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

Differentiation arrest and stromal cell-independent growth of murine erythroleukemia cells are associated with elevated expression of ets-related genes but not with mutation of p53

The ELM erythroleukemia is novel in that long-term survival of leukemic cells in culture (ELM-D cells) is dependent on contact with a bone marrow-derived stromal feeder cell layer. However, a number of stroma-independent (ELM-I) mutants that vary in their ability to differentiate in vitro in response to erythropoietin and interleukin-3 have been derived. We have attempted to define the genetic changes responsible for these different phenotypes. At the p53 locus in the primary leukemic cells, one copy of the gene has been lost whereas the other contains an 18-bp depletion, implicating its mutation as an early step in the development of the leukemia. Changes in ets gene expression have also been found. The Fli-1 gene region is rearranged in the primary tumor because of the insertion of a retrovirus inserted upstream of one Fli-1 allele, but this does not result in Fli-1 gene activation in any of the ELM-D or ELM-I cell lines except one. It seems significant that this line is the only one to have lost the ability to differentiate in response to erythropoietin. In addition, up-regulation of erg is associated with stromal cell-independent growth, since all ELM-I mutants have moderate levels of erg mRNA, whereas only low or undetectable levels are found in primary leukemic cells in vivo or in ELM-D cells in vitro. This up-regulation of erg mRNA seems to be important for stromal cell-independent growth, since ELM-D cells show elevated expression of the erg gene after separation from stromal cells. This seems to be made permanent in ELM-I mutants, since they do not down-regulate erg mRNA when grown in contact with stromal cells. We therefore propose that ets family members regulate both the survival and differentiation of erythroid cells.

Characterization of the human CD4 gene promoter: transcription from the CD4 gene core promoter is tissue-specific and is activated by Ets proteins

We analyzed the 5' transcription control sequences of the human CD4 gene. We located the transcription initiation site and showed that the CD4 core promoter (positions -40 to +16) lacks a classical "TATA" or initiator positioning consensus sequence but directs precise and efficient transcription when coupled to the ubiquitously active simian virus 40 enhancer. The transcriptional activity of the CD4 gene promoter correlated with CD4 expression in various cell types. Interestingly, the CD4 core promoter also displayed a tissue-specific transcriptional activity. Within this fragment, three nucleic acid sequences are completely conserved in the murine CD4 gene. One of these sequences contains a perfect ETS consensus sequence. Another ETS consensus sequence is located 1060 nt upstream. Electrophoretic-mobility-shift assays showed that the core promoter ETS motif binds an Ets-related protein specifically expressed at high levels in CD4+ cells. Moreover, in CD4- cells, overexpression of Ets-1 or Ets-2 efficiently and specifically activated transcription from the CD4 promoter and core promoter. These data indicate that Ets transcription factors play a central role in controlling CD4 gene expression, by binding to both a classical remote site and an unusual proximal activator sequence.

The genomic structure of the murine ICSBP gene reveals the presence of the gamma interferon-responsive element, to which an ISGF3 alpha subunit (or similar) molecule binds

ICSBP, a member of the interferon regulatory factor family, is expressed predominantly in lymphoid tissues and is induced by gamma interferon (IFN-gamma). We have studied the genomic organization of the murine ICSBP gene and its 5' upstream region. The murine ICSBP gene (Icsbp) is present as a single copy on chromosome 8 and consists of nine exons. Transcription initiates at two juxtaposed sites downstream from the TATA and CAAT boxes and produces two species of ICSBP mRNA (3.0 and 1.7 kb), presumably by differential usage of poly(A)+ signals. A sequence from -175 to -155 was identified to be an IFN response region that conferred IFN-gamma induction upon a heterologous promoter in lymphoid cell line EL4. This region includes a motif, TTCNNGGAA, designated the palindromic IFN response element (pIRE), to which an IFN-gamma-inducible, cycloheximide-sensitive factor(s) binds. A similar palindromic motif was found in the upstream region of the murine IRF-1 gene, the IFN-gamma activation site of the guanylate-binding protein gene and the IFN-gamma-responsive region of the Fc receptor type I gene, all of which competed with the pIRE for factor binding in gel mobility shift assays. We show that the pIRE binding factor reacts with the antibody against the 91-kDa subunit of ISGF3 alpha recently shown to bind to the IFN-gamma activation site. These results suggest that this factor is related to the IFN-gamma activation factor and contains the 91-kDa subunit of ISGF3 alpha. Taken together, pIRE represents an IRE that is distinct from the classical IFN-stimulated response element and that is capable of conferring IFN-gamma induction through the binding of the 91-kDa ISGF3 alpha subunit (or an antigenically similar molecule).

The genomic structure of the murine ICSBP gene reveals the presence of the gamma interferon-responsive element, to which an ISGF3 alpha subunit (or similar) molecule binds

ICSBP, a member of the interferon regulatory factor family, is expressed predominantly in lymphoid tissues and is induced by gamma interferon (IFN-gamma). We have studied the genomic organization of the murine ICSBP gene and its 5' upstream region. The murine ICSBP gene (Icsbp) is present as a single copy on chromosome 8 and consists of nine exons. Transcription initiates at two juxtaposed sites downstream from the TATA and CAAT boxes and produces two species of ICSBP mRNA (3.0 and 1.7 kb), presumably by differential usage of poly(A)+ signals. A sequence from -175 to -155 was identified to be an IFN response region that conferred IFN-gamma induction upon a heterologous promoter in lymphoid cell line EL4. This region includes a motif, TTCNNGGAA, designated the palindromic IFN response element (pIRE), to which an IFN-gamma-inducible, cycloheximide-sensitive factor(s) binds. A similar palindromic motif was found in the upstream region of the murine IRF-1 gene, the IFN-gamma activation site of the guanylate-binding protein gene and the IFN-gamma-responsive region of the Fc receptor type I gene, all of which competed with the pIRE for factor binding in gel mobility shift assays. We show that the pIRE binding factor reacts with the antibody against the 91-kDa subunit of ISGF3 alpha recently shown to bind to the IFN-gamma activation site. These results suggest that this factor is related to the IFN-gamma activation factor and contains the 91-kDa subunit of ISGF3 alpha. Taken together, pIRE represents an IRE that is distinct from the classical IFN-stimulated response element and that is capable of conferring IFN-gamma induction through the binding of the 91-kDa ISGF3 alpha subunit (or an antigenically similar molecule).

The PU.1/Spi-1 proto-oncogene is a transcriptional regulator of a lentivirus promoter

The enhancer unit present in the retrovirus equine infectious anemia virus (EIAV) was previously shown to contain binding sites for proteins belonging to MDBP, PEA2, AP-1, and ets families. The EIAV ets motif matches the consensus sequence for both PEA3- and PU.1-binding sites. Here, we show by gel shift analysis that PU.1, present in nuclear extracts from monocyte and B-lymphocyte cell lines, binds to oligonucleotides containing the EIAV ets element. HeLa cells transiently transfected with a PU.1 expression plasmid expressed nuclear factors that formed complexes indistinguishable from those seen with monocyte extracts. Antibodies to PU.1 protein either supershifted or abolished formation of these complexes, depending on the PU.1 epitopes recognized. The binding of PU.1 to the EIAV ets motif in vitro correlated with transcriptional activity of the EIAV promoter in transfected monocyte cell lines. In HeLa cells, the product of PU.1 cDNA bound to the EIAV ets motif and activated transcription from the EIAV promoter. The PU.1-binding site was the primary determinant of EIAV promoter activity in cell lines that express PU.1. Nucleotide determinants of PU.1 binding and a consensus PU.1 binding sequence were defined in gel shift assays using a panel of mutated oligonucleotides. To our knowledge, this is the first report of a retroviral promoter controlled by PU.1.

Differential regulation of the human immunodeficiency virus type 2 enhancer in monocytes at various stages of differentiation

We have demonstrated that stimulation of the human immunodeficiency virus type 2 (HIV-2) enhancer in T cells is dependent upon at least four cis-acting elements, including two purine-rich binding sites, PuB1 and PuB2, which are capable of binding members of the ets family of proto-oncogenes, the pets (peri-ets) site, which lies just upstream of the PuB2 site, and a single kappa B site (D. M. Markovitz, M. Smith, J. M. Hilfinger, M. C. Hannibal, B. Petryniak, and G. J. Nabel, J. Virol. 66:5479-5484, 1992). In this study, we examined the regulation of the HIV-2 enhancer in cells of monocytic lineage. We found that in immature monocytic cell lines, the HIV-2 enhancer is markedly induced by phorbol esters and that all four cis-acting elements are required for activation. In mature monocytic cells, constitutive activity is high, with only modest stimulation following phorbol ester treatment. Mutation of any of the four cis-acting elements resulted in greatly reduced basal expression in mature monocytes. This is in contrast to HIV-1, in which developmentally controlled expression of the enhancer in monocytes is mediated largely through the kappa B sites alone [G. E. Griffin, K. Leung, T. M. Folks, S. Kunkel, and G. J. Nabel, Nature (London) 339:70-73, 1989]. Further, we demonstrated that although both Elf-1, an ets family member with significant similarity to the drosophila developmental regulatory protein E74, and Pu.1, a monocyte- and B-cell-specific member of the ets family, bind the purine-rich enhancer region, Elf-1 is the protein which binds predominantly in vivo. A nuclear factor(s) which binds the pets site, an element which has been described only in HIV-2, was detected in extracts of all of the monocytic cells tested. These findings indicate that the mechanism by which cellular factors regulate HIV-2 enhancer function in monocytic cells differs significantly from that of HIV-1 and may offer a partial explanation for the differences in the biological and clinical characteristics of the two viruses.

Expression of mRNA encoding the macrophage colony-stimulating factor receptor (c-fms) is controlled by a constitutive promoter and tissue-specific transcription elongation

The gene encoding the receptor for macrophage colony-stimulating factor 1 (CSF-1), the c-fms protooncogene, is selectively expressed in immature and mature mononuclear phagocytes and trophoblasts. Exon 1 is expressed only in trophoblasts. Isolation and sequencing of genomic DNA flanking exon 2 of the murine c-fms gene revealed a TATA-less promoter with significant homology to human c-fms. Reverse transcriptase primer extension analysis using exon 2 primers identified multiple clustered transcription initiation sites. Their position was confirmed by RNase protection. The same primer extension products were detected in equal abundance from macrophage or nonmacrophage sources of RNA. c-fms mRNA is acutely down-regulated in primary macrophages by CSF-1, bacterial lipopolysaccharide (LPS), and phorbol myristate acetate (PMA). Each of these agents reduced the abundance of c-fms RNA detectable by primer extension using an exon 3 primer without altering the abundance of presumptive short c-fms transcripts detected with exon 2 primers. Primer extension analysis with an intron 2 primer detected products at greater abundance in nonmacrophages. Templates detected with the intronic primer were induced in macrophages by LPS, PMA, and CSF-1, suggesting that each of the agents caused a shift from full-length c-fms mRNA production to production of unspliced, truncated transcripts. The c-fms promoter functioned constitutively in the RAW264 macrophage cell line, the B-cell line MOPC.31C, and several nonhematopoietic cell lines. Macrophage-specific expression and responsiveness to selective repression by LPS and PMA was achieved by the incorporation of intron 2 into the c-fms promoter-reporter construct. The results suggest that expression of the c-fms gene in macrophages is controlled by sequences in intron 2 that act by regulating transcription elongation.

Expression of mRNA encoding the macrophage colony-stimulating factor receptor (c-fms) is controlled by a constitutive promoter and tissue-specific transcription elongation

The gene encoding the receptor for macrophage colony-stimulating factor 1 (CSF-1), the c-fms protooncogene, is selectively expressed in immature and mature mononuclear phagocytes and trophoblasts. Exon 1 is expressed only in trophoblasts. Isolation and sequencing of genomic DNA flanking exon 2 of the murine c-fms gene revealed a TATA-less promoter with significant homology to human c-fms. Reverse transcriptase primer extension analysis using exon 2 primers identified multiple clustered transcription initiation sites. Their position was confirmed by RNase protection. The same primer extension products were detected in equal abundance from macrophage or nonmacrophage sources of RNA. c-fms mRNA is acutely down-regulated in primary macrophages by CSF-1, bacterial lipopolysaccharide (LPS), and phorbol myristate acetate (PMA). Each of these agents reduced the abundance of c-fms RNA detectable by primer extension using an exon 3 primer without altering the abundance of presumptive short c-fms transcripts detected with exon 2 primers. Primer extension analysis with an intron 2 primer detected products at greater abundance in nonmacrophages. Templates detected with the intronic primer were induced in macrophages by LPS, PMA, and CSF-1, suggesting that each of the agents caused a shift from full-length c-fms mRNA production to production of unspliced, truncated transcripts. The c-fms promoter functioned constitutively in the RAW264 macrophage cell line, the B-cell line MOPC.31C, and several nonhematopoietic cell lines. Macrophage-specific expression and responsiveness to selective repression by LPS and PMA was achieved by the incorporation of intron 2 into the c-fms promoter-reporter construct. The results suggest that expression of the c-fms gene in macrophages is controlled by sequences in intron 2 that act by regulating transcription elongation.

Genomic structure of the human CD53 gene

The genomic structure of the gene encoding human pan-leukocyte surface glycoprotein CD53 (a member of the "tetraspan family" of membrane proteins) was determined. The gene consists of eight exons encoding all sequences found in cDNA and is spread over more than 26 kilobases of genomic DNA. The exon-intron organization of the CD53 gene is strikingly similar to the CD63 and TAPA-1 genes, which suggests a close evolutionary relationship between these genes. The 5' end of the gene upstream of the first exon contains at least three close transcription start points (approximately 20 base pairs 5' of the 5' end of the published cDNA). The region upstream of the transcription initiation sites is not G+C rich; it contains potential binding sites for several transcriptional factors but no TATA or CCAAT boxes.

Identification of cell-specific and developmentally regulated nuclear factors that direct myeloid and lymphoid expression of the CD11a gene

Human CD11a/CD18 is a noncovalently associated heterodimeric receptor expressed exclusively on the surface of lymphocytes and myeloid cells. To begin to understand the mechanisms that direct the expression of the genes encoding this receptor, we have cloned and characterized the promoter region of the CD11a gene and localized cis-acting elements involved in its expression in lymphoid and myeloid cells. One such element is the "LYM" box, which interacts with two sets of DNA-binding activities, one primarily expressed in lymphocytes and preerythroid cells and the other expressed predominantly in myeloid cells. A second element required for expression of the CD11a gene contains the "GAGA" sequence RRRGAGGAAG (R indicates a purine), which interacts with the DNA-binding activities MS-1 and MS-2. MS-1 is expressed exclusively in myeloid cells and probably represents a member of the Ets family of transcription activators. MS-2 is present in epithelial, preerythroid, and lymphoid cells but is only detected in myeloid cells after differentiation. MS-2 also binds to a second element within the CD11a promoter and homologous elements present in the promoter regions of the CD11b and CD43 genes. Since MS-2 interacts with a number of different gene promoters and is developmentally regulated in myeloid cells, it may play a major role in regulating myeloid gene expression.

Both LyF-1 and an Ets protein interact with a critical promoter element in the murine terminal transferase gene

Terminal deoxynucleotidyltransferase (TdT) is a template-independent DNA polymerase that is expressed transiently during the earliest stages of B- and T-cell ontogeny. Previously, we characterized the promoter for the murine TdT gene and identified a novel DNA-binding protein, called LyF-1, that interacts with a DNA sequence element found to be critical for transcriptional activity in lymphoid cell lines. Here, we present a more detailed analysis of this 30-bp control element, called the TdT D' element, which is centered approximately 60 bp upstream of the transcription start site. We found that both the murine and human D' elements are recognized by multiple proteins, including LyF-1 and at least two Ets family proteins, Ets-1 and Fli-1. Additional protein-DNA interactions were identified through studies using unfractionated nuclear extracts, in which the D' element was apparently incorporated into a multiprotein complex, possibly containing an Ets protein as a core component. By analyzing a series of substitution mutations, two adjacent binding sites for LyF-1 were identified in the murine D' element, with the Ets protein binding site closely coinciding with the proximal, lower-affinity LyF-1 site. Transient transfection analysis with these mutations revealed that only a 10-bp region, containing precisely the Ets and proximal LyF-1 binding sites, was needed for D' activity. These results suggest an important role for an Ets family protein in the expression of the TdT gene. The role of LyF-1 is less clear; it might act in conjunction with the Ets protein bound at the D' element or it might be unnecessary for D' activity.

Mouse beta-globin DNA-binding protein B1 is identical to a proto-oncogene, the transcription factor Spi-1/PU.1, and is restricted in expression to hematopoietic cells and the testis

The hematopoietic-specific DNA-binding protein B1 binds to the DNA consensus sequence AAAGRGGAARYG located twice in intervening sequence 2 of both of the mouse beta-globin genes (D. L. Galson and D.E. Housman, Mol. Cell. Biol. 8:381-392, 1988). B1 was cloned by expression of a murine erythroleukemia (MEL) cell cDNA library in transfected COS cells and screening by electrophoretic mobility shift analysis. B1 is identical to the proto-oncogene Spi-1/PU.1 (Spi-1), an ets family member. Protein-DNA contacts are shown to resemble those of the helix-turn-helix homeodomain proteins. By Northern (RNA) analysis, we found that Spi-1 mRNA is present at low levels during murine CFU-E maturation and is at least 20-fold higher in uninduced MEL, a transformed proerythroblast-like cell line which contains an activating/transforming insertion of spleen focus-forming virus at the Spi-1 locus. Dimethyl sulfoxide-induced MEL cell differentiation decreases Spi-1 mRNA to approximately 20% of the uninduced level before commitment occurs. In addition to erythroid cells, Spi-1 mRNA is present in B cells, myelomonocytes, and mast cells but not in T cells and nonhematopoietic cell types. In situ hybridization demonstrated Spi-1 mRNA expression in bone marrow, spleen, interstitial nonhepatocytes of the liver, and interstitial nontubular cells of the testis. The Spi-1 locus was mapped on human chromosome 11 to the same interval as ACP2 (lysosomal acid phosphatase), between the anonymous DNA markers D11S33 and D11S14. This region has not yet been found to be associated with a human malignancy.

Identification of a novel interleukin-6 response element containing an Ets-binding site and a CRE-like site in the junB promoter

Interleukin-6 (IL-6) activation of the immediate-early gene junB has been shown to require both a tyrosine kinase and an unknown 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H7)-sensitive pathway. Here we report the identification and characterization of an IL-6 immediate-early response element in the junB promoter (designated JRE-IL6) in HepG2 cells. The JRE-IL6 element, located at -149 to -124, contains two DNA motifs, an Ets-binding site (EBS) (CAGGAAGC) and a CRE-like site (TGACGCGA). Functional studies using variously mutated JRE-IL6 elements showed that both motifs were necessary and sufficient for IL-6 response of the promoter. The EBS of the JRE-IL6 element (JEBS) appears to bind a protein in the Ets family or a related protein which could also form a major complex with the EBSs of the murine sarcoma virus long terminal repeat or human T-cell leukemia virus type 1 long terminal repeat. The CRE-like site appears to weakly bind multiple CREB-ATF family proteins. Despite the similarity in the structure between the JRE-IL6 element and the polyomavirus enhancer PyPEA3, composed of an EBS and an AP1-binding site and known to be activated by a variety of oncogene signals, JRE-IL6 could not be activated by activated Ha-Ras, Raf-1, or 12-O-tetradecanoylphorbol-13-acetate. We show that IL-6 activates JRE-IL6 through an H7-sensitive pathway that does not involve protein kinase C, cyclic AMP-dependent kinase, Ca(2+)- or calmodulin-dependent kinases, Ras, Raf-1, or NF-IL6 (C/EBP beta). The combination of JEBS and the CRE-like site appears to form the basis for the selective and efficient response of JRE-IL6 to IL-6 signals, but not to signals generated by activated Ha-Ras, Raf-1, or protein kinase C.

Characterization of cytokine LD78 gene promoters: positive and negative transcriptional factors bind to a negative regulatory element common to LD78, interleukin-3, and granulocyte-macrophage colony-stimulating factor gene promoters

Cytokine LD78 is a human counterpart of the mouse macrophage inflammatory protein 1 alpha/hematopoietic stem cell inhibitor. Promoters of the LD78 alpha and LD78 beta genes showed similar inducible activities in two leukemic cell lines, K562 and Jurkat, but the induction mechanisms differed between the two cell lines. Further characterization of the LD78 alpha promoter indicated that multiple positive and negative regulatory elements are present, some of which are differentially required for induction and repression of the promoter activity in different cells. One of the negative regulatory elements, ICK-1, functioned in both cell lines in the absence and presence of stimulation and was shown to be a recognition site for positive and negative transcriptional factors. This ICK-1 element contained a direct repeat, and similar repeats were also found in the negative regulatory elements of hematopoietic growth factor interleukin-3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF) gene promoters. Nuclear extracts from K562 and Jurkat cells formed several protein-DNA complexes with the LD78 alpha ICK-1 element, one of which was also observed with the IL-3 and GM-CSF ICK-1 elements. Results from in vivo and in vitro analyses suggested that the protein forming this complex functions as a negative factor. The binding affinity of this protein, ICK-1A, to the LD78 alpha ICK-1 element was low and was significantly affected by the incubation temperature and the salt concentration in the binding buffer. ICK-1B, another protein bound specifically by the LD78 alpha ICK-1 element, was shown to be a positive factor important for induction of the promoter. These results suggested that ICK-1A plays an important role in balanced expression of LD78, IL-3, and GM-CSF during hematopoietic cell growth and differentiation.

Characterization of cytokine LD78 gene promoters: positive and negative transcriptional factors bind to a negative regulatory element common to LD78, interleukin-3, and granulocyte-macrophage colony-stimulating factor gene promoters

Cytokine LD78 is a human counterpart of the mouse macrophage inflammatory protein 1 alpha/hematopoietic stem cell inhibitor. Promoters of the LD78 alpha and LD78 beta genes showed similar inducible activities in two leukemic cell lines, K562 and Jurkat, but the induction mechanisms differed between the two cell lines. Further characterization of the LD78 alpha promoter indicated that multiple positive and negative regulatory elements are present, some of which are differentially required for induction and repression of the promoter activity in different cells. One of the negative regulatory elements, ICK-1, functioned in both cell lines in the absence and presence of stimulation and was shown to be a recognition site for positive and negative transcriptional factors. This ICK-1 element contained a direct repeat, and similar repeats were also found in the negative regulatory elements of hematopoietic growth factor interleukin-3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF) gene promoters. Nuclear extracts from K562 and Jurkat cells formed several protein-DNA complexes with the LD78 alpha ICK-1 element, one of which was also observed with the IL-3 and GM-CSF ICK-1 elements. Results from in vivo and in vitro analyses suggested that the protein forming this complex functions as a negative factor. The binding affinity of this protein, ICK-1A, to the LD78 alpha ICK-1 element was low and was significantly affected by the incubation temperature and the salt concentration in the binding buffer. ICK-1B, another protein bound specifically by the LD78 alpha ICK-1 element, was shown to be a positive factor important for induction of the promoter. These results suggested that ICK-1A plays an important role in balanced expression of LD78, IL-3, and GM-CSF during hematopoietic cell growth and differentiation.

Mouse beta-globin DNA-binding protein B1 is identical to a proto-oncogene, the transcription factor Spi-1/PU.1, and is restricted in expression to hematopoietic cells and the testis

The hematopoietic-specific DNA-binding protein B1 binds to the DNA consensus sequence AAAGRGGAARYG located twice in intervening sequence 2 of both of the mouse beta-globin genes (D. L. Galson and D.E. Housman, Mol. Cell. Biol. 8:381-392, 1988). B1 was cloned by expression of a murine erythroleukemia (MEL) cell cDNA library in transfected COS cells and screening by electrophoretic mobility shift analysis. B1 is identical to the proto-oncogene Spi-1/PU.1 (Spi-1), an ets family member. Protein-DNA contacts are shown to resemble those of the helix-turn-helix homeodomain proteins. By Northern (RNA) analysis, we found that Spi-1 mRNA is present at low levels during murine CFU-E maturation and is at least 20-fold higher in uninduced MEL, a transformed proerythroblast-like cell line which contains an activating/transforming insertion of spleen focus-forming virus at the Spi-1 locus. Dimethyl sulfoxide-induced MEL cell differentiation decreases Spi-1 mRNA to approximately 20% of the uninduced level before commitment occurs. In addition to erythroid cells, Spi-1 mRNA is present in B cells, myelomonocytes, and mast cells but not in T cells and nonhematopoietic cell types. In situ hybridization demonstrated Spi-1 mRNA expression in bone marrow, spleen, interstitial nonhepatocytes of the liver, and interstitial nontubular cells of the testis. The Spi-1 locus was mapped on human chromosome 11 to the same interval as ACP2 (lysosomal acid phosphatase), between the anonymous DNA markers D11S33 and D11S14. This region has not yet been found to be associated with a human malignancy.

The c-ets-1 proto-oncogenes in Xenopus laevis: expression during oogenesis and embryogenesis

We previously reported the cloning and sequencing of two cDNAs derived from the Xenopus laevis ets-1 gene (Stiegler et al., 1990). The Xl-ets-1a cDNA encodes a polypeptide highly homologous to known ets-1 proteins. The 3'-UTR contains two AATAAA polyadenylation signals together with three copies of the TTTTTAT sequence thought to confer a maturation-specific polyadenylation and implicated in the deadenylation of dormant mRNAs. Several transcripts with maternal characteristics were detected in oogenesis and early embryogenesis. A marked augmentation of the major transcript in the poly(A)+ fraction was detected at fertilization. Ets-1 transcripts were observed at constant levels during the cleavage stages but decreased abruptly at gastrulation, to reappear from neurulation to late embryogenesis. The possible contribution of 3'-UTR sequence elements to this behavior is discussed.

Description of the leukocyte function-associated antigen 1 (LFA-1 or CD11a) promoter

The CD11a/CD18 (leukocyte function-associated antigen 1 or LFA-1) leukocyte integrin is expressed at high levels on the cell surface of T lymphocytes and macrophages, where it mediates homotypic and heterotypic adherence between leukocytes and other cell types by binding to intracellular adhesion molecules 1 and 2 on the conjugate cell. To initiate studies of the molecular regulation of expression of the CD11a molecule, we isolated genomic clones corresponding to the 5'-flanking region of CD11a, identified the transcriptional start sites for CD11a, and characterized the CD11a promoter sequence in transient expression assays. The CD11a promoter (1.7 kb) directed functional activity of a heterologous reporter gene in the T-lymphocyte cell line Jurkat and the myeloid cell line HL-60 but did not direct functional activity in three different nonleukocyte cell lines. Deletional analysis of the CD11a promoter sequence indicated the presence of distinct, cell-type-specific regulatory sequences with the region from -40 to -17 relative to the transcription start sites responsible for most of the in vitro activity of the CD11a promoter in the Jurkat T-cell line, and the promoter sequence located within the first 17 bp relative to the transcription start sites responsible for CD11a promoter activity in the HL-60 cell line. Identification of the CD11a promoter provides the opportunity to identify unique cis-acting elements and trans-acting factors responsible for the cell-type-specific expression of CD11a in human leukocytes. Further, the CD11a promoter may be useful in transgenic constructs and in retroviral vectors to direct expression of heterologous genes selectively in leukocytes.

Identification of a novel interleukin-6 response element containing an Ets-binding site and a CRE-like site in the junB promoter

Interleukin-6 (IL-6) activation of the immediate-early gene junB has been shown to require both a tyrosine kinase and an unknown 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H7)-sensitive pathway. Here we report the identification and characterization of an IL-6 immediate-early response element in the junB promoter (designated JRE-IL6) in HepG2 cells. The JRE-IL6 element, located at -149 to -124, contains two DNA motifs, an Ets-binding site (EBS) (CAGGAAGC) and a CRE-like site (TGACGCGA). Functional studies using variously mutated JRE-IL6 elements showed that both motifs were necessary and sufficient for IL-6 response of the promoter. The EBS of the JRE-IL6 element (JEBS) appears to bind a protein in the Ets family or a related protein which could also form a major complex with the EBSs of the murine sarcoma virus long terminal repeat or human T-cell leukemia virus type 1 long terminal repeat. The CRE-like site appears to weakly bind multiple CREB-ATF family proteins. Despite the similarity in the structure between the JRE-IL6 element and the polyomavirus enhancer PyPEA3, composed of an EBS and an AP1-binding site and known to be activated by a variety of oncogene signals, JRE-IL6 could not be activated by activated Ha-Ras, Raf-1, or 12-O-tetradecanoylphorbol-13-acetate. We show that IL-6 activates JRE-IL6 through an H7-sensitive pathway that does not involve protein kinase C, cyclic AMP-dependent kinase, Ca(2+)- or calmodulin-dependent kinases, Ras, Raf-1, or NF-IL6 (C/EBP beta). The combination of JEBS and the CRE-like site appears to form the basis for the selective and efficient response of JRE-IL6 to IL-6 signals, but not to signals generated by activated Ha-Ras, Raf-1, or protein kinase C.

Both LyF-1 and an Ets protein interact with a critical promoter element in the murine terminal transferase gene

Terminal deoxynucleotidyltransferase (TdT) is a template-independent DNA polymerase that is expressed transiently during the earliest stages of B- and T-cell ontogeny. Previously, we characterized the promoter for the murine TdT gene and identified a novel DNA-binding protein, called LyF-1, that interacts with a DNA sequence element found to be critical for transcriptional activity in lymphoid cell lines. Here, we present a more detailed analysis of this 30-bp control element, called the TdT D' element, which is centered approximately 60 bp upstream of the transcription start site. We found that both the murine and human D' elements are recognized by multiple proteins, including LyF-1 and at least two Ets family proteins, Ets-1 and Fli-1. Additional protein-DNA interactions were identified through studies using unfractionated nuclear extracts, in which the D' element was apparently incorporated into a multiprotein complex, possibly containing an Ets protein as a core component. By analyzing a series of substitution mutations, two adjacent binding sites for LyF-1 were identified in the murine D' element, with the Ets protein binding site closely coinciding with the proximal, lower-affinity LyF-1 site. Transient transfection analysis with these mutations revealed that only a 10-bp region, containing precisely the Ets and proximal LyF-1 binding sites, was needed for D' activity. These results suggest an important role for an Ets family protein in the expression of the TdT gene. The role of LyF-1 is less clear; it might act in conjunction with the Ets protein bound at the D' element or it might be unnecessary for D' activity.

Two cis-DNA elements involved in myeloid-cell-specific expression and gamma interferon (IFN-gamma) activation of the human high-affinity Fc gamma receptor gene: a novel IFN regulatory mechanism

The human high-affinity receptor for the constant region of immunoglobulin G (human Fc gamma R1) is encoded by two mRNAs induced selectively by gamma interferon (IFN-gamma) and expressed in cells of myeloid lineage. The cis-DNA element (GRR) previously found to confer IFN-gamma responsiveness to this gene acts as an inducible enhancer and is the target of an IFN-gamma-activated factor(s) (GIRE-BP) in cells of different origins. Although the GRR motif is not related to the DNA elements involved in the regulation of other IFN-stimulated genes, GIRE-BP binding depends on the IFN-gamma-dependent activation of the 91-kDa protein known to be one of the factors of a transcriptional complex activated by IFN-alpha. Deletions of the Fc gamma R1 promoter allowed us to identify a 25-bp element, downstream from the GRR motif, conferring cell-type-specific expression. This element, called MATE (myeloid activating transcription element), is the DNA target for constitutive factors forming two complexes, MATE-BP1 and MATE-BP2. In accordance with the functional analysis, MATE-BP binding activities were detected in extracts prepared from myeloid cell lines such as THP-1, HL-60, and U-937 but not in HeLa cell extracts. The MATE motif is present not only in the promoter of other Fc receptor genes but also in several promoters of genes whose expression is restricted to monocytic cells. Our results suggest that human Fc gamma R1 gene expression in myeloid cells is initiated by the interaction of IFN-gamma-activated factors with cell-type-specific factors through their binding to the GRR and MATE motifs.

Two cis-DNA elements involved in myeloid-cell-specific expression and gamma interferon (IFN-gamma) activation of the human high-affinity Fc gamma receptor gene: a novel IFN regulatory mechanism

The human high-affinity receptor for the constant region of immunoglobulin G (human Fc gamma R1) is encoded by two mRNAs induced selectively by gamma interferon (IFN-gamma) and expressed in cells of myeloid lineage. The cis-DNA element (GRR) previously found to confer IFN-gamma responsiveness to this gene acts as an inducible enhancer and is the target of an IFN-gamma-activated factor(s) (GIRE-BP) in cells of different origins. Although the GRR motif is not related to the DNA elements involved in the regulation of other IFN-stimulated genes, GIRE-BP binding depends on the IFN-gamma-dependent activation of the 91-kDa protein known to be one of the factors of a transcriptional complex activated by IFN-alpha. Deletions of the Fc gamma R1 promoter allowed us to identify a 25-bp element, downstream from the GRR motif, conferring cell-type-specific expression. This element, called MATE (myeloid activating transcription element), is the DNA target for constitutive factors forming two complexes, MATE-BP1 and MATE-BP2. In accordance with the functional analysis, MATE-BP binding activities were detected in extracts prepared from myeloid cell lines such as THP-1, HL-60, and U-937 but not in HeLa cell extracts. The MATE motif is present not only in the promoter of other Fc receptor genes but also in several promoters of genes whose expression is restricted to monocytic cells. Our results suggest that human Fc gamma R1 gene expression in myeloid cells is initiated by the interaction of IFN-gamma-activated factors with cell-type-specific factors through their binding to the GRR and MATE motifs.

Two factors that bind to highly conserved sequences in mammalian type C retroviral enhancers

The transcriptional enhancers of the Moloney and Friend murine leukemia viruses (MLV) are important determinants of viral pathogenicity. We used electrophoretic mobility shift and methylation interference assays to study nuclear factors which bind to a region of these enhancers whose sequence is identical between Moloney and Friend viruses and particularly highly conserved among 35 mammalian type C retroviruses whose enhancer sequences have been aligned (E. Golemis, N. A. Speck, and N. Hopkins, J. Virol. 64:534-542, 1990). Previous studies identified sites for the leukemia virus factor b (LVb) and core proteins in this region (N. A. Speck and D. Baltimore, Mol. Cell. Biol. 7:1101-1110, 1987) as well as a site, overlapping those for LVb and core, for a third factor (N. R. Manley, M. A. O'Connell, P. A. Sharp, and N. Hopkins, J. Virol. 63:4210-4223, 1989). Surprisingly, the latter factor appeared to also bind two sites identified in the Friend MLV enhancer, Friend virus factor a and b1 (FVa and FVb1) sites, although the sequence basis for the ability of the protein to bind these diverse sites was not apparent. Here we describe the further characterization of this binding activity, termed MCREF-1 (for mammalian type C retrovirus enhancer factor 1), and the identification of a consensus sequence for its binding, GGN8GG. We also identify a factor, abundant in mouse T-cell lines and designated LVt, which binds to two sites in the Moloney MLV enhancer, overlapping the previously identified LVb and LVc binding sites. These sites contain the consensus binding site for the Ets family of proteins. We speculate on how distinct arrays of these factors may influence the disease-inducing phenotype.

Growth suppression of Friend virus-transformed erythroleukemia cells by p53 protein is accompanied by hemoglobin production and is sensitive to erythropoietin

The murine allele temperature-sensitive (ts) p53Val-135 encodes a ts p53 protein that behaves as a mutant polypeptide at 37 degrees C and as a wild-type polypeptide at 32 degrees C. This ts allele was introduced into the p53 nonproducer Friend erythroleukemia cell line DP16-1. The DP16-1 cell line was derived from the spleen cells of a mouse infected with the polycythemia strain of Friend virus, and like other erythroleukemia cell lines transformed by this virus, it grows independently of erythropoietin, likely because of expression of the viral gp55 protein which binds to and activates the erythropoietin receptor. When incubated at 32 degrees C, DP16-1 cells expressing ts p53Val-135 protein, arrested in the G0/G1 phase of the cell cycle, rapidly lost viability and expressed hemoglobin, a marker of erythroid differentiation. Erythropoietin had a striking effect on p53Val-135-expressing cells at 32 degrees C by prolonging their survival and diminishing the extent of hemoglobin production. This response to erythropoietin was not accompanied by down-regulation of viral gp55 protein.

Distinctive growth requirements and gene expression patterns distinguish progenitor B cells from pre-B cells

Long-term bone marrow cultures have been useful in determining gene expression patterns in pre-B cells and in the identification of cytokines such as interleukin 7 (IL-7). We have developed a culture system to selectively grow populations of B lineage restricted progenitors (pro-B cells) from murine bone marrow. Pro-B cells do not grow in response to IL-7, Steel locus factor (SLF), or a combination of the two. c-kit, the SLF receptor, and the IL-7 receptor are both expressed by pro-B cells, indicating that the lack of response is not simply due to the absence of receptors. Furthermore, SLF is not necessary for the growth of pro-B cells since they could be expanded on a stromal line derived from Steel mice that produces no SLF. IL-7 responsiveness in pre-B cells is associated with an increase in n-myc expression and is correlated with immunoglobulin (Ig) gene rearrangements. Although members of the ets family of transcription factors and the Pim-1 kinase are expressed by pro-B cells, n-myc is not expressed. Pro-B cells maintain Ig genes in the germline configuration, which is correlated with a low level of recombination activating genes 1 and 2 (Rag-1 and 2) mRNA expression, but high expression of sterile mu and terminal deoxynucleotidyl transferase. Pro-B cells are unable to grow separated from the stromal layer by a porous membrane, indicating that stromal contact is required for growth. These results suggest that pro-B cells are dependent on alternative growth signals derived from bone marrow stroma and can be distinguished from pre-B cells by specific patterns of gene expression.

Growth suppression of Friend virus-transformed erythroleukemia cells by p53 protein is accompanied by hemoglobin production and is sensitive to erythropoietin

The murine allele temperature-sensitive (ts) p53Val-135 encodes a ts p53 protein that behaves as a mutant polypeptide at 37 degrees C and as a wild-type polypeptide at 32 degrees C. This ts allele was introduced into the p53 nonproducer Friend erythroleukemia cell line DP16-1. The DP16-1 cell line was derived from the spleen cells of a mouse infected with the polycythemia strain of Friend virus, and like other erythroleukemia cell lines transformed by this virus, it grows independently of erythropoietin, likely because of expression of the viral gp55 protein which binds to and activates the erythropoietin receptor. When incubated at 32 degrees C, DP16-1 cells expressing ts p53Val-135 protein, arrested in the G0/G1 phase of the cell cycle, rapidly lost viability and expressed hemoglobin, a marker of erythroid differentiation. Erythropoietin had a striking effect on p53Val-135-expressing cells at 32 degrees C by prolonging their survival and diminishing the extent of hemoglobin production. This response to erythropoietin was not accompanied by down-regulation of viral gp55 protein.

CD14: cell surface receptor and differentiation marker

In the past, CD14 has been viewed simply as a useful marker molecule for monocytes and macrophages. Now, new findings on its role in binding of LPS-LBP complexes and in signal transduction have engendered renewed interest in the properties of CD14. Here, CD14 function, its expression in different cell types and the regulation of expression, including the generation of soluble CD14, are described, and the diagnostic value of CD14 in various diseases is discussed.

Characterization of the mouse type X collagen gene

Type X collagen, a homotrimer of alpha 1 (X) polypeptide chains, is specifically expressed by hypertrophic chondrocytes in regions of cartilage undergoing endochondral ossification. We have previously characterized a genomic clone containing the major part of the mouse type X collagen gene (col10a1) and assigned the locus for col10a1 to mouse chromosome 10 (Apte et al., Eur. J. Biochem. 224: 217-224, 1992). In this paper, through additional characterization of cDNA and genomic clones, we describe the complete organization of the col10a1 gene. The col10a1 gene is 7.2 kb in size and, as in the chick, col10a1 gene transcripts are generated from only three exons. Exon 1 encodes only the 5' untranslated (5' UT) region of the mRNA and is separated from exon 2 by an intron 562 bp in length. Exon 2 (169 bp) encodes 15 bp of 5' UT message, the translation start plus 17-amino acid residues of the putative signal peptide, and 33 1/3 codons of the putative N-terminal non-collagenous (NC2) domain of type X collagen. Exon 3 is 2854 bp in size and encodes 4 2/3 codons of the NC2 domain, the entire collagenous domain of 463 residues (COL), the entire C-terminal non-collagenous (NC1) domain (161 amino acid residues) and the entire 965 bp 3' untranslated (3' UT) sequence of the mRNA. Two TATA boxes are present in tandem in the col10a1 promotor. Both TATA boxes are active in transcription, generating two populations of transcripts with different 5'-termini; the longer transcript is of low abundance and is detectable only by PCR in newborn mice. The col10a1 promotor contains a CCAAT box as well as other consensus sequence elements required for binding of potential transcription factors. Characterization of the col10a1 gene provides data essential for studies of the regulation of type X collagen expression during mammalian endochondral bone growth and development. Knowledge of the complete structure of the mouse type X collagen gene will also be useful for the investigation of type X collagen gene abnormalities in murine chondrodysplasias and for the generation of transgenic mice.

Human FLI-1 localizes to chromosome 11Q24 and has an aberrant transcript in neuroepithelioma

The v-ets oncogene family shares a conserved motif, termed the ETS-domain, that mediates sequence-specific DNA binding. This motif is unique among transcription factor families. Using partially degenerate oligonucleotides to highly conserved amino acids in this motif as primers for the polymerase chain reaction, a novel ETS-domain cDNA fragment was generated. This fragment was subsequently used to clone both mouse and human full length cDNAs for this gene. The amino acid sequence of the longest open reading frame showed that this gene was homologous to the mouse FLI-I gene, an ETS family gene activated by Friend erythroleukemia virus insertion. The gene is normally expressed only in hematopoietic cells. The gene was localized to chromosome 11q24, a region of aberrations in Ewing's sarcoma and neuroepithelioma. In the neuroepithelioma cell line TC-32 the FLI-1 transcript is present but has an aberrant structure, indicating that it may be rearranged in neuroepithelioma.

Identification of a nuclear protein that constitutively recognizes the sequence containing a heat-shock element. Its binding properties and possible function modulating heat-shock induction of the rat heme oxygenase gene

Heme oxygenase is an essential enzyme in heme catabolism, and also known as a 32-kDa heat-shock protein in rat. The rat heme-oxygenase gene promoter contains a functional heat-shock element (HSE) designated as HSE1 (-290 to -276 from the transcriptional initiation site), which consists of three copies of a 5-bp unit (5'-NGAAN-3';-->) in alternating orientation. Here we identified a putative HSE (-221 to -212), designated as HSE2, consisting of an inverted repeat of this 5-bp unit (<==>). Using transient expression assays, we show that HSE1 is sufficient to confer the heat-inducibility (a three fold to fourfold increase) on the reporter gene located downstream from the rat heme-oxygenase gene promoter, but HSE2 alone is not, suggesting that HSE2, a HSE of a tail-to-tail configuration, is not functional in vivo. However, the presence of both HSE1 and HSE2 in the promoter region increased the heat-mediated induction of the reporter-gene expression by more than 15-fold. Gel mobility-shift assays indicate that both HSE1 and HSE2 are recognized by activated heat-shock factor present only in heat-shocked rat glioma cells. Interestingly, the sequence containing HSE2 is also bound by a protein that is present in nuclear extracts prepared from either heat-shocked or non-shocked glioma cells, but this nuclear protein is unable to bind to HSE1. We suggest that a protein binding to the sequence containing HSE2 may be involved in transcriptional regulation of the rat heme oxygenase gene under thermal stress.

The activation domain of transcription factor PU.1 binds the retinoblastoma (RB) protein and the transcription factor TFIID in vitro: RB shows sequence similarity to TFIID and TFIIB

The retinoblastoma (RB) tumor suppressor protein and the TATA-box-binding protein TFIID form contacts with a number of viral transactivator proteins. One of these, the adenovirus E1A protein, can bind to both proteins. Here we present evidence that the cellular transcription factor PU.1 can bind to both RB and TFIID. Like E1A, PU.1 binds to the conserved C-terminal domain of TFIID and to the RB "pocket" domain. The PU.1 sequences required to bind either protein lie within a 75-amino acid region which functions as an independent activation domain in vivo. The ability of PU.1 to contact directly both RB and TFIID through the same 75-residue domain prompted us to look for sequence similarity between these two proteins. We find that the previously defined domain A of the RB pocket shows sequence similarity to the conserved C terminus of TFIID, whereas domain B shows sequence similarity to a second general transcription factor, TFIIB. The potential for RB to influence transcription by using TFIID- and TFIIB-related functions is discussed.

Isolation of a cDNA encoding the adenovirus E1A enhancer binding protein: a new human member of the ets oncogene family

The cDNA encoding adenovirus E1A enhancer-binding protein E1A-F was isolated by screening a HeLa cell lambda gt11 expression library for E1A-F site-specific DNA binding. One cDNA clone produced recombinant E1A-F protein with the same DNA binding specificity as that endogenous to HeLa cells. Sequence analysis of the cDNA showed homology with the ETS-domain, a region required for sequence-specific DNA binding and common to all ets oncogene members. Analysis of the longest cDNA revealed about a 94% identity in amino acids between human E1A-F and mouse PEA3 (polyomavirus enhancer activator 3), a recently characterized ets oncogene member. E1A-F was encoded by a 2.5kb mRNA in HeLa cells, which was found to increase during the early period of adenovirus infection. In contrast, ets-2 mRNA was significantly reduced in infected HeLa cells. The results indicate that E1A enhancer binding protein E1A-F is a member of the ets oncogene family and is probably a human homologue of mouse PEA3.

GATA and Ets cis-acting sequences mediate megakaryocyte-specific expression

The human glycoprotein IIB (GPIIB) gene is expressed only in megakaryocytes, and its promoter displays cell type specificity. We show that this specificity involved two cis-acting sequences. The first one, located at -55, contains a GATA binding site. Point mutations that abolish protein binding on this site decrease the activity of the GPIIB promoter but do not affect its tissue specificity. The second one, located at -40, contains an Ets consensus sequence, and we show that Ets-1 or Ets-2 protein can interact with this -40 GPIIB sequence. Point mutations that impair Ets binding decrease the activity of the GPIIB promoter to the same extent as do mutations that abolish GATA binding. A GPIIB 40-bp DNA fragment containing the GATA and Ets binding sites can confer activity to a heterologous promoter in megakaryocytic cells. This activity is independent of the GPIIB DNA fragment orientation, and mutations on each binding site result in decreased activity. Using cotransfection assays, we show that c-Ets-1 and human GATA1 can transactive the GPIIB promoter in HeLa cells and can act additively. Northern (RNA) blot analysis indicates that the ets-1 mRNA level is increased during megakaryocyte-induced differentiation of erythrocytic/megakaryocytic cell lines. Gel retardation assays show that the same GATA-Ets association is found in the human GPIIB enhancer and the rat platelet factor 4 promoter, the other two characterized regulatory regions of megakaryocyte-specific genes. These results indicate that GATA and Ets cis-acting sequences are an important determinant of megakaryocytic specific gene expression.

The Ets family of transcription factors

Interest in the Ets proteins has grown enormously over the last decade. The v-ets oncogene was originally discovered as part of a fusion protein expressed by a transforming retrovirus (avian E26), and later shown to be transduced from a cellular gene. About 30 related proteins have now been found in species ranging from flies to humans, that resemble the vEts protein in the so-called 'ets domain'. The ets domain has been shown to be a DNA-binding domain, that specifically interacts with sequences containing the common core trinucleotide GGA. Furthermore, it is involved in protein-protein interactions with co-factors that help determine its biological activity. Many of the Ets-related proteins have been shown to be transcription activators, like other nuclear oncoproteins and anti-oncoproteins (Jun, Fos, Myb, Myc, Rel, p53, etc.). However, Ets-like proteins may have other functions, such as in DNA replication and a general role in transcription activation. Ets proteins have been implicated in regulation of gene expression during a variety of biological processes, including growth control, transformation, T-cell activation, and developmental programs in many organisms. Signals regulating cell growth are transmitted from outside the cell to the nucleus by growth factors and their receptors. G-proteins, kinases and transcription factors. We will discuss how several Ets-related proteins fit into this scheme, and how their activity is regulated both post- and pre-translationally. Loss of normal control is often associated with conversion to an oncoprotein. vEts has been shown to have different properties from its progenitor, which might explain how it has become oncogenic. Oncogene-related products have been implicated in the control of various developmental processes. Evidence is accumulating for a role for Ets family members in Drosophila development, Xenopus oocyte maturation, lymphocyte differentiation, and viral infectious cycles. An ultimate hope in studying transformation by oncoproteins is to understand how cells become cancerous in humans, which would lead to more effective treatments. vEts induces erythroblastosis in chicken. Cellular Ets-family proteins can be activated by proviral insertion in mice and, most interestingly, by chromosome translocation in humans. We are at the beginning of understanding the multiple facets of regulation of Ets activity. Future work on the Ets family promises to provide important insights into both normal control of growth and differentiation, and deregulation in illness.

GATA and Ets cis-acting sequences mediate megakaryocyte-specific expression

The human glycoprotein IIB (GPIIB) gene is expressed only in megakaryocytes, and its promoter displays cell type specificity. We show that this specificity involved two cis-acting sequences. The first one, located at -55, contains a GATA binding site. Point mutations that abolish protein binding on this site decrease the activity of the GPIIB promoter but do not affect its tissue specificity. The second one, located at -40, contains an Ets consensus sequence, and we show that Ets-1 or Ets-2 protein can interact with this -40 GPIIB sequence. Point mutations that impair Ets binding decrease the activity of the GPIIB promoter to the same extent as do mutations that abolish GATA binding. A GPIIB 40-bp DNA fragment containing the GATA and Ets binding sites can confer activity to a heterologous promoter in megakaryocytic cells. This activity is independent of the GPIIB DNA fragment orientation, and mutations on each binding site result in decreased activity. Using cotransfection assays, we show that c-Ets-1 and human GATA1 can transactive the GPIIB promoter in HeLa cells and can act additively. Northern (RNA) blot analysis indicates that the ets-1 mRNA level is increased during megakaryocyte-induced differentiation of erythrocytic/megakaryocytic cell lines. Gel retardation assays show that the same GATA-Ets association is found in the human GPIIB enhancer and the rat platelet factor 4 promoter, the other two characterized regulatory regions of megakaryocyte-specific genes. These results indicate that GATA and Ets cis-acting sequences are an important determinant of megakaryocytic specific gene expression.

Structural organization of the 5' flanking region of the human corticotropin releasing hormone gene

We have determined the nucleotide sequence of the proximal 3625 nucleotides 5' flanking the major mRNA start site of the human corticotropin releasing hormone gene (hCRH) and identified several putative regulatory elements. Interestingly, we did not detect any glucocorticoid responsive elements; we did however find five interspersed perfect half palindromic estrogen responsive elements, which might confer estrogen regulatability to the hCRH gene. We have identified a segment spanning from -2835 to -2972, which has about 72% homology to the 3' terminal half of the human Alu I family of highly repetitive elements, and another one, which spans from -2213 to -2580 and has greater than 80% homology to members of human type O family of repetitive elements. These elements may confer DNA fragility, since the loci for hCRH and the human fragile site FRA8F colocalize in human chromosome 8. The structural information reported represents a first step in the study of regulation of the hCRH gene at the molecular level.

Different binding site requirements for binding and activation for the bipartite enhancer factor EF-1A

The human transcription factor EF-1A binds to the purine-rich E1A core enhancer sequence in the adenovirus E1A and E4 and polyomavirus enhancer regions. The consensus binding site for EF-1A resembles that of members of the ets domain protein family. EF-1A activation of transcription requires a dimeric binding site. Analysis of binding sites containing point mutations revealed that EF-1A binding is determined by the core nucleotides of the binding site, while transcriptional activation is determined both by the core and some peripheral nucleotides that do not affect binding. We have purified EF-1A and analyzed its two constituent subunits, EF-1A alpha and EF-1A beta. EF-1A alpha (MW approximately 60kD) makes the primary DNA contacts. EF-1A beta (MW approximately 50 kD) forms a heteromultimeric complex with EF-1A alpha both in solution and on a dimeric binding site. Binding of both EF-1A subunits is necessary, but not sufficient, for transcriptional activation. We present immunochemical and functional evidence that EF-1A alpha is related to the murine ets-related protein GABP alpha and that EF-1A beta is related to the murine protein GABP beta.

Analysis of proviruses integrated in Fli-1 and Evi-1 regions in Cas-Br-E MuLV-induced non-T-, non-B-cell leukemias

The DNAs of the Cas-Br-E MuLV-induced leukemias always contain somatically acquired mink cell focus-forming (MCF) recombinant proviruses. MCF recombinants could be involved during leukemogenesis at both preleukemic times and in late-stage tumors. Among the Cas-Br-E-induced non-T-, non-B-cell leukemias, viral integrations were found in the Fli-1 and Evi-1 region in 71% (36 out of 51) and 22% (16 out of 72) of the tumors analyzed, respectively. As an approach to evaluate the contribution of Cas-Br-E MCF recombinant formation in cis-activation of proto-oncogenes, we analyzed the structure of the Fli-1- and Evi-1-associated proviruses by Southern blot hybridization. In Fli-1, we found that the proviruses, ecotropic as well as MCF, are all integrated within a very short DNA region immediately upstream of the initiator ATG, toward the 3' end of a 5' exon (Ben-David, Giddens, Letwin, and Bernstein, 1991, Genes Dev. 5, 908-918). All proviruses are oriented the same way, in the 5' to 3' transcriptional sense. Both provirus types are able to direct the Fli-1 expression to the same extent presumably via a promoter insertion mechanism. Most of the proviruses had no detectable deletion and contained both 5' and 3' LTR sequences with similar U3 sequences. MCF recombinants did not show any selective advantage over ecotropic proviruses for the Fli-1 locus since the frequency of ecotropic to MCF-recombinant virus at the Fli-1 locus was identical to that observed at any other locus. This suggests that the formation of these MCF recombinants is not essential for activation of Fli-1 and that ecotropic Cas-Br-E already possesses the required sequences for full cis-activation of Fli-1. On the other hand, in Evi-1, there is a strict selection for ecotropic proviruses. Presumably, viral genetic elements outside of the U3 region could be critical for the Evi-1 cis-activation.

Pur-1, a zinc-finger protein that binds to purine-rich sequences, transactivates an insulin promoter in heterologous cells

Purine-rich stretches of nucleotides (GAGA boxes) are often found just upstream of transcription start sites in many genes, including insulin. Mutational analysis suggests that the GAGA box plays an important role in transcription of the rat insulin I gene. We identify here at least four different proteins that bind specifically to the insulin GAGA box. Using a GAGA oligonucleotide, we have isolated a cDNA encoding a sequence-specific protein from a HIT (hamster insulinoma cell line) lambda gt11 library. This protein, which we designate Pur-1 (for purine binding), binds to the GAGA boxes of the rat insulin I and II genes and the human islet amyloid polypeptide gene. Pur-1 is a potent transactivator in both pancreatic and nonpancreatic cells. Furthermore, Pur-1 is able to activate an intact insulin promoter in HeLa cells, where it is normally inactive.

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.

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.

A positive regulator of the ribosomal protein gene, beta factor, belongs to the ETS oncoprotein family

The beta factor, which interacts with the rpL32 promoter, binds to the sequence 5'-GAGCCGGAAGTG and trans-activates this gene. Comparison of the DNA sequences bound by the beta factor with those bound by other known DNA-binding proteins revealed that the ETS proteins interact with similar DNA sequences. Consequently we have examined the relationship of the beta factor to the several ETS proteins so far reported. Antibody and oligonucleotide competition experiments, performed by using electrophoretic shift analysis, revealed that the beta factor contains ETS epitopes and that it is immunologically related to both of the GA-binding proteins (GABPs), implying that the beta factor may consist of two separate protein subunits.