Members of the Sp transcription factor family control transcription from the uteroglobin promoter

Estrogen regulated transcription of the non-estrogen-regulated hamster uteroglobin gene in MCF-7 cells

To study the estrogen regulated transcription of the uteroglobin (UG) gene, the founding member of the secretoglobin family widely expressed in many different mammalian species, we re-created functional estrogen response elements (EREs) in the UG gene promoter from a species where UG expression is not regulated by estrogens: the hamster Mesocricetus auratus (Ma), to ascertain if the lack of functional EREs is the real cause of its estrogen insensitivity. Functional EREs in the hamster promoter, including the consensus ERE (cERE), failed to respond to an appropriate estrogen stimulus compared with its estrogen regulated ortholog from the brown hare Lepus capensis (Lc). As the nucleotide sequence is the only difference between genetic constructs from these two species, we suspected that the UG promoter from the hamster probably contains cis-acting genetic elements that negatively impairs the estrogen-regulated transcription mediated by the functional ERE. Accordingly, we prepared chimeric DNA constructs which eventually allowed to identify a region located 29 base pairs (bp) downstream of the ERE as responsible for the lack of estrogen-responsiveness of the Ma-UG gene in the breast cancer cell line MCF-7. This region contains the sequence ACACCCC which has been identified as the core sequence of the Sp/ Krüppel-like factor (KLF) family of transcription factors. This finding is relevant, not only due to the observation on a novel mechanism that control estrogen-induced transcription, but also because it may encourage further investigation for better defining specific genes with an ERE that do not respond to estrogen signaling in MCF-7 cells, a cell line widely employed as an in vitro model in breast cancer research.

Estrogen-regulated transcription of the uteroglobin gene from the brown hare (Lepus capensis)

To get further insights on the estrogen regulation of the uteroglobin (UG) gene, the 5'-flanking region of the UG gene from the brown hare (Lepus capensis) (Lc) was cloned and compared with those from two phylogenetically related species: the rabbit (Orictolagus cuniculus) (Oc) and the volcano rabbit (Romerolagus diazi) (Rd). The Lc-UG gene is very similar to those from rabbits (94%) and volcano rabbits (95%), and shares a number of genetic elements, including an estrogen response element (ERE). The estrogen-regulated transcription of a series of progressive 5'-deletion mutants of the Lc-UG gene, identified a functional ERE in the promoter region exhibiting the same orientation and relative position than that previously described in rabbits. The Lc-ERE is identical to the Oc-ERE, but different from both the Rd-ERE and the consensus ERE (c-ERE) by one nucleotide. We also detected important species-specific differences in the estrogen-regulated transcription of the UG gene. A luciferase reporter driven by 333 base pairs (bp) of the Lc-UG promoter elicited a higher response to estradiol than its related counterparts when expressed in estrogen-sensitive MCF-7 cells. Several ERE-like motifs which failed to act as functional EREs were also identified; one of them exhibited two mismatches in its palindromic sequence, a characteristic exhibited in many other natural occurring EREs, including the Rd-ERE.

Cloning the uteroglobin gene promoter from the relic volcano rabbit (Romerolagus diazi) reveals an ancient estrogen-response element

To gain further insight on the estrogen-dependent transcriptional regulation of the uteroglobin (UG) gene, we cloned the 5'-flanking region of the UG gene from the phylogenetically ancient volcano rabbit (Romerolagus diazi; Rd). The cloned region spans 812 base pairs (bp; -812/-1) and contains a noncanonical TATA box (TACA). The translation start site is 48 bp downstream from the putative transcription initiation site (AGA), and is preceded by a consensus Kozak box. Comparison of the Rd-UG gene with that previously isolated from rabbits (Oryctolagus cuniculus) showed 93% in sequence identity as well as a number of conserved cis-acting elements, including the estrogen-response element (ERE; -265/-251), which differs from the consensus by two nucleotides. In MCF-7 cells, 17β-estradiol (E(2)) induced transcription of a luciferase reporter driven by the Rd-UG promoter in a similar manner as in an equivalent rabbit UG reporter; the Rd-UG promoter was 30% more responsive to E(2) than the rabbit promoter. Mutagenesis studies on the Rd-ERE confirmed this cis-element as a target of E(2) as two luciferase mutant reporters of the Rd-promoter, one with the rabbit and the other with the consensus ERE, were more responsive to the hormone than the wild-type reporter. Gel shift and super-shift assays showed that estrogen receptor-α indeed binds to the imperfect palindromic sequence of the Rd-ERE.

Association of the CD14 Gene Polymorphism C-159T with Allergic Rhinitis

Background

Altered expression of the cluster differentiation antigen, CD14, may affect the proportion of T-helper type 1 (Th1) to Th2 cells, thereby influencing the immunoglobulin E (IgE) response and associated inflammatory phenotype in allergic conditions. Therefore, the gene encoding CD14 is considered as a positional candidate gene for atopy. Recently, a functional C-159 T polymorphism has been described in the promoter region of the gene and has been associated with increased gene expression and atopic phenotypes in various ethnic populations. We evaluated the relationship between the C-159 T polymorphism in the promoter of the CD14 gene and the total serum IgE level in Chinese adult patients with allergic rhinitis.

Methods

Polymerase chain reaction with restriction fragment length polymorphism (RFLP) analysis was used to determine the C-159 T polymorphism in subjects with allergic rhinitis (n = 92) and nonallergic disease controls (n = 72). Total serum IgE was also measured.

Results

In the allergic rhinitis group, the frequency of the TT homozygotes was significantly higher than for the control group (p < 0.05). In both groups, the C-159 T polymorphism is not associated with serum IgE levels.

Conclusions

TT homozygotes are more common in adult patients with allergic rhinitis among the Chinese population.

Nuclear factor Y is required for basal activation and chromatin accessibility of fibroblast growth factor receptor 2 promoter in osteoblast-like cells

Fibroblast growth factor receptor 2 (FGFR2) plays an important regulatory role in bone development. However, the regulatory mechanisms controlling FGFR2 expression remain poorly understood. Here we have identified a role for the nuclear factor Y (NF-Y) in constitutive activation of FGFR2. A unique DNase I hypersensitive site was detected in the region encompassing nucleotides -270 to +230 after scanning a large range covering 33.3 kilobases around the transcription start site of FGFR2. Using a PCR-based chromatin accessibility assay, an open chromatin conformation was detected around the proximal 5′ fragment of FGFR2 gene. Deletion constructs of the 5′-flanking region of FGFR2 were fused to a luciferase reporter gene. After transient transfection in C3H10T1/2, ME3T3-E1, and C2C12 as well as primary osteoblasts, a minimal region -86/+139 that is highly homologous to the human sequence and bears a CCAAT box was identified as the core promoter. Electrophoretic mobility shift assay supershift and chromatin immunoprecipitation demonstrated that the CCAAT box was the binding site for NF-Y. Deletion of NF-Y consensus sequence resulted in the total loss of NF-Y promoter activity. Overexpression of NF-Y protein and transfection of NF-Y small interfering RNAs in the cells substantially changed the promoter activity. Moreover, NF-Y small interfering RNAs greatly inhibited the endogenous FGFR2 transcription level and the chromatin accessibility and H3 acetylation across the promoter. Taken together, our results demonstrate that interaction of NF-Y at the CCAAT box is pivotal to FGFR2 gene transcription partly through the construction of a local open chromatin configuration across the promoter.

Transcription factors Sp1 and C/EBP regulate NRAMP1 gene expression

The natural resistance-associated macrophage protein 1 (Nramp1), which belongs to a conserved family of membrane metal transporters, contributes to phagocyte-autonomous antimicrobial defense mechanisms. Genetic polymorphisms in the human NRAMP1 gene predispose to susceptibility to infectious or inflammatory diseases. To characterize the transcriptional mechanisms controlling NRAMP1 expression, we previously showed that a 263 bp region upstream of the ATG drives basal promoter activity, and that a 325 bp region further upstream confers myeloid specificity and activation during differentiation of HL-60 cells induced by vitamin D. Herein, the major transcription start site was mapped in the basal region by S1 protection assay, and two cis-acting elements essential for myeloid transactivation were characterized by in vitro DNase footprinting, electrophoretic mobility shift experiments, in vivo transfection assays using linker-mutated constructs, and chromatin immunoprecipitation assays in differentiated monocytic cells. One distal cis element binds Sp1 and is required for NRAMP1 myeloid regulation. Another site in the proximal region binds CCAAT enhancer binding proteins alpha or beta and is crucial for transcription. This study implicates Sp1 and C/EBP factors in regulating the expression of the NRAMP1 gene in myeloid cells.

Keep your fingers off my DNA: protein-protein interactions mediated by C2H2 zinc finger domains

Cys2-His2 (C2H2) zinc finger domains (ZFs) were originally identified as DNA-binding domains, and uncharacterized domains are typically assumed to function in DNA binding. However, a growing body of evidence suggests an important and widespread role for these domains in protein binding. There are even examples of zinc fingers that support both DNA and protein interactions, which can be found in well-known DNA-binding proteins such as Sp1, Zif268, and Ying Yang 1 (YY1). C2H2 protein-protein interactions (PPIs) are proving to be more abundant than previously appreciated, more plastic than their DNA-binding counterparts, and more variable and complex in their interactions surfaces. Here we review the current knowledge of over 100 C2H2 zinc finger-mediated PPIs, focusing on what is known about the binding surface, contributions of individual fingers to the interaction, and function. An accurate understanding of zinc finger biology will likely require greater insights into the potential protein interaction capabilities of C2H2 ZFs.

Uteroglobin: a steroid-inducible immunomodulatory protein that founded the Secretoglobin superfamily

Blastokinin or uteroglobin (UG) is a steroid-inducible, evolutionarily conserved, secreted protein that has been extensively studied from the standpoint of its structure and molecular biology. However, the physiological function(s) of UG still remains elusive. Isolated from the uterus of rabbits during early pregnancy, UG is the founding member of a growing superfamily of proteins called Secretoglobin (Scgb). Numerous studies demonstrated that UG is a multifunctional protein with antiinflammatory/ immunomodulatory properties. It inhibits soluble phospholipase A(2) activity and binds and perhaps sequesters hydrophobic ligands such as progesterone, retinols, polychlorinated biphenyls, phospholipids, and prostaglandins. In addition to its antiinflammatory activities, UG manifests antichemotactic, antiallergic, antitumorigenic, and embryonic growth-stimulatory activities. The tissue-specific expression of the UG gene is regulated by several steroid hormones, although a nonsteroid hormone, prolactin, further augments its expression in the uterus. The mucosal epithelia of virtually all organs that communicate with the external environment express UG, and it is present in the blood, urine, and other body fluids. Although the physiological functions of this protein are still under investigation, a single nucleotide polymorphism in the UG gene appears to be associated with several inflammatory/autoimmune diseases. Investigations with UG-knockout mice revealed that the absence of this protein leads to phenotypes that suggest its critical homeostatic role(s) against oxidative damage, inflammation, autoimmunity, and cancer. Recent studies on UG-binding proteins (receptors) provide further insight into the multifunctional nature of this protein. Based on its antiinflammatory and antiallergic properties, UG is a potential drug target.

Developmental regulation of lumenal lung fluid and electrolyte transport

In the fetus, there is a net secretion of liquid (LL) by the lung as a result of active transport of chloride ions. The rate of secretion and the resulting volume of LL are vital for normal lung growth but how volume is sensed and how secretion may be regulated are still unknown. Towards term under the influence of thyroid and adrenocorticoid hormones, the epithelial sodium channel (ENaC) is increasingly expressed in the pulmonary epithelium. Adrenaline released by the fetus during labour activates ENaC and produces rapid absorption of liquid in preparation for air breathing; absence of ENaC is incompatible with survival. There may be other mechanisms involved in aiding liquid clearance including changes in epithelial permeability, an effect of oxygen on both ENaC and Na/K ATPase and perhaps the influence of additional hormones on ENaC activity. Some time after birth there are further developmental changes with the appearance of other cation channels (CNG1 and perhaps NSCC) which contribute to the liquid absorptive side of the balance existing across the epithelium between secretion and absorption to produce essentially almost no net liquid movement in the postnatal lung. The evidence for these processes is discussed and areas of uncertainty indicated.

The transcription factor SOX17 is involved in the transcriptional control of the uteroglobin gene in rabbit endometrium

The transcription of the uteroglobin gene (ug) is induced by progesterone in the rabbit endometrium, primarily through the binding of the progesterone receptor to the distal region of the ug promoter. However, other transcription factors participate in the progesterone action. The proximal ug promoter contains several putative consensus sequences for the binding of various progesterone-dependent endometrial nuclear factors (Perez Martinez et al. [1996] Arch Biochem Biophys 333: 12-18), suggesting that several transcription factors might be implicated in the hormonal induction of ug. We report here that one of these progesterone-dependent factors specifically binds to the sequence CACAATG (-183/-177) of the rabbit ug promoter. This sequence (hereafter called element G') is very similar to the consensus sequence for binding of the SOX family of transcription factors. Mutation of the element G' reduced transcription from the ug promoter in transient expression experiments. The endometrial factor was purified and analyzed by nano-liquid chromatography and ion trap coupled mass spectrometry yielding two partial amino acid sequences corresponding to a region of SOX17 that is highly conserved inter-species. This identification was confirmed by immunological techniques using a specific anti-SOX17 antibody. In agreement with the above findings, overexpression of SOX17 in transfected endometrial cells increased transcription from the ug promoter. SOX17 gradually accumulated in the nucleus in vivo concomitant with the induction of ug expression by progesterone in the endometrium. Thus, these findings implicate, for the first time, SOX17 in the transcriptional control of rabbit ug.

Sp3 inhibits Sp1-mediated activation of the cardiac troponin T promoter and is downregulated during pathological cardiac hypertrophy in vivo

Combinatorial interactions between cis elements and trans-acting factors are required for regulation of cardiac gene expression during normal cardiac development and pathological cardiac hypertrophy. Sp factors bind GC boxes and are implicated in recruitment and assembly of the basal transcriptional complex. In this study, we show that the cardiac troponin T (cTnT) promoter contains a GC box that is necessary for basal and cAMP-mediated activity of cTnT promoter constructs transfected in embryonic cardiomyocytes. Cardiac nuclear proteins bind the cTnT GC box in a sequence-specific fashion and consist of Sp1, Sp2, and Sp3 protein factors. By chromatin immunoprecipitation, Sp1 binds the cTnT promoter "in vivo." Cotransfected Sp1 trans-activates the cTnT promoter in cardiomyocytes in culture. Sp3 represses Sp1-mediated transcriptional activation of the cTnT gene in embryonic cardiomyocytes. Sp3 repression of Sp1-mediated cTnT promoter activation is dose dependent, inferring a mechanism of competitive binding/inhibition. To evaluate the role of Sp factors in cardiac gene expression in vivo, we have established a clinically relevant animal model of pathological cardiac hypertrophy where the fetal cardiac program is activated. In this animal model, cardiac hypertrophy results from increased left-right shunting, volume loading of the left ventricle, and pressure loading of the right ventricle. Sp1 expression is increased in all four hypertrophied cardiac chambers, whereas Sp3 expression is diminished. This observation is consistent with the in vitro activating function of Sp1 and inhibitory effects of Sp3 on activity of cTnT promoter constructs. Sp factor levels are modulated during the hypertrophic cardiac program in vivo.

Sp3 is involved in the regulation of SOCS3 gene expression

Cytokine-induced expression of SOCS (suppressor of cytokine signalling) molecules is important for the negative regulatory control of STAT (signal transduction and activators of transcription)-dependent cytokine signalling, e.g. for the signal transduction of IL-6 (interleukin-6)-type cytokines through the JAK (Janus kinase)/STAT cascade. STAT activation itself represents an important step in the transcriptional activation of SOCS3 gene expression. However, downstream of the STAT-responsive element, the SOCS3 gene contains a GC-rich element in its 5'-upstream region. The aim of the present study was to investigate the implications of this GC-rich element in the transcriptional control of SOCS3 gene expression. In the present study, we show that mutation of this GC-rich element abolishes IL-6-dependent transcriptional activation of the SOCS3 promoter and that Sp3 (specificity protein 3), a ubiquitously expressed transcription factor, but not Sp1 binds to this GC-rich motif, suggesting that Sp3 is involved in the regulation of SOCS3 expression. The results suggest that Sp3 is important for IL-6-induced transcriptional activation of the SOCS3 (gene) promoter and acts as an enhancer of basal as well as induced transcriptional activity, resulting in enhanced SOCS3 mRNA and protein expression. Mutation of Lys-483, a potential target for Sp3 acetylation, inhibited Sp3-mediated enhancement of SOCS3 mRNA expression and SOCS3 promoter activation, indicating that the acetylation of this lysine residue of Sp3 is important for the enhancing effect of Sp3 on SOCS3 expression.

Activation of the RNA-dependent protein kinase PKR promoter in the absence of interferon is dependent upon Sp proteins

The protein kinase regulated by RNA (PKR) is interferon (IFN)-inducible and plays important roles in many cellular processes, including virus multiplication, cell growth, and apoptosis. The TATA-less PKR promoter possesses a novel 15-bp DNA element (kinase conserved sequence (KCS)) unique to the human and mouse PKR genes that is conserved in sequence and position. We found that Sp1 and Sp3 of the Sp family of transcription factors bind at the KCS element. Their involvement was analyzed in the activation of basal and IFN-inducible PKR promoter activity. Both the small and large isoforms of Sp3 co-purified with KCS protein binding activity (KBP) by using nuclear extracts from HeLa cells not treated with IFN. Two forms of the KCS-binding protein complex were demonstrated by electrophoretic mobility shift assay analysis; one contained Sp1 and the other Sp3. In mouse cells null for all Sp3 isoforms, PKR expression was reduced to approximately 50% that of wild-type cells in the absence of IFN. The IFN-inducible expression of PKR, however, was Sp3-independent but STAT1- and JAK1-dependent. Overexpression of Sp1 in human U cells resulted in increased PKR promoter activity. In Drosophila SL2 cells lacking Sp proteins, both Sp1 and Sp3 large but not small isoforms activated PKR promoter expression, with the Sp1-mediated activation dominant. Mutational analysis of the PKR promoter region indicated a cooperative interaction between two different Sp sites, one of which is within the KCS element. These results establish that, in the absence of IFN treatment, activation of PKR basal expression is mediated by Sp1 and Sp3 proteins in a cooperative manner.

Sp1 and Sp3 regulate basal transcription of the human CYP2F1 gene

Selective transcription of the human CYP2F1 gene in lung tissues may control the susceptibilities of this organ to diverse pneumotoxicants and lung carcinogens. However, the mechanisms responsible for CYP2F1 organ-selective transcription have not been elucidated. The objectives of the current studies were to identify and characterize basal transcription elements within the TATA-less promoter region of CYP2F1. Four putative Sp1-like sites were identified in the CYP2F1 promoter. Competitive electrophoretic mobility shift assay analysis with mutated oligonucleotide probes and lung A549 cell nuclear extract, along with supershift studies using antibodies to either Sp1 or Sp3 proteins, demonstrated that all four sites formed three specific protein-DNA complexes. Mutations in any of the four core Sp1-like motifs abolished protein-DNA binding. Western blot analysis of both human tissues and cells showed that Sp1 was considerably higher in lung than liver and that Sp3 was much higher in liver than lung. Promoter activation of a luciferase reporter construct was sequentially increased by addition of each of the four Sp1-like motifs in lung A549 cells but not in liver HepG2 cells. Cotransfection of a Sp1 expression vector with the reporter construct dramatically increased luciferase activity in either A549 cells or Sp1-deficient Drosophila Schneider line 2 (SL-2) cells. However, similar cotransfections with an Sp3 expression vector failed to increase activity. Cotransfection of both the Sp1 and Sp3 expression vectors considerably decreased Sp1-mediated activity in A549 cells and abolished activity in SL-2 cells. Thus, these studies demonstrated that four Sp1-dependent proximal promoter elements drive organ-selective CYP2F1 gene transcription, and that Sp1 and Sp3 factors interact to modulate constitutive CYP2F1 transcription in lung cells.

Transcriptional Activity of Sp1 Is Regulated by Molecular Interactions between the Zinc Finger DNA Binding Domain and the Inhibitory Domain with Corepressors, and This Interaction Is Modulated by MEK

Sp1 activates the transcription of many cellular and viral genes with the GC-box in either the proximal promoter or the enhancer. Sp1 is composed of several functional domains, such as the inhibitory domain (ID), two serine/threonine-rich domains, two glutamine-rich domains, three C2H2-type zinc finger DNA binding domains (ZFDBD), and a C-terminal D domain. The ZDDBD is the most highly conserved domain among the Sp-family transcription factors and plays a critical role in GC-box recognition. In this study, we investigated the protein-protein interactions occurring at the Sp1ZFDBD and the Sp1ID, and the molecular mechanisms controlling the interaction. Our results found that Sp1ZFDBD and Sp1ID repressed transcription once they were targeted to the proximal promoter of the pGal4 UAS reporter fusion gene system, suggesting molecular interaction with the repressor molecules. Indeed, mammalian two-hybrid assays, GST fusion protein pull-down assays, and co-immunoprecipitation assays showed that Sp1ZFDBD and Sp1ID are able to interact with corepressor proteins such as SMRT, NcoR, and BCoR. The molecular interactions appear to be regulated by MAP kinase/Erk kinase kinase (MEK). The molecular interactions between Sp1ID and the corepressor might explain the role of Sp1 as a repressor under certain circumstances. The siRNA-induced degradation of the corepressors resulted in an up-regulation of Sp1-dependent transcription. The cellular context of the corepressors and the regulation of molecular interaction between corepressors and Sp1ZFDBD or Sp1ID might be important in controlling Sp1 activity.

Sumoylation of internally initiated Sp3 isoforms regulates transcriptional repression via a Trichostatin A-insensitive mechanism

Sp3 is a ubiquitously expressed member of the Sp family of transcription factors that encodes three proteins, Sp3, M1 and M2, with differing capacities to stimulate or repress transcription. As part of ongoing efforts to study the functions of Sp3 isoforms, we employed a yeast "two-hybrid" screen to identify Sp3-binding proteins. This screen resulted in the identification of Ubc9, a SUMO-1 conjugating enzyme, as an M2-binding protein, and consistent with these results sequence analyses identified consensus sumoylation motifs within several Sp family members. Western blots probed with anti-Sp3 detected a high molecular weight Sp3 isoform that is stabilized by a SUMO-1 hydrolase inhibitor, and this protein is also bound by anti-SUMO-1 antiserum. Transient transfection assays with epitope-tagged-SUMO-1 and GFP-SUMO-1 fusion proteins confirmed that Sp3, M1 and M2 proteins are sumoylated in vivo. Substitution of arginine for lysine at one putative site of sumoylation, lysine(551), blocked sumoylation of all Sp3 isoforms in vivo and led to a marginal increase in Sp3-mediated trans-activation in insect and mammalian cells. In contrast, introduction of this amino acid substitution within M1 converted it into a potent transcriptional trans-activator. We conclude that Sp3 isoforms are sumoylated in vivo and this post-translational modification plays an important role in the regulation of Sp3-mediated transcription.

The CD14 C-159T polymorphism is not associated with asthma or asthma severity in an Australian adult population

BACKGROUND

CD14 functions as a multifunctional receptor for bacterial cell wall components including endotoxin and lipopolysaccharide and is likely to play a role in the polarisation of T lymphocytes into Th1 and Th2 subsets, thereby influencing the cytokine profile and subsequent IgE production in response to antigen/allergen contact in allergic phenotypes. A functional C-159T polymorphism has been described in the promoter region of the gene and has been associated with increased gene expression, atopy, and non-atopic asthma in different ethnic populations. A study was undertaken to examine the association between the C-159T polymorphism and asthma, asthma severity, and atopy in a large Australian white population.

METHODS

PCR-RFLP analysis was used to characterise the C-159T polymorphism in mild (n = 264), moderate (n = 225) and severe (n = 79) asthmatic patients and non-asthmatic controls (n = 443), including atopic (n = 688) and non-atopic (n = 323) individuals. Association analyses were performed using chi(2) tests.

RESULTS

There was no association between the polymorphism and asthma (p = 0.468) or asthma severity (p = 0.727), and only a very weak association with atopy (p = 0.084). A meta-analysis of all studies conducted to date revealed similar genotypic frequencies in white ethnic populations and confirmed that there was no overall association with atopy (p = 0.52) or asthma (p = 0.23), although there was significant between study heterogeneity (p = 0.01).

CONCLUSIONS

This study confirms that there is no association between the CD14 C-159T polymorphism and asthma or asthma severity and a weak association between this polymorphism and atopy in an adult population.

cDNA sequence, 5′-flanking region, and promoter activity of the Neotomodon alstoni alstoni Clara cell secretory protein gene

To better understand the phylogenetic divergence and the species-specific characteristics of the Clara cell secretory protein (CCSP), we cloned the cDNA encoding the neotomodon CCSP (nCCSP) and analyzed its tissue-specific expression. The full-length cDNA is 451bp long and predicts an amino acid sequence of 93 residues. Northern blot analysis from different neotomodon tissues demonstrated that the mRNA of CCSP appears to be solely expressed in the lung. To study the transcriptional regulation of the CCSP gene, we cloned the 5'-flanking region of the nCCSP gene and compared its features with those previously reported for the hamster gene. The neotomodon and hamster genes share 89% sequence homology in their promoter region as well as a number of conserved cis-acting elements. However, in H441 cells the expression of a reporter gene driven by the nCCSP promoter was about 4-fold greater than its hamster counterpart. Functional analysis of progressive 5'-deletion mutants identified a region involved in the higher transcriptional activity of the neotomodon promoter.

Tissue-specific activity of the proximal human calcitonin receptor promoter is mediated by Sp1 and an epigenetic phenomenon

To identify cis-acting sequences transcriptionally regulating the human calcitonin receptor (hCTR) gene, hCTR promoter/luciferase gene constructs were transiently or stably transfected into hCTR-positive and -negative cell lines. Luciferase assays demonstrated that the proximal hCTR promoter (hCTRP1) was transcriptionally active in all cell lines tested. High-level hCTRP1 activity depended on an 11 bp Sp1/Sp3 binding site. Electrophoretic mobility shift assay showed that this region bound the transcription factors Sp1 and Sp3. We further showed that hCTRP1 was strongly activated by the 11 bp Sp1/Sp3 binding site in hCTRP1/luciferase-, Sp1-transfected Drosophila S2 cells. Bisulphite-mediated sequencing of genomic DNA from hCTR-expressing and -non-expressing cell lines demonstrated that the endogenous hCTRP1 was hypomethylated in all cell lines tested. These results suggest that the hCTRP1 is activated by the tissue-ubiquitous transcription factor Sp1 and that an epigenetic process unrelated to CpG methylation represses its activity in hCTR-negative tissues.

Impaired hematopoiesis in mice lacking the transcription factor Sp3

As the zinc-finger transcription factor specificity protein 3 (Sp3) has been implicated in the regulation of many hematopoietic-specific genes, we analyzed the role of Sp3 in hematopoiesis. At embryonic day 18.5 (E18.5), Sp3-/- mice exhibit a partial arrest of T-cell development in the thymus and B-cell numbers are reduced in liver and spleen. However, pre-B-cell proliferation and differentiation into immunoglobulin M-positive (IgM+) B cells in vitro are not affected. At E14.5 and E16.5, Sp3-/- mice exhibit a significant delay in the appearance of definitive erythrocytes in the blood, paralleled by a defect in the progression of differentiation of definitive erythroid cells in vitro. Perinatal death of the null mutants precludes the analysis of adult hematopoiesis in Sp3-/- mice. We therefore investigated the ability of E12.5 Sp3-/- liver cells to contribute to the hematopoietic compartment in an in vivo transplantation assay. Sp3-/- cells were able to repopulate the B- and T-lymphoid compartment, albeit with reduced efficiency. In contrast, Sp3-/- cells showed no significant engraftment in the erythroid and myeloid lineages. Thus, the absence of Sp3 results in cell-autonomous hematopoietic defects, affecting in particular the erythroid and myeloid cell lineages.

Genomic organization, chromosomal localization and adipocytic expression of the murine gene for CORS-26 (collagenous repeat-containing sequence of 26 kDa protein)

The murine gene for CORS-26 shows striking homologies to the adipocyte-specific secretory protein adiponectin (belonging to the newly discovered C1q/TNF molecular superfamily) and its expression has been reported to be restricted to fibroblasts, cartilage and kidney. However, the present data demonstrate specific induction of CORS-26 mRNA expression in hormonally differentiated 3T3-L1 adipocytes, but not in preadipocytes. Furthermore, CORS-26 mRNA expression could be demonstrated in human synovial adipocytes of the knee by in situ hybridization. Since the genes for CORS-26 and adiponectin are homologous for their COOH-terminal globular domain and of their N-terminal collagenous domain, they might have originated by divergence from an innate mesenchymal precursor molecule directing the development of myocytes, adipocytes and chondrocytes from a mesenchymal stem cell. Here, the complete genomic organization with exon/intron boundaries together with exon-specific primer combinations are presented. Additionally, approximately 1 kb of the TATA-box-containing promoter region was cloned and analyzed for putative transcription factor binding sites. The chromosomal localization of the murine CORS-26 gene was mapped to mouse chromosome 15 A2 by fluorescence in situ hybridization (FISH). Since the linkage loci for proteoglycan-induced arthritis and MRL/lpr arthritis in mice have been mapped to that chromosomal region, CORS-26 might represent the underlying mechanism of disease. The present data provide the basis for further investigation of the CORS-26 gene regulation in the context of mesenchymal tissue development, chondrocyte/adipocyte function and bone or skeletal disease.

Regulation of prothymosin alpha by estrogen receptor alpha: molecular mechanisms and relevance in estrogen-mediated breast cell growth

Prothymosin alpha (PTalpha) is a small highly acidic protein found in the nuclei of virtually all mammalian tissues. Its high conservation in mammals and wide tissue distribution suggest an essential biological role. While the exact mechanism of action of PTalpha remains elusive, the one constant has been its relationship with the proliferative state of the cell and its requirement for cellular growth and survival. Recently PTalpha was found to promote transcriptional activity by sequestering the anticoactivator, REA from the Estrogen Receptor (ER) complex. We now report that Estradiol (E2) upregulates PTalpha mRNA and protein expression. Further studies indicate that ERalpha regulates PTalpha gene transcriptional activity. We have also delimited the region of PTalpha gene promoter involved in ERalpha-mediated transcriptional regulation and identified a novel ERalpha-binding element. Increased intracellular PTalpha expression in the presence of estrogens is accompanied by increased nuclear/decreased cytoplasmic localization. Increased nuclear expression of PTalpha is correlated with increased proliferation as measured by expression of Ki67 nuclear antigen. Conversely, inhibition of nuclear PTalpha expression in breast cancer cells using antisense methodology resulted in the inhibition of E2-induced breast cancer cell proliferation. Overall these studies underscore the importance of PTalpha in estrogen-induced breast cell proliferation.

Sp1- and Sp3-mediated transcriptional regulation of the fibroblast growth factor receptor 1 gene in chicken skeletal muscle cells

Expression of the fibroblast growth factor receptor 1 (FGFR1) gene in skeletal muscle is positively regulated in proliferating myoblasts and declines during differentiation. We have characterized the cis-regulatory elements in the proximal region of the FGFR1 promoter which render positive transcriptional activity. Multiple elements between -69 and -14 activate the FGFR1 promoter. Myoblast transfections revealed that potential Sp transcription factor binding sites are required for promoter activity. Electromobility shift assays indicated that myoblast nuclear proteins specifically bind to these cis-elements and that differentiated myotube nuclear extracts do not form these same complexes. In addition, Southwestern blot analysis detected binding of the most proximal Sp motif to a Sp1-like protein present in myoblast nuclear extracts but not in myotubes. In corroboration, Sp1 and Sp3 proteins were detected only in myoblasts and not in differentiated myotubes. Finally, transfection of Drosophila SL2 cells showed that Sp1 is a positive regulator of FGFR1 promoter activity and that Sp3 is a coactivator via the proximal Sp binding sites. These studies demonstrate that the FGFR1 promoter is activated by Sp transcription factors in proliferating myoblasts and demonstrate at least part of the mechanism by which FGFR1 gene expression is down-regulated in differentiated muscle fibers.

Molecular markers of endometrial epithelial cell mitogenesis mediated by the Sp/Krüppel-like factor BTEB1

Basic transcription element binding (BTEB1) protein is one of at least 20 Sp/KLF family members that function as transcriptional activators or repressors by binding to GC/GT-rich sequences within target genes to influence cellular homeostasis in mammals. Previously, we demonstrated that increased expression of BTEB1 in a human endometrial epithelial cell line Hec-1-A resulted in serum dependent-enhanced proliferation, which was accompanied by heightened expression of cell cycle- and growth-associated genes. In the present study, we examined the mechanism underlying the altered proliferative potential associated with BTEB1 by the identification of additional BTEB1 downstream gene targets and by the demonstration of BTEB1 transactivation of promoters for a number of growth-associated genes. Using mRNA differential display in the analysis of RNA populations from Hec-1-A sublines with high (4S, 9S) and low (2As, 3As) BTEB1 cellular content, we identified 10 distinct differentially expressed transcripts, nine of which had higher levels in S than in As sublines. The expression levels of two of these cDNAs, Axl receptor tyrosine kinase and mitosin, whose encoded products are implicated in cellular proliferation, were modestly induced by serum, albeit in a BTEB1-independent manner. Moreover, insulin-like growth factor-I, a mitogen present in serum, had no significant effect on their expression in either subline. In transient reporter assays, the basal activities of the Axl gene promoter and those for two other growth-regulatory genes, namely p21(WAF1) and IGFBP-2, were increased by serum and were significantly higher in 4S than in 2As lines. However, while BTEB1 and its ubiquitous family member Sp1 increased basal p21(WAF1) and IGFBP-2 transcription when added as expression constructs in the parental Hec-1-A cell line, only Sp1 activated Axl transcription, despite the presence in all three gene promoters of GC-enriched regions that presumably can bind BTEB1 and Sp1 with similar affinities. To elucidate intracellular signaling pathways that might involve BTEB1, inhibitors of specific kinase-dependent transducers were used in transient transfection assays involving the IGFBP-2 gene promoter in 4S and 2As sublines. While inhibitors of the MAPK, PI-3K, and PKA pathways elicited similar effects on the IGFBP-2 gene promoter activity, irrespective of cellular BTEB1 content, that for JNK had a more pronounced effect on Hec-1-A sublines exhibiting higher BTEB1 expression levels. Taken together, the results suggest that BTEB1 mediates the expression of growth-associated genes through direct and indirect transactivation mechanisms, one of which may involve the participation of a JNK family member.

Reciprocal regulation of beta(1)-adrenergic receptor gene transcription by Sp1 and early growth response gene 1: induction of EGR-1 inhibits the expression of the beta(1)-adrenergic receptor gene

The beta(1)-adrenergic receptor (beta(1)-AR) plays a key role in regulating heart rate and contractility in response to catecholamines. Our studies have focused on defining the factors that regulate the expression of the beta(1)-AR gene. We determined that a 65-base-pair (bp) region in the beta(1)-AR promoter between bp -394 and bp -330 directs basal transcription. An element located between -377 and -365 can bind Sp1 and Sp3. In Drosophila melanogaster SL2 cells, Sp1 stimulated the expression of the beta(1)-AR promoter, whereas Sp3 was unable to activate transcription. Site-directed mutagenesis indicated that an intact Sp1-binding site is essential for maintaining the activity of the basal promoter. In addition to binding Sp family members, the nucleotides between -381 and -367 can bind the zinc-finger transcription factor Egr-1. The Egr-1 and Sp1 binding sites are partially overlapping and their binding sequence is conserved among mammalian beta(1)-AR genes. The induction of Egr-1 in rat neonatal ventricular myocytes with phorbol-12-myristate-13-acetate or in HeLa S3 cells by regulated expression of Egr-1 in a tetracycline-responsive promoter, suppressed expression from the beta(1)-AR promoter. Overexpression of Sp1 in SK-N-MC cells increased beta(1)-AR mRNA by 2.4-fold, whereas overexpression of Egr-1 reduced beta(1)-AR mRNA by 40%. Coexpression of Egr-1 with Sp1 reduced Sp1-mediated up-regulation of beta(1)-AR mRNA by 60%. Mutagenesis revealed that an intact Sp1-binding site is essential for observing transcriptional repression by Egr-1 and that Egr-1 suppressed the transcription of the beta(1)-AR gene by competing with Sp1 for binding to their overlapping sites. These results reveal a novel physiologically relevant transcriptional mechanism for reciprocal regulation of beta(1)-AR gene expression.

Transcription factor Sp3 is regulated by acetylation

Sp3 is a ubiquitous transcription factor closely related to Sp1. Previous analyses showed that, unlike Sp1, Sp3 fails to activate transcription in certain promoter settings. This is due to the presence of an inhibitory domain located between the second glutamine-rich activation domain and the DNA-binding domain. To further analyze the transcriptional properties of Sp3, we have expressed and purified recombinant Sp3 and Sp1 as epitope-tagged proteins from stable transfected insect cells. We found that Sp3 does act as a strong activator similar to Sp1 in an in vitro transcription assay using Sp1/Sp3-depleted HeLa nuclear extract. However, on the same promoter Sp3 is almost inactive when transfected into cells. Mutational studies demonstrate that a single lysine residue is responsible for the low transcriptional activity of Sp3 in vivo. We show that Sp3, but not a mutant of Sp3 that lacks this lysine residue, is highly acetylated in vivo. Our results strongly suggest that the transcriptional activity of Sp3 is regulated by acetylation. The consequences of acetylation for the activity of Sp3 are discussed.

Role of the Sp family of transcription factors on glucagon receptor gene expression

The glucagon receptor mediates the actions of glucagon on carbohydrate metabolism by the liver and on insulin release by the pancreatic beta-cell, which are key processes in the control of glucose homeostasis. The 5'-region of the mouse glucagon receptor gene has been recently cloned and two functional promoters were characterized. In the present study, we show that most of the glucagon receptor mRNA was transcribed from the distal promoter, in the mouse liver. In the distal promoter region, a GC-rich sequence with five putative binding sites for the Sp family of transcription factors was localized. To elucidate the role of these Sp1-binding sites in the mouse MIN6 beta-cell line, the expression of reporter gene constructs containing deletion or point mutation of each site was carried out. Selective mutation of the second Sp1-binding site decreased the activity of the distal promoter. Electrophoretic mobility shift assay with a DNA fragment spanning the three first Sp1 sites confirmed that the second site bound specifically MIN6 nuclear proteins, and supershift using specific Sp antibodies demonstrated that it interacted with Sp3 but not Sp1 transcription factors. These data illustrate that the basal expression of the mouse glucagon receptor gene, driven by the distal promoter, requires an Sp1-binding site that binds Sp3 proteins.

Expression of TCF, TPF/YY1, and the Sp family transcription factors in rabbit endometrium throughout pregnancy

BACKGROUND

TCF, TPF/YY1, and the Sp family are specific transcription factors that bind sequences found within the uteroglobin (UG) gene promoter region that are necessary for transcription. To date, UG gene expression and regulation in vivo are not fully understood. The purpose of this study was to assess the expression patterns of these factors in the rabbit endometrium throughout pregnancy.

METHODS

Endometrial nuclear extracts were obtained from female rabbits on days 0, 3, 5, 7, 15, and 28 after mating. Transcription factor expression was assessed by DNA-protein binding assays using endometrial nuclear proteins and specific oligonucleotides. Band shifts were observed on 4% acrylamide gels and analyzed by densitometry.

RESULTS

The expression patterns of the transcription factors analyzed here differed, as TPF/YY1 and Sp3/SpR-2 were expressed constitutively while TCF and Sp1 showed variable expression patterns throughout pregnancy.

CONCLUSIONS

Our results suggest that UG gene expression in the intact pregnant rabbit is controlled by two constitutive and two regulated factors, and that the DNA-binding sites are located at the TATA box and the GT1 sites within the gene promoter.

Cellular transcription factors that interact with p6 promoter elements of parvovirus B19

All transcripts of the human parvovirus B19 identified so far are regulated by a single promoter at map unit 6 of the viral genome, the so-called p6 promoter. This promoter is active in a wide variety of different cells. In order to identify cellular transcription factors involved in regulating promoter activity, we performed gel-retardation and supershift assays using the parts of the p6 promoter sequence shown previously to be protected in footprint experiments. Thereby, binding was demonstrated of the Oct-1 protein to an octamer motif within the p6 promoter and of the transcription factor Sp1 to three GC boxes. A specific preferential interaction of the factor Sp3 with one of these boxes was observed, indicating that the ratio Sp1:Sp3 may be involved in the regulation of promoter activity. Consensus sites for the regulatory protein YY1 are located close to the GC boxes and the octamer motif, to which this factor binds efficiently.

Transcriptional activation of genes by 17 beta-estradiol through estrogen receptor-Sp1 interactions

Estrogen receptor-alpha (ER alpha) is a ligand-activated transcription factor and a member of the nuclear receptor superfamily. The classic mechanism of ER alpha action is associated with estrogen-induced formation of a nuclear ER alpha homodimer, binding to 5'-regulatory estrogen response elements (EREs) in target gene promoters, interaction with other nuclear proteins, and general transcription factors to activate gene expression. ER alpha also interacts with Sp1 protein to transactivate genes through binding Sp1(N)xERE or Sp1(N)xERE half-site (1/2) motifs where both ER alpha and Sp1 bind DNA elements. Activation through Sp1(N)xERE1/2 requires interactions of both proteins with their cognate DNA elements as well as additional nuclear factors to form a functional ER alpha/Sp1-DNA complex. Recent studies also show that ER alpha and Sp1 physically interact and ER alpha preferentially binds to the C-terminal DNA-binding domain of Sp1 protein. Moreover, ER alpha/Sp1 can activate transcription from a consensus GC-rich Sp1 binding site in transient transfection studies in MCF-7 human breast cancer cells, and this response is also observed with ER alpha variants that do not contain the DNA-binding domain. Several genes that are induced by estrogens in MCF-7 cells are activated through one or more GC-rich sites in their regulatory regions and these include the cathepsin D, E2F1, bcl-2, c-fos, adenosine deaminase, insulinlike growth factor binding protein 4, and retinoic acid receptor alpha 1 genes. ER alpha/Sp1 and ER beta/Sp1 action is dependent on ligand structure and cell context and ER beta/Sp1 is primarily associated with decreased ligand-dependent gene expression. ER alpha/Sp1, like ER alpha/AP1, represents a pathway for hormone activation of genes in which the receptor does not bind DNA, and results of ongoing studies suggest that ER alpha/Sp1 plays an important role in transcriptional activation of multiple growth regulatory genes in breast cancer cells.

Cell cycle regulation of the murine cdc25B promoter: essential role for nuclear factor-Y and a proximal repressor element

Expression of the cdc25B gene is up-regulated late during cell cycle progression (S/G(2)). We have cloned the murine cdc25B promoter to identify elements involved in transcriptional regulation. A detailed structure-function analysis led to the identification of several elements that are located upstream of a canonical Inr motif at the site of transcription initiation and are involved in transcriptional activation and regulation. Activation of the promoter is largely mediated by NF-Y and Sp1/3 interacting with one and four proximal binding sites, respectively. In addition, NF-Y plays an essential role in cell cycle regulation in conjunction with a repressor element (cell cycle-regulated repressor) located approximately 30 nucleotides upstream of the putative Inr element and overlapping a consensus TATA motif. The cell cycle-regulated repressor is unrelated to the previously described cell cycle-regulated repressor elements. Taken together, our observations suggest that expression of the cdc25B gene is controlled through a novel mechanism of cell cycle-regulated transcription.

Regulation of the Clara cell secretory protein/uteroglobin promoter in lung

Clara cell secretory protein/uteroglobin (CCSP/UG) is specifically expressed in the conducting airway epithelium of the lung in a differentiation-dependent manner. The proximal promoter region of the rodent CCSP/UG gene directs Clara cell specificity. Previously, it was shown that the forkhead transcription factors HNF-3 alpha and beta and the homeodomain factor TTF-1 are important transcription factors acting through this region, suggesting that they contribute to cell specificity of the CCSP/UG gene. Members of the C/EBP family of transcription factors can also interact with elements of the proximal rat and mouse CCSP/UG promoters. The onset of C/EBP alpha expression in Clara cells correlates with the strong increase of CCSP/UG expression. Thus, C/EBP alpha may play a crucial role for differentiation-dependent CCSP/UG expression. Transfection studies demonstrate that C/EBP alpha and TTF-1 can synergistically activate the murine CCSP/UG promoter. Altogether, these results suggest that C/EBP alpha, TTF-1, and HNF-3 determine the Clara cell-specific, differentiation-dependent expression of the CCSP/UG gene in murine lung. The relative importance of these three transcription factors, however, differs in rabbits and humans.

Uteroglobin gene transcription: what's the RUSH?

Prolactin enhances progesterone-dependent transcription of the rabbit uteroglobin gene. RUSH transcription factors are implicated in the signal transduction pathway. The RUSH acronym identifies key features of these nuclear phosphoproteins, that is, RING-finger motif, binds the uteroglobin promoter, structurally related to the SWI/SNF family of transcription factors, and helicase-like. Cloned by recognition site screening, RUSH proteins bind to an 85-bp region (-170/-85) of the uteroglobin promoter that was subsequently identified as a novel prolactin-responsive region by promoter deletion analysis. Gel shift and linker-scanning assays further reduced the RUSH target site to -160/-110. A hexameric core of MCWTDK was identified as the RUSH-specific DNA-binding site (-126/-121) by CASTing. This site overlaps authentic HNF3 beta and OCT-1 binding sites. A unique Type IV P-type ATPase that is embedded in the inner nuclear membrane binds the RING domain of RUSH. The conformationally flexible loop portion of this RING-finger binding protein (RFBP) extends into the nucleoplasm to contact euchromatin. The physical association of RFBP with transcriptionally active chromatin supports the speculation that RFBP targets RUSH transcription factors to the active uteroglobin promoter.

ZIC2 and Sp3 repress Sp1-induced activation of the human D1A dopamine receptor gene

The human D(1A) dopamine receptor is transcribed from a tissue-specific regulated gene under the control of two promoters. An activator region (AR1) located between nucleotides -1154 and -1136 (relative to the first ATG) enhances transcription from the upstream promoter that is active in the brain. In this investigation, we sought to identify the nuclear factors that regulate the D(1A) gene through their binding to AR1 using yeast one-hybrid screening. Sp3 and Zic2 were among the positive clones isolated. Although Sp1 was not isolated from this screening and purified Sp1 alone does not bind to AR1 in gel shift experiments, this general transcription factor binds to AR1 in the presence of D(1A) expressing NS20Y nuclear extract and activates the D(1A) promoter. Thus, Sp1 appears to require an unknown factor(s) or post-translational modification to interact with AR1. On the other hand, Zic2 and Sp3 inhibit Sp1-induced activation of the D(1A) gene in an AR1-dependent manner. Zic2 and D(1A) genes have reciprocal brain regional distributions; Zic2 is expressed primarily in the cerebellum, and D(1A) is highly expressed in corpus striatum. These observations collectively suggest that one of the physiologic functions of Zic2 is repression of D(1A) gene transcription and that the intracellular balance among Sp1, Sp3 and Zic2 is important for regulating the tissue-specific expression of this dopamine receptor.

Sp1 and Sp3 activate p21 (WAF1/CIP1) gene transcription in the Caco-2 colon adenocarcinoma cell line

The CDK inhibitor p21WAF1/CIP1 is a negative regulator of the cell cycle, and its expression is induced during terminal differentiation in vitro and in vivo. Expression of p21 is controlled at the transcriptional level by both p53-dependent and -independent mechanisms. Our previous studies established that p21 is expressed in the Caco-2 adenocarcinoma cell line, and its expression is induced by a p53-independent mechanism during differentiation of these cells. Here we have found that transcription of p21 in Caco-2 cells is controlled primarily by the transcription factors Sp1 and Sp3 through two Sp1 binding sites, Sp1-1 and Sp1-2, located between -119 and -114 bp and between -109 and -104 bp of the p21 promoter, respectively. Sp1 and Sp3 binding to the p21 promoter increased during Caco-2 cell differentiation, while the absolute level of Sp1 did not change and the absolute level of Sp3 increased approximately twofold. Transfection experiments in the SL2 Drosophila cell line that lacks endogenous Sp3 activity demonstrated that Sp1 transactivates the p21 promoter primarily through the Sp1-2 site, while Sp3 acts through the Sp1-1 site. In these cells Sp3 is a stronger transactivator of the p21 promoter than Sp1. Our data suggest that induction of p21 transcription during Caco-2 differentiation is modulated by Sp1/Sp3 interactions with the p21 promoter.

Kinetic analysis of Sp1-mediated transcriptional activation of the human DNA polymerase beta promoter

In the present studies, we have examined the effect of Sp1 on the activation of the human DNA polymerase beta (beta-pol), a TATA-less promoter. A HeLa cell nuclear extract (NE) based in vitro runoff transcription system of core beta-pol promoter human DNA (pbetaP8) three-step kinetic model of transcription initiation were used to describe the kinetic effect of Sp1. The results showed that distal Sp1-binding sites in the core beta-pol promoter are important for transcriptional activation of the pbetaP8 promoter. A detailed kinetic analysis showed that Sp1 stimulates the activity of the pbetaP8 promoter through distal Sp1-binding sites by increasing the amount of recruitment, instead of stimulating the apparent rate of RPc assembly (k1). There was no significant effect of Sp1 on the apparent rate of open complex (RPo) formation (k2) or on the apparent rate of promoter clearance (k3) of the pbetaP8 promoter. These studies define the kinetic mechanisms by which Sp1 may regulate the rate of transcript formation of the pbetaP8 promoter, and these results may have implications for Sp1 regulation of TATA-less promoters.

Inhibition of vascular endothelial growth factor expression in HEC1A endometrial cancer cells through interactions of estrogen receptor alpha and Sp3 proteins

Treatment of HEC1A endometrial cancer cells with 10 nm 17beta-estradiol (E2) resulted in decreased vascular endothelial growth factor (VEGF) mRNA expression, and a similar response was observed using a construct, pVEGF1, containing a VEGF gene promoter insert from -2018 to +50. In HEC1A cells transiently transfected with pVEGF1 and a series of deletion plasmids, it was shown that E2-dependent down-regulation was dependent on wild-type estrogen receptor alpha (ERalpha) and reversed by the anti-estrogen ICI 182, 780, and this response was not affected by progestins. Deletion analysis of the VEGF gene promoter identified an overlapping G/GC-rich site between -66 to -47 that was required for decreased transactivation by E2. Protein-DNA binding studies using electrophoretic mobility shift and DNA footprinting assays showed that both Sp1 and Sp3 proteins bound this region of the VEGF promoter. Coimmunoprecipitation and pull-down assays demonstrated that Sp3 and ERalpha proteins physically interact, and the interacting domains of both proteins are different from those previously observed for interactions between Sp1 and ERalpha proteins. Using a dominant negative form of Sp3 and transcriptional activation assays in Schneider SL-2 insect cells, it was confirmed that ERalpha-Sp3 interactions define a pathway for E2-mediated inhibition of gene expression, and this represents a new mechanism for decreased gene expression by E2.

Involvement of Sp1 in the transcriptional regulation of the rat insulin-like growth factor-1 gene

Most insulin-like growth factor-I (IGF-I) transcripts are initiated in exon 1, but mechanisms of regulation are not well understood. Since potential Sp1 sites are found in footprinted regions within approximately 360 bp upstream and downstream from the major initiation sites in exon 1, we explored the involvement of Sp1 and Sp3 in regulation of IGF-1 expression. Gel shift assays showed strong Sp1 binding to the downstream site, but binding to the upstream site was weak; Sp1 bound to a CCTGCCCA sequence in downstream footprint region V, and Sp3 binding was centered on the same sequence. IGF-I basal promoter constructs containing a mutation in the downstream Sp1 site exhibited a 32% decrease in expression in CHO cells and a 75% decrease in HepG2 cells, indicating the importance of Sp1 for expression in vivo. Sp1 and Sp3 expression vectors provided three- to five-fold stimulation of wild-type IGF-I constructs, but had little effect on a construct containing a mutation in the downstream Sp1 site, and Sp1 had comparable effects in Drosophila SL2 cells. IGF-I heterologous promoter constructs exhibited similar responses: in both SL2 cells and CHO cells, stimulation by Sp1 was enhanced with constructs containing downstream region V. Since Sp1 also stimulated expression of concatamers of putative cis-acting sites fused to the SV40 promoter enhancer in pGL3, the results in combination indicate that the presence of IGF-I region V is sufficient to permit stimulation by Sp1.

CONCLUSION

Sp1 and related factors may play an important role in the regulation of IGF-I gene transcription, through interactions with region V downstream from the major initiation sites in exon 1.

Identification of functional TTF-1 and Sp1/Sp3 sites in the upstream promoter region of rabbit SP-B gene

Surfactant protein B (SP-B) is essential for the maintenance of biophysical properties and physiological function of pulmonary surfactant. SP-B mRNA is expressed in a cell type-restricted manner in alveolar type II and bronchiolar (Clara) epithelial cells of the lung and is developmentally induced. In NCI-H441 cells, a lung cell line with characteristics of Clara cells, a minimal promoter region comprising -236 to +39 nucleotides supports high-level expression of chloramphenicol acetyltransferase reporter activity. In the present investigation, we characterized the upstream promoter region, -236 to -140 nucleotides, that is essential for promoter activity. Deletion mapping identified two segments, -236 to -170 and -170 to -140 nucleotides, that are important for promoter activity. Mutational analysis and gel mobility shift experiments identified thyroid transcription factor-1, Sp1, and Sp3 as important trans-acting factors that bind to sequences in the upstream promoter region. Our data suggest that SP-B promoter activity is dependent on interactions between factors bound to upstream and downstream regions of the promoter.

Transcription factor Sp3 is essential for post-natal survival and late tooth development

Sp3 is a ubiquitously expressed transcription factor closely related to Sp1 (specificity protein 1). We have disrupted the mouse Sp3 gene by homologous recombination. Sp3-deficient embryos are growth retarded and invariably die at birth of respiratory failure. The cause for the observed breathing defect remains obscure since only minor morphological alterations were observed in the lung, and surfactant protein expression is indistinguishable from that in wild-type mice. Histological examinations of individual organs in Sp3(-/-) mice show a pronounced defect in late tooth formation. In Sp3 null mice, the dentin/enamel layer of the developing teeth is impaired due to the lack of ameloblast-specific gene products. Comparison of the Sp1 and Sp3 knockout phenotype shows that Sp1 and Sp3 have distinct functions in vivo, but also suggests a degree of functional redundancy.

Kinetic analysis of Sp1-mediated transcriptional activation of a TATA-containing promoter

Using a HeLa cell nuclear extract (NE)-based in vitro runoff transcription system, we have examined the effect of Sp1 on the activation of a TATA-containing chimeric DNA polymerase beta (pAS8) promoter. The results demonstrated that the TATA element-dependent basal activity of the pAS8 promoter was stimulated 4-fold by supplementation of a Sp1-depleted HeLa cell nuclear extract (NEd) with purified human Sp1, indicating that pAS8 promoter activity is dependent upon Sp1. A detailed kinetic analysis based on a three-step kinetic model of transcription initiation showed that Sp1 stimulates the activity of the pAS8 promoter by increasing the amount of closed preinitiation complex (RP(c)) assembly as well as by enhancing the rate of promoter clearance (k(3)). There was no significant effect of Sp1 on the apparent rate of open complex (RP(o)) formation (k(2)) of the pAS8 promoter. These studies define more precisely the kinetic mechanisms by which Sp1 may regulate the rate of transcript formation of a TATA-containing promoter.

Mechanisms of transcriptional activation of bcl-2 gene expression by 17beta-estradiol in breast cancer cells

bcl-2 gene expression is induced by 17beta-estradiol (E2) in T47D and MCF-7 human breast cancer cells, and the mechanism of E2 responsiveness was further investigated by analysis of the bcl-2 gene promoter. The -1602 to -1534 distal region (bcl-2j) of the promoter was E2-responsive; however, in gel mobility shift assays, the estrogen receptor alpha (ER(alpha)) did not bind [(32)P]bcl-2j, whereas Sp1 protein formed a retarded band complex. Further analysis demonstrated that the upstream region (-1603 to -1579) of the bcl-2 gene promoter contained two GC/GA-rich sites at -1601 (5'-GGGCTGG-3') and -1588 (3'-GGAGGG-5') that bound Sp1 protein. Subsequent studies confirmed that transactivation by E2 was dependent on ER(alpha)/Sp1 interactions with both GC-rich sites, and this was confirmed by in vitro footprinting. In contrast, a 21-base pair E2-responsive downstream region (-1578 to -1534) did not bind Sp1 or ER(alpha) protein; however, analysis of a complex binding pattern with nuclear extracts showed that ATF-1 and CREB-1 bound to this motif. These data coupled with results of transient transfection studies demonstrated that transcriptional activation by E2 of the -1578 to -1534 region of the bcl-2 gene promoter was dependent on induction of cAMP and subsequent activation through a cAMP response element. Thus, hormone regulation of bcl-2 gene expression in breast cancer cells involves multiple enhancer elements and E2-mediated transactivation does not require direct binding of the estrogen receptor with promoter DNA.

The Sp-family of transcription factors

GC-boxes and related motifs are frequently occurring DNA-elements present in many promoters and enhancers. In contrast to other elements it was generally thought that the transcription factor Sp1 is the only factor acting through these motifs. The cloning of paralogous genes of the Sp1 factor uncovered the existence of a small protein family consisting of Sp1, Sp2, Sp3 and Sp4. All four proteins exhibit very similar structural features. They contain a highly conserved DNA-binding domain composed of three zinc fingers close the C-terminus and serine/threonine- and glutamine-rich domains in their N-terminal regions. The high degree of structural conservation between these four proteins suggested that they do exert similar functions. Molecular, genetic and biochemical analyses, however, demonstrated that Sp2, Sp3 and Sp4 are not simply functional equivalents of Sp1. Here, I will summarize and discuss recent advances which have been made towards understanding the mode of action and biological function of individual family members.

Composite action of three GC/GT boxes in the proximal promoter region is important for gastrin gene transcription

The proximal region of the human gastrin gene promoter contains three GC/GT boxes at positions -140 to -134 bp, -108 to -102 bp and -67 to -61 bp. In this study we have examined the significance of the three elements, and their role in Sp1 and Sp3 mediated gastrin transcription. In AGS cells, mutation of each of the boxes caused a moderate decrease in promoter activity from 33 to 63%, whereas double or triple mutations reduced activity to 3-12%. In Drosophila cells Sp1 activated the promoter, mainly through the distal GC box. Similarly, co-transfection of heterologous promoter constructs revealed that only the distal GC box increased activation by Sp1. The effect of Sp3 was cell-line dependent, since Sp3 inhibited the gastrin promoter activity in AGS cells and caused a synergistic activation of the Sp1 stimulated gastrin promoter in Drosophila cells. Both effects were dependent on the C-terminal DNA binding domain of Sp3. The results indicates that the combined effect of the GC/GT boxes and the ratio between Sp1 and Sp3 are important for gastrin gene expression.

Insulin-induced early growth response gene (Egr-1) mediates a short term repression of rat malic enzyme gene transcription

In this report we have studied insulin regulation of malic enzyme (ME) gene transcription in rat H-35 hepatoma cells and localized the insulin-responsive region of the ME promoter between positions -177 and -102. This region contains a putative insulin response element (IRE-II). When nuclear extracts from untreated or insulin-treated H-35 cells were incubated with IRE-II, transcription factors Sp1 and Sp3 were observed to bind constitutively to this element, whereas insulin induces the quick and transient binding of an insulin response factor. This induction requires de novo protein synthesis. Competition and supershift assays demonstrated that the insulin response factor is the immediate-early gene Egr-1. In vitro assays revealed that Egr-1 displaces Sp1 from its binding site in IRE-II. Insulin induces Egr-1 mRNA, with a time course pattern that corresponds perfectly to the Egr-1 binding to IRE-II. This induction depends on the activation of mitogen-activated protein (MAP) kinase, and it is phosphatidylinositol 3-kinase-independent, as demonstrated with specific inhibitors for both pathways. By cotransfecting the wild-type or a dominant negative Ras, an upstream regulator of MAP kinase, we show that Ras inhibits ME promoter activity. Furthermore, overexpression of Egr-1 in H-35 cells represses the ME gene promoter in a dose-dependent manner. These results suggest that insulin induces a quick, transient, and Ras/MAP kinase-dependent activation of Egr-1 which leads to a transient repression of ME gene transcription. On a late phase, insulin would activate a different, Egr-1-independent pathway, which would result in activation of the ME gene.

Trans-activation functions of the Sp-related nuclear factor, basic transcription element-binding protein, and progesterone receptor in endometrial epithelial cells

The present study examined the trans-activation potential of basic transcription element-binding protein (BTEB), a recently identified member of the Sp family of GC box-binding transcription factors, on the expression of the gene encoding the pregnancy-associated, epithelial-specific, and progesterone (P)-induced porcine uterine endometrial secretory protein, uteroferrin (UF). Endometrial expression of BTEB, P receptor (PR), and UF genes was analyzed by RT-PCR as a function of pregnancy stage and cell type and was correlated with the levels of endometrial BTEB that were quantified by Western blot and/or electrophoretic mobility shift assay. PR, BTEB, and UF messenger RNAs (mRNAs) were present in early (day 12) and mid(day 60) pregnancy pig endometrium, although expression levels varied for each mRNA (UF, day 12 << day 60; PR and BTEB, day 12 = day 60). Within the endometrium, glandular epithelial (GE) cells manifested higher amounts of UF mRNA than stromal fibroblastic cells, whereas both cell types had comparable amounts of BTEB and PR mRNAs. Expression of BTEB, however, was limited to endometrial GE cells. A BTEB expression vector (pcDNA-3BTEB) was used to examine the effect of increased BTEB protein on UF gene expression and promoter activity in primary cultures of pig endometrial GE cells. Cells transiently transfected with pcDNA-3BTEB had 2-fold higher UF mRNA levels than those transfected with the empty expression vector (pcDNA-3). Further, cells cotransfected with a UF promoter-luciferase (-1935UF-Luc) reporter gene and the BTEB expression vector had 2-fold higher Luc activity than those cotransfected with reporter gene and pcDNA-3. This effect of BTEB was not observed in transfected endometrial stromal fibroblastic cells, but was apparent in the human endometrial epithelial carcinoma cell lines ECC-1 and Hec-1-A, which exhibit low levels of BTEB protein and low or undetectable PR mRNA levels, respectively. The respective contributions of BTEB and PR to the modulation of UF promoter activity were examined by cotransfection of Hec-1-A and ECC-1 cells with expression plasmids for BTEB and PR and one of two UF promoter constructs (-831UF-Luc or -1935UF-Luc) in the absence or presence of P. The increase in UF promoter activity with BTEB was mimicked by PR in a P-dependent manner in both cell lines. The combined effect of PR/P and BTEB appeared additive in Hec-1-A cells and was synergistic in ECC-1 cells. These results highlight the cell context dependence of the trans-activation potential of BTEB and suggest its unique role, in concert with PR, in directing the temporal expression of endometrial epithelial genes of pregnancy.

Perinatal regulation of the ClC-2 chloride channel in lung is mediated by Sp1 and Sp3

Mechanisms responsible for regulation of pulmonary epithelial chloride-channel expression in the perinatal period are under investigation to better understand normal lung development and airway disease pathogenesis. The ClC-2 epithelial chloride channel is regulated by changes in pH and volume and is most abundant in lung during fetal development. In this study, we identify and sequence the ClC-2 promoter, which is GC rich and lacks a TATA box. By construction of a series of promoter-luciferase constructs, a 67-bp GC box-containing sequence in the promoter is shown to be critical to ClC-2 expression in primary and immortalized fetal lung epithelial cells. Electrophoretic mobility shift assays and antibody supershifts demonstrate that the Sp1 and Sp3 transcription factors are expressed in fetal lung nuclei and interact with the GC box sequences in the promoter. Immunoblotting techniques demonstrate that Sp1 and Sp3 are perinatally downregulated in the lung with the same temporal sequence as ClC-2 downregulation. This work suggests that Sp1 and Sp3 activate ClC-2 gene transcription and that reduction in Sp1 and Sp3 at birth explains perinatal downregulation of ClC-2 in the lung.

Two progesterone-dependent endometrial nuclear factors bind to an E-box in the rabbit uteroglobin gene promoter: involvement in tissue-specific transcription

We studied the implications of progesterone-dependent transcription factors in the hormonal and tissue-specific induction of the uteroglobin gene (ug) in the rabbit endometrium. Previously, we have observed the interaction of two progesterone-dependent endometrial nuclear proteins (TRBPs) with sequences downstream from the ug TATA box. Using electrophoretic mobility shift assays (EMSA) we show here that TRBPs specifically interacted with an E-box localized almost immediately downstream from the ug TATA box. UV crosslinking of affinity-purified TRBPs to the radiolabeled oligonucleotide probe confirmed that these factors were proteins with molecular mass of about 40-50 kDa. Ferguson's analysis of the Mr of the DNA-TRBP complexes suggested that TRBPs interacted with the E-box either as homo- or heterodimers. This interaction did not result in detectable bending of the DNA. EMSA analysis with nuclear extracts from different rabbit tissues suggested that TRBPs might be endometrium-specific nuclear factors. Involvement of the E-box in the tissue-specific transcription from the ug promoter was assessed by transient expression experiments using different cell lines transfected with a reporter gene driven by the ug promoter which contained either the intact E-box or a mutated version that completely abolished its interaction with TRBPs. These experiments indicated that, in all cell lines of nonendometrial lineage, destruction of the E-box increased transcription from the ug promoter, whereas in two cell lines of endometrial origin this mutation either had no appreciable effect or slightly reduced the transcription from the promoter. Thus, this E-box and endometrial helix-loop-helix proteins might be involved in the hormonal and tissue-specific regulation of ug transcription.