Many transcription coactivators interact with nuclear receptors in a ligand-and C-terminal transactivation function (AF2)-dependent manner. We isolated a nuclear factor (designated ASC-2) with such properties by using the ligand-binding domain of retinoid X receptor as a bait in a yeast two-hybrid screening. ASC-2 also interacted with other nuclear receptors, including retinoic acid receptor, thyroid hormone receptor, estrogen receptor ␣, and glucocorticoid receptor, basal factors TFIIA and TBP, and transcription integrators CBP/p300 and SRC-1. In transient cotransfections, ASC-2, either alone or in conjunction with CBP/p300 and SRC-1, stimulated ligand-dependent transactivation by wild type nuclear receptors but not mutant receptors lacking the AF2 domain. Consistent with an idea that ASC-2 is essential for the nuclear receptor function in vivo, microinjection of anti-ASC-2 antibody abrogated the liganddependent transactivation of retinoic acid receptor, and this repression was fully relieved by coinjection of ASC-2-expression vector. Surprisingly, ASC-2 was identical to a gene previously identified during a search for genes amplified and overexpressed in breast and other human cancers. From these results, we concluded that ASC-2 is a bona fide transcription coactivator molecule of nuclear receptors, and its altered expression may contribute to the development of cancers.The nuclear receptor superfamily is a group of ligand-dependent transcriptional regulatory proteins that function by binding to specific DNA sequences named hormone response elements in the promoters of target genes (for a review, see Ref.1). The superfamily includes receptors for a variety of small hydrophobic ligands such as steroids, T3, 1 and retinoids as well as a large number of related proteins that do not have known ligands, referred to as orphan nuclear receptors (reviewed in Ref.2). Functional analysis of nuclear receptors has shown that there are two major activation domains. The activation function-2 (AF-2) at the extreme C-terminal region of the ligandbinding domain (LBD) exhibits ligand-dependent transactivation, whereas the N-terminal activation function-1 contains a ligand-independent transactivation domain. The AF-2 region is conserved among nuclear receptors, and deletion or point mutations in this region impair transcriptional activation without changing ligand and DNA binding affinities. X-ray crystallographic studies of the LBD of nuclear receptors revealed that the ligand binding induces a major conformational change in the AF-2 region (3-7), suggesting that this region may play a critical role in mediating transactivation by a ligand-dependent interaction with coactivators. As expected, many coactivators fail to interact with AF-2 mutants of nuclear receptors (8 -10). Transcriptional activation of most nuclear receptors involves at least two separate processes as follows: derepression and activation. Repression is mediated in part by interaction of unliganded receptors with corepressors such as N-CoR (11) and SMRT (12). H...

Many transcription coactivators interact with nuclear receptors in a ligandThe nuclear receptor superfamily is a group of proteins that regulate, in a ligand-dependent manner, transcriptional initiation of target genes by binding to specific DNA sequences named hormone response elements (reviewed in reference 23). Functional analysis of nuclear receptors has shown that there are two major activation domains. The N-terminal domain (AF1) contains a ligand-independent activation function, whereas the ligand-binding domain (LBD) exhibits ligand-dependent transactivation function (AF2). The AF2 core region, located at the extreme C terminus of the receptor LBDs, is conserved among nuclear receptors and undergoes a major conformational change upon ligand binding (23). This region has been shown to play a critical role in mediating transactivation by serving as a ligand-dependent interaction interface with many different coactivators (reviewed in reference 9). These coactivators, including the p160 family members (i.e., SRC-1, SRC-2/GRIP1/TIF2, and SRC-3/ACTR/pCIP/AIB1/ RAC3/TRAM1), CBP/p300, p/CAF, TRAP/DRIP, activating signal cointegrator 2 (ASC-2), and many others, bridge nuclear receptors and the basal transcription apparatus and/or remodel the chromatin structures (9).Chromatin, the physiological template of all eukaryotic genetic information, undergoes a diverse array of posttranslational modifications that largely impinge on histone amino termini, thereby regulating access to the underlying DNA (reviewed in reference 12). SRC-1 and the p160 family member ACTR, along with CBP and p300, were recently shown to contain histone acetyltransferase (HAT) activities and associate with yet another HAT protein, p/CAF (9). In contrast, SMRT and N-CoR, nuclear receptor corepressors, form complexes with Sin3 and histone deacetylase proteins (9). These results are consistent with the notion that the acetylation of histones destabilizes nucleosomes and relieves transcriptional repression by allowing transcription factors to access recognition elements, whereas deacetylation of the histones stabilizes the repressed state. More recently, the histone arginine methyltransferases CARM1 and PRMT1 were newly defined as transcriptional coactivators of nuclear receptors (4, 40). NSD1 and

The Mediator complex of Saccharomyces cerevisiae is required for both general and regulated transcription of RNA polymerase II (PolII) and is composed of two stable subcomplexes (Srb4 and Rgr1 subcomplexes). To decipher the function of each Mediator subcomplex and to delineate the functional relationship between the subcomplexes, we characterized the compositions and biochemical activities of PolII-Mediator complexes (holoenzymes) prepared from several Mediator mutant strains of S. cerevisiae. We found that holoenzymes devoid of a functional Gal11 module were defective for activated but not basal transcription in a reconstituted in vitro system. This activation-specific defect was correlated with a crippled physical interaction to transcriptional activator proteins, which could be bypassed by artificial recruitment of a mutant holoenzyme to a promoter. Consistent with this observation, a direct interaction between Gal11 and gene-specific transcriptional activator proteins was detected by far-Western analyses and column binding assays. In contrast, the srb5 deletion mutant holoenzyme was defective for both basal and activated transcription, despite its capacity for activator binding that is comparable to that of the wild-type holoenzyme. These results demonstrate that the Gal11 module of the Rgr1 subcomplex is required for the efficient recruitment of PolII holoenzyme to a promoter via activator-specific interactions, while the Srb4 subcomplex functions in the modulation of general polymerase activity.

mRNA synthesis requires pol 1 II and a set of general transcription factors (GTFs) including TFIIA, TFIIB, TFIID, TFIIF, and TFIIH. The regulation of this process requires a number of coactivator complexes involved in chromatin remodeling and recruitment of transcriptional machinery to the promoter (1-5). In particular, the yeast Mediator complex is required for diverse aspects of transcriptional regulation, including activated transcription and transcriptional repression (7-9). In addition, Mediator improves the efficiency of basal transcription and the phosphorylation of the C-terminal domain (CTD) of the largest subunit of pol II (Rpb1) (6). To accommodate these diverse activities, the Mediator complex is composed of more than 20 polypeptides, including Srb subunits (Srb2, -4, -5, -6, and -7), Med subunits

Indoor air pollution (IAP) is a serious threat to human health, causing millions of deaths each year. A plethora of pollutants can result in IAP; therefore, it is very important to identify their main sources and concentrations and to devise strategies for the control and enhancement of indoor air quality (IAQ). Herein, we provide a critical review and evaluation of the major sources of major pollutant emissions, their health effects, and issues related to IAP-based illnesses, including sick building syndrome (SBS) and building-related illness (BRI). In addition, the strategies and approaches for control and reduction of pollutant concentrations are pointed out, and the recent trends in efforts to resolve and improve IAQ, with their respective advantages and potentials, are summarized. It is predicted that the development of novel materials for sensors, IAQ-monitoring systems, and smart homes is a promising strategy for control and enhancement of IAQ in the future.

Silencing mediator of retinoic acid and thyroid hormone receptors (SMRT) is known to interact with Sin3 and recruit the histone deacetylases (HDACs) that lead to hypoacetylation of histones and transrepression of target transcription factors. Herein, we found that coexpression of SMRT significantly repressed transactivations by activating protein-1 (AP-1), nuclear factor-B (NFB), and serum response factor (SRF) in a dose-dependent manner, but not in the presence of trichostatin A, a specific inhibitor of HDAC. Similarly, coexpression of HDAC1 and mSin3A also showed repressive effects. Consistent with these results, the C-terminal region of SMRT directly interacted with SRF, the AP-1 components c-Jun and c-Fos, and the NFB components p50 and p65, as demonstrated by the yeast and mammalian two hybrid tests as well as the glutathione S-transferase pull down assays. Thus, we concluded that SMRT serves to recruit Sin3/HDACs to SRF, NFB, and AP-1 in vivo and modulate their transactivation.Retinoic acid and thyroid hormone receptor bind to their target genes and repress transcription (for a review see Ref. 1). The silencing mediator of retinoic acid and thyroid hormone receptors (SMRT) 1 (2) and the nuclear hormone receptor corepressors (N-CoR) (3) were originally isolated as factors associated with the hinge and ligand binding D/E domains of unliganded receptors. These corepressors interact with Sin3 and recruit the histone deacetylases (HDAC1 or Rpd-3⅐HDAC2) that lead to hypoacetylation of the histones, consistent with the concept that histone hypoacetylation correlates with gene repression (4 -7). Two groups have recently reported the isolation of histone deacetylase core complexes (mSin3 and the NuRD complex) that are critically involved in this transcriptional repression (8,9). A few components of the NuRD complex are also present in the mSin3 complex that consists of seven polypeptides. In particular, SAP30 directly interacts with NCoR, although N-CoR does not appear to be stably associated with this mSin3 complex. Antibody-blocking experiments and studies with histone deacetylase inhibitors also supported the idea that N-CoR/SMRT may serve as an adapter molecule between the core mSin3 complex and sequence-specific transcriptional repressors such as unliganded nuclear receptors (8, 9). However, recent evidence also showed that N-Cor/SMRT and Sin3 directly interact with the key components of the transcriptional initiation process (TFIIB, and the TBP-associating factors) to inhibit basal transcription, suggesting an alternative repression pathway (10, 11). Interestingly, the N-CoR⅐Sin3⅐HDAC complex is also known to mediate transcriptional repression from a wide variety of other nonreceptormediated pathways. These include MyoD (12), the bHLH-LZ proteins Mad and Mxi that mediate repression of myc activities and tumor suppression (13), E2F-repressive retinoblastoma protein (14), and the oncoproteins PLZF-RAR (15) and LAZ3/ BCL6 (16), which are involved in acute promyelocytic leukemia and non-Hodgkin lymphomas, respect...

No abstract

Human activating signal cointegrator 1 (hASC-1) was originally isolated as a transcriptional coactivator of nuclear receptors. Here we report that ASC-1 exists as a steady-state complex associated with three polypeptides, P200, P100, and P50, in HeLa nuclei; stimulates transactivation by serum response factor (SRF), activating protein 1 (AP-1), and nuclear factor B (NF-B) through direct binding to SRF, c-Jun, p50, and p65; and relieves the previously described transrepression between nuclear receptors and either AP-1 or NF-B. Interestingly, ectopic expression of Caenorhabditis elegans ASC-1 (ceASC-1), an ASC-1 homologue that binds P200 and P100, like hASC-1, while weakly interacting only with p65, in HeLa cells appears to replace endogenous hASC-1 from the hASC-1 complex and exerts potent dominant-negative effects on AP-1, NF-B, and SRF transactivation. In addition, neutralization of endogenous P50 by single-cell microinjection of a P50 antibody inhibits AP-1 transactivation; the inhibition is relieved by coexpression of wild-type P50, but not of P50⌬KH, a mutant form that does not interact with P200. Overall, these results suggest that the endogenous hASC-1 complex appears to play an essential role in AP-1, SRF, and NF-B transactivation and to mediate the transrepression between nuclear receptors and either AP-1 or NF-B in vivo.