PubMed Health⌕ Search

Biomedical subjects

C Séguin

Publications and source records attributed to C Séguin.

At least 19 recordsLinked to original sources
PubMed2001

Phosphorylation is involved in the activation of metal-regulatory transcription factor 1 in response to metal ions.

We have studied the role of phosphorylation in the activation of metal-regulatory transcription factor-1 (MTF-1) and metallothionein (MT) gene expression. We showed that MTF-1 is phosphorylated in vivo and that zinc stimulates MTF-1 phosphorylation 2-4-fold. Several kinase inhibitors were used to examine the possible involvement of kinase cascades in the activation of MTF-1. Metal-induced MT gene expression was abrogated by protein kinase C (PKC), c-Jun N-terminal kinase (JNK), phosphoinositide 3-kinase, and tyrosine-specific protein kinases inhibitors, as assayed by Northern analysis and by cotransfection experiments using a metal regulatory element-luciferase reporter plasmid. The extracellular signal-activated protein kinase and the p38 kinase cascades did not appear to be essential for the activation of MT gene transcription by metals. By using dominant-negative mutants of PKC, JNK, mitogen-activated kinase kinase 4 (MKK4), and MKK7, we provide further evidence supporting a role for PKC and JNK in the activation of MTF-1 in response to metals. Notably, increased MTF-1 DNA binding in response to zinc and MTF-1 nuclear localization was not inhibited in cells preincubated with the different kinase inhibitors despite strong inhibition of MTF-1-mediated gene expression. This suggests that phosphorylation is essential for MTF-1 transactivation function. We hypothesize that metal-induced phosphorylation of MTF-1 is one of the primary events leading to increased MTF-1 activity. Thus, metal ions such as cadmium could activate MTF-1 and induce MT gene expression by stimulating one or several kinases in the MTF-1 signal transduction pathway.

Animals↗
PubMed2001

Characterization of the mouse metal-regulatory-element-binding proteins, metal element protein-1 and metal regulatory transcription factor-1.

Metal activation of metallothionein gene transcription depends mainly on the presence of regulatory DNA sequences termed metal-regulatory elements (MREs) and involves MRE-binding transcription factor-1 (MTF-1) interacting with the MREs in a Zn(2+)-dependent manner. We previously identified and characterized a nuclear protein, termed metal element protein-1 (MEP-1), specifically binding with high affinity to MRE elements. The precise relationship between MTF-1 and MEP-1 was unclear, and to determine whether MEP-1 and MTF-1 were distinct protein species, we performed DNA binding analyses to characterize the binding properties of both proteins. Electrophoretic mobility-shift assays showed that MTF-1, produced in COS cells, produces a slower-migrating band compared with that obtained with purified MEP-1. Using an anti-MTF-1 antibody, we showed that both the MTF-1-MRE and the MEP-1-MRE complexes are supershifted by an anti-MTF-1 antibody, thus demonstrating that MEP-1 is antigenically related to MTF-1. RNase protection analyses carried out with RNA prepared from different tissues and cell lines failed to reveal the presence of MTF-1 splicing variants. This indicates that MEP-1 may be a proteolytic fragment of MTF-1. MTF-1 DNA-binding activity was rapidly activated in vivo by Zn(2+) ions but not by Cd(2+), UV irradiation or PMA, and occurred on ice as well as at 21 degrees C. In control and Zn(2+)-treated cell extracts, DNA-binding activity was not enhanced in vitro following the addition of exogenous Zn(2+) or a preincubation at 37 degrees C. However, recombinant MTF-1 produced in vitro required Zn(2+) activation for DNA binding. Interestingly, treatment of nuclear extracts with calf intestine phosphatase completely abrogated MTF-1 DNA-binding activity, thus suggesting that phosphorylation is involved in the regulation of MTF-1 activity.

Animals↗
PubMed2001

The value of clonality in the diagnosis and follow-up of patients with cutaneous T-cell infiltrates.

The diagnosis of early stages of cutaneous T-cell lymphoma (CTCL) is often difficult, especially for lesions that are at the borderline between reactive and neoplastic skin T-cell infiltrates. T-cell monoclonality in these lesions is considered by some to be an important prognostic factor of neoplastic evolution, whereas others claim that clonality can also be found in benign skin infiltrates and is therefore of limited diagnostic value. To address this controversy, the authors analyzed retrospectively eight patients with lymphocytic skin lesions who progressed to CTCL, and three patients with recurrent T-cell lymphocytic infiltrates who had not developed CTCL. From a total of 65 biopsies of eight progressing patients, 32 were diagnosed as histologically malignant and 33 were diagnosed as benign or borderline. The authors found clonality by either polymerase chain reaction or Southern blot analysis in 88% of malignant and in 79% of nonmalignant lesions. None of the 37 biopsies of non-progressing patients was clonal. These results indicate strongly that the presence of monoclonality in T-cell skin infiltrates is related closely to the risk of developing CTCL. The value of clonality as a marker of malignancy is supported by the absence of T-cell clonal populations in all infiltrates from patients who had not progressed to lymphoma.

Blotting, Southern↗
PubMed2000

Cloning of cDNAs encoding retinoic acid receptors RAR gamma 1, RAR gamma 2, and a new splicing variant, RAR gamma 3, from Aambystoma mexicanum and characterization of their expression during early development.

To analyze retinoic acid (RA) receptor (RAR) expression during early development in the urodele embryo, we have isolated cDNAs for four members of the axolotl (Ambystoma mexicanum) RAR family, namely RAR alpha (NR1B1), aRAR gamma 1 (NR1B3a), aRAR gamma 2 (NR1B3b), and a new splicing variant of aRAR gamma 2, aRAR gamma 3 (NR1B3c), which contains an insertion of five hydrophobic amino acids in the C-terminal region of the DNA binding domain. The temporal expression pattern of the RAR gamma isoforms was established by RT-PCR using total RNA from embryos of different stages. The expression of aRAR gamma 2 coincides with neurulation and is enhanced in the extremities of the embryo's anteroposterior axis. The aRAR gamma 3 is specifically expressed during gastrulation and early neurulation, whereas aRAR gamma 1 is expressed later during organogenesis. Global aRAR gamma 2 mRNA levels, as well as their spatio-temporal expression pattern in the neurula, were not affected by treatment with RA. These results show that several RARs are expressed in the axolotl embryo during early development, and reveal the existence of a new RAR gamma variant.

Alternative Splicing↗
PubMed2000

Characterization of cis-acting elements in the promoter of the mouse metallothionein-3 gene. Activation of gene expression during neuronal differentiation of P19 embryonal carcinoma cells.

The metallothionein (MT)3 gene is expressed predominantly in the brain and the organs of the reproductive system, and fails to respond to metal ions in vivo. A CTG repeat was proposed to function as a potential repressor element in nonpermissive cells, and a sequence similar to the JC virus silencer element was found to function as a negative element in permissive primary astrocytes. The objective of this study was to characterize further the mechanisms governing cell-type specific MT-3 gene transcription. We searched for a suitable cell line expressing the MT-3 gene to be used for determination of MT-3 promoter tissue specificity, and showed that MT-3 expression is activated during neuroectodermal differentiation of P19 cells induced by retinoic acid to levels similar to those found in whole brain. Deletion of the CTG repeat or of the JC virus silencer did not promote MT-3 promoter activity in nonpermissive cells, or enhance expression in permissive cells. We identified MT-3 promoter sequences interacting with liver and brain nuclear proteins, as assayed by DNase I footprinting analyses and electrophoretic mobility shift assay, and assessed the role of these sequences in the regulation of MT-3 expression by cotransfection experiments. We generated stable transfectants in permissive C6 and nonpermissive NIH-3T3 cells, and analysed the methylation status of the MT-3 gene. These studies show that regulation of tissue-specific MT-3 gene expression does not appear to involve a repressor, and suggest that other mechanisms such as chromatin organization and epigenetic modifications could account for the absence of MT-3 gene transcription in nonpermissive cells.

3T3 Cells↗
PubMed1998

Post-transcriptional control of c-myc RNA during early development analyzed in vivo with a Xenopus-axolotl heterologous system.

We have set up a heterologous in vivo system to study gene regulation at the post-transcriptional level during early development. This system uses two amphibian species, Xenopus laevis and Ambystoma mexicanum (axolotl), the development of which is three to four times slower than that of X. laevis. The stability of three different synthetic X. laevis c-myc transcripts was followed after injection into fertilized axolotl eggs. One transcript is 2.2 kilobases (kb) long (full-length). The second is 1.5-kb long with most of the 3' untranslated region (3'UTR) removed, and the third corresponds to the 3'UTR (0.7-kb). The behavior of the endogenous axolotl c-myc RNA was compared with the exogenous injected c-myc transcripts. Our results show the existence of several developmental timers controlling degradation of the c-myc molecules. The first is activated at oocyte maturation and affects both the endogenous and exogenous (2.2- and 1.5-kb) transcripts containing the coding regions. A second timer could be linked to the number of cell divisions since fertilization (6th-7th cleavages) and involves the endogenous c-myc RNAs. Another timer could involve the c-myc mRNA molecule itself, because when injected into axolotl eggs, the half-life of the 2.2-kb X. laevis transcript appears to be independent of the axolotl context. After injection into axolotl fertilized eggs, the behavior of this X. laevis full-length c-myc molecule reveals an unexpected increase in the intensity of its autoradiographic signals. This increase occurs independently of events linked to mid-blastula transition and preliminary investigations are discussed.

Amanitins↗
PubMed1998

Expression of the gene encoding metallothionein-3 in organs of the reproductive system.

Metallothionein-3 (MT-3) is a new MT gene-family member that inhibits survival of rat neurons cultured in presence of brain extracts. Contrary to other MT genes, which are expressed in most tissues and which are highly inducible by metals, MT-3 expression was reported to be mainly in the brain, and it failed to respond to metals in vivo. We show here that MT-3 mRNA is present in several organs other than the brain, as assayed by Northern analyses. In the rat, MT-3 mRNA was detected in the testis, prostate, epididymis, tongue, ovary, uterus, stomach, heart, and seminal vesicles. The MT-3 mRNA levels in the testis, epididymis, prostate, and tongue were 22% of those in brain, while in ovary, uterus, and stomach, they were 4% of the brain level, and they were lower still in the other organs. The MT-3 gene was not inducible by CdCl2 or lipopolysaccharide in rat testis and prostate. In the mouse and the human, relative MT-3 mRNA levels were lower than those found in the rat when compared with those present in brain. Testicular MT-3 transcript levels remained quite constant during rat postnatal development in animals aged from 6 to 43 days. In situ hybridization analyses on human testis sections showed that MT-3 mRNA was present at different levels in both the Leydig cells and the seminiferous tubules. In orchiectomized rats, prostatic MT-3 mRNA was decreased by 75%, and injections of dihydrotestosterone restored MT-3 mRNA levels to control values. Overall, these results show that MT-3 tissue-specific gene expression is broader than previously reported and provide new experimental systems to study the function and mechanism of action of the MT-3 protein.

Animals↗
PubMed1998

Cloning of a complementary DNA encoding an Ambystoma mexicanum metallothionein, AmMT, and expression of the gene during early development.

We have used a polymerase chain reaction strategy to isolate a metallothionein (MT) cDNA from the amphibian Ambystoma mexicanum (axolotl). This cDNA is 875-bp long and encodes a 60 amino acid protein, AmMT, typical for family 1 MTs. It contains 20 cysteine (Cys) residues that can be aligned with those of other vertebrate MTs. The overall structure of the protein is unique among vertebrates in having only two amino acid residues before the first Cys at the amino-terminal end. Northern analyses showed that AmMT is expressed throughout embryogenesis, giving rise to three mRNA species of 650, 750, and 1,600 nucleotides (nt). The 750 and 1,600 nt transcripts appear to result from differential use of polyadenylation signals, whereas the 650 nt RNA could arise from deadenylation of the 750-nt transcript. Both the 750- and 1,600-nt RNAs were presented in embryos before the mid-blastula transition (MBT). After the MBT, the 750-nt RNA was replaced by the 650-nt RNA which was gradually degraded to undetectable levels in post-neurulation embryos. Levels of the 1,600-nt transcript increased at gastrulation and reach a maximum in Stage 30 embryos. In adult animals, levels of the 750-nt RNA were high in liver and testes, and very low in lung, gut, skin, and oviducts, whereas levels of the 1,600-nt transcript were similar and moderately elevated in all tissues examined. In contrast, in Xenopus laevis, Northern analysis did not detect XIMT-A mRNA in embryos before late neurulation (Stage 24). XIMT-A mRNA levels then increased sharply in Stage 36 hatched embryos at levels similar to those found in adult livers. These results show that AmMT presents a unique expression pattern among metazoans being transcribed as two transcripts differing in the length of their 3' untranslated regions, the levels of which vary during embryogenesis and in adult tissues.

Ambystoma↗
PubMed1998

Cloning of a cDNA for xDOR2, a novel TR2-related nuclear orphan receptor, expressed during neurulation in Xenopus laevis embryos.

We isolated from neurulating Xenopus laevis (X. laevis) embryos a cDNA encoding a novel nuclear orphan receptor, Developmental Orphan Receptor 2 (xDOR2), closely related to Ambystoma mexicanum DORI (aDOR1) and to Testicular Receptor-2 (TR2) orphan receptor family members. The xDOR2 cDNA sequence which is truncated both at its 5' and 3' ends predicts a protein sequence of 542 amino acids. While the DNA-binding domain of xDOR2 shares 91%, and 92%, identity with those of aDOR1 and the TR2s, respectively, considerable divergence is observed at both extremities of the peptides. At the N-terminus, xDOR2 is 66% identical to aDOR1 and 64% to the TR2s. At the C-terminus, xDOR2 which is longer by 126 amino acids compared to aDOR1, shares 62%, identity with aDOR1 and appears to contain a complete ligand-binding domain. The DOR receptors appear to form a subtype distinct from the TR2s, and may play a role in the development and differentiation of neural tissues.

Amino Acid Sequence↗
PubMed1997

Subgroup specific protection of mice from respiratory syncytial virus infection with peptides encompassing the amino acid region 174-187 from the G glycoprotein: the role of cysteinyl residues in protection.

We identified subgroup specific protective epitopes represented by the amino acid regions 174-187 and 171-187 of the G glycoproteins from respiratory syncytial virus (RSV), subgroups A and B. Mice immunized with coupled synthetic peptides corresponding to either the region 174-187 containing a Cys186-->Ser substitution or to the native region 171-187 were completely resistant to RSV infection but only to the respective virus. The protective activities of the peptides 174-187 were dependent on the Cys186-->Ser substitution. In addition, a recombinant protein representing the region 125-203 of the A subgroup G glycoprotein expressed in Escherichia coli was capable without further treatment to completely protect animals against RSV subgroup A infection. We show that the combinations of cysteinyl residues (positions 173, 176, 182, and 186) retained within either synthetic peptides or the recombinant protein G125-203 greatly influenced their protective activities. This indicates that the region 171-187 is essential for the protection conferred by the G125-203 protein. Furthermore, our results strongly suggest that the peptides' and recombinant protein's potencies are a function of a loop-like structure which is stabilized by intramolecular disulfide linkages between Cys176-Cys182 and Cys173-Cys186. This is further supported by the observation that chemical blocking of the sulfidryl groups in synthetic peptides completely eliminated their protective activity.

Amino Acid Sequence↗
PubMed1997

Molecular cloning from neurulating Ambystoma mexicanum embryos of the cDNA encoding an orphan nuclear receptor (aDOR1) closely related to TR2-11.

We have isolated a cDNA encoding a novel orphan nuclear receptor, aDOR1, closely related to testicular receptor-2 (TR2) orphan receptor family members, from neurulating Ambystoma mexicanum embryos. The cDNA sequence predicts a protein primary sequence of 416 amino acids with a calculated molecular weight of 45.8 kDa. While the DNA-binding domains of aDOR1 and hTR2-11 share 96% identity, considerable divergence is observed at both extremities of the peptides. At the N-terminus, aDOR1 is 66% identical to hTR2-11 and longer by 37 amino acids. At the C-terminus, despite a greater similarity (69%), aDOR1 is much shorter than the hTR2 isoforms and seems to encode a distinct ligand-binding domain. Expression of aDOR1 was studied by the reverse transcription polymerase chain reaction assay (RT-PCR). High mRNA levels were detected during oogenesis, they remained high during the cleavage stage, and decreased at the mid-blastula transition (MBT). Transcripts increased again at the end of gastrulation, reached a peak level during neurulation, and leveled off after closure of the neural tube. In neurulas dissected along the anteroposterior axis, aDOR1 mRNA was enriched at both extremities of the embryo, while no particular distribution was favored along the dorsoventral axis. Retinoic acid (RA) treatments at the beginning of gastrulation did not affect overall mRNA levels in the neurula nor its distribution along both axes. In the adult, expression was predominant in the brain; lower levels (about 15%) were detectable in all germ layer derivatives, except muscle. These results suggest that aDOR1 may be required for the early determination events occurring during the cleavage stages of development, and may be involved in embryogenesis and in brain function.

Ambystoma↗
PubMed1995

Structure and metal-regulated expression of the gene encoding Xenopus laevis metallothionein-A.

To investigate the regulation of amphibian metallothionein(MT)-encoding genes, we have isolated and sequenced the XlMT-A gene encoding Xenopus laevis (Xl) MT-A. The gene displays an overall structure similar to that of mammalian MT, with three exons interrupted by two introns. The promoter region contains a typical TATA box and two metal regulatory elements (MRE) within the first 100 bp upstream from the transcription start point (tsp). The transition metal ion (Mc2+) inducibility of the promoter was studied by transient expression experiments in CV-1 African green monkey kidney cells, using different DNA fragments from the 5'-flanking region of XlMT-A fused to the bacterial cat reporter gene. The first 145 bp upstream from the tsp are sufficient to confer inducibility of cat by Cd2+. Constructs bearing only the most proximal MRE are not inducible by Me2+, thus suggesting that both MRE are required for Me2+ induction. Recognition sites for the transcription factors, AP-1 and AP-2, are located within the first 180 bp of the promoter region and these elements appear to be involved in controlling the constitutive basal level of expression of this MT.

Amino Acid Sequence↗
PubMed1995

Evidence that the amino acid region 124-203 of glycoprotein G from the respiratory syncytial virus (RSV) constitutes a major part of the polypeptide domain that is involved in the protection against RSV infection.

The first 230 residues of the 298-amino acid glycoprotein G of respiratory syncytial virus (RSV) are sufficient to confer complete resistance to challenge with live RSV, whereas the first 180 residues completely failed (Olmsted et al. (1989) J. Virol. 63, 411-420). The characterization of a protective epitope corresponding to the amino acid region 174-187 of the G protein (Trudel et al. (1991) Virology 185, 749-757) suggests that interruption of this region in the 180 residue truncated polypeptide may be responsible for its inability to confer protection and consequently that the 174-187 region may play a major role in the protection effected by the protein G. To support these hypotheses, we examined the ability of the amino acid region 124-203 of glycoprotein G to confer protection. The corresponding peptide was expressed as a non-fusion protein in a recombinant vaccinia virus designated VG27. Immunization of BALB/c mice with this recombinant efficiently induced the production of antibodies capable of recognizing both the parental glycoprotein G and peptide 174-187. Furthermore, upon challenge with RSV, a significant decrease of infectious particles was found in the lungs of mice immunized with VG27 as compared with non-immunized mice. Our results suggest that the 124-203 amino acid region of the RSV G protein constitutes a major part of the domain involved in protection.

Animals↗
PubMed1993

Purification of mouse MEP-1, a nuclear protein which binds to the metal regulatory elements of genes encoding metallothionein.

Metal regulatory elements (MREs) shared by metallothionein (MT) gene promoters are essential for metal induction of MT genes. MEP-1, a nuclear protein which binds to these elements has been purified from heavy metal-resistant mouse L cells using footprinting, Southwestern and UV cross-linking techniques to assay its binding activity. The purification scheme, starting from crude nuclear extracts, involved a combination of heparin-Sepharose and MRE-DNA affinity chromatography. The purified protein preparation showed a single polypeptide band of 108 kDa on polyacrylamide gel electrophoresis, and 2D-gel analyses revealed the presence of a protein species migrating as a single population of approximately 110 kDa. MEP-1 does not appear to be glycosylated since it eluted with the flow-through on a Wheat Germ Sepharose column. It was retained by a zinc-Chelating Sepharose column suggesting that amino acid residues (i.e., cysteine, histidine) which have an affinity for zinc ions are exposed on the protein surface. Binding studies with the purified protein indicated that it binds specifically to MRE sequences and that the binding can be abolished by a point mutation in the MRE core consensus sequence or by the addition of the chelating agent 1,10-phenanthroline. Binding activity can be restored by the addition of zinc ions to the chelated protein. These results suggest that MEP-1 is one of the major proteins interacting with MRE sequences.

Animals↗
PubMed1993

Isolation of cDNAs for two closely related members of the axolotl Wnt family, Awnt-5A and Awnt-5B, and analysis of their expression during development.

To characterize molecular interactions between cells in the early amphibian embryo, we have isolated cDNAs for two members of the axolotl (Ambystoma mexicanum) Wnt family, Awnt-5A and Awnt-5B. The encoded proteins share 83% amino acid identity. Using a reverse transcription-polymerase chain reaction (RT-PCR) assay, we find that Awnt-5A transcripts are abundant in the blastula until gastrulation, barely detectable during gastrulation, and increase again during neurulation. They are detected throughout the remaining development and in hatched larvae. In contrast, transcripts for Awnt-5B are undetectable in the blastula. They appear with gastrulation, are present throughout neurulation and organogenesis, and decrease to barely detectable levels in hatched larvae. PCR reactions performed using cDNA library-phage DNA templates derived from whole neurulae versus embryos with the neuroectoderm removed suggest that, in the neurula, Awnt-5A transcripts are present in neuroectodermal as well as non-neuroectodermal tissues while Awnt-5B mRNAs are predominantly localized in the neuroectoderm. To localize Awnt-5A expression in embryos before gastrulation, early gastrulae were dissected by cutting along the animal-vegetal and future dorso-ventral axes and analyzed by RT-PCR. At this early stage, Awnt-5A transcripts appear to be predominantly localized in the dorso-vegetal region of the embryo. These results suggest that the two closely related Awnt-5 genes participate in different morphogenetic processes during early axolotl development.

Ambystoma mexicanum↗
PubMed1993

Cloning and nucleotide sequence of a complementary DNA encoding Xenopus laevis metallothionein: mRNA accumulation in response to heavy metals.

A cDNA encoding Xenopus laevis metallothionein (MT) was cloned from a cDNA library constructed using liver poly(A+)RNA of X. laevis adult males treated with CdCl2. The probe used to screen the library was a MT-specific DNA fragment obtained by means of the polymerase chain reaction (PCR) and degenerate oligodeoxynucleotide primers. The cDNA clone encodes a putative protein of 62 amino acids, of which 20 are cysteine residues. The position of all the cysteine residues is conserved with respect to mammalian MT sequences. The amino acid sequence of this X. laevis MT, designated XIMT-A, shares between 60% and 67% identity with various vertebrate MTs. Overall, the structure of XIMT-A is no similar in sequence to MT-1 than it is to MT-2 isoforms of various vertebrates. Ten different X. laevis MT cDNA isolates were partially sequenced and turned out to be identical, suggesting a single species of MT mRNA. Southern blot analysis of X. laevis DNA reveals that the XlMT-A gene is present in at least two copies. This result is consistent with the suggestion that a genome duplication occurred in a X. laevis ancestor. The in vivo response to increasing doses of Cd2+, Zn2+, and Cu2+ metal salts was tested. In the liver, all three metals proved to be potent inducers, raising MT mRNA levels between 50- and 100-fold. The maximum response to Cd2+ was at 12 hr after injection and to Zn2+ at 24 hr after injection. High levels of mRNA were maintained for more than 48 hr. Cd2+ and Zn2+ induced XlMT-A mRNA in all tissues examined (kidney, spleen, heart, intestine, testes, and brain). Dexamethasone did not induce MT mRNA synthesis in the liver.

Amino Acid Sequence↗