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Les protéines à « Methyl-CpG-binding domain » (MBD) jouent un rôle important dans l’interprétationde la méthylation de l’ADN conduisant à la répression transcriptionnelle via le recrutement decomplexes remodelant la chromatine. Dans les cancers, MBD2 jouerait un rôle essentiel dans la perted’expression des gènes hyperméthylés. Ainsi, MBD2 serait une cible potentielle pour rétablir, enpartie au moins, leur expression. Caractériser, à l’échelle du génome, la distribution de MBD2 et sesconséquences sur la répression transcriptionnelle au cours de la cancérogenèse est donc une étapeincontournable. (1) L’impact sur l’expression génique de l’inhibition de MBD2 par interférence àl’ARN, a été étudié en utilisant des puces, dans des cellules normales MRC5. La perte de MBD2n’induit pas de surexpression génique globale et la densité en CpG des promoteurs méthylés sembleêtre une composante importante dans la force de répression par MBD2. (2) Les profils de méthylationde l’ADN, de liaisons de MBD2 et de l’ARN polymérase II dans les cellules HeLa ont été analysés parChIP-on-chip avec des puces promoteurs. Ces mêmes approches couplées à l’analyse de l’acétylationdes histones H3 ont été réalisées dans un modèle cellulaire syngénique de progression tumoralemammaire humain. Dans les modèles étudiés, une forte proportion de gènes silencieux et méthylés estliée par MBD2. Les comparaisons entre cellules immortalisées et transformées ne montrent pas dechangements majeurs de la méthylation de l’ADN ou de la répression transcriptionnelle, par contreune redistribution de MBD2 parmi ces sites est observée, suggérant une redondance entre les protéinesliant l’ADN méthylé. / The Methyl-CpG-Binding Domain (MBD) proteins represent key molecules in the interpretation ofDNA methylation signals leading to gene silencing through recruitment of chromatin remodelingcomplexes. In cancer, a member of this protein family, MBD2, seems to play an important role in theloss of expression of aberrantly methylated genes. Thus, MBD2 may be a potential target toreestablish their expression. Mapping of MBD2 binding sites and the relationship between MBD2binding and transcriptional activity was, therefore, a crucial step. (1) We investigated the impact ofMBD2 inhibition by RNA interference on gene expression, using microarray analysis, in a normalhuman fibroblastic cell line, MRC-5. MBD2 depletion did not induce global gene overexpression andCpG density of the methylated promoters seems to be an important parameter in the strength of thetranscriptional repression mediated by MBD2. (2) Global profiling for different layers of epigeneticmodifications (DNA methylation, MBD2 association) and RNA polymerase II binding sites in HeLacells was analyzed by a ChIP-chip method using human promoter arrays. This approach, combinedwith an analysis of H3 histone acetylation patterns, was performed in a syngenic model of breastcancer progression. In the models analyzed MBD2 appeared to be a true methylation-dependenttranscriptional repressor. Furthermore, MBD2 binds to a high proportion of methylated silent genes.Comparisons between immortalized and transformed cells did not indicate major changes of DNAmethylation or gene silencing, while a redistribution of MBD2 among these sites was observed,suggesting a redundancy between methylated binding proteins.

(EN) Chronic lymphocytic leukemia (B-CLL) represents a disease of mature-like B-cells. Due to failed apoptosis but also due to enhanced proliferative signals, the leukemic B-cells accumulate in the peripheral blood, bone marrow, lymph nodes and spleen. The clinical course of B-CLL is very heterogeneous; in some patients B-CLL progresses very rapidly into an aggressive form. Such patients need therapy sooner while in other patients with indolent B-CLL the onset of therapy takes years. Several standard prognostic and disease progression markers are used for disease staging and monitoring, however a reliable marker that will suggest when to start therapy is unknown. Expression of small, non-coding microRNAs is often deregulated and represent important prognostic markers in variety of cancers including leukemia. Hence in our study we concentrated to miR-155, an important molecule regulating differentiation of hematopoietic cells, inflammation process and antibody production. Its aberrant expression was described in Hodgkin`s as well as in non-Hodgkin`s lymphoma, including indolent lymphoproliferations like B- CLL. Our results confirmed elevated levels of both, primary miR-155 transcript and mature form of miR-155 in our B-CLL patient samples (N=239). The aberrant expression of miR-155 in B-CLL samples...

It is well known that chromatin posttranslational state, transcription and splicing influence each other. Nevertheless, the details of this coupling are not fully understood. In S. cerevisiae, it is possible to induce conditions, in which splicing is uncoupled from transcription. Such situation occurred in cells expressing a mutated splicing factor Prp45, whose human homolog has been proved to participate in transcription regulation and also in splicing reactions. Based on previously indicated interactions in high throughput two-hybrid screens, we have been looking for physical links between Prp45 and proteins involved in chromatin posttranslational modifications. Finding of such a link would provide insight into the relationships of gene expression processes. Using coimmunoprecipitation and affinity purification, we were unable to detect physical interactions between Prp45 and our candidate chromatin regulators. Alternative approaches are discussed. Using the precipitation techniques, we mapped the interaction of Prp46 with truncated variants of Prp45. This observation contributes to our knowledge of protein-protein interactions within the spliceosome.

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