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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Transient transfections of mutated MMTV LTRs, driving the luciferase reporter gene, have shown the presence of at least one cis-acting element cooperating with the GREs. Studies of the chromatin structure of two glucocorticoid-regulated promoters, the mouse mammary tumor virus (MMTV) long terminal repeat (LTR), a retroviral promoter, and the rat tyrosine aminotransferase (TAT) promoter, demonstrate that both DNAs are organized into precisely positioned nucleosomes. Hormonal activation of transcription is accompanied by structural changes of one (MMTV LTR) or two (TAT promoter) nucleosomes associated with the hormone-response elements (HREs). These changes can be visualized by the appearance of DNasel hypersensitive sites. Association of the hormone-receptor complex with the nucleus is necessary to induce the DNasel hypersensitive site and to maintain transcription, but is not necessary to maintain DNasel hypersensitivity. Anti-hormones, even when able to promote a strong binding of the receptor to the nucleus, are unable to induce the chromatin structural change. Using cell lines containing approx. 200 copies of a MMTV LTR/Hv-ras chimeric construct, we have demonstrated a strong, hormono-independent nuclear matrix interaction of sequences located just upstream and downstream of the ras coding sequences.
J Steroid Biochem Mol Biol 1991
PMID:Chromatin structure of hormono-dependent promoters. 168 63

The mechanism of glucocorticoid resistance has been studied in a rat hepatoma cell variant (6.10.2), which contains low levels of glucocorticoid receptor (GR). These cells seem to have lost all the glucocorticoid-induced transcriptional responses as measured by the lack of induction of expression of stably integrated mouse mammary tumor virus (MMTV) and the endogenous gene tyrosine aminotransferase (TAT), as well as the transcriptional suppression of GR gene expression. Physico-chemical characterization of the GR in the glucocorticoid resistant 6.10.2 cells revealed that the receptor is indistinguishable from the wild-type receptor with regard to size, hormone- and DNA-binding. The levels of the receptor mRNA and the total immunoreactive protein found in 6.10.2 cells were about 20% of those found in wild-type cells. Further analysis of 6.10.2 cells demonstrated that the receptor was indeed biologically functional. Treatment of 6.10.2 cells with 8-bromo-cAMP, which induced the endogenous GR level two-fold, restored responsiveness to glucocorticoids. Secondly, pretreatment of the cells with cycloheximide also led to reacquisition of cellular responsiveness to glucocorticoids. We propose that there exists a "threshold" level of GR, which is required for responsiveness and that under normal culture conditions, the level of GR in 6.10.2 cells is below this threshold. Glucocorticoid responsiveness can be restored by raising the GR level above the threshold with 8-bromo-cAMP or, alternatively, by removing the threshold barrier (repressor protein) with cycloheximide. Finally, the existence of such a repressor protein for MMTV induction was shown by in vivo titration with an isolated negative cis-element from the MMTV promoter.
J Steroid Biochem Mol Biol 1991
PMID:The mechanism for glucocorticoid-resistance in a rat hepatoma cell variant that contains functional glucocorticoid receptor. 168 64

Wnt-1 (int-1) is a cellular oncogene often activated by insertion of proviral DNA of the mouse mammary tumor virus. We have mapped the 5' end and the promoter area of the Wnt-1 gene by nuclease protection and primer extension assays. In differentiating P19 embryonal carcinoma cells, in which Wnt-1 is naturally expressed, two start sites of transcription were found, one preceded by two TATA boxes and one preceded by several GC boxes. In P19 cells, a 1-kilobase upstream sequence of Wnt-1 was able to confer differentiation-specific expression on a heterologous gene. We have investigated how Wnt-1 transcription was affected by mouse mammary tumor virus proviral integrations in various configurations near the promoters of the gene. One provirus has been inserted in the 5' nontranslated part of Wnt-1, in the same transcriptional orientation, and has functionally replaced the Wnt-1 promoters. Wnt-1 transcription in this tumor starts in the right long terminal repeat of the provirus, with considerable readthrough transcription from the left long terminal repeat. Another provirus has been inserted in the orientation opposite that of Wnt-1 into a GC box, disrupting the first Wnt-1 transcription start site but not the downstream start site. Most insertions have not structurally altered the Wnt-1 transcripts and have enhanced the activity of the normal two promoters.
Mol Cell Biol 1990 Aug
PMID:The Wnt-1 (int-1) oncogene promoter and its mechanism of activation by insertion of proviral DNA of the mouse mammary tumor virus. 169 22

Mouse mammary tumor virus (MMTV) is an endogenous murine retrovirus that is expressed in the epithelial cells of the mammary and salivary glands, lungs, kidneys, and seminal vesicles and in the lymphoid cells of the spleen and thymus. Several studies have shown that the long terminal repeat (LTR) of this virus can direct the expression of reporter genes to the same tissues in transgenic mice. To determine whether multiple regulatory elements within the LTR are involved in this tissue-specific expression, we have established lines of transgenic mice containing transgenes that have deletions in the MMTV LTR. Deletions of all LTR sequences upstream of -364 or of LTR sequences from -165 to -665 both result in the expression of linked reporter genes such as the simian virus 40 early region or the bacterial enzyme chloramphenicol acetyltransferase in novel sites, such as the heart, brain, and skeletal muscle; expression of endogenous MMTV and transgenes containing the full-length LTR is not detected in these organs. Negative regulation appears to involve more than one region, since deletion of sequences between either -201 and -471 or -201 and -344, as well as sequences upstream of -364, results in inappropriate expression in heart, brain, and skeletal muscle. Therefore, a negative regulatory element(s) in the MMTV LTR can suppress transcription from the viral promoter in several different organs. This represents the first example of generalized negative regulatory elements that act in many different tissues in transgenic mice to prevent inappropriate expression of a gene.
Mol Cell Biol 1990 Nov
PMID:Negative regulation in correct tissue-specific expression of mouse mammary tumor virus in transgenic mice. 170 Feb 74

In vivo expression of the mouse mammary tumor virus (MMTV) is restricted to a few organs, with the highest rate of transcription found in the mammary gland. Using a series of mammary and nonmammary murine cell lines, we have identified two regulatory elements, located upstream of the hormone responsive element, that specifically regulate the MMTV promoter. The first element displays an enhancerlike activity and is coincident with the binding of a nuclear factor (designated MP4; position -1078 to -1052 in the long terminal repeat) whose presence is apparently restricted to mammary cell lines. The second regulatory region mediates a repressive activity and is mapped to the long terminal repeat segment from -415 to -483. This repression is specific for a particular subtype of mammary cells (RAC cells) able to grow under two differentiation states (A. Sonnenberg, H. Daams, J. Calafat, and J. Hilgers, Cancer Res. 46:5913-5922, 1986). The MMTV promoter in mammary cell lines thus appears to be modulated by two cis-acting elements that are likely to be involved in tissue-specific expression in vivo.
Mol Cell Biol 1991 May
PMID:Two regions of the mouse mammary tumor virus long terminal repeat regulate the activity of its promoter in mammary cell lines. 170 94

Expression of the glycoprotein hormone alpha gene is regulated divergently by glucocorticoids in different cell types. Coexpression of the glucocorticoid receptor (GR) with an alpha-CAT reporter gene caused activation of alpha promoter activity in fibroblasts, but repression in JEG-3 choriocarcinoma cells, indicating that cell-specific factors dictate positive vs. negative regulation of this promoter by GR. Cell-specific sequences and other enhancer elements in the the alpha gene have been relatively well characterized in JEG-3 cells, and this model was used to further examine the mechanism of transcriptional repression by glucocorticoids. Promoter mutagenesis indicated that the degree of GR-mediated repression was impaired by a variety of deletional and site-directed mutations between -171 and -111 bp, a region that includes both cell-specific and cAMP response elements (CREs). In an attempt to further localize a negative glucocorticoid response element (GRE) sequence, binding studies were used to assess GR interactions with alpha promoter DNA sequences. Using avidin-biotin complex DNA binding assays, a series of overlapping alpha promoter DNA sequences between -170 to 29 basepairs were tested, but each failed to bind GR, whereas a control GRE avidly bound receptor. Similarly, in competition assays in transfected CV-1 cells, the alpha gene 5'-flanking sequence did not compete for GR stimulation of a glucocorticoid responsive reporter gene, whereas a sequence that contains known GR-binding sites (murine mammary tumor virus) effectively inhibited GR-mediated expression. The absence of high affinity GR-binding sites in the alpha promoter suggested that mutations that affected GR inhibition may have eliminated recognition sites for transactivators, which are themselves targets for the GR, rather than altering specific negative GRE sites in the DNA sequence. To examine this possibility, GR repression was studied using chimeric transcription factors. The transcription-activating domains of several different proteins (CREB, thyroid hormone receptor, or VP16) were linked to the DNA-binding domain of Gal-4, and transcription was driven by the Gal-4 recognition site (UAS). GR markedly repressed transactivation by Gal-4-CREB and, to a lesser degree, the Gal-4-thyroid hormone receptor and Gal-4-VP16 chimeric proteins. Repression occurred when UAS was linked to either the alpha promoter or to the E1B promoter. Thus, inhibition occurs in the absence of either the CRE or the proximal alpha promoter. These results support a mechanism in which GR-mediated repression in JEG-3 cells occurs by receptor interference with the transactivating potential of enhancer-binding proteins or associated transcription factors.
Mol Endocrinol 1991 Jan
PMID:Repression of the human glycoprotein hormone alpha-subunit gene by glucocorticoids: evidence for receptor interactions with limiting transcriptional activators. 170 98

Viral transformation and DNA-transfection assays were employed to investigate the differential toxic effect of caffeic acid phenethyl ester (CAPE), an extract of the honeybee hive product propolis, on adenovirus type 5 (Ad5)-transformed cloned rat embryo fibroblast (CREF) cells. CAPE inhibited, in a dose-dependent manner, both de novo and carcinogen-enhanced transformation of CREF cells by H5hr1, the cold-sensitive (cs) host-range mutant of Ad5. CAPE had a selective inhibitory effect on Ad5-induced transformation when a wild-type (wt) Ad5 E1A gene or a cs Ad5 E1A gene (at 37 degrees C, but not at 32 degrees C) was cotransfected into CREF cells with a dominant-acting bacterial hygromycin-resistance gene. A requirement for the expression of Ad5 E1A-encoded mRNAs and transforming proteins and sensitivity to CAPE was demonstrated using CREF cells stably transformed by a cs Ad5 E1A gene and an Ad5 E1A gene under the transcriptional control of a mouse mammary tumor virus promoter. To distinguish between the effects of the two Ad5 E1A-encoded proteins of 289 amino acids (aa) and 243 aa, CREF cells were stably transformed with cDNAs encoding either the 13S or the 12S E1A mRNA. CREF cells expressing the 13S E1A-encoded 289-aa protein were more sensitive to the growth-suppressing effect of CAPE than cells producing only the 12S E1A-encoded 243-aa protein. However, the growth-suppressing and toxic effects of CAPE were greatest in cells expressing both E1A-encoded transforming proteins. Analysis of the effect of CAPE on E1A and beta-actin gene expression in wt and cs E1A and H5hr1-transformed CREF cells indicated that low levels of CAPE, which were growth suppressive, did not selectively suppress E1A expression. These results demonstrated that cellular changes induced in CREF cells by the 13S E1A-encoded 289-aa protein of Ad5, when expressed alone or in combination with the 12S E1A-encoded 243-aa protein, rendered transformed cells sensitive to the growth-suppressing and toxic effects of CAPE.
Mol Carcinog 1991
PMID:Suppression of adenovirus type 5 E1A-mediated transformation and expression of the transformed phenotype by caffeic acid phenethyl ester (CAPE). 171 5

We have previously reported the identification of a glucocorticoid and cell-density inducible gene (clone 5) that appears to play a regulatory role in adipocyte differentiation. In the current studies we have more carefully investigated the interplay between cell growth or differentiation and the glucocorticoid responsiveness of clone 5 RNA. We find that inducibility by steroid hormone is independent of the differentiated state but surprisingly, occurs only when cells are at high cell density. In subconfluent TA1 cells clone 5 RNA is refractory to induction whereas well characterized glucocorticoid-inducible promoters such as the those from mouse mammary tumor virus and alpha-1-acid glycoprotein are induced under all conditions. These results point to the necessity of ancillary factors, absent in low density cell culture, that are required for glucocorticoid responsiveness of the clone 5 gene.
Mol Endocrinol 1991 May
PMID:Glucocorticoid induction of the adipocyte clone 5 gene requires high cell density. 171 9

Previous studies have demonstrated that the entire rat beta-casein (R beta C) gene and a -524/+490 R beta C fragment-chloramphenicol acetyltransferase (CAT) fusion gene are expressed preferentially in the mammary gland of transgenic mice in a developmentally regulated fashion. However, transgene expression was infrequent, less than 1% of that observed for the endogenous gene, and varied as much as 500-fold, presumably due to the site of chromosomal integration. To determine whether a heterologous hormone-responsive enhancer could be used to increase both the level and frequency of expression in the mammary gland, a fragment derived from the mouse mammary tumor virus long terminal repeat containing four hormone response elements (HREs) was inserted into the R beta C promoter at a site not known to contain transcriptional regulatory elements. Transgenic mice generated which carried HRE-enhanced R beta C-CAT fusion genes expressed CAT activity in the mammary glands of all founder lines examined at levels that were on average 13-fold greater than for lines generated with similar constructs not carrying HREs. In the highest expressing line, the level of HRE-enhanced transgene expression was found to be developmentally regulated, increasing 14-fold in the mammary gland from virgin to day 10 of lactation. In this line, expression was also observed in the thymus and spleen; however, the level of CAT activity was 4-fold lower than in the mammary gland and was not developmentally regulated. In adrenalectomized mice, the administration of dexamethasone stimulated CAT expression in the mammary gland but not in the thymus and spleen. These studies demonstrate that in the context of the R beta C promoter, the HRE functions in the mammary gland to increase both the frequency and level of transgene expression.
Mol Endocrinol 1991 Oct
PMID:A heterologous hormone response element enhances expression of rat beta-casein promoter-driven chloramphenicol acetyltransferase fusion genes in the mammary gland of transgenic mice. 177 34

A fragment of the mouse mammary tumor virus (MMTV) promoter was reconstituted from pure histones into a dinucleosome with uniquely positioned octamer cores. Core boundaries for the in vitro-assembled dinucleosome corresponded to the observed in vivo phasing pattern for long terminal repeat nucleosomes A and B. Nuclear factor 1 (NF1), a constituent of the MMTV transcription initiation complex, was excluded from the assembled dinucleosome, whereas the glucocorticoid receptor was able to bind. During transcription of MMTV in vivo, displacement of nucleosome B was necessary to permit assembly of the initiation complex. These results indicate that the nucleoprotein structure of the promoter can provide differential access to sequence-specific DNA-binding proteins and that active chromatin remodeling can occur during transcription activation.
Mol Cell Biol 1991 Feb
PMID:Transcription factor access is mediated by accurately positioned nucleosomes on the mouse mammary tumor virus promoter. 184 70


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