly, ROS-induced EMT and tumor progression in HCC cells was epigenetically mediated through an increased formation of repressive chromatin H4K20me3.
ABSTRACT
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.
