Probing the interaction between the histone methyltransferase/deacetylase subunit RBBP4/7 and the transcription factor BCL11A in epigenetic complexes

Abstract

The transcription factor BCL11A has recently been reported to be a driving force in triple-negative breast cancer (TNBC), contributing to the maintenance of a chemoresistant breast cancer stem cell (BCSC) population. Although BCL11A was shown to suppress γ-globin and p21 and to induce MDM2 expression in the hematopoietic system, its downstream targets in TNBC are still unclear. For its role in transcriptional repression, BCL11A was found to interact with several corepressor complexes; however, the mechanisms underlying these interactions remain unknown. Here, we reveal that BCL11A interacts with histone methyltransferase (PRC2) and histone deacetylase (NuRD and SIN3A) complexes through their common subunit, RBBP4/7. In fluorescence polarization assays, we show that BCL11A competes with histone H3 for binding to the negatively charged top face of RBBP4. To define that interaction, we solved the crystal structure of RBBP4 in complex with an N-terminal peptide of BCL11A (residues 2-16, BCL11A(2-16)). The crystal structure identifies novel interactions between BCL11A and the side of the β-propeller of RBBP4 that are not seen with histone H3. We next show that BCL11A(2-16) pulls down RBBP4, RBBP7, and other components of PRC2, NuRD, and SIN3A from the cell lysate of the TNBC cell line SUM149. Furthermore, we demonstrate the therapeutic potential of targeting the RBBP4-BCL11A binding by showing that a BCL11A peptide can decrease aldehyde dehydrogenase-positive BCSCs and mammosphere formation capacity in SUM149. Together, our findings have uncovered a previously unidentified mechanism that BCL11A may use to recruit epigenetic complexes to regulate transcription and promote tumorigenesis.

PRC2 is high maintenance

“…Thus, RBAP46/48 likely enhances PRC2 affinity for its target sites as previously proposed (Margueron and Reinberg 2011), thereby promoting PRC2 activity. The significance of the interaction between RBAP46/48 and the histone H3 or H4 tail under physiological conditions warrants further investigation; however, it is important to stress that RBAP46/48 are components of a large number of chromatin associated complexes (Margueron and Reinberg 2011;Millard et al 2016;Moody et al 2018), and their function is likely providing stable binding to chromatin, perhaps in a dynamic way.…”

Tspan8-Tumor Extracellular Vesicle-Induced Endothelial Cell and Fibroblast Remodeling Relies on the Target Cell-Selective Response

“…This tempted us speculating on upregulation of Tf that was confirmed for 44 mRNA versus only 3 mRNA in AS-TEX treated EC. Strongly upregulated ARID3a mRNA promotes IFNα expression [104], BCL11a 1 binds to selective histone subunits, particularly RBP4 [105], FOXE1 together with ETV1 1 promotes telomerase reverse transcription promoter activation [106] and also affects via GLI2 1 Wnt/β-catenin pathway activation [107]. HES7 is best known for its dominant role in somitogenesis with synergistic signaling including TBX6 1 and Notch [108].…”

Transcriptional Repressors of Fetal Globin Genes as Novel Therapeutic Targets in Beta-Thalassemia

“…In the last years, many efforts have been aimed at clarifying the repression mechanism exerted by BCL11A at the HBB locus. At this regard, an important contribution has been provided by the identification of the multiprotein complex Transcriptional repressor mechanisms of fetal globin genes in adult erythropoiesis involving BCL11A and CSDA multiprotein complexes [23][24][25][26][27].…”

“…interacting with BCL11A that includes GATA-1, FOG-1, RUNX1, KLF1, and SOX6 [24,31,32]. In addition, further insights have been provided regarding the BCL11A repression mechanisms by demonstrating how these protein complexes drive the recruitment of a variety of epigenetic factors such as the nucleosome remodeling and deacetylase (NuRD) repressor complex, histone deacetylase (HDAC1 and HDAC2), lysine-specific demethylase (LSD1), and DNA methyl-transferase (DNMT1) [25][26][27] (Figure 3). ChiP analysis also revealed binding sites for BCL11A at regulatory elements within the LCR, as well as at the promoter regions of both embryonic and fetal globin genes and in an intergenic region between the fetal and adult genes, thus indicating that these protein complexes are directly involved in fetal globin gene silencing as well as in long-range interactions that contribute to reshape chromatin loop domains in order to spatially separate the fetal and adult globin genes from the transcriptional machinery and, in the meantime, to promote long-range LCR interactions with the adult globin genes [33][34][35].…”