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Accueil > Publications > Recherche par années > Années 1990 > 1999

1999

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In vitro and in vivo antitumour activity and cellular pharmacological properties of new platinum-iminoether complexes with different configuration at the iminoether ligands

In order to widen our knowledge on antitumour trans-[PtCl2(iminoether)(2)] complexes, we have synthesised two new derivatives, trans[PtCl2(E-HN=C(OEt)Me)(2)] (1) and trarzs-[PtCl2(Z-HN=C(OEt)Me)(2)] (2), which differ in the configuration of the iminoether ligands. Isomer 1 showed an in vitro cytotoxicity similar to that of cisplatin in a panel of human tumour cell lines (mean IC50 = 8 and 7.7 mu M, respectively), whereas isomer 2 showed a lower activity (IC50 = 14.3 mu M). Both I and 2 isomers overcame cisplatin resistance of ovarian cancer cell line A2780/Cp8.

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In vitro characterization of peptidoglycan-associated lipoprotein (PAL)-peptidoglycan and PAL-TolB interactions

The Tol-peptidoglycan-associated lipoprotein (PAL) system of Escherichia call is a multiprotein complex of the envelope involved in maintaining outer membrane integrity. PAL and the periplasmic protein TolB, two components of this complex, are interacting with each other, and they have also been reported to interact with OmpA and the major lipoprotein, two proteins interacting with the peptidoglycan. All these interactions suggest a role of the Tol-PAL system in anchoring the outer membrane to the peptidoglycan. Therefore, we were interested in better understanding the interaction between PAL and the peptidoglycan, We designed an in vitro interaction assay based on the property of purified peptidoglycan to be pelleted by ultracentrifugation, Using this assay, we showed that a purified PAL protein interacted in vitro with pure peptidoglycan, A peptide competition experiment further demonstrated that the region from residues 89 to 130 of PAL was sufficient to bind the peptidoglycan. Moreover, the fact that this same region of PAL was also binding to TolB suggested that these two interactions were exclusive. Indeed, the TolB-PAL complex appeared not to be associated with the peptidoglycan. This led us to the conclusion that PAL may exist in two forms in the cell envelope, one bound to TolB and the other bound to the peptidoglycan.

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In vitro effect of acetyl-N-Ser-Asp-Lys-Pro (AcSDKP) analogs resistant to angiotensin I-converting enzyme on hematopoietic stem cell and progenitor cell proliferation

The tetrapeptide Acetyl-N-Ser-Asp-Lys-Pro (AcSDKP), an inhibitor of hematopoietic stem cell proliferation, is known to reduce in vivo the damage resulting from treatment with chemotherapeutic agents or ionizing radiation on the stem cell compartment, Recently, AcSDKP has been shown to be a physiological substrate of the N-active site of angiotensin I-converting enzyme (ACE), Four analogs of the tetrapeptide expressing a high stability towards ACE degradation in vitro have been synthesized in order to provide new molecules likely to improve the myeloprotection displayed by AcSDKP, These analogs are three pseudopeptides with a modified peptidic bond, Ac-Ser Psi(CH2-NH)Asp-Lys-Pro, Ac-Ser-Asp-Psi(CH2-NH)Lys-Pro, Ac-Ser-Asp-Lys Psi(CH2-N)Pro, and one C-terminus modified peptide (AcSDKP-NH2), We report here that these analogs reduce in vitro the proportion of murine colony-forming units-granulocyte/macrophage in S-phase and inhibit the entry into cycle of high proliferative potential colony-forming cells, The efficacy of AcSDKP analogs in preventing in vitro primitive hematopoietic stem cells from entering into cycle suggests that these molecules could be new candidates for the powerful inhibition of hematopoietic stem and progenitor cell proliferation in vivo.

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In vivo evidence for back and forth oscillations of the transcription elongation complex

We have used a combination of DNA and RNA footprinting experiments to analyze the structural rearrangements experienced by a transcription elongation complex that was halted in vivo by a protein readblock, We show that the complex readblocked within an (ATC/TAG)(n), sequence is in a dynamic equilibrium between upstream- and downstream-translocated conformers. By increasing the strength of the putative RNA-DNA hybrid, the ternary complex is readily trapped in the downstream-translocated conformation, where the melted DNA region is limited to 8 bp, The shift of the equilibrium towards the downstream location is also achieved by introducing within the 5’ end of the message an RNA sequence that can pair with a segment of the transcript in the vicinity of the halted ternary complex. Our results demonstrate that within certain template DNA sequences, the back and forth oscillations of the ternary complex actually occur in a multipolymerase system and inside the cell. Furthermore, the cis-acting effect of the upstream RNA sequence underscores an important phenomenon in gene regulation where a transcript may regulate its own elongation.

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Inhibition of neutrophil cathepsin G by oxidized mucus proteinase inhibitor. Effect of heparin

Oxidation of mucus proteinase inhibitor (MPI) transforms Met(73), the P-1’ residue of its active center into methionine sulfoxide and lowers its affinity for neutrophil elastase [Boudier, C., and Bieth, J. G. (1994) Biochem. J. 303, 61-68]. Here, we show that the oxidized inhibitor has also a decreased affinity for neutrophil cathepsin G and pancreatic chymotrypsin. The K-i of the oxidized MPI-cathepsin G complex (1.2 mu M) is probably too high to be compatible with significant inhibition of cathepsin G in inflammatory lung secretions. Stopped-flow kinetics shows that, within the inhibitor concentration range used, the mechanism of inhibition of cathepsin G and chymotrypsin by oxidized MPI is consistent with a one-step reaction, E + I (kdiss)reversible arrow(kass) EI, whereas the inhibition of elastase takes place in two steps, E + I reversible arrow(Ki*) EI* (k-2)reversible arrow(k2) EI. Heparin, which accelerates the inhibition of the three proteinases by native MPI, also favors their interaction with oxidized MPI.

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Interaction between lectins and neoglycoproteins containing new sialylated glycosynthons

Neoglycoconjugates are useful tools to study carbohydrate/protein interactions. In order to discover new lectins, to define their fine specificity or to study their intracellular trafficking, there is a need for neoglycoconjugates containing complex oligosaccharides. We recently set up a simple way to transform native oligosaccharides into glycosynthons. The present paper describes i) the synthesis of such glycosynthons starting with sialylated oligosides, ii) the preparation of sialylated neoglycoproteins and iii) their binding to sialic acid-specific lectins assessed by surface plasmon resonance experiments.

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Interstrand cross-links of cisplatin induce striking distortions in DNA

In the reaction between cellular DNA and cisplatin, different bifunctional adducts are formed including intrastrand and interstrand crosslinks. The respective role of these lesions in the cytotoxicity of the drug is not yet elucidated. This paper deals with the current knowledge on cisplatin interstrand cross-links and presents results on the formation, stability and structure of these adducts. A key step in the studies of these lesions is the recent determination of solution and crystallographic structures of double-stranded oligonucleotides containing a unique interstrand cross-link.

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