The human histone deacetylase family

Deletion of histone deacetylase 3 reveals critical roles in S phase progression and DNA damage control

Histone deacetylases (HDACs) are enzymes that modify key residues in histones to regulate chromatin architecture, and they play a vital role in cell survival, cell-cycle progression, and tumorigenesis. To understand the function of Hdac3, a critical component of the N-CoR/SMRT repression complex, a conditional allele of Hdac3 was engineered. Cre-recombinase-mediated inactivation of Hdac3 led to a delay in cell-cycle progression, cell-cycle-dependent DNA damage, and apoptosis in mouse embryonic fibroblasts (MEFs). While no overt defects in mitosis were observed in Hdac3-/- MEFs, including normal H3Ser10 phosphorylation, DNA damage was observed in Hdac3-/- interphase cells, which appears to be associated with defective DNA double-strand break repair. Moreover, we noted that Hdac3-/- MEFs were protected from DNA damage when quiescent, which may provide a mechanistic basis for the action of HDAC inhibitors on cycling tumor cells.

A shifting paradigm: histone deacetylases and transcriptional activation

Transcriptional repression and silencing have been strongly associated with hypoacetylation of histones. Accordingly, histone deacetylases, which remove acetyl groups from histones, have been shown to participate in mechanisms of transcriptional repression. Therefore, current models of the role of acetylation in transcriptional regulation focus on the acetylation status of histones and designate histone acetyltransferases, which add acetyl groups to histones, as transcriptional coactivators and histone deacetylases as corepressors. In recent years, an accumulation of studies have shown that these enzymes also target non-histone proteins and that histone deacetylases have clear roles as coactivators at a variety of genes, some of which are key regulators of cell growth and survival. This review summarizes the evidence for histone deacetylases as coactivators and provides models of coactivation mechanisms, some of which integrate roles of acetylated histones and non-histone proteins in transcription.

Nuclear histone deacetylases are not required for global histone deacetylation during meiotic maturation in porcine oocytes

Histone acetylation plays an important role in the regulation of chromatin structure and gene function. In mammalian oocytes, histones H3 and H4 are highly acetylated during the germinal vesicle (GV) stage, and global histone deacetylation takes place via a histone deacetylase (HDAC)-dependent mechanism after GV breakdown (GVBD). The presence of HDACs in the GVs of mammalian oocytes in spite of the high acetylation states of nuclear histones indicates that the HDACs in the nucleus are inactive but become activated after GVBD. However, the fluctuation pattern, the localization of HDAC activity during meiotic maturation and, moreover, the responsibility of nuclear HDACs for global histone deacetylation are still unknown. Here, we demonstrated using porcine oocytes that total HDAC activity was maintained throughout meiotic maturation, and high HDAC activity was observed in both the nucleus and the cytoplasm at the GV stage. The experiments with valproic acid (VPA), a specific class I HDAC inhibitor, revealed that the HDACs in GVs were class I, and those in the cytoplasm were other than class I. Interestingly, VPA had no effect on global histone deacetylation after GVBD, indicating that nuclear HDACs were not required for global histone deacetylation. To confirm this possibility, we removed the nuclei from immature oocytes, injected somatic cell nuclei into the enucleated oocytes, and showed that injected somatic cell nuclei were dramatically deacetylated after nuclear envelope breakdown. These results revealed that nuclear contents, including class I HDACs, are not required for the global histone deacetylation during meiosis, and that cytoplasmic HDACs other than class I are responsible for this process.

Cholesterylbutyrate solid lipid nanoparticles as a butyric acid prodrug

Cholesterylbutyrate (Chol-but) was chosen as a prodrug of butyric acid. Butyrate is not often used in vivo because its half-life is very short and therefore too large amounts of the drug would be necessary for its efficacy. In the last few years butyric acid's anti-inflammatory properties and its inhibitory activity towards histone deacetylases have been widely studied, mainly in vitro. Solid Lipid Nanoparticles (SLNs), whose lipid matrix is Chol-but, were prepared to evaluate the delivery system of Chol-but as a prodrug and to test its efficacy in vitro and in vivo. Chol-but SLNs were prepared using the microemulsion method; their average diameter is on the order of 100-150 nm and their shape is spherical. The antineoplastic effects of Chol-but SLNs were assessed in vitro on different cancer cell lines and in vivo on a rat intracerebral glioma model. The anti-inflammatory activity was evaluated on adhesion of polymorphonuclear cells to vascular endothelial cells. In the review we will present data on Chol-but SLNs in vitro and in vivo experiments, discussing the possible utilisation of nanoparticles for the delivery of prodrugs for neoplastic and chronic inflammatory diseases.

Histone deacetylase inhibitors: mechanisms and clinical significance in cancer: HDAC inhibitor-induced apoptosis

Epigenic modifications, mainly DNA methylation and acetylation, are recognized as the main mechanisms contributing to the malignant phenotype. Acetylation and deacetylation are catalyzed by specific enzymes, histone acetyltransferases (HATs) and histone deacetylases (HDACs), respectively. While histones represent a primary target for the physiological function of HDACs, the antitumor effect of HDAC inhibitors might also be attributed to transcription-independent mechanisms by modulating the acetylation status of a series of non-histone proteins. HDAC inhibitors may act through the transcriptional reactivation of dormant tumor suppressor genes. They also modulate expression of several other genes related to cell cycle, apoptosis, and angiogenesis. Several HDAC inhibitors are currently in clinical trials both for solid and hematologic malignancies. Thus, HDAC inhibitors, in combination with DNA-demethylating agents, chemopreventive, or classical chemotherapeutic drugs, could be promising candidates for cancer therapy. Here, we review the molecular mechanisms and therapeutic potential of HDAC inhibitors for the treatment of cancer.

Biochemical characterization of Plasmodium falciparum Sir2, a NAD+-dependent deacetylase

In Plasmodium falciparum, the causative agent of cerebral malaria, silent information regulator 2 (Sir2) has been implicated in pathogenesis through its role in var gene silencing. P. falciparum Sir2 (PfSir2) in addition to the catalytic core, has a 13 residue N-terminal and 4 residue C-terminal extension over the shorter Archaeoglobus fulgidus Sir2. In this paper, we highlight our studies aimed at understanding the kinetic mechanism of PfSir2 and the role of N- and C-terminal extensions in protein function and oligomerization. Bisubstrate kinetic analysis showed that PfSir2 exhibits a rapid equilibrium ordered sequential mechanism, with peptide binding preceding NAD(+). This study also reports on surfactin as a novel Sir2 inhibitor exhibiting competitive inhibition with respect to NAD(+) and uncompetitive inhibition with acetylated peptide. This inhibition pattern with surfactin provides further support for ordered binding of substrates. Surfactin was also found to be a potent inhibitor of intra-erythrocytic growth of P. falciparum with 50% inhibitory concentration in the low micromolar range. PfSir2, like the yeast homologs (yHst2 and Sir2p), is a trimer in solution. However, dissociation of trimer to monomers in the presence of NAD(+) is characteristic of the parasite enzyme. Oligomerization studies on N- and/or C-terminal deletion constructs of PfSir2 highlight the role of C-terminus of the protein in mediating homotrimerization. N-terminal deletion resulted in reduced catalytic efficiency although substrate affinity was not altered in the constructs. Interestingly, deletion of both the ends relaxed NAD(+) specificity.

Histone Deacetylase 7 Silencing Alters Endothelial Cell Migration, a Key Step in Angiogenesis

Global inhibition of class I and II histone deacetylases (HDACs) impairs angiogenesis. Herein, we have undertaken the identification of the specific HDAC(s) with activity that is necessary for the development of blood vessels. Using small interfering RNAs, we observed that HDAC7 silencing in endothelial cells altered their morphology, their migration, and their capacity to form capillary tube-like structures in vitro but did not affect cell adhesion, proliferation, or apoptosis. Among several factors known to be involved in angiogenesis, platelet-derived growth factor-B ( PDGF-B ) and its receptor ( PDGFR -β) were the most upregulated genes following HDAC7 silencing. We demonstrated that their increased expression induced by HDAC7 silencing was partially responsible for the inhibition of endothelial cell migration. In addition, we have also shown that treatment of endothelial cells with phorbol 12-myristate 13-acetate resulted in the exportation of HDAC7 out of the nucleus through a protein kinase C/protein kinase D activation pathway and induced, similarly to HDAC7 silencing, an increase in PDGF-B expression, as well as a partial inhibition of endothelial cell migration. Collectively, these data identified HDAC7 as a key modulator of endothelial cell migration and hence angiogenesis, at least in part, by regulating PDGF-B/PDGFR-β gene expression. Because angiogenesis is required for tumor progression, HDAC7 may represent a rational target for therapeutic intervention against cancer.

Histone deacetylases: target enzymes for cancer therapy

Epigenic regulation of gene transcription has recently been the subject of a fast growing interest particularly in the field of cancer. Enzymatic acetylation and deacetylation of the epsilon-amino groups of lysine residues from nucleosomal histones, represents major molecular epigenic mechanisms controlling gene expression. Histone deacetylases (HDACs) and histone acetyl transferases (HAT) represent the two families of enzymes in charge of the control of the level of acetylation of the histone tails. By removing the acetyl groups that abrogate the positive charge of the lysine residues that maintain the histone tails attached to DNA, HDACs repress transcription. In mammals, these latter enzymes form three groups of related enzymes based on their sequence homology and are classified as HDACs I, II and III. Global inhibition of the HDACs I and II groups results in cell growth arrest and apoptosis of cancer cells and alters tumor growth in in vivo experimental models. Their surprisingly low general toxicity and their impressive efficiency in preclinical cancer models has led to consider HDAC inhibitors as very promising new anticancer pharmacological agents. In this review, we attempt to give a comprehensive overview of the role and the involvement of HDAC in carcinogenesis as well as the current progress on the development of HDAC general and specific inhibitors as new cancer therapies.

Complementary roles for histone deacetylases 1, 2, and 3 in differentiation of pluripotent stem cells

In eukaryotic cells, covalent modifications to core histones contribute to the establishment and maintenance of cellular phenotype via regulation of gene expression. Histone acetyltransferases (HATs) cooperate with histone deacetylases (HDACs) to establish and maintain specific patterns of histone acetylation. HDAC inhibitors can cause pluripotent stem cells to cease proliferating and enter terminal differentiation pathways in culture. To better define the roles of individual HDACs in stem cell differentiation, we have constructed "dominant-negative" stem cell lines expressing mutant, Flag-tagged HDACs with reduced enzymatic activity. Replacement of a single residue (His-->Ala) in the catalytic center reduced the activity of HDACs 1 and 2 by 80%, and abolished HDAC3 activity; the mutant HDACs were expressed at similar levels and in the same multiprotein complexes as wild-type HDACs. Hexamethylene bisacetamide-induced MEL cell differentiation was potentiated by the individual mutant HDACs, but only to 2%, versus 60% for an HDAC inhibitor, sodium butyrate, suggesting that inhibition of multiple HDACs is required for full potentiation. Cultured E14.5 cortical stem cells differentiate to neurons, astrocytes, and oligodendrocytes upon withdrawal of basic fibroblast growth factor. Transduction of stem cells with mutant HDACs 1, 2, or 3 shifted cell fate choice toward oligodendrocytes. Mutant HDAC2 also increased differentiation to astrocytes, while mutant HDAC1 reduced differentiation to neurons by 50%. These results indicate that HDAC activity inhibits differentiation to oligodendrocytes, and that HDAC2 activity specifically inhibits differentiation to astrocytes, while HDAC1 activity is required for differentiation to neurons.

HDAC10 promoter polymorphism associated with development of HCC among chronic HBV patients

Histone deacetylases (HDACs) are key enzymes responsible for the removal of acetyl groups from acetylated histone and non-histone proteins, and play important roles in various biological processes including transcription regulation and DNA repair. In this study, we identified 22 sequence variants by direct DNA sequencing in 24 individuals and five common variant were selected for genotyping in larger-scale subjects (n=1095). Statistical analysis revealed that HDAC10-589C>T was significantly associated with HCC occurrence among chronic HBV patients (OR=2.39, P(cor)=0.04) as well as HCC acceleration among chronic HBV patients (RH=1.97, Pcor=0.002). Functional assay also revealed that luciferase activity of "T" allele was significantly higher than that of "C" allele of HDAC10-589C>T (P=0.023). These results suggest that the "T" allele of HDAC10-589C>T affect on the increased transcription activity, and might accelerate HCC development through increased expression of HDAC10.

Gene profile analysis of osteoblast genes differentially regulated by histone deacetylase inhibitors

Background

Osteoblast differentiation requires the coordinated stepwise expression of multiple genes. Histone deacetylase inhibitors (HDIs) accelerate the osteoblast differentiation process by blocking the activity of histone deacetylases (HDACs), which alter gene expression by modifying chromatin structure. We previously demonstrated that HDIs and HDAC3 shRNAs accelerate matrix mineralization and the expression of osteoblast maturation genes (e.g. alkaline phosphatase, osteocalcin). Identifying other genes that are differentially regulated by HDIs might identify new pathways that contribute to osteoblast differentiation.

Results

To identify other osteoblast genes that are altered early by HDIs, we incubated MC3T3-E1 preosteoblasts with HDIs (trichostatin A, MS-275, or valproic acid) for 18 hours in osteogenic conditions. The promotion of osteoblast differentiation by HDIs in this experiment was confirmed by osteogenic assays. Gene expression profiles relative to vehicle-treated cells were assessed by microarray analysis with Affymetrix GeneChip 430 2.0 arrays. The regulation of several genes by HDIs in MC3T3-E1 cells and primary osteoblasts was verified by quantitative real-time PCR. Nine genes were differentially regulated by at least two-fold after exposure to each of the three HDIs and six were verified by PCR in osteoblasts. Four of the verified genes (solute carrier family 9 isoform 3 regulator 1 (Slc9a3r1), sorbitol dehydrogenase 1, a kinase anchor protein, and glutathione S-transferase alpha 4) were induced. Two genes (proteasome subunit, beta type 10 and adaptor-related protein complex AP-4 sigma 1) were suppressed. We also identified eight growth factors and growth factor receptor genes that are significantly altered by each of the HDIs, including Frizzled related proteins 1 and 4, which modulate the Wnt signaling pathway.

Conclusion

This study identifies osteoblast genes that are regulated early by HDIs and indicates pathways that might promote osteoblast maturation following HDI exposure. One gene whose upregulation following HDI treatment is consistent with this notion is Slc9a3r1. Also known as NHERF1, Slc9a3r1 is required for optimal bone density. Similarly, the regulation of Wnt receptor genes indicates that this crucial pathway in osteoblast development is also affected by HDIs. These data support the hypothesis that HDIs regulate the expression of genes that promote osteoblast differentiation and maturation.

HDAC3 is linked to cell cycle machinery in MiaPaCa2 cells by regulating transcription of skp2

OBJECTIVE

Histone deacetylases (HDACs) have been linked to cell cycle control in various models, involving regulation of the cyclin-dependent kinase inhibitor p27(Kip1).

RESULTS

Here, we demonstrate that HDAC inhibition by trichostatin A reduces S-phase kinase-associated protein 2 mRNA and protein abundance. Furthermore, in contrast to HDAC1, recruited to the skp2 promoter in the G(0) phase, HDAC3 is bound in early S phase. Activating function of HDAC3 towards the skp2 gene has been validated using RNA interference techniques. siRNAs, targeting HDAC3 specifically, reduced skp2 transcription.

CONCLUSION

These findings propose that the skp2 gene is a novel target of HDAC3, mediating cell cycle control and oncogenesis.

Histone deacetylase as therapeutic target in a rodent model of hemorrhagic shock: effect of different resuscitation strategies on lung and liver

BACKGROUND

DNA transcription is regulated in part by acetylation of nuclear histones, controlled by 2 groups of enzymes: histone deacetylases (HDAC) and histone acetyl transferases (HAT). We have shown previously that hemorrhage and resuscitation are associated with HDAC/HAT imbalance, which influences the acetylation status of cardiac histones. The goals of this study were to determine whether: (1) resuscitation after hemorrhage affects histone acetylation in a fluid- and organ-specific fashion; and (2) administration of HDAC inhibitors influences histone acetylation and subsequent gene expression.

METHODS

In the first experiment, rats (n = 6/group) were subjected to volume-controlled hemorrhage and resuscitated with: (1) racemic lactated Ringer's (DL-LR); (2) L-lactated Ringer's (L-LR); (3) 7.5% hypertonic saline (HTS); (4) ketone Ringer's (KR); or (5) pyruvate Ringer's (PR). Control groups included: (6) no hemorrhage (Sham); and (7) hemorrhage with no resuscitation (NR). In the second experiment (n = 5/group), 3 HDAC inhibitors, valproic acid (VPA), trichostatin A (TSA), and suberoylanilide hydroxamic acid (SAHA), were added to normal saline and used as fluid for resuscitation. At the end of resuscitation, lung and liver tissues were subjected to subcellular protein fractionation and Western blotting to analyze histone acetylation. In addition, cDNA microarrays and RT-PCR were used to measure expression of selected genes.

RESULTS

Hemorrhage did not change the level of histone acetylation in lungs, whereas resuscitation predominantly hyperacetylated histones. An analysis of histone acetylation on 10 lysine sites showed that L-LR, HTS, and KR resuscitation caused the largest number of changes (7, 6, and 6 respectively). SAHA hyperacetylated 7 sites in liver and affected expression of 57 genes (44 up, 13 down).

CONCLUSIONS

Resuscitation with various fluids, as well as infusion of pharmacologic HDAC inhibitors affects histone acetylation in a fluid- and organ-specific fashion, even when administered post-insult for a limited period of time. Uniquely affected genes are associated with metabolism, cellular growth, proliferation, differentiation, transformation, and cellular signaling.

Histone deacetylase inhibitors: biology and mechanism of action

Histone deacetylases (HDACs) and histone acetyltransferases are enzymes that regulate chromatin structure and function through the removal and addition, respectively, of the acetyl group from the lysine residues of core nucleosomal histones. This posttranslational modification of histones is an important process in the regulation of gene expression. Aberrant expression and recruitment and disrupted activities of HDACs and histone acetyltransferases have been found in malignant tissues, implicating their involvement in cancer. HDAC inhibitors (HDACIs) function through diverse mechanisms, including the promotion of cell cycle arrest and apoptosis and the inhibition of angiogenesis. Malignant cells appear more sensitive to the proapoptotic effects of HDACIs, underscoring the therapeutic potential of these agents. Multiple HDACIs are currently under investigation in clinical trials, including vorinostat (suberoylanilide hydroxamic acid), which was recently approved by the U.S. Food and Drug Administration for the treatment of cutaneous manifestations of cutaneous T-cell lymphoma in patients with progressive, persistent, or recurrent disease on or after 2 systemic therapies.

Effects of a novel histone deacetylase inhibitor, N-(2-aminophenyl) benzamide, on a reversible hypertrophy induced by isoproterenol in in situ rat hearts

The aim of the present study was performed to determine whether a novel histone deacetylase (HDAC) inhibitor, N-(2-aminophenyl)-4-{[benzyl(2-hydroxyethyl)amino]methyl} benzamide (K-183), prevents a reversible cardiac hypertrophy induced by isoproterenol and improves left ventricular (LV) dysfunction in rats. Either isoproterenol or vehicle was infused for 3 days by osmotic minipump. One hour prior to the implantation of isoproterenol, K-183 or trichostatin A (TSA) was injected twice a day for 3 days. We recorded continuous LV pressure-volume (P-V) loops of in situ hearts one hour after removal of the osmotic minipump. LV work capability (systolic P-V area at midrange LV volume: PVA(mLVV)) and hemodynamics were evaluated. K-183 per se induced neither cardiac hypertrophy nor collagen production. Although K-183 did not prevent the hypertrophy, where PVA(mLVV) remained decreased, K-183, differently from TSA, significantly attenuated the decrease of cardiac output and the increase of effective arterial elastance in the hypertrophied heart. These results indicate that the novel HDAC inhibitor K-183 has some beneficial effects on hemodynamics, although K-183 has no effects of anti-hypertrophic modalities.

Structural basis of inhibition of the human NAD+-dependent deacetylase SIRT5 by suramin

Sirtuins are NAD(+)-dependent protein deacetylases and are emerging as molecular targets for the development of pharmaceuticals to treat human metabolic and neurological diseases and cancer. To date, several sirtuin inhibitors and activators have been identified, but the structural mechanisms of how these compounds modulate sirtuin activity have not yet been determined. We identified suramin as a compound that binds to human SIRT5 and showed that it inhibits SIRT5 NAD(+)-dependent deacetylase activity with an IC(50) value of 22 microM. To provide insights into how sirtuin function is altered by inhibitors, we determined two crystal structures of SIRT5, one in complex with ADP-ribose, the other bound to suramin. Our structural studies provide a view of a synthetic inhibitory compound in a sirtuin active site revealing that suramin binds into the NAD(+), the product, and the substrate-binding site. Finally, our structures may enable the rational design of more potent inhibitors.

Inhibitors of histone deacetylases as potential therapeutic tools for high-risk embryonal tumors of the nervous system of childhood

The origin of malignant embryonal tumors is incompletely understood and certain risk groups remain difficult to treat. The epigenetic structure of DNA and its lesions play a role in the origin of these neoplasms. Manipulation of the epigenome may offer novel treatment options. The authors evaluated the cytotoxicity of histone deacetylase inhibitors (HDI) [MS-275, SAHA, TSA, M344, M360, D85, SW55, SW187 and valproic acid (VPA)] on 13 embryonal tumor cell lines [4 medulloblastomas, 5 neuroblastomas, 2 atypical teratoid/rhabdoid tumors (AT/RT), and 2 malignant rhabdoid tumors of the kidney (RTK)] in MTT assay. In addition, HDI effects on hyperacetylation, reexpression of growth regulatory genes and apoptosis were characterized by Western analysis, RT-PCR and annexin-V staining. All HDI inhibited cell proliferation in a time- and dose-dependent manner. VPA was least cytotoxic with GI50 values after 72 hr ranging from 53.6 to 332.9 microM, while TSA was most efficient with GI50 values after 72 hr ranging from 0.01 to 8.8 microM. M344 and M360 were also highly effective. Western blot revealed hyperacetylation of histone H4 after HDI treatment. Reactivation of several genes including the proapoptotic CASP8 was identified by RT-PCR. Annexin-V staining demonstrated a dose and time dependent induction of apoptosis. HDI inhibited the growth of medulloblastoma, neuroblastoma and rhabdoid tumors in vitro. Treatment with HDI induced the reactivation of growth regulatory genes and consequently apoptosis. Our results warrant further studies and may help in the design of new protocols geared at the treatment of high risk embryonal tumors.

Sirtuin 2, a mammalian homolog of yeast silent information regulator-2 longevity regulator, is an oligodendroglial protein that decelerates cell differentiation through deacetylating alpha-tubulin

Silent information regulator-2 (SIR2) proteins regulate lifespan of diverse organisms, but their distribution and roles in the CNS remain unclear. Here, we show that sirtuin 2 (SIRT2), a mammalian SIR2 homolog, is an oligodendroglial cytoplasmic protein and localized to the outer and juxtanodal loops in the myelin sheath. Among cytoplasmic proteins of OLN-93 oligodendrocytes, alpha-tubulin was the main substrate of SIRT2 deacetylase. In cultured primary oligodendrocyte precursors (OLPs), SIRT2 emergence accompanied elevated alpha-tubulin acetylation and OLP differentiation into the prematurity stage. Small interfering RNA knockdown of SIRT2 increased the alpha-tubulin acetylation, myelin basic protein expression, and cell arbor complexity of OLPs. SIRT2 overexpression had the opposite effects, and counteracted the cell arborization-promoting effect of overexpressed juxtanodin. SIRT2 mutation concomitantly reduced its deacetylase activity and its impeding effect on OLP arborization. These results demonstrated a counterbalancing role of SIRT2 against a facilitatory effect of tubulin acetylation on oligodendroglial differentiation. Selective SIRT2 availability to oligodendroglia may have important implications for myelinogenesis, myelin-axon interaction, and brain aging.

Histone deacetylase inhibitors for epigenetic therapy of cancer

Histone acetylation and histone deacetylation play key roles in the epigenetic regulation. Thus, inhibition of deacetylation controlled by histone deacetylases may result in chromatin remodeling, upregulation of key tumor repressor genes, differentiation or apoptosis. Therefore many naturally occurring and synthetic histone deacetylase inhibitors have been shown to display potent anticancer activities in preclinical studies. The exact mechanism by which histone deacetylases exert their effect, however, is still obscure; in any case it is more complicated than originally understood. Although several representatives of this novel class of therapeutic agents are currently at early stages of clinical development, rational design leading to highly selective histone deacetylase inhibitors against histone deacetylase isoforms will not only probably offer more potent anticancer drugs, but also critical insights into their mechanism of action.

IFI16 in human prostate cancer

Increased expression of IFI16 protein (encoded by the IFI16 gene) in normal human prostate epithelial cells is associated with cellular senescence-associated cell growth arrest. Consistent with a role for IFI16 protein in cellular senescence, the expression of IFI16 protein is either very low or not detectable in human prostate cancer cell lines. We now report that treatment of DU-145 and LNCaP prostate cancer cell lines with histone deacetylase inhibitor trichostatin A (TSA) or CGK1026 resulted in transcriptional activation of the IFI16 gene. The induction of IFI16 protein in LNCaP cells was dependent on the duration of TSA treatment. Furthermore, TSA treatment of LNCaP cells up-regulated the expression of Janus-activated kinase 1 protein kinase and modulated the transcription of certain IFN-activatable genes. However, overexpression of exogenous Janus-activated kinase 1 protein in LNCaP cells and treatment of cells with IFNs (alpha and gamma) did not increase the expression of IFI16. Instead, the transcriptional activation of IFI16 gene by TSA treatment of LNCaP cells was dependent on transcriptional activation by c-Jun/activator protein-1 transcription factor. Importantly, increased expression of IFI16 in LNCaP cells was associated with decreases in the expression of androgen receptor and apoptosis of cells. Conversely, knockdown of IFI16 expression in TSA-treated LNCaP cells increased androgen receptor protein levels with concomitant decreases in apoptosis. Together, our observations provide support for the idea that histone deacetylase-dependent transcriptional silencing of the IFI16 gene in prostate epithelial cells contributes to the development of prostate cancer.

Suberoylanilide hydroxamic acid, a histone deacetylase inhibitor: effects on gene expression and growth of glioma cells in vitro and in vivo

PURPOSE

Histone acetylation is one of the main mechanisms involved in regulation of gene expression. During carcinogenesis, tumor-suppressor genes can be silenced by aberrant histone deacetylation. This epigenetic modification has become an important target for tumor therapy. The histone deacetylation inhibitor, suberoylanilide hydroxamic acid (SAHA), can induce growth arrest in transformed cells. The aim of this study is to examine the effects of SAHA on gene expression and growth of glioblastoma multiforme (GBM) cells in vitro and in vivo.

EXPERIMENTAL DESIGN

The effect of SAHA on growth of GBM cell lines and explants was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide. Changes of the cell cycle and relative gene expression were detected by fluorescence-activated cell sorting, real-time reverse transcription-PCR, and Western blotting. After glioma cells were implanted in the brains of mice, the ability of SAHA to decrease tumor growth was studied.

RESULTS

Proliferation of GBM cell lines and explants were inhibited in vitro by SAHA (ED50, 2x10(-6) to 2x10(-5) mol/L, 5 days). SAHA exposure of human U87 and T98G glioma cell lines, DA66 and JM94 GBM explants, as well as a murine GL26 GBM cell line resulted in an increased accumulation of cells in G2-M of the cell cycle. Many proapoptotic, antiproliferative genes increased in their expression (DR5, TNFalpha, p21WAF1, p27KIP1), and many antiapoptotic, progrowth genes decreased in their levels (CDK2, CDK4, cyclin D1, cyclin D2) as measured by real-time reverse transcription-PCR and/or Western blot after these GBM cells were cultured with SAHA (2.5x10(-6) mol/L, 1 day). Chromatin immunoprecipitation assay found that acetylation of histone 3 on the p21(WAF1) promoter was markedly increased by SAHA. In vivo murine experiments suggested that SAHA (10 mg/kg, i.v., or 100 mg/kg, i.p.) could cross the blood-brain barrier as shown by prominent increased levels of acetyl-H3 and acetyl-H4 in the brain tissue. Furthermore, the drug significantly (P<0.05) inhibited the proliferation of the GL26 glioma cells growing in the brains of mice and increased their survival.

CONCLUSIONS

Taken together, SAHA can slow the growth of GBM in vitro and intracranially in vivo. SAHA may be a welcome addition for the treatment of this devastating disease.

Histone deacetylase inhibitors: insights into mechanisms of lethality

Histone deacetylases (HDACs) have recently emerged as an important target for therapeutic intervention in cancer and potentially other human diseases. By modulating the acetylation status of histones, histone deacetylase inhibitors (HDACIs) alter the transcription of genes involved in cell growth, maturation, survival and apoptosis, among other processes. Early clinical results suggest a potentially useful role for HDACIs in the treatment of certain forms of lymphoma (e.g., cutaneous T cell lymphoma) and acute leukaemia. An unresolved question is how HDACIs induce cell death in tumour cells. Recent studies suggest that acetylation of nonhistone proteins may play an important role in the biological effects of this class of compounds, and may explain lack of correlation between histone acetylation and induction of cell death by HDACIs in some circumstances. Recently, attention has focussed on the effects of HDACIs on disruption of co-repressor complexes, induction of oxidative injury, upregulation of the expression of death receptors, generation of lipid second messengers such as ceramide, interference with the function of chaperone proteins and modulation of the activity of NF-kappaB as critical determinants of lethality. Aside from providing critical insights into the mechanism of action of HDACIs in neoplastic disease, these findings may provide a foundation for the rational development of combination studies, involving HDACIs in combination with either conventional cytotoxic drugs as well as more novel targeted agents.

Assays for pharmacodynamic analysis of histone deacetylase inhibitors

Histone deacetylase inhibitors (HDACIs) are a promising new class of targeted anticancer drugs. The pharmacodynamic (PD) assessment of whether a drug has hit its target is critically important to the successful development of any molecular targeted therapy. In the case of HDACIs there are many issues to be considered in PD development and implementation. Although originally it was thought that measurement of core histone hyperacetylation in peripheral blood mononuclear cells might suffice as a PD marker, as the field is evolving it is becoming evident that other measures may be essential, and are likely to be tumour context specific. This paper provides an overview of the assays that have been performed thus far in HDACI clinical trials, with an analysis of relative strengths and weaknesses, and a delineation of the complexity of HDACI PD analysis. Consideration is given to where new approaches are needed and potential approaches for future monotherapy and combination therapy trials are suggested.

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.

Histone deacetylase inhibitor trichostatin A inhibits the growth of bladder cancer cells through induction of p21WAF1 and G1 cell cycle arrest

PURPOSE

To investigate whether Trichostatin A (TSA) possesses antitumor activity against human bladder cancer cells, and if any, its mechanism.

MATERIALS AND METHODS

A human bladder cancer cell line, BIU-87, was treated with different concentrations of TSA. After treatment, cell growth was measured by MTT assay. Cell apoptosis and cell cycle changes were examined by means of flow cytometry (FCM). Apoptosis was confirmed by apoptotic ladder formation assay. mRNA expression of p21WAF1 and p53 was assessed by differential reverse transcription-polymerase chain reaction.

RESULTS

Trichostatin A significantly inhibited the proliferation of bladder cancer cell at nanomolar concentrations in a time- and dose-dependent fashion. TSA treatment caused cell cycle arrest at the G1 phase and increased apoptotic cell death as shown by FCM and DNA fragmentation analysis, accompanied by increased p21WAF1 mRNA expression. In addition, TSA treatment did not alter p53 mRNA expression.

CONCLUSION

Our results indicate that TSA is able to inhibit bladder cancer cell growth in vitro, possibly through p21WAF1 mediated cell cycle arrest and apoptotic cell death. This study suggests that TSA may be a potential therapeutic agent for the treatment of bladder cancer.

Targeting histone deacetylase in cancer therapy

Histone deacetylase (HDAC) is recognized as one of the promising targets for cancer treatment as many HDAC inhibitors have entered clinical trials for both solid and liquid tumors. Nevertheless, the mechanisms underlying the antiproliferative effects of HDAC inhibitors remain elusive. Although they have been shown to regulate the transcription of a defined set of genes through chromatin remodeling, increasing evidence suggests that modifications of the epigenetic histone code may not be the primary mechanism for HDAC inhibitor-mediated growth inhibition and apoptosis in cancer cells. While histones still represent a primary target for the physiological function of HDACs, the antitumor effect of HDAC inhibitors might also be attributed to transcription-independent mechanisms by modulating the acetylation status of a series of nonhistone targets. Also noteworthy is the effect of HDAC inhibitors on Akt downregulation through the alteration of protein phosphatase 1 (PP1) complex formation. To provide an overview of the use of HDAC inhibitors in cancer treatment, this review addresses the following subjects: (1) the physiological relevance of HDAC-mediated acetylation of histone and nonhistone substrates, (2) the chemical biology of HDACs and development of a novel class of HDAC inhibitors, and (3) the protein acetylation-independent effect of HDAC inhibitors on the activation status of signaling kinases.

HDAC activity regulates entry of mesoderm cells into the cardiac muscle lineage

Class II histone deacetylases (HDAC4, HDAC5, HDAC7 and HDAC9) have been shown to interact with myocyte enhancer factors 2 (MEF2s) and play an important role in the repression of cardiac hypertrophy. We examined the role of HDACs during the differentiation of P19 embryonic carcinoma stem cells into cardiomyocytes. Treatment of aggregated P19 cells with the HDAC inhibitor trichostatin A induced the entry of mesodermal cells into the cardiac muscle lineage, shown by the upregulation of transcripts Nkx2-5, MEF2C, GATA4 and cardiac alpha-actin. Furthermore, the overexpression of HDAC4 inhibited cardiomyogenesis, shown by the downregulation of cardiac muscle gene expression. Class II HDAC activity is inhibited through phosphorylation by Ca2+/calmodulin-dependent kinase (CaMK). Expression of an activated CaMKIV in P19 cells upregulated the expression of Nkx2-5, GATA4 and MEF2C, enhanced cardiac muscle development, and activated a MEF2-responsive promoter. Moreover, inhibition of CaMK signaling downregulated GATA4 expression. Finally, P19 cells constitutively expressing a dominant-negative form of MEF2C, capable of binding class II HDACs, underwent cardiomyogenesis more efficiently than control cells, implying the relief of an inhibitor. Our results suggest that HDAC activity regulates the specification of mesoderm cells into cardiomyoblasts by inhibiting the expression of GATA4 and Nkx2-5 in a stem cell model system.

CRA-026440: a potent, broad-spectrum, hydroxamic histone deacetylase inhibitor with antiproliferative and antiangiogenic activity in vitro and in vivo

CRA-026440 is a novel, broad-spectrum, hydroxamic acid-based inhibitor of histone deacetylase (HDAC) that shows antitumor and antiangiogenic activities in vitro and in vivo preclinically. CRA-026440 inhibited pure recombinant isozymes HDAC1, HDAC2, HDAC3/SMRT, HDAC6, HDAC8, and HDAC10 in the nanomolar range. Treatment of cultured tumor cell lines grown in vitro with CRA-026440 resulted in the accumulation of acetylated histone and acetylated tubulin, leading to an inhibition of tumor cell growth and the induction of apoptosis. CRA-026440 inhibited ex vivo angiogenesis in a dose-dependent manner. CRA-026440 parenterally given to mice harboring HCT116 or U937 human tumor xenografts resulted in a statistically significant reduction in tumor growth. CRA-026440, when used in combination with Avastin, achieved greater preclinical efficacy in HCT 116 colorectal tumor model. Inhibition of tumor growth was accompanied by an increase in the acetylation of alpha-tubulin in peripheral blood mononuclear cells and an alteration in the expression of many genes in the tumors, including several involved in angiogenesis, apoptosis, and cell growth. These results reveal CRA-026440 to be a novel HDAC inhibitor with potent antitumor activity.

Class II HDACs mediate CaMK-dependent signaling to NRSF in ventricular myocytes

We recently reported that a transcriptional repressor, neuron-restrictive silencer factor (NRSF), represses expression of fetal cardiac genes, including atrial and brain natriuretic peptide (ANP and BNP), by recruiting class I histone deacetylase (HDAC) and that attenuation of NRSF-mediated repression contributes to the reactivation of fetal gene expression during cardiac hypertrophy. The molecular mechanism by which the activity of the NRSF-HDAC complex is inhibited in cardiac hypertrophy remains unresolved, however. In the present study, we show that class II HDACs (HDAC4 and 5), which are Ca/calmodulin-dependent kinase (CaMK)-responsive repressors of hypertrophic signaling, associate with NRSF and participate in NRSF-mediated repression. Blockade of the CaMK-class II HDAC signaling pathway using a CaMK-resistant HDAC5 mutant, a CaMK inhibitor (KN62) or a dominant-negative CaMK mutant inhibited ET-1-inducible ANP and BNP promoter activity, but that inhibitory effect was abolished by mutation of the neuron-restrictive silencer element (NRSE) within the ANP and BNP promoter. In addition, adenovirus-mediated expression of a dominant-negative NRSF mutant abolished the inhibitory effect of KN62 on ET-1-inducible endogenous ANP gene expression in ventricular myocytes. Finally, the interaction between NRSF and class II HDACs was decreased in both in vitro and in vivo models of cardiac hypertrophy. These findings show that ET-1-induced CaMK signaling disrupts class II HDAC-NRSF repressor complexes, thereby enabling activation of ANP and BNP gene transcription in ventricular myocytes, and shed light on a novel mechanism by which the fetal cardiac gene program is reactivated.

Valproate inhibition of histone deacetylase 2 affects differentiation and decreases proliferation of endometrial stromal sarcoma cells

Covalent modifications of histone proteins, in particular deacetylation of lysine residues, are important for the regulation of gene transcription both in normal and malignant cells. These processes are controlled by histone acetyltransferases and histone deacetylases (HDAC) and have up to now not been described in solid mesenchymal tumors. The present study shows differences in the HDAC1 and HDAC2 expression in endometrial stromal sarcomas (ESS) and a cognate cell line (ESS-1) compared with nonneoplastic endometrial stroma. We show for the first time that HDAC2 expression is consistently increased in ESS. In contrast, HDAC1 expression is generally lower than HDAC2 both in nonneoplastic stroma and in ESS, suggesting that these two proteins, although closely related, are regulated in different ways. In vitro experiments with an ESS cell line showed that valproate, an inhibitor of the class I HDACs, led to significant HDAC2 decrease and to cell differentiation. HDAC2 inhibition in ESS-1 cells caused significant changes in the cell cycle by inhibiting G1-S transition and influencing expression of p21WAF1 and cyclin D1. Moreover, in ESS-1 cells, increased expression of the p21WAF1 was associated with reduction of HDAC2 expression after transfection with small interfering RNA directed against HDAC2. Our results suggest that HDAC2 might be considered as potential drug target in the therapy of ESS and that HDAC inhibitors should be further evaluated in clinical trials in ESS.

Epigenetics--an epicenter of gene regulation: histones and histone-modifying enzymes

The treatment of cancer through the development of new therapies is one of the most important challenges of our time. The decoding of the human genome has yielded important insights into the molecular basis of physical disorders, and in most cases a connection between failures in specific genes and the resulting clinical symptoms can be made. The modulation of epigenetic mechanisms enables, by definition, the alteration of cellular phenotype without altering the genotype. The information content of a single gene can be crucial or harmful, but the prerequisite for a cellular effect is active gene transcription. To this end, epigenetic mechanisms play a very important role, and the transcription of a given gene is directly influenced by the modification pattern of the surrounding histone proteins as well as the methylation pattern of the DNA. These processes are effected by different enzymes which can be directly influenced through the development of specific modulators. Of course, all genetic information is written as a four-character code in DNA. However, epigenetics describes the art of reading between the lines.

HDAC3 is crucial in shear- and VEGF-induced stem cell differentiation toward endothelial cells

Reendothelialization involves endothelial progenitor cell (EPC) homing, proliferation, and differentiation, which may be influenced by fluid shear stress and local flow pattern. This study aims to elucidate the role of laminar flow on embryonic stem (ES) cell differentiation and the underlying mechanism. We demonstrated that laminar flow enhanced ES cell–derived progenitor cell proliferation and differentiation into endothelial cells (ECs). Laminar flow stabilized and activated histone deacetylase 3 (HDAC3) through the Flk-1–PI3K–Akt pathway, which in turn deacetylated p53, leading to p21 activation. A similar signal pathway was detected in vascular endothelial growth factor–induced EC differentiation. HDAC3 and p21 were detected in blood vessels during embryogenesis. Local transfer of ES cell–derived EPC incorporated into injured femoral artery and reduced neointima formation in a mouse model. These data suggest that shear stress is a key regulator for stem cell differentiation into EC, especially in EPC differentiation, which can be used for vascular repair, and that the Flk-1–PI3K–Akt–HDAC3–p53–p21 pathway is crucial in such a process.

Dexamethasone-induced protein degradation in cultured myotubes is p300/HAT dependent

Muscle proteolysis during sepsis and other catabolic conditions is, at least in part, regulated by glucocorticoids. Dexamethasone-treated myotubes are a commonly used in vitro model of muscle wasting. We reported recently that treatment of cultured L6 myotubes with dexamethasone resulted in increased gene and protein expression of the nuclear cofactor p300 but it is not known whether glucocorticoids upregulate p300 histone acetyl transferase (HAT) activity in muscle and whether p300/HAT activity regulates glucocorticoid-induced muscle proteolysis. Here, we found that treatment of cultured L6 myotubes with dexamethasone resulted in increased nuclear p300/HAT activity. Treatment of myotubes with p300 siRNA or transfection of muscle cells with a plasmid expressing p300 that was mutated in its HAT activity domain blocked the dexamethasone-induced increase in protein degradation, supporting a role of p300/HAT in glucocorticoid-induced muscle proteolysis. In addition to increased HAT activity, treatment of the myotubes with dexamethasone resulted in reduced nuclear expression and activity of histone deacetylases (HDACs) 3 and 6. When myotubes were treated with the HDAC inhibitor trichostatin A, protein degradation increased to the same degree as in dexamethasone-treated myotubes. The results suggest that glucocorticoids increase HAT and decrease HDAC activities in muscle, changes that both favor hyperacetylation. The results also provide evidence that dexamethasone-induced protein degradation in cultured myotubes is, at least in part, regulated by p300/HAT activity.

ATM regulates ionizing radiation-induced disruption of HDAC1:PP1:Rb complexes

Ionizing radiation elicits signaling events that coordinate DNA repair and interruption of cell cycle progression. We previously demonstrated that ionizing radiation (IR) of cells activates nuclear protein phosphatase-1 (PP1) by promoting dephosphorylation of Thr320, an inhibitory site in the enzyme and that the ATM kinase is required for this response. We sought to identify potential targets of IR-activated PP1. Untreated and IR-treated Jurkat cells were labeled with (32)P orthophosphate, and nuclear extracts were subjected to microcystin affinity chromatography to recover phosphatase complexes that were analyzed by 2D-PAGE and mass spectrometry. Several proteins associated with protein phosphatases demonstrated a significant decrease in (32)P intensity following IR, and one of these was identified as HDAC1. Co-immunoprecipitation revealed complexes containing PP1 with HDAC1 and Rb in cell extracts. In response to IR, there was an ATM-dependent activation of PP1, dephosphorylation of HDAC1, dissociation of HDAC1-PP1-Rb complexes and increased HDAC1 activity. These results suggest that IR regulates HDAC1 phosphorylation and activity through ATM-dependent activation of PP1.

Restoration of tamoxifen sensitivity in estrogen receptor-negative breast cancer cells: tamoxifen-bound reactivated ER recruits distinctive corepressor complexes

Breast tumors expressing estrogen receptor-alpha (ER) respond well to therapeutic strategies using selective ER modulators, such as tamoxifen. However, approximately 30% of invasive breast cancers are hormone independent because they lack ER expression due to hypermethylation of ER promoter. Treatment of ER-negative breast cancer cells with demethylating agents [5-aza-2'-deoxycytidine (5-aza-dC)] and histone deacetylase (HDAC) inhibitors (trichostatin A) leads to expression of ER mRNA and functional protein. Here, we examined whether epigenetically reactivated ER is a target for tamoxifen therapy. Following treatment with trichostatin A and 5-aza-dC, the formerly unresponsive ER-negative MDA-MB-231 breast cancer cells became responsive to tamoxifen. Tamoxifen-mediated inhibition of cell growth in these cells is mediated at least in part by the tamoxifen-bound ER. Tamoxifen-bound reactivated ER induces transcriptional repression at estrogen-responsive genes by ordered recruitment of multiple distinct chromatin-modifying complexes. Using chromatin immunoprecipitation, we show recruitment of two different corepressor complexes to ER-responsive promoters in a mutually exclusive and sequential manner: the nuclear receptor corepressor-HDAC3 complex followed by nucleosome remodeling and histone deacetylation complex. The mechanistic insight provided by this study might help in designing therapeutic strategies directed toward epigenetic mechanisms in the prevention or treatment of breast cancer.

Neuronal SIRT1 Activation as a Novel Mechanism Underlying the Prevention of Alzheimer Disease Amyloid Neuropathology by Calorie Restriction

Nicotinamide adenine dinucleotide (NAD)+-dependent sirtuins have been identified to be key regulators in the lifespan extending effects of calorie restriction (CR) in a number of species. In this study we report for the first time that promotion of the NAD+-dependent sirtuin, SIRT1-mediated deacetylase activity, may be a mechanism by which CR influences Alzheimer disease (AD)-type amyloid neuropathology. Most importantly, we report that the predicted attenuation of beta-amyloid content in the brain during CR can be reproduced in mouse neurons in vitro by manipulating cellular SIRT1 expression/activity through mechanisms involving the regulation of the serine/threonine Rho kinase ROCK1, known in part for its role in the inhibition of the non-amyloidogenic alpha-secretase processing of the amyloid precursor protein. Conversely, we found that the expression of constitutively active ROCK1 in vitro cultures significantly prevented SIRT1-mediated response, suggesting that alpha-secretase activity is required for SIRT1-mediated prevention of AD-type amyloid neuropathology. Consistently we found that the expression of exogenous human (h) SIRT1 in the brain of hSIRT1 transgenics also resulted in decreased ROCK1 expression and elevated alpha-secretase activity in vivo. These results demonstrate for the first time a role for SIRT1 activation in the brain as a novel mechanism through which CR may influence AD amyloid neuropathology. The study provides a potentially novel pharmacological strategy for AD prevention and/or treatment.

Histone deacetylase inhibitors induce antigen specific anergy in lymphocytes: a comparative study

Induction of immune tolerance to transplanted tissue continues to be a challenge for organ transplantation. In the present study, six widely used histone deacetylase inhibitors (HDAI), sodium butyrate (n-butyrate), Trichostatin A, Oxamflatin, Scriptaid, HDAC I and HDAC III, were examined for ability to induce antigen-specific immune anergy in cloned and naïve murine CD4(+) T cells. When first compared for their ability to inhibit histone deacetylation Trichostatin A was found to be 10 times more potent than HDAC III, Oxamflatin and Scriptaid and 10(4) times more potent than n-butyrate. When we compared ability to inhibit CD4(+) T cell proliferation in response to IL-2 stimulation, Trichostatin A was the most potent with 100% inhibition using 100 nM Trichostatin A, while 1 muM of HDAC III, Oxamflatin and Scriptaid and 1 mM of n-butyrate were required for this effect. When the tolerogenic activity of Trichostatin A, Scriptaid and n-butyrate were compared using cloned Th1 cells specific for keyhole limpet hemocyanin (KLH), all three HDAI were effective, but Trichostatin A was again the most potent. Finally, Trichostatin A (0.05 mM) was shown to induce anergy in OT-II ovalbumin-specific naïve CD4(+) T-cells. We concluded that Trichostatin A was the most potent HDAI with regard to inhibition of histone deacetylation and the ability to induce antigen-specific anergy in both cloned and naïve CD4(+) T cells. These results will guide future studies examining HDAIs for ability to induce clinical tolerance in organ transplantation.

Curcumin-induced histone hypoacetylation enhances caspase-3-dependent glioma cell death and neurogenesis of neural progenitor cells

Acetylation of histones and nonhistone proteins is an important post-translational modification involved in the regulation of gene expression in mammalian cells. Dysfunction of histone acetyltransferase (HAT) is often associated with the manifestation of several diseases. In this report, HATs are new targets for the development of therapeutics. Our studies first proved that curcumin induces histone hypoacetylation in brain cancer cells and finally induces apoptotic cell death through a (PARP)- and caspase 3-mediated manner. In addition, curcumin induces recontrolling of neural stem cell fates. It induces effective neurogenesis, synaptogenesis, and migration of neural progenitor cells in vitro in brain-derived adult neural stem cells. We also confirmed the neurogenic effect of curcumin in our in vivo experiments. Curcumin actively suppressed differentiation in astrocytes while promoting differentiation into the neurons associated with decrease of histone H3 and H4 acetylation. We suggest that histone hypoacetylation plays an important role in determine stem cell fate through controlling the simultaneous expression of many genes. Thus, the present finding that curcumin, a nontoxic dietary compound, is a histone acetyltransferase inhibitor would supply a new window to understand further the molecular mechanism of histone acetylase inhibitors (HAI) in cancer and neural stem cells and provide a new target molecule for treating central nervous system disorders.

Histone deacetylase inhibitor-mediated radiosensitization of human cancer cells: class differences and the potential influence of p53

Histone deacetylase inhibitors (HDI) are emerging as potentially useful components of the anticancer armamentarium and as useful tools to dissect mechanistic pathways. HDIs that globally inhibit histone deacetylases (HDAC) have radiosensitizing effects, but the relative contribution of specific HDAC classes remains unclear. Newly characterized HDIs are now available that preferentially inhibit specific HDAC classes, including SK7041 (inhibits class I HDACs) and splitomicin (inhibits class III HDACs). We investigated in human cancer cells the relative radiosensitizations that result from blocking specific HDAC classes. We found that trichostatin A (TSA; inhibitor of both class I and II HDACs) was the most effective radiosensitizer, followed by the class I inhibitor SK7041, whereas splitomicin (inhibitor of class III) had least effect. Interestingly, radiosensitization by TSA in cell lines expressing p53 was more pronounced than in isogenic lines lacking p53. Radiosensitization of cells expressing p53 by TSA was reduced by pifithrin-alpha, a small-molecule inhibitor of p53. In contrast, the radiosensitization by TSA of cells expressing low levels of p53 was enhanced by transfection of wild-type p53-expressing vector or pretreatment with leptomycin B, an inhibitor of nuclear export that increased intracellular levels of p53. These effects on radiosensitization were respectively muted or not seen in cells treated with SK7041 or splitomicin. To our knowledge, this may be among the first systematic investigations of the comparative anticancer effects of inhibiting specific classes of HDACs, with results suggesting differences in the degrees of radiosensitization, which in some cell lines may be influenced by p53 expression.

Sir2 protein deacetylases: evidence for chemical intermediates and functions of a conserved histidine

Sir2 NAD+-dependent protein deacetylases are implicated in a variety of cellular processes such as apoptosis, gene silencing, life-span regulation, and fatty acid metabolism. Despite this, there have been relatively few investigations into the detailed chemical mechanism. Sir2 proteins (sirtuins) catalyze the chemical conversion of NAD+ and acetylated lysine to nicotinamide, deacetylated lysine, and 2'-O-acetyl-ADP-ribose (OAADPr). In this study, Sir2-catalyzed reactions are shown to transfer an 18O label from the peptide acetyl group to the ribose 1'-position of OAADPr, providing direct evidence for the formation of a covalent alpha-1'-O-alkylamidate, whose existence is further supported by the observed methanolysis of the alpha-1'-O-alkylamidate intermediate to yield beta-1'-O-methyl-ADP-ribose in a Sir2 histidine-to-alanine mutant. This conserved histidine (His-135 in HST2) activates the ribose 2'-hydroxyl for attack on the alpha-1'-O-alkylamidate. The histidine mutant is stalled at the intermediate, allowing water and other alcohols to compete kinetically with the attacking 2'-hydroxyl. Measurement of the pH dependence of kcat and kcat/Km values for both wild-type and histidine-to-alanine mutant enzymes confirms roles of this residue in NAD+ binding and in general-base activation of the 2'-hydroxyl. Also, transfer of an 18O label from water to the carbonyl oxygen of the acetyl group in OAADPr is consistent with water addition to the proposed 1',2'-cyclic intermediate formed after 2'-hydroxyl attack on the alpha-1'-O-alkylamidate. The effect of pH and of solvent viscosity on the kcat values suggests that final product release is rate-limiting in the wild-type enzyme. Implications of this new evidence on the mechanisms of deacetylation and possible ADP-ribosylation catalyzed by Sir2 deacetylases are discussed.

Acetylation of human 8-oxoguanine-DNA glycosylase by p300 and its role in 8-oxoguanine repair in vivo

The human 8-oxoguanine-DNA glycosylase 1 (OGG1) is the major DNA glycosylase responsible for repair of 7,8-dihydro-8-oxoguanine (8-oxoG) and ring-opened fapyguanine, critical mutagenic DNA lesions that are induced by reactive oxygen species. Here we show that OGG1 is acetylated by p300 in vivo predominantly at Lys338/Lys341. About 20% of OGG1 is present in acetylated form in HeLa cells. Acetylation significantly increases OGG1's activity in vitro in the presence of AP-endonuclease by reducing its affinity for the abasic (AP) site product. The enhanced rate of repair of 8-oxoG in the genome by wild-type OGG1 but not the K338R/K341R mutant, ectopically expressed in oxidatively stressed OGG1-null mouse embryonic fibroblasts, suggests that acetylation increases OGG1 activity in vivo. At the same time, acetylation of OGG1 was increased by about 2.5-fold after oxidative stress with no change at the polypeptide level. OGG1 interacts with class I histone deacetylases, which may be responsible for its deacetylation. Based on these results, we propose a novel regulatory function of OGG1 acetylation in repair of its substrates in oxidatively stressed cells.

Acetylation of estrogen receptor alpha by p300 at lysines 266 and 268 enhances the deoxyribonucleic acid binding and transactivation activities of the receptor

Using a variety of biochemical and cell-based approaches, we show that estrogen receptor alpha (ERalpha) is acetylated by the p300 acetylase in a ligand- and steroid receptor coactivator-dependent manner. Using mutagenesis and mass spectrometry, we identified two conserved lysine residues in ERalpha (Lys266 and Lys268) that are the primary targets of p300-mediated acetylation. These residues are acetylated in cells, as determined by immunoprecipitation-Western blotting experiments using an antibody that specifically recognizes ERalpha acetylated at Lys266 and Lys268. The acetylation of ERalpha by p300 is reversed by native cellular deacetylases, including trichostatin A-sensitive enzymes (i.e. class I and II deacetylases) and nicotinamide adenine dinucleotide-dependent/nicotinamide-sensitive enzymes (i.e. class III deacetylases, such as sirtuin 1). Acetylation at Lys266 and Lys268, or substitution of the same residues with glutamine (i.e. K266/268Q), a residue that mimics acetylated lysine, enhances the DNA binding activity of ERalpha in EMSAs. Likewise, substitution of Lys266 and Lys268 with glutamine enhances the ligand-dependent activity of ERalpha in a cell-based reporter gene assay. Collectively, our results implicate acetylation as a modulator of the ligand-dependent gene regulatory activity of ERalpha. Such regulation is likely to play a role in estrogen-dependent signaling outcomes in a variety of estrogen target tissues in both normal and pathological states.

Potentiation of the lethality of the histone deacetylase inhibitor LAQ824 by the cyclin-dependent kinase inhibitor roscovitine in human leukemia cells

Interactions between the novel histone deacetylase inhibitor LAQ824 and the cyclin-dependent kinase inhibitor roscovitine were examined in human leukemia cells. Pretreatment (24 hours) with a subtoxic concentration of LAQ824 (30 nmol/L) followed by a minimally toxic concentration of roscovitine (10 micromol/L; 24 hours) resulted in greater than additive effects on apoptosis in U937, Jurkat, and HL-60 human leukemia cells and blasts from three patients with acute myelogenous leukemia. These events were associated with enhanced conformational changes in Bax; mitochondrial release of cytochrome c, Smac/DIABLO, and apoptosis-inducing factor; and a marked increase in caspase activation. LAQ824/roscovitine-treated cells displayed caspase-dependent down-regulation of p21(CIP1) and Mcl-1 and a pronounced caspase-independent reduction in X-linked inhibitor of apoptosis (XIAP) expression. The lethality of this regimen was significantly attenuated by ectopic expression of XIAP, a nuclear localization signal-defective p21(CIP1) mutant, Mcl-1, and Bcl-2. Combined exposure to LAQ824 and roscovitine resulted in a significant reduction in XIAP mRNA levels and diminished phosphorylation of the carboxyl-terminal domain of RNA polymerase II. Notably, roscovitine blocked LAQ824-mediated differentiation. Finally, LAQ824 and roscovitine individually and in combination triggered an increase in generation of reactive oxygen species; moreover, coadministration of the free radical scavenger N-acetylcysteine prevented LAQ824/roscovitine-mediated mitochondrial injury and apoptosis. Collectively, these findings suggest that combined treatment of human leukemia cells with LAQ824 and roscovitine disrupts maturation and synergistically induces apoptosis, lending further support for an antileukemic strategy combining novel histone deacetylase and cyclin-dependent kinase inhibitors.

Characterization of the two catalytic domains in histone deacetylase 6

Histone deacetylase 6 (HDAC6) is the only known HDAC with two potentially functional catalytic domains, yet the role towards substrate played by these two domains remains ambiguous. Most studies report HDAC6 activities measured using either immune complexes or in vitro translated products. Here, we characterize the activity of highly purified recombinant HDAC6, mutants with active site histidine mutations in each domain (H216A and H611A), and individual catalytic domains. The deacetylase activities of these proteins, as well as their kinetic parameters, were measured using histone, alpha-tubulin, and fluorogenic acetylated lysine as substrates. Mutant H216A only slightly lowers the catalytic rate. However, mutant H611A decreases the catalytic rate more than 5000-fold. The first domain expressed alone is not catalytically active. In contrast, the second domain shows only a modest decrease in substrate binding and product formation rate. Our results indicate that the in vitro deacetylase activity of HDAC6 resides in the C-terminal second catalytic domain.

Histone deacetylase enzymes as potential drug targets in cancer and parasitic diseases

The elucidation of the mechanisms of transcriptional activation and repression in eukaryotic cells has shed light on the important role of acetylation-deacetylation of histones mediated by histone acetyltransferases (HATs) and histone deacetylases (HDACs), respectively. Another group belonging to the large family of sirtuins (silent information regulators (SIRs)) has an (nicotinamide adenine dinucleotide) NAD(+)-dependent HDAC activity. Several inhibitors of HDACs (HDIs) have been shown to exert antitumor effects. Interestingly, some of the HDIs exerted a broad spectrum of antiprotozoal activity. The purpose of this review is to analyze some of the current data related to the deacetylase enzymes as a possible target for drug development in cancer and parasitic diseases with special reference to protozoan infections. Given the structural differences among members of this family of enzymes, development of specific inhibitors will not only allow selective therapeutic intervention, but may also provide a powerful tool for functional study of these enzymes.

Histone deacetylation as a target for radiosensitization

Due to an increase in the understanding of molecular radiobiology, strategies for enhancing tumor radiosensitivity have begun to focus on targeting the molecules and processes that regulate cellular radioresponse. Toward this end, histone acetylation has begun to receive considerable attention as a potential target for radiosensitization. Histone acetylation, which is determined by the competing actions of histone acetylases (HATs) and histone deacetylases (HDACs), plays a role in regulating chromatin structure and gene expression--two parameters that have long been considered determinants of radioresponse. As a means of modifying histone acetylation status, considerable effort has been put into the development of inhibitors of HDAC activity, which is often aberrant in tumor cells. This has led to the generation of a relatively large number of structurally diverse compounds that inhibit HDAC activity and result in histone hyperacetylation, and importantly, are applicable to patient treatment. Whereas a number of these HDAC inhibitors have antitumor activity in preclinical cancer models when delivered as single agents, recent studies have indicated that these compounds also significantly enhance tumor cell radiosensitivity. A structurally diverse set of HDAC inhibitors have been shown to enhance the in vitro radiosensitivity of human tumor cell lines generated from a spectrum of solid tumors. Moreover, HDAC inhibitors increased the radiosensitivity of human tumor xenografts. Although the mechanism responsible for this radiosensitization has not been definitely elucidated, data suggest that inhibiting the repair of radiation-induced DNA damage may be involved. Whereas HDAC inhibitors are currently in clinical trials as single modalities and in combination with chemotherapeutic agents, recent results suggest that these compounds may also enhance the antitumor effectiveness of radiotherapy.

Gβγ Binds Histone Deacetylase 5 (HDAC5) and Inhibits Its Transcriptional Co-repression Activity

In a yeast two-hybrid screen designed to identify novel effectors of the G betagamma subunit of heterotrimeric G proteins, we found that G betagamma binds to histone deacetylase 5 (HDAC5), an enzyme involved in a pathway not previously recognized to be directly impacted by G proteins. Formation of the G beta1gamma2-HDAC5 complex in mammalian cells can be blocked by overexpression of G alpha(o), and this inhibition is relieved by activation of alpha2A-adrenergic receptor, suggesting that the interaction occurs in a signal-dependent manner. The C-terminal domain of HDAC5 binds directly to G betagamma through multiple motifs, and overexpression of this domain mimics the C terminus of G protein-coupled receptor kinase 2, a known G betagamma scavenger, in its ability to inhibit the G betagamma/HDAC5 interaction. The C terminus of HDAC4 shares significant similarity with that of HDAC5, and accordingly, HDAC4 is also able to form complexes with G beta1gamma2 in cultured cells, suggesting that the C-terminal domain of class II HDACs is a general G betagamma binding motif. Activation of a G(i/o)-coupled receptor results in a time-dependent activation of MEF2C, an HDAC5-regulated transcription factor, whereas inhibition of the interaction with a G betagamma scavenger inhibits MEF2C activity, suggesting a reduced potency of HDAC5-mediated inhibition. Taken together, these data imply that HDAC5 and possibly other class II HDACs can be added to the growing list of G betagamma effectors.

Histone deacetylase inhibitors promote osteoblast maturation

HDIs are potential therapeutic agents for cancer and neurological diseases because of their abilities to alter gene expression, induce growth arrest or apoptosis of tumors cells, and stimulate differentiation. In this report, we show that several HDIs promote osteoblast maturation in vitro and in calvarial organ cultures.

INTRODUCTION

Histone deacetylase inhibitors (HDIs) are currently in phase I and II clinical trials as anticancer agents. Some HDIs are also commonly prescribed treatments for epilepsy and bipolar disorders. Although administered systemically, the effects of HDIs on osteoblasts and bone formation have not been extensively examined. In this study, we investigated the effect of histone deacetylase inhibition on osteoblast proliferation and differentiation.

MATERIALS AND METHODS

MC3T3-E1 cells, calvarial-derived primary osteoblasts, and calvarial organ cultures were treated with various commercially available HDIs (trichostatin A [TSA], sodium butyrate [NaB], valproic acid [VPA], or MS-275). The effects of these inhibitors on cell proliferation, viability, cell cycle progression, Runx2 transcriptional activity, alkaline phosphatase production, and matrix mineralization were determined. Expression levels of osteoblast maturation genes, type I collagen, osteopontin, bone sialoprotein, and osteocalcin in response to TSA were measured by quantitative PCR.

RESULTS

Concentrations of HDIs that caused hyperacetylation of histone H3 induced transient increases in osteoblast proliferation and viability but did not alter cell cycle profiles. These concentrations of HDIs also increased the transcriptional activity of Runx2. TSA accelerated alkaline phosphatase production in MC3T3-E1 cells and calvarial organ cultures. In addition, TSA accelerated matrix mineralization and the expression of osteoblast genes, type I collagen, osteopontin, bone sialoprotein, and osteocalcin in MC3T3-E1 cells.

CONCLUSIONS

These studies show that histone deacetylase activity regulates osteoblast differentiation and bone formation at least in part by enhancing Runx2-dependent transcriptional activation. Therefore, HDIs are a potentially new class of bone anabolic agents that may be useful in the treatment of diseases that are associated with bone loss such as osteoporosis and cancer.

Histone-modifying complexes regulate gene expression pertinent to the differentiation of the protozoan parasite Toxoplasma gondii

Pathogenic apicomplexan parasites like Toxoplasma and Plasmodium (malaria) have complex life cycles consisting of multiple stages. The ability to differentiate from one stage to another requires dramatic transcriptional changes, yet there is a paucity of transcription factors in these protozoa. In contrast, we show here that Toxoplasma possesses extensive chromatin remodeling machinery that modulates gene expression relevant to differentiation. We find that, as in other eukaryotes, histone acetylation and arginine methylation are marks of gene activation in Toxoplasma. We have identified mediators of these histone modifications, as well as a histone deacetylase (HDAC), and correlate their presence at target promoters in a stage-specific manner. We purified the first HDAC complex from apicomplexans, which contains novel components in addition to others previously reported in eukaryotes. A Toxoplasma orthologue of the arginine methyltransferase CARM1 appears to work in concert with the acetylase TgGCN5, which exhibits an unusual bias for H3 [K18] in vitro. Inhibition of TgCARM1 induces differentiation, showing that the parasite life cycle can be manipulated by interfering with epigenetic machinery. This may lead to new approaches for therapy against protozoal diseases and highlights Toxoplasma as an informative model to study the evolution of epigenetics in eukaryotic cells.