Jiuhong Kang

Involvement of histone hypoacetylation in Ni2+-induced bcl- 2 down-regulation and human hepatoma cell apoptosis.

Although induction of cell apoptosis is known to be involved in the cytotoxicity of Ni2+, little research has been aimed at the mechanism of Ni2+-induced apoptosis. Recent studies showed that Ni2+ induces histone hypoacetylation in different cell lines. Since histone hypoacetylation plays important roles in the control of cell cycle progress and apoptosis, we hypothesized that histone hypoacetylation may be an unrevealed pathway in Ni2+-induced apoptosis. To address this, effects of Ni2+ on cell apoptosis, bcl-2 gene expression and histone acetylation were examined in human hepatoma Hep3B cells. We found that Ni2+ treatment resulted in cell proliferation arrest, the appearance of detached cells, condensed chromatin, apoptotic bodies and specific DNA fragmentation, indicating the occurrence of cell apoptosis. At the same time, Ni2+ induced a significant decrease in bcl-2 expression and histone acetylation; the decrease of histone H4 acetylation in nucleosomes associated with the bcl-2 promoter region was also proven by a chromatin immunoprecipitation assay, indicating the involvement of histone hypoacetylation in Ni2+-induced bcl-2 down-regulation. Further studies showed that increasing histone acetylation by either 100xa0nM of trichostatin A or over-expressing histone acetyltranferase p300 in Hep3B cells obviously attenuated the bcl-2 down-regulation and cell apoptosis caused by Ni2+. Considering the importance of bcl-2 in determining cell survival and apoptosis, the data presented here suggest that histone hypoacetylation may represent one unrevealed pathway in Ni2+-induced cell apoptosis, where bcl-2 is one of its targets.

Synergistic killing of human leukemia cells by antioxidants and trichostatin A

PurposeAntioxidants and trichostatin A (TSA) are promising anticancer drugs, and are capable of enhancing the neoplastic toxicity of other chemicals that exert anticancer activity via different mechanisms. Since antioxidants and TSA (the specific inhibitor of histone deacetylase) are believed to combat cancer via different mechanisms, we sought to determine whether combining them would improve their anticancer activity in human leukemia cells (HL-60).Materials and methodsHL-60 cells were treated with antioxidants (ascorbic acid, AA and N-acetyl-cysteine, NAC), TSA or their combination, and cell proliferation arrest, lactate dehydrogenase (LDH) release and cell viability were measured as indicators of cell damage. Accumulation of reactive oxygen species (ROS) and the acetylation of histones were also measured.ResultsThe cytotoxicity of AA, NAC and TSA increased in a time- and dose-dependent manner. AA (1, 2 and 4xa0mM) and NAC (0.2, 0.5 and 1xa0mM) were able to diminish ROS generation but showed no influence on histone acetylation in HL-60 cells. In contrast, TSA (20, 50, 100 and 200xa0nM) did not inhibit ROS generation but significantly increased histone acetylation, indicating a possible role for both scavenging ROS and increasing histone acetylation in the induction of cell death in HL-60 cells. This conclusion was further confirmed by the finding that the combination of antioxidant and TSA not only diminished ROS generation, but also increased histone acetylation, and hence showed greater cytotoxicity in HL-60 cells than either component alone.ConclusionsOur findings show that combining antioxidants and TSA can enhance their neoplastic toxicity at least in human leukemia HL-60 cells, providing a new approach to the design of chemotherapy strategies and the development of anticancer drugs.