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C K Glass

Publications and source records attributed to C K Glass.

At least 91 records · Page 5Linked to original sources
PubMed1994

Combinatorial interactions between AP-1 and ets domain proteins contribute to the developmental regulation of the macrophage scavenger receptor gene.

Macrophage development is regulated by a complex set of hormone-like molecules and cell adhesion events that control the growth and differentiation of progenitor cells. The macrophage scavenger receptor (SR) gene becomes markedly upregulated during the final stages of monocyte-to-macrophage differentiation and provides a model for the identification and characterization of transcription factors that control this process. In this report, we have identified three genomic regulatory elements that are required for transactivation of the SR gene in the THP-1 monocytic leukemia cell line following induction of macrophage differentiation by tetradecanoyl phorbol acetate. Each of these regulatory elements contains a near-consensus binding site for members of the AP-1 gene family, while the two most quantitatively important elements also contain juxtaposed binding sites for ets domain transcription factors. We demonstrate that tetradecanoyl phorbol acetate treatment results in a marked and prolonged increase in AP-1 binding activity on these elements, which can be accounted for almost entirely by c-jun and junB. These proteins in turn form ternary complexes with additional factors that bind to the adjacent ets recognition motifs. Several indirect lines of evidence indicate that ets2 represents a component of this ternary complex. The combined expression of c-jun, ets2, and a constitutive form of ras result in synergistic increases in transcription from promoters containing the SR regulatory elements. These observations suggest that SR gene expression is regulated via a signal transduction pathway involving ras, AP-1, and ets domain proteins and imply that at least some of the signalling components involved in ras-dependent growth are also utilized to promote the expression of genes involved in terminal differentiation.

Base Sequence↗
PubMed1994

Cell-specific expression of the macrophage scavenger receptor gene is dependent on PU.1 and a composite AP-1/ets motif.

The type I and II scavenger receptors (SRs) are highly restricted to cells of monocyte origin and become maximally expressed during the process of monocyte-to-macrophage differentiation. In this report, we present evidence that SR genomic sequences from -245 to +46 bp relative to the major transcriptional start site were sufficient to confer preferential expression of a reporter gene to cells of monocyte and macrophage origin. This profile of expression resulted from the combinatorial actions of multiple positive and negative regulatory elements. Positive transcriptional control was primarily determined by two elements, located 181 and 46 bp upstream of the major transcriptional start site. Transcriptional control via the -181 element was mediated by PU.1/Spi-1, a macrophage and B-cell-specific transcription factor that is a member of the ets domain gene family. Intriguingly, the -181 element represented a relatively low-affinity binding site for Spi-B, a closely related member of the ets domain family that has been shown to bind with relatively high affinity to other PU.1/Spi-1 binding sites. These observations support the idea that PU.1/Spi-1 and Spi-B regulate overlapping but nonidentical sets of genes. The -46 element represented a composite binding site for a distinct set of ets domain proteins that were preferentially expressed in monocyte and macrophage cell lines and that formed ternary complexes with members of the AP-1 gene family. In concert, these observations suggest a model for how interactions between cell-specific and more generally expressed transcription factors function to dictate the appropriate temporal and cell-specific patterns of SR expression during the process of macrophage differentiation.

Animals↗
PubMed1993

Interaction between the thyroid hormone receptor and co-factors on the promoter of the gene encoding phospho enol pyruvate carboxykinase.

Using transient transfection studies we localized a thyroid hormone-responsive element on the promoter of the rat phospho-enol pyruvate carboxykinase gene between 355 and 174 bp upstream of the transcription start site. DNAse 1 footprinting analysis within this region showed that a 28 bp fragment at position -324 to -297 was protected by the thyroid-hormone receptor. This receptor was overexpressed in HeLa cells using a vaccinia virus expression vector. DNA-binding assays with this receptor-enriched nuclear HeLa cell extract revealed that only 20% of the thyroid hormone receptor was able to bind the target-sequence with high affinity (4 nM). Titration with nuclear extract from hepatocytes increased the percentage of c-erbA molecules able to bind to this thyroid hormone-responsive element 4-fold without a change in affinity. Our data show that the complex of the thyroid hormone responsive element of the promoter of the phosphoenol pyruvate carboxykinase gene and the thyroid hormone receptor contains only a single receptor molecule suggesting the formation of a heterodimer complex. Accordingly, this thyroid hormone receptor/DNA complex is formed only in the presence of co-factors that are present in limiting amounts in the hepatocyte nucleus.

Animals↗
PubMed1993

Differential orientations of the DNA-binding domain and carboxy-terminal dimerization interface regulate binding site selection by nuclear receptor heterodimers.

Retinoic acid, thyroid hormone, and vitamin D receptors preferentially activate target genes through response elements that consist of direct repeat arrangements of a core recognition motif of consensus sequence AGGTCA. We present evidence that the preference for direct repeat elements arises from two fundamental differences from steroid hormone receptors. First, retinoic acid, thyroid hormone, and vitamin D receptors are demonstrated to preferentially form heterodimers with the retinoid X receptors. These interactions are mediated by the carboxy-terminal dimerization interface, with heterodimer preference specified by actions of the DNA-binding domain. Second, the DNA-binding domains of heterodimeric receptors appear to be rotationally flexible with respect to the carboxy-terminal dimerization interface. Several independent lines of evidence suggest that, relative to the retinoid X and steroid hormone receptors, the DNA-binding domain of the thyroid hormone receptor is preferentially rotated by approximately 180 degrees with respect to its carboxy-terminal dimerization interface. As a result, solution interactions between the carboxy-terminal dimerization interfaces of the retinoid X and thyroid hormone receptors are predicted to lead to the preferential alignment of their respective DNA-binding domains in a direct repeat configuration. This alignment would position the retinoid X receptor over the upstream recognition motif of direct repeat response elements. Differential orientations of the DNA-binding domain, which contribute to the polarity of heterodimer binding, are regulated by a short sequence (the A box) that is located between the conserved DNA-binding and carboxy-terminal dimerization domains.

Amino Acid Sequence↗
PubMed1993

Synergistic interactions between Pit-1 and other elements are required for effective somatotroph rat growth hormone gene expression in transgenic mice.

The role of the pituitary-specific POU-domain protein, Pit-1, in GH gene activation has been established by in vitro analyses and by the observation that mutations affecting the Pit-1 genomic locus result in genetically transmitted dwarfism. To define the quantitative contribution of the two Pit-1 response elements and the potential role of other factors in GH gene activation, we systematically assessed the ability of a series of GH promoter regions to activate transgenes in the mouse anterior pituitary gland. These studies revealed that the two GH Pit-1 binding sites are necessary, but not sufficient, for efficient transcriptional activation. Transgenes containing information including only these cis-active regions are expressed at extremely low levels in the pituitary glands of transgenic mice. The addition of 35 base pairs of 5'-flanking information, contributing other elements including a thyroid hormone/retinoic acid response element, results in much higher levels of transgene expression. Sequences located upstream of this segment contribute a further 5- to 10-fold activation. Thus, while Pit-1 is required for GH gene activation, it alone can only direct minimal expression in transgenic animals. Rather, synergistic interactions between other promoter elements and Pit-1 appear to be required for expression of the transgenes at approximately the 100-fold higher levels that are characteristic of somatotrophs, and are therefore likely to be critical components of somatotroph-specific expression of the GH gene.

Animals↗
PubMed1992

Regulated expression of the human acetylated low density lipoprotein receptor gene and isolation of promoter sequences.

The acetylated low density lipoprotein (AcLDL) receptor is expressed on tissue macrophages after their differentiation from monocyte precursors and has been proposed to play a role in the generation of foam cells in atherosclerotic lesions. In the present studies, THP-1 human monocytic leukemia cells were used to investigate mechanisms responsible for expression of the AcLDL receptor gene after treatment with phorbol 12-myristate 13-acetate (TPA). TPA-dependent accumulation of AcLDL receptor mRNA was not detected until after a lag phase of 12 hr and was blocked by concurrent treatment with cycloheximide. In addition, the TPA-dependent induction of AcLDL receptor activity and mRNA levels was inhibited by retinoic acid and dexamethasone treatment. Isolation and sequence analysis of the promoter regions for the human and bovine AcLDL receptor genes indicated high sequence similarity. Binding sites for AP-1 proteins or other known transcription factors were not conserved between the two species, suggesting that novel factors are required for AcLDL receptor expression.

Base Sequence↗
PubMed1992

A negative retinoic acid response element in the rat oxytocin promoter restricts transcriptional stimulation by heterologous transactivation domains.

Retinoic acid receptors are ligand-dependent transcription factors that stimulate gene transcription from promoters containing retinoic acid or thyroid hormone response elements. We describe a high-affinity binding site from the rat oxytocin promoter that mediates negative transcriptional regulation by the retinoic acid receptor. To examine whether strong, constitutive transactivation domains would be capable of stimulating gene transcription when bound to this DNA binding site that normally mediates transcriptional repression, we fused the transactivation domain of the herpes simplex viral protein VP16 to the amino terminus of the retinoic acid receptor and tested the activity of the chimeric protein on the negative retinoic acid response element. This chimeric retinoic acid receptor acted as a strong, constitutive transactivator when bound to promoters containing palindromic thyroid hormone/retinoic acid response elements but surprisingly it still repressed gene transcription when bound to promoters containing the oxytocin-negative retinoic acid response element. These results suggest that a negative DNA binding site itself can inhibit the function of even potent constitutive transactivation domains, and provide evidence that tethering of a constitutive transactivation domain to DNA is insufficient to activate gene transcription.

Animals↗
PubMed1991

RXR beta: a coregulator that enhances binding of retinoic acid, thyroid hormone, and vitamin D receptors to their cognate response elements.

The retinoic acid receptor (RAR) requires coregulators to bind effectively to response elements in target genes. A strategy of sequential screening of expression libraries with a retinoic acid response element and RAR identified a cDNA encoding a coregulator highly related to RXR alpha. This protein, termed RXR beta, forms heterodimers with RAR, preferentially increasing its DNA binding and transcriptional activity on promoters containing retinoic acid, but not thyroid hormone or vitamin D, response elements. Remarkably, RXR beta also heterodimerizes with the thyroid hormone and vitamin D receptors, increasing both DNA binding and transcriptional function on their respective response elements. RXR alpha also forms heterodimers with these receptors. These observations suggest that retinoid X receptors meet the criteria for biochemically characterized cellular coregulators and serve to selectively target the high affinity binding of retinoic acid, thyroid hormone, and vitamin D receptors to their cognate DNA response elements.

Amino Acid Sequence↗
PubMed1991

The orientation and spacing of core DNA-binding motifs dictate selective transcriptional responses to three nuclear receptors.

Characterization of several thyroid hormone (T3), retinoic acid, and estrogen response elements has led to the identification of conserved DNA half-sites (core binding motifs). We present evidence that differences in both the relative orientation and spacing of these motifs within hormone response elements determine the distinct transcriptional responses of three members of the nuclear receptor superfamily. When separated by 3 bp, direct repeat, palindromic, and inverted palindromic arrangements of these motifs impart selective transcriptional responses to retinoic acid, estrogen, and T3 receptors, respectively. Varying the spacing between core motifs alters the specificity. Without spacing, a direct repeat of the core motif paradoxically configures the T3 receptor to confer transactivation in the absence of T3 and repression in its presence. Such an element occurs naturally in the mouse beta-thyrotropin promoter, physiologically under negative regulation by T3. The orientation and spacing of core binding motifs may thus function in concert as a code that accounts for the selective patterns of transcriptional responses of hormonally regulated promoters.

Animals↗
PubMed1990

Multiple cell type-specific proteins differentially regulate target sequence recognition by the alpha retinoic acid receptor.

Retinoic acid receptors appear to exert profound effects on vertebrate development by regulating the transcription of distinct sets of target genes within different cell types. Several lines of evidence are presented for the existence of multiple, cell type-specific nuclear proteins that function to differentially increase the binding affinity of the alpha retinoic acid receptor for a variety of response elements. These proteins, which we refer to as retinoic acid receptor coregulators, interact with the retinoic acid receptor via a common dimerization interface that overlaps with its ligand binding domain. These observations raise the intriguing possibility that coregulator proteins serve to restrict and/or direct the effects of retinoic acid receptors on patterns of gene expression during development.

Animals↗
PubMed1990

Ligand-activated thyroid hormone and retinoic acid receptors inhibit growth factor receptor promoter expression.

Thyroid hormone (T3) and retinoic acid (RA) receptors mediate ligand-dependent inhibition of epidermal growth factor (EGF) receptor and c-erbB2/neu promoter activities. Ligand-activated T3 and RA receptors act via a 36 bp 5' fragment of the EGF receptor gene in vivo and, in the presence of nuclear extract, bind with high affinity to this region in vitro. Both ligand binding and DNA binding domains of T3 and RA receptors are required for promoter inhibition. When both receptors are expressed in the presence of a single ligand, inhibition is reversed, indicating that the hormone-activated receptor is competed by the unliganded receptor. These results suggest that ligand regulates transcriptional inhibitory functions of the T3 and RA receptors and describe novel regulation of growth factor receptor gene expression.

Base Sequence↗
PubMed1990

Colocalization of 15-lipoxygenase mRNA and protein with epitopes of oxidized low density lipoprotein in macrophage-rich areas of atherosclerotic lesions.

Oxidation of low density lipoprotein (LDL) enhances its atherogenicity, and inhibition of such oxidation decreases the rate of progression of atherosclerotic lesions. The mechanism of LDL oxidation in vivo remains uncertain, but in vitro studies have suggested that cellular lipoxygenases may play a role by initiating lipid peroxidation in LDL. In situ hybridization studies using a 15-lipoxygenase riboprobe and immunostaining using antibodies against 15-lipoxygenase showed strongly positive reactivity largely confined to macrophage-rich areas of atherosclerotic lesions. Polymerase chain reaction with 15-lipoxygenase-specific oligonucleotides and restriction enzyme digestions of the amplified fragment were used to confirm the presence of 15-lipoxygenase message in the reverse-transcribed lesion mRNA. Immunostaining with antibodies reactive with oxidized LDL (but not with native LDL) indicated that the lipoxygenase colocalizes with epitopes of oxidized LDL, compatible with a role for macrophage lipoxygenase in the oxidation of LDL in vivo. Since oxidized LDL is chemotactic for blood monocytes, early lesions might progress at a markedly accelerated rate because of further recruitment of more monocytes which, in turn, would increase further the rate of oxidation of LDL. These data suggest that therapy targeted to block macrophage lipoxygenase activity might decrease the rate of development of atherosclerotic lesions.

Animals↗
PubMed1990

The C'-terminal interaction domain of the thyroid hormone receptor confers the ability of the DNA site to dictate positive or negative transcriptional activity.

To investigate mechanisms responsible for positive and negative transcriptional control, we have utilized two types of promoters that are differentially regulated by thyroid hormone (T3) receptors. Promoters containing the palindromic T3 response element TCAGGTCA TGACCTGA are positively regulated by the T3 receptor after the administration of T3, whereas otherwise identical promoters containing the estrogen response element TCAGGTCA CTG TGACCTGA can be regulated negatively; converse effects are observed with the estrogen receptor. We describe evidence that the transcriptional inhibitory effects of the T3 or estrogen receptors on the estrogen or T3 response elements, respectively, are imposed by amino acid sequences in the C'-terminal region that colocalize with dimerization and hormone-binding domains and that these sequences can transfer inhibitory functions to other classes of transcription factors. Removal of the C'-terminal dimerization and hormone-binding domains of either the alpha T3 or estrogen receptors permits each receptor to act constitutively to enhance transcription on both T3 and estrogen response elements. It is, therefore, suggested that protein-protein interactions between receptor C' termini limit the subset of DNA binding sites on which transcriptional activation occurs.

Animals↗
PubMed1989

Positive and negative regulation of gene transcription by a retinoic acid-thyroid hormone receptor heterodimer.

We present evidence that the human thyroid hormone receptor forms a heterodimer with the human retinoic acid receptor. This interaction results in a cooperative increase in binding of the alpha retinoic acid receptor to a subset of thyroid hormone response elements. Mutations within the DNA binding domain or near the C-terminus abolish either receptor's ability to interact cooperatively on these elements. The thyroid hormone-retinoic acid receptor heterodimer exhibits novel transcriptional properties in that coexpression of both receptors at low levels in Green monkey kidney (CV1) cells results in a positive transcriptional effect on promoters containing a palindromic thyroid hormone response element, but has a surprisingly negative effect on a thyroid hormone response element derived from the alpha myosin heavy chain gene. These results suggest that by forming heterodimers, more elab-orate control of transcription can be achieved by creating receptor combinations with differing activities.

Amino Acid Sequence↗