Elucidation of the mechanisms by which cells recognize and respond to different levels of androgens

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An unanswered fundamental question in andrology is how cells recognize and respond in a different manner to different levels of physiological and synthetic androgens. It is assumed that since androgens differ primarily in their relative binding affinity for the androgen receptor (AR) that they are distinguished by how well they enable the formation of similar receptor-coregulator complexes and that this manifests as a quantitative continuum of the same responses. However, leveraging compelling new data we propose the alternate, albeit not mutually exclusive, possibility that androgen dose regulates the relative abundance of AR monomers and dimers in cells and that these forms of the receptor have different coregulator binding preferences resulting in different biological outputs. Indeed, using in vitro systems that model exposure from castrate (low dose; LD) to eugonadal levels and above (high dose; HD), we have determined that the global changes in chromatin architecture, transcription factor cistrome, and gene expression in cells are substantially different, with the changes induced by LD androgens (monomeric AR) being associated with cell proliferation and HD androgens (dimeric AR) inducing a program associated with a differentiated phenotype. A similar distinction in response to androgen levels was observed in vivo. Further, we made the surprising observation that both LD and HD androgens facilitate an AR dependent, non-genomic activation of mTOR but that the resulting translational outputs are different, such that LD but not HD androgens facilitate increased translation of mRNAs encoding key cell cycle proteins (i.e. E2F1, FOXM1). Importantly, we have identified high affinity AR ligands that do not allow receptor dimerization and have shown that their actions phenocopy those of LD androgens. Thus, by using receptor oligomerization state as a biosensor cells are able to respond differently to different levels of androgens; a process that can be exploited in the development of new AR modulators for the treatment of cancer and other androgenopathies. Hypothesis: Androgen receptor expressing cells possess biochemical mechanisms that enable them to manifest qualitatively distinct biological responses to different exposure levels of androgens enabling the same hormone to exhibit different activities in the same cell. Aims: (1) Define the mechanism(s) that enable cells to sense and respond to different levels of androgens, (2) Elucidate the mechanisms by which androgens activate mTOR and regulate mRNA translational specificity, and (3) Use small molecule-based approaches to explore the physiological and pathological importance of pathways and processes that enable cells to respond differently to different levels of androgens. Impact: In addition to probing the pharmacology of AR this study will formally test the “coregulator hypothesis” that differential engagement of functionally distinct coregulators allows the same ligand to exhibit different activities in and between cells. This will also enable the establishment of a conceptual framework that will inform the mechanisms that determine the molecular pharmacology of other ligand-regulated nuclear receptors.