Project description:We determined genomic binding of HDAC3 in mouse hypothalamus by ChIP-seq, and identified target genes of the NCOR/HDAC3 complex in hypothalamus of NS-DADm (mutated deacetylase activation domain in NCORs) mice by RNA-seq.
Project description:We determined genomic binding of HDAC3 in mouse hypothalamus by ChIP-seq, and identified target genes of the NCOR/HDAC3 complex in hypothalamus of NS-DADm (mutated deacetylase activation domain in NCORs) mice by RNA-seq.
Project description:Repression of peroxisome proliferator-activated receptor ? (PPAR?)-dependent transcription by the nuclear receptor corepressor (NCoR) is important for homeostatic expression of PPAR? target genes in vivo. The current model states that NCoR-mediated repression requires its direct interaction with PPAR? in the repressive conformation. Previous studies, however, have shown that DNA-bound PPAR? is incompatible with a direct, high-affinity association with NCoR because of the inherent ability of PPAR? to adopt the active conformation. Here we show that NCoR acquires the ability to repress active PPAR?-mediated transcription via G protein pathway suppressor 2 (GPS2), a component of the NCoR corepressor complex. Unlike NCoR, GPS2 can recognize and bind the active state of PPAR?. In GPS2-deficient mouse embryonic fibroblast cells, loss of GPS2 markedly reduces the corepressor function of NCoR for PPAR?, leading to constitutive activation of PPAR? target genes and spontaneous adipogenesis of the cells. GPS2, however, is dispensable for repression mediated by unliganded thyroid hormone receptor ? or a PPAR? mutant unable to adopt the active conformation. This study shows that GPS2, although dispensable for the intrinsic repression function of NCoR, can mediate a novel corepressor repression pathway that allows NCoR to directly repress active PPAR?-mediated transcription, which is important for the optimal corepressor function of NCoR for PPAR?. Interestingly, GPS2-dependent repression specifically targets PPAR? but not PPAR? or PPAR?. Therefore, GPS2 may serve as a unique target to manipulate PPAR? signaling in diseases.
Project description:The thyroid hormone receptor (TR) has been proposed to regulate expression of target genes in the absence of triiodothyronine (T(3)) through the recruitment of the corepressors, NCoR and SMRT. Thus, NCoR and SMRT may play an essential role in thyroid hormone action, although this has never been tested in vivo. To accomplish this, we developed mice that express in the liver a mutant NCoR protein (L-NCoRDeltaID) that cannot interact with the TR. L-NCoRDeltaID mice appear grossly normal, however, when made hypothyroid the repression of many positively regulated T(3)-target genes is abrogated, demonstrating that NCoR plays a specific and sufficient role in repression by TR in the absence of T(3). Remarkably, in the euthyroid state, expression of many T(3)-targets is also up-regulated in L-NCoRDeltaID mice, demonstrating that NCoR also determines the magnitude of the response to T(3) in euthyroid animals. Although positive T(3) targets were up-regulated in L-NCoRDeltaID mice in the hypo- and euthyroid state, there was little effect seen on negatively regulated T(3) target genes. Thus, NCoR is a specific regulator of T(3)-action in vivo and mediates repression by the unliganded TR in hypothyroidism. Furthermore, NCoR appears to play a key role in determining the tissue-specific responses to similar levels of circulating T(3). Interestingly, NCoR recruitment to LXR is also impaired in this model, leading to activation of LXR-target genes, further demonstrating that NCoR recruitment regulates multiple nuclear receptor signaling pathways.
Project description:Histone deacetylases (HDACs) are believed to regulate gene transcription by catalyzing deacetylation reactions. HDAC3 depletion in mouse liver upregulates lipogenic genes and results in severe hepatosteatosis. Here we show that pharmacologic HDAC inhibition in primary hepatocytes causes histone hyperacetylation but does not upregulate expression of HDAC3 target genes. Meanwhile, deacetylase-dead HDAC3 mutants can rescue hepatosteatosis and repress lipogenic genes expression in HDAC3-depleted mouse liver, demonstrating that histone acetylation is insufficient to activate gene transcription. Mutations abolishing interactions with the nuclear receptor corepressor (NCOR or SMRT) render HDAC3 nonfunctional in vivo. Additionally, liver-specific knockout of NCOR, but not SMRT, causes metabolic and transcriptomal alterations resembling those of mice without hepatic HDAC3, demonstrating that interaction with NCOR is essential for deacetylase-independent function of HDAC3. These findings highlight nonenzymatic roles of a major HDAC in transcriptional regulation in vivo and warrant reconsideration of the mechanism of action of HDAC inhibitors.
Project description:Histone deacetylase 3 (HDAC3) is an epigenome-modifying enzyme that is required for normal mouse development and tissue-specific functions. In vitro, HDAC3 protein itself has minimal enzyme activity, but gains its histone deacetylation function from stable association with the conserved deacetylase activation domain (DAD) contained in nuclear receptor corepressors NCOR1 and SMRT. Here we show that HDAC3 enzyme activity is undetectable in mice bearing point mutations in the DAD of both NCOR1 and SMRT (NS-DADm), despite normal levels of HDAC3 protein. Local histone acetylation is increased, and genomic HDAC3 recruitment is reduced though not abrogated. Remarkably, the NS-DADm mice are born and live to adulthood, whereas genetic deletion of HDAC3 is embryonic lethal. These findings demonstrate that nuclear receptor corepressors are required for HDAC3 enzyme activity in vivo, and suggest that a deacetylase-independent function of HDAC3 may be required for life. This SuperSeries is composed of the SubSeries listed below. Refer to individual Series.
