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Junn Yanagisawa

Publications and source records attributed to Junn Yanagisawa.

15 recordsLinked to original sources
PubMed2005

Splicing potentiation by growth factor signals via estrogen receptor phosphorylation.

Mitogen-activated protein kinase-mediated growth factor signals are known to augment the ligand-induced transactivation function of nuclear estrogen receptor alpha (ERalpha) through phosphorylation of Ser-118 within the ERalpha N-terminal transactivation (activation function-1) domain. We identified the spliceosome component splicing factor (SF)3a p120 as a coactivator specific for human ERalpha (hERalpha) activation function-1 that physically associated with ERalpha dependent on the phosphorylation state of Ser-118. SF3a p120 potentiated hERalpha-mediated RNA splicing, and notably, the potentiation of RNA splicing by SF3a p120 depended on hER Ser-118 phosphorylation. Thus, our findings suggest a mechanism by which growth factor signaling can regulate gene expression through the modulation of RNA splicing efficiency via phosphorylation of sequence-specific activators, after association between such activators and the spliceosome.

Animals↗
PubMed2005

TRRAP as a hepatic coactivator of LXR and FXR function.

TBP-free TAF II-containing-type HAT complex subclasses, which contain hGCN5 HAT and TRRAP, appear to act as common coactivator complexes for nuclear receptors. However, their physiological significance with respect to each nuclear receptor remains to be established. To address this issue, we used hepatic cell lines (HepG2) with reduced endogenous TRRAP expression through antisense RNA expression or with overexpressed TRRAP or other major coactivators. The ligand-induced transactivation function of liver X receptor alpha (LXRalpha) and farnesoid X receptor/bile acid receptor reflected TRRAP expression levels, while that of PPARgamma did not. A GST pull-down assay indicated that TRRAP contains two potential LXRalpha-interacting domains in the C-terminal and central domains. Expression of antisense TRRAP RNA in HepG2 cells abolished the ligand-induced expression of LXRalpha target genes. These results suggested that TRRAP plays an important role as a coactivator, presumably part of a complex, in lipid metabolism through regulation of the LXRalpha-mediated gene cascade in hepatic cells.

Adaptor Proteins, Signal Transducing↗
PubMed2004

Ligand-dependent switching of ubiquitin-proteasome pathways for estrogen receptor.

Recent evidence indicates that the transactivation of estrogen receptor alpha (ERalpha) requires estrogen-dependent receptor ubiquitination and degradation. Here we show that estrogen-unbound (unliganded) ERalpha is also ubiquitinated and degraded through a ubiquitin-proteasome pathway. To investigate this ubiquitin-proteasome pathway, we purified the ubiquitin ligase complex for unliganded ERalpha and identified a protein complex containing the carboxyl terminus of Hsc70-interacting protein (CHIP). CHIP preferentially bound to misfolded ERalpha and ubiquitinated it to induce degradation. Ligand binding to the receptor induced the dissociation of CHIP from ERalpha. In CHIP-/- cells, the degradation of unliganded ERalpha was abrogated; however, estrogen-induced degradation was observed to the same extent as in CHIP+/+ cells. Our findings suggest that ERalpha is regulated by two independent ubiquitin-proteasome pathways, which are switched by ligand binding to ERalpha. One pathway is necessary for the transactivation of the receptor and the other is involved in the quality control of the receptor.

Animals↗
PubMed2004

Characterization of BHC80 in BRAF-HDAC complex, involved in neuron-specific gene repression.

BRAF-HDAC complex (BHC) has been shown to contain six components, including BHC80, and to mediate REST-dependent transcriptional repression of neuron-specific genes in non-neuronal cells. In this study, we have examined the functional role(s) of BHC80 in mouse tissues and human cultured cells. Two isoforms of mouse BHC80 were predominantly present in the central nervous system and spermatogenic cells. Human cultured cells also contained two isoforms of BHC80. Immunohistochemical analysis showed the presence of mouse BHC80 in the nucleus of neuronal cells in the hippocampus and cerebellum. The C-terminal region of human BHC80 containing PHD zinc-finger domain was capable of binding directly to each of five other components of BHC, and of organizing BHC mediating transcriptional repression. Moreover, two isoforms of human BHC80 were distinguished from each other by reduced binding to HDAC1 and HDAC2, despite the presence of the PHD finger domain. These results suggest that BHC80 presumably serves as a scaffold protein in BHC in neuronal as well as non-neuronal cells. A possible role of BHC80 in spermatogenesis is also suggested.

Alternative Splicing↗
PubMed2004

BRCA1 function mediates a TRAP/DRIP complex through direct interaction with TRAP220.

Breast cancer susceptibility gene 1 (BRCA1) is a tumor suppressor gene mutated in a high percentage of hereditary breast and ovarian cancers. The multifunctional BRCA1 protein acts on cell cycle control, exerting several highly specialized DNA repair processes through diverse domains. Gene regulation through its C-terminal domain (BRCT) is indispensable for BRCA1-mediated tumor suppression, suggesting the possibility that the BRCT domain interacts with co-regulator complexes. Using a biochemical approach with HeLa S3 nuclear extracts, we isolated BRCT-associated complexes and identified one of the purified components as TRAP220. We then performed interaction studies in vivo (co-immunoprecipitation) and in vitro (glutathione S-transferase pull-down assays) and showed that BRCT directly interacted with TRAP220. This in vitro interaction was completely abolished by BRCT point mutations typical of those found in patients with BRCA1 that lack transactivation function. BRCA1 transactivation function was dependent on TRAP220 expression level in a transient expression assay. Moreover, a cell survival assay showed that antisense TRAP220 expression to disrupt endogenous TRAP220 expression significantly reduced the survival rate potentiated by BRCA1 after DNA damage. These results suggested that a TRAP220 complex play an important role as putative co-activator complexes in BRCA1-mediated tumor suppression.

BRCA1 Protein↗
PubMed2004

Transrepression by a liganded nuclear receptor via a bHLH activator through co-regulator switching.

Vitamin D receptor (VDR) is essential for ligand-induced gene repression of 25(OH)D3 1alpha-hydroxylase (1alpha(OH)ase) in mammalian kidney, while this gene expression is activated by protein kinase A (PKA) signaling downstream of the parathyroid hormone action. The mapped negative vitamin D response element (1alphanVDRE) in the human 1alpha(OH)ase gene promoter (around 530 bp) was distinct from those of the reported DR3-like nVDREs, composed of two E-box-like motifs. Unlike the reported nVDREs, no direct binding of VDR/RXR heterodimer to 1alphanVDRE was detected. A bHLH-type factor, designated VDIR, was identified as a direct sequence-specific activator of 1nVDRE. The transactivation function of VDIR was further potentiated by activated-PKA signaling through phosphorylation of serine residues in the transactivation domains, with the recruitment of a p300 histone acetyltransferase co-activator. The ligand-dependent association of VDR/RXR heterodimer with VDIR bound to 1alphanVDRE caused the dissociation of p300 co-activators from VDIR, and the association of HDAC co-repressor complex components resulting in ligand-induced transrepression. Thus, the present study deciphers a novel mechanism of ligand-induced transrepression by nuclear receptor via co-regulator switching.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗
PubMed2003

Both N- and C-terminal transactivation functions of DNA-bound ERalpha are blocked by a novel synthetic estrogen ligand.

Estrogen receptors (ERs) play a central role in the diverse actions of estrogen. A number of synthetic ER ligands have been generated that can modulate various ER functions. Here we show that TAS-108, representing a novel class of synthetic ER ligands, blocked both ER transactivation functions without inhibiting DNA-binding activity. A transient expression assay showed that similar to ICI182,780, TAS-108 exhibited pure antagonistic activity as it blocked both the N-terminal AF-1 and C-terminal AF-2 transactivation functions. However, unlike ICI182,780, TAS-108 promoted the recruitment of the SMRT co-repressor that abolished ER transactivation function without inhibition of the ability of ERalpha to bind to its target DNA. Both TAS-108 and ICI182,780 acted as antagonists for the transactivation functions of the D351Y mutant, derived from tamoxifen-resistant breast cancer cells, while estrogen and known selective estrogen receptor modulators (SERMs), 4-OH tamoxifen and raloxifene, stimulated D351Y-mediated transcription. Thus, our findings indicated that TAS-108 acts as a novel estrogen antagonist that recruits co-repressors to ERs without AF-1 activation or prevention of DNA binding. Therefore, TAS-108 may be effective against tamoxifen-resistant breast cancer via a different mechanism than that for ICI182,780.

Animals↗
PubMed2003

Protein kinase A potentiates adrenal 4 binding protein/steroidogenic factor 1 transactivation by reintegrating the subcellular dynamic interactions of the nuclear receptor with its cofactors, general control nonderepressed-5/transformation/transcription domain-associated protein, and suppressor, dosage-sensitive sex reversal-1: a laser confocal imaging study in living KGN cells.

The mechanism through which protein kinase A (PKA) potentiates the transactivation ability of adrenal 4 binding protein/steroidogenic factor 1 (Ad4BP/SF-1) is currently unclear. In the present study, we investigated the mechanism by applying laser confocal microscopy and fluorescence recovery after photobleaching technique. In KGN cells, forskolin (a PKA stimulator) could reorganize wild-type Ad4BP/SF-1, but not mutant Ad4BP/SF-1 (G35E), from a diffuse distribution pattern to foci formation in the nucleus. The subcellular distributions of GCN5 (general control nonderepressed) and TRRAP (transformation/transcription domain-associated protein), both of which were recently proved to be working in the same complex as the third class of nuclear receptor coactivators, were unexpectedly diffuse inside and outside the nucleus, respectively, when they were separately transfected. However TRRAP was translocated into the nucleus in the presence of GCN5, and together with GCN5 colocalized with Ad4BP/SF-1 in the same foci when PKA was activated. A luciferase assay also indicated that these two cofactors enhanced Ad4BP/SF-1 transactivation.Dosage-sensitive sex reversal (DAX-1) interacts with and thus inhibits Ad4BP/SF-1 transactivation. The coexistence of the two proteins dramatically altered their respective subnuclear distributions. They colocalized extensively, suggestive of binding, and Ad4BP/SF-1 was sharply immobilized when DAX-1 was coexpressed, whereas PKA could maintain mobility, as evidenced by Fluorescence Recovery After Photobleaching showing that Ad4BP/SF-1 mobility recovered after forskolin treatment.Therefore, the PKA signal pathway may modify the interaction between Ad4BP/SF-1 and its activators and repressor (GCN5 and TRRAP are integrated, whereas DAX-1 is disassociated), and thus stimulate the Ad4BP/SF-1 transactivation.

Adaptor Proteins, Signal Transducing↗
PubMed2003

The chromatin-remodeling complex WINAC targets a nuclear receptor to promoters and is impaired in Williams syndrome.

We identified a human multiprotein complex (WINAC) that directly interacts with the vitamin D receptor (VDR) through the Williams syndrome transcription factor (WSTF). WINAC has ATP-dependent chromatin-remodeling activity and contains both SWI/SNF components and DNA replication-related factors. The latter might explain a WINAC requirement for normal S phase progression. WINAC mediates the recruitment of unliganded VDR to VDR target sites in promoters, while subsequent binding of coregulators requires ligand binding. This recruitment order exemplifies that an interaction of a sequence-specific regulator with a chromatin-remodeling complex can organize nucleosomal arrays at specific local sites in order to make promoters accessible for coregulators. Furthermore, overexpression of WSTF could restore the impaired recruitment of VDR to vitamin D regulated promoters in fibroblasts from Williams syndrome patients. This suggests that WINAC dysfunction contributes to Williams syndrome, which could therefore be considered, at least in part, a chromatin-remodeling factor disease.

Active Transport, Cell Nucleus↗
PubMed2003

Modulation of oestrogen receptor signalling by association with the activated dioxin receptor.

Environmental contaminants affect a wide variety of biological events in many species. Dioxins are typical environmental contaminants that exert adverse oestrogen-related effects. Although their anti-oestrogenic actions are well described, dioxins can also induce endometriosis and oestrogen-dependent tumours, implying possible oestrogenic effects. However, the molecular mechanism underlying oestrogen-related actions of dioxins remains largely unknown. A heterodimer of the dioxin receptor (AhR) and Arnt, which are basic helix-loop-helix/PAS-family transcription factors, mediates most of the toxic effects of dioxins. Here we show that the agonist-activated AhR/Arnt heterodimer directly associates with oestrogen receptors ER-alpha and ER-beta. This association results in the recruitment of unliganded ER and the co-activator p300 to oestrogen-responsive gene promoters, leading to activation of transcription and oestrogenic effects. The function of liganded ER is attenuated. Oestrogenic actions of AhR agonists were detected in wild-type ovariectomized mouse uteri, but were absent in AhR-/- or ER-alpha-/- ovariectomized mice. Our findings suggest a novel mechanism by which ER-mediated oestrogen signalling is modulated by a co-regulatory-like function of activated AhR/Arnt, giving rise to adverse oestrogen-related actions of dioxin-type environmental contaminants.

Animals↗
PubMed2003

Full activation of estrogen receptor alpha activation function-1 induces proliferation of breast cancer cells.

The effects of estrogen and anti-estrogen are mediated through the estrogen receptors (ER) alpha and beta, which function as ligand-induced transcriptional factors. Recently, one of the phthalate esters, n-butylbenzyl phthalate (BBP), has been shown to induce estrogen receptor-mediated responses. By using the truncated types of ER mutants, we revealed that activation function-1 (AF-1) activity was necessary for the BBP-dependent transactivation function of ERalpha. AF-1 is also known to be responsible for the partial agonistic activity of tamoxifen. Whereas tamoxifen exhibits an anti-estrogenic effect on proliferation of the MCF-7 breast cancer cell line, BBP showed an estrogenic effect on MCF-7 to stimulate proliferation. In vivo and in vitro binding assays revealed that whereas 4-hydroxytamoxifen (OHT) induced binding of ERalpha to both an AF-1 coactivator complex (p68/p72 and p300) and corepressor complexes (N-CoR/SMRT), BBP selectively enhanced the binding to the AF-1 coactivators. We also showed that the transcriptional activity of OHT-bound ERalpha was modulated by the ratio between the AF-1 coactivator and corepressor complexes. Expression of a dominant-negative type of N-CoR inhibited the interaction between OHT-bound ERalpha and N-CoR/SMRT and enhanced the transcriptional activity of OHT-bound ERalpha. Furthermore, the cell growth of MCF-7 stably expressing the dominant-negative type of N-CoR was enhanced by the addition of OHT. These results indicated that fully activated AF-1 induces the stimulation of breast cancer growth and that the ratio between AF-1 coactivators and corepressors plays a key role to prevent proliferation of tumor by tamoxifen.

3T3 Cells↗
PubMed2003

Cytokines suppress adipogenesis and PPAR-gamma function through the TAK1/TAB1/NIK cascade.

Pluripotent mesenchymal stem cells in bone marrow differentiate into adipocytes, osteoblasts and other cells. Balanced cytodifferentiation of stem cells is essential for the formation and maintenance of bone marrow; however, the mechanisms that control this balance remain largely unknown. Whereas cytokines such as interleukin-1 (IL-1) and tumour-necrosis factor-alpha (TNF-alpha) inhibit adipogenesis, the ligand-induced transcription factor peroxisome proliferator-activated receptor-gamma (PPAR-gamma), is a key inducer of adipogenesis. Therefore, regulatory coupling between cytokine- and PPAR-gamma-mediated signals might occur during adipogenesis. Here we show that the ligand-induced transactivation function of PPAR-gamma is suppressed by IL-1 and TNF-alpha, and that this suppression is mediated through NF-kappaB activated by the TAK1/TAB1/NF-kappaB-inducing kinase (NIK) cascade, a downstream cascade associated with IL-1 and TNF-alpha signalling. Unlike suppression of the PPAR-gamma transactivation function by mitogen-activated protein kinase-induced growth factor signalling through phosphorylation of the A/B domain, NF-kappaB blocks PPAR-gamma binding to DNA by forming a complex with PPAR-gamma and its AF-1-specific co-activator PGC-2. Our results suggest that expression of IL-1 and TNF-alpha in bone marrow may alter the fate of pluripotent mesenchymal stem cells, directing cellular differentiation towards osteoblasts rather than adipocytes by suppressing PPAR-gamma function through NF-kappaB activated by the TAK1/TAB1/NIK cascade.

Adaptor Proteins, Signal Transducing↗
PubMed2002

Nuclear receptor function requires a TFTC-type histone acetyl transferase complex.

Nuclear receptors (NRs) regulate transcription in a ligand-dependent way through two types of coactivator complexes: the p160/CBP histone acetyl transferase (HAT) complex and the DRIP/TRAP/SMCC complex without HAT activity. Here we identified a large human (h) coactivator complex necessary for the estrogen receptor alpha (ERalpha) transactivation. This complex contains the GCN5 HAT, the c-Myc interacting protein TRRAP/PAF400, TAF(II)30, and other subunits. Similarly to known TFTC (TBP-free TAF(II)-containing)-type HAT complexes (hTFTC, hPCAF, and hSTAGA), TRRP directly interacted with liganded ER alpha, or other NRs. ER alpha transactivation was enhanced by the purified complex in vitro. Antisense TRRAP RNA inhibited estrogen-dependent cell growth of breast cancer cells. Thus, the isolated TFTC-type HAT complex acts as a third class of coactivator complex for NR function.

Acetyltransferases↗
PubMed2002

Ligand-selective potentiation of rat mineralocorticoid receptor activation function 1 by a CBP-containing histone acetyltransferase complex.

The rat mineralocorticoid receptor (MR) has two activation functions in distinct regions of the A/B domain, designated activation function 1a (AF-1a; amino acids 1 to 169) and AF-1b (amino acids 451 to 600). Since the p160 family protein TIF2, a known component of the AF-2 coactivator complex, potentiates the transactivation function of AF-1b but not that of AF-1a, it is likely that some other, novel protein complex interacts with the AF-1a region. Therefore, we attempted to identify such coactivator complexes from HeLa nuclear extracts by biochemical purification using a glutathione S-transferase-MR AF-1a fusion protein. Purified AF-1a region-interacting proteins were found to contain RNA helicase A (RHA) and CBP. Further analysis showed that RHA interacted with the AF-1a region directly and then recruited a complex with histone acetyltransferase (HAT) activity that contained CBP. For full-length MR, aldosterone, but not hydrocortisone, was found to induce the binding of RHA/CBP complexes to the AF-1a region, as well as to allow the cooperative potentiation of MR transcriptional activity by RHA and CBP. In addition, a chromatin immunoprecipitation assay showed that aldosterone-bound MR, but not hydrocortisone-bound MR, recruited RHA/CBP complexes to native MR target gene promoters. Our results suggested that an altered conformation of the A/B region induced by aldosterone, but not hydrocortisone, might determine the accessibility of MR AF-1a to RHA/CBP complexes.

Acetyltransferases↗