Abstract PR03: Exploring the link between Kras and histone acetylation

Abstract

Abstract KRAS mutations in pancreatic ductal adenocarcinoma (PDAC) have been shown to extensively rewire cellular metabolism to promote macromolecular biosynthesis and maintain redox homeostasis. Recently, compelling evidence has emerged demonstrating that many epigenetic modifications are sensitive to the availability of cellular metabolites. For example, acetyl-CoA is the donor substrate for lysine acetylation, and histone acetylation is responsive to levels of acetyl-CoA, which is produced largely from glucose metabolism. We thus hypothesized that oncogenic metabolic reprogramming alters metabolite levels in a way that impacts the epigenome and could thus contribute to tumorigenesis. Indeed, we find that oncogenic Akt activation promotes elevated histone acetylation, and that this effect is mediated by ATP-citrate-lyase (ACLY), a nucleocytoplasmic enzyme that converts glucose-derived citrate into acetyl-CoA. In order to understand what cellular processes are affected by such AKT-ACLY-mediated increase in histone acetylation, we employed a mouse model of pancreatic ductal adenocarcinoma, driven by oncogenic Kras (Pdx1-Cre; LSL-KrasG12D; TP53L/+). In this model, the PI3K/Akt pathway is activated downstream of Kras. By immunohistochemistry we found that, in mice with WT Kras, pancreatic acinar cells exhibit very low levels of histone H4 (K5/8/12/16) acetylation (AcH4), although AcH4 is clearly detectable in ductal epithelial cells and islets. By contrast, in mice expressing oncogenic Kras in the pancreas (LSL-KrasG12D; p53L/+; Pdx1-Cre), acinar H4 acetylation is dramatically increased. Remarkably, this overt increase in histone acetylation precedes the appearance of histological abnormalities and persists during several steps in tumor progression. Moreover, Kras and Akt-dependent reuglation of histone acetylation levels can be recapitulated in ex vivo acinar cell culture, suggesting that this is a primary effect of oncogene activation in these cells. Akt inhibition also significantly reduced glucose consumption and phosphorylation of ACLY and ultimately decreased acetyl-CoA levels. Akt inhibition in vitro reduces Kras-induced acinar cell hyperacetylation and block acinar-to-ductal metaplasia, an initiating event of pancreatic carcinoma. Our data indicate that Akt orchestrates a metabolic rewiring in pancreatic tumorigenesis, which promotes histone hyperacetylation, a phenotype evident before the manifestation of the disease and that might conceivably contribute to cell plasticity and tumor progression. Citation Format: Alessandro Carrer, Joyce V. Lee, Supriya Shah, Nicole M. Aiello, Nathaniel W. Snyder, Andrew J. Worth, Ian A. Blair, Ben Z. Stanger, Kathryn E. Wellen. Exploring the link between Kras and histone acetylation. [abstract]. In: Proceedings of the AACR Special Conference on Chromatin and Epigenetics in Cancer; Sep 24-27, 2015; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2016;76(2 Suppl):Abstract nr PR03.