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

The A2 vitellogenin gene of Xenopus laevis, which is expressed liver specifically, contains an A-activator-binding site (AABS) that mediates high in vitro transcriptional activity in rat liver nuclear extracts. Footprint experiments with DNase I and gel retardation assays revealed the binding of several proteins to AABS. Using binding sites of known DNA-binding proteins as competitors in the gel retardation assay, we found that the transcription factor C/EBP and/or one of its "iso-binders" as well as LFB1/HNF1 bound AABS. These interactions were confirmed by in vitro transcription experiments using various oligonucleotides as competitors. However, saturating amounts of C/EBP- and LFB1/HNF1-binding sites as competitors only partially blocked AABS-mediated transcriptional activity. This finding implies that at least a third distinct transcription factor interacts with AABS. In vitro transcription experiments revealed that AABS was present not only in the closely related Xenopus A1 vitellogenin gene but also in acute-phase genes as a liver-specific regulatory element known to confer the interleukin-6 response. Both AABS and the interleukin-6 response element are promoter modules interacting with at least three distinct transcription factors, including C/EBP and LFB1/HNF1.
Mol Cell Biol 1991 Jan
PMID:Liver-specific gene expression: A-activator-binding site, a promoter module present in vitellogenin and acute-phase genes. 170 15

The hepatic transcription of the angiotensinogen gene is regulated by both glucocorticoids and cytokines generated as products of the acute phase reaction. We have identified a multimodular enhancer in the 5'-flanking region of the rat angiotensinogen gene that mediates these responses and consists of an acute phase response element (APRE) flanked on both sides by adjacent glucocorticoid response element consensus motifs (GREs). Induction of transcription by the cytokine interleukin-1 (IL-1) is glucocorticoid dependent and mediated through the APRE. The APRE binds in a mutually exclusive manner a cytokine/phorbol ester-inducible protein (BPi), indistinguishable from nuclear factor kB, and a family of constitutive liver proteins (BPcs) related to the heat-stable transcription factor C/EBP. Using mutated 5'-flanking sequences of the angiotensinogen gene fused to a firefly luciferase reporter gene transfected into hepatoblastoma (HepG2) cells, we have mapped enhanson sequences required for the transcriptional response to glucocorticoids. Two functionally distinct GREs are identified by deletion and site-directed mutagenesis, both of which mediate glucocorticoid-stimulated transcription in vivo. Glucocorticoid-induced transcription mediated by the angiotensinogen gene enhancer is, furthermore, dependent on the occupancy of the APRE by either the BPi or a member of the BPc family because a mutant APRE that binds neither BPi nor BPc exhibits an attenuated glucocorticoid responsiveness. Mutant APREs that permit exclusive binding of either BPi or BPc synergistically transmit the glucocorticoid response mediated by one or the other of the adjacent GREs. Thus, the induction of angiotensinogen gene transcription involves interaction between the glucocorticoid receptor and either one of the APRE-binding proteins: either the cytokine-inducible NFkB or the constitutive family of C/EBP-like proteins, bound to adjacent enhansons in a mutually synergistic enhancer complex.
Mol Endocrinol 1990 Dec
PMID:Synergistic enhansons located within an acute phase responsive enhancer modulate glucocorticoid induction of angiotensinogen gene transcription. 170 27

Transcription of the rat alpha 1-acid glycoprotein (AGP) gene is induced by glucocorticoids. In addition to the glucocorticoid response element which maps to bases -120 to -107, sequences located between bases -106 to -42 have been shown to be necessary for hormone induction. We have previously identified multiple sites of C/EBP interaction with the AGP promoter in the region -106 to -64. In this study, we purify and identify a C/EBP family member, AGP/EBP(LAP), present in the rat hepatoma cell line HTC (JZ.1) which also binds to the C/EBP recognition sites in this region. Mutations in the recognition sites that prevent binding are analyzed, and the results suggest a positive as well as a possible inhibitory role for AGP/EBP(LAP) in the glucocorticoid induction of the gene in HTC (JZ.1) cells.
Mol Cell Biol 1991 Oct
PMID:AGP/EBP(LAP) expressed in rat hepatoma cells interacts with multiple promoter sites and is necessary for maximal glucocorticoid induction of the rat alpha-1 acid glycoprotein gene. 171 23

Understanding the nature and importance of protein-protein interactions in the mechanisms of eukaryotic gene expression is essential to understanding the normal and aberrant regulation of gene transcription. Using 125I-labeled cAMP response element-binding protein (CREB) and activating transcription factor-2 (ATF-2) recombinant peptides to probe Western blots of HeLa nuclear extracts, we have identified multiple separate nuclear factors that form specific protein-protein interactions with these leucine zipper-containing transcriptional regulatory proteins. The interaction is specific because preincubation of blots with cold homologous protein blocks the binding of labeled protein, whereas preincubation of blots with cold heterologous protein has no effect on labeled protein interactions. Although these studies focus on two specific transactivators, CREB and ATF-2, the approach is of general use for the study of other leucine zipper-containing mammalian transcription factors. Furthermore, in addition to allowing the detection of protein-protein interactions of CREB and ATF-2 with nuclear factors, we have used this strategy to isolate cDNA clones expressing these nuclear proteins. We demonstrate that CREB will form heterodimers with ATF-1, but not ATF-2, Jun, Fos, or C/EBP whereas, ATF-2 will form heterodimers with Jun and Fos, but not with C/EBP or ATF-1. This strategy, therefore, allows a systematic approach to identifying, characterizing, and cloning proteins involved in the control of eukaryotic transcriptional regulation. The identification and characterization of the components of eukaryotic transcription complexes will allow studies that address the molecular mechanisms of normal and abnormal control of cellular gene expression.
Mol Endocrinol 1991 Feb
PMID:Identification of multiple nuclear factors that interact with cyclic adenosine 3',5'-monophosphate response element-binding protein and activating transcription factor-2 by protein-protein interactions. 182 7

Intracisternal A-particle (IAP) expression in mouse cells has been correlated with hypomethylation of HhaI and HpaII sites in proviral long terminal repeats (LTRs). In a previous study, in vitro methylation of three HhaI sites in the U3 region of the LTR from the cloned genomic IAP element, MIA14, was shown to inhibit promoter activity in vivo. In this study, we found by site-directed mutagenesis that the two more downstream HhaI sites within this LTR were responsible for the methylation effects on promoter activity in vivo; methylation of the other (5') HhaI site, which lies within a putative SP1 binding domain, did not affect promoter activity. Methylation of the HhaI sites also inhibited promoter activity of the LTR in a cell-free transcription system. Exonuclease III footprinting demonstrated methylation-induced changes in protein binding over the region encompassing the downstream HhaI site, designated the Enh2 domain. The protein that interacts specifically with this domain, EBP-80, was characterized in a previous study (M. Falzon and E. L. Kuff, J. Biol. Chem. 264:21915-21922, 1989). We show here that the presence of methylcytosine in the HhaI site within the Enh2 domain inhibited binding of EBP-80 in vitro. The methylated MIA14 LTR construct was much less responsive to added EBP-80 in an in vitro transcription system than was the unmethylated construct. These data suggest that CpG methylation within the Enh2 domain may exert its effect on transcription in vivo by altering the interaction between EBP-80 and its cognate DNA sequence.
Mol Cell Biol 1991 Jan
PMID:Binding of the transcription factor EBP-80 mediates the methylation response of an intracisternal A-particle long terminal repeat promoter. 189 60

A cDNA clone encoding a thyroid-specific enhancer-binding protein (T/EBP) was isolated from a rat thyroid-derived FRTL-5 cell lambda gt 11 expression library, using a double-stranded oligonucleotide probe. This oligonucleotide was previously demonstrated to have the strongest binding affinity among three cis-acting DNA elements within the thyroid-specific enhancer region located 5.5 kbp upstream of the human thyroid peroxidase gene transcription start site. Nucleotide and deduced amino acid sequences of the cDNA revealed that T/EBP is identical to the previously reported thyroid-specific transcription factor 1 (TTF-1), which binds to the promoter of the rat thyroglobulin gene and controls its thyroid-specific expression. Expression of the T/EBP cDNA under control of the human cytomegalovirus major immediate-early gene promoter conferred thyroid-specific enhancer activity of as high as 26-fold to nonpermissive human hepatoma HepG2 cells when cotransfected with a vector containing 6.3 kbp of upstream sequence of the human thyroid peroxidase gene connected to a luciferase reporter gene. T/EBP was further expressed in HepG2 cells by using the vaccinia virus expression system. The expressed protein was partially purified by using sequence-specific affinity column chromatography and was further shown, by gel mobility shift experiments, to specifically bind to the enhancer-derived double-stranded oligonucleotide. These results clearly indicate that the binding of T/EBP (TTF-1) to the specific cis-acting enhancer element is largely responsible for thyroid-specific enhancer activity.
Mol Cell Biol 1991 Oct
PMID:Thyroid-specific enhancer-binding protein (T/EBP): cDNA cloning, functional characterization, and structural identity with thyroid transcription factor TTF-1. 192 26

The second enhancer (enhancer II) of hepatitis B virus is functionally liver specific. Located within an open reading frame of the virus and immediately upstream of the initiation sites of viral major transcripts, enhancer II furnishes a unique model for use in investigating the structure and function of an enhancer. In this study, two functional constituents, a 23-bp box-alpha and a 12-bp box-beta, are identified as being both necessary and sufficient for enhancer II function. Examination of the box-alpha and box-beta sequences reveals a weak homology to the extended consensus for a C/EBP binding site. Gel shift and footprinting analyses indicate that multiple proteins bind to these sequences and thus are candidate transcription factors that mediate the enhancer function. One heat-resistant protein, protein a, and one heat-sensitive protein, protein b, bind to box-alpha. Protein a, which binds to box-alpha in a way indistinguishable from that seen with a recombinant C/EBP, appears not to be identical to C/EBP in that the binding of protein a requires a minimal sequence larger than the canonical C/EBP sites. Two box-beta-binding proteins, c and d, show greater affinity for the C/EBP consensus than for box-beta. However, both proteins c and d are relatively heat sensitive and display a distinct sequence preference from the recombinant C/EBP protein. Since the function of enhancer II is strictly dependent on a bipartite architecture, this system provides a unique model for studies of how the interactions of its binding proteins lead to the enhancer function.
Mol Cell Biol 1991 Oct
PMID:C/EBP-like proteins binding to the functional box-alpha and box-beta of the second enhancer of hepatitis B virus. 192 32

A complex cell culture environment has been shown to maintain the differentiated state of hepatocytes, yet the mechanisms by which environmental cues selectively maintain liver-specific gene transcription have been unknown. In this paper we show that the hepatic environment regulates the activities of at least three liver-enriched transcription factors, eE-TF, eG-TF/HNF3, and eH-TF, that activate the mouse serum albumin enhancer. eE-TF is a heat-stable factor that has a DNA-binding specificity similar to that of the liver transcription factor C/EBP, but is a distinct protein. eG-TF/HNF3 contributes to the liver-specific transcription of several other serum protein genes. eH-TF binds to a TGTTTGC sequence that occurs at regulatory sites of the albumin promoter, the hepatitis B virus enhancer, and other hepatic genes. eE-TF, eG-TF/HNF3, and eH-TF are regulated by different combinations of the following cell culture conditions: a hormonally defined serum-free medium; an extracellular matrix gel; and a transformation-competent simian virus 40 large T antigen. We propose a regulatory network model to explain how cues from the cell lineage and the extracellular environment coordinately help maintain the activities of transcription factors involved in hepatocyte differentiation.
Mol Cell Biol 1991 Feb
PMID:Extracellular signals that regulate liver transcription factors during hepatic differentiation in vitro. 199 Feb 82

C/EBP is a rat liver DNA-binding protein which can act as a transcription factor. Its N-terminal portion contains three distinct domains. The first domain (amino acids 1 to 107) appears to be a highly potent transactivator. The second domain (amino acids 107 to 170) does not appear to exhibit either activation or repression activity. This domain is defined as an "attenuator domain" because its presence under four different sequence contexts reproducibly decreases the effect of transactivation of C/EBP. The third domain (amino acids 171 to 245) is a relatively weaker transactivator with a striking proline-rich motif. Deletional analysis of this third domain has shown that a 45-amino-acid region is sufficient for transactivation. This region (amino acids 171 to 215) contains 12 proline, 6 histidine, and mainly hydrophobic or noncharged amino acids. Further mutational analysis of a highly conserved proline-octamer region within this domain indicates that a specific proline content is not crucial for transactivation.
Mol Cell Biol 1991 Mar
PMID:An "attenuator domain" is sandwiched by two distinct transactivation domains in the transcription factor C/EBP. 199 5

Human preadipocytes contain nuclear factors that specifically bind to the AE-1 sequence, previously demonstrated as an enhancer element in the regulation of adipose P2 gene expression during 3T3 adipose differentiation. By transient transfection and in vivo competition experiments, the trans-acting factors were found to bind either to the C/EBP recognition site in the AE-1 sequence and act as a negative regulator or to the adjacent site (termed 3' AE-1) and act as a positive regulator of adipose P2 gene activity in human preadipocytes.
Mol Cell Biol 1991 Apr
PMID:The C/EBP-binding region and adjacent sites regulate expression of the adipose P2 gene in human preadipocytes. 200 13


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