Transcription of the mouse secretory protease inhibitor p12 gene is activated by the developmentally regulated positive transcription factor Sp1

Characterization of the human α9 integrin subunit gene: Promoter analysis and transcriptional regulation in ocular cells

α9β1 is the most recent addition to the integrin family of membrane receptors and consequently remains the one that is the least characterized. To better understand how transcription of the human gene encoding the α9 subunit is regulated, we cloned the α9 promoter and characterized the regulatory elements that are required to ensure its transcription. Transfection of α9 promoter/CAT plasmids in primary cultured human corneal epithelial cells (HCECs) and uveal melanoma cell lines demonstrated the presence of both negative and positive regulatory elements along the α9 promoter and positioned the basal α9 promoter to within 118 bp from the α9 mRNA start site. In vitro DNaseI footprinting and in vivo ChIP analyses demonstrated the binding of the transcription factors Sp1, c-Myb and NFI to the most upstream α9 negative regulatory element. The transcription factors Sp1 and NFI were found to bind the basal α9 promoter individually but Sp1 binding clearly predominates when both transcription factors are present in the same extract. Suppression of Sp1 expression through RNAi also caused a dramatic reduction in the expression of the α9 gene. Most of all, addition of tenascin-C (TNC), the ligand of α9β1, to the tissue culture plates prior to seeding HCECs increased α9 transcription whereas it simultaneously decreased expression of the α5 integrin subunit gene. This dual regulatory action of TNC on the transcription of the α9 and α5 genes suggests that both these integrins must work together to appropriately regulate cell adhesion, migration and differentiation that are hallmarks of tissue wound healing.

Electrophoretic mobility shift assays for the analysis of DNA-protein interactions

Electromobility shift assay is a simple, efficient, and rapid method for the study of specific DNA-protein interactions. It relies on the reduction in the electrophoretic mobility conferred to a DNA fragment by an interacting protein. The technique is suitable to qualitative, quantitative, and kinetic analyses. It can also be used to analyze conformational changes.

Transcriptional regulation of the cyclin-dependent kinase inhibitor 1A (p21) gene by NFI in proliferating human cells

The cyclin-dependent kinase inhibitor 1A (CDKN1A), also known as p21 (WAF1/CIP1) modulates cell cycle, apoptosis, senescence and differentiation via specific protein-protein interactions with the cyclins, cyclin-dependent kinase (Cdk), and many others. Expression of the p21 gene is mainly regulated at the transcriptional level. By conducting both ligation-mediated PCR (LMPCR) and chromatin immunoprecipitation (ChIP) in vivo, we identified a functional target site for the transcription factor, nuclear factor I (NFI), in the basal promoter from the p21 gene. Transfection of recombinant constructs bearing mutations in the p21 NFI site demonstrated that NFI acts as a repressor of p21 gene expression in various types of cultured cells. Inhibition of NFI in human skin fibroblasts through RNAi considerably increased p21 promoter activity suggesting that NFI is a key repressor of p21 transcription. Over-expression of each of the four NFI isoforms in HCT116 cells established that each of them contribute to various extend to the repression of the p21 gene. Most of all, over-expression of NFI-B in doxorubicin, growth-arrested HCT116 increased the proportion of cells in the S-phase of the cell cycle whereas NFI-A and NFI-X reduced it, thereby establishing a role for NFI in the cell cycle dependent expression of p21.

Regulation of the Rhox5 Homeobox Gene in Primary Granulosa Cells: Preovulatory Expression and Dependence on SP1/SP3 and GABP1

Homeobox genes encode transcription factors that regulate embryonic development and postnatal events. Rhox5 (previously called Pem), the founding member of a homeobox gene cluster that we recently identified on the X chromosome, is selectively expressed in granulosa cells in the ovary and other somatic-cell types in other reproductive organs. In this report, we investigate its regulation in granulosa cells in the rat ovary. We found that Rhox5 expression in the ovary is governed by the Rhox5 distal promoter and is expressed at least as early as Day 5 postpartum. Rhox5 mRNA levels are regulated during the ovarian cycle, peaking before ovulation. Deletion analysis revealed a 25-nt element essential for distal promoter transcription in primary granulosa cells. This distal promoter element contains two ETS and one SP1 transcription-factor family binding sites that mutagenesis analysis indicated were essential for high-level transcription. This element was both necessary and sufficient for transcription, because it activated transcription when placed upstream of a heterologous minimal promoter. Cold competition and electrophoretic mobility shift assay studies demonstrated that SP1, SP3, and the ETS family transcription factor GABP bound this element. Dominant-negative forms of GABP and SP3 repressed distal promoter expression in primary rat granulosa, showing that these factors are crucial for Rhox5 expression. Cotransfection of dominant-negative mutants indicated that Rhox5 expression in granulosa cells is regulated by the c-Jun N-terminal protein kinase (JNK, MAPK8) and RAS pathways, which are known to be upstream of ETS family transcription factors. The discovery that Rhox5 expression in granulosa cells is regulated by MAPK pathways and ETS and SP1 family members provides an opportunity to understand how these regulatory pathways and factors collaborate to regulate gene expression during the ovarian cycle.

Expression of the alpha 5 integrin subunit gene promoter is positively regulated by the extracellular matrix component fibronectin through the transcription factor Sp1 in corneal epithelial cells in vitro

The accumulation of fibronectin (FN) in response to corneal epithelium injury has been postulated to turn on expression of the FN-binding integrin alpha(5)beta(1). In this work, we determined whether the activity directed by the alpha(5) gene promoter can be modulated by FN in rabbit corneal epithelial cells (RCEC). The activity driven by chloramphenicol acetyltransferase/alpha(5) promoter-bearing plasmids was drastically increased when transfected into RCEC grown on FN-coated culture dishes. The promoter sequence mediating FN responsiveness was shown to bear a perfect inverted repeat that we designated the fibronectin-responsive element (FRE). Analyses in electrophoretic mobility shift assays provided evidence that Sp1 is the predominant transcription factor binding the FRE. Its DNA binding affinity was found to be increased when RCEC are grown on FN-coated dishes. The addition of the MEK kinase inhibitor PD98059 abolished FN responsiveness suggesting that alteration in the state of phosphorylation of Sp1 likely accounts for its increased binding to the alpha(5) FRE. The FRE also proved sufficient to confer FN responsiveness to an otherwise unresponsive heterologous promoter. However, site-directed mutagenesis indicated that only the 3' half-site of the FRE was required to direct FN responsiveness. Collectively, binding of FN to its alpha(5)beta(1) integrin activates a signal transduction pathway that results in the transcriptional activation of the alpha(5) gene likely through altering the phosphorylation state of Sp1.

MAP kinase pathway signalling is essential for extracellular matrix determined mammary epithelial cell survival

Mammary epithelial cells in primary cell culture require both growth factors and specific extracellular matrix (ECM)-attachment for survival. Here we demonstrate for the first time that inhibition of the ECM-induced Erk 1/Erk 2 (p42/44 MAPK) pathway, by PD 98059, leads to apoptosis in these cells. Associated with this cell death is a possible compensatory signalling through the p38 MAP kinase pathway the inhibition of which, by SB 203580, leads to a more rapid onset of apoptosis. This provides evidence for a hitherto undescribed Erk 1/Erk 2 to p38 MAP kinase pathway 'cross-talk' that is essential for the survival of these cells. The cell death associated with inhibition of these two MAP kinase pathways however, occurred in the presence of insulin that activates the classical PI-3 kinase-dependent Akt/PKB survival signals and Akt phosphorylation. Cell death induced by inhibition of the MAP kinase pathways did not affect Akt phosphorylation and may, thus, be independent of PI-3 kinase signalling.

Transcription from the P2 promoter of the growth hormone receptor gene involves members of the Sp transcription factor family

The P2 promoter of the gene for growth hormone receptor is developmentally regulated and is differentially active in a number of tissues. Little is known about the identity of the transcription factors that participate to effect this pattern of transcription. Deletion analysis and transient transfection were used to localize a previously identified cis-acting element within the sheep P2 promoter to between positions -99 and -87. Gel mobility-shift assays with nuclear extracts from Chinese hamster ovary (CHO-K1) fibroblasts revealed that this sequence encompasses an atypical binding site for both Sp1 and two isoforms of Sp3. A gel mobility-shift scan of promoter sequences between -88 and +21 indicated the existence of three other binding sites for Sp1 and Sp3. One of these, designated site II and found by using a probe spanning -74 to -54, corresponds to a classical GC box consensus sequence. Site III (-63 to -41) and site IV (-27 to -5) harbour atypical Sp1/Sp3-binding sequences. Site-directed mutagenesis of site II or site IV decreased promoter activity by approx. 40%, whereas a promoter construct incorporating both mutations exhibited negligible (approx. 1%) activity. Co-transfection of expression plasmids encoding either Sp1 or Sp3 significantly transactivated reporter gene activity from a P2 promoter construct carrying all four Sp1/Sp3-binding sites (8-fold compared with 7.1-fold induction respectively). Sp1 is known to interact with a variety of other transcription factors to regulate the transcription of a number of differentially expressed genes. The identification of four binding sites for Sp1 and Sp3 within the P2 promoter of the gene for growth hormone receptor might point to other factors that interact to regulate the activity of this promoter in different tissues during foetal and post-natal development.

Oxidative stress and superoxide dismutase in development, aging and gene regulation

Free radicals and other reactive oxygen species are produced in the metabolic pathways of aerobic cells and affect a number of biological processes. Oxidation reactions have been postulated to play a role in aging, a number of degenerative diseases, differentiation and development as well as serving as subcellular messengers in gene regulatory and signal transduction pathways. The discovery of the activity of superoxide dismutase is a seminal work in free radical biology, because it established that free radicals were generated by cells and because it made removal of a specific free radical substance possible for the first time, which greatly accelerated research in this area. In this review, the role of reactive oxygen in aging, amyotrophic lateral sclerosis (a neurodegenerative disease), development, differentiation, and signal transduction are discussed. Emphasis is also given to the role of superoxide dismutases in these phenomena.

Stimulation of the preprothyrotropin-releasing hormone gene by epidermal growth factor

Regulation of the expression of the prepro-TRH (ppTRH) gene by epidermal growth factor (EGF) was investigated. The i.p. injection of EGF significantly stimulated hypothalamic ppTRH messenger RNA levels in rats. To clarify whether this stimulatory effect of EGF could be exerted at the level of gene transcription, the 5'-flanking region (-1893/+127) of the mouse ppTRH gene fused to a luciferase reporter gene was transiently transfected into pituitary GH4C1 cells, and the effect of EGF on gene transcription was measured by a luciferase assay. EGF stimulated ppTRH gene promoter activity in a time- and dose-dependent manner. Deletion analysis revealed that two different regions of the promoter, between -254 and -218 [EGF response element-1 (EGFRE1)] and between -130 and -84 (EGFRE2) were required for full stimulation by EGF. The two EGFREs possessed putative binding sequences for the transcription factor Sp1, and they functioned cooperatively in heterologous promoters. Nuclear extracts from GH4C1 cells specifically bound those two EGFREs in gel retardation assays. Two protein-DNA complexes were found on EGFRE1, whereas four complexes were observed on EGFRE2. Although the binding of nuclear extracts to EGFRE1 was competed for by the consensus Sp1 binding sequence, the complexes on EGFRE1 were not supershifted by an Sp1 antibody. Formation of the slower migrating protein complex on EGFRE1 was prevented by EDTA, suggesting that one of the EGFRE1-binding proteins might be an Sp1-related zinc finger protein. Competition and supershift experiments demonstrated that the EGFRE2-binding protein showing that the slowest migration possessed a characteristic similar to that of Sp1. Selective mutations of the Sp1-binding site in EGFRE2 markedly diminished the EGF-induced stimulation. These results suggest that EGF may function as a positive regulator of ppTRH gene expression, and that the stimulatory effect may be mediated through a cooperative interaction between Sp1 or Sp1-related proteins and additional factors that bind to two separate DNA regions.

Transcriptional regulation of the rat poly(ADP-ribose) polymerase gene by Sp1

Expression of the gene encoding poly(ADP-ribose) polymerase (PARP), although ubiquitous, nevertheless varies substantially between tissues. We have recently shown that Sp1 binds five distinct target sequences (US-1 and F1-F4) in the rat PARP (rPARP) gene promoter. Here we used deletion analyses and site-directed mutagenesis to address the regulatory function played by these Sp1 sites on the basal transcriptional activity directed by the rPARP promoter. Transfection experiments revealed that the most proximal Sp1 site is insufficient by itself to direct any promoter activity. In addition, a weak negative regulatory element was identified between positions -101 and -60. The rPARP promoter directed high levels of chloramphenicol acetyltransferase activity in Jurkat T-lymphoblastoid and Ltk- fibroblast cells but only moderate levels in pituitary GH4C1 and liver HTC cells, correlating with the amounts of PARP detected in these cells by western blot analysis. However, the reduced promoter efficiency in HTC and GH4C1 cells did not result from the lack of Sp1 activity in these cells but suggested that yet uncharacterized regulatory proteins might turn off PARP gene expression by binding negative regulatory elements from the rPARP promoter. Similarly, site-directed mutagenesis on the three most proximal Sp1 elements suggested the influence exerted by Sp1 on the rPARP promoter activity to vary substantially between cell types. It also provided evidence for a basal rPARP promoter activity driven through the recognition of unidentified cis-acting elements by transcription factors other than Sp1.

Genomic organization and molecular characterization of a gene encoding HsPXF, a human peroxisomal farnesylated protein

A protein modification essential for the cellular sorting of many biologically relevant proteins is the covalent attachment of prenyl lipids by specific transferases. Isoprenylation is known to render protein domains hydrophobic, thereby facilitating the interaction with lipid bilayers and/or membrane proteins. The target for the modification with farnesyl groups is the COOH-terminal sequence CaaX. Among the variety of farnesylated proteins the only one reported so far to be located to peroxisomes is the 37-kDa peroxisomal farnesylated hamster protein PxF. Recently we published data on the cDNA of the human gene HK33 (A. Braun et al., 1994, Gene 146: 291-295), which was revealed to be the human ortholog of PxF and was consequently renamed HsPXF. The genomic structure, molecular characterization, and evolutionary conservation of HsPXF are described herein. The exact location of the gene was defined as chromosome 1q22. The gene spans a region of approximately 9 kb, containing eight exons and seven introns. The 5' upstream region showed two potential Sp1-binding sites and an Alu repetitive sequence. Luciferase reporter activating capacity confirmed the presumed promoter activity of this region. On the transcriptional level, we detected four splice variants originating either from exon skipping or from alternative splicing events. For the HsPXF protein, a carboxyterminal farnesylation at cysteine residues was demonstrated. Through the use of HsPXF-specific antibodies, the protein was shown to be attached to the outer surface of peroxisomes. This localization together with the similarity to a peroxisomal assembly protein from Saccharomyces cerevisiae suggests HsPXF is involved in the process of peroxisomal biogenesis or assembly.

The rat growth hormone and human cellular retinol binding protein 1 genes share homologous NF1-like binding sites that exert either positive or negative influences on gene expression in vitro

High levels of expression for the rat growth hormone (rGH) gene are restricted to the somatotroph cells of the anterior pituitary. Previously, we have shown that rGH cell-specific repression results in part from the recognition of negatively acting silencers by a number of nuclear proteins that repress basal promoter activity. Examination of these silencers revealed the presence of binding sites for proteins that belong to the NF1 family of transcription factors. Indeed, proteins from this family were shown to bind the rGH proximal silencer (designated silencer-1) in in vitro assays. Furthermore, this silencer site is capable of repressing chloramphenicol acetyltransferase (CAT) gene expression driven by an heterologous promoter (that of the mouse p12 gene), even in pituitary cells. Recently, we identified in the 5' untranslated region of the gene encoding human cellular retinol binding protein 1 (hCRBP1) a negative regulatory element (Fp1) that also bears an NF1 binding site very similar to that of rGH silencer-1. However, although deletion of Fp1 in the hCRBP1 gene yielded increased CAT activity, pointing toward a negative regulatory function exerted by this element, its insertion upstream of the p12 basal promoter results in an impressive positive stimulation of CAT gene expression. By exploiting NaDodSO4 gel protein fractionation and renaturation, we identified a 40-kD nuclear protein (designated Bp1) present in GH4C1 cells that binds very strongly to rGH silencer-1 but only weakly to hCRBP1 Fp1. Similarly, we also detected a 29-kD nuclear factor (designated Bp2) that recognizes exclusively the Fp1 element as its target site, therefore suggesting that different, but likely related, proteins bind these homologous elements to either activate or repress gene transcription. Although they bind DNA through the recognition of the NF1-like target sequence contained on these elements, competition and supershift experiments in electrophoretic mobility shift assays provided evidence that neither of these proteins belong to the NF1 family.

A GT-rich sequence binding the transcription factor Sp1 is crucial for high expression of the human type VII collagen gene (COL7A1) in fibroblasts and keratinocytes

Type VII collagen is the major component of anchoring fibrils, structural elements that stabilize the attachment of the basement membrane to the underlying dermis. In this study, we have dissected the human type VII collagen gene (COL7A1) promoter to characterize the cis-elements responsible for the expression of the gene in cultured fibroblasts and keratinocytes. Using transient cell transfections with various 5' end deletion COL7A1 promoter/chloramphenicol acetyltransferase reporter gene plasmid constructs, we determined that the region between nucleotides -524 and -456, relative to the transcription start site, is critical for high promoter activity in both cell types studied. Gel mobility shift assays using several DNA fragments spanning this region identified a GT-rich sequence between residues -512 and -505, necessary for the binding of nuclear proteins to this region of the promoter. Point mutations abolished the binding of nuclear proteins in gel shift assays and drastically diminished the activity of the promoter in transient cell transfections. Supershift assays with antibodies against various transcription factors including Sp1, Sp3, c-Jun/AP-1, and AP-2, and competition experiments with oligonucleotides containing consensus sequences for Sp1 and AP-1 binding identified Sp1 as the transcription factor binding to this region of the COL7A1 promoter. Indeed, recombinant human Sp1 was shown to bind the COL7A1 promoter GT-rich element but not its mutated form in gel mobility shift assays. In addition, co-transfection of pPacSp1, an expression vector for Sp1, together with the COL7A1 promoter/chloramphenicol acetyltransferase construct into Sp1-deficient Drosophila Schneider SL2 cells unequivocally demonstrated that Sp1 is essential for high expression of the COL7A1 gene. These data represent the first in-depth analysis of the human COL7A1 promoter transcriptional control.

Involvement of two Sp1 elements in basal endothelial prostaglandin H synthase-1 promoter activity

Prostaglandin H synthase-1 (PGHS-1) is a constitutively expressed key enzyme in the biosynthesis of physiologically important prostanoids. The promoter of the human PGHS-1 gene lacks a TATA box, has a very GC-rich region, and contains multiple transcription start sites. To identify the elements involved in the constitutive expression of the PGHS-1 gene, we constructed a 2075-base pair fragment (-2095 to -21 relative to the translation start codon) and a series of 5'-deletion mutants into a promoterless luciferase expression vector, which was transfected in HUVEC. Two important regions were identified. DNase I footprinting identified a protected segment, which contains an Sp1 binding site proximal to the transcription start sites. Band shift assays confirmed specific binding of Sp1 to this segment. Band shift assays further revealed specific binding of Sp1 to a distal region containing a canonical Sp1 site. Mutation of either Sp1 binding site significantly reduced the promoter activity. When both sites were mutated, the activity was reduced to 29% of that of the wild type. Mutation of Sp1 sites did not abrogate promoter activity stimulated by phorbol ester. These results indicate that binding of Sp1 or its related proteins to two widely separated Sp1 sites on the promoter region activates the basal PGHS-1 gene transcription.

Negative transcriptional regulation of the chicken Na+/K(+)-ATPase alpha 1-subunit gene

Although the Na+/K(+)-ATPase alpha 1-subunit gene is ubiquitously expressed in vertebrates, its level of expression varies among tissue and cell types. In spite of similar mRNA distribution in tissues of mammals and birds, the 5'-flanking regions of alpha 1-subunit genes exhibit remarkable diversity; i.e., the core promoter activity of the TATA-less chicken alpha 1 gene strongly depends upon multiple Sp1-based regulation (six Sp1 sites), whereas the promoter activity of the TATA-like rat alpha 1-subunit gene relies on the two Sp1 and additional positive regulatory factors. Further analysis of the regulatory regions of the Na+/K(+)-ATPase alpha 1-subunit genes revealed that the vertebrate alpha 1-subunit genes may share common inhibitory mechanisms for subtle transcriptional regulation; the core promoter activities can be either enhanced or repressed depending on the availability of inhibitory factors. Two potential candidates for such inhibitory elements in both avian and mammalian Na+/K(+)-ATPase alpha 1-subunit genes are (1) a newly identified element, GCCCTC, and (2) a GCF-binding sequence, NN[G/c]CG[G/c][G/c][G/c]CN, or its reverse complement. Gel retardation assays using the inhibitory region of the chicken gene and crude nuclear extracts from tissue-cultured chicken and mouse cells showed the existence of a set of proteins that bind to this region. The amounts of individual regulatory proteins in different cell types seem to vary, resulting in differential formation of DNA/protein complexes in different cell types. Thus, the regulation of Na+/K(+)-ATPase alpha 1-subunit gene expression under different cellular environment as well as in different cell types can be achieved by a shared mechanism; modulation of the ratio of the abundance of individual inhibitory factors.

Expression of a 74-kDa nuclear factor 1 (NF1) protein is induced in mouse mammary gland involution. Involution-enhanced occupation of a twin NF1 binding element in the testosterone-repressed prostate message-2/clusterin promoter

Testosterone repressed prostate message-2 (TRPM-2)/clusterin gene expression is rapidly induced in early involution of the mouse mammary gland, after weaning, and in the rat ventral prostate, after castration. A search for involution-enhanced DNaseI footprints in the proximal mouse TRPM-2/clusterin gene promoter led to the identification and characterization (by DNase I footprinting and EMSA) of a twin nuclear factor 1 (NF1) binding element at -356/-309, relative to the proposed transcription start site; nuclear extracts from 2-day involuting mouse mammary gland showed an enhanced footprint over the proximal NF1 element; extracts from involuting prostate showed enhanced occupancy of both NF1 binding elements. Subsequent EMSA and Western analysis led to the detection of a 74-kDa NF1 protein whose expression is triggered in early involution in the mouse mammary gland; such an induced protein is not found in the involuting rat ventral prostate. This protein was not found in lactation where three other NF1 proteins of 114, 68, and 46 kDa were detected. Reiteration of the epithelial cell apoptosis associated with early mammary gland involution, in vitro, in a primary cell culture system, triggered the appearance of the 74-kDa NF1. Overlaying the cells with laminin-rich extracellular matrix suppressed the apoptosis and the expression of the 74-kDa NF1 and, in the presence of lactogenic hormones, initiated milk protein gene expression and the expression of two of the lactation-associated NF1 proteins (68 and 46 kDa). This study, thus, identifies for the first time the occurrence of a switch in expression of different members of the family of NF1 transcription factors as mammary epithelial cells move from the differentiated to the involution/apoptotic state, and it is likely that the involution-specific 74-kDa NF1 accounts for the enhanced NF1 footprint detected on the TRPM-2/clusterin promoter with extracts of mouse mammary gland.

Isolation and characterization of the human cytochrome P450 CYP1B1 gene

Previously, we identified a novel human cytochrome P450 cDNA that is inducible by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and represents the first member of a new subfamily designated cytochrome P4501B1 (CYP1B1; Sutter, T. R., Tang, Y. M., Hayes, C. L., Wo, Y. P., Jabs, E. W., Li, X., Yin, H., Cody, C. W., and Greenlee, W. F. (1994) J. Biol. Chem. 269, 13092-13099). Here, we report on the isolation and initial characterization of the CYP1B1 gene. The CYP1B1 gene maps to human chromosome 2 at 2p21-22 and contains three exons and two introns. The putative open reading frame starts in the second exon and is 1629 base pairs in length. Southern analysis using DNA probes directed to each of the three exons confirmed that CYP1B1 is a single copy gene. Human CYP1B1 differs from its two most closely related members of the cytochrome P450 superfamily, CYP1A1 and CYP1A2, in the number of exons (3 versus 7) and chromosome location (2 versus 15). A single transcription initiation site was identified by primer extension analysis and S1 nuclease mapping. Based on nucleotide sequence analysis, the CYP1B1 gene lacks a consensus TATA box in the promoter region and contains nine TCDD-responsive enhancer core binding motifs (5'-GCGTG-3') located within a 2.5-kilobase pair genomic fragment 5'-ward of the transcription initiation start site. Deletion analysis of chloramphenicol acetyltransferase reporter gene constructs containing 5' CYP1B1 genomic fragments indicates that a region from -1022 to -835 containing three of the nine core binding motifs contributes to the TCDD-inducible expression of CYP1B1.

Multiple nuclear regulatory proteins bind a single cis-acting promoter element to control basal transcription of the human alpha 4 integrin gene in corneal epithelial cells

Expression of the fibronectin-binding integrin alpha 4 beta 1 has been postulated to be an important event in the process of corneal epithelial wound healing. In a previous study, we identified upstream positive and negative cis-acting regulatory elements that are needed to modulate the transcriptional activity of the human alpha 4 integrin subunit gene promoter in primary cultures of rabbit corneal epithelial cells. We have shown that most of the basal activity directed by this promoter was dependent on the presence of a cis-acting DNA sequence designated the alpha 4.1 element, centered at position -45 relative to the human alpha 4 mRNA start site. Here, we demonstrate that five distinct nuclear regulatory proteins (designated Bp1 to Bp5) from rabbit corneal epithelial cells possess the ability to bind the alpha 4.1 element in a specific manner in vitro. However, when they are combined together, only two of them (Bp2 and Bp5) retained their ability to interact with their specific target sequence in in vitro assays. The apparent molecular masses of the Bp1 to Bp5 proteins were determined and found to be of 91, 74, 59, 45, and 39 kD, respectively. Electrophoretic mobility-shift assays (EMSAs) indicated that only Bp2 also possesses the ability to bind the alpha 4.2 element, a site homologous to alpha 4.1 which plays a minor role in alpha 4 gene expression. Despite the presence of three Ets binding sites in the immediate vicinity of alpha 4.1, competition experiments in EMSA clearly indicate that Bp1, Bp2, Bp4, and Bp5 do not belong to the Ets family of transcription factors. Insertion of both alpha 4.1 and alpha 4.2 upstream from the basal promoter of the mouse p12 gene provided evidence that both elements have the ability to modulate basal expression driven from a heterologous promoter. alpha 4.1 was shown to function as an activator, whereas alpha 4.2 acted as a repressor in a manner that is dependent on its orientation, further stressing the critical regulatory function played by these two elements on alpha 4 gene basal expression.

Transcriptional regulation of murine beta1,4-galactosyltransferase in somatic cells. Analysis of a gene that serves both a housekeeping and a mammary gland-specific function

beta1,4-Galactosyltransferase (beta4-GT) is a constitutively expressed enzyme that synthesizes the beta4-N-acetyllactosamine structure in glycoconjugates. In mammals, beta4-GT has been recruited for a second biosynthetic function, the production of lactose which occurs exclusively in the lactating mammary gland. In somatic tissues, the murine beta4-GT gene specifies two mRNAs of 4. 1 and 3.9 kilobases (kb), as a consequence of initiation at two different start sites approximately 200 base pairs apart. We have proposed that the region upstream of the 4.1-kb start site functions as a housekeeping promoter, while the region adjacent to the 3.9-kb start site functions primarily as a mammary gland-specific promoter (Harduin-Lepers, A., Shaper, J. H., and Shaper, N. L. (1993) J. Biol. Chem. 268, 14348-14359). Using DNase I footprinting and electrophoretic mobility shift assays, we show that the region immediately upstream of the 4.1-kb start site is occupied mainly by the ubiquitous factor Sp1. In contrast, the region adjacent to the 3.9-kb start site is bound by multiple proteins which include the tissue-restricted factor AP2, a mammary gland-specific form of CTF/NF1, Sp1, as well as a candidate negative regulatory factor that represses transcription from the 3.9-kb start site. These data experimentally support our conclusion that the 3.9-kb start site has been introduced into the mammalian beta4-GT gene to accommodate the recruited role of beta4-GT in lactose biosynthesis.

Expression and regulation of superoxide dismutase activity in human skin fibroblasts from donors of different ages

We have determined the activities, protein, and mRNA abundances as well as the level of transcriptional activation of two intracellular forms of the free radical metabolizing enzyme superoxide dismutase in 29 human skin fibroblast lines established from donors of different ages. SOD-1 (a copper and zinc containing form of SOD) and SOD-2 (a manganese containing form of the enzyme) activities were both observed to be significantly lower in cell lines derived from fetal skin than in lines established from postnatal skin (ages 17-94 years). The percent of total activity contributed by SOD-1 decreased in an age-associated manner from approximately 50% in the fetal lines to less than 20% in lines established from old tissue donors. All of the cell lines were screened to exclude the possibility that they contained a polymorphism known to influence SOD-2 activity. Northern blot analysis revealed three SOD-1 mRNA transcripts that were 0.5, 0.7, and 1.9 kb in length. Although SOD-1 protein abundance was lower in fetal lines than in lines derived from postnatal donors, SOD-1 mRNA abundance did not differ between fetal cells and cell lines derived from young donors. SOD-2 protein abundance and mRNA abundance were both significantly lower in fetal lines than in postnatal lines. No postnatal age-dependent differences were observed in any of the SOD-2 parameters examined. Nuclear run-on analysis revealed that fetal cell lines exhibited a lower level of transcriptional initiation for SOD-1 than postnatal lines. The transcription of SOD-2 was readily detected in postnatal lines, but undetectable in fetal lines. These results are consistent with multiple levels of control for SOD-1 expression and with a strong transcriptional influence on SOD-2 expression.

A novel expression vector composed of a regulatory element of the human leukosialin-encoding gene in different types of mammalian cells

The regulatory element (RE) of the human leukosialin (LS)-encoding gene, that encodes a major sialoglycoprotein of human leukocyte and platelet membranes, was used to develop a novel expression vector, pKX. The vector was constructed by cloning a RE fragment and the SV40 fragment containing polyadenylation and splicing signals between HindIII and BamHI sites of the pCAT-Basic vector. The transcription level controlled by this vector was evaluated in six different cell lines using a transient expression assay of chloramphenicol acetyltransferase (CAT). The CAT activity of the pKX vector was compared to the other common expression vectors, namely pMSG (driven by the mouse mammary tumor virus LTR), pcDL-SR alpha (SV40 promoter/enhancer and HTLV-I LTR), pcDNAI (cytomegalovirus promoter/enhancer) and pCAT-Control (SV40 promoter/enhancer). The level of expression provided by the pKX vector was comparable to that observed with pcDNAI and pcDL-SR alpha vectors. In different mammalian cell lines, the highest efficiency of expression of the pKX vector was observed in the human T-cell lines, Jurkat and CEM, although the expression of pcDL-SR alpha-CAT in those cell lines was in the same range. The expression of the pKX vector driven by a non-viral promoter and/or enhancer can be as efficient as that driven by a viral promoter and/or enhancer. Potential uses of this vector may be found in studies of transient gene expression in hematopoietic cells and for gene therapy, particularly the ones involving T-cells.

The human medium chain Acyl-CoA dehydrogenase gene promoter consists of a complex arrangement of nuclear receptor response elements and Sp1 binding sites

Expression of the gene encoding the mitochondrial fatty acid. beta-oxidation enzyme, medium-chain acyl-CoA dehydrogenase (MCAD), is regulated among tissues during development and in response to alterations in substrate availability. To identify and characterize cis-acting MCAD gene promoter regulatory elements and corresponding transcription factors, DNA-protein binding studies and mammalian cell transfection analyses were performed with hjman MCAD gene promoter fragments. DNA:protein binding studies with nuclear protein extracts prepared from hepatoma G2 cells, 3T3 fibroblasts, or Y-1 adrenal tumor cells identified three sequences (nuclear receptor response element 1 or NRRE-1, NRRE-2, and NRRE-3) that bind orphan members of the steroid/thyroid nuclear receptor superfamily including chicken ovalbumin upstream promoter transcription factor and steroidogenic factor 1. Sp1 binding sites (A-C) were identified in close proximity to each of the NRREs. NRRE-3 conferred cell line-specific transcriptional repression by interacting with chicken ovalbumin upstream promoter transcription factor or activation via steroidogenic factor 1. In contrast, the Sp1 binding site A behaved as a transcriptional activator in all cell lines examined. We propose that multiple nuclear receptor transcription factors interact with MCAD gene promoter elements to differentially regulate transcription among a variety of cell types.

Transcriptional analysis of acetylcholine receptor alpha 3 gene promoter motifs that bind Sp1 and AP2

In this study, we performed an analysis of the neuronal nicotinic acetylcholine receptor alpha 3 subunit gene promoter region, -238/+47, to identify cis and trans elements that are important for basal activity in PC12 cells. Sequence analyses of the alpha 3 promoter and footprint assays revealed an Sp1 binding site between -79 and -57 (termed the alpha 3 GA motif) and an AP2 binding site between -30 and -7. Using mobility shift analysis, we found that PC12 cell extracts contain proteins that specifically bind to the alpha 3 GA motif and are immunologically related to Sp1. Mutation of the alpha 3 GA motif, which prevented binding of Sp1, resulted in a 75% decrease in promoter activity. Mutation of the AP2 site resulted in only a minor loss of promoter activity, which is consistent with the lack of AP2 binding activity in PC12 extracts. In Drosophila Schneider line 2 (S2) cell cotransfection assays, Sp1 activated the alpha 3 promoter in a GA motif-dependent manner. Furthermore, multimerization of the GA motif upstream of the beta-globin TATA box conferred Sp1 responsiveness. Our results indicate that Sp1 can activate transcription through direct interaction with the alpha 3 GA motif and that this motif plays a major role in alpha 3 promoter basal activity in PC12 cells.

Multiple regulatory elements control the basal promoter activity of the human alpha 4 integrin gene

It has been suggested that expression of the genes encoding the alpha 4/beta 1 integrin increases during wound healing of the cornea. As a first step in understanding the mechanisms required to stimulate alpha 4 gene expression during this process, we defined the minimal upstream sequence required to direct basal promoter activity for this gene. Using deletion analyses of the alpha 4 gene upstream sequence, we identified two functionally important negative regulatory elements. Dimethylsulfate (DMS) methylation interference assays provided evidence for the binding of a single nuclear protein to tandemly repeated homologous cis-acting elements (designated alpha 4.1 and alpha 4.2) from the alpha 4 basal promoter that share the core sequence 5'-GTGGGT-3'. The formation of a protection only at alpha 4.1 in DNase I footprinting suggested that it is the primary target element for the binding of nuclear proteins. Three distinct nuclear proteins bound a double-stranded oligonucleotide bearing the DNA sequence of alpha 4.1 to produce specific DNA-protein complexes (R1 to R3) in gel-shift assays, from which that producing R3 was identified as the protein yielding DNase I protection at alpha 4.1. Detailed mutational analysis of alpha 4.1 and alpha 4.2 indicated that both elements positively regulate gene expression in primary cultures of corneal epithelial cells and Jurkat tissue culture cells, which is consistent with the deletion analysis. However, when transiently transfected into pituitary GH4C1, the alpha 4.2 mutants yielded increased chloramphenicol acetyl transferase activity therefore demonstrating that these elements have the ability to function either as positive or negative regulators of gene transcription in a manner that is dependent on the type of cell transfected.

The rat growth hormone proximal silencer contains a novel DNA-binding site for multiple nuclear proteins that represses basal promoter activity

Cell-type-specific expression of the rat growth hormone (rGH) gene is determined by the interaction of both positive as well as negative regulatory proteins with cis-acting elements located upstream of the rGH mRNA start site. We have recently shown that the rat liver transcription factor NF1-L binds to the proximal rGH silencer (called silencer-1) to repress its transcriptional activity. However, this single factor proved to be insufficient by itself to confer cell-specific gene repression. We therefore attempted to identify other regulatory proteins interacting with silencer 1, which might be needed to achieve full cell-specific repression of that gene. A common recognition site for three yet uncharacterized nuclear proteins (designated as SBP1, SBP2 and SBP3) which bind a DNA sequence adjacent to the NF1-L-binding site in the rGH silencer-1 element were identified. UV crosslinking of DNA/protein complexes and nuclear protein fractionation/renaturation from SDS/polyacrylamide gels further indicated that the molecular masses for SBP1-3 are 41, 26 and 17 kDa respectively, the major species being the 26-kDa protein (SBP2) which account for 83% of the shifted SBP double-stranded oligonucleotide in gel mobility-shift assays. For this reason, most of this study focussed on the characterization of SBP2. We demonstrated that binding of NF1-L and SBP2 to their respective recognition sequence is a mutually exclusive event. Although an SBP-binding activity has been found in every non-pituitary tissue or cell line tested, no such activity could be detected in either rat pituitaries or rat pituitary GH4C1 cells. Insertion of the SBP element upstream of the basal promoter of the mouse p12 heterologous gene resulted in a consistent decrease in chloramphenicol acetyl transferase reporter gene expression following transient transfections in non-pituitary cells only, suggesting that the related SBP1-3 proteins might be involved in generally repressing gene transcription in a cell-specific manner.

Transcriptional activation of human leukosialin (CD43) gene by Sp1 through binding to a GGGTGG motif

Human leukosialin (CD43) is expressed on the surface of hematopoietic cells in cell-type specific and differentiation-stage-specific manners. Previously we found that the sequence from -53 to -40 was critically involved in the promoter function [Kudo, S. & Fukuda, M. (1991) J. Biol. Chem. 266, 8483-8489]. A transient-expression assay using a chloramphenicol acetyltransferase reporter gene revealed that the promoter could confer a high basal transcriptional activity in both leukosialin-producing and non-producing cells. The transcription factor interacting with the promoter sequence was determined by DNase I footprinting and gel-mobility-shift assays. The nuclear extracts from both leukosialin-producing Jurkat cells and non-producing Hela cells showed a footprint on the 5' flanking region from -58 to -34. Gel-mobility-shift assays revealed that DNA-protein complexes were formed with both nuclear extracts, and these complex formations were inhibited by an oligonucleotide containing the Sp1-binding consensus sequence. Prior incubation of anti-Sp1 antibody with nuclear extracts in this assay resulted in the supershift of the band for the DNA-protein complex. In addition, the footprint produced by the purified Sp1 transcription factor was identical to those produced by nuclear extracts of Jurkat and Hela cells. The mutational analyses revealed that the binding affinities of Sp1 to mutated promoter sequences were parallel to the transcriptional activity of these promoter sequences. Transient expression analyses in Drosophila Schneider cells demonstrated that cotransfection with Sp1 expression plasmid increased the transcriptional activity. These results establish that Sp1 can bind to the promoter and positively regulates the expression of the leukosialin gene. Even the stable expression of CAT constructs in non-producing Hela cells showed high transcriptional activity. The leukosialin expression thus appears to be regulated by the unique mechanism, that is the repression of high basal transcriptional activity rather than the activation of the basal transcriptional level. Tissue-specific expression is probably achieved by suppression of the basal transcriptional activity in non-producing cells.

The 30-kDa rat liver transcription factor nuclear factor 1 binds the rat growth-hormone proximal silencer

Transcription of the gene encoding rat growth hormone is under the influence of cis-acting negative regulatory elements termed silencers. We showed previously that one such element, designated the rat growth hormone proximal silencer-1 site, binds a nuclear protein, the nuclear-factor-1-like protein that is probably a member of the CAAT transcription factor/nuclear-factor-1 (CTF/NF-I) family of transcription factors. This nuclear protein possesses DNA-binding activity as well as biochemical properties similar to those reported for the 30-kDa rat liver form of nuclear factor 1 (NF1-L). Results from both gel mobility supershift assays and Western-blot analyses, performed in combination with a polyclonal antibody directed against the DNA-binding domain of NF1-L, indicated that rat liver nuclear factor 1 might indeed correspond to one of the transcription factors interacting with the rat growth-hormone proximal silencer element. Further experiments using gel mobility shift assays also indicated that, as for NF1-L, multiple proteins among the 52-66-kDa CTF/NF-I isoforms from human HeLa cells also possess the ability to bind the rat growth-hormone silencer.

Anomalous interaction of Sp1 and specific binding of an E-box-binding protein with the regulatory elements of the Na,K-ATPase alpha 2 subunit gene promoter

We identified cis elements in the 5'-flanking region of rat Na,K-ATPase alpha 2 subunit gene (Atp1a2) using transient transfection assays in L6 rat skeletal muscle myoblast cells. By 5'-deletion mutation analysis, the region between nucleotide positions -175 and -108 was identified as a positive regulatory region. In the region, the distal E box (nucleotides -144 to -139) acts as a negative regulatory element, and the Sp1 consensus sequence (nucleotides -123 to -118) and the GGGAGG sequence (nucleotides -114 to -109) act as positive regulatory elements. Gel-retardation analysis revealed that binding factors are an E-box-binding protein and Sp1. DNase I footprinting and methylation-interference analyses revealed that Sp1 binds to the region from nucleotides -122 to -101 and the E-box-binding protein to the region from nucleotides -144 to -136. T4 DNA polymerase footprinting revealed that there are three Sp1-binding sites in the region and that Sp1 binds to one of the three sites in a mutually exclusive manner. The mechanism by which Sp1 activates the Atp1a2 promoter is discussed.

The US-1 element from the gene encoding rat poly(ADP-ribose) polymerase binds the transcription factor Sp1

By comparing the upstream DNA sequence of the rat and human genes encoding poly(ADP-ribose) polymerase (PARP), we have defined a 16-bp conserved region and designated it as US-1 for 'upstream sequence 1'. This element is homologous to the recently described binding site for the transcription factor Sp1 in the promoter sequence of the mouse p12 gene which encodes a protease inhibitor. Analyses in gel mobility shift assays revealed that a nuclear protein, produced by all tissue-culture cells tested, specifically binds the US-1 element. The pattern of shifted DNA protein complexes obtained was strikingly similar to that for Sp1, which is supported by the positive displacement of these complexes by an oligomer containing the Sp1 binding site in gel shift competition experiments. Replacement of the Sp1 binding site from the basal promoter of the mouse p12 gene by the rPARP US-1 element did not result in any significant variations in the level of expression of the chloramphenicol acetyltransferase (CAT) reporter gene upon transient transfection of tissue-culture cells. However, when point mutations are introduced in the US-1 element in a similar substitution experiment, a significant reduction in CAT gene expression could be observed. These data are consistent with Sp1 interacting with the US1 element. Results from DNase I footprinting experiments clearly indicated that purified Sp1 not only binds to the US-1 element but also to four other closely located cis-acting sites scattered in the promoter of the rat PARP gene, therefore suggesting that Sp1 is likely to modulate strongly the expression of that gene in different tissues.

Sp1 binds to the adhesion-molecule-on-glia regulatory element that functions as a positive transcription regulatory element in astrocytes

We analyzed cis-acting elements regulating the expression of the gene encoding adhesion molecule on glia (AMOG) in primary cultured astrocytes from newborn rat cerebrum and cerebellum. The relative promoter activities among the series of 5' sequential deletion mutants are similar to those observed in B103 (rat neuroblastoma cell line) cells. The previously identified AMRE (AMOG regulatory element) of the GAGGCGGGG sequence functions as a positive regulatory element, not only in B103 cells, but also in astrocytes. Binding factors to the element were identified as Sp1 based on the following observations using nuclear extracts from the astrocytes and B103 cells: (1) The interaction of the factors with AMRE analyzed by DNase I footprinting and methylation interference analyses was similar to that of Sp1; (2) The binding of the factors to AMRE competed with an oligonucleotide containing the authentic Sp1 consensus sequence; (3) Sp1-specific antibody interfered with the formation of the AMRE gel retardation complexes. The functional implications of the factors in AMOG gene regulation are discussed.

Expression of the rat growth-hormone gene is under the influence of a cell-type-specific silencer element

We have previously shown that a cell-type-specific negative-regulatory element, or silencer, acts to specifically restrict rat-growth-hormone(rGH)-promoter activity to pituitary cells. Here we report a detailed characterization of this element. The activity of the silencer is dependent on its position relative to the promoter. The negative regulatory effect can be diminished by cotransfection with a high-copy-number, silencer-containing competitor plasmid, suggesting that the function of the element is mediated by specific binding of a trans-acting negative-regulatory factor. The minimal region required for silencer function is contained between positions -309 and -266 relative to the start of the rGH mRNA. The specific interaction of a nuclear protein from non-pituitary cells with this rGH DNA segment was shown by DNaseI as well as dimethylsulfate methylation-interference footprinting. A detailed examination of the DNA-binding site for that protein clearly suggest that it belongs to the NF1 family of transcription factors.