Non-invasive imaging of estrogen receptor-coregulator interaction by luciferase fragment complementation

• Main Author: Lake, Madryn
• Other Authors: Nguyen, Quang-De ; Ali, Simak ; Aboagye, Eric
• Published: Imperial College London 2012
• Subjects: 616.99449
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.551101

Breast cancer is the most common cancer in the UK and approximately 1 in 8 women will be affected by the disease. Estrogen regulates breast cancer growth through the action of the estrogen receptors ERα and ERβ. Antiestrogens, in particular tamoxifen, have contributed greatly to the reduction in breast cancer mortality. Tamoxifen is a tissue selective antiestrogen; it is antiestrogenic in the breast but estrogenic in other tissues, thereby enabling it to promote the beneficial effects of estrogen, such as maintaining bone density. However, like estrogen, tamoxifen also promotes endometrial cancer, so there is an impetus for the development of novel tissue selective ERα ligands. Regulation of gene expression by the estrogen receptors requires the ligand-regulated recruitment of transcription coregulator proteins. In breast cancer ERα-coactivator interactions are associated with tumour progression while ERα-corepressor interactions are associated with receptor antagonism and a therapeutic block of ERα signalling. This thesis details the development of a luciferase fragment complementation assay to image the interaction of ERα with the coactivator AIB1 and corepressor SMRT. It is hoped that elucidation of these interactions will enable a greater appreciation of the tissue selective actions of ERα ligands and aid in the screening of novel ERα antagonists. By means of complimentary luciferase fragment fusion proteins, it is shown that ligand dependent ERα-coregulator interaction can be imaged in vitro and in vivo. ERα and AIB1 luciferase fusion proteins indicate an E2 induced increase in luciferase fragment complementation which is modulated by antiestrogens. The complementation observed correlates with ERα transcriptional activity and the specificity has been further validated by ERα fusion protein mutants. Consistent with the notion that the ERα-SMRT interaction is characteristic of ERα antagonism, ERα and SMRT fusion proteins show increased luciferase fragment complementation with antiestrogens compared with estrogen.