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U Strähle

Publications and source records attributed to U Strähle.

48 records · Page 3Linked to original sources
PubMed1989

Glucocorticoid- and progesterone-specific effects are determined by differential expression of the respective hormone receptors.

Although glucocorticoids and progestins control vastly different physiological processes, the receptors mediating the effects of these hormones interact with the same DNA sequences. Transfer experiments involving synthetic genes and in vitro binding studies have shown that progesterone and glucocorticoid receptors both recognize the same 15-base pair DNA element (TGTACAGGATGTTCT), raising the question of how the two steroids affect gene expression selectively. We considered the possibility that their selectivity arises from either the differential expression of the receptors in target cells or the differential dependence of receptor function on additional transcription factors. To test these alternatives we introduced a progesterone-receptor expression plasmid into the rat hepatoma cell line Fto2B-3 which contains glucocorticoid receptor but is devoid of progesterone receptor. We report that expression of the progesterone receptor in Fto2B-3 cells renders endogenous glucocorticoid-regulated genes inducible by progestins. Our data show that the responsiveness of a cell to external stimuli can be reprogrammed by the expression of a single transcription factor and that differential expression of hormone receptors is at least one mechanism by which steroid-specific gene activation is achieved.

Animals↗
PubMed1989

Glucocorticoid receptor binds cooperatively to adjacent recognition sites.

In order to define the mechanism of synergistic induction mediated by multiple glucocorticoid response elements (GRE), the affinity of the glucocorticoid receptor to a single or duplicated GRE was analyzed by gel retardation, nitrocellulose filter binding and by footprinting experiments. Direct measurement of the relative affinity and indirect determination by competition showed greater than 10-fold higher affinity of the glucocorticoid receptor to a duplicated GRE when compared to a single element. Maximal stability of the GRE-receptor complex was obtained using two closely spaced GREs positioned on the same side of the DNA helix. Increasing the distance or changing the helical position of the GREs considerably increased the off rate of the receptor. DNase I footprinting shows in addition to the protection of the GRE region, an altered pattern in the nonprotected intervening DNA indicating structural alteration of the DNA helix by the receptor bound to adjacent GREs.

Animals↗
PubMed1988

Synergistic action of the glucocorticoid receptor with transcription factors.

Steroid responsive elements (SRE) have been mapped at variable positions relative to the transcription start site and are often adjacent to binding sites of transcription regulatory proteins. In order to define the role of these transcriptional control sequences in the induction process, we inserted the previously defined 15-bp glucocorticoid response element (GRE) or 15-bp estrogen response element (ERE) immediately upstream of the TATA box of the thymidine kinase promoter, deleting all distal promoter elements. Both ERE and GRE confer inducibility by the respective hormone to the truncated promoter. These data suggest that the steroid receptor protein, possibly in conjunction with the TATA box binding protein, is able to form an active transcription complex. In contrast, the GRE when inserted 351 bp upstream of the start site of transcription of the tyrosine aminotransferase gene (TAT) is not capable of mediating hormone inducibility. Inducibility can be attained at this position by either two GREs or a single GRE in combination with a CCAAT motif. A cluster of point mutations in the CCAAT box abolishes hormone inducibility, strongly suggesting a synergistic action between the glucocorticoid receptor and the factor recognizing the CCAAT motif. The CCAAT box can be replaced by a CACCC box, an NF I and an SP1 binding site, thus demonstrating that synergistic action is not restricted to the CCAAT box binding protein. These combinations of a GRE with different transcription factor binding sites show a pronounced cell-type-dependent glucocorticoid induction of expression.

Animals↗
PubMed1988

Synergistic action of glucocorticoid and estradiol responsive elements.

Modulation of gene expression by steroid hormones is mediated by receptor proteins that associate with regulatory elements of responsive genes upon binding the hormone ligand. The finding that two glucocorticoid responsive elements act cooperatively to stimulate transcription of the tyrosine aminotransferase gene prompted us to explore whether synergistic effects also occur when two different steroid hormone receptors are involved. A region of the chicken vitellogenin II gene that displays homologies to glucocorticoid and estradiol responsive elements was tested for its capability to confer estradiol and glucocorticoid inducibility to a heterologous promoter. When positioned immediately upstream of the thymidine kinase gene promoter, this element enhances expression by either steroid. Combination of both hormones results in a synergistic increase of transcription. Mutational analysis shows that sequences that show similarities of glucocorticoid and estradiol responsive elements are absolutely required for hormone induction. Analysis of the dose dependence of induction by both steroids demonstrates that half-maximal activity is observed at lower hormone concentrations when the other steroid is present in saturating amounts, which suggests that the synergistic induction observed with the combination of hormones is based on a functional interaction of the two hormone receptors.

Adenocarcinoma↗
PubMed1987

Cooperativity of glucocorticoid response elements located far upstream of the tyrosine aminotransferase gene.

Two glucocorticoid response elements (GREs) located 2.5 kb upstream of the transcription initiation site of the tyrosine aminotransferase gene were identified by gene transfer experiments and shown to bind to purified glucocorticoid receptor. Although the proximal GRE has no inherent capacity by itself to stimulate transcription, when present in conjunction with the distal GRE, this element synergistically enhances glucocorticoid induction of gene expression. Cooperativity of the two GREs is maintained when they are transposed upstream of a heterologous promoter. An oligonucleotide of 22 bp representing the distal GRE is sufficient to confer glucocorticoid inducibility. As evidenced by the mapping of DNAase I hypersensitive sites, local alterations in the structure of chromatin at the GREs take place as a consequence of hormonal treatment.

Base Sequence↗
PubMed1987

A DNA sequence of 15 base pairs is sufficient to mediate both glucocorticoid and progesterone induction of gene expression.

To define the recognition sequence of the glucocorticoid receptor and its relationship with that of the progesterone receptor, oligonucleotides derived from the glucocorticoid response element of the tyrosine aminotransferase gene were tested upstream of a heterologous promoter for their capacity to mediate effects of these two steroids. We show that a 15-base-pair sequence with partial symmetry is sufficient to confer glucocorticoid inducibility on the promoter of the herpes simplex virus thymidine kinase gene. The same 15-base-pair sequence mediates induction by progesterone. Point mutations in the recognition sequence affect inducibility by glucocorticoids and progesterone similarly. Together with the strong conservation of the sequence of the DNA-binding domain of the two receptors, these data suggest that both proteins recognize a sequence that is similar, if not the same.

Base Sequence↗
PubMedDate not supplied

In vivo protein-DNA interactions in a glucocorticoid response element require the presence of the hormone.

Transcriptional activation of gene expression by glucocorticoid hormones is mediated by the interaction of hormone-receptor complexes with specific DNA sequences called glucocorticoid responsive elements (GREs) (refs 1-3, see ref. 4 for review). Deletion of this sequence abolishes glucocorticoid induction of transcription. According to a current model, activation of the cytoplasmic receptor protein by hormone binding leads to its increased affinity for and translocation to the nucleus. However, recent reports that the oestradiol and progesterone receptors are localized in the nucleus in the absence of steroid led us to examine whether the free receptor interacts in vivo with its DNA binding site in the absence of hormone binding. We used the genomic footprinting technique to show that changes in in vivo protein-DNA interactions within the GREs of the tyrosine aminotransferase gene (TAT) can be detected only after hormone treatment in hepatoma cells. Such changes are not detected in fibroblast cells, in which the TAT gene is not expressed. Many of the changes in dimethylsulphate reactivity observed in the living cell are also found in vitro using cloned DNA and a partially purified glucocorticoid receptor.

Animals↗
PubMedDate not supplied

Oestrogen and glucocorticoid responsive elements are closely related but distinct.

DNA sequences recognized by the glucocorticoid receptor are termed glucocorticoid-responsive elements because of their stimulatory effect on transcription. An oligonucleotide of 15 base pairs having partial or perfect symmetry is necessary for glucocorticoid induction and this same oligonucleotide is surprisingly also recognized by the progesterone receptor. Here we define a palindromic sequence of 15 base pairs, modelled after a sequence element shared by the vitellogenin genes of frog and chicken, which confers oestrogen inducibility on a heterologous promoter and can be converted into a glucocorticoid-responsive element by substitution of one or two bases at homologous positions in the palindrome. Considered with the observation that the DNA-binding domains of steroid receptors are closely related, this finding demonstrates that the steroid-responsive elements constitute a family of related DNA sequences.

Base Sequence↗