Abstract PS17-40: Fatty acid metabolism at the connection of histone methylation and mammary cell plasticity
Authors: Yadav Shivangi , Virk Ranya KA , Chung Carolina H , Chandrasekaran Sriram , Backman Vadim , Khan Seema Ahsan , Clare Susan Elizabeth 
Published: February 2021

INTRODUCTION:Metabolic switching has been linked with cancer progression. We initially reported increased expression of lipids metabolism genes in the contralateral breasts of women with unilateral estrogen receptor negative (ER-) breast cancer. We then demonstrated chromatin remodeling in normal mammary epithelial cells following exposure to lipids. Metabolites from intermediate metabolism are substrates that generate chromatin modifications, connecting metabolism to epigenetics. Key to this crosstalk is the fact that the kinetic and thermodynamic properties of chromatin modification reactions are in line with the dynamic range of the physiological concentrations of the corresponding intermediates in metabolism. Since substrates for histone methylation and acetylation reactions often have cellular concentrations that are commensurate with enzyme Km values, and are sensitive and responsive to changes in metabolism, we now present evidence regarding changes in metabolic flux and cellular plasticity connecting lipid metabolism to ER- cancer progression.

Methods:MCF-10A cells were grown in the presence of medium chain fatty acid- octanoic acid (5mM) for 24 hours. RNA sequencing was performed on the treated and control cells using Illumina Next Seq 500 for 75bp single-read sequencing. Differential expression and gene set enrichment analyses were utilized to identify significantly enriched biological processes and molecular functions upon fatty acid treatment. Differential metabolic flux was determined using flux balance analysis. For proteomic analysis of post-translational histone modifications, histones were acid extracted from nuclei and LC-MS based mass spectrometry was used to quantitate the modifications and data is represented as the relative abundance in %.

Results:Transcriptome data from RNA sequencing, incorporated into the human metabolic network reconstruction, revealed a significant increase in methylation flux in octanoate treated MCF10-A cells. The treated cells showed an increase in the flux in fatty acid oxidation and one-carbon metabolism reactions. The proteomic histone modification profile showed an increase in histone methylation specifically at H3K9, H3K4, H3K27 and H3K36, which corroborates with the GSEA analysis showing a significant correlation of H3K27 methylation (NES = 2.47, q-value = 0.05), a marker of constitutive heterochromatin, in the octanoate treated phenotype. Further, RNA-Seq of octanoate treated MCF-10A cells revealed prominent upregulation of cell-fate commitment and cell differentiation pathways, specifically neural differentiation, and adenylate cyclase-activating adrenergic receptor signaling.

Conclusion:Lipids are a source of acetyl-CoA which serves as a donor for histone acetylation; our data shows that resultant increased flux through metabolic reactions produces s-adenosine methionine (SAM), an important methylating agent. These post-translational modifications have profound effects on chromatin structure, effecting changes that range from the expression of a single gene to a complete conversion of phenotype. We observe both an alteration of the molecular phenotype, as well as adenylate cyclase-activating adrenergic receptor signaling, which may be a clue to the development of ER- disease as GWAS have revealed that the adenylate cyclase-activating pathway is enriched in susceptibility to ER-negative disease.

Citation Format: Shivangi Yadav, Ranya KA Virk, Carolina H Chung, Sriram Chandrasekaran, Vadim Backman, Seema Ahsan Khan, Susan Elizabeth Clare. Fatty acid metabolism at the connection of histone methylation and mammary cell plasticity [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS17-40.