P53-dependent antiproliferative and pro-apoptotic effects of trichostatin A (TSA) in glioblastoma cells.

Glioblastomas are known to be highly chemoresistant, but HDAC inhibitors (HDACi) have been shown to be of therapeutic relevance for this aggressive tumor type. We treated U87 glioblastoma cells with trichostatin A (TSA) to define potential epigenetic targets for HDACi-mediated antitumor effects. Using a cDNA array analysis covering 96 cell cycle genes, cyclin-dependent kinase inhibitor p21(WAF1) was identified as the major player in TSA-induced cell cycle arrest. TSA slightly inhibited proliferation and viability of U87 cells, cumulating in a G1/S cell cycle arrest. This effect was accompanied by a significant up-regulation of p53 and its transcriptional target p21(WAF1) and by down-regulation of key G1/S regulators, such as cdk4, cdk6, and cyclin D1. Nevertheless, TSA did not induce apoptosis in U87 cells. As expected, TSA promoted the accumulation of total acetylated histones H3 and H4 and a decrease in endogenous HDAC activity. Characterizing the chromatin modulation around the p21(WAF1) promoter after TSA treatment using chromatin immunoprecipitation, we found (1) a release of HDAC1, (2) an increase of acetylated H4 binding, and (3) enhanced recruitment of p53. p53-depleted U87 cells showed an abrogation of the G1/S arrest and re-entered the cell cycle. Immunofluorescence staining revealed that TSA induced the nuclear translocation of p21(WAF1) verifying a cell cycle arrest. On the other hand, a significant portion of p21(WAF1) was present in the cytoplasmic compartment causing apoptosis resistance. Furthermore, TSA-treated p53-mutant cell line U138 failed to show an induction in p21(WAF1), showed a deficient G2/M checkpoint, and underwent mitotic catastrophe. We suggest that HDAC inhibition in combination with other clinically used drugs may be considered an effective strategy to overcome chemoresistance in glioblastoma cells.

Chrysin inhibits propagation of HeLa cells by attenuating cell survival and inducing apoptotic pathways.

OBJECTIVE: Chrysin, one of the main active constituents of flavonoids, is known for demonstrating protective effects against various types of cancer including cervical cancer. The aim of this study was to determine apoptosis induction and antiproliferative action of chrysin on human cervical cancer cells. MATERIALS AND METHODS: In this study, attempts have been made to establish anticancer role of chrysin on HeLa cells. MTT, mitochondrial potential, DNA fragmentation, annexin V/propidium iodide assays, qPCR and protein profiling were performed. RESULTS: Chrysin treated HeLa cells showed time and dose dependent decrease in cell viability and demonstrated profound effects on nuclear morphology and DNA fragmentation. Chrysin treatment increased the expression of proapoptotic genes BAD, BAX, BID, BOK and APAF1, TNF, FASL, FAS, FADD and caspases (like caspase 3, caspase 7, caspase 8 and caspase 9), whereas it decreased the expression level of antiapoptotic genes MCL-1, NAIP, XIAP and Bcl-2 and cell cycle regulatory genes CCNB1, CCNB2, CCND1, CCND2, CCND3, CCNE2, CDK4 and CDK2 at transcript level. Furthermore, chrysin significantly upregulated pro-apoptotic proteins, like TRAILR2/DR5, TRAILR1/DR4, Fas/TNFRSF6/CD95, phosphoP53(S15), BAD, BAX, cleaved caspase 3, procaspase 3, HTRA2/Omi and SMAC/Diablo, while downregulated anti-apoptotic proteins like BCL-X, BCL2, XIAP and CIAPs that support chrysin mediated apoptosis in HeLa cells. Remarkably, chrysin downregulated the phosphorylated AKT pathway proteins, (p-473) AKT, (p-Ser 2448) mTOR, (p-Ser241) PDK1, (p-Ser112) BAD, and upregulated (p-Ser21) GSK3b, (p-Thr172) AMPKa, P27 (p-Thr198) and (p-Ser15) P53, which endorses chrysin mediated apoptosis. CONCLUSIONS: Chrysin significantly inhibited proliferation and induced apoptosis by modulation of various apoptotic genes and AKT/MAPK pathway genes.

Trichostatin A causes p53 to switch oxidative-damaged colorectal cancer cells from cell cycle arrest into apoptosis.

Many studies aim at improving therapeutic efficacy by combining strategies with oxidative stress-inducing drugs and histone deacetylase (HDAC) inhibitors in colorectal cancer. As p53 and p21(WAF1) are essential in oxidative stress-induced DNA damage, we investigated epigenetic regulation of p21(WAF1) promoter. Firstly, HCT116 p53(+)/(+) and p53(-)/(-) colorectal cancer cells were treated with H(2)O(2) for 6 hrs and 24 hrs (early/late response). Chromatin immunoprecipitation revealed transcriptional transactivation of p21(WAF1) in HCT116 p53(+)/(+) cells as shown by increased binding of p53 and acetylated H4 around two p21(WAF1) promoter sites, the responsible element (RE) and the Sp1 site, while both proteins bound preferentially on the RE. Interestingly, H3 was not involved, suggesting H4-specific transactivation of the p21(WAF1) promoter. H(2)O(2) addition resulted in G(2)/M arrest of both HCT116 cell lines without significant cell death. To investigate whether a HDAC inhibitor strengthens G(2)/M arrest, we pretreated cells with Trichostatin A (TSA). In HCT116 p53(+)/(+) cells, we found (i) remarkably increased acetylated H4 around both p21(WAF1) promoter regions, especially at the Sp1 site; (ii) increased acetylation of p53 at lysines 320 and 382;(iii) displacement of HDAC1 from the Sp1 site, thus inhibiting its repression effect and increasing p53 binding.p53 seems to trigger H4-acetylation around the p21(WAF1) promoter because there was nearly no H4 acetylation in HCT116 p53(-)/(-) cells. For the first time we show that there is a time-dependent TSA mode of action with increased p53-dependent histone H4 acetylation at the p21(WAF1) promoter in early response, and decreased acetylation in late response. Reduced p53-triggered transactivation of p21(WAF1) in late response allows cells to re-enter cell cycle, and TSA causes p53 to simultaneously induce apoptosis.