Biomedical subjects

Hung-Ying Kao

Publications and source records attributed to Hung-Ying Kao.

9 recordsLinked to original sources

PubMed2006

Alpha-actinin 4 potentiates myocyte enhancer factor-2 transcription activity by antagonizing histone deacetylase 7.

Histone deacetylase 7 (HDAC7) is a member of class IIa HDACs that regulate myocyte enhancer factor-2 (MEF2)-mediated transcription and participate in multiple cellular processes such as T cell apoptosis. We have identified alpha-actinin 1 and 4 as class IIa HDAC-interacting proteins. The interaction domains are mapped to C terminus of alpha-actinin 4 and amino acids 72-172 of HDAC7. A point mutation in HDAC7 that disrupts its association with MEF2A also disrupts its association with alpha-actinin 4, indicating that MEF2A and alpha-actinin 4 binding sites largely overlap. We have also isolated a novel splice variant of alpha-actinin 4 that is predominantly localized in the nucleus, a pattern distinct from the full-length alpha-actinin 4, which is primarily distributed in the cytoplasm and plasma membrane. Using small interfering RNA, chromatin immunoprecipitation, and transient transfection assays, we show that alpha-actinin 4 potentiates expression of TAF55, a putative MEF2 target gene. Loss of MEF2A interaction correlates with loss of the ability of alpha-actinin 4 to potentiate TAF55 promoter activity. Ectopic expression of alpha-actinin 4, but not the mutant defective in MEF2A association, leads to disruption of HDAC7.MEF2A association and enhancement of MEF2-mediated transcription. Taken together, we have identified a novel mechanism by which HDAC7 activity is negatively regulated and uncovered a previously unknown function of alpha-actinin 4.

Actinin↗

PubMed2006

CRM1 mediates nuclear export of HDAC7 independently of HDAC7 phosphorylation and association with 14-3-3s.

CRM1, 14-3-3 proteins, and CaMK play important roles in trafficking of HDAC7, but the interplay between these proteins in this process is not clearly understood. Here, we show that CRM1 is capable of promoting cytoplasmic localization of wild-type and mutant HDAC7 (S178A/S344A/S479A), which is normally found in the nucleus. Using phospho-specific antibodies to HDAC7, we demonstrate that CaMK I promotes phosphorylation of S178, S344, and S479 of HDAC7. We also show that endogenous S178-phosphorylated HDAC7 is localized in both the nucleus and the cytoplasm, whereas S344- and S479-phosphorylated HDAC7 are exclusively localized in the nucleus. An HDAC7 mutant, S178E/S344E/S479E, which lost the ability to bind 14-3-3s, is localized in both the nucleus and the cytoplasm. Furthermore, the nuclear export of S178E/S344E/S479E is inhibited by LMB, but is enhanced by the CRM1. Taken together, these results strongly suggest that CRM1 mediated-nuclear export of HDAC7 is independent of HDAC7 phosphorylation and its association with 14-3-3s.

14-3-3 Proteins↗

PubMed2004

Retinoid X receptor alpha (RXRalpha) helix 12 plays an inhibitory role in the recruitment of the p160 co-activators by unliganded RXRalpha/retinoic acid receptor alpha heterodimers.

Retinoid X receptor (RXR)/retinoic acid receptor (RAR) heterodimers control gene expression through recruitment of co-repressors or co-activators, depending on their hormone binding status. We show that the helix 12 of RXRalpha and RARalpha is critical for recruitment of the co-regulators and transcriptional regulation by RXRalpha, RARalpha, and RXRalpha/RARalpha. LG268, an RXR-specific agonist, was able to promote co-activator association with the heterodimers, but was unable to dissociate co-repressors. Reconstitution experiments in yeast demonstrated that LG268 was capable of activating transcription by RXRalpha/RARalpha through recruitment of the co-activator. We hypothesize that the inability to release co-repressors from RXRalpha/RARalpha is responsible for the inability of LG268 to activate RXRalpha/RARalpha heterodimers in mammalian cells. Deletion of RARalpha helix 12 (RXRalpha/RARalpha Delta403) abolished both hormone-dependent dissociation from co-repressors and hormone-dependent association with co-activators. Deletion of RXRalpha helix 12 (RXRalpha Delta443/RARalpha) resulted in a higher binding affinity for co-repressors. Unexpectedly, RXRalpha Delta443/RARalpha also gained hormone-independent co-activator binding activity. Moreover, LG268 became an antagonist to RXRalpha Delta443/RARalpha heterodimers. These data suggest that the helix 12 of RXRalpha plays an inhibitory role in the recruitment of co-activators by unliganded RXRalpha/RARalpha.

Amino Acid Sequence↗

PubMed2004

Phosphorylation of the histone deacetylase 7 modulates its stability and association with 14-3-3 proteins.

Class II histone deacetylases (HDACs) play a role in myogenesis and inhibit transcriptional activation by myocyte enhancer factors 2. A distinct feature of class II HDACs is their ability to shuttle between the nucleus and the cytoplasm in a cell type- and signal-dependent manner. We demonstrate here that treatment with the 26 S proteosome inhibitors, MG132 and ALLN, leads to detection of ubiquitinated HDAC7 and causes accumulation of cytoplasmic HDAC7. We also show that treatment with calyculin A, a protein phosphatase inhibitor, leads to a marked increase of HDAC7 but not HDAC5. The increase in HDAC7 is accompanied by enhanced interaction between 14-3-3 proteins and HDAC7. HDAC7 mutations that prevent the interaction with 14-3-3 proteins also block calyculin A-mediated stabilization. Expression of constitutively active calcium/calmodulin-dependent kinase I stabilizes HDAC7 and causes an increased association between HDAC7 and 14-3-3. Together, our results suggest that calcium/calmodulin-dependent kinase I-mediated phosphorylation of HDAC7 acts, in part, to promote association of HDAC7 with 14-3-3 and stabilizes HDAC7.

14-3-3 Proteins↗

PubMed2004

Ataxin 1, a SCA1 neurodegenerative disorder protein, is functionally linked to the silencing mediator of retinoid and thyroid hormone receptors.

Ataxin 1 (Atx1) is a foci-forming polyglutamine protein of unknown function, whose mutant form causes type 1 spinocerebellar ataxia in humans and exerts neurotoxicity in transgenic mouse and fly expressing mutant Atx1. In this study, we demonstrate that Atx1 interacts with the transcriptional corepressor SMRT (silencing mediator of retinoid and thyroid hormone receptors) and with histone deacetylase 3. Atx1 binds chromosomes and mediates transcriptional repression when tethered to DNA. Interaction with SMRT-related factors is a conserved feature of Atx1, because Atx1 also binds SMRTER, a Drosophila cognate of SMRT. Significantly, mutant Atx1 forms aggregates in Drosophila, and such mutant Atx1-mediated aggregates sequester SMRTER. Consistently, the neurodegenerative eye phenotype caused by mutant Atx1 is enhanced by a Smrter mutation and, conversely, is suppressed by a chromosomal duplication that contains the wild type Smrter gene. Together, our results suggest that Atx1 is a transcriptional factor whose mutant form exerts its deleterious effects in part by perturbing corepressor-dependent transcriptional pathways.

Animals↗

PubMed2003

Tip60 is a co-repressor for STAT3.

Tip60 (Tat-interactive protein, 60 kDa), a cellular protein with intrinsic histone acetyltransferase activity, is involved in DNA damage repair and apoptosis. Recent studies have suggested that Tip60 acts either as a co-activator or a co-repressor to modulate transcription. In this study, we demonstrate that Tip60 represses reporter gene expression when it is fused to the Gal4 DNA binding domain. We also show that Tip60 associates with histone deacetylase 7 (HDAC7) through its N-terminal zinc finger-containing region and that HDAC7 activity is required for the repressive effect of Tip60. Because endogenous Tip60 interacts with STAT3, we hypothesized that Tip60 might complex with STAT3 and HDAC7 and modulate STAT3-mediated trans-activation. Consistent with this hypothesis, the overexpression of Tip60 represses STAT3-driven reporter gene expression, which can be further potentiated by the co-transfection of HDAC7. Furthermore, interleukin-9-induced c-myc expression, which depends on STAT3 activity, is abrogated by exogenous expression of Tip60. This is the first demonstration of which Tip60 represses STAT3 activity in part through the recruitment of HDAC7.

Acetyltransferases↗

PubMed2002

Co-repressor release but not ligand binding is a prerequisite for transcription activation by human retinoid acid receptor alpha ligand-binding domain.

Nuclear hormone receptors coordinately regulate the activity of genetic networks through the recruitment of transcriptional co-regulators, including co-repressors and co-activators. Allosteric modulation of the ligand-binding domain by hormonal activators shifts the co-factor binding preference by defined structural changes in overlapping docking sites. We report here that mutations at conserved residues within the docking motif of the retinoic acid receptor alpha cause defects in dimerization, co-regulator association, and transcriptional regulation. Furthermore, although a minimal co-repressor receptor interaction domain is sufficient for receptor binding, flanking sequences appear to stabilize this interaction without interfering with ligand sensitivity. However, ligand sensitivity is changed by the K262A mutation, which requires much higher concentrations of all-trans-retinoic acid to promote co-repressor dissociation. Consequently, K262A functions as a dominant-negative mutant at low concentrations of all-trans-retinoic acid. As a result, transcriptional activation is mechanistically linked to co-repressor release.

Amino Acid Sequence↗

PubMed2002

Class II histone deacetylases are directly recruited by BCL6 transcriptional repressor.

BCL6 is a member of the POZ/zinc finger (POK) family involved in survival and/or differentiation of a number of cell types and in B cell lymphoma upon chromosomal alteration. Transcriptional repression by BCL6 is thought to be achieved in part by recruiting a repressor complex containing two class I histone deacetylases (HDACs). In this study we investigated whether BCL6 could also target members of class II HDACs. Our results indicate that three related class II deacetylases, HDAC4, HDAC5, and HDAC7 can associate with BCL6 in vivo and in vitro. Using electron microscopy, we found that endogenous BCL6 and class II HDACs partially co-localize in the nucleus. Overexpression experiments showed that BCL6 and HDAC4, -5, or -7 are intermingled onto common nuclear substructures and form stable complexes. A highly conserved domain in the N-terminal region of HDAC5 and HDAC7 as well as the zinc finger region of BCL6 were found necessary for the complex formation in vivo and in vitro. Moreover, our data point to the zinc finger region of BCL6 as a multifunctional domain which, beside its known capacity to bind DNA, is involved in the nuclear targeting of the protein and in the recruitment of the class II HDACs, and hence constitutes an autonomous repressor domain. Since PLZF, a BCL6 relative, could also interact with HDAC4, -5, and 7, we suggest that class II HDACs are largely involved in the control of the POK transcription factors activity.

Animals↗

PubMed2001

Isolation and characterization of mammalian HDAC10, a novel histone deacetylase.

Acetylation of histone core particles plays an important role in modulating chromatin structure and gene expression. The acetylation status of the histone tails is determined by two opposing enzymatic activities, histone acetyltransferases and histone deacetylases (HDACs). Here we describe the isolation and characterization of HDAC10, a novel class II histone deacetylase. Molecular cloning and Northern blot analyses reveal that the HDAC10 transcript is widely expressed and subjected to alternative splicing. HDAC10 is both nuclear and cytoplasmic, a feature reminiscent of HDACs 4, 5, and 7. Distinct from other family members, HDAC10 harbors an amino-terminal catalytic domain and a carboxyl pseudo-repeat that shares significant homology with its catalytic domain. Mutational analysis reveals that transcriptional repression by HDAC10 requires its intrinsic histone deacetylase activity. Taken together, HDAC10 represents a distinct HDAC that may play a role in transcription regulation.

Amino Acid Sequence↗