A transcriptional switch mediated by cofactor methylation

We describe a molecular switch based on the controlled methylation of nucleosome and the transcriptional cofactors, the CREB-binding proteins (CBP)/p300. The CBP/p300 methylation site is localized to an arginine residue that is essential for stabilizing the structure of the KIX domain, which mediates CREB recruitment. Methylation of KIX by coactivator-associated arginine methyltransferase 1 (CARM1) blocks CREB activation by disabling the interaction between KIX and the kinase inducible domain (KID) of CREB. Thus, CARM1 functions as a corepressor in cyclic adenosine monophosphate signaling pathway via its methyltransferase activity while acting as a coactivator for nuclear hormones. These results provide strong in vivo and in vitro evidence that histone methylation plays a key role in hormone-induced gene activation and define cofactor methylation as a new regulatory mechanism in hormone signaling.

Nuclear receptors and lipid physiology: opening the X-files

Cholesterol, fatty acids, fat-soluble vitamins, and other lipids present in our diets are not only nutritionally important but serve as precursors for ligands that bind to receptors in the nucleus. To become biologically active, these lipids must first be absorbed by the intestine and transformed by metabolic enzymes before they are delivered to their sites of action in the body. Ultimately, the lipids must be eliminated to maintain a normal physiological state. The need to coordinate this entire lipid-based metabolic signaling cascade raises important questions regarding the mechanisms that govern these pathways. Specifically, what is the nature of communication between these bioactive lipids and their receptors, binding proteins, transporters, and metabolizing enzymes that links them physiologically and speaks to a higher level of metabolic control? Some general principles that govern the actions of this class of bioactive lipids and their nuclear receptors are considered here, and the scheme that emerges reveals a complex molecular script at work.

Transcriptional regulation in acute promyelocytic leukemia

It has been 10 years since the seminal discovery that a mutant form of a retinoid acid receptor (RARalpha) is associated with acute promyelocytic leukemia (APL). This finding, coupled with the remarkable success of retinoic acid (RA), the natural ligand of RARalpha, in the treatment of APL, has made APL a unique model system in the study of oncogenic conversion of transcription factors in hematological malignancies. Indeed, subsequent basic and clinical studies showed that chromosomal translocation involving the RARalpha gene is the cytogenetic hallmark of APL and that these mutant forms of RARs are the oncogenes in APL that interfere with the proliferation and differentiation pathways controlled by both RAR and their fusion partners. However, it was not until recently that the role of aberrant transcriptional regulation in the pathogenesis of APL was revealed. In this review, we summarize the biochemical and biological mechanisms of transcriptional regulation by mutant RARs and their corresponding wild-type fusion partner PML and PLZF. These studies have been instrumental in our understanding of the process of leukemogenesis in general and have laid the scientific foundation for the novel concept of transcription therapy in the treatment of human cancer.

Vitamin A deprivation results in reversible loss of hippocampal long-term synaptic plasticity

Despite its long history, the central effects of progressive depletion of vitamin A in adult mice has not been previously described. An examination of vitamin-deprived animals revealed a progressive and ultimately profound impairment of hippocampal CA1 long-term potentiation and a virtual abolishment of long-term depression. Importantly, these losses are fully reversible by dietary vitamin A replenishment in vivo or direct application of all trans-retinoic acid to acute hippocampal slices. We find retinoid responsive transgenes to be highly active in the hippocampus, and by using dissected explants, we show the hippocampus to be a site of robust synthesis of bioactive retinoids. In aggregate, these results demonstrate that vitamin A and its active derivatives function as essential competence factors for long-term synaptic plasticity within the adult brain, and suggest that key genes required for long-term potentiation and long-term depression are retinoid dependent. These data suggest a major mental consequence for the hundreds of millions of adults and children who are vitamin A deficient.

Phase transition kinetics in colloid-polymer mixtures at triple coexistence: kinetic maps from free-energy landscapes

We report a detailed experimental study of the kinetics of separation into coexisting gas, liquid, and crystal phases in a colloid-polymer mixture. Distinct kinetic regimes are identified, and interpreted in terms of the underlying "free-energy landscape" of the system.

Classification of ordering kinetics in three-phase systems

Though equations of motion containing transport coefficients are required to quantitatively predict the phase-ordering dynamics of any given system, a great deal can be gleaned just from the shape of the free-energy landscape. We demonstrate how to extract the most information concerning phase-ordering phenomenology from a knowledge of a system's free-energy function, or phase diagram. Many putative pathways to equilibrium can be ruled out on the grounds of the second law of thermodynamics. In some parts of the phase diagram, these considerations are sufficient to completely determine the phase-ordering process without ever having to calculate a transport coefficient, even when three phases are present. The results include a large number of regions of the phase diagram with distinct phase-ordering kinetics, and some surprisingly elaborate routes to the equilibrium state. A process is found whereby a crystalline condensation nucleus becomes coated with a shell of gas, buffering it from a majority metastable liquid phase. Our results, based on thermodynamic arguments, are supported by numerical solution of model B, which describes diffusive phase-ordering kinetics. Some of our predictions are tested against experimental observations of colloid-polymer mixtures, described in more detail in the preceding paper [F. Renth, W. C. K. Poon, and R. M. L. Evans, Phys. Rev. E 64, 031402 (2001)]. A compact notation is developed to represent intricate phase-ordering pathways.

Diffusive growth of polydisperse hard-sphere crystals

Unlike atoms, colloidal particles are not identical, but can only be synthesised within a finite size tolerance. Colloids are therefore polydisperse, i.e., mixtures of infinitely many components with sizes drawn from a continuous distribution. We model the crystallization of hard-sphere colloids (with/without attractions) from an initially amorphous phase. Although the polydisperse hard-sphere phase diagram has been widely studied, it is not straightforwardly applicable to real colloidal crystals, since they are inevitably out of equilibrium. The process by which colloidal crystals form determines the size distribution of the particles that comprise them. Once frozen into the crystal lattice, the particles are caged so that the composition cannot subsequently relax to the equilibrium optimum. We predict that the mean size of colloidal particles incorporated into a crystal is smaller than anticipated by equilibrium calculations. This is because small particles diffuse fastest and therefore arrive at the crystal in disproportionate abundance.

A dynamic role for HDAC7 in MEF2-mediated muscle differentiation

The overlapping expression profile of MEF2 and the class-II histone deacetylase, HDAC7, led us to investigate the functional interaction and relationship between these regulatory proteins. HDAC7 expression inhibits the activity of MEF2 (-A, -C, and -D), and in contrast MyoD and Myogenin activities are not affected. Glutathione S-transferase pulldown and immunoprecipitation demonstrate that the repression mechanism involves direct interactions between MEF2 proteins and HDAC7 and is associated with the ability of MEF2 to interact with the N-terminal 121 amino acids of HDAC7 that encode repression domain 1. The MADS domain of MEF2 mediates the direct interaction of MEF2 with HDAC7. MEF2 inhibition by HDAC7 is dependent on the N-terminal repression domain and surprisingly does not involve the C-terminal deacetylase domain. HDAC7 interacts with CtBP and other class-I and -II HDACs suggesting that silencing of MEF2 activity involves corepressor recruitment. Furthermore, we show that induction of muscle differentiation by serum withdrawal leads to the translocation of HDAC7 from the nucleus into the cytoplasm. This work demonstrates that HDAC7 regulates the function of MEF2 proteins and suggests that this class-II HDAC regulates this important transcriptional (and pathophysiological) target in heart and muscle tissue. The nucleocytoplasmic trafficking of HDAC7 and other class-II HDACs during myogenesis provides an ideal mechanism for the regulation of HDAC targets during mammalian development and differentiation.

Sharp, an inducible cofactor that integrates nuclear receptor repression and activation

A yeast two-hybrid screen using the conserved carboxyl terminus of the nuclear receptor corepressor SMRT as a bait led to the isolation of a novel human gene termed SHARP (SMRT/HDAC1 Associated Repressor Protein). SHARP is a potent transcriptional repressor whose repression domain (RD) interacts directly with SMRT and at least five members of the NuRD complex including HDAC1 and HDAC2. In addition, SHARP binds to the steroid receptor RNA coactivator SRA via an intrinsic RNA binding domain and suppresses SRA-potentiated steroid receptor transcription activity. Accordingly, SHARP has the capacity to modulate both liganded and nonliganded nuclear receptors. Surprisingly, the expression of SHARP is itself steroid inducible, suggesting a simple feedback mechanism for attenuation of the hormonal response.

HATs on and beyond chromatin

The role of histone acetylation as a key mechanism of transcriptional regulation has been well established. Recent advances suggest that histone acetyltransferases also play important roles in histone-modulated processes such as DNA replication, recombination and repair. In addition, acetylation of transcriptional cofactors and other proteins is an efficient means of regulating a diverse range of molecular interactions. As new histone acetyltransferases and substrates are rapidly emerging, it is becoming apparent that protein acetylation may rival phosphorylation as a mechanism to transduce cellular regulatory signals.

Ocular safety of INS365 ophthalmic solution: a P2Y(2) agonist in healthy subjects

The purpose of this study was to evaluate the ocular safety and tolerability of the P2Y(2) receptor agonist, INS365, when applied as eye drops in normal human subjects. This study was a double-masked, placebo-controlled, randomized, within subject paired-comparison, dose-escalation study in five cohorts of ten healthy subjects. The concentrations of INS365 ophthalmic solution were 0.5, 1.0, 2.0, and 5.0% given three times over six hours. Safety was assessed by general and ophthalmic examination and symptomatology. Unanesthetized Schirmer tests were performed in the last cohort of 10 subjects to evaluate the acute effects of INS365 on tear secretion. There were no significant differences in the number of subjects with ocular events reported in placebo-treated eyes compared to INS365-treated eyes. Two adverse events were possibly related to INS365: painless blepharospasm and an increase in lacrimation after 5.0% INS365 instillation. Unanesthetized Schirmer testing showed no acute effects of INS365 on tear secretion, compared to its vehicle, in healthy subjects, in which reflex tearing often produced maximal Schirmer values. INS365 ophthalmic solution was well-tolerated when administered by ocular instillation. Stimulation of ocular surface P2Y(2) receptors was not associated with ocular tolerability issues in healthy subjects.

The dual role of ultraspiracle, the Drosophila retinoid X receptor, in the ecdysone response

The Drosophila homolog of the retinoid X receptor, ultraspiracle (USP), heterodimerizes with the ecdysone receptor (EcR) to form a functional complex that mediates the effects of the steroid molting hormone ecdysone by activating and repressing expression of ecdysone response genes. As with other retinoid X receptor heterodimers, EcR/USP affects gene transcription in a ligand-modulated manner. We used in vivo, cell culture, and biochemical approaches to analyze the functions of two usp alleles, usp(3) and usp(4), which encode stable proteins with defective DNA-binding domains. We observed that USP is able to activate as well as repress the Z1 isoform of the ecdysone-responsive broad complex (BrC-Z1). Activation of BrC-Z1 as well as EcR, itself an ecdysone response gene, can be mediated by both the USP3 and USP4 mutant proteins. USP3 and USP4 also activate an ecdysone-responsive element, hsp27EcRE, in cultured cells. These results differ from the protein null allele, usp(2), which is unable to mediate activation [Schubiger, M. & Truman, J. W. (2000) Development 127, 1151--1159]. BrC-Z1 repression is compromised in all three usp alleles, suggesting that repression involves the association of USP with DNA. Our results distinguish two mechanisms by which USP modulates the properties of EcR: one that involves the USP DNA-binding domain and one that can be achieved solely through the ligand-binding domain. These newly revealed properties of USP might implicate similar properties for retinoid X receptor.

Paranemin and the organization of desmin filament networks

De novo expression of vimentin, GFAP or peripherin leads to the assembly of an extended intermediate filament network in intermediate filament-free SW13/cl.2 cells. Desmin, in contrast, does not form extended filament networks in either SW13/cl.2 or intermediate filament-free mouse fibroblasts. Rather, desmin formed short thickened filamentous structures and prominent spot-like cytoplasmic aggregates that were composed of densely packed 9–11 nm diameter filaments. Analysis of stably transfected cell lines indicates that the inability of desmin to form extended networks is not due to a difference in the level of transgene expression. Nestin, paranemin and synemin are large intermediate filament proteins that coassemble with desmin in muscle cells. Although each of these large intermediate filament proteins colocalized with desmin when coexpressed in SW-13 cells, expression of paranemin, but not synemin or nestin, led to the formation of an extended desmin network. A similar rescue of desmin network organization was observed when desmin was coexpressed with vimentin, which coassembles with desmin, or with keratins, which formed a distinct filament network. These studies demonstrate that desmin filaments differ in their organizational properties from the other vimentin-like intermediate filament proteins and appear to depend upon coassembly with paranemin, at least when they are expressed in non-muscle cells, in order to form an extended filament network.

An essential role for nuclear receptors SXR/PXR in detoxification of cholestatic bile acids

Hepatic hydroxylation is an essential step in the metabolism and excretion of bile acids and is necessary to avoid pathologic conditions such as cholestasis and liver damage. In this report, we demonstrate that the human xenobiotic receptor SXR (steroid and xenobiotic receptor) and its rodent homolog PXR (pregnane X receptor) serve as functional bile acid receptors in both cultured cells and animals. In particular, the secondary bile acid derivative lithocholic acid (LCA) is highly hepatotoxic and, as we show here, a metabolic substrate for CYP3A hydroxylation. By using combinations of knockout and transgenic animals, we show that activation of SXR/PXR is necessary and sufficient to both induce CYP3A enzymes and confer resistance to toxicity by LCA, as well as other xenotoxicants such as tribromoethanol and zoxazolamine. Therefore, we establish SXR and PXR as bile acid receptors and a role for the xenobiotic response in the detoxification of bile acids.

Incidence of dementia and Alzheimer disease in 2 communities: Yoruba residing in Ibadan, Nigeria, and African Americans residing in Indianapolis, Indiana

CONTEXT

Alzheimer disease (AD) represents a major and increasing public health problem. If populations were identified with significantly lower or higher incidence rates of AD, the search for risk factors in the genesis of AD could be greatly enhanced.

OBJECTIVE

To compare incidence rates of dementia and AD in 2 diverse, elderly community-dwelling populations.

DESIGN

The Indianapolis-Ibadan Dementia Project, a longitudinal, prospective population-based study consisting of a baseline survey (1992-1993) and 2 subsequent follow-up waves after 2 years (1994-1995) and 5 years (1997-1998). Each wave followed a 2-stage design, with an in-home screening interview followed by a full diagnostic workup of a subsample of participants based on screening performance.

SETTING AND PARTICIPANTS

A total of 2459 community-dwelling Yoruba residents of Ibadan, Nigeria, without dementia, and 2147 community-dwelling African American residents of Indianapolis, Ind, without dementia (all aged 65 years or older). The cohorts were followed up for a mean of 5.1 years and 4.7 years, respectively.

MAIN OUTCOME MEASURES

Incident cases of dementia and AD in each of the 2 populations.

RESULTS

The age-standardized annual incidence rates were significantly lower among Yoruba than among African Americans for dementia (Yoruba, 1.35% [95% confidence interval [CI], 1.13%-1.56%]; African Americans, 3.24% [95% CI, 2.11%-4.38%]) and for AD (Yoruba, 1.15% [95% CI, 0.96%-1.35%]; African Americans, 2.52% [95% CI, 1.40%-3.64%]).

CONCLUSION

This is the first report of incidence rate differences for dementia and AD in studies of 2 populations from nonindustrialized and industrialized countries using identical methods and the same group of investigators in both sites. Further explorations of these population differences may identify potentially modifiable environmental or genetic factors to account for site differences in dementia and AD.

The structure of the ultraspiracle ligand-binding domain reveals a nuclear receptor locked in an inactive conformation

Ultraspiracle (USP) is the invertebrate homologue of the mammalian retinoid X receptor (RXR). RXR plays a uniquely important role in differentiation, development, and homeostasis through its ability to serve as a heterodimeric partner to many other nuclear receptors. RXR is able to influence the activity of its partner receptors through the action of the ligand 9-cis retinoic acid. In contrast to RXR, USP has no known high-affinity ligand and is thought to be a silent component in the heterodimeric complex with partner receptors such as the ecdysone receptor. Here we report the 2.4-A crystal structure of the USP ligand-binding domain. The structure shows that a conserved sequence motif found in dipteran and lepidopteran USPs, but not in mammalian RXRs, serves to lock USP in an inactive conformation. It also shows that USP has a large hydrophobic cavity, implying that there is almost certainly a natural ligand for USP. This cavity is larger than that seen previously for most other nuclear receptors. Intriguingly, this cavity has partial occupancy by a bound lipid, which is likely to resemble the natural ligand for USP.

PPAR-gamma dependent and independent effects on macrophage-gene expression in lipid metabolism and inflammation

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is highly expressed in lipid-accumulating macrophages of the coronary artery. In light of this, the wide-spread clinical use of thiazolidinediones (TZDs) in the treatment of type II diabetes raises concerns about the role of PPAR-gamma in macrophage function and disease progression. To define the role of PPAR-gamma in macrophage biology, we used homologous recombination to create embryonic stem cells that were homozygous for a null mutation in the PPAR-gamma gene. We demonstrate here that PPAR-gamma is neither essential for nor substantially affects the development of the macrophage lineage both in vitro and in vivo. In contrast, we show it is an important regulator of the scavenger receptor CD36, which has been genetically linked to lipid accumulation in macrophages. Both 15-deoxy-Delta12,14prostaglandin J2 and thiazolidinediones have anti-inflammatory effects that are independent of PPAR-gamma. We show that PPAR-gamma is required for positive effects of its ligands in modulating macrophage lipid metabolism, but that inhibitory effects on cytokine production and inflammation may be receptor independent.

A PPAR gamma-LXR-ABCA1 pathway in macrophages is involved in cholesterol efflux and atherogenesis

Previous work has implicated PPAR gamma in the regulation of CD36 expression and macrophage uptake of oxidized LDL (oxLDL). We provide evidence here that in addition to lipid uptake, PPAR gamma regulates a pathway of cholesterol efflux. PPAR gamma induces ABCA1 expression and cholesterol removal from macrophages through a transcriptional cascade mediated by the nuclear receptor LXR alpha. Ligand activation of PPAR gamma leads to primary induction of LXR alpha and to coupled induction of ABCA1. Transplantation of PPAR gamma null bone marrow into LDLR -/- mice results in a significant increase in atherosclerosis, consistent with the hypothesis that regulation of LXR alpha and ABCA1 expression is protective in vivo. Thus, we propose that PPAR gamma coordinates a complex physiologic response to oxLDL that involves particle uptake, processing, and cholesterol removal through ABCA1.

Identification of ligands and coligands for the ecdysone-regulated gene switch

The ecdysone-inducible gene switch is a useful tool for modulating gene expression in mammalian cells and transgenic animals. We have identified inducers derived from plants as well as certain classes of insecticides that increase the versatility of this gene regulation system. Phytoecdysteroids share the favorable kinetics of steroids, but are inert in mammals. The gene regulation properties of one of these ecdysteroids have been examined in cell culture and in newly developed strains of ecdysone-system transgenic mice. Ponasterone A is a potent regulator of gene expression in cells and transgenic animals, enabling reporter genes to be turned on and off rapidly. A number of nonsteroidal insecticides have been identified that also activate the ecdysone system. Because the gene-controlling properties of the ecdysone switch are based on a heterodimer composed of a modified ecdysone receptor (VgEcR) and the retinoid X receptor (RXR), we have tested the effect of RXR ligands on the VgEcR/RXR complex. Used alone, RXR ligands display no activity on the ecdysone switch. However, when used in combination with a VgEcR ligand, RXR ligands dramatically enhance the absolute levels of induction. This property of the heterodimer has allowed the development of superinducer combinations that increase the dynamic range of the system.

Check radiography after fixation of hip fractures: is it necessary?

Technological advances in radiography in the form of image intensification has not only made internal fixation of femoral neck fracture much easier but these high resolution films can be saved as hard copies and can also be reversed into 'positives' at a later date. However, requesting routine post-operative check radiographs for these fractures are still a common practice. A retrospective study was carried out to compare the quality of image intensifier films with conventional post-operative radiographs. 79 sets of films were reviewed with particular reference to adequacy of fixation and possible joint penetration by the screws. No significant difference was noted between the two sets of films. We suggest that routine post-operative radiographs after femoral neck fracture fixation are unnecessary unless there is some clinical indication. This has significant implications in relation to patient discomfort, radiation exposure and cost-effectiveness.