Elements of the rabbit uteroglobin promoter mediating its transcription in epithelial cells from the endometrium and lung

The rabbit uteroglobin gene is specifically expressed in certain epithelial cells of ontogenetically unrelated origin. In the endometrium, expression is restricted to the glandular and luminal epithelium and is inducible by progesterone and estradiol. In the lung, Clara cells lining the bronchiolar epithelium show constitutive expression of uteroglobin, which is modulated by glucocorticoids. To explore the molecular basis for this cell type specificity, we have transiently transfected the uteroglobin promoter region fused to the chloramphenicol acetyl transferase gene (CAT gene) in the endometrial cell line Ishikawa; in the human lung cell line NCI-H441, which shows morphological Clara cell characteristics; in HeLa cells; and in three fibroblast cell lines. The uteroglobin promoter efficiently drives expression of the CAT gene in Ishikawa and NCI-H441 cells, but not in HeLa and fibroblast cells. To identify the responsible elements we have analyzed progressive promoter 5'-deletion mutants and randomly generated linker scanning mutants spanning the sequence from -258 to -14 of the uteroglobin promoter. Transfection experiments reveal seven mutation-sensitive regions located around -30, -70, -95, -130, -190, -230, and -255. Several mutants display strong cell type-specific phenotypes. Most significantly, the integrity of the region around -190 is essential for full CAT gene expression in Ishikawa cells, but not in NCI-H441 cells.

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.

Sp3 represses the Sp1-mediated transactivation of the human COL2A1 gene in primary and de-differentiated chondrocytes

Sp1 and Sp3 effects on the transcription of the human alpha1(II) procollagen gene (COL2A1) were investigated in both differentiated and de-differentiated rabbit articular chondrocytes. Transient transfection with constructs of deleted COL2A1 promoter sequences driving the luciferase reporter gene revealed that the region spanning -266 to +121 base pairs showed Sp1-enhancing effects, whatever the differentiation state. In contrast, Sp3 did not influence COL2A1 gene transcription. Concomitant overexpression of the two Sp proteins demonstrated that Sp3 blocked the Sp1 induction of COL2A1 promoter activity. Moreover, inhibition of Sp1/Sp3 binding to their target DNA sequence decreased both COL2A1 gene transcription and Sp1-enhancing effects. DNase I footprinting and gel retardation assays revealed that Sp1 and Sp3 bind specifically to cis-sequences of the COL2A1 gene promoter whereby they exert their transcriptional effects. Sp1 and Sp3 levels were found to be reduced in de-differentiated chondrocytes, as revealed by DNA-binding and immunochemical study. Sp1 specifically activated collagen neosynthesis whatever the differentiation state of chondrocytes, suggesting that this factor exerts a major role in the expression of collagen type II. However, our data indicate that type II collagen-specific expression in chondrocytes depend on both the Sp1/Sp3 ratio and cooperation of Sp1 with other transcription factors, the amounts of which are also modulated by phenotype alteration.

Complex phenotype of mice homozygous for a null mutation in the Sp4 transcription factor gene

BACKGROUND

Sp4 is a zinc finger transcription factor which is closely related to Sp1 and Sp3. All three proteins recognize the same DNA elements and can act as transcriptional activators through glutamine-rich activation domains. Unlike Sp1 and Sp3, which are ubiquitous proteins, Sp4 is highly abundant in the central nervous system, but also detectable in many other tissues.

RESULTS

We have disrupted the mouse Sp4 gene by a targeted deletion of the exons encoding the N-terminal activation domains. Sp4 knockout mice show a complete absence of Sp4 expression. They develop until birth without obvious abnormalities. After birth, two-thirds die within 4 weeks. Surviving mice are growth retarded. Male Sp4null mice do not breed. The cause for the breeding defect remains obscure since they show complete spermatogenesis. In addition, pheromone receptor genes in the vomeronasal organ appear unaffected. Female Sp4null mice have a smaller thymus, spleen and uterus. In addition, they exhibit a pronounced delay in sexual maturation.

CONCLUSIONS

The phenotype of the Sp4null mice differs significantly from those described for Sp1-/- and Sp3-/- mice. Thus, the structural similarities, the common recognition motif and the overlapping expression pattern of these three transcription factors do not reflect similar physiological functions.

Impaired ossification in mice lacking the transcription factor Sp3

Sp3 is a ubiquitously expressed member of the Sp family of transcription factors. Recently, the mouse Sp3 gene has been disrupted by homologous recombination. Sp3 null mice die immediately after birth due to respiratory failure. In addition, these mice show a pronounced defect in late tooth formation. Here we show that Sp3 is also required for proper skeletal ossification. Both endochondral and intramembranous ossification are impaired in E18.5 Sp3-/- embryos. The delay in ossification is reflected by reduced expression of the osteoblast-specific marker gene osteocalcin. The transcription factor - core binding factor 1 (Cbfa1)--that is essential for bone formation, however, is expressed at normal levels. In vitro differentiation studies using Sp3-/- ES cells further support the conclusion that Sp3 is needed for correct bone formation. The capacity of Sp3-/- cells to undergo osteogenic differentiation in vitro is reduced and osteocalcin expression is significantly diminished. Our studies establish Sp3 as an essential transcription factor for late bone development.

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.

Characterization and promoter analysis of the mouse gene for transcription factor Sp4

Transcription factor Sp4 is a member of the Sp1 family. It functions differently from other members of this family, such as Sp1 and Sp3, and the gene for Sp4 is transcribed in a tissue-specific manner. Recent studies in mice suggest that Sp4 might play an important role in growth, viability, and male fertility. We report here the isolation and characterization of the gene for Sp4 from a mouse genomic library. The mouse gene for Sp4 was about 80 kb in length and it consisted of six exons and five introns. The promoter was found in a CpG island and had a high G+C content. The proximal promoter contained multiple putative binding sites for the transcription factors Sp1 and MAZ but lacked a consensus TATA box. Multiple sites for the initiation of transcription were mapped in a GC-rich region from 286 bp to 211 bp upstream of the ATG triplet at the site of initiation of translation, and all of the sites were either C or G. Transfection experiments and deletion analysis allowed us to localize the promoter to a region that was no more than 93 bp upstream from the first site of initiation of transcription. We also found that ectopic expression of Sp1 and of MAZ, but not of Sp3, suppressed expression of the Sp4 promoter in a dose-dependent manner.

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.

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.

A tale of three fingers: the family of mammalian Sp/XKLF transcription factors

One of the most common regulatory elements is the GC box and the related GT/CACC box, which are widely distributed in promoters, enhancers and locus control regions of housekeeping as well as tissue-specific genes. For long it was generally thought that Sp1 is the major factor acting through these motifs. Recent discoveries have shown that Sp1 is only one of many transcription factors binding and acting through these elements. Sp1 simply represents the first identified and cloned protein of a family of transcription factors characterised by a highly conserved DNA-binding domain consisting of three zinc fingers. Currently this new family of transcription factors has at least 16 different mammalian members. Here, we will summarise and discuss recent advances that have been directed towards understanding the biological role of these proteins.

Functional interactions between Sp1 or Sp3 and the helicase-like transcription factor mediate basal expression from the human plasminogen activator inhibitor-1 gene

Basal expression of the human plasminogen activator inhibitor-1 (PAI-1) is mediated by a promoter element named B box that binds the helicase-like transcription factor (HLTF), homologous to SNF/SWI proteins. Electrophoretic mobility shift assays performed on a set of B box point mutants demonstrated two HLTF sites flanking and partially overlapping with a GT box binding Sp1 and Sp3. Mutations affecting either the Sp1/Sp3 or the two HLTF sites inhibited by 6- and 2.5-fold, respectively, transient expression in HeLa cells of a reporter gene fused to the PAI-1 promoter. In Sp1/Sp3-devoid insect cells, co-expression of PAI-1-lacZ with Sp1 or Sp3 led to a 14-26-fold induction while HLTF had no effect. Simultaneous presence of Sp1 or Sp3 and the short HLTF form (initiating at Met-123) provided an additional 2-3-fold synergistic activation suppressed by mutations that prevented HLTF binding. Moreover, a DNA-independent interaction between HLTFMet123 and Sp1/Sp3 was demonstrated by co-immunoprecipitation from HeLa cell extracts and glutathione S-transferase pull-down experiments. The interaction domains were mapped to the carboxyl-terminal region of each protein; deletion of the last 85 amino acids of HLTFMet123 abolished the synergy with Sp1. This is the first demonstration of a functional interaction between proteins of the Sp1 and SNF/SWI families.

Role of Sp1 in cAMP-dependent transcriptional regulation of the bovine CYP11A gene

The pituitary peptide hormone ACTH regulates transcription of the cholesterol side chain cleavage cytochrome P450 (CYP11A) gene via cAMP and activation of cAMP-dependent protein kinase. A G-rich sequence element conferring cAMP-dependent regulation has been found to reside within region -118 to -100 of the bovine CYP11A promoter. Previous studies have suggested that it binds a protein antigenically related to the transcription factor Sp1. We now report that the -118/-100 element binds both Sp1 and Sp3, members of the Sp family of transcription factors. We have made use of Drosophila SL2 cells, which lack endogenous Sp factors, to dissect the possible functional roles of Sp1, Sp3, and Sp4. All factors stimulated the activity of cotransfected reporter constructs in which the promoter of the bovine CYP11A gene regulates luciferase expression. Sp3 did not repress Sp1-dependent activation, as has previously been shown for other G-rich promoters. Mutation of the -118/-100 element of CYP11A abolished Sp1-mediated activation of a CYP11A reporter gene in SL2 cells as well as cAMP responsiveness in human H295R cells. Furthermore, cotransfection of SL2 cells with the catalytic subunit of cAMP-dependent protein kinase together with Sp1 and a CYP11A reporter construct enhanced Sp1-dependent activation of the reporter 4.2-fold, demonstrating that Sp1 confers cAMP responsiveness in these cells. Thus, we show that introduction of Sp1 alone in an Sp-negative cell such as SL2 is sufficient to achieve the cAMP-dependent regulation observed using the -118/-100 element of CYP11A in adrenocortical cells.

Synergistic activation of the human Btk promoter by transcription factors Sp1/3 and PU.1

Analysis of the human Bruton's agammaglobulinemia tyrosine kinase (Btk) gene promoter revealed that 280 bp upstream of the transcriptional start site is sufficient for a cell restricted expression pattern. Here, the interplay of the transcription factors Sp1, Sp3, and PU.1 binding to this promoter area was analysed. All three proteins are able to independently activate the promoter in Drosophila Schneider (SL2) cells lacking endogenous Sp- or PU.1-like activities. Furthermore, PU.1 is able to act synergistically with Sp1 as well as Sp3 to transactivate the promoter. This transactivation is mediated through adjacent binding sites rather than through the more distant Sp binding site, suggesting a possible direct interaction between PU.1 and Sp1/3. Expression of Btk was found in ES cells and levels of expression were the same as in ES cells with a targeted deletion of the Sp1 gene, suggesting that Sp3 acts as a positive regulator of Btk in vivo, in the absence of Sp1.

Combinatorial action of HNF3 and Sp family transcription factors in the activation of the rabbit uteroglobin/CC10 promoter

It has been reported that respiratory epithelium-specific transcription is mediated by thyroid transcription factor 1 and members of the HNF3/forkhead family of transcription factors. Here, we show that the uteroglobin/Clara cell 10-kDa promoters from rabbit and man are regulated by HNF3alpha and HNF3beta but not by HFH-4 and TTF-1. We have identified two HNF3-responsive elements in the rabbit uteroglobin/CC10 promoter located around 95 and 130 base pairs upstream of the transcriptional start site. Both elements contribute to promoter activity in H441 cells expressing uteroglobin/CC10 and HNF3alpha. Gene transfer experiments into Drosophila Schneider cells that lack many mammalian transcription factor homologs revealed that HNF3alpha and HNF3beta on their own cannot activate the uteroglobin/CC10 promoter. However, HNF3alpha and HNF3beta strongly enhanced Sp1-mediated promoter activation. Synergistic activation by HNF3alpha and Sp1 was absolutely dependent on the integrity of two Sp1 sites located at around -65 and -230. We show further that multiple activation domains of Sp1 are required for cooperativity with HNF3alpha. These studies demonstrate that transcription from the rabbit uteroglobin/CC10 promoter in lung epithelium is controlled by the combinatorial action of the cell-specific factor HNF3alpha and the ubiquitous factor Sp1.

RAP1-like binding activity in islet cells corresponds to members of the Sp1 family of transcription factors

Deletion and mutational analyses of the gastrin promoter have identified a binding site for the yeast transcription factor RAP1 relevant for transcriptional activation in islet cells. We here report that the mammalian transcription factors binding to this site in islet cells are the Sp transcription factor members Sp1 and Sp3. Furthermore, functional analyses revealed Sp1- and Sp3-mediated transcriptional activation of gastrin. These data reveal that the zinc finger proteins Sp1 and Sp3 do have similar binding specificities as the multifunctional yeast RAP1 protein.

Binding of the ubiquitous cellular transcription factors Sp1 and Sp3 to the ZI domains in the Epstein-Barr virus lytic switch BZLF1 gene promoter

Induction of the Epstein-Barr virus lytic cycle in latently infected B cells requires the expression of the immediate-early lytic gene BZLF1. We have previously identified several cis-elements within the BZLF1 promoter that are required for induction by known inducers of the lytic cycle [E. Flemington and S. H. Speck (1990)J. Virol. 64, 1217-1226]. These include four elements termed the ZI domains (ZIA, ZIB, ZIC, and ZID) that share extensive homology and that have recently been shown to bind several cellular transcription factors [A. M. Borras, J. L. Strominger, and S. H. Speck (1996) J. Virol. 70, 3894-3901]. Here Sp1 and Sp3 are identified as the cellular factors present in crude B cell nuclear extract preparations that bind to the ZIC domain. In addition, three of the four complexes observed in electrophoretic mobility shift analyses employing probes containing either the ZIA or the ZID domains also represent Sp1 or Sp3 binding. Binding of Sp1 and Sp3 to the ZI domains was shown to be significantly weaker than binding of these factors to a consensus Sp1 site. A heterologous promoter construct containing three repeats of a consensus Sp1 site, cloned upstream of a single copy of the ZII (CREB/ AP1) element from the BZLF1 promoter linked to the beta-globin TATA box, exhibited phorbol ester inducibility. The latter observation was consistent with the functional behavior exhibited by a heterologous promoter construct containing multiple copies of the ZIC domain liked to the ZII element. However, the basal activity of the heterologous promoter construct driven by the consensus Sp1 sites was ca. 10-fold higher than that of the heterologous reporter construct containing multimerized ZIC sites. Thus, the low affinity of Sp1 binding to the ZI domains may contribute to the low-level basal activity of the BZLF1 promoter.

An inhibitor domain in Sp3 regulates its glutamine-rich activation domains

Sp3 is a ubiquitously expressed human transcription factor closely related to Sp1 and Sp4. All three proteins contain a highly conserved DNA binding domain and two glutamine-rich regions, suggesting that they possess similar activation functions. In our previous experiments, however, Sp3 failed to activate transcription. Instead, it repressed Sp1-mediated transcriptional activation, suggesting that it is an inhibitory member of this family of regulatory factors. Here we show that Sp3 can also act as a positive regulator of transcription. The glutamine-rich domains on their own have a strong activation function and interact with the TATA box binding protein (TBP)-associated factor dTAFII110. However, in full-length Sp3 as well as in Gal4-Sp3 fusion proteins, both activation domains are silenced by an inhibitory domain located between the second glutamine-rich region and the DNA binding domain. The inhibitory domain completely suppressed transcriptional activation when fused to a heterologous glutamine-rich domain but only moderately suppressed transcription when linked to an acidic activation domain. Site-directed mutagenesis identified a stretch of highly charged amino acid residues essential for inhibitor function. Substitution of the amino acid triplet KEE by alanine residues within this region changed the almost transcriptionally inactive Sp3 into a strong activator. Our results suggest that the transcriptional activity of Sp3 might be regulated in vivo by relief of inhibition.

High Sp1/Sp3 ratios in epithelial cells during epithelial differentiation and cellular transformation correlate with the activation of the HPV-16 promoter

Gene expression of human papillomavirus type 16 (HPV-16) and other HPV types is epithelial specific. Specificity is brought about by synergism between several different transcription factors that seem to occur ubiquitously but differ qualitatively and quantitatively between cells in which HPV genomes are transcriptionally active or inactive. Here, we report on the contribution to this combinatorial mechanism by the activator Sp1 and the related antagonist Sp3, both of which can bind a single site at the E6 promoter of all genital HPVs. In the Sp-factor-free background of Drosophila cells, Sp1 activates HPV-16 transcription, while Sp3 fails to do so and even inhibits the activation by Sp1. The same differential activation occurs in the case of promoters of the epithelial-specific cellular genes encoding keratin 18 and E-cadherin. All cell types that we examined contain similar amounts of Sp3 factor. In contrast, Sp1 levels, determined by supershifts and Western blots, are higher in several human epithelial cell lines that support HPV transcription than in human fibroblasts, liver, and muscle cells. This suggests that cell-type differential transcription is regulated by Sp1 and Sp3. In primary keratinocytes, Sp3 levels exceed those of Sp1. This ratio became inverted after differentiating these cells in high calcium, or methyl cellulose containing medium. The simultaneous transcriptional stimulation of the HPV promoter points to a role of the Sp1-Sp3 antagonism during a differentiation of stratified epithelia in vivo, as these culture techniques mimick this process in vitro. Transformation in vivo or in vitro seems to override these cell-type-specific controls and leads to a general increase of Sp1 activity.

Influence of early postnatal dexamethasone therapy on ventilator dependency in surfactant-substituted preterm infants

We examined 26 preterm infants with respiratory distress syndrome in a randomized controlled prospective study to determine whether early postnatal dexamethasone therapy (< 2 h; 0.5 mg/kg per day) over 5 days in addition to substitution of surfactant (100 mg/kg) facilitates extubation and the course of RDS. Control (n = 12) and treated (n = 14) groups were comparable in birthweight (mean +/- SD: 1219 +/- 292 versus 1446 +/- 442 g), gestational age (29.3 +/- 2.2 versus 30.6 +/- 2.7 weeks), prenatal characteristics and initial respiratory and blood gas parameters. In both groups one infant died. Infants in the dexamethasone group responded better to surfactant (12/14 versus 3/12; p < 0.01), were extubated earlier (6.6 versus 14.2 days; p < 0.02) and required less time on supplemental oxygen (4.2 versus 12.5 days; p < 0.02). Pulmonary complications tended to be lower in the dexamethasone group (1/14 versus 4/12), as was the frequency of retinopathy (2/14 versus 6/12; p < 0.05). We conclude that early postnatal dexamethasone therapy improves response to surfactant therapy resulting in better weaning and earlier extubation in premature infants.

Transcriptional regulation of the SIS/PDGF-B gene in human osteosarcoma cells by the Sp family of transcription factors

Expression of PDGF-B, the gene encoding the platelet-derived growth factor B chain, has been implicated as a participant in an autocrine growth loop in the human osteosarcoma cell line U2-OS. In previous work, we identified a primary site in the PDGF-B promoter, the SIS proximal element (SPE), which is critical for transcription of the PDGF-B gene in U2-OS cells. We also identified Sp1 as one of the SPE-binding proteins in U2-OS nuclear extracts. In the present work, we have identified another SPE-binding protein to be Sp3. Gel mobility shift assays showed that both Sp1 and Sp3 require the CACCC motif within the SPE for binding. In vitro transcription assays showed that Sp1 or/and Sp3 is necessary for transcription of the PDGF-B gene. Cotransfection experiments functionally demonstrated that Sp1 and Sp3 can independently or additively activate the PDGF-B promoter through the SPE as well as a synthetic promoter. However, the CACCC motif within the SPE is not the only site within the minimal PDGF-B promoter through which Sp1/Sp3 acts; additional nested deletion analyses showed that multiple cis-acting elements within the minimal promoter are required for full level transcription of the PDGF-B gene in U2-OS cells.

ARDS infolge schwerer RSV-Infektion Therapeutische Optionen

We report on a strikingly frequent referral of former preterm babies with respiratory syncytial virus (RSV) infection and subsequent ARDS in our hospital during the winter 1994/95 with regard to the clinical course under application of alternative treatment modalities. Treatment modalities like inhalational ribavirin, use of bronchodilators and instillation of surfactant had been tried without success. All children (age: 1-43 months) were ventilated for 6.6 (1-17) days with FiO₂ = 1.0 and a mean airway pressure of 16.4 (10-24) cm H₂O. Mean arterial blood gases were 49 (paO₂) and 41 (pCO₂) mm Hg, the OI was 33.4. By inhalational NO in combination with IPPV or HFOV 4 patients could be stabilized, in the other 6 ECMO became necessary. Two of them died in spite of several weeks on ECMO; 8 children survived and could be discharged home after a mean hospital stay of 3 months. Even in very severe cases of RSV infection treatment modalities like NO, HFOV and ECMO can be used successfully. The use of these treatment modalities must be considered before the lung damage is irreversible; in those cases a pre-existing BPD is no contraindication even for extracorporeal lung support.

Sp1 trans-activation of cell cycle regulated promoters is selectively repressed by Sp3

The transcription factor Sp1 plays a key role in the activation of many cellular and viral gene promoters, including those that are regulated during the cell cycle. However, recent evidence indicates that Sp1 belongs to a larger family of factors which bind G/C box elements in order to either activate or repress transcription. Sp3, a member of this family, functions to repress transcriptional activation in two viral promoters, most likely by competing with Sp1 for GC box/Sp binding sites. However, the physiological role of Sp3 in the repression of endogenous cellular promoters has not been experimentally addressed. In the present study, we analyze the activity and binding of Sp3 on several eukaryotic promoters that contain G/C boxes and are known to be regulated during cellular proliferation and the cell cycle. Using antibodies specific for Sp1 and Sp3, we observe that both of these factors localize to the cell nucleus and have a similar, dispersed subnuclear distribution. Further, using gel mobility shift assays, we show that both Sp1 and Sp3 interact specifically with the histone H4 promoter. Transient cotransfections of Drosophila cells with Sp1 and Sp3 expression vectors and with the histone H4, thymidine kinase (TK), or dihydrofolate reductase (DHFR) promoters show that only the DHFR promoter, containing multiple functional GC boxes, displays Sp3 repression of Sp1 activation. In contrast, the single G/C boxes within the histone H4 or TK promoters, which confer transcriptional activation via Sp1 binding, are not responsive to repression by Sp3. Therefore, we demonstrate that the endogenous cellular DHFR promoter is selectively responsive to Sp3 repression. The data suggest that Sp3 may contribute to the control of proliferation- and/or cell-regulated promoters depending upon the context and/or number of functional Sp1 binding sites.

Functional analyses of the transcription factor Sp4 reveal properties distinct from Sp1 and Sp3

Sp4 is a human sequence-specific DNA binding protein with structural features similar to those described for the transcription factors Sp1 and Sp3. These three proteins contain two glutamine-rich regions and a highly conserved DNA binding domain composed of three zinc fingers. Consistently, Sp1, Sp3, and Sp4 do have the same DNA binding specificities. In this report, we have embarked on a detailed analysis of the transcriptional properties of Sp4 in direct comparison to Sp1 and Sp3. Cotransfection experiments into Drosophila SL2 cells lacking endogenous Sp factors demonstrate that Sp4 is an activator protein like Sp1. However, in contrast to Sp1, Sp4 is not able to act synergistically through adjacent binding sites. The transactivation function of Sp4 resides, like that of Sp1, in the N-terminal glutamine-rich region. Sp4 can function as a target for the Sp1 activation domains in a superactivation assay, suggesting that the activation domains of Sp1 and Sp4 are functionally related. Furthermore, we show that Sp4-mediated transcriptional activation can be repressed by Sp3. Taken together, our results demonstrate that the transcription factor Sp4 exhibits specific functional properties distinct from Sp1 and Sp3.

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

Previous analyses of the uteroglobin promoter revealed seven distinct regions, which contribute to its overall activity in epithelial cells from endometrium and lung. Most significantly, a mutation of the promoter sequence around 65 base pairs upstream of the transcriptional start site severely impairs promoter activity. The transcription factor acting through this sequence has not been identified yet. Here, we report that members of the Sp transcription factor family specifically recognize this non-classical GC box, in addition to another functional motif located 230 base pairs upstream of the transcriptional start site. We have characterized in detail the interaction of recombinant Sp3 with both motifs by DNase I footprinting and methylation protection using the wild-type uteroglobin promoter and various linker scanning mutants as templates. Electrophoretic mobility shift analyses show that Sp1 and Sp3 both bind with similar affinity to these elements. We demonstrate that the DNA-binding proteins in the endometrial cell line Ishikawa which recognize these motifs are also Sp1 and Sp3. Gene transfer experiments into Drosophila Schneider cells that do not contain endogenous Sp factors revealed that both DNA motifs respond to transiently expressed Sp1 and Sp3. Our results show thus that the level of transcription from the uteroglobin promoter is controlled by members of the Sp transcription factor family through unusual Sp binding sites.

Differential transcriptional regulation of c-myc promoter through the same DNA binding sites targeted by Sp1-like proteins

Sp1 and Sp3 are closely related members of a gene family encoding proteins with very similar structural features. The zinc finger DNA binding domains of Sp1 and Sp3 are highly conserved and they bind to GC and GT box with comparable affinities. To begin to delineate the specific roles of these two members of the Sp1-like gene family, here we have analysed the DNA binding specificity and their effects on activation of human c-myc promoter. We found that both proteins bind to the same sites of c-myc promoter, upstream to both the P1 and P2 initiation sites. Cotransfection experiments, in mammalian and insect cells, indicated that Sp1 trans-activate c-myc promoter, whereas Sp3 did not. In addition, enforced expression of Sp3 repressed Sp1-mediated activation of c-myc. Finally, we found that Sp1 and E2F-1/DP-1 cooperatively trans-activate c-myc promoter. In contrast enforced expression of Sp3 fails to repress E2F-1/DP-1-mediated activation.

Progesterone binding to uteroglobin: two alternative orientations of the ligand

Progesterone binding to a homodimer of uteroglobin takes place in a hydrophobic cavity formed by the two subunits. Previous mutational analyses have shown that the tyrosine (21 and 21') and threonine (60 and 60') residues of the uteroglobin dimer are directly involved in progesterone binding. To analyze the contribution of each of the two tyrosines and threonines in the dimer, we have constructed a covalently linked uteroglobin dimer (UGcl) by fusing two uteroglobin cDNAs via a synthetic linker sequence. Escherichia coli expressed UGcl bound progesterone with the same affinity as the native dimeric protein. Replacement of both tyrosines by phenylalanines abolished progesterone binding. Replacement of either the C-terminal tyrosine 21 or the N-terminal tyrosine 21' separately, reduced the affinity for progesterone 3- to 4-fold, suggesting that both tyrosines participate in progesterone binding. In contrast, substitutions of the threonine residues of the C- or N-terminal moities had no effect, whereas the replacement of both threonines reduced the affinity for progesterone 2- to 3-fold. These data, together with computer models, suggest that progesterone docks in the internal binding pocket of uteroglobin in two different orientations.

A transgenic mouse model for lung adenocarcinoma

Lung cancer is a leading cause of tumor-related deaths in humans but its origin and development are poorly understood. To study the biology of these tumors, appropriate animal and cell culture models will be of eminent importance. Uteroglobin is a marker protein for the nonciliated epithelial Clara cells lining the respiratory and terminal bronchioli of the lung. We have used the promoter and 5'-flanking sequences of the rabbit uteroglobin gene to target expression of the SV40 T antigen to the lung of transgenic mice. All transgenic founders as well as the descendants from an established line, UT7.1, developed multifocal bronchioloalveolar adenocarcinomas originating from Clara cells. At least three different stages in tumor development with progressive loss of the differentiated phenotype can be distinguished by immunohistochemical data and in situ hybridization. Only in the initial stage did bronchiolar cells express both uteroglobin and SV40 T antigen, whereas at later stages, only SV40 T antigen was detected, and the most advanced tumors were negative for both proteins. Starting from the lungs of UT7.1 mice, a bronchiolar cell line was established that maintains the features of differentiated Clara cells. This system provides a useful model for further studying the development and progression of lung adenocarcinomas in vivo and in vitro.

Different members of the Sp1 multigene family exert opposite transcriptional regulation of the long terminal repeat of HIV-1

Recently, a family of transcription factors structurally related to Sp1 has been described; thus, more than one activator may bind to the GC boxes present in a number of viral and cellular promoters. We have compared the transactivation potentials of Sp1, Sp3 and Sp4 proteins on the human immunodeficiency virus type 1 (HIV-1) promoter. The long terminal repeat (LTR) of HIV-1 contains three binding sites for the transcription factor Sp1 (GC boxes) which are involved in both basal and Tat-mediated transcriptional activation. Moreover, a cooperative interaction between NF-kappa B and Sp1 is required for HIV enhancer activation. We now demonstrate that Sp4 is an activator, while the Sp3 protein represses basal expression of HIV promoter. Remarkably, we found that over-expression of the transcription factor Sp3 was able to suppress Tat-mediated transactivation. These inhibitory effects of Sp3 correlate with its DNA binding activity, suggesting that Sp3 inhibition involves competition with Sp1 for occupancy of the GC boxes. Next, we have analyzed the role of different Sp1-related proteins in the stimulation of HIV-1 promoter in response to mitogens. We found that the binding of NF-kappa B is not by itself sufficient to induce HIV gene expression. Instead, an interaction between NF-kappa B and the trans-acting domain (A domain) of Sp1 bound to an adjacent site must occur. We found that the cooperative interaction between NF-kappa B and Sp1 is highly specific, since neither Sp3 nor Sp4 is capable of cooperating with NF-kappa B.

The uteroglobin promoter targets expression of the SV40 T antigen to a variety of secretory epithelial cells in transgenic mice

Adenocarcinomas derived from the lining epithelia of various organs are the most common malignant tumors in human pathology and about 50% are hormone dependent. The tissue-specific and hormally regulated expression of the rabbit uteroglobin gene is secretory epithelial cells could provide a means of establishing in vivo models for a variety of human tumors originating from such tissues. We have generated trangenic mice inheriting a hybrid gene containing 4.7 kb of the rabbit uteroglobin 5'-flanking sequences fused to the SV40 T antigen encoding region. All transgenic founders examined exhibited bronchio-alveolar adenocarcinomas, probably due to expression of the transgene in Clara cells. Most founders also developed tumors of the submandibular salivary gland, and adenocarcinomas of the stomach. Adenocarcinomas and dysplasias in epithelial cells of the male and female genital tract were found in single founders. Immunohistochemical analysis showed that T antigen expression interfered with stable maintenance of the differentiated phenotype as documented by expression of the endogenous uteroglobin gene. One founder gave rise to a mouse line, UT7.1. Transgenic descendants of UT7.1 developed lung adenocarcinomas and, depending on the genetic background, exhibited tumors of the stomach, the salivary gland and the pancreas. Sporadically male descendants developed prostatic adenocarcinoma whereas females developed dysplasias and adenocarcinomas of the uterus and the oviduct. Thus, the UT7.1 mouse line could be a useful model for several epithelial neoplasias.

Sp1-mediated transcriptional activation is repressed by Sp3

Sp1, Sp3 (SPR-2) and Sp4 (SPR-1) are human sequence-specific DNA binding proteins with very similar structural features. In this report, we have analyzed Sp3 in direct comparison with Sp1. We have raised antibodies against both Sp1 and Sp3, and show that Sp3 protein, like Sp1, is expressed in various cell lines. Co-transfection experiments in different mammalian cell lines reveal that in contrast to Sp1 and Sp4, Sp3 is not able to activate several Sp1 responsive promoters. In addition, Sp3 also fails to activate reporter constructs in Drosophila SL2 cells lacking endogenous Sp factors. Instead, we find that Sp3 represses Sp1-mediated activation in a linear dose-dependent manner. A mutant of Sp3 lacking the DNA binding domain does not affect activation by Sp1, suggesting that the inhibition is most likely due to the competition with Sp1 for their common binding sites. To determine if any structurally similar domain of Sp3 is able to replace partially homologous domains of Sp1, we have generated chimeric proteins and tested their activation characteristics in gene transfer experiments. It appears that neither the glutamine-rich domains A and B nor the D domain of Sp1 can be replaced by the homologous regions of Sp3. Our results suggest that Sp3 is an inhibitory member of the Sp family.

Uteroglobin, an apically secreted protein of the uterine epithelium, is secreted non-polarized form MDCK cells and mainly basolaterally from Caco-2 cells

A complete cDNA encoding rabbit uteroglobin was constructed and expressed in MDCK and Caco-2 cells. The MDCK cells secrete uteroglobin in approximately equal amounts to the apical and the basolateral side, whereas the Caco-2 cells secrete uteroglobin mainly to the basolateral side. Both MDCK and Caco-2 cells thus secrete uteroglobin in a non-sorted manner. It has, however, previously been shown that uteroglobin is secreted exclusively at the apical membrane in primary cell culture of endometrial epithelial cells [S.K. Mani et al. (1991) Endocrinology 128, 1563-1573]. This suggests that either the endometrial epithelium has an apical default pathway or recognises a sorting signal not recognised by MDCK cells and Caco-2 cells. Our data thus show that a soluble molecule can be secreted at the apical, the basolateral or both membranes depending on the cell type.

[Extracorporeal membrane oxygenation (ECMO) in acute cardiovascular failure caused by myocarditis]

Main indication for extracorporeal membrane oxygenation (ECMO) is respiratory failure in the newborn. Less frequently ECMO is used for cardiac support. We report on a 4 months old boy, who suddenly fell ill with an acute viral myocarditis and heart failure (left-ventricular shortening fraction lowered to 17%). After failure of conventional management and resuscitation (twice) due to asystolic, veno-arterial ECMO was installed for a total time of 4 days. Under ECMO there was complete recovery of left-ventricular function; the infant was discharged 1 month after admission to hospital. ECMO-therapy should not only be considered in children with respiratory failure, but also in those with potentially reversible cardiac failure.

Cloning by recognition site screening of two novel GT box binding proteins: a family of Sp1 related genes

Previous analyses of the uteroglobin gene promoter revealed a GT1 box which is also found in the SV40 enhancer. The GT1 element in the context of the uteroglobin promoter is active in Ishikawa cells, a human endometrial cell line, but not in HeLa cells. Here we report the cloning by recognition site screening of two factors (SPR-1 and SPR-2) which bind to this GT1 motif. SPR-1 and SPR-2 are homologues of the transcription factor Sp1. All three proteins are closely related members of a gene family encoding proteins with very similar structural features. Like Sp1, SPR-1 and SPR-2 contain glutamine and serine/threonine rich amino acid stretches. Most significantly, the DNA binding domains of all three proteins are highly conserved and they recognize GT as well as GC boxes identically. SPR-2 mRNA is expressed ubiquitously, whereas SPR-1 transcripts are abundant in the brain but barely detectable in other organs. The possible function of these factors for the activity of the uteroglobin promoter is discussed.

High frequency oscillatory ventilation and extracorporeal membrane oxygenation in severe persistent pulmonary hypertension of the newborn

We report on 50 term and near-term neonates (birth weight greater than 1800 g, gestational age greater than 33 weeks) with severe persistent pulmonary hypertension of the newborn (PPHN), referred to us from January 1987 to July 1991 after failure of maximum conventional treatment. All infants had paO2 less than 45 mm Hg when ventilated with peak inspiratory pressure greater than 38 cm H2O and FiO2 = 1.0, hence meeting entry criteria for extracorporeal membrane oxygenation (ECMO). High frequency oscillatory ventilation (HFOV) was tried in all patients. If sufficient oxygenation could not be achieved (paO2 less than 40 mm Hg for at least 2 h), ECMO therapy was begun, which was the case in 25 children. Neonates responding to HFOV (n = 25) were of a slightly younger gestational age (37.0 weeks vs 38.8 weeks, P less than 0.05), had higher Apgar scores and were less hypoxaemic before HFOV (paO2 36.6 mm Hg vs 28.8 mm Hg, P less than 0.01); during HFOV there was a significant rise in paO2 (greater than 150 mm Hg; P less than 0.001) and a fall in pCO2 to 21.6 mm Hg (P less than 0.001). Due to air leaks, which was the main complication of HFOV (52%), ECMO therapy had to be begun in two additional infants after an initial positive effect. HFOV tended to be successful in cases of primary PPHN, meconium aspiration and sepsis, but not in infants with lung hypoplasia as a result of diaphragmatic hernia or other reasons. Success or failure of HFOV could not be reliably predicted by any parameter.(ABSTRACT TRUNCATED AT 250 WORDS)

Human CC10, the homologue of rabbit uteroglobin: genomic cloning, chromosomal localization and expression in endometrial cell lines

Human and rat cDNAs to Clara Cell 10 kDa protein (CC10) have been previously isolated. Comparison of the amino acid sequences showed that CC10 is homologous to rabbit uteroglobin. Here we present further evidence that human CC10 is the human counterpart of rabbit uteroglobin. We have isolated the gene and have mapped its genomic localization to chromosome 11q11-qter. Sequence analysis of the 5'-flanking region reveals that the homology between the human and the rabbit gene starts at the first exon/intron boundary and extends up to -1.4 kb. A second region of 0.74 kb from -1.77 to -2.51 kb in the human 5'-flanking gene region is homologous to rabbit sequences that include four progesterone receptor binding sites which have been implicated in progesterone regulation of rabbit uteroglobin gene expression in endometrium. Sequence alignment of this region on the nucleotide level shows that only two weak progesterone receptor binding sites are partially conserved. In addition, close inspection of the human and rabbit promoters reveals that the estrogen responsive element and two recently identified cis elements of the rabbit promoter located between -177 and -258 bp are also absent in the human uteroglobin promoter. Despite these differences in the 5'-flanking regions of the genes, we report that the human uteroglobin mRNA is expressed in a human cell line of endometrial origin indicating that human uteroglobin is expressed in the uterus like its rabbit homologue. Thus, it appears that human uteroglobin is not only a marker for lung Clara cells but also an endometrial differentiation marker.(ABSTRACT TRUNCATED AT 250 WORDS)

Interchain cysteine bridges control entry of progesterone to the central cavity of the uteroglobin dimer

The progesterone-binding protein uteroglobin has been expressed in Escherichia coli in an unfused, soluble form. Like mature uteroglobin from rabbit endometrium (UG), the E.coli produced uteroglobin (UG1) dimerizes in vitro, forms an antiparallel dimer with Cys3-Cys69' and Cys69-Cys3' disulfide bonds and binds progesterone under reducing conditions. In order to analyze the dimerization and the reduction dependence of progesterone binding in more detail, we separately replaced cysteine 3 and cysteine 69 by serines. Under reducing conditions, both uteroglobin variants (UG1-3Ser and UG1-69Ser) bind progesterone with the same affinity as the wild-type suggesting that both cysteine residues are not directly involved in progesterone binding. In contrast to the wild-type protein, both cysteine variants also bind progesterone with high affinity in the absence of reducing agents. In addition, UG1-3Ser and UG1-69Ser both form covalently linked homodimers. Thus, unnatural Cys69-69' and Cys3-3' disulfide bonds exist in UG1-3Ser and UG1-69Ser, respectively. These data together with computer models based on X-ray diffraction data strongly support the idea that progesterone reaches its binding site located in an internal hydrophobic cavity via a hydrophobic tunnel along helices 1 and 4. Under non-reducing conditions the tunnel is closed by two disulfide bridges (Cys3-Cys69' and Cys69-Cys3') that lie in the most flexible region of the dimer. Reduction or replacement of a cysteine residue enables conformational changes that open the channel allowing progesterone to enter.

Novel upstream elements and the TATA-box region mediate preferential transcription from the uteroglobin promoter in endometrial cells

To understand the mechanisms responsible for endometrium-specific expression of the uteroglobin gene, we have compared transcription from the uteroglobin promoter in a human endometrial cell line (Ishikawa) and in HeLa cells. In transient transfection experiments and in nuclear extracts, sequences from -395 to +14 of the uteroglobin gene are able to promote transcription of a reporter gene more efficiently in Ishikawa cells than in HeLa cells relative to the RSV or the SV40 early promoter. Analysis of progressive 5'-deletion mutants identifies three promoter regions, -258/-220, -205/-177, and -96/-35, that are important for preferential transcription in endometrial cells. DNase I footprinting experiments with nuclear extracts from Ishikawa and HeLa cells reveal a series of defined protections overlapping these regions. The relative intensity of individual protections differs between the two cell lines. Oligonucleotide competition experiments suggest that similar factor(s) bind(s) to the two relevant upstream regions of the promoter that share no homology to known regulatory elements. A protection over the TATA-box is detected only with extracts from Ishikawa cells. Band shift experiments show that an Ishikawa-specific factor binds to sequences overlapping the TATA-box region that are partially conserved in other endometrium-expressed genes. We propose that novel transcription factors mediate endometrium-specific expression of the uteroglobin gene in conjunction with a tissue-specific factor that binds to the TATA-box region.

Expression of the uteroglobin promoter in epithelial cell lines from endometrium

To understand the molecular mechanism of endometrial differentiation we have initiated an analysis of the uteroglobin promoter. Uteroglobin is normally expressed in endometrial tissues under the control of ovarian hormones. In gene transfer experiments with the Ishikawa cell line, derived from a human endometrial adenocarcinoma, we have identified several regions in the promoter of the uteroglobin gene that are responsible for its endometrium-specific expression. To evaluate the generality of these findings, we have begun cloning the promoter regions of potential endometrial markers, including the rat, mouse, and human uteroglobin gene. In the rat, expression of the uteroglobin-like gene, CC10, is dominant in the lung but is also observed in the endometrium of progesterone treated animals. A comparison of the 5'-flanking sequence of the rat and rabbit uteroglobin gene resulted in the detection of similarities and differences that could explain their differential expression in vivo. To substantiate these findings we have established several cell lines from rat endometrium using murine retroviral vectors containing a positive selection marker and various viral oncogenes, such as SV40 large T antigen, adenovirus E1A, and Ha-ras. Cell lines immortalized by SV40 T-antigen were subsequently transformed with the Ha-ras oncogene. Several cell lines exhibit properties of epithelial endometrial cells. Two cell lines generated with a temperature sensitive mutant of the SV40 large T-antigen grow as transformed cells at the permissive temperature, but differentiate upon shifting to the non-permissive temperature. These rat endometrial cell lines should be useful for the analysis of endometrium-specific gene expression and as model systems for endometrial carcinoma.

Cell-specific, developmentally and hormonally regulated expression of the rabbit uteroglobin transgene and the endogenous mouse uteroglobin gene in transgenic mice

We have generated a transgenic mouse line by introducing the rabbit uteroglobin gene with 4 kb of 5'-flanking DNA and 1 kb of 3'-flanking DNA into the mouse germ line via microinjection into fertilized oocytes. Expression of the rabbit uteroglobin transgene was examined and compared with the endogenous mouse uteroglobin gene. Both genes are expressed in the lung, male genital tract and uterus. In the lung, mRNA expression is enhanced by glucocorticoids and restricted to the Clara cells that line terminal and respiratory bronchioli. During embryonic lung development, transcripts are first detected at day 17. Expression in the uterus is restricted to the glandular epithelium and can be induced by sequential treatment with estrogens and progesterone. In the uterus of these pseudopregnant mice the level of rabbit uteroglobin transcripts is higher than that of the mouse endogenous uteroglobin transcripts. In the male genital tract, expression of both genes is restricted to the epithelial layers of the vesicular gland, vas deferens and epididymis. Our results indicate that the rabbit uteroglobin gene together with 4 kb of 5'-flanking DNA and 1 kb of 3'-flanking DNA contains the information required for cell type-specific, developmentally, and hormonally regulated expression.

Identification of residues essential for progesterone binding to uteroglobin by site-directed mutagenesis

In order to identify amino acids directly involved in progesterone binding to rabbit uteroglobin we have mutated Phe 6, Tyr 21 and Thr 60 by site-directed mutagenesis of the uteroglobin cDNA. These residues have been postulated previously to participate in progesterone binding. High-level expression of the mutated uteroglobin cDNAs in Escherichia coli yields recombinant protein mutants that, like natural uteroglobin, form stable dimers, suggesting that the tertiary structure of the protein has not been altered. Substitution of Phe 6 by Ser or Ala does not change the progesterone binding characteristics. In contrast, replacement of Tyr 21 by Phe or Ala, drastically decreases progesterone binding. In addition, replacement of Thr 60 by Ala reduces the affinity for progesterone by a factor of three. These data suggest a direct interaction of progesterone with these two amino acids and support the idea of direct hydrogen bonding of the carbonyl (C3 and C20) of progesterone with the hydroxyl groups of Tyr 21 and Thr 60, respectively.

A comparison of mouse and rabbit embryos for the production of transgenic animals by pronuclear microinjection

Procedures for the production of transgenic animals have low overall efficiency. To evaluate factors responsible for low efficiency, zygotes of two species, varying intensities of microscope light, different qualities of injection pipettes, and six different genes were tested for their influence on the efficiency of pronuclear gene injection for the production of transgenic rabbits and mice. Rabbit zygotes were less sensitive to mechanical manipulation during injection than mouse zygotes. Exposing zygotes to a microscope light intensity of 5550 lx significantly reduced their cleavage rate, while a lower intensity (2280 lx) did not. Using pipettes with a filament for pronuclear gene injection of mouse zygotes resulted in a higher cleavage rate of zygotes after injection than when pipettes were used without filament (30.3 vs 20.6%). Implantation rates varied between 2.9% (HB72CAT) and 23.1% (ts 58-2) depending on the gene used. No transgenic animals were obtained after injection of uteroglobin-CAT-hybrid genes (B2B3UGCAT, HB72CAT), while all other genes used (UG 11.8, UGTAg, RSV lacZ, ts 58-2) resulted in transgenic embryos, fetuses, and newborn animals.

Tissue-specific expression, hormonal regulation and 5'-flanking gene region of the rat Clara cell 10 kDa protein: comparison to rabbit uteroglobin

The amino acid sequence of rat Clara Cell 10 kDa secretory protein (CC10) shows 55% identity to rabbit uteroglobin. In order to define the relationship between rat CC10 and rabbit uteroglobin in detail, the tissue-specific expression and hormonal regulation of rat CC10 mRNA was analyzed. We report that like rabbit uteroglobin, rat CC10 mRNA is expressed in lung and esophagus, as well as in uteri of estrogen- and progesterone-treated females. Expression of CC10 mRNA in lung is regulated by glucocorticoids. The similarity in expression pattern of rat CC10 mRNA and rabbit uteroglobin mRNA is reflected by a striking similarity in the 5'-flanking regions of the two genes. Despite this overall similarity, two regions of 0.3 kb and 2.1 kb are absent in the rat CC10 upstream gene region. The larger region includes a cluster of hormone receptor binding sites, believed to be responsible for differential regulation of rabbit uteroglobin by glucocorticoids and progesterone. Thus, while the sequence identities in the coding and 5'-flanking regions point towards a common ancestor for the uteroglobin and CC10 gene, later events (deletions/insertions) might have caused species-specific differences in their regulation.

The uteroglobin promoter contains a noncanonical estrogen responsive element

Uteroglobin is expressed in various tissues of the rabbit under complex hormonal control. In the endometrium the uteroglobin gene is transcribed only in epithelial cells after administration of ovarian hormones. In this paper we demonstrate that within the promoter region of the rabbit uteroglobin gene, there is a functional estrogen-responsive element (ERE) located between -265 and -252. Hybrid constructions containing sequences of the uteroglobin promoter up to -299, linked to the chloramphenicol acetyltransferase gene of E. coli respond to estrogens in gene transfer experiments, whereas a deletion that removes half of the ERE does not. A synthetic oligonucleotide corresponding to the putative ERE is able to confer estrogen inducibility to an otherwise unresponsive promoter. Binding experiments with purified estrogen receptor from calf uterus reveal a DNase-I footprint over the ERE. Within this protected region six guanine residues that have been shown to be contacted by the receptor in other EREs are protected against methylation by dimethylsulfate in the presence of the estrogen receptor. We compare this ERE with the vitellogenin A2 ERE from Xenopus and find that the relative affinity of the uteroglobin ERE is slightly lower than that of the vitellogenin ERE. Thus, this uteroglobin ERE could be involved in physiological regulation of uteroglobin expression in the genital tract.

Recombinant rabbit uteroglobin expressed at high levels in E. coli forms stable dimers and binds progesterone

In order to express uteroglobin in Escherichia coli we have constructed a DNA coding for complete mature rabbit uteroglobin by fusing genomic sequences from the second exon of the gene to an incomplete cDNA. This DNA was inserted into various positions of the polylinker cloning region of pDS expression vectors and the uteroglobin gene was expressed in E. coli by IPTG induction. Four different uteroglobin-derived proteins were produced containing 1, 3, 5 and 7 more N-terminal amino acids than the naturally occurring mature protein. The yield of soluble protein strongly increased with increasing length of the N-terminal additions. Protein and RNA analysis showed that this variation is most likely due to progressively higher translation efficiencies of the larger recombinants. UG7, the most efficiently synthesized recombinant protein, carrying seven additional N-terminal amino acids, was purified and further characterized. Like natural uteroglobin, UG7 forms a dimer and binds progesterone with an affinity indistinguishable to the natural protein. This bacterially produced protein can be used for detailed structure-function investigations of uteroglobin.