Application of a protein-blotting procedure to the study of human glucocorticoid receptor interactions with DNA

Identification of sequence-specific DNA-binding proteins by southwestern blotting

We describe a Southwestern blotting method for characterization of both DNA-binding proteins and their specific sites. Proteins are first separated on a sodium dodecyl sulfate (SDS) polyacrylamide gel, then renatured in SDS-free buffer and transferred by electroblotting to an immobilizing membrane, and detected by their ability to bind radiolabeled DNA. The protein(s) interacting with the labeled DNA is visualized by autoradiography. This technique was used in our laboratory to visualize the metal regulatory consensus sequence-binding protein MTF-1 in L cell crude nuclear extracts.

Identification of beta-cell-specific insulin gene transcription factor RIPE3b1 as mammalian MafA

Of the three critical enhancer elements that mediate beta-cell-specific and glucose-responsive expression of the insulin gene, only the identity of the transcription factor binding to the RIPE3b element (RIPE3b1) has remained elusive. Using a biochemical purification approach, we have identified the RIPE3b1 factor as a mammalian homologue of avian MafA/L-Maf (mMafA). The avian MafA is a cell-type determination factor that expressed ectopically can trigger lens differentiation program, but no mammalian homologue of avian MafA has previously been identified. Here, we report cloning of the human mafA (hMafA) and demonstrate that it can specifically bind the insulin enhancer element RIPE3b and activate insulin-gene expression. In addition, mMafA has a very restrictive cellular distribution and is selectively expressed in pancreatic beta but not in alpha cells. We suggest that mMafA has an essential role in the function and differentiation of beta-cells and thus may be associated with the pathophysiological origins of diabetes.

Genomic cloning of the Hsc71 gene in the hermaphroditic teleost Rivulus marmoratus and analysis of its expression in skeletal muscle: identification of a novel muscle-preferred regulatory element

To further our understanding of the role of stress proteins in development as well as in adaptation of fish to adverse environmental conditions, we undertook molecular analyses of stress protein encoding genes from the hermaphroditic teleost Rivulus marmoratus. We isolated a genomic clone containing the Hsc71 gene (rm-hsc71m) and its upstream sequences. rm-Hsc71m is not induced by external stress, but is enriched in a tissue-specific manner during early development. In adult, the strongest expression appeared in skeletal muscle, whereas lower expression was seen in the gill, eye and brain. To understand the regulatory basis of high muscle expression of rm-hsc71m, transfection of R.marmoratus muscle tissue was performed using 5' deletion fragments containing the rm-hsc71m promoter driving EGFP expression. An upstream region from -2.7 to -1.9 kb was identified as a muscle-specific regulatory region. Within this region, we identified at least three sites with the novel sequence TGTnACA interacting with a fish muscle factor having an M(r) of 32 000. Our data indicate that rm-hsc71m expression in skeletal muscle is controlled by a muscle-specific regulatory element containing this novel motif.

Proinflammatory cytokines regulate human glucocorticoid receptor gene expression and lead to the accumulation of the dominant negative beta isoform: a mechanism for the generation of glucocorticoid resistance

Inflammatory responses in many cell types are coordinately regulated by the opposing actions of NF-kappaB and the glucocorticoid receptor (GR). The human glucocorticoid receptor (hGR) gene encodes two protein isoforms: a cytoplasmic alpha form (GRalpha), which binds hormone, translocates to the nucleus, and regulates gene transcription, and a nuclear localized beta isoform (GRbeta), which does not bind known ligands and attenuates GRalpha action. We report here the identification of a tumor necrosis factor (TNF)-responsive NF-kappaB DNA binding site 5' to the hGR promoter that leads to a 1.5-fold increase in GRalpha mRNA and a 2.0-fold increase in GRbeta mRNA in HeLaS3 cells, which endogenously express both GR isoforms. However, TNF-alpha treatment disproportionately increased the steady-state levels of the GRbeta protein isoform over GRalpha, making GRbeta the predominant endogenous receptor isoform. Similar results were observed following treatment of human CEMC7 lymphoid cells with TNF-alpha or IL-1. The increase in GRbeta protein expression correlated with the development of glucocorticoid resistance.

Cold shock domain factors activate the granulocyte-macrophage colony-stimulating factor promoter in stimulated Jurkat T cells

Cold shock domain (CSD) family members have been shown to play roles in either transcriptional activation or repression of many genes in various cell types. We have previously shown that CSD proteins dbpAv and dbpB (also known as YB-1) act to repress granulocyte-macrophage colony-stimulating factor transcription in human embryonic lung (HEL) fibroblasts via binding to single-stranded DNA regions across the promoter. Here we show that the same CSD factors are involved in granulocyte-macrophage colony-stimulating factor transcriptional activation in Jurkat T cells. Unlike the mechanisms of CSD repression in HEL fibroblasts, CSD-mediated activation in Jurkat T cells is not mediated through DNA binding but presumably through protein-protein interactions via the C terminus of the CSD protein with transcription factors such as RelA/NF-kappaB p65. We demonstrate that Jurkat T cells lack truncated CSD factor subtypes present in HEL fibroblasts, which raises the possibility that the cellular content of CSD proteins may determine their final role as activators or repressors of transcription.

Multiple binding sites for nuclear proteins of the anterior pituitary are located in the 5'-flanking region of the porcine follicle-stimulating hormone (FSH) beta-subunit gene

Gonadotropins, follicle-stimulating hormone (FSH), and luteinizing hormone (LH), are synthesized specifically in the gonadotropes of the anterior pituitary. The aim of this study was to investigate nuclear factors that bind specifically to the porcine FSH beta-subunit gene. We examined nuclear protein binding to 2.75 kilobase pairs (kbp) of DNA adjacent to the porcine FSH beta-subunit gene: about 2.32 kbp of upstream DNA and 0.43 kbp of downstream DNA. The upstream region contains only TATA box, CACCC element, and some imperfect sequences of cAMP-responsive element, activator protein-1 binding site, and activator protein-2 binding site. Gel mobility shift assay using nuclear proteins extracted from the porcine anterior pituitary revealed that the proteins bound to a limited region of DNA, 107 bp long (designated as Fd2), located about -800 bp upstream from the transcription initiation site. Competitive binding assays demonstrated that the protein binding was sequence specific; the addition of excess amounts of several putative regulatory sequences and plasmid (non-homologous) DNA fragments did not reduce the binding. Furthermore, all five subfragments of Fd2 were also bound by the pituitary nuclear proteins, showing that the entire region of Fd2 is involved in this interaction. Southwestern blotting demonstrated that at least seven protein species of 110, 98, 78, 63, 52, 42, and 35 kDa recognize Fd2. Nuclear proteins from several other porcine tissues were also able to bind to the Fd2 fragment but the gel shift patterns were different and the bindings were weak, although only the cerebellum showed a pattern of binding that was similar to that of the anterior pituitary. These data suggest that multiple proteins of the anterior pituitary recognize a specific region of the porcine FSH beta-subunit gene.

The RIIbeta regulatory subunit of protein kinase A binds to cAMP response element: an alternative cAMP signaling pathway

cAMP, through the activation of cAMP-dependent protein kinase (PKA), is involved in transcriptional regulation. In eukaryotic cells, cAMP is not considered to alter the binding affinity of CREB/ATF to cAMP-responsive element (CRE) but to induce serine phosphorylation and consequent increase in transcriptional activity. In contrast, in prokaryotic cells, cAMP enhances the DNA binding of the catabolite repressor protein to regulate the transcription of several operons. The structural similarity of the cAMP binding sites in catabolite repressor protein and regulatory subunit of PKA type II (RII) suggested the possibility of a similar role for RII in eukaryotic gene regulation. Herein we report that RIIbeta subunit of PKA is a transcription factor capable of interacting physically and functionally with a CRE. In contrast to CREB/ATF, the binding of RIIbeta to a CRE was enhanced by cAMP, and in addition, RIIbeta exhibited transcriptional activity as a Gal4-RIIbeta fusion protein. These experiments identify RIIbeta as a component of an alternative pathway for regulation of CRE-directed transcription in eukaryotic cells.

Identification of an HMG-like protein involved in regulation of Na+/H+ exchanger expression

In this study we characterized regulation of the Na+/H+ exchanger promoter in several tissue types. A conserved poly (dA:dT) region was important in regulation of the promoter. Nuclear extracts from rat myocardium and from mouse proximal tubule cells protected the poly (dA:dT) region of the NHE1 promoter. A protein from nuclear extracts also bound to the poly (dA:dT) element in gel mobility shift binding assays. The binding was specific and was removed by mutations in the poly (dA:dT) region. Characterization of the binding to the poly (dA:dT) region in gel mobility shift assays showed that it was reduced by high concentrations of the divalent cations Mg++ and Mn++. The inhibition by divalent cations was reduced by decreasing the pH of the binding assay. N-terminal sequencing of the poly (dA:dT) binding protein showed that it was a member of the HMG (high mobility group) family of nuclear proteins which are important in cell growth and proliferation. The results are the first direct detection of a protein that regulates the NHE1 promoter.

Characterization of a 50-kDa component of epithelial basement membranes using GDA-J/F3 monoclonal antibody

Using the monoclonal antibody GDA-J/F3, a 50-kDa noncollagenous component of human skin basement membrane zone was identified. Immunofluorescence stainings of normal human skin with the GDA-J/F3 antibody showed a linear fluorescence decorating the basement membrane zone. With immunoelectron microscopy, the epitope was localized to the insertion points of the anchoring fibrils into the lamina densa. The antigen is distinct from collagen VII, from the main structural protein of the anchoring fibrils, and from several other structural molecules of the basement membrane zone, because the GDA-J/F3 antibody did not react with purified basement membrane components in vitro. In serum-free cultures, the antigen was synthesized and secreted by normal and transformed human keratinocytes and to a lesser extent by normal human skin fibroblasts. Immunoprecipitation of radiolabeled epithelial cell-conditioned medium with the GDA-J/F3 antibody yielded two polypeptides that migrated on SDS-polyacrylamide gel electrophoresis with apparent molecular masses of 46 and 50 kDa under nonreducing conditions. Using reducing gels, only the 50-kDa polypeptide was observed. The antigen was resistant to digestion with bacterial collagenase but sensitive to trypsin and pepsin. It also bound to heparin and DEAE cellulose at low ionic strength and alkaline pH. These findings indicate that the GDA-J/F3 antigen is a small globular disulphide-bonded protein with a potential to interact with basement membrane proteoglycans. Integration of the GDA-J/F3 antigen into the histoarchitecture of the dermo-epidermal junction is dependent on the presence of collagen VII, because the GDA-J/F3 epitope was missing in several patients with a genetic blistering disorder of the skin, epidermolysis bullosa dystrophica, who lacked collagen VII and anchoring fibrils.

Mouse glucocorticoid receptor phosphorylation status influences multiple functions of the receptor protein

Although studies have shown that the mouse glucocorticoid receptor (mGR) contains eight phosphorylation sites (Bodwell, J. E., Ortí, E. , Coull, J. M., Pappin, D. J. C., Smith, L. I., and Swift, F. (1991) J. Biol. Chem. 266, 7549-7555), the effect of phosphorylation on receptor function is unclear. We have examined the consequences of single or multiple phosphorylation site mutations on several properties of mGR including receptor expression, ligand-dependent nuclear translocation, hormone-mediated transactivation, ligand-dependent down-regulation of mGR, and receptor protein half-life. Mutations had little effect on receptor expression, subcellular distribution, ligand-dependent nuclear translocation, or on the ability to activate hormone-mediated transcription from a complex (murine mammary tumor virus) promoter. In contrast, the phosphorylation status of the mGR had a profound effect on the ability to transactivate a minimal promoter containing simple glucocorticoid response elements after hormone administration. Similarly, ligand-dependent down-regulation by glucocorticoids of both receptor mRNA and protein was abrogated in mutants containing three or more phosphorylation site alterations. Finally, we show that the phosphorylation status of mGR has a profound effect on the stability of the glucocorticoid receptor protein. Receptors containing seven or eight mutated sites have a markedly extended half-life and do not show the ligand-dependent destabilization seen with wild type receptor. These data show that receptor phosphorylation may play a crucial role in regulating receptor levels and hence control receptor functions.

Cloning of a cDNA encoding a plasma membrane-associated, uronide binding phosphoprotein with physical properties similar to viral movement proteins

Oligogalacturonides are structural and regulatory homopolymers from the extracellular pectic matrix of plants. In vitro micromolar concentrations of oligogalacturonates and polygalacturonates were shown previously to stimulate the phosphorylation of a small plasma membrane-associated protein in potato. Immunologically cross-reactive proteins were detected in plasma membrane-enriched fractions from all angiosperm subclasses in the Cronquist system. Polygalacturonate-enhanced phosphorylation of the protein was observed in four of the six dicotyledon subclasses but not in any of the five monocotyledon subclasses. A cDNA for the protein was cloned from potato. The deduced protein is extremely hydrophilic and has a proline-rich N terminus. The C-terminal half of the protein was predicted to be a coiled coil, suggesting that the protein interacts with other macromolecules. The recombinant protein was found to bind both simple and complex galacturonides. The behavior of the protein suggests several parallels with viral proteins involved in intercellular communication.

Up-regulation of hormone response of human papillomavirus type 16 expression and increased DNA-protein binding by consensus mutations of viral glucocorticoid response elements

Human papillomaviruses (HPVs) and steroid hormones are linked to the development of cervical cancer. Studies from our laboratory and others showed that the steroid glucocorticoid and progesterone hormones activated the expression of HPV type 16. This activation was attributed to the specific interaction of the glucocorticoid receptor (GR) with the three glucocorticoid response elements (GREs) in the HPV16 regulatory region. In the present study, we first examined the glucocorticoid response mediated through the GREs, using GRE consensus (GREc) mutations and expression assays from a heterologous basal promoter. Both single and triple HPV16 GREc constructs increased expression in the presence of the dexamethasone glucocorticoid in HeLa cervical carcinoma cells and primary baby rat kidney epithelial cells, in comparison with the triple wild-type GREs. Further, the hormone increased significantly the expression of the viral E6-E7 oncogene mRNA from intact HPV in primary human ectocervical cells in in situ hybridization assays. Three in vitro assays of DNA-protein interaction with oligonucleotides and HeLa cell extracts showed a higher binding of protein to two of the HPV16 GREcs than to the wild-type GREs. This applied especially to the GRE containing an overlapping NF1 half site, that also had a greater differential induction by dexamethasone of expression in vivo. The NF1 site was mutated in the GREc that also was bound by unique, lower-mobility complexes in electrophoretic mobility shift assays. UV-crosslinking assays confirmed the increased binding and showed binding by a 96-kDa protein, probably the GR. Our results show an important role of glucocorticoids in HPV16 expression. The direct action through the HPV16 GREs is suggested to be mediated by the hormone-activated GR in association with other factors.

Regulation of Na+/H+ exchanger gene expression. Role of a novel poly(dA.dT) element in regulation of the NHE1 promoter

In this study we examine regulation of expression of the Na+/H+ exchanger promoter in L6 and NIH 3T3 cells. We have identified a highly conserved poly(dA dT)-rich region that appears to be important in regulation of expression of the NHE1 gene. Deletion or mutation of this region results in dramatic decreases in promoter activity in both L6 and NIH 3T3 cells. In addition, DNase I footprinting experiments demonstrated that this region is protected by nuclear extracts from both cell types, and gel mobility shift assays showed that a protein or proteins specifically binds to the poly(dA dT)-rich element. Using Southwestern blotting, we determined that a 33-kDa protein binds to the poly(dA dT)-containing region. Mutations that abolished protein binding to this element diminished activity of the promoter. Insertion of the poly(dA dT)-rich element into a plasmid containing the SV40 promoter demonstrated that this element can also enhance the activity of a foreign promoter. Together, the results we have presented here show that the poly(dA dT)-rich region is important in regulation of NHE1 expression in different cell types.

A developmental stage-specific histone H1 homolog of Coxiella burnetii

Two DNA-binding proteins have been detected in Coxiella burnetii by southwestern (DNA-protein) blotting. One of these, termed Hq1, is enriched in the small cell variant stage of the developmental cycle and displays compositional and primary amino acid sequence similarities to eukaryotic histone H1. C. burnetii appears to be another example of an intracellular parasite with morphologically distinct developmental forms whose nucleoid structure may be controlled by histone H1 homologs.

Identification of the DNA damage-responsive elements of the rhp51+ gene, a recA and RAD51 homolog from the fission yeast Schizosaccharomyces pombe

The Schizosaccharomyces pombe rhp51+ gene encodes a recombinational repair protein that shares significant sequence identities with the bacterial RecA and the Saccharomyces cerevisiae RAD51 protein. Levels of rhp51+ mRNA increase following several types of DNA damage or inhibition of DNA synthesis. An rhp51::ura4 fusion gene was used to identify the cis-acting promoter elements involved in regulating rhp51+ expression in response to DNA damage. Two elements, designated DRE1 and DRE2 (for damage-responsive element), match a decamer consensus URS (upstream repressing sequence) found in the promoters of many other DNA repair and metabolism genes from S. cerevisiae. However, our results show that DRE1 and DRE2 each function as a UAS (upstream activating sequence) rather than a URS and are also required for DNA-damage inducibility of the gene. A 20-bp fragment located downstream of both DRE1 and DRE2 is responsible for URS function. The DRE1 and DRE2 elements cross-competed for binding to two proteins of 45 and 59 kDa. DNase I footprint analysis suggests that DRE1 and DRE2 bind to the same DNA-binding proteins. These results suggest that the DRE-binding proteins may play an important role in the DNA-damage inducibility of rhp51+ expression.

Induction of differentiation in the cultured F9 teratocarcinoma stem cells by triterpene acids

The effects of the triterpene acids, ursolic acid and oleanolic acid, on the differentiation of F9 teratocarcinoma stem cells were studied. These agents caused the morphological change of F9 cells into endoderm cells, as did retinoic acid (RA). Moreover, expression of laminin B1, type IV collagen and retinoic acid receptor beta (RAR beta) increased in ursolic- and oleanolic-acid treated F9 cells. Since these agents are structurally similar to the glucocorticoid hormone, we studied the effects of dexamethasone, a synthetic glucocorticoid, on F9 cells. Dexamethasone also induced the morphological change and altered the expression of laminin B1, type IV collagen, and RAR beta in F9 cells. In addition, transcription of glucocorticoid receptor was detected after treatment with these three agents. According to Southwestern blot analysis, a 94-kDa protein, thought to be a glucocorticoid receptor, was detected in F9 cells treated with these agents. In a gel-shift assay, we identified protein factors binding to the glucocorticoid-responsive element (GRE) in the nuclear proteins from F9 cells treated with ursolic or oleanolic acid. The binding activity of the GRE-binding protein disappeared on the addition of unlabeled GRE oligonucleotide. Taken together, these results suggest that UA and OA can induce the differentiation of F9 cells and may regulate the expression of differentiation-specific genes, probably by forming a complex with the glucocorticoid receptor or its analogous nuclear receptor.

Multiple human papillomavirus type 16 glucocorticoid response elements functional for transformation, transient expression, and DNA-protein interactions

We have previously shown that human papillomavirus type 16 (HPV-16) can efficiently transform primary baby rat kidney cells in the presence of the steroid hormones progesterone and the glucocorticoid dexamethasone. To study this effect of hormone, different combinations of the previously identified glucocorticoid response element (GRE) at nucleotide 7640 of HPV-16 and the other two GREs that we have recently identified, at nucleotides 7385 and 7474, were mutated. The previously described GRE and the other two GREs were shown to be functional for the induction of transformation by dexamethasone. In addition, transient assays in cervical HeLa cells demonstrated the functional importance of the three individual GREs. Assays for in vitro interaction demonstrated the specific binding of a 97-kDa protein, the glucocorticoid receptor, to both recently identified HPV-16 GREs.

Both a ubiquitous factor mTEF-1 and a distinct muscle-specific factor bind to the M-CAT motif of the myosin heavy chain beta gene

The A element, a fourteen base pair sequence in the rabbit myosin heavy chain (HC) beta promoter (-276/-263), contains the M-CAT motif, a cis-acting element found in several muscle-specific genes. The A element is essential for muscle-specific transcription of the myosin HC beta gene. Recently, we have identified both muscle-specific and ubiquitous factors (A1 and A2 factors, respectively) that bind to the A element. Since the sequence of the A element is very similar to the GTIIC motif in the SV40 enhancer, we examined the relationship between A-element-binding factors and a GTIIC binding factor TEF-1, recently isolated from HeLa cells. The GTIIC motif was bound by the A1 and A2 factors in muscle nuclear extracts and competed with the A element for DNA-protein complex formation. Antibody against human TEF-1 'supershifted' the ubiquitous A2 factor-DNA complex, but did not alter the mobility of the muscle-specific A1 factor-DNA complex. We isolated a murine cDNA clone (mTEF-1) from a cardiac cDNA library. The clone is highly homologous to Hela cell TEF-1. The in vitro transcription/translation product of mTEF-1 cDNA bound to the A element, and the DNA binding property of mTEF-1 was identical to that of the A2 factor. Transfection of mTEF-1 cDNA into muscle and non-muscle cells confirmed that mTEF-1 corresponds to A2, but not to A1 factors. The mTEF-1 mRNA is expressed abundantly in skeletal and cardiac muscles, kidney and lung, but it is also expressed at lower levels in other tissues. These results suggest that the M-CAT binding factors consist of two different factors; the ubiquitous A2 is encoded by mTEF-1, but the muscle-specific A1 factor is distinct from mTEF-1.

Protein-DNA interactions in the cAMP responsive promoter region of the murine ornithine decarboxylase gene

To evaluate the function of the murine ornithine decarboxylase (ODC) gene promoter, expression of chimeric ODC-chloramphenicol acetyltransferase (CAT) plasmids (pODCcat) containing 1,658 nt of the ODC promoter sequence and its various 5'-deletions was analyzed. In transient expression assays with NIH/3T3 mouse cells, pODCcat constructs exhibited fairly strong promoter activity yielding CAT values up to 40% of those obtained with the viral promoter RSV. Interestingly, 5'-deletions of the pODCcat constructs increased the promoter activity over that achieved using the entire 1.6-kb 5'-flanking region, with the highest activity being observed with about 750 nt of the ODC promoter. This finding suggests that the distal part of the promoter includes DNA elements which are involved in repressing its function. The promoter region could be deleted down to the proximal 97 nt and still be stimulated by cAMP to the same extent as the 1.6-kb promoter. DNase I footprinting and methylation interference studies showed that a specific protein binds to the region from -59 to -39, which encompasses a DNA motif resembling the consensus cyclic AMP response element (CRE). However, comparative gel retardation and Southwestern blotting experiments with the putative ODC-CRE and the somatostatin promoter CRE indicated that the 70-kDa protein interacting with the CRE-like element of the ODC promoter is different from the well-characterized nuclear CRE-binding protein CREB.

NF-AB, a liver-specific and cytokine-inducible nuclear factor that interacts with the interleukin-1 response element of the rat alpha 1-acid glycoprotein gene

The 142-bp cytokine response element of the rat alpha 1-acid glycoprotein (AGP) gene is a complex of several additively contributing regulatory sequences. By using deletions and point mutations, a minimal interleukin-1 (IL-1) response element was localized to the region from positions 1 to 36 within the 5'-most AB fragment of the cytokine response element. Two distinct sequence motifs were contained within this element, both of which were required to achieve full IL-1 response in rat and human hepatoma cells. This element showed a minor response to phorbol ester treatment only in human hepatoma cells. Southwestern (DNA-protein) blot analysis of nuclear proteins of rat liver and hepatoma cells revealed the presence of a heat-labile nuclear factor (NF-AB). NF-AB migrated as a basic protein with an apparent molecular mass of 37 kDa and bound specifically to the DNA sequence at positions 10 to 37 of the AB fragment. The NF-AB binding activity was detected neither in the cytoplasmic fraction of rat hepatoma cells nor in nuclear extracts from control or acute-phase rat kidney. The binding activity of NF-AB correlated with the transcriptional activity of the endogenous AGP gene in rat liver and hepatoma cells. Nuclear extract from human HepG2 cells showed a similar binding activity with an apparent molecular mass of 34.5 kDa. The human NF-AB binding activity was detectable only after 13 h of cytokine treatment and was not induced by phorbol ester. Tissue distribution, DNA sequence binding specificity, and kinetics of cytokine induction of NF-AB do not coincide with the characteristics of any other described factors that have been associated with cytokine regulation. Therefore, NF-AB is considered a new candidate involved in IL-1 regulation of the rat AGP gene.

NF-AB, a liver-specific and cytokine-inducible nuclear factor that interacts with the interleukin-1 response element of the rat alpha 1-acid glycoprotein gene

The 142-bp cytokine response element of the rat alpha 1-acid glycoprotein (AGP) gene is a complex of several additively contributing regulatory sequences. By using deletions and point mutations, a minimal interleukin-1 (IL-1) response element was localized to the region from positions 1 to 36 within the 5'-most AB fragment of the cytokine response element. Two distinct sequence motifs were contained within this element, both of which were required to achieve full IL-1 response in rat and human hepatoma cells. This element showed a minor response to phorbol ester treatment only in human hepatoma cells. Southwestern (DNA-protein) blot analysis of nuclear proteins of rat liver and hepatoma cells revealed the presence of a heat-labile nuclear factor (NF-AB). NF-AB migrated as a basic protein with an apparent molecular mass of 37 kDa and bound specifically to the DNA sequence at positions 10 to 37 of the AB fragment. The NF-AB binding activity was detected neither in the cytoplasmic fraction of rat hepatoma cells nor in nuclear extracts from control or acute-phase rat kidney. The binding activity of NF-AB correlated with the transcriptional activity of the endogenous AGP gene in rat liver and hepatoma cells. Nuclear extract from human HepG2 cells showed a similar binding activity with an apparent molecular mass of 34.5 kDa. The human NF-AB binding activity was detectable only after 13 h of cytokine treatment and was not induced by phorbol ester. Tissue distribution, DNA sequence binding specificity, and kinetics of cytokine induction of NF-AB do not coincide with the characteristics of any other described factors that have been associated with cytokine regulation. Therefore, NF-AB is considered a new candidate involved in IL-1 regulation of the rat AGP gene.

Identification of a multiprotein complex interacting with the c-fos serum response element

The serum response element (SRE) is essential for serum and growth factor stimulation of the c-fos gene. We have examined the nuclear proteins, obtained from tissues with elevated expression of the c-fos gene (proliferating rat liver and hepatocarcinoma), that bind to the SRE sequence. A synthetic oligonucleotide containing the SRE sequence from the mouse c-fos gene promoter (-299 to -322) was radioactively labeled, used as a probe for the mobility shift assay and Southwestern (DNA-protein) blotting, and also used for sequence-specific affinity chromatography. We have identified a group of nuclear proteins of molecular sizes 36, 45, 62, 67, 72, and 112 kDa capable of interacting with the SRE sequence. The 36-, 67-, and 112-kDa proteins have DNA-binding properties, but the presence of the others in the SRE-protein complex could be the result of protein-protein interaction. All of these protein factors were present in nuclei obtained from intact and proliferating rat liver as well as from 5123tc Morris hepatoma. The DNA-binding activity (on Southwestern blots) of the 67- and 112-kDa proteins was not affected by alkaline phosphatase treatment, but the ability of the dephosphorylated nuclear proteins to form the complex with the SRE sequence under gel shift assay conditions was severely impaired. The same alkaline phosphatase treatment completely abolished the DNA-binding properties of the c-fos cyclic AMP-responsive element-specific proteins. Therefore, transcriptional activation of the c-fos gene at the SRE must require the presence of a multiprotein complex the formation of which is governed by phosphorylation. The binding of the 67- and 62-kDa proteins to the c-fos SRE has been previously reported; however, the 36-. 45-, 72-, and 112-kDa proteins are novel factors involved in the multifaceted regulation of c-fos gene expression in vivo.

Identification of a multiprotein complex interacting with the c-fos serum response element

The serum response element (SRE) is essential for serum and growth factor stimulation of the c-fos gene. We have examined the nuclear proteins, obtained from tissues with elevated expression of the c-fos gene (proliferating rat liver and hepatocarcinoma), that bind to the SRE sequence. A synthetic oligonucleotide containing the SRE sequence from the mouse c-fos gene promoter (-299 to -322) was radioactively labeled, used as a probe for the mobility shift assay and Southwestern (DNA-protein) blotting, and also used for sequence-specific affinity chromatography. We have identified a group of nuclear proteins of molecular sizes 36, 45, 62, 67, 72, and 112 kDa capable of interacting with the SRE sequence. The 36-, 67-, and 112-kDa proteins have DNA-binding properties, but the presence of the others in the SRE-protein complex could be the result of protein-protein interaction. All of these protein factors were present in nuclei obtained from intact and proliferating rat liver as well as from 5123tc Morris hepatoma. The DNA-binding activity (on Southwestern blots) of the 67- and 112-kDa proteins was not affected by alkaline phosphatase treatment, but the ability of the dephosphorylated nuclear proteins to form the complex with the SRE sequence under gel shift assay conditions was severely impaired. The same alkaline phosphatase treatment completely abolished the DNA-binding properties of the c-fos cyclic AMP-responsive element-specific proteins. Therefore, transcriptional activation of the c-fos gene at the SRE must require the presence of a multiprotein complex the formation of which is governed by phosphorylation. The binding of the 67- and 62-kDa proteins to the c-fos SRE has been previously reported; however, the 36-. 45-, 72-, and 112-kDa proteins are novel factors involved in the multifaceted regulation of c-fos gene expression in vivo.

FVB/N: an inbred mouse strain preferable for transgenic analyses

FVB/N mice offer a system suitable for most transgenic experiments and subsequent genetic analyses. The inbred FVB/N strain is characterized by vigorous reproductive performance and consistently large litters. Moreover, fertilized FVB/N eggs contain large and prominent pronuclei, which facilitate microinjection of DNA. The phenotype of large pronuclei in the zygote is a dominant trait associated with the FVB/N oocyte but not the FVB/N sperm. In experiments to generate transgenic mice, the same DNA constructs were injected into three different types of zygotes: FVB/N, C57BL/6J, and (C57BL/6J x SJL/J)F1. FVB/N zygotes survived well after injection, and transgenic animals were obtained with efficiencies similar to the F1 zygotes and much better than the C57BL/6J zygotes. Genetic markers of the FVB/N strain have been analyzed for 44 loci that cover 15 chromosomes and were compared with those of commonly used inbred strains. In addition to the albino FVB/N strain, pigmented congenic strains of FVB/N are being constructed. These features make the FVB/N strain advantageous to use for research with transgenic mice.

Specificity of autoantibodies to histone H1 in SLE: relationship to DNA-binding domains

Autoantibodies in the sera of patients with systemic lupus erythematosus were examined with respect to their specificity for proteolytic fragments of histone H1 that retain, or do not retain, DNA-binding domains. 16 of 31 sera contained IgG and IgM antibodies to histone H1. IgM antibodies to H1 in 8 sera (50%) were directed at 18 kD and 20 kD alpha-chymotrypic H1 fragments that bore binding sites for DNA, as identified by staining immunoblots containing the fragments with ssDNA plus 6/0, a mouse monoclonal antibody against ssDNA, IgM with this type of histone H1 specificity did not react with comparably-sized V8 protease fragments of H1. IgM antibodies to H1 in the other patients were directed against entirely different epitopes which were preserved in V8 protease digests of H1. In serial studies of three patients during different phase of their SLE, the level of antibodies against the 18 kD and 20 kD histone H1 fragments varied in parallel with the level of anti-ssDNA antibodies in one and varied inversely in the other two. The data suggest that a significant proportion of autoantibodies to histone H1 are directed at a limited number of epitopes localized to H1 fragments containing DNA-binding sites.

Increased expression and DNA-binding activity of transcription factor Sp1 in doxorubicin-resistant HL-60 leukemia cells

The processes responsible for the multidrug-resistant (Mdr) phenotype in Adriamycin (doxorubicin)-resistant HL-60 leukemia cells (HL-60/AR) are not defined. Since enhanced transcription of resistance-related proteins is associated with Mdr cells, we sought to determine whether changes in the expression of specific transcription factors were a feature characteristic of the Mdr process. Nuclear extracts were prepared from wild-type and resistant cells and compared for their ability to bind DNA consensus sequences for the transcription factors Sp1 and NF kappa B contained in the 5' long terminal repeat region of human immunodeficiency virus type 1. Southwestern (DNA-protein) blots showed a family of DNA-binding proteins of 105 kilodaltons (kDa) that were present only in HL-60/AR cells. Competitive gel shift assays indicated that these factors were related to transcription factor Sp1, and immunoblotting with an Sp1 antibody identified this factor as Sp1. DNase footprinting of the promoter region in the human immunodeficiency virus type 1 5' long terminal repeat showed that protection occurred at two Sp1 sites as well as two NF kappa B sites and the trans-acting region with nuclear extracts only from resistant cells. Preliminary evidence also suggests that phosphorylation may play a negative regulatory role in the activity of Sp1, since calf intestine alkaline phosphatase stimulated the DNA-binding activity of Sp1 in vitro. These results indicate that HL-60/AR cells contain an abundance of DNA-binding proteins, particularly Sp1, which probably interact with other cis-acting regulatory proteins in a cooperative manner.

Increased expression and DNA-binding activity of transcription factor Sp1 in doxorubicin-resistant HL-60 leukemia cells

The processes responsible for the multidrug-resistant (Mdr) phenotype in Adriamycin (doxorubicin)-resistant HL-60 leukemia cells (HL-60/AR) are not defined. Since enhanced transcription of resistance-related proteins is associated with Mdr cells, we sought to determine whether changes in the expression of specific transcription factors were a feature characteristic of the Mdr process. Nuclear extracts were prepared from wild-type and resistant cells and compared for their ability to bind DNA consensus sequences for the transcription factors Sp1 and NF kappa B contained in the 5' long terminal repeat region of human immunodeficiency virus type 1. Southwestern (DNA-protein) blots showed a family of DNA-binding proteins of 105 kilodaltons (kDa) that were present only in HL-60/AR cells. Competitive gel shift assays indicated that these factors were related to transcription factor Sp1, and immunoblotting with an Sp1 antibody identified this factor as Sp1. DNase footprinting of the promoter region in the human immunodeficiency virus type 1 5' long terminal repeat showed that protection occurred at two Sp1 sites as well as two NF kappa B sites and the trans-acting region with nuclear extracts only from resistant cells. Preliminary evidence also suggests that phosphorylation may play a negative regulatory role in the activity of Sp1, since calf intestine alkaline phosphatase stimulated the DNA-binding activity of Sp1 in vitro. These results indicate that HL-60/AR cells contain an abundance of DNA-binding proteins, particularly Sp1, which probably interact with other cis-acting regulatory proteins in a cooperative manner.

The influence of vitamin B6 on the structure and function of the glucocorticoid receptor

Pyridoxal phosphate influences several properties of steroid hormone receptors in vitro, but its role in vivo has not been clearly established. In an effort to address this issue, we have investigated the in vivo effects of vitamin B6 on the physical properties and biological function of the human glucocorticoid receptor. We demonstrate that vitamin B6 treatment of whole cells in culture produces an alteration in the isoelectric point of the receptor, as well as changes in the steroid and DNA binding capacities. Furthermore, glucocorticoid dependent transcriptional activation properties of the receptor are also altered by modulation of the vitamin B6 status. High concentrations of vitamin B6 suppress activation of transcription, while vitamin deficiency enhances responsiveness to steroid hormone. Together, these studies imply a physiological role for vitamin B6 in glucocorticoid hormone action.

VIP: molecular biology and neurobiological function

In the mammalian brain, a major regulatory peptide is vasoactive intestinal peptide (VIP). This 28 amino acid peptide, originally isolated from the porcine duodenum, was later found in the central and peripheral nervous systems and in endocrine cells, where it exhibits neurotransmitter and hormonal roles. Increasing evidence points to VIP's importance as a mediator or a modulator of several basic functions. Thus, VIP is a major factor in brain activity, neuroendocrine functions, cardiac activity, respiration, digestion, and sexual potency. In view of this peptide's importance, the mechanisms controlling its production and the pathways regulating its functions have been reviewed. VIP is a member of a peptide family, including peptides such as glucagon, secretin, and growth hormone releasing hormone. These peptides may have evolved by exon duplication coupled with gene duplication. The human VIP gene contains seven exons, each encoding a distinct functional domain on the protein precursor or the mRNA. VIP gene transcripts are mainly found in neurons or neuron-related cells. VIP gene expression is regulated by neuronal and endocrine signals that contribute to its developmental control. VIP exerts its function via receptor-mediated systems, activating signal transduction pathways, including cAMP. It can act as a neurotransmitter, neuromodulator, and a secretagog. As a growth and developmental regulator, VIP may have a crucial effect as a neuronal survival factor. We shall proceed from the gene to its multiple functions.

Resolution and partial characterization of factors required for in vitro transcription by mammalian RNA polymerase II

Multiple protein factors from HeLa cells are necessary for the accurate initiation of transcription on minimal promoters in vitro. We have partially purified these factors by chromatographic methods. In addition to RNA polymerase II, six factors A-F (FA, FB, FC, FD, FE, and FF) necessary for initiation at the beta-globin promoter start site in vitro have been identified. Certain of these (FA, FC, and FE) have been purified to near homogeneity. The present purification scheme yields sufficient amounts of purified material for the more detailed characterization and cloning of the genes for these activities. Among these factors, FD and FF were required with template DNA at an early step of formation of the initiation complex, whereas FB, FA together with FC, and FE were effective when added at successively later stages in the process of complex formation.

In vitro characterization of tissue-specific nuclear proteins preferentially bound to the mouse beta-globin gene during MEL cell terminal differentiation

Using DNA restriction fragments of the mouse beta-globin gene and other promoter-containing DNA fragments (LTR-MMTV and pBR322) as controls, we have characterized by protein blotting, in extracts of mouse erythroleukemia (MEL) cells, specific nuclear DNA binding proteins with a preferential affinity for the beta-globin DNA. Some proteins (110 and 75 kDa) appear in differentiated MEL cells while others (100, 95, and 35 kDa) are present in immature MEL and normal erythroblast cells and bind selectively to the far-upstream region of the gene. These proteins could modulate either positively or negatively the expression of the beta-globin gene and maybe, of other genes, during the terminal differentiation of erythroid cells.

An Auxin-Regulated Gene of Arabidopsis thaliana Encodes a DNA-Binding Protein

We have isolated a single-copy gene from the plant Arabidopsis thaliana, called dbp, which encodes a lysine-rich, DNA-binding protein. The Dbp protein has a molecular weight and a composition resembling histone H1. When the dbp gene was expressed in bacteria, the protein product bound DNA nonspecifically. The dbp gene is expressed constitutively in all parts of the plant but is induced five times above this basal level in apical zones. In vitro hormone-depletion experiments showed that the expression in the shoot apex could be induced by exogenous auxin. In situ hybridizations in the root apex indicated that the expression of dbp is enhanced in the region of cell division.

Detection of a nuclear protein that interacts with a metal regulatory element of the mouse metallothionein 1 gene

Metallothionein (MT) genes contain multiple metal regulatory elements (MREs) that are responsible for metal induction. A protein blotting procedure and a synthetic oligonucleotide have been used to identify nuclear factors interacting with a MRE (MREd) of the mouse MT-1 gene. We report the specific binding of the probe to a protein of apparent Mr 108,000 (p108). The specificity of the interaction was demonstrated by mutation analysis and competition experiments. Furthermore, the probe contains the Sp1 consensus binding sequence 5'CCGCCC3', in addition to the MRE consensus sequence, 5'TGCAC3', and we show that a Simian Virus 40 DNA fragment which contains six Sp1 binding sites did not bind p108 nor did it compete for the protein(s) interacting with MREd in a DNA footprinting assay. These results show that a metal regulatory element of the mouse MT-1 gene interacts specifically with a nuclear protein of Mr 108,000 and that this protein is distinct from the transcription factor Sp1.