LAUSR

Breast and prostate cancer are the leading cancer diagnoses for women and men, respectively, second only to cutaneous cancers. Breast and prostate cancer arise from aberrant estrogen/estrogen receptor (ER) and testosterone/androgen receptor signaling (AR), respectively. These sex hormone receptors are members of the steroid hormone receptor family, which also includes the glucocorticoid receptor (GR), mineralocorticoid receptor (MR), and progesterone receptor (PR). Although these receptors canonically function through homodimerization, recent evidence has suggested that receptor crosstalk can amplify or dampen the actions of heterologous receptors. However, these interactions have not been extensively studied in all possible combinations of steroid hormone receptor crosstalk. In this project, we hypothesize that heterodimerization may amplify or repress the transcriptional response(s) elicited by the various receptor complexes depending upon conditions such as concentration of ligands, type of ligand, physiological states, and the types/functions of promoter regions. To test this hypothesis, we investigated the significance of ligand-induced interactions between different homo- and heterodimer combinations of AR, ARV7, GR, MR, PR, and ERα in HEK293 cells using IncuCyte live-cell imaging and NanoBRET technology. Ultimately, the combination of transfection experiments, live-cell imaging, and NanoBRET assays provided insight into which combination of steroid receptors successfully interact to amplify (or dampen) the HaloTag expression, luminescence intensity at 450nM (i.e., NanoLuc expression), and NanoBRET ratio (i.e., acceptor emission luminescence at 610nM divided by donor emission luminescence at 450nM) in HEK293 cells. Our studies revealed that heterodimerization of ERα-PR, ERα-MR, AR-GR, AR-PR, ARV7-MR, ARV7-PR, and GR-MR produced significant ligand-induced changes in signaling intensity compared to no ligand conditions for each fusion protein construct. Additionally, to demonstrate the value of the NanoBRET method for modelling clinically relevant disease conditions, we assessed the physical interaction of ERα and PR in the context of the ERα Y537S mutation - a mutation associated with endocrine therapy resistance in breast cancer that results in a constitutively active ERα. The results showed that ERα-Y537S mutation increases ERα/PR physical interaction upon PR-B stimulation in a NanoBRET proximity-based assay. Future directions include testing these interactions in breast and prostate cancer cell lines and identifying the receptors’ localization within the cell, the results of which may be of clinical importance. Citation Format: Amira Ishag-Osman, David Hosfield, Rosemary Huggins, Geoffrey Greene. Evaluating nuclear receptor heterodimerization using live cell proximity assays: Implications for novel therapeutic approaches for hormone driven cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3439.