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E Taillandier

Publications and source records attributed to E Taillandier.

At least 19 recordsLinked to original sources
PubMed2000

Parallel self-associated structures formed by T,C-rich sequences at acidic pH.

Oligonucleotides of nonregular heteropyrimidine sequences incorporating or not incorporating purine residues 5'-d(ACTCCCTTCTCCTCTCTA), 5'-d(ACTCCCTGGTCCTCTCTA), 5'-d(TCTCTCCTGGTCCCTCC), and 5'-d(TCTCTCCTCTTCCCTCC) can form self-associated parallel-stranded (ps) structures at pH 4-5.5. The ps structures were identified by studying at neutral and acidic pH UV melting transitions, FTIR spectra, and fluorescence of pyrene-labeled oligonucleotides as well as by chemical joining of 5'-phosphorylated oligonucleotides. A gel electrophoresis run for oligonucleotides 5'-d(TCTCTCCTCTTCCCTCC) and 5'-d(ACTCCCTTCTCCTCTCTA) has shown the formation of homoduplexes at low DNA strand concentrations. Ps structures are held by C-C(+) base pairs and have N- and S-types of sugar puckering as detected by FTIR spectroscopy in the millimolar concentration range. Guanine inserts as well as thymine and purine inserts into an oligomeric cytosine sequence make the formation of the tetraplex i-motif unfavorable. MvaI restriction endonuclease, which recognizes the CCT/AGG sequence in DNA, does not cleave parallel pseudosubstrates.

Acids↗
PubMed2000

Parallel intramolecular DNA triple helix with G and T bases in the third strand stabilized by Zn(2+) ions.

We present evidence of formation of an intramolecular parallel triple helix with T*A.T and G*G.C base triplets (where * represents the hydrogen bonding interaction between the third strand and the duplex while. represents the Watson-Crick interactions which stabilize the duplex). The third GT strand, containing seven GpT/TpG steps, targets the polypurine sequence 5'-AGG-AGG-GAG-GAG-3'. The triple helix is obtained by the folding back twice of a 36mer, formed by three dodecamers tethered by hydroxyalkyl linkers (-L-). Due to the design of the oligonucleotide, the third strand orientation is parallel with respect to the polypurine strand. Triple helical formation has been studied in concentration conditions in which native gel electrophoresis experiments showed the absence of intermolecular structures. Circular dichroism (CD) and UV spectroscopy have been used to evidence the triplex structure. A CD spectrum characteristic of triple helical formation as well as biphasic UV and CD melting curves have been obtained in high ionic strength NaCl solutions in the presence of Zn(2+) ions. Specific interactions with Zn(2+) ions in low water activity conditions are necessary to stabilize the parallel triplex.

Base Pairing↗
PubMed2000

Current Awareness.

In order to keep subscribers up-to-date with the latest developments in their field, John Wiley & Sons are providing a current awareness service in each issue of the journal. The bibliography contains newly published material in the field of NMR in biomedicine. Each bibliography is divided into 9 sections: 1 Books, Reviews ' Symposia; 2 General; 3 Technology; 4 Brain and Nerves; 5 Neuropathology; 6 Cancer; 7 Cardiac, Vascular and Respiratory Systems; 8 Liver, Kidney and Other Organs; 9 Muscle and Orthopaedic. Within each section, articles are listed in alphabetical order with respect to author. If, in the preceding period, no publications are located relevant to any one of these headings, that section will be omitted.

Journal Article↗
PubMed2000

Magnetic resonance spectroscopy of cellular lipid extracts from sensitive, resistant and reverting K562 cells and flow cytometry for investigating the P-glycoprotein function in resistance reversion.

The proton NMR spectra of K562 cells contain resonances of lipids. When these cells acquire multidrug resistance phenotype, the NMR lipid signals are modified and partially recovered when the resistance is reversed. The goals of the present study are to elucidate the mechanism of the resistance phenotype reversion and to investigate the possible origin of lipid signals detected in whole cells with proton NMR spectroscopy. Therefore, the K562 drug-sensitive cell line, its adriamycin resistant counterpart and two reverting derivates, obtained by verapamil treatment and long term culture in drug-free medium, were used in this study. The P-glycoprotein (P-gp) pump function was measured by flow cytometry and lipids were extracted to be analysed by proton and phosphorus spectroscopy. The phenotype reversion is due to the decrease of the P-gp function and an increased entrance of anthracycline drug when compared with the resistant cells. The spectra obtained on extracts showed no modification of the fatty acid composition and of the ratio of total cholesterol to fatty acid content. A different phospholipid composition in sensitive and resistant cells was found, but the reversion of resistance did not produce a recovery of these lipids. Thus, the lipid NMR spectra of extracts could not explain the spectral modifications observed on whole cells, in relation to acquiring and reverting drug resistance. These results are in favour of a different lipid organization or of localization within the cell.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2000

Delivery and pathway in MCF7 cells of DNA vectorized by cationic liposomes derived from cholesterol.

We have investigated the delivery and the pathway in tumoral MCF7 cells of DNA carried by liposomes prepared from (trimethyl aminoethane carbamoyl cholesterol iodide (TMAE-Chol), a cholesterol-based cationic lipid with a quaternary ammonium on the polar head. The structure of DNA-liposome complexes depends on the length of DNA and on the lipid-DNA charge ratio X. Spherical beads constitute fine structures of the observed complexes even when they appear as aggregates. For oligonucleotide transfer, dissociation from liposomes after transfection, penetration of the oligonucleotides into nuclei, and a long resident time were observed. For plasmid transfer, a correlation between the variation in the transfection level and the ultrastructure of complexes was demonstrated. The results showed a cellular route of lipid/plasmid complexes from the beginning by endocytosis, entrapped into endosomes, released by the latter until entry in the perinuclear area, and then penetration of plasmids inside the nuclei resulting in the observed expression of the beta-galactosidase gene.

Biological Transport↗
PubMed1999

Parallel and antiparallel triple helices with G, A-containing third strands.

A triple helix, formed by a 13 nucleotide (nt) all-purine oligonucleotide, containing six contiguous guanines, oriented parallel to a homopurine strand present in the polypurine tract of Friend leukemia virus, was obtained in 0.1 M LiCl. Its dissociation constant at 25 degrees C, given by electrophoretic titration, of the order of 50 nM, is at least ten times lower than that of the corresponding antiparallel triplex formed on the same target. At 4 degrees C, the parallel orientation of the homopurine strands is favored to the point that the guanine block of 6 nt, present in the 'antiparallel' oligonucleotide, attaches in a parallel fashion to the corresponding block in the target strand, to generate a partial, parallel triplex, that coexists with the antiparallel one.

Adenine↗
PubMed1998

FTIR and UV spectroscopy of parallel-stranded DNAs with mixed A*T/G*C sequences and their A*T/I*C analogues.

The infrared spectra of parallel-stranded (ps) hairpin duplexes with mixed A*T/G*C composition and either isolated or sequential G*C pairs were studied in comparison with antiparallel-stranded (aps) duplexes and a corresponding set of molecules with hypoxanthine as a G base analogue lacking the exocyclic amino group. The ps duplexes showed the characteristic bands for the C2=O2 and C4=O4 stretching vibrations of thymine residues in trans-Watson-Crick A*T pairing at 1683 and 1668 cm-1. The latter band was superimposed on the stretching vibration of the free C6=O6 group of guanine. Substitution of guanine by hypoxanthine inhibited the formation of ps hairpin duplexes whatever the sequence, demonstrating that in the H-bonding between G and C the 2-NH2 group is necessary for stabilizing all of the investigated ps duplexes. This result is in agreement with a model of trans-Watson-Crick G*C base pairs with two H-bonds [N2H2(G)-N3(C) and N1H(G)-O2(C)]. However, trans-Watson-Crick A*T and G*C base pairs with two H-bonds are not isomorphous, which may explain the decreased stability of the ps, but not the aps, duplexes upon increasing the number of A*T/G*C steps. Molecular modeling studies performed on two of the ps duplexes reveal the existence of propeller twist for avoiding a clash between the N2(G) and N4(C) amino groups, and favorable stacking of sequential G*C base pairs. The optimized hairpin ps duplexes invariably incorporated G*C base pairs with two H-bonds, regardless of the initial structures adopted for the force field calculations.

Adenine↗
PubMed1998

Joint molecular modeling and spectroscopic studies of DNA complexes of a bis(arginyl) conjugate of a tricationic porphyrin designed to target the major groove.

To target selectively the major groove of double-stranded B DNA, we have designed and synthesized a bis(arginyl) conjugate of a tricationic porphyrin (BAP). Its binding energies with a series of double-stranded dodecanucleotides, having in common a central d(CpG)2 intercalation site were compared. The theoretical results indicated a significant energy preference favoring major groove over minor groove binding and a preferential binding to a sequence encompassing the palindrome GGCGCC encountered in the Primary Binding Site of the HIV-1 retrovirus. Spectroscopic studies were carried out on the complexes of BAP with poly(dG-dC) and poly(dA-dT) and a series of oligonucleotide duplexes having either a GGCGCC, CCCGGG, or TACGTA sequence. The results of UV-visible and circular dichroism spectroscopies indicated that intercalation of the porphyrin takes place in poly(dG-dC) and all the oligonucleotides. Thermal denaturation studies showed that BAP increased significantly the melting temperature of the oligonucleotides having the GGCGCC sequence, whereas it produced only a negligible stabilization of sequences having CCCGGG or TACGTA in place of GGCGCC. This indicates a preferential binding of BAP to GGCGCC, fully consistent with the theoretical predictions. IR spectroscopy on d(GGCGCC)2 indicated that the guanine absorption bands, C6=O6 and N7-C8-H, were shifted by the binding of BAP, indicative of the interactions of the arginine arms in the major groove. Thus, the de novo designed compound BAP constitutes one of the very rare intercalators which, similar to the antitumor drugs mitoxantrone and ditercalinium, binds DNA in the major groove rather than in the minor groove.

Arginine↗
PubMed1998

Triple helix-forming oligonucleotides which make imperfect Watson-Crick duplexes that compete with the creation of the triplex.

Because of the repetitive nature of the sequence, when titrating a G,A-rich, triple helix-forming oligonucleotide (TFO) with increasing concentrations of target duplex in order to obtain the dissociation constant of the complex, a duplex is sometimes first generated at intermediate concentrations of the target. This duplex is based on an imperfect Watson-Crick pairing of the TFO to the pyrimidine-rich strand of the target. An explanation is proposed for this duplex being obtained only in a certain domain of the titration range, before the triple helix becomes predominant.

Base Pairing↗
PubMed1998

Conformational study of DNA-RNA duplexes containing MMI substituted phosphodiester linkages by FTIR spectroscopy.

Six methylene(methylimino) (MMI, Bhat et al. J. Org. Chem., 61, 8186, 1996) linked oligonucleotides a-f (* = MMI linkage; 5'-GCGT*TT*TT*TT*TT*TGCG-3') containing various combinations of 2'-O-methyl and 2'-fluoro substituent were synthesized as a model to study the global conformational change upon hybridization to the complement RNA. Fourier transform infrared (FTIR) spectroscopic technique has been used to study and compare the influence of these modifications on the solution conformation of 2'-modified MMI DNA-RNA duplexes. FTIR analysis of the single-stranded RNA (5'-CGCAAAAAAAAAACGC-3') and the modified oligonucleotides a-f showed that all sugar residues adopted a C3'-endo conformation (North-type). Stable duplexes were formed when oligonucleotides a-f were hybridized to the complement RNA. These duplexes retained the original C3'-endo conformation for all sugar residues, hallmark of an A-form of duplex. We postulate that the observed preorganization of the sugar residues and oligonucleotides containing 2'-modified MMI modifications may play an important role in both improving the recognition of RNA target and enhancing the stability of duplex formation with RNA.

Carbohydrates↗
PubMed1997

Triple helix formation and homologous strand exchange in pyrene-labeled oligonucleotides.

The orientations of the symmetrical third strands (G3A4G3) and (G3T4G3) within the triplexes (C3T4C3) - (G3A4G3) x (G3A4G3) and (C3T4C3) - (G3A4G3) x (G3T4G3) were investigated by fluorescence spectroscopy and thermal denaturation using pyrene-labeled oligodeoxynucleotides. In the two triplex structures, both parallel and antiparallel orientations of the third strand with respects to the purine Watson-Crick one were identified by means of pyrene excimer formation. The pyrene labels do not modify the melting temperature of the (C3T4C3) - (G3A4G3) x (G3T4G3) triplex but somewhat stabilize the corresponding duplex against thermal denaturation. The absorption melting profiles of the (C3T4C3) - (G3A4G3) x (G3A4G3) triplex are monophasic in agreement with previous reports. In contrast, the melting of this structure, when monitored by the pyrene excimer band, reveals a biphasic behavior. These data, together with kinetics measurements, strongly suggest exchange mechanisms between the homologous oligomers (G3A4G3), Hoogsteen, and Watson-Crick strands.

DNA↗
PubMed1997

Hydration of the dTn.dAn x dTn parallel triple helix: a Fourier transform infrared and gravimetric study correlated with molecular dynamics simulations.

We present a comparative analysis of the water organization around the dTn.dAn x dTn triple helix and the Watson-Crick double helix dTn.dAn respectively by means of gravimetric measurements, infrared spectroscopy and molecular dynamics simulations. The hydration per nucleotide determined by gravimetric and spectroscopic methods correlated with the molecular dynamics simulations shows that at high relative humidity (98% RH) the triple helix is less solvated than the duplex (17 +/- 2 water molecules per nucleotide instead of 21 +/-1). The experimental desorption curves are different for both structures and indicate that below 81% RH the triplex becomes more hydrated than the duplex. At this RH the FTIR spectra show the emergence of N-type sugars in the adenosine strand of the triplex. When the third strand is bound in the major groove of the Watson-Crick duplex molecular dynamics simulations show the formation of a spine of water molecules between the two thymidine strands.

DNA↗
PubMed1997

A macrocyclic bis-acridine shifts the equilibrium from duplexes towards DNA hairpins.

Nucleic acids can undergo dynamic conformational changes associated with the regulation of biological processes. A molecule presenting larger affinities for alternative structures relative to a duplex is expected to modify such conformational equilibria. We have previously reported that macrocyclic bis-acridine binds preferentially to single-stranded regions, especially DNA hairpins, due to steric effects. Here, we show, using gel electrophoresis, fluorescence and melting temperature experiments, that the macrocycle bis-acridine shifts an equilibrium from a duplex towards the corresponding hairpins. Competition experiments enlighten the higher affinity of the macrocycle for hairpins compared with double-stranded DNA. The macrocycle bis-acridine destabilizes a synthetic polynucleotide, by the formation of premelted areas. By extrapolation, the macrocycle bis-acridine should be able to disrupt, at least locally, genomic DNA duplexes and to stabilize unpaired areas, especially palindromic ones forming hairpins. Such macrocyclic compounds may have potential applications in the therapy of diseases involving hairpins.

Acridines↗
PubMed1997

A physico-chemical study of triple helix formation by an oligodeoxythymidylate with N3'--> P5' phosphoramidate linkages.

Non-denaturing gel retardation assay, DNA melting experiments and FTIR spectroscopy were used to characterize the triple helix formed by a 15mer 2'-deoxythymidylate with N3'-->P5'phosphoramidate linkages with its target sequence. The results indicate that: (i) the pentadecadeoxythymidylate with phosphoramidate linkages [dT15(np)] is highly potent to form a triple helix with a dT15*dA15target duplex through Hoogsteenbase-pairing; (ii) it forms a dT15(np)*dA15xdT15(np) triplex with the single-stranded oligo-2'-deoxyadenylate (dA15) without detectable double-helical intermediate; (iii) it does not only form a triple helix on the dT15*dA15target duplex, but also partially displaces the dT15 strand from the dT15*dA15duplex to form a dT15(np)*dA15xdT15(np) complex.

DNA↗
PubMed1996

Parallel and antiparallel A*A-T intramolecular triple helices.

Intramolecular triple helices have been obtained by folding back twice oligonucleotides formed by decamers bound by non-nucleotide linkers: dA10-linker-dA10-linker-dT10 and dA10-linker-dT10-linker-dA10. We have thus prepared two triple helices with forced third strand orientation, respectively antiparallel (apA*A-T) and parallel (pA*A-T) with respect to the adenosine strand of the Watson-Crick duplex. The existence of the triple helices has been shown by FTIR, UV and fluorescence spectroscopies. Similar melting temperatures have been obtained in very different oligomer concentration conditions (micromolar solutions for thermal denaturation classically followed by UV spectroscopy, milimolar solutions in the case of melting monitored by FTIR spectroscopy) showing that the triple helices are intramolecular. The stability of the parallel triplex is found to be slightly lower than that of the antiparallel (deltaT(m) = 6 degrees C). The sugar conformations determined by FTIR are different for both triplexes. Only South-type sugars are found in the antiparallel triplex whereas both South- and North-type sugars are detected in the parallel triplex. In this case, thymidine sugars have a South-type geometry, and the adenosine strand of the Watson-Crick duplex has North-type sugars. For the antiparallel triplex the experimental results and molecular modeling data are consistent with a reverse-Hoogsteen like third-strand base pairing and South-type sugar conformation. An energetically optimized model of the parallel A*A-T triple helix with a non-uniform distribution of sugar conformations is discussed.

Carbohydrate Conformation↗
PubMed1996

Temporary ex vivo inhibition of the expression of the human oncogene HER2 (NEU) by a triple helix-forming oligonucleotide.

A 28-base phosphodiester triple helix-forming oligonucleotide, mostly G and A containing, targeted to a polypurine tract interrupted by a purine-pyrimidine inversion, situated upstream from the TATA box of the promoter of the human HER2 gene, was conceived by computer modeling. The "energetically best choice" was oligo 28(C), which formed the triple helix in vitro, as proved by gel retardation and Fourier transform infrared spectroscopy. When administered as a complex with lipofectin, fluorescence confocal microscopy and electrophoresis confirmed the delivery and persistence of this unprotected oligonucleotide inside MCF7 (breast cancer) cells. At a concentration of 2 microM, the oligonucleotide reduced within 6 h the HER2 mRNA level to 42% (Northern blot) but did not interfere with the transcription of a housekeeping gene, glyceraldehyde-3-phosphate dehydrogenase. During the first day of administration at 0.22 microM, it lowered to 59% the HER2 protein in treated, as compared to nontreated, cells (ELISA). The effect was sequence specific when compared to that of five different negative controls, and it was target selective when compared to the expression of a related, nontargeted protein, the epidermal growth factor receptor. By day 2, the inhibitory effect was overcome by replenishment reactions.

Base Sequence↗
PubMed1996

Ligand-induced formation of hoogsteen-paired parallel DNA.

INTRODUCTION: Based on molecular modeling studies, a model has been proposed for intercalation of triple-helix-specific ligands (benzopyridoindole (BPI) derivatives) into triple helices, in which the intercalating compounds interact mainly with the Hoogsteen-paired strands of the triple helix. We set out to test this model experimentally using DNA duplexes capable of forming parallel Hoogsteen base-paired structures. RESULTS: We have investigated the possible formation of a parallel DNA structure involving Hoogsteen hydrogen bonds by thermal denaturation, FTIR spectroscopy and gel-shift experiments. We show that BPI derivatives bind to Hoogsteen base-paired duplexes and stabilize them. The compounds induce a reorganization from a non-perfectly matched antiparallel Watson- Crick duplex into a perfectly matched parallel Hoogsteen-paired duplex. CONCLUSIONS: These results suggest that preferential intercalation of BPI derivatives in triple helices is due to their ability to interact specifically with the Hoogsteen-paired bases. The results are consistent with a model proposed on the basis of molecular modeling studies using energy minimization, and they open a new field of investigations regarding the biological relevance of Hoogsteen base-pairing.

DNA↗