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Etude des histones déacétylases (HDACs) de classes I et III du parasite plathelminthe Schistosoma mansoni

Abstract : Schistosomes are platyhelminth parasites that infect 200 million people and cause the death of 200,000 people each year throughout the world. Currently one drug, praziquantel, is used against all species of schistosome, but resistant strains have been isolated in endemic areas as well as in laboratory studies. The need to find new drugs and new therapies is therefore urgent. Enzymes involved in gene regulation are promising targets for new drugs because of their essential role in the cell. We have targetted the enzymes responsible for histone deacetylation, the histone deacetylases (HDACs) that are generally involved in repressing transcription. These enzymes are already studied as potential therapeutic targets in cancer and parasitic diseases such as paludism. They form a family highly conserved throughout evolution that is composed of four classes. Classes I, II and IV are HDACs that require an active site zinc ion, whereas the third class is made up of the sirtuins that are NAD+-dependent. The first part of the work was focused on class I HDACs. To investigate the conservation of these enzymes in Schistosoma mansoni, we cloned and characterized three class I HDACs, orthologues of mammalian HDAC1, 3 and 8, and confirmed their identities by phylogenetic analysis. The identification of an HDAC8 orthologue shows that it is not vertebrate-specific as previously thought and insertions in its catalytic domain suggest specific enzymatic properties. SmHDAC1, 3, and 8 mRNAs are expressed at all schistosome life-cycle stages. SmHDAC1 represses transcriptional activity in a mammalian cell line and this activity is dependent on its catalytic activity since transcription is partially restored by treatment with an HDAC inhibitor (HDACi) trichostatin A (TSA) and a catalytic site mutant fails to repress transcription. In order to determine the extent and importance of histone acetylation in S. mansoni, we tested the effects of three HDACi on both larval and adult worms in culture. TSA, valproic acid (VPA) and suberoylanilide hydroxamic acid (SAHA) inhibited global HDAC activity at all life-cycle stages. TSA and VPA, but not SAHA, cause mortality of schistosomula and adults, with TSA showing the most rapid effect. Moreover, TSA causes an increase in apoptosis in schistosomula shown by the TUNEL assay and an increase in caspase 3/7 activity. Both TSA and VPA are shown to cause an increase in general levels of protein acetylation in schistosomes ; more particularly of histone 4 whereas histone 3 acetylation is less affected. In the case of TSA treatment this histone hyperacetylation is correlated with the increased expression of caspases 3 and 7 transcripts. Finally, quantitative chromatin immunoprecipitation shows that the proximal promoter region of the S. mansoni caspase 7 gene is hyperacetylated on histone H4 after TSA treatment The second part of the work targetted class III HDACs, sirtuins. The first of these enzymes, Sir2, was discovered in yeast and 7 orthologs, SIRT1 to 7, have been described in humans. We cloned and characterized a SIRT1 ortholog from S. mansoni that contains an insertion in its catalytic domain that may modify its activity and exhibits a potential phosphorylation site for PKB/Akt kinases. Sir2 and its orthologs have a very important role in lifespan regulation. Indeed, in the yeast as well as in other organisms such as C. elegans or the mouse, they interact with the transcription factor "Forkhead-Box Others" (FOXO) to extend lifespan in response to calorie restriction and are implicated in the regulation of the insulin receptor-dependent pathway, which involves PKB/Akt, FOXO and SIRT1 and controls cell metabolism, survival mechanisms and lifespan. Some of S. mansoni particularities are a long lifespan (more than 30 years in human), high calorie consumption and extreme fertility (more than 300 eggs laid each day by S. mansoni female worms). Taken together these characteristics are paradoxiacal since, in other organisms, calorie restriction increases lifespan and reduces reproduction. In order to dissect the mechanisms involved in this disregulation, we have also characterized SmFOXO. Transcripts of SmSIRT1 and SmFOXO are differentially expressed in the various S. mansoni life-cycle stages, but the expressed proteins interact positively to drive transcription in transfected mammalian cell lines. Future work will focus on the role of the insulin pathway on SmSIRT1/SmFOXO dependent gene transcription in vivo
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https://tel.archives-ouvertes.fr/tel-00451179
Contributor : Florence Dubois <>
Submitted on : Friday, January 29, 2010 - 10:18:01 AM
Last modification on : Thursday, February 21, 2019 - 9:56:02 AM
Long-term archiving on: : Wednesday, November 30, 2016 - 11:38:35 AM

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  • HAL Id : tel-00451179, version 1

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Florence Dubois. Etude des histones déacétylases (HDACs) de classes I et III du parasite plathelminthe Schistosoma mansoni. Biochimie [q-bio.BM]. Université du Droit et de la Santé - Lille II, 2009. Français. ⟨tel-00451179⟩

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