| Popis: |
Two estrogen receptors exist, ERα and ERβ. ERα is often over-expressed in breast cancers, frequently coupled with ERβ downregulation. The complex function of ERβ is not fully understood. There are 5 ERβ isoforms, ERβ1-5, and three are present in breast tissue (ERβ1, -2 and -5). Knowledge surrounding the role of the ERβ2 in breast cancer is limited; however its cellular location has been demonstrated to have predictive prognostic ability; nuclear expression was associated with better prognosis and cytoplasmic with poorer prognosis. Aside from acting as a repressor of ERα in breast cancer cells, little is known about the function of ERβ2. The aim of this thesis was to improve our understanding of ERβ2 and its potential role in breast cancer. ERβ2 expression was characterised in a range of breast cancer cell lines representative of five major molecular subgroups where it was expressed in both the nucleus and cytoplasm. Nuclear ERβ2 was largely expressed in a speckled pattern while cytoplasmic ERβ2 colocalised with mitochondria in all cell lines. ERβ nuclear speckles were explored further by immunofluorescence. ERβ2 speckles did not colocalise with other known nuclear speckled proteins, including nuclear speckles, PML and cajal bodies. Speckle numbers changed in response to 4-OHT, DPN and genistein treatment but not E2, and disappeared following transcriptional or translational inhibition with actinomycin D and cyclohexamide respectively. Numbers of ERβ2 speckles decreased during G2/M phase of the cell cycle. The physiological function of ERβ2 was explored by overexpressing ERβ2 in luminal and triple negative cell lines. ERβ2 overexpression resulted in suppression of proliferation in luminal cells whereas in triple negative cells, proliferative response was cell line-dependent. Cell migration was decreased in all cell lines. ERβ2 overexpression additionally influenced gene transcription of some nuclear genes i.e. BCL-2, CDK6, S100A7 and RIP140 and also some mitochondrially transcribed genes i.e. ND1, ND2, CYB and ATP6. In summary, ERβ2 was expressed in the nucleus as speckles; dynamic structures which changed in number in response to external stimuli. Cytoplasmically expressed ERβ2 colocalised with the mitochondria may influence transcription of some mitochondrial genes. |
