UNIPROT:P51532 - FACTA Search

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Query: UNIPROT:P51532 (transcriptional activator)
6,546 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The human progesterone receptor (PR) is a member of the steroid/thyroid hormone superfamily of nuclear receptors. The receptor is expressed as two forms, PR-B and the shorter PR-A, which lacks the NH2-terminal 164 amino acids of PR-B; whereas PR-B seems to be predominantly a transcriptional activator, PR-A also functions as a repressor. Our previous studies of PR expressed in T47D breast cancer cells have shown that PR is a phosphoprotein whose phosphorylation is enhanced in response to hormone. There is an initial rapid (minutes) increase in phosphorylation followed by a slower, less substantial increase, which results in decreased mobility of the receptor on sodium dodecyl sulfate gels. We now report the identification of three phosphorylation sites, which are predominantly phosphorylated during the later phase of the response to hormone. These sites, Ser102, Ser294, and Ser345, are all found in Ser-Pro consensus sequences. Whereas Ser294 and Ser345 are common to PR-A and PR-B, Ser102 is unique to PR-B. Finally, we demonstrate that phosphorylation of Ser345 is associated with the altered mobility on sodium dodecyl sulfate gels.
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PMID:Identification of a group of Ser-Pro motif hormone-inducible phosphorylation sites in the human progesterone receptor. 747 77

The biological response to progesterone is mediated by two distinct forms of the human progesterone receptor (hPR-A and hPR-B). In most cell contexts, hPR-B functions as a transcriptional activator of progesterone-responsive genes, whereas hPR-A functions as a transcriptional inhibitor of all steroid hormone receptors. We have created mutations within the carboxyl terminus of hPR which differentially effect the transcriptional activity of hPR-B in a cell- and promoter-specific manner. Analogous mutations, when introduced into hPR-A, have no effect on its ability to inhibit the transcriptional activity of other steroid hormone receptors. The observed differences in the structural requirements for hPR-B and hPR-A function suggest that transcriptional activation and repression by PR are mediated by two separate pathways within the cell. In support of this hypothesis, we have shown that hPR-A mediated repression of human estrogen receptor (hER) transcriptional activity is not dependent on hER expression level but depends largely on the absolute expression level of hPR-A. Thus, it appears that hPR-A inhibits hER transcriptional activity as a consequence of a noncompetitive interaction of hPR-A with either distinct cellular targets or different contact sites on the same target. We propose that hPR-A expression facilitates a ligand-dependent cross-talk among sex steroid receptor signaling pathways within the cell. It is likely, therefore, that alterations in the expression level of hPR-A or its cellular target can have profound effects on the physiological or pharmacological responses to sex steroid hormone receptor ligands.
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PMID:The A and B isoforms of the human progesterone receptor operate through distinct signaling pathways within target cells. 796 70

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.
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PMID:A regulatory system for use in gene transfer. 805 76

We have used circular permutation and phasing electrophoretic mobility shift assays to determine the ability of the A and B forms of human progesterone receptor (PR) to bend target DNA. Studies were done with baculovirus-expressed full-length receptors purified to apparent homogeneity. By circular permutation analysis, both forms of PR induced substantial distortions in the structure of target DNA with calculated distortion angles (alpha D) of 57 degrees for PR-A and 84 degrees for PR-B. The apparent bend centers for both forms of PR were similarly located a few base pairs (-4 to -2 bp) from the middle of the progesterone response element. No differences were detected in the magnitude of distortion or apparent bend centers when PR was bound to hormone agonist (R5020) or the antagonist RU486. Phasing analysis, which can determine the orientation of a DNA bend, revealed that both forms of PR mediated directional bends toward the major groove of the DNA helix. Calculated directed bend angles (alpha B) were 40 degrees for PR-B and 31 degrees for PR-A. The chromatin high mobility group protein HMG-1, which acts as an accessory factor to enhance the binding affinity of purified PR for progesterone response elements, had minimal influence on PR-mediated DNA bending. This result, taken together with the fact that HMG-1 can form a ternary complex with PR and DNA, is consistent with the conclusion that HMG-1 facilitates PR binding by stabilizing a receptor-induced DNA conformation that is required for assembly of a high affinity PR-DNA complex. The results of this study also suggest that DNA bending may be coupled to transcriptional regulation since PR-B is generally a stronger transcriptional activator than PR-A and also mediates a larger bend in target DNA than PR-A.
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PMID:Progesterone receptor-induced bending of its target DNA: distinct effects of the A and B receptor forms. 872 84

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.
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PMID:Positive and negative regulation of gene expression in eukaryotic cells with an inducible transcriptional regulator. 927 20

In humans, the biological response to progesterone is mediated by two distinct forms of the progesterone receptor (human (h) PR-A, 94 kDa and hPR-B, 114 kDa). These two isoforms are transcribed from distinct estrogen-inducible promoters within a single copy PR gene; the only difference between them is that the first 164 amino acids of hPR-B (B-upstream sequence) are absent in hPR-A. In most cell lines such as MCF-7 (human breast cancer cells), CV-1 (monkey kidney fibroblasts), and HeLa (human cervical carcinoma cells), hPR-A functions as a transcriptional repressor, whereas hPR-B functions as a transcriptional activator of progesterone-responsive genes. Interestingly, in these cell contexts, hPR-A also acts as a trans-dominant repressor of the transcriptional activity of other steroid hormone receptors. In contrast to hPR-A, which functions predominantly as a ligand-dependent transcriptional repressor, we show in this study that the A isoform of the chicken PR (cPR-A) lacks this trans-dominant repressor function and is a transcriptional activator in all contexts examined. By constructing chimeras between the N-terminal domains of the chicken and human PR, we mapped the trans-dominant repressor function of hPR-A to the first 140 amino acids of the protein. Notably, when this 140-amino acid "repressor" domain is placed onto chicken PR-A, the activity of the latter changes from a transcriptional activator to a repressor. Interestingly, however, this "repressor domain" is necessary, but not sufficient, for trans-repression as it is inactive when it is tethered to a heterologous protein. This suggests that the trans-repression function is comprised not only of the repressor domain of hPR-A but also requires the context of the receptor to function. The identification of a discrete inhibitory region within hPR-A which is transferable to another receptor implies that this region interacts with a set of transcription factors or adaptors that are distinct from those recognized by hPR-B, the identification of which will be required to define the mechanism by which hPR-A modulates steroid hormone receptor transcriptional activity. Thus, although chickens and humans both produce two very similar forms of the progesterone receptor, it is clear from these studies that the mechanism of action of progesterone in these two systems is quite different.
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PMID:Mapping and characterization of the functional domains responsible for the differential activity of the A and B isoforms of the human progesterone receptor. 940 67

Synthetic steroid hormone antagonists are clinically important compounds that regulate physiological responses to steroid hormones. The antagonists bind to the hormone receptors, which are ligand-inducible transcription factors, and modulate their gene-regulatory activities. In most instances, a steroid receptor, such as progesterone receptor (PR) or estrogen receptor (ER), is transcriptionally inactive when complexed with an antagonist and competitively inhibits transactivation of a target steroid-responsive gene by the cognate hormone-occupied receptor. In certain cellular and promoter contexts, however, antagonist-occupied PR or ER acquires paradoxical agonist-like activity. The cellular mechanisms that determine the switch from the negative to the positive mode of transcriptional regulation by an antagonist-bound steroid receptor are unknown. We now provide strong evidence supporting the existence of a cellular inhibitory cofactor that interacts with the B form of human PR (PR-B) complexed with the antiprogestin RU486 to maintain it in a transcriptionally inactive state. In the presence of unliganded thyroid hormone receptor (TR) or ER complexed with the antiestrogen 4-hydroxytamoxifen, which presumably sequesters a limiting pool of the inhibitory cofactor, RU486-PR-B functions as a transcriptional activator of a progesterone-responsive gene even in the absence of hormone agonist. In contrast, hormone-occupied TR or ER fails to induce transactivation by RU486-PR-B. Recent studies revealed that a transcriptional corepressor, NCoR (nuclear receptor corepressor), interacts with unliganded TR but not with liganded TR. Interestingly, coexpression of NCoR efficiently suppresses the partial agonistic activity of antagonist-occupied PR-B but fails to affect transactivation by agonist-bound PR-B. We further demonstrate that RU486-PR-B interacts physically with NCoR in vitro. These novel observations suggest that the inhibitory cofactor that associates with RU486-PR-B and represses its transcriptional activity is either identical or structurally related to the corepressor NCoR. We propose that cellular mechanisms that determine the switch from the antagonistic to the agonistic activity of RU486-PR-B involve removal of the corepressor from the antagonist-bound receptor so that it can effect partial but significant gene activation.
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PMID:A nuclear receptor corepressor modulates transcriptional activity of antagonist-occupied steroid hormone receptor. 954 87

The progesterone receptor (PR) occurs in two major forms, the full-length PRB and the amino-truncated PRA, which lacks 164 amino-terminal residues. PRB functions as a strong transcriptional activator of progesterone-responsive genes, whereas PRA is inactive in several cell types where it may even act as a trans-dominant repressor of PRB and other steroid receptors, like the glucocorticoid receptor or, reportedly, the estrogen receptor. We initially observed that a PR deleted of its entire amino domain (PR538-C) is incapable of trans-repressing PRB or glucocorticoid receptor, suggesting that a negative modulation domain must be contained in the region between position 165 and 538. After testing progressive deletion mutants and chimeras, we demonstrate that this negative modulating domain is confined within 120 residues in the amino-terminal region and that it contains a subdomain of 40 residues that is crucial for intermolecular transrepression. Duplication, deletion, and transplantation of the negative modulation domain show that the negative modulation domain has only a limited functional autonomy. In our hands, transrepression of estrogen receptor could not be substantiated, and, under our conditions, at least an equimolar concentration of PRA expression plasmid is required for transrepression. Our deletion studies reveal domains that correlate with strong homology patches between the amino-terminal domains of mammalian and avian PR.
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PMID:Definition of a negative modulation domain in the human progesterone receptor. 973 2

In the present study we describe the set-up of a new one-hybrid reporter gene assay in Saccharomyces cerevisiae composed of the human progesterone receptor fused to the DNA-binding domain of the yeast transcriptional activator Gal4. This assay allows the convenient estimation of receptor mediated progestogenic as well as antiprogestogenic actions of compounds. The induction of the beta-galactosidase reporter gene expression correlated well with the progesterone receptor affinity and the concentration of the progestins tested. The results corresponded to those obtained from a reporter gene assay in the cancer cell line CV-1 and in vitro binding experiments using rabbit uterus cytosol. In both the yeast and CV-1 cells the activity of antiprogestins was detectable by inhibition of the progestin-induced reporter gene expression. Secondary reporter genes under the transcriptional control of receptor unrelated promoters have been introduced into yeast and mammalian test strains to distinguish between specific receptor mediated antihormone actions and nonspecific effects on cellular metabolism.
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PMID:Dual reporter systems in yeast and mammalian cells for assessing progesterone receptor modulators. 1008 31

In humans, the biological response to progesterone is mediated by two forms of the progesterone receptor (hPR-A; 94kDa and hPR-B; 114kDa). These two isoforms are transcribed from distinct, estrogen-inducible promoters within a single-copy progesterone receptor (PR) gene; the only difference between them is that the first 164 amino acids of hPR-B are absent in hPR-A. In most cell lines, hPR-A functions as a transcriptional repressor of progesterone-responsive promoters, whereas hPR-B functions as a transcriptional activator of the same genes. The observation, made in the early 1990s, that shorter isoforms of some transcriptional activators can act as transrepressors of the transcriptional activity of the larger isoforms, initiated a line of investigation that led to the discovery that hPR-A is a strong transrepressor of hPR-B activity. Interestingly, hPR-A also functions as a transdominant repressor of the transcriptional activity of the estrogen, glucocorticoid, androgen, and mineralocorticoid receptors. A specific inhibitory domain (ID) within hPR-A responsible for this activity has been mapped to the extreme amino terminus of the receptor. Interestingly, although this inhibitory domain is contained within both PR isoforms, its activity is manifest only in the context of hPR-A. The identification of a discrete inhibitory region within hPR-A, whose activity was masked in the context of hPR-B, suggests that these two receptor isoforms may interact with different proteins (transcription factors, co-activators, co-repressors) within the cell. In support of this hypothesis, we have recently observed that the co-repressor SMRT (silencing mediator of retinoid and thyroid receptors) interacts much more tightly with hPR-A than with hPR-B. This important finding led to the initial conclusion that the ability of hPR-A to repress hPR-B transcriptional activity could occur as a consequence of hPR-B/A heterodimerization, where the presence of SMRT in the complex could prevent transcriptional activation. The observation, however, that hPR-A also inhibits human estrogen receptor (hER) transcriptional activity, a receptor with which hPR-A is not able to heterodimerize, suggests that there must be additional complexity. This chapter outlines what is known about the mechanism of action of hPR-A and hPR-B and how this knowledge has enhanced our understanding of PR pharmacology.
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PMID:The A and B isoforms of the human progesterone receptor: two functionally different transcription factors encoded by a single gene. 1054 81

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