Role for peroxisome proliferator-activated receptor alpha in oxidized phospholipid-induced synthesis of monocyte chemotactic protein-1 and interleukin-8 by endothelial cells

The attraction, binding, and entry of monocytes into the vessel wall play an important role in atherogenesis. We have previously shown that minimally oxidized/modified LDL (MM-LDL), a pathogenically relevant lipoprotein, can activate human aortic endothelial cells (HAECs) to produce monocyte chemotactic activators. In the present study, we demonstrate that MM-LDL and oxidation products of 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphocholine (PAPC) activate endothelial cells to synthesize monocyte chemotactic protein-1 (MCP-1) and interleukin-8 (IL-8). Several lines of evidence suggest that this activation is mediated by the lipid-dependent transcription factor peroxisome proliferator-activated receptor alpha (PPARalpha), the most abundant member of the PPAR family in HAECs. Treatment of transfected CV-1 cells demonstrated activation of the PPARalpha ligand-binding domain by MM-LDL, Ox-PAPC, or its component phospholipids, 1-palmitoyl-2-oxovalaroyl-sn-glycero-phosphocholine and 1-palmitoyl-2-glutaroyl-sn-glycero-phosphocholine; these lipids also activated a consensus peroxisome proliferator-activated receptor response element (PPRE) in transfected HAECs. Furthermore, activation of PPARalpha with synthetic ligand Wy14,643 stimulates the synthesis of IL-8 and MCP-1 by HAECs. By contrast, troglitazone, a PPARgamma agonist, decreased the levels of IL-8 and MCP-1. Finally, we demonstrate that unlike wild-type endothelial cells, endothelial cells derived from PPARalpha null mice do not produce MCP-1/JE in response to Ox-PAPC and MM-LDL. Together, these data demonstrate a proinflammatory role for PPARalpha in mediation of the activation of endothelial cells to produce monocyte chemotactic activity in response to oxidized phospholipids and lipoproteins.

Identification of a nuclear domain with deacetylase activity

Here, we describe the identification and characterization of a nuclear body (matrix-associated deacetylase body) whose formation and integrity depend on deacetylase activity. Typically, there are 20-40 0.5-microM bodies per nucleus, although the size and number can vary substantially. The structure appears to contain both class I and the recently described class II histone deacetylases (HDAC)5 and 7 along with the nuclear receptor corepressors SMRT (silencing mediator for retinoid and thyroid receptor) and N-CoR (nuclear receptor corepressor). Addition of the deacetylase inhibitors trichostatin A and sodium butyrate completely disrupt these nuclear bodies, providing a demonstration that the integrity of a nuclear body is enzyme dependent. We demonstrate that HDAC5 and 7 can associate with at least 12 distinct proteins, including several members of the NuRD and Sin3A repression complexes, and appear to define a new but related complex.

Association of an interleukin 1 alpha polymorphism with Alzheimer's disease

BACKGROUND

Retrospective epidemiologic studies suggest that individuals exposed to anti-inflammatory agents such as nonsteroidal anti-inflammatory drugs have a lower probability of developing AD as well as an older age at onset for the illness. Neuroinflammation may play an important role in the pathogenesis of AD. Interleukin 1 (IL-1), a potent proinflammatory cytokine, is colocalized immunohistochemically to neuritic plaques, a requisite neuropathologic feature for AD. A polymorphism in the 5'-flanking regulatory region at -889 of the IL-1 alpha gene (a C-to-T transition designated as IL-1A[-889] allele 2) may cause an overexpression of IL-1 alpha, a finding shown to be associated with inflammatory diseases. The IL-1A(-889) allele 2 polymorphism may be associated with AD pathogenesis.

METHODS

A total of 259 patients with AD and 192 nondemented control subjects were included from two different centers (Indianapolis, IN, and Munich, Germany). Genotyping for APOE alleles and IL-1A(-889) allele 2 was performed by PCR-based amplification followed by restrictive endonuclease digestion. Statistical analyses were conducted by center-, gender group-, and age group-stratified Mantel-Haenszel odds ratios, CI, and p values.

RESULTS

The allele frequency of IL-1A(-889) allele 2 was 46% in clinically diagnosed patients with probable AD versus 34% in control subjects from the combined centers.

CONCLUSION

The authors found an increased risk for AD with an estimated Mantel-Haenszel odds ratio of 1.68 (95% CI 1.1 to 2.6; p = 0.022) for heterozygous carriers and 7.2 (95% CI 2.0 to 24.5; p = 0.003) for individuals homozygous for IL-1A(-889) allele 2. They found no evidence for an interaction between the IL-1A and the apoE epsilon 4 polymorphisms (carriers and homozygotes), age, or gender with regard to conferred risk. The data strongly support an association between the IL-1A(-889) allele 2, especially in homozygotes, and later-onset AD.

Humanized xenobiotic response in mice expressing nuclear receptor SXR

The cytochrome CYP3A gene products, expressed in mammalian liver, are essential for the metabolism of lipophilic substrates, including endogenous steroid hormones and prescription drugs. CYP3A enzymes are extremely versatile and are inducible by many of their natural and xenobiotic substrates. Consequently, they form the molecular basis for many clinical drug-drug interactions. The induction of CYP3A enzymes is species-specific, and we have postulated that it involves one or more cellular factors, or receptor-like xeno-sensors. Here we identify one such factor unequivocally as the nuclear receptor pregnenolone X receptor (PXR) and its human homologue, steroid and xenobiotic receptor (SXR). We show that targeted disruption of the mouse PXR gene abolishes induction of CYP3A by prototypic inducers such as dexamethasone or pregnenolone-16alpha-carbonitrile. In transgenic mice, an activated form of SXR causes constitutive upregulation of CYP3A gene expression and enhanced protection against toxic xenobiotic compounds. Furthermore, we show that the species origin of the receptor, rather than the promoter structure of CYP3A genes, dictates the species-specific pattern of CYP3A inducibility. Thus, we can generate 'humanized' transgenic mice that are responsive to human-specific inducers such as the antibiotic rifampicin. We conclude that SXR/PXR genes encode the primary species-specific xeno-sensors that mediate the adaptive hepatic response, and may represent the critical biochemical mechanism of human xenoprotection.

Acquisition of oncogenic potential by RAR chimeras in acute promyelocytic leukemia through formation of homodimers

The t(15;17) chromosomal translocation in acute promyelocytic leukemia (APL) generates the PML-RARalpha fusion protein. The recruitment of nuclear receptor corepressor SMRT/N-CoR and subsequent repression of retinoid target genes is critical for the oncogenic function of PML-RARalpha. Here we show that the ability of PML-RARalpha to form homodimers is both necessary and sufficient for its increased binding efficiency to corepressor and inhibitory effects on hormonal responses in myeloid differentiation. We further provide evidence that altered stoichiometric interaction of SMRT with PML-RARalpha homodimers may underlie these processes. Finally, we demonstrate that a RXR AF2 mutant recapitulates many biochemical and functional properties of PML-RARalpha. Taken together, our results provide an example that altered dimerization of a transcription factor can be directly linked to cellular transformation and implicate dimerization interfaces of oncogenes as potential drug targets.

Alteration of a single amino acid in peroxisome proliferator-activated receptor-alpha (PPAR alpha) generates a PPAR delta phenotype

Three pharmacologically important nuclear receptors, the peroxisome proliferator-activated receptors (PPARs alpha, gamma, and delta), mediate key transcriptional responses involved in lipid homeostasis. The PPAR alpha and gamma subtypes are well conserved from Xenopus to man, but the beta/delta subtypes display substantial species variations in both structure and ligand activation profiles. Characterization of the avian cognates revealed a close relationship between chick (c) alpha and gamma subtypes to their mammalian counterparts, whereas the third chicken subtype was intermediate to Xenopus (x) beta and mammalian delta, establishing that beta and delta are orthologs. Like xPPAR beta, cPPAR beta responded efficiently to hypolipidemic compounds that fail to activate the human counterpart. This provided the opportunity to address the pharmacological problem as to how drug selectivity is achieved and the more global evolutionary question as to the minimal changes needed to generate a new class of receptor. X-ray crystallography and chimeric analyses combined with site-directed mutagenesis of avian and mammalian cognates revealed that a Met to Val change at residue 417 was sufficient to switch the human and chick phenotype. These results establish that the genetic drive to evolve a novel and functionally selectable receptor can be modulated by a single amino acid change and suggest how nuclear receptors can accommodate natural variation in species physiology.

The orphan nuclear receptor Tlx regulates Pax2 and is essential for vision

Although the development of the vertebrate eye is well described, the number of transcription factors known to be key to this process is still limited. The localized expression of the orphan nuclear receptor Tlx in the optic cup and discrete parts of the central nervous system suggested the possible role of Tlx in the formation or function of these structures. Analyses of Tlx targeted mice revealed that, in addition to the central nervous system cortical defects, lack of Tlx function results in progressive retinal and optic nerve degeneration with associated blindness. An extensive screen of Tlx-positive and Tlx-negative P19 neural precursors identified Pax2 as a candidate target gene. This identification is significant, because Pax2 is known to be involved in retinal development in both the human and the mouse eye. We find that Pax2 is a direct target and that the Tlx binding site in its promoter is conserved between mouse and human. These studies show that Tlx is a key component of retinal development and vision and an upstream regulator of the Pax2 signaling cascade.

Improved insulin-sensitivity in mice heterozygous for PPAR-gamma deficiency

The thiazolidinedione class of insulin-sensitizing, antidiabetic drugs interacts with peroxisome proliferator-activated receptor gamma (PPAR-gamma). To gain insight into the role of this nuclear receptor in insulin resistance and diabetes, we conducted metabolic studies in the PPAR-gamma gene knockout mouse model. Because homozygous PPAR-gamma-null mice die in development, we studied glucose metabolism in mice heterozygous for the mutation (PPAR-gamma(+/-) mice). We identified no statistically significant differences in body weight, basal glucose, insulin, or FFA levels between the wild-type (WT) and PPAR-gamma(+/-) groups. Nor was there a difference in glucose excursion between the groups of mice during oral glucose tolerance test, but insulin concentrations of the WT group were greater than those of the PPAR-gamma(+/-) group, and insulin-induced increase in glucose disposal rate was significantly increased in PPAR-gamma(+/-) mice. Likewise, the insulin-induced suppression of hepatic glucose production was significantly greater in the PPAR-gamma(+/-) mice than in the WT mice. Taken together, these results indicate that - counterintuitively - although pharmacological activation of PPAR-gamma improves insulin sensitivity, a similar effect is obtained by genetically reducing the expression levels of the receptor.

Serum cholesterol, APOE genotype, and the risk of Alzheimer's disease: a population-based study of African Americans

A significant interaction among total serum cholesterol (TC), APOE genotype, and AD risk was found in a population-based study of elderly African Americans. Increasing TC was associated with increased AD risk in the group with no epsilon4 alleles, whereas TC was not associated with increased AD risk in the group with one or more epsilon4 alleles. Further study of the relationship between cholesterol and APOE genotype is needed to confirm this association, but the results suggest that cholesterol may be a potentially modifiable environmental risk factor for AD.

Isolation of a novel histone deacetylase reveals that class I and class II deacetylases promote SMRT-mediated repression

The transcriptional corepressor SMRT functions by mediating the repressive effect of transcription factors involved in diverse signaling pathways. The mechanism by which SMRT represses basal transcription has been proposed to involve the indirect recruitment of histone deacetylase HDAC1 via the adaptor mSin3A. In contrast to this model, a two-hybrid screen on SMRT-interacting proteins resulted in the isolation of the recently described HDAC5 and a new family member termed HDAC7. Molecular and biochemical results indicate that this interaction is direct and in vivo evidence colocalizes SMRT, mHDAC5, and mHDAC7 to a distinct nuclear compartment. Surprisingly, HDAC7 can interact with mSin3A in yeast and in mammalian cells, suggesting association of multiple repression complexes. Taken together, our results provide the first evidence that SMRT-mediated repression is promoted by class I and class II histone deacetylases and that SMRT can recruit class II histone deacetylases in a mSin3A-independent fashion.

Mechanism of corepressor binding and release from nuclear hormone receptors

The association of transcription corepressors SMRT and N-CoR with retinoid and thyroid receptors results in suppression of basal transcriptional activity. A key event in nuclear receptor signaling is the hormone-dependent release of corepressor and the recruitment of coactivator. Biochemical and structural studies have identified a universal motif in coactivator proteins that mediates association with receptor LBDs. We report here the identity of complementary acting signature motifs in SMRT and N-CoR that are sufficient for receptor binding and ligand-induced release. Interestingly, the motif contains a hydrophobic core (PhixxPhiPhi) similar to that found in NR coactivators. Surprisingly, mutations in the amino acids that directly participate in coactivator binding disrupt the corepressor association. These results indicate a direct mechanistic link between activation and repression via competition for a common or at least partially overlapping binding site.

Constitutive activation of transcription and binding of coactivator by estrogen-related receptors 1 and 2

In this report, we demonstrate that, in contrast to most previously characterized nuclear receptors, hERR1 and hERR2 (human estrogen receptor-related protein 1 and -2) are constitutive activators of the classic estrogen response element (ERE) as well as the palindromic thyroid hormone response element (TRE(pal)) but not the glucocorticoid response element (GRE). This intrinsically activated state of hERR1 and hERR2 resides in the ligand-binding domains of the two genes and is transferable to a heterologous receptor. In addition, we show that members of the p160 family of nuclear receptor coactivators, ACTR (activator of thyroid and retinoic acid receptors), GRIP1 (glucocorticoid receptor interacting protein 1), and SRC-1 (steroid receptor coactivator 1), potentiate the transcriptional activity by hERR1 and hERR2 in mammalian cells, and that both orphan receptors bind the coactivators in a ligand-independent manner. Together, these results suggest that hERR1 and hERR2 activate gene transcription through a mechanism different from most of the previously characterized steroid hormone receptors.

Pbx-Hox heterodimers recruit coactivator-corepressor complexes in an isoform-specific manner

Homeobox (hox) proteins have been shown to regulate cell fate and segment identity by promoting the expression of specific genetic programs. In contrast to their restricted biological action in vivo, however, most homeodomain factors exhibit promiscuous DNA binding properties in vitro, suggesting a requirement for additional cofactors that enhance target site selectivity. In this regard, the pbx family of homeobox genes has been found to heterodimerize with and thereby augment the DNA binding activity of certain hox proteins on a subset of potential target sites. Here we examine the transcriptional properties of a forced hox-pbx heterodimer containing the pancreas-specific orphan homeobox factor pdx fused to pbx-1a. Compared to the pdx monomer, the forced pdx-pbx1a dimer, displayed 10- to 20-fold-higher affinity for a consensus hox-pbx binding site but was completely unable to bind a hox monomer recognition site. The pdx-pbx dimer stimulated target gene expression via an N-terminal trans-activation domain in pdx that interacts with the coactivator CREB binding protein. The pdx-pbx dimer was also found to repress transcription via a C-terminal domain in pbx-1a that associates with the corepressors SMRT and NCoR. The transcriptional properties of the pdx-pbx1 complex appear to be regulated at the level of alternative splicing; a pdx-pbx polypeptide containing the pbx1b isoform, which lacks the C-terminal extension in pbx1a, was unable to repress target gene expression via NCoR-SMRT. Since pbx1a and pbx1b are differentially expressed in endocrine versus exocrine compartments of the adult pancreas, our results illustrate a novel mechanism by which pbx proteins may modulate the expression of specific genetic programs, either positively or negatively, during development.

PPAR gamma is required for placental, cardiac, and adipose tissue development

The nuclear hormone receptor PPAR gamma promotes adipogenesis and macrophage differentiation and is a primary pharmacological target in the treatment of type II diabetes. Here, we show that PPAR gamma gene knockout results in two independent lethal phases. Initially, PPAR gamma deficiency interferes with terminal differentiation of the trophoblast and placental vascularization, leading to severe myocardial thinning and death by E10.0. Supplementing PPAR gamma null embryos with wild-type placentas via aggregation with tetraploid embryos corrects the cardiac defect, implicating a previously unrecognized dependence of the developing heart on a functional placenta. A tetraploid-rescued mutant surviving to term exhibited another lethal combination of pathologies, including lipodystrophy and multiple hemorrhages. These findings both confirm and expand the current known spectrum of physiological functions regulated by PPAR gamma.

Transcriptional repression by wild-type p53 utilizes histone deacetylases, mediated by interaction with mSin3a

There is growing evidence that the p53 tumor suppressor protein not only can function to activate gene transcription but also to repress the expression of specific genes. Although recent studies have implicated the transcriptional repression function of p53 in the pathway of apoptosis, the molecular basis of this activity remains poorly understood. This study takes a first step toward elucidating this mechanism. We report that trichostatin A (TSA), an inhibitor of histone deacetylases (HDACs), abrogates the ability of p53 to repress the transcription of two genes that it negatively regulates, Map4 and stathmin. Consistent with this finding, we report that p53 physically associates in vivo with HDACs. This interaction is not direct but, rather, is mediated by the corepressor mSin3a. Both wild-type p53 and mSin3a, but not mutant p53, can be found bound to the Map4 promoter at times when this promoter preferentially associates with deacetylated histones in vivo. Significantly, inhibition of p53-mediated transcriptional repression with TSA markedly inhibits apoptosis induction by p53. These data offer the first mechanistic insights for p53-mediated transcriptional repression and underscore the importance of this activity for apoptosis induction by this protein.

Multiple left-right asymmetry defects in Shh(-/-) mutant mice unveil a convergence of the shh and retinoic acid pathways in the control of Lefty-1

Asymmetric expression of Sonic hedgehog (Shh) in Hensen's node of the chicken embryo plays a key role in the genetic cascade that controls left-right asymmetry, but its involvement in left-right specification in other vertebrates remains unclear. We show that mouse embryos lacking Shh display a variety of laterality defects, including pulmonary left isomerism, alterations of heart looping, and randomization of axial turning. Expression of the left-specific gene Lefty-1 is absent in Shh(-/-) embryos, suggesting that the observed laterality defects could be the result of the lack of Lefty-1. We also demonstrate that retinoic acid (RA) controls Lefty-1 expression in a pathway downstream or parallel to Shh. Further, we provide evidence that RA controls left-right development across vertebrate species. Thus, the roles of Shh and RA in left-right specification indeed are conserved among vertebrates, and the Shh and RA pathways converge in the control of Lefty-1.

Regulation of hormone-induced histone hyperacetylation and gene activation via acetylation of an acetylase

Nuclear receptors have been postulated to regulate gene expression via their association with histone acetylase (HAT) or deacetylase complexes. We report that hormone induces dramatic hyperacetylation at endogenous target genes through the HAT activity of p300/CBP. Unexpectedly, this hyperacetylation is transient and coincides with attenuation of hormone-induced gene activation. In exploring the underlying mechanism, we found that the acetylase ACTR can be acetylated by p300/CBP. The acetylation neutralizes the positive charges of two lysine residues adjacent to the core LXXLL motif and disrupts the association of HAT coactivator complexes with promoter-bound estrogen receptors. These results provide strong in vivo evidence that histone acetylation plays a key role in hormone-induced gene activation and define cofactor acetylation as a novel regulatory mechanism in hormonal signaling.

Vimentin-dependent utilization of LDL-cholesterol in human adrenal tumor cells is not associated with the level of expression of apoE, sterol carrier protein-2, or caveolin

SW-13 adrenal tumor cells that lack detectable intermediate filaments (IF-free) exhibit an impaired capacity to esterify lipoprotein-derived cholesterol compared with cells that contain vimentin filaments. IF-free cells were found to synthesize and secrete significant amounts of apoE, while apoE secretion was nearly undetectable in cell lines that spontaneously express vimentin. However, stable transfectants that express a mouse vimentin cDNA exhibited elevated levels of cholesterol esterification and apoE secretion compared with untransfected IF-free cells, indicating that apoE secretion is not directly related to the capacity of these cells to esterify cholesterol. Some of the cell lines that differed in the level of apoE synthesis and secretion had similar levels of apoE mRNA, suggesting that the differences in expression involve a post-transcriptional mechanism. Treatment of these cells with forskolin and IBMX, 8br-cAMP, or TPA had no effect on apoE secretion. The level of sterol carrier protein-2 (SCP(2)) synthesis and the distribution of SCP(2) between membrane and soluble cellular fractions was not observably different in cells that contained or lacked vimentin. SW-13 cell lines contained little or no detectable caveolin-1 or caveolin-2. These studies demonstrate that the difference in the capacity of these adrenal tumor cells that contain or lack vimentin filaments to esterify low density lipoprotein-cholesterol is not obviously associated with the level of expression or distribution of apoE, SCP(2), or caveolins.

Percutaneous dilatational tracheostomy under ultrasound guidance

Diagnostic ultrasound may be used to assess the suitability of patients for percutaneous dilatational tracheostomy (PDT) in the intensive care unit (ICU). It may identify patients unsuitable for PDT, prevent puncture of aberrant vessels, estimate the distance from the surface of the skin to the trachea, and ensure accurate placement of the needle in the trachea. We conclude that diagnostic ultrasound permits careful evaluation of patients for whom PDT is being considered, and adds to the safety of the procedure.

SMRTER, a Drosophila nuclear receptor coregulator, reveals that EcR-mediated repression is critical for development

The Drosophila ecdysone receptor (EcR)/ultraspiracle (USP) heterodimer is a key regulator in molting and metamorphoric processes, activating and repressing transcription in a sequence-specific manner. Here, we report the isolation of an EcR-interacting protein, SMRTER, which is structurally divergent but functionally similar to the vertebrate nuclear corepressors SMRT and N-CoR. SMRTER mediates repression by interacting with Sin3A, a repressor known to form a complex with the histone deacetylase Rpd3/HDAC. Importantly, we identify an EcR mutant allele that fails to bind SMRTER and is characterized by developmental defects and lethality. Together, these results reveal a novel nuclear receptor cofactor that exhibits evolutionary conservation in the mechanism to achieve repression and demonstrate the essential role of repression in hormone signaling.

Molecular genetics of acute promyelocytic leukemia

The remarkable success of retinoic acid in the treatment of acute promyelocytic leukemias and the subsequent discovery that mutant forms of a retinoid acid receptor (RARalpha) are invariably associated with this disease has generated considerable interest among both clinicians and basic scientists. Studies both in cell culture and in transgenic animals suggest that mutant RARs interfere with normal retinoid-mediated transactivation and granulocytic differentiation. More recently, a pivotal link between transcriptional silencing, the oncogenic functions of RAR mutants, and hormonal responses in APL patients has been established. These studies have greatly advanced our understanding of the molecular changes involved in leukemogenesis, have helped to reveal new aspects of cellular differentiation, and might lead to improved treatment strategies for human leukemias.

Metabolic costs of heat solicitation calls in relation to thermal need in embryos of American white pelicans

Chilled embryos of pelicans, Pelecanus erythrorhynchos, begin to vocally solicit parental heat at the pipped-egg stage. Honest signalling models predict that if vocal heat solicitation is a true reflection of need, then solicitation should be costly and costs should increase with the embryo's need for warmth. Using open-flow respirometry, we measured the metabolic costs associated with vocal heat solicitation by exposing embryos to either a decreasing or increasing series of body temperatures, ranging from 25 to 37.8 degrees C. We measured baseline costs (stable temperature, embryo silent) and costs associated with cold-induced calling at each temperature. At natural incubation temperature (37.8 degrees C), call rates and costs associated with calling were negligible, as was thermal need. Metabolic costs relative to baseline costs and costs per call increased with thermal need as body temperature declined. Absolute metabolic costs increased between 37.8 and 35 degrees C, then remained stable down to 25 degrees C. Call rates increased as embryos were chilled within the range of temperatures most frequently experienced in nature (35-37.8 degrees C), then decreased significantly for all lower temperatures, probably owing to reduced overall metabolic rate at lower temperatures (25-37.8 degrees C). The results generally support the honest signalling prediction that vocal heat solicitation is metabolically costly, and that costs increase with need. Copyright 1999 The Association for the Study of Animal Behaviour.