GlcNAcylation of histone H2B facilitates its monoubiquitination.

Chromatin reorganization is governed by multiple post-translational modifications of chromosomal proteins and DNA. These histone modifications are reversible, dynamic events that can regulate DNA-driven cellular processes. However, the molecular mechanisms that coordinate histone modification patterns remain largely unknown. In metazoans, reversible protein modification by O-linked N-acetylglucosamine (GlcNAc) is catalysed by two enzymes, O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA). However, the significance of GlcNAcylation in chromatin reorganization remains elusive. Here we report that histone H2B is GlcNAcylated at residue S112 by OGT in vitro and in living cells. Histone GlcNAcylation fluctuated in response to extracellular glucose through the hexosamine biosynthesis pathway (HBP). H2B S112 GlcNAcylation promotes K120 monoubiquitination, in which the GlcNAc moiety can serve as an anchor for a histone H2B ubiquitin ligase. H2B S112 GlcNAc was localized to euchromatic areas on fly polytene chromosomes. In a genome-wide analysis, H2B S112 GlcNAcylation sites were observed widely distributed over chromosomes including transcribed gene loci, with some sites co-localizing with H2B K120 monoubiquitination. These findings suggest that H2B S112 GlcNAcylation is a histone modification that facilitates H2BK120 monoubiquitination, presumably for transcriptional activation.

Williams syndrome is an epigenome-regulator disease.

A human multi-protein complex (WINAC), composed of SWI/SNF components and DNA replication-related factors, that directly interacts with the vitamin D receptor (VDR) through the Williams syndrome transcription factor (WSTF), was identified with an ATP-dependent chromatin remodeling activity. This novel ATP-dependent chromatin remodeling complex facilitates VDR-mediated transrepression as well as transactivation with its ATP-dependent chromatin remodeling activity and promoter targeting property for the activator to access to the DNA. It also suggested that in this complex, WSTF serves as a signaling sensor to receive intra-cellular singalings to switch the activity of WINAC as well as WICH, another ATP-dependent chromatin remodeling complex containing hSNF2h. By making WSTF-deficient mice, some of the heart defects as well as abnormal calcium metabolism observed in Williams syndrome are attributed to the abnormal chromatin remodeling activity caused by WSTF deficiency. Thus, we would propose to designate Williams syndrome as an epigenome-regulator disease.

Testis-specific protein on Y chromosome (TSPY) represses the activity of the androgen receptor in androgen-dependent testicular germ-cell tumors.

Testis-specific protein on Y chromosome (TSPY) is an ampliconic gene on the Y chromosome, and genetic interaction with gonadoblastoma has been clinically established. However, the function of the TSPY protein remains to be characterized in physiological and pathological settings. In the present study, we observed coexpression of TSPY and the androgen receptor (AR) in testicular germ-cell tumors (TGCTs) in patients as well as in model cell lines, but such coexpression was not seen in normal testis of humans or mice. TSPY was a repressor for androgen signaling because of its trapping of cytosolic AR even in the presence of androgen. Androgen treatment stimulated cell proliferation of a TGCT model cell line, and TSPY potently attenuated androgen-dependent cell growth. Together with the finding that TSPY expression is reduced in more malignant TGCTs in vivo, the present study suggests that TSPY serves as a repressor in androgen-induced tumor development in TGCTs and raises the possibility that TSPY could be used as a clinical marker to assess the malignancy of TGCTs.

Double PHD fingers protein DPF2 recognizes acetylated histones and suppresses the function of estrogen-related receptor alpha through histone deacetylase 1.

Estrogen-related receptor alpha (ERRalpha) is a member of the nuclear receptor superfamily and regulates many physiological functions, including mitochondrial biogenesis and lipid metabolism. ERRalpha enhances the transactivation function without endogenous ligand by associating with coactivators such as peroxisome proliferator-activated receptor gamma coactivator 1 alpha and beta (PGC-1alpha and -beta) and members of the steroid receptor coactivator family. However, the molecular mechanism by which the transactivation function of ERRalpha is converted from a repressive state to an active state is poorly understood. Here we used biochemical purification techniques to identify ERRalpha-associated proteins in HeLa cells stably expressing ERRalpha. Interestingly, we found that double PHD fingers protein DPF2/BAF45d suppressed PGC-1alpha-dependent transactivation of ERRalpha by recognizing acetylated histone H3 and associating with HDAC1. DPF2 directly bound to ERRalpha and suppressed the transactivation function of nuclear receptors such as androgen receptor. DPF2 was recruited to ERR target gene promoters in myoblast cells, and knockdown of DPF2 derepressed the level of mRNA expressed by target genes of ERRalpha. These results show that DPF2 acts as a nuclear receptor-selective co-repressor for ERRalpha by associating with both acetylated histone H3 and HDAC1.

NF-YC functions as a corepressor of agonist-bound mineralocorticoid receptor.

The role of aldosterone has been implicated in the metabolic syndrome and cardiovascular diseases. The biological actions of aldosterone are mediated through mineralocorticoid receptor (MR). Nuclear receptor-mediated gene expression is regulated by dynamic and coordinated recruitment of coactivators and corepressors. To identify new coregulators of the MR, full-length MR was used as bait in yeast two-hybrid screening. We isolated NF-YC, one of the subunits of heterotrimeric transcription factor NF-Y. Specific interaction between MR and NF-YC was confirmed by yeast two-hybrid, mammalian two-hybrid, coimmunoprecipitation assays, and fluorescence subcellular imaging. Transient transfection experiments in COS-7 cells demonstrated that NF-YC repressed MR transactivation in a hormone-sensitive manner. Moreover, reduction of NF-YC protein levels by small interfering RNA potentiated hormonal activation of endogenous target genes in stably MR-expressing cells, indicating that NF-YC functions as an agonist-dependent MR corepressor. The corepressor function of NF-YC is selective for MR, because overexpression of NF-YC did not affect transcriptional activity mediated by androgen, progesterone, or glucocorticoid receptors. Chromatin immunoprecipitation experiments showed that endogenous MR and steroid receptor coactivator-1 were recruited to an endogenous ENaC gene promoter in a largely aldosterone-dependent manner, and endogenous NF-YC was sequentially recruited to the same element. Immunohistochemistry showed that endogenous MR and NF-YC were colocalized within the mouse kidney. Although aldosterone induces interaction of the N and C termini of MR, NF-YC inhibited the N/C interaction. These findings indicate that NF-YC functions as a new corepressor of agonist-bound MR via alteration of aldosterone-induced MR conformation.

CDP/cut is an osteoblastic coactivator of the vitamin D receptor (VDR).

Vitamin D plays an important role in regulating bone and calcium metabolism. The actions of vitamin D are mediated through the nuclear vitamin D receptor (VDR), and gene disruption of the VDR in mice causes skeletal disorders. However, the precise role of the VDR in each stage of osteoblastogenesis is not well understood. To address this issue, we used a biochemical approach to identify an osteoblast-specific coregulator of the VDR. Using a GST-fused VDR ligand-binding domain as bait, proteins associated with liganded VDR were purified from nuclear extracts of HOS osteoblastic cells and compared with those of HeLa cells. Among the interactants identified by mass fingerprinting, CCAAT displacement protein (CDP) was found as a novel ligand-dependent VDR interactant in HOS cells, together with other previously reported DRIP/TRAP complex components. Further biochemical analysis showed that complex formation between the VDR and CDP was distinct from the previously known DRIP/TRAP complex and the p160 family coactivator complexes. Transient expression of CDP potentiated VDR-mediated transcriptional activation in HOS cells. Furthermore, modulation of CDP expression levels in osteoblastic SaM-1 cells affected vitamin D-dependent osteoblast differentiation before the maturation (mineralization) stage. These findings suggest that CDP is a novel differentiation stage-specific coactivator of the VDR in osteoblasts.

DNA demethylation in hormone-induced transcriptional derepression.

Epigenetic modifications at the histone level affect gene regulation in response to extracellular signals. However, regulated epigenetic modifications at the DNA level, especially active DNA demethylation, in gene activation are not well understood. Here we report that DNA methylation/demethylation is hormonally switched to control transcription of the cytochrome p450 27B1 (CYP27B1) gene. Reflecting vitamin-D-mediated transrepression of the CYP27B1 gene by the negative vitamin D response element (nVDRE), methylation of CpG sites ((5m)CpG) is induced by vitamin D in this gene promoter. Conversely, treatment with parathyroid hormone, a hormone known to activate the CYP27B1 gene, induces active demethylation of the (5m)CpG sites in this promoter. Biochemical purification of a complex associated with the nVDRE-binding protein (VDIR, also known as TCF3) identified two DNA methyltransferases, DNMT1 and DNMT3B, for methylation of CpG sites, as well as a DNA glycosylase, MBD4 (ref. 10). Protein-kinase-C-phosphorylated MBD4 by parathyroid hormone stimulation promotes incision of methylated DNA through glycosylase activity, and a base-excision repair process seems to complete DNA demethylation in the MBD4-bound promoter. Such parathyroid-hormone-induced DNA demethylation and subsequent transcriptional derepression are impaired in Mbd4(-/-) mice. Thus, the present findings suggest that methylation switching at the DNA level contributes to the hormonal control of transcription.

Phosphorylation of Williams syndrome transcription factor by MAPK induces a switching between two distinct chromatin remodeling complexes.

Changes in the environment of a cell precipitate extracellular signals and sequential cascades of protein modification and elicit nuclear transcriptional responses. However, the functional links between intracellular signaling-dependent gene regulation and epigenetic regulation by chromatin-modifying proteins within the nucleus are largely unknown. Here, we describe novel epigenetic regulation by MAPK cascades that modulate formation of an ATP-dependent chromatin remodeling complex, WINAC (WSTF Including Nucleosome Assembly Complex), an SWI/SNF-type complex containing Williams syndrome transcription factor (WSTF). WSTF, a specific component of two chromatin remodeling complexes (SWI/SNF-type WINAC and ISWI-type WICH), was phosphorylated by the stimulation of MAPK cascades in vitro and in vivo. Ser-158 residue in the WAC (WSTF/Acf1/cbpq46) domain, located close to the N terminus of WSTF, was identified as a major phosphorylation target. Using biochemical analysis of a WSTF mutant (WSTF-S158A) stably expressing cell line, the phosphorylation of this residue (Ser-158) was found to be essential for maintaining the association between WSTF and core BAF complex components, thereby maintaining the ATPase activity of WINAC. WINAC-dependent transcriptional regulation of vitamin D receptor was consequently impaired by this WSTF mutation, but the recovery from DNA damage mediated by WICH was not impaired. Our results suggest that WSTF serves as a nuclear sensor of the extracellular signals to fine-tune the chromatin remodeling activity of WINAC. WINAC mediates a previously unknown MAPK-dependent step in epigenetic regulation, and this MAPK-dependent switching mechanism between the two functionally distinct WSTF-containing complexes might underlie the diverse functions of WSTF in various nuclear events.

Distinct function of 2 chromatin remodeling complexes that share a common subunit, Williams syndrome transcription factor (WSTF).

A number of nuclear complexes modify chromatin structure and operate as functional units. However, the in vivo role of each component within the complexes is not known. ATP-dependent chromatin remodeling complexes form several types of protein complexes, which reorganize chromatin structure cooperatively with histone modifiers. Williams syndrome transcription factor (WSTF) was biochemically identified as a major subunit, along with 2 distinct complexes: WINAC, a SWI/SNF-type complex, and WICH, an ISWI-type complex. Here, WSTF(-/-) mice were generated to investigate its function in chromatin remodeling in vivo. Loss of WSTF expression resulted in neonatal lethality, and all WSTF(-/-) neonates and approximately 10% of WSTF(+/-) neonates suffered cardiovascular abnormalities resembling those found in autosomal-dominant Williams syndrome patients. Developmental analysis of WSTF(-/-) embryos revealed that Gja5 gene regulation is aberrant from E9.5, conceivably because of inappropriate chromatin reorganization around the promoter regions where essential cardiac transcription factors are recruited. In vitro analysis in WSTF(-/-) mouse embryonic fibroblast (MEF) cells also showed impaired transactivation functions of cardiac transcription activators on the Gja5 promoter, but the effects were reversed by overexpression of WINAC components. Likewise in WSTF(-/-) MEF cells, recruitment of Snf2h, an ISWI ATPase, to PCNA and cell survival after DNA damage were both defective, but were ameliorated by overexpression of WICH components. Thus, the present study provides evidence that WSTF is shared and is a functionally indispensable subunit of the WICH complex for DNA repair and the WINAC complex for transcriptional control.

GlcNAcylation of a histone methyltransferase in retinoic-acid-induced granulopoiesis.

The post-translational modifications of histone tails generate a 'histone code' that defines local and global chromatin states. The resultant regulation of gene function is thought to govern cell fate, proliferation and differentiation. Reversible histone modifications such as methylation are under mutual controls to organize chromosomal events. Among the histone modifications, methylation of specific lysine and arginine residues seems to be critical for chromatin configuration and control of gene expression. Methylation of histone H3 lysine 4 (H3K4) changes chromatin into a transcriptionally active state. Reversible modification of proteins by beta-N-acetylglucosamine (O-GlcNAc) in response to serum glucose levels regulates diverse cellular processes. However, the epigenetic impact of protein GlcNAcylation is unknown. Here we report that nuclear GlcNAcylation of a histone lysine methyltransferase (HKMT), MLL5, by O-GlcNAc transferase facilitates retinoic-acid-induced granulopoiesis in human HL60 promyelocytes through methylation of H3K4. MLL5 is biochemically identified in a GlcNAcylation-dependent multi-subunit complex associating with nuclear retinoic acid receptor RARalpha (also known as RARA), serving as a mono- and di-methyl transferase to H3K4. GlcNAcylation at Thr 440 in the MLL5 SET domain evokes its H3K4 HKMT activity and co-activates RARalpha in target gene promoters. Increased nuclear GlcNAcylation by means of O-GlcNAc transferase potentiates retinoic-acid-induced HL60 granulopoiesis and restores the retinoic acid response in the retinoic-acid-resistant HL60-R2 cell line. Thus, nuclear MLL5 GlcNAcylation triggers cell lineage determination of HL60 through activation of its HKMT activity.

Coactivation of estrogen receptor beta by gonadotropin-induced cofactor GIOT-4.

Estrogen exerts its diverse effects through two subtypes of estrogen receptors (ER), ERalpha and ERbeta. Each subtype has its own distinct function and expression pattern in its target tissues. Little, however, is known about the transcriptional regulatory mechanism of ERbeta in the major ERbeta-expressing tissues. Using biochemical methods, we identified and described a novel ERbeta coactivator. This protein, designated GIOT-4, was biochemically purified from 293F cells. It coactivated ERbeta in ovarian granulosa cells. GIOT-4 expression was induced by stimulation with follicle-stimulating hormone (FSH). GIOT-4 recruited an SWI/SNF-type complex in a ligand-independent manner to ERbeta as an ER subtype-specific physical bridging factor and induced subsequent histone modifications in the ERbeta target gene promoters in a human ovarian granulosa cell line (KGN). Indeed, two ERbeta-specific target genes were upregulated by FSH at a specific stage of a normal ovulatory cycle in intact mice. These findings imply the presence of a novel regulatory convergence between the gonadotropin signaling cascade and ERbeta-mediated transcription in the ovary.

Spermatogenesis-specific association of SMCY and MSH5.

The status of chromatin during spermatogenesis is dynamically regulated by specific histone codes or stage-specific histone changes. The functional links between such epigenetic regulation and proteins regulating meiosis are largely unknown. In mammals, genes encoded on the Y chromosome are thought to possess male-specific biological functions. While genes located within the azoospermia factor region (AZF) are known to be involved in spermatogenesis, the physiological function of individual genes is not known. SMCY is a gene mapped to the AZF, and in this report, we analyzed the function of SMCY protein during spermatogenesis. Biochemical identification of the proteins with which it interacted showed that SMCY formed a distinct complex with MSH5, a critical meiosis-regulatory protein in the human testicular germ cell line, NEC8. As anticipated, histone H3K4 demethylase activity was detected. Immunohistochemical analysis revealed the co-localization of SMCY with MSH5 at a specific stage of meiotic prophase progression during murine spermatogenesis. Our results suggest that SMCY may have a male-specific function as a histone H3K4 demethylase by recruiting a meiosis-regulatory protein to condensed DNA.

Switching of chromatin-remodelling complexes for oestrogen receptor-alpha.

The female sex steroid hormone oestrogen stimulates both cell proliferation and cell differentiation in target tissues. These biological actions are mediated primarily through nuclear oestrogen receptors (ERs). The ligand-dependent transactivation of ERs requires several nuclear co-regulator complexes; however, the cell-cycle-dependent associations of these complexes are poorly understood. By using a synchronization system, we found that the transactivation function of ERalpha at G2/M was lowered. Biochemical approaches showed that ERalpha associated with two discrete classes of ATP-dependent chromatin-remodelling complex in a cell-cycle-dependent manner. The components of the NuRD-type complex were identified as G2/M-phase-specific ERalpha co-repressors. Thus, our results indicate that the transactivation function of ERalpha is cell-cycle dependent and is coupled with a cell-cycle-dependent association of chromatin-remodelling complexes.

Transrepressive function of TLX requires the histone demethylase LSD1.

TLX is an orphan nuclear receptor (also called NR2E1) that regulates the expression of target genes by functioning as a constitutive transrepressor. The physiological significance of TLX in the cytodifferentiation of neural cells in the brain is known. However, the corepressors supporting the transrepressive function of TLX have yet to be identified. In this report, Y79 retinoblastoma cells were subjected to biochemical techniques to purify proteins that interact with TLX, and we identified LSD1 (also called KDM1), which appears to form a complex with CoREST and histone deacetylase 1. LSD1 interacted with TLX directly through its SWIRM and amine oxidase domains. LSD1 potentiated the transrepressive function of TLX through its histone demethylase activity as determined by a luciferase assay using a genomically integrated reporter gene. LSD1 and TLX were recruited to a TLX-binding site in the PTEN gene promoter, accompanied by the demethylation of H3K4me2 and deacetylation of H3. Knockdown of either TLX or LSD1 derepressed expression of the endogenous PTEN gene and inhibited cell proliferation of Y79 cells. Thus, the present study suggests that LSD1 is a prime corepressor for TLX.