Mediation of Sonic hedgehog-induced expression of COUP-TFII by a protein phosphatase

A Sonic hedgehog (Shh) response element was identified in the chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) promoter that binds to a factor distinct from Gli, a gene known to mediate Shh signaling. Although this binding activity is specifically stimulated by Shh-N (amino-terminal signaling domain), it can also be unmasked with protein phosphatase treatment in the mouse cell line P19, and induction by Shh-N can be blocked by phosphatase inhibitors. Thus, Shh-N signaling may result in dephosphorylation of a target factor that is required for activation of COUP-TFII-, Islet1-, and Gli response element-dependent gene expression. This finding identifies another step in the Shh-N signaling pathway.

Alcohol problems and long-term psychosocial outcome in Chinese patients with bipolar disorder

BACKGROUND

A high comorbidity of alcohol use disorders among Western bipolar patients is recognized and worsens the outcome of bipolar illness. In view of lower prevalence of alcohol use disorders in some Asian groups, we attempted to investigate the alcohol problems among Chinese bipolar patients in Taiwan.

METHODS

The clinical data of bipolar patients (DSM-III-R) having been followed-up naturally for at least 15 years were obtained by a combination of chart reviews and interviews with patients and family members.

RESULTS

Based on a retrospective chart review of 158 patients, 8.2% of them were found to have alcohol problems. The lifetime prevalence of alcohol abuse was 6.9%, and of alcohol dependence 3.0% among 101 subjects accepting interview. According to the Global Assessment of Functioning Scale (APA, 1994) nearly one-third of them were clearly dysfunctional.

LIMITATION

As subjects had a greater mean age, the age-related effects probably worsened the psychosocial outcome and reduced the incidence of new substance abuse.

CONCLUSION

Chinese bipolar patients, despite a lower comorbidity of alcohol use disorders, do not have a more favorable long-term psychosocial outcome (marriage, work, and social adjustment) than Western patients.

Regulation of androgen-dependent prostatic cancer cell growth: androgen regulation of CDK2, CDK4, and CKI p16 genes

Growth of prostatic epithelial cells is androgen-dependent; however, the mechanism of androgen action on cell growth is not well defined. We investigated whether androgen-dependent prostatic epithelial cell growth is mediated by androgen regulation of expression of genes controlling cell cycle progression. For this purpose, we used an androgen-dependent prostatic cancer cell line, LNCaP-FGC, as an in vitro model. We found that expression of CDK2 and CDK4 genes were up-regulated within hours of androgen treatment as detected in Northern and Western blot analyses. Kinase assay also confirmed that there was increased CDK2 kinase activity upon androgen stimulation. Moreover, androgen down-regulated expression of the cyclin-dependent kinase inhibitor p16 (MTS1, CDKN2) gene. The overall effects of these androgen actions result in an increased cyclin-dependent kinase activity and stimulation of the cell to enter S phase of the cell cycle, thereby enhancing cell proliferation. In contrast, an androgen-independent PC-3 cell line lost its response to androgen stimulation, and higher basal levels of CDK2, CDK4, and p16 genes were constitutively expressed in PC-3 cells. Collectively, these data suggest a possible signaling pathway of androgen in stimulating cell growth. These results also imply that in androgen-dependent prostate cancer, increased androgen receptor (AR) activity, resulting from AR gain-of-function mutations, AR gene amplification, or AR gene overexpression, malignantly stimulates proliferation of prostatic epithelial cells and constitutes one possible mechanism of androgen-dependent tumorigenesis.

Identification of a novel sonic hedgehog response element in the chicken ovalbumin upstream promoter-transcription factor II promoter

Sonic hedgehog (Shh) is a secreted morphogen that regulates dorso-ventral patterning within the neural tube during embryonic development. It is well established that Shh can induce motor-neuron differentiation that coincides with the appearance of specific motor-neuron markers including chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) and Isl1. However, the mechanism of Shh-induced signaling pathway in vertebrates is not clearly defined. In this report we have identified COUP-TFII as a target gene for Shh. In addition we have used a 1.6-kb region of the COUP-TFII promoter to identify a target element that mediates the Shh-induced activity. Extensive deletions introduced within this region have further enabled us to identify a novel sonic hedgehog response element (ShhRE) in the COUP-TFII promoter. Point mutations introduced within the ShhRE reveal some key nucleotides that are essential for protein(s)-binding activity. Finally, the ShhRE is capable of functioning as a true enhancer element and can mediate Shh-induced transactivation of reporter gene via a heterologous promoter.

Steroid receptor coactivator-1 is a histone acetyltransferase

Steroid receptors and coactivator proteins are thought to stimulate gene expression by facilitating the assembly of basal transcription factors into a stable preinitiation complex. What is not clear, however, is how these transcription factors gain access to transcriptionally repressed chromatin to modulate the transactivation of specific gene networks in vivo. The available evidence indicates that acetylation of chromatin in vivo is coupled to transcription and that specific histone acetyltransferases (HATs) target histones bound to DNA and overcome the inhibitory effect of chromatin on gene expression. The steroid-receptor coactivator SRC-1 is a coactivator for many members of the steroid-hormone receptor superfamily of ligand-inducible transcription factors. Here we show that SRC-1 possesses intrinsic histone acetyltransferase activity and that it also interacts with another HAT, p300/CBP-associated factor (PCAF). The HAT activity of SRC-1 maps to its carboxy-terminal region and is primarily specific for histones H3 and H4. Acetylation by SRC-1 and PCAF of histones bound at specific promoters may result from ligand binding to steroid receptors and could be a mechanism by which the activation functions of steroid receptors and associated coactivators enhance formation of a stable preinitiation complex, thereby increasing transcription of specific genes from transcriptionally repressed chromatin templates.

Identification of a novel sonic hedgehog response element in the chicken ovalbumin upstream promoter-transcription factor II promoter

Sonic hedgehog (Shh) is a secreted morphogen that regulates dorso-ventral patterning within the neural tube during embryonic development. It is well established that Shh can induce motor-neuron differentiation that coincides with the appearance of specific motor-neuron markers including chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) and Isl1. However, the mechanism of Shh-induced signaling pathway in vertebrates is not clearly defined. In this report we have identified COUP-TFII as a target gene for Shh. In addition we have used a 1.6-kb region of the COUP-TFII promoter to identify a target element that mediates the Shh-induced activity. Extensive deletions introduced within this region have further enabled us to identify a novel sonic hedgehog response element (ShhRE) in the COUP-TFII promoter. Point mutations introduced within the ShhRE reveal some key nucleotides that are essential for protein(s)-binding activity. Finally, the ShhRE is capable of functioning as a true enhancer element and can mediate Shh-induced transactivation of reporter gene via a heterologous promoter.

Null mutation of mCOUP-TFI results in defects in morphogenesis of the glossopharyngeal ganglion, axonal projection, and arborization

The COUP-TFs are orphan members of the steroid/thyroid hormone receptor superfamily. Multiple COUP-TF members have been cloned and they share a high degree of sequence homology between species as divergent as Drosophila and humans, suggesting a conservation of function through evolution. The COUP-TFs are highly expressed in the developing nervous systems of several species examined, indicating their possible involvement in neuronal development and differentiation. In the mouse, there are two very homologous COUP-TF genes (I and II) and their expression patterns overlap extensively. To study the physiological function of mCOUP-TFI, a gene-targeting approach was undertaken. We report here that mCOUP-TFI null animals die perinataly. Mutant embryos display an altered morphogenesis of the ninth cranial ganglion and nerve. The aberrant formation of the ninth ganglion is most possibly attributable to extra cell death in the neuronal precursor cell population. In addition, at midgestation, aberrant nerve projection and arborization were oberved in several other regions of mutant embryos. These results indicate that mCOUP-TFI is required for proper fetal development and is essential for postnatal development. Furthermore, mCOUP-TFI possesses vital physiological functions that are distinct from mCOUP-TFII despite of their high degree of homology and extensive overlapping expression patterns.

Steroid receptor induction of gene transcription: a two-step model

Coactivators, such as steroid receptor coactivator 1 (SRC-1A) and CREB (cAMP response element binding protein)-binding protein (CBP), are required for efficient steroid receptor transactivation. Using an in vitro transcription assay, we found that progesterone receptor (PR)-driven transcription is inhibited by a dominant negative PR ligand-binding domain-interacting region of SRC-1A, indicating that SRC-1A is required for actual transcriptional processes. In addition, these coactivators also possess intrinsic histone acetyltransferase (HAT) activity and bind to each other and another HAT, p300/CBP-associated factor. Here we show that the human PR also interacts with p300/CBP-associated factor in vitro. Recruitment of multiple HATs to target promoters suggests an important role for chromatin remodeling in transcriptional activation of genes by steroid receptors. In transient transfection assays, we found that addition of a histone deacetylase inhibitor, trichostatin A, strongly potentiated PR-driven transcription. In contrast, directing histone deacetylase-1 (HD1) to a promoter using the GAL4 DNA binding domain inhibited transcription. Furthermore, PR transactivation was repressed by recruiting HD1 into the PR-DNA complex by fusing HD1 to a PR ligand-binding domain-interacting portion of SRC-1. Collectively, these results suggest that targeted histone acetylation by recruited HAT cofactors and histone deacetylation are important factors affecting PR transactivation. Recruitment of coactivators and HATs by the liganded PR in vivo may result in (i) remodeling of transcriptionally repressed chromatin to facilitate assembly and (ii) enhanced stabilization of the preinitiation complex by the activation functions of coactivators and the liganded PR itself.

Effects of occupational and nonoccupational factors on liver function tests in workers exposed to solvent mixtures

A total of 368 workers from six paint-manufacturing factories participated in this study. The workers were classified according to type of exposure: direct, intermittent, and no exposure. The workers' liver-function tests were influenced greatly by gender, hepatitis B, alcohol consumption, and body mass index. Both the serum concentration and the odds of abnormality of total serum bile acids were elevated among the directly exposed group. The authors concluded that analysis of covariance should take into account occupational and nonoccupational factors on liver-function tests to avoid any errors. Total serum bile acids also indicated liver dysfunction from solvent exposure.

Microglia in the pineal gland of the neonatal rat: characterization and effects on pinealocyte neurite length and serotonin content

Microglia in the pineal gland of 1-day-old Sprague-Dawley rats were examined by OX-42 immunocytochemistry and DiI-acetylated-LDL uptake in pineal cell suspension and were found to comprise 3-5% of the total cells in the pineal gland of the neonates. In order to investigate the effects of microglia on pinealocyte structure and function, microglia-depleted and microglia-enriched pineal cell cultures were generated from 1-day-old neonate by fluorescence activated cell sorting (FACS). After 7 days of culture, tissues were processed for either immunocytochemistry for pinealocyte S-antigen and serotonin or high performance liquid chromatography to measure serotonin. Morphometric analysis of immunoreacted cells revealed that pinealocyte neurite length was enhanced in microglia-depleted cultures and was inhibited in a microglia-enriched environment (ANOVA, P < 0.001). Serotonin content of pineal cultures decreased in microglia-depleted cultures and was elevated in microglia-enriched cultures (ANOVA, P < 0.001) without any significant change in pinealocyte numbers. These findings are consistent with a working hypothesis that microglia function to mediate neuroendocrine-immune interactions of the gland.

Gene silencing by chicken ovalbumin upstream promoter-transcription factor I (COUP-TFI) is mediated by transcriptional corepressors, nuclear receptor-corepressor (N-CoR) and silencing mediator for retinoic acid receptor and thyroid hormone receptor (SMRT)

Chicken ovalbumin upstream promoter-transcription factors (COUP-TFs) are orphan receptors that belong to the steroid/thyroid hormone receptor (TR) superfamily and can repress the transcriptional activity of several target genes; however, the precise mechanism of this repression is unknown. Transfection of a Gal4 DNA-binding domain fused to the putative ligand-binding domain of COUP-TFI (Gal4-COUP-TFI) significantly represses the basal transcriptional activity of a reporter gene containing Gal4-binding sites. Cotransfection of COUP-TFI can relieve the Gal4-COUP-TFI repression in a dose-dependent manner. In contrast, COUP-TFI delta35, which lacks the repressor domain (the C-terminal 35 amino acids), fails to relieve this repression. This finding suggests that the repressor domain of COUP-TFI may squelch a limiting amount of corepressor in HeLa cells. In addition, increasing concentrations of TRbeta also can relieve the COUP-TFI repression in a hormone-sensitive manner. Similarly, overexpression of increasing concentration of COUP-TFI, but not COUP-TFI delta35, can squelch the silencing activity of the unliganded TRbeta. Collectively, these results indicate that COUP-TFI and TRbeta share a common corepressor(s) for their silencing activity. To determine which corepressor is involved in the COUP-TF-silencing activity, we used a yeast two-hybrid and in vitro GST pull-down assays to demonstrate that COUP-TFI can interact with the fragment of N-CoR (nuclear receptor-corepressor) encoding amino acids 921-2453 and the fragments of SMRT (silencing mediator for retinoic acid receptor and TR) encoding amino acids 29-564 and 565-1289, respectively. Interestingly, the fragment of SMRT encoding amino acids 1192-1495, which strongly interacts with TRbeta, interacts very weakly with COUP-TFI. Furthermore, overexpression of N-CoR or SMRT potentiates the silencing activity of COUP-TFI and can relieve the COUP-TFI-mediated squelching of Gal4-COUP-TFI activity. Therefore, our studies indicate that N-CoR and SMRT act as corepressors for the COUP-TFI silencing activity.

Positive and negative regulation of gene expression in eukaryotic cells with an inducible transcriptional regulator

To facilitate the understanding of the complex process of target gene expression and its control, we report a modified inducible system for activation or repression of target gene expression in response to an exogenously administered compound. The main component of this inducible system is a chimeric transcriptional activator (GLVP) consisting of an N-terminal VP16 transcriptional activation domain fused to a yeast GAL4 DNA binding domain and a mutated human progesterone receptor (hPR) ligand binding domain (LBD). This chimeric regulator binds to a target gene containing the 17-mer GAL4 upstream activation sequence (UAS) in the presence of anti-progesterone, RU486. We showed that the combination of two different types of domains (VP16 and poly-glutamine stretch) into one chimeric molecule could result in a further increase in transcriptional activation potency. Through mutational analysis, we modified the original GLVP and generated a more potent version of the RU486 inducible regulator GL914 VPc with a 19 amino acid deletion of the hPR-LBD (delta C19) and a C-terminally located VP16 activation domain. More importantly, this new chimeric regulator can effectively activate target gene expression at a much lower concentration of RU486 (0.01 nM). The concept of RU486 regulatable gene expression is not limited to gene activation. By replacing the VP16 activation domain with a KRAB transcriptional repression domain, we are able to achieve inducible repression of target gene expression. We also present evidence that individual functional domains within a chimeric protein could modulate each other's function depending on their relative positions within the molecule. Using this potent regulator, we demonstrate that inducible nerve growth factor (NGF) secretion into conditioned media can elicit neurite outgrowth in co-cultured PC12 cells. This new versatile inducible system can potentially be used to control target gene expression in a mammalian system in vivo.

Concomitant chemotherapy and radiotherapy for locally advanced nasopharyngeal carcinoma

BACKGROUND

The prognosis of stage III and IV nasopharyngeal carcinoma treated with radiation therapy alone is poor. To improve outcome, concomitant chemotherapy was incorporated into the treatment of locally advanced nasopharyngeal carcinoma.

METHODS AND PATIENTS

Seventy-four patients with locally advanced nasopharyngeal carcinoma were prospectively treated with a combination of concomitant chemotherapy and computerized-tomography-assisted radiotherapy at Koo Foundation Sun Yat-Sen Cancer Center, Taipei, Taiwan, between April 1990 and December 1995. The first 29 patients who had a minimum of 2 years of follow-up were included in this report. Their median interval of follow-up was 42 months. The dose of radiation was 7000 cGy given in 35 fractions. Two courses of chemotherapy, consisting of cisplatin and 5-fluorouracil, were delivered simultaneously with radiotherapy during weeks 1 and 6, and two additional monthly courses were given after radiotherapy. Included in this study were four patients with stage III and 25 patients with stage IV disease.

RESULTS

Toxicities of concomitant radiotherapy and chemotherapy were acceptable and reversible. The locoregional control rate at 50 months was 88.2%, and the disease-free survival rate was 74.6%.

DISCUSSION

Our results demonstrate an improved survival with the addition of computerized tomography treatment planning and concomitant chemotherapy to radiotherapy in the treatment of locally advanced nasopharyngeal carcinoma when compared with data in the current literature. However, a randomized trial comparing computerized-tomography-assisted radiotherapy with and without chemotherapy is necessary to confirm the contribution of chemotherapy.

Ligand-inducible and liver-specific target gene expression in transgenic mice

Transgenic mice have been used as models for tissue-specific gene regulation and to examine the molecular and cellular effects of altered expression of specific gene in disease processes such as tumorigenesis. Because of the deleterious effects of constitutive expression of transgenes, which frequently result in prenatal or postnatal death, only a limited number of disease models have been established in transgenic mice. We report an inducible binary transactivation system that permits the control of transgene expression in a tissue-specific and inducible fashion in mice. In this system, transcription of the target transgene is kept silent until turned on by the administration of an exogenous compound. We also demonstrate that expression level of the target gene can be induced three to four orders of magnitude and can be controlled by the administrated compound in a dose-dependent manner.

Role of co-activators and co-repressors in the mechanism of steroid/thyroid receptor action

Steroid/thyroid hormone receptors are ligand-dependent transcription factors that regulate diverse aspects of growth, development, and homeostasis by binding as homodimers or heterodimers to their cognate DNA response elements to modulate transcription of target genes. Transactivation by steroid/ thyroid hormone receptors involves a conserved AF-2 domain located in the distal carboxy-terminus of the receptors. The existence of co-factors, termed co-activators or adapters, was first suggested by transcriptional squelching between progesterone receptors and estrogen receptors. Co-repressors were also postulated to contribute to the silencing function of unliganded thyroid hormone receptor (TR). The yeast two-hybrid system and Far-Western blotting have been used to identify several proteins that interact with members of the steroid/thyroid hormone receptor superfamily in a ligand-sensitive manner. Our laboratory cloned the first functional co-activator, termed steroid receptor co-activator-one (SRC-1), that appears to be a general co-activator for all steroid receptors tested and enhances transactivation of steroid hormone-dependent target genes. Subsequently, many more putative co-activators have been reported, including the SRC-1 related proteins, TIF2 and GRIP1, and other putative and unrelated co-activators such as ARA70, Trip1, RIP140, and TIF1. In addition, another co-activator, CREB-binding protein (CBP), has been shown to enhance steroid receptor-dependent target gene transcription. CBP and SRC-1 interact and synergistically enhance transcriptional activation by the ER and PR. Therefore, a ternary complex-consisting of CBP, SRC-1, and liganded steroid receptors-may form to increase the rate of hormone-responsive gene transcription. Similarly, co-repressors, such as SMRT and N-CoR, for TR and retinoic acid receptors (RAR) have been identified. The unliganded TR and RAR have been shown to inhibit basal promoter activity; this silencing of target gene transcription by unliganded receptors is mediated by these co-repressors. Collectively, available evidence supports the following model of steroid-responsive gene transcription. Upon binding of agonist the receptor changes its conformation in the ligand-binding domain that enables recruitment of co-activators, which allows the receptor to interact with the basal transcriptional machinery more efficiently and to activate transcription. In contrast, binding of antagonists induces a different conformational change in the receptor. Although some antagonist-bound receptor can dimerize and bind to its cognate DNA element, it fails to dislodge the associated co-repressors, which results in a nonproductive interaction with the basal transcriptional machinery. Similarly, the TR and RAR associate with co-repressors in the absence of ligand, thereby resulting in a negative interaction with the transcriptional machinery that silences target gene expression. In the case of mixed agonist/antagonists, such as 4-hydroxytamoxifen, activation of gene transcription may depend on the relative ratio of co-activators and co-repressors in the cell or cell-specific factors that determine the relative agonistic or antagonistic potential of different compounds. These co-activators and co-repressors appear to act as an accelerator and/or a brake that modulates transcriptional regulation of hormone-responsive target gene expression. Thus, the recent discovery of co-activators and co-repressors expands our knowledge of the mechanisms of steroid receptor action.

Neurobehavioral effects of occupational exposure to low-level organic solvents among Taiwanese workers in paint factories

At six paint factories in northern Taiwan, 325 workers participated in a detailed evaluation that included medical and occupational questionnaires, blood sampling, neurobehavioral tests, vibratory perception threshold tests, and thermal perception threshold tests. Because of cultural differences, a Chinese test battery was modified from the Neurobehavioral Evaluation System 2. Eleven tests were performed: finger tapping, continuous performance, associated learning, symbol-digit, pattern comparison, pattern memory, visual digit span, switch attention, associated delayed recognition, mood scales, and vocabulary. Air concentrations of organic solvents were measured by passive personal samplers and analyzed by gas chromatography. Results showed that major solvents to which the workers were exposed were toluene, xylene, n-hexane, methyl iso-butyl ketone, and n-butyl acetate. The exposure index (EI) was classified by different exposure patterns and different air concentrations in the breathing zone as follows: EI 0, nonexposure; EI 1, low exposure; and EI 2, high exposure (the medians of 8-hr hygienic effects were 0, 0.03, and 0.25, respectively). Because of their diverse socioeconomic status and demographic characteristics, the workers were divided into two groups for additional analysis: one group comprised white-collar workers, including technicians and administrative staff, and the other comprised blue-collar workers. By using multiple linear regression analysis controls for age, sex, education, and alcohol intake, significant associations were found between increased exposure to solvent mixtures and performance on some neuropsychologic tests. In the blue-collar group, significantly prolonged response latencies were observed in the tests of continuous performance, pattern comparison, and pattern memory. Among white-collar workers, significant impairment was observed in the continuous performance test. All three tests involved visual attention and perceptual (speed and memory) functions. It was concluded that these may be the earliest neurotoxic signs of occupational exposure to low-level organic solvents in paint manufacturing workers.

Interferon regulatory factors and TFIIB cooperatively regulate interferon-responsive promoter activity in vivo and in vitro

Interferon regulatory factors (IRFs) bind to the interferon-stimulated response element (ISRE) and regulate interferon- and virus-mediated gene expression. IRF-1 acts as a transcriptional activator, while IRF-2 acts as a repressor. Here we show that IRF-1 and IRF-2 bind to both cellular TFIIB, a component of the basal transcription machinery, and recombinant TFIIB (rTFIIB) and that this protein-protein interaction facilitates binding of IRFs to the ISRE. A functional interaction between TFIIB and IRF was assessed by a newly established in vitro transcription assay in which recombinant IRF-1 (rIRF-1) stimulated transcription specifically from an ISRE-containing template. With this assay we show that rIRF-1 and rTFIIB cooperatively enhance the ISRE promoter in vitro. We found that the activity of an ISRE-containing promoter was cooperatively enhanced upon cotransfection of TFIIB and IRF-1 cDNAs into P19 embryonal carcinoma cells, further demonstrating functional interactions in vivo. The cooperative enhancement by TFIIB and IRF-1 was independent of the TATA sequence in the ISRE promoter but dependent on the initiator sequence (Inr) and was abolished when P19 cells were induced to differentiate by retinoic acid treatment. In contrast, cotransfection of TFIIB and IRF-1 into NIH 3T3 cells resulted in a dose-dependent repression of promoter activation which occurred in a TATA-dependent manner. Our results indicate the presence of a cell type-specific factor that mediates the functional interaction between IRFs and TFIIB and that acts in conjunction with the requirement of TATA and Inr for promoter activation.

The extreme C terminus of progesterone receptor contains a transcriptional repressor domain that functions through a putative corepressor

Binding of a hormone agonist to a steroid receptor leads to the dissociation of heat shock proteins, dimerization, specific DNA binding, and target gene activation. Although the progesterone antagonist RU486 can induce most of these events, it fails to activate human progesterone receptor (hPR)-dependent transcription. We have previously demonstrated that a conformational change is a key event leading to receptor activation. The major conformational distinction between hormone- and antihormone-bound receptors occurs within the C-terminal portion of the molecule. Furthermore, hPR mutants lacking the C terminus become transcriptionally active in the presence of RU486. These results suggest that the C terminus contains a repressor domain that inhibits the transcriptional activity of the RU486-bound hPR. In this study, we have defined a 12 amino acid (12AA) region in the C terminus of hPR that is necessary and sufficient for the repressor function when fused to the C-terminal truncated hPR or to the GAL4 DNA-binding domain. Mutations in the 12AA domain (aa 917-928) generate an hPR that is active in the presence of RU486. Furthermore, overexpression of the 12AA peptide activates the RU486-bound wild-type hPR without affecting progesterone-dependent activation. These results suggest that association of the 12AA repressor region with a corepressor might inactivate hPR activity when it is bound to RU486. We propose that binding of a hormone agonist to the receptor changes its conformation in the ligand-binding domain so that association with coactivator is promoted and activation of target gene occurs.

Mechanism of catecholamine-induced proliferation of vascular smooth muscle cells

BACKGROUND

Catecholamines have been shown to aggravate atherosclerosis in animals and humans, and abnormal proliferation of vascular smooth muscle cells (VSMC) is a key event in the early stage of atherosclerosis. Catecholamines may be involved in such cell growth. Therefore, a series of experiments using cultured VSMC was performed to elucidate their possible mitogenic effect.

METHODS AND RESULTS

We examined the mitogenic effect of catecholamines using rat aortic smooth muscle cells (VSMC) by measuring [3H]thymidine incorporation, checking with flow cytometry, and counting the cell number directly. Furthermore, the catecholamine-activated signal transduction pathway was assessed by measurement of the formation of inositol 1, 4, 5-triphosphate, intracellular Ca2+ concentration, mitogen-activated protein kinase (MAPK) activity, and mitogenic gene expression. Norepinephrine (NE) and phenylephrine stimulated [3H]thymidine incorporation and cell growth. Clonidine and isoproterenol showed little of such effects. Prazosin was more effective than either yohimbine or propranolol in suppressing the mitogenic effect of NE, indicating that catecholamine-induced VSMC proliferation is mediated by alpha 1-adrenoceptors. The alpha 1-adrenoceptor activation was coupled to pertussis toxin-insensitive Gq-protein and triggered phosphoinositide hydrolysis with subsequent activation of protein kinase C and MAPK in VSMC. In response to NE, both 42- and 44-kD MAPK were activated and tyrosine was phosphorylated. alpha 1-Adrenoceptor stimulation with NE also caused accumulation of c-fos, c-jun, and c-myc mRNA. Chloroethylclonidine completely blocked the alpha 1-adrenoceptor-mediated mitogenesis.

CONCLUSIONS

The effect of catecholamines appears to be mediated via the activation of the chloroethylclonidine-sensitive alpha 1-adrenoceptors that triggers the phosphoinositide hydrolysis and activates the MAPK pathway, leading to DNA synthesis and cell proliferation.

Neurobehavioral effects of occupational exposure to low-level styrene

Eighty-six workers in six fiberglass-reinforced plastics manufacturing plants in Taiwan were given a detailed evaluation including medical and occupational questionnaires, symptom questionnaires, blood sampling, and neurobehavioral tests, including cognitive performance, vibratory perception threshold, and thermal perception threshold. A Chinese version of cognitive tests modified from the Neurobehavioral Evaluation System 2 was applied. Forty-one workers directly exposed to styrene at the mean concentration of 22 ppm are compared with 45 workers not subject to styrene exposure. Multiple linear regression analysis controlling for age, sex, education, and alcohol intake revealed significant associations between styrene exposure and responses in some neuropsychologic measurements. No acute or chronic symptom had significant correlation with styrene exposure. Among the neurobehavioral tests, only the continuous performance test and vibration threshold were significantly and adversely affected in workers exposed to styrene. Significant changes in the central and peripheral nervous system were thus detected at a mean styrene exposure of 22 ppm.

Inhibition of platelet function by A02131-1, a novel inhibitor of cGMP-specific phosphodiesterase, in vitro and in vivo

The effect of A02131-1 [3-(5'-hydroxymethyl-2'-furyl)-1-benzyl thieno (3,2-c)pyrazole], a cGMP-specific phosphodiesterase (PDE) inhibitor, on platelet function was investigated. The compound was found to inhibit the aggregation of and adenosine triphosphate (ATP) release from human platelet-rich plasma and washed platelets that were induced by aggregation inducing drugs such as arachidonic acid (AA), collagen, U46619, platelet-activating factor (PAF), adenosine diphosphate (ADP) and A23187, and the inhibitory effect was concentration-dependent. A02131-1 also disaggregated the performed platelet aggregates induced by these inducers. Thromboxane B2 (TXB2) formations caused by collagen, PAF, ADP, and A23187 were inhibited by A02131-1 at concentrations that did not affect the AA-induced formation of TXB2 and prostaglandin D2 (PGD2). A02131-1 suppressed both the generation of inositol 1,4,5-triphosphate (IP3) and the increase of intracellular Ca2+ concentration stimulated by these aggregation inducers. A02131-1 was shown to increase the cAMP and cGMP levels in platelets and the extent was found to be dependent on concentration as well as time. A02131-1 increased the cAMP level much more slowly than the cGMP level. Activities of adenylate cyclase, guanylate cyclase, and PDEs (type I and III) were not altered by A02131-1. However, the activity of cGMP-specific PDE (type V) was inhibited by A02131-1. The antiplatelet aggregation activity and the effect on raising cAMP level of A02131-1 were both potentiated by prostaglandin E1 (PGE1). In the mouse tail bleeding test, A02131-1 was clearly shown to be more effective than dipyridamole in prolonging the tail bleeding time of conscious mice. These data indicate that A02131-1 is a cGMP-specific PDE (type V) inhibitor in human platelets.

Molecular mechanisms of COUP-TF-mediated transcriptional repression: evidence for transrepression and active repression

COUP-TF, an orphan member of the nuclear receptor superfamily, has been proposed to play a key role in regulating organogenesis, neurogenesis, and cellular differentiation during embryonic development. Since heterodimierization is a common theme within the nuclear receptor superfamily and has been demonstrated to modulate transcriptional properties of heterodimeric partners via allosteric interactions, we have devised a strategy to examine the silencing function of COUP-TF in a heterodimeric context. We find that the intrinsic active repression function of COUP-TF is not affected by heterodimerization. Moreover, COUP-TF can transrepress the ligand-dependent activation of its heterodimeric partners without its own DNA binding site. Using receptor deletion mutants in transfection assays, we show that the region necessary for COUP-TF silencing function is not sufficient for its transrepression activity. Furthermore, our studies indicate that in addition to its active repression function, COUP-TF can repress several different types of activator-dependent transactivation. However, this active repression function of COUP-TF may be differentially regulated by some other activator(s). These studies provide new insights into the molecular mechanism(s) of COUP-TF-mediated repression.

Breast-conserving surgery and radiotherapy for early breast cancer

Breast conservation is not a commonly prescribed treatment option for breast cancer in Taiwan. We report 42 patients with 43 early-stage breast cancers who were treated with breast-conserving surgery and radiotherapy at the Koo Foundation Sun Yat-Sen Cancer Center from April 1990 to December 1994. Included in this study were 33 patients with stage I cancers and 10 with stage II. Breast-conserving surgery consisted of wide local excision and ipsilateral axillary lymph node dissection. Radiotherapy was given 2 to 6 weeks after surgery, with a dose of 46 to 50 Gy, 2 Gy per fraction per day, to the whole breast, and an additional 14 to 18 Gy to the original tumor site. Irradiation to the regional lymph nodes was not performed in patients with negative axillary lymph nodes. Sixteen out of 43 (37%) patients were treated with adjuvant chemotherapy. The local control rate 3 years after treatment was 97% and relapse-free survival was 91%. The cosmetic outcome in 41 treated breasts that were rendered relapse-free by conserving treatment were evaluated and graded by the physicians as excellent, good, fair or poor using a standardized scale. Forty breasts (98%) were scored as excellent or good for their cosmetic results. Breast-conserving surgery and radio-therapy offer Taiwanese women with early breast cancer excellent local control and a highly satisfactory cosmetic outcome.

Hepatoblastoma in an infant with Beckwith-Wiedemann Syndrome

A 3-month-old Chinese male infant with typical manifestations of Beckwith-Wiedemann Syndrome (BWS), such as macroglossia, hepatomegaly, umbilical hernia and hypoglycemia, presented with a large hepatic tumor. The tumor measured 7.6 x 8.0 x 7.5 cm. An open biopsy of the tumor revealed hepatoblastoma. The family refused chemotherapy, so only supportive care was given. The tumor grew very rapidly and the infant died 17 days after admission due to respiratory failure. To our knowledge, this is the first report of BWS associated with hepatoblastoma in a Chinese infant. This patient was a typical example of the association of BWS and hepatoblastoma, and the possible effect of growth factors on the rapid proliferation of the neoplasm in BWS.

Chicken ovalbumin upstream promoter-transcription factors and their regulation

COUP-TFs are orphan members of the steroid/thyroid hormone receptor superfamily. COUP-TF homologues have been cloned in several species, from Drosophila to man. The vertebrate COUP-TFs can be classified into four subgroups according to sequence homology in their ligand-binding domain. COUP-TFs bind to AGGTCA direct repeats or palindromes with various spacings. These include the response elements of several other members of the superfamily, the vitamin D receptor, the thyroid hormone receptor, the retinoic acid receptor, the retinoid X receptor, the peroxisome proliferation activated regulator, and the hepatocyte nuclear factor-4. COUP-TF response elements have been identified in the promoters of many genes and COUP-TFs have been shown to act as negative regulators both in vitro and in vivo. They can compete with the above mentioned receptors for binding to the common response elements. The ratio of COUP-TF and the other positive regulator determines the transcriptional state of the particular gene in any given moment. COUP-TFs are expressed in the developing central nervous system of mouse and zebra-fish. In addition, they are also expressed in many organs during mouse organogenesis. The expression pattern and profile of COUP-TFs favor the hypothesis that they are involved in development and differentiation. The expression of COUP-TFs are also highly regulated. P19 embryonal carcinoma cells have been used as a model system to study COUP-TF regulation. COUP-TFs are up-regulated in retinoic acid (RA) treated P19 cells. Transient transfection assay showed that mouse COUP-TFII promoter directly responded to RA treatment, suggesting that COUP-TF expression is directly regulated by RA signaling pathway.

Regulation of synaptic ribbons in rat pineal gland explants by norepinephrine and sympathetic neurons in a co-culture model

The hypothesis that synaptic ribbons in the mammalian pinealocyte are influenced by adrenergic mechanisms was tested in the present study using a co-culture model of pineal glands and superior cervical ganglia from neonatal rats. Pineal gland explants survived and showed a high degree of differentiation when cultured for up to 30 days regardless of the presence or absence of superior cervical ganglia. Pineal glands also had neurotrophic properties promoting the survival and neurite extension from superior cervical ganglia. Synaptic ribbons were a common ultrastructural feature in all pineal cultures. There was a significant decline in synaptic ribbon numbers when co-cultured with superior cervical ganglia for both 7 and 30 days. A similar significant decrease in synaptic ribbon frequency was observed after treatment of pineal explants with norepinephrine (10(-5 )M) for both 7 and 30 days. These findings are consistent with the hypothesis that neural mechanisms play an important role in regulating synaptic ribbon numbers, at least during early development. The study also illustrates the utility of pineal gland-superior cervical ganglia co-cultures as a model for future investigations of neuron-target interactions in the pineal.

Sequence and characterization of a coactivator for the steroid hormone receptor superfamily

A yeast two-hybrid system was used to identify a protein that interacts with and enhances the human progesterone receptor (hPR) transcriptional activity without altering the basal activity of the promoter. Because the protein stimulated transactivation of all the steroid receptors tested, it has been termed steroid receptor coactivator-1 (SRC-1). Coexpression of SRC-1 reversed the ability of the estrogen receptor to squelch activation by hPR. Also, the amino terminal truncated form of SRC-1 acted as a dominant-negative repressor. Together, these results indicate that SRC-1 encodes a coactivator that is required for full transcriptional activity of the steroid receptor superfamily.

The mouse bone morphogenetic protein-4 gene. Analysis of promoter utilization in fetal rat calvarial osteoblasts and regulation by COUP-TFI orphan receptor

Bone morphogenetic protein-4 (BMP-4) is one of a member of related polypeptides that are important in bone formation and other developmental processes. We isolated the BMP-4 gene from a mouse genomic library and characterized the exon-intron structure and one of the candidate promoters. Two alternative 5'-noncoding exons, 1A and 1B, were identified by reverse transcription polymerase chain reaction assays. Quantitative competitive polymerase chain reaction using Exon 1A, Exon 1B, and Exon 3 primers indicate the 1A-containing transcript is the primary BMP-4 mRNA expressed in bone cell cultures. Primer extension analysis supports that 1A is the major promoter utilized in bone cell cultures as well as in 9.5-day mouse embryos. 1A promoter activity indicate selective DNA regions functional in bone cells. We found potential regulatory response regions in the 1A 5'-flanking region of the BMP-4 gene for the chicken ovalbumin upstream-transcription factor I (COUP-TFI). Specific binding to the COUP-TFI response regions in the BMP-4 1A promoter was demonstrated. By co-transfection of a COUP-TFI expression plasmid with the BMP-4 1A promoter in fetal rat calvarial osteoblasts, we demonstrated that COUP-TFI inhibits the BMP-4 promoter activity. This suggests that COUP-TFI could act as a silencer for BMP-4 transcription in vivo.

Isolation, characterization, and chromosomal localization of mouse and human COUP-TF I and II genes

Chicken ovalbumin upstream promoter transcription factors (COUP-TFs) are orphan members of the steroid/thyroid hormone receptor superfamily. COUP-TF homologues have been cloned in many species, from Drosophila to human. The protein sequences of COUP-TFs are highly homologous across species, suggesting functional conservation. Two COUP-TF genes have been cloned from human, and their genomic organizations have been characterized. To determine whether the genomic organization is conserved between human and mouse, we isolated two mouse COUP-TF genes (I and II) and characterized their genomic structures. Both genes have relatively simple structures that are similar to those of their human counterparts. In addition, we mapped mouse COUP-TF I to the distal region of chromosome 13 and COUP-TF II to the central region of chromosome 7. Furthermore, we mapped human COUP-TF I to 5q14 of chromosome 5 and COUP-TF II to 15q26 of chromosome 15. The results demonstrate that COUP-TF genes are located in chromosomal regions that are syntenic between mouse and human.

Stimulation of human insulin receptor gene expression by retinoblastoma gene product

Multiple cis-acting elements have been defined to be important for the transcriptional regulation of the human insulin receptor (hIR) gene expression. We report here that one of these elements also mediated the stimulation of hIR promoter activity by the retinoblastoma gene product (Rb). The cis-element responsible for Rb stimulation was localized to the GA and GC boxes situated between -643 to -607 of the hIR gene. We have previously demonstrated that these GA and GC boxes bind Sp1 with high affinity and are responsible for E1a activation of hIR promoter activity. Mutation of these sequences completely abolished Rb-dependent enhancement of hIR promoter activity. In addition, we localized three regions in the N-terminal domain of Rb to be involved in stimulation of hIR promoter activity. Our results represent one of the first studies to demonstrate a functional importance assigned to the multiple phosphorylation sites in the N terminus of Rb. Finally, the mechanism by which Rb activates the hIR promoter are presented.

Neurotrophic effects of the pineal gland: role of non-neuronal cells in co-cultures of the pineal gland and superior cervical ganglia

The pineal gland (PG) is a source of several trophic factors. In this study, PG and superior cervical ganglia (SCG) from Sprague-Dawley neonates (1-day-old) were co-cultured to test the hypothesis that endogenous release of PG NGF (or an NGF-like cytokine) is sufficient to promote survival of SCG neurons. Neuronal density of SCG neurons was significantly enhanced when co-cultured with PG for 7 days compared to SCG cultured alone. SCG survival and neurite formation in PG co-cultures was less than in SCG treated with exogenous NGF (100 ng/ml). The neurotrophic effect of PG co-cultures was abolished when 1% anti-NGF was added to the medium. Co-cultures of SCG neurons with established 7-day PG cultures induced extensive SCG neurite formation within 24 hr compared to SCG co-cultured with 1-day PG cultures. This suggests that PG neurotrophic effects are due to PG non-neuronal cells (nnc) that proliferate to confluency by 7 days in culture. S-antigen-positive pinealocytes did not proliferate in culture. There was decreased SCG survival when neurons were seeded onto PG cultures that had been previously killed by drying, which suggests that the neurotrophic effects of nnc are not substrate-dependent. Immunocytochemical characterization of PG nnc revealed a heterogenous mixture of astrocytes, macrophage/microglia, and fibroblasts. These findings support the hypothesis that NGF is actively secreted by PG and that nnc are the principal source of this neurotophin.

Chicken ovalbumin upstream promoter transcription factor (COUP-TF): expression during mouse embryogenesis

Members of the steroid/thyroid hormone receptor superfamily such as TR, RAR, RXR and VDR are known to play important roles in regulation of gene expression during development, differentiation and homeostasis. COUP-TFs are orphan members of this superfamily of nuclear receptors and have been shown to negatively regulate the ability of these nuclear receptors to transactivate target genes. Two different mechanisms are implicated in this repression. First, COUP-TFs bind to AGGTCA direct repeats and palindromes with various spacings, which include response elements for TR, RAR, RXR and VDR, allowing for direct competition of COUP-TFs for the response elements. Second, COUP-TFs can heterodimerize with RXRs, the essential cofactor for effective binding of VDR, TRs and RARs to their cognate response elements. The physiological significance of this negative effect of COUP-TF on the activity of these receptors has been analyzed. Detection of COUP-TF transcripts during mouse development reveal discrete spatial and temporal expression domains consistent with COUP-TFs being involved in regulation of gene expression during embryogenesis. Transcripts are localized within discrete regions of the central and peripheral nervous system including the inner ear. In addition, COUP-TFs are found in many tissues including testes, ovary, prostate, skin, kidney, lung, stomach, intestine, pancreas and salivary gland. Some of these expression domains colocalize with those of TR, RAR, and RXR. The simultaneous expression of these genes raise the possibility that COUP-TFs can act as negative regulatory factors during development and differentiation.

Transcription factor TFIIB and the vitamin D receptor cooperatively activate ligand-dependent transcription

The active metabolite of vitamin D, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], regulates gene transcription through binding to the vitamin D receptor (VDR), a member of the nuclear hormone receptor superfamily. Sequence-specific transcription factors, including nuclear hormone receptors, are thought to interact with the basal transcription complex to regulate transcription. In glutathione S-transferase fusion-based protein-protein binding assays we found that VDR specifically binds to TFIIB, a component of the basal complex, and that the interaction requires select domains of each protein. To assess the functional significance of this interaction, transfection assays were performed with a 1,25(OH)2D3-responsive reporter construct. In P19 embryonal carcinoma cells cotransfection of VDR and TFIIB cooperatively activated reporter transcription, while each factor alone gave very low to no activation. This activation was dependent on 1,25(OH)2D3 and the dose of TFIIB and VDR transfected, demonstrating that a nuclear hormone receptor functionally interacts with TFIIB in vivo. In contrast, transfection of NIH 3T3 cells generated strong reporter activation by 1,25(OH)2D3 in the presence of VDR alone, and cotransfection of TFIIB led to specific dose-dependent repression of reporter activity. Taken together, these results indicate that TFIIB-nuclear hormone receptor interaction plays a critical role in ligand-dependent transcription, which is apparently modulated by a cell-type-specific accessory factor.

E1a activation of insulin receptor gene expression is mediated by Sp1-binding sites

E1a adenoviral oncoproteins have been known to modulate genes important for the growth and differentiation of cells. Our laboratory is interested in understanding how insulin promotes the growth and proliferation of cells. In this report, we have examined the ability of E1a to modulate the insulin receptor gene expression. In HepG2 cells, expression of the 243-amino acid E1a protein stimulated expression of the chloramphenicol acetyltransferase reporter under the control of the insulin receptor promoter. 5'-Deletion analysis of the insulin receptor promoter indicated that the region between -630 and -607 is important for regulation by E1a. This region contains two GA and four overlapping GC boxes that are putative Sp1-binding sites. A DNA fragment containing these sites was used as a probe in gel retardation assays. Three specific protein-DNA complexes were detected with HepG2 nuclear extract. These complexes could be competed partially by the DNA fragments with mutations in either the GA or GC boxes, but not by the DNA fragment with a mutation in both the GA and GC boxes. In addition, mutation of each of these sites lowered the basal activity of the promoter and partially reduced transactivation by E1a. Simultaneous mutation in both GA and GC boxes further reduced the basal activity and abrogated transactivation by E1a. Taken together, these results indicate that the loss of binding ability of Sp1 (or Sp1-like factors) is concomitant with reduction of the basal activity and the loss of E1a inducibility of the gene.(ABSTRACT TRUNCATED AT 250 WORDS)

Mouse retinoid X receptor contains a separable ligand-binding and transactivation domain in its E region

Steroid, thyroid, and retinoid hormones exert their biological functions by interacting with their cognate nuclear receptors. Upon binding receptors, hormones induce a protease-resistant structural change in the receptor ligand-binding domain and subsequently activate the receptors. Utilizing partial proteolysis, we have been able to delineate a region in the mouse retinoid X receptor beta (mRXR beta) required for ligand binding. A separable activation domain within the mRXR beta E region has been identified. The activation domain, which is 21 amino acids in length, is located at the extreme C terminus of mRXR beta. This domain is not required for ligand binding since removal of this sequence neither eliminates the ligand-induced, protease-resistant conformational change nor alters the ligand-enhanced DNA binding. Furthermore, deletion of this activation domain converts the receptor into a transcriptional silencer. Finally, a further truncation of 9 amino acids (for a total of 30 amino acids) from the C terminus results in a mutant which does not undergo the protease-resistant conformational change and cannot bind DNA as a homodimer. Nevertheless, this mutant is still able to form a heterodimer with the thyroid hormone receptor. Therefore, homodimerization and heterodimerization can be distinguished by this nine-amino-acid sequence.

The tau 4 activation domain of the thyroid hormone receptor is required for release of a putative corepressor(s) necessary for transcriptional silencing

The C terminus of nuclear hormone receptors is a complex structure that contains multiple functions. We are interested in the mechanism by which thyroid hormone converts its receptor from a transcriptional silencer to an activator of transcription. Both regulatory functions are localized in the ligand binding domain of this receptor superfamily member. In this study, we have identified and characterized several functional domains within the ligand binding domain of the human thyroid hormone receptor (TR beta) conferring transactivation. Interestingly, these domains are localized adjacent to hormone binding sites. One activation domain, designated tau 4, is only 17 amino acids in length and is localized at the extreme C terminus of TR. Deletion of six amino acids of tau 4 resulted in a receptor that could still bind hormone but acted as a constitutive silencer, indicating that tau 4 is required for both transactivation and relief of the silencing functions. In addition, we performed in vivo competition experiments, the results of which suggest that in the absence of tau 4 or hormone, TR is bound by a corepressor protein(s) and that one role of hormone is to release corepressor from the receptor. We propose a general model in which the role of hormone is to induce a conformational change in the receptor that subsequently affects the action of tau 4, leading to both relief of silencing and transcriptional activation.

Mechanisms for synergistic activation of thyroid hormone receptor and retinoid X receptor on different response elements

The thyroid hormone receptors (TR) form heterodimers with the retinoid X receptors (RXR) and activate target genes through thyroid-responsive elements (TRE). Heterodimerization elevates the DNA binding efficiency and thus can result in functional synergism between TR and RXR. Here we demonstrate that DNA sequences dictate the cooperative activation between TR and RXR despite the high affinity binding of the heterodimer to those TREs. We provide evidence that the C-terminal activation domain of RXR can modulate the triiodothyronine (T3) responsiveness of TR/RXR heterodimers on reporter genes without altering the DNA binding properties of the heterodimers. The modulation function of this relatively small region is under the control of specific TRE sequences and promoter context. These data indicate that this C-terminal region of RXR is likely involved in receptor-cellular factor(s) interactions. Finally, we propose that the synergistic activation by TR and RXR is achieved through elevated DNA binding and, dependent on the DNA sequence, the interaction of RXR with other transcription factors.

A rapid one-step method to purify baculovirus-expressed human estrogen receptor to be used in the analysis of the oxytocin promoter

We have produced a truncated form of the human estrogen receptor (hER) as a fusion protein with glutathione S-transferase (GST) in Spodoptera frugiperda (Sf) cells using the baculovirus expression vector (BEV) system. The protein is correctly produced and can be purified from crude whole-cell extracts by a single-step, batch-wise affinity-purification procedure. We show that this GST-hER fusion protein binds at its DNA-binding site specifically and in a hormone-inducible manner. Furthermore, we used the purified hER to analyze the complex estrogen response element (ERE) in the promoter of the oxytocin-encoding gene.

A regulatory system for use in gene transfer

We recently have demonstrated that a C-terminal deletion mutant of the human progesterone receptor (hPRB891) fails to bind to progesterone but can bind RU 486 (Mifepristone) and other progesterone antagonists. Most significantly, this mutant receptor activates transcription of a reporter gene containing the progesterone response element in the presence of these antagonists. Taking advantage of this finding and the modular nature of functional domains of steroid receptors, we constructed a chimeric regulator (pGL-VP) by fusing the ligand-binding domain of human progesterone receptor hPRB891 to the yeast transcriptional activator GAL4 DNA-binding domain and the herpes simplex virus protein VP16 activation domain. We demonstrated that this chimeric regulator activates target genes containing the GAL4-binding sites in transient transfection assays in response to RU 486. In addition, this regulatory system has been validated by ex vivo transplantation of a stable cell line containing both the regulator and a reporter gene into rats. The dosage of RU 486 used is significantly lower than that required for antagonizing progesterone action. The gene-switch system reported here represents a regulatory system, which could be applicable for gene-transfer studies involving animals, as well as humans, in which the delivered gene(s) can be specifically turned on/off in response to an exogenous compound.

COUP-TF an orphan member of the steroid/thyroid hormone receptor superfamily

COUP-TFs are orphan members of the steroid/thyroid hormone receptor superfamily. They are transcription factors that are highly conserved across species and have a wide spectrum of binding specificity. In tissue cultures, COUP-TFs repress the transactivation function of several other members of the steroid/thyroid hormone receptor superfamily, and they also negatively regulate the transcription from promoters of many other genes. The expression profile of COUP-TFs in several species suggests that they play an important role in development and differentiation.

Negative regulation by the R2 element of the MHC class I enhancer in adenovirus-12 transformed cells correlates with high levels of COUP-TF binding

The transcriptional down-regulation of the major histocompatibility complex (MHC) class I antigens in adenovirus type 12 (Ad12) transformed cells gives them the potential to escape immunosurveillance and to form tumors. The enhancer of the class I promoter is the target of transcriptional repression which is mediated by the E1A gene of Ad12. The R2 region within the class I enhancer acts as a negative element in Ad12-transformed cells and exhibits a stronger binding activity than is observed in nontumorigenic Ad5-transformed cells, which are not reduced in class I expression. The R2 element contains a nuclear hormone receptor half-site consensus sequence, AGGTCA, which is required for both the binding activity and the ability of R2 to act as a negative element in Ad12-transformed cells. In this study, we show that an orphan hormone receptor protein, COUP-TF, contributes to the differential R2 binding activity observed between Ad12- and Ad5-transformed cells. Additionally, COUP-TF was shown to bind as a dimer to the R2 element and to use the consensus AGGTCA as one half-site and its 3' flanking sequence as a probable second degenerate half-site. Since COUP-TF can act as a transcriptional repressor, we suggest that the higher COUP-TF binding activity to the R2 element in Ad12-transformed cells contributes to down-regulation of class I transcription and, consequently, tumorigenesis.

Detection of potential ligands for nuclear receptors in cellular extracts

In response to external stimuli, steroid receptors are directly influenced to transactivate gene expression. Assuming they exist, identification of ligands for orphan steroid receptors is a key to understanding their physiology. In the orphan subgroup of the steroid receptor superfamily, the putative carboxyl terminal ligand-binding domain (LBD) is well conserved among members of the superfamily, which suggests a role in ligand binding. A consequence of ligand binding is the induction of a significant conformational change within the LBD which is necessary for the transactivation function. This characteristic conformational change can be detected by partial proteolytic digestion and has been localized by mutational analysis and epitopic mapping of the LBD using monoclonal antibodies. Based on this finding, a sensitive in vitro assay was developed for the rapid screening and identification of potential ligands for orphan receptors. We examined the patterns of conformational changes in the androgen receptor, glucocorticoid receptor, and progesterone receptor induced by binding of their cognate agonists and antagonists. We demonstrated that the conformational changes induced by ligands can serve as characteristic and reliable markers to distinguish between the ligand-bound and apoprotein states of a receptor. The sensitivity and feasibility of employing this assay to detect new endogenous ligands using fractionated cellular extracts were also tested. The results strongly suggest that unknown compounds can be defined as potential ligands for orphan receptors using this approach.

Repression of estrogen-dependent stimulation of the oxytocin gene by chicken ovalbumin upstream promoter transcription factor I

The orphan receptor chicken ovalbumin upstream promoter transcription factor I (COUP-TF I) fully prevented not only the activation of the oxytocin gene by retinoic acid and thyroid hormone but also completely repressed the estrogen-dependent stimulation in transfected P19 EC cells. DNase I footprinting showed that the COUP-TF I protein bound to the 5'-flanking region of the oxytocin gene at the site of the distal composite hormone response element, which mediates the responses to estrogen, retinoic acid, and thyroid hormone. Electrophoretic mobility shift assay using this composite hormone response element as probe showed that COUP-TF I and the estrogen receptor competed for binding but did not form a heterodimer. The binding by COUP-TF I was stronger than the binding of the estrogen receptor. Thus, the mechanism of repression involves occupancy of integrated binding sites. By mutagenesis of the composite hormone response element, the COUP-TF I binding site and the estrogen response element could be separated, resulting in functional dissociation of the repressive action of COUP-TF I and the induction by estrogen. The results show that repression of gene expression by COUP-TF I is not limited to receptors that act through heterodimerization but also extends to the homodimer-forming estrogen receptor in a context-dependent manner. This interaction between COUP-TF I and the estrogen receptor may provide a physiological mechanism of selective antagonism of gene regulation by estrogens.

Spatiotemporal expression patterns of chicken ovalbumin upstream promoter-transcription factors in the developing mouse central nervous system: evidence for a role in segmental patterning of the diencephalon

Chicken ovalbumin upstream promoter-transcription factor (COUP-TF) genes encode transcription factors belonging to the orphan subfamily of the steroid/thyroid hormone receptor superfamily. Two COUP-TF counterparts have been cloned from mouse. In an attempt to study the function of these genes in the developing central nervous system (CNS), the spatiotemporal expression patterns of the two mouse genes have been examined by in situ hybridization. Both genes are widely expressed in the developing CNS, with patterns that are overlapping yet distinct from each other. The differential expression of murine COUP-TFI and -II in the diencephalon is striking in that high levels of expression from each gene are confined to specific segmental compartments--the neuromeres. Our results suggest that murine COUP-TFs may play important roles in the development and differentiation of the CNS, including the specification of diencephalic neuromeres.

Multiple hormone response elements can confer glucocorticoid regulation on the human insulin receptor gene

Glucocorticoids have been shown to increase the levels of cell surface insulin receptors and their mRNA in many different cell types. Previously, we have reported that glucocorticoids induce the transcription of the human insulin receptor (hIR) gene in rat 208F cells and we also identified a putative glucocorticoid response element (GRE) to which the glucocorticoid receptor binds in a specific manner. In this study we have mapped four additional regions of the hIR promoter to which glucocorticoid receptor binds specifically; one residues at -1340 and the others are distributed within a 100 base pair region from -750 to -650. Within each DNase I footprinting region resides at least one putative GRE sequence. They function as GREs to confer glucocorticoid inducibility when fused to a heterologous promoter-chloramphenicol acetyltransferase reporter construct. The functional significance of these putative GREs was further substantiated by mutational analysis. Taken together, our results indicate that these GREs are capable of conferring glucocorticoid-dependent transcriptional induction similar to those observed in vivo. Therefore, the increase of hIR mRNA and insulin binding to surface receptor in response to glucocorticoids is likely mediated by enhancement of transcription. The functional redundancy of the GREs may reflect the biological mechanism which ensures the glucocorticoid regulation of the hIR gene at the transcriptional level.

Functional characterization of a unique liver gene promoter

Human phenylalanine hydroxylase (PAH) is specifically expressed in the liver to convert L-phenylalanine to L-tyrosine. Deficiency of the PAH enzyme causes classic phenylketonuria, a common genetic disorder. The human PAH gene has a TATA-less promoter with multiple transcriptional initiation sites. A 9-kilobase DNA fragment 5'-flanking to the human PAH gene is sufficient to confer tissue- and developmental stage-specific expression of a reporter gene in transgenic mice. Deletion studies showed that the -121-base pair proximal promoter still retained a significant level of activity in hepatic cells. At least two protein binding sites, PAH-A and PAH-B, were identified in the proximal region of the human PAH promoter using rat liver nuclear extract. The PAH-A site covers a unique palindromic sequence, and the PAH-B site contains CCCTCCC repeats. Both elements are ubiquitous and essential regulatory elements for transcriptional activity. Nuclear protein factors that bind to the PAH-A and -B sites are detected in different cell types and are distinct from previously characterized transcription factors. No tissue-specific transcription factor binding sites have been detected within the proximal promoter region of the human PAH gene. These results suggest that the PAH gene promoter has a unique organization of regulatory elements for its tissue-specific expression in comparison with other liver gene promoters.