Search PubMed⌕ Search

Biomedical subjects

M Yaniv

Publications and source records attributed to M Yaniv.

At least 109 records · Page 6Linked to original sources
PubMed1991

Unregulated expression of c-Jun or c-Fos proteins but not Jun D inhibits oestrogen receptor activity in human breast cancer derived cells.

We present evidence that oestrogen receptor activity in human MCF-7 breast cancer cells is reduced by over-expression of c-Jun or c-Fos proteins and to a lesser extent by Jun B overexpression. In contrast, overexpression of Jun D protein does not affect the activity of the oestrogen receptor. A region of c-Jun found to be required for repression of oestrogen receptor activity is located outside the DNA binding domain and is not conserved among the three Jun proteins. Finally, we suggest that c-Jun and c-Fos act independently to inactivate the oestrogen receptor.

Base Sequence↗
PubMed1991

Several different upstream promoter elements can potentiate transactivation by the BPV-1 E2 protein.

The enhancer and upstream promoter regions of RNA polymerase II transcribed genes modulate the rate of transcription initiation and establish specific patterns of gene expression. Both types of region consist of clusters of DNA binding sites for nuclear proteins. To determine how efficiently the same factor can activate transcription when acting as an enhancer or promoter factor, we have studied transactivation by the BPV-1 E2 protein, a papillomavirus transcriptional regulator. By cotransfecting a BPV-1 E2 expression vector and a series of reporter plasmids containing well-defined chimeric promoters we have found that whilst E2 can strongly stimulate complex promoters such as that of the HSV tk gene, it does not efficiently activate constructions containing only a TATA box and initiation site. We show that insertion of upstream promoter elements, but not of spacer DNA, between E2 binding sites and the TATA box greatly increases E2 activation. This effect was observed with more than one type of upstream promoter element, is not related to the strength of the promoter and is unlikely to result from co-operative DNA binding by E2 and the transcription factors tested. These results would suggest that E2 has the properties of an enhancer rather than promoter factor and that in certain cases promoter and enhancer factors may affect different steps in the process of transcriptional activation.

Base Sequence↗
PubMed1991

vHNF1 is expressed in epithelial cells of distinct embryonic origin during development and precedes HNF1 expression.

HNF1 (Hepatic Nuclear Factor 1) and vHNF1 are transcriptional regulators containing a highly divergent homeodomain. The first was initially found in liver nuclear extracts and is crucial for the transcription of albumin and many other hepatocyte specific genes, while the second was found in dedifferentiated hepatoma cells. Both recognize the same DNA binding site and can form homo and heterodimers in vitro and in vivo. In situ hybridization analyses have been performed to delineate the spatial and temporal pattern of expression of vHNF1 relative to HNF1 during mouse embryogenesis. The results show that accumulation of vHNF1 mRNAs expression is detected in several tissues of the embryo of both endodermal and mesodermal origin. Expression occurs in the yolk sac, the primitive gut, the liver primordium, and at different stages of kidney development in polarized epithelial structures and usually precedes that of HNF1. vHNF1 expression seems particularly prevalent with morphogenetic events in the kidney and may be a marker for certain polarized epithelium.

Animals↗
PubMed1991

Nuclear oncogenes.

Ample evidence has accumulated in recent years to establish that most, if not all, nuclear proto-oncogenes are in fact sequence-specific DNA-binding proteins that modulate gene expression. Their synthesis or activity is modulated by extracellular signals or by cross talk between different classes of transcription factors.

Animals↗
PubMed1991

The papillomavirus E2 protein: a factor with many talents.

The products of the papillomavirus E2 open reading frame play a key role in the regulation of the viral cycle. E2 proteins can activate or repress viral promoters by several distinct mechanisms and viral DNA replication requires the expression of the full-length E2 protein together with the product of the E1 open reading frame. This is an interesting example of how a single eukaryotic DNA-binding protein has evolved to perform several different functions and it provides a valuable model system for studying the regulation of eukaryotic transcription and DNA replication.

Animals↗
PubMed1991

Structural analysis of the human papillomavirus type 16-E2 transactivator with antipeptide antibodies reveals a high mobility region linking the transactivation and the DNA-binding domains.

In order to probe the structure of the transcription factor encoded by the E2 Open Reading Frame of papillomaviruses, we raised polyclonal antibodies against a series of synthetic peptides that cover the HPV16-E2 protein. In gel shift experiments with the native form of the protein, we detected supershifts (caused by the binding of antibodies to the E2-DNA complex) with antibodies synthesized against peptides covering a central region 50 residues long in the E2 protein. On the contrary, antibodies raised against peptides from the NH2- and COOH-termini did not give any supershifted band. Western blot experiments showed that several of these non reacting antibodies did however interact with the denatured protein. These results suggest that the central region that connects the NH2-terminal domain responsible for transcriptional activation and the COOH-domain involved in DNA-binding is exposed and maintained in a conformation resembling the peptide, indicating a high mobility region. In contrast, the DNA-binding and transactivation domains were not recognized by the antipeptide antibodies, in line with secondary structure predictions and sequence comparisons indicating that the E2 protein consists of structured and conserved NH2 and COOH-terminal regions separated by a non-conserved and unstructured region. This flexible 'hinge' region may facilitate contacts between E2 dimers at distance in mechanisms of transcriptional activation steps that involve homosynergy or DNA-looping.

Amino Acid Sequence↗
PubMed1991

The functional BPV-1 E2 trans-activating protein can act as a repressor by preventing formation of the initiation complex.

The products encoded by the E2 open reading frame of the papillomaviruses are DNA-binding transcription factors involved in the positive or negative regulation of multiple viral promoters. To further understand the mechanisms by which the same transcription factor may act differentially, the full-length BPV-1 E2 protein was expressed and purified from yeast and assayed in vitro for its capacity to modulate transcription. E2 stimulated transcription of the HSV thymidine kinase (TK) promoter when E2-binding sites were positioned in an enhancer configuration approximately 100 bp upstream of the promoter start site. In contrast, the same full-length E2 protein repressed transcription of the HPV-18 E6/E7 P105 promoter. This repression was mediated through binding to the E2 DNA-binding site immediately upstream of the P105 promoter TATA box and could be abrogated by preincubation of the HPV-18 P105 promoter template with the nuclear extract allowing the formation of the preinitiation complex. In vitro DNA-binding experiments with purified E2 and TFIID showed that binding of E2 to its DNA target placed at different positions with respect to the TATA box differentially affects binding of TFIID to its cognate site. In these respects, E2 is similar to the bacteriophage lambda repressor, which can act either as a repressor or an activator of transcription depending on the position of its binding sites relative to the promoter sequences.

Animals↗
PubMed1991

Hepatic nuclear factor 1 (HNF1) shows a wider distribution than products of its known target genes in developing mouse.

Hepatic nuclear factor 1 (HNF1) is a highly diverged homeoprotein that is crucial for transcription of many liver-specific genes including albumin. In particular, a minimal promoter, consisting of an HNF1-binding-site and a TATA box, is highly active only in hepatoma cell lines. The expression of the HNF1 and albumin genes has been examined in mouse embryos by in situ hybridization. At 10.5 days of gestation, the HNF1 mRNA was detected in both the hepatic primordia and visceral endoderm of the yolk sac whereas the albumin transcript was present only in the nascent liver. At later stages of development, HNF1 was detected in liver, in the epithelial cells of most of the digestive tract and in the cortex of the kidney, whereas albumin was again found only in the liver. The presence of HNF1 protein in adult kidney was demonstrated by immunodetection in gel-retardation assays and western blot analysis. These experiments show that, even though the HNF1 homeo-protein is essential for expression of many liver-specific genes, it cannot, by itself, force high expression levels of these genes, in non-hepatic tissues.

Albumins↗
PubMed1991

Two DNA-bound E2 dimers are required for strong transcriptional activation and for cooperation with cellular factors in most cells.

The E2 transcriptional activator encoded by papillomaviruses binds as a dimer to the palindromic sequence ACCGNNNNCGGT present in several copies in the viral genomes. We show that strong activation requires that a minimum of two E2 binding sites are actually occupied by the protein. Studies with constructs bearing two E2 sites separated by variable lengths of DNA showed that there is no stereospecific constraint for E2 homosynergy. The capacity of E2 to cooperate with cellular factors interacting with the promoter/enhancer sequences of the genomes of human papilloma virus types 16, 18, or 33 was further investigated. In epithelial cells, one E2 dimer could not cooperate with the AP1 complex, the glucocorticoid receptor, or the NF1/K factor, whereas several E2 dimers could. These results lead to the notion of the "functional E2 tetramer" as the unit for strong transcriptional activation by E2 and for cooperativity with other cellular factors in this process. Finally, our results suggest that activators such as E2 or the glucocorticoid receptor may interact with partially different targets in the transcriptional machinery.

Animals↗
PubMed1991

[Functional interaction between estrogen receptor and proto-oncogene products c-Jun and c-Fos].

We show here that TPA treatment of MCF-7 cells represses estrogen receptor dependent transcriptional activity, while increasing the AP1 binding activity. These two events are probably linked, since the transcriptional activity of the estrogen receptor in these cells is repressed by overexpression of both cJun or cFos, the components of the AP1 transcripts factor. On the contrary no repression was observed after overexpression of another member of the jun family, the JunD. The repression caused by cJun or cFos may depend on partially different pathways. Our results suggest that the inhibition of TPA of the estrogen dependent growth of the MCF-7 cells is caused by over expression of cJun and cFos.

Drug Interactions↗
PubMed1991

Transfected mouse c-jun can inhibit transformation of primary rat embryo fibroblasts.

The c-jun gene, which encodes a transcriptional regulatory protein, is the cellular homologue of the transforming gene of avian sarcoma virus 17. In an attempt to assess the biological activities of mouse c-jun, we studied the consequences of its overproduction in an in vitro transformation assay. A c-jun expression plasmid failed to cooperate with either ras, myc or mutant p53 in this focus formation assay. On the other hand, it dramatically inhibited the ability of various oncogene combinations to elicit foci upon transfection into primary rat embryo fibroblasts. Deletion plasmids lacking either the transactivating domain or the leucine repeat of c-jun still displayed a pronounced inhibitory activity. On the contrary, a plasmid encoding only the first 187 amino acids of c-jun had no such activity. The data suggests that enhanced c-jun expression may interfere with the induction or proliferation of transformed cells in this system, and that the inhibitory activity resides in the C-terminal half of the molecule.

Animals↗
PubMed1990

A distal dimerization domain is essential for DNA-binding by the atypical HNF1 homeodomain.

Hepatic Nuclear Factor 1 (HNF1, also referred to as LFB1, HP1 or APF) is a liver-specific transcription factor required for the expression of many hepatocyte specific genes. We report here the purification of this rat liver nuclear protein and the cloning of its cDNA using a PCR-derived approach. Seven independent clones reveal 3 alternative polyadenylation sites and a unique open reading frame. Both a motif homologous to the homeodomain and a distal dimerization domain are required for specific DNA binding. Sequence comparisons reveal several atypical features at key positions in the segment corresponding to helices III and IV of the Antaennapedia homeodomain as well as a potential 24 amino acid loop in place of the universal turn between helices II and III. Together with its property to dimerize in the presence or absence of DNA, these features place HNF1 as the prototype of a novel subclass of transcription factors distantly related to homeoproteins.

Amino Acid Sequence↗
PubMed1990

Hepatocyte dedifferentiation and extinction is accompanied by a block in the synthesis of mRNA coding for the transcription factor HNF1/LFB1.

The promoter proximal sequences of a group of liver-specific genes including that of albumin interact with the same hepato-specific factor named HNF1, LFB1, APF or HP1, a distant member of the homeoprotein family. A distinct protein, termed variant HNF1 (vHNF1), of lower mol. wt but displaying identical sequence specificity is found both in dedifferentiated variants and in an extinguished somatic hybrid that fail to express most or all of the tissue-specific traits, including albumin. We show here that HNF1 transcripts are present only in differentiated hepatoma cells. No transcripts are detected in dedifferentiated variants or in the extinguished cell hybrid, strongly suggesting that the vHNF1 protein is encoded by a distinct gene. Finally, HNF1 transcripts reappear in revertants to the hepatic phenotype. Run-on transcription analysis in isolated nuclei demonstrates that the expression of HNF1 in these cell lines is regulated primarily at the transcriptional level. Contrary to HNF1, the mRNAs coding for two other nuclear factors involved in albumin transcription, C/EBP and NF1, do not follow the distribution of albumin transcripts in these cell lines. These results indicate that extinction in somatic hybrids or loss of expression upon dedifferentiation of liver-specific genes possessing an HNF1 recognition site is caused, at least in part, by a block in HNF1 gene expression.

Animals↗
PubMed1990

Cloning of human hepatic nuclear factor 1 (HNF1) and chromosomal localization of its gene in man and mouse.

HNF1 is a transcription factor that is required for hepatocyte-specific expression of several genes, including albumin and fibrinogen. Rat HNF1-encoding cDNAs have recently been cloned, revealing that this factor is a distant member of the homeoprotein family. We have now isolated HNF1 clones from a human liver cDNA library by using a rat HNF1 cDNA-derived probe. The longest clone, HCL20, contains a sequence corresponding to the intact rat HNF1-coding region followed by a 3' nontranslated region and a poly(A) tail, hence representing an almost full-length HNF1 cDNA. Alignment of the human and rat sequences shows that HNF1 is highly conserved between the two species. The HNF1 gene was mapped by in situ hybridization and by RFLP analysis of interspecific mouse backcrosses to chromosomes 12q24.3 and 5F in human and mouse, respectively, establishing a new segmental homology between these two chromosomes.

Albumins↗
PubMed1990

Fos and Jun oncogenes transactivate chimeric or native promoters containing AP1/GCN4 binding sites in plant cells.

The function of mammalian transcription factors of the leucine zipper class was investigated in leaf-derived protoplasts of tobacco. In transient expression experiments, Fos and Jun strongly activated chimeric promoters composed of the TATA box region of the cauliflower mosaic virus 35S transcript preceded by one to five copies of an AP1/GCN4 binding site. Fos and Jun also stimulated a wheat high molecular weight glutenin promoter in which similar binding sites are located more than 500 base pairs from its transcription start site. Both the DNA binding and the transcription activation domains of these proteins were required for proper promoter stimulation by Fos and Jun. Each factor alone was partially active, suggesting that at least the Fos protein can associate with an endogenous plant transcription factor. These observations support the hypothesis that sequences related to AP1/GCN4 binding sites could be cis-acting modules involved in the transcriptional regulation of plant genes.

Base Sequence↗
PubMed1990

Cooperative activation of transcription by bovine papillomavirus type 1 E2 can occur over a large distance.

The viral transcriptional factors encoded by the E2 open reading frame bind to the specific DNA sequence elements ACCGNNNNCGGT, allowing activation or repression of transcription. We have analyzed bovine papillomavirus type 1 E2 transactivation using recombinant genes containing E2-binding sites inserted at either 3' or 5' positions relative to the heterologous transcriptional initiation site of the herpes simplex virus thymidine kinase gene. In these hybrid plasmids, strong transactivation required the presence of a minimum of two E2-binding sites in close proximity to the promoter or five binding sites at a distance. The presence of a single E2-binding motif 5', close to the initiation site, increased the efficiency of E2 transactivation from a distance in a more-than-additive manner. Since each E2-binding site bound a dimer of the E2 protein, these experiments suggest that transactivation by E2 requires the interaction between several E2 dimers with other essential transcription factors. This interaction may be facilitated by DNA looping, which would bring E2 molecules close to the promoter.

Base Sequence↗
PubMed1990

Chromosomal localization of the three members of the jun proto-oncogene family in mouse and man.

The three members of the jun proto-oncogene family c-jun, jun b and jun D were mapped on the mouse chromosome by in situ hybridization. The c-jun locus is on chromosome 4 subregion C5----C7, whereas jun B and jun D are co-localized on chromosome 8 subregion C. RFLP analysis of interspecific hybrids confirmed the mapping of jun B and D and showed that they are situated about 7.3 +/- 3.5 cM apart. Thus despite their possible origin from a single ancestral gene they are not closely linked on the chromosome. Using the same probes, we showed that the human genome also contains sequences homologous to the mouse jun B and jun D. They are located on human chromosome 19 p13.2, a region that may be involved in chromosomal translocation in acute lymphocytic leukemia (ALL), acute nonlymphocytic leukemia (ANLL) and malignant melanoma (MEL). Finally, the present data identify a new segmental homology between mouse and human chromosomes.

Animals↗