Biomedical subjects

Y Le Dréan

Publications and source records attributed to Y Le Dréan.

7 recordsLinked to original sources

PubMed2007

Low-power millimeter wave radiations do not alter stress-sensitive gene expression of chaperone proteins.

This article reports experimental results on the influence of low-power millimeter wave (MMW) radiation at 60 GHz on a set of stress-sensitive gene expression of molecular chaperones, namely clusterin (CLU) and HSP70, in a human brain cell line. Selection of the exposure frequency is determined by its near-future applications for the new broadband civil wireless communication systems including wireless local area networks (WLAN) for domestic and professional uses. Frequencies around 60 GHz are strongly attenuated in the earth's atmosphere and such radiations represent a new environmental factor. An exposure system operating in V-band (50-75 GHz) was developed for cell exposure. U-251 MG glial cell line was sham-exposed or exposed to MMW radiation for different durations (1-33 h) and two different power densities (5.4 microW/cm(2) or 0.54 mW/cm(2)). As gene expression is a multiple-step process, we analyzed chaperone proteins induction at different levels. First, using luciferase reporter gene, we investigated potential effect of MMWs on the activation of transcription factors (TFs) and gene promoter activity. Next, using RT-PCR and Western blot assays, we verified whether MMW exposure could alter RNA accumulation, translation, or protein stability. Experimental data demonstrated the absence of significant modifications in gene transcription, mRNA, and protein amount for the considered stress-sensitive genes for the exposure durations and power densities investigated. The main results of this study suggest that low-power 60 GHz radiation does not modify stress-sensitive gene expression of chaperone proteins.

Cell Line↗

PubMed2000

A zebrafish ftz-F1 (Fushi tarazu factor 1) homologue requires multiple subdomains in the D and E regions for its transcriptional activity.

A zebrafish Ftz-F1 homologue, zFF1A (zebrafish Ff1a or Nr5a2, a member of nuclear receptor superfamily) and its C-terminally truncated variant (zFF1B) were previously identified. Due to lack of the identity box (I-box) and activation function 2 (AF-2) domain, zFF1B lacks transactivation function and fails to synergize with estrogen receptor (ER) in regulating promoters. It was speculated that the I-box might be involved in the zFF1A/ER interaction. In the present study, the function of the I-box was examined. In the absence of the I-box or with an altered heptad 9, the AF-2 of zFF1A was not functional, either in the presence or absence of ER. The GST pull-down assay showed that zFF1A and its mutants exerted similar physical contacts with ER-LBD, suggesting that the "dimerization" domain (I-box) is essential for the transcriptional activity of zFF1A. Moreover, nuclear receptor coactivator selectively activated zFF1 with the I-box but exerted no effect on zFF1B, indicating that the I-box is able to interact with the coactivators. By deletion study and analysis of the identified domains in GAL4-DNA binding domain, other regions of zFF1A critical for its AF were also delineated. Consistent with the mutation analysis, AF-2 was active only in the presence of the I-box. We also identified a novel AF domain (AF-3) located in the hinge region (amino acids 155-267), although the activity of AF-3 was inhibited by its flanking region. We suggest that the D and E regions of zFF1A possess both positive and negative transactivation functions, and interdomain "cross-talk" may confer the full transcriptional activity of the protein.

Amino Acid Sequence↗

PubMed2000

Interplay between liganded and orphan nuclear receptors controls reproductive pathways.

Nuclear receptors are transcription factors that belong to an evolutionary ancient superfamily. These proteins, which are even present in primitive metazoans, are implicated in all levels of cell fate: proliferation, differentiation, and apoptosis. Some of these nuclear receptors behave as ligand-inducible transcription factors, as they have acquired during evolution the ability to bind ligands. This is the case for some proteins that recognize small hydrophobic signaling molecules, and particularly the estrogen receptor (ER or NR3A1), which regulates the target gene's transcription rate under estrogen binding. It is now known that the ER alone regulates the transcription of many genes, such as those implicated in reproductive functions. However, this ER-mediated signaling pathway could be modulated by other transcription factors. Our work has established that two other orphan nuclear receptors (SF-1 or NR5A1 and the COUP-TFs, NR2F1 and NR2F2) can enhance two ER-regulated genes implicated in salmonid reproductive functions: the ER gene itself, and the sGTHIIbeta gene. Moreover, some xenoestrogens could disturb these regulations. Therefore, our data contribute to the concept that interplay between nuclear receptors is an important event for the transcriptional regulation of genes controlling cellular functions.

Animals↗

PubMed1999

Eukaryotic conditional expression system.

Existing conditional expression systems can be classified in two major categories that are based either on the induction or on the de-repression of transcription. The system described here combines both mechanisms, since a unique transcription factor can be shifted from a repression to a stimulation activity by simply changing its ligand. The resulting advantage of this system is the complete absence of basal expression before active induction. The principle of this method is based on the unexpected ability of the chimeric protein containing the DNA-binding domain of the yeast Gal4 transcription factor fused to the COOH half of the estradiol receptor (GalER), to act as a repressor when bound to the drug 4OH-tamoxifen, in the context of a previously described optimized Gal4-responsive promoter. The efficacy of this system has been assessed in transient expression assays using the chloramphenicol acetyl transferase (CAT), and in situ, through the activity of a Gal4 responsive beta-galactosidase gene.

Animals↗

PubMed1997

Presence of distinct cis-acting elements on gonadotropin gene promoters in diverse species dictates the selective recruitment of different transcription factors by steroidogenic factor-1.

The nuclear receptor steroidogenic factor-1 (SF-1) regulates the cell-specific expression of the pituitary gonadotropin subunit genes. Several potential DNA-binding sites for SF-1, estrogen receptor (ER) and the immediate-early transcription factor NGFI-A are found in LHbeta genes from many species. In this study, we have examined the action and interaction of these transcription factors on LHbeta gene promoters from two representative vertebrate species, i.e. rat and salmon. Cotransfection studies in COS-1 cells have shown that the action of SF-1 on salmon gonadotropin IIbeta (sGTHIIbeta) gene promoter was dramatically enhanced when combined with ER. The rat LHbeta promoter was activated by SF-I or ER individually, but these two factors, however, were unable to act in synergism on this promoter. In contrast, NGFI-A, specifically in cooperation with SF-1, transactivated the rat LHbeta gene expression but was ineffective on the sGTHIIbeta gene. Gel shift experiments showed that this lack of activation was due to the low affinity of the salmon NGFI-A-responsive element for its binding protein. In conclusion, our studies demonstrate that differential recruitment of distinct transcription factors by SF-1 might be a common mechanism to activate the cell-specific gonadotropin gene expression in different species.

Animals↗

PubMed1995

Rainbow trout estrogen receptor presents an equal specificity but a differential sensitivity for estrogens than human estrogen receptor.

The estrogen receptor is a transcription factor that mediates the actions of estrogens which plays a major role in salmonid vitellogenesis. Previously, we cloned and described the estradiol receptor in rainbow trout. To study the transactivation characteristics, the full length cDNA was inserted in an expression vector and tested by transfection on an estrogen-dependent promoter (pERE-TK-CAT). For the first time, direct comparison between the trout receptor (rtER) and human receptor (hER) in an analogous system has been possible. We demonstrate that rtER can, like hER, transactivate transcription in a strictly hormone-dependent manner. The specificity and sensitivity of the rtER response to different steroids have been studied. With rtER, the E2 concentration needed for half maximal activation is 10 times higher than with hER. In addition, we show that rtER has a weak affinity for androgens and transactivation could be induced using high testosterone concentration. Experiments show that both rtER and hER have an equal specificity for estrogens but that the rtER binds its ligand with a lower sensitivity than hER. Several hypotheses concerning the role of main amino acids within the receptor protein are proposed based on the different properties of the receptors and comparison of sequences.

Animals↗

PubMed1995

Characterization of an estrogen-responsive element implicated in regulation of the rainbow trout estrogen receptor gene.

We previously reported that the expression of the rainbow trout estrogen receptor (rtER) gene is markedly increased by estradiol (E2). In this paper, we have used transient transfection assays with reporter plasmids expressing chloramphenicol acetyl transferase (CAT), linked to 5' flanking regions of the rtER gene promoter, to identify cis-elements responsible for E2 inducibility. Deletion analysis localized an estrogen-responsive element (ERE), at position +242, with one mutation on the first base compared with the consensus sequence. This element confers estrogen responsiveness to CAT reporter linked to both the herpes simplex virus thymidine kinase promoter and the homologous rtER promoter. Moreover, using a 0.2 kb fragment of the rtER promoter encompassing the ERE and the rtER DNA binding domain obtained from a bacterial expression system, DNase I footprinting experiments demonstrated a specific protection covering 20 bp (+240/+260) containing the ERE sequence. Based on these studies, we believe that this ERE sequence, identified in the rtER gene promoter, may be a major cis-acting element involved in the regulation of the gene by estrogen.

Animals↗