| 11. |
- Indukuri, Rajitha
(author)
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Estrogen receptor beta transcriptional regulation: A potential mechanism for colon cancer prevention
- 2021
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Doctoral thesis (other academic/artistic)abstract
- Colorectal cancer (CRC) is the third leading cause of death from cancer in both men andwomen in the Western world. Improved screening efforts, surveillance, and treatment havereduced CRC mortality in older patients. However, the incidence is increasing in young adults,even in the absence of CRC family history. This may indicate an influence of increasingobesity, changed dietary patterns, and lifestyle factors. The progression of CRC is a multistepprocedure that takes 10-15 years, thus offering a time to implement preventative measures andearly detection. There is a critical need to develop more effective preventive therapies due tothe risks posed by current prevention therapies. The best CRC prophylactic agent should beboth safe and suitable to use for a long time (1).In preclinical studies, estrogen has been shown to protect from CRC, and substantial evidencesuggests it is through estrogen receptor beta (ERβ). Natural ERβ selective agonists have beentested in phase II clinical trials to treat menopause symptoms and proven to be safe and welltolerated with no side effects (2, 3). Thus, selective activation of ERβ with selective agonists,which do not activate estrogen receptor alpha (ERα), is a potential clinical approach inpreventing adenomatous polyps progression into CRC. However, the mechanism of thesebeneficial ERβ effects is not well understood, and there is a significant knowledge gap in thisarea.The overall aim of this thesis was to identify the mechanistic background of the intestinal ERβmediated antitumorigenic effects in the colon and further to explore ERβ as a preventativeapproach in CRC. One specific aim was to determine whether ERβ present specifically in colonepithelium is responsible for protecting from CRC, which is addressed in Paper I. Tounderstand the impact of ERβ in protecting from colitis-associated CRC (CA-CRC), we haveinduced colitis in intestinal-specific ERβ knockout mice of both sexes. The loss of intestinalERβ aggravated CA-CRC in a sex-dependent manner. The incidence of tumors increased inmales, while in females, the size of the tumors was enhanced. We identified that ERβ attenuatestumor necrosis factor alpha (TNFα) induced epithelial cell damage and modulates theregulation of key nuclear factor-κB (NFκB) members. As a direct consequence, ERβ was foundto reduce inflammation and to control intestinal crypt cell proliferation.Another aim was to explore transcriptional regulation by ERβ through mapping of chromatinbinding sites and interaction with NFκB, which is studied in Paper II and IV. Commonly usedERβ antibodies have been shown to be unspecific towards ERβ; this study used a validatedERβ antibody to map genome-wide ERβ binding sites in colon cancer cells. We observed thatthe presence of ERβ also modulated the regulatory chromatin mark H3K27AC in potentialenhancers of transcriptional regulation, Wnt signaling, and cell proliferation. Further, motifanalysis indicated a novel ERβ colon-specific cross-talk with TCF, and KLF motifs supporteda interaction between β-catenin/TCF and ERβ. We found that ERβ binds and regulates severalimportant tumor suppressors and oncogenes in CRC cells, such as CST5 and LRP6, consistentwith its proposed antitumorigenic activity. We also revealed the p65 cistrome in CRC cell lines and showed that ERβ alters the p65 chromatin binding in a cell-type-dependent manner. Wefound that ERβ chromatin binding sites were enriched among circadian clock genes and alsothat ERβ modulates p65 binding to core clock genes in CRC cells, indicating potential crosstalk between ERβ and circadian clock gene regulation.The final aim was to investigate the impact of ERβ, and estrogen signaling in high-fat diet(HFD) induced inflammation in colon, explored in paper III. We fed mice with an HFD for 13weeks and treated them with estrogenic ligands for the last three weeks prior to sacrifice. Thecolon transcriptome showed predominant sex differences, and selective activation of ERβreduced macrophage infiltration and epithelial cell proliferation induced by HFD. Wedemonstrated that ERβ opposes HFD-induced dysregulation of core circadian clock genes invivo, further strengthening the role of ERβ in circadian rhythm.Taken together, these results highlight the chemopreventive potential of ERβ in CRC in bothsexes. The identified cross-talk with TNFα/NFκB pathway, Wnt signaling, regulating genesinvolved circadian clock, and tumorigenesis reflected ERβ protection/antitumor activityagainst CRC progression and development (as illustrated in Figure 1).
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| 12. |
- Indukuri, Rajitha, et al.
(author)
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Genome-wide estrogen receptor β chromatin binding in humancolon cancer cells reveals its tumor suppressor activity
- 2021
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In: International Journal of Cancer. - : Wiley. - 0020-7136 .- 1097-0215.
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Journal article (peer-reviewed)abstract
- Colorectal cancer (CRC) is the third leading cause of cancer death in the western world. In women, menopausal hormone therapy has been shown to reduce CRC incidence by 20%. Studies demonstrate that estrogen activating estrogen receptor beta (ERβ) protects against CRC. ERβ is a nuclear receptor that regulates gene expression through interactions with the chromatin. This molecular mechanism is, however, not well characterized in colon. Here, we present for the first time, the cistrome of ERβ in different colon cancer cell lines. We use cell lines engineered to express ERβ, optimize and validate an ERβ antibody for chromatin-immunoprecipitation (ChIP), and perform ChIP-Seq. We identify key binding motifs, including ERE, AP-1, and TCF sites, and we determine enrichment of binding to cis-regulatory chromatin sites of genes involved in tumor development, cell migration, cell adhesion, apoptosis, and Wnt signaling pathways. We compare the corresponding cistromes of colon and breast cancer and find that they are conserved for about a third of genes, including GREB1, but that ERβ tethering to TCF and KLF family motifs is characteristic for colon. We exemplify upregulation of putative CRC tumor suppressor gene CST5 where ERβ in colon cells binds to cis-regulatory regions nearby (−351 bp) the transcriptional start site. Our work provides a foundation for understanding the mechanism of action of ERβ in CRC prevention.
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| 13. |
- Song, Dandan, et al.
(author)
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ER alpha and ER beta Homodimers in the Same Cellular Context Regulate Distinct Transcriptomes and Functions
- 2022
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In: Frontiers in Endocrinology. - : Frontiers Media SA. - 1664-2392. ; 13
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Journal article (peer-reviewed)abstract
- The two estrogen receptors ER alpha and ER beta are nuclear receptors that bind estrogen (E2) and function as ligand-inducible transcription factors. They are homologues and can form dimers with each other and bind to the same estrogen-response element motifs in the DNA. ER alpha drives breast cancer growth whereas ER beta has been reported to be anti-proliferative. However, they are rarely expressed in the same cells, and it is not fully investigated to which extent their functions are different because of inherent differences or because of different cellular context. To dissect their similarities and differences, we here generated a novel estrogen-dependent cell model where ER alpha homodimers can be directly compared to ER beta homodimers within the identical cellular context. By using CRISPR-cas9 to delete ER alpha in breast cancer MCF7 cells with Tet-Off-inducible ER beta expression, we generated MCF7 cells that express ER beta but not ER alpha. MCF7 (ER beta only) cells exhibited regulation of estrogen-responsive targets in a ligand-dependent manner. We demonstrated that either ER was required for MCF7 proliferation, but while E2 increased proliferation via ER alpha, it reduced proliferation through a G2/M arrest via ER beta. The two ERs also impacted migration differently. In absence of ligand, ER beta increased migration, but upon E2 treatment, ER beta reduced migration. E2 via ER alpha, on the other hand, had no significant impact on migration. RNA sequencing revealed that E2 regulated a transcriptome of around 800 genes via each receptor, but over half were specific for either ER alpha or ER beta (417 and 503 genes, respectively). Functional gene ontology enrichment analysis reinforced that E2 regulated cell proliferation in opposite directions depending on the ER, and that ER beta specifically impacted extracellular matrix organization. We corroborated that ER beta bound to cis-regulatory chromatin of its unique proposed migration-related direct targets ANXA9 and TFAP2C. In conclusion, we demonstrate that within the same cellular context, the two ERs regulate cell proliferation in the opposite manner, impact migration differently, and each receptor also regulates a distinct set of target genes in response to E2. The developed cell model provides a novel and valuable resource to further complement the mechanistic understanding of the two different ER isoforms.
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