Biomedical subjects

J F Riou

Publications and source records attributed to J F Riou.

97 records · Page 6Linked to original sources

PubMed1986

Purification and characterization of Plasmodium berghei DNA topoisomerases I and II: drug action, inhibition of decatenation and relaxation, and stimulation of DNA cleavage.

It has recently been suggested that topoisomerases could be important targets for drugs used in several diseases. This prompted us to purify and characterize the topoisomerases I and II present in the erythrocytes of protozoan parasites of the genus Plasmodium, the causative agent of malaria, in order to later use these enzymatic systems in antimalarial drug assays. The topoisomerases were purified from Plasmodium berghei, a parasite of mouse red cells. The Plasmodium topoisomerase II consists of two subunits with a molecular weight of about 160K. The enzyme is ATP- and Mg2+-dependent. The conditions for the reactions of relaxation, unknotting, decatenation, and catenation were found to be similar to those observed with enzymes from other eukaryotic cells. The Plasmodium topoisomerase I is a monomeric enzyme with a Mr of 70K-100K. It is ATP-independent and K+- or Na-dependent. Mg2+ is not required for relaxation but stimulates the reaction. Topoisomerase II was more sensitive to drug action than topoisomerase I. The most active drugs were the ellipticine derivatives. The antimalarial drugs, currently used in human clinical therapy, were poor inhibitors. Some antitumoral drugs stimulated the double-stranded DNA cleavage activity of Plasmodium topoisomerase II, like that of mammalian topoisomerases II. Antimalarial drugs had no stimulating activity. It is therefore suggested that Plasmodium topoisomerases are not good targets for antimalarial drugs.

Alkaloids↗

PubMed1986

Synthesis and distribution of laminin-related polypeptides in early amphibian embryos.

Western blotting experiments carried out with several heterospecific antibodies against mouse-derived laminin allowed the identification of four laminin-related polypeptides in early Pleurodeles waltlii embryos. Synthesis of all four polypeptides was detected from the early blastula stage to late gastrula stage. Immunofluorescent staining with anti-laminin and anti-fibronectin antibodies provided evidence for a close association of these laminin-related polypeptides with the fibronectin fibrillar network.

Animals↗

PubMed1986

ATP-independent type II topoisomerase from trypanosomes.

We have characterized in Trypanosoma cruzi a DNA topoisomerase capable of decatenating complex trypanosomal kinetoplast DNA networks in the absence of ATP. The enzymatic activity requires Mg2+ and K+. Using a defined DNA topoisomer we showed that the linking number changes by steps of 2, which characterizes the enzyme as a type II topoisomerase. The enzyme can catenate supercoiled DNA molecules, unknot DNA, and cleave double-stranded DNA. The enzyme has no ATPase activity. The native enzyme has an Mr of about 200,000. Crude extracts and partially purified fractions contain an aggregating factor that can substitute spermidine in catenating reactions. Because of the presence of this factor, the kinetoplast DNA can only be decatenated by purified fractions. The enzyme is inhibited by certain drugs and provides a potential target for chemotherapy. Such an enzyme was also characterized in Trypanosoma equiperdum.

Adenosine Triphosphate↗

PubMed1986

Cell surface glycoproteins change during gastrulation in Pleurodeles waltlii.

Identification of the cell surface glycoproteins is an essential requirement for elucidating the mechanisms that mediate intercellular adhesion and cell migration in gastrulating amphibian embryos. In our experiments the glycoproteins present at the surface of isolated cells at blastula and gastrula stages were labelled with 3H-labelled sodium borohydride. The procedure included the oxidation of either galactosyl and, or, N-acetylgalactosaminyl residues with galactose oxidase or sialic acid with sodium metaperiodate. The tritiated components were analysed by two-dimensional gel electrophoresis. On the surface of isolated embryonic cells, 23 glycoproteins have been identified. The most important observation was the labelling of 15 new glycoproteins during gastrulation. At the late blastula stage, eight glycoproteins containing galactosyl or N-acetyl-galactosaminyl residues are labelled, while 23 are labelled at the late gastrula stage. In other experiments, glycoproteins labelled by [3H]fucose or [3H]mannose or precipitated by concanavalin A(ConA)-, or wheat-germ agglutinin (WGA)-Sepharose were studied by two-dimensional gel electrophoresis in order to provide supplementary data on the synthesis and lectin-binding properties of major cell surface glycoproteins. It appears that approximately 100 different glycoproteins are revealed by these methods. Among them, 13 have been identified as major cell surface glycoproteins, 12 being labelled by [3H]mannose, four by [3H]fucose, 10 bearing an affinity for ConA and five for WGA. These 13 glycoproteins are synthesized throughout gastrulation without qualitative variation.

Animals↗

PubMed1986

[A DNA topoisomerase from trypanosomes able to catenate, decatenate and unknot DNA without ATP].

A novel DNA-topoisomerase from Trypanosoma cruzi was partially purified. The enzyme, without ATP addition, catalyzes decatenation of kinetoplast DNA, catenation of circular supercoiled DNAs and unknotting of P4 phage DNA. The presence of Mg++ is required as well as a suitable concentration of KCl. In stoichiometric conditions the trypanosome enzyme induces double-strand DNA cleavage. The reaction is highly stimulated by some chemicals. Such characteristics allow to include this enzyme into the type II class of DNA-topoisomerases.

Adenosine Triphosphate↗

PubMedDate not supplied

Alternative splicing directs the expression of two D2 dopamine receptor isoforms.

Dopamine receptors are classified into D1 and D2 subtypes on the basis of their pharmacological properties and the intracellular responses they mediate. The cerebral D2 dopamine receptor is the target of drugs used to alleviate the main symptoms of schizophrenia. Although it is considered to be a single molecular entity, there is evidence that multiple D2-receptor subtypes exist. A complementary DNA encoding a D2 receptor has recently been cloned and the deduced 415-amino-acid sequence indicates that it belongs to the large superfamily of receptors coupled to G proteins, and that its topology consists of seven transmembrane domains. In this family, the genes are frequently without introns and each is believed to encode a unique polypeptide product. Here we show that the gene for the D2 receptor produces two receptor isoforms by alternative messenger RNA splicing, providing a route to receptor diversity in this family. One isoform corresponds to the D2(415) receptor, but the second contains an additional sequence encoding a 29-amino-acid fragment, defining a novel D2(444) receptor isoform. Expression of the two isoforms is tissue-specific, and both are regulated by guanyl nucleotides. As the extra sequence is located within a putative cytoplasmic loop that binds to G proteins, the two isoforms might interact with different G proteins and thereby initiate distinct intracellular signals.

Amino Acid Sequence↗

PubMedDate not supplied

The amphibian embryo: an experimental model for the in vivo analysis of interactions between embryonic cells and extracellular matrix molecules.

The early amphibian embryo provides an attractive model for the in vivo analysis of cell interactions with extracellular matrix components. During gastrulation, mesodermal cells use an anastomosing network of extracellular fibrils as substratum for their migration. These fibrils contain glycosaminoglycans and non collagenous proteins including laminin and fibronectin. The function of these extracellular components in the mesodermal cell migration process has been inferred from grafting experiments and microinjection of probes such as specific antibodies or GRGDS-containing peptides. Using the amphibian embryo as an experimental system, combination of microsurgical, cell behavioral and molecular approaches will provide new insights into cell-extracellular matrix interactions directing morphogenetic cell movements.

Amino Acid Sequence↗