Periprosthetic fractures about total knee arthroplasty

Periprosthetic fracture after total knee arthroplasty presents a difficult complication for many orthopaedic surgeons. These fractures occur most frequently around the distal femur followed by the patella and then tibia. These fractures are frequently complicated by poor bone quality or compromised bone due to the presence of the implants. Surgical treatment is typically necessary and requires varied techniques of open fixation, intramedullary fixation, or revision arthroplasty. Outcomes of these injuries vary widely. This review aims to describe the epidemiology, classification, treatment options and outcomes for periprosthetic fractures following total knee arthroplasty.

A novel chemically modified curcumin reduces inflammation-mediated connective tissue breakdown in a rat model of diabetes: periodontal and systemic effects

BACKGROUND AND OBJECTIVE

Periodontal disease is the most common chronic inflammatory disease known to mankind (and the major cause of tooth loss in the adult population) and has also been linked to various systemic diseases, particularly diabetes mellitus. Based on the literature linking periodontal disease with diabetes in a "bidirectional manner", the objectives of the current study were to determine: (i) the effect of a model of periodontitis, complicated by diabetes, on mechanisms of tissue breakdown including bone loss; and (ii) the response of the combination of this local and systemic phenotype to a novel pleiotropic matrix metalloproteinase inhibitor, chemically modified curcumin (CMC) 2.24.

MATERIAL AND METHODS

Diabetes was induced in adult male rats by intravenous injection of streptozotocin (nondiabetic rats served as controls), and Escherichia coli endotoxin (lipopolysaccharide) was repeatedly injected into the gingiva to induce periodontitis. CMC 2.24 was administered by oral gavage (30 mg/kg) daily; untreated diabetic rats received vehicle alone. After 3 wk of treatment, the rats were killed, and gingiva, jaws, tibia and skin were collected. The maxillary jaws and tibia were dissected and radiographed. The gingival tissues of each experimental group (n = 6 rats/group) were pooled, extracted, partially purified and, together with individual skin samples, analyzed for matrix metalloproteinase (MMP)-2 and MMP-9 by gelatin zymography; MMP-8 was analyzed in gingival and skin tissue extracts, and in serum, by western blotting. The levels of three bone-resorptive cytokines [interleukin (IL)-1β, IL-6 and tumor necrosis factor-α], were measured in gingival tissue extracts and serum by ELISA.

RESULTS

Systemic administration of CMC 2.24 to diabetic rats with endotoxin-induced periodontitis significantly inhibited alveolar bone loss and attenuated the severity of local and systemic inflammation. Moreover, this novel tri-ketonic phenylaminocarbonyl curcumin (CMC 2.24) appeared to reduce the pathologically excessive levels of inducible MMPs to near-normal levels, but appeared to have no significant effect on the constitutive MMPs required for physiologic connective tissue turnover. In addition to the beneficial effects on periodontal disease, induced both locally and systemically, CMC 2.24 also favorably affected extra-oral connective tissues, skin and skeletal bone.

CONCLUSION

This study supports our hypothesis that CMC 2.24 is a potential therapeutic pleiotropic MMP inhibitor, with both intracellular and extracellular effects, which reduces local and systemic inflammation and prevents hyperglycemia- and bacteria-induced connective tissue destruction.

Performance of Coopworth ewe lambs exposed to low levels of ryegrass endophyte (Neotyphodium lolii) alkaloids and allowed access to a mycotoxin deactivator

During February–April, Coopworth ewe lambs grazing a pasture dominated by naturalised perennial ryegrass (PRG) exhibited slight signs of ill-thrift and heat stress. PRG represented 85% of the herbage; 90% of the PRG population was infected with Neotyphodium endophyte. Concentrations of ergovaline and lolitrem B in perennial ryegrass were each within the range 0.5–1.0 mg/kg DM during this period. Two groups of 30 lambs rotated weekly between two paddocks that offered 6 t DM/ha of mature, low-quality pasture. They received an allowance of crushed barley and peas (80 : 20) at 100 g/head per day. One group was treated with a mycotoxin deactivator, Mycofix® Plus, mixed into their mash during processing (5 g/100 g). No sign of ‘staggers’ was observed in the lambs at any time. Lambs with access to Mycofix Plus made great use of shade; their occupancy of shade increased steeply with ambient temperature over the range 18−38°C (P < 0.001). For the control group, occupancy of shade was low (P < 0.001) and independent of temperature (P < 0.001). Instead of using shade on hot days, the control lambs whose respiration rate was higher than treated ewes (P < 0.001) commonly stood by the wire fence, huddled in the open. Over the first 56 days of treatment, while pasture remained dry, weight change in control and treated lambs was –13 and +16 g/day, respectively (P < 0.010). The need for greater investigation of the effects of endophyte alkaloids on livestock is discussed.

Impact of mycotoxins and of a mycotoxin deactivator on alpacas grazing perennial ryegrass infected with wild endophyte (Neotyphodium spp.)

Liveweight gain, animal health and the effectiveness of a mycotoxin deactivator were studied on an old pasture that contained 61% perennial ryegrass. Sixty-seven percent of the ryegrass population was infected with endophyte (Neotyphodium spp.). The pasture was fenced into two halves and two groups of 28 alpaca male weaners were rotated between the two plots. Nine to 10 Suris and 18–19 Huacayas were allocated to each group. One group was fed a concentrate supplement (100 g/head per day) and the other was fed the same supplement to which was added the toxin deactivator, Mycofix® Plus (5 g/100 g). Mean liveweight gain on the low-quality pasture over late summer and early autumn was not significantly (P > 0.05) different between the groups. For the control group it was 41 g/day but individual rates of gain ranged from 67 to 0 g/day, depending on the severity of signs of perennial ryegrass toxicosis (r = 0.82, P < 0.001). Liveweight gain was independent of neurotoxic signs in the Mycofix® Plus treated group. Ergovaline concentration in perennial ryegrass varied from 0.43 to a peak in early autumn (March) of 1.05 mg/kg. Mean urine lysergol alkaloid concentration peaked in mid-summer (January) at 109 ng/mg creatinine (control group) and was consistently lower in the Mycofix® Plus group, although the difference approached significance (P = 0.06) only in March. Lolitrem B concentration in perennial ryegrass varied from 0.78 to 1.57 mg/kg. Neurotoxic signs in alpacas were observed throughout the study and peaked in early autumn, coinciding with peak lolitrem B concentration; at this time, 84% of alpacas exhibited neurotoxic signs. Over the 145-day study, the Mycofix® Plus treated group exhibited a lower mean rating of perennial ryegrass toxicosis signs (P < 0.05). Variation in liveweight gain and signs of toxicosis were not associated with significant differences in liver enzyme activity.

A preliminary survey of zearalenone and other mycotoxins in Australian silage and pasture

The oestrogenic mycotoxin zearalenone can occur in pasture and fodder infected with various Fusarium spp., and at concentrations exceeding 1 mg/kg, it has been associated with a reduction in the fertility of grazing ruminants. Pasture and fodder samples collected in four small studies from cattle and sheep farms in south-eastern Australia were tested for zearalenone and other mycotoxins using high performance liquid chromatography. Zearalenone in winter pasture was detected (viz. >0.1 and up to 5.0 mg/kg DM) in 8 of 22 pastures; three exceeded the tolerance concentration, 1.0 mg/kg. Zearalenone was detected in 15 of 24 samples of silage that were submitted by farmers for nutritional assessment, but that were not suspected of toxicity; 12 were in the range 1.0–80 mg/kg. Zearalenone was correlated with crude protein concentration (r = 0.59, P < 0.05); it was high in legume-dominant compared with grass-dominant silage (P < 0.04). In a separate investigation of 28 feed samples submitted for mycotoxin screening by nutritionists/veterinarians, zearalenone was detected in 7 of 13 pastures, in two of two hays and 9 of 13 silages (6 of 28 exceeded 1 mg/kg). Deoxynivalenol was detected in 6 of 13 pastures, one of two hays and 10 of 13 silages. Deoxynivalenol was high (0.64–1.76 mg/kg) in five silages of excellent/average appearance. Ergovaline and lolitrem B were detected at above tolerable concentrations in four of eight perennial ryegrass-dominant samples examined. Aflatoxins, ochratoxin A and fumonisins were detected in some samples although the concentrations were low. Two samples contained either zearalenone and ergovaline, or zearalenone and deoxynivalenol, where both mycotoxins exceeded tolerable concentrations.

trans-Stilbene oxide induces expression of genes involved in metabolism and transport in mouse liver via CAR and Nrf2 transcription factors

trans-Stilbene oxide (TSO) induces drug metabolizing enzymes in rat and mouse liver. TSO is considered a phenobarbital-like compound because it induces Cyp2B mRNA expression in liver. Phenobarbital increases Cyp2B expression in liver via activation of the constitutive androstane receptor (CAR). The purpose of this study was to determine whether TSO induces gene expression in mouse liver via CAR activation. TSO increased CAR nuclear localization in mouse liver, activated the human Cyp2B6 promoter in liver in vivo, and activated a reporter plasmid that contains five nuclear receptor 1 (NR1) binding sites in HepG2 cells. TSO administration increased expression of Cyp2b10, NAD(P)H:quinone oxidoreductase (Nqo1), epoxide hydrolase, heme oxygenase-1, UDP-glucuronosyl-transferase (Ugt) 1a6 and 2b5, and multidrug resistance-associated proteins (Mrp) 2 and 3 mRNA in livers from male mice. Cyp2b10 and epoxide hydrolase induction by TSO was decreased in livers from CAR-null mice, compared with wild-type mice, suggesting CAR involvement. In contrast, TSO administration induced Nqo1 and Mrp3 mRNA expression equally in livers from wild-type and CAR-null mice, suggesting that TSO induces expression of some genes through a mechanism independent of CAR. TSO increased nuclear staining of the transcription factor Nrf2 in liver, and activated an antioxidant/electrophile response element luciferase reporter construct that was transfected into HepG2 cells. In summary, in mice, TSO increases Cyp2b10 and epoxide hydrolase expression in mice via CAR, and potentially induces Nqo1 and Mrp3 expression via Nrf2. Moreover, our data demonstrate that a single compound can activate both CAR and Nrf2 transcription factors in liver.

CAR, The Continuously Advancing Receptor, in Drug Metabolism and Disease

The detoxification and elimination of potentially toxic foreign and endogenous compounds depends on the concerted action of xenobiotic metabolizing enzymes. Nuclear hormone receptors (NHRs) have emerged as key regulators of the expression of these enzymes and his review focuses on the xenosenor CAR (Constitutive Androstane Receptor, NR1I3). CAR is highly expressed in the liver and the small intestine, two key tissues expressing xenobiotic metabolizing enzymes, and mediates the induction of their expression by the widely used antiepileptic drug, phenobarbital (PB) and the potent synthetic inducer 1, 4-bis-(2-(3, 5, -dichloropyridyloxy)) benzene (TCPOBOP). TCPOBOP is an agonist ligand for CAR. PB induces its nuclear translocation, which results in increased expression of CAR target genes since, unlike the classical, ligand-dependent nuclear receptors, CAR is an apparently constitutive transactivator. This constitutive activity is inhibited by the inverse agonist ligands androstanol and androstenol. The CAR mediated induction of the expression of xenobiotic metabolizing enzymes is generally protective, but can be deleterious if toxic metabolites are produced. CAR also has a protective role in the stress response elicited by hyperbilirubinemia, as well as lithocholic acid induced cholestasis. In addition, recent studies show that CAR activation disrupts thyroid hormone homeostasis. Finally, CAR activation promotes hepatocyte proliferation and blocks apoptosis, and is essential for the tumorigenesis induced by its activators PB and TCPOBOP. The role of CAR in endobiotic and xenobiotics metabolism has clinical implications in disease prevention, drug-drug interactions, and the development of better drug treatments.

CAR/PXR provide directives for Cyp3a41 gene regulation differently from Cyp3a11

This study reports that Cyp3a41 gene contains 13 exons and is localized on the chromosome 5. CYP3A41 is a female-specific isoform that is predominantly expressed in the liver. Estrogen signaling is not responsible for its female specificity. CYP3A41 expression in kidney and brain is observed only in 50% of mice examined. PXR mediates dexamethasone-dependent suppression of CYP3A41. In contrast to CYP3A11, CYP3A41 expression is not induced by pregnenolone-16alpha-carbonitrile (PCN) in wild-type mice, but is significantly suppressed by PCN in PXR(-/-) mice. Phenobarbital and TCPOBOP induce CYP3A11 expression only in the presence of CAR, but have no effect on CYP3A41 expression. Immunoblot and erythromycin demethylase activity analysis reveal robust CYP3A induction after PCN treatment, which is poorly correlated to CYP3A41. These findings suggest a differential role for CAR/PXR in regulating individual CYP3A isoforms by previously characterized CYP3A inducers.

Specific and overlapping functions of the nuclear hormone receptors CAR and PXR in xenobiotic response

The products of the cytochrome P450 (CYP) genes play an important role in the detoxification of xenobiotics and environmental contaminants, and many foreign chemicals or xenobiotics can induce their expression. We have previously shown that the nuclear hormone receptor CAR (Constitutive Androstane Receptor, NR113) mediates the well studied induction of CYP2B10 gene expression by phenobarbital (PB) and 1, 4-bis-[2-(3, 5,-dichloropyridyloxy)] benzene (TCPOBOP). We have used the CAR knockout mouse model to explore the broader functions of this xenobiotic receptor. In addition to the liver, CAR is expressed in the epithelial cells of the villi in the small intestine, and this expression is required for CYP2B10 induction in response to PB and TCPOBOP in those cells. In agreement with previous observations that CAR can bind to regulatory elements in CYP3A genes, CAR is also required for induction of expression of CYP3A11 in response to both PB and TCPOBOP in liver. In males, CAR is also required for induction of liver CYP2A4 expression. In wild type animals, pretreatment with the CAR inverse agonist androstenol blocks the response of both the CYP2B10 and CYP3A11 genes to PB and TCPOBOP, and decreases basal CYP3A11 expression. CAR is also required for the response of CYP2B10 to several additional xenobiotic inducers, including chlorpromazine, clotrimazole and dieldrin, but not dexamethasone, an agonist for both the xenobiotic receptor PXR (Pregnane X Receptor NR112) and the glucocorticoid receptor. Chlorpromazine induction of CYP3A11 is also absent in CAR-deficient animals, but the responses to clotrimazole and dieldrin are retained, indicating that both of these inducers can also activate PXR (Pregnane X Receptor NR112). We conclude that CAR has broad functions in xenobiotic responses. Some are specific to CAR but others, including induction of the important drug metabolizing enzyme CYP3A, overlap with those of PXR.

Involvement of toll-like receptor 4 in innate immunity to respiratory syncytial virus

The mammalian Toll-like receptor 4, TLR4, is an important component in the innate immune response to gram-negative bacterial infection. The role of TLR4 in antiviral immunity has been largely unexplored. In this study, the in vivo immune responses to respiratory syncytial virus (RSV) and influenza virus infection were examined in TLR4-deficient (C57BL/10ScNCr) and TLR4-expressing (C57BL/10Sn) mice. TLR4-deficient mice challenged with RSV, but not influenza virus, exhibited impaired natural killer (NK) cell and CD14(+) cell pulmonary trafficking, deficient NK cell function, impaired interleukin-12 expression, and impaired virus clearance compared to mice expressing TLR4. These findings suggest that Toll signaling pathways have an important role in innate immunity to RSV.

Genomic DNA libraries

Genomic DNA libraries are almost always screened by hybridization using a radioactive nucleic acid probe. Since this approach is essentially independent of a particular vector or type of target DNA, the main problem faced when considering creation of a genomic DNA library is simply generating a large enough number of recombinant DNA clones. The basic strategies used to address this problem have included both minimizing the number of clones necessary by incorporating large fragments of genomic DNA, and maximizing cloning efficiency by using vectors based on bacteriophage lambda. This unit discusses the appropriate numerical considerations for both ordinary genomic DNA libraries and subgenomic DNA libraries, and then describes a limited number of appropriate vectors.

cDNA libraries

This unit provides a basic description of issues that require careful consideration before undertaking construction of cDNA libraries. Topics include: generating a double-stranded DNA copy of the mRNA, the quality of the mRNA, the relative abundance of the clone of interest, the choice of screening method, the size of the library that will be necessary to include the clone of interest, and choices of linkers or adaptors for insertion into the vector.

Mutations in the small heterodimer partner gene are associated with mild obesity in Japanese subjects

Mutations in several genes encoding transcription factors of the hepatocyte nuclear factor (HNF) cascade are associated with maturity-onset diabetes of the young (MODY), a monogenic form of early-onset diabetes mellitus. The ability of the orphan nuclear receptor small heterodimer partner (SHP, NR0B2) to modulate the transcriptional activity of MODY1 protein, the nuclear receptor HNF-4alpha, suggested SHP as a candidate MODY gene. We screened 173 unrelated Japanese subjects with early-onset diabetes for mutations in this gene and found five different mutations (H53fsdel10, L98fsdel9insAC, R34X, A195S, and R213C) in 6 subjects as well as one apparent polymorphism (R216H), all present in the heterozygous state. Interestingly, all of the subjects with the mutations were mildly or moderately obese at onset of diabetes, and analysis of the lineages of these individuals indicated that the SHP mutations were associated with obesity rather than with diabetes. Therefore, an additional group of 101 unrelated nondiabetic subjects with early-onset obesity was screened for mutations in the SHP gene. Two of the previously observed mutations (R34X and A195S) and two additional mutations (R57W and G189E) were identified in 6 subjects, whereas no mutations were identified in 116 young nondiabetic lean controls (P = 0.0094). Functional studies of the mutant proteins show that the mutations result in the loss of SHP activity. These results suggest that genetic variation in the SHP gene contributes to increased body weight and reveal a pathway leading to this common metabolic disorder in Japanese.

Role reversal: new insights from new ligands for the xenobiotic receptor CAR

In the classic model of nuclear receptor signaling, specific hormone binding results in the recruitment of coactivator proteins and transcriptional activation. Recent results with newly characterized nuclear receptors have expanded this model to include new types of ligands and novel transcriptional responses. Both inverse agonists and conventional agonist ligands have been identified for the xenobiotic receptor constitutive androstane receptor (CAR), a constitutive activator of transcription in the absence of ligands.

New insights into receptor ligand binding domains from a novel assembly assay

Previous studies have demonstrated that hormone binding stabilizes the ligand binding domain (LBD) of the nuclear hormone receptors against proteolysis. We have confirmed and extended this observation using a newly developed assembly assay. In this assay, the LBD is divided into two parts, of which one includes the first helix of this domain and the other corresponds to the remainder of the LBD. Several independent criteria demonstrate that these two fragments can assemble into a functional LBD in the presence of a ligand, but not in its absence, and that this is a reflection of the stabilizing effect of ligand. We have also used this assay to demonstrate that binding of the nuclear receptor corepressor NCoR can directly stabilize the LBD. Overall, these results highlight the dynamic nature of the LBD and suggest that current models for activation based solely on allosteric effects on the C-terminal helix may be too limited.

The farnesoid X-activated receptor mediates bile acid activation of phospholipid transfer protein gene expression

Bile acids facilitate the absorption of dietary lipids and fat-soluble vitamins and are physiological ligands for the farnesoid X-activated receptor (FXR), a member of the nuclear hormone receptor superfamily. FXR functions as a heterodimer with the retinoid X receptor and in the presence of ligand, the heterodimer binds to specific DNA sequences in the promoters of target genes to regulate gene transcription. Phospholipid transfer protein (PLTP) has been identified as a possible target gene for FXR because the human promoter contains a potential FXR response element, an inverted repeat in which consensus receptor-binding hexamers are separated by one nucleotide (inverted repeat-1). PLTP is essential in the transfer of very low density lipoprotein phospholipids into high density lipoprotein (Jiang, X. C., Bruce, C., Mar, J., Lin, M., Ji, Y., Francone, O. L., and Tall, A. R. (1999) J. Clin. Invest. 103, 907-914). Here we report the regulation of PLTP gene expression by FXR and bile acids. In CV-1 cells, cotransfection of FXR and the retinoid X receptor resulted in bile acid-dependent transactivation of a luciferase reporter construct containing the human PLTP promoter. Mutation analysis demonstrated that the inverted repeat-1 (IR-1) in the PLTP promoter is required for this transactivation. Finally, we demonstrate that bile acids are able to regulate PLTP gene expression in vivo. Mice fed a chow diet supplemented with bile acid showed increased hepatic PLTP mRNA levels. These results suggest that FXR may play a role in high density lipoprotein metabolism via the regulation of PLTP gene expression.

The nuclear receptor CAR mediates specific xenobiotic induction of drug metabolism

Organisms encounter a wide range of foreign compounds--or 'xenobiotics'--with potentially harmful consequences. The cytochrome P450 (CYP) enzymes metabolize xenobiotics and thus are a primary defence against these compounds. Increased expression of specific CYP genes in response to particular xenobiotics is a central component of this defence, although such induction can also increase production of toxic metabolites. Here we show that the nuclear receptor CAR mediates the response evoked by a class of xenobiotics known as the 'phenobarbital-like inducers'. The strong activation of Cyp2b10 gene expression by phenobarbital, or by the more potent TCPOBOP, is absent in mice lacking the CAR gene. These animals also show decreased metabolism of the classic CYP substrate zoxazolamine and a complete loss of the liver hypertrophic and hyperplastic responses to these inducers. Cocaine causes acute hepatotoxicity in wild-type mice previously exposed to phenobarbital-like inducers and this toxicity is also absent in the CAR-deficient animals. Thus, loss of CAR function alters sensitivity to toxins, increasing or decreasing it depending on the compound. Modulation of CAR activity in humans may significantly affect metabolism of drugs and other xenobiotics.

Dynamic stabilization of nuclear receptor ligand binding domains by hormone or corepressor binding

We have developed a novel assembly assay to examine structural changes in the ligand binding domain (LBD) of the thyroid hormone receptor (TR). Fragments including the first helix of the TR LBD interact only weakly with the remainder of the LBD in the absence of hormone, but this interaction is strongly enhanced by the addition of either hormone or the corepressor NCoR. Since neither the ligand nor the corepressor shows direct interaction with this helix, we propose that both exert their effects by stabilizing the overall structure of the LBD. Current models of activation of nuclear hormone receptors focus on a ligand-induced allosteric shift in the position of the C-terminal helix 12 that generates the coactivator binding site. Our results suggest that ligand binding also has more global effects that dynamically alter the structure of the receptor LBD.

The xenobiotic compound 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene is an agonist ligand for the nuclear receptor CAR

A wide range of xenobiotic compounds are metabolized by cytochrome P450 (CYP) enzymes, and the genes that encode these enzymes are often induced in the presence of such compounds. Here, we show that the nuclear receptor CAR can recognize response elements present in the promoters of xenobiotic-responsive CYP genes, as well as other novel sites. CAR has previously been shown to be an apparently constitutive transactivator, and this constitutive activity is inhibited by androstanes acting as inverse agonists. As expected, the ability of CAR to transactivate the CYP promoter elements is blocked by the inhibitory inverse agonists. However, CAR transactivation is increased in the presence of 1,4-bis[2-(3, 5-dichloropyridyloxy)]benzene (TCPOBOP), the most potent known member of the phenobarbital-like class of CYP-inducing agents. Three independent lines of evidence demonstrate that TCPOBOP is an agonist ligand for CAR. The first is that TCPOBOP acts in a dose-dependent manner as a direct agonist to compete with the inhibitory effect of the inverse agonists. The second is that TCPOBOP acts directly to stimulate coactivator interaction with the CAR ligand binding domain, both in vitro and in vivo. The third is that mutations designed to block ligand binding block not only the inhibitory effect of the androstanes but also the stimulatory effect of TCPOBOP. Importantly, these mutations do not block the apparently constitutive transactivation by CAR, suggesting that this activity is truly ligand independent. Both its ability to target CYP genes and its activation by TCPOBOP demonstrate that CAR is a novel xenobiotic receptor that may contribute to the metabolic response to such compounds.

SF-36 as a predictor of health states

BACKGROUND

There are a number of claims that Medical Outcomes Study Short Form 36 (MOS SF-36) mean scores can be used to discriminate between healthy and nonhealthy persons and determine various levels of health.

OBJECTIVES

The purpose of this study was to evaluate the ability of the SF-36 to predict whether or not respondents reported health problems.

METHODS

We used structural equation modeling (SEM) techniques to evaluate the SF-36 and its ability to discriminate between those who reported health problems or reported physician-determined illness and those who did not in a sample from the 1990 National Survey of Functional Health Status (NHS).

RESULTS

The correlation between physician-determined illness and Physical Health was -.404, resulting in 16.32% shared variance. The correlation between reported health problems and Physical Health was -.360, resulting in 12.96% shared variance. These correlations are markedly lower than those to the eight first-order scales or between Physical and Mental Health (r = .889). Mental Health could not predict physician-determined illness or reported health problems independent of Physical Health.

CONCLUSIONS

The SF-36 is relatively poor at accounting for the health status of respondents. There are significant paths but the variance accounted for in absolute and relative terms is small. Physical Health does a much better job of accounting for general mental health than it does for perceived health problems or physician-determined illness. These findings suggest that the SF-36 may not discriminate well between healthy and nonhealthy groups and that objective measures of health status may be required in conjunction with the use of the SF-36.

Identification of the DNA binding specificity and potential target genes for the farnesoid X-activated receptor

The farnesoid X-activated receptor (FXR; NR1H4) is a member of the nuclear hormone receptor superfamily and functions as a heterodimer with the 9-cis-retinoic acid receptor (RXR). In order to determine the optimal DNA binding sequence for the FXR/RXR heterodimer, we have utilized the selected and amplified binding sequence imprinting technique. This technique identified a number of related sequences that interacted with FXR/RXR in vitro. The consensus sequence contained an inverted repeat of the sequence AGGTCA with a 1-base pair spacing (IR-1). This sequence was shown to be a high affinity binding site for FXR/RXR in vitro and to confer ligand-dependent transcriptional activation by FXR/RXR to a heterologous promoter. Electrophoretic mobility shift assays and transient transfection assays were used to investigate the importance of the core half-site sequences, spacing nucleotide, flanking sequences, and orientation and spacing of the core half-sites on DNA binding and ligand-dependent transcriptional activation by FXR/RXR. These studies demonstrated that the FXR/RXR heterodimer binds to the consensus IR-1 sequence with the highest affinity, although FXR/RXR can bind to and activate through a variety of elements including IR-1 elements with changes in the core half-site sequence, spacing nucleotide, and flanking nucleotides. In addition, FXR/RXR can bind to and transactivate through direct repeats. Three genes were identified that contain IR-1 sequences in their proximal promoters. These elements were shown to bind FXR/RXR in vitro and to confer FXR/RXR-dependent transcriptional activation to a heterologous promoter in response to a bile acid or synthetic retinoid. The endogenous mRNA levels of one of these genes, phospholipid transfer protein, were shown to be induced by FXR and FXR ligands. The identification of the IR-1 and related elements as high affinity binding sites and functional response elements for FXR/RXR and the identification of a target gene for FXR/RXR should assist in the identification of additional genes regulated by FXR/RXR.

The orphan nuclear receptor SHP inhibits hepatocyte nuclear factor 4 and retinoid X receptor transactivation: two mechanisms for repression

The orphan nuclear hormone receptor SHP interacts with a number of other nuclear hormone receptors and inhibits their transcriptional activity. Several mechanisms have been suggested to account for this inhibition. Here we show that SHP inhibits transactivation by the orphan receptor hepatocyte nuclear factor 4 (HNF-4) and the retinoid X receptor (RXR) by at least two mechanisms. SHP interacts with the same HNF-4 surface recognized by transcriptional coactivators and competes with them for binding in vivo. The minimal SHP sequences previously found to be required for interaction with other receptors are sufficient for interaction with HNF-4, although deletion results indicate that additional C-terminal sequences are necessary for full binding and coactivator competition. These additional sequences include those associated with direct transcriptional repressor activity of SHP. SHP also competes with coactivators for binding to ligand-activated RXR, and based on the ligand-dependent interaction with other nuclear receptors, it is likely that coactivator competition is a general feature of SHP-mediated repression. The minimal receptor interaction domain of SHP is sufficient for full interaction with RXR, as previously described. This domain is also sufficient for full coactivator competition. Functionally, however, full inhibition of RXR transactivation requires the presence of the C-terminal repressor domain, with only weak inhibition associated with this receptor interaction domain. Overall, these results suggest that SHP represses nuclear hormone receptor-mediated transactivation via two separate steps: first by competition with coactivators and then by direct effects of its transcriptional repressor function.

Bradycardia and asystole with the use of vagus nerve stimulation for the treatment of epilepsy: a rare complication of intraoperative device testing

PURPOSES

A 56-year-old man with mild mental retardation, right congenital hemiparesis, and refractory partial seizures was referred for vagus nerve stimulation (VNS).

METHODS

Routine lead diagnostic testing during the surgical procedure (1.0 mA, 20 Hz, and 500 micros, for approximately 17 s) resulted, during the initial two stimulations, in a bradycardia of approximately 30 beats/min. A third attempt led to transient asystole that required atropine and brief cardiopulmonary resuscitation.

RESULTS

The procedure was immediately terminated, the device removed, and the patient recovered completely. A postoperative cardiologic evaluation, including an ECG, 24-h Holter monitor, echocardiogram, and a tilt-table test, was normal.

CONCLUSIONS

Possible mechanisms for the bradycardia/asystole include stimulation of cervical cardiac branches of the vagus nerve either by collateral current spread or directly by inadvertent placement of the electrodes on one of these branches; improper plugging of the electrodes into the pulse generator, resulting in erratic varying intensity of stimulation; reverse polarity; and idiosyncratic-type reaction in a hypersusceptible individual. The manufacturer reports the occurrence rate in approximately 3,500 implants for this intraoperative event to be approximately one in 875 cases or 0.1%.

Activating signal cointegrator 1, a novel transcription coactivator of nuclear receptors, and its cytosolic localization under conditions of serum deprivation

Activating signal cointegrator 1 (ASC-1) harbors an autonomous transactivation domain that contains a putative zinc finger motif which provides binding sites for basal transcription factors TBP and TFIIA, transcription integrators steroid receptor coactivator 1 (SRC-1) and CBP-p300, and nuclear receptors, as demonstrated by the glutathione S-transferase pull-down assays and the yeast two-hybrid tests. The ASC-1 binding sites involve the hinge domain but not the C-terminal AF2 core domain of nuclear receptors. Nonetheless, ASC-1 appears to require the AF2-dependent factors to function (i.e., CBP-p300 and SRC-1), as suggested by the ability of ASC-1 to coactivate nuclear receptors, either alone or in cooperation with SRC-1 and p300, as well as its inability to coactivate a mutant receptor lacking the AF2 core domain. By using indirect immunofluorescence, we further show that ASC-1, a nuclear protein, is localized to the cytoplasm under conditions of serum deprivation but is retained in the nucleus when it is serum starved in the presence of ligand or coexpressed CBP or SRC-1. These results suggest that ASC-1 is a novel coactivator molecule of nuclear receptors which functions in conjunction with CBP-p300 and SRC-1 and may play an important role in establishing distinct coactivator complexes under different cellular conditions.

Activation of the promoter of the orphan receptor SHP by orphan receptors that bind DNA as monomers

Small heterodimer partner (SHP) is an orphan nuclear receptor that lacks a conventional DNA binding domain. It interacts with several other members of the nuclear receptor superfamily and inhibits receptor transactivation. In order to characterize the regulation of SHP expression, a number of receptors and other transcription factors were tested for effects on the SHP promoter. Among these, the orphan receptor steroidogenic factor-1 (SF-1) was found to potently transactivate the SHP promoter. Detailed footprinting studies show that the SHP promoter contains at least five SF-1 binding sites, and mutagenesis studies demonstrate each of the three strongest binding sites is required for SF-1 transactivation. SHP is coexpressed with SF-1 in adrenal glands, but is also expressed in tissues that lack SF-1, including liver. However, liver expresses a close relative of SF-1, the orphan fetoprotein transcription factor (FTF), and FTF can also transactivate the SHP promoter. These results suggest that alterations in the levels or activities of SF-1 or FTF could modulate SHP expression in appropriate tissues and thereby affect a variety of receptor dependent signaling pathways.

Bile acids: natural ligands for an orphan nuclear receptor

Bile acids regulate the transcription of genes that control cholesterol homeostasis through molecular mechanisms that are poorly understood. Physiological concentrations of free and conjugated chenodeoxycholic acid, lithocholic acid, and deoxycholic acid activated the farnesoid X receptor (FXR; NR1H4), an orphan nuclear receptor. As ligands, these bile acids and their conjugates modulated interaction of FXR with a peptide derived from steroid receptor coactivator 1. These results provide evidence for a nuclear bile acid signaling pathway that may regulate cholesterol homeostasis.

Linkage of the nuclear hormone receptor genes NR1D2, THRB, and RARB: evidence for an ancient, large-scale duplication

The THRA gene encoding thyroid hormone receptor alpha shares an unusual partial overlap with the NR1D1 gene encoding the orphan receptor Rev-ErbAalpha. Though THRA and NR1D1 have close relatives in THRB and NR1D2, which encode TRbeta and Rev-ErbAbeta, these beta isoforms do not share an analogous overlap. Here we report that the human THRB and NR1D2 genes are separated by approximately 1 Mb on chromosome 3 and that these two genes are also linked to the RARB gene, which encodes retinoic acid receptor beta. Since previous results indicate that the THRA/NR1D1 locus is also linked to the RARA gene, these results suggest that the two receptor gene clusters were generated by a single large-scale duplication.

Examining the relationship between gender and drug-using behaviors in adolescents: the use of diagnostic assessments and biochemical analyses of urine samples

The present study examined the relationship between gender and drug-use among adolescents using diagnostic assessments and biochemical analyses of urine samples. The data were collected in the context of a referral and assessment program for adolescents suspected of using drugs, using the Adolescent Substance Battery [1]. A six-month random sample of 20 percent of adolescents assessed for drug use were targeted for biochemical assay. Compliance for urine delivery was relatively high at 91 percent. Urine samples were quantitatively screened for pharmaceuticals using a standard thin-layer chromatography (TLC) technique [2]. Statistical significance was found in the relationship between gender and marijuana use (p < .05). This study confirms that gender and drug-using behaviors among adolescents need additional research and evaluation.

Androstane metabolites bind to and deactivate the nuclear receptor CAR-beta

The orphan receptor CAR-beta binds DNA as a heterodimer with the retinoid-X receptor and activates gene transcription in a constitutive manner. Here we show that, in contrast to the classical nuclear receptors, the constitutive activity of CAR-beta results from a ligand-independent recruitment of transcriptional co-activators. While searching for potential ligands of CAR-beta, we found that the steroids androstanol and androstenol inhibit the constitutive activity of CAR-beta. This effect is stereospecific: only 3alpha-hydroxy, 5alpha-reduced androstanes are active. These androstanes do not interfere with heterodimerization or DNA binding of CAR-beta; instead, they promote co-activator release from the ligand-binding domain. These androstane ligands are examples of naturally occurring inverse agonists that reverse transcriptional activation by nuclear receptors. CAR-beta (constitutive androstane receptor-beta), therefore, defines an unanticipated steroidal signalling pathway that functions in a manner opposite to that of the conventional nuclear receptor pathways.

Inhibition of estrogen receptor action by the orphan receptor SHP (short heterodimer partner)

SHP (short heterodimer partner) is an unusual orphan receptor that lacks a conventional DNA-binding domain. Previous results have shown that it interacts with several other nuclear hormone receptors, including the retinoid and thyroid hormone receptors, and inhibits their ligand-dependent transcriptional activation. Here we show that SHP also interacts with estrogen receptors and inhibits their function. In mammalian and yeast two-hybrid systems as well as glutathione-S-transferase pull-down assays, SHP interacts specifically with estrogen receptor-alpha (ERalpha) in an agonist-dependent manner. The same assay systems using various deletion mutants of SHP map the interaction domain with ERalpha to the same SHP sequences required for interaction with the nonsteroid hormone receptors such as retinoid X receptor and thyroid hormone receptor. In transient cotransfection assays, SHP inhibits estradiol -dependent activation by ERalpha by about 5-fold. In contrast, SHP interacts with ERbeta independent of ligand and reduces its ability to activate transcription by only 50%. These data suggest that SHP functions to regulate estrogen signaling through a direct interaction with ERalpha.

Structure and expression of the orphan nuclear receptor SHP gene

To determine the organization of the orphan nuclear receptor SHP gene (Seol, W., Choi, H.-S., and Moore, D.D. (1996) Science 272, 1336-1339), genomic clones were isolated from human and mouse genomic libraries. The SHP gene was composed of two exons interrupted by a single intron spanning approximately 1.8 kilobases in human and 1.2 kilobases in mouse. Genomic Southern blot analysis and fluorescence in situ hybridization of human metaphase chromosomes indicated that the SHP gene is located at the human chromosome 1p36.1 subband. The 5'-flanking regions of human and mouse SHP genes were highly conserved, showing 77% homology in the region of approximately 600 nucleotides upstream from the transcription start site. Primer extension analysis was carried out to determine the transcription start site of human SHP to 32 nucleotides downstream of a potential TATA box. The human SHP gene was specifically expressed in fetal liver, fetal adrenal gland, adult spleen, and adult small intestine. As expected from this expression pattern, the activity of the mouse SHP promoter measured by transient transfection was significantly higher in the adrenal-derived Y1 cells than HeLa cells.

Alternative splicing variants of IkappaB beta establish differential NF-kappaB signal responsiveness in human cells

To release transcription factor NF-kappaB into the nucleus, the mammalian IkappaB molecules IkappaB alpha and IkappaB beta are inactivated by phosphorylation and proteolytic degradation. Both proteins contain conserved signal-responsive phosphorylation sites and have conserved ankyrin repeats. To confer specific physiological functions to members of the NF-kappaB/Rel family, the different IkappaB molecules could vary in their specific NF-kappaB/Rel factor binding activities and could respond differently to activation signals. We have demonstrated that both mechanisms apply to differential regulation of NF-kappaB function by IkappaB beta relative to IkappaB alpha. Via alternative RNA processing, human IkappaB beta gives rise to different protein isoforms. IkappaB beta1 and IkappaB beta2, the major forms in human cells, differ in their carboxy-terminal PEST sequences. IkappaB beta2 is the most abundant species in a number of human cell lines tested, whereas IkappaB beta1 is the only form detected in murine cells. These isoforms are indistinguishable in their binding preferences to cellular NF-kappaB/Rel homo- and heterodimers, which are distinct from those of IkappaB alpha, and both are constitutively phosphorylated. In unstimulated B cells, however, IkappaB beta1, but not IkappaB beta2, is found in the nucleus. Furthermore, the two forms differ markedly in their efficiency of proteolytic degradation after stimulation with several inducing agents tested. While IkappaB beta1 is nearly as responsive as IkappaB alpha, indicative of a shared activation mechanism, IkappaB beta2 is only weakly degraded and often not responsive at all. Alternative splicing of the IkappaB beta pre-mRNA may thus provide a means to selectively control the amount of IkappaB beta-bound NF-kappaB heteromers to be released under NF-kappaB stimulating conditions.

IkappaBbeta interacts with the retinoid X receptor and inhibits retinoid-dependent transactivation in lipopolysaccharide-treated cells

To elucidate the molecular action of the NFkappaB inhibitor IkappaBbeta, we isolated a number of IkappaBbeta interactors using the yeast two-hybrid system. These include the retinoid X receptor (RXR), whose interaction with IkappaBbeta is significantly stimulated by the RXR ligand 9-cis-retinoic acid, as shown in the yeast system as well as the glutathione S-transferase pull down assays. RXR is a nuclear protein, whereas IkappaBbeta accumulates in the nucleus only in cells stimulated with lipopolysaccharide or other inducers that result in prolonged activation of NFkappaB. Consistent with this, cotransfection with IkappaBbeta specifically repressed the 9-cis-RA-induced transcriptional activities of RXR in an lipopolysaccharide-dependent manner. These results suggest a novel IkappaBbeta-mediated antagonism between the signaling pathways of NFkappaB and RXR.

The Nuclear Receptor Resource: a growing family

Last year, the original Glucocorticoid Receptor Resource was expanded into a comprehensive project: the Nuclear Receptor Resource (NRR, http:// nrr.georgetown.edu/nrr/nrr.html ). The NRR has since been offering comprehensive information on nuclear receptor structure and function, as well as general facts of interest to the scientific community on meetings, funding and employment opportunities. The project now includes individual resources as part of a network which integrates information on glucocorticoid, androgen, mineralocorticoid, thyroid hormone, Vitamin D and peroxisome-proliferator activated receptors. Many investigators have joined the NRR network by filling the Who is who? form available in the NRR home page. This has facilitated communication among scientists in the field and dissemination of data nor otherwise published. Because several investigators have contacted NRR authors over the past few months asking for advice and materials for educational purposes, we have recently decided to include in our project an educational resource on nuclear receptors termed the 'Graphics Library'. The input and suggestions of NRR users do shape the future direction of the project, so we encourage user to give us feedback.

Novel receptor interaction and repression domains in the orphan receptor SHP

SHP (short heterodimer partner) is a novel orphan receptor that lacks a conventional DNA binding domain and interacts with other members of the nuclear hormone receptor superfamily. We have characterized the SHP sequences required for interaction with other superfamily members, and have defined an SHP repressor domain. In the mammalian two-hybrid system, a fusion of full-length SHP to the GAL4 DNA binding domain shows 9-cis-retinoic acid-dependent interaction with a VP16-retinoid X receptor alpha (RXR alpha) fusion. By deletion analysis, sequences required for this RXR interaction map to the central portion of SHP (amino acids 92 to 148). The same region is required for interaction with RXR in vitro and in the yeast two-hybrid system, and results from the yeast system suggest that the same SHP sequences are required for interaction with other members of the nuclear hormone receptor superfamily such as thyroid hormone receptor and retinoic acid receptor. In mammalian cells, a GAL4-SHP fusion protein shows about 10-fold-decreased transcriptional activation relative to GAL4 alone, and fusion of SHP to the C terminus of a GAL4-VP16 fusion to generate a triple chimera also results in a strong decrease in transactivation activity. Sequences required for this repressor function were mapped to the C terminus of SHP. This region is distinct from that required for corepressor interaction by other members of the nuclear hormone receptor superfamily, and SHP did not interact with N-CoR in either the yeast or mammalian two-hybrid system. Together, these results identify novel receptor interaction and repressor domains in SHP and suggest two distinct mechanisms for inhibition of receptor signaling pathways by SHP.

Differential transactivation by two isoforms of the orphan nuclear hormone receptor CAR

We have identified a new murine orphan member of the nuclear hormone receptor superfamily, termed mCAR, that is closely related to the previously described human orphan MB67, referred to here as hCAR. Like hCAR, mCAR expression is highest in liver. In addition to the most abundant mCAR1 isoform, the mCAR gene expresses a truncated mCAR2 variant that is missing the C-terminal portion of the ligand binding/dimerization domain. The mCAR gene has 8 introns, and this mCAR2 variant is generated by a splicing event that skips the 8th exon. mCAR1, like hCAR, binds as a heterodimer with the retinoid X receptor to the retinoic acid response element from the promoter of the retinoic acid receptor beta2 isoform. Consistent with its lack of a critical heterodimerization interface, the mCAR2 variant does not bind this site. Both mCAR1 and hCAR are apparently constitutive transcriptional activators. This activity is dependent on the presence of the conserved C-terminal AF-2 transcriptional activation motif. As expected from its inability to bind DNA, the mCAR2 variant neither transactivates by itself nor inhibits transactivation by hCAR or mCAR1.

Activation of the orphan receptor RIP14 by retinoids

Retinoids are crucial regulators of a wide variety of processes in both developing and adult animals. These effects are thought to be mediated by the retinoic acid (RA) receptors and the retinoid X receptors (RXRs). We have identified an additional retinoid-activated receptor that is neither a retinoic acid receptors nor an RXR. RXR-interacting protein 14 (RIP14), a recently described orphan member of the nuclear receptor superfamily, can be activated by either all-trans-RA (tRA) or the synthetic retinoid TTNPB [[E]-4-[2-(5, 6, 7, 8-tetrahydro-5, 5, 8, 8-tetramethyl-2-naphthalenyl)propen-1-yl]benzoic acid].RIP14 binds to DNA as a heterodimer with RXR. In the presence of either tRA or TTNPB, the addition of 9-cis-RA or the RXR-specific agonist LG1069 [4-[1-(3, 5, 5, 8, 8-pentamethyl-5, 6, 7, 8-tertrahydro-2-naphthyl)ethenyl]benzoic acid] results in additional activation. Mutations of the ligand-dependent transcriptional activation functions indicate that TTNPB activates the RIP14 component of the RIP14-RXR heterodimer, that 9-cis-RA and LG1069 activate RXR, and that tRA activates via both RIP14 and RXR. Despite the very effective activation of RIP14 by tRA or TTNPB, relatively high concentrations of these compounds are required, and no evidence for direct binding of either compound was obtained using several approaches. These results suggest that RIP14 is the receptor for an as-yet-unidentified retinoid metabolite.

Direct modulation of simian virus 40 late gene expression by thyroid hormone and its receptor

Transcription of the late genes of simian virus 40 (SV40) is repressed during the early phase of the lytic cycle of infection of primate cells by the binding of cellular factors, called IBP-s, to the SV40 late promoter; repression is relieved after the onset of viral DNA replication by titration of these repressors (S. R. Wiley, R. J. Kraus, F. R. Zuo, E. E. Murray, K. Loritz, and J. E. Mertz, Genes Dev. 7:2206-2219, 1993). Recently, we showed that IBP-s consists of several members of the steroid/thyroid hormone receptor superfamily (F. Zuo and J. E. Mertz, Proc. Natl. Acad. Sci. USA 92:8586-8590, 1995). Here, we show that the thyroid hormone receptor TRalpha1, in combination with retinoid X receptor alpha (RXRalpha), is specifically bound at the transcriptional initiation site of the major late promoter of SV40. This binding repressed transcription from the SV40 late promoter by preventing the formation of pre-initiation complexes. Addition of the thyroid hormone 3,5,3'-L-triiodothyronine (T3) resulted in reversal of this repression in cotransfected CV-1 cells. Interestingly, repression did not occur when this thyroid response element (TRE) was translocated to 50 bp upstream of the major late initiation site. Binding of TRalpha1/RXRalpha heterodimers to this TRE induced bending of the promoter DNA. We conclude that hormones and their receptors can directly affect the expression of SV40, probably by affecting protein-protein and protein-DNA interactions involved in the formation of functional preinitiation complexes.

The Nuclear Receptor Resource Project

We have expanded the original Glucocorticoid Receptor Resource (GRR) database to include several individual resources as part of a larger project called the Nuclear Receptor Resource (NRR). In addition to the GRR, the NRR currently features the Thyroid Hormone Receptor Resource, the Androgen Receptor Resource, the Mineralocorticoid Receptor Resource, the Vitamin D Receptor Resource, and the Steroid Receptor Associated Proteins Resource. The goal of the NRR project is to provide a comprehensive resource for information on the nuclear receptor superfamily, and to provide a forum for the dissemination and discussion of both published and unpublished material on these proteins. Although the individual resources are managed from different servers, all the files are integrated and can be accessed through the project's Home Page, housed at http://nrr. georgetown.edu/nrr.html. In the near future, we hope to expand the project to contain information on other nuclear receptors and to better our electronic publication system. To accomplish this, we encourage the involvement of nuclear receptor investigators in the NRR.

Two receptor interacting domains in the nuclear hormone receptor corepressor RIP13/N-CoR

The thyroid hormone receptor (TR) and the retinoic acid receptor (RAR) act as transcriptional repressors when they are not occupied by their cognate ligands. This repressor function is mediated by proteins called corepressors. One of the nuclear hormone receptor corepressors, N-CoR, was originally isolated as a retinoid X receptor-interacting protein called RIP13. We have isolated a new potential variant of RIP13/N-CoR that is missing previously described transcriptional repressor domains but is similar in structure to the related corepressor termed SMRT or TRAC-2. Detailed analysis of the interaction with TR and RAR demonstrates that RIP13/N-CoR contains a new receptor interaction domain, termed ID-II, in addition to the previously described domain, referred to here as ID-I. Both ID-I and ID-II are capable of interacting independently with either TR or RAR, as assessed by the yeast two-hybrid system, by a mammalian two-hybrid system, or by direct in vitro binding. Results with all three approaches confirm that RIP13/N-CoR also interacts with retinoid X receptor, but this interaction is weaker than that with TR or RAR. Together, these results demonstrate that RIP13/N-CoR can interact with several different nuclear hormone receptors via two separate receptor interaction domains. Differences between the interactions observed in the different systems suggest that corepressor function may be modified by additional factors present in various cell types.

An orphan nuclear hormone receptor that lacks a DNA binding domain and heterodimerizes with other receptors

SHP is an orphan member of the nuclear hormone receptor superfamily that contains the dimerization and ligand-binding domain found in other family members but lacks the conserved DNA binding domain. In the yeast two-hybrid system, SHP interacted with several conventional and orphan members of the receptor superfamily, including retinoid receptors, the thyroid hormone receptor, and the orphan receptor MB67. SHP also interacted directly with these receptors in vitro. In mammalian cells, SHP specifically inhibited transactivation by the superfamily members with which it interacted. These results suggest that SHP functions as a negative regulator of receptor-dependent signaling pathways.

A component of the 26S proteasome binds on orphan member of the nuclear hormone receptor superfamily

The 26S proteasome complex plays a general role in turnover of both short and long lived proteins by specifically degrading ubiquitinated proteins. Recent evidence suggests that this large protease has more specific functions in a number of important cellular processes, ranging from activation of the transcription factor NFkB and antigen processing to transit through mitosis. We have identified a component of the 26S proteasome that interacts specifically with MB67, an orphan member of the nuclear hormone receptor superfamily. MIP224 (MB67 interacting protein) was isolated using the yeast two hybrid system and is apparently identical to the human 26S proteasome component TBP7. MIP224/TBP7 is one of several proteasomal proteins that share a strongly conserved ATPase domain (CAD) which is also present in a rapidly expanding superfamily of proteins with diverse functions. In yeast, MIP224 interacts specifically with MB67 and another closely related orphan receptor, but does not interact with several other receptor superfamily members tested. In mammalian cells, coexpression of MIP224 inhibits transactivation by MB67. MIP224 also interacts in yeast with other CAD proteins, including MSS1, which is proteasomal, and TRIP1, which is associated with transcriptional activation. This interaction of a proteasomal protein with a transcriptional protein suggests a previously unexpected link between the processes of protein degradation and transcriptional regulation.

Early prevention of alcohol and other drug use among adolescents

Among a variety of methods to prevent drug use among adolescents, school-community based prevention and intervention programs are prevalent. The impact of such programs will be compromised, however, if drug use among adolescents is impacted by forces apart from the impact of school-community prevention and intervention, such as the function of the family. On the other hand, prevention and intervention programs can have a powerful impact if teenage drug use is responded to through early intervention. The purpose of this study was to review a sample of students referred for drug assessments to determine how early intervention should occur and how involved high school and middle school students are with alcohol and other drugs.

Characterization and mapping of the Xiphophorus maculatus (Teleostei: Poeciliidae) RPS15 gene

We have determined the nucleotide sequence and gene map location of the Xiphophorus maculatus homologue of RPS15 (ribosomal protein S15, alias RIG). The Xiphophorus RPS15 cDNA encodes 145 amino acids, which show 94% identity compared to deduced mammalian and avian RPS15 amino acid sequences. At the nucleotide level, 84% sequence identity is maintained between the fish and human gene, while homologous amphibian and avian sequences show about 80% nucleotide identity compared to the Xiphophorus sequence. Nucleotide identity substantially decreases when the fish gene is compared to Arabidopsis S15 (64%) and yeast S21 (55%) genes. Genetic linkage analysis of an RPS15 restriction fragment length polymorphism in backcross hybrids generated from the cross X. helleri x (X. maculatus Jp 163 B x X. helleri) demonstrated linkage of Xiphophorus RPS15 to the EGFR, UMPK and YES loci in Xiphophorus Linkage Group VI.

Interaction of thyroid-hormone receptor with a conserved transcriptional mediator

The thyroid-hormone receptors are hormone-dependent transcription factors that control expression of many target genes. This regulation is presumably a consequence of hormone-dependent contacts between the receptors and the basal transcription machinery. We used the yeast two-hybrid system to identify a candidate human transcriptional mediator that interacts with both the thyroid-hormone receptor and the retinoid-X receptor in a ligand-dependent fashion. This protein, Trip1 (for thyroid-hormone-receptor interacting protein), shares striking sequence conservation with the yeast transcriptional mediator Sug1 (refs 6, 7). Here we show that Trip1 can functionally substitute for Sug1 in yeast, and that both proteins interact in vitro with the thyroid-hormone receptor, and with the transcriptional activation domains of yeast GAL4 and of herpes virus VP16.

Cyclopamine, a steroidal alkaloid, disrupts development of cranial neural crest cells in Xenopus

Cyclopamine is a steroidal alkaloid which causes limb and craniofacial defects in many vertebrate species. We have used Xenopus laevis as a model system to characterize the defects caused by cyclopamine at the cellular level. The most dramatic consequence of cyclopamine treatment in the Xenopus embryo is a defect in formation of craniofacial cartilage. Much of this cartilage is absent in treated animals. As in avian and mammalian species, Xenopus craniofacial cartilage is derived primarily from cells of the cranial neural crest. Grafting experiments show that development of the cartilaginous derivatives of the cranial neural crest is impaired after cyclopamine treatment, and this is at least partially due to a direct effect on presumptive crest cells. A culture system was used to determine the cellular response to the drug. Cyclopamine did not block the initial emigration of cells from a neural plate explant. However, cell death is seen in treated cultures after 4 days. Trunk neural crest cells and transformed cell lines are resistant to cyclopamine. We therefore conclude that cyclopamine specifically causes death of cranial neural crest cells and that lethality is likely to account for the teratogenic effects of this compound.

Two classes of proteins dependent on either the presence or absence of thyroid hormone for interaction with the thyroid hormone receptor

The thyroid hormone (T3) receptors (TRs) are hormone-dependent transcription factors that regulate expression of a variety of specific target genes. To help elucidate the mechanisms that underlie this transcriptional regulation and other potential TR activities, we used the yeast interaction trap to isolate clones encoding proteins that specifically interact with the ligand binding domain of the rat TR beta. Several such proteins, called Trips (TR-interacting proteins), were isolated from independent selections carried out either in the presence or absence of T3. Surprisingly, all of the Trips were dependent on hormone for interaction with the TR, with some interacting only when T3 is present and others only when it is absent. Nearly all of the Trips also show similar ligand-dependent interaction with the retinoid X receptor (RXR), but none interact with the glucocorticoid receptor under any conditions. The sequences of three of the Trips predict specific functional roles: one is an apparent human homolog of a yeast transcriptional coactivator, one is a new member of a class of nonhistone chromosomal proteins, and one contains a conserved domain associated with ubiquitination of specific target proteins. Consistent with the pleiotropic effects of TR and RXR, several other Trips show significant amino acid sequence similarity with proteins involved in various regulatory pathways. The inherent transcriptional activity of the Trips was tested in yeast, and a chimeric protein consisting of a fusion of Trip4 to the bacterial LexA repressor protein is a relatively strong transcriptional activator. Similar LexA fusions to Trip9 and Trip10 had no transcriptional activity on their own but, when coexpressed with both TR and RXR, conferred T3-dependent activation to a reporter gene controlled by LexA binding sites. We suggest that this indirect T3 response provides a novel mechanism for hormonal activation of gene expression, and that studies of the Trips will provide important insights into the specific mechanisms of action of TRs and other receptors.