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

Retroviral insertions downstream of the heterogeneous nuclear ribonucleoprotein A1 gene in erythroleukemia cells: evidence that A1 is not essential for cell growth

A large number of novel cellular proto-oncogenes have been identified and cloned by analysis of common integration sites in retrovirally induced malignancies. In the multistage erythroleukemias induced by the various strains of Friend leukemia virus, the analysis of proviral-integration events has led to the identification of two genes, Fli-1 and Spi-1, both novel members of the ets oncogene family of transcription factors. In this report, we describe the identification of another integration site, designated Fli-2 (Friend leukemia virus integration-2), in an erythroleukemia cell line induced by Friend murine leukemia virus (F-MuLV). Rearrangements at the Fli-2 locus were found in two erythroleukemia cell lines independently induced by F-MuLV and one leukemic cell line derived from the spleen of a mouse infected with the polycythemia strain of Friend leukemia virus. The deduced amino acid sequence of a cDNA corresponding to a transcript originating from genomic DNA adjacent to Fli-2 is identical to that of the human heterogeneous nuclear ribonucleoprotein A1 gene, a member of the gene family of RNA-binding proteins involved in RNA splicing. In one erythroleukemia cell line, A1 expression was undetectable as a result of F-MuLV integration in one allele and loss of the other allele. These results suggest that perturbations in RNA splicing mechanisms may contribute to malignant transformation and provide direct evidence that the A1 protein is not required for cell growth.

Definition of interferon gamma-response elements in a novel human Fc gamma receptor gene (Fc gamma RIb) and characterization of the gene structure

The human Fc gamma RI (CD64) is a high affinity receptor for the Fc portion of immunoglobulin (Ig), and its constitutively low expression on the cell surface of monocyte/macrophage and neutrophils is selectively upregulated by interferon gamma (IFN-gamma) treatment (Perussia, B., E. T. Dayton, R. Lazarus, V. Fanning, and G. Trinchieri. 1983. J. Exp. Med. 158:1092). Three distinct cDNAs have been cloned and code for proteins that predict three extracellular Ig-like domains (Allen, J.M., and B. Seed. 1989. Science [Wash. DC]. 243:378). Several differences in the coding region of these cDNAs suggest that in addition to polymorphic differences a second Fc gamma RI gene could possibly exist. This alternative Fc gamma RI gene (Fc gamma RIb) was defined by the lack of a genomic HindIII restriction site (van der Winkel, J. G. J., L. U. Ernst, C. L. Anderson, and I. M. Chiu. 1991. J. Biol. Chem. 266:13449). We describe the characterization a second gene (Fc gamma RIb) that has a termination codon in the third extracellular domain and therefore predicts a soluble form of a termination codon in the third extracellular domain and therefore predicts a soluble form of the receptor. We also define two distinct IFN-gamma-responsive regions in the 5' flanking sequence of Fc gamma RIb that resemble motifs that have been defined in the class II major histocompatibility complex promoter. The Fc gamma RIb promoter does not possess canonical TATA or CCAAT boxes, but does possess a palindromic motif that closely resembles the initiator sequence identified in the terminal deoxynucleotidyl transferase/human leukocyte IFN/adeno-associated virus type II P5 gene promoters (Smale, S. T., and D. Baltimore. 1989. Cell. 57:103; Seto, E., Y. Shi, and T. Shenk. 1991. Nature [Lond.]. 354:241; Roy, A. L., M. Meisterernst, P. Pognonec, and R. C. Roeder. 1991. Nature [Lond.]. 354:245) virus type II P5 gene promoters raising interesting questions as to its role in the basal and myeloid-specific transcription of this gene.

An inhibitory carboxyl-terminal domain in Ets-1 and Ets-2 mediates differential binding of ETS family factors to promoter sequences of the mb-1 gene

The mb-1 gene is expressed only during the early stages of B-lymphocyte differentiation. Here we show that the mb-1 proximal promoter region contains a functionally important binding site for members of the ETS family of DNA-binding proteins. We found that both the E26 virus-encoded v-ets and the myeloid/B-cell-specific factor PU.1 bind efficiently to this site in vitro. By contrast, Ets-1, the lymphocyte-specific cellular homologue of v-ets, and the related, more ubiquitously expressed Ets-2 protein interacted weakly with this binding site. DNA binding by both Ets-1 and Ets-2, however, could be increased 20- to 50-fold by deleting as few as 16 carboxyl-terminal amino acids. The inhibitory carboxyl-terminal amino acid sequence is highly conserved between Ets-1 and Ets-2 but is not present in either v-ets or PU.1. Replacement of the carboxyl-terminal amino acids of v-ets with those of Ets-1 decreased DNA binding by v-ets drastically. Cotranslation of Ets-1 transcripts encoding proteins of different lengths suggested that Ets-1 binds DNA as a monomer. Therefore, the carboxyl-terminal inhibitory domain appears to interfere directly with DNA binding and not with homodimerization. Finally, the functional relevance of ETS factor binding to the mb-1 promoter site was evidenced by the stimulation of transcription through this site by a v-myb-v-ets fusion protein. Together, these data suggest that one or more ETS family factors are involved in the regulation of mb-1 gene expression.

A novel Ets-related transcription factor, Elf-1, binds to human immunodeficiency virus type 2 regulatory elements that are required for inducible trans activation in T cells

Human immunodeficiency virus type 1 (HIV-1) and HIV-2 are structurally related retroviruses which both cause AIDS in humans. Although both viruses establish latency in quiescent human-peripheral-blood T cells, the asymptomatic phase of HIV-2 infection may be more prolonged than that of HIV-1. The latent phases of both HIV-1 and HIV-2 infection have been shown to be disrupted by T-cell activation, a process that requires host cell transcription factors. In the case of HIV-1, the transcription factor NF-kappa B is sufficient for inducible transcriptional activation. In contrast, factors in addition to NF-kappa B are required to activate HIV-2 transcription in infected T cells. In this report, we demonstrate that a novel Ets-related transcription factor, Elf-1, binds specifically to two purine-rich motifs in the HIV-2 enhancer. Mutagenesis experiments demonstrated that these Elf-1 binding sites are required for induction of HIV-2 transcription following T-cell-receptor-mediated T-cell activation. Moreover, Elf-1 is the only factor present in activated T-cell nuclear extracts that binds to these sites in electrophoretic mobility shift assays. Thus, Elf-1 is a novel transcription factor that appears to be required for the T-cell-receptor-mediated trans activation of HIV-2 gene expression. These results may explain differences in the clinical spectra of diseases caused by HIV-1 and HIV-2 and may also have implications for the design of therapeutic approaches to HIV-2 infection.

DNA binding sites 5' of the IgG1 switch region comprising IL4 inducibility and B cell specificity

Immunoglobulin class switch recombination is directed to the same switch region on both chromosomes of a B cell by an as yet unknown mechanism. The cytokine interleukin 4 (IL4) targets recombination in activated B lymphocytes to the gamma 1 switch region (s gamma 1). Here we report two DNA-binding-proteins which bind to a sequence 5' of s gamma 1. One protein is B cell specific, while binding of the other one is induced by IL4. These two proteins bind to a region 700 bp upstream of the putative promoter region of the gamma 1 germline transcripts and may be involved in the process of recombination and/or transcription.

A cDNA clone for a novel nuclear protein with DNA binding activity

In an effort to identify trans-acting factors regulating specific genes, we cloned a novel human gene, DBP-5. The cDNA clone contains a predicted open reading frame coding for a potential 1,179 amino acid protein. The mRNA corresponding to DBP-5 is ubiquitously distributed, and the gene is phylogenetically conserved. Immunofluorescence analyses with several cell lines indicate that the protein is localized to the nucleus. Sequence analysis revealed unusual features of the predicted protein structure, including four completely conserved repeats. The phylogenetic conservation of DBP-5, the ubiquity of its expression, its nuclear localization, and its ability to bind DNA sequences, raise the possibility that DBP-5 may play a role in the organization of interphase chromatin and/or in transcriptional regulation.

Characterization of Spi-B, a transcription factor related to the putative oncoprotein Spi-1/PU.1

We have cloned a human cDNA from a new gene, spi-B, on the basis of its homology with the DNA-binding domain of the Spi-1/PU.1 putative oncogene product. spi-B codes for a protein of 262 amino acids presenting 43% overall identity with Spi-1. Its highly basic carboxy-terminal region exhibits 34% sequence identity with the DNA-binding domain of the Ets-1 protein. We showed that the Spi-B protein is able to bind the purine-rich sequence (PU box) recognized by Spi-1/PU.1 and to activate transcription of a reporter plasmid containing PU boxes. Chromosome in situ hybridization allowed us to map spi-B to the 19q13.3-19q13.4 region of the human genome. spi-B, like spi-1, was found to be expressed in various murine and human hematopoietic cell lines except T lymphoid cell lines.

Functional analysis of the human adenosine deaminase gene thymic regulatory region and its ability to generate position-independent transgene expression

We previously observed that human ADA gene expression, required for the intrathymic maturation of T cells, is controlled by first-intron sequences. Used as a cis activator, the intron generates copy-dependent reporter expression in transgenic thymocytes, and we here dissect its critical determinants. Of six DNase I-hypersensitive sites (HS sites) in the intron, only HS III was a transfection-active classic enhancer in T cells. The enhancer contains a critical core region, ACATGGCAGTTGGTGGTGGAGGGGAACA, that interacts with at least two factors, ADA-NF1 and ADA-NF2. Activity of the core is strongly augmented by adjacent elements contained within a 200-bp domain corresponding to the limits of HS III hypersensitivity. These core-adjacent sequences include consensus matches for recognition by the AP-1, TCF-1 alpha, mu E, and Ets transcription factor families. In contrast, considerably more extensive sequences flanking the enhancer domain were required for position-independent and copy-proportional expression in transgenic mouse thymocytes. The additionally required upstream segment encompassed the nonenhancer HS II site. The required downstream segment, composed largely of Alu-repetitive DNA, was non-DNase I hypersensitive. Transgenes that lacked either segment were subject to strong positional effects. Among these variably expressing lines, the expression level correlated with the degree of hypersensitivity at HS III. This finding suggests that formation of hypersensitivity is normally facilitated by the flanking segments. These results delineate a complex thymic regulatory region within the intron and indicate that a series of interactions is necessary for the enhancer domain to function consistently within chromatin.

Identification of Ets-like lymphoid specific elements within the immunoglobulin heavy chain 3' enhancer

Recently we identified an additional enhancer in the 3' end of the immunoglobulin heavy chain (IgH) locus. To identify individual regulatory elements within the rat IgH 3' enhancer, deletion analysis was performed. Transfection experiments using reporter constructs suggest that the enhancer contains three functionally distinct domains, two of which are lymphoid specific and one domain is active in both lymphoid and in nonlymphoid cells. The three domains together contribute to enhancer function and act synergistically. Further analyses suggest that a putative mu E1 site, octanucleotide motif, mu E3 site, and mu B/Ets-like motif are important for the overall transcriptional activity of the IgH 3' enhancer. Moreover, we provide evidence that an additional Ets-like element, micro A, is involved in the tissue specific regulation of enhancer activity and that binding of a protein to this element correlates with the transcriptional activity of one of the lymphoid restricted domains.

Activation of the human immunodeficiency virus type 2 enhancer is dependent on purine box and kappa B regulatory elements

Human immunodeficiency virus type 2 (HIV-2) displays several features which distinguish it from HIV-1. Among the differences in these two viruses are the responses of their enhancer regions to T-cell activation. For example, stimulation of HIV-1 transcription is largely dependent on two kappa B regulatory elements. In contrast, the HIV-2 enhancer has a single kappa B site and contains additional cis-acting sequences responsive to induction. One of these sites, previously termed CD3R, is a purine-rich site, also called PuB1, which is responsive to stimulation of the CD3 component of the T-cell receptor complex and binds Elf-1, a member of the ets proto-oncogene family. In this report, we examine the interaction of the PuB1 site with other sites in the HIV-2 enhancer. We demonstrate that the PuB1 site confers responsiveness to T-cell activators only in cooperation with additional enhancer elements. Induction of the HIV-2 enhancer is dependent on at least two other cis-acting regulatory elements in addition to PuB1 and kappa B. One of these elements is another purine-rich site (PuB2), which also binds recombinant Elf-1. An adjacent region, proximal to the PuB2 ets (pets) site, shows protection in DNase footprinting experiments with extracts from Jurkat T cells. Mutation of either the kappa B, PuB1, PuB2, or pets site significantly reduces the response of the HIV-2 enhancer to T-cell stimulation, an effect which is mediated at the RNA level. Therefore, activation of the HIV-2 enhancer is dependent on at least four cis-acting elements, only one of which is found in HIV-1, which act in synergy with one another. Despite their sequence similarity, the organization and function of the HIV-2 enhancer have diverged considerably from those of HIV-1.

Functional analysis of the human adenosine deaminase gene thymic regulatory region and its ability to generate position-independent transgene expression

We previously observed that human ADA gene expression, required for the intrathymic maturation of T cells, is controlled by first-intron sequences. Used as a cis activator, the intron generates copy-dependent reporter expression in transgenic thymocytes, and we here dissect its critical determinants. Of six DNase I-hypersensitive sites (HS sites) in the intron, only HS III was a transfection-active classic enhancer in T cells. The enhancer contains a critical core region, ACATGGCAGTTGGTGGTGGAGGGGAACA, that interacts with at least two factors, ADA-NF1 and ADA-NF2. Activity of the core is strongly augmented by adjacent elements contained within a 200-bp domain corresponding to the limits of HS III hypersensitivity. These core-adjacent sequences include consensus matches for recognition by the AP-1, TCF-1 alpha, mu E, and Ets transcription factor families. In contrast, considerably more extensive sequences flanking the enhancer domain were required for position-independent and copy-proportional expression in transgenic mouse thymocytes. The additionally required upstream segment encompassed the nonenhancer HS II site. The required downstream segment, composed largely of Alu-repetitive DNA, was non-DNase I hypersensitive. Transgenes that lacked either segment were subject to strong positional effects. Among these variably expressing lines, the expression level correlated with the degree of hypersensitivity at HS III. This finding suggests that formation of hypersensitivity is normally facilitated by the flanking segments. These results delineate a complex thymic regulatory region within the intron and indicate that a series of interactions is necessary for the enhancer domain to function consistently within chromatin.

Role of the PU.1 transcription factor in controlling differentiation of Friend erythroleukemia cells

Both viral and cellular genes have been directly implicated in pathogenesis of Friend viral erythroleukemia. The virus-encoded gp55 glycoprotein binds to erythropoietin receptors to cause mitogenesis and differentiation of erythroblasts. However, if the provirus integrates adjacent to the gene for the PU.1 transcription factor, the cell loses its commitment to terminally differentiate and becomes immortal, as indicated by its transplantability and by its potential for indefinite growth in culture (C. Spiro, B. Gliniak, and D. Kabat, J. Virol. 63:4434-4437, 1989; R. Paul, S. Schuetze, S. L. Kozak, and D. Kabat, J. Virol. 65:464-467, 1991). To test the implications of these results, we produced polyclonal antiserum to bacterially synthesized PU.1, and we used it to analyze PU.1 expression throughout leukemic progression and during chemically induced differentiation of Friend erythroleukemia (F-MEL) cell lines. This antiserum identified three electrophoretically distinct PU.1 components in extracts of F-MEL cells and demonstrated their nuclear localization. Although PU.1 proteins are abundant in F-MEL cells, they are absent or present in only trace amounts in normal erythroblasts or in differentiating erythroblasts from the preleukemic stage of Friend disease. Furthermore, chemicals (dimethyl sulfoxide or N,N'-hexamethylenebisacetamide) that overcome the blocked differentiation of F-MEL cells induce rapid declines of PU.1 mRNA and PU.1 proteins. The elimination of PU.1 proteins coincides with recommitment to the program of erythroid differentiation and with loss of immortality. These results support the hypothesis that PU.1 interferes with the commitment of erythroblasts to differentiate and that chemicals that reduce PU.1 expression reinstate the erythropoietic program.

Phenotypic characterization of KU812, a cell line identified as an immature human basophilic leukocyte

The knowledge about the differentiation of basophilic leukocytes is fragmentary. This report discusses a detailed phenotypic characterization of molecular markers for hematopoietic differentiation in a basophilic leukemia cell line, KU812. The expression of markers for lymphoid, erythroid, neutrophil, eosinophil, monocytic, megakaryocytic, mast cell and basophil differentiation was analyzed at the mRNA level by Northern blots in the KU812 cells, and for reference, in a panel of human cell lines representative of the different hematopoietic differentiation lineages. KU812 was found to express a number of mast cell and basophil-related proteins, i.e. mast cell tryptase, mast cell carboxypeptidase A, high-affinity immunoglobulin (IgE) receptor alpha and gamma chains and the core protein for heparin and chondroitin sulphate synthesis. We found no expression of a number of monocyte/-macrophage or neutrophil leukocyte markers except for lysozyme. From earlier studies, it has been shown that lysozyme is not expressed in murine mucosal mast cell lines. This finding, together with the expression of the mast cell carboxypeptidase in KU812 might distinguish the phenotype of this cell line from that typical of mucosal mast cell lines in rodents. We found a low level of expression of the eosinophil and basophil marker, major basic protein, which might indicate a relationship between basophils and eosinophils. No expression is, however, detected with the eosinophil-specific markers eosinophil cationic protein, eosinophil-derived neurotoxin or eosinophil peroxidase. We also report an extensive screening for inducers of basophilic differentiation of the KU812 cells. The most efficient protocol of induction included serum starvation which led to a dramatic increase in a number of markers specific for mast cells and basophils such as tryptase, carboxypeptidase A and the heparin core protein. Finally, diisopropylfluorophosphate analysis of total protein extracts from KU812 show four labeled protein bands with sodium dodecyl sulfate-polyacrylamide gel electrophoresis, indicating that this cell line expresses at least three previously undescribed serine proteases of which one or more could be a potential basophil-specific marker(s).

Elk-1 protein domains required for direct and SRF-assisted DNA-binding

The Ets-related Elk-1 protein can bind to purine-rich DNA target sites in a sequence specific fashion and, in addition, can form a ternary complex with the c-fos serum response element (SRE) and the serum response factor (SRF). We demonstrate that Elk-1 can readily interchange between its different interaction partners. The amino terminal ETS-domain of Elk-1 was shown to be necessary and sufficient for direct DNA-binding activity. For ternary complex formation with the SRE and SRF, both the Elk-1 ETS-domain as well as flanking sequences up to amino acid 169 were required. Removal of sequences between the ETS-domain and amino acids 137-169 did not abolish ternary complex formation. This suggests the Elk-1 region spanning amino acids 137-169 to contain a protein-protein interaction domain. Furthermore, we have shown that a single amino acid exchange introduced into the ETS-domain can drastically alter the direct DNA-binding affinity of Elk-1 without severely affecting SRF-assisted binding to the SRE. Thus, Elk-1 requires different propensities of the ETS-domain to exert its different modes of DNA sequence recognition.

Characterization and chromosomal mapping of the gene encoding the cellular DNA binding protein ILF

Recently we isolated a cellular DNA binding protein, designated interleukin enhancer binding factor (ILF), that binds to purine-rich regulatory motifs in both the HIV-1 LTR and the IL2 promoter. Further analysis of the ILF gene reveals the existence of two mRNA species, both of which encode proteins containing the recently described fork head DNA binding domain. Gel retardation analysis demonstrates that the portion of the ILF protein with homology to the fork head domain is sufficient to mediate DNA binding to a number of related purine-rich sequences. ILF mRNA is expressed constitutively in both lymphoid and nonlymphoid tissues. Chromosomal mapping localizes the ILF gene to human chromosome 17q25, which is a site of chromosomal translocations in some cases of human acute myelogous leukemias. These studies further characterize the structure of the cellular DNA binding protein ILF and may prove valuable in the molecular analysis of possible translocations affecting this gene.

Characterization and chromosomal mapping of the gene encoding the cellular DNA binding protein HTLF

A region of the human T-cell leukemia virus long terminal repeat (HTLV-I LTR) located between -155 and -117 is important in the regulation of gene expression by the ets family of transcription factors. In an attempt to identify additional cellular transcription factors that bind to this portion of the HTLV-I LTR, we used lambda gt11 expression cloning with oligonucleotides corresponding to this element. A 1239-bp cDNA was isolated from a Jurkat cDNA library, which encoded a protein capable of binding to this purine-rich region. This protein, which we designated human T-cell leukemia virus enhancer factor (HTLF), contains a domain with homology to the recently described fork head DNA binding domain. Chromosome mapping of the HTLF gene demonstrated that it was localized to human chromosome 2p16-p22. HTLF is a unique cellular gene that may function in the transcriptional regulation of HTLV-I LTR.

Role of the PU.1 transcription factor in controlling differentiation of Friend erythroleukemia cells

Both viral and cellular genes have been directly implicated in pathogenesis of Friend viral erythroleukemia. The virus-encoded gp55 glycoprotein binds to erythropoietin receptors to cause mitogenesis and differentiation of erythroblasts. However, if the provirus integrates adjacent to the gene for the PU.1 transcription factor, the cell loses its commitment to terminally differentiate and becomes immortal, as indicated by its transplantability and by its potential for indefinite growth in culture (C. Spiro, B. Gliniak, and D. Kabat, J. Virol. 63:4434-4437, 1989; R. Paul, S. Schuetze, S. L. Kozak, and D. Kabat, J. Virol. 65:464-467, 1991). To test the implications of these results, we produced polyclonal antiserum to bacterially synthesized PU.1, and we used it to analyze PU.1 expression throughout leukemic progression and during chemically induced differentiation of Friend erythroleukemia (F-MEL) cell lines. This antiserum identified three electrophoretically distinct PU.1 components in extracts of F-MEL cells and demonstrated their nuclear localization. Although PU.1 proteins are abundant in F-MEL cells, they are absent or present in only trace amounts in normal erythroblasts or in differentiating erythroblasts from the preleukemic stage of Friend disease. Furthermore, chemicals (dimethyl sulfoxide or N,N'-hexamethylenebisacetamide) that overcome the blocked differentiation of F-MEL cells induce rapid declines of PU.1 mRNA and PU.1 proteins. The elimination of PU.1 proteins coincides with recommitment to the program of erythroid differentiation and with loss of immortality. These results support the hypothesis that PU.1 interferes with the commitment of erythroblasts to differentiate and that chemicals that reduce PU.1 expression reinstate the erythropoietic program.

Upstream region of a genomic gene for human mitochondrial transcription factor 1

A genomic gene for human mitochondrial transcription factor 1 was cloned from a human genomic library and its 5' flanking region was sequenced. No typical TATA and three consensus sequences for potential Sp1 binding site were found in its 5' flanking region of 2 kilobase pairs. There were, at least, four common sequences among some nuclear genes for mitochondrial-related proteins.

Serum, AP-1 and Ets-1 stimulate the human ets-1 promoter

The ets-1 proto-oncogene codes for a transcription factor. In order to understand how ets-1 is regulated, we have cloned its promoter. We show that the promoter is inducible by serum and expression of c-Fos and c-Jun, and it is positively auto-regulated by its gene product. A 50 base-pair sequence is sufficient to confer c-Fos + c-Jun and c-Ets-1 responsiveness to a heterologous promoter. This element contains two AP1 and one Ets-1 like motifs. Striking, AP-1 and Ets-1 motifs are found in oncogene responsive units (ORU's) of other promoters, suggesting that combining these motifs is a common mechanism for generating mitogen responsive transcription elements.

Characterization and uses of monoclonal antibody derived against DNA binding domain of the ets family of genes

A monoclonal antibody recognizing ets proteins from a variety of species has been developed. This antibody recognizes ets1, ets2, erg, and other related proteins. It has a high affinity for the ets1 protein. The epitope for the pan ets mAb consists of about 13 amino acids. This antibody can be used to isolate and characterize new members of ets gene family derived from a c-DNA expression library, as well as to identify other "ets motif" binding proteins.

Interaction of murine ets-1 with GGA-binding sites establishes the ETS domain as a new DNA-binding motif

The proto-oncogene ets-1 is the founding member of a new family of eukaryotic transcriptional regulators. Using deletion mutants of murine ets-1 cDNA expressed in Escherichia coli, we show that the DNA-binding domain corresponds closely to the ETS domain, an 85-amino-acid region that is conserved among ets family members. To investigate the specificity of DNA binding of the ETS domain, we mapped the DNA contacts of a monomeric Ets-1 fragment by chemical protection and interference assays. DNA backbone interactions span a 20-nucleotide region and are localized on one face of the helix. Close phosphate and base contacts are restricted to 10 central nucleotides. Contacts map to the major groove in the center of the site. Flanking minor groove interactions also are predicted. To determine the sequence preference in the close contact zone, we selected a pool of high-affinity binding sites using a purified Ets-1 carboxy-terminal fragment. Our Ets-1-selected consensus, 5'-A/GCCGGAA/TGT/C-3', differs from the binding consensus for the Drosophila ETS domain protein E74A, suggesting that specificity of action of ets family members is mediated by the ETS domain. Compared to other well-characterized classes of DNA-binding proteins, Ets-1 produces a unique pattern of DNA contacts. These studies demonstrate that the ETS domain proteins bind DNA in a novel manner.

Activation of the human immunodeficiency virus type 1 enhancer is not dependent on NFAT-1

The function of a putative NFAT-1 site in the human immunodeficiency virus type 1 enhancer has been analyzed. Activation by the T-cell antigen receptor is minimal in Jurkat cells and is mediated by the kappa B sites. The putative NFAT-1 region is not required for the response to anti-CD3 or to mitogens in T-cell, B-cell, or monocyte/macrophage leukemia lines, nor is it a cis-acting negative regulatory element.

Structure of the mouse activin receptor type II gene

Knowledge of the structures of the activin receptor genes is crucial to our understanding of the role of the activins, inhibins, and their receptors in developmental and physiological processes. The type II activin receptor (ActRc) has been shown to be a transmembrane protein with putative serine/threonine kinase activity. Using a human ActRc type II cDNA as a probe, 18 overlapping lambda clones containing portions of the mouse ActRc type II gene were isolated from a mouse 129SvE genomic library. Sequence analysis of the exons, exon-intron boundaries, and 5' and 3' non-translated regions as well as Southern blot analysis of mouse genomic DNA were used to establish the structure of the mouse ActRc type II gene. The mouse ActRc type II gene is encoded by 11 exons and spans greater than 66 kilobases. Two large introns (introns 1 and 4) contribute the majority of the gene size and are found to delineate exons which encode important domains of the activin receptor. Analysis of the 5' region of the gene reveals several putative transcription factor binding sites which may be important for the complex transcriptional regulation of this gene.

Expression of a 91-kilodalton PEA3-binding protein is down-regulated during differentiation of F9 embryonal carcinoma cells

Proteins binding to the PEA3 enhancer motif (AGGAAG) activate the polyomavirus early promoter and help comprise the viral late mRNA initiator element (W. Yoo, M. E. Martin, and W. R. Folk, J. Virol. 65:5391-5400, 1991). Because many developmentally regulated cellular genes have PEA3 motifs near their promoter sequences, and because Ets family gene products activate the PEA3 motif, we have studied the expression of PEA3-binding proteins and Ets-related proteins during differentiation of F9 embryonal carcinoma cells. An approximately 91-kDa protein (PEA3-91) was identified in F9 cell nuclear extracts by UV cross-linking to a radiolabeled PEA3 oligonucleotide probe, and expression of PEA3-91 was down-regulated after differentiation of F9 cells to parietal endoderm. The c-ets-1 gene product binds to a sequence in the murine sarcoma virus long terminal repeat that is similar to the PEA3 motif (cGGAAG), but PEA3-91 was not cross-linked to this Ets-1-binding motif, nor did antiserum which recognizes murine c-ets-1 and c-ets-2 proteins have any effect on PEA3-binding activity in mobility shift assays. Furthermore, c-ets-1 mRNA was not detected in undifferentiated or differentiated F9 cells, and c-ets-2 mRNA levels remained high after differentiation. Antiserum against the Drosophila Ets-related E74A protein, however, recognized an approximately 92-kDa protein in F9 cells whose expression during differentiation varied in a manner identical to that of PEA3-91. These data suggest that PEA3-91 is not the product of the ets-1 or ets-2 genes but is likely to be the product of a murine homolog of the Drosophila E74 gene.

Isolation and characterization of five Drosophila genes that encode an ets-related DNA binding domain

The recent determination of the site-specific DNA binding properties of several proteins related to the ets oncoprotein has allowed the definition of a novel DNA binding domain, designated the ETS domain. In Drosophila, an ETS domain is present in the early ecdysone-induced E74A protein, which binds DNA in a site-specific manner and interacts with many ecdysone-induced polytene chromosome puffs at the onset of metamorphosis. As a first step toward determining the function of ETS-domain proteins during Drosophila development, we have used PCR amplification with degenerate oligonucleotides to isolate five other ets-related genes. Two of these genes, D-ets-2 and D-elg, have been previously identified. The proteins encoded by these genes are highly related to one another and to the seven identified vertebrate ETS-domain proteins, within the approximately 85-amino-acid DNA binding domain. In situ hybridization to polytene chromosomes revealed that these ets-related genes are not clustered in the genome and that only E74 corresponds to an ecdysone-inducible puff locus. These five ets-related genes are distinguished further from E74 in that they are transcribed through most of development, suggesting that they do not perform a stage-specific function. They are, however, expressed in a variety of patterns in early embryos, suggesting roles in the development of specific cell types. D-ets-2 is expressed in a complex pattern that changes dynamically during early embryogenesis. D-ets-3 and D-ets-6 are expressed in the ventral nervous system. The expression of D-ets-3 is higher in the three thoracic segments and lower in the abdominal segments. The high levels of expression in the thoracic segments are dependent on the presence of the bithorax complex. D-ets-4 and D-elg are expressed at their highest levels in the pole cells, suggesting a role in the development of the germline. This study represents the first effort in any organism to systematically isolate members of the ets gene family. The identification of six independent ets-related genes demonstrates that the ETS-domain proteins constitute a new family of potential transcriptional regulators encoded by the Drosophila genome.

Evolutionarily conserved Ets family members display distinct DNA binding specificities

Members of the Ets family of proto-oncogenes encode sequence-specific transcription factors that bind to a purine-rich motif centered around a conserved GGA trinucleotide. Ets binding sites have been identified in the transcriptional regulatory regions of multiple T cell genes including the T cell receptor alpha and beta (TCR-alpha and -beta) enhancers and the IL-2 enhancer, as well as in the enhancers of several T cell-trophic viruses including Maloney sarcoma virus, human leukemia virus type 1, and human immunodeficiency virus-2. T cells express multiple members of the Ets gene family including Ets-1, Ets-2, GABP alpha, Elf-1, and Fli-1. The different patterns of expression and protein-protein interactions of these different Ets family members undoubtedly contribute to their ability to specifically regulate distinct sets of T cell genes. However, previous studies have suggested that different Ets family members might also display distinct DNA binding specificities. In this report, we have examined the DNA binding characteristics of two Ets family members, Ets-1 and Elf-1, that are highly expressed in T cells. The results demonstrate that the minimal DNA binding domain of these proteins consists of adjacent basic and putative alpha-helical regions that are conserved in all of the known Ets family members. Both regions are required for DNA binding activity. In vitro binding studies demonstrated that Ets-1 and Elf-1 display distinct DNA binding specificities, and, thereby interact preferentially with different naturally occurring Ets binding sites. A comparison of known Ets binding sites identified three nucleotides at the 3' end of these sequences that control the differential binding of the Ets-1 and Elf-1 proteins. These results are consistent with a model in which different Ets family members regulate the expression of different T cell genes by binding preferentially to purine-rich sequences that share a GGA core motif, but contain distinct flanking sequences.

Expression of a 91-kilodalton PEA3-binding protein is down-regulated during differentiation of F9 embryonal carcinoma cells

Proteins binding to the PEA3 enhancer motif (AGGAAG) activate the polyomavirus early promoter and help comprise the viral late mRNA initiator element (W. Yoo, M. E. Martin, and W. R. Folk, J. Virol. 65:5391-5400, 1991). Because many developmentally regulated cellular genes have PEA3 motifs near their promoter sequences, and because Ets family gene products activate the PEA3 motif, we have studied the expression of PEA3-binding proteins and Ets-related proteins during differentiation of F9 embryonal carcinoma cells. An approximately 91-kDa protein (PEA3-91) was identified in F9 cell nuclear extracts by UV cross-linking to a radiolabeled PEA3 oligonucleotide probe, and expression of PEA3-91 was down-regulated after differentiation of F9 cells to parietal endoderm. The c-ets-1 gene product binds to a sequence in the murine sarcoma virus long terminal repeat that is similar to the PEA3 motif (cGGAAG), but PEA3-91 was not cross-linked to this Ets-1-binding motif, nor did antiserum which recognizes murine c-ets-1 and c-ets-2 proteins have any effect on PEA3-binding activity in mobility shift assays. Furthermore, c-ets-1 mRNA was not detected in undifferentiated or differentiated F9 cells, and c-ets-2 mRNA levels remained high after differentiation. Antiserum against the Drosophila Ets-related E74A protein, however, recognized an approximately 92-kDa protein in F9 cells whose expression during differentiation varied in a manner identical to that of PEA3-91. These data suggest that PEA3-91 is not the product of the ets-1 or ets-2 genes but is likely to be the product of a murine homolog of the Drosophila E74 gene.

Identification of the promoter of the myelomonocytic leukocyte integrin CD11b

The CD11b (or macrophage-1 antigen; MAC-1) subunit of the leukocyte integrin family forms a noncovalently associated heterodimeric structure with the CD18 (beta) subunit on the surface of human granulocytes and monocyte/macrophages, where it enables these myeloid cells to participate in a variety of adherence-related activities. Expression of the CD11b subunit is restricted to cells of the myelomonocytic lineage and depends upon the stage of differentiation with the most mature myeloid cells expressing the highest levels of CD11b. To study the regulation of CD11b expression, a genomic clone corresponding to the 5' region of the CD11b gene was isolated from a human chromosome 16 library. Primer extension and RNase protection assays identified two major transcriptional start sites, located 90 base pairs and 54 base pairs upstream from the initiation methionine. DNA sequence analysis of 1.7 kilobases of the 5' flanking sequence of the CD11b gene indicated the absence of a "CAAT" or "TATA" box; however, potential binding sites for the transcription activators Sp1, PU.1, ets, and AP-2 are present, as well as retinoic acid response elements. The 1.7-kilobase CD11b promoter sequence displayed functional activity in transient transfection assays in the monocytic cell line THP-1 and the myeloid cell line HL-60. In contrast, this 1.7-kilobase promoter sequence did not display functional activity in the Jurkat T-lymphoid cell line. Detailed characterization of the CD11b promoter sequence should provide insight into the molecular events regulating the tissue-specific and developmental stage-specific expression of the CD11b molecule in myelomonocytic cells.

BLyF, a novel cell-type- and stage-specific regulator of the B-lymphocyte gene mb-1

The mb-1 gene encodes an integral membrane protein that appears to be required for the surface expression and signalling function(s) of the immunoglobulin receptor on B lymphocytes. The gene is expressed in a lineage-restricted manner. It is activated early in B-cell ontogeny, continues to be expressed in mature B cells, but is turned off in terminally differentiated plasma cells. We have identified the mb-1 promoter and functionally tested its activity by transient transfections. A 737-bp promoter fragment preferentially stimulates accurately initiated transcription in mb-1-expressing B cells. Deletion analysis of the promoter suggests the presence of two functional domains, proximal and distal. Both domains independently activate transcription from a heterologous promoter. The distal domain functions in a cell-type- and stage-specific manner, activating transcription in B cells but not in T cells or plasma cells. A 25-bp element within this domain is necessary and sufficient for activity. This element is recognized by a novel cell-type- and stage-specific transcription factor termed BLyF. The binding of BLyF completely correlates with the ability of the regulatory element to stimulate transcription. Thus, BLyF appears to positively regulate transcription of the mb-1 gene. Our results also suggest that the inactivity of the mb-1 locus in plasma cells is not simply due to the loss of BLyF activity.

cis-acting sequences required for inducible interleukin-2 enhancer function bind a novel Ets-related protein, Elf-1

The recent definition of a consensus DNA binding sequence for the Ets family of transcription factors has allowed the identification of potential Ets binding sites in the promoters and enhancers of many inducible T-cell genes. In the studies described in this report, we have identified two potential Ets binding sites, EBS1 and EBS2, which are conserved in both the human and murine interleukin-2 enhancers. Within the human enhancer, these two sites are located within the previously defined DNase I footprints, NFAT-1 and NFIL-2B, respectively. Electrophoretic mobility shift and methylation interference analyses demonstrated that EBS1 and EBS2 are essential for the formation of the NFAT-1 and NFIL-2B nuclear protein complexes. Furthermore, in vitro mutagenesis experiments demonstrated that inducible interleukin-2 enhancer function requires the presence of either EBS1 or EBS2. Two well-characterized Ets family members, Ets-1 and Ets-2, are reciprocally expressed during T-cell activation. Surprisingly, however, neither of these proteins bound in vitro to EBS1 or EBS2. We therefore screened a T-cell cDNA library under low-stringency conditions with a probe from the DNA binding domain of Ets-1 and isolated a novel Ets family member, Elf-1. Elf-1 contains a DNA binding domain that is nearly identical to that of E74, the ecdysone-inducible Drosophila transcription factor required for metamorphosis (hence the name Elf-1, for E74-like factor 1). Elf-1 bound specifically to both EBS1 and EBS2 in electrophoretic mobility shift assays. It also bound to the purine-rich CD3R element from the human immunodeficiency virus type 2 long terminal repeat, which is required for inducible virus expression in response to signalling through the T-cell receptor. Taken together, these results demonstrate that multiple Ets family members with apparently distinct DNA binding specificities regulate differential gene expression in resting and activated T cells.

Structure of the genes encoding the CD19 antigen of human and mouse B lymphocytes

CD19 is a B lymphocyte cell-surface marker that is expressed early during pre-B-cell differentiation with expression persisting until terminal differentiation into plasma cells. CD19 is a member of the Ig gene superfamily with two extracellular Ig-like domains separated by a non-Ig-like domain, and with an extensive approximately 240 amino acid cytoplasmic domain. In this study, Southern blot analysis revealed that the human and mouse CD19 genes were compact single copy genes. Both the human and mouse CD19 genes were isolated and the nucleotide sequences flanking each exon were determined. Both genes were composed of 15 exons and spanned approximately 8 kilobases (kb) of DNA in human and approximately 6 kb in mouse. The positions of exon-intron boundaries were identical between human and mouse and correlated with the putative functional domains of the CD19 protein. The 200 bp region 5' of the putative translation initiation AUG codon was well conserved in sequence between human and mouse and contained potential transcription regulatory elements. In addition, the 3' untranslated regions (UT) of the CD19 genes following the termination codon were conserved in sequence. The high level of conservation of nucleotide sequences between species in all exons and 5' and 3' UT suggests that expression of the CD19 gene may be regulated in a similar fashion in human and mouse.

cis-acting sequences required for inducible interleukin-2 enhancer function bind a novel Ets-related protein, Elf-1

The recent definition of a consensus DNA binding sequence for the Ets family of transcription factors has allowed the identification of potential Ets binding sites in the promoters and enhancers of many inducible T-cell genes. In the studies described in this report, we have identified two potential Ets binding sites, EBS1 and EBS2, which are conserved in both the human and murine interleukin-2 enhancers. Within the human enhancer, these two sites are located within the previously defined DNase I footprints, NFAT-1 and NFIL-2B, respectively. Electrophoretic mobility shift and methylation interference analyses demonstrated that EBS1 and EBS2 are essential for the formation of the NFAT-1 and NFIL-2B nuclear protein complexes. Furthermore, in vitro mutagenesis experiments demonstrated that inducible interleukin-2 enhancer function requires the presence of either EBS1 or EBS2. Two well-characterized Ets family members, Ets-1 and Ets-2, are reciprocally expressed during T-cell activation. Surprisingly, however, neither of these proteins bound in vitro to EBS1 or EBS2. We therefore screened a T-cell cDNA library under low-stringency conditions with a probe from the DNA binding domain of Ets-1 and isolated a novel Ets family member, Elf-1. Elf-1 contains a DNA binding domain that is nearly identical to that of E74, the ecdysone-inducible Drosophila transcription factor required for metamorphosis (hence the name Elf-1, for E74-like factor 1). Elf-1 bound specifically to both EBS1 and EBS2 in electrophoretic mobility shift assays. It also bound to the purine-rich CD3R element from the human immunodeficiency virus type 2 long terminal repeat, which is required for inducible virus expression in response to signalling through the T-cell receptor. Taken together, these results demonstrate that multiple Ets family members with apparently distinct DNA binding specificities regulate differential gene expression in resting and activated T cells.

BLyF, a novel cell-type- and stage-specific regulator of the B-lymphocyte gene mb-1

The mb-1 gene encodes an integral membrane protein that appears to be required for the surface expression and signalling function(s) of the immunoglobulin receptor on B lymphocytes. The gene is expressed in a lineage-restricted manner. It is activated early in B-cell ontogeny, continues to be expressed in mature B cells, but is turned off in terminally differentiated plasma cells. We have identified the mb-1 promoter and functionally tested its activity by transient transfections. A 737-bp promoter fragment preferentially stimulates accurately initiated transcription in mb-1-expressing B cells. Deletion analysis of the promoter suggests the presence of two functional domains, proximal and distal. Both domains independently activate transcription from a heterologous promoter. The distal domain functions in a cell-type- and stage-specific manner, activating transcription in B cells but not in T cells or plasma cells. A 25-bp element within this domain is necessary and sufficient for activity. This element is recognized by a novel cell-type- and stage-specific transcription factor termed BLyF. The binding of BLyF completely correlates with the ability of the regulatory element to stimulate transcription. Thus, BLyF appears to positively regulate transcription of the mb-1 gene. Our results also suggest that the inactivity of the mb-1 locus in plasma cells is not simply due to the loss of BLyF activity.

Molecular cloning and characterization of PEA3, a new member of the Ets oncogene family that is differentially expressed in mouse embryonic cells

The PEA3 motif, first recognized in the polyomavirus enhancer, is an oncogene, serum growth factor, and phorbol ester-responsive element. An activity capable of binding to this sequence, termed PEA3 (polyomavirus enhancer activator 3), was identified in mouse 3T6 cell nuclear extracts. We have cloned cDNAs that encode PEA3 from a mouse FM3A cell cDNA library. A continuous open reading frame in the longest cDNA predicts a 555-amino-acid protein with a calculated molecular mass of 61 kD. Recombinant PEA3 binds to DNA with the same sequence specificity as that endogenous to FM3A cells and activates transcription through the PEA3 motif in HeLa cells. Deletion mapping of the protein revealed that the DNA-binding domain is located within a stretch of 102 amino acids near the carboxyl terminus. This region shares extensive sequence similarity with the ETS domain, a conserved protein sequence common to all ets gene family members. PEA3 is encoded by a 2.4-kb mRNA that is expressed to differing extents in fibroblastic and epithelial cell lines but not in hematopoietic cell lines. In the mouse, PEA3 expression is highly restricted; only the epididymis and the brain contain readily detectable amounts of its mRNA. Interestingly, the amount of PEA3 mRNA is down-regulated during retinoic acid-induced differentiation of mouse embryonic cell lines. These findings suggest that PEA3 plays a regulatory role during mouse embryogenesis.

Identification of nucleotide preferences in DNA sequences recognised specifically by c-Ets-1 protein

The protooncogene Ets-1 is a member of the c-Ets family of genes originally identified through their sequence homology to the v-ets gene of the avian erythroblastosis virus E26. Ets-like factors are characterised by a conserved 85 amino acid domain which appears to be essential for binding to purine rich DNA sequences. Sequences binding to Ets-1 were selected from a random oligonucleotide pool by immunoprecipitation and amplified using the Polymerase Chain Reaction. Oligonucleotides enriched by this procedure were cloned in plasmids and sequenced. Alignment of DNA sequences revealed GGAA and GGAT cores at about a 1.4:1 ratio. Preferred sequences were identified both 5' and 3' of the GGAW core, extending the binding site to ACMGGAWRTT. Analysis of the flanking sequences associated with GGAA and GGAT cores revealed differences which may have compensated for the generally lower affinity of binding sites containing a GGAT core. Lastly mutational analysis of one particular Ets-1 binding site was used to establish the relative importance for binding of some nucleotides within the core and to show that Ets-1 and the closely related Ets-2 proteins bind to similar sequences.

Myb and Ets proteins cooperate in transcriptional activation of the mim-1 promoter

In the generation of the acutely transforming avian retrovirus E26, both myb and ets genes have been transduced, leading to the production of a Gag-Myb-Ets fusion protein. This co-occurrence of v-myb and v-ets oncogenes suggests that the two might have a functional relationship. To look for such a relationship, we tested the transcriptional activation activity of Myb alone or with coexpressed Ets-1 or Ets-2. Using the promoter of the v-Myb-inducible mim-1 gene as a target, we found that full-length c-Myb gene products were poor activators of transcription, while an oncogenic (truncated) form of this protein was a strong trans-activator. However, coexpression of Ets-2 with full-length or truncated forms of Myb greatly increased trans-activation. Coexpression of Ets-1, Fos, Jun, or Myc with Myb did not increase trans-activation of the mim-1 promoter. The ability of Myb and Ets-2 to transactivate was cooperative, since Ets-2 alone gave little or no activation. Bacterially synthesized Ets-2 protein was found to bind specifically to the mim-1 promoter, suggesting that it may be a target for both Myb and Ets proteins. Thus, Myb and Ets proteins can cooperate in transcriptional activation, and their co-occurrence in the E26 virus may reflect a functional relationship between these two oncoproteins. Truncated forms of Myb may have a reduced need for cooperating factors such as Ets-2, and this might constitute an important mechanism associated with oncogenic activation.

PU.1 recruits a second nuclear factor to a site important for immunoglobulin kappa 3' enhancer activity

PU.1 is a B-cell- and macrophage-specific transcription factor. By an electrophoretic mobility shift assay and dimethyl sulfate methylation interference assays, we show that PU.1 binds to DNA sequences within the immunoglobulin kappa 3' enhancer (kappa E3'). Binding of PU.1 to the kappa E3' enhancer assists the binding of a second tissue-restricted factor, NF-EM5, to an adjacent site. Binding of NF-EM5 to kappa E3' DNA sequences requires protein-protein interaction with PU.1 as well as specific protein-DNA interactions. This is the first known instance of PU.1 interacting with another cellular protein. NF-EM5 does not cofractionate with PU.1, suggesting that it is a distinct protein and is not a posttranslational modification of PU.1. UV-crosslinking studies and elution from sodium dodecyl sulfate-polyacrylamide gels indicate that NF-EM5 is a protein of approximately 46 kDa. Site-directed mutagenesis studies of the PU.1- and EM5-binding sites indicate that these sites play important roles in kappa E3' enhancer activity. By using a series of PU.1 deletion constructs, we have identified a region in PU.1 that is necessary for interaction with NF-EM5. This segment encompasses a 43-amino-acid region with PEST sequence homology, i.e., one that is rich in proline (P), glutamic acid (E), serine (S), and threonine (T).

Characterization of SAP-1, a protein recruited by serum response factor to the c-fos serum response element

We used a yeast genetic screen to isolate cDNAs that encode a protein, SRF accessory protein-1 (SAP-1), that is recruited to the c-fos serum response element (SRE) as part of a ternary complex that includes serum response factor (SRF). SAP-1 requires DNA-bound SRF for ternary complex formation and makes extensive DNA contacts to the 5' side of SRF, but does not bind DNA autonomously. Ternary complex formation by SAP-1 requires only the DNA-binding domain of SRF, which can be replaced by that of the related yeast protein MCM1. We isolated cDNAs encoding two forms of SAP-1 protein, SAP-1a and SAP-1b, which differ at their C termini. Both SAP-1 proteins contain three regions of striking homology with the elk-1 protein, including an N-terminal ets domain. Ternary complex formation by SAP-1 requires both the ets domain and a second conserved region 50 amino acids to its C-terminal side. SAP-1 has similar DNA binding properties to the previously characterized HeLa cell protein p62/TCF.

Regulation of transcription of immunoglobulin germ-line gamma 1 RNA: analysis of the promoter/enhancer

Antibody class switching is achieved by recombinations between switch (S) regions which consist of tandemly repeated sequences located 5' to Ig heavy chain constant (CH) region genes. RNA transcripts from specific unrearranged or germ-line Ig CH genes are induced in IgM+ B cells prior to their undergoing class switch recombination to the same CH genes. Thus, the antibody class switch appears to be directed by induction of accessibility, as assayed by transcription of germ line CH genes. For example, IL-4 induces transcripts from the mouse germ-line C gamma 1 and C epsilon genes to which it also directs switch recombination. We report here that the 150 bp region upstream of the first initiation site of RNA transcribed from the murine germ-line C gamma 1 gene, contains promoter and enhancer elements responsible for basal level transcription and inducibility by anti-Ig phorbol myristate acetate (PMA) and for synergy of these inducers with IL-4 in a surface IgM+ B cell line, L10A6.2 and a surface IgG2a+ B cell line, A20.3. Linker-scanning mutations demonstrated that multiple interdependent elements are required for inducibility by PMA and also for synergy with IL-4. Within the 150 bp region are several consensus sequences that bind known or putative transcription factors, including a C/EBP binding site--IL-4 responsive element, four CACCC boxes, a PU box, a TGF beta inhibitory element (TIE), an alpha beta-interferon response element (alpha beta-IRE) and an AP-3 site. The relationship between transcription regulated by these elements and the regulation of endogenous germ-line gamma 1 transcripts and switching to IgG1 is discussed.

PU.1 recruits a second nuclear factor to a site important for immunoglobulin kappa 3' enhancer activity

PU.1 is a B-cell- and macrophage-specific transcription factor. By an electrophoretic mobility shift assay and dimethyl sulfate methylation interference assays, we show that PU.1 binds to DNA sequences within the immunoglobulin kappa 3' enhancer (kappa E3'). Binding of PU.1 to the kappa E3' enhancer assists the binding of a second tissue-restricted factor, NF-EM5, to an adjacent site. Binding of NF-EM5 to kappa E3' DNA sequences requires protein-protein interaction with PU.1 as well as specific protein-DNA interactions. This is the first known instance of PU.1 interacting with another cellular protein. NF-EM5 does not cofractionate with PU.1, suggesting that it is a distinct protein and is not a posttranslational modification of PU.1. UV-crosslinking studies and elution from sodium dodecyl sulfate-polyacrylamide gels indicate that NF-EM5 is a protein of approximately 46 kDa. Site-directed mutagenesis studies of the PU.1- and EM5-binding sites indicate that these sites play important roles in kappa E3' enhancer activity. By using a series of PU.1 deletion constructs, we have identified a region in PU.1 that is necessary for interaction with NF-EM5. This segment encompasses a 43-amino-acid region with PEST sequence homology, i.e., one that is rich in proline (P), glutamic acid (E), serine (S), and threonine (T).

Three essential promoter elements mediate tumour necrosis factor and interleukin-1 activation of the granulocyte-colony stimulating factor gene

Granulocyte-colony stimulating factor (G-CSF) is a haemopoietic growth factor produced by mesenchymal cells but not T lymphocytes after stimulation with specific cytokines or mitogens. A 330 bp promoter fragment of the human G-CSF gene induced reporter gene expression in human embryonic lung fibroblasts in response to tumor necrosis factor-alpha (TNF-alpha) or interleukin-1 beta (IL-1 beta). The same promoter fragment was not active in Jurkat T cells nor did it respond to phorbol ester in either cell type. At least three distinct elements, the CK-1 sequence, a decanucleotide present in haemopoietic growth factor genes, an NF-IL-6 consensus sequence and a consensus octamer sequence, were essential in the G-CSF promoter for TNF-alpha and IL-1 beta response. Mutation of any of these sequences abolished promoter function. In contrast, mutation of two other consensus protein binding sequences, i.e. a Pu-1 site and a CK-2-like sequence, did not eliminate promoter function. Both the CK-1 and octamer sequences acted independently as TNF-alpha and IL-1 beta responsive elements upstream of a heterologous promoter. The response of the octamer sequence and the 330 bp promoter but not the CK-1 sequence was greater with IL-1 beta than TNF-alpha reflecting a similar response of the endogenous gene.

Transcriptional regulation during T-cell development: the alpha TCR gene as a molecular model

The regulation of gene expression during lymphocyte differentiation is a complex process involving interactions between multiple positive and negative transcriptional regulatory elements. In this article, transcriptional regulation of the archetypal T-cell-specific gene, alpha TCR, is discussed. Major recent developments, including the identification of novel families of transcription factors that regulate multiple T-cell genes during thymocyte ontogeny and T-cell activation, are described.