Transactivation of bad by vorinostat-induced acetylated p53 enhances doxorubicin-induced cytotoxicity in cervical cancer cells

Vorinostat (VOR) has been reported to enhance the cytotoxic effects of doxorubicin (DOX) with fewer side effects because of the lower DOX dosage in breast cancer cells. In this study, we investigated the novel mechanism underlying the synergistic cytotoxic effects of VOR and DOX co-treatment in cervical cancer cells HeLa, CaSki and SiHa cells. Co-treatment with VOR and DOX at marginal doses led to the induction of apoptosis through caspase-3 activation, poly (ADP-ribose) polymerase cleavage and DNA micronuclei. Notably, the synergistic growth inhibition induced by the co-treatment was attributed to the upregulation of the pro-apoptotic protein Bad, as the silencing of Bad expression using small interfering RNA (siRNA) abolished the phenomenon. As siRNA against p53 did not result in an increase in acetylated p53 and the consequent upregulation of Bad, the observed Bad upregulation was mediated by acetylated p53. Moreover, a chromatin immunoprecipitation analysis showed that the co-treatment of HeLa cells with VOR and DOX increased the recruitment of acetylated p53 to the bad promoter, with consequent bad transactivation. Conversely, C33A cervical cancer cells containing mutant p53 co-treated with VOR and DOX did not exhibit Bad upregulation, acetylated p53 induction or consequent synergistic growth inhibition. Together, the synergistic growth inhibition of cervical cancer cell lines induced by co-treatment with VOR and DOX can be attributed to the upregulation of Bad, which is induced by acetylated p53. These results show for the first time that the acetylation of p53, rather than histones, is a mechanism for the synergistic growth inhibition induced by VOR and DOX co-treatments.

The effect of combined treatment with cisplatin and histone deacetylase inhibitors on HeLa cells

OBJECTIVE

To investigate the combined effects of cisplatin and the histone deacetylase (HDAC) inhibitors suberoylanilide hydroxamic acid (SAHA) or sirtinol on HeLa cells and assess the mechanism underlying HDAC inhibitor-cisplatin synergy.

METHODS

The antineoplastic actions of cisplatin, SAHA and sirtinol, alone and in combination, were evaluated using the tetrazolium dye-based MTT cell proliferation assay, DAPI nuclear staining and cytotoxicity analysis.

RESULTS

Exposure to cisplatin, SAHA or sirtinol alone induced a dose-dependent reduction in HeLa cell viability. Combined treatment with cisplatin and SAHA or sirtinol was significantly more cytotoxic than cisplatin alone. Individually, cisplatin, SAHA and sirtinol activated caspase-3 and induced apoptosis, but the effects of combined treatment were greater. Importantly, both HDAC inhibitors dose-dependently inhibited the expression of the antiapoptotic proteins Bcl-2 and x-linked inhibitor of apoptosis protein (XIAP).

CONCLUSION

The combination of cisplatin and SAHA or sirtinol had synergistic effect on the HeLa cell viability. This potentiation of cisplatin activity was associated with HDAC inhibitor-mediated down-regulation of Bcl-2 and XIAP. These may result from the relaxation of chromatin by these HDAC inhibitors that increase cisplatin sensitivity by enhancing the accessibility of DNA to cisplatin and transcriptional regulators.

Analysis of a genome-wide set of gene deletions in the fission yeast Schizosaccharomyces pombe

We report the construction and analysis of 4,836 heterozygous diploid deletion mutants covering 98.4% of the fission yeast genome providing a tool for studying eukaryotic biology. Comprehensive gene dispensability comparisons with budding yeast--the only other eukaryote for which a comprehensive knockout library exists--revealed that 83% of single-copy orthologs in the two yeasts had conserved dispensability. Gene dispensability differed for certain pathways between the two yeasts, including mitochondrial translation and cell cycle checkpoint control. We show that fission yeast has more essential genes than budding yeast and that essential genes are more likely than nonessential genes to be present in a single copy, to be broadly conserved and to contain introns. Growth fitness analyses determined sets of haploinsufficient and haploproficient genes for fission yeast, and comparisons with budding yeast identified specific ribosomal proteins and RNA polymerase subunits, which may act more generally to regulate eukaryotic cell growth.

A novel role for methyl CpG-binding domain protein 3, a component of the histone deacetylase complex, in regulation of cell cycle progression and cell death

Histone deacetylases (HDACs) form HDAC-associated complexes and play an essential role in transcriptional repression. The functional significance of HDAC-associated proteins in the progression of the cell cycle and in cell death remains to be established. Here, we investigated the molecular mechanisms by which methyl CpG-binding domain protein 3 (MBD3), a component of the HDAC complex, modulates these processes via its functional interplay with HDAC. Depletion of MBD3 induced an arrest at the G(2)/M transition and resulted in defective mitosis in cancer cells. These effects appear to be associated with the transcriptional modulation of key cell cycle-regulator genes, including CylinB1, Plk1, and Survivin. Chromatin immunoprecipitation analyses revealed that the transcription of these cell cycle regulators is modulated by MBD3, supporting its direct role in their transcriptional repression. These findings collectively support a role for MBD3 in cell cycle progression and cell death as a modulator of HDAC-mediated transcription.

An HDAC inhibitor, trichostatin A, induces a delay at G2/M transition, slippage of spindle checkpoint, and cell death in a transcription-dependent manner

Histone deacetylases (HDACs), a promising target for cancer therapy, play a role in regulating cell-cycle progression. The mechanisms for HDAC inhibition-induced regulation of G(2)/M transition and mitotic progression remain to be elucidated. Herein, we report that trichostatin A (TSA), an HDAC inhibitor, induces a delay at the G(2)/M transition, chromosome missegregation and multi-nucleation, and thereby leads to cell death by promoting exit from aberrant mitosis without spindle checkpoint. These results are associated with a transcriptional modulation of key regulator genes of the cell cycle, including CyclinB1, Plk1, Survivin, and p21(WAF1/Cip1). Actinomycin D, a transcriptional inhibitor, abrogated the TSA-induced delay of G(2)/M transition and transcriptional modulation of cell-cycle regulator genes, indicating that the impact of TSA in this manner is transcription dependent. Overall, our findings indicate that TSA provides a barrier to cell-cycle progression for antiproliferation and promotes escape from mitotic catastrophe and cell death, by inhibiting an HDAC-mediated transcriptional action.

Methyl CpG-binding domain protein 3 mediates cancer-selective cytotoxicity by histone deacetylase inhibitors via differential transcriptional reprogramming in lung cancer cells

Histone deacetylase inhibitors (HDI) have been reported to inhibit the growth and survival of cancer cells while leaving normal cells untouched. However, the mechanisms underlying this selective cell death are poorly understood. Gene expression analysis revealed that HDI treatment induced up-regulation of p21(WAF1/Cip1) and down-regulation of ErbB2 in cancer cells but not normal cells. Overexpression of p21(WAF1/Cip1) and/or silencing of ErbB2 enhanced cancer cell growth inhibition, suggesting that HDI-induced up-regulation/down-regulation of these genes play critical roles in HDI-induced growth inhibition of cancer cells. Most importantly, we found that the gene silencing factor methyl CpG-binding domain protein 3 (MBD3) was not only released from cancer-selective promoter of the HDI up-regulated p21(WAF1/Cip1) gene but also recruited to that of the HDI-down-regulated ErbB2 gene. Furthermore, silencing of MBD3 by small interfering RNA abrogated the HDI-induced gene regulation and growth inhibition in lung cancer but not in normal cells. Together, our results support the critical potential of MBD3 in HDI-induced cancer-selective cell death via cancer differential gene expression.

Sodium butyrate sensitizes human glioma cells to TRAIL-mediated apoptosis through inhibition of Cdc2 and the subsequent downregulation of survivin and XIAP

In TNF-related apoptosis-inducing ligand (TRAIL)-resistant glioma cells, co-treatment with nontoxic doses of sodium butyrate and TRAIL resulted in a marked increase of TRAIL-induced apoptosis. This combined treatment was also cytotoxic to glioma cells overexpressing Bcl-2 or Bcl-xL, but not to normal human astrocytes, thus offering an attractive strategy for safely treating resistant gliomas. Cotreatment with sodium butyrate facilitated completion of proteolytic processing of procaspase-3 that was partially blocked by treatment with TRAIL alone. We also found that treatment with sodium butyrate significantly decreased the protein levels of survivin and X-linked inhibitor of apoptosis protein (XIAP), two major caspase inhibitors. Overexpression of survivin and XIAP attenuated sodium butyrate-stimulated TRAIL-induced apoptosis, suggesting its involvement in conferring TRAIL resistance to glioma cells. Furthermore, the kinase activities of Cdc2 and Cdk2 were significantly decreased following sodium butyrate treatment, accompanying downregulation of cyclin A and cyclin B, as well as upregulation of p21. Forced expression of Cdc2 plus cyclin B, but not Cdk2 plus cyclin A, attenuated sodium butyrate/TRAIL-induced apoptosis, overriding sodium butyrate-mediated downregulation of survivin and XIAP. Therefore, Cdc2-mediated downregulation of survivin and XIAP by sodium butyrate may contribute to the recovery of TRAIL sensitivity in glioma cells.

Subcellular localization and transcriptional repressor activity of HBx on p21WAF1/Cip1 promoter is regulated by ERK-mediated phosphorylation

The protein encoded by the hepatitis B viral X-gene, HBx, is essential for viral infection and has been shown to regulate gene transcription and the Ras signaling pathway including Raf, MEK, and ERK. To better understand regulatory mechanism of HBx functions, we investigated whether ERK1/2-induced phosphorylation of HBx regulates its transcriptional activity on p21(WAF1/Cip1) promoter. HBx-genotype A (WT1) and its modified HBx (WT2; (38)SSPSPS(43) in WT1 was substituted by (38)PPSSPS(43) in HBx-genotype F) were phosphorylated by ERK1/2 in vitro, although their Ser --> Ala constructs, SA1 (S(43) of WT1 to A) and SA2 (S(41) of WT2 to A), were not. HBx WT1 and WT2, but not SA2, repressed transcription from the p21(WAF1/Cip1) promoter. This repression was blocked by treatment with PD98059, an inhibitor of MEK, or by overexpression of dominant negative MEK1. Furthermore, WT1 and WT2 localized predominantly in the nucleus, whereas SA1 and SA2 localized to the cytoplasm, suggesting that the subcellular localization of HBx is controlled by its phosphorylation. Overall, our findings provide insight that ERK1/2-mediated phosphorylation of HBx regulates HBx function and localization, and may contribute to dysregulation of cell cycle progression leading to hepatocarcinogenesis in HBV-infected cells.

Functional interplay between modulation of histone deacetylase activity and its regulatory role in G2-M transition

The acetylation status of histones plays an essential role in regulating transcription and replication, and is thus involved in the proliferation and differentiation of normal and neoplastic cells. Here, we investigated the effect of trichostatin A (TSA), an inhibitor of histone deacetylases (HDACs), on G2-M transition during the cell cycle. HDAC inhibition by TSA arrested the cell cycle at G2 and also induced escape from the mitotic arrest into G1. TSA reduced the expression of cyclin B1, a key cyclin for G2-M transition, but stimulated expression of p21(WAF1/Cip1), an inhibitor of CDK and Cdc2. In contrast, the expression of cyclin B1 but not p21(WAF1/Cip1) is enhanced during M. Moreover, histone acetylation at promoters of these two genes was regulated by TSA. TSA augmented acetylation of the p21(WAF1/Cip1) promoter but reduced that of the cyclin B1 promoter, suggesting the relationship between TSA-induced modulation of histone acetylation and differential expression of these genes. Taken together, our observations suggest that modulation of HDAC activity is implicated in the G2-M transition by regulating the transcription of cell cycle regulators, p21(WAF1/Cip1) and cyclin B1, via modulating acetylation status of the histones at their promoters.

Characterization of mycoplasma arginine deiminase expressed in E. coli and its inhibitory regulation of nitric oxide synthesis

We previously reported that a cytostatic protein that is found in ASC-17D Sertoli cell-conditioned media was Mycoplasma arginine deiminase (ADI), which hydrolyzes L-arginine into L-citrulline and ammonia. Here, we report the over-expression of recombinant ADI (rADI) in E. coli and the down-regulation of lipopolysaccharide (LPS) induced-nitric oxide (NO) production by rADI treatment. We cloned the ADI gene from Mycoplasma arginini genomic DNA by a polymerase chain reaction, and changed five TGA tryptophan codons (stop codon in E. coli) to TGG codons in the coding region by site-directed mutagenesis in order to express in E. coli. The rADI was purified to apparent homogeneity by DEAE-Sepharose and arginine-affinity chromatography. The rADI expressed in E. coli was identified as 45 kDa on SDS-PAGE and 90 kDa on native PAGE, implying that it exists as a dimer like ADI of M. arginini. The Km for arginine of rADI was approximately 370+/-50 microM. Its optimal temperature and pH were 41 degrees C and pH 6.4, respectively, and enzyme activity remained > or = 50% for 5 d at physiological temperature and pH. Treatment of purified rADI suppressed NO production in macrophage-like RAW 264.7 and primary glial cells that were exposed to LPS. Furthermore, an intraperitoneal injection of rADI significantly suppressed the rise of blood nitrite/nitrate levels that were induced by the systemic administration of bacterial endotoxin LPS to mice, resulting in an improvement in their survival rate. These results suggest that the depletion of blood arginine with an arginine-metabolizing enzyme, such as ADI, could suppress excessive production of NO that is caused by inducible NOS (iNOS) during the endotoxemia. Also, rADI may be used as a new approach to control NO-related diseases, such as sepsis.