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Uterine Epithelial Development and Enhancer of Zeste Homolog 2

It Is Important for More than Just Cancer
  • Xiyin Wang
    Affiliations
    Department of Obstetrics and Gynecology, Indiana University School of Medicine, Indianapolis, Indiana
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  • Shannon M. Hawkins
    Correspondence
    Address correspondence to Shannon M. Hawkins, M.D., Ph.D., Department of Obstetrics and Gynecology, Indiana University School of Medicine, 550 N University Blvd., UH2440, Indianapolis, IN 46202.
    Affiliations
    Department of Obstetrics and Gynecology, Indiana University School of Medicine, Indianapolis, Indiana
    Search for articles by this author
Open ArchivePublished:April 13, 2019DOI:https://doi.org/10.1016/j.ajpath.2019.03.007
      Enhancer of zeste homolog 2 (EZH2) functions as a master regulator via epigenetic regulation of gene expression. EZH2 may function to methylate nonhistone proteins, methylate histone proteins, or act as a transcription factor, which up-regulates or down-regulates gene expression on the basis of context within the cell.
      • Kim K.H.
      • Roberts C.W.
      Targeting EZH2 in cancer.
      As a master regulator, EZH2 can have long-standing effects on development that lead to increased risk of disease later in life. For example, early work showed that treatment of mice with xenoestrogens, such as diethylstilbestrol, led to inactivation of EZH2, subsequent reprogramming of estrogen-responsive genes, and increased sensitivity to the proliferative effects of estradiol in the uterus.
      • Walker C.L.
      Epigenomic reprogramming of the developing reproductive tract and disease susceptibility in adulthood.
      • Bredfeldt T.G.
      • Greathouse K.L.
      • Safe S.H.
      • Hung M.C.
      • Bedford M.T.
      • Walker C.L.
      Xenoestrogen-induced regulation of EZH2 and histone methylation via estrogen receptor signaling to PI3K/AKT.
      However, the role of EZH2 in uterine development has not been described. In this issue of The American Journal of Pathology, Fang et al
      • Fang X.
      • Ni N.
      • Lydon J.P.
      • Ivanov I.
      • Bayless K.J.
      • Rijnkels M.
      • Li Q.
      EZH2 is required for uterine epithelial integrity.
      report on the impact of conditional deletion of Ezh2 in the mouse uterus, using a progesterone-driven Cre recombinase [Ezh2 conditional knockout (cKO)].

      Uterine Epithelial Development

      Mouse and human endometrium is composed of luminal epithelium that invaginates to form glandular epithelium, which is surrounded by endometrial stromal cells.
      • Cha J.
      • Sun X.
      • Dey S.K.
      Mechanisms of implantation: strategies for successful pregnancy.
      • Filant J.
      • Spencer T.E.
      Uterine glands: biological roles in conceptus implantation, uterine receptivity and decidualization.
      Several genes, including catenin β 1 (Ctnnb1), forkhead box A2 (Foxa2), leucine-rich repeat-containing G-protein–coupled receptor 4 (Lgr4), wingless-related mouse mammary tumor virus (MMTV) integration site 4 (Wnt4), and Wnt7a, regulate uterine epithelium development and differentiation.
      • Spencer T.E.
      Biological roles of uterine glands in pregnancy.
      Fang et al
      • Fang X.
      • Ni N.
      • Lydon J.P.
      • Ivanov I.
      • Bayless K.J.
      • Rijnkels M.
      • Li Q.
      EZH2 is required for uterine epithelial integrity.
      add Ezh2 to the list of genes important in uterine epithelial cell development.
      The key function of the endometrium is in the implantation process of the blastocyst. Each component of the endometrium plays a unique molecular role in embryo implantation. Both luminal epithelium and glandular epithelium are histologically columnar epithelial cells. However, they differ in shape, location, and molecular function, particularly regarding steroid hormone and non–steroid hormone signaling cascades.
      • Cha J.
      • Sun X.
      • Dey S.K.
      Mechanisms of implantation: strategies for successful pregnancy.
      • Evans G.E.
      • Martinez-Conejero J.A.
      • Phillipson G.T.
      • Sykes P.H.
      • Sin I.L.
      • Lam E.Y.
      • Print C.G.
      • Horcajadas J.A.
      • Evans J.J.
      In the secretory endometria of women, luminal epithelia exhibit gene and protein expressions that differ from those of glandular epithelia.
      Luminal epithelium is critical for uterine receptivity, embryo attachment, and furthering differentiation-signaling cascades. Glandular epithelium is important for angiogenesis and successful implantation and continuation of pregnancy.
      • Cha J.
      • Sun X.
      • Dey S.K.
      Mechanisms of implantation: strategies for successful pregnancy.
      • Evans G.E.
      • Martinez-Conejero J.A.
      • Phillipson G.T.
      • Sykes P.H.
      • Sin I.L.
      • Lam E.Y.
      • Print C.G.
      • Horcajadas J.A.
      • Evans J.J.
      In the secretory endometria of women, luminal epithelia exhibit gene and protein expressions that differ from those of glandular epithelia.
      The Ezh2 cKO mouse uterine epithelium exhibits a unique morphologic change. Specifically, the normal single layer of columnar glandular epithelium is replaced by stratified columnar epithelium. Consistent with endometrial hyperplasia, the endometrium contains an increased number of dilated glands separated by normal stroma. More important, deletion of Ezh2 in the uterus results in fertility defects.
      • Fang X.
      • Ni N.
      • Lydon J.P.
      • Ivanov I.
      • Bayless K.J.
      • Rijnkels M.
      • Li Q.
      EZH2 is required for uterine epithelial integrity.

      Molecular Impact

      In Ezh2 cKO mice, uterine epithelium development was dysregulated at the molecular level. In particular, there was an aberrant expression of basalis cell markers.
      • Fang X.
      • Ni N.
      • Lydon J.P.
      • Ivanov I.
      • Bayless K.J.
      • Rijnkels M.
      • Li Q.
      EZH2 is required for uterine epithelial integrity.
      The endometrium is composed of the stratum compactum, stratum spongiosum, and stratum basalis. Both the stratum compactum and stratum spongiosum make up the stratum functionalis, which exhibits large changes through the menstrual cycle.
      • Huang E.C.
      • Crum C.P.
      • Hornstein M.D.
      Chapter 16 - Evaluation of the cyclic endometrium and benign endometrial disorders. Diagnostic and Gynecologic and Obstetric Pathology.
      In contrast, the stratum basalis remains more histologically constant and is changed with replacing tissue lost during menstruation, potentially through stem-like or progenitor cells in the basalis.
      • Prianishnikov V.A.
      On the concept of stem cell and a model of functional-morphological structure of the endometrium.
      • Gargett C.E.
      • Chan R.W.
      • Schwab K.E.
      Hormone and growth factor signaling in endometrial renewal: role of stem/progenitor cells.
      • Schwab K.E.
      • Hutchinson P.
      • Gargett C.E.
      Identification of surface markers for prospective isolation of human endometrial stromal colony-forming cells.
      Transformation-related protein 63 (p63), alias tumor protein p63, is involved in the development of the epithelial basal layer.
      • O'Connell J.T.
      • Mutter G.L.
      • Cviko A.
      • Nucci M.
      • Quade B.J.
      • Kozakewich H.P.
      • Neffen E.
      • Sun D.
      • Yang A.
      • McKeon F.D.
      • Crum C.P.
      Identification of a basal/reserve cell immunophenotype in benign and neoplastic endometrium: a study with the p53 homologue p63.
      The p63 gene contains two main isoforms by alternative promoters that contain a p53-like N-terminal transactivation domain and lack this domain.
      • Murray-Zmijewski F.
      • Lane D.P.
      • Bourdon J.C.
      p53/p63/p73 Isoforms: an orchestra of isoforms to harmonise cell differentiation and response to stress.
      The uterine epithelium of Ezh2 cKO mice contained high levels of p63 that lacked the N-terminal transactivation domain, consistent with an increased basal cell phenotype.
      • Fang X.
      • Ni N.
      • Lydon J.P.
      • Ivanov I.
      • Bayless K.J.
      • Rijnkels M.
      • Li Q.
      EZH2 is required for uterine epithelial integrity.
      Recent work has shown that neonatal exposure to estrogenic chemicals, such as diethylstilbestrol, affects p63 expression by increasing the number and location of basal cells and increasing the risk of uterine carcinoma in adults.
      • Suen A.A.
      • Jefferson W.N.
      • Williams C.J.
      • Wood C.E.
      Differentiation patterns of uterine carcinomas and precursor lesions induced by neonatal estrogen exposure in mice.
      The p63 may be a marker of metaplastic differentiation and/or initiation of epithelial stratification.
      • Koster M.I.
      • Kim S.
      • Mills A.A.
      • DeMayo F.J.
      • Roop D.R.
      p63 Is the molecular switch for initiation of an epithelial stratification program.
      EZH2 may play a similar role and/or regulate p63 expression.

      The Future of EZH2 Inhibitors

      EZH2 inhibitors hold significant promise as new therapies for switch/sucrose non–fermentable (SWI/SNF)-mutated cancers.
      • Bitler B.G.
      • Aird K.M.
      • Garipov A.
      • Li H.
      • Amatangelo M.
      • Kossenkov A.V.
      • Schultz D.C.
      • Liu Q.
      • Shih I.-M.
      • Conejo-Garcia J.R.
      • Speicher D.W.
      • Zhang R.
      Synthetic lethality by targeting EZH2 methyltransferase activity in ARID1A-mutated cancers.
      The SWI/SNF complex, involved in chromatin remodeling, is composed of approximately 15 subunits, such as ARID1A and SMARCA4. Next-generation sequencing studies across multiple different cancer types have shown that members of the SWI/SNF complex are frequently mutated in cancer, with a range of mutation frequency from 9% in triple-negative breast cancer to 75% in ovarian clear cell carcinoma.
      • Shain A.H.
      • Pollack J.R.
      The spectrum of SWI/SNF mutations, ubiquitous in human cancers.
      Important translational studies have shown that EZH2 inhibitors demonstrate increased efficacy in ARID1A-mutated cancers.
      • Bitler B.G.
      • Aird K.M.
      • Garipov A.
      • Li H.
      • Amatangelo M.
      • Kossenkov A.V.
      • Schultz D.C.
      • Liu Q.
      • Shih I.-M.
      • Conejo-Garcia J.R.
      • Speicher D.W.
      • Zhang R.
      Synthetic lethality by targeting EZH2 methyltransferase activity in ARID1A-mutated cancers.
      The function of EZH2 in the endometrium is critical to understanding normal development, but also, it is critical to understanding the pharmacologic effects of EZH2 inhibitors on tissues other than cancer. Deletion of Ezh2 in the mouse uterus results in simple hyperplasia that is histologically similar to the endometrial histology of women treated with ulipristal, a selective progesterone receptor modulator.
      • Bressler L.H.
      • Bernardi L.A.
      • Snyder M.A.
      • Wei J.J.
      • Bulun S.
      Treatment of endometriosis-related chronic pelvic pain with ulipristal acetate and associated endometrial changes.
      On the basis of data from this Ezh2 cKO mouse model,
      • Fang X.
      • Ni N.
      • Lydon J.P.
      • Ivanov I.
      • Bayless K.J.
      • Rijnkels M.
      • Li Q.
      EZH2 is required for uterine epithelial integrity.
      as clinical trials progress for EZH2 inhibitors, careful consideration for fertility and endometrial evaluation are critical.

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      Linked Article

      • Enhancer of Zeste 2 Polycomb Repressive Complex 2 Subunit Is Required for Uterine Epithelial Integrity
        The American Journal of PathologyVol. 189Issue 6
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          Normal proliferation and differentiation of uterine epithelial cells are critical for uterine development and function. Enhancer of zeste 2 polycomb repressive complex 2 subunit (EZH2), a core component of polycomb repressive complexes 2, possesses histone methyltransferase activity that catalyzes the trimethylation of lysine 27 of histone H3. EZH2 has been involved in epithelial-mesenchymal transition, a key event in development and carcinogenesis. However, its role in uterine epithelial cell function remains unknown.
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