Epigenetic regulation by RARα maintains ligand-independent transcriptional activity

Abstract

Retinoic acid receptors (RARs) α, β and γ are key regulators of embryonic development. Hematopoietic differentiation is regulated by RARα, and several types of leukemia show aberrant RARα activity. Through microarray expression analysis, we identified transcripts differentially expressed between F9 wild-type (Wt) and RARα knockout cells cultured in the absence or presence of the RAR-specific ligand all trans retinoic acid (RA). We validated the decreased Mest, Tex13, Gab1, Bcl11a, Tcfap2a and HMGcs1 transcript levels, and increased Slc38a4, Stmn2, RpL39l, Ref2L, Mobp and Rlf1 transcript levels in the RARa knockout cells. The decreased Mest and Tex13 transcript levels were associated with increased promoter CpG-island methylation and increased repressive histone modifications (H3K9me3) in RARα knockout cells. Increased Slc38a4 and Stmn2 transcript levels were associated with decreased promoter CpG-island methylation and increased permissive histone modifications (H3K9/K14ac, H3K4me3) in RARα knockout cells. We demonstrated specific association of RARα and RXRα with the Mest promoter. Importantly, stable expression of a dominant negative, oncogenic PML–RARα fusion protein in F9 Wt cells recapitulated the decreased Mest transcript levels observed in RARα knockout cells. We propose that RARα plays an important role in cellular memory and imprinting by regulating the CpG methylation status of specific promoter regions.

RARγ is Essential for Retinoic Acid Induced Chromatin Remodeling and Transcriptional Activation in Embryonic Stem Cells

“…Several genes, including DNMT3L, Suv39h1, and Tex13, were differentially expressed between WT and RARc 2/2 ES cells independent of RA treatment. Consequently, RARc may have ligand-independent functions similar to those recently reported for RARa (Laursen et al, 2012). Our research data also lead to novel conclusions about epigenetic modifications of RA-responsive genes in ES cells.…”

“…1; supplementary material Table S2B). These data suggest a role for RARc in regulating gene expression in the absence of the ligand, as we demonstrated in teratocarcinoma stem cells for RARa (Laursen et al, 2012). Furthermore, a total of 56 and 72 transcripts were differentially regulated by threefold or more in WT versus RARc 2/2 ES cells upon 8 and 24 h of RA treatment, respectively (Fig.…”

Imprinted genes in myeloid lineage commitment in normal and malignant hematopoiesis

“…The fact that RARa is involved in hematopoiesis made the authors assume that the regulation of both IGs by RARa might occur during HSCs differentiation in an epigenetic manner. 126 …”

Genes involved in cell adhesion and signaling: A new repertoire of Retinoic Acid Receptors target genes in mouse embryonic fibroblasts

“…According to the classical model (Dilworth and Chambon, 2001), unliganded and DNAbound RARa represses transcription through the recruitment of corepressor complexes that maintain chromatin in a condensed and repressed state. However, recent studies reported that RARa can mediate substantial levels of transcriptional activation in the absence of ligand through the recruitment of complexes that regulate the methylation of specific promoter regions (Delacroix et al, 2010;Laursen et al, 2012). RARc has been also shown to control gene transcription in the absence of ligand (Su and Gudas, 2008) and it has been proposed that this property would reflect its weak ability to bind corepressors Hauksdottir et al, 2003).…”