Dissecting the Role of EZH2 and H3K27me3 in Endometriosis

Background Endometriosis, defined as the growth and development of endometrial like tissue, ( i.e., glands and stroma) outside the uterine cavity, is a gynecological condition that affects 10% of women in their reproductive age. Cumulative evidence has demonstrated that candidate genes which are related with cellular behaviors characteristic of endometriosis are epigenetically regulated by DNA methylation and histone acetylation. However, the specific role of histone methylation and the enzymes responsible for setting these histone marks ( e.g., histone methyltransferases‐HMT's) in the regulation of these candidate genes is still unknown. EZH2 is an HMT that sets the H3K27me3 histone mark, a repressor of the transcriptional machinery. We have previously reported that endometriotic lesions are characterized by high levels of H3K27me3; therefore, we aimed to assess basal and hormone‐regulated protein expression levels of EZH2 isoforms (α and β) and also elucidate if H3K27me3 is enriched within or near promoter regions of candidate genes. Methods Western Blot (WB) was performed to determine basal and ovarian steroid EZH2 protein levels in cell lines. Immunohistochemistry (IHC) of an endometriosis‐TMA was used to assess EZH2 α and β protein levels in tissue samples. Chromatin immunoprecipitation (ChIP‐qPCR) with an H3K27me3 antibody was conducted using endometrial and endometriotic samples. Scratch Assay was performed to determine the effect of EZH2 inhibition on proliferative cellular behavior Results WB results suggest that endometriotic cells expressed higher levels of EZH2α, compared to non‐endometriotic cells. Also, hormonal treatments did not modulate EZH2 isoform expression in any of the cell lines tested. IHC indicated that in endometriotic lesions the glands and stroma had higher EZH2α and β protein levels compared to eutopic endometrium from patients. ChIP‐qPCR results showed higher levels of H3K27me3 levels within promoter regions of candidate genes in at least some of the endometriotic lesions. Pharmacological inhibition of EZH2 reduced the proliferative rate of the endometriotic cells. Conclusions The present study is the first in reporting that EZH2 isoform protein expression is elevated in endometriosis but not regulated by steroid hormones. We also showed that H3K27me3 is elevated in the promoter region of candidate genes in some lesions. Elucidating the expression profile and function of HMTs may support the use of novel histone methyltransferases inhibitors (HMTi) as a possible treatment for this enigmatic disease. Support or Funding Information R01HD050509, NCI1U56CA126379‐01, R25GM082406.