Showing papers on "Regulation of gene expression published in 1992"
TL;DR: A functionally tripartite, 50-nt hypoxia-inducible enhancer which binds several nuclear factors, one of which is induced by Hypoxia via de novo protein synthesis.
Abstract: We have identified a 50-nucleotide enhancer from the human erythropoietin gene 3'-flanking sequence which can mediate a sevenfold transcriptional induction in response to hypoxia when cloned 3' to a simian virus 40 promoter-chloramphenicol acetyltransferase reporter gene and transiently expressed in Hep3B cells Nucleotides (nt) 1 to 33 of this sequence mediate sevenfold induction of reporter gene expression when present in two tandem copies compared with threefold induction when present in a single copy, suggesting that nt 34 to 50 bind a factor which amplifies the induction signal DNase I footprinting demonstrated binding of a constitutive nuclear factor to nt 26 to 48 Mutagenesis studies revealed that nt 4 to 12 and 19 to 23 are essential for induction, as substitutions at either site eliminated hypoxia-induced expression Electrophoretic mobility shift assays identified a nuclear factor which bound to a probe spanning nt 1 to 18 but not to a probe containing a mutation which eliminated enhancer function Factor binding was induced by hypoxia, and its induction was sensitive to cycloheximide treatment We have thus defined a functionally tripartite, 50-nt hypoxia-inducible enhancer which binds several nuclear factors, one of which is induced by hypoxia via de novo protein synthesis
2,523 citations
TL;DR: In this article, the authors proposed a method to solve the problem of the "missing link" problem, i.e., "missing links" and "missing connections" problem.
Abstract: 0749-503X/92/060423-66 $38.00
1,280 citations
TL;DR: It is clear that PEPCK mRNA is stabilized by agents that increase the rate of transcription of the gene, and under appropriate metabolic signals this dual control of mRNA synthesis and stability provides for a long-term increase in PEPCk mRNA and protein.
Abstract: Understanding the regulation of hepatic glucose metabolism had its foundation in the elucidation of several pathways, but recent advances have come from the application of molecular genetics. Five years ago little was known about the primary structure of the key regulatory enzymes. Since then, the primary sequence of liver GK, 6-PF-1-K, Fru-1,6-P2ase, PK, PEPCK, and 6-PF-2-K/Fru-2,6-P2ase have been derived from cDNA sequences and/or determined by direct protein sequencing. This has provided new insights into the molecular mechanisms of catalysis and the regulation of these enzymes by covalent modification. Isolation of the cDNAs for these enzymes also has allowed for the quantitation of specific mRNAs and permitted analysis of hormonal control of specific gene expression. The genes for these enzymes have been isolated and sequenced, and their promoter regions are being identified and characterized. Hormone response elements have been delineated in several of the promoters. The promoter regions for 6-PF-2-K/Fru-2,6-P2ase and Fru-1,6-P2ase have also been identified, and future research will focus on the elucidation of the mechanisms whereby hormones regulate the expression of these genes. A number of generalizations can be made about the regulation of gene expression of glycolytic/gluconeogenic enzymes. First, there is coordinate hormonal regulation of gene expression and these effects are consonant with their physiologic actions. Insulin induces the mRNAs that encode glycolytic enzymes and represses the mRNAs that encode gluconeogenic enzymes; cAMP has opposite effects. Both can increase or decrease transcription. Whereas insulin and cAMP affect all of these mRNAs, glucocorticoids appear to have a more restricted action. Second, transcriptional and posttranscriptional regulatory mechanisms are involved. The synthesis of all of the mRNAs discussed is regulated by hormones. Relatively little is known about how mRNA stability is regulated in general, but it is clear that PEPCK mRNA is stabilized by agents that increase the rate of transcription of the gene. Under appropriate metabolic signals this dual control of mRNA synthesis and stability provides for a long-term increase in PEPCK mRNA and protein. Studies with PK mRNA are less direct, but suggest a similar dual mechanism. It will be interesting to see whether multilevel regulation is restricted to these two mRNAs, both of which are involved in the same substrate cycle, or whether the stability of other mRNAs involved in hepatic glucose metabolism is also affected. Third, glucose appears to be important in the regulation of these hepatic genes.(ABSTRACT TRUNCATED AT 400 WORDS)
845 citations
TL;DR: Results imply that the MDR1 gene could be activated during tumor progression associated with mutations in Ras and p53, and imply that drug resistance in human cancer is associated with overexpression of the multidrug resistance (MDR1) gene.
Abstract: Drug resistance in human cancer is associated with overexpression of the multidrug resistance (MDR1) gene, which confers cross-resistance to hydrophobic natural product cytotoxic drugs. Expression of the MDR1 gene can occur de novo in human cancers in the absence of drug treatment. The promoter of the human MDR1 gene was shown to be a target for the c-Ha-Ras-1 oncogene and the p53 tumor suppressor gene products, both of which are associated with tumor progression. The stimulatory effect of c-Ha-Ras-1 was not specific for the MDR1 promoter alone, whereas a mutant p53 specifically stimulated the MDR1 promoter and wild-type p53 exerted specific repression. These results imply that the MDR1 gene could be activated during tumor progression associated with mutations in Ras and p53.
746 citations
TL;DR: The model that a steroidogenic cell-selective protein interacts with related promoter elements from three steroidogenic enzymes to regulate their coordinate expression is supported and a cDNA is isolate and characterize that very likely encodes this protein.
Abstract: We proposed that a cell-selective regulatory protein coordinately regulates the expression of three enzymes that are required for the biosynthesis of corticosteroids: cholesterol side chain cleavage enzyme, steroid 21-hydroxylase, and the aldosterone synthase isozyme of steroid 11 beta-hydroxylase. In this report, we identify a 53-kilodalton protein, termed steroidogenic factor 1 (SF-1), that interacts with the related promoter elements from these steroidogenic enzymes, and we isolate and characterize a cDNA that very likely encodes this protein. We first showed that nuclear extracts from bovine adrenal glands interact with the mouse steroidogenic regulatory elements, forming complexes indistinguishable from those produced by nuclear extracts from mouse Y1 adrenocortical cells. These bovine adrenal extracts were subjected to sequential ion exchange and affinity chromatography to yield a highly enriched preparation of SF-1. The predominant protein in the affinity-purified preparation comigrated with shift ...
670 citations
TL;DR: Evidence is presented that the ras proteins in malignant tumour cell lines from patients with type 1 neurofibromatosis are in a constitutively activated state, as judged by the guanine nucleotide bound to them, and are necessary for cellular proliferation, and support the hypothesis that NF1 is a tumour-suppressor gene whose product acts upstream of ras.
Abstract: Defects in the NF1 gene have been implicated in the inherited disorder neurofibromatosis type 1, which is characterized by several developmental abnormalities including an increased frequency of benign and malignant tumours of neural crest origin (neurofibromas and neurofibrosarcomas respectively). The NF1 gene encodes a ubiquitous protein homologous to p120GAP, the GTPase-activating protein (GAP) for the products of the ras protooncogenes. When expressed in non-mammalian systems, the region of the NF1 gene homologous to p120GAP produces a protein with GAP-like activity. Here we present evidence that the ras proteins in malignant tumour cell lines from patients with type 1 neurofibromatosis are in a constitutively activated state, as judged by the guanine nucleotide bound to them, and are necessary for cellular proliferation. These cells contain p21ras and p120GAP that are both functionally wild type, but barely any functional NF1 protein. Our results show that the NF1 protein is normally essential for correct negative regulation of ras proteins in the cell, even in the presence of normal p120GAP, and they support the hypothesis that NF1 is a tumour-suppressor gene whose product acts upstream of ras.
622 citations
TL;DR: It is shown that intact purified wild-type human and murine p53 proteins strongly activate transcription in vitro, and this activation depends on the ability of p53 to bind to a template bearing a p53-binding sequence.
Abstract: The p53 protein is an important determinant in human cancer and regulates the growth of cells in culture. It is known to be a sequence-specific DNA-binding protein with a powerful activation domain, but it has not been established whether it regulates transcription directly. Here we show that intact purified wild-type human and murine p53 proteins strongly activate transcription in vitro. This activation depends on the ability of p53 to bind to a template bearing a p53-binding sequence. By contrast, tumour-derived mutant p53 proteins cannot activate transcription from the template at all, and when complexed to wild-type p53, these mutants block transcriptional activation by the wild-type protein. Moreover, the simian virus 40 large T antigen inhibits wild-type p53 from activating transcription. Our results support a model in which p53 directly activates transcription but this activity can be inhibited by mutant p53 and SV40 large T antigen through interaction with wild-type p53.
613 citations
TL;DR: It is found that oncogene expression in proliferating osteoblasts contributes to the suppression of genes expressed postproliferatively, and that chromatin structure and the presence of nucleosomes contribute to three-dimensional organization of gene promoters that support synergistic and/or antagonistic activities of physiologic mediators of bone cell growth and differentiation.
Abstract: The combined application of molecular, biochemical, histochemical, and ultrastructural approaches has defined a temporal sequence of gene expression associated with development of the bone cell phenotype in primary osteoblast cultures. The peak levels of expressed genes reflect a developmental sequence of bone cell differentiation characterized by three principal periods: proliferation, extracellular matrix maturation and mineralization, and two restriction points to which the cells can progress but cannot pass without further signals. The regulation of cell growth and bone-specific gene expression has been examined during this developmental sequence and is discussed within the context of several unique concepts. These are (1) that oncogene expression in proliferating osteoblasts contributes to the suppression of genes expressed postproliferatively, (2) that hormone modulation of a gene is dependent upon the maturational state of the osteoblast, and (3) that chromatin structure and the presence of nucleosomes contribute to three-dimensional organization of gene promoters that support synergistic and/or antagonistic activities of physiologic mediators of bone cell growth and differentiation.
571 citations
TL;DR: Physiopathological implications for the protection of mucins against proteolysis by human leucocyte elastase and the interplay of temperature and protons in the modulation of oxygen binding by squid blood are studied.
Abstract: RESEARCH PAPERS' Proteins Generation of forms of fragment E with differing thrombin-binding properties during digestion of fibrinogen by plasmin Association between diphtheria toxin Aand B-fragment and their fusion proteins The interplay of temperature and protons in the modulation of oxygen binding by squid blood Interaction between secretory leucocyte proteinase inhibitor and bronchial mucins or glycopeptides. Physiopathological implications for the protection ofmucins against proteolysis by human leucocyte elastase Purification, characterization and function of bacterioferritin from the cyanobacterium Synechocystis P.C.C. 6803
543 citations
TL;DR: A katF Salmonella mutant has increased susceptibility to nutrient deprivation, oxidative stress, acid stress, and DNA damage, conditions which are relevant to the intraphagosomal environment of host macrophages.
Abstract: Nutrient limitation is a critical signal in Salmonella virulence gene regulation. The katF (rpoS) gene mediates the expression of the Salmonella spv plasmid virulence genes during bacterial starvation. A katF Salmonella mutant has increased susceptibility to nutrient deprivation, oxidative stress, acid stress, and DNA damage, conditions which are relevant to the intraphagosomal environment of host macrophages. Moreover, the katF mutant has significantly reduced virulence in mice. katF encodes an alternative sigma factor of RNA polymerase which coordinately regulates Salmonella virulence.
535 citations
TL;DR: The two-hybrid system is used to suggest that RIF1 is a cofactor or mediator for RAP1 in the establishment of a repressed chromatin state at these loci and support the idea that the rap1s phenotypes are attributable to a failure to recruit Rif1 to silencers and telomeres.
Abstract: The yeast RAP1 protein is a sequence-specific DNA-binding protein that functions as both a repressor and an activator of transcription. RAP1 is also involved in the regulation of telomere structure, where its binding sites are found within the terminal poly(C1-3A) sequences. Previous studies have indicated that the regulatory function of RAP1 is determined by the context of its binding site and, presumably, its interactions with other factors. Using the two-hybrid system, a genetic screen for the identification of protein-protein interactions, we have isolated a gene encoding a RAP1-interacting factor (RIF1). Strains carrying gene disruptions of RIF1 grow normally but are defective in transcriptional silencing and telomere length regulation, two phenotypes strikingly similar to those of silencing-defective rap1s mutants. Furthermore, hybrid proteins containing rap1s missense mutations are defective in an interaction with RIF1 in the two-hybrid system. Taken together, these data support the idea that the rap1s phenotypes are attributable to a failure to recruit RIF1 to silencers and telomeres and suggest that RIF1 is a cofactor or mediator for RAP1 in the establishment of a repressed chromatin state at these loci. By use of the two-hybrid system, we have isolated a mutation in RIF1 that partially restores the interaction with rap1s mutant proteins.
TL;DR: Experiments with model sequences containing various nucleotide substitutions established that (C/T)CAAGG(T/C)CA is the strongest binding sequence for Ad4 BP, which strongly suggests that Ad4BP is an indispensable transcription factor for the expression of all the steroidogenic P-450 genes.
TL;DR: Analysis of a T-cell antigen receptor (TCR) alpha promoter from a variable gene segment (V) revealed a critical GT box element which is also found in upstream regions of several V alpha genes, TCR enhancer, and regulatory elements of other genes.
Abstract: Analysis of a T-cell antigen receptor (TCR) alpha promoter from a variable gene segment (V) revealed a critical GT box element which is also found in upstream regions of several V alpha genes, TCR enhancer, and regulatory elements of other genes. This element is necessary for TCR gene expression and binds several proteins. These GT box-binding proteins were identified as members of a novel Sp1 multigene family. Two of them, which we term Sp2 and Sp3, were cloned. Sp2 and Sp3 contain zinc fingers and transactivation domains similar to those of Sp1. Like Sp1, Sp2 and Sp3 are expressed ubiquitously, and their in vitro-translated products bind to the GT box in TCR V alpha promoters. Sp3, in particular, also binds to the Sp1 consensus sequence GC box and has binding activity similar to that of Sp1. As the GT box has also previously been shown to play a role in gene regulation of other genes, these newly isolated Sp2 and Sp3 proteins might regulate expression not only of the TCR gene but of other genes as well.
TL;DR: In vitro DNA binding studies show that DEF A binds to specific DNA motifs as a heterodimer, together with the protein product of the floral homeotic globosa gene, thus demonstrating that the protein encoded by deficiens is a DNA binding protein.
Abstract: We have determined the structure of the floral homeotic deficiens (defA) gene whose mutants display sepaloid petals and carpelloid stamens, and have analysed its spatial and temporal expression pattern. In addition, several mutant alleles (morphoalleles) were studied. The results of these analyses define three functional domains of the DEF A protein and identify in the deficiens promoter a possible cis-acting binding site for a transcription factor which specifically upregulates expression of deficiens in petals and stamens. In vitro DNA binding studies show that DEF A binds to specific DNA motifs as a heterodimer, together with the protein product of the floral homeotic globosa gene, thus demonstrating that the protein encoded by deficiens is a DNA binding protein. Furthermore, Northern analysis of a temperature sensitive allele at permissive and non-permissive temperatures provides evidence for autoregulation of the persistent expression of deficiens throughout flower development. A possible mechanism of autoregulation is discussed.
TL;DR: Observations implicate phagosome acidification as an intracellular inducer of PhoP-regulated gene expression and suggest that Salmonella survival is dependent on its ability to attenuate phagosomes acidification.
Abstract: Survival of Salmonella typhimurium within macrophage phagosomes requires the coordinate expression of bacterial gene products. This report examines the contribution of phagosomal pH as a signal for expression of genes positively regulated by the S. typhimurium virulence regulators PhoP and PhoQ. Several hours after bacterial phagocytosis by murine bone marrow-derived macrophages, PhoP-activated gene transcription increased 50- to 77-fold. In contrast, no difference in PhoP-activated gene expression was observed after infection of cultured epithelial cells, suggesting that the membrane sensor PhoQ recognized signals unique to macrophage phagosomes. The increase in PhoP-regulated gene expression was abolished when macrophage culture medium contained NH4Cl or chloroquine, weak bases that raise the pH of acidic compartments. Measurements of pH documented that S. typhimurium delayed and attenuated acidification of its intracellular compartment. Phagosomes containing S. typhimurium required 4-5 hr to reach pH < 5.0. In contrast, within 1 hr vacuoles containing heat-killed bacteria were measured at pH < 4.5. The eventual acidification of phagosomes to pH < 5.0 correlated with the period of maximal PhoP-dependent gene expression. These observations implicate phagosome acidification as an intracellular inducer of PhoP-regulated gene expression and suggest that Salmonella survival is dependent on its ability to attenuate phagosome acidification.
TL;DR: The identification of Max and the specific DNA-binding activities of Myc and Max provides an opportunity for directly testing the transcriptional activities of these proteins in mammalian cells and reports here that Myc overexpression activates, whereas Max overeexpression represses, transcription of a reporter gene.
Abstract: The Myc family proteins are thought to be involved in transcription because they have both a carboxy-terminal basic-helix-loop-helix-zipper (bHLH-Z) domain, common to a large class of transcription factors, and an amino-terminal fragment which, for c-Myc, has transactivating function when assayed in chimaeric constructs. In addition, c-, N- and L-Myc proteins heterodimerize, in vitro and in vivo, with the bHLH-Z protein Max. In vitro, Max homodimerizes but preferentially associates with Myc, which homodimerizes poorly. Furthermore Myc-Max heterodimers specifically bind the nucleotide sequence CACGTG with higher affinity than either homodimer alone. The identification of Max and the specific DNA-binding activities of Myc and Max provides an opportunity for directly testing the transcriptional activities of these proteins in mammalian cells. We report here that Myc overexpression activates, whereas Max overexpression represses, transcription of a reporter gene. Max-induced repression is relieved by overexpression of c-Myc. Repression requires the DNA-binding domain of Max, whereas relief of repression requires the dimerization and transcriptional activation activities of Myc. Both effects require Myc-Max-binding sites in the reporter gene.
TL;DR: Findings support the previous contention that the segmental distribution and variable expression of the cutaneous, skeletal, and endocrine manifestations of MAS reflect an underlying somatic mosaicism and suggest that the molecular basis of MAS is a postzygotic mutation in Gs alpha that causes constitutive activation of adenylyl cyclase.
Abstract: McCune-Albright syndrome (MAS) is characterized by polyostotic fibrous dysplasia, cafe-au-lait lesions, and a variety of endocrine disorders, including precocious puberty, hyperthyroidism, hypercortisolism, growth hormone excess, and hyperprolactinemia. The diverse metabolic abnormalities seen in MAS share the involvement of cells that respond to extracellular signals through activation of the hormone-sensitive adenylyl cyclase system (EC 4.6.1.1). Mutations that lead to constitutive activation of Gs alpha, the guanine nucleotide-binding regulatory protein that stimulates adenylyl cyclase activity, have been identified in a subset of human growth hormone-secreting pituitary tumors and human thyroid tumors. We report here the identification of a mutation in the gene encoding Gs alpha in a patient with MAS. Denaturing gradient gel electrophoresis was used to analyze amplified DNA fragments including exon 8 or exon 9 of the Gs alpha gene. In one subject with MAS a G-to-A transition was found in exon 8 of one of the two alleles encoding Gs alpha. This single-base substitution results in the replacement of arginine by histidine at position 201 of the mature Gs alpha protein. Semiquantitative analysis of amplified DNA indicated that the mutant allele was less prevalent than the wild-type allele in peripheral leukocytes and was present in very low levels in skin. These findings support the previous contention that the segmental distribution and variable expression of the cutaneous, skeletal, and endocrine manifestations of MAS reflect an underlying somatic mosaicism. Further, these results suggest that the molecular basis of MAS is a postzygotic mutation in Gs alpha that causes constitutive activation of adenylyl cyclase.
TL;DR: A number of anaerobic genes that show heme-independent, oxygen-repressed expression have been identified, suggesting that there are at least two different regulatory circuitries.
TL;DR: Regulation of chromosomally determined nutrient cation and anion uptake systems shows important similarities to regulation of plasmid-determined toxic ion resistance systems that mediate the outward transport of deleterious ions.
TL;DR: A cDNA encoding a unique hyaluronan receptor has been molecularly cloned from a lambda GT11 3T3 cDNA expression library and is named RHAMM, an acronym for receptor for hyAluronan-mediated motility, which appears to be a new type of hyalonson receptor that is involved in cell locomotion.
Abstract: A cDNA encoding a unique hyaluronan receptor has been molecularly cloned from a lambda GT11 3T3 cDNA expression library. Immunoblot analyses of cell lysates, using antibodies to peptides encoded in the cDNA, specifically react with a 58-kD protein. This protein is regulated by the mutant H-ras gene in cells containing a metallothionein promoter H-ras hybrid gene. Further, antibodies to peptide sequences encoded in the cDNA block the increase in locomotion resulting from induction of the mutant H-ras gene in this cell line. In a transblot assay, the bacterially expressed protein binds to biotinylated hyaluronan. Antibodies to peptides encoded in the cDNA react in immunoblot assays with the 58- and 52-kD proteins of a novel hyaluronan receptor complex previously implicated in cell locomotion. Furthermore, antibodies specific to the 58- and 52-kD proteins, which block ras-induced locomotion, also cross-react with the expressed, encoded protein. The gene product described here appears to be a new type of hyaluronan receptor that is involved in cell locomotion. It is named RHAMM, an acronym for receptor for hyaluronan-mediated motility.
TL;DR: To identify DNA sequences that may mediate transcriptional repression in response to 1,25(OH)2D3 in GH4C1 cells but not in ROS 17/2.8 cells, a down-regulatory element is distinguished both in sequence composition and in the requirement for particular cellular factors other than the 1, 25(OH), 2D3 receptor for repressing transcription.
Abstract: 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], plays an important role in the regulation of mineral ion homeostasis. As well as being the major steroid hormone that regulates calcium metabolism, 1,25(OH)2D3 suppresses transcription of the gene encoding parathyroid hormone, a peptide that plays a dominant role in regulating extracellular calcium levels. To identify DNA sequences that may mediate this transcriptional repression, nuclear extracts containing the 1,25(OH)2D3 receptor were examined for binding to sequences in the 5'-flanking region of the human parathyroid hormone gene. A 25-base-pair (bp) oligonucleotide containing the sequences from -125 to -101 from the start of exon I binds nuclear proteins recognized by monoclonal antibodies against the 1,25(OH)2D3 receptor. The sequences in this region contain a single copy of a motif (AGGTTCA) homologous to the motifs repeated in the up-regulatory 1,25(OH)2D3-response elements. When placed upstream to a heterologous viral promoter, the sequences contained in this 25-bp oligonucleotide mediate transcriptional repression in response to 1,25(OH)2D3 in GH4C1 cells but not in ROS 17/2.8 cells. This down-regulatory element, therefore, differs from the up-regulatory 1,25(OH)2D3-response elements both in sequence composition and in the requirement for particular cellular factors other than the 1,25(OH)2D3 receptor for repressing transcription.
TL;DR: The present study set out to determine whether activation of full virus latent-gene expression was a necessary accompaniment to induction of the lytic cycle in Burkitt's lymphoma lines, and revealed three response pathways of EBV gene activation from EBNA1-positive latency.
Abstract: Previous studies on Epstein-Barr virus (EBV)-positive B-cell lines have identified two distinct forms of virus latency. Lymphoblastoid cell lines generated by virus-induced transformation of normal B cells in vitro, express the full spectrum of six EBNAs and three latent membrane proteins (LMP1, LMP2A, and LMP2B); furthermore, these lines often contain a small fraction of cells spontaneously entering the lytic cycle. In contrast, Burkitt's lymphoma-derived cell lines retaining the tumor biopsy cell phenotype express only one of the latent proteins, the nuclear antigen EBNA1; such cells do not enter the lytic cycle spontaneously but may be induced to do so by treatment with such agents as tetradecanoyl phorbol acetate and anti-immunoglobulin. The present study set out to determine whether activation of full virus latent-gene expression was a necessary accompaniment to induction of the lytic cycle in Burkitt's lymphoma lines. Detailed analysis of Burkitt's lymphoma lines responding to anti-immunoglobulin treatment revealed three response pathways of EBV gene activation from EBNA1-positive latency. A first, rapid response pathway involves direct entry of cells into the lytic cycle without broadening of the pattern of latent gene expression; thereafter, the three "latent" LMPs are expressed as early lytic cycle antigens. A second, delayed response pathway in another cell subpopulation involves the activation of full latent gene expression and conversion to a lymphoblastoidlike cell phenotype. A third response pathway in yet another subpopulation involves the selective activation of LMPs, with no induction of the lytic cycle and with EBNA expression still restricted to EBNA1; this type of latent infection in B lymphocytes has hitherto not been described. Interestingly, the EBNA1+ LMP+ cells displayed some but not all of the phenotypic changes normally induced by LMP1 expression in a B-cell environment. These studies highlight the existence of four different types of EBV infection in B cells, including three distinct forms of latency, which we now term latency I, latency II, and latency III.
TL;DR: These experiments show that yeast cells can activate a transcription factor that stimulates expression of a nuclear gene in response to the accumulation of unfolded proteins in another cellular compartment.
Abstract: The KAR2 gene of Saccharomyces cerevisiae codes for an essential chaperone protein (BiP) that is localized in the lumen of the endoplasmic reticulum (ER). The high basal rate of transcription of KAR2 is increased transiently by heat shock: prolonged induction occurs when unfolded proteins accumulate in the ER. Three cis-acting elements in the KAR2 promoter control expression of KAR2: (i) a GC-rich region that contributes to the high level of constitutive expression, (ii) a functional heat shock element (HSE) and (iii) an element (UPR) that is involved in the induction of BiP mRNA by unfolded proteins. By analyzing internal deletion mutants of the KAR2 promoter, we demonstrate here that these three elements regulate transcription of KAR2 independently. Furthermore, the 22 bp UPR element causes a heterologous (CYC1) promoter to respond to the presence of unfolded proteins in the ER. Extracts of both stressed and unstressed yeast cells contain proteins that bind specifically to synthetic HSE and UPR elements and retard their migration through gels. Binding proteins specific for the UPR element can be fractionated by ammonium sulfate precipitation. Two of the proteins UPRF-1 and UPRF-2 (which is apparently a proteolytic degradation product of UPRF-1) bind inefficiently to mutant versions of the UPR that are unable to confer responsiveness to unfolded proteins to the (CYC1) promoter. UPRF-1 therefore displays the properties expected of a transcription factor that is involved in the sustained response of the KAR2 promoter to unfolded proteins in the ER. These experiments show that yeast cells can activate a transcription factor that stimulates expression of a nuclear gene in response to the accumulation of unfolded proteins in another cellular compartment.
TL;DR: A functional consequence of the promiscuous DNA binding of COUP-TF is its ability to down-regulate hormonal induction of target gene expression by other members of the steroid-thyroid hormone receptor superfamily such as the vitamin D3, thyroid hormone, and retinoic acid receptors.
Abstract: Alignment of natural chicken ovalbumin upstream promoter transcription factor (COUP-TF) response elements shows that, in addition to the predominant direct repeat of the GGTCA motif with a 2-bp spacing, there are other functional COUP elements with variations in the GGTCA orientation and spacing. We systematically analyzed the binding of in vitro-synthesized COUP-TFs and showed that COUP-TF is capable of binding to oligonucleotides containing both direct repeats and palindromes and with different spacings of the GGTCA repeats. Subsequently, we analyzed four possible mechanisms proposed to explain how COUP-TF could bind to these spatial variations of the GGTCA repeat. We demonstrated that the functional DNA-binding form of COUP-TF is a dimer which requires two GGTCA half-sites to bind DNA. We demonstrated that the COUP-TF dimer undergoes a remarkable structural adaptation to accommodate binding to these spatial variants of the GGTCA repeats. A functional consequence of the promiscuous DNA binding of COUP-TF is its ability to down-regulate hormonal induction of target gene expression by other members of the steroid-thyroid hormone receptor superfamily such as the vitamin D3, thyroid hormone, and retinoic acid receptors. Our data indicate that COUP-TF may have an important role in hormonal regulation of gene expression by these receptors.
TL;DR: Genomic clones of the human cdc2 gene containing 5′ flanking sequences were isolated and shown to function as a growth regulated promoter in vivo when fused to a CAT reporter gene.
Abstract: Transcription of the human cdc2 gene is cell cycle regulated and restricted to proliferating cells Nuclear run-on assays show that cdc2 transcription is high in S and G2 phases of the cell cycle but low in G1 To investigate transcriptional control further, genomic clones of the human cdc2 gene containing 5' flanking sequences were isolated and shown to function as a growth regulated promoter in vivo when fused to a CAT reporter gene In primary human fibroblasts, the human cdc2 promoter is negatively regulated by arrest of cell growth in a similar fashion to the endogenous gene This requires specific 5' flanking upstream negative control (UNC) sequences which mediate repression The retinoblastoma susceptibility gene product (Rb) specifically represses cdc2 transcription in cycling cells via 136 bp of 5' flanking sequence located between -245 and -109 within the UNC region E2F binding sites in this region were shown to be essential for optimal repression A model is proposed where Rb negatively regulates the cdc2 promoter in non-cycling and cycling G1 cells
TL;DR: Examination of c-myc expression in mutant embryos indicates the existence of coordinate regulation of myc genes during mouse embryogenesis and suggests further that there are linked regulatory mechanisms for normal expression in the embryo.
Abstract: myc genes are thought to function in the processes of cellular proliferation and differentiation. To gain insight into the role of the N-myc gene during embryogenesis, we examined its expression in embryos during postimplantation development using RNA in situ hybridization. Tissue- and cell-specific patterns of expression unique to N-myc as compared with the related c-myc gene were observed. N-myc transcripts become progressively restricted to specific cell types, primarily to epithelial tissues including those of the developing nervous system and those in developing organs characterized by epithelio-mesenchymal interaction. In contrast, c-myc transcripts were confined to the mesenchymal compartments. These data suggest that c-myc and N-myc proteins may interact with different substrates in performing their function during embryogenesis and suggest further that there are linked regulatory mechanisms for normal expression in the embryo. We have mutated the N-myc locus via homologous recombination in embryonic stem (ES) cells and introduced the mutated allele into the mouse germ line. Live-born heterozygotes are under-represented but appear normal. Homozygous mutant embryos die prenatally at approximately 11.5 days of gestation. Histologic examination of homozygous mutant embryos indicates that several developing organs are affected. These include the central and peripheral nervous systems, mesonephros, lung, and gut. Thus, N-myc function is required during embryogenesis, and the pathology observed is consistent with the normal pattern of N-myc expression. Examination of c-myc expression in mutant embryos indicates the existence of coordinate regulation of myc genes during mouse embryogenesis.
TL;DR: It is indicated that high levels of expression of the human NAD(P)H:quinone oxidoreductase gene in tumor cells and its induction by beta-naphthoflavone and 3-(2)-tert-butyl-4-hydroxyanisole are mediated by human antioxidant response element (hARE).
TL;DR: DII may serve as a downstream target gene through which the homeotic genes control abdominal segment identity in the Drosophila embryo and is identified as a minimal cis-regulatory enhancer element that directs DII expression in the larval leg primordia.
TL;DR: All three TSPs demonstrate characteristic patterns of expression in the developing and adult mouse, and it is likely that each protein subserves a discrete function.
Abstract: Thrombospondin (TSP) is a large, trimeric, modular glycoprotein that is a major constituent of platelet alpha granules. TSP is also secreted by a wide variety of epithelial and mesenchymal cells in patterns that reflect developmental changes in the embryo and response to injury in the adult. In addition to its role in blood coagulation, TSP has been reported to serve both adhesive and anti-adhesive functions, to foster neurite outgrowth, stimulate and inhibit cell growth and migration, and inhibit angiogenesis. Although this diversity in apparent function can be attributed, in part, to the ability of a single TSP to interact with several different cell-surface receptors, it is now known that the TSPs are encoded by at least three homologous genes in both human and mouse. TSP1, the commonly recognized protein isolated from platelets, is similar to TSP2 in structure. Both proteins contain NH2-terminal, COOH-terminal, and procollagen homology domains, and type I (TSP or properdin), type II (EGF-like), and type III (Ca(2+)-binding) repeats. However, the two TSPs differ in amino acid sequence and in the regulation of their expression. TSP1 is rapidly induced by serum and growth factors. An SRE and a binding site for NF-Y have been shown to mediate the serum response of the human TSP1 gene. On the other hand, TSP2 is far less responsive to serum than TSP1 and lacks the promoter elements that mediate the serum responsiveness of TSP1. TSP3 resembles TSP1 and TSP2 in its COOH-terminal domain and type III repeats, but contains four rather than three type II repeats and lacks type I repeats and a procollagen homology. The NH2-terminal domain of TSP3 also differs from that of either TSP1 or TSP2. All three TSPs demonstrate characteristic patterns of expression in the developing and adult mouse. It is therefore likely that each protein subserves a discrete function. In the future it will be necessary to distinguish among the three TSPs in addressing the function of these proteins.
TL;DR: Evidence is presented herein that transcriptional regulation of hsp gene expression is linked with the regulation of overall protein synthesis as well as with the accumulation of proteins denatured by stressful events.
Abstract: Heat shock genes encode proteins (hsp's) that play important structural roles under normal cir- cumstances and are essential to the ceils' ability to survive environmental insults. Evidence is presented herein that transcriptional regulation of hsp gene ex- pression is linked with the regulation of overall protein synthesis as well as with the accumulation of proteins denatured by stressful events. The factor that connects the three processes appears to be one of the hsp's, pre- sumably a member(s) of the hsp70 family. Biochemical experiments demonstrate that complexes containing hsp70 and heat shock transcription factor, the specific regulator of hsp gene activity, are formed in the cells.