Valérie Martin

Involvement of DNA methylation in the control of the expression of an estrogen‐induced breast‐cancer‐associated protein (pS2) in human breast cancers

pS2 gene has been used to investigate the relationship between alterations of DNA methylation patterns in human tumors and gene expression. The expression of pS2, which is transcriptionally controlled by estrogens in breast cancer cell lines, is restricted to estrogen‐receptor‐rich human breast tumors. We found that the CCGG site within the promoter/enhancer sequence of pS2 was hypomethylated in estrogen‐receptor‐rich breast tumors expressing this gene. The amount of DNA molecules unmethylated at this site was related to the amount of pS2 mRNA detected in the samples. The demethylation of this region, which contains the estrogen responsive element, was confirmed by genomic sequencing. Transient expression of functional human estrogen receptors stimulated the expression of the endogenous pS2 in HeLa cells, but failed, in BT‐20 cells, to stimulate expression of this gene. Since the promoter/enhancer region of pS2 is unmethylated in HeLa cells and methylated in BT‐20 cells, these data also support the hypothesis that DNA methylation might be involved in the control of pS2 expression. J. Cell. Biochem. 65:95–106.

Ultrastructural features of "solid cell nest" of the human thyroid gland: a study of 8 cases.

The ultrastructural features of solid cell nests (SCN), made of squamous cells, and associated calcitonin cells (C cells), of the thyroid gland were studied in only a few cases in humans. A study was performed on 8 paraffin-embedded SCN, postembedded in Epon, to look for their ultastructural features. Immunohistochemical analysis using calcitonin antibody was performed on semithin sections of SCN to explore the presence of C cells. Three cases (37.5%) of SCN were positive for calcitonin, and electron-dense secretory granules were observed in the cytoplasm. In two of these cases, an increased number of C cells in the adjacent thyroid parenchyma was observed. The presence of ciliated and lymphoid cells, in addition to intracytoplasmic microvacuolar and microfollicular (microglandular) structures, was noticed. Ciliated cells have already been reported in embryonic rests of human and animals, but ultrastructurally for the first time in human SCN. The presence of microfollicular structures, intracytoplasmic microvacuolar, secretory granules features, and ciliated cells, in addition to lymphoid cell, suggests the existence of a common ultimobranchial stem cell for C cells or for one or more cell types of the thyroid gland.

Pulsed remineralisation in the northwestern Mediterranean Sea: a hypothesis

Abstract A general study of biogeochemical processes (DYNAPROC cruise) was conducted in May 1995 at a time-series station in the open northwestern Mediterranean Sea where horizontal advection was weak. Short-term variations of the vertical distributions of pico- and nanophytoplankton were investigated over four 36-h cycles, along with parallel determinations of metabolic CO2 production rates and amino acid-containing colloid (AACC) concentrations at the chlorophyll maximum depth. The vertical (0–1000-m depth) distributions of (i) AACC, (ii) suspended particles and (iii) metabolic CO2 production rate were documented during the initial and final stages of these 36-h cycles. This study was concerned with diel vertical migration (DVM) of zooplankton, which provided periodic perturbations. Accordingly, the time scale of the experimental work varied from a few hours to a few days. Although all distributions exhibited a periodic behaviour, AACC distributions were generally not linked to diel vertical migrations. In the subsurface layer, Synechococcus made the most abundant population and large variations in concentration were observed both at day and at night. The corresponding integrated (over the upper 90 m) losses of Synechococcus during one night pointed to a potential source of exported organic matter amounting to 534 mg C m−2. This study stresses the potential importance of organic matter export from the euphotic zone through the daily grazing activity of vertically migrating organisms, which would not be accounted for by measurements at longer time scales. The metabolic CO2 production exhibited a peak of activity below 500 m that was shifted downward, apparently in a recurrent way and independently of the vertical distributions of AACC or of suspended particulate material. To account for this phenomenon, a «sustained wave train» hypothesis is proposed that combines the effect of the diel superficial faecal pellet production by swarming migrators and the repackaging activity of the nonmigrating midwater populations. Our results confirm the recent finding that the particulate compartment is not the major source of the observed instantaneous remineralisation rate and shed a new light on the fate of organic matter in the aphotic zone.

The estrogen responsive element of the pS2 gene is recognized by a methylation sensitive DNA binding protein.

The human pS2 gene is specifically expressed is a subclass of estrogen receptor containing human breast cancer cells. In the MCF7 cell line, its induction by estradiol is a primary transcriptional event. The exact location of its estrogen responsive element has been determined using a chimeric recombinant transfected into HeLa cells and a transient expression assay. In this study we found, using electrophoretic mobility shift experiments, that in HeLa cells the estrogen responsive element (ERE) of the pS2 gene is recognized by a methylation sensitive DNA binding protein (MSDBP) different from the estrogen receptor. Competition experiments have shown that the binding of this protein requires at least one CpG in the center of the palindromic sequence and that imperfect palindromic sequences are also recognized. Although the presence of CpG is necessary, CpG-rich oligonucleotides, containing consensus sequences for Sp1 or AP2, do not interfere with its binding to the pS2 oligonucleotide, indicating that the ERE sequence itself participates in the specificity of its binding. This protein binds the pS2 sequence with a relatively high affinity (apparent Kd = 10(-10) M) and its binding is strongly reduced by the methylation of the cytosines at CpG sites. UV cross-linking experiments and peptide mapping indicate that this protein has an apparent molecular weight of 46 kDa and is present in several cell lines, including non-human cell lines. Taken together, these data suggest that this protein might have a potential role in regulating gene activity or in chromatin structure of some genes possessing an ERE.

1-Bromo-3-trifluoromethylbut-2-ene: synthesis and electrophilic reactivity

Abstract A three-step synthesis of 1-bromo-3-trifluoromethylbut-2-ene in 54% overall yield isreported starting from 1,1,1-trifluoroacetone. The electrophilic reactivity of this compoundtowards various nucleophiles has been studied. Thus, for example, condensation withthe sodium salt of diethyl malonate gave ethyl 2-carboethoxy-5-trifluoromethylhex-4-enoate in 66% yield.

1-BROMO-4,4,4-TRIFLUORO-3-(TRIFLUOROMETHYL)BUT-2-ENE : SYNTHESIS AND ELECTROPHILIC REACTIVITY

Abstract A two-step synthesis of 1-bromo-4,4,4-trifluoro-3-(trifluoromethyl)but-2-ene in 35% overall yield is reported starting from commercially available hexafluoroacetone. The electrophilic reactivity of this new compound towards various nucleophilic reagents has been studied. Substitution products or ones arising from allylic rearrangement are obtained depending on the nature of the nucleophile.

Preparation of 1-Aryl-4-(trifluoromethyl)penta-1,3-dienes by Wittig-Horner Condensation

Abstract A direct route to 1-aryl-4-(trifluoromethyl)penta-1,3-dienes is described using the Wittig-Horner reaction of diethyl (3-(trifluoromethyl)-but-2-enyl)phosphonate anion with aromatic aldehydes or trifluoroaceto-phenone.

Regioselective nucleophilic additon-elimination to β,β-bis(trifluoromethyl) acrylic esters

Abstract Reaction of β,β-bis(trifluoromethyl)acrylic esters 1 with nucleophilic reagents in aprotic media has been studied. A regioselective addition-elimination is observed leading to compounds 3 (ethyl α substituted 3-trifluoromethyl-4,4-difluorobut-3-enoate). The second CF 3 dramatically changes the reactivity of the acrylic ester as there is no classical Michael addition as for β-trifluoromethylacrylic ester [1]. In the case of amines, a mixture of 3 and saturated products 4 is obtained. Traces of 4 are also formed with anionic reagents. So, regioselective formation of carbanion 2 followed by a fluoride ion elimination is postulated.