Ctbp2 modulates chromatin states during embryonic stem cell differentiation

Abstract

The chromatin status is essential for cell fate determination. Accordingly, chromatin regulators are important for cell state transition process, such as deve1elopment and differentiation. Embryonic stem cells (ESCs) are maintained by core transcription factors (CTFs), which are closely connected with chromatin regulators to modulate chromatin environment and gene expression. The transcriptional corepressor C-terminal binding protein 2 (Ctbp2), which makes chromatin structures less accessible for transcription, is known as gating factor for pluripotency exit, but the underlying mechanism of Ctbp2 in ESC differentiation is poorly understood. Here, we show that Ctbp2 and ESC CTFs are co-occupied in active ESC genes and Ctbp2 mediates H3K27ac deacetylation in association with nucleosome remodeling and deacetylation (NuRD) complex during mouse embryonic stem cell (mESC) differentiation. In addition, it was confirmed that Ctbp2 occupies most of super-enhancers, regulatory region of CTFs. In undifferentiated conditions, knockdown of Ctbp2 causes aberrantly high H3K27ac level but the gene expression levels are not significantly changed. Even if differentiation signal is given, Ctbp2-knockdown cells fail to down-regulate ESC CTF expression, thereby sustaining ESC maintenance. The fact that Ctbp2 and NuRD complex preoccupy in super-enhancers accounts for the recent finding that super-enhancers are sensitive to perturbation. We validated above findings in human breast cancer cell line MCF7 by analyzing public genomewide ChIP-sequencing data, which shows that CTBP1/2 is associated with master transcription factors ERα, FOXA1, and GATA3 in ER positive breast cancer. Furthermore, CTBP1/2 is enriched in active chromatin regions, especially in most of super-enhancers. These suggest that CTBP1/2 is critical for not only mESC differentiation but also cancer differentiation and progression processes in human.