Abstract P6-12-03: Proinflammatory and estrogen signaling modulates the chemoresistance and metastasis of breast cancer cells through post-translational modifications of pioneering factor FOXA1

Abstract

Abstract ER-positive breast cancers compose most breast cancers at the time of diagnosis and are primarily driven by mitogenic estrogen signaling. In ER-positive breast cancers, the pioneer transcription factor FOXA1 plays a critical role in the estrogen receptor (ER) function. It binds to condensed chromatin and promotes chromatin accessibility for subsequent ER binding upon estrogen stimulation. We have reported that TNFa-stimulated proinflammatory signaling relocates FOXA1 to a new set of latent enhancers, which initiates the binding of estrogen liganded ER and subsequent expression of a unique transcriptome with clinical significance. The redistribution of FOXA1 occurs within 40 mins of the TNFa treatment, which implies a rapid signaling cascade that arises from changes to either FOXA1’s post-translational modifications (PTMs) or its binding partners. To understand this genomic redistribution of FOXA1, we compared the post-translational modifications (PTMs) of FOXA1 from Vehicle, E2, TNFa, and E2+TNFa treated MCF-7 breast cancer cells. More than five acetylation and phosphorylation events have been identified around the DNA binding domain of FOXA1 by semi-quantitative and quantitative mass spectrometry approaches, and their abundance varies across treatments. To study these PTMs of FOXA1, we used CRISPR/Cas9 to create specific knock-in mutations to mimic or prevent acetylation events in MCF-7 cells. Specifically, we engineered MCF-7 cell lines where K270 was mutated to glutamine (K270Q) to mimic acetylation. And for comparison, we also created cell lines where K270 was mutated to arginine (K270R) to prevent acetylation of FOXA1. Our data, including FOXA1 ChIP-seq and RNA-seq, revealed the genomic redistribution of FOXA1 with these PTMs, which subsequently alters gene expression programs and promotes cell growth, migration, or chemoresistance. These results were confirmed in other ER+ cell lines (such as T47D cells) providing evidence for the generalizability of our findings. Taken together, our data suggest that inflammatory signaling signaling can reshape the enhancer landscape of FOXA1 through post-translational modifications, resulting in changes to estrogen signaling that have profound effects on breast cancer biology. Citation Format: Shen Li, Hector L. Franco, Hyunsoo Kim, Rosemary N. Plagens, Raul Mendez-Giraldez, Colby Tubbs, Venkat Malladi, Joseph Garay. Proinflammatory and estrogen signaling modulates the chemoresistance and metastasis of breast cancer cells through post-translational modifications of pioneering factor FOXA1 [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-12-03.