The human histone deacetylase family

Histone deacetylases augment cytokine induction of the iNOS gene

The inducible nitric oxide synthase (iNOS) gene plays an important role in renal diseases. Transcription is the principal mode of regulation. This study explores the role of acetylation in cytokine-mediated iNOS induction in cultured murine mesangial cells and RAW 264.7 cells. Nitric oxide production was measured by the Griess reaction. The activity of the iNOS promoter and a nuclear factor-kappa B (NF-kappa B) element promoter were assessed in transient transfection assays. Gel shift and supershift assays were used to identify NF-kappa B in nuclear extracts. Protein-protein interactions were assayed by co-immunoprecipitation and GST pull-down assays. Treatment with the histone deacetylase (HDAC) inhibitor trichostatin A (TSA) and overexpression of HDAC isoforms were used to assess the impact of acetylation status on iNOS and NF-kappa B element promoter activity. TSA inhibited induction of endogenous NO production and iNOS as well as NF-kappa B element promoter activity in response to interleukin-1 beta (IL-1 beta) or lipopolysaccharide (LPS) + interferon-gamma (IFN-gamma) in both cell types without altering NF-kappa B DNA binding activity. Overexpression of specific HDAC isoforms enhanced cytokine induction of both the iNOS and the NF-kappa B element promoter. HDAC2 and NF-kappa B p65 co-immunoprecipitated from mesangial cell nuclear extracts, and in vitro translated HDAC2 specifically interacted with an NF-kappa B p65 GST fusion protein. Hyperacetylation diminishes cytokine induction of iNOS transcription activity, at least partially, by limiting the functional efficacy of NF-kappa B. The specific recruitment of HDAC2 to NF-kappa B at target promoters and the consequent effects on acetylation status may play an important role in regulating iNOS as well as other NF-kappa B-dependent genes involved in inflammation.

Tip60 and histone deacetylase 1 regulate androgen receptor activity through changes to the acetylation status of the receptor

The androgen receptor (AR), a member of the nuclear hormone receptor superfamily, is thought to play an important role in the development of prostate cancer. The AR is a hormone-dependent transcription factor that activates expression of numerous androgen-responsive genes. Histone acetyltransferase-containing proteins have been shown to increase activity of several transcription factors, including nuclear hormone receptors, by eliciting histone acetylation, which facilitates promoter access to the transcriptional machinery. Conversely, histone deacetylases (HDACs) have been identified which reduce levels of histone acetylation and are associated with transcriptional repression by various transcription factors. We have previously shown that Tip60 (Tat-interactive protein, 60 kDa) is a bona fide co-activator protein for the AR. Here we show that Tip60 directly acetylates the AR, which we demonstrate is a requisite for Tip60-mediated transcription. To define a mechanism for repression of AR function, we demonstrate that AR activity is specifically down-regulated by the histone deacetylase activity of HDAC1. Furthermore, using both mammalian two-hybrid and immunoprecipitation experiments, we show that AR and HDAC1 interact, suggestive of a direct role for down-regulation of AR activity by HDAC1. In chromatin immunoprecipitation assays, we provide evidence that AR, Tip60, and HDAC1 form a trimeric complex upon the endogenous AR-responsive PSA promoter, suggesting that acetylation and deacetylation of the AR is an important mechanism for regulating transcriptional activity.

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.

JDP2, a repressor of AP-1, recruits a histone deacetylase 3 complex to inhibit the retinoic acid-induced differentiation of F9 cells

Up-regulation of the c-jun gene is a critical event in the retinoic acid (RA)-mediated differentiation of embryonal carcinoma F9 cells. Activating transcription factor 2 (ATF-2) and p300 cooperate in the activation of transcription of the c-jun gene during the differentiation of F9 cells. We show here that the overexpression of Jun dimerization protein 2 (JDP2), a repressor of AP-1, inhibits the transactivation of the c-jun gene by ATF-2 and p300 by recruitment of the histone deacetylase 3 (HDAC3) complex, thereby repressing the RA-induced transcription of the c-jun gene and inhibiting the RA-mediated differentiation of F9 cells. Moreover, chromatin immunoprecipitation assays showed that the JDP2/HDAC3 complex, which binds to the differentiation response element within the c-jun promoter in undifferentiated F9 cells, was replaced by the p300 complex in response to RA, with an accompanying change in the histone acetylation status of the chromatin, the initiation of transcription of the c-jun gene, and the subsequent differentiation of F9 cells. These results suggest that JDP2 may be a key factor that controls the commitment of F9 cells to differentiation and shed new light on the mechanism by which an AP-1 repressor functions.

Inhibitory molecules in signal transduction pathways of cardiac hypertrophy

Cardiac hypertrophy is induced by a variety of diseases, such as hypertension, valvular diseases, myocardial infarction, and endocrine disorders. Although cardiac hypertrophy may initially be a beneficial response that normalizes wall stress and maintains normal cardiac function, prolonged hypertrophy is a leading cause of heart failure and sudden death. A number of studies have elucidated molecules responsible for the development of cardiac hypertrophy, including the mitogen-activated protein (MAP) kinases pathway, Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway, and calcium/calmodulin-dependent protein phosphatase calcineurin pathway. These molecules may be targets for therapies designed to prevent the progression of cardiac hypertrophy. Numerous studies have focused on characterization of the intracellular signal transduction molecules that promote cardiac hypertrophy in order to clarify the molecular mechanisms, but there have been only a few reports on the inhibitory regulators of hypertrophic response. Recently, several molecules have attracted much attention as endogenous inhibitory regulators of cardiac hypertrophy. Enhancement of these inhibitory regulators would also seem to be a potential approach for the pharmacological treatment of hypertrophy. In this review, we summarize the inhibitory molecules of cardiac hypertrophy.

Histone deacetylases as therapeutic targets in hematologic malignancies

During the past 5 years, it has become increasingly apparent that deregulated transcriptional control is a root cause of hematologic malignancy. Chromosomal translocations yield novel fusion transcription factors that in turn either activate genes critical for cell growth or repress genes important for normal cellular differentiation. Many of the fusion proteins of myeloid leukemia are aberrant transcriptional repressors and share the property of recruiting histone deacetylases (HDACs) to target genes. HDACs, by acting on chromatin and on transcription factors themselves, can modulate gene regulation. HDACs also play major roles in the function of well-characterized tumor suppressors such as p53 and Rb. Thus, HDACs are a compelling therapeutic target for cancer therapy. Several classes of HDAC inhibitors induce differentiation and cell death in myeloid and lymphoid model systems. Some of these are now in clinical trials for hematologic malignancies. The nature of HDAC function, the classes of inhibitors available, and recent experimental and clinical data will be reviewed.

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.

Regulation of lifespan by histone deacetylase

Aging is a universal biological phenomenon in eukaryotes, but why and how we age still remain mysterious. It would be of great biological interest and practical importance if we could uncover the molecular mechanism of aging, and find a way to delay the aging process while maintaining physical and mental strengths of youth. Histone deacetylases (HDACs) such as SIR2 and RPD3 are known to be involved in the extension of lifespan in yeast and Caenorhabditis elegans. An inhibitor of HDACs, phenylbutyrate, also can significantly increase the lifespan of Drosophila, without diminution of locomotor vigor, resistance to stress, or reproductive ability. Treatment for a limited period, either early or late in adult life, is also effective. Alteration in the pattern of gene expression, including induction or repression of numerous genes involved in longevity by changing the level and the pattern of histone acetylation may be an important factor in determining the longevity of animals.

Human SIR2 deacetylates p53 and antagonizes PML/p53-induced cellular senescence

The yeast Sir2 protein mediates chromatin silencing through an intrinsic NAD-dependent histone deacetylase activity. Sir2 is a conserved protein and was recently shown to regulate lifespan extension both in budding yeast and worms. Here, we show that SIRT1, the human Sir2 homolog, is recruited to the promyelocytic leukemia protein (PML) nuclear bodies of mammalian cells upon overexpression of either PML or oncogenic Ras (Ha-rasV12). SIRT1 binds and deacetylates p53, a component of PML nuclear bodies, and it can repress p53-mediated transactivation. Moreover, we show that SIRT1 and p53 co-localize in nuclear bodies upon PML upregulation. When overexpressed in primary mouse embryo fibroblasts (MEFs), SIRT1 antagonizes PML-induced acetylation of p53 and rescues PML-mediated premature cellular senescence. Taken together, our data establish the SIRT1 deacetylase as a novel negative regulator of p53 function capable of modulating cellular senescence.

Functional requirement for histone deacetylase 1 in Caenorhabditis elegans gonadogenesis

Histone acetylation and deacetylation have been implicated in the regulation of gene expression. Molecular studies have shown that histone deacetylases (HDACs) function as transcriptional repressors. However, very little is known about their roles during development in multicellular organisms. We previously demonstrated that inhibition of maternal and zygotic expression of histone deacetylase 1 (HDA-1) causes embryonic lethality in Caenorhabditis elegans. Here, we report the identification of an hda-1 genetic mutant which has also been called a gon-10 mutant (for gonadogenesis defective 10) and show that loss of HDA-1 zygotic expression results in specific postembryonic defects in gonadogenesis and vulval development. We provide evidence that the lag-2 gene, which plays a role in gonadogenesis and vulval development and encodes a Notch ligand, is derepressed in gon-10 animals, suggesting that lag-2 may be a target of HDA-1. Our findings reveal a novel and specific function for the ubiquitously expressed HDA-1 in C. elegans gonadogenesis and place hda-1 in the Notch signaling pathway.

Conserved enzymatic production and biological effect of O-acetyl-ADP-ribose by silent information regulator 2-like NAD+-dependent deacetylases

Silent information regulator 2 (Sir2) family of enzymes has been implicated in many cellular processes that include histone deacetylation, gene silencing, chromosomal stability, and aging. Yeast Sir2 and several homologues have been shown to be NAD(+)-dependent histone/protein deacetylases. Previously, it was demonstrated that the yeast enzymes catalyze a unique reaction mechanism in which the cleavage of NAD(+) and the deacetylation of substrate are coupled with the formation of O-acetyl-ADP-ribose, a novel metabolite. We demonstrate that the production of O-acetyl-ADP-ribose is evolutionarily conserved among Sir2-like enzymes from yeast, Drosophila, and human. Also, endogenous yeast Sir2 complex from telomeres was shown to generate O-acetyl-ADP-ribose. By using a quantitative microinjection assay to examine the possible biological function(s) of this newly discovered metabolite, we demonstrate that O-acetyl-ADP-ribose causes a delay/block in oocyte maturation and results in a delay/block in embryo cell division in blastomeres. This effect was mimicked by injection of low nanomolar levels of active enzyme but not with a catalytically impaired mutant, indicating that the enzymatic activity is essential for the observed effects. In cell-free oocyte extracts, we demonstrate the existence of cellular enzymes that can efficiently utilize O-acetyl-ADP-ribose.

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.

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 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.

Isolation and characterization of a novel class II histone deacetylase, HDAC10

A novel histone deacetylase, HDAC10, was isolated from a mixed tissue human cDNA library. HDAC10 was classified as a class II subfamily member based upon similarity to HDAC6. The genomic structure of HDAC10 was found to consist of 20 exons. HDAC10 has two sequence variants, HDAC10v1 and HDAC10v2, and two transcripts were detectable by Northern blot analysis. HDAC10v1 and HDAC10v2 were found to be identical through exon 17 but diverged after this exon. HDAC10v2 has an 82-bp alternate exon that generates a frameshift and shortens the sequence by 11 amino acids. In this study, the characterization of HDAC10v1 was performed. HDAC10v1 has an N-terminal catalytic domain, two putative C-terminal retinoblastoma protein binding domains, and a nuclear hormone receptor binding motif. The HDAC10v1 enzyme was found to be catalytically active based upon its ability to deacetylate a (3)H-acetylated histone H4 N-terminal peptide. Immunofluorescence detection of transfected HDAC10v1-FLAG indicated that the enzyme is a nuclear protein. Furthermore, coimmunoprecipitation experiments indicated that HDAC10v1 associated with HDAC2 and SMRT (silencing mediator for retinoid and thyroid hormone receptors). In addition, based upon the public data base, a single nucleotide polymorphism was found in the C terminus of HDAC10 which changes a Gly residue to Cys, suggesting that HDAC10 molecules containing these single nucleotide polymorphisms may be folded improperly. HDAC10 extends the HDAC superfamily and adds to a growing number of HDACs that have been found to have splice variants, suggesting that RNA processing may play a role in mediating the activity of HDACs.

Biological roles and mechanistic actions of co-repressor complexes

Transcriptional repression, which plays a crucial role in diverse biological processes, is mediated in part by non-DNA-binding co-repressors. The closely related co-repressor proteins N-CoR and SMRT, although originally identified on the basis of their ability to associate with and confer transcriptional repression through nuclear receptors, have been shown to be recruited to many classes of transcription factor and are in fact components of multiple protein complexes containing histone deacetylase proteins. This association with histone deacetylase activity provides an important component of the mechanism that allows DNA-binding proteins interacting with N-CoR or SMRT to repress transcription of specific target genes. Both N-CoR and SMRT are important targets for cell signaling pathways, which influence their expression levels, subcellular localization and association with other proteins. Recently, the biological importance of these proteins has been revealed by studies of genetically engineered mice and human diseases such as acute promyelocytic leukemia (APL) and resistance to thyroid hormone(RTH).

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.

MEF2: a calcium-dependent regulator of cell division, differentiation and death

The decision of a cell to divide, differentiate or die is dependent on the coupling of cytoplasmic signals to the activation and repression of specific sets of genes in the nucleus. Many of the signal transduction pathways that control these cellular decisions are activated by elevation of intracellular calcium. Recent studies have revealed a central role for the myocyte enhancer factor-2 (MEF2) family of transcription factors in linking calcium-dependent signaling pathways to the genes responsible for cell division, differentiation and death. This article describes the post-translational mechanisms that confer calcium-sensitivity to MEF2 and its downstream target genes, and considers how this transcription factor can control diverse and mutually exclusive cellular decisions.

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?

Expression profile of histone deacetylase 1 in gastric cancer tissues

Although histone deacetylases (HDACs) appear to play a crucial role in carcinogenesis, the expression status of HDACs in primary human cancer tissues has not yet been reported. In this study, we investigated the expression level of HDAC1 in 25 paired primary human gastric cancer (GC) tissues and corresponding normal tissues through semi-quantitative RT-PCR and immunoblot analysis. The HDAC1 expression pattern was also topologically examined through immunohistochemistry. Overexpression of HDAC1 mRNA was detected in 68% of GC tissues (17 of 25), and the relative density of HDAC1 mRNA in GC tissue was increased 1.8-fold versus the normal counterpart (P < 0.01). Elevated expression of HDAC1 protein was also detected in 61% of GC samples (11 of 18), which also showed an increased mRNA level of HDAC. Immunohistochemically, overexpression of HDAC1 was predominantly localized in the nuclei of most neoplastic cells, including embolic tumor cells, whereas normal glandular epithelial cells revealed only weak HDAC1 expression that was focal in distribution. Thus, the present study clearly demonstrates that HDAC1 is overexpressed in GC and probably plays a significant role in gastric carcinogenesis.

Identification of components of the murine histone deacetylase 6 complex: link between acetylation and ubiquitination signaling pathways

The immunopurification of the endogenous cytoplasmic murine histone deacetylase 6 (mHDAC6), a member of the class II HDACs, from mouse testis cytosolic extracts allowed the identification of two associated proteins. Both were mammalian homologues of yeast proteins known to interact with each other and involved in the ubiquitin signaling pathway: p97/VCP/Cdc48p, a homologue of yeast Cdc48p, and phospholipase A2-activating protein, a homologue of yeast UFD3 (ubiquitin fusion degradation protein 3). Moreover, in the C-terminal region of mHDAC6, a conserved zinc finger-containing domain named ZnF-UBP, also present in several ubiquitin-specific proteases, was discovered and was shown to mediate the specific binding of ubiquitin by mHDAC6. By using a ubiquitin pull-down approach, nine major ubiquitin-binding proteins were identified in mouse testis cytosolic extracts, and mHDAC6 was found to be one of them. All of these findings strongly suggest that mHDAC6 could be involved in the control of protein ubiquitination. The investigation of biochemical properties of the mHDAC6 complex in vitro further supported this hypothesis and clearly established a link between protein acetylation and protein ubiquitination.

Independent dynamic regulation of histone phosphorylation and acetylation during immediate-early gene induction

Induction of c-fos and c-jun is associated with phosphoacetylation of histone H3 and acetylation of histone H4. Upon induction, a large population of nucleosomes becomes highly acetylated on histones H3 and H4, whereas a much smaller population of comparable nucleosomes at similar positions along the gene becomes phosphoacetylated. Inhibiting histone H3 phosphorylation with kinase inhibitors does not measurably alter the enhanced acetylation of these nucleosomes. Finally, whereas H3 phosphorylation is a MAP kinase-mediated inducible event, we found acetylation to be continuously turning over by the targeted action of HATs and HDACs in the absence of any stimulation or gene transcription. These studies suggest that phosphorylation and acetylation are independently and dynamically regulated at these genes and reveal the complexity of multiple histone modifications at immediate-early gene chromatin.

Update on immunologic basis of celiac disease

During the past few years several seminal studies have greatly expanded our knowledge on celiac disease pathogenesis. This review focuses on aspects that have been most properly addressed and where substantial new information has been gathered include. Topics covered include (a) the identification of T-cell epitopes in gluten and the mechanisms of specific T-cell response in celiac disease small intestine; (b) the mechanisms of induction of mucosal lesion; and (c) the putative role of non-T-cell factors in driving mucosal response to gliadin. After discussing a brief history of the "quest for the cause of celiac disease," we examine the development of the typical celiac lesion (the crypt hyperplastic mucosal atrophy) as it generally unfolds: the increased entry of dietary antigens; the early changes, linked to specific components of the innate immunity rather than to its adaptive branch; the most thoroughly investigated subsequent response, involving a strong T-cell response and cytokines; and the factors responsible for enterocytes' death. The emerging pattern is that of a complex interaction of factors, although far from being completely understood, but fascinating as it opens an incredible window of knowledge on an autoimmune disorder whose environmental factor is known, whose autoantigen is known, whose autoantibodies are known: a truly unique situation in medicine.

Histone deacetylase inhibitors as new cancer drugs

Histone deacetylase inhibitors are potent inducers of growth arrest, differentiation, or apoptotic cell death in a variety of transformed cells in culture and in tumor bearing animals. Histone deacetylases and the family of histone acetyl transferases are involved in determining the acetylation of histones, which play a role in regulation of gene expression. Radiograph crystallographic studies reveal that the histone deacetylase inhibitors, suberoylanilide hydroxamic acid and trichostatin A, fit into the catalytic site of histone deacetylase, which has a tubular structure with a zinc atom at its base. The hydroxamic acid moiety of the inhibitor binds to the zinc. Histone deacetylase inhibitors cause acetylated histones to accumulate in both tumor and peripheral circulating mononuclear cells. Accumulation of acetylated histones has been used as a marker of the biologic activity of the agents. Hydroxamic acid-based histone deacetylase inhibitors limit tumor cell growth in animals with little or no toxicity. These compounds act selectively on genes, altering the transcription of only approximately 2% of expressed genes in cultured tumor cells. A number of proteins other than histones are substrates for histone deacetylases. The role that these other targets play in histone deacetylase inducement of cell growth arrest, differentiation, or apoptotic cell death is not known. This review summarizes the characteristics of a variety of inhibitors of histone deacetylases and their effects on transformed cells in culture and tumor growth in animal models. Several structurally different histone deacetylase inhibitors are in phase I or II clinical trials in patients with cancers.

Inhibition of histone deacetylase activity causes cell type-specific induction of the PDGF-B promoter only in the absence of activation by its enhancer

There is a strong correlation between the acetylation status of nucleosomal histones and transcriptional activity. Here we show that the histone deacetylase inhibitor trichostatin A (TSA) activates reporter gene constructs driven by the human platelet-derived growth factor B (PDGF-B) gene promoter. This activation showed an inverse correlation with the cell type-specific transcriptional activities of the promoter. The TSA response was minimal in three tumor cell lines that exhibit high-level promoter activity. In JEG-3 choriocarcinoma cells, however, where the basal promoter activity is considerably lower, there was a strong response to TSA. This was in contrast to constructs that included a PDGF-B enhancer, which were refractory to TSA effects, indicating a possible function of the enhancer in modulating acetylation status. Analysis of PDGF-B promoter mutants with respect to TSA induction revealed no specific TSA-responsive element, but suggested that association of nonacetylated histones to the PDGF-B promoter may be a default process in the absence of enhancer activation. TSA treatment of JEG-3 cells, either alone or in combination with the demethylating agent 5-azacytidine, failed to activate the silenced endogenous PDGF-B transcript, however, which appears to be repressed by additional mechanisms.

The hairless gene mutated in congenital hair loss disorders encodes a novel nuclear receptor corepressor

The mammalian hairless (hr) gene plays a critical role in the maintenance of hair growth. Although the hr gene has been identified, the biochemical function of its encoded protein (Hr) has remained obscure. Here, we show that Hr functions as a transcriptional corepressor for thyroid hormone receptors (TRs). We find that two independent regions of Hr mediate TR binding and that interaction requires a cluster of hydrophobic residues similar to the binding motifs proposed for nuclear receptor corepressors (N-CoR and SMRT). Similarly, we show that Hr binds to the same region of TR as known corepressors. We show that Hr interacts with histone deacetylases (HDACs) and is localized to matrix-associated deacetylase (MAD) bodies, indicating that the mechanism of Hr-mediated repression is likely through associated HDAC activity. Thus, Hr is a component of the corepressor machinery, and despite its lack of sequence identity with previously described corepressors, its mode of action is remarkably conserved. On the basis of its thyroid hormone-inducible and tissue- and developmental-specific expression, Hr likely defines a new class of nuclear receptor corepressors that serve a more specialized role than ubiquitous corepressors. The discovery that Hr is a corepressor provides a molecular basis for specific hair loss syndromes in both humans and mice.

Control of muscle development by dueling HATs and HDACs

Skeletal muscle cells have provided an especially auspicious system in which to dissect the roles of chromatin structure in the control of cell growth, differentiation, and development. The MyoD and MEF2 families of transcription factors act cooperatively to regulate the expression of skeletal muscle-specific genes. Recent studies have shown that these two classes of transcription factors associate with histone acetyltransferases and histone deacetylases to control the activation and repression, respectively, of the muscle differentiation program. Signaling systems that regulate the growth and differentiation of muscle cells act, at least in part, by regulating the intracellular localization and associations of these chromatin remodeling enzymes with myogenic transcription factors. We describe the molecules and mechanisms involved in chromatin remodeling during skeletal muscle development.

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.

The modular nature of histone deacetylase HDAC4 confers phosphorylation-dependent intracellular trafficking

In C2C12 myoblasts, endogenous histone deacetylase HDAC4 shuttles between cytoplasmic and nuclear compartments, supporting the hypothesis that its subcellular localization is dynamically regulated. However, upon differentiation, this dynamic equilibrium is disturbed and we find that HDAC4 accumulates in the nuclei of myotubes, suggesting a positive role of nuclear HDAC4 in muscle differentiation. Consistent with the notion of regulation of HDAC4 intracellular trafficking, we reveal that HDAC4 contains a modular structure consisting of a C-terminal autonomous nuclear export domain, which, in conjunction with an internal regulatory domain responsive to calcium/calmodulin-dependent protein kinase IV (CaMKIV), determines its subcellular localization. CaMKIV phosphorylates HDAC4 in vitro and promotes its nuclear-cytoplasmic shuttling in vivo. However, although 14-3-3 binding of HDAC4 has been proposed to be important for its cytoplasmic retention, we find this interaction to be independent of CaMKIV. Rather, the HDAC4.14-3-3 complex exists in the nucleus and is required to confer CaMKIV responsiveness. Our results suggest that the subcellular localization of HDAC4 is regulated by sequential phosphorylation events. The first event is catalyzed by a yet to be identified protein kinase that promotes 14-3-3 binding, and the second event, involving protein kinases such as CaMKIV, leads to efficient nuclear export of the HDAC4.14-3-3 complex.

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.

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.

Trichostatin A, an inhibitor of histone deacetylase, inhibits hypoxia-induced angiogenesis

Trichostatin A (TSA), a hydroxamate-type inhibitor of mammalian histone deacetylases has been reported to inhibit angiogenesis both in vitro and in vivo. TSA inhibits hypoxia-induced production of the angiogenic mediator vascular endothelial cell growth factor (VEGF) by tumour cells and also inhibits directly endothelial cell migration and proliferation. HDAC inhibitors such as TSA are currently of major interest as potential anticancer therapeutics, largely because of their well-documented properties of inhibiting proliferation and inducing apoptosis of tumour cells. The finding that HDAC appears to be a critical regulator of angiogenesis in addition to tumour cell growth will heighten interest in the development of HDAC inhibitors as potential anticancer drugs.

Silencing of gene expression: implications for design of retrovirus vectors

Transcriptional silencing of retroviruses poses a major obstacle to their use as gene therapy vectors. Silencing is most pronounced in stem cells which are desirable targets for therapeutic gene delivery. Many vector designs combat silencing through cis-modifications of retroviral vector sequences. These designs include mutations of known retroviral silencer elements, addition of positive regulatory elements and insulator elements to protect the transgene from negative position effects. Similar strategies are being applied to lentiviral vectors that readily infect non-dividing quiescent stem cells. Collectively these cis-modifications have significantly improved vector design but optimal expression may require additional intervention to escape completely the trans-factors that scan for foreign DNA, establish silencing in stem cells and maintain silencing in their progeny. Cytosine methylation of CpG sites was proposed to cause retroviral silencing over 20 years ago. However, several studies provide evidence that retrovirus silencing acts through methylase-independent mechanisms. We propose an alternative silencing mechanism initiated by a speculative stem cell-specific "somno-complex". Further understanding of retroviral silencing mechanisms will facilitate better gene therapy vector design and raise new strategies to block transcriptional silencing in transduced stem cells.

The transcriptional corepressor MITR is a signal-responsive inhibitor of myogenesis

Activation of muscle-specific genes by members of the myocyte enhancer factor 2 (MEF2) and MyoD families of transcription factors is coupled to histone acetylation and is inhibited by class II histone deacetylases (HDACs) 4 and 5, which interact with MEF2. The ability of HDAC4 and -5 to inhibit MEF2 is blocked by phosphorylation of these HDACs at two conserved serine residues, which creates docking sites for the intracellular chaperone protein 14-3-3. When bound to 14-3-3, HDACs are released from MEF2 and transported to the cytoplasm, thereby allowing MEF2 to stimulate muscle-specific gene expression. MEF2-interacting transcription repressor (MITR) shares homology with the amino-terminal regions of HDAC4 and -5, but lacks an HDAC catalytic domain. Despite the absence of intrinsic HDAC activity, MITR acts as a potent inhibitor of MEF2-dependent transcription. Paradoxically, however, MITR has minimal inhibitory effects on the skeletal muscle differentiation program. We show that a substitution mutant of MITR containing alanine in place of two serine residues, Ser-218 and Ser-448, acts as a potent repressor of myogenesis. Our findings indicate that promyogenic signals antagonize the inhibitory action of MITR by targeting these serines for phosphorylation. Phosphorylation of Ser-218 and Ser-448 stimulates binding of 14-3-3 to MITR, disrupts MEF2:MITR interactions, and alters the nuclear distribution of MITR. These results reveal a role for MITR as a signal-dependent regulator of muscle differentiation.

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.