Specific Histone Acetyltransferases Research Articles

Structural and functional insights into the epigenetic regulator MRG15.

MORF4-related gene on chromosome 15 (MRG15), a chromatin remodeller, is evolutionally conserved and ubiquitously expressed in mammalian tissues and cells. MRG15 plays vital regulatory roles in DNA damage repair, cell proliferation and division, cellular senescence and apoptosis by regulating both gene activation and gene repression via associations with specific histone acetyltransferase and histone deacetylase complexes. Recently, MRG15 has also been shown to rhythmically regulate hepatic lipid metabolism and suppress carcinoma progression. The unique N-terminal chromodomain and C-terminal MRG domain in MRG15 synergistically regulate its interaction with different cofactors, affecting its functions in various cell types. Thus, how MRG15 elaborately regulates target gene expression and performs diverse functions in different cellular contexts is worth investigating. In this review, we provide an in-depth discussion of how MRG15 controls multiple physiological and pathological processes.

Novel Tip60 HAT activators as neuroepigenetic therapeutic modulators for Alzheimer’s Disease

AbstractBackgroundAlzheimer’s Disease (AD) etiology involves a complex interplay of genetics, age, and environmental factors that influence neuroepigenetic mediated neural gene control. Reduced histone acetylation in the AD brain is a widespread hallmark underlying neural gene repression and cognitive impairment in AD etiology. As histone acetylation is dynamically regulated by antagonistic histone deacetylases (HDACs) and histone acetyltransferases (HATs), pharmacological treatments aiming to restore histone acetylation via HDAC inhibition are a research hotspot for developing AD cognitive enhancing drugs. Although promising, HDAC inhibitor treatments in the AD animal models are rarely translated into clinical trials due to non‐specific global hyperacetylation. Alternatively, enhancing activity of specific HATs with non‐redundant functions serves as an exciting new therapeutic strategy that remains unexplored. To this end, our lab has identified and published a neuroprotective role for HAT Tip60 in multiple neural circuits impaired in AD pathology. Human and Drosophila AD brains exhibit reduced Tip60 and enhanced repressor HDAC2 that triggers histone deacetylation with concomitant repression of cognition genes. All these deficits are prevented by genetically increasing Tip60 in the Drosophila AD brain. Here, we test that pharmacologically enhancing Tip60’s HAT function replicates this AD neuroprotective function.MethodWe used in silico structural modeling and a novel pharmacophore based virtual screening approach to design and synthesize novel small molecule compounds strongly predicted to target and enhance Tip60’s HAT activity.ResultOur screen produced 19,000 hits that we individually docked on Tip60’s HAT domain using GOLD docking software. 13 compounds were identified that exhibited significantly high Tip60 docking scores, and optimal ease of synthesis, drug like properties and blood brain barrier peneteration. These compounds were custom synthesized. We show that several of these compounds fully rescue locomotor neural based deficits and cognition gene expression alterations in both Tip60 knockdown and AD Drosophila in vivo models with no observable side effects, underscoring their therapeutic effectiveness. These compounds will ultimately be assessed for further specificity and for their therapeutic effectiveness in AD animal models in vivo.ConclusionWe propose our first‐in‐class small molecule Tip60 HAT activators will serve as powerful novel chemical entities for development of specific acetylation‐based cognition enhancing drugs for AD.

Histone acetyltransferase Gcn5-mediated histone H3 acetylation facilitates cryptococcal morphogenesis and sexual reproduction.

Eukaryotic gene transcription is typically regulated by a series of histone modifications, which play a crucial role in adapting to complex environmental stresses. In the ubiquitous human fungal pathogen Cryptococcus neoformans, sexual life cycle is a continuous intracellular differentiation process that strictly occurs in response to mating stimulation. Despite the comprehensive identification of the regulatory factors and genetic pathways involved in its sexual cycle, understanding of the epigenetic modifications involved in this process remains quite limited. In this research, we found that histone acetyltransferase Gcn5-mediated histone H3 acetylation plays a crucial role in completing the cryptococcal sexual cycle, including yeast-hyphae morphogenesis and the subsequent sexual reproduction. Furthermore, we demonstrated that Gcn5 participates in this process primarily through regulating the key morphogenesis regulator Znf2 and its targets. This study thus provided a comprehensive understanding of how histone acetylation modification impacts sexual life cycle in a high-risk human pathogenic fungus.

Repression of the major immediate early promoter of human cytomegalovirus allows transcription from an alternate promoter.

Following infection, the human cytomegalovirus (HCMV) genome becomes rapidly associated with host histones which can contribute to the regulation of viral gene expression. This can be seen clearly during HCMV latency where silencing of the major immediate early promoter (MIEP), normally responsible for expression of the key lytic proteins IE72 and IE86, is mediated by histone methylation and recruitment of heterochromatin protein 1. Crucially, reversal of these histone modifications coupled with histone acetylation drives viral reactivation which can be blocked with specific histone acetyltransferase inhibitors (HATi). In lytic infection, a role for HATi is less clear despite the well-established enhancement of viral replication observed with histone deacetylase inhibitors. Here we report that a number of different broad-acting HATi have a minor impact on viral infection and replication during lytic infection with the more overt phenotypes observed at lower multiplicities of infection. However, specific analyses of the regulation of major immediate early (MIE) gene expression reveal that the HATi C646, which targets p300/CBP, transiently repressed MIE gene expression via inhibition of the MIEP but by 24 h post-infection MIE gene expression was rescued due to compensatory activation of an alternative IE promoter, ip2. This suggested that silencing of the MIEP promoted alternative ip2 promoter activity in lytic infection and, consistent with this, ip2 transcription is impaired in cells infected with a recombinant HCMV that does not auto-repress the MIEP at late times of infection. Furthermore, inhibition of the histone methyltransferases known to be responsible for auto-repression is similarly inhibitory to ip2 transcription in wild-type infected cells. We also observe that these discrete transcriptional activities of the MIEP and ip2 promoter are also reflected in reactivation; essentially in cells where the MIEP is silenced, ip2 activity is easier to detect at very early times post-reactivation whereas in cells where robust activation of the MIEP is observed ip2 transcription is reduced or delayed. Finally, we observe that inhibition of pathways demonstrated to be important for reactivation of HCMV in dendritic cells, e.g. in response to IL-6, are preferentially important for activation of the MIEP and not the ip2 promoter. Together, these data add to the hypothesis that the existence of multiple promoters within the MIE region of HCMV can drive reactivation in a cell type- and ligand-specific manner and also suggest that inter-dependent regulatory activity between the two promoters exists.

Acetylation State of Lysine 14 of Histone H3.3 Affects Mutant Huntingtin Induced Pathogenesis.

Huntington's Disease (HD) is a fatal neurodegenerative disorder caused by the expansion of a polyglutamine-coding CAG repeat in the Huntingtin gene. One of the main causes of neurodegeneration in HD is transcriptional dysregulation that, in part, is caused by the inhibition of histone acetyltransferase (HAT) enzymes. HD pathology can be alleviated by increasing the activity of specific HATs or by inhibiting histone deacetylase (HDAC) enzymes. To determine which histone's post-translational modifications (PTMs) might play crucial roles in HD pathology, we investigated the phenotype-modifying effects of PTM mimetic mutations of variant histone H3.3 in a Drosophila model of HD. Specifically, we studied the mutations (K→Q: acetylated; K→R: non-modified; and K→M: methylated) of lysine residues K9, K14, and K27 of transgenic H3.3. In the case of H3.3K14Q modification, we observed the amelioration of all tested phenotypes (viability, longevity, neurodegeneration, motor activity, and circadian rhythm defects), while H3.3K14R had the opposite effect. H3.3K14Q expression prevented the negative effects of reduced Gcn5 (a HAT acting on H3K14) on HD pathology, while it only partially hindered the positive effects of heterozygous Sirt1 (an HDAC acting on H3K14). Thus, we conclude that the Gcn5-dependent acetylation of H3.3K14 might be an important epigenetic contributor to HD pathology.

A toolbox for class I HDACs reveals isoform specific roles in gene regulation and protein acetylation.

The class I histone deacetylases are essential regulators of cell fate decisions in health and disease. While pan- and class-specific HDAC inhibitors are available, these drugs do not allow a comprehensive understanding of individual HDAC function, or the therapeutic potential of isoform-specific targeting. To systematically compare the impact of individual catalytic functions of HDAC1, HDAC2 and HDAC3, we generated human HAP1 cell lines expressing catalytically inactive HDAC enzymes. Using this genetic toolbox we compare the effect of individual HDAC inhibition with the effects of class I specific inhibitors on cell viability, protein acetylation and gene expression. Individual inactivation of HDAC1 or HDAC2 has only mild effects on cell viability, while HDAC3 inactivation or loss results in DNA damage and apoptosis. Inactivation of HDAC1/HDAC2 led to increased acetylation of components of the COREST co-repressor complex, reduced deacetylase activity associated with this complex and derepression of neuronal genes. HDAC3 controls the acetylation of nuclear hormone receptor associated proteins and the expression of nuclear hormone receptor regulated genes. Acetylation of specific histone acetyltransferases and HDACs is sensitive to inactivation of HDAC1/HDAC2. Over a wide range of assays, we determined that in particular HDAC1 or HDAC2 catalytic inactivation mimics class I specific HDAC inhibitors. Importantly, we further demonstrate that catalytic inactivation of HDAC1 or HDAC2 sensitizes cells to specific cancer drugs. In summary, our systematic study revealed isoform-specific roles of HDAC1/2/3 catalytic functions. We suggest that targeted genetic inactivation of particular isoforms effectively mimics pharmacological HDAC inhibition allowing the identification of relevant HDACs as targets for therapeutic intervention.

Histone Acetyltransferases p300 and CBP Coordinate Distinct Chromatin Remodeling Programs in Vascular Smooth Muscle Plasticity.

Vascular smooth muscle cell (VSMC) phenotypic switching contributes to cardiovascular diseases. Epigenetic regulation is emerging as a key regulatory mechanism, with the methylcytosine dioxygenase TET2 acting as a master regulator of smooth muscle cell phenotype. The histone acetyl-transferases p300 and CREB-binding protein (CBP) are highly homologous and often considered to be interchangeable, and their roles in smooth muscle cell phenotypic regulation are not known. We assessed the roles of p300 and CBP in human VSMC with knockdown, in inducible smooth muscle-specific knockout mice (inducible knockout [iKO]; p300iKO or CBPiKO), and in samples of human intimal hyperplasia. P300, CBP, and histone acetylation were differently regulated in VSMCs undergoing phenotypic switching and in vessel remodeling after vascular injury. Medial p300 expression and activity were repressed by injury, but CBP and histone acetylation were induced in neointima. Knockdown experiments revealed opposing effects of p300 and CBP in the VSMC phenotype: p300 promoted contractile protein expression and inhibited migration, but CBP inhibited contractile genes and enhanced migration. p300iKO mice exhibited severe intimal hyperplasia after arterial injury compared with controls, whereas CBPiKO mice were entirely protected. In normal aorta, p300iKO reduced, but CBPiKO enhanced, contractile protein expression and contractility compared with controls. Mechanistically, we found that these histone acetyl-transferases oppositely regulate histone acetylation, DNA hydroxymethylation, and PolII (RNA polymerase II) binding to promoters of differentiation-specific contractile genes. Our data indicate that p300 and TET2 function together, because p300 was required for TET2-dependent hydroxymethylation of contractile promoters, and TET2 was required for p300-dependent acetylation of these loci. TET2 coimmunoprecipitated with p300, and this interaction was enhanced by rapamycin but repressed by platelet-derived growth factor (PDGF) treatment, with p300 promoting TET2 protein stability. CBP did not associate with TET2, but instead facilitated recruitment of histone deacetylases (HDAC2, HDAC5) to contractile protein promoters. Furthermore, CBP inhibited TET2 mRNA levels. Immunostaining of cardiac allograft vasculopathy samples revealed that p300 expression is repressed but CBP is induced in human intimal hyperplasia. This work reveals that p300 and CBP serve nonredundant and opposing functions in VSMC phenotypic switching and coordinately regulate chromatin modifications through distinct functional interactions with TET2 or HDACs. Targeting specific histone acetyl-transferases may hold therapeutic promise for cardiovascular diseases.

Abstract 467: The Histone Acetyltransferases P300 And Cbp Coordinate Distinct Chromatin Remodeling Programs In Vascular Smooth Muscle Plasticity

Vascular smooth muscle cell (VSMC) phenotypic switching contributes to cardiovascular diseases. Epigenetic regulation is emerging as a key regulatory mechanism, with the methyl cytosine dioxygenase TET2 acting as a master regulator of SMC phenotype. The histone acetyltransferases (HATs) p300 and CBP are highly homologous and often considered to be interchangeable, and their roles in SMC phenotypic regulation are not known. We assessed the roles of p300 and CBP in human VSMC with knockdown, in inducible smooth muscle-specific knockout mice ( p300 iKO or CBP iKO ), and in human intimal hyperplasia. P300, CBP, and histone acetylation were differently regulated in VSMCs undergoing phenotypic switching and in injury-induced vessel remodeling. Knockdown experiments revealed opposing effects of p300 and CBP in VSMC phenotype: p300 promoted contractile protein expression and inhibited migration, but CBP inhibited contractile genes and enhanced migration. p300 iKO mice exhibited severe intimal hyperplasia following arterial injury while CBP iKO mice were entirely protected. In normal aorta, p300 iKO reduced, but CBP iKO enhanced, contractile proteins and contractility. Mechanistically, we found that these HATs oppositely regulate histone acetylation, DNA hydroxy methylation, and RNA PolII binding to promoters of differentiation-specific contractile genes. We report p300 and TET2 function together, as p300 was required for TET2-dependent hydroxy methylation of contractile promoters, and TET2 was required for p300-dependent acetylation of these loci. TET2 co-immunoprecipitated with p300 and this interaction was enhanced by rapamycin but repressed by PDGF, with p300 promoting TET2 protein stability. CBP did not associate with TET2, instead facilitated recruitment of histone deacetylases (HDAC2, HDAC5) to contractile gene promoters. Immunostaining revealed, p300 expression is repressed but CBP is induced in human intimal hyperplasia. This work reveals that p300 and CBP serve non-redundant and opposing functions in VSMC phenotypic switching and coordinately regulate chromatin modifications through distinct functional interactions with TET2 or HDACs. Targeting specific HATs may hold therapeutic promise for cardiovascular diseases.

On-going consequences of in utero exposure of Pb: An epigenetic perspective.

Epigenetic modifications by toxic heavy metals are one of the intensively investigated fields of modern genomic research. Among a diverse group of heavy metals, lead (Pb) is an extensively distributed toxicant causing an immense number of abnormalities in the developing fetus via a wide variety of epigenetic changes. As a divalent cation, Pb can readily cross the placental membrane and the fetal blood brain barrier leading to far-reaching alterations in DNA methylation patterns, histone protein modifications, and micro-RNA expression. Over recent years, several human cohorts and animal model studies have documented hypermethylation and hypomethylation of developmental genes along with altered DNA methyl-transferase expression by in utero Pb exposure in a dose-, duration-, and sex-dependent manner. Modifications in the expression of specific histone acetyltransferase enzymes along with histone acetylation and methylation levels have been reported in rodent and murine models. Apart from these, down-regulation and up-regulation of certain microRNAs crucial for fetal development have been shown to be associated with in utero Pb exposure in human placenta samples. All these modifications in the developing fetus during the prenatal and perinatal stages reportedly caused severe abnormalities in early or adult age, such as impaired growth, obesity, autism, diabetes, cardiovascular diseases, risks of cancer development, and Alzheimer's disease. In this review, currently available information on Pb-mediated alterations in the fetal epigenome is summarized. Further research on Pb-induced epigenome modification will help to understand the mechanisms in detail and will enable us to formulate safety guidelines for pregnant women and developing children.

Two Related Coactivator Complexes SAGA and ATAC Control Embryonic Stem Cell Self-Renewal Through Two Different Acetyltransferase-Independent Mechanisms

SAGA and ATAC are two related transcriptional coactivator complexes, sharing the same histone acetyltransferase (HAT) subunit. The HAT activities of SAGA and ATAC are required for metazoan development but the precise role of the two complexes in RNA polymerase II transcription in mammals is less understood. To determine whether SAGA and ATAC have redundant or specific functions dependent on their HAT activities, we compared the effects of HAT inactivation in each complex with that of complete inactivation of either SAGA or ATAC in mouse embryonic stem cells (ESCs) . We show that core subunits of SAGA or ATAC subunits are required for complex assembly, mouse ESC growth and self-renewal. Additionally, ATAC, but not SAGA subunits are required for ESC viability by regulating the transcription of translation-related genes. Surprisingly, depletion of a shared or specific HAT module subunits caused a global decrease in histone H3K9 acetylation, but did not result in significant phenotypic or transcriptional defects. Thus, our results indicate that SAGA and ATAC are differentially required for viability and self-renewal of mouse ESCs by regulating transcription through different pathways, but in a HAT-independent manner.

GPS-PAIL: prediction of lysine acetyltransferase-specific modification sites from protein sequences.

Protein acetylation catalyzed by specific histone acetyltransferases (HATs) is an essential post-translational modification (PTM) and involved in the regulation a broad spectrum of biological processes in eukaryotes. Although several ten thousands of acetylation sites have been experimentally identified, the upstream HATs for most of the sites are unclear. Thus, the identification of HAT-specific acetylation sites is fundamental for understanding the regulatory mechanisms of protein acetylation. In this work, we first collected 702 known HAT-specific acetylation sites of 205 proteins from the literature and public data resources, and a motif-based analysis demonstrated that different types of HATs exhibit similar but considerably distinct sequence preferences for substrate recognition. Using 544 human HAT-specific sites for training, we constructed a highly useful tool of GPS-PAIL for the prediction of HAT-specific sites for up to seven HATs, including CREBBP, EP300, HAT1, KAT2A, KAT2B, KAT5 and KAT8. The prediction accuracy of GPS-PAIL was critically evaluated, with a satisfying performance. Using GPS-PAIL, we also performed a large-scale prediction of potential HATs for known acetylation sites identified from high-throughput experiments in nine eukaryotes. Both online service and local packages were implemented, and GPS-PAIL is freely available at: http://pail.biocuckoo.org.

Acetylation of Mammalian ADA3 Is Required for Its Functional Roles in Histone Acetylation and Cell Proliferation.

Alteration/deficiency in activation 3 (ADA3) is an essential component of specific histone acetyltransferase (HAT) complexes. We have previously shown that ADA3 is required for establishing global histone acetylation patterns and for normal cell cycle progression (S. Mohibi et al., J Biol Chem 287:29442-29456, 2012, http://dx.doi.org/10.1074/jbc.M112.378901). Here, we report that these functional roles of ADA3 require its acetylation. We show that ADA3 acetylation, which is dynamically regulated in a cell cycle-dependent manner, reflects a balance of coordinated actions of its associated HATs, GCN5, PCAF, and p300, and a new partner that we define, the deacetylase SIRT1. We use mass spectrometry and site-directed mutagenesis to identify major sites of ADA3 acetylated by GCN5 and p300. Acetylation-defective mutants are capable of interacting with HATs and other components of HAT complexes but are deficient in their ability to restore ADA3-dependent global or locus-specific histone acetylation marks and cell proliferation in Ada3-deleted murine embryonic fibroblasts (MEFs). Given the key importance of ADA3-containing HAT complexes in the regulation of various biological processes, including the cell cycle, our study presents a novel mechanism to regulate the function of these complexes through dynamic ADA3 acetylation.

589 - Stratification of breast cancer patients using Tip60 staining paired with evaluation of a designed Tip60 specific histone acetyltransferase inhibitor for targeted treatment

589 - Stratification of breast cancer patients using Tip60 staining paired with evaluation of a designed Tip60 specific histone acetyltransferase inhibitor for targeted treatment

ROCK1 Plays a Crucial Role to Maintain Cardiac Function in Response to Pressure-Overload in Mice

acetylation by p300 histone acetyltransferase (HAT) activity was associated with GATA4 transcriptional activity, as well as pathological cardiomyocyte hypertrophy and the development of heart failure in vivo. However, little is known to what extent histone modifications can directly impact on cardiac hypertrophy. Aims: We hypothesized that the epigenetic histone modifications relate to cardiac hypertrophic responses. Methods and Results: In cardiomyocytes, phenylephrine (PE) stimulus increased the acetylation among H3K122, H3K9, and H3K14. These acetylations were significantly inhibited by knockdown of p300 and curcumin, a p300 specific HAT inhibitor. Chromatin-immunoprecipitation assay demonstrated that PE stimulus increased the recruitment of the acetylated H3K122 and H3K9 onto ANF and BNP promoters containing the GATA element. Moreover, we utilized in vivo ChIP assays with Dahl salt-sensitive rats and found that acetylation and H3K9 were increased around ANF and BNP promoters at the LVH stage and those of H3K122 were increased at the CHF stage. Conclusion: This study indicate that epigenetic hypertrophic responses via acetylations of tail and globular domains of histone were involved in the transition from LVH to CHF.

Abstract 3613: P300 inhibition enhances cytotoxic effect of Gemcitabine through E2F1 activation in pancreatic cancer

Abstract Background: Transcriptional cofactor, P300 has been reported to regulate cell cycle on G1/S transition. Previously, we shown that prolonged S-phase is associated with increased apoptosis induced by Gemcitabine (GEM) in pancreatic cancer cells. Thus, we hypothesized that targeting P300 enhances the cytotoxic effect of GEM on pancreatic cancer. Methods: We studied 2 human pancreatic cancer cell lines, Panc1 and MIAPaCa2. P300 was gene-silenced using siRNA, and P300 histone acetyltransferase (HAT) activity was inhibited by specific inhibitor C646. Cell viability was measured by WST-8 assay and GEM-induced apoptosis was measured using Caspase3 and PARP by Western blotting, Tunel assay by immunofluorescence staining, and Annexin V-PI staining by flow cytometry. CDK4/6 inhibitor Palbociclib was used to block S-phase entry. Results: Robust P300 expression was observed in pancreatic cancer cell lines and human pancreatic adenocarcinoma tissues. When P300 expression was depleted by specific P300 siRNA, cell viability after GEM treatment was decreased significantly compared with the control pancreatic cancer cells (43% decrease in MIAPaCa2 and 39% decrease in Panc1, respectively, p<0.05). Increased GEM-induced apoptosis was confirmed by increased cleaved forms of Caspase3 and PARP, increased tunel positive cells, and increased Annexin positive cells in P300-depleted cells compared to the control cells. When S phase entry was blocked by Palbociclib, the effect of gene silencing of P300 on GEM-induced apoptosis was abolished. As Rb-E2F1 complex is known as the key regulator of the S phase specific gene transcriptions, we evaluated the effect of P300 gene silencing on Rb and E2F1. While P300 gene-silencing did not affect Rb phosphorylation after GEM treatment, it increased E2F1 expression significantly (56% increase in MIAPaCa2 and 119% increase in Panc1, respectively, p<0.05). When pancreatic cancer cells were treated with combination of GEM and C646, P300 specific HAT inhibitor, the cell viability was reduced significantly compared with when treated with GEM alone (48% decrease for Panc1, and 58% for MIAPaCa2, respectively, p<0.05). Conclusion: Targeting P300 by siRNA or HAT inhibitor enhances the efficacy of GEM on pancreatic cancer cells. Our observation suggests the presence of Rb-independent E2F1 regulatory mechanism in pancreatic cancer cells. This pathway may be an important therapeutic target to potentiate GEM chemotherapy in the treatment of pancreatic cancer. Citation Format: Hiroaki Ono, Marc D. Basson, Hiromichi Ito. P300 inhibition enhances cytotoxic effect of Gemcitabine through E2F1 activation in pancreatic cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3613. doi:10.1158/1538-7445.AM2015-3613

Acetylation as a mechanism that regulates axonal regeneration.

The capacity for adult axons to regenerate after injury is diminished compared with developing axons. In the case of central nervous system (CNS) axons, injury causes a total failure to regenerate. This failure is due to both the intrinsic developmental decrease in growth capacity and the extrinsic inhibitory environment formed because of the injury. One way to re-invigorate mature axons into a regrowth state is to induce regenerative gene expression in the nucleus to increase the intrinsic growth state of the neuron. One potential mechanism is through changes in epigenetic factors. Another possible method is to alter posttranslational modifications in axonal and growth cone microtubules of the axonal cytoplasm (Trakhtenberg and Goldberg, 2012; Cho and Cavalli, 2014). An increasing number of studies have turned to epigenetic manipulation using pharmacological inhibitors to try and enhance axonal growth. Numerous reversible posttranslational modifications are considered important for axonal growth and regeneration but such modifications are regulated by families of enzymes which affect system wide changes in the body, sometimes shuttling between the nucleus and the cytoplasm as well as between the cell body and axon. Two families of enzymes, histone acetyl transferases (HATs) and histone deacetylases (HDACs), act antagonistically to affect acetylation and de-acetylation respectively on many proteins throughout the body. Acetylation in neurons is critical for many physiological events such as cell division, cell growth and proliferation. This paper will focus on the potential implications of acetylation homeostasis on axonal growth.

Epigenetic control of learning and memory in Drosophila by Tip60 HAT action.

Disruption of epigenetic gene control mechanisms in the brain causes significant cognitive impairment that is a debilitating hallmark of most neurodegenerative disorders, including Alzheimer's disease (AD). Histone acetylation is one of the best characterized of these epigenetic mechanisms that is critical for regulating learning- and memory- associated gene expression profiles, yet the specific histone acetyltransferases (HATs) that mediate these effects have yet to be fully characterized. Here, we investigate an epigenetic role for the HAT Tip60 in learning and memory formation using the Drosophila CNS mushroom body (MB) as a well-characterized cognition model. We show that Tip60 is endogenously expressed in the Kenyon cells, the intrinsic neurons of the MB, and in the MB axonal lobes. Targeted loss of Tip60 HAT activity in the MB causes thinner and shorter axonal lobes while increasing Tip60 HAT levels cause no morphological defects. Functional consequences of both loss and gain of Tip60 HAT levels in the MB are evidenced by defects in immediate-recall memory. Our ChIP-Seq analysis reveals that Tip60 target genes are enriched for functions in cognitive processes, and, accordingly, key genes representing these pathways are misregulated in the Tip60 HAT mutant fly brain. Remarkably, we find that both learning and immediate-recall memory deficits that occur under AD-associated, amyloid precursor protein (APP)-induced neurodegenerative conditions can be effectively rescued by increasing Tip60 HAT levels specifically in the MB. Together, our findings uncover an epigenetic transcriptional regulatory role for Tip60 in cognitive function and highlight the potential of HAT activators as a therapeutic option for neurodegenerative disorders.

Increasing Tip60 HAT Levels Rescues Axonal Transport Defects and Associated Behavioral Phenotypes in aDrosophilaAlzheimer's Disease Model

Axonal transport defects and axonopathy are prominent in early preclinical stages of Alzheimer's disease (AD), often preceding known disease-related pathology by over a year. As epigenetic transcriptional regulatory mechanisms, such as histone acetylation, are critical for neurogenesis, it is postulated that their misregulation might be linked to early pathophysiological mechanisms that contribute to AD. The histone acetyltransferase (HAT) Tip60 epigenetically regulates genes enriched for neuronal functions and is implicated in AD via its formation of a transcriptional regulatory complex with the amyloid precursor protein (APP) intracellular domain. Disruption of APP function is associated with axonal transport defects, raising the possibility that an epigenetic role for Tip60 might also be involved. Here, we examine whether Tip60 HAT activity functions in axonal transport using Drosophila CNS motor neurons as a well-characterized transport model. We show that reduction of Tip60 HAT activity in the nervous system causes axonopathy and transport defects associated with epigenetic misregulation of certain axonal transport-linked Tip60 target genes. Functional consequences of these defects are evidenced by reduced locomotion activity of the mutant Tip60 larvae, and these phenotypes can be partially rescued with certain histone deacetylase inhibitors. Finally, we demonstrate that Tip60 function in axonal transport is mediated by APP and that, remarkably, excess Tip60 exerts a neuroprotective role in APP-induced axonal transport and functional locomotion defects. Our observations highlight a novel functional interactive role between Tip60 HAT activity and APP in axonal transport and provide insight into the importance of specific HAT modulators for cognitive disorder treatment.

Abstract 1597: C646, a selective small molecule inhibitor of p300, radiosensitizes cancer cells through enhancement of mitotic catastrophe.

Abstract Background: The histone acetyltransferases (HATs) including p300, CBP and TIP60 are transcriptional co-activators implicated in many gene regulatory pathways and protein acetylation events. We have previously shown that siRNA-mediated ablation of p300 and CBP sensitized cancer cells to ionizing radiation (IR) (Ogiwara, Oncogene 2011), and that garcinol, curcumin and anacardic acid, natural compounds with multi-HATs inhibitory activity, had radiosensitizing effect in cancer cells (Oike, Int J Radiat Oncol Biol Phys 2012). However, radiosensitization by selective small molecule inhibitors targeting activity of a specific HAT, that can have much potential for clinical use, have not been well investigated. C646 is a selective small molecule inhibitor of p300 identified by structure-based and active site-directed in silico screening (Bowers, Chem Biol 2010). In this study, we investigated the in vitro effect of C646 on radiosensitization and cell death in human cancer cells. Materials and Methods: The radiosensitizing effect in A549 (lung adenocarcinoma), H460 (lung squamous cell carcinoma) and H157 (lung large cell carcinoma) cells were assessed by colony formation assay, while that in MRC-5 (fibroblast) cells lacking in colony-forming ability was examined by ATP assay. Cell cycle distribution in A549 cells was analyzed using flow cytometry. The effect on mitotic catastrophe, apoptosis and senescence in A549 cells was evaluated by DAPI, annexin V and senescence-associated β-galactosidase staining, respectively. C646 was used at concentrations less than IC50. Results: C646 radiosensitized A549, H460 and H157 cancer cells with dose enhancement ratio at 10% surviving fraction of 1.4, 1.2 and 1.2, respectively. Meanwhile, C646 unaffected the radiosensitivity of MRC-5 cells. Cell cycle analysis showed that the hyperploid cell population (> 4N DNA cells) increased in C646-treated A549 cells after IR. Analyses of mode of cell death revealed that C646 enhanced mitotic catastrophe, but not apoptosis nor senescence, induced by IR in A549 cells. Conclusion: These data indicate that C646 is a radiosensitizer which enhances mitotic catastrophe induced by IR. Citation Format: Takahiro Oike, Mayumi Komachi, Hideaki Ogiwara, Jun Yokota, Takashi Nakano, Takashi Kohno. C646, a selective small molecule inhibitor of p300, radiosensitizes cancer cells through enhancement of mitotic catastrophe. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1597. doi:10.1158/1538-7445.AM2013-1597

Targeting specific HATs for neurodegenerative disease treatment: translating basic biology to therapeutic possibilities

Dynamic epigenetic regulation of neurons is emerging as a fundamental mechanism by which neurons adapt their transcriptional responses to specific developmental and environmental cues. While defects within the neural epigenome have traditionally been studied in the context of early developmental and heritable cognitive disorders, recent studies point to aberrant histone acetylation status as a key mechanism underlying acquired inappropriate alterations of genome structure and function in post-mitotic neurons during the aging process. Indeed, it is becoming increasingly evident that chromatin acetylation status can be impaired during the lifetime of neurons through mechanisms related to loss of function of histone acetyltransferase (HAT) activity. Several HATs have been shown to participate in vital neuronal functions such as regulation of neuronal plasticity and memory formation. As such, dysregulation of such HATs has been implicated in the pathogenesis associated with age-associated neurodegenerative diseases and cognitive decline. In order to counteract the loss of HAT function in neurodegenerative diseases, the current therapeutic strategies involve the use of small molecules called histone deacetylase (HDAC) inhibitors that antagonize HDAC activity and thus enhance acetylation levels. Although this strategy has displayed promising therapeutic effects, currently used HDAC inhibitors lack target specificity, raising concerns about their applicability. With rapidly evolving literature on HATs and their respective functions in mediating neuronal survival and higher order brain function such as learning and memory, modulating the function of specific HATs holds new promises as a therapeutic tool in neurodegenerative diseases. In this review, we focus on the recent progress in research regarding epigenetic histone acetylation mechanisms underlying neuronal activity and cognitive function. We discuss the current understanding of specific HDACs and HATs in neurodegenerative diseases and the future promising prospects of using specific HAT based therapeutic approaches.