Trichostatin A activates p18INK4c gene: differential activation and cooperation with p19INK4d gene

Investigation of the Effect of 5-Aza-2'-Deoxycytidine in Comparison to and in Combination with Trichostatin A on p16INK4a, p14ARF, p15INK4b Gene Expression, Cell Growth Inhibition and Apoptosis Induction in Colon Cancer Caco-2 Cell Line

Background

The cell cycle is divided into four phases, G1, G2, S, and M phase. The mammalian cell cycle is controlled and governed by the kinase complexes including cyclin and the cyclin-dependent kinase (CDK), cyclin-CDK complexes. The activity of the complexes is regulated by cyclin-dependent kinase inhibitors (CDKIs), the INK4, and the CDK interacting protein/kinase inhibitory protein (CIP/KIP) families. Promoter hypermethylation and histone deacetylation of CDKIs have been reported in several cancers. These changes can be reversed by DNA demethylating agents, such as decitabine, 5-Aza-2'-deoxycytidine (5-Aza-CdR), and histone deacetylase inhibitors (HDACIs), such as trichostatin A. Previously, we reported the effect of 5-Aza-CdR and trichostatin A (TSA) on hepatocellular carcinoma (HCC). The present study aimed to investigate the effect of 5-Aza-CdR in comparison to and in combination with trichostatin A on p16INK4a, p14ARF, p15INK4b genes expression, cell growth inhibition and apoptosis induction in colon cancer Caco-2 cell line.

Methods

The Caco-2 cells were cultured and treated with 5-Aza-CdR and TSA (alone and combined). The cell viability, apoptosis, and relative gene expression were determined by MTT assay, flow cytometry, and real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR), respectively.

Results

Both compounds inhibited cell growth, induced apoptosis, and up-regulated the p16INK4a, p14ARF, p15INK4b gene significantly. The TSA had a more significant effect in comparison to 5-Aza-CdR. Furthermore, maximal apoptosis and up-regulation were observed with combined treatment.

Conclusions

our finding indicated that 5-Aza-CdR and TSA can epigenetically re-activate the p16INK4a, p14ARF, p15INK4b gene resulting in cell growth inhibition and apoptosis induction in colon cancer.

Host Tumor Suppressor p18INK4c Functions as a Potent Cell-Intrinsic Inhibitor of Murine Gammaherpesvirus 68 Reactivation and Pathogenesis

Gammaherpesviruses are common viruses associated with lifelong infection and increased disease risk. Reactivation from latency aids the virus in maintaining infection throughout the life of the host and is responsible for a wide array of disease outcomes. Previously, we demonstrated that the virus-encoded cyclin (v-cyclin) of murine gammaherpesvirus 68 (γHV68) is essential for optimal reactivation from latency in normal mice but not in mice lacking the host tumor suppressor p18^INK4c (p18). Whether p18 plays a cell-intrinsic or -extrinsic role in constraining reactivation remains unclear. Here, we generated recombinant viruses in which we replaced the viral cyclin with the cellular p18^INK4c gene (p18KI) for targeted expression of p18, specifically within infected cells. We find that the p18KI virus is similar to the cyclin-deficient virus (cycKO) in lytic infection, establishment of latency, and infected cell reservoirs. While the cycKO virus is capable of reactivation in p18-deficient mice, expression of p18 from the p18KI virus results in a profound reactivation defect. These data demonstrate that p18 limits reactivation within latently infected cells, functioning in a cell-intrinsic manner. Further, the p18KI virus showed greater attenuation of virus-induced lethal pneumonia than the cycKO virus, indicating that p18 could further restrict γHV68 pathogenesis even in p18-sufficient mice. These studies demonstrate that host p18 imposes the requirement for the viral cyclin to reactivate from latency by functioning in latently infected cells and that p18 expression is associated with decreased disease, thereby identifying p18 as a compelling host target to limit chronic gammaherpesvirus pathogenesis.IMPORTANCE Gammaherpesviruses are ubiquitous viruses associated with multiple malignancies. The propensity to cycle between latency and reactivation results in an infection that is never cleared and often difficult to treat. Understanding the balance between latency and reactivation is integral to treating gammaherpesvirus infection and associated disease outcomes. This work characterizes the role of a novel inhibitor of reactivation, host p18^INK4c, thereby bringing more clarity to a complex process with significant outcomes for infected individuals.

Molecular-targeting therapies against quantitative abnormalities in gene expression with malignant tumors

Genetic mutations in exons of oncogenes and tumor-suppressor genes causing qualitative abnormalities result in activation of the oncogenes and inactivation of the tumor-suppressor genes, thereby causing cancer. In contrast, we have previously demonstrated that decreases in the RB promoter activity by genetic or epigenetic abnormalities can also cause carcinogenesis. In addition, activation and inactivation of a variety of oncogenes and tumor-suppressor genes finally cause quantitative abnormalities in gene expression. Interestingly, we discovered effective molecular-targeting agents, such as a novel MEK inhibitor, trametinib, by screening for agents upregulating the expression of cyclin-dependent kinase inhibitors. In the present review, we focused on the quantitative abnormalities in gene expression with carcinogenesis, and discuss the importance of normalizing the quantitative abnormalities in gene expression with several molecular-targeting agents.

Characterization of the regulation and function of zinc-dependent histone deacetylases during rodent liver regeneration

The studies reported here were undertaken to define the regulation and functional importance of zinc-dependent histone deacetylase (Zn-HDAC) activity during liver regeneration using the mouse partial hepatectomy (PH) model. The results showed that hepatic HDAC activity was significantly increased in nuclear and cytoplasmic fractions following PH. Further analyses showed isoform-specific effects of PH on HDAC messenger RNA (mRNA) and protein expression, with increased expression of the class I HDACs, 1 and 8, and class II HDAC4 in regenerating liver. Hepatic expression of (class II) HDAC5 was unchanged after PH; however, HDAC5 exhibited transient nuclear accumulation in regenerating liver. These changes in hepatic HDAC expression, subcellular localization, and activity coincided with diminished histone acetylation in regenerating liver. The significance of these events was investigated by determining the effects of suberoylanilide hydroxyamic acid (SAHA, a specific inhibitor of Zn-HDAC activity) on hepatic regeneration. The results showed that SAHA treatment suppressed the effects of PH on histone deacetylation and hepatocellular bromodeoxyuridine (BrdU) incorporation. Further examination showed that SAHA blunted hepatic expression and activation of cell cycle signals downstream of induction of cyclin D1 expression in mice subjected to PH.

CONCLUSION

The data reported here demonstrate isoform-specific regulation of Zn-HDAC expression, subcellular localization, and activity in regenerating liver. These studies also indicate that HDAC activity promotes liver regeneration by regulating hepatocellular cell cycle progression at a step downstream of cyclin D1 induction.

Combination of a novel HDAC inhibitor OBP-801/YM753 and a PI3K inhibitor LY294002 synergistically induces apoptosis in human endometrial carcinoma cells due to increase of Bim with accumulation of ROS

OBJECTIVE

In most endometrial carcinoma, it has been observed that the PI3K/Akt pathway is abnormally accelerated in association with mutations in PIK3CA and PTEN. The present study aimed to examine the combined effect of a novel histone deacetylase (HDAC) inhibitor OBP-801/YM753 and a PI3K inhibitor LY294002 against human endometrial carcinoma cells.

METHODS

The effects of OBP-801/YM753 and LY294002 on the growth of human endometrial carcinoma HEC-1A cells were examined using WST-8 and colony formation assays. The distribution of the cell cycle or apoptosis was analyzed by flow cytometry. The accumulation of intracellular reactive oxygen species (ROS) was measured with a 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate, acetyl ester (CM-H2DCFDA) dye. The expression of apoptosis-related proteins was investigated by Western blotting. Mice engrafted with 1×10(8) HEC-1A cells were treated with OBP-801/YM753, LY294002 or the combination, and tumor volumes were measured.

RESULTS

The combination of OBP-801/YM753 and LY294002 significantly inhibited the cell growth on comparison with each agent alone and synergistically increased apoptosis with the induction of Bim, a well-known apoptosis inducer. Additionally, the apoptosis induced by the combination was shown to be dependent on intracellular ROS accumulation and Bim induction. Moreover, the apoptosis-inducing effect of OBP-801/YM753 with LY294002 was more potent than that of SAHA with LY294002. Combined treatment with OBP-801/YM753 and LY294002 significantly suppressed tumor growth compared to the control in vivo.

CONCLUSIONS

The combination of OBP-801/YM753 and LY294002 is effective on the inhibition of the growth of HEC-1A cells, and we suggest that this combination is promising a novel therapeutic strategy for endometrial carcinoma.

HDAC modulation and cell death in the clinic

Histone acetyltransferases (HATs) and histone deacetylases (HDACs) are two opposing classes of enzymes, which finely regulate the balance of histone acetylation affecting chromatin packaging and gene expression. Imbalanced acetylation has been associated with carcinogenesis and cancer progression. In contrast to genetic mutations, epigenetic changes are potentially reversible. This implies that epigenetic alterations are amenable to pharmacological interventions. Accordingly, some epigenetic-based drugs (epidrugs) have been approved by the Food and Drug Administration (FDA) and the European Medicines Agency (EMA) for cancer treatment. Here, we focus on the biological features of HDAC inhibitors (HDACis), analyzing the mechanism(s) of action and their current use in clinical practice.

["Molecular-targeting prevention" of cancer. The theory and its possibilities]

In previous prevention studies, molecular targets were not intended. We then proposed the concept termed "molecular-targeting prevention" and applied it to cancer prevention. In most malignant tumors, tumor-suppressor genes, the retinoblastoma gene (RB) and/or the p53 gene are considered to be inactivated. We therefore hypothesized that RB and/or p53 might be good candidates for the molecular-targeting prevention of cancer. Interestingly, many cancer-preventive food factors were found to reactivate the lost functions of RB and/or p53 by a "gene-regulating chemoprevention" strategy. We next proposed the concept termed "combination-oriented molecular-targeting prevention", in which only the preventive effects are synergistically enhanced. We then investigated the TNF-related apoptosis-inducing ligand (TRAIL)-death receptor 5 (DR5) pathway as a candidate of the target, and found that many cancer-preventive food factors could enhance the pathway resulting in the synergistic apoptosis of various cancer cells. We hope that these strategies will contribute to the prevention of cancer.

Downregulation of survivin and aurora A by histone deacetylase and RAS inhibitors: a new drug combination for cancer therapy

Histone deacetylase (HDAC) inhibitors, such as valproic acid (VPA), constitute a novel class of anticancer agents that cause an increase in acetylated histones and thus restore the expression of dormant tumor-suppressor and other genes related to cell differentiation, cell-cycle arrest or apoptosis of tumor cells. The Ras inhibitor farnesylthiosalicylic acid (FTS, salirasib) attenuates cancer cell proliferation in vitro and in vivo and, under certain circumstances, induces cell death. FTS by itself does not induce differentiation or complete growth arrest. The abovementioned activity of VPA as a differentiation agent suggested that it might be worth investigating its possible therapeutic potential in synergistic combination with FTS. Here, we examined whether the combined application of VPA and FTS could synergistically inhibit the proliferation of cancer cells that express oncogenic K-Ras (A549 nonsmall-cell lung carcinoma cells), DLD1 (colon carcinoma cells) or chronically active wild-type K-Ras and constitutively active B-Raf (ARO, thyroid carcinoma cells). The results showed that combined treatment with VPA and FTS synergistically reduces proliferation in all of these cancer cell lines by downregulating Ras and blocking the expression of Survivin and Aurora A. These alterations, which were most pronounced following the combined treatment, led to a mitotic crisis, as reflected by mislocalization of the chromosomal passenger complex. Our findings thus demonstrate that combination therapy with VPA and FTS might offer a promising therapeutic approach to the treatment of epithelial tumors.

"Combination-oriented molecular-targeting prevention" of cancer: a model involving the combination of TRAIL and a DR5 inducer

Malignant tumors carry a high risk of death, and the prevention of malignant tumors is a crucial issue in preventive medicine. To this end, many chemopreventive agents have been tested, but the effects of single agents have been found to be insufficient to justify clinical trials. We have therefore hypothesized that combinations of different chemopreventive agents may synergistically enhance the preventive effect of chemopreventive agents used singly. To provide the treating physician with some guideline by which to choose the most effective agents to be combined, we propose a strategy which we have termed the "combination-oriented molecular-targeting prevention" of cancer. As the molecular target of our model, we focused on tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), which specifically causes apoptosis in malignant tumor cells. Many of these agents were found to up-regulate the expression of death receptor 5, a TRAIL receptor. They were also found to synergistically induce apoptosis in malignant tumor cells when combined with TRAIL. Here, we strongly advocate that the strategy of "combination-oriented molecular-targeting prevention" of cancer will be a practical approach for chemoprevention against human malignant tumors.

Sodium butyrate-induced upregulation of p18( INK4C ) gene affects K562 cell G (0)/G (1) arrest and differentiation

Histone deacetylase inhibitor sodium butyrate (NaBu) can induce G(0)/G(1) arrest and erythroid differentiation in K562 cells, but the molecular mechanisms underlying this process are unclear. Here we show that both p18( INK4C ) mRNA and protein levels were upregulated during K562 cell erythroid differentiation induced by NaBu. Moreover, the NaBu activation of p18( INK4C ) was dependent on the integrity of Sp1 clusters in the promoter. NaBu caused hyperacetylation of histones H3 and H4 on endogenous p18( INK4C ) promoter and enhanced binding of transcription factor Sp1 in vivo. Also, overexpression of p18( INK4C ) in K562 cells resulted in G(0)/G(1) arrest and partial erythroid differentiation. Our results suggested that NaBu-mediated p18( INK4C ) regulation played a role in cell cycle arrest and erythroid differentiation in K562 cells.

Distinct HDACs regulate the transcriptional response of human cyclin-dependent kinase inhibitor genes to Trichostatin A and 1alpha,25-dihydroxyvitamin D3

The anti-proliferative effects of histone deacetylase (HDAC) inhibitors and 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] converge via the interaction of un-liganded vitamin D receptor (VDR) with co-repressors recruiting multiprotein complexes containing HDACs and via the induction of cyclin-dependent kinase inhibitor (CDKI) genes of the INK4 and Cip/Kip family. We investigated the effects of the HDAC inhibitor Trichostatin A (TSA) and 1alpha,25(OH)2D3 on the proliferation and CDKI gene expression in malignant and non-malignant mammary epithelial cell lines. TSA induced the INK4-family genes p18 and p19, whereas the Cip/Kip family gene p21 was stimulated by 1alpha,25(OH)2D3. Chromatin immunoprecipitation and RNA inhibition assays showed that the co-repressor NCoR1 and some HDAC family members complexed un-liganded VDR and repressed the basal level of CDKI genes, but their role in regulating CDKI gene expression by TSA and 1alpha,25(OH)2D3 were contrary. HDAC3 and HDAC7 attenuated 1alpha,25(OH)2D3-dependent induction of the p21 gene, for which NCoR1 is essential. In contrast, TSA-mediated induction of the p18 gene was dependent on HDAC3 and HDAC4, but was opposed by NCoR1 and un-liganded VDR. This suggests that the attenuation of the response to TSA by NCoR1 or that to 1alpha,25(OH)2D3 by HDACs can be overcome by their combined application achieving maximal induction of anti-proliferative target genes.

ZD1839 induces p15INK4b and causes G1 arrest by inhibiting the mitogen-activated protein kinase/extracellular signal–regulated kinase pathway

Inactivation of the retinoblastoma protein pathway is the most common abnormality in malignant tumors. We therefore tried to detect agents that induce the cyclin-dependent kinase inhibitor p15(INK4b) and found that ZD1839 (gefitinib, Iressa) could up-regulate p15(INK4b) expression. ZD1839 has been shown to inhibit cell cycle progression through inhibition of signaling pathways such as phosphatidylinositol 3'-kinase-Akt and mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) cascades. However, the mechanism responsible for the differential sensitivity of the signaling pathways to ZD1839 remains unclear. We here showed that ZD1839 up-regulated p15(INK4b), resulting in retinoblastoma hypophosphorylation and G(1) arrest in human immortalized keratinocyte HaCaT cells. p15(INK4b) induction was caused by MAPK/ERK kinase inhibitor (PD98059), but not by Akt inhibitor (SH-6, Akt-III). Moreover, mouse embryo fibroblasts lacking p15(INK4b) were resistant to the growth inhibitory effects of ZD1839 compared with wild-type mouse embryo fibroblasts. Additionally, the status of ERK phosphorylation was related to the antiproliferative activity of ZD1839 in human colon cancer HT-29 and Colo320DM cell lines. Our results suggest that induction of p15(INK4b) by inhibition of the MAPK/ERK pathway is associated with the antiproliferative effects of ZD1839.

Trichostatin A down-regulate DNA methyltransferase 1 in Jurkat T cells

Histone deacetylase inhibitor Trichostatin A (TSA), alone, is able to activate the transcription of DNA methylation-mediated silenced genes in human cancer cells. Increase in expression and half-life of the DNA methyltransferase DNMT1 has been found in carcinomas of the colon, lung, liver, prostate, and breast cancer. This overexpression of DNMT1 is responsible for hypermethylation of regulatory sequences of many genes involved in tumorigenesis. Using quantitative real-time PCR and Western blot analysis, we found that TSA down-regulate DNMT1 mRNA and protein expression in Jurkat T leukemia cells clone E6-1. We also observed that TSA decreased DNMT1 mRNA stability and reduced this transcript half-life from approximately 7 to 2h. We also found that protein biosynthesis is needed for posttranscriptional regulation of DNMT1 mRNA, which suggests the involvement of an RNase and/or mRNA stabilization protein entity in DNMT1 transcript stabilization. Our findings suggest that TSA not only alters histone acetylation, but also may affect DNA methylation.