Abstract
Simple SummaryBoth Yin Yang 1 (YY1) and enhancer of zeste homolog 2 (EZH2) are oncogenes with overexpressed statuses in cancers. As a transcription factor, YY1 recruits EZH2 through its oncoprotein binding (OPB) domain to repress gene expression. In this study, we identified the interaction domain of YY1 on EZH2 protein with amino acids 493–519, named the YY1 protein binding (YPB) domain. Synthetic peptides using YPB and OPB domain sequences effectively blocked endogenous YY1-EZH2 interaction. Functionally, YPB and OPB peptides could efficiently inhibit the proliferation of breast cancer cells, promote their apoptosis, and reduce tumor growth in a xenograft mouse model. Using chromatin immunoprecipitation DNA sequencing (ChIP-seq) analysis, we discovered that YPB and OPB peptides could interfere with H3K27 trimethylation of multiple genes. Eventually, we identified that YPB and OPB peptides primarily targeted the PTENP1 gene and validated its importance in the anticancer activity of the two peptides.Enhancer of zeste homolog 2 (EZH2) is a methyltransferase to mediate lysine 27 trimethylation in histone H3 (i.e., H3K27me3) and repress gene expression. In solid tumors, EZH2 promotes oncogenesis and is considered a therapeutic target. As a transcription factor, Yin Yang 1 (YY1) recruits EZH2 through its oncoprotein binding (OPB) domain to establish gene repression. In this study, we mapped the YY1 protein binding (YPB) domain on EZH2 to a region of 27 amino acids. Both YPB and OPB domain synthetic peptides could disrupt YY1EZH2 interaction, markedly reduce breast cancer cell viability, and efficiently inhibit tumor growth in a xenograft mouse model. We analyzed MDA-MB-231 cells treated with YPB, OPB, and control peptides by chromatin immunoprecipitation DNA sequencing (ChIP-seq) using an antibody against H3K27me3. YPB and OPB treatments altered H3K27me3 on 465 and 1137 genes, respectively, compared to the control. Of these genes, 145 overlapped between the two peptides. Among them, PTENP1, the PTEN pseudogene, showed reduced H3K27me3 signal when treated by either YPB or OPB peptide. Consistently, the two peptides enhanced both PTENP1 and PTEN expression with concomitantly reduced AKT activation. Further studies validated PTENP1′s contribution to the anticancer activity of YPB and OPB peptides.
Highlights
Epigenetic regulation plays a key role in cell proliferation, differentiation, and embryonic development
We first carried out reciprocal co-immunoprecipitation using the lysates of MDA-MB-231 cells, and observed the association of endogenous Yin Yang 1 (YY1) and enhancer of zeste homolog 2 (EZH2) (Figure 1B)
In vitro binding assays demonstrated that GST-EZH2 (385–618) could interact with His×6-YY1 (Figure 1E), suggesting that the YY1 binding site resided in the residues 385–618 of EZH2
Summary
Epigenetic regulation plays a key role in cell proliferation, differentiation, and embryonic development. EZH2 has been demonstrated to promote cancer cell proliferation, migration, invasion, and metastasis through regulating the expression of a large array of target genes [7,8,9,10]. Like many other transcriptional cofactors, EZH2 does not directly bind DNA, but can be recruited by other molecules to its target promoters, where it exerts its regulatory activity. Other transcription factors or chromatin binding proteins, such as TCF1 and CDYL, could help EZH2 bind its target genes to regulate their expression [17,18]. Since the discovery that long noncoding RNA HOTAIR could recruit EZH2 and other histone modifiers to chromatin [19], understanding of the regulation of EZH2 s epigenetic activity has been greatly extended. The RNA binding affinity of EZH2 and its recruitment to chromatin by many other lncRNAs, including PVT1, MALAT1, HOXD-AS1, FOXC2-AS1, and GATA6-AS1, have been frequently reported [20,21,22,23,24]
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