Abstract
Obesity, a major risk factor for colorectal cancer (CRC), has been shown to promote the upregulation of estrogens, oxysterols such as 27-hydroxycholesterol (27-OHC), and insulin-like growth factors (IGFs) in vivo. Epidemiological data, however, suggest that hormone replacement therapy (HRT) provides a protective effect against CRC and reduces CRC-related mortality, particularly in postmenopausal women, indicating a beneficial role of estrogen. Estrogen and 27-OHC signal through two nuclear receptors-estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ)-as well as the seven-transmembrane G-protein-coupled receptor GPER1, with ERβ being the predominant receptor in the colon. The goal of this study was to elucidate the relationship between obesity, estrogen receptors, and CRC.This PhD thesis demonstrated the inhibitory effects of estradiol (E2) and 27-OHC on CRC, as shown by tritiated thymidine incorporation and transwell migration assays. A reduction in insulin like growth factor binding protein-5 (IGFBP5) levels was detected via western blotting, though the expression of ERβ did not show consistent changes upon treatment with E2 or 27-OHC in colon cancer cells. Notably, silencing ERβ inhibited cell proliferation and invasion. ERβ may partially mediate the inhibitory effects of E2 and 27-OHC on colon cancer growth. Alternatively, the observed effects of E2 and 27-OHC treatment may involve additional mechanisms beyond ERβ activity. The regulatory role of ERβ in IGFBP5 expression was identified through TCGA analysis, qRT-PCR, immunoprecipitation, immunofluorescence, and Western blotting. Silencing ERβ resulted in a more pronounced decrease in IGFBP5 levels in response to E2 and 27-OHC, and evidence of a physical interaction between ERβ and IGFBP5 was observed. Although survival analyses did not indicate a significant role for ERβ, high IGFBP5 expression was associated with reduced survival in CRC patients, suggesting that IGFBP5 could serve as a prognostic marker. Moreover, a strong positive correlation between IGFBP5 and epithelial-mesenchymal transition (EMT) markers was identified. Short-term treatment (15 minutes) with E2 and 27-OHC led to reduced cell proliferation, indicating that GPER1, rather than the nuclear receptor ERβ, may be the primary mediator of these effects in colon cell lines. Mechanistic studies involving qRT-PCR, RNA sequencing, calcium signalling, and cAMP analyses revealed that GPER1 may play a central role in linking obesity to CRC.
In summary, this thesis highlights the prognostic significance of IGFBP5, the protective role of ERβ silencing, and the potential of GPER1 as a therapeutic target in CRC. These findings provide valuable insights into the interplay between estrogen signalling, cholesterol metabolism, and CRC progression, while also proposing directions for future research into their potential clinical applications.
| Date of Award | 4 Feb 2025 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Kalina Biernacka (Supervisor), Rachel M Barker (Supervisor) & Claire M Perks (Supervisor) |