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.

Sequence specific binding of Ets-1 to the mouse cytokeratin EndoA gene enhancer

Expression of the mouse cytokeratin EndoA gene is regulated by an enhancer that is located 1 kilobases (kb) 3' downstream from the gene. The EndoA enhancer consists of six direct repeats with homology to the PEA3 motif in the polyoma virus enhancer core. The PEA3 motif binds to the proto-oncogene Ets product. In this report we show that GST-c-Ets-1 fusion protein binds specifically to the EndoA enhancer unit sequence by gel shift analysis. Footprinting showed that the Ets-1 binding site consisted of 20 bases in each repeat. Ets-1 also moderately activated the EndoA enhancer. These results demonstrate that Ets-1 binds in a sequence specific fashion to the mouse EndoA enhancer and suggest that c-Ets-1 or other related Ets family genes function in regulating EndoA gene expression.

Requirement of an ETS-binding element for transcription of the human lck type I promoter

The requirement for cis-acting DNA sequences for transcriptional activity of the human lck type I promoter was investigated in two human cell lines that express type I transcripts, the leukemic T-cell line, Jurkat, and the colon carcinoma line, SW620. Transient transfection assays in Jurkat and SW620 cells revealed negative and positive cis-acting regulatory elements in the lck type I promoter between -570 and -480 and between -128 and -63 respectively. For the latter, a triple point mutation of a sequence, GCAGGAAGT, from -99 and -91 resulted in complete loss of lck type I promoter activity in both Jurkat and SW620 cells. In vitro binding assays indicated that this sequence, denoted the ETS-binding element or EBE, can interact with the lymphoid-specific transcription factor ETS-1. Thus, a protein(s) in the ETS family appears to be required for transcription of the lck type I promoter in T cells and may be important for the activation of the lck gene in human colon carcinoma.

c-Ets-1 protein is hyperphosphorylated during mitosis

The ets-1 and ets-2 proto-oncogene products can serve as transcription factors and become phosphorylated in response to Ca(2+)-mediated signals. We have examined expression of Ets proteins during the cell cycle in cells synchronized by centrifugal elutriation or nocodazole-induced mitotic block. Both methods revealed the presence of a hyperphosphorylated isoform of Ets-1 during the mitotic phase. This isoform showed a characteristic mobility shift and was observed during mitosis in each of four cell lines (three human T-cell lines and a human astrocytoma) that express ets-1. In elutriated cells, only a small portion of the Ets-1 in cells from the G2/M fractions was hyperphosphorylated, while in nocodazole-arrested cells more of the Ets-1 was shifted. When cells were released from nocodazole arrest, this isoform disappeared within 1-2 h as cells completed mitosis and entered G1. This suggests that hyperphosphorylated Ets-1 is present transiently during early mitosis, before or around the time of the metaphase-anaphase transition. Exposure of unsynchronized cells to okadaic acid resulted in a dramatic hyperphosphorylation of virtually all Ets-1, suggesting that changes in cellular phosphatase activity are important for cell cycle regulation of Ets-1. Hyperphosphorylated Ets-1 appears to arise from multiple phosphorylations on serine in the exon 7-encoded domain of the protein and did not appear to alter sequence-specific DNA-binding activity. Although enhanced phosphorylation of Ets-2 was detected in nocodazole-arrested cells, no Ets-2 hyperphosphorylation was seen.

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.

Mis-splicing yields circular RNA molecules

We previously identified novel human ets-1 transcripts in which the normal order of exons is inverted, and demonstrated that although the order of exons is different than in the genomic DNA, splicing of these exons out of order occurs in pairs using genuine splice sites (1). Here we determine the structure of these novel transcripts, showing that they correspond to circular RNA molecules containing only exons in genomic order. These transcripts are stable molecules, localized in the cytoplasmic component of the cells. To our knowledge, this is the first case of circular transcripts being processed from nuclear pre-mRNA in eukaryotes. This new type of transcript might represent a novel aspect of gene expression and hold some interesting clues about the splicing mechanism.

Negative regulatory elements in the human ETS1 gene promoter

The human ETS1 gene promoter contains binding sites for transcription factors AP1, AP2 and ETS. These factors have been previously shown to be positive regulators for the expression of the ETS1 gene. In our previous report it was inferred that the ETS1 gene promoter also contains negative regulatory elements that might balance and prevent the overexpression of the ETS1 gene product. The studies reported here show that the ETS1 gene promoter also contains binding site motifs for transcription factors PEA3 and OCT. By subjecting deletion constructs of the ETS1 gene promoter to functional analysis, two negative regulatory elements (NREs) were located: NRE1 was mapped to 230 nt at the 5' end of the promoter, and NRE2 was mapped to 350 nt located between the second OCT motif and a 120-base sequence downstream from the SacI site. These NREs can also reduce the activity of a heterogenous promoter. Gel mobility-shift assays showed that nuclear extracts from B-lymphoid (Daudi), T-lymphoid (HPB) and erthyromyeloid (K562) cells each form one major and several minor complexes with NRE1 and NRE2. The nuclear extract from promyelocytic (HL60) cells does not form complexes with either NRE1 or NRE2. The identification of NREs in the ETS1 gene promoter suggests that these elements play an important role in regulating the ETS1 gene expression in hematopoietic cells.

Specificities of protein-protein and protein-DNA interaction of GABP alpha and two newly defined ets-related proteins

The ets-related protein GABP alpha interacts with the four ankyrin-type (ANK) repeats of GABP beta to form a high-affinity DNA-binding complex that recognizes a site important for herpes simplex virus type I immediate early gene activation. To investigate the selectivity and specificity of the GABP complex, we have isolated two new ETS family members, termed ER81 and ER71. ER81 and GABP alpha were present in most tissues of adult mice, whereas ER71 was restricted to testis. We have compared the DNA-binding specificities of these proteins by binding site selection. GABP alpha, ER71, and ER81 recognized the common pentanucleotide DNA sequence 5'-CGGAA/T-3'. Although subtle differences were observed for nucleotide preferences flanking this pentanucleotide core, the overall similarity of the selected sequences was most striking. Given the observation that GABP alpha interaction with GABP beta requires its intact ETS domain, we further compared the ability of GABP beta to interact with other ETS proteins. GABP beta did not augment the DNA-binding activity of the highly similar ETS domains of ER81, ER71, or Ets-1. Moreover, probing of total tissue extracts with radiolabeled GABP beta demonstrated its exceedingly stringent specificity for GABP alpha. Given that the DNA-binding specificities of these ETS proteins are similar and that the protein-protein interactions between GABP beta and GABP alpha are highly specific, we conclude that the protein interactions determine the target site selection by GABP alpha.

C-ets-1 protooncogene expression alters the growth properties of immortalized rat fibroblasts

Ets family genes have been cloned and characterized from a variety of species ranging from human to Drosophila. The ets proteins encode transcription factors that activate transcription via specific binding to GGAA core sequence present in various promoter/enhancers. To investigate the role of ets protooncogene expression on the growth properties of rat embryo fibroblasts (REF), we constructed and introduced ets expression vectors into primary, as well as immortalized REF cells. The transfected cells contained multiple copies of the vector DNA, and the Northern blot analysis demonstrated overexpression of the c-ets-1-specific mRNA. Although the expression of the ets genes was unable to immortalize primary rat embryo fibroblasts, the expression of ets-1 in REF-1 cells enabled their growth in serum-free medium and effected tumorigenic activity in nude mice.

A phorbol ester response element within the human T-cell receptor beta-chain enhancer

The activity of the T-cell receptor beta-chain gene enhancer is increased by activators of the protein kinase C pathway during T-cell activation. Analysis of mutant enhancer constructs identified two elements, beta E2 and beta E3, conferring phorbol ester inducibility. Multimerized beta E2 acted in isolation as a phorbol ester-responsive element. Both beta E2 and beta E3, which contain a consensus Ets-binding site, were shown to bind directly to the product of the c-ets-1 protooncogene. Both regions also bound a second factor, core-binding factor. Mutation of the beta E2 Ets site abolished the inducibility of the beta E2 multimer. beta E2 and beta E3 Ets site mutations also profoundly affected activity and inducibility of the enhancer. In contrast, enhancer activity but not its inducibility was affected by mutation of the beta E2 core-binding factor site. Cotransfection studies showed that Ets-1 specifically repressed activity of the multimerized beta E2 element and the complete T-cell receptor beta-chain enhancer. These data show that the T-cell receptor beta-chain enhancer responds to protein kinase C-mediated activation signals via a functional domain, composed of two elements, which contains binding sites for Ets transcription factors and which is negatively regulated by Ets-1.

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.

Human ETS1 oncoprotein. Purification, isoforms, -SH modification, and DNA sequence-specific binding

The human ETS1 proto-oncogene proteins have been isolated from the T-cell leukemia line, CEM, by immunoaffinity chromatography and their identity confirmed by NH2-terminal amino acid sequencing. Incubation of CEM cells with N alpha-p-tosyl-L-lysine chloromethyl ketone (TLCK) indicates that ETS proteins can be modified in their cellular context and that pretreatment of the cells with N-ethylmaleimide (NEM) protects ETS1 proteins from TLCK modification. These data show that ETS1 proteins can exist in at least two different states, -SH-available and -SH-protected. Renatured human ETS1 has DNA sequence-specific binding to the PEA3 (CAGGAAGT) motif. The ETS1.PEA3 complex can be observed by electrophoretic mobility shift assays (EMSA). Purified ETS1 retards a band which is exactly the same size as a complex that is retarded from nuclear extracts prepared from CEM cells. Reduced ETS1 is required to form the ETS1.PEA3 complex, however; modification of the ETS1 -SH groups by either NEM or by TLCk does not inhibit formation of the complex. The ETS1.PEA3 complex formed with TLCK-modified ETS1 has a slower mobility than the complex formed with unmodified ETS1. Zone sedimentation analysis of purified ETS1 indicates that it is the monomer of ETS1 which binds to the PEA3 oligonucleotide.

Oncogenic conversion alters the transcriptional properties of ets

The vEts oncoprotein and its progenitor cEts1(p68) belong to a growing family of transcription factors that are related by the conserved ets domain. We show here that the ets domain and adjacent COOH-terminal amino acids are required for DNA binding by cEts1(p68). vEts differs from cEts1(p68) in both the COOH-terminal sequence and an amino acid substitution in the ets domain. The change in the COOH-terminal sequence markedly decreases its affinity for specific DNA, and the ets domain mutation further diminishes binding. vEts does not trans-activate through the ets (PEA3) motif in vivo. Surprisingly, vEts still efficiently trans-activates the promoters of two genes, stromelysin and collagenase, that are found to be overexpressed in transformed cells. The AP1 motifs of both promoters are required for efficient activation. vEts does not bind to the AP1 motif, even in the presence of cJun and cFos. The DNA-binding domain of Ets1 is required for activation through the AP1 element. Activation is inhibited by the expression of the glucocorticoid and retinoic acid receptors, suggesting that activation by Ets does not involve reversal of negative regulators of AP1. We suggest that activation is by an indirect mechanism involving activation of endogenous genes. Our results show that vEts differs from its progenitor cEts1(p68) in its trans-activating properties. The findings suggest that activation of the Jun and Fos oncoprotein pathway is important for transformation by Ets.

Ets-1 and Ets-2 protooncogene expression in theca cells of the adult mouse ovary

We have investigated the mRNA expression of the Ets-1 and Ets-2 genes in murine gonads and found expression in adult ovaries. In situ hybridization experiments show that the Ets genes are predominantly expressed in theca cells and cells of ovarian interstitium. By gel retardation experiments we detected DNA binding proteins in ovaries that specifically bind to the ETS motif, suggesting the expression of Ets or Ets-related proteins. Our results raise the possibility of Ets-2 involvement in ovarian pathology seen in patients with Down's syndrome.

Genomic dispersal of the ets gene family during metazoan evolution

Evolutionary homologs of the ets proto-oncogene have been discovered in the genomes of widely divergent eucaryote species from Drosophila to sea urchin to vertebrates. The prototype mammalian ets-1 and ets-2 genes are divided into three coding domains that differ in their rate of accumulation of sequence divergence. An analysis of sequence divergence of ets gene homologs in various species has produced a phylogenetic history of the ets gene family in the context of metazoan evolutionary radiation. A minimum of five duplication events of ets primordial genes were evident, namely (1) a duplication that separates primitive ets genes (Drosophila precursor of 74E, mouse PU.1 and human ELK1) from the ets-1, ets-2, erg ancestor; (2) and (3) two duplications that established separate ets, erg and elg/GABP-alpha lineages which occurred prior to invertebrate-vertebrate divergence; (4) divergence of ets-1 and ets-2 gene family also associated with vertebrate-invertebrate divergence; (5) duplication of ets-1 and ets-2 in Xenopus laevis to produce two ets-1 genes and two ets-2 genes during genomic tetraploidation in the recent ancestry of this species.

XbaI RFLP of ETS-1 oncogene in chronic B-cell leukaemia

The influence of a polymorphic variant of the ETS-1 oncogene on the predisposition to develop chronic B-cell leukemia (CLL) was investigated. A total of 59 patients with CLL and 59 controls were examined for the frequency of an XbaI restriction fragment length polymorphism RFLP of the ETS-1 oncogene which has been reported to occur more frequently in patients with hematological malignancies than in normal controls. We found no significant difference in the allele frequency between the CLL patients and the normal controls. These data suggest that the presence of the XbaI RFLP is not associated with CLL.

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.

A novel modulator domain of Ets transcription factors

The ets gene family is composed of several oncogenes and codes for transcription factors. The Ets proteins have a similar sequence called the ets domain and bind to the core motif A/CGGAA. We show here that several members of the ets family have different trans-activating properties. The ets domain of Ets-1 is required for DNA binding. Adjacent to this domain there is a novel element that inhibits DNA binding. It appears to alter the structure of the DNA-binding domain before it interacts with DNA. There is a similar sequence in Ets-2 that also inhibits DNA binding. This sequence is absent in alternative splice products of h-Ets-1. PU1, the most distantly related member of the ets gene family, lacks this novel element. It has a distinct DNA-binding specificity that is determined by DNA sequences outside the core motif. These results have important implications for both the oncogenic and normal functions of ets family members.

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.

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.

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.

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.

c-ets1 proto-oncogene is a transcription factor expressed in endothelial cells during tumor vascularization and other forms of angiogenesis in humans

The c-ets1 proteins are transcriptional activators expressed within endothelial cells during blood vessel development in chick embryos. The authors show by in situ hybridization that c-ets1 is transcribed in the endothelia during angiogenesis in human embryos, in granulation tissue, and especially during tumor vascularization. c-ets1 mRNAs were also detected in the fibrocytes of tumor stroma and in the spindle cells of Kaposi's sarcomas, regarded as cells of endothelial origin. It has been shown that the c-ets proteins activate transcription through a PEA3 motif that plays a role in the stimulation of transcription of urokinase-type plasminogen-activator (u-PA), stromelysin and collagenase genes. The authors demonstrate in vitro that the angiogenic factor TNF alpha increases transiently the amount of both c-ets1 and u-PA mRNA in confluent human umbilical vein endothelial cells. Therefore, the authors suggest that the c-ets1 proteins might regulate the transcription of the genes coding for matrix-degrading proteases, which are necessary for both angiogenesis and tumor invasion.

High-affinity DNA-protein interactions of the cellular ETS1 protein: the determination of the ETS binding motif

ETS1 protein purified from CEM cells was used to select its optimum DNA-binding sequence (pu) G/CCaGGA-AGTc (py). The sequence CCGGAAGT (ETS1-3) was preferred 5:1 over CAGGAAGT (PEA3). Quantitative electrophoretic mobility-shift assays (EMSA) indicated that the purified ETS1 protein binds to either ETS1-3 or PEA3 oligonucleotide probes with high affinity (Ka = 0.5-4.0 x 10(10) M-1) and that the purified ETS1 has different binding capacities for ETS1-3 and PEA3 oligonucleotide probes. The ETS1 protein binds 2-5 times more ETS1-3 than PEA3. Competitive binding experiments showed that the ETS1-3 and PEA3 probes effectively compete for the binding of ETS1-3. However, changing the core DNA-binding sequence from GGAA to AGAA eliminates competition. Since the human ETS1 protein selected the same DNA sequence from a mixture of random oligonucleotides as did the Drosophila E74A protein (one of the most divergent members of the ETS family), this strongly suggests that all proteins containing the ETS 85 amino acid domain (sequences which define the ETS family) will bind to the same sequence.

Structural and functional analysis of the regulatory sequences of the ets-1 gene

The ets-1 gene is a human homolog of the oncogene v-ets of avian acute leukemia virus E26. The ets-1 gene is preferentially expressed in lymphoid cells. To understand the regulation of the ets-1 gene expression the regulatory sequences of this gene were identified and isolated. The promoter is found to be functioning in the lymphoid cell line Daudi and the erythromyeloid cell line K562 but not in the promyelocytic cell line HL60. Sequence analysis indicates that the ets-1 promoter does not contain the TATA or CAT box. It contains multiple transcription initiation sites in a tight cluster. The promoter contains one binding site each for AP1 and AP2. It has one definitive and five presumptive sp1-binding sites. In addition, the ets-1 promoter contains one ets-1 protein-binding site. Functional analysis has shown that c-jun enhances the activity of the ets-1 promoter, whereas the combination of c-fos and c-jun expressions has no synergistic effect. The expression of exogenous AP2 and ets-1 also enhances the activity of the ets-1 promoter. These results suggest that the AP1, AP2 and ets-1 proteins have a positive regulatory effect. The presence of the ets-1 protein-binding site indicates the existence of an autoregulatory mechanism for the expression of the ets-1 gene. Our results suggested that the presence of a negative regulatory element upstream of the region where most of the positive regulators are located.

Transcriptional activation through ETS domain binding sites in the cytochrome c oxidase subunit IV gene

A mutational analysis of the rat cytochrome c oxidase subunit IV (RCO4) promoter region revealed the presence of a major control element consisting of a tandemly repeated pair of binding sites for a nuclear factor from HeLa cells. This factor was designated NRF-2 (nuclear respiratory factor 2) because a functional recognition site was also found in the human ATP synthase beta-subunit gene. Deletion or site-directed point mutations of the NRF-2 binding sites in the RCO4 promoter resulted in substantial loss of transcriptional activity, and synthetic oligomers of the NRF-2 binding sites from both genes stimulated a heterologous promoter when cloned in cis. NRF-2 binding and transcriptional activation required a purine-rich core sequence, GGAA. This motif is characteristic of the recognition site for a family of activators referred to as ETS domain proteins because of the similarity within their DNA-binding domains to the ets-1 proto-oncogene product. NRF-2 recognized an authentic Ets-1 site within the Moloney murine sarcoma virus long terminal repeat, and this site was able to compete for NRF-2 binding to the RCO4 promoter sequence. In addition, a single polypeptide of 55 kDa was detected following cross-linking of a partially purified NRF-2 fraction to RCO4, the human ATP synthase beta subunit, or Moloney murine sarcoma virus binding sites. However, in contrast to Ets-1, which appears to be exclusive to lymphoid tissues, NRF-2 has the broad tissue distribution expected of a regulator of respiratory chain expression.

Sequence-specific interaction of the Ets1 protein with the long terminal repeat of the human T-lymphotropic virus type I

We recently demonstrated that members of the c-ets proto-oncogene family, Ets1 and Ets2, are sequence-specific transcriptional activators of the human T-lymphotropic virus type I (HTLV-I) long terminal repeat (LTR). We now report that the HTLV-I LTR contains two distinct Ets1-responsive regions, ERR-1 and ERR-2. Expression of Ets1 with reporter plasmids containing ERR-1 or ERR-2 upstream of a basal promoter resulted in an increase in transcriptional activity. By gel mobility shift assay, the interaction of Ets1 with the downstream ERR-1-binding region was found to be more stable than its interaction with the upstream ERR-2 region. By DNase I footprint, gel mobility shift, and methylation interference analyses, ERR-1 was found to contain two Ets1 binding sites, ERE-A and ERE-B. A recombinant Ets1 protein was found to bind with higher affinity to ERE-A than to ERE-B. Binding of Ets1 to these sites appears to result in a specific and sequential protection of a 37-nucleotide sequence of the HTLV-I LTR from -154 to -118. In view of the high-level expression of Ets1 in lymphoid cells, the c-ets proto-oncogenes encode transcription factors which could play an important role in both basal and Tax1-mediated HTLV-I transcription.

Identification of Ets- and notch-related subunits in GA binding protein

Recombinant cDNA clones that encode two distinct subunits of the transcription factor GA binding protein (GABP) have been isolated. The predicted amino acid sequence of one subunit, GABP alpha, exhibits similarity to the sequence of the product of the ets-1 protooncogene in a region known to encompass the Ets DNA binding domain. The sequence of the second subunit, GABP beta, contains four 33-amino acid repeats located close to the NH2-terminus of the subunit. The sequences of these repeats are similar to repeats in several transmembrane proteins, including Notch from Drosophila melanogaster and Glp-1 and Lin-12 from Caenorhabditis elegans. Avid, sequence-specific binding to DNA required the presence of both polypeptides, revealing a conceptual convergence of nuclear transforming proteins and membrane-anchored proteins implicated in developmentally regulated signal transduction processes.

Erythroleukemia induction by Friend murine leukemia virus: insertional activation of a new member of the ets gene family, Fli-1, closely linked to c-ets-1

The retroviral integration site Fli-1 is rearranged in 75% of the erythroleukemia cell clones induced by Friend murine leukemia virus (F-MuLV), whereas Spi-1/PU.1, a member of the ets family of DNA-binding proteins, is rearranged in 95% of the erythroleukemias induced by Friend spleen focus-forming virus (SFFV). To determine the transcriptional domain defined by Fli-1, we have isolated a cDNA clone that is highly expressed only in erythroleukemia cell lines with Fli-1 rearrangements. The protein sequence of this cDNA is very similar to Erg2, another member of the ets gene family. The hydrophilic carboxy-terminal end of the Fli-1 cDNA shares significant sequence similarity to the DNA-binding ETS domain found in all members of the ets family. PFGE analysis localized Fli-1 within 240 kb of the ets-1 proto-oncogene on mouse chromosome 9 and human chromosome 11q23, suggesting that ets-1 and Fli-1 arose from a common ancestral gene by gene duplication. The involvement of the murine Fli-1, Spi-1, and avian v-ets genes in erythroleukemia induction suggests that activation of ets gene family members plays an important role in the progression of these multistage malignancies.

The human ETS1 gene: genomic structure, promoter characterization and alternative splicing

Genomic clones encompassing the human ETS1 gene were isolated and utilized to define its molecular organization. This gene consists of eight exons spanning over 60 kb. The 5' end of the human ETS1 gene was subcloned and characterized. S1 nuclease, primer extension and RNAase protection analyses of human mRNAs showed multiple transcription initiation sites. DNA sequence analysis indicated a high G + C content in the promoter region and the absence of either a 'TATA' box or a 'CAAT' box. Six consensus recognition sequences for the transcription factor SP1, two AP1 consensus sequences and one consensus AP2 recognition sequence were identified, as well as two GC elements with dyad symmetry. A palindromic region similar to the serum response element of the c-fos gene and two octamer consensus recognition sequences were located upstream of the promoter region. A series of promoter deletion constructs positioned upstream from the bacterial chloramphenicol acetyl transferase gene were transfected into HeLa cells and their functional promoter activity assayed. The deletion constructs identified the 5' boundary for maximum promoter activity at 486 bp upstream of the first initiation site and suggest possible positive and negative regulatory regions. Polymerase chain reaction analysis of ETS1 cDNA identified several amplified products, indicating alternative splicing. In addition to the presence of mRNA products lacking exon VII, products lacking exon IV, as well as ones lacking both exons IV and VII, were found.

Ligation of membrane Ig leads to calcium-mediated phosphorylation of the proto-oncogene product, Ets-1

Recent studies have demonstrated that the nuclear protein, Ets-1, which is preferentially expressed in lymphocytes, binds to the long terminal repeat of Moloney murine sarcoma virus and HTLV-1 and regulates gene expression. The association of Ets-1 with DNA has been shown to be lost when the protein is phosphorylated. Thus, Ets-1 may regulate gene expression in lymphocytes and this activity may be determined by its phosphorylation state. To address the possibility that Ets-1 activity may be altered by membrane (m) Ig-mediated signal transduction, we analyzed the effect of mIgM and mIgD ligation on the phosphorylation state of Ets-1. Monoclonal anti-IgM or anti-IgD antibody stimulation of normal mouse B cells led to increased phosphorylation of Ets-1 within 2 min. This response was absolutely dependent on calcium mobilization and could be induced by elevation of intracellular free calcium using the calcium ionophore, ionomycin. Calcium release from intracellular stores was sufficient to mediate the phosphorylation of Ets-1. Treatment of resting B cells with IL-4, TGF beta-1, IFN-gamma, anti-class I, or anti-class II antibodies did not induce Ets-1 phosphorylation. In summary, calcium mobilization from intracellular stores after mIgM or mIgD ligation provides a necessary and sufficient signal for activation of Ets-1 phosphorylation. This phosphorylation event may act in the alteration of gene expression during B cell activation.

Ets1, when fused to the GAL4 DNA binding domain, efficiently enhances galactose promotor dependent gene expression in yeast

Ets1, the translation product of the c-ets1 proto-oncogene and the related Ets2 protein, act as sequence-specific transcriptional factors in transient transfection experiments in animal cells. We report here that in S. cerevisiae, expression of a lacZ test gene placed under the control of the GAL1 promoter is stimulated efficiently by a fusion protein in which the chicken Ets1 sequence starting from amino acid 37, is linked to the DNA binding domain of the yeast GAL4 transcriptional activator. This suggests that Ets1 contains one or more intrinsic transcription activation domain(s). However, the GAL4 integral of Ets1 fusion protein was unable to restore growth of a gal4 deletion mutant on galactose, implying that the fusion product cannot substitute for GAL4 enhancement on all GAL genes.

Ataxia-telangiectasia (group A): localization of ATA gene to chromosome 11q22-23 and pathogenetic implications

Ataxia-telangiectasia (AT) is an autosomal recessive disorder resulting from a single defective gene in each family. Complementation studies suggest that the same syndrome is associated with defects of at least four AT genes (ATA, ATC, ATD and ATE). The syndrome is multifaceted and involves the cerebellum, skin, immunological system, chromosomes, cancer susceptibility, radiosensitivity, premature ageing and serum alphafetoprotein levels. In order to further develop understanding of how these seemingly unrelated physiological systems interact in this disease, we attempted to localize the gene by linkage analysis, using a single large Group A AT family to screen 171 genetic markers and 30 additional AT families to confirm any positive linkages. We found a linkage to AT (Group A) with genetic markers on chromosome 11q22-23. This region of the human genome is syntenic with a large region of the mouse genome on chromosome 9 and includes such "candidate" genes as THY1, NCAM, CD3G-D-3, ets-1, and APOA1-C3-A4. In addition, studies of human chromosomes identify fragile sites in this region as well as breakpoints associated with translocation 4: 11 and 9; 11 in acute non- lymphocytic leukemias. The pathogenetic implications of this localization to 11q22-23 are considered.

The c-ets-1 proto-oncogene has oncogenic activity and is positively autoregulated

The proto-oncogene ets-1 is a member of the ets family of genes that share homology with the viral oncogene, v-ets, of the avian leukemia virus E26. By using expression vectors, we demonstrate that the ets-1 gene transforms NIH3T3 cells and the ets-1 transfected cells form colonies in soft agar and induce tumors in nude mice. We have also determined that the ets-1 protein contains homology with the helix-loop-helix motif of the HLH family proteins, but lacks the basic domain upstream of helix I. Transfection of the NIH3T3 cells with ets-1 vectors results in the activation of the endogenous ets-1 gene. Using hybridization probes that can distinguish between transcripts from endogenous and exogenous templates, we show that the endogenous ets-1 gene is activated by the expression of the transfected exogenous ets-1. In contrast, the expression of transfected ets-2 has no effect on the endogenous ets-1 gene expression. The results indicate that the ets-1 proto-oncogene is positively autoregulated by its product.

Sequence-specific binding of human Ets-1 to the T cell receptor alpha gene enhancer

Expression of the human T cell receptor (TCR) alpha gene is regulated by a T cell-specific transcriptional enhancer that is located 4.5 kilobases (kb) 3' to the C alpha gene segment. The core enhancer contains two nuclear protein binding sites, T alpha 1 and T alpha 2, which are essential for full enhancer activity. T alpha 1 contains a consensus cyclic adenosine monophosphate (cAMP) response element (CRE) and binds a set of ubiquitously expressed CRE binding proteins. In contrast, the transcription factors that interact with the T alpha 2 site have not been defined. In this report, a lambda gt11 expression protocol was used to isolate a complementary DNA (cDNA) that programs the expression of a T alpha 2 binding protein. DNA sequence analysis demonstrated that this clone encodes the human ets-1 proto-oncogene. Lysogen extracts produced with this cDNA clone contained a beta-galactosidase-Ets-1 fusion protein that bound specifically to a synthetic T alpha 2 oligonucleotide. The Ets-1 binding site was localized to a 17-base pair (bp) region from the 3' end of T alpha 2. Mutation of five nucleotides within this sequence abolished both Ets-1 binding and the activity of the TCR alpha enhancer in T cells. These results demonstrate that Ets-1 binds in a sequence-specific fashion to the human TCR alpha enhancer and suggest that this developmentally regulated proto-oncogene functions in regulating TCR alpha gene expression.

The product of the c-ets-1 proto-oncogene and the related Ets2 protein act as transcriptional activators of the long terminal repeat of human T cell leukemia virus HTLV-1

The c-ets-1 proto-oncogene and the related c-ets-2 gene encode related nuclear chromatin-associated proteins which bind DNA in vitro. To investigate the possibility that Ets1 and Ets2 are transcriptional activators, we analyzed the ability of these proteins to trans-activate promoter/enhancer sequences in transient co-transfection experiments. A CAT construct driven by the long terminal repeat of the human T cell leukemia virus, HTLV-1 was found to be trans-activated by both Ets1 and Ets2 in NIH3T3 and HeLa cells. The increased levels of CAT activity were paralleled by increased levels of correctly initiated CAT mRNA. Mutant Ets1 proteins unable to accumulate in the nucleus were found to be inactive. An ets-responsive sequence between positions -117 and -160 of the LTR was identified by analyses of a series of 5' deletion mutants of the HTLV-1 LTR and of dimerized versions of specific motifs of the LTR enhancer region. Using a gel shift binding assay, Ets1 was found to bind specifically to an oligonucleotide corresponding to region -117 to -160. This sequence, which also contributes to Tax1 responsiveness of the HTLV-1 LTR, is characterized by the presence of four repeats of a pentanucleotide sequence of the type CC(T/A)CC. Competition experiments show that integrity of repeats 1 and 4 is important for Ets1 binding. These results show that Ets1 and Ets2 are sequence-specific transcriptional activators. In view of the high level expression of Ets1 in lymphoid cells, Ets1 could be part of the transcription complex which mediates the response to Tax1 and the control of HTLV-1 replication. More generally, Ets1 and Ets2 could regulate transcription of cellular genes.

The c-ets proto-oncogenes encode transcription factors that cooperate with c-Fos and c-Jun for transcriptional activation

Cell transformation by oncogenes leads to changes in gene expression. A key event in this process seems to be activation of the transcription factors AP-1 and PEA 3. Their synergistic activities are required for efficient activation of transcription from different promoters by many different oncogenes, serum growth factors and the tumour promoter TPA. We show here that the products of the ets-1 and -2 proto-oncogenes, whose biological function was previously unknown, are transcription factors that activate transcription through the PEA 3 motif. The p68c-ets-1 protein specifically binds to DNA and contains a transcriptional activation domain. The ets-like gene family therefore seems to encode a new family of transcription factors, apparently unrelated to other transcription factors. The p68c-ets-1 protein cooperates with c-Fos and c-Jun (components of AP-1) for activation of transcription from the oncogene-responsive domain of the polyoma enhancer, indicating that combined activity of all three oncoproteins could be involved in the response of cells to growth stimuli.

Reciprocal expression of human ETS1 and ETS2 genes during T-cell activation: regulatory role for the protooncogene ETS1

The expression of the protooncogenes ETS1 and ETS2 has been studied in purified human T cells activated either by cross-linking of the T-cell receptor-CD3 complex on their cell surface or by direct stimulation with phorbol esters and ionomycin. Our results show that resting T cells express high levels of ETS1 mRNA and protein, while expression of ETS2 is undetectable. Upon T-cell activation, ETS2 mRNA and proteins are induced, while ETS1 gene expression decreases to very low levels. Late after stimulation, ETS1 mRNA is reinduced and maintained at a high level, while ETS2 gene expression decreases to undetectable levels. Therefore, it appears that in human T cells, ETS2 gene products are associated with cellular activation and proliferation, while ETS1 gene products are preferentially expressed in a quiescent state.

Isoforms of the human ets-1 protein: generation by alternative splicing and differential phosphorylation

The ets-1 gene belongs to the ets gene family (ets-1, ets-2, erg, and elk) and is homologous to the v-ets oncogene found in the avian leukemia virus E26. The ets-1 gene products were characterized using a specific monoclonal antibody developed against a bacterially expressed v-ets protein. The ets-1 gene product in the human T-cell line CEM was found to consist of at least six species: four major species with apparent molecular weights of 51 kDa (p51), 48 kDa (p48), 42 kDa (p42), and 39 kDa (p39); and two minor species of 52 kDa (pp52) and 49 kDa (pp49), which are demonstrated to be the phosphorylated forms of p51 and p48, respectively. All of the ets-1 proteins are related to each other and are considered products of the ets-1 gene. Subcellular localization showed that the pp52 and p51 are found mainly in the cytoplasm, while p48 and p39 are found mainly in the nucleus. Specific antibodies against various exons of ets-1 showed that both p42 and p39 lack a region corresponding to exon VII. Polymerase chain reaction analyses revealed the presence of an additional RNA product that corresponds to mRNA lacking exon VII. These results suggest that the human ets-1 gene encodes multiple proteins that are generated by at least two distinct mechanisms: alternative splicing of mRNA and protein phosphorylation.

Sequence-specific DNA binding of the proto-oncoprotein ets-1 defines a transcriptional activator sequence within the long terminal repeat of the Moloney murine sarcoma virus

The ets proto-oncogene family is a group of sequence-related genes whose normal cellular function is unknown. In a study of cellular proteins involved in the transcriptional regulation of murine retroviruses in T lymphocytes, we have discovered that a member of the ets gene family encodes a sequence-specific DNA-binding protein. A mouse ets-1 cDNA clone was obtained by screening a mouse thymus cDNA expression library with a double-stranded oligonucleotide probe representing 20 bp of the Moloney murine sarcoma virus (MSV) long terminal repeat (LTR). The cDNA sequence has an 813-bp open reading frame (ORF) whose predicted amino acid sequence is 97.6% identical to the 272 carboxy-terminal amino acids of the human ets-1 protein. The ORF was expressed in bacteria, and the 30-kD protein product was shown to bind DNA in a sequence-specific manner by mobility-shift assays, Southwestern blot analysis, and methylation interference. A mutant LTR containing four base pair substitutions in the ets-1 binding site was constructed and was shown to have reduced binding in vitro. Transcriptional efficiency of the MSV LTR promoter containing this disrupted ets-1 binding site was compared to the activity of a wild-type promoter in mouse T lymphocytes in culture, and 15- to 20-fold reduction in expression of a reporter gene was observed. We propose that ets-1 functions as a transcriptional activator of mammalian type-C retroviruses and speculate that ets-related genes constitute a new group of eukaryotic DNA-binding proteins.

Identification of a Ets1 variant protein unaffected in its chromatin and in vitro DNA binding capacities by T cell antigen receptor triggering and intracellular calcium rises

We previously showed that thymocytes express high levels of c-ets-1 protein (Ets1) that can be rapidly phosphorylated following mitogenic stimulation using lectins. We demonstrate here that T cell receptor (TCR) specific stimulation with monoclonal antibodies of mature CD8+ or CD4+ T cells also results in the rapid phosphorylation of Ets1, reinforcing the hypothesis of a possible role for Ets1 in T cell activation. In addition to the major Ets1 product (mu-p63c-ets-1), we identify in mouse thymocytes and mature T cells a distinct 52 Kd Ets1 related protein (mu-p52c-ets-1). In contrast to the major Ets1 protein, mu-p52c-ets-1 is poorly phosphorylated in unstimulated cells. Furthermore, mitogenic stimulation of thymocytes and T cells failed to induce in mu-p52c-ets-1 the Ca2(+)-dependent phosphorylation events which are known to drastically affect the migration of the major Ets1 protein in SDS polyacrylamide gels. Mu-p52c-ets-1, like mu-p63c-ets-1, is a nuclear-chromatin associated protein which exhibits DNA binding activity in vitro. However, in contrast to the major Ets1 protein, the association of mu-p53c-ets-1 with chromatin and its ability to bind to DNA in vitro are unaffected by activation stimuli resulting in an increase in [Ca2+]i. Finally, we present indications suggesting that mu-p52c-ets-1 might be the murine equivalent of the translation product of an alternatively c-ets-1 spliced mRNA described in human cells by others.

Polymorphism of the proto-oncogene ETS-1 in hematological malignancies

We studied a novel restriction fragment length polymorphism (RFLP) of the proto-oncogenes ETS-1 that we detected in a patient with an acute monocytic leukemia by the presence of two, 3.7 and 10 kb, Xbal fragments on Southern blots of DNA from blast cells and remission blood samples. RFLP analysis of a series of 114 normal donors revealed that only four (3.6%) shared the 10 kb fragment. By contrast, this unusual allele was found in 20 (all lymphocytic or monocytic) of 108 (18.5%) hematological malignancies (p less than 0.001). DNA sequence analysis indicated the disappearance in the rare allele of a Xbal site due to a single point mutation at the 3' end of ETS-1 locus. Molecular consequences of this mutation point to a possible pathogenic involvement of ETS-1 in these disorders and to the question of genetic susceptibility to hematological malignancies.

Definition of an Ets1 protein domain required for nuclear localization in cells and DNA-binding activity in vitro

Ets1 and Ets2 are nuclear phosphoproteins which bind to DNA in vitro and share two domains of strong identity. Deletion analyses of each of these conserved regions in Ets1 demonstrated that integrity of the carboxy-terminal domain, also conserved in the more distantly related elk and erg gene products, is essential for both nuclear targeting and DNA-binding activity in vitro.

Expression of ets genes in mouse thymocyte subsets and T cells

The cellular ets genes (ets-1, ets-2, and erg) have been identified by their sequence similarity with the v-ets oncogene of the avian erythroblastosis virus, E26. Products of the ets-2 gene have been detected in a wide range of normal mouse tissues and their expression appears to be associated with cell proliferation in regenerating liver. In contrast, the ets-1 gene was previously shown to be more highly expressed in the mouse thymus than in other tissues. Because the thymic tissue contains various subsets of cells in different stages of proliferation and maturation, we have examined ets gene expression in fetal thymocytes from different stages of development, in isolated subsets of adult thymocytes, and in peripheral T lymphocytes. Expression of the ets-1 gene was first detected at day 18 in fetal thymocytes, corresponding to the first appearance of CD4+ (CD4+, CD8-) thymocytes, and reaches maximal/plateau levels of expression in the thymus at 1 to 2 days after birth. The ets-2 gene expression is detected at least 1 day earlier, coinciding with the presence of both double-positive (CD4+, CD8+) and double-negative (CD4-, CD8-) blast thymocytes and reaches maximal/plateau levels 1 day before birth. In the adult thymus, ets-1 and ets-2 mRNA expression is 10- to 8-fold higher respectively in the CD4+ subset than in the other subsets examined. Higher levels of p55 ets-1 protein were also shown to exist in the CD4+ subset. Because the CD4+ thymic subset is the pool from which the CD4+ peripheral, helper/inducer T cells are derived, the ets gene expression was examined in lymph node T cells. Both the CD4+ and the CD8+ T cells subsets had lower ets RNA levels than the CD4+ thymocytes. These results suggest that ets-2 and more particularly ets-1 gene products play an important role in T cell development and differentiation and are not simply associated with proliferating cells, which are observed at a higher frequency in fetal thymocytes, or dull Ly-1 (low CD5+), and double-negative (CD4-, CD8-) adult thymocytes. Selectively enhanced expression of ets-1 gene may be observed in thymic CD4+ thymocytes because these cells have uniquely encountered MHC class II or other Ag in the thymic environment. These cells may have been subsequently stimulated to activate the ets genes in conjunction with their differentiation of helper/inducer function(s) and expression of mature TCR.(ABSTRACT TRUNCATED AT 400 WORDS)

The oncogene ETS1 is distant from the chromosome 11 breakpoint in leukaemic cells with the t(11;19)(q23;p13)

Field inversion gel electrophoresis of DNA from a leukemic clone characterized by the t(11;19)(q23;p13) allowed us to exclude any genomic rearrangement within more than 900 kb of DNA encompassing ETS1 on chromosome 11. Although ETS1 was moved to the derivative chromosome 19 as a result of the t(11;19), we conclude that this oncogene is not close to the chromosome 11 breakpoint and is unlikely to be involved in this leukaemia.

Deletion of c-ets1 and T3 gamma loci from the 11q- chromosome in the human monoblastic cell line U937

The 11q- chromosome in the human monoblastic cell line U937 appears to be derived from an interstitial deletion in bands 11q21-23/24 or a translocation with an unknown chromosome. We show here by in situ hybridisation that this chromosome has lost the c-ets1 and T3 gamma loci. C-ets1 and T3 gamma sequences were not detected on any chromosomes besides the normal 11, indicating either that they were lost from the genome or that the chromosome to which they were translocated was not present in a high enough proportion of the cells to be detected by in situ hybridisation. No DNA rearrangements were found with three different restriction enzymes in the c-ets1, N-CAM, Thy-1 and c-sea genes detected by our probes. There was also no detectable rearrangement in the c-fms gene which was shown to be translocated from chromosome 5 to chromosome 1 in a subline of U937. The size of the c-fms and c-ets1 messages were normal. The possible significance of these findings is discussed.

Restriction fragment length polymorphisms in the ETS-1 proto-oncogene. Comparison of Saudi and Western populations

We have cloned part of the ETS 1 proto-oncogene and demonstrated the presence of two polymorphic Sst I restriction sites. A probe derived from one of our clones revealed the presence of 8.3 kb, 9.5 kb and/or 11.5 kb fragments on Southern blots of human DNA samples. The relative frequencies of these alleles appear to be significantly different between Saudi and Western populations, but there are no apparent differences in these frequencies between Saudi non-leukemic and leukemic individuals.

A unique amino-terminal sequence predicted for the chicken proto-ets protein

Avian cellular sequences homologous to the ets domain of the avian leukemia retrovirus, E26, have been characterized, and shown to contain nine discrete regions within a single locus of about 60 kb. The structure of the viral homologous and nonhomologous domains of this chicken ets-1 gene is characterized and seen to define the unique amino acid sequences of the ets protein. We have isolated and sequenced an avian ets-1 cDNA clone obtained from chicken thymus. This cDNA clone contains an open reading frame (ORF) encoding the normal cellular product of 441 amino acids. This product is significantly smaller than that encoded by the v-ets domain of the E26 transforming protein, p135, which contains 491 amino acids. The open reading frame predicted by our sequence data results in a protein calculated to be 50 kDa, which is slightly smaller than that actually observed in chicken cells. The presence of termination codons 5' to this ORF demonstrates that the cDNA characterized contains the entire coding region for the chicken ets gene.