EZH2 overexpression dampens tumor-suppressive signals via an EGR1 silencer to drive breast tumorigenesis

Abstract

The mechanism underlying EZH2 overexpression in breast cancer and its involvement in tumorigenesis remain poorly understood. In this study, we developed an approach to systematically identify the trans-acting factors regulating the EZH2 expression, and identified more than 20 such factors. We revealed reciprocal regulation of early growth response 1 (EGR1) and EZH2: EGR1 activates the expression of EZH2, and EZH2 represses EGR1 expression. Using CRISPR-mediated genome/epigenome editing, we demonstrated that EHZ2 represses EGR1 expression through a silencer downstream of the EGR1 gene. Deletion of the EGR1 silencer resulted in reduced cell growth, invasion, tumorigenicity of breast cancer cells, and extensive changes in gene expression, such as upregulation of GADD45, DDIT3, and RND1; and downregulation of genes encoding cholesterol biosynthesis pathway enzymes. We hypothesize that EZH2/PRC2 acts as a “brake” for EGR1 expression by targeting the EGR1 silencer, and EZH2 overexpression dampens tumor-suppressive signals mediated by EGR1 to drive breast tumorigenesis.

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Fig. 1: The approach used to identify the transcription factors (TFs)/chromatin-binding proteins that regulate the expression of EZH2.
Fig. 2: EGR1 upregulates the expression of EZH2 in breast cancer cells.
Fig. 3: EZH2 represses EGR1 expression in a PRC2-dependent manner in breast cancer cells.
Fig. 4: Identification of a distal silencer that represses the expression of EGR1.
Fig. 5: Deletion of the EGR1+26 kb silencer region represses the tumorigenic phenotype of MDA-MB-231 cells in vitro and in vivo.
Fig. 6: Extensive changes in gene expression in EGR1+26 kb silencer-knockout cells.
Fig. 7: Reciprocal regulation of EZH2 and EGR1 is implicated in breast tumorigenesis.

Data availability

The RNA-seq data are deposited in the Gene Expression Omnibus (GEO) database under the accession number GSE134876.

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Acknowledgements

This work was funded by the Science and Technology Development Fund, Macau SAR (File no. 137/2014/A3 and 095/2015/A3), the Science and Technology Program of Guangzhou, China (201807010101), and the Research & Development Administration Office of the University of Macau (MYRG201700099, MYRG2018-00022) awarded to GL.

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GL conceived and supervised the study. XG, HD, ZL, and YY carried out the experiments. XG, XZ, and GL analyzed data. ULC, YL, and JZ performed bioinformatic analysis. XW and GL drafted the paper. All authors have read and approved the paper.

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Correspondence to Gang Li.

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Guan, X., Deng, H., Choi, U.L. et al. EZH2 overexpression dampens tumor-suppressive signals via an EGR1 silencer to drive breast tumorigenesis. Oncogene 39, 7127–7141 (2020). https://doi.org/10.1038/s41388-020-01484-9

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