Identification of a second promoter in the human c-ets-2 proto-oncogene

We localized and characterized a new regulatory element with promoter activity in the human c-ets-2 intron 1. This promoter governs the expression of 5' divergent c-ets-2 transcripts through multiple start sites dispersed within 300 bp. Among the multiple start sites detected, three are major transcriptional initiation points. We detected transcripts initiated from this new promoter in various cell lines such as COLO 320, NBE, or HepG2 cells. This promoter exhibits transcriptional activity when linked to the CAT gene, and deletion constructs reveal that it contains activating and repressing elements. The sequence of the promoter reveals putative binding sites for ETS, MYB, GATA, and Oct factors. In addition, we show that this promoter is functionally conserved in the chicken.

Stromelysin-1 expression is activated in vivo by Ets-1 through palindromic head-to-head Ets binding sites present in the promoter

Regulation of the gene expression of Stromelysin-1 (matrix metalloproteinase-3), a member of the matrix metalloproteinase family, is critical for tissue homeostasis. The Stromelysin-1 promoter is known to be transactivated by Ets proteins through palindromic head-to-head Ets binding sites (EBS), an unusual configuration among metalloproteinase promoters. Patterns of increased co-expression of Stromelysin-1 and Ets-1 genes have been observed in pathological processes such as rheumatoid arthritis, glomerulonephritis and tumor invasion. In this context, we show in a synovial fibroblastic model cell line (HIG-82), which is able to co-express Stromelysin-1 and Ets-1, that the EBS palindrome is essential for the expression of Stromelysin-1. More precisely, using electrophoretic mobility shift assays, DNA affinity purification and chromatin immunoprecipitation, we demonstrate that endogenous Ets-1, but not Ets-2, is present on this palindrome. The use of a dominant-negative form of Ets-1 and the decrease of Ets-1 amount either by fumagillin, an antiangiogenic compound, or by short interfering RNA show that the activation rate of the promoter and the expression of Stromelysin-1 correlate with the level of endogenous Ets-1. Thus, it is the first demonstration, using this cellular model, that endogenously expressed Ets-1 is actually a main activator of the Stromelysin-1 promoter through its effective binding to the EBS palindrome.

Cloning of the rat IL-5Ralpha gene: analysis of 5'-upstream region and expression by B cells

Although rats are widely used for the analysis of allergic reactions and parasitic infections where IL-5 is involved, nothing is currently known of the expression of IL-5 receptor in this species. In this study, the cDNA sequence, genomic structure and the transcriptional regulation of the rat IL-5Ralpha were analyzed. The rat IL-5Ralpha gene, which we localized to chromosome 4q34-q41, spans more than 25 kb and consists of 12 exons. Promoter activity was seen in different cell lines and analysis by deletion experiments allowed to identify two negative regulatory regions which did not differ when tested either with IL-5Ralpha-negative or positive cells. Finally, the investigation of the expression of IL-5Ralpha showed that it is expressed in lung, spleen, liver, and purified rat B cells from normal rat. This can provide an explanation for the role of rat IL-5 as B-cell growth factor and a relevant model in order to better understand the activity of IL-5 on human B cells.

Expression of a functional IL-13Ralpha1 by rat B cells

IL-13 mediates its effects through a complex receptor system including IL-4Ralpha and a functional IL-13Ralpha1. IL-13 has been reported to have no effects on mouse B cells due to a lack of receptor expression. However, on human B cells a functional IL-13Ralpha1 has been described. Here, we identified the rat IL-13Ralpha1 in order to analyze its expression and function in rat B cells. The expression of IL-13Ralpha1 has been shown by the presence of mRNA and the corresponding protein in purified rat B cells and in rat hybridoma B cell line. Rat B cells are able to bind IL-13 and to proliferate when cultured with CD40 ligand and IL-13. In vivo experiments showed that administration of IL-13 did enhance IgE production. These results suggest a direct interaction of rat B cells with IL-13 through a functional receptor with an increase of IgE production and provide a relevant model to further study the activity of IL-13 and to better understand its role in human diseases.

Targeting of PML/RARalpha is lethal to retinoic acid-resistant promyelocytic leukemia cells

Acute promyelocytic leukemia (APL) cells, containing the t(15;17) rearrangement, express the fusion protein, PML/RARalpha. Clinically, patients respond to all-trans retinoic acid (ATRA) through complete remissions associated with myeloid maturation of leukemic cells. This clinical ATRA response of APL is linked to PML/RARalpha expression. Unfortunately, these remissions are transient and relapsed APL is often ATRA-resistant. The role PML/RARalpha plays in the growth and maturation of these APL cells with acquired ATRA resistance has not been fully explored. This study uses an ATRA-resistant NB4 cell line (NB4-R1) to investigate the contribution of PML/RARalpha expression to ATRA resistance. Targeting of PML/RARalpha in NB4-R1 cells was undertaken using two approaches: homologous recombination and hammerhead ribozyme-mediated cleavage. Reducing PML/RARalpha protein in NB4-R1 cells rendered these cells more sensitive to ATRA. These cells were growth-inhibited in ATRA, apoptosis was induced, and there was no apparent signaling of differentiation. Sequence analysis identified a mutation in the ligand binding domain (LBD) of the RARalpha portion of PML/RARalpha. Results show that these retinoid-resistant NB4 cells require persistent PML/RARalpha expression for leukemic cell growth. Taken together, these findings can account for why these cells do not respond to ATRA and how reduction of PML/RARalpha abrogates the antiapoptotic effect it confers to these leukemic cells.

[Registry of cancer in Reunion: data of the first five years of registration (1988-1992)]

After explaining the purposes of a general cancer register in Reunion Island and describing objectives and running, main results from 1988 to 1992 are introduced. Comparison with EUROCIM network shows that cancer standardized incidence (all sites) in Reunion Island is at the same level as in Martinique and lower than in other registers. Nevertheless some cancers are particularly frequent. For men, as for most European registers, lung cancer (15%) is the most frequent diagnosed cancer, followed by esophagus and stomach cancers. Reunion Island belongs to areas with highest incidence rates for esophagus cancer. Breast cancer (21%), despite a lower incidence than in Europe, is still the first female cancer, followed by cervix cancer (18%) which incidence, as in Martinique, is very high. We don't notice high discrepancies between mortality rates and incidence rates in Reunion Island during that period.

The homeobox-containing Engrailed (En-1) product down-regulates the expression of Pax-6 through a DNA binding-independent mechanism

By in situ hybridization of quail neuroretinas, we observed that Engrailed (En-1) is expressed both in the ganglionic and the amacrine cell layers, similarly to Pax-6. Because we observed a decrease of Pax-6 expression in the neuroretina of hatched animals, we studied the effect of the chicken En-1 and En-2 proteins on Pax-6 expression. En-1 and to some extent En-2 were able to repress the basal and the p46Pax-6-activated transcription from the two Pax-6 promoters. Infection of retinal pigmented epithelium by a virus encoding the En-1 protein repressed the endogenous Pax-6, and a similar effect was observed with a homeodomain-deleted En-1. In vitro interaction indicates that En proteins are able to interact with the p46Pax-6 through the paired domain. This interaction negatively regulates the DNA-binding properties of the p46Pax-6. These results suggest an interplay between En-1 and Pax-6 during the central nervous system development and indicate that En-1 may be a negative regulator of Pax-6.

Structure and organization of the mouse elk1 gene

In the ets gene family of transcription factors, elk1 belongs to the subfamily of Ternary Complex Factors (TCFs) which bind to the Serum Response Element (SRE) in conjunction with a dimer of Serum Response Factors (SRFs). In this communication we report the isolation of cDNAs from the mouse elk1 gene, containing the full coding sequence homologous (87% identical) to the human gene, and the structure and organization of 22 kb of the mouse elk1 locus. The coding sequence is spread through 5 exons (numbered 1 to 5): exons 1 to 4 range from 102 bp to 447 bp and exon 5 is at least 620 bp. Exon 0 was not found in the 8.5 kb sequence upstream of exon 1. The intron between exons 1 and 2 is 4 kb long and the 3 other introns are less than 500 bp long. This information will be useful to engineer targeted mutations of this gene in mice and to determine the genomic structure of the other TCF genes.

Characterization of a new melanocyte-specific gene (QNR-71) expressed in v-myc-transformed quail neuroretina

Quail neuroretina cells (QNR) infected with the v-myc-expressing retrovirus MC29 become pigmented after several passages in vitro. After differential screening of a cDNA library constructed from these cells, we have isolated a cDNA clone (QNR-71) which identifies an RNA expressed only in the pigmented layer of the retina and in the epidermis. This gene can also be induced in other cell types transformed by MC29, suggesting that QNR-71 may be regulated by the v-myc protein. Sequence analysis showed that the QNR-71 cDNA exhibits stretches of homologies with melanosomal proteins encoding genes. From bacterially expressed QNR-71 peptides we obtained rabbit antisera able to specifically recognize two proteins of 95 and 100 kDa in pigmented retinal cells, but not in the neuroretina. To study the regulation of QNR-71, we used promoter fragments linked to the CAT reporter gene, in transient co-expression assay. We observed an increase in CAT expression with a c-MYC and microphtalmia (mi) expression vectors. Both MYC and mi activate the QNR-71 promoter through direct binding to a CATGTG site present in the promoter fragment.

A functional Rev-erb alpha responsive element located in the human Rev-erb alpha promoter mediates a repressing activity

Rev-erb alpha belongs to the nuclear receptor superfamily, which contains receptors for steroids, thyroid hormones, retinoic acid, and vitamin D, as well as "orphan" receptors. No ligand has been found for Rev-erb alpha to date, making it one of these orphan receptors. Similar to some other orphan receptors, Rev-erb alpha has been shown to bind DNA as a monomer on a specific sequence called a Rev-erb alpah responsive element (RevRE), but its transcriptional activity remains unclear. In this paper, we characterize a functional RevRE located in the human Rev-erb alpha promoter itself. We also present evidence that (i) Rev-erb alpha mediates transcriptional repression of its own promoter in vitro, (ii) this repressing effect strictly depends on the binding of Rev-erb alpha to its responsive element and is transferable to a heterologous promoter; and (iii) Rev-erb alpha binds to this responsive sequence as a homodimer.

Identification of two ets related genes in a marine worm, the polychaete annelid Nereis diversicolor

The ETS family includes a growing number of transcription factors with a highly conserved DNA-binding domain, the ETS domain. We have used PCR amplification with degenerated oligonucleotides to isolate two putative ETS DNA-binding coding domains in a primitive form of coelomate, the polychaete annelid Nereis diversicolor. These sequences are highly related to the ETS and ERG groups of the ets gene family. For the erg sequence an adjacent region encoding for 91 amino acids has been characterized after library screening, and we show an expression in cells isolated from the coelomic cavity of the animal. A phylogenic analysis confirms that the ets-1/ets-2 and the erg/fli dichotomy arose specifically in the vertebrate lineage.

Expression of the non-structural proteins of parvovirus MVMp from recombinant retroviruses: predominant role of the parvoviral NS-1 product in host cell disturbance

Stable Psi-2 cell transformants were selected for their resistance to neomycin after transfection with a retroviral pZipNeo-SVX vector carrying sequences encoding for the non-structural proteins of parvovirus minute virus of mice (prototype strain, MVMp). Cells producing both NS-1 and NS-2 proteins (PsiNS) or only the NS-2 polypeptide (PsiNS2) were obtained. PsiNS cells exhibited morphological abnormalities and had a reduced clone-forming ability, whereas PsiNS2 cells were indistinguishable from the parental line. These cellular systems produced recombinant retroviral particles which transduced the NS gene(s) into mouse A9 cells. As in the case of Psi-2 cells, A9 transformants expressing both NS-1 and NS-2 proteins were impaired in their cloning efficiency. These results provided a direct confirmation of the predominant role of protein NS-1 in the cytopathic effect of parvoviruses.

Overexpression of c-erbA proto-oncogene enhances myogenic differentiation

Triiodothyronine (T3) positively regulates both the expression of the MyoD gene, a key myogenic regulator, and C2 muscle cell differentiation. To directly examine the role of its nuclear receptors in the control of myogenesis, we introduced a c-erbA expression vector into C2 muscle cells by transient or stable transfection. Our results show that c-erbA can play a potent role in the triggering of muscle terminal differentiation since its overexpression leads to: (1) a complete abrogation of the activity of the myogenesis inhibitor AP-1 (fos/jun) transcription factor; (2) an enhanced induction of MyoD expression upon T3 treatment; (3) the acquisition by T3 of the ability to trigger both growth arrest and terminal differentiation in the presence of large amounts of serum mitogens, a property that is otherwise specific to retinoic acid (RA). Thus, c-erbA is one of the two protooncogenes (with c-ski) that acts as positive regulator of muscle differentiation. Furthermore, the fact that c-erbA overexpression allows T3 to largely mimic the RA effects indicates that their biological differences in the modulation of myogenic program primarily rely on the differential expression of their receptors in C2 muscle cells rather than on an intrinsic specificity of their target genes.