Estrogen receptor α wields treatment-specific enhancers between morphologically similar endometrial tumors

Abstract

The DNA-binding sites of estrogen receptor α (ERα) show great plasticity under the control of hormones and endocrine therapy. Tamoxifen is a widely applied therapy in breast cancer that affects ERα interactions with coregulators and shifts the DNA-binding signature of ERα upon prolonged exposure in breast cancer. Although tamoxifen inhibits the progression of breast cancer, it increases the risk of endometrial cancer in postmenopausal women. We therefore asked whether the DNA-binding signature of ERα differs between endometrial tumors that arise in the presence or absence of tamoxifen, indicating divergent enhancer activity for tumors that develop in different endocrine milieus. Using ChIP sequencing (ChIP-seq), we compared the ERα profiles of 10 endometrial tumors from tamoxifen users with those of six endometrial tumors from nonusers and integrated these results with the transcriptomic data of 47 endometrial tumors from tamoxifen users and 64 endometrial tumors from nonusers. The ERα-binding sites in tamoxifen-associated endometrial tumors differed from those in the tumors from nonusers and had distinct underlying DNA sequences and divergent enhancer activity as marked by histone 3 containing the acetylated lysine 27 (H3K27ac). Because tamoxifen acts as an agonist in the postmenopausal endometrium, similar to estrogen in the breast, we compared ERα sites in tamoxifen-associated endometrial cancers with publicly available ERα ChIP-seq data in breast tumors and found a striking resemblance in the ERα patterns of the two tissue types. Our study highlights the divergence between endometrial tumors that arise in different hormonal conditions and shows that ERα enhancer use in human cancer differs in the presence of nonphysiological endocrine stimuli.E strogen receptor α (ERα) is a steroid hormone receptor that behaves as a transcription factor by interacting with the DNA. The DNA-binding profile (cistrome) of ERα is dependent on context and tissue type (1). The hormonal environment of the cell greatly influences this cistrome because estrogen activates ERα by binding its ligand-binding domain. Upon activation, ERα's structural conformation changes to interact with cofactors at the DNA (2) and to regulate a transcriptional program that drives cell proliferation (3). Hence, the hormonal environment modulates the ERα cistrome and thereby rewires downstream effects.Endocrine therapies, as exemplified by tamoxifen, manipulate the DNA-binding capacities of the steroid hormone receptor ERα. Tamoxifen, a small-molecule inhibitor that competes with estrogens to bind ERα, is a major endocrine agent used in treating ERα-positive breast cancer patients. Studies in the breast cancer cell line MCF-7 show that prolonged tamoxifen exposure shifts the ERα cistrome, which consequently changes gene expression (4-6).Tamoxifen is a well-known selective estrogen receptor modulator (SERM) with tissue-selective physiological action. Early reports on tamoxifen's effects on transplanted MCF-7 cells in athymic mice revealed decreased tumor c...

Estrogen-independent molecular actions of mutant estrogen receptor 1 in endometrial cancer

“…The regulatory proteins used by ESR1 to mediate gene expression in breast cancer cells have been well characterized by multiple laboratories (Carroll et al 2005;Hurtado et al 2011;Magnani et al 2011;Tan et al 2011;Mohammed et al 2013). However, the proteins responsible for mediating these interactions in endometrial cancer have not been established, but ETV4 (Gertz et al 2013) and FOXA1 (Droog et al 2017) have been proposed as key transcription factors. To understand the relationship between mutant ESR1 binding and these factors, we overlapped ESR1 binding sites with the binding sites of FOXA1, which is reported to overlap with 8% of ESR1's binding sites in parental Ishikawa cells, and ETV4, which is reported to overlap with 45% of ESR1's binding sites in parental Ishikawa cells (Gertz et al 2013).…”

“…Although these studies have uncovered important features of the molecular and phenotypic consequences of ESR1 mutations in breast cancer, similar analyses have not been performed in endometrial cancer cells. Because gene expression responses to estrogens and ESR1 genomic binding are highly dissimilar between breast and endometrial cancer (Gertz et al 2012(Gertz et al , 2013Droog et al 2017), the impact of ESR1 LBD mutations in endometrial cancer cells could be different than the effects observed in breast cancer cells.…”

Estrogen-independent molecular actions of mutant estrogen receptor alpha in endometrial cancer

“…The use of multiple ESR1 mutant and wildtype clones enabled the discovery of molecular changes that can be reproducibly attributed to the mutation. Wildtype ESR1 binds to different loci in breast cancer and endometrial cancer cells (Gertz et al 2013) and primary tumors (Droog 2017) leading to different transcriptional responses to E2. Mutant ESR1 exhibits a similar cell type-specific pattern in which the genes regulated by mutant ESR1 are different between endometrial cancer cells and breast cancer cells.…”

“…The regulatory proteins utilized by ESR1 to mediate gene expression in breast cancer cells have been well characterized by multiple labs (Carroll 2005;Hurtado 2010;Magnani 2011;Tan 2011;Mohammed 2013). However, the proteins responsible for mediating these interactions in endometrial cancer have not been established, but ETV4 (Gertz et al 2013) and FOXA1 (Droog 2017) have been proposed as key transcription factors. To understand the relationship between mutant ESR1 binding and these factors, we overlapped ESR1 binding sites with the binding sites of FOXA1, which is reported to overlap with 8% of ESR1's binding sites in parental Ishikawa cells, and ETV4, which is reported to overlap with 45% of ESR1's binding sites in parental Ishikawa cells (Gertz et al 2013).…”

“…While these studies have uncovered important features of the molecular and phenotypic consequences of ESR1 mutations in breast cancer, similar analyses have not been performed in endometrial cancer cells. Because gene expression responses to estrogens and ESR1 genomic binding are highly dissimilar between breast and endometrial cancer (Gertz 2012;Gertz et al 2013;Droog 2017), the impact of ESR1 LBD mutations in endometrial cancer cells could be different than the effects observed in breast cancer cells.…”