Histone deacetylase inhibitor, Trichostatin A, activates p21WAF1/CIP1 expression through downregulation of c-myc and release of the repression of c-myc from the promoter in human cervical cancer cells

HDAC3 overexpression and colon cancer cell proliferation and differentiation

An immunohistochemical analysis of human colorectal adenocarcinomas showed that cancer cells express widely varying levels of HDAC3. The SW480 colon cancer cell line was found to express high levels of HDAC3 compared to other colon cancer cell lines. p21 was poorly induced in SW480 cells relative to the lower HDAC3-expressing HT-29 cells. RNAi-induced reduction of HDAC3 in SW480 cells increased their constitutive, butyrate-, TSA-, and TNF-alpha-induced expression of p21, but did not cause all the gene expression changes induced upon general histone deacetylase (HDAC) inhibition. SW480 cells with lower HDAC3 expression appeared to be poised for gene expression responses with increased histone H4-K12 acetylation, but not K5, K8, or K16 acetylation. Even though p21 was readily activated in HT29 cells, HDAC3 siRNA nonetheless stimulated p21 expression in these cells to a greater degree than HDAC1 and HDAC2 siRNA. SW480 cells with lower HDAC3 levels displayed an enhanced cell cycle arrest and growth inhibition by butyrate, but without changes in apoptosis or sensitivity to chemotherapeutic agents. As reported for other colon cancer cell lines, butyrate induced the rapid downregulation of the secretory cell differentiation markers mucin 2 and intestinal trefoil factor in SW480 cells. Interestingly, selective HDAC3 inhibition was sufficient to downregulate these genes. Our data support a central role for HDAC3 in regulating the cell proliferation and differentiation of colon cancer cells and suggest a potential mechanism by which colon cancers may become resistant to luminal butyrate.

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.

Nuclear receptor hepatocyte nuclear factor 4alpha1 competes with oncoprotein c-Myc for control of the p21/WAF1 promoter

The dichotomy between cellular differentiation and proliferation is a fundamental aspect of both normal development and tumor progression; however, the molecular basis of this opposition is not well understood. To address this issue, we investigated the mechanism by which the nuclear receptor hepatocyte nuclear factor 4alpha1 (HNF4alpha1) regulates the expression of the human cyclin-dependent kinase inhibitor gene p21/WAF1 (CDKN1A). We found that HNF4alpha1, a transcription factor that plays a central role in differentiation in the liver, pancreas, and intestine, activates the expression of p21 primarily by interacting with promoter-bound Sp1 at both the proximal promoter region and at newly identified sites in a distal region (-2.4 kb). Although HNF4alpha1 also binds two additional regions containing putative HNF4alpha binding sites, HNF4alpha1 mutants deficient in DNA binding activate the p21 promoter to the same extent as wild-type HNF4alpha1, indicating that direct DNA binding by HNF4alpha1 is not necessary for p21 activation. We also observed an in vitro and in vivo interaction between HNF4alpha1 and c-Myc as well as a competition between these two transcription factors for interaction with promoter-bound Sp1 and regulation of p21. Finally, we show that c-Myc competes with HNF4alpha1 for control of apolipoprotein C3 (APOC3), a gene associated with the differentiated hepatic phenotype. These results suggest a general model by which a differentiation factor (HNF4alpha1) and a proliferation factor (c-Myc) may compete for control of genes involved in cell proliferation and differentiation.

Trichostatin-A induces differential changes in histone protein dynamics and expression in HeLa cells

Trichostatin-A (TSA), a histone deacetylase (HDAC) inhibitor, results in enhanced acetylation of core histones thereby disrupting chromatin organization within living cells. We report on changes in chromatin organization and the resultant alteration in nuclear architecture following treatment with TSA using fluorescence imaging. TSA triggers an expected increase in the euchromatin fraction which is accompanied by a significant increase in nuclear volume and alterations in chromatin compaction mapped using fluorescence anisotropy imaging. We observe differential changes in the mobility of core and linker histones as measured by fluorescence recovery after photo-bleaching (FRAP) and fluorescence correlation spectroscopy (FCS) methods. Further TSA induces a differential increase in linker histone transcription and increased phosphorylation of linker histone proteins accompanying an expected increase in core histone acetylation patterns. Thus subtle feedback responses triggered by changes in chromatin configurations impinge selectively on linker histone mobility and its expression. These observations have implications for understanding the role of HDAC in the dynamic maintenance of chromatin organization.

Histone Deacetylase 2 Modulates p53 Transcriptional Activities through Regulation of p53-DNA Binding Activity

Histone deacetylase (HDAC) inhibitors are emerging as promising cancer therapeutics. HDAC inhibitors have been found to induce cellular activities that are strikingly similar to p53-mediated responses to genotoxic stress. For example, HDAC inhibitors induce cell cycle arrest, apoptosis, and cellular senescence. Because at least 11 HDACs are affected by the current HDAC inhibitors, the HDAC critical for tumor cell survival and proliferation remains unknown. Thus, we sought to characterize the distinct roles of HDACs in the p53 pathway. Through the use of stable MCF7 cell lines which inducibly express short hairpin RNA targeting HDAC2, we found that HDAC2 plays important roles in the p53 pathway. Specifically, we found that knockdown of HDAC2 inhibited cellular proliferation in a dose-dependent manner which was also partly p53-dependent. Furthermore, knockdown of HDAC2 induced cellular senescence. Importantly, we found that knockdown of HDAC2 enhanced p53-dependent trans-repression and trans-activation of a subset of target genes. We found that the enhancement was due to increased p53-DNA binding activity but not alterations in p53 stability or posttranslational modification(s). Thus, for the first time, our data suggest that HDAC inhibitors function through the p53 pathway, at least in part, by activating p53-DNA binding activity.

Differential role of epigenetic modulators in malignant and normal stem cells: a novel tool in preclinical in vitro toxicology and clinical therapy

Adult stem cells are primitive cells that undergo asymmetric division, thereby giving rise to one clonogenic, self-renewing cell and one cell able to undergo multipotent differentiation. Disturbance of this controlled process by epigenetic alterations, including imbalance of histone acetylation/histone deacetylation and DNA methylation/demethylation, may result in uncontrolled growth, formation of self-renewing malignant stem cells and eventually cancer. In view of this notion, several epigenetic modulators, in particular those with histone deacetylase inhibiting activity, are currently being tested in phase I and II clinical trials for their promising chemotherapeutic properties in cancer therapy. As chromatin modulation is also involved in regulation of differentiation, normal development, embryonic and adult stem cell functions and maintenance of their plasticity during embryonic organogenesis, the question can be raised whether predestined cell fate can be modified through epigenetic interference. And if so, could this strategy enforce adult stem cells to differentiate into different types of functional cells? In particular, functional hepatocytes seem important for preclinical toxicity screening of candidate drugs. This paper reviews the potential use and relevance of epigenetic modifiers, including inhibitors of histone deacetylases and DNA methyltransferases (1) to change cell fate and 'trans'differentiate normal adult stem cells into hepatocyte-like cells and (2) to cure disorders, caused by uncontrolled growth of malignant stem cells.

Histone deacetylase inhibitors: signalling towards p21cip1/waf1

Chromatin-modifying enzymes such as histone deacetylases (HDAC) facilitate a closed chromatin structure and hence transcriptional repression. HDAC are commonly affected in human cancer diseases. Thus, inhibition of HDAC represents a novel therapeutic approach. Several studies have shown that HDAC inhibitors strongly activate the expression of the cyclin-dependent kinase inhibitor p21(cip1/waf1) through (i) enhanced histone acetylation around the p21(cip1/waf1) promoter and (ii) the Sp1 sites on the p21(cip1/waf1) promoter releasing the repressor HDAC1 from its binding. p21(cip1/waf1) expression is regulated in a p53-dependent and p53-independent manner. The decision if p21(cip1/waf1) up-regulation results in cell cycle arrest or apoptosis, decides about the therapeutic efficacy of an anti-cancer treatment with HDAC inhibitors.

Trichostatin A, an inhibitor of histone deacetylase, inhibits smooth muscle cell proliferation via induction of p21(WAF1)

The proliferation of vascular smooth muscle cells (VSMCs) can contribute to a variety of pathological states, including atherosclerosis and post-angioplasty restenosis. The p21(WAF1) cyclin-dependent kinase inhibitor regulates cell-cycle progression, senescence, and differentiation in injured blood vessels. Histone deacetylase (HDAC) inhibitors have shown utility in controlling proliferation in a wide range of tumor cell lines, possibly by inducing the expression of p21(WAF1). Our goal was to investigate the effect of trichostatin A (TSA), a specific and potent HDAC inhibitor, on the proliferation of vascular smooth muscle cells (VSMCs) isolated from rat thoracic aorta. TSA suppressed the HDAC activity of VSMCs in a dose-dependent manner and inhibited VSMC proliferation as demonstrated by cell number counting and the degree of [3H] thymidine incorporation. Further, TSA reduced the phosphorylation of Rb protein, a regulator of cell-cycle progression. TSA treatment also induced the expression of p21(WAF1) but not of p16(INK4), p27(KIP1) or p53. Finally, TSA inhibited HDAC activity of VSMCs from p21(WAF1) knock-out mice but had no effect on VSMC proliferation in these animals. In conclusion, TSA inhibits VSMC proliferation via the induction of p21(WAF1) expression and subsequent cell-cycle arrest with reduction of the phosphorylation of Rb protein at the G1-S phase.

Epigenetic regulation of immune escape genes in cancer

According to the concept of immune surveillance, the appearance of a tumor indicates that it has earlier evaded host defenses and subsequently must have escaped immunity to evolve into a full-blown cancer. Tumor escape mechanisms have focused mainly on mutations of immune and apoptotic pathway genes. However, data obtained over the past few years suggest that epigenetic silencing in cancer may be as frequent a cause of gene inactivation as are mutations. Here, we discuss the evidence that tumor immune evasion is mediated by non-mutational epigenetic events involving chromatin and that epigenetics collaborates with mutations in determining tumor progression. Since epigenetic changes are potentially reversible, the relative contribution of mutations and epigenetics, to the gene defects in any given tumor, may be a factor in determining the efficacy of treatments. We review new developments in basic chromatin mechanisms and in this context describe the rationale for the current use of epigenetic agents in cancer therapy and for a novel epigenetically generated tumor vaccine model. We emphasize that epigenetic cancer treatments are currently a 'blunt-sword' and suggest future directions for designing chromatin-based programs of potential value in the diagnosis and treatment of cancer.

Acetylation of p53 at lysine 373/382 by the histone deacetylase inhibitor depsipeptide induces expression of p21(Waf1/Cip1)

Generally, histone deacetylase (HDAC) inhibitor-induced p21(Waf1/Cip1) expression is thought to be p53 independent. Here we found that an inhibitor of HDAC, depsipeptide (FR901228), but not trichostatin A (TSA), induces p21(Waf1/Cip1) expression through both p53 and Sp1/Sp3 pathways in A549 cells (which retain wild-type p53). This is demonstrated by measuring relative luciferase activities of p21 promoter constructs with p53 or Sp1 binding site mutagenesis and was further confirmed by transfection of wild-type p53 into H1299 cells (p53 null). That p53 was acetylated after depsipeptide treatment was tested by sequential immunoprecipitation/Western immunoblot analysis with anti-acetylated lysines and anti-p53 antibodies. The acetylated p53 has a longer half-life due to a significant decrease in p53 ubiquitination. Further study using site-specific antiacetyllysine antibodies and transfection of mutated p53 vectors (K319/K320/K321R mutated and K373R/K382R mutations) into H1299 cells revealed that depsipeptide specifically induces p53 acetylation at K373/K382, but not at K320. As assayed by coimmunoprecipitation, the K373/K382 acetylation is accompanied by a recruitment of p300, but neither CREB-binding protein (CBP) nor p300/CBP-associated factor (PCAF), to the p53 C terminus. Furthermore, activity associated with the binding of the acetylated p53 at K373/K382 to the p21 promoter as well as p21(Waf1/Cip1) expression is significantly increased after depsipeptide treatment, as tested by chromatin immunoprecipitations and Western blotting, respectively. In addition, p53 acetylation at K373/K382 is confirmed to be required for recruitment of p300 to the p21 promoter, and the depsipeptide-induced p53 acetylation at K373/K382 is unlikely to be dependent on p53 phosphorylation at Ser15, Ser20, and Ser392 sites. Our data suggest that p53 acetylation at K373/K382 plays an important role in depsipeptide-induced p21(Waf1/Cip1) expression.

HDAC inhibitor treatment of hepatoma cells induces both TRAIL-independent apoptosis and restoration of sensitivity to TRAIL

Hepatocellular carcinoma (HCC) displays a striking resistance to chemotherapeutic drugs or innovative tumor cell apoptosis-inducing agents such as tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Recently, we found 2 histone deacetylase inhibitors (HDAC-I), valproic acid and ITF2357, exhibiting inherent therapeutic activity against HCC. In TRAIL-sensitive cancer cells, the mechanism of HDAC-I-induced cell death has been identified to be TRAIL-dependent by inducing apoptosis in an autocrine fashion. In contrast, in HCC-derived cells, a prototype of TRAIL-resistant tumor cells, we found a HDAC-I-mediated apoptosis that works independently of TRAIL and upregulation of death receptors or their cognate ligands. Interestingly, TRAIL resistance could be overcome by a combinatorial application of HDAC-I and TRAIL, increasing the fraction of apoptotic cells two- to threefold compared with HDAC-I treatment alone, whereas any premature HDAC-I withdrawal rapidly restored TRAIL resistance. Furthermore, a tumor cell-specific downregulation of the FLICE inhibitory protein (FLIP) was observed, constituting a new mechanism of TRAIL sensitivity restoration by HDAC-I. In contrast, FLIP levels in primary human hepatocytes (PHH) from different donors were upregulated by HDAC-I. Importantly, combination HDAC-I/TRAIL treatment did not induce any cytotoxicity in nonmalignant PHH. In conclusion, HDAC-I compounds, exhibiting a favorable in vivo profile and inherent activity against HCC cells, are able to selectively overcome the resistance of HCC cells toward TRAIL. Specific upregulation of intracellular FLIP protein levels in nonmalignant hepatocytes could enhance the therapeutic window for clinical applications of TRAIL, opening up a highly specific new treatment option for advanced HCC.

Sodium butyrate induces apoptosis and cell cycle arrest in primary effusion lymphoma cells independently of oxidative stress and p21(CIP1/WAF1) induction

Primary effusion lymphoma, a peculiar type of B cell non-Hodgkin lymphoma, preferentially develops in immunodeficient individuals and its pathogenesis is closely linked with human herpesvirus 8 (HHV-8). HHV-8 is present primarily persistence in primary effusion lymphoma cells, and the lytic cycle of HHV-8 can be induced by sodium butyrate (NaB) treatment. HHV-8 gene expression is affected by NaB in BCBL-1 cells, but the cellular response of BCBL-1 cells upon NaB treatment has not been investigated to date. Using BCBL-1 cells, a HHV-8 harboring cell line, we demonstrated that sodium butyrate could induce the reactive oxygen species generation, apoptosis and cell cycle arrest in BCBL-1 cells. The sodium butyrate-induce cell cycle arrest was associated with the decrease of Cdc2, Cdk4 and cyclin A in BCBL-1 cells without altering the protein levels of p21(CIP1/WAF1). The apoptosis induced by sodium butyrate in BCBL-1 cells was independent of oxidative stress.

Rational development of histone deacetylase inhibitors as anticancer agents: a review

The epigenome is defined by DNA methylation patterns and the associated post-translational modifications of histones. This histone code determines the expression status of individual genes dependent upon their localization on the chromatin. The histone deacetylases (HDACs) play a major role in keeping the balance between the acetylated and deacetylated states of chromatin and eventually regulate gene expression. Recent developments in understanding the cancer cell cycle, specifically the interplay with chromatin control, are providing opportunities for developing mechanism-based therapeutic drugs. Inhibitors of HDACs are under considerable exploration, in part because of their potential roles in reversing the silenced genes in transformed tumor cells by modulating transcriptional processes. This review is an effort to summarize the nonclinical and clinical status of HDAC inhibitors currently under development in anticancer therapy.

Histone deacetylases as transcriptional activators? Role reversal in inducible gene regulation

Histone deacetylation enzymes have often been associated with the suppression of eukaryotic gene transcription. In contrast, recent studies of inducible gene regulation indicate that protein deacetylation can also be required as a transcriptional activation signal. The concept of protein deacetylation as a requirement for transcription activation seems to contradict earlier conclusions about the function of deacetylation in gene suppression. However, in the context of a more global interpretation, these opposing effects of deacetylation imply its dynamic role in the overall control of gene expression. The exact requirement for deacetylation differs among promoters, depending on their specific architecture and regulation scenario.

Lost in transcription: p21 repression, mechanisms, and consequences

The cyclin-dependent kinase inhibitor p21WAF1/CIP1 is a major player in cell cycle control and it is mainly regulated at the transcriptional level. Whereas induction of p21 predominantly leads to cell cycle arrest, repression of p21 may have a variety of outcomes depending on the context. In this review, we concentrate on transcriptional repression of p21 by cellular and viral factors, and delve in detail into its possible biological implications and its role in cancer. It seems that the major mode of p21 transcriptional repression by negative regulators is the interference with positive transcription factors without direct binding to the p21 promoter. Specifically, the negative factors may either inhibit binding of positive regulators to the promoter or hinder their transcriptional activity. The ability of p21 to inhibit proliferation may contribute to its tumor suppressor function. Because of this, it is not surprising that a number of oncogenes repress p21 to promote cell growth and tumorigenesis. However, p21 is also an inhibitor of apoptosis and p21 repression may also have an anticancer effect. For example, c-Myc and chemical p21 inhibitors, which repress p21, sensitize tumor cells to apoptosis by anticancer drugs. Further identification of factors that repress p21 is likely to contribute to the better understanding of its role in cancer.