Abstract 4744: Epigenetic reprogramming induced by lipids fosters mammary cell plasticity in non-transformed breast epithelial cells
Authors: Eduardo Mariana Bustamante , Cottone Gannon , Liu Shiyu , Khan Seema , Clare Susan 
Published: June 2023

Abstract
Introduction. Lipid exposure of non-transformed breast epithelial cells results in increased flux modifications, and profound changes in gene expression. The upregulated genes are involved in stemness, neural development, and neural crest pathways. Neural genes are highly expressed in an estrogen receptor negative breast cancer (ERnegBC): the triple negative subtype. We aim to identify mechanisms that link lipids and epigenetic reprogramming to the genesis of ERnegBC.
Methods. Non-transformed MCF-10A cells exposed to octanoic acid (OA) were utilized for U13C-glucose tracing. S-adenosylmethionine (SAM), 2-HG and other metabolites were analyzed following treatment with OA ± PHGDH inhibitor. CUT&RUN for H3K4me3 and H3K27me3 was performed, and genes affected by OA (PMID: 28263391) were compared with OA-responsive peaks. OA-induced genes with CUT&RUN peaks were measured in breast organoids derived from reduction mammoplasty samples exposed to OA. The Aldefluour assay was used to identify stem-like (ALDH+) cells.
Results. U13C-glucose tracing in presence of OA showed decreased glucose uptake, glycolysis and pentose phosphate pathway flux, with little effect on the TCA cycle. One-carbon (1C)-THF was redirected to the methionine cycle increasing flux to methylation. The methyl donor SAM and the demethylase inhibitor 2-HG increased after 15- and 30-min OA exposure, respectively; PHGDH inhibitor blocked these increases likely via effects on 1C metabolism. H3K4me3 CUT&RUN revealed 661 differential peaks (FDR &lt; 0.05) comparing OA to control. The genes associated with these peaks are involved in neuron differentiation, neural crest, EMT and neural genes expressed in ERnegBC. 73% of H3K4me3 OA-associated peaks were in regulatory regions of OA-induced genes (FDR &lt; 0.01), including NGFR (log2FC = 11.7), NGF (log2FC = 8), NTRK1 (log2FC = 2.1). OA-induced genes with enriched H3K4me3 peaks were also upregulated in breast organoids exposed to OA, such as NGFR (FC = 2.2), NGF (FC = 4.7), NTRK1 (FC = 6.6). Motif analysis revealed an overrepresentation of transcription factors (p &lt; 0.05) associated with EMT (Zeb1, Slug), neural functions (E2A, AP1, JunB), neuronal-injury (Atf3) and stress response (Chop, Atf4). Twelve H3K27me3 peaks were enriched in control (FDR &lt; 0.05) and associated with increased gene expression in OA, among them were LGR6 (log2FC = 1.9), a gene associated with ERnegBC and PLAG1 (log2FC = 2.8) a stem cell marker. ALDH+ cells’ percentage increased by at least 10% after OA exposure.
Conclusions. Lipid exposure affects the production of SAM and 2-HG, which results in epigenetic fostered plasticity, leading to reprogramming/selecting cells with a multi-potential embryonic or stem-like state and/or differentiation to a neural/neural crest-like state which may facilitate ERnegBC genesis.
Citation Format: Mariana Bustamante Eduardo, Gannon Cottone, Shiyu Liu, Seema Khan, Susan Clare. Epigenetic reprogramming induced by lipids fosters mammary cell plasticity in non-transformed breast epithelial cells. [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 4744.