Metabolic and epigenetic reprogramming are two key hallmarks of cancer. Rapidly proliferating cancer cells often exhibit a higher and differentially reprogrammed transcriptional activity than normal cells of the same tissue. To support transcriptional reprogramming and increased transcriptional load, sustained chromatin acetylation is required to loosen the chromatin and enable RNA transcription. Histone acetylation also requires a constant supply of acetyl-CoA, a labile, membrane impermeable metabolite that is the obligatory donor of the acetyl groups for histone acetylation. However, the pathways responsible for increased synthesis of acetyl-CoA inside the nucleus remain largely elusive. Using estrogen-responsive (MCF7) and their matched endocrine therapy resistant breast cancer cells (LCC9 and MCF7:5C), we show that blocking p300-mediated acetyltransferase activity is crucial for proliferation of endocrine therapy-resistant breast cancer cells. Furthermore, we found nuclear expression of two acetyl-CoA producing enzymes, i.e., pyruvate dehydrogenase complex (PDC), and ATP citrate lyase (ACLY), which implies their functional role inside the nucleus. PDC is a multimeric protein complex enzyme made up of five different subunits. Canonically, PDC is found in mitochondria and is responsible for the conversion of pyruvate to acetyl-CoA, linking glycolysis to the tricarboxylic acid (TCA) cycle. Our results show that multiple PDC enzyme subunits, e.g., pyruvate dehydrogenase (PDH) E1 alpha (E1 alpha), dihydrolipoal dehydrogenase (DLD), and PDHX (also known as E3BP) are expressed in the nucleus of MCF7, LCC9 and MCF7:5C cells. Moreover, expression of nuclear DLD and PDHX subunit is higher in endocrine resistant cells (LCC9 and MCF7:5C) than in their parental MCF7 cells, strongly suggesting a possible role in endocrine resistance. Notably, high expression of PDHX is correlated with poor relapse-free survival in estrogen-receptor positive breast cancer patients in four independent publicly available datasets. ACLY is a tetramer of identical subunits catalyzes conversion of citric acid and co-enzyme A to acetyl-CoA. ACLY is also overexpressed in the nucleus of endocrine-resistant breast cancer cells (LCC9 and MCF7:5C) when compared with their endocrine sensitive MCF7 controls. This study investigates the role of nuclear PDC and ACLY mediated acetyl-CoA synthesis and its impact on histone acetylation enabling reprogrammed transcriptional activity supporting proliferation of endocrine therapy-resistant breast cancer cells.
Citation Format: Surojeet Sengupta, Shuait Nair, Lu Jin, Catherine M Sevigny, Brandon Jones, Robert Clarke. Nuclear expression of acetyl-CoA producing enzymes and their roles in epigenetic reprogramming in breast cancer cells [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 PS17-50.