RF03 | PMON297 Connecting Fluctuations in Estrogen Production, Release, and Action with Hormone-Dependent Gene Expression in Breast Cancers

Abstract

Abstract Estrogens are steroid hormones that play a key role in a wide range of physiological and pathological processes. Estrogen receptor-alpha, ERɑ, functions primarily as a nuclear transcription factor (TF) through ligand-dependent activation by 17β-estradiol (E2), the predominant naturally-occurring estrogen. This results in dimerization, DNA binding to cis-regulatory elements called enhancers, and gene regulatory function of ERɑ. In vivo, E2 production and action fluctuates during reproductive cycles and possibly even in a circadian manner. In tissues and cells, E2-regulated gene expression is dynamic, with rapid induction of enhancer formation and target gene expression (or repression), followed by enhancer "decommissioning" and cessation of the gene regulatory effects. The effects of sustained E2 production and signaling, fluctuations in E2 levels, and removal of E2 on estrogen-regulated gene expression are unknown. Classical experiments exploring the gene regulatory effects of E2 involve stimulation of cultured cells throughout the duration of the experiment with a continuous dose of hormone, with the cells harvested at the end of the stimulation period. While this has allowed us to understand the molecular underpinnings of signal-dependent transcription, it has not allowed analysis of physiological fluctuations in estrogen signaling involving periods of stimulation and non-stimulation. In our studies, we are applying a combination of next generation sequencing techniques and fluorescence microscopy to investigate signal-dependent responses to fluctuating E2 levels using ERɑ-positive MCF-7 human breast cancer cells after E2 treatment and removal. Our initial results suggest that different E2 target genes respond differently to E2 withdrawal. Moreover, for some E2 traget genes, sustained E2 treatment may not be required for a complete E2 transcriptional response. With these studies, we hope to connect physiological aspects of E2 production, release, and action with the molecular mechanisms of E2-dependent gene expression - an aspect of our understanding of estrogen signaling that has been lacking. This work is supported by grants from the NIH/NIDDK (DK058110) and CPRIT (RP160319) to W.L.K. Presentation: Saturday, June 11, 2022 1:12 p.m. - 1:17 p.m., Monday, June 13, 2022 12:30 p.m. - 2:30 p.m.