Interaction of a tissue-specific factor with an essential rat growth hormone gene promoter element

Differential placental hormone gene expression during pregnancy in a transgenic mouse containing the human growth hormone/chorionic somatomammotropin locus

The human (h) growth hormone/chorionic somatomammotropin (GH/CS) gene locus presents a unique model to gain insight into the molecular mechanisms that have allowed a closely related family of genes to be expressed in two distinct cell lineages/tissues: pituitary somatotrophs and placental syncytiotrophoblasts. However, studies of external factors that regulate gene expression have been somewhat limited by (i) a lack of human cell lines expressing endogenous GH or CS appropriately; and (ii) the fact that the GH/CS locus is unique to primates and thus does not exist in rodents. In the current study, a transgenic (171 h GH/CS-TG) mouse was generated containing the intact hGH/CS gene cluster and hGH locus control region (LCR) in a 171-kilobase DNA fragment. Pituitary and placental-specific expression of hGH/CS RNA was detected at embryonic day (E) 18.5. Immunostaining of hGH was seen in somatotrophs of the anterior pituitary beginning in late gestation. The presence of hCS protein was detected in the placental labyrinth in trophoblasts functionally analogous to the syncytiotrophoblast of the chorionic villi. This pattern of gene expression is consistent with the presence of essential components of the hGH/CS LCR. Transcript levels for hCS-A, hCS-B and placental hGH-variant increased in 171 hGH/CS-TG placenta during gestation (E11.5-E18.5), as previously observed in human placental development. Throughout gestation, hCS-A RNA levels were proportionately higher, accounting for 91% of total CS RNA by E18.5, comparable to term human placenta. Finally, the previous correlation between the transcription factor AP-2alpha and hCS RNA expression observed in developing primary human cytotrophoblast cultures, was extended to pregnancy in the 171 hGH/CS-TG mouse. The 171 hGH/CS-TG mouse thus provides a model to investigate hGH/CS gene expression, including in pregnancy.

In vivo genomic footprinting of thyroid hormone-responsive genes in pituitary tumor cell lines

We studied the effects of thyroid hormone (T3) on nuclear protein-DNA interactions by using dimethyl sulfate (DMS) and DNase I ligation-mediated PCR footprinting. We examined an endogenous gene the growth hormone (GH) gene, and a stably transfected plasmid containing the chicken lysozyme silencer (F2) T3 response element (TRE) gene, F2-TRE-TK-CAT, both in pituitary tumor (GC) cells. The 235-1 cell line, which expresses prolactin (PRL) and Pit-1, but not the T3 receptor (TR) or GH, was used as a control. DMS and DNase I footprinting identified protected G residues in the Pit-1, Sp1, and Zn-15 binding sites of the GH gene in GC, but not in 235-1, cells. There was no specific protection of the tripartite GH TRE at -180 bp against either DMS or DNase I in the absence or presence of T3 in either cell line. However, T3 increased protection of the Pit-1 and Sp1 binding sites against DMS in GC cells. In GC cells stably transfected with a plasmid containing F2-TRE-TK-CAT or TRalpha, chloramphenicol acetyltransferase expression was T3 inducible and DMS footprinting revealed both F2 TRE TR-binding half sites in a pattern suggesting the binding of TR homodimers before and during T3 exposure. We conclude that the GH gene is accessible to specific nuclear proteins in GC, but not in 235-1, cells and that T3 enhances this interaction, although there is no evidence of TR binding to the low-affinity rat GH TRE. The presence of TR binding to the high-affinity F2 TRE before and during T3 exposure suggests that reversible interaction of T3 with DNA-bound TRs, rather than transient T3-TR contact with TREs, determines the level of T3-stimulated transcriptional activation.

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

We have previously shown that a trans-acting protein produced in some tissue culture cells positively control the transcriptional activity directed by the mouse p12 promoter. This nuclear protein exerts its positive activity by interacting with a regulatory sequence designated p12.A and located between the TATA and CCAAT box elements on the p12 gene promoter. Using DNase I and dimethyl sulfate methylation interference footprinting techniques coupled with gel retardation assays, we found evidence that the protein which binds to the p12.A element is the well-known transcription factor Sp1. Mutational analysis in transient transfection assays confirmed the positive activity exerted by this protein in every cell line tested. In agreement with this observation, we detected a p12.A-Sp1 binding activity in nuclear extracts prepared from all cell lines used. However, a similar binding activity could not be detected in a number of nuclear extracts prepared from normal mouse tissues. In this report, we provide the evidence that the lack of Sp1-binding activity results from the degradation of Sp1 in the kidney, liver, and pancreas of the mouse.

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

We have previously shown that a trans-acting protein produced in some tissue culture cells positively control the transcriptional activity directed by the mouse p12 promoter. This nuclear protein exerts its positive activity by interacting with a regulatory sequence designated p12.A and located between the TATA and CCAAT box elements on the p12 gene promoter. Using DNase I and dimethyl sulfate methylation interference footprinting techniques coupled with gel retardation assays, we found evidence that the protein which binds to the p12.A element is the well-known transcription factor Sp1. Mutational analysis in transient transfection assays confirmed the positive activity exerted by this protein in every cell line tested. In agreement with this observation, we detected a p12.A-Sp1 binding activity in nuclear extracts prepared from all cell lines used. However, a similar binding activity could not be detected in a number of nuclear extracts prepared from normal mouse tissues. In this report, we provide the evidence that the lack of Sp1-binding activity results from the degradation of Sp1 in the kidney, liver, and pancreas of the mouse.

Interaction of basal positive and negative transcription elements controls repression of the proximal rat prolactin promoter in nonpituitary cells

The proximal rat prolactin (rPRL) promoter contains three cell-specific elements, designated footprints I, III, and IV, which restrict rPRL gene expression to anterior pituitary lactotroph cells. Footprint II (-130 to -120) binds a factor, which we have termed F2F, present in pituitary and nonpituitary cell types. Here we demonstrate that a key role of the footprint II site is to inhibit rPRL promoter activity in nonpituitary cells, specifically, by interfering with the basal activating function of a vicinal element. Gene transfer analysis revealed 20-fold activation of the rPRL promoter in nonpituitary cell types when footprint II was either deleted or specifically mutated. Similar activation of the intact rPRL promoter was obtained by in vivo F2F titration studies. In GH4 rat pituitary cells, the footprint II inhibitory activity was masked by the redundant, positively acting cell-specific elements and was inhibitory only if the two upstream sites, footprints III and IV, were deleted. Deletion of the -112 to -80 region in the footprint II site-specific mutant background resulted in complete loss of rPRL promoter activity in both pituitary and nonpituitary cell types, mapping a basal activating element that is operative irrespective of cell type to this region. While the basal activating element imparted an activating function in a heterologous promoter assay, the footprint II sequence did not display any inherent repressor function and actually induced several minimal heterologous promoters. However, the inhibitory activity of the footprint II site was detected only if it was in context with the basal activating element. These data underscore the importance of ubiquitous activating and inhibitory factors in establishing cell-specific gene expression and further emphasize the complexity of the molecular mechanisms which restrict gene expression to specific cell types. We provide a novel paradigm to study rPRL promoter function and hormone responsiveness independently of lactotroph cell-specific requirements.

Interaction of basal positive and negative transcription elements controls repression of the proximal rat prolactin promoter in nonpituitary cells

The proximal rat prolactin (rPRL) promoter contains three cell-specific elements, designated footprints I, III, and IV, which restrict rPRL gene expression to anterior pituitary lactotroph cells. Footprint II (-130 to -120) binds a factor, which we have termed F2F, present in pituitary and nonpituitary cell types. Here we demonstrate that a key role of the footprint II site is to inhibit rPRL promoter activity in nonpituitary cells, specifically, by interfering with the basal activating function of a vicinal element. Gene transfer analysis revealed 20-fold activation of the rPRL promoter in nonpituitary cell types when footprint II was either deleted or specifically mutated. Similar activation of the intact rPRL promoter was obtained by in vivo F2F titration studies. In GH4 rat pituitary cells, the footprint II inhibitory activity was masked by the redundant, positively acting cell-specific elements and was inhibitory only if the two upstream sites, footprints III and IV, were deleted. Deletion of the -112 to -80 region in the footprint II site-specific mutant background resulted in complete loss of rPRL promoter activity in both pituitary and nonpituitary cell types, mapping a basal activating element that is operative irrespective of cell type to this region. While the basal activating element imparted an activating function in a heterologous promoter assay, the footprint II sequence did not display any inherent repressor function and actually induced several minimal heterologous promoters. However, the inhibitory activity of the footprint II site was detected only if it was in context with the basal activating element. These data underscore the importance of ubiquitous activating and inhibitory factors in establishing cell-specific gene expression and further emphasize the complexity of the molecular mechanisms which restrict gene expression to specific cell types. We provide a novel paradigm to study rPRL promoter function and hormone responsiveness independently of lactotroph cell-specific requirements.

DAL82, a second gene required for induction of allantoin system gene transcription in Saccharomyces cerevisiae

Several highly inducible enzyme activities are required for the degradation of allantoin in Saccharomyces cerevisiae. Induction of these pathway enzymes has been shown to be regulated at transcription, and response to inducer is lost in dal81 and dal82/durM mutants. The similar phenotypes generated by dal81 and dal82 mutations prompted the question of whether they were allelic. We demonstrated that the DAL81 and DAL82 loci are distinct, unlinked genes situated on chromosomes IX and XIV. DAL82 gene expression did not respond to induction by the allantoin pathway inducer or to nitrogen catabolite repression. Expression was also not significantly affected by mutation of the dal80 locus. From the nucleotide sequence of the DAL82 gene, we deduced that it encodes a protein with a mass of 29,079 Da that may possess the structural motifs expected of a regulatory protein. This protein was shown to be required for the function mediated by the cis-acting upstream induction sequence situated in the 5'-flanking regions of the inducible allantoin pathway genes.

Somatotroph- and lactotroph-specific interactions with the homeobox protein binding sites in the rat growth hormone gene promoter

Nuclear extracts prepared from growth hormone-secreting (GC) and prolactin-secreting (235-1) rat anterior pituitary cell lines were compared for their ability to bind to the DNA sequences conferring tissue-specificity to the expression of the rat growth hormone (rGH) gene promoter. Cell-specific differences in the interaction of Pit-1, a tissue-specific member of the POU-domain transcription factor family, with the pGHF1 binding site were detected by methylation interference experiments; otherwise the Pit-1 proteins present in GC cell and 235-1 cell extracts were similar. Two other protein/DNA complexes, GHF5 and GHF7, were detected by gel mobility shift assays and the binding of both complexes to the rGH promoter depended upon DNA sequences contained within the two binding sites for Pit-1. In contrast to Pit-1 which can bind to either of the two sites independently, a single Pit-1 binding site was insufficient for GHF5 and GHF7 binding; i.e. both Pit-1 binding sites within the rGH promoter were required. Whereas GHF5 was present in nuclear extracts of GC cells and a variety of cells not producing growth hormone, GHF7 binding activity was detected only in the GC cell line (and not in the 235-1 cell line). GHF7 binding activity was therefore more closely correlated with growth hormone gene transcription than was Pit-1. rGH promoters containing mutations which inhibited GHF5, GHF7 and Pit-1 binding were expressed less efficiently than the wild type promoter after transfection into GC cells. One promoter mutation to which the GHF7 complex but not the Pit-1 factor can bind was also transcription deficient demonstrating that Pit-1 binding, independent of GHF7 binding, was nevertheless important to the expression of the rat growth hormone promoter.

Human chorionic somatomammotropin and growth hormone gene expression in rat pituitary tumour cells is dependent on proximal promoter sequences

Human placental chorionic somatomammotropin (hCS-A or hCS-B) and pituitary growth hormone (hGH-N) are related by structure and function. The hCS-A gene is expressed in rat pituitary tumour (GC) cells after gene transfer. Deletion of hCS-A 5'-flanking DNA reveals repressor activity upstream of nucleotide -132, and a region essential for expression in GC cells between nucleotides -94 and -61. The sequences in this region differ from the equivalent hGH-N gene DNA by one nucleotide, and include the binding site (-92 to -65) for a pituitary-specific factor (GHF-1), required for hGH-N expression in GC cells. Exchange of hGH-N with hCS-A gene DNA in this region maintains expression in GC cells. By contrast, modification of these sequences blocks expression. These data indicate that proximal promoter sequences, equivalent to those bound by GHF-1 on the hGH-N gene, are required for hCS-A expression in GC cells.

Purified hepatocyte nuclear factor 1 interacts with a family of hepatocyte-specific promoters

During development cell types arise through the activation or repression of classes of specific genes. One hypothesis is that this phenomenon is realized by tissue-specific factors playing a role at the transcription level. Recently we have described a liver-specific nuclear protein, hepatocyte nuclear factor 1, that appears to be involved in the transcription of the fibrinogen and alpha 1-antitrypsin genes. In this report we describe the purification of hepatocyte nuclear factor 1 and demonstrate that it interacts with essential promoter regions of many liver-specific genes, including albumin, alpha-fetoprotein, and transthyretin. This finding suggests that hepatocyte nuclear factor 1 could be one factor necessary for establishing the liver phenotype. We also show that this protein binds to the promoter of the surface-antigen gene of the hepatitis B virus, a virus characterized by a high degree of hepatotropism.

Identification of rat growth hormone genomic sequences targeting pituitary expression in transgenic mice

Constructs containing different segments of the 5' flanking region of the rat growth hormone gene fused to the human growth hormone coding sequences were introduced into fertilized mouse oocytes. As few as 181 base pairs of the rat growth hormone promoter targeted reporter gene expression to the pituitary gland of the resulting transgenic mice. A construct containing only 45 base pairs of the promoter failed to target expression of the reporter to the pituitary, indicating that the pituitary expression is directed by information contained in the segment spanning positions -181 to -45. In the pituitary, immunohistochemistry showed transgene expression mainly in the growth hormone-producing cells (somatotrophs), in a subset of cells producing thyrotropin, and occasionally in prolactin-producing cells. These data establish that cis-active elements contained within the first 180 base pairs of the promoter are sufficient for transcriptional activation of the growth hormone gene in somatotrophs and suggest a functional relationship among growth hormone, prolactin, and thyrotropin gene activation.

Regulation of gene expression by thyroid hormone

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Tissue-specific activity of the pro-opiomelanocortin gene promoter

The pro-opiomelanocortin (POMC) gene is specifically expressed in corticotroph cells of the anterior pituitary. To define the POMC promoter sequences responsible for tissue-specific expression, we assessed POMC promoter activity by gene transfer into POMC-expressing pituitary tumor cells (AtT-20) and fibroblast L cells. The rat POMC promoter was only efficiently utilized and correctly transcribed in AtT-20 cells. 5'-End deletion analysis revealed two promoter regions required for activity in AtT-20 cells. When tested by fusion to a heterologous promoter, DNA fragments corresponding to both regions exhibited tissue-specific activity, suggesting the presence of at least two tissue-specific DNA sequence elements within the promoter. In summary, POMC promoter sequences from -480 to -34 base pairs appear sufficient to mimic the specificity of anterior pituitary expression.

Tissue-specific activity of the pro-opiomelanocortin gene promoter

The pro-opiomelanocortin (POMC) gene is specifically expressed in corticotroph cells of the anterior pituitary. To define the POMC promoter sequences responsible for tissue-specific expression, we assessed POMC promoter activity by gene transfer into POMC-expressing pituitary tumor cells (AtT-20) and fibroblast L cells. The rat POMC promoter was only efficiently utilized and correctly transcribed in AtT-20 cells. 5'-End deletion analysis revealed two promoter regions required for activity in AtT-20 cells. When tested by fusion to a heterologous promoter, DNA fragments corresponding to both regions exhibited tissue-specific activity, suggesting the presence of at least two tissue-specific DNA sequence elements within the promoter. In summary, POMC promoter sequences from -480 to -34 base pairs appear sufficient to mimic the specificity of anterior pituitary expression.