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PML-RARa/RXR alters the epigenetic landscape in Acute Promyelocytic Leukemia

ABSTRACT: Many different molecular mechanisms have been suggested to be associated with PML-RAR dependent transformation of haematopoietic progenitors. Here, we investigated the role of PML-RAR and RXR in the organization of epigenetic structures at a genome-wide level. We identified 2722 high confidence PML-RAR binding sites in the leukemic model cell line NB4 and found PML-RAR colocalization with RXR to the vast majority of these binding regions. Importantly, these results could be corroborated and extended in primary blast cells of two APL patients. Through genome-wide epigenetic studies we show that treatment with pharmacological doses of all-trans retinoic acid ATRA induces global alterations in active H3 acetylation and repressive H3K27me3, H3K9me3 and DNA methylation chromatin modifications. However at the PML-RAR/RXR binding sites, ATRA only induces changes in H3 acetylation. These H3 acetylation alterations triggered by the loss of PML-RAR/RXR binding affect H3 acetylation and RNA polymerase II occupancy at nearby genes. Our results suggest that PML-RAR/RXR functions as a local chromatin modulator and that specific recruitment of histone deacetylase activities to genes important for haematopoietic differentiation, RAR signaling and epigenetic control is crucial to the transforming potential of PML-RAR/RXR.

ORGANISM(S): Homo sapiens

PROVIDER: GSE18886 | GEO | 2009/12/17

SECONDARY ACCESSION(S): PRJNA121283

REPOSITORIES: GEO

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Project description:We defined the RARα interactome in the MDA-MB453 breast cancer cell line genetically engineered to over-express an N-terminally tagged version of the nuclear retinoic acid receptor. Twenty eight nuclear proteins which interact with RARα and whose interaction is stimulated or reduced by the pan-RAR ligand, all-trans retinoic acid (ATRA) were identified. Given the potential significance of the S100A3 calcium-binding protein in the control of tumor progression, we focused our attention on this factor. Using the two models represented by the ATRA-sensitive SKBR3 and MCF7 breast cancer cell lines characterized by constitutive expression of S100A3 and RARα, we demonstrate that the endogenous forms of S100A3 and RARα interact in physiological conditions. The interaction of S100A3 with RARα is cell context independent and it is observed not only in breast cancer but also in acute promyelocytioc leukemia (APL) cells, characterized by expression of the RARα-derived PML-RARα oncogene, which is the product of the t(15:17) chromosomal translocation. S100A3 interacts directly and specifically with RARα and PML-RARα, being unable to bind other members of the RAR/RXR family of retinoid nuclear receptors. The interaction surface maps to the carboxyl-terminal region of the RARα ligand binding domain. Binding of S100A3 to RARα and PML-RARα controls the constitutive and ATRA-dependent degradation of the two receptors. Silencing of the S100A3 gene decreases the amounts of RARα in breast SK-BR-3 and lung A549 cancer cells, rendering them more refractory to the anti-proliferative action of ATRA. In SK-BR-3 cells, this effect is accompanied by a decrease in the lactogenic/differentiating action of ATRA. In APL-derived NB4 cells, S100A3 knock-down reduces the amounts of both RARα and PML-RARα. Contemporaneous down-regulation of the two receptors is associated with an increase in the basal and ATRA-induced expression of many granulocytic differentiation markers. Opposite on RARα and PML-RARα levels as well as ATRA induced differentiation markers are observed upon over-expression of S100A3 in NB4 cells.

Project description:In mouse embryonic cells, a retinoic acid (RA) stimulation triggers a massive change of gene expression leading the pluripotent, proliferating cells to a lineage-specific differentiation process. The retinoic acid receptor (RAR) plays a key role in this response by inhibiting pluripotency-maintaining genes and simultaneously activating some major actors of cell differentiation. To investigate the mechanism underlying this dual regulation, we performed joint RAR/RXR ChIP-seq and mRNA-seq time series during the first 48 hours of the RA-induced Primitive Endoderm differentiation process in F9 embryonic carcinoma cells. We detected significantly more RAR/RXR binding regions than previous studies and identified among them a handful of typical binding intensity patterns during differentiation. We demonstrate that these patterns are correlated with the coincidental binding of essential transcription factors (TFs) for pluripotency maintenance or PrE differentiation of embryonic stem (ES) cells, as well as the presence of variants of RAR binding motifs. Most importantly, early-bound regions coincide with pluripotency-associated transcription factor binding in ES (like Pou5f1, Sox2, Esrrb and Nr5a2) and display an increased frequency of the DR0 type RAR binding motifs; late-bound sites are associated to the PrE marker Sox17 and are enriched in the canonical DR5 binding motif. Our data offer an unprecedently detailed view on the action of RA in triggering pluripotent cell differentiation. Altogether, this work sheds light on the relocation of RAR/RXR binding sites throughout differentiation, and shows how RAR/RXR progressively shift from DR0 enriched regions, which were specifically identified in undifferentiated models, to canonical RAR binding sites containing loci. Time course (0, 2, 6, 12, 24, 48h) after stimulation of F9 cultured cells by retinoic acid: PanRAR and PanRXR ChIP-seq at 0, 2, 24 and 48h (no replicate); WCE-seq at 0h (no replicate); mRNA-seq at 0, 6, 12, 24, 48h (2 replicates except for time 0h, 4 replicates). Additionally, a control time course (culture in DMSO) sampled at 24 and 48h (no replicates).

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PML-RARa/RXR alters the epigenetic landscape in Acute Promyelocytic Leukemia

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