As an engineered nanomaterial, zinc oxide nanoparticles (ZnO NPs) are used frequently in biological applications and can make contact with human skin. Here, we systematically investigated the effects of ZnO NPs on non-tumorigenic human epidermal keratinocytes, which were used as a test model for this in vitro study, at the epigenetic and molecular levels. Our results showed that ZnO NPs induced cell cycle arrest at the G2/M checkpoint before the viability of human epidermal keratinocytes was reduced, which was associated with the chromatin changes at the epigenetic level, including increased methylation of histone H3K9 and decreased acetylation of histone H4K5 accompanied by chromatin condensation at 24 hours. The mRNA expression of the methyltransferase genes G9a and GLP was also increased upon treatment with ZnO NPs, and the acetyltransferase genes GCN5 , P300 , and CBP were downregulated. Reactive oxygen species were found to be more abundant after treatment with ZnO NPs for 6 hours, and DNA damage was observed at 24 hours. Transmission electron microscopy and flow cytometry confirmed that ZnO NPs were absorbed into the cell when they were added to the medium. Apoptotic human epidermal keratinocytes were detected, and the expression of the proapoptotic genes Bax , Noxa , and Puma increased significantly, while the expression of the antiapoptotic gene Bcl-xl decreased 24 hours after exposure to ZnO NPs. These findings suggest that the ZnO NPs induced cell cycle arrest at G2/M, which was associated with epigenetic changes and accompanied by p53-Bax mitochondrial pathway-mediated apoptosis.

The cereal aleurone layer plays an important role in seed germination, and reactive oxygen species (ROS) in aleurone layers act as crucial signal molecules in this progression. Recent studies have revealed that epigenetic modification is involved in plant development and seed germination. However, little is known about a possible relationship between histone modification and the ROS signaling pathway in cereal aleurone layers during seed germination. Here, we found that the expression of both histone acetyltransferases (HATs) and histone deacetylases (HDACs) was increased gradually during seed germination, accompanied by an increase in global acetylation levels of histones H3 and H4 in maize aleurone layers. The acetylation was found to be promoted by GA(3) and suppressed by ABA. However, when the HDAC inhibitor trichostatin A (TSA) was used, the increased H3K9ac and H4K5ac level correlated with an inhibition of the germination. These results indicated that the overall histone acetylation in the aleurone layers is not required for germination. Similarly these two hormones, GA(3) and ABA, exerted opposed effects on the expression of the ROS-related gene sodCp. Furthermore, chromatin immunoprecipitation experiments showed that the promoter region of the sodCp gene was hyperacetylated during germination, and this acetylation was promoted by GA(3) and inhibited by both ABA and TSA. These results suggested that GA(3)-mediated expression of the sodCp gene in aleurone layers is associated with histone hyperacetylation on the promoter and coding region of this gene, consequently leading to an accumulation of H(2)O(2) which regulated production of α-amylase during seed germination.

DNA methylation plays a crucial role in lots of biological processes and cancer. 5-azacytidine (5-AC), a DNA methylation inhibitor, has been used as a potential chemotherapeutic agent for cancer. In this study, we used 5-AC treatment to investigate whether DNA methylation was involved in regulation of programmed cell death (PCD) in mouse embryo fibroblast NIH-3T3 cells which could undergo PCD after treatment with TNF-α and cycloheximide (CHX). The results showed that the genomic DNA of NIH-3T3 cells was hypermethylated during PCD induced by TNF-α and CHX, and 5-AC might prevent this PCD process. However, treatment with the other three DNA methylation inhibitors, 5-aza-deoxycytidine, 6-thioguanine and RG108, did not interfere with the NIH-3T3 cell PCD process. Additionally, knockdown of DNMT1 did not affect the apoptosis process. The present results and observations indicated that 5-AC specifically inhibited the NIH-3T3 apoptosis process via a genomic DNA methylation-independent pathway. During the TNF-α and CHX-inducing apoptosis process, the PCD related BCL-2 family proteins were significantly down-regulated. Furthermore, after the small interference RNA-mediated knockdown of BCL-XL, one of the BCL-2 family proteins, 5-AC did not inhibit the apoptosis process, suggesting that 5-AC inhibited the PCD process induced by TNF-α and CHX by affecting the anti-apoptotic protein BCL-XL.