DNA sequences bound specifically by glucocorticoid receptor in vitro render a heterologous promoter hormone responsive in vivo

Generation of glucocorticoid-responsive Moloney murine leukemia virus by insertion of regulatory sequences from murine mammary tumor virus into the long terminal repeat

The glucocorticoid-regulatory sequences from the murine mammary tumor virus long terminal repeat (MMTV LTR) were introduced into the LTR of Moloney murine leukemia virus (M-MuLV) by recombinant DNA techniques. The site of insertion was in the M-MuLV LTR U3 region at -150 base pairs with respect to the RNA cap site. Infectious M-MuLVs carrying the altered LTRs (Mo + MMTV M-MuLVs) were recovered by transfection of proviral clones into NIH-3T3 cells. The Mo + MMTV M-MuLVs were hormonally responsive in that infection was 3 logs more efficient when performed in the presence of dexamethasone, irrespective of the orientation of the inserted MMTV sequences. However, even in the presence of hormone, the Mo + MMTV M-MuLVs were less infectious than wild-type M-MuLV. In contrast to the large effect on infectivity, dexamethasone induced virus-specific RNA levels in chronically Mo + MMTV M-MuLV-infected cells only two- to fourfold. Fusion plasmids between the altered LTRs and the bacterial chloramphenicol acetyltransferase gene allowed the investigation of LTR promoter strength by the transient chloramphenicol acetyltransferase expression assay. The chloramphenicol acetyltransferase assays indicated that the insertion of MMTV sequences into the M-MuLV LTR reduced promoter activity in the absence of glucocorticoids but that promoter activity could be induced two- to fivefold by dexamethasone. The Mo + MMTV M-MuLVs were also tested for the possibility that viral DNA synthesis or integration during initial infection was enhanced by dexamethasone. However, no significant difference was detected between cultures infected in the presence or absence of hormone. The insertion of MMTV sequences into an M-MuLV LTR deleted of its enhancer sequences did not yield infectious virus or active promoters, even in the presence of dexamethasone.

The TGGCA protein binds to the MMTV-LTR, the adenovirus origin of replication, and the BK virus enhancer

TGGCA-binding proteins are nuclear proteins with high affinity for double-stranded DNA homologous to the prototype recognition sequence 5'YTGGCANNNTGCCAR 3'. Their ubiquitous tissue distribution in higher vertebrates characterizes them as a class of highly conserved proteins which may exert a basic function. To obtain clues to this function, specific binding sites were mapped on three viral genomes. Recognition sites were identified in the enhancer region of the BK virus, in the LTR of the mouse mammary tumor virus, and in the origin of replication of adenovirus 12. The TGGCA-binding protein from HeLa cells appears to be identical to nuclear factor I described by others, which stimulates initiation of adenovirus DNA replication in vitro. However, data from MMTV, BKV, and from cellular genes suggest that this specific protein-DNA interaction may also be involved in the control of gene activity.

High-affinity binding site for a specific nuclear protein in the human IgM gene

Proteins binding to specific regions of DNA with high affinity frequently govern or regulate reactions at the gene level. We have identified a high-affinity binding site in the immunoglobulin mu gene that binds a specific nuclear protein, and have now characterized it fully using nuclear factor 1 (NF-1), a protein purified from the nuclei of HeLa cells and required for the in vitro replication of adenovirus (Ad) DNA. NF-1 protects a 25-base pair (bp) double-stranded segment of DNA which shares a consensus sequence, 5' TGGA/CNNNNNGCCAA 3', with similar binding sites in the Ad-5 terminal repeat and the human c-myc gene. Although this site differs from the enhancer region, a biological function is suggested by the fact that it is DNase I hypersensitive in immunoglobulin-producing lymphoblastoid cells. The binding site for the NF-1 protein in the mu gene, by analogy with the site in the Ad-5 terminal repeat, may represent one component of a cellular origin of replication; alternatively, it may be responsible for the activation of the chromatin in this region.

Rous sarcoma virus encodes a transcriptional activator

Rous sarcoma virus expresses a transcriptional activator that affects the LTR as well as other promoters. We discern this activity as a stimulation of the transient expression of an LTR-promoted hybrid transcriptional unit and also of the rat preproinsulin II gene in transfected NIH 3T3 cells. We map the activity to an alternate reading frame in the p19-p10 region of the gag gene and identify a mRNA whose spliced structure would direct translation of this reading frame from the Pr76gag initiation codon. This mRNA probably differs from genomic RNA only by the 282 nucleotide splice. The predicted translation product is a 124 residue polypeptide; the first six amino acids arise from gag. The target for the action of this transcriptional modulator at the LTR lies between 111 and 620 nucleotides upstream of the cap site.

Glucocorticoid and progesterone receptors bind to the same sites in two hormonally regulated promoters

The glucocorticoid receptor of rat liver recognizes nucleotide sequences near the promoter of mouse mammary tumour virus (MMTV) required for hormonal induction in gene transfer experiments. Similar nucleotide sequences have been found in the human metallothionein gene IIA and in the chicken lysozyme gene, the later induced also by oestrogen, progesterone and androgens. In microinjection experiments, deletion of only 44 base pairs (bp) of the lysozyme promoter (from -208 to -164) results in coordinated loss of progesterone and glucocorticoid-dependent gene expression. We show here that purified glucocorticoid receptor from rat liver and progesterone receptor from rabbit uterus yield similar or overlapping exonuclease III footprints in the promoter regions of MMTV and chicken lysozyme. Thus, the regulatory elements for different steroid hormones may be similar or at least share structural features.

A trans-acting factor is responsible for the simian virus 40 enhancer activity in vitro

Stimulation of in vitro transcription by the simian virus 40 enhancer involves a rapid and stable binding of a trans-acting factor with both the 5'- and 3'-domains of the enhancer sequence. The enhancer factor, which differs from other types of transcriptional factors, can interact with other enhancer elements.

Selective binding of the estradiol receptor to a region at least one kilobase upstream from the rat prolactin gene

The interaction of the estradiol receptor with cloned DNA fragments from the prolactin gene was investigated using a competitive binding assay. A DNA fragment from the 5'-flanking region of the rat prolactin gene was able to bind the estradiol receptor selectively. DNA fragments representing most of the remaining 10 kb of the prolactin gene showed little or no selective binding to the estradiol receptor. The fragment from the 5'-flanking region which selectively binds the receptor is located between 1.2 and 2.0 kb upstream from the transcription initiation site rather than in a more proximal position as has been observed for the interaction of several other steroid hormone receptors with specific genes. Nucleotide sequence analysis demonstrated that this region of DNA contains two large segments of alternating purine-pyrimidine sequence. One of the alternating purine-pyrimidine regions is very large, containing more than 160 nucleotides of almost perfect poly(dG-dT). Further studies will be required to determine if the receptor interacts specifically with these interesting sequences. However, the ability of the estradiol receptor to bind to an upstream 5'-flanking region of the prolactin gene may be part of the mechanism which allows the receptor to stimulate the transcription of this gene selectively.

Hormonal response region in the mouse mammary tumor virus long terminal repeat can be dissociated from the proviral promoter and has enhancer properties

The proviral DNA of mouse mammary tumor virus (MMTV) contains a regulatory region closely associated with its promoter, which subjects transcription to the control of glucocorticoid hormones. Delimitation analysis of a chimeric MMTV long terminal repeat-thymidine kinase gene (LTR-tk) has shown that the hormonal regulation sequence is confined to 202 nucleotides preceding the LTR-specific RNA initiation site. A second RNA initiation site (tk-specific mRNA) placed close to the regulatory MMTV sequence by in vitro recombination is also subjected to hormonal stimulation in transfected cells. A series of plasmids with deletions around the LTR cap site progressing from 3' to 5' was made and functionally tested. In vitro deletion of MMTV LTR sequences comprising the RNA initiation sequence and the "TATA" box do not effect hormonal regulation at the tk-specific mRNA start site. Nucleotides up to position -59 from the LTR initiation site could be deleted without influence on the glucocorticoid regulation, whereas deletions to position -65 abolished the hormonal effect on the tk gene transcription. A short MMTV LTR segment containing nucleotides -236 to -52 from the LTR initiation site was recombined with the tk gene or the alpha-globin gene. This fragment confers hormonal inducibility onto the heterologous genes over distances of 0.4 or 1.1 kilobases. The hormonal response region functions when it is placed either 5' or 3' of the regulated gene in both of the possible orientations and is reminiscent of an enhancer sequence.

The first intron of the human growth hormone gene contains a binding site for glucocorticoid receptor

Glucocorticoid receptor (GCR) protein stimulates transcription from a variety of cellular genes. We show here that GCR partially purified from rat liver binds specifically to a site within the first intron of the human growth hormone (hGH) gene, approximately 100 base pairs downstream from the start of hGH transcription. GCR binding is selectively inhibited by methylation of two short, symmetrically arranged clusters of guanine residues within this site. A cloned synthetic 24-base-pair deoxyoligonucleotide containing the predicted GCR binding sequence interacts specifically with GCR. The hGH binding site shares sequence homology with a GCR binding site upstream from the human metallothionein II gene and a subset of GCR binding sites from mouse mammary tumor virus. All of these binding sites for this eukaryotic transcriptional regulatory protein show remarkable similarity in overall geometry to the binding sites for several prokaryotic transcriptional regulatory proteins.

Saccharomyces cerevisiae GAL1-GAL10 divergent promoter region: location and function of the upstream activating sequence UASG

The GAL1 and GAL10 genes, separated by 680 base pairs and divergently transcribed on chromosome 2 of Saccharomyces cerevisiae, were separately fused to the lacZ gene of Escherichia coli so that beta-galactosidase synthesis in S. cerevisiae reflected GAL1 and GAL10 promoter function. Analysis of two sets of deletions defined a 75-base-pair sequence, located ca. midway between the transcription initiation regions of GAL1 and GAL10, that mediates GAL4-dependent induction of both genes. Deletion of various parts of this sequence (called the GAL upstream activating sequence or UASG) reduced GAL1 and GAL10 induction about equally. Sequences in the GAL10-proximal half of UASG in some sequence contexts functioned independently of sequences in the GAL1-proximal half of UASG. A 33-base-pair deletion of the GAL10-proximal half of UASG drastically reduced induction. Deletions between UASG and the GAL1 TATA box caused beta-galactosidase to be synthesized at an unexpectedly high basal level, that is, in the absence of galactose and GAL4 product. Some of these mutations also reduced the repression caused by glucose.

Bovine leukemia virus long terminal repeat: a cell type-specific promoter

The functional activity of the promoter unit contained within the long terminal repeat (LTR) of bovine leukemia virus (BLV) was examined by monitoring transient expression of a heterologous gene placed under its control. Various cell lines were transfected with recombinant plasmids carrying the bacterial chloramphenicol acetyltransferase (CAT) gene coupled to the BLV LTR (pBL-cat). Transient expression of CAT activity directed by the BLV LTR was observed only in the established BLV-producer cell lines derived from fetal lamb kidney (FLK) cells and bat lung cells. The amount of CAT activity transiently expressed in FLK-BLV cells was decreased approximately tenfold by deletion of LTR sequences located within a region 100 to 170 nucleotides upstream of the RNA start site. Surprisingly, removal of the region 50 base pairs downstream of the RNA initiation site to the 3'-end of the LTR reduced the expression of CAT activity by 87 percent. The BLV LTR thus appears to be an unusual promoter unit, functioning in a cell type-specific manner and possessing sequences on both the 5' and 3' sides of the RNA start site that influence gene expression.

B lineage--specific interactions of an immunoglobulin enhancer with cellular factors in vivo

The mouse heavy chain immunoglobulin gene contains a tissue-specific enhancer. The enhancer and flanking sequences were studied in vivo by carrying out dimethyl sulfate protection experiments on living cells, in combination with genomic sequencing. Relative to reactions on naked DNA, there are changes (protections and enhancements) in the reactivity of guanine residues to dimethyl sulfate within the enhancer sequence in myeloma, B, and early B cells, whereas virtually no alterations appear in cells of non-B lineage. Most of the affected residues are in four clusters, in sequences homologous to the octamer 5'CAGGTGGC 3' (C, cytosine; A, adenine; G. guanine; T, thymine). The alterations in the pattern of G reactivity are consistent with the tissue-specific binding of molecules to the mouse immunoglobulin heavy chain enhancer.

An enhancer-like element in the adenovirus E2 promoter contains sequences essential for uninduced and E1A-induced transcription

Using a chloramphenicol acetyltransferase gene under the control of a series of adenovirus E2 promoter mutants, we have determined the sequence requirements for E1A-induced as well as uninduced expression of the E2 promoter. Fully induced expression requires 79 nucleotides of upstream sequence, and the same sequences are required for uninduced expression. A promoter containing 70 nucleotides of upstream sequence is inducible, although to a lower level than wild type, while a promoter containing 59 nucleotides of upstream sequence is not inducible. The sequences required for induction as well as for uninduced promoter activity map between 21 and 79 nucleotides upstream of the transcriptional initiation site and function in either orientation and at a distance. We suggest that E1A-mediated induction involves the effective increase in a factor utilizing this upstream site and that the factor can functionally interact with the site irrespective of its location relative to the start of transcription.

Analysis of gene expression during hematopoiesis: present and future applications

Recombinant DNA technology now provides the strategies required to identify genes whose expression controls the development of normal and pathologic blood cells. Characterization of the gene families responsible for synthesis of hemoglobins, immunoglobulins, histocompatibility antigens, and cellular enzymes have already, or are about to, provide major insights into the mechanisms producing normal erythroid cells, immunocytes, and immune surface features. Hemoglobinopathies, leukemias, and autoimmune diseases of the bone marrow can now be examined to a degree of detail previously inaccessible to investigators. Oncogene translocation analysis is shedding new light on the pathogenesis of leukemias and lymphomas. Recent basic advances now permit direct cloning and identification of genes in host organisms which express their protein products, thus allowing isolation of genes coding for the hematopoietic surface markers and growth factors which characterize and regulate blood cell progenitors. This review summarizes the molecular genetic approach to analysis of normal and pathologic hematopoiesis, surveys major findings which have resulted, and examines the potential use of refined gene cloning strategies for improved understanding of blood cell development.

A synthetic HIS4 regulatory element confers general amino acid control on the cytochrome c gene (CYC1) of yeast

Hybrid promoters constructed from upstream sequences of the yeast HIS4 promoter and the downstream element of the yeast CYC1 promoter place iso-1-cytochrome c (CYC1) expression under the general amino acid control, typical of HIS4. HIS4 fragments that confer regulation contain at least one copy of the sequence T-G-A-C-T-C that is repeated at HIS4 and other genes subject to the general control. A 14-base-pair synthetic oligonucleotide containing a single copy of the HIS4 repeat places CYC1 under the general control. Two copies of this oligonucleotide produce a derepressed level of expression nearly equivalent to that conferred by the largest HIS4 5' noncoding fragments we examined and direct regulated expression of a set of transcripts with 5' ends typical of the CYC1 promoter. Comparison of the expression levels conferred by the short synthetic repeat and larger HIS4 5' fragments reveals additional promoter elements required for maintaining efficient gene expression under repressing growth conditions.

Pretranslational regulation of tyrosine aminotransferase and phosphoenolpyruvate carboxykinase (GTP) synthesis by glucagon and dexamethasone in adult rat hepatocytes

The regulation of synthesis of the gluconeogenic cytosolic enzyme phosphoenolpyruvate carboxykinase (PEPCK) and of tyrosine aminotransferase (TAT) by glucagon and glucocorticoid hormones was studied in hepatocytes maintained in suspension culture for 7 h. Specific antibodies were used to measure relative rates of enzyme synthesis after pulse-labelling of the cells with [3H]leucine or [35S]methionine. Concomitantly, amounts of mRNA were quantified after translation in vitro in a reticulocyte lysate and specific immunoprecipitation of the proteins. Glucagon stimulated the rate of synthesis of PEPCK by 4-6-fold and that of TAT by 6-8-fold in 2h. In contrast, dexamethasone had little effect on PEPCK synthesis, whereas it increased TAT synthesis by 5-9-fold. When used in combination, the two hormones displayed additive effects on TAT synthesis, whereas the glucocorticoid hormone strongly potentiated stimulation of PEPCK synthesis by glucagon. In every instance, changes in rates of synthesis of the two enzymes were totally accounted for by increases in amounts of the corresponding functional mRNA, suggesting a pretranslational site of action for both glucagon and dexamethasone.

Effect of cell cycle position on transformation by microinjection

We have investigated the effect of cell cycle position on the efficiency of transformation by microinjection. Linear recombinant plasmids transform synchronized cells with similar frequencies following injections at all cell cycle stages, whereas supercoiled molecules show a decreased ability to generate transformants in early S phase. This inhibition is not due to an inability to transiently express a transferred gene, since cells at all stages of the cycle efficiently expressed a hamster adenine phosphoribosyltransferase gene introduced on a supercoiled plasmid. Southern transfer analyses of the cell cycle specific transformants revealed that tandem arrays of plasmids, integrated into the host chromosomes, could be generated at all cell cycle stages.

Effects of glucagon, dexamethasone and triiodothyronine on phosphoenolpyruvate carboxykinase (GTP) synthesis and mRNA level in rat liver cells

Acute hormonal effects on the synthesis rate of the cytosolic form of the gluconeogenic enzyme, phosphoenolpyruvate carboxykinase (GTP), were investigated using rat hepatocytes maintained in short-term suspension culture. Cells were pulse-labeled with [3H]leucine or [35S]methionine and the rate of synthesis of phosphoenolpyruvate carboxykinase was estimated after immunoprecipitation of cell extracts with specific antibodies or following high-resolution two-dimensional gel electrophoresis of cell proteins. Total RNA was also extracted from cultured cells and subsequently translated in a wheat germ cell-free protein-synthesis system, in order to quantify the level of functional mRNA coding for phosphoenolpyruvate carboxykinase. Glucagon, the single most effective inducer, causes a 15--20-fold increase in the level of specific mRNA in 2 h, accompanied by a similar increase in enzyme synthesis rate. The extent of induction is further amplified about threefold when dexamethasone is added to the culture medium. The synergistic action of dexamethasone does not require pre-exposure of the cells to the glucocorticoid, but on the contrary occurs without lag upon simultaneous addition of glucagon and dexamethasone. The induction of phosphoenolpyruvate carboxykinase mRNA by glucagon is markedly depressed in hepatocytes inhibited for protein synthesis by cycloheximide. Cycloheximide-inhibited cells, however, display a considerable induction of the message after joint stimulation with dexamethasone and glucagon. Thus, the synergistic action of dexamethasone does not require concomitant protein synthesis. These data provide indirect evidence for a primary effect of the glucocorticoids on the expression of the phosphoenolpyruvate carboxykinase gene. Besides glucagon and dexamethasone, the thyroid hormones are shown to influence the rate of phosphoenolpyruvate carboxykinase synthesis in isolated liver cells. The stimulatory effect of 3,5,3'-triiodothyronine (T3) is best demonstrated as a twofold increase in relative rate of enzyme synthesis in cells supplied with T3 plus glucagon, as compared to cells challenged with glucagon alone. The effect of T3 relies on a pretranslational mechanism, as shown by a commensurate increase in functional mRNA coding for phosphoenolpyruvate carboxykinase. Dose-response experiments with T3 as well as dexamethasone demonstrate effects at very low hormone levels, consistent with a role for these hormones as physiological modulators of phosphoenolpyruvate carboxykinase expression.

Adenovirus-2 E1A products repress enhancer-induced stimulation of transcription

The adenovirus-2 early region 1A (E1A) products repress activation of transcription induced by the simian virus 40, polyoma virus and adenovirus-2 E1A enhancers. The repression probably involves an interaction between the enhancer elements and a trans-acting factor(s), possibly the E1A products themselves.

tk Enzyme expression in differentiating muscle cells is regulated through an internal segment of the cellular tk gene

Thymidine kinase (tk) enzyme expression is shut down when cultured skeletal muscle cells terminally differentiate. This regulation is mediated by a rapid and specific decline in the abundance of cellular tk mRNA. tk-deficient mouse myoblasts were transformed to the tk-positive phenotype by using both the cellular tk gene of the chicken and the herpesvirus tk gene. Myoblasts transformed with the cellular tk gene effectively regulate tk enzyme activity upon terminal differentiation. Conversely, myoblasts transformed with the herpesvirus tk gene continue to express tk enzyme activity in postreplicative muscle cells. A regulated pattern of expression is retained when the promoter of the cellular tk gene is replaced by the promoter of the herpesvirus tk gene. Moreover, the cellular tk gene is appropriately regulated during terminal muscle differentiation when its 3' terminus is removed and replaced by the terminus of the viral tk gene. Thus, the element of the cellular tk gene sufficient to specify its regulation is entirely intragenic.

Upstream activation sites of the CYC1 gene of Saccharomyces cerevisiae are active when inverted but not when placed downstream of the "TATA box"

The ability of the upstream activation sites (UASs) of the yeast CYC1 gene to function when inverted or when positioned downstream of the "TATA box" is investigated. Inversion of a 130-base-pair DNA fragment bearing the UASs leaves the activity of the sites almost completely intact. In contrast, positioning the sites downstream of the TATA box or in the intron of a CYC1-ribosomal protein 51-lacZ tribrid gene almost totally abolishes their activity. In the latter construct, the separation between the UASs and TATA box is roughly equivalent to that between the elements in the intact CYC1 promoter region. The UASs are shown not to interrupt transcription of splicing in this construct since a GAL10 UAS positioned upstream of the TATA box gives rise to galactose-inducible expression of the tribrid gene. The inability of the UASs to function in the intron is partly due to sequences between the intron and the TATA box that block the activation signal. However, a large component of the inactivity of the sites in the intron appears to be their downstream location. This result is discussed in light of possible mechanisms of upstream activation in yeast.

Characterization of a steroid hormone receptor gene and mRNA in wild-type and mutant cells

The effects of steroid hormones are mediated by intracellular hormone-specific receptor proteins; the interaction between the hormone and its receptor increases the affinity of the receptor for nuclear binding sites, thereby modulating the expression of specific genes. The glucocorticoid receptor is a soluble protein of relative molecular mass (Mr) 94,000 (94K), present at a low relative abundance (less than or equal to 0.01%); it has been purified to near-homogeneity, and specific antisera and monoclonal antibodies have been produced. Purified glucocorticoid receptor binds in vitro with high affinity to defined regions of DNA near regulated promoters, and sequences essential for these interactions are functional in vivo as hormone-dependent transcriptional enhancer elements. We have now cloned complementary DNA (cDNA) for the rat liver glucocorticoid receptor and we describe here a 2.6-kilobase (kb) receptor cDNA isolated following polysome immuno-enrichment of receptor messenger RNA with glucocorticoid receptor-specific antibodies. The receptor appears to be encoded by a single-copy gene which specifies a approximately 6-kb transcript in rat and mouse cells; this mRNA is altered quantitatively and qualitatively in several mutant cell lines with specific defects in receptor function.

Genetic properties and chromatin structure of the yeast gal regulatory element: an enhancer-like sequence

DNA molecules created by fusing a 365-base-pair segment of yeast DNA encoding the galactose-regulated upstream promoter element (gal) to a set of derivatives that systematically delete sequences upstream from the his3 gene are introduced in single copy back into the yeast genome precisely at the his3 locus and then assayed for transcription. Fusions of the gal regulatory element to his3 derivatives containing all normal mRNA coding sequences but lacking essentially the entire promoter region fail to express his3 under any growth conditions. Fusions to derivatives lacking the his3 upstream promoter element but containing the "TATA box" place his3 expression under gal control--i.e., extremely high RNA levels in galactose-containing medium and essentially no his3 RNA in glucose-containing medium. However, of the two normal his3 initiation sites, only the downstream one is activated by the gal element. In fusions of this type, neither the orientation of the gal element nor the distance between the element and the his3 TATA box affects the level or the initiation points of transcription. However, the gal element does not influence transcription when placed 100 or 300 base pairs downstream from the normal mRNA start sites. Fusions to derivatives containing the entire his3 promoter region restore the basal level of his3 transcription in glucose-grown cells, and both transcriptional initiation sites are used. Furthermore, RNA levels in galactose-grown cells, although somewhat higher than in glucose-grown cells, are significantly below the fully induced level. The distance from his3 coding sequences does not affect RNA levels, suggesting that specific sequences, possibly corresponding to the his3 upstream promoter element, reduce the ability of the gal element to activate transcription. Analysis of chromatin from some of these strains indicates a DNase I-hypersensitive site(s) in the middle of the gal element. However, this structural feature is not correlated with transcriptional initiation because it is found when cells are grown in glucose medium and also in derivatives lacking a TATA box. Thus, the gal upstream element possesses most, but not all, of the properties of viral and cellular enhancer sequences of higher eukaryotes. In addition, it appears that the his3 and gal upstream sequences represent two distinct classes of promoter elements, which activate transcription from different initiation sites.

Organization and expression of genes encoding prostatic steroid binding protein

We have cloned the genes for prostatic steroid binding protein to study the mechanism whereby their expression is regulated by testosterone. The genes for the C1 and C2 polypeptides are probably unique whereas there are two genes C3(1) and C3(2) for the C3 polypeptide of which only the former is transcribed in vivo. The state of DNA methylation associated with the two genes for C3 also differ, insofar as C3(1) is demethylated in ventral prostate from 14-28 days of age, whereas the C3(2) gene remains hypermethylated. The organization of all four genes is similar and appreciable DNA sequence homologies suggest that they may have arisen from a single ancestral gene. To study C3 expression and its hormonal regulation we have introduced the cloned genes into mouse S115 cells, an androgen-responsive cell line. Both genes were accurately transcribed and their expression was stimulated up to fivefold by 10(-8) M testosterone in approximately one third of the clones tested. To delineate the site of action of the hormone we have constructed chimeric genes consisting of putative C3 promoters and regulatory sequences together with a marker gene, interferon. This chimeric gene resulted in interferon production but its expression was stimulated by less than twofold in all clones tested. Therefore, these results indicate that, in mouse cells, testosterone does not interact directly with the rat C3 promoter but, in certain clones, may act post-transcriptionally.

Tissue-specific expression of the rat pancreatic elastase I gene in transgenic mice

The gene for rat pancreatic elastase I is selectively expressed to high levels in the rat exocrine pancreas. When the cloned rat elastase I gene with 7 kb upstream and 5 kb downstream flanking sequences was introduced into mice by microinjection into fertilized eggs, the gene was expressed in a pancreas-specific manner. In four of five transgenic mice, the level of rat elastase I mRNA in the pancreas was equal to or greater than the normal rat level (10,000 mRNAs per cell) and correlated with the number of integrated gene copies. In nonpancreatic tissues the levels were at least 10(3)-fold lower, except for expression in the liver of one mouse. Thus transfer of a 23 kb genomic DNA segment containing the rat elastase I gene to a foreign chromosomal location in the mouse can give rise to qualitatively and quantitatively normal expression.

A retroviral provirus closely associated with the Ren-2 gene of DBA/2 mice

We have determined the entire nucleotide sequence of an intra-cisternal A particle (IAP) genome, associated with the Ren-2 gene of DBA/2 mice. This genome (MIARN) displays features common to other IAP retroviral-like genomes. Long terminal repeats (LTRs) are approximately 430 base pairs (bp) in length and show typical retroviral U3-R-U5 organisation, though the R-region, at 120 bp, is much larger than the average IAP. This difference probably arose by the amplification of a pyrimidine-rich sequence, by a slippage-mispairing mechanism. Flanking the 5' LTR is a sequence complementary to a phenylalanine tRNA, strongly conserved in all rodent IAP genomes and probably required to prime the initiation of (-) strand synthesis. Flanking the 3' LTR, is a purine-rich sequence probably required for (+) strand synthesis. The tRNA binding site (TBS) is flanked by six tandem copies of a sequence homologous to the TBS. The relationship of the MIARN element to other IAP genomes and the significance of its association with the highly expressed Ren-2 is discussed.

Control of gene expression by glucocorticoid hormones

Glucocorticoids control the expression of a small number of transcriptionally active genes by increasing or decreasing mRNA concentration. Either effect can result from a transcriptional or a post-transcriptional mechanism. Induction of mouse mammary tumour virus RNA results from a stimulation of transcription initiation and depends on the presence of defined regions in proviral DNA. These regions bind the glucocorticoid receptor and behave functionally as proto-enhancers. Glucocorticoid-inducible genes can retain their sensitivity to the hormone after transfer to a heterologous cell by transfection techniques. Non-inducible genes can become inducible when linked to the promoter region of an inducible gene. The mechanisms by which the receptor-steroid complex stimulates or inhibits transcription or influences mRNA stability are unknown. Receptor binding to nucleic acids appears to be a necessary but not sufficient condition. It is likely that the receptor also interacts with chromatin proteins. This might lead to a catalytic modification of these proteins, resulting in a modulation of gene expression. Development of glucocorticoid-sensitive, biochemically defined, cell-free transcription systems should provide a tool to delineate the molecular determinants of this essential regulatory mechanism.

Regulation of glucose-6-phosphate dehydrogenase mRNA by insulin and the glucocorticoids in primary cultures of rat hepatocytes

The levels of functional mRNA encoding glucose-6-phosphate dehydrogenase (G6PDH; EC 1.1.1.49) were examined in hepatocytes from fasted and fasted/carbohydrate-refed rats and in hepatocytes inoculated into primary culture. Functional G6PDH mRNA was assessed in a cell-free protein synthesis system in vitro. We observed that hepatocytes from fasted/carbohydrate-refed rats had a 12-fold higher level of mRNA than did hepatocytes from fasted rats. The possibility that the adrenal glucocorticoids and insulin were responsible for the increase in G6PDH mRNA in refed rats was examined by studying the effect of insulin and the synthetic glucocorticoid, dexamethasone, on the level of functional G6PDH mRNA in primary cultures of rat hepatocytes maintained in a chemically defined medium. Hepatocytes from fasted rats were inoculated into primary culture and maintained for 48 h either in the absence of hormones or in the presence of insulin alone, dexamethasone alone or both hormones together. We observed that dexamethasone alone caused a fourfold increase in G6PDH mRNA while insulin caused about a twofold increase. Both hormones together elicited an increase that was additive. A comparison of functional G6PDH mRNA levels with the effect of the hormones on G6PDH activity and relative rate of enzyme synthesis suggests that the glucocorticoid elevates the level of G6PDH mRNA within the cell without causing a concommitant increase in the rate of synthesis of the enzyme or the level of G6PDH activity. The results obtained with the primary cultures of hepatocytes indicate that insulin and the glucocorticoids are probably involved with the regulation of hepatic G6PDH mRNA. However, involvement of other hormones, such as thyroid hormone, seems likely since the induced levels of G6PDH mRNA in hepatocytes in culture was one-third of that observed in refed rats.

Structure and nucleotide sequence of the putative mammary oncogene int-1; proviral insertions leave the protein-encoding domain intact

Many mammary tumors induced by mouse mammary tumor virus (MMTV) contain a provirus in the same region of the host-cell genome, leading to expression of a putative cellular oncogene called int-1. Here we present the structure and nucleotide sequence of int-1. We have established several proviral insertion sites exactly by nuclease S1 analysis or by molecular cloning and DNA sequencing. The protein-encoding domain of int-1 is distributed over four exons. At the 5' end of the gene two overlapping exons were detected, one of which is preceded by a TATA box. The deduced int-1-encoded protein has 370 amino acids, with a preponderance of hydrophobic residues at the NH2 terminus. Proviruses are found at both sides of the gene, usually oriented away from the gene. Downstream integrations occur frequently in the long 3' untranslated region of the last exon. One upstream provirus is inserted in the 5' untranslated region and, unlike the other upstream insertions, in the same orientation as the int-1 gene. Proviral integrations always leave the protein-encoding domain intact, providing further evidence that the int-1 protein contributes an essential step in mammary tumorigenesis.

Saccharomyces cerevisiae GAL1-GAL10 divergent promoter region: location and function of the upstream activating sequence UASG

The GAL1 and GAL10 genes, separated by 680 base pairs and divergently transcribed on chromosome 2 of Saccharomyces cerevisiae, were separately fused to the lacZ gene of Escherichia coli so that beta-galactosidase synthesis in S. cerevisiae reflected GAL1 and GAL10 promoter function. Analysis of two sets of deletions defined a 75-base-pair sequence, located ca. midway between the transcription initiation regions of GAL1 and GAL10, that mediates GAL4-dependent induction of both genes. Deletion of various parts of this sequence (called the GAL upstream activating sequence or UASG) reduced GAL1 and GAL10 induction about equally. Sequences in the GAL10-proximal half of UASG in some sequence contexts functioned independently of sequences in the GAL1-proximal half of UASG. A 33-base-pair deletion of the GAL10-proximal half of UASG drastically reduced induction. Deletions between UASG and the GAL1 TATA box caused beta-galactosidase to be synthesized at an unexpectedly high basal level, that is, in the absence of galactose and GAL4 product. Some of these mutations also reduced the repression caused by glucose.

Hormonal regulation of the Rous sarcoma virus src gene via a heterologous promoter defines a threshold dose for cellular transformation

We have derived rat cell lines producing different and regulatable amounts of pp60v-src by introducing the src gene of Rous sarcoma virus (RSV) under the control of the glucocorticoid-responsive transcriptional promoter from the mouse mammary tumor virus (MMTV). We find that the cellular phenotype is strictly dependent upon the dose of pp60v-src with a distinct threshold for changes indicative of neoplastic potential. Cells with low constitutive levels of pp60v-src are not phenotypically distinguishable from cells without v-src, but as little as a 4-fold increment in pp60v-src produces morphological transformation and anchorage-independent growth. These properties of the transformed state are achieved at levels of pp60v-src far below levels found in an RSV-transformed cell line, without detectable increase in phosphorylation of the major cellular target for tyrosine phosphorylation.

Molecular cloning of a cDNA for the chicken progesterone receptor B antigen

A cDNA for the chicken progesterone receptor B subunit antigen (Mr, 108,000) has been isolated from a cDNA library prepared from size-selected chicken oviduct poly(A)+RNA. A specific monoclonal antibody raised against hen progesterone receptor B subunit (alpha PR-B) was used to screen the library. Recombinant clones reacting with the antibody by virtue of antigen expression were used in hybrid-selected translation. A single clone, pPRB-1, hybridized specifically to a mRNA that yielded a Mr 108,000 protein when translated in vitro and which was immunoprecipitable by the alpha PR-B antibody. This cDNA represents a 470-base-pair portion of the PR-B nucleotide sequence. Additional clones have been subsequently isolated from the recombinant library using the insert from pPRB-1 as a specific probe. A mRNA size of approximately 3000 nucleotides was determined for the chicken progesterone receptor B subunit by formaldehyde/agarose gel electrophoresis and blot hybridization using pPRB-1 as a probe. Preliminary studies show that withdrawal of hormone from chickens treated chronically with estrogen leads to a dramatic decrease in the cellular RNA concentration of receptor B, indicating that target tissue levels of receptor B RNA are under hormonal control.

Control of neuronal gene expression

Some 30,000 genes are expressed exclusively in the rat brain, many of which contain a genetic element called an identifier sequence located in at least one of their introns. The identifier sequences are transcribed by RNA polymerase III exclusively in neurons to produce two RNA species, BC1 and BC2, of 160 and 100 to 110 nucleotides. This transcriptional event may define regions of chromatin that contain neuronal-specific genes and may poise these genes for transcription by polymerase II by rendering the gene promoters accessible to soluble trans-acting molecules.

Transcriptionally active chromatin

Eukaryotic chromatin has a dynamic, complex hierarchical structure. Active gene transcription takes place on only a small proportion of it at a time. While many workers have tried to characterize active chromatin, we are still far from understanding all the biochemical, morphological and compositional features that distinguish it from inactive nuclear material. Active genes are apparently packaged in an altered nucleosome structure and are associated with domains of chromatin that are less condensed or more open than inactive domains. Active genes are more sensitive to nuclease digestions and probably contain specific nonhistone proteins which may establish and/or maintain the active state. Variant or modified histones as well as altered configurations or modifications of the DNA itself may likewise be involved. Practically nothing is known about the mechanisms that control these nuclear characteristics. However, controlled accessibility to regions of chromatin and specific sequences of DNA may be one of the primary regulatory mechanisms by which higher cells establish potentially active chromatin domains. Another control mechanism may be compartmentalization of active chromatin to certain regions within the nucleus, perhaps to the nuclear matrix. Topological constraints and DNA supercoiling may influence the active regions of chromatin and be involved in eukaryotic genomic functions. Further, the chromatin structure of various DNA regulatory sequences, such as promoters, terminators and enhancers, appears to partially regulate transcriptional activity.

Mouse kidney and submaxillary gland renin genes differ in their 5' putative regulatory sequences

The genomic DNAs that specify the renin mRNAs found in the submaxillary gland and in the kidney of Swiss mice have been isolated by molecular cloning in phage lambda. The Ren1 and Ren2 genes, encoding the kidney and submaxillary renins, respectively, span about 9.5 kilobases each. Restriction maps of both renin genes and their flanking sequences are presented. To correlate the differential expression of the renin genes with their structures, a sequence analysis of the putative 5' regulatory sequences of both genes was conducted. The results show that the leader sequences and promoter regions of both genes are highly homologous to a point located 179 nucleotides upstream from the transcription start point; the sequences diverge beyond this position.

tk Enzyme expression in differentiating muscle cells is regulated through an internal segment of the cellular tk gene

Thymidine kinase (tk) enzyme expression is shut down when cultured skeletal muscle cells terminally differentiate. This regulation is mediated by a rapid and specific decline in the abundance of cellular tk mRNA. tk-deficient mouse myoblasts were transformed to the tk-positive phenotype by using both the cellular tk gene of the chicken and the herpesvirus tk gene. Myoblasts transformed with the cellular tk gene effectively regulate tk enzyme activity upon terminal differentiation. Conversely, myoblasts transformed with the herpesvirus tk gene continue to express tk enzyme activity in postreplicative muscle cells. A regulated pattern of expression is retained when the promoter of the cellular tk gene is replaced by the promoter of the herpesvirus tk gene. Moreover, the cellular tk gene is appropriately regulated during terminal muscle differentiation when its 3' terminus is removed and replaced by the terminus of the viral tk gene. Thus, the element of the cellular tk gene sufficient to specify its regulation is entirely intragenic.

Dexamethasone increases the number of RNA polymerase II molecules transcribing integrated mouse mammary tumor virus DNA and flanking mouse sequences

In mouse Ltk- cells that were transfected with recombinant bacteriophage DNA containing a complete proviral copy of an integrated endogenous mouse mammary tumor virus (MMTV) with its flanking cellular sequences, the newly acquired MMTV proviruses were transcribed in a glucocorticoid-responsive fashion. After hormone treatment of selected cell clones in culture we isolated the nuclei, elongated the nascent RNA chains in vitro, and determined the number of RNA polymerase II molecules on the transcribed MMTV DNA as well as on the flanking mouse DNA sequences. We found that the specific increase in the polymerase loading after hormone treatment is proportional to the increase in the amount of stable MMTV mRNA. When the DNA sequences which are responsible for hormone-receptor binding and for the increased MMTV mRNA levels were deleted, no increase in RNA polymerase II loading on MMTV DNA was observed. Nuclear RNA chains which were transcribed in response to hormone treatment were detected not only from the transfected MMTV DNA but also from the mouse DNA sequences adjacent to the 3' end of the provirus.

Reversible and persistent changes in chromatin structure accompany activation of a glucocorticoid-dependent enhancer element

A derivative of mouse mammary tumor virus (MTV) DNA, LTL, was constructed in vitro and introduced into the genome of mouse L cells. Transcription of LTL was stimulated by dexamethasone, a glucocorticoid hormone. Two features of LTL chromatin structure are altered upon hormone treatment. First, "moderate" DNAase I sensitivity of the entire LTL element increases following addition of dexamethasone; this alteration persists after hormone withdrawal, when LTL transcription is shut off. Second, a discrete DNAase I-hypersensitive region is induced with a time course that closely parallels the rate of increasing transcription from the MTV promoter; this structure disappears upon hormone removal. The induced hypersensitive region coincides with a segment of the MTV long terminal repeat sequence that specifically binds purified glucocorticoid receptor in vitro and functions as a hormone-dependent enhancer element in vivo. We suggest that specific glucocorticoid receptor-DNA interactions may alter the configuration of DNA or chromatin in the vicinity of the binding sites, thereby creating an active transcriptional enhancer.

Adenovirus 5 E2 transcription unit: an E1A-inducible promoter with an essential element that functions independently of position or orientation

Utilizing deletion mutants of a plasmid containing the adenovirus E2 gene, an E1A-inducible transcription unit, we determined the promoter sequences required for full expression in transient transfection assays. Wild-type expression was obtained from plasmids containing only 79 nucleotides of upstream sequence relative to the transcription initiation site. Removal of an additional nine nucleotides lowered expression 10-fold, and deletion to -59 resulted in near total loss of transcription. Wild-type levels of expression were restored to a -28 deletion mutant by insertion of the sequence from -21 to -262 from the wild-type promoter at the -28 position, in either orientation, even though when inserted in the opposite orientation the relevant sequences were ca. 270 nucleotides upstream from their normal position. Finally, this sequence could be placed at a distance of 4,000 nucleotides from the E2 cap site and still retain near total function. Thus, the E2 promoter element can function independent of orientation and position, properties characteristic of enhancer elements.

How damaged is the biologically active subpopulation of transfected DNA?

Relatively little is known about the damage suffered by transfected DNA molecules during their journey from outside the cell into the nucleus. To follow selectively the minor subpopulation that completes this journey, we devised a genetic approach using simian virus 40 DNA transfected with DEAE-dextran. We investigated this active subpopulation in three ways: (i) by assaying reciprocal pairs of mutant linear dimers which differed only in the arrangement of two mutant genomes; (ii) by assaying a series of wild-type oligomers which ranged from 1.1 to 2.0 simian virus 40 genomes in length; and (iii) by assaying linear monomers of simian virus 40 which were cleaved within a nonessential region to leave either sticky, blunt, or mismatched ends. We conclude from these studies that transfected DNA molecules in the active subpopulation are moderately damaged by fragmentation and modification of ends. As a whole, the active subpopulation suffers about one break per 5 to 15 kilobases, and about 15 to 20% of the molecules have one or both ends modified. Our analysis of fragmentation is consistent with the random introduction of double-strand breaks, whose cause and exact nature are unknown. Our analysis of end modification indicated that the most prevalent form of damage involved deletion or addition of less than 25 base pairs. In addition we demonstrated directly that the efficiencies of joining sticky, blunt, or mismatched ends are identical, verifying the apparent ability of cells to join nearly any two DNA ends and suggesting that the efficiency of joining approaches 100%. The design of these experiments ensured that the detected damage preceded viral replication and thus should be common to all DNAs transfected with DEAE-dextran and not specific for viral DNA. These measurements of damage within transfected DNA have important consequences for studies of homologous and nonhomologous recombination in somatic cells as is discussed.

Remodeling the estrogen receptor model

The estrogen receptor model has revised to make it compatible with new data on subcellular localization of the receptor and physical characteristics of solubilized versus immobilized receptors. Our current model suggests that receptors, with or without bound estrogen, are present in the nuclear fraction. Furthermore, the receptor behaves as if it were immobilized or bound to some nuclear constituent at all times. Thus, the association of the estrogen-free receptor (unbound receptor) to a target site in the nucleus is considered to be the critical event in defining the nature of the response to estrogenic hormones.