Search results for HDAC3

Showing 20 results out of 33

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Protein (2 results from a total of 2)

Identifier: R-HSA-442464
Species: Homo sapiens
Compartment: nucleoplasm
Primary external reference: UniProt: HDAC3: O15379
Identifier: R-HSA-6813777
Species: Homo sapiens
Compartment: cytosol
Primary external reference: UniProt: HDAC3: O15379

Reaction (6 results from a total of 16)

Identifier: R-HSA-9008137
Species: Homo sapiens
Compartment: nucleoplasm
Based on studies in mice, RUNX2 forms a complex with ZNF521 (ZNP521) and a histone deacetylase HDAC3. Binding to ZNF521 does not inhibit RUNX2 binding to target genes, such as the BGLAP (Osteocalcin) gene promoter, but inhibits RUNX2-mediated activation of these genes. HDAC3 is needed for ZNF521 to inhibit RUNX2-mediated transcription from the BGLAP promoter. Action of ZNF521 antagonizes RUNX2 during mesenchymal commitment to the osteoblast lineage and during osteoblast maturation (Hesse et al. 2010).
Identifier: R-HSA-3777129
Species: Homo sapiens
Compartment: nucleoplasm
HDAC3 mediates the gene silencing activity of Retinoic acid and thyroid hormone receptor (SMRT) complex or the homologous nuclear receptor corepressor (NCoR). These coregulators are involved in a wide range of developmental and homeostatic processes, including metabolism, inflammation, and circadian rhythms (Mottis et al. 2013). HDAC3 interacts with a conserved SANT-like domain known as the deacetylase activating domain (DAD) within NCOR2 (SMRT) or NCOR1 (Li et al. 2000, Wen et al. 2000, Zhang et al. 2002, Yoon et al. 2003, Oberoi et al. 2011). This interaction both recruits and activates HDAC3 (Wen et al. 2000, Guenther et al. 2001, Zhang et al. 2002). Recruitment of HDAC3 to the DAD is essential for repression by the nuclear thyroid hormone receptor and for the maintenance of normal circadian physiology (You et al. 2010, Yin et al. 2007). A second SANT-like domain has been reported to interact directly with histone tails and termed the histone interaction domain (HID) (Hartman et al. 2005, Yu et al. 2003). NCORs are largely unstructured platform proteins that act as a scaffold upon which the enzymatic machinery of the repression complex is built (Watson et al. 2012). They can recruit other deacetylases such as HDAC4 (Fischle et al. 2002), HDAC5, HDAC7 (Kao et al. 2000), Sirt1 (Picard et al. 2004), and via mSin3, HDAC1 (Heinzel et al. 1997, Nagy et al. 1997). The importance of these deacetylase enzymes is not yet established. It has been demonstrated HDAC3 was shown to be responsible for deacetylase activities associated with HDAC4 and HDAC7 (Fischle et al. 2002). Corepressor complexes are heterogeneous, context-specific and transient in nature, but in addition to HDAC3, some additional partners are regularly found in stoichiometric association with NCOR1/NCOR2 and are essential for repressive function. These partners include the G protein pathway suppressor (GPS2) and transducing beta-like 1 (TBL1) and its homologue, TBL-related 1 (TBLR1), which together form the core repression complex (Oberoi et al. 2011). Ins(1,4,5,6)P4 is a further component of the complex (Watson et al. 2012).
Identifier: R-HSA-9024326
Species: Homo sapiens
Compartment: nucleoplasm
In macrophages, excess of cholesterol leads to the formation of oxysterols, the natural ligands of liver X receptors LXRα (NR1H3) and LXRβ (NR1H2), which belong to the nuclear receptor superfamily of ligand-activated transcription factors. Activation of NR1H2,3 induces expression of ATP-binding cassette transporter A1 (ABCA1), which acts in the plasma membrane and endosomal system to promote cellular cholesterol transfer to lipid-poor apolipoproteins, such as ApoA1 and ApoE associated with high density lipoprotein (HDL) formation (Ignatova ID et al. 2013; Vedhachalam C et a. 2007). NR1H3 (LXRα) was found to be a stronger activator of ABCA1 expression in response to LXR agonists in mouse bone marrow-derived macrophages and in human primary macrophages (Bischoff ED et al. 2010; Ishibashi M et al. 2013). Cholesteryl esters accumulate in various tissues of mice lacking NR1H3, and in cells of the male reproductive system this is directly attributable to reduced expression of ABCA1 (Ouvrier A et al. 2009). Moreover, loss of ABCA1 in humans results in Tangier disease, a condition in which patients have extremely low levels of circulating HDL, massive accumulation of cholesterol in macrophages, and an increased risk for developing atherosclerosis (Rust S et al. 1999). Treatment with the synthetic NR1H2,3 agonist, T0901317, increased expression of ABCA1 mRNA in cells and tissues of wild type, but not NR1H2,3-null mice (Wagner BL et al. 2003; Repa JJ et al. 2000). At the same time, “unliganded” NR1H2,3 repressed basal expression of ABCA1 in a tissue-specific manner, occurring in macrophages and intestinal mucosa but not in several other mouse tissues (Wagner BL et al. 2003). Treatment of human THP-1 macrophages with endogenous (25-hydroxycholesterol) or synthetic (T0901317) NR1H2,3 ligands stimulated both transcriptional and posttranscriptional pathways affecting ABCA1 expression (Ignatova ID et al. 2013).

NR1H2 or NR1H3 heterodimerizes with retinoid X receptors (RXR) and binds to LXR-response elements (LXREs) consisting of a direct repeat of the core sequence 5'-AGGTCA-3' separated by 4 nucleotides (DR4) in the DNA of target genes (Wiebel FF & Gustafsson JA 1997). The human ABCA1 promoter was found to contain a LXRE located about 50 bp upstream of the transcription start site (Costet P et al. 2000). Gel shift experiments showed that NR1H2,3:RXR heterodimers bind to the isolated LXREs from human ABCA1 (Costet P et al. 2000). Further, the ligand-selective regulation of ABCA1 was observed when ABCA1 promoter-luciferase reporter constructs were transfected into human embryonic kidney 293T cells or human liver carcinoma HepG2 cells that were then treated with T0901317 or 25-hydroxycholesterol to show enhanced luciferase activity (Ignatova ID et al. 2013). Unliganded LXR:RXR actively suppresses transcription by recruiting a corepressor complex. A mammalian two-hybrid analysis, using GAL4 fusions of the receptor interaction domains (ID) from the nuclear receptor corepressor (NCOR1) and the silencing mediator of retinoic acid and thyroid hormone receptors (SMRT or NCOR2) transiently co-expressed with VP-16 fusions of NR1H3 or NR1H2 ligand binding domains in monkey kidney fibroblasts CV-1 cells showed that in the absence of ligand, both NR1H2 and NR1H3 interacted with the corepressor IDs of NCOR and SMRT (Wagner BL et al. 2003). Biochemical work has identified a core complex consisting of NCOR, histone deacetylase 3 (HDAC3), transducin β-like proteins (TBL1, TBLR1), and G protein pathway suppressor 2 (GPS2) (Zhang J et al. 2002). The chromatin immunoprecipitation (ChIP) assays in HepG2 cells revealed that, in the absence of GW3965, a synthetic NR1H2,3 agonist, NCOR and HDAC3 were associated with ABCA1 promoter, while agonist treatment caused their dissociation and induced recruitment of histone acetyltransferase (HAT) CBP and RNA polymerase II (Jakobsson T et al. 2009). TBLR1 was also present at the promoter and unaffected by the ligand status. GPS2 was found to occupy the ABCA1 promoter in the absence of ligand but was released upon GW3965 treatment, while NR1H2,3 (LXR) recruitment was observed already in the absence of ligand and further enhanced upon ligand activation (Jakobsson T et al. 2009). The inclusion of RXR in the re-ChIP assays demonstrates that GPS2 associates with the LXR:RXR heterodimer. Importantly, similar recruitment patterns were obtained in human THP-1 macrophages. Thus, at the ABCA1 promoter, NR1H2,3 ligand triggers exchange of a GPS corepressor complex (containing NCoR, HDAC3, TBLR1) for the coactivator complex devoid of GPS2 (Jakobsson T et al. 2009).

Identifier: R-HSA-8877922
Species: Homo sapiens
Compartment: nucleoplasm, endoplasmic reticulum lumen
Binding of RUNX2 to the OSE2 element in the promoter of the BGLAP (osteocalcin, OC) gene stimulates BGLAP transcription (Ducy and Karsenty 1995, Ducy et al. 1997). When RUNX2 binds the OSE2 element in complex with the MAF transcription factor, BGLAP transcription is enhanced (Nishikawa et al. 2010). BGLAP gene transcription is also directly stimulated by the complex of RUNX2 and WWTR1 (TAZ) (Hong et al. 2005), as well as the complex of RUNX2 and RB1 (Thomas et al. 2001). Phosphorylation of RUNX2, in the context of the RUNX2:CBFB complex, increases its association with the BGLAP promoter and enhances BGLAP transcription (Wee et al. 2002, Ge et al. 2009). Osteocalcin, a bone-derived hormone, is one of the most abundant non-collagenous proteins of the bone extracellular matrix (reviewed in Karsenty and Olson 2016).
Association of the activated androgen receptor (AR) with RUNX2 prevents binding of RUNX2 to the BGLAP promoter (Baniwal et al. 2009). Based on studies in rat, when YAP1, phosphorylated on an unknown tyrosine residue by SRC and/or YES1, is present in the complex with RUNX2 at the BGLAP gene promoter, transcription of the BGLAP gene is inhibited (Zaidi et al. 2004). Signaling by SRC is known to inhibit osteoblast differentiation (Marzia et al. 2000). Based on studies in mice, binding to ZNF521 (ZNP521) inhibits RUNX2-mediated activation of target promoters, such as BGLAP. HDAC3 is needed for ZNF521 to inhibit RUNX2-mediated transcription from the BGLAP promoter. Action of ZNF521 antagonizes RUNX2 during mesenchymal commitment to the osteoblast lineage and during osteoblast maturation (Hesse et al. 2010).
Identifier: R-HSA-5663258
Species: Homo sapiens
Compartment: nucleoplasm
NR1D1 (REV-ERBA) binds heme and the promoter of the PGC-1alpha (PPARGC1A) gene. The REV-ERBA:heme complex recruits the corepressors NCoR and HDAC3 and represses transcription.
Identifier: R-HSA-8986939
Species: Homo sapiens
Compartment: nucleoplasm
MECP2 binds the nuclear receptor co-repressor complex (NCoR/SMRT). This interaction is inhibited by MECP2 phosphorylation at threonine residue T308. The following NCoR/SMRT complex components were co-immunoprecipitated with MECP2: NCOR1, NCOR2, HDAC3, TBL1 (TBL1X), TBLR1 (TBL1XR1) and GPS2 (Lyst et al. 2013, Ebert et al. 2013). Direct interaction was confirmed between the transcriptional repressor domain of MECP2 and NCOR1, NCOR2, TBL1X and TBLR1 (Lyst et al. 2013). NCoR/SMRT complex consists of either NCOR1 (NCoR) or NCOR2 (SMRT), GPS2, HDAC3 and tetramers of either TBL1X or TBL1XR1 (Oberoi et al. 2011, reviewed by Watson et al. 2012).

Complex (6 results from a total of 9)

Identifier: R-HSA-9024349
Species: Homo sapiens
Compartment: nucleoplasm
Identifier: R-HSA-4663830
Species: Homo sapiens
Compartment: nucleoplasm
Identifier: R-HSA-9024373
Species: Homo sapiens
Compartment: nucleoplasm
Identifier: R-HSA-9008155
Species: Homo sapiens
Compartment: nucleoplasm
Identifier: R-HSA-9024368
Species: Homo sapiens
Compartment: nucleoplasm
Identifier: R-HSA-6807075
Species: Homo sapiens
Compartment: nucleoplasm

Set (2 results from a total of 2)

Identifier: R-HSA-6808476
Species: Homo sapiens
Compartment: nucleoplasm
Identifier: R-HSA-6808474
Species: Homo sapiens
Compartment: nucleoplasm

Pathway (4 results from a total of 4)

Identifier: R-HSA-1368071
Species: Homo sapiens
Compartment: nucleoplasm
REV-ERBA binds DNA elements very similar to those bound by the transcription activator RORA. RORAREV-ERBA bound to DNA and heme recruits the corepressors NCoR and HDAC3 to repress transcription. Thus REV-ERBA and RORA appear to compete to repress or activate genes, repectively.
Identifier: R-HSA-3214815
Species: Homo sapiens
Lysine deacetylases (KDACs), historically referred to as histone deacetylases (HDACs), are divided into the Rpd3/Hda1 metal-dependent 'classical HDAC family' (de Ruijter et al. 2003, Verdin et al. 2003) and the unrelated sirtuins (Milne & Denu 2008). Phylogenetic analysis divides human KDACs into four classes (Gregoretti et al. 2004): Class I includes HDAC1, 2, 3 and 8; Class IIa includes HDAC4, 5, 7 and 9; Class IIb includes HDAC6 and 10; Class III are the sirtuins (SIRT1-7); Class IV has one member, HDAC11 (Gao et al. 2002). Class III enzymes use an NAD+ cofactor to perform deacetylation (Milne & Denu 2008, Yang & Seto 2008), the others classes use a metal-dependent mechanism (Gregoretti et al. 2004) to catalyze the hydrolysis of acetyl-L-lysine side chains in histone and non-histone proteins yielding L-lysine and acetate. X-ray crystal structures are available for four human HDACs; these structures have conserved active site residues, suggesting a common catalytic mechanism (Lombardi et al. 2011). They require a single transition metal ion and are typically studied in vitro as Zn2+-containing enzymes, though in vivo HDAC8 exhibits increased activity when substituted with Fe2+ (Gantt et al. 2006). The structurally-related enzyme acetylpolyamine amidohydrolase (APAH) (Leipe & Landsman 1997) exhibits optimal activity with Mn2+, followed closely by Zn2+ (Sakurada et al. 1996).

HDACs are often part of multi-protein transcriptional complexes that are recruited to gene promoters, regulating transcription without direct DNA binding. With the exception of HDAC8, all class I members can be catalytic subunits of multiprotein complexes (Yang & Seto 2008). HDAC1 and HDAC2 interact to form the catalytic core of several multisubunit complexes including Sin3, nucleosome remodeling deacetylase (NuRD) and corepressor of REST (CoREST) complexes (Grozinger & Schreiber 2002). HDAC3 is part of the silencing mediator of retinoic acid and thyroid hormone receptor (SMRT) complex or the homologous nuclear receptor corepressor (NCoR) (Li et al. 2000, Wen et al. 2000, Zhang et al. 2002, Yoon et al. 2003, Oberoi et al. 2011) which are involved in a wide range of processes including metabolism, inflammation, and circadian rhythms (Mottis et al. 2013).

Class IIa HDACs (HDAC4, -5, -7, and -9) shuttle between the nucleus and cytoplasm (Yang & Seto 2008, Haberland et al. 2009). The nuclear export of class IIa HDACs requires phosphorylation stimulated by calcium or other stimuli. They appear to have been evolutionarily inactivated as enzymes, having acquired a histidine substitution of the tyrosine residue in the active site of the mammalian deacetylase domain (H976 in humans) (Lahm et al. 2007, Schuetz et al. 2008). Instead they function as transcriptional corepressors for the MEF2 family of transcription factors (Yang & Gregoire 2005) .

Histones are the primary substrate for most HDACs except HDAC6 which is predominantly cytoplasmic and acts on alpha-tublin (Hubbert et al. 2002, Zhang et al. 2003, Boyault et al. 2007). HDACs also deacetylate proteins such as p53, E2F1, RelA, YY1, TFIIE, BCL6 and TFIIF (Glozak et al. 2005).

Histone deacetylases are targeted by structurally diverse compounds known as HDAC inhibitors (HDIs) (Marks et al. 2000). These can induce cytodifferentiation, cell cycle arrest and apoptosis of transformed cells (Marks et al. 2000, Bolden et al. 2006). Some HDIs have significant antitumor activity (Marks and Breslow 2007, Ma et al. 2009) and at least two are approved anti-cancer drugs.

The coordinates of post-translational modifications represented and described here follow UniProt standard practice whereby coordinates refer to the translated protein before any further processing. Histone literature typically refers to coordinates of the protein after the initiating methionine has been removed. Therefore the coordinates of post-translated residues in the Reactome database and described here are frequently +1 when compared with the literature.
Identifier: R-HSA-381340
Species: Homo sapiens
Compartment: nucleoplasm, cytosol, plasma membrane
Adipogenesis is the process of cell differentiation by which preadipocytes become adipocytes. During this process the preadipocytes cease to proliferate, begin to accumulate lipid droplets and develop morphologic and biochemical characteristics of mature adipocytes such as hormone responsive lipogenenic and lipolytic programs. The most intensively studied model system for adipogenesis is differentiation of the mouse 3T3-L1 preadipocyte cell line by an induction cocktail of containing mitogens (insulin/IGF1), glucocorticoid (dexamethasone), an inducer of cAMP (IBMX), and fetal serum (Cao et al. 1991, reviewed in Farmer 2006). More recently additional cellular models have become available to study adipogenesis that involve almost all stages of development (reviewed in Rosen and MacDougald 2006). In vivo knockout mice lacking putative adipogenic factors have also been extensively studied. Human pathways are traditionally inferred from those discovered in mouse but are now beginning to be validated in cellular models derived from human adipose progenitors (Fischer-Posovszky et al. 2008, Wdziekonski et al. 2011).
Adipogenesis is controlled by a cascade of transcription factors (Yeh et al. 1995, reviewed in Farmer 2006, Gesta et al. 2007). One of the first observable events during adipocyte differentiation is a transient increase in expression of the CEBPB (CCAAT/Enhancer Binding Protein Beta, C/EBPB) and CEBPD (C/EBPD) transcription factors (Cao et al. 1991, reviewed in Lane et al. 1999). This occurs prior to the accumulation of lipid droplets. However, it is the subsequent inductions of CEBPA and PPARG that are critical for morphological, biochemical and functional adipocytes.
Ectopic expression of CEBPB alone is capable of inducing substantial adipocyte differentiation in fibroblasts while CEBPD has a minimal effect. CEBPB is upregulated in response to intracellular cAMP (possibly via pCREB) and serum mitogens (possibly via Krox20). CEBPD is upregulated in response to glucocorticoids. The exact mechanisms that upregulate the CEBPs are not fully known.
CEBPB and CEBPD act directly on the Peroxisome Proliferator-activated Receptor Gamma (PPARG) gene by binding its promoter and activating transcription. CEBPB and CEBPD also directly activate the EBF1 gene (and possibly other EBFs) and KLF5 (Jimenez et al. 2007, Oishi 2005). The EBF1 and KLF5 proteins, in turn bind, and activate the PPARG promoter. Other hormones, such as insulin, affect PPARG expression and other transcription factors, such as ADD1/SREBP1c, bind the PPARG promoter. This is an area of ongoing research.
During adipogenesis the PPARG gene is transcribed to yield 2 variants. The adipogenic variant 2 mRNA encodes 30 additional amino acids at the N-terminus compared to the widely expressed variant 1 mRNA.
PPARG encodes a type II nuclear hormone receptor (remains in the nucleus in the absence of ligand) that forms a heterodimer with the Retinoid X Receptor Alpha (RXRA). The heterodimer was initially identified as a complex regulating the aP2/FABP4 gene and named ARF6 (Tontonoz et al. 1994).
The PPARG:RXRA heterodimer binds a recognition sequence that consists of two hexanucleotide motifs (DR1 motifs) separated by 1 nucleotide. Binding occurs even in the absence of ligands, such as fatty acids, that activate PPARG. In the absence of activating ligands, the PPARG:RXRA complex recruits repressors of transcription such as SMRT/NCoR2, NCoR1, and HDAC3 (Tontonoz and Spiegelman 2008).
Each molecule of PPARG can bind 2 molecules of activating ligands. Although, the identity of the endogenous ligands of PPARG is unknown, exogenous activators include fatty acids and the thiazolidinedione class of antidiabetic drugs (reviewed in Berger et al. 2005, Heikkinen et al. 2007, Lemberger et al. 1996). The most potent activators of PPARG in vitro are oxidized derivatives of unsaturated fatty acids.. Upon binding activating ligands PPARG causes a rearrangement of adjacent factors: Corepressors such as SMRT/NCoR2 are lost and coactivators such as TIF2, PRIP, CBP, and p300 are recruited (Tontonoz and Spiegelman). PPARG also binds directly to the TRAP220 subunit of the TRAP/Mediator complex that recruits RNA polymerase II. Thus binding of activating ligand by PPARG causes transcription of PPARG target genes.
Targets of PPARG include genes involved in differentiation (PGAR/HFARP, Perilipin, aP2/FABP4, CEBPA), fatty acid transport (LPL, FAT/CD36), carbohydrate metabolism (PEPCK-C, AQP7, GK, GLUT4 (SLC2A4)), and energy homeostasis (LEPTIN and ADIPONECTIN) (Perera et al. 2006).
Within 10 days of differentiation CEBPB and CEBPD are no longer located at the PPARG promoter. Instead CEBPA is present. EBF1 and PPARG bind the CEBPA promoter and activate transcription of CEBPA, one of the key transcription factors in adipogenesis. A current hypothesis posits a self-reinforcing loop that maintains PPARG expression and the differentiated state: PPARG activates CEBPA and CEBPA activates PPARG. Additionally EBF1 (and possibly other EBFs) activates CEBPA, CEBPA activates EBF1, and EBF1 activates PPARG.
Identifier: R-HSA-350054
Species: Homo sapiens
THE NOTCH-HLH TRANSCRIPTION PATHWAY:

Notch signaling was first identified in Drosophila, where it has been studied in detail at the genetic, molecular, biochemical and cellular levels (reviewed in Justice, 2002; Bray, 2006; Schweisguth, 2004; Louvri, 2006). In Drosophila, Notch signaling to the nucleus is thought always to be mediated by one specific DNA binding transcription factor, Suppressor of Hairless. In mammals, the homologous genes are called CBF1 (or RBPJkappa), while in worms they are called Lag-1, so that the acronym "CSL" has been given to this conserved transcription factor family. There are at least two human CSL homologues, which are now named RBPJ and RBPJL.

CSL is an example of a bifunctional DNA-binding transcription factor that mediates repression of specific target genes in one context, but activation of the same targets in another context. This bifunctionality is mediated by the association of specific Co-Repressor complexes vs. specific Co-Activator complexes in different contexts, namely in the absence or presence of Notch signaling.

In Drosophila, Su(H) represses target gene transcription in the absence of Notch signaling, but activates target genes during Notch signaling. At least some of the mammalian CSL homologues are believed also to be bifunctional, and to mediate target gene repression in the absence of Notch signaling, and activation in the presence of Notch signaling.

Notch Co-Activator and Co-Repressor complexes: This repression is mediated by at least one specific co-repressor complexes (Co-R) bound to CSL in the absence of Notch signaling. In Drosophila, this co-repressor complex consists of at least three distinct co-repressor proteins: Hairless, Groucho, and dCtBP (Drosophila C-terminal Binding Protein). Hairless has been show to bind directly to Su(H), and Groucho and dCtBP have been shown to bind directly to Hairless (Barolo, 2002). All three of the co-repressor proteins have been shown to be necessary for proper gene regulation during Notch signaling in vivo (Nagel, 2005).

In mammals, the same general pathway and mechanisms are observed, where CSL proteins are bifunctional DNA binding transcription factors (TFs), that bind to Co-Repressor complexes to mediate repression in the absence of Notch signaling, and bind to Co-Activator complexes to mediate activation in the presence of Notch signaling. However, in mammals, there may be multiple co-repressor complexes, rather than the single Hairless co-repressor complex that has been observed in Drosophila.

During Notch signaling in all systems, the Notch transmembrane receptor is cleaved and the Notch intracellular domain (NICD) translocates to the nucleus, where it there functions as a specific transcription co-activator for CSL proteins. In the nucleus, NICD replaces the Co-R complex bound to CSL, thus resulting in de-repression of Notch target genes in the nucleus. Once bound to CSL, NICD and CSL proteins recruit an additional co-activator protein, Mastermind, to form a CSL-NICD-Mam ternary co-activator (Co-A) complex. This Co-A complex was initially thought to be sufficient to mediate activation of at least some Notch target genes. However, there now is evidence that still other co-activators and additional DNA-binding transcription factors are required in at least some contexts (reviewed in Barolo, 2002).

Mammalian CSL Corepressor Complexes: In the absence of activated Notch signaling, DNA-bound CSL proteins recruit a corepressor complex to maintain target genes in the repressed state until Notch is specifically activated. The mammalian corepressor complexes include NCOR complexes, but may also include additional corepressor proteins, such as SHARP (reviewed in Mumm, 2000 and Kovall, 2007). The exact composition of the CSL NCOR complex is not known, but in other pathways the "core" NCOR corepressor complex includes at least one NCOR protein (NCOR1, NCOR2, CIR), one Histone Deacetylase protein (HDAC1, HDAC2, HDAC3, etc), and one TBL1 protein (TBL1X, TBL1XR1) (reviewed in Rosenfeld, 2006). In some contexts, the core NCOR corepressor complex may also recruit additional corepressor proteins or complexes, such as the SIN3 complex, which consists of SIN3 (SIN3A, SIN3B), and SAP30, or other SIN3-associated proteins. An additional CSL - NCOR binding corepressor, SHARP, may also contribute to the CSL corepressor complex in some contexts (Oswald, 2002). The CSL corepressor complex also includes a bifunctional cofactor, SKIP, that is present in both CSL corepressor complexes and CSL coactivator complexes, and may function in the binding of NICD and displacement of the corepressor complex during activated Notch signaling (Zhou, 2000).

Mammalian CSL Coactivator Complexes: Upon activation of Notch signaling, cleavage of the transmembrane Notch receptor releases the Notch Intracellular Domain (NICD), which translocates to the nucleus, where it binds to CSL and displaces the corepressor complex from CSL (reviewed in Mumm, 2000 and Kovall, 2007). The resulting CSL-NICD "binary complex" then recruits an additional coactivator, Mastermind (Mam), to form a ternary complex. The ternary complex then recruits additional, more general coactivators, such as CREB Binding Protein (CBP), or the related p300 coactivator, and a number of Histone Acetytransferase (HAT) proteins, including GCN5 and PCAF (Fryer, 2002). There is evidence that Mam also can subsequently recruit specific kinases that phosphorylate NICD, to downregulate its function and turn off Notch signaling (Fryer, 2004).

Combinatorial Complexity in Transcription Cofactor Complexes: HDAC9 has at least 7 splice isoforms, with some having distinct interaction and functional properties. Isoforms 6 and 7 interact with NCOR1. Isoforms 1 and 4 interact with MEF2 (Sparrow, 1999), which is a specific DNA-binding cofactor for a subset of HLH proteins. Isoform 3 interacts with both NCOR1 and MEF2. Although many HDACs only have one or two isoforms, this complexity for HDAC9 illustrates the level of transcript complexity and functional specificity that such "general" transcriptional cofactors can have.
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