The macrophage and B cell-specific transcription factor PU.1 is related to the ets oncogene

The murine L-plastin gene promoter: identification and comparison with the human L-plastin gene promoter

Plastins (or fimbrins) are a family of actin-binding proteins that are conserved from yeast to humans. In mammals, three tissue-specific plastin isoforms have been identified. The L isoform (L-plastin) is normally expressed only in leukocytes but is also found in >90% of neoplastic nonleukocyte human cells. Because L-plastin expression in tissue-specifically regulated in both humans and rodents, it is likely that similar mechanisms regulate L-plastin gene expression in human and rodent cells and that they could be identified by comparing the function and nucleotide sequences of the human and murine L-plastin gene promoters. Previously, we reported the isolation and characterization of the human L-plastin gene promoter. In this study, we isolated a murine L-plastin 5' end cDNA and used it as a probe to isolate several murine genomic clones. A representative clone contained 7 kb of the flanking region, 0.1 kb of the first exon, and 9.9 kb of the first intron. A continuous 1,354-bp sequence was identified around the first exon. Five transcription initiation sites were found 40 to 73 bp downstream from a perfect TATA box. Alignment of the sequence with its human counterpart revealed approximately 60% homology in a 1-kb region spanning the first exon and the flanking region. The TATA box, one ER binding site, and two ETS binding sites were completely conserved. An Sp1 binding sequence in the human promoter was partially conserved in the murine promoter but could still bind to Sp1. A second ER binding sequence, lying 5' adjacent to the TATA box in the human promoter, was conserved only at the 3' half-site in the murine promoter; the 5' half-site was changed into a potential AP1 binding site. This AP1/ER hybrid sequence was incapable of binding to ER. However, both human and murine promoters were found to function equally well in either human or murine leukocytes.

The family of the small leucine-rich proteoglycans: key regulators of matrix assembly and cellular growth

The focus of this review is on conceptual and functional advances in our understanding of the small leucine-rich proteoglycans. These molecules belong to an expanding gene class whose distinctive feature is a structural motif, called the leucine-rich repeat, found in an increasing number of intracellular and extracellular proteins with diverse biological attributes. Three-dimensional modeling of their prototype protein core proposes a flexible, arch-shaped binding surface suitable for strong and distinctive interactions with ligand proteins. Changes in the properties of individual proteoglycans derive from amino acid substitutions in the less conserved surface residues, changes in the number and length of the leucine-rich repeats, and/or variation in glycosylation. These proteoglycans are tissue organizers, orienting and ordering collagen fibrils during ontogeny and in pathological processes such as wound healing, tissue repair, and tumor stroma formation. These properties are rooted in their bifunctional character: the protein moiety binding collagen fibrils at strategic loci, the microscopic gaps between staggered fibrils, and the highly charged glycosaminoglycans extending out to regulate interfibrillar distances and thereby establishing the exact topology of fibrillar collagens in tissues. These proteoglycans also interact with soluble growth factors, modulate their functional activity, and bind to cell surface receptors. The latter interaction affects cell cycle progression in a variety of cellular systems and could explain the purported changes in the expression of these gene products around the invasive neoplastic cells and in regenerating tissues.

Regulation of CSF-1 receptor expression

Cells of the mononuclear phagocyte lineage possess receptors for macrophage colony-stimulating factor (CSF-1) encoded by the c-fms protooncogene and respond to CSF-1 with increased survival, growth, differentiation, and reversible changes in function. The c-fms gene is itself a macrophage differentiation marker. In whole mount analyses of mRNA expression in embryos, c-fms is expressed at very high levels on placental trophoblasts. It is detectable on individual cells in the yolk sac around 8.5 to 9 days postcoitus, appears on isolated cells in the head of the embryo around 9.5 dpc, and appears on numerous cells throughout the embryo by day 10.5. The extent of c-fms expression is much greater than for other macrophage-specific genes including lysozyme and a macrophage-specific protein tyrosine phosphatase. Our studies of the cis-acting elements of the c-fms promoter have indicated a key role for collaboration between the macrophage-specific transcription factor, Pu.1, which functions in determining the site of transcription initiation, and other members of the Ets transcription factor family. This is emerging as a common pattern in macrophage-specific promoters. We have shown that two PU box elements alone can function as a macrophage-specific promoter. The activity of both the artificial promoter and the c-fms promoter is activated synergistically by coexpression of Pu.1 and another Ets factor, c-Ets-2. A 3.5kb c-fms exon 2 promoter (but not the 300bp proximal promoter) is also active in a wide diversity of tumor cell lines. The interesting exception is the melanoma cell line K1735, in which the promoter is completely shut down and expression of c-fms causes growth arrest and cell death. The activity of the exon 2 promoter in these nonmacrophages is at least as serum responsive as the classic serum-responsive promoter of the c-fos gene. It is further inducible in nonmacrophages by coexpression of the c-fms product. Unlike other CSF-1/c-fms-responsive promoters, the c-fms promoter is not responsive to activated Ras even when c-Ets-2 is coexpressed. In most lines, production of full length c-fms is prevented by a downstream intronic terminator, but in Lewis lung carcinoma, read-through does occur, and expression of both c-fms and other macrophage-specific genes such as lysozyme and urokinase becomes detectable in conditions of serum deprivation.

Specific binding of the ETS-domain protein to the interferon-stimulated response element

Interferon (IFN) activation of genes bearing an IFN-stimulated response element (ISRE) is regulated through binding of IFN-stimulated gene factors (ISGF) to the ISRE found in many IFN-stimulated genes. Using a multimerized human 2-5A synthetase ISRE as probe, we screened lambda gt11 expression libraries for cDNA encoding ISRE-binding activity and isolated a clone for murine proto-oncogene ets-1. The Ets-1 protein binds to the 2-5A synthetase ISRE at a site that also binds ISGF3, a multicomponent factor whose ISRE binding correlates with IFN-induced activation of transcription from ISRE-containing promoters. IFN-induced ISGF3 complex formation on the ISRE can be inhibited by specific Ets-1 antibody. Coexpression of Ets-1 represses ISRE-dependent reporter activity, suggesting that one or more members of the Ets protein family may negatively regulate transcriptional activity mediated by the 2-5A synthetase ISRE.

Human proteinase-3 expression is regulated by PU.1 in conjunction with a cytidine-rich element

Human proteinase-3 is one of three serine proteinases present in the azurophil granules of polymorphonuclear leukocytes along with elastase and cathepsin G. Proteinase-3 gene expression is confined to the promyelocytic stage of polymorphonuclear leukocyte maturation. The present investigation identifies elements responsible for this highly controlled tissue- and developmental-specific expression of proteinase-3. Within the first 200 base pairs of the proteinase-3 promoter, two elements were identified as important for expression, these elements at -101 and -190 confer the majority of the activity. The element at -101 has a PU.1 consensus. It binds a myeloid nuclear protein of approximately 45 kDa that "supershifts" with PU.1 antibody and is competed by the CD11b PU.1 element. The element at -190 has a core sequence of CCCCGCCC (CG element). The cytidines but not the guanidine are essential for promoter activity. The CG element binds a second nuclear protein with a molecular mass of approximately 40 kDa that is found in cells of myeloid lineage as well as non-myeloid HeLa cells. However, the proteinase-3 promoter is not active in HeLa cells which suggests that the CG element alone is not sufficient for proteinase-3 gene expression. Maturation of promyelocytic cells results in an inhibition of proteinase-3 gene expression and a reduction in nuclear protein binding to the PU.1 and CG elements. Similar elements occur in the elastase and cathepsin G promoters. Using the elastase and cathepsin G PU.1 and CG-like elements as probes results in identical band-shift patterns to that obtained with proteinase-3 PU.1 and CG elements. These data suggest that there is cooperative interaction between a PU.1 and a CG element with a consensus of CCCCXCCC and that they are important control elements for tissue- and developmental-specific expression of azurophil serine proteinases of polymorphonuclear leukocytes.

Identification of the promoter for the gene encoding the bifunctional enzyme, peptidylglycine alpha-amidating monooxygenase

The gene encoding rat peptidylglycine alpha-amidating monooxygenase (PAM) contains 26 protein-coding exons. We identified two non-overlapping genomic clones encoding the 5' untranslated region (UTR) of the PAM gene. Exon 1 has 69 nucleotides flanked by perfect splice acceptor and donor sites, with a TATA motif 25 nucleotides upstream. Exon 0 lacks TATA or CAAT motifs and is embedded in a G + C-rich 800-nucleotide CpG island. The major products identified by RNase protection initiated in exon 0; only a minority of mRNAs initiated in exon 1. 5'-rapid amplification of cDNA ends (RACE) identified the same major transcriptional start sites in exon 0 in the atrium and neurointermediate pituitary. The 2.0-kb fragment upstream of exon 0 and the 1.3-kb fragment upstream of exon 1 were placed upstream of a luciferase-based reporter gene in both sense and antisense orientations. Expression of luciferase was observed in neuroendocrine and nonneuroendocrine cells with both sense constructs. A 0.2-kb fragment of the exon 0 PAM promoter containing multiple GC box elements supported expression of luciferase activity in all cell types. Expression of reporter genes in cells that do not normally express PAM suggests a need for more upstream or intronic information, a role for methylation, or a need for chromatin scaffolding for tissue-specific expression of the endogenous gene.

The structure of the gene for the second chain of the human interferon-gamma receptor

The gene for the second chain of the human interferon-gamma receptor was analyzed from cosmid DNA clones. The gene spans over 33 kilobases of DNA and contains seven exons. The signal peptide is encoded by exons 1 and 2, the extracellular domain by exons 2, 3, 4, 5, and by part of 6. Exon 6 also encodes the whole transmembrane domain and part of the intracellular domain. Exon 7 encodes the remainder of the intracellular domain and contains the 3'-untranslated region. The sequences at the exon/intron boundaries are well conserved with respect to canonical acceptor/donor sites (AG/GT). The 5'-flanking region was sequenced and analyzed for transcription factor binding sites. No TATA or CAAT boxes in the promoter region were identified. Consistent with the lack of a TATA box, analysis of the mRNAs by primer extension showed multiple transcription start sites. Promoter activity of the 5'-flanking region was investigated with a luciferase reporter gene and the cytomegalovirus minimal promoter. Segments of the 5' region with promoter activity were identified.

In vivo transcriptional regulation of the human immunodeficiency virus in the central nervous system in transgenic mice

Human immunodeficiency virus type 1 (HIV-1) causes infections of the central nervous system (CNS) and has been implicated as the causative agent of AIDS-associated encephalopathy and the AIDS dementia complex. The development of in vivo models of HIV-1-mediated gene expression has shown that the HIV long terminal repeat (LTR) from the viral isolate HIV(JR-CSF) specifically supports gene expression in adult and developing CNS. To determine the molecular basis for HIV-1 developmental CNS gene expression, in vivo footprinting analysis by the ligation-mediated PCR technique was performed on CNS tissue from the brain stem of a transgenic mouse. The association of cellular proteins in the CNS with sequences in the LTR was found over sequences that defined the TATA region, the Sp-1 and NF-kappaB sites, and two upstream regions (-111 to -150 and -260 to -300). A purine-rich sequence at positions -256 to -296 of the HIV(JR-CSF) LTR but not of the HIV(IIIB) LTR specifically bound protein in nuclear extracts of newborn brain tested in electrophoretic mobility shift assays. No specific protein binding was observed to this region in liver or HeLa cell nuclear extracts. This suggests the presence of a newly identified transcription factor involved in regulation of HIV-1 gene expression in the CNS.

ELF-1 interacts with and transactivates the IgH enhancer pi site

We previously identified a B-cell-specific regulatory element in the immunoglobulin heavy chain (IgH) enhancer, pi, with striking similarity to binding sites for ets-related transcription factors. Whereas the ability of ets-related factors to bind to and transactivate the pi site has been substantiated, the identification of the particular member of the ets family responsible for B-cell-specific regulation of the pi site has remained controversial. We have used antibodies specific for individual members of the ets family to evaluate which ets-related factor in B-cell nuclear extracts interacts with the IgH pi site. We present strong evidence that ELF-1 is highly expressed in B-cells and is one of two major factors specifically interacting with the murine IgH enhancer pi site in B-cell nuclear extracts. Binding of ELF-1 correlates with activity of the pi site, since mutations abolishing function of pi also inhibit binding of ELF-1. Furthermore, we demonstrate that ELF-1 can transactivate the IgH enhancer in HeLa cells, suggesting a role for ELF-1 in B-cell-specific IgH gene expression.

Synergistic up-regulation of the myeloid-specific promoter for the macrophage colony-stimulating factor receptor by AML1 and the t(8;21) fusion protein may contribute to leukemogenesis

AML1 is involved in the (8;21) translocation, associated with acute myelogenous leukemia (AML)-type M2, which results in the production of the AML1-ETO fusion protein: the amino-terminal 177 amino acids of AML1 and the carboxyl-terminal 575 amino acids of ETO. The mechanism by which AML1-ETO accomplishes leukemic transformation is unknown; however, AML1-ETO interferes with AML1 transactivation of such AML1 targets as the T-cell receptor beta enhancer and the granulocyte-macrophage colony-stimulating factor promoter. Herein, we explored the effect of AML1-ETO on regulation of a myeloid-specific AML1 target, the macrophage colony-stimulating factor (M-CSF) receptor promoter. We found that AML1-ETO and AML1 work synergistically to transactivate the M-CSF receptor promoter, thus exhibiting a different activity than previously described. Truncation mutants within the ETO portion of AML1-ETO revealed the region of ETO necessary for the cooperativity between AML1 and AML1-ETO lies between amino acids 347 and 540. Endogenous M-CSF receptor expression was examined in Kasumi-1 cells, derived from a patient with AML-M2 t(8;21) and the promonocytic cell line U937. Kasumi-1 cells exhibited a significantly higher level of M-CSF receptor expression than U937 cells. Bone marrow from patients with AML-M2 t(8;21) also exhibited a higher level of expression of M-CSF receptor compared with normal controls. The upregulation of M-CSF receptor expression by AML1-ETO may contribute to the development of a leukemic state in these patients.

Redox regulation of GA-binding protein-alpha DNA binding activity

We have investigated the reduction/oxidation (redox) regulation of the heteromeric transcription factor GA-binding protein (GABP). GABP, also known as nuclear respiratory factor 2, regulates the expression of nuclear encoded mitochondrial proteins involved in oxidative phosphorylation, including cytochrome c oxidase subunits IV and Vb, as well as the expression of mitochondrial transcription factor 1. GABP is composed of two subunits, the Ets-related GABP-alpha, which mediates specific DNA binding, and GABP-beta, which forms heterodimers and heterotetramers on DNA sequences containing the PEA3/Ets motif ((C/A)GGA(A/T)(G/A)). We demonstrate here that GABP DNA binding activity and GABP-dependent gene expression in 3T3 cells are inhibited by pro-oxidant conditions. DNA binding of recombinant GABP-alpha was activated by chemical reduction (dithiothreitol) and by thioredoxin; however, GSSG inhibited GABP DNA binding activity. Treatment of GABP-alpha, but not GABP-beta1, with sulfhydryl-alkylating agents also inhibited GABP DNA binding activity. Our results suggest that GABP DNA binding activity is redox-regulated in vivo, possibly by thioredoxin-mediated reduction and by GSSG-mediated oxidation of the GABP-alpha subunit. The regulation of GABP (nuclear respiratory factor 2) DNA binding activity by cellular redox changes provides an important link between mitochondrial and nuclear gene expression and the redox state of the cell.

An interleukin-2 signal relieves BSAP (Pax5)-mediated repression of the immunoglobulin J chain gene

Cytokine regulation of B cell development was analyzed using interleukin-2 (IL-2)-induced transcription of the J chain gene as a model system. A nuclear target of the IL-2 signal was identified as the Pax5 transcription factor, BSAP, which recognizes a negative regulatory motif in the J chain promoter. Functional assays showed that BSAP mediates the silencing of the J chain gene during the early stages of B cell development, but repression is relieved during the antigen-driven stages in a concentration-dependent manner by an IL-2-induced down-regulation of BSAP RNA expression. At the low levels present in J chain-expressing plasma cells, BSAP repression could be overridden by positive-acting factors binding to down-stream J chain promoter elements. Overexpression of BSAP in these cells reversed the positive regulation and inhibited J chain gene transcription. Thus, IL-2 regulation of BSAP concentration may provide a mechanism for controlling both repressor and activator functions of BSAP during a B cell immune response.

Transformation by the Bmi-1 oncoprotein correlates with its subnuclear localization but not its transcriptional suppression activity

The bmi-1 oncogene cooperates with c-myc in transgenic mice, resulting in accelerated lymphoma development. Altering the expression of Bmi-1 affects normal embryogenesis. The protein product of bmi-1 is homologous to certain Drosophila Polycomb group proteins that regulate homeotic gene expression through alteration of chromatin structure. Chimeric LexA-Bmi-1 protein has previously been shown to repress transcription. How Bmi-1 functions in embryogenesis and whether this relates to the ability of Bmi-1 to mediate cellular transformation is unknown. We demonstrate here that Bmi-1 is able to transform rodent fibroblasts in vitro, providing a system that has allowed us to correlate its molecular properties with its ability to transform cells. We map functional domains of Bmi-1 involved in transcriptional suppression by using the GAL4 chimeric transcriptional regulator system. Deletion analysis shows that the centrally located helix-turn-helix-turn-helix-turn (HTHTHT) motif is necessary for transcriptional suppression whereas the N-terminal RING finger domain is not required. We demonstrate that nuclear localization requires KRMK (residues 230 to 233) and that the absence of nuclear entry ablates transformation. In addition, we find that the subnuclear localization of wild-type Bmi-1 to the rim of the nucleus requires the RING finger domain and correlates with its ability to transform. Our studies with Bmi-1 deletion mutants suggest that the ability of Bmi-1 to mediate cellular transformation correlates with its unique subnuclear localization but not its transcriptional suppression activity.

RREB-1, a novel zinc finger protein, is involved in the differentiation response to Ras in human medullary thyroid carcinomas

An activated ras oncogene induces a program of differentiation in the human medullary thyroid cancer cell line TT. This differentiation process is accompanied by a marked increase in the transcription of the human calcitonin (CT) gene. We have localized a unique Ras-responsive transcriptional element (RRE) in the CT gene promoter. DNase I protection indicates two domains of protein-DNA interaction, and each domain separately can confer Ras-mediated transcriptional inducibility. This bipartite RRE was also found to be Raf responsive. By affinity screening, we have cloned a cDNA coding for a zinc finger transcription factor (RREB-1) that binds to the distal RRE. The consensus binding site for this factor is CCCCAAACCACCCC. RREB-1 is expressed ubiquitously in human tissues outside the adult brain. Overexpression of RREB-1 protein in TT cells confers the ability to mediate increased transactivation of the CT gene promoter-reporter construct during Ras- or Raf-induced differentiation. These data suggest that RREB-1 may play a role in Ras and Raf signal transduction in medullary thyroid cancer and other cells.

Molecular cloning of Elk-3, a new member of the Ets family expressed during mouse embryogenesis and analysis of its transcriptional repression activity

We isolated a cDNA clone, Elk-3, that encodes a novel Ets transcription factor from 16-day mouse embryos. The deduced amino acid sequence of the protein was homologous to human ELK-1 and SAP-1. This protein, ELK-1, and SAP-1 shared some unique structural properties such as an Ets DNA-binding site in the amino-terminal region, a serum response factor interacting domain and phosphorylation sites of serine or threonine residues in the carboxy-terminal region. Northern blotting weakly revealed that two transcripts of 4 and 2.1 kb are expressed in the adult ovary and lung and a 2.1-kb transcript predominated in 8- to 14-day embryos. We assayed the transcriptional activities of Elk-3 protein on the cytokeratin EndoA enhancer containing Ets binding sites in endodermal cells. Elk-3 protein strongly repressed enhancer activity but did not affect the activity of the basal promoter in the absence of the enhancer. Furthermore, Elk-3 can suppress the activity of Ets-2 as the transcriptional activator on the EndoA enhancer. These data suggested that the Elk-3 gene product plays a role in transcriptional regulation during embryogenesis.

Regulation of the myeloperoxidase enhancer binding proteins Pu1, C-EBP alpha, -beta, and -delta during granulocyte-lineage specification

We have compared the molecular architecture and function of the myeloperoxidase upstream enhancer in multipotential versus granulocyte-committed hematopoietic progenitor cells. We show that the enhancer is accessible in multipotential cell chromatin but functionally incompetent before granulocyte commitment. Multipotential cells contain both Pu1 and C-EBP alpha as enhancer-binding activities. Pu1 is unphosphorylated in both multipotential and granulocyte-committed cells but is phosphorylated in B lymphocytes, raising the possibility that differential phosphorylation may play a role in specifying its lymphoid versus myeloid functions. C-EBP alpha exists as multiple phosphorylated forms in the nucleus of both multipotential and granulocyte-committed cells. C-EBP beta is unphosphorylated and cytoplasmically localized in multipotential cells but exists as a phosphorylated nuclear enhancer-binding activity in granulocyte-committed cells. Granulocyte colony-stimulating factor-induced granulocytic differentiation of multipotential progenitor cells results in activation of C-EBP delta expression and functional recruitment of C-EBP delta and C-EBP beta to the nucleus. Our results implicate Pu1 and the C-EBP family as critical regulators of myeloperoxidase gene expression and are consistent with a model in which a temporal exchange of C-EBP isoforms at the myeloperoxidase enhancer mediates the transition from a primed state in multipotential cells to a transcriptionally active configuration in promyelocytes.

New insights on DNA recognition by ets proteins from the crystal structure of the PU.1 ETS domain-DNA complex

Transcription factors belonging to the ets family regulate gene expression and share a conserved ETS DNA-binding domain that binds to the core sequence 5'-(C/A)GGA(A/T)-3'. The domain is similar to alpha+beta ("winged") helix-turn-helix DNA-binding proteins. The crystal structure of the PU.1 ETS domain complexed to a 16-base pair oligonucleotide revealed a pattern for DNA recognition from a novel loop-helix-loop architecture (Kodandapani, R., Pio, F., Ni. C.-Z., Piccialli, G., Klemsz, M., McKercher, S., Maki, R. A., and Ely, K. R. (1996) Nature 380, 456-460). Correlation of this model with mutational analyses and chemical shift data on other ets proteins confirms this complex as a paradigm for ets DNA recognition. The second helix in the helix-turn-helix motif lies deep in the major groove with specific contacts with bases in both strands in the core sequence made by conserved residues in alpha3. On either side of this helix, two loops contact the phosphate backbone. The DNA is bent (8 degrees) but uniformly curved without distinct kinks. ETS domains bind DNA as a monomer yet make extensive DNA contacts over 30 A. DNA bending likely results from phosphate neutralization of the phosphate backbone in the minor groove by both loops in the loop-helix-loop motif. Contacts from these loops stabilize DNA bending and may mediate specific base interactions by inducing a bend toward the protein.

Interferon regulatory factor-2 directs transcription from the gp91phox promoter

Repressor elements in the gp91(phox) promoter are necessary to restrict tissue-specific transcription to mature phagocytes. Deletion of these elements leads to significant promoter activity in cell lines such as HEL and K562 that do not normally express gp91(phox). The -100 to +12 base pair gp91(phox) promoter region is sufficient to direct maximal de-repressed transcription in these cells. However, promoter activity is dramatically decreased following a 16-base pair truncation that deletes an interferon-stimulated response element. This element interacts with IRF-1 and IRF-2, members of the interferon regulatory factor family of transcription factors. In addition, this promoter region is bound by a factor with properties similar to BID, a DNA-binding protein that also interacts with three upstream sites within the gp91(phox) promoter. Transient transfection studies using mutated promoters indicate that both the IRF and BID binding sites are required for maximal gp91(phox) promoter activity. Overexpression of IRF-1 or IRF-2 in K562 cells leads to transactivation of gp91(phox) promoter constructs, which is dependent on the presence of an intact IRF binding site. IRF-2 predominates in macrophages that express the gp91(phox) gene as well as in HEL and K562 cells. We conclude that IRF-2 and BID activate gp91(phox) promoter activity in the absence of transcriptional repression.

Pip, a lymphoid-restricted IRF, contains a regulatory domain that is important for autoinhibition and ternary complex formation with the Ets factor PU.1

Pip is a lymphoid-restricted IRF transcription factor that is recruited to composite elements within immunoglobulin light-chain gene enhancers through a specific interaction with the Ets factor PU.1. We have examined the transcriptional regulatory properties of Pip as well as the requirements for its interaction with PU.1 and DNA to form a ternary complex. We demonstrate that Pip is a dichotomous regulator; it specifically stimulates transcription in conjunction with PU.1, but represses alpha/beta-interferon-inducible transcription in the absence of PU.1. Thus, during B-cell activation and differentiation, Pip may function both as an activator to promote B cell-specific gene expression and as a repressor to inhibit the antiproliferative effects of alpha/beta-interferons. Mutational analysis of Pip reveals a carboxy-terminal segment that is important for autoinhibition of DNA binding and ternary complex formation. A domain of Pip containing this segment confers autoinhibition and PU.1-dependent binding activity to the DNA-binding domain of the related IRF family member, p48. On the basis of these and other data we propose a model for PU.1/Pip ternary complex formation.

Characterization of the human myeloid cell nuclear differentiation antigen gene promoter

MNDA (myeloid cell nuclear differentiation antigen) is an interferon alpha regulated nuclear protein expressed only in cells of the human myelomonocytic lineage. To identify mechanisms responsible for this lineage-specific and interferon-regulated expression, the 5' flanking sequence of the gene has been characterized. Two interferon-stimulated response elements (ISRE) flank a multiple transcription start site region identifying MNDA as a TATA-less interferon-regulated gene. Other DNA elements present include a cluster of Myb sites, several Ets, an Ets related PU.1 site and an Sp1 site located within 600 bp of the transcription start sites. In addition, DNA methylation was revealed as one of the possible factors in establishing MNDA expression. The 5' flanking sequence has promoter activity which is elevated by interferon alpha. The findings indicate that MNDA expression is regulated by mechanisms similar to other myelomonocytic cell specific genes and genes up-regulated by interferon alpha.

Kainic acid increases the expression of the prohormone convertases furin and PC1 in the mouse hippocampus

Prohormone convertases (PCs) belong to the mammalian family of subtilisin/kexin-like enzymes which have been implicated in the posttranslational processing of precursor proteins. Several PCs are produced in the central and peripheral nervous system, and only a few specific precursor-substrates have been identified in vivo. In the nervous system, PCs may be involved in intracellular processing of precursors for neuropeptides, hormones and neurotrophic factors, including nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF). To study the interrelationships between the convertases furin, PC1 and PC2, and the neurotrophins NGF, BDNF and NT-3, we compared their mRNA distribution in different tissues. We also examined their expression in the hippocampus of mice undergoing kainic acid-induced seizures. In this experiment, in situ hybridization (ISH) demonstrated that the levels of mRNA for furin, PC1 and BDNF increased maximally at 3 h after kainic acid administration, followed by a decline to normal levels by 96 h. NGF showed small changes, while NT-3 was downregulated with minimal expression levels between 3 to 12 h. Double ISH with radioactively-labeled riboprobes and digoxigenin-labeled riboprobes demonstrated colocalization of furin with NGF and BDNF in the mouse submaxillary gland, and of furin and PC1 with BDNF in the trigeminal ganglion. Based on colocalization studies and evidence of coordinate expression with NGF and BDNF, we suggest the involvement of furin in processing of proNGF, and of both furin and PC1 in processing of proBDNF.

Characterization of NERF, a novel transcription factor related to the Ets factor ELF-1

We have cloned the gene for a novel Ets-related transcription factor, new Ets-related factor (NERF), from human spleen, fetal liver, and brain. Comparison of the deduced amino acid sequence of NERF with those of other members of the Ets family reveals that the level of homology to ELF-1, which is involved in the regulation of several T- and B-cell-specific genes, is highest. Homologies are clustered in the putative DNA binding domain in the middle of the protein, a basic domain just upstream of this domain, and several shorter stretches of homology towards the amino terminus. The presence of two predominant NERF transcripts in various fetal and adult human tissues is due to at least three alternative splice products, NERF-1a, NERF-1b, and NERF-2, which differ in their amino termini and their expression in different tissues. Only NERF-2 and ELF-1, and not NERF-1a and NERF-1b, function as transcriptional activators of the lyn and blk gene promoters, although all isoforms of NERF bind with affinities similar to those of ELF-1 to a variety of Ets binding sites in, among others, the blk, lck, lyn, mb-1, and immunoglobulin H genes and are expressed at similar levels. Since NERF and ELF-1 are coexpressed in B and T cells, both might be involved in the regulation of the same genes.

Establishment and characterization of choroid plexus carcinoma cell lines: connection between choroid plexus and immune systems

Murine choroid plexus cell lines were produced from choroid plexus carcinoma generated in transgenic mice harboring the viral oncogene simian virus 40 large tumor antigen under transcriptional control of an intronic enhancer region from the human immunoglobulin heavy chain (IgH) gene. Two morphologically distinct cell lines have been cloned. These established cell lines retained the characteristics of choroid plexus cells in that they expressed such choroid plexus cell marker or related proteins as transthyretin and alpha2-macroglobulin. They were tumorigenic in nude mice. In the cell lines, the muA and muB (HE2) motifs within the IgH intronic enhancer were active and we also demonstrated the existence of the proteins binding to these motifs, suggesting a potential link between the choroid plexus and immune systems. It is considered that these binding proteins act as trans-activators for the enhancer and may belong to the class of ETS-related proteins. These cell lines and xenografts should be useful materials for analyses of choroid plexus functions.

The transcription factor PU.1 is involved in macrophage proliferation

PU.1 is a tissue-specific transcription factor that is expressed in cells of the hematopoietic lineage including macrophages, granulocytes, and B lymphocytes. Bone marrow-derived macrophages transfected with an antisense PU.1 expression construct or treated with antisense oligonucleotides showed a decrease in proliferation compared with controls. In contrast, bone marrow macrophages transfected with a sense PU.1 expression construct displayed enhanced macrophage colony-stimulating factor (M-CSF)-dependent proliferation. Interestingly, there was no effect of sense or antisense constructs of PU.1 on the proliferation of the M-CSF-independent cell line, suggesting that the response was M-CSF dependent. This was further supported by the finding that macrophages transfected with a sense or an antisense PU.1 construct showed, respectively, an increased or a reduced level of surface expression of receptors for M-CSF. The enhancement of proliferation seems to be selective for PU.1, since transfections with several other members of the ets family, including ets-2 and fli-1, had no effect. Various mutants of PU.1 were also tested for their ability to affect macrophage proliferation. A reduction in macrophage proliferation was found when cells were transfected with a construct in which the DNA-binding domain of PU.1 was expressed. The PEST (proline-, glutamic acid-, serine-, and threonine-rich region) sequence of the PU.1 protein, which is an important domain for protein-protein interactions in B cells, was found to have no influence on PU.1-enhanced macrophage proliferation when an expression construct containing PU.1 minus the PEST domain was transfected into bone marrow-derived macrophages. In vivo, PU.1 is phosphorylated on several serine residues. The transfection of plasmids containing PU.1 with mutations at each of five serines showed that only positions 41 and 45 are critical for enhanced macrophage proliferation. We conclude that PU.1 is necessary for the M-CSF-dependent proliferation of macrophages. One of the proliferation-relevant targets of this transcription factor could be the M-CSF receptor.

RNA polymerase II inhibitor, 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) causes erythroleukemic differentiation and transcriptional activation of erythroid genes

Friend virus-transformed murine erythroleukemia (MEL) cells are a useful system for studying the regulation of erythroid growth and differentiation. As a manifestation of the leukemic process, these erythroblasts are blocked in their ability to terminally differentiate. However, this block is reversible as a variety of different agents are capable of inducing differentiation of these malignant erythroblasts. The mechanisms by which these agents cause differentiation remains unknown. We report here that 5,6-dichlorobenzimidazole (DRB), which inhibits RNA polymerase II by causing premature termination of transcription, induces differentiation of these cells, including the transcriptional activation of erythroid genes. The effects of DRB on nonerythroid gene expression and on cell growth are substantially different than that of the commonly used inducer, dimethyl sulfoxide (DMSO). The shared ability of DMSO, DRB, and other unrelated agents to induce erythroid gene expression in MEL cells while having differing effects on nonerythroid gene expression and on cell growth suggests that expression of the terminally differentiated phenotype represents a common pathway that can be triggered by different mechanisms.

The Ets protein Spi-B is expressed exclusively in B cells and T cells during development

Spi-B and PU.1 are hematopoietic-specific transcription factors that constitute a subfamily of the Ets family of DNA-binding proteins. Here we show that contrary to previous reports, PU.1 and Spi-B have very different expression patterns. PU.1 is expressed at high levels in B cells, mast cells, megakaryocytes, macrophages, neutrophils, and immature erythroid cells and at lower levels in mature erythrocytes. PU.1 is completely absent from peripheral T cells and most T cell lines based on sensitive RT-PCR assays. In contrast, Spi-B is expressed exclusively in lymphoid cells and can be detected in early fetal thymus and spleen. In situ hybridizations of adult murine tissues demonstrate Spi-B mRNA in the medulla of the thymus, the white pulp of the spleen, and the germinal centers of lymph nodes. Spi-B expression is very abundant in B cells and both Spi-B mRNA and protein are detected in some T cells. In situ hybridization and Northern blot analysis suggest that Spi-B gene expression increases during B cell maturation and decreases during T cell maturation. Gel-retardation experiments show that Spi-B can bind to all putative PU.1 binding sites, but do not reveal any preferred Spi-B binding site. Finally, both PU.1 and Spi-B function as transcriptional activators of the immunoglobulin light-chain enhancer E lambda 2.4 when coexpressed with Pip (PU.1-interaction partner) in NIH-3T3 cells. Taken together, these data suggest that differences in patterns of expression between Spi-B and PU.1 distinguish the function of each protein during development of the immune system.

Novel DNase I hypersensitive sites in the 3'-flanking region of the human c-myc gene

DNase I hypersensitivity regions correlate with genetic regulatory loci and binding sites for sequence-specific DNA-binding proteins. We present data supporting the presence of novel DNase 1 hypersensitive sites (which we have designated sites VI-IX) in both the body of the human c-myc gene downstream from exon 2 and the 3'-flanking region of the c-myc gene in HL-60 cells. All of these novel DH sites are markedly decreased when HL-60 cells are treated with either dimethyl sulfoxide (DMSO) or retinoic acid. Moreover, a similar pattern of DNase I hypersensitive sites in this region of c-myc was present in MCF-7 human breast cancer cells growing in culture. Our results suggest a potential role for these sites in transcriptional regulation of the human c-myc gene.

Octamer binding factors and their coactivator can activate the murine PU.1 (spi-1) promoter

PU.1 (spi-1), a member of the Ets transcription factor family, is predominantly expressed in myeloid and B cells, activates many B cell and myeloid genes, and is critical for development of both of these lineages. Our previous studies (Chen, H. M., Ray-Gallet, D., Zhang, P., Hetherington, C. J., Gonzalez, D. A., Zhang, D.-E., Moreau-Gachelin, F., and Tenen, D. G. (1995) Oncogene 11, 1549-1560) demonstrate that the PU.1 promoter directs cell type-specific reporter gene expression in myeloid cell lines, and that PU.1 activates its own promoter in an autoregulatory loop. Here we show that the murine PU.1 promoter is also specifically and highly functional in B cell lines as well. Oct-1 and Oct-2 can bind specifically to a site at base pair -55 in vitro, and this site is specifically protected in B cells in vivo. We also demonstrate that two other sites contribute to promoter activity in B cells; an Sp1 binding site adjacent to the octamer site, and the PU.1 autoregulatory site. Finally, we show that the B cell coactivator OBF-1/Bob1/OCA-B is only expressed in B cells and not in myeloid cells, and that OBF-1/Bob1/OCA-B can transactivate the PU.1 promoter in HeLa and myeloid cells. This B cell restricted coactivator may be responsible for the B cell specific expression of PU.1 mediated by the octamer site.

Regulatory function of delta/YY-1 on the locus control region-like sequence of mouse glycophorin gene in erythroleukemia cells

The far upstream region (-1.2-0.9 kilobase pairs) of the mouse glycophorin gene contains the locus control region (LCR)-like region, which acts as an erythroid-specific enhancer dependent on chromosomal integration in murine erythroleukemia (MEL) cells. In the present study, we demonstrated that this region binds six nuclear factors. The binding of GATA-1 to corresponding sites did not show any change before or after induction with dimethyl sulfoxide, but the binding of Spi-1/PU.l and an unidentified factor called glycophorin regulatory element binding factor (GRBF) showed a change during induction. While binding activity of Spi-l/PU.l dropped soon after induction, the GRBF activity increased after induction when expression of the glycophorin gene began. After identification of the consensus binding site of GRBF, we cloned cDNA for that factor by Southwestern method, and it was identified as a previously reported transcription factor, delta, a murine form of YY-l which is a versatile transcription factor. Mutation analysis in the delta/YY-1 binding site within the LCR-like region indicated that delta/YY-1 acts as a regulatory protein in combination with the E-box-binding protein that binds to the neighboring sequence.

The transcription factor Spi-1/PU.1 binds RNA and interferes with the RNA-binding protein p54nrb

The protooncogene for Spi-1/PU.1 is an Ets-related transcription factor overexpressed during Friend erythroleukemia. The molecular basis by which Spi-1/PU.1 is involved in the erythroleukemic process remains to be elucidated. By using an immobilized protein binding assay, we have identified a 55-kDa protein as a putative partner of Spi-1/PU.1 protein. Microsequence analysis revealed that this 55-kDa protein was p54nrb (nuclear RNA-binding protein, 54 kDa) a RNA-binding protein highly similar to the splicing factor PSF (polypyrimidine tract-binding protein-associated splicing factor). In this paper, we show that Spi-1/PU.1 impedes the binding of p54nrb to RNA and alters the splicing process in vitro. Moreover, we present evidence that the transcriptional factor Spi-1/PU.1, unlike other Ets proteins, is able to bind RNA. Altogether, these results raise the intriguing possibility that the functional interference observed between Spi-1/PU.1 and RNA-binding proteins might represent a novel mechanism in malignant erythropoiesis.

Transcriptional regulation of c-Fes in myeloid leukemia cells

The c-Fes proto-oncogene encodes a myeloid-specific protein-tyrosine kinase that is expressed preferentially in differentiated myeloid cells, but not in early myeloblast progenitor cells. To examine the basis for the phenotypic expression of c-Fes, the transcription initiation sites of the human c-Fes gene were mapped in myeloid leukemia cells and regulatory elements in the genomic c-Fes sequence were characterized. Two major transcription initiation sites were found in the myeloid leukemia cell line THP-1 which delineated exon 1 to be 72-83 bp. When the activity of the CAT reporter gene under the control of the c-Fes promoter region, untranslated exon 1 and intron 1 was measured in TF-1, K562 and MCF-7 cells, only TF-1 cells exhibited chloramphenicol acetyltransferase activity. In contrast, all cell lines supported reporter gene activity when intron 1 was deleted. Deletion analyses revealed a negative regulatory region in intron 1, which was localized by Southwestern analysis and DNA footprinting to a 14 bp region. This negative regulatory region suppressed reporter CAT activity in K562 and TF-1 cells when inserted downstream to the SV40 early promoter. These results suggest that the tissue-specific expression of c-Fes may result, in part, from the negative regulation of transcription in myeloid and nonmyeloid cells.

Spi-1/PU.1 transgenic mice develop multistep erythroleukemias

Insertional mutagenesis of the spi-1 gene is associated with the emergence of malignant proerythroblasts during Friend virus-induced acute erythroleukemia. To determine the role of spi-1/PU.1 in the genesis of leukemia, we generated spi-1 transgenic mice. In one founder line the transgene was overexpressed as an unexpected-size transcript in various mouse tissues. Homozygous transgenic animals gave rise to live-born offspring, but 50% of the animals developed a multistep erythroleukemia within 1.5 to 6 months of birth whereas the remainder survived without evidence of disease. At the onset of the disease, mice became severely anemic. Their hematopoietic tissues were massively invaded with nontumorigenic proerythroblasts that express a high level of Spi-1 protein. These transgenic proerythroblasts are partially blocked in differentiation and strictly dependent on erythropoietin for their proliferation both in vivo and in vitro. A complete but transient regression of the disease was observed after erythrocyte transfusion, suggesting that the constitutive expression of spi-1 is related to the block of the differentiation of erythroid precursors. At relapse, erythropoietin-independent malignant proerythroblasts arose. Growth factor autonomy could be partially explained by the autocrine secretion of erythropoietin; however, other genetic events appear to be necessary to confer the full malignant phenotype. These results reveal that overexpression of spi-1 is essential for malignant erythropoiesis and does not alter other hematopoietic lineages.

Constitutive expression of c-fos and c-jun, overexpression of ets-2, and reduced expression of metastasis suppressor gene nm23-H1 in rheumatoid arthritis

OBJECTIVES

To identify genes that are involved in the development and progression of rheumatoid arthritis (RA).

METHODS

We used a multiple gene analysis system and a set of available genes participating in processes such as proliferation, differentiation, tumour progression, and metastasis, to identify their RA related expression. Synovial tissues from 22 patients with RA were evaluated in comparison with those from six patients with osteoarthritis and two patients with non-inflamed joints as controls, using northern blot and reverse transcriptase polymerase chain reaction experiments.

RESULTS

Our data confirm the role of c-fos and c-jun as constitutive signal transmitters in solid RA tissues, thus demonstrating the potential of the approach. Activation of both genes persisted through multiple passages of the cells in tissue cultures derived from the synovial lining of RA tissues. There was an increased expression of ets-2 in 30% of RA samples and an up to 30-fold decreased expression of the potential metastasis suppressor gene nm23-H1 in 90% of RA tissues, compared with control tissues.

CONCLUSIONS

The data presented show for the first time a significant decrease of nm23-H1 expression in RA, which is possibly involved in local invasiveness, and a strong activation of the ets-2 nuclear oncogene in about one third of RA tissues, which may also be part of a pathway leading to advanced disease stages. The constitutive expression of c-fos and c-jun in RA tissue most probably results from a continuing inflammatory stimulus. These findings with cell cultures suggest an intrinsic activation mechanism of these early response genes in RA.

Transcription factor PU.1 mediates induction of c-fms in vascular smooth muscle cells: a mechanism for phenotypic change to phagocytic cells

The macrophage colony-stimulating factor receptor encoded by the c-fms gene is expressed in vascular intimal smooth muscle cells isolated from atherosclerotic lesions. A combination of platelet-derived growth factor-BB and epidermal growth factor induces stable expression of c-fms in normal vascular medial smooth muscle cells. The mechanism by which these growth factors induce c-fms expression has now been investigated in an attempt to gain insight into the events that underlie the phenotypic conversion of vascular smooth muscle cells in atherosclerosis. Deletion analysis of the c-fms promoter revealed that the region including a binding site for transcription factor PU.1 was required for transcriptional activity in human aortic medial smooth muscle cells. Mutation in the PU.1 binding site markedly reduced promoter activity. Northern (RNA) blot analysis demonstrated that growth factors induced the expression of PU.1 mRNA in vascular medial smooth muscle cells and that PU.1 mRNA was expressed in vascular intimal smooth muscle cells. PU.1 antisense oligonucleotides inhibited growth factor-induced c-fms expression and foam cell formation. These results suggest that transcription factor PU.1 plays an essential role in the phenotypic conversion of vascular smooth muscle cells to macrophagelike cells by mediating the induction of c-fms.

A new pattern for helix-turn-helix recognition revealed by the PU.1 ETS-domain-DNA complex

The Ets family of transcription factors, of which there are now about 35 members regulate gene expression during growth and development. They share a conserved domain of around 85 amino acids which binds as a monomer to the DNA sequence 5'-C/AGGAA/T-3'. We have determined the crystal structure of an ETS domain complexed with DNA, at 2.3-A resolution. The domain is similar to alpha + beta (winged) 'helix-turn-helix' proteins and interacts with a ten-base-pair region of duplex DNA which takes up a uniform curve of 8 degrees. The domain contacts the DNA by a novel loop-helix-loop architecture. Four of amino acids that directly interact with the DNA are highly conserved: two arginines from the recognition helix lying in the major groove, one lysine from the 'wing' that binds upstream of the core GGAA sequence, and another lysine, from the 'turn' of the 'helix-turn-helix' motif, which binds downstream and on the opposite strand.

Gene targeting reveals a hierarchy of transcription factors regulating specification of lymphoid cell fates

Specification of B- and T-lymphoid cell fates appears to involve the expression of a shared set of genes encoding recombination proteins and of genes encoding lineage-specific components of antigen receptors. Recent studies using gene targeting have identified transcription factors that are required for the proper specification of lymphoid cell fates. On the basis of these data, a regulatory gene hierarchy which orchestrates the development of lymphoid progenitors from hematopoietic stem cells can be proposed.

The myeloid-cell-specific c-fes promoter is regulated by Sp1, PU.1, and a novel transcription factor

The protein product of the c-fps/fes (c-fes) proto-oncogene has been implicated in the normal development of myeloid cells (macrophages and neutrophils). mRNA for c-fes has been detected exclusively in myeloid cells and vascular endothelial cells in adult mammals. Although a 13-kilobase-pair (kb) human c-fes transgene exhibits high levels of expression in mice, the sequences that confer myeloid-cell-specific expression of the human c-fes gene have not been defined. Transient-transfection experiments demonstrated that plasmids containing 446 bp of c-fes 5'-flanking sequences linked to a luciferase reporter gene were active exclusively in myeloid cells. No other DNA element within the 13-kb human c-fes locus contained positive cis-acting elements, with the exception of a weakly active region within the 3'-flanking sequences. DNase I footprinting assays revealed four distinct sites that bind myeloid nuclear proteins (-408 to -386, -293 to -254, -76 to -65, and -34 to +3). However, the first two footprints resided in sequences that were largely dispensable for transient activity. Plasmids containing 151 bp of 5'-flanking sequences confer myeloid-cell-specific gene expression. Electrophoretic mobility shift analyses demonstrated that the 151-bp region contains nuclear protein binding sites for Sp1, PU.1, and/or Elf-1, and a novel factor. This unidentified factor binds immediately 3' of the PU.1/Elf-1 sites and appears to be myeloid cell specific. Mutation of the PU.1/Elf-1 site or the 3' site (FP4-3') within the context of the c-fes promoter resulted in substantially reduced activity in transient transfections. Furthermore, transient-cotransfection assay demonstrated that PU.1 (and not Elf-1) can transactivate the c-fes promoter in nonmyeloid cell lines. We conclude that the human c-fes gene contains a strong myeloid-cell-specific promoter that is regulated by Sp1, PU.1, and a novel transcription factor.

Interaction of C/EBPbeta and v-Myb is required for synergistic activation of the mim-1 gene

The retroviral oncogene v-myb encodes a transcription factor (v-Myb) which activates the myelomonocyte-specific mim-1 gene, a natural myb target gene, by cooperating with members of the C/EBP transcription factor family. The finding that v-Myb, together with C/EBP, is sufficient to activate the mim-1 gene in heterologous cell types has implicated Myb and C/EBP as a bipartite molecular switch, which regulates the expression of myelomonocyte-specific genes. To understand the relationship between v-Myb and C/EBP in more detail, we have examined the molecular basis of the activation of the mim-1 promoter by v-Myb and C/EBPbeta, a member of the C/EBP transcription factor family highly expressed in myelomonocytic cells. We have identified a composite Myb and C/EBP response element which mediates synergistic activation of the mim-1 promoter by both factors and consists of closely spaced Myb- and C/EBP-binding sites. In vitro and in vivo protein-binding studies indicate that v-Myb and C/EBPbeta interact with each other via their DNA-binding domains. We show that this interaction is essential for the synergistic activation of the mim-1 promoter by v-Myb and C/EBPbeta. Our work therefore identifies C/EBPbeta as an interaction partner of v-Myb involved in myelomonocyte gene expression.

Expression of the human acute myeloid leukemia gene AML1 is regulated by two promoter regions

The human chromosome 21 AML1 gene is expressed predominantly in the hematopoietic system. In several leukemia-associated translocations AML1 is fused to other genes and transcription of the fused regions is mediated by upstream sequences that normally regulate the expression of AML1. The 5' genomic region of AML1 was cloned and sequenced. The two 5' untranslated regions (UTRs) previously identified in AML1 cDNAs were located in this region and the distance between them was established. The distal 5' UTR maps over 7 kb upstream of the proximal one. Using primer extension with mRNA, transcription start sites were identified at two distinct sites above these 5' uTRs. Sequence analysis revealed the absence of a TATA motif and the presence of Sp1, PU.1, Oct, CRE, Myb, Ets, and Ets-like binding sites in both upstream regions. Several initiator elements (Inr) that overlap the transcription start sites were also identified. These proximal and distal upstream regions and their deletion mutants were cloned in front of a luciferase reporter gene and used in transfection assays. We demonstrate that both upstream regions function as promoters in hematopoietic (Jurkat) and nonhematopoietic (HEK) cell lines. The activity of both promoters was orientation dependent and was enhanced, in a cell-type specific manner, by a heterologous enhancer sequence. These results indicate that additional control elements, either negative or positive, regulate the tissue-specific expression of AML1.

The human lambda immunoglobulin enhancer is controlled by both positive elements and developmentally regulated negative elements

We have recently reported the localization of the first transcriptional enhancer in the human lambda (lambda) immunoglobulin light chain locus. Enhancer activity was contained on a 1.2 kb SstI fragment, with partial activity retained on a core 111 bp PstI-SstI fragment. This enhancer is located 11.7 kb downstream of C lambda 7, the most 3' lambda constant region gene. Using a chloramphenicol acetyl transferase (CAT) assay system, we have now determined the boundaries of the complete enhancer and find it is two- to four-fold as active as the core fragment in both pre-B and B cell lines. Interestingly, a larger fragment, containing the complete enhancer as well as 5' and 3' flanking sequences has four- to eight-fold reduced activity when tested in pre-B cell lines, but full activity in B cell lines. This suggests the presence of developmentally regulated negative elements flanking the human lambda enhancer which prevent or reduce its activity at a developmentally incorrect time. By using in vivo footprinting we have begun to examine the protein interactions within this enhancer in a more physiologically relevant manner and have identified motifs which are shared with the murine lambda enhancers, as well as motifs unique to the human lambda enhancer.

CCAAT enhancer-binding protein (C/EBP) and AML1 (CBF alpha2) synergistically activate the macrophage colony-stimulating factor receptor promoter

Transcription factors play a key role in the development and differentiation of specific lineages from multipotential progenitors. Identification of these regulators and determining the mechanism of how they activate their target genes are important for understanding normal development of monocytes and macrophages and the pathogenesis of a common form of adult acute leukemia, in which the differentiation of monocytic cells is blocked. Our previous work has shown that the monocyte-specific expression of the macrophage colony-stimulating factor (M-CSF) receptor is regulated by three transcription factors interacting with critical regions of the M-CSF receptor promoter, including PU.1 and AML1.PU.1 is essential for myeloid cell development, while the AML1 gene is involved in several common leukemia-related chromosome translocations, although its role in hematopoiesis has not been fully identified. Along with AML1, a third factor, Mono A, interacts with a small region of the promoter which can function as a monocyte-specific enhancer when multimerized and linked to a heterologous basal promoter. Here, we demonstrate by electrophoretic mobility shift assays with monocytic nuclear extracts, COS-7 cell-transfected factors, and specific antibodies that the monocyte-enriched factor Mono A is CCAAT enhancer-binding protein (C/EBP). C/EBP has been shown previously to be an important transcription factor involved in hepatocyte and adipocyte differentiation; in hematopoietic cells, C/EBP is specifically expressed in myeloid cells. In vitro binding analysis reveals a physical interaction between C/EBP and AML1. Further transfection studies show that C/EBP and AML1 in concert with the AML1 heterodimer partner CBF beta synergistically activate M-CSF receptor by more then 60 fold. These results demonstrate that C/EBP and AML1 are important factors for regulating a critical hematopoietic growth factor receptor, the M-CSF receptor, suggesting a mechanism of how the AML1 fusion protein could contribute to acute myeloid leukemia. Furthermore, they demonstrate physical and functional interactions between AML1 and C/EBP transcription factor family members.

Expression of the transcription factor, Spi-1 (PU.1), in differentiating murine erythroleukemia cells Is regulated post-transcriptionally. Evidence for differential stability of transcription factor mRNAs following inducer exposure

Increased expression of the transcription factor Spi-1 (PU.1) results from retroviral insertion in nearly all Friend spleen focus-forming virus-transformed murine erythroleukemia cell lines and exposure of these cells to Me2SO, induces their differentiation and decreases Spi-1 mRNA level by 4-5-fold. While these results suggest that alterations in Spi-1 expression have significant effects on erythroblast growth and differentiation, neither the cause nor the effect of the decrease in Spi-1 expression that follows Me2SO exposure has been established. The experiments described here demonstrate that the effect of inducers on Spi-1 expression is regulated post-transcriptionally. Nuclear run-off transcriptions demonstrated that Spi-1 transcription was not decreased following Me2SO exposure. Additionally, expression of a recombinant Spi-1 mRNA under transcriptional control of a constitutively active Rous sarcoma virus promoter was regulated identically to endogenous Spi-1 mRNA. The ability of Me2SO to destabilize Spi-1 mRNA was selective, as the stability of the erythroid transcription factors GATA-1 and NF-E2 were not similarly effected. The effect of Me2SO on the stability of Spi-1 mRNA provides a novel means of altering gene expression in these cells and is likely to have significance for the differentiation of these cells.

Regulation of the leukocyte integrin gene CD11c is mediated by AP1 and Ets transcription factors

The leukocyte integrin gene, CD11c, encodes the chi subunit of the p150,95 (CD11c.CD18) receptor. Expression of the CD11c gene is predominately seen in monocytes, but has also been detected in some B- and T-cell neoplasms and in some large-cell lymphomas of uncertain origin. To elucidate the molecular mechanisms that govern the expression of CD11c, we have cloned and characterized the promoter region of this gene. The DNase I footprint and mobility shift analyses revealed five sites within the -86 to +40 region that interact with nuclear proteins. The -62 to -44 region contains two consensus sequences for AP1 (referred to as AP1-1 and AP1-2) and were shown to bind purified c-jun protein. Co-transfection of c-fos and c-jun expression constructs with a CD11c promoter-CAT fusion into HL60 cells led to a 6.7-fold increase in CD11c promoter activity. We show that c-fos and c-jun mediate their effects through both AP1-1 and AP1-2 which function in an additive manner. Regions -42 to -34 and -13 to -5 contain consensus sequences for Ets factors (referred to as Ets C and Ets A, respectively). Deletion of Ets resulted in a significant reduction in phorbol ester-induced expression of CD11c, whereas deletion of Ets A led to only a modest loss in CD11c expression. We show that Ets C cooperates with the AP1 sites to regulate CD11c expression.

Genomic organization and FISH mapping of human Pmel 17, the putative silver locus

The Pmel 17 gene is expressed preferentially in pigment cells. It has been mapped to human chromosome 12 pter-q21 and mouse chromosome 10, near the silver locus. The Pmel 17 gene contains an insertional mutation at its carboxyl terminus in the silver mouse, suggesting that the silver locus might correspond to the gene. In the current studies, we have isolated and characterized human Pmel 17 genomic clones and employed FISH mapping for a precise localization of this gene in the human chromosome. The FISH mapping placed the Pmel 17 gene at human chromosome 12 q12-q13. The human gene consists of nine exons and eight introns, and the entire coding region of the gene spans approximately 7.9 kb of the human chromosome 12. The putative functional domains, such as the signal sequence, histidine-rich, 26-amino acid repeats, cysteinerich, transmembrane and cytoplasmic domains, were encoded by separate exons. Cistranscription elements such as a TATA, a CAT and other potential elements for pigment cell-specific gene expression were found within 1100 base pairs of the 5' flanking region.

Structural organization, sequence, and expression of the chicken NRAMP1 gene encoding the natural resistance-associated macrophage protein 1

One of the most common causes of food poisoning in humans is salmonellosis, which is frequently caused by ingestion with Salmonella-contaminated poultry products. Several lines of evidence suggest that genetic factors control resistance and susceptibility of chickens to infection with Salmonellae. In the mouse, innate resistance to infection with intracellular pathogens such as Salmonella typhimurium, several species of Mycobacteria, and Leishmania donovani is controlled by the mouse chromosome 1 Nramp1Bcg gene. To investigate the role of NRAMP1 in the differential resistance and susceptibility of chickens to infections with S. typhimurium, we have cloned and characterized cDNA clones corresponding to the chicken NRAMP1 gene. Nucleotide and predicted amino acid sequence analyses indicate that the chicken NRAMP1 polypeptide encodes a 555-amino-acid residue membrane protein with 12 putative transmembrane domains, two N-linked glycosylation sites, and an evolutionary conserved consensus transport motif. The peptide sequence identity among chicken, mouse, and human NRAMP1 is 68%. The chicken NRAMP1 gene contains 15 exons and spans 5 kb of genomic DNA. One major and two minor transcription initiation sites were detected using primer extension. Nucleotide sequencing of the promoter region revealed the presence of a classical TATAA element and consensus sequences for binding the myeloid specific PU.1 factor and several lipopolysaccharide (LPS) (NF-IL6 and NF-kappa B) and interferon-gamma (IFN-gamma)-inducible response elements. Similar regulatory elements are found in the promoters of mouse and human NRAMP1. Northern blot analyses revealed NRAMP1 expression in reticuloendothelial organs (spleen and liver), lung, and thymus. As demonstrated in mice and humans, the macrophage is also a major site of NRAMP1 mRNA expression in chickens. However, the high levels of expression detected in chicken thymus contrast with the absence of expression of the mammalian Nramp1 gene in this tissue.