Cloning and characterization of the murine histone deacetylase (HDAC3)

Histone Deacetylase 3 Inhibition Decreases Cerebral Edema and Protects the Blood–Brain Barrier After Stroke

We have previously shown that selective inhibition of histone deacetylase 3 (HDAC3) decreases infarct volume and improves long-term functional outcomes after stroke. In this study, we examined the effects of HDAC3 inhibition on cerebral edema and blood–brain barrier (BBB) leakage and explored its underlying mechanisms. Adult male Wistar rats were subjected to 2-h middle cerebral artery occlusion (MCAO) and randomly treated i.p. with either vehicle or a selective HDAC3 inhibitor (RGFP966) at 2 and 24 h after stroke. Modified neurological severity scores (mNSS) were calculated at 2 h, 1 day, and 3 days. H&E, Evans blue dye (EBD) assay, and fluorescein isothiocyanate (FITC)-dextran were employed to assess cerebral edema and BBB leakage. Western blot for matrix metalloproteinase-9 (MMP9), MMP-9 zymography, and immunostaining for HDAC3, GFAP, Iba-1, albumin, aquaporin-4, claudin-5, ZO-1, and NF-kB were performed. Early RGFP966 administration decreased cerebral edema (p = 0.002) and BBB leakage, as measured by EBD assay, FITC-dextran, and albumin extravasation (p < 0.01). RGFP966 significantly increased tight junction proteins (claudin-5 and ZO-1) in the peri-infarct area. RGFP966 also significantly decreased HDAC3 in GFAP + astrocytes, which correlated with better mNSS (r = 0.67, p = 0.03) and decreased cerebral edema (r = 0.64, p = 0.04). RGFP966 decreased aquaporin-4 in GFAP + astrocytes (p = 0.002), as well as, the inflammatory markers Iba-1, NF-kB, and MMP9 in the ischemic brain (p < 0.05). Early HDAC3 inhibition decreases cerebral edema and BBB leakage. BBB protection by RGFP966 is mediated in part by the upregulation of tight junction proteins, downregulation of aquaporin-4 and HDAC3 in astrocytes, and decreased neuroinflammation.

Neuroprotective Effects of Selective Inhibition of Histone Deacetylase 3 in Experimental Stroke

Histone deacetylase 3 (HDAC3) has been implicated as neurotoxic in several neurodegenerative conditions. However, the role of HDAC3 in ischemic stroke has not been thoroughly explored. We tested the hypothesis that selective inhibition of HDAC3 after stroke affords neuroprotection. Adult male Wistar rats (n = 8/group) were subjected to 2 h of middle cerebral artery occlusion (MCAO), and randomly selected animals were treated intraperitoneally twice with either vehicle (1% Tween 80) or a selective HDAC3 inhibitor (RGFP966, 10 mg/kg) at 2 and 24 h after MCAO. Long-term behavioral tests were performed up to 28 days after MCAO. Another set of rats (n = 7/group) were sacrificed at 3 days for histological analysis. Immunostaining for HDAC3, acetyl-Histone 3 (AcH3), NeuN, TNF-alpha, toll-like receptor 4 (TLR4), cleaved caspase-3, cleaved poly (ADP-ribose) polymerase (PARP), Akt, and TUNEL were performed. Selective HDAC3 inhibition improved long-term functional outcome (p < 0.05) and reduced infarct volume (p < 0.0001). HDAC3 inhibition increased levels of AcH3 in the ischemic brain (p = 0.016). Higher levels of AcH3 were significantly correlated with better neurological scores and smaller infarct volumes (r = 0.74, p = 0.002; r = 0.6, p = 0.02, respectively). The RGFP966 treatment reduced apoptosis-TUNEL+, cleaved caspase-3+, and cleaved PARP+ cells-and neuroinflammation-TNF-alpha+ and TLR4+ cells-in the ischemic border compared to vehicle control (p < 0.05). The RGFP966 treatment also increased Akt expression in the ipsilateral cortex (p < 0.001). Selective HDAC3 inhibition after stroke improves long-term neurological outcome and decreases infarct volume. The neuroprotective effects of HDAC3 inhibition are associated with a reduction in apoptosis and inflammation and upregulation of the Akt pathway.

HDAC3 promotes meiotic apparatus assembly in mouse oocytes by modulating tubulin acetylation

Histone deacetylases (HDACs) have been shown to deacetylate numerous cellular substrates that govern a wide array of biological processes. HDAC3, a member of the Class I HDACs, is a highly conserved and ubiquitously expressed protein. However, its roles in meiotic oocytes are not known. In the present study, we find that mouse oocytes depleted of HDAC3 are unable to completely progress through meiosis, and are blocked at metaphase I. These HDAC3 knockdown oocytes show spindle/chromosome organization failure, with severely impaired kinetochore-microtubule attachments. Consistent with this, the level of BubR1, a central component of the spindle assembly checkpoint, at kinetochores is dramatically increased in metaphase oocytes following HDAC3 depletion. Knockdown and overexpression experiments reveal that HDAC3 modulates the acetylation status of α-tubulin in mouse oocytes. Importantly, the deacetylation mimetic mutant tubulin-K40R can partly rescue the defective phenotypes of HDAC3 knockdown oocytes. Our data support a model whereby HDAC3, through deacetylating tubulin, promotes microtubule stability and the establishment of kinetochore-microtubule interaction, consequently ensuring proper spindle morphology, accurate chromosome movement and orderly meiotic progression during oocyte maturation.

Involvement of HDAC1 and HDAC3 in the Pathology of Polyglutamine Disorders: Therapeutic Implications for Selective HDAC1/HDAC3 Inhibitors

Histone deacetylases (HDACs) enzymes, which affect the acetylation status of histones and other important cellular proteins, have been recognized as potentially useful therapeutic targets for a broad range of human disorders. Emerging studies have demonstrated that different types of HDAC inhibitors show beneficial effects in various experimental models of neurological disorders. HDAC enzymes comprise a large family of proteins, with18 HDAC enzymes currently identified in humans. Hence, an important question for HDAC inhibitor therapeutics is which HDAC enzyme(s) is/are important for the amelioration of disease phenotypes, as it has become clear that individual HDAC enzymes play different biological roles in the brain. This review will discuss evidence supporting the involvement of HDAC1 and HDAC3 in polyglutamine disorders, including Huntington's disease, and the use of HDAC1- and HDAC3-selective HDAC inhibitors as therapeutic intervention for these disorders. Further, while HDAC inhibitors are known alter chromatin structure resulting in changes in gene transcription, understanding the exact mechanisms responsible for the preclinical efficacy of these compounds remains a challenge. The potential chromatin-related and non-chromatin-related mechanisms of action of selective HDAC inhibitors will also be discussed.

HDAC3 and the molecular brake pad hypothesis

Successful transcription of specific genes required for long-term memory processes involves the orchestrated effort of not only transcription factors, but also very specific enzymatic protein complexes that modify chromatin structure. Chromatin modification has been identified as a pivotal molecular mechanism underlying certain forms of synaptic plasticity and memory. The best-studied form of chromatin modification in the learning and memory field is histone acetylation, which is regulated by histone acetyltransferases and histone deacetylases (HDACs). HDAC inhibitors have been shown to strongly enhance long-term memory processes, and recent work has aimed to identify contributions of individual HDACs. In this review, we focus on HDAC3 and discuss its recently defined role as a negative regulator of long-term memory formation. HDAC3 is part of a corepressor complex and has direct interactions with Class II HDACs that may be important for its molecular and behavioral consequences. And last, we propose the "molecular brake pad" hypothesis of HDAC function. The HDACs and associated corepressor complexes may function in neurons, in part, as "molecular brake pads." HDACs are localized to promoters of active genes and act as a persistent clamp that requires strong activity-dependent signaling to temporarily release these complexes (or brake pads) to activate gene expression required for long-term memory formation. Thus, HDAC inhibition removes the "molecular brake pads" constraining the processes necessary for long-term memory and results in strong, persistent memory formation.

Histone deacetylase 3 localizes to the mitotic spindle and is required for kinetochore-microtubule attachment

Protein acetylation and deacetylation play key roles in multiple physiological functions. Histone deacetylase 3 (HDAC3) is a highly conserved, ubiquitously expressed protein that forms multiprotein corepressor complexes to repress gene transcription. Recent studies show that HDAC3 may play a role in cell proliferation. Altered HDAC3 level increases G(2)/M cells, but the mechanism remains unknown. Here we show for the first time, to our knowledge, that the HDAC3 complex, including nuclear receptor corepressor (N-CoR), transducin-beta-like protein 1 (TBL1), and TBL1-related protein 1 (TBLR1), is localized on the mitotic spindle. Knockdown of HDAC3 or N-CoR resulted in a collapsed mitotic spindle that was surrounded by chromosomes arranged in a dome-like configuration. Treatment of mitotic cells with Trichostatin A, an HDAC inhibitor, resulted in similar spindle defects independent of transcriptional regulation. In addition, wild-type HDAC3 but not a deacetylase-dead mutant HDAC3 rescued the phenotypes of HDAC3-depleted cells, suggesting that the enzymatic activity of HDAC3 is important for proper spindle function. Whereas the kinetochores and the spindle assembly checkpoint appeared intact in HDAC3-deficient cells, kinetochore-microtubule attachments were impaired because spindle microtubules were unstable in response to cold treatment. These data suggest that the HDAC3 complex is involved in the formation of functional mitotic spindles and proper kinetochore-microtubule attachment. The level or distribution of acetylated alpha-tubulin was not altered in HDAC3-deficient cells. Taken together, our studies raise the interesting possibility that acetylation-deacetylation of mitotic spindle components may be essential for mitotic spindle function.

Histone deacetylase inhibitors: discovery and development as anticancer agents

Histone deacetylase (HDAC) inhibitors are a new class of targeted anticancer agents. Several HDAC inhibitors are in clinical trials and have shown significant activity against a spectrum of both haematological and solid tumours at doses that are well tolerated by patients. HDACs and histone acetyltransferases can, by reversible acetylation, modify the structure and function of histones and proteins in transcription factor complexes, which are involved in the regulation of gene expression, as well as many non-histone proteins that are involved in regulating cell proliferation and cell death. HDAC inhibitors are a structurally diverse group of molecules; these agents selectively alter the expression of genes. HDAC inhibitors can induce cancer cell death, whereas normal cells are relatively resistant to HDAC inhibitor-induced cell death.

Histone deacetylase 3 (HDAC3) activity is regulated by interaction with protein serine/threonine phosphatase 4

Histone deacetylase 3 (HDAC3) is one of four members of the human class I HDACs that regulates gene expression by deacetylation of histones and nonhistone proteins. Early studies have suggested that HDAC3 activity is regulated by association with the corepressors N-CoR and SMRT. Here we demonstrate that, in addition to protein-protein interactions with NCoR/SMRT, the activity of HDAC3 is regulated by both phosphorylation and dephosphorylation. A protein kinase CK2 phosphoacceptor site in the HDAC3 protein was identified at position Ser424, which is a nonconserved residue among the class I HDACs. Mutation of this residue was found to reduce deacetylase activity. Interestingly, unlike other class I HDACs, HDAC3 uniquely copurifies with the catalytic and regulatory subunits of the protein serine/threonine phosphatase 4 complex (PP4c/PP4R1). Furthermore, HDAC3 complexes displayed protein phosphatase activity and a series of subsequent mutational analyses revealed that the N terminus of HDAC3 (residues 1-122) was both necessary and sufficient for HDAC3-PP4c interactions. Significantly, both overexpression and siRNA knock-down approaches, and analysis of cells devoid of PP4c, unequivocally show that HDAC3 activity is inversely proportional to the cellular abundance of PP4(c). These findings therefore further highlight the importance of protein-protein interactions and extend the significance of dephosphorylation in the regulation of HDAC activity, as well as present a novel alternative pathway by which HDAC3 activity is regulated.

Characterization of Progenitor-Cell-Specific Genes Identified by Subtractive Suppression Hybridization

We have utilized subtractive suppression hybridization (SSH) to identify differentially expressed genes present in either neuroepithelial (NEP) cells or glial restricted precursor (GRP) cells. Eighteen clones enriched in GRP cells and 28 in NEP cells were identified. Five of the GRP-specific clones (tenascin C, cystatin C, GABA transporter 3, extracellular matrix molecule 2 and H2-4) were characterized further, and their glial specificity was confirmed by RT-PCR, in situ hybridization and immunocytochemistry. H2-4 (an expressed sequence tag) was shown to be part of chondroitin sulfate proteoglycan 3. Overall, our results show that SSH can be used to identify lineage- and stage-specific markers and that extracellular matrix molecules likely play important roles in the migration and differentiation of GRPs.

Modulation of splicing events in histone deacetylase 3 by various extracellular and signal transduction pathways

Within the context of the chromatin environment histone deacetylases are important transcriptional regulators. Three classes of human histone deacetylases have currently been identified on the basis of their similarity to yeast proteins. The class I enzymes contain four members: HDACs 1-3 and HDAC8. Of these, HDAC3 is known to generate transcript variants with altered amino-terminal regions. Here we describe the identification of a novel splice variant of HDAC3, in which exon 3 is alternatively spliced from the messenger RNA transcript. We show that this human HDAC3 splice transcript is upregulated by treatments with histone deacetylase inhibitors. We also demonstrate evidence of splicing events in murine HDAC3 as a response to various signals, including switching between splice transcript isoforms following treatments with kinase inhibitors or by osmotic shock. In contrast, such switching events were not observed in human cells. These results indicate that differential pathways in mouse and human may control the regulation of HDAC3, and that splice variants may play important roles in responding to exogenous stimuli that act via signal transduction pathways.

Mammalian histone deacetylase 1 protein is posttranslationally modified by phosphorylation

HDAC1, a member of the histone deacetylase family, is involved in transcription regulation through the modification of chromatin structure. Several studies also implicated HDAC1 in tumorigenesis. Much attention has been concentrated on protein-protein interactions involving HDAC1 and the possibility that posttranslational modifications may occur in mammalian HDAC1 proteins has not been carefully and systematically investigated. In this study, we utilized in vivo labeling assays to demonstrate that both human and murine HDAC1 proteins are phosphorylated in cells. Assays using HDAC1 deletion mutants indicated that phosphorylation occurs in its C-terminal domain. cAMP-dependent kinase and casein kinase II, but not protein kinase C, cdc2, or MAP kinase, could phosphorylate HDAC1 in vitro, although HDAC1 contains several protein kinase C consensus sites. We also found that phosphorylation did not influence HDAC1 enzymatic activity using a human histone H4 N-terminal peptide as the substrate. Interestingly, HDAC1-FLAG fusion protein immunoprecipitated from transfected cells was found to be in association with a kinase activity, providing an in vitro assay for further studies of this posttranslational modification.

Histone deacetylases, transcriptional control, and cancer

A key event in the regulation of eukaryotic gene expression is the posttranslational modification of nucleosomal histones, which converts regions of chromosomes into transcriptionally active or inactive chromatin. The most well studied posttranslational modification of histones is the acetylation of epsilon-amino groups on conserved lysine residues in the histones' amino-terminal tail domains. Significant advances have been made in the past few years toward the identification of histone acetyltransferases and histone deacetylases. Currently, there are over a dozen cloned histone acetyltransferases and at least eight cloned human histone deacetylases. Interestingly, many histone deacetylases can function as transcriptional corepressors and, often, they are present in multi-subunit complexes. More intriguing, at least some histone deacetylases are associated with chromatin-remodeling machines. In addition, several studies have pointed to the possible involvement of histone deacetylases in human cancer. The availability of the cloned histone deacetylase genes has provided swift progress in the understanding of the mechanisms of deacetylases, their role in transcription, and their possible role in health and disease.