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Open Access Research article

Concomitant heterochromatinisation and down-regulation of gene expression unveils epigenetic silencing of RELB in an aggressive subset of chronic lymphocytic leukemia in males

Jean-Brice Marteau1, Odile Rigaud1, Thibaut Brugat156, Nathalie Gault1, Laurent Vallat2, Mogens Kruhoffer3, Torben F Orntoft3, Florence Nguyen-Khac2, Sylvie Chevillard4, Hélène Merle-Beral2 and Jozo Delic14*

Author affiliations

1 Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA) Direction des Sciences du Vivant (DSV) Institut de Radiobiologie Cellulaire et Moléculaire (IRCM), Laboratoire d’Onco-Hématologie (LOH), France

2 GH Pitié Salpêtrière, Service d’Hématologie Biologique, AP-HP, Université Paris 6, Inserm U543, 47, Bd de l’Hôpital, Paris (75013), France

3 University of Aarhus, Department of Clinical Biochemistry, Brendstrupgaardsvej 100, Aarhus DK-8200, Denmark

4 Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA) Direction des Sciences du Vivant (DSV) Institut de Radiobiologie Cellulaire et Moléculaire (IRCM), Laboratoire de Cancérologie Expérimentale (LCE), 18, Av du Panorama, Fontenay-aux-Roses (92265), France

5 Université René Descartes-Paris V, 4, Av de l'Observatoire, Paris (75006), France

6 Current Address: Jean Langhorne's Lab, Division of Parasitology, National Institute for Medical Research, The Ridgeway London, NW71AA, UK

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Citation and License

BMC Medical Genomics 2010, 3:53  doi:10.1186/1755-8794-3-53

Published: 10 November 2010

Abstract

Background

The sensitivity of chronic lymphocytic leukemia (CLL) cells to current treatments, both in vitro and in vivo, relies on their ability to activate apoptotic death. CLL cells resistant to DNA damage-induced apoptosis display deregulation of a specific set of genes.

Methods

Microarray hybridization (Human GeneChip, Affymetrix), immunofluorescent in situ labeling coupled with video-microscopy recording/analyses, chromatin-immunoprecipitation (ChIP), polymerase chain reactions (PCR), real-time quantitative PCR (RT-QPCR) and bisulfite genome sequencing were the main methods applied. Statistical analyses were performed by applying GCRMA and SAM analysis (microarray data) and Student's t-test or Mann & Whitney's U-test.

Results

Herein we show that, remarkably, in a resistant male CLL cells the vast majority of genes were down-regulated compared with sensitive cells, whereas this was not the case in cells derived from females. This gene down-regulation was found to be associated with an overall gain of heterochromatin as evidenced by immunofluorescent labeling of heterochromatin protein 1α (HP-1), trimethylated histone 3 lysine 9 (3metH3K9), and 5-methylcytidine (5metC). Notably, 17 genes were found to be commonly deregulated in resistant male and female cell samples. Among these, RELB was identified as a discriminatory candidate gene repressed in the male and upregulated in the female resistant cells.

Conclusion

The molecular defects in the silencing of RELB involve an increase in H3K9- but not CpG-island methylation in the promoter regions. Increase in acetyl-H3 in resistant female but not male CLL samples as well as a decrease of total cellular level of RelB after an inhibition of histone deacetylase (HDAC) by trichostatin A (TSA), further emphasize the role of epigenetic modifications which could discriminate two CLL subsets. Together, these results highlighted the epigenetic RELB silencing as a new marker of the progressive disease in males.