Histone deacetylases, transcriptional control, and cancer

Structure-activity relationships on phenylalanine-containing inhibitors of histone deacetylase: in vitro enzyme inhibition, induction of differentiation, and inhibition of proliferation in Friend leukemic cells

Inhibitors of histone deacetylases (HDACs) are a new class of anticancer agents that affect gene regulation. We had previously reported the first simple synthetic HDAC inhibitors with in vitro activity at submicromolar concentrations. Here, we present structure-activity data on modifications of a phenylalanine-containing lead compound including amino acid amides as well as variations of the amino acid part. The compounds were tested for inhibition of maize HD-2, rat liver HDAC, and for the induction of terminal cell differentiation and inhibition of proliferation in Friend leukemic cells. In the amide series, in vitro inhibition was potentiated up to 15-fold, but the potential to induce cell differentiation decreased. Interestingly, an HDAC class selectivity was indicated among some of these amides. In the amino acid methyl ester series, a biphenylalanine derivative was identified as a good enzyme inhibitor, which blocks proliferation in the submicromolar range and is also a potent inducer of terminal cell differentiation.

Cloning and functional characterization of HDAC11, a novel member of the human histone deacetylase family

We have cloned and characterized a human cDNA that belongs to the histone deacetylase family, which we designate as HDAC11. The predicted HDAC11 amino acid sequence reveals an open reading frame of 347 residues with a corresponding molecular mass of 39 kDa. Sequence analyses of the putative HDAC11 protein indicate that it contains conserved residues in the catalytic core regions shared by both class I and II mammalian HDAC enzymes. Putative orthologues of HDAC11 exist in primate, mouse, Drosophila, and plant. Epitope-tagged HDAC11 protein expressed in mammalian cells displays histone deacetylase activity in vitro. Furthermore, HDAC11's enzymatic activity is inhibited by trapoxin, a known histone deacetylase inhibitor. Multiple tissue Northern blot and real-time PCR experiments show that the high expression level of HDAC11 transcripts is limited to kidney, heart, brain, skeletal muscle, and testis. Epitope-tagged HDAC11 protein localizes predominantly to the cell nucleus. Co-immunoprecipitation experiments indicate that HDAC11 may be present in protein complexes that also contain HDAC6. These results indicate that HDAC11 is a novel and unique member of the histone deacetylase family and it may have distinct physiological roles from those of the known HDACs.

The SIN3/RPD3 deacetylase complex is essential for G(2) phase cell cycle progression and regulation of SMRTER corepressor levels

The SIN3 corepressor and RPD3 histone deacetylase are components of the evolutionarily conserved SIN3/RPD3 transcriptional repression complex. Here we show that the SIN3/RPD3 complex and the corepressor SMRTER are required for Drosophila G(2) phase cell cycle progression. Loss of the SIN3, but not the p55, SAP18, or SAP30, component of the SIN3/RPD3 complex by RNA interference (RNAi) causes a cell cycle delay prior to initiation of mitosis. Loss of RPD3 reduces the growth rate of cells but does not cause a distinct cell cycle defect, suggesting that cells are delayed in multiple phases of the cell cycle, including G(2). Thus, the role of the SIN3/RPD3 complex in G(2) phase progression appears to be independent of p55, SAP18, and SAP30. SMRTER protein levels are reduced in SIN3 and RPD3 RNAi cells, and loss of SMRTER by RNAi is sufficient to cause a G(2) phase delay, demonstrating that regulation of SMRTER protein levels by the SIN3/RPD3 complex is a vital component of the transcriptional repression mechanism. Loss of SIN3 does not affect global acetylation of histones H3 and H4, suggesting that the G(2) phase delay is due not to global changes in genome integrity but rather to derepression of SIN3 target genes.

SUMO-1 modification of histone deacetylase 1 (HDAC1) modulates its biological activities

Histone deacetylation plays a central role in the regulation of genes linked to virtually all biological processes. This modification reaction is dependent on a family of related histone deacetylases (HDACs), which function as key components of large multiprotein complexes involved in the development of normal and neoplastic cells. The mechanisms regulating HDACs and their roles in such processes are not understood, and these form the major focus for the current study. Here, in the course of assessing possible post-translational modifications of HDAC1, we demonstrated that HDAC1 is a substrate for SUMO-1 (small ubiquitin-related modifier) modification in vitro and in vivo. The HDAC1 lysines targeted for modification were identified as C-terminal Lys-444 and Lys-476, which are also present in mammalian HDAC2 and lower vertebrate HDAC1/2 orthologs yet absent from other HDAC family members, pointing to a means of differential regulation among HDAC proteins. Mutation of these target residues (lysine to arginine substitution) profoundly reduced HDAC1-mediated transcriptional repression in reporter assays without affecting HDAC1 ability to associate with mSin3A and eliminated HDAC1-induced cell cycle and apoptotic responses upon overexpression. Together, the results demonstrate that HDAC1 is modified by SUMO-1, and this modification can dramatically affect HDAC1 activity in a number of surrogate biological assays.

Essential function of histone deacetylase 1 in proliferation control and CDK inhibitor repression

Histone deacetylases (HDACs) modulate chromatin structure and transcription, but little is known about their function in mammalian development. HDAC1 was implicated previously in the repression of genes required for cell proliferation and differentiation. Here we show that targeted disruption of both HDAC1 alleles results in embryonic lethality before E10.5 due to severe proliferation defects and retardation in development. HDAC1-deficient embryonic stem cells show reduced proliferation rates, which correlate with decreased cyclin-associated kinase activities and elevated levels of the cyclin-dependent kinase inhibitors p21(WAF1/CIP1) and p27(KIP1). Similarly, expression of p21 and p27 is up-regulated in HDAC1-null embryos. In addition, loss of HDAC1 leads to significantly reduced overall deacetylase activity, hyperacetylation of a subset of histones H3 and H4 and concomitant changes in other histone modifications. The expression of HDAC2 and HDAC3 is induced in HDAC1-deficient cells, but cannot compensate for loss of the enzyme, suggesting a unique function for HDAC1. Our study provides the first evidence that a histone deacetylase is essential for unrestricted cell proliferation by repressing the expression of selective cell cycle inhibitors.

Paradigms of growth control: relation to Cdk activation

The cyclin-dependent kinases (CDKs) play a key role in cell cycle control, and in this review, we focus on the events that regulate their activities. Emphasis is placed on the CDKs that function during the G(1) phase of the cell cycle and on the CDK inhibitor p27(Kip1). We discuss how CDK activation relates to two basic concepts of cell cycle regulation: (i) the need for multiple mitogens for the proliferation of nontransformed cells and (ii) the inhibitory effect of high culture density on proliferative capacity. We also describe how Cdk2 modulates the expression of the alpha subunit of the interleukin-2 receptor in T cells, and address the question of whether p27(Kip1) functions as an activator or inhibitor of the CDKs associated with the D cyclins.

Histone deacetylase 1 inactivation by an adenovirus early gene product

Gam1 is an early gene product of the avian adenovirus CELO and is essential for viral replication. Gam1 has no homology to any known proteins; however, its early expression and nuclear localization suggest that the protein functions to influence transcription in the infected cell. A determinant of eukaryotic gene expression is the acetylation state of chromosomal histones and other nuclear proteins. We find that Gam1 expression increases the level of transcription from a variety of eukaryotic promoters, similar to the effect of treating cells with the histone deacetylase (HDAC) inhibitor trichostatin A (TSA ). We show that Gam1 can effectively inhibit histone deacetylation by HDAC1 and that Gam1 binds to HDAC1 both in vitro and in vivo. A CELO virus lacking Gam1 (CELOdG) is replication defective, but the defect can be overcome by either expressing an interfering HDAC1 mutant or by treating infected cells with TSA. The identification of a viral early gene product having the specific function of binding and inactivating HDAC suggests that deacetylase complexes play an important role in limiting early gene expression from invading viruses.

Histone-deacetylase inhibitors: novel drugs for the treatment of cancer

The opposing actions of histone acetyltransferases (HATs) and histone deacetylases (HDACs) allow gene expression to be exquisitely regulated through chromatin remodelling. Aberrant transcription due to altered expression or mutation of genes that encode HATs, HDACs or their binding partners, is a key event in the onset and progression of cancer. HDAC inhibitors can reactivate gene expression and inhibit the growth and survival of tumour cells. The remarkable tumour specificity of these compounds, and their potency in vitro and in vivo, underscore the potential of HDAC inhibitors as exciting new agents for the treatment of cancer.

Acetyltransferase machinery conserved in p300/CBP-family proteins

CREB-binding protein (CBP) and p300 are highly conserved and functionally related transcription coactivators and histone/protein acetyltransferases. They are tumor suppressors, participate in a wide variety of physiological events, and serve as integrators among different signal transduction pathways. In this study, 11 distinct proteins that have a high degree of homology with the amino acid sequence of p300 have been identified in current protein databases. All of these 11 proteins belong to either animal or plant multicellular organisms (higher eucaryotes). Conservation of p300/CBP domains among these proteins was examined further by sequence alignment and pattern search. The domains of p300/CBP that are required for the HAT function, including PHD, putative CoA-binding, and ZZ domains, are conserved in all of these 11 proteins. This observation is consistent with the previous functional assays and indicates that they are a family of acetyltransferases, i.e. p300/CBP acetyltransferases (PCAT). TAZ domains (TAZ1 and/or TAZ2) of PCAT proteins may allow them to participate in transcription regulation by either directly recruiting transcription factors, acetylating them subsequently, or directing targeted acetylation of nucleosomal histones.

Functional domains of histone deacetylase-3

Post-translational modifications of histones, in general, and acetylation/deacetylation, in particular, can dramatically alter gene expression in eukaryotic cells. In humans, four highly homologous class I HDAC enzymes (HDAC1, HDAC2, HDAC3, and HDAC8) have been identified to date. Although HDAC3 shares some structural and functional similarities with other class I HDACs, it exists in multisubunit complexes separate and different from other known HDAC complexes, implying that individual HDACs might function in a distinct manner. In this current study, to understand further the cellular function of HDAC3 and to uncover possible unique roles this protein may have in gene regulation, we performed a detailed analysis of HDAC3 using deletion mutations. Surprisingly, we found that the non-conserved C-terminal region of HDAC3 is required for both deacetylase and transcriptional repression activity. In addition, we discovered that the central portion of the HDAC3 protein possesses a nuclear export signal, whereas the C-terminal part of HDAC3 contributes to the protein's localization in the nucleus. Finally, we found that HDAC3 forms oligomers in vitro and in vivo and that the N-terminal portion of HDAC3 is necessary for this property. These data indicate that HDAC3 comprises separate, non-overlapping domains that contribute to the unique properties and function of this protein.

Identification of novel E2F1-regulated genes by microarray

The E2F pathway has been proposed to regulate genes involved in the transition from quiescence into DNA synthesis. However, this hypothesis has not been rigorously tested on a genomic scale. Toward this end, we have infected quiescent mouse fibroblasts, which do not express E2F1, with an E2F1-expressing adenovirus and examined the expression of more than 6000 genes using high-density microarrays. Microarray results clearly support the current paradigm; however, they suggest that E2F1 may also regulate unanticipated cellular functions including pathways involved in apoptosis, signal transduction, transcriptional control, and membrane biology. Most surprisingly, we identified a number of genes that are repressed by E2F1 expression, suggesting that E2F1 may have the potential to repress transcription of numerous genes through an unknown mechanism.

A microplate reader-based nonisotopic histone deacetylase activity assay

Recent years have brought an enormous increase in knowledge concerning the involvement of histone deacetylase (HDAC) in gene regulation and the potential use of its inhibitors in transcription therapy. This also stimulates research toward new methods for the determination of HDAC activity and thus the potency of potential inhibitors. We have previously succeeded in developing a nonisotopic assay for HDAC using a fluorescent coumarin derivative of epsilon-acetyllysine. Here we present plate reader-based quantitation as an alternative means for the determination of substrate conversion. A new validated assay procedure with a boradiazaindacene (BODIPY 530/550) rather than a coumarin internal standard was established to allow for fluorescence measurement without chromatographic separation. The method is equal in its sensitivity, accuracy, and precision to the previously published HPLC method. A comparison with a new commercially available homogeneous plate reader assay leads to similar inhibition constants for the HDAC inhibitor trichostatin A. The commercial assay has a higher throughput but its procedure for the detection of HDAC activity could not be applied to our enzyme preparation, while our substrate is also converted by HeLa HDAC. This indicates a broader range of potential applications for our system.

Identification of HDAC10, a novel class II human histone deacetylase containing a leucine-rich domain

Histone acetylation is important for regulating chromatin structure and gene expression. Three classes of mammalian histone deacetylases have been identified. Among class II, there are five known members, namely HDAC4, HDAC5, HDAC6, HDAC7 and HDAC9. Here we describe the identification and characterization of a novel class II member termed HDAC10. It is a 669 residue polypeptide with a bipartite modular structure consisting of an N-terminal Hda1p-related putative deacetylase domain and a C-terminal leucine-rich domain. HDAC10 is widely expressed in adult human tissues and cultured mammalian cells. It is enriched in the cytoplasm and this enrichment is not sensitive to leptomycin B, a specific inhibitor known to block the nuclear export of other class II members. The leucine-rich domain of HDAC10 is responsible for its cytoplasmic enrichment. Recombinant HDAC10 protein possesses histone deacetylase activity, which is sensitive to trichostatin A, a specific inhibitor for known class I and class II histone deacetylases. When tethered to a promoter, HDAC10 is able to repress transcription. Furthermore, HDAC10 interacts with HDAC3 but not with HDAC4 or HDAC6. These results indicate that HDAC10 is a novel class II histone deacetylase possessing a unique leucine-rich domain.

Inhibitors of human histone deacetylase: synthesis and enzyme and cellular activity of straight chain hydroxamates

Inhibitors of histone deacetylase (HDAC) have been shown to induce terminal differentiation of human tumor cell lines and to have antitumor effects in vivo. We have prepared analogues of suberoylanilide hydroxamic acid (SAHA) and trichostatin A and have evaluated them in a human HDAC enzyme inhibition assay, a p21(waf1) (p21) promoter assay, and in monolayer growth inhibition assays. One compound, 4-(dimethylamino)-N-[7-(hydroxyamino)-7-oxoheptyl]-benzamide, was found to affect the growth of a panel of eight human tumor cell lines differentially.

Role of the Sin3-histone deacetylase complex in growth regulation by the candidate tumor suppressor p33(ING1)

Sin3 is an evolutionarily conserved corepressor that exists in different complexes with the histone deacetylases HDAC1 and HDAC2. Sin3-HDAC complexes are believed to deacetylate nucleosomes in the vicinity of Sin3-regulated promoters, resulting in a repressed chromatin structure. We have previously found that a human Sin3-HDAC complex includes HDAC1 and HDAC2, the histone-binding proteins RbAp46 and RbAp48, and two novel polypeptides SAP30 and SAP18. SAP30 is a specific component of Sin3 complexes since it is absent in other HDAC1/2-containing complexes such as NuRD. SAP30 mediates interactions with different polypeptides providing specificity to Sin3 complexes. We have identified p33ING1b, a negative growth regulator involved in the p53 pathway, as a SAP30-associated protein. Two distinct Sin3-p33ING1b-containing complexes were isolated, one of which associates with the subunits of the Brg1-based Swi/Snf chromatin remodeling complex. The N terminus of p33ING1b, which is divergent among a family of ING1 polypeptides, associates with the Sin3 complex through direct interaction with SAP30. The N-terminal domain of p33 is present in several uncharacterized human proteins. We show that overexpression of p33ING1b suppresses cell growth in a manner dependent on the intact Sin3-HDAC-interacting domain.

Histone deacetylase inhibitor FK228 inhibits tumor angiogenesis

FK228 (formerly FR901228) was recently isolated from Chromobacterium violaceum as a potent antitumor agent and its biologic target protein was identified as histone deacetylase (HDAC). Because of its unique chemical structure (i.e., bicyclic depsipeptide) and activity profile in the National Cancer Institute's developmental therapeutics program, FK228 is currently in a phase I clinical trial for cancer therapy. In the present study, we investigated the antiangiogenic activity of FK228 in vivo and in vitro. FK228 potently blocked the hypoxia-stimulated proliferation, invasion, migration, adhesion and tube formation of bovine aortic endothelial cells at the same concentration at which the agent inhibited the HDAC activity of cells. In addition, FK228 inhibited the neovascularization of chick embryo and that of adult mice in the Matrigel plug assay. Interestingly, the expression of angiogenic-stimulating factors such as vascular endothelial growth factor or kinase insert domain receptor were suppressed by FK228, whereas that of angiogenic-inhibiting factors such as von Hippel Lindau and neurofibromin2 were induced, suggesting that a gene-transcription effect was involved in the inhibition of angiogenesis by FK228. These results indicate that FK228 is a novel antiangiogenic agent and may suppress tumor expansion, at least in part, by the inhibition of neovascularization.

Regulation of gene expression by the proto-oncogene BCL-6

The proto-oncogene BCL-6 encodes a transcriptional repressor protein that is expressed at high levels in germinal center B cells and lymphomas with a germinal center B cell phenotype. The BCL-6 gene is a frequent target of chromosomal translocations, micro-deletions, and point mutations in non-Hodgkin's lymphoma. Studies of BCL-6-deficient mice have revealed that BCL-6 is critical for normal lymphocyte differentiation and also that BCL-6 is a negative regulator of inflammation. Recent studies have shed light on how BCL-6 controls these processes by showing that BCL-6 regulates a broad spectrum of target genes. BCL-6 represses transcription of genes involved in lymphocyte activation, differentiation, proliferation, and migration. Although much progress has been made in understanding gene regulation by BCL-6, many important questions are unresolved.

Histone deacetylase inhibitors in cancer treatment

Histone deacetylase (HDAC) inhibitors are emerging as an exciting new class of potential anticancer agents for the treatment of solid and hematological malignancies. In recent years, an increasing number of structurally diverse HDAC inhibitors have been identified that inhibit proliferation and induce differentiation and/or apoptosis of tumor cells in culture and in animal models. HDAC inhibition causes acetylated nuclear histones to accumulate in both tumor and normal tissues, providing a surrogate marker for the biological activity of HDAC inhibitors in vivo. The effects of HDAC inhibitors on gene expression are highly selective, leading to transcriptional activation of certain genes such as the cyclin-dependent kinase inhibitor p21WAF1/CIP1 but repression of others. HDAC inhibition not only results in acetylation of histones but also transcription factors such as p53, GATA-1 and estrogen receptor-alpha. The functional significance of acetylation of non-histone proteins and the precise mechanisms whereby HDAC inhibitors induce tumor cell growth arrest, differentiation and/or apoptosis are currently the focus of intensive research. Several HDAC inhibitors have shown impressive antitumor activity in vivo with remarkably little toxicity in preclinical studies and are currently in phase I clinical trial. The focus of this review is the development and clinical application of HDAC inhibitors for the treatment of cancer.

Enzymatic activity associated with class II HDACs is dependent on a multiprotein complex containing HDAC3 and SMRT/N-CoR

Histone deacetylases (HDACs) play a key role in regulating eukaryotic gene expression. The HDAC domain, homologous to the yeast repressors RPD3 and HDA1, is considered necessary and sufficient for enzymatic activity. Here, we show that the catalytic domain of HDAC4 interacts with HDAC3 via the transcriptional corepressor N-CoR/SMRT. All experimental conditions leading to the suppression of HDAC4 binding to SMRT/N-CoR and to HDAC3 result in the loss of enzymatic activity associated with HDAC4. In vitro reconstitution experiments indicate that HDAC4 and other class II HDACs are inactive in the context of the SMRT/N-CoR-HDAC3 complex and do not contribute to its enzymatic activity. These observations indicate that class II HDACs regulate transcription by bridging the enzymatically active SMRT/N-CoR-HDAC3 complex and select transcription factors independently of any intrinsic HDAC activity.

Histone deacetylase 1 phosphorylation promotes enzymatic activity and complex formation

Accessibility of the genome to DNA-binding transcription factors is regulated by proteins that control the acetylation of amino-terminal lysine residues on nucleosomal histones. Specifically, histone deacetylase (HDAC) proteins repress transcription by deacetylating histones. To date, the only known regulatory mechanism of HDAC1 function is via interaction with associated proteins. Although the control of HDAC1 function by protein interaction and recruitment is well precedented, we were interested in exploring HDAC1 regulation by post-translational modification. Human HDAC1 protein was analyzed by ion trap mass spectrometry, and two phosphorylated serine residues, Ser(421) and Ser(423), were unambiguously identified. Loss of phosphorylation at Ser(421) and Ser(423) due to mutation to alanine or disruption of the casein kinase 2 consensus sequence directing phosphorylation reduced the enzymatic activity and complex formation of HDAC1. Deletion of the highly charged carboxyl-terminal region of HDAC1 also decreased its deacetylase activity and protein associations, revealing its requirement in maintaining HDAC1 function. Our results reinforce the importance of protein associations in modulating HDAC1 function and provide the first step toward characterizing the role of post-translational modifications in regulating HDAC activity in vivo.

FIH-1: a novel protein that interacts with HIF-1alpha and VHL to mediate repression of HIF-1 transcriptional activity

Hypoxia-inducible factor 1 (HIF-1) is a master regulator of oxygen homeostasis that controls angiogenesis, erythropoiesis, and glycolysis via transcriptional activation of target genes under hypoxic conditions. O(2)-dependent binding of the von Hippel-Lindau (VHL) tumor suppressor protein targets the HIF-1alpha subunit for ubiquitination and proteasomal degradation. The activity of the HIF-1alpha transactivation domains is also O(2) regulated by a previously undefined mechanism. Here, we report the identification of factor inhibiting HIF-1 (FIH-1), a protein that binds to HIF-1alpha and inhibits its transactivation function. In addition, we demonstrate that FIH-1 binds to VHL and that VHL also functions as a transcriptional corepressor that inhibits HIF-1alpha transactivation function by recruiting histone deacetylases. Involvement of VHL in association with FIH-1 provides a unifying mechanism for the modulation of HIF-1alpha protein stabilization and transcriptional activation in response to changes in cellular O(2) concentration.

Structure of histone deacetylases: insights into substrate recognition and catalysis

Histone deacetylases catalyze the removal of the acetyl moiety from acetyl-lysine within histones to promote gene repression and silencing. These enzymes fall into distinct families based on primary sequence homology and functional properties in vivo. Recent structural studies of histone deacetylases and their homologs from bacteria have provided important insights into the mode of substrate recognition and catalysis by these enzymes.

Histone deacetylases and cancer: causes and therapies

Together, histone acetyltransferases and histone deacetylases (HDACs) determine the acetylation status of histones. This acetylation affects the regulation of gene expression, and inhibitors of HDACs have been found to cause growth arrest, differentiation and/or apoptosis of many tumours cells by altering the transcription of a small number of genes. HDAC inhibitors are proving to be an exciting therapeutic approach to cancer, but how do they exert this effect?

Interaction of EVI1 with cAMP-responsive element-binding protein-binding protein (CBP) and p300/CBP-associated factor (P/CAF) results in reversible acetylation of EVI1 and in co-localization in nuclear speckles

EVI1 is a very complex protein with two domains of zinc fingers and is inappropriately expressed in many types of human myeloid leukemias. Using reporter gene assays, several investigators showed that EVI1 is a transcription repressor, and recently it was shown that EVI1 interacts with the co-repressor carboxyl-terminal binding protein 1 (CtBP1). Earlier, we showed that the inappropriate expression of EVI1 in murine hematopoietic precursor cells leads to their abnormal differentiation and to increased proliferation. Using biochemical assays, we have identified two groups of transcription co-regulators that associate with EVI1 presumably to regulate gene expression. One group of co-regulators includes the CtBP1 and histone deacetylase. The second group includes the two co-activators cAMP-responsive element-binding protein-binding protein (CBP) and p300/CBP-associated factor (P/CAF), both of which have histone acetyltransferase (HAT) activity. All of these proteins require separate regions of EVI1 for efficient interaction, and they divergently affect the ability of EVI1 to regulate gene transcription in reporter gene assays. Confocal microscopy analysis shows that in the majority of the cells, EVI1 is nuclear and diffused, whereas in about 10% of the cells EVI1 localizes in nuclear speckles. However, in the presence of the added exogenous co-repressors histone deacetylase or CtBP1, all of the nuclei have a diffuse EVI1 staining, and the proteins do not appear to reside together in obvious nuclear structures. In contrast, when CBP or P/CAF are added, defined speckled bodies appear in the nucleus. Analysis of the staining pattern indicates that EVI1 and CBP or EVI1 and P/CAF are contained within these structures. These nuclear structures are not observed when CBP is substituted with a point mutant HAT-inactive CBP with which EVI1 also physically interacts. Finally, we show that the interaction of EVI1 with either CBP or P/CAF leads to acetylation of EVI1. These results suggest that the assembly of EVI1 in nuclear speckles requires the intact HAT activity of the co-activators.

Inhibitor of histone deacetylation, depsipeptide (FR901228), in the treatment of peripheral and cutaneous T-cell lymphoma: a case report

Depsipeptide, FR901228, has demonstrated potent in vitro and in vivo cytotoxic activity against murine and human tumor cell lines. In the laboratory, it has been shown to be a histone deacetylase (HDAC) inhibitor. In a phase I trial of depsipeptide conducted at the National Cancer Institute, 3 patients with cutaneous T-cell lymphoma had a partial response, and 1 patient with peripheral T-cell lymphoma, unspecified, had a complete response. Sézary cells isolated from patients after treatment had increased histone acetylation. These results suggest that inhibition of HDAC is a novel and potentially effective therapy for patients with T-cell lymphoma.

FIH-1: a novel protein that interacts with HIF-1alpha and VHL to mediate repression of HIF-1 transcriptional activity

Hypoxia-inducible factor 1 (HIF-1) is a master regulator of oxygen homeostasis that controls angiogenesis, erythropoiesis, and glycolysis via transcriptional activation of target genes under hypoxic conditions. O(2)-dependent binding of the von Hippel-Lindau (VHL) tumor suppressor protein targets the HIF-1alpha subunit for ubiquitination and proteasomal degradation. The activity of the HIF-1alpha transactivation domains is also O(2) regulated by a previously undefined mechanism. Here, we report the identification of factor inhibiting HIF-1 (FIH-1), a protein that binds to HIF-1alpha and inhibits its transactivation function. In addition, we demonstrate that FIH-1 binds to VHL and that VHL also functions as a transcriptional corepressor that inhibits HIF-1alpha transactivation function by recruiting histone deacetylases. Involvement of VHL in association with FIH-1 provides a unifying mechanism for the modulation of HIF-1alpha protein stabilization and transcriptional activation in response to changes in cellular O(2) concentration.

pRb2/p130 and p107 control cell growth by multiple strategies and in association with different compartments within the nucleus

It has been recently reported that retinoblastoma family proteins suppress cell growth by regulating not only E2F-dependent mRNA transcription but also rRNA and tRNA transcription and, through HDAC1 recruitment, chromatin packaging. In the present study we report data showing that these various control strategies are correlated, at least in part, with nuclear compartmentalization of retinoblastoma proteins. In a first series of experiments, we showed that pRb2/p130 and p107 are not evenly distributed within the nucleus and that cell cycle-dependent binding with E2F4 changes also as a function of their subnuclear localization. Namely, in the nucleoplasm pRb2/p130-E2F4 complexes are more numerous during G0/G1 while in the nucleolus they increase in S phase. Partially different functions for p107 are suggested since p107-E2F4 complexes in the nucleoplasm are more numerous is S phase with respect to G0/G1 and no cell cycle change is observed in the nucleolus. In a second series of experiments we showed that pRb2/p130, p107, E2F4, and pRb2/p130-HDAC1 complexes are all inner nuclear matrix-associated proteins and localize to sites different from pRb/p105 ones. We provide further evidence of multiple and partially distinct retinoblastoma protein family functional roles during cell cycle. Moreover, our data support emerging evidence for functional interrelationships between nuclear structure and gene expression.

Involvement of histone deacetylase at two distinct steps in gene regulation during intestinal development in Xenopus laevis

Amphibian metamorphosis is marked by dramatic thyroid hormone (T(3))-induced changes including de novo morphogenesis, tissue remodeling and organ resorption through programmed cell death. These changes involve cascades of gene regulation initiated by thyroid hormone and its receptors. Previous studies suggest that chromatin remodeling involving changes in core histone acetylation plays a fundamental role in transcriptional regulation. A basic model has been suggested where targeted histone deacetylation is involved in transcriptional repression and histone acetylation is involved in transcriptional activation. On the other hand, the developmental roles of histone acetylation remain to be elucidated. Here we demonstrate that tadpole treatment with trichostatin A, a specific potent histone deacetylase inhibitor, blocks metamorphosis. Gene expression analyses show that trichostatin A induces the release of T(3)-response gene repression without affecting T(3)-induction of direct T(3)-response genes. However, the drug blocks the regulation of late T(3)-response genes, which may be responsible for its inhibitory effects on metamorphosis. These data support a role of deacetylases in transcriptional repression by unliganded T(3) receptor during premetamorphosis and another role at a downstream step of the gene regulation cascade induced by T(3) during metamorphosis.

Human HDAC7 histone deacetylase activity is associated with HDAC3 in vivo

Histone deacetylases (HDACs) are part of transcriptional corepressor complexes and play key roles in regulating chromatin structure. Three different classes of human HDACs have been defined based on their homology to HDACs found in Saccharomyces cerevisiae: RPD3 (class I), HDA1 (class II), and SIR2 (class III). Here we describe the identification and functional characterization of HDAC7, a new member of the human class II HDAC family. Although HDAC7 is localized mostly to the cell nucleus, it is also found in the cytoplasm, suggesting nucleocytoplasmic shuttling. The HDAC activity of HDAC7 maps to a carboxyl-terminal domain and is dependent on the interaction with the class I HDAC, HDAC3, in the cell nucleus. Cytoplasmic HDAC7 that is not bound to HDAC3 is enzymatically inactive. We provide evidence that the transcriptional corepressors SMRT and N-CoR could serve as critical mediators of HDAC7 activity by binding class II HDACs and HDAC3 by two distinct repressor domains. Different class II HDACs reside in the cell nucleus in stable and autonomous complexes with enzymatic activity, but the enzymatic activities associated with HDAC7 and HDAC4 rely on shared cofactors, including HDAC3 and SMRT/N-CoR.

Regulation of transcription factor YY1 by acetylation and deacetylation

YY1 is a sequence-specific DNA-binding transcription factor that has many important biological roles. It activates or represses many genes during cell growth and differentiation and is also required for the normal development of mammalian embryos. Previous studies have established that YY1 interacts with histone acetyltransferases p300 and CREB-binding protein (CBP) and histone deacetylase 1 (HDAC1), HDAC2, and HDAC3. Here, we present evidence that the activity of YY1 is regulated through acetylation by p300 and PCAF and through deacetylation by HDACs. YY1 was acetylated in two regions: both p300 and PCAF acetylated the central glycine-lysine-rich domain of residues 170 to 200, and PCAF also acetylated YY1 at the C-terminal DNA-binding zinc finger domain. Acetylation of the central region was required for the full transcriptional repressor activity of YY1 and targeted YY1 for active deacetylation by HDACs. However, the C-terminal region of YY1 could not be deacetylated. Rather, the acetylated C-terminal region interacted with HDACs, which resulted in stable HDAC activity associated with the YY1 protein. Finally, acetylation of the C-terminal zinc finger domain decreased the DNA-binding activity of YY1. Our findings suggest that in the natural context, YY1 activity is regulated through intricate mechanisms involving negative feedback loops, histone deacetylation, and recognition of the cognate DNA sequence affected by acetylation and deacetylation of the YY1 protein.

Common themes in the pathogenesis of acute myeloid leukemia

The pathogenesis of acute myeloid leukemia is associated with the appearance of oncogenic fusion proteins generated as a consequence of specific chromosome translocations. Of the two components of each fusion protein, one is generally a transcription factor, whereas the other partner is more variable in function, but often involved in the control of cell survival and apoptosis. As a consequence, AML-associated fusion proteins function as aberrant transcriptional regulators that interfere with the process of myeloid differentiation, determine a stage-specific arrest of maturation and enhance cell survival in a cell-type specific manner. The abnormal regulation of transcriptional networks occurs through common mechanisms that include recruitment of aberrant co-repressor complexes, alterations in chromatin remodeling, and disruption of specific subnuclear compartments. The identification and analysis of common and specific target genes regulated by AML fusion proteins will be of fundamental importance for the full understanding of acute myeloid leukemogenesis and for the implementation of disease-specific drug design.

The FK506-binding protein 25 functionally associates with histone deacetylases and with transcription factor YY1

FK506-binding proteins (FKBPs) are cellular receptors for immunosuppressants that belong to a subgroup of proteins, known as immunophilins, with peptidylprolyl cis-trans isomerase (PPIase) activity. Sequence comparison suggested that the HD2-type histone deacetylases and the FKBP-type PPIases may have evolved from a common ancestor enzyme. Here we show that FKBP25 physically associates with the histone deacetylases HDAC1 and HDAC2 and with the HDAC-binding transcriptional regulator YY1. An FKBP25 immunoprecipitated complex contains deacetylase activity, and this activity is associated with the N-terminus of FKBP25, distinct from the FK506/rapamycin-binding domain. Furthermore, FKBP25 can alter the DNA-binding activity of YY1. Together, our data firmly establish a relationship between histone deacetylases and the FKBP enzymes and provide a novel and critical function for the FKBPs.

Regulation of transcription factor YY1 by acetylation and deacetylation

YY1 is a sequence-specific DNA-binding transcription factor that has many important biological roles. It activates or represses many genes during cell growth and differentiation and is also required for the normal development of mammalian embryos. Previous studies have established that YY1 interacts with histone acetyltransferases p300 and CREB-binding protein (CBP) and histone deacetylase 1 (HDAC1), HDAC2, and HDAC3. Here, we present evidence that the activity of YY1 is regulated through acetylation by p300 and PCAF and through deacetylation by HDACs. YY1 was acetylated in two regions: both p300 and PCAF acetylated the central glycine-lysine-rich domain of residues 170 to 200, and PCAF also acetylated YY1 at the C-terminal DNA-binding zinc finger domain. Acetylation of the central region was required for the full transcriptional repressor activity of YY1 and targeted YY1 for active deacetylation by HDACs. However, the C-terminal region of YY1 could not be deacetylated. Rather, the acetylated C-terminal region interacted with HDACs, which resulted in stable HDAC activity associated with the YY1 protein. Finally, acetylation of the C-terminal zinc finger domain decreased the DNA-binding activity of YY1. Our findings suggest that in the natural context, YY1 activity is regulated through intricate mechanisms involving negative feedback loops, histone deacetylation, and recognition of the cognate DNA sequence affected by acetylation and deacetylation of the YY1 protein.

Histone deacetylase as a therapeutic target

The maintenance of health depends on the coordinated and tightly regulated expression of genetic information. Certain forms of leukemia have become paradigms for the pathogenic role of aberrant repression of differentiation genes. In these acute leukemias, fusion proteins generated by chromosomal translocations no longer function as transcriptional activators, but instead repress target genes by recruiting histone deacetylases (HDACs). The potential benefit of HDAC inhibition has been established by the use of enzyme inhibitors in vitro and in a single reported case of experimental therapy. Because recently identified HDAC inhibitors appear to overcome many drawbacks of early inhibitory compounds in clinical use, the stage is set to test the therapeutic value of HDAC inhibition in leukemias and in other diseases, including solid tumors and aberrant hormonal signaling. This review summarizes the range of diseases expected to respond to HDAC inhibition.

Histone deacetylase 4 possesses intrinsic nuclear import and export signals

Nucleocytoplasmic trafficking of histone deacetylase 4 (HDAC4) plays an important role in regulating its function, and binding of 14-3-3 proteins is necessary for its cytoplasmic retention. Here, we report the identification of nuclear import and export sequences of HDAC4. While its N-terminal 118 residues modulate the nuclear localization, residues 244 to 279 constitute an authentic, strong nuclear localization signal. Mutational analysis of this signal revealed that three arginine-lysine clusters are necessary for its nuclear import activity. As for nuclear export, leucine-rich sequences located in the middle part of HDAC4 do not function as nuclear export signals. By contrast, a hydrophobic motif (MXXLXVXV) located at the C-terminal end serves as a nuclear export signal that is necessary for cytoplasmic retention of HDAC4. This motif is required for CRM1-mediated nuclear export of HDAC4. Furthermore, binding of 14-3-3 proteins promotes cytoplasmic localization of HDAC4 by both inhibiting its nuclear import and stimulating its nuclear export. Unlike wild-type HDAC4, a point mutant with abrogated MEF2-binding ability remains cytoplasmic upon exogenous expression of MEF2C, supporting the notion that direct MEF2 binding targets HDAC4 to the nucleus. Therefore, HDAC4 possesses intrinsic nuclear import and export signals for its dynamic nucleocytoplasmic shuttling, and association with 14-3-3 and MEF2 proteins affects such shuttling and thus directs HDAC4 to the cytoplasm and the nucleus, respectively.

Duration of nuclear NF-kappaB action regulated by reversible acetylation

The nuclear expression and action of the nuclear factor kappa B (NF-kappaB) transcription factor requires signal-coupled phosphorylation and degradation of the IkappaB inhibitors, which normally bind and sequester this pleiotropically active factor in the cytoplasm. The subsequent molecular events that regulate the termination of nuclear NF-kappaB action remain poorly defined, although the activation of de novo IkappaBalpha gene expression by NF-kappaB likely plays a key role. Our studies now demonstrate that the RelA subunit of NF-kappaB is subject to inducible acetylation and that acetylated forms of RelA interact weakly, if at all, with IkappaBalpha. Acetylated RelA is subsequently deacetylated through a specific interaction with histone deacetylase 3 (HDAC3). This deacetylation reaction promotes effective binding to IkappaBalpha and leads in turn to IkappaBalpha-dependent nuclear export of the complex through a chromosomal region maintenance-1 (CRM-1)-dependent pathway. Deacetylation of RelA by HDAC3 thus acts as an intranuclear molecular switch that both controls the duration of the NF-kappaB transcriptional response and contributes to the replenishment of the depleted cytoplasmic pool of latent NF-kappaB-IkappaBalpha complexes.

Structure of histone acetyltransferases

Histone acetyltranferase (HAT) enzymes are the catalytic subunits of multisubunit protein complexes that acetylate specific lysine residues on the N-terminal regions of the histone components of chromatin to promote gene activation. These enzymes, which now include more than 20 members, fall into distinct families that generally have high sequence similarity and related substrate specificity within families, but have divergent sequence and substrate specificity between families. Significant insights into the mode of catalysis and histone substrate binding have been provided by the structure determination of the divergent HAT enzymes Hat1, Gcn5/PCAF and Esa1. A comparison of these structures reveals a structurally conserved central core domain that mediates extensive interactions with the acetyl-coenzyme A cofactor, and structurally divergent N and C-terminal domains. A correlation of these structures with other studies reveals that the core domain plays a particularly important role in histone substrate catalysis and that the N and C-terminal domains play important roles in histone substrate binding. These correlations imply a related mode of catalysis and histone substrate binding by a diverse group of HAT enzymes.

Signal transduction pathways and chromatin structure in cancer cells

Molecular mechanisms controlling gene expression include cell shape, mechanical and chemical signal transduction pathways, chromatin remodeling, and DNA methylation. In this article, we will review the contribution of these molecular mechanisms and structural alterations in the malignant transformation of cells. The mechanical signaling pathway consists of the tissue matrix system that links together the three-dimensional skeletal networks, the extracellular matrix, cytoskeleton, and nuclear matrix. The cytoskeleton array is a dynamic system that transmits signals from the cell exterior to nuclear DNA. The composition and function of this mechanical signaling pathway is altered in cancer cells. Chemical signaling pathways such as the Ras/mitogen-activated protein kinase (MAPK) pathway stimulate the activity of kinases that modify transcription factors, histones, and chromatin remodeling factors. Oncoproteins deregulating this signaling pathway set in motion a series of events that cumulate to chromatin remodeling and aberrant gene expression. J. Cell. Biochem. Suppl. 35:27-35, 2000.

Ca2+ and BMP-6 signaling regulate E2F during epidermal keratinocyte differentiation

The epidermis consists of a squamous epithelium continuously replenished by committed stem cells, which can either self-renew or differentiate. We demonstrated previously that E2F genes are differentially expressed in developing epidermis (Dagnino, L., Fry, C. J., Bartley, S. M., Farnham, P., Gallie, B. L., and Phillips, R. A. (1997) Cell Growth Differ. 8, 553-563). Thus, we hypothesized that various E2F proteins likely play distinct growth regulatory roles in the undifferentiated stem cells and in terminally differentiated keratinocytes. To further understand the function of E2F genes in epidermal morphogenesis, we have examined the expression, regulation, and protein-protein interactions of E2F factors in undifferentiated cultured murine primary keratinocytes or in cells induced to differentiate with Ca(2+) or BMP-6 (bone morphogenetic protein 6). We find similar patterns of E2F regulation with both differentiating agents and demonstrate a switch in expression from E2F-1, -2, and -3 in undifferentiated, proliferating cells to E2F-5 in terminally differentiated keratinocytes. Inhibition of keratinocyte proliferation by transforming growth factor-beta1 did not enhance E2F-5 protein levels, suggesting that this response is specific to differentiation rather than reversible cell cycle withdrawal. E2F-5 up-regulation is also accompanied by formation of heteromeric nuclear complexes containing E2F5, p130, and histone deacetylase (HDAC) 1. Overexpression of E2F5 specifically inhibited DNA synthesis in undifferentiated keratinocytes in an HDAC-dependent manner, suggesting that E2F-5.p130.HDAC1 complexes are likely involved in the permanent withdrawal from the cell cycle of keratinocytes responding to differentiation stimuli.

TEL contacts multiple co-repressors and specifically associates with histone deacetylase-3

TEL (Translocation-ETS-Leukemia or ETV 6) is disrupted by multiple chromosomal translocations in acute leukemia. The loss of heterozygosity at the TEL locus in leukemias and the hemizygous deletion of TEL that is observed in various tumors, suggests that TEL is a tumor suppressor. Overexpression of TEL alters cellular morphology and represses the expression of the matrix metalloproteinase stromelysin-1. Based on these studies, deletion analysis was used to define the minimal repression domains of TEL. TEL-mediated repression required both the N-terminal pointed domain and a central region composed of amino acids 268-303. The mSin3A and N-CoR corepressors bind to the pointed domain and the central repression domain of TEL, respectively. Unexpectedly, histone deacetylase-3, but not other histone deacetylases, also associates with the central region of TEL. Histone deacetylase-3 interacts with a TEL mutant that cannot bind N-CoR, suggesting that this is a direct interaction with TEL. In addition, histone H3 was under-acetylated near the TEL-binding sites in the endogenous stromelysin-1 promoter when TEL was expressed. Furthermore, trichostatin A, a potent histone deacetylase inhibitor, impaired TEL-dependent repression of the stromelysin-1 promoter. Finally, while TEL-expression induced cellular aggregation of Ras-transformed cells, Trichostatin A reversed the TEL-induced cellular aggregation phenotype. Thus, the cumulative data suggests that histone deacetylase-3 activity is required for the transcriptional functions of TEL.

Protein modules that manipulate histone tails for chromatin regulation

Histones are the predominant protein components of chromatin and are subject to specific post-translational modifications that are correlated with transcriptional competence. Among these histone modifications are acetylation, phosphorylation and methylation, and recent studies reveal that conserved protein modules mediate the attachment, removal or recognition of these modifications. It is becoming clear that appropriate coordination of histone modifications and their manipulations by conserved protein modules are integral to gene-specific transcriptional regulation within chromatin.

Class II histone deacetylases: Structure, function, and regulation

Acetylation of histones, as well as non-histone proteins, plays important roles in regulating various cellular processes. Dynamic control of protein acetylation levels in vivo occurs through the opposing actions of histone acetyltransferases and histone deacetylases (HDACs). In the past few years, distinct classes of HDACs have been identified in mammalian cells. Class I members, such as HDAC1, HDAC2, HDAC3, and HDAC8, are well-known enzymatic transcriptional corepressors homologous to yeast Rpd3. Class II members, including HDAC4, HDAC5, HDAC6, HDAC7, and HDAC9, possess domains similar to the deacetylase domain of yeast Hda1. HDAC4, HDAC5, and HDAC7 function as transcriptional corepressors that interact with the MEF2 transcription factors and the N-CoR, BCoR, and CtBP corepressors. Intriguingly, HDAC4, HDAC5, and probably HDAC7 are regulated through subcellular compartmentalization controlled by site-specific phosphorylation and binding of 14-3-3 proteins; the regulation of these HDACs is thus directly linked to cellular signaling networks. Both HDAC6 and HDAC9 possess unique structural modules, so they may have special biological functions. Comprehension of the structure, function, and regulation of class II deacetylases is important for elucidating how acetylation regulates functions of histones and other proteins in vivo.Key words: histone acetylation, protein acetylation, histone deacetylase, 14-3-3 proteins.

Histone modifications and apoptosis: Cause or consequence?

Since the first description of apoptosis, genetic and biochemical studies have led to a greater understanding of the multiple pathways that eukaryotic cells can take to terminate their existence. These findings have also proven useful in understanding the development of various diseases such as AIDS, Alzheimer's, and Parkinson's and have provided potential targets for possible therapies. Despite all these studies, the mechanism of chromatin condensation, a morphological hallmark of apoptosis, remains elusive. This review describes the work to date on the post-translational modifications of histones during apoptosis and discusses the models that have been presented to explain the apoptotic condensation of chromatin.Key words: histones, nucleosomes, chromatin, apoptosis.

The emerging role of class II histone deacetylases

Histone acetylation and deacetylation play essential roles in modifying chromatin structure and regulating gene expression in all eukaryotes. Several histone acetyltransferases have been identified that act as transcriptional coactivators. In contrast, histone deacetylases (HDACs) are part of transcriptional corepressor complexes. Based on their similarity to known yeast factors, the human HDACs are grouped into three classes. Class I HDACs are similar to the yeast transcriptional repressor yRPD3, while class II HDACs are related to yHDA1 and class III HDACs to ySIR2. In this review, we focus on the biology of class II HDACs. These newly discovered enzymes have been implicated in cell differentiation and development, and many molecular details are emerging that shed light on class II HDAC function and regulation. We discuss the biological role of these factors in the context of physiological processes.Key words: transcriptional regulation, histone deacetylases, class II HDACs, nucleocytoplasmic shuttling, MEF2.

Avian erythroleukemia: a model for corepressor function in cancer

Transcriptional regulation at the level of chromatin plays crucial roles during eukaryotic development and differentiation. A plethora of studies revealed that the acetylation status of histones is controlled by multi-protein complexes containing (de)acetylase activities. In the current model, histone deacetylases and acetyltransferases are recruited to chromatin by DNA-bound repressors and activators, respectively. Shifting the balance between deacetylation, i.e. repressive chromatin and acetylation, i.e. active chromatin can lead to aberrant gene transcription and cancer. In human acute promyelocytic leukemia (APL) and avian erythroleukemia (AEL), chromosomal translocations and/or mutations in nuclear hormone receptors, RARalpha [NR1B1] and TRalpha [NR1A1], yielded oncoproteins that deregulate transcription and alter chromatin structure. The oncogenic receptors are locked in their 'off' mode thereby constitutively repressing transcription of genes that are critical for differentiation of hematopoietic cells. AEL involves an oncogenic version of the chicken TRalpha, v-ErbA. Apart from repression by v-ErbA via recruitment of corepressor complexes, other repressors and corepressors appear to be involved in repression of v-ErbA target genes, such as carbonic anhydrase II (CAII). Reactivation of repressed genes in APL and AEL by chromatin modifying agents such as inhibitors of histone deacetylase or of methylation provides new therapeutic strategies in the treatment of acute myeloid leukemia.

Homo-oligomerisation and nuclear localisation of mouse histone deacetylase 1

Reversible histone acetylation changes the chromatin structure and can modulate gene transcription. Mammalian histone deacetylase 1 (HDAC1) is a nuclear protein that belongs to a growing family of evolutionarily conserved enzymes catalysing the removal of acetyl residues from core histones and other proteins. Previously, we have identified murine HDAC1 as a growth factor-inducible protein in murine T-cells. Here, we characterise the molecular function of mouse HDAC1 in more detail. Co-immunoprecipitation experiments with epitope-tagged HDAC1 protein reveal the association with endogenous HDAC1 enzyme. We show that HDAC1 can homo-oligomerise and that this interaction is dependent on the N-terminal HDAC association domain of the protein. Furthermore, the same HDAC1 domain is also necessary for in vitro binding of HDAC2 and HDAC3, association with RbAp48 and for catalytic activity of the enzyme. A lysine-rich sequence within the carboxy terminus of HDAC1 is crucial for nuclear localisation of the enzyme. We identify a C-terminal nuclear localisation domain, which is sufficient for the transport of HDAC1 and of reporter fusion proteins into the nucleus. Alternatively, HDAC1 can be shuttled into the nucleus by association with another HDAC1 molecule via its N-terminal HDAC association domain. Our results define two domains, which are essential for the oligomerisation and nuclear localisation of mouse HDAC1.

Sex-dependent regulation by dexamethasone of murine hydroxysteroid sulfotransferase gene expression

To determine whether glucocorticoid-inducible expression of hepatic hydroxysteroid sulfotransferase is conserved in mouse, the effects of dexamethasone (DEX) on hydroxysteroid sulfotransferase (mSULT2A) gene expression were investigated in primary cultured hepatocytes prepared from C57BL/6J mice. In female mouse hepatocytes, DEX (10(-7) and 10(-5) M, respectively) produced 8.2- and 17.8-fold increases, respectively, in the amounts of mSULT2A mRNA relative to control. By contrast, mSULT2A mRNA levels were undetectable in male mouse hepatocytes. Female-predominant mSULT2A mRNA expression was also observed in liver samples from C57BL/6J and three other mouse strains. Treatment of primary cultured female mouse hepatocytes with dihydrotestosterone in the presence of DEX suppressed mSULT2 expression. Transfection of primary cultured male or female mouse hepatocytes with a rat SULT2-40/41 reporter construct revealed that hepatocytes of both sexes have sufficient machinery to achieve DEX-inducible SULT2 transcription. However, treatment with the potent histone deacetylase inhibitor trichostatin A failed to elicit mSULT2A expression in male mouse hepatocytes.

Trichostatin A reverses skewed expression of CD154, interleukin-10, and interferon-gamma gene and protein expression in lupus T cells

In systemic lupus erythematosus (SLE), T helper cells exhibit increased and prolonged expression of cell-surface CD40 ligand (CD154), spontaneously overproduce interleukin-10 (IL-10), but underproduce interferon-gamma (IFN-gamma). We tested the hypothesis that the imbalance of these gene products reflects skewed expression of CD154, IL-10, and IFN-gamma genes. Here, we demonstrate that the histone deacetylase inhibitor, trichostatin A, significantly down-regulated CD154 and IL-10 and up-regulated IFN-gamma gene expression in SLE T cells. This reversal corrected the aberrant expression of these gene products, thereby enhancing IFN-gamma production and inhibiting IL-10 and CD154 expression. That trichostatin A can simultaneously reverse the skewed expression of multiple genes implicated in the immunopathogenesis of SLE suggests that this pharmacologic agent may be a candidate for the treatment of this autoimmune disease.