Abstract 1033: Cigarette smoke and bile acids induce metabolic reprogramming mediated by uncoupling protein-2 (UCP2) during esophageal carcinogenesis
Authors: Xu Yuan , Brown Kate , Depew Deborah R. , Feingold Paul L. , Rao Mahadev , Davis Jeremy , Schrump David S. , Ripley. R. Taylor 
Published: July 2016

Background: In cancer cells, glucose is processed not through mitochondrial respiration, but mainly through glycolysis to form lactate and minimal ATP (Warburg effect). Glutamine is an essential amino acid in cancer cells and the primary fuel for the mitochondria. Uncoupling protein 2 (UCP2) decreases mitochondrial proton membrane potential and reduces reactive oxygen species (ROS). Limited information is available regarding mechanisms that link environmental risk factors such as gastro-esophageal reflux and cigarette smoking to metabolomic alterations in esophageal adenocarcinoma (EAC). The present study was undertaken to examine the effects of cigarette smoke and bile acids on UCP2 expression, metabolic activity, and malignant phenotype of EAC cells.

Methods: Ten EAC lines were screened for UCP2 expression using qRT-PCR and immunoblot techniques. Two EAC lines, Flo-1 and NCI-SB-ESC2 (Esc2), had low and high UCP2 expression, respectively. Flo-1 and Esc2 cells were exposed to normal media with or without cigarette smoke condensate (CSC) and/or the bile acid, deoxycholic acid (DCA) for 5 days. Cell growth, migration, invasion, and clonogenicity were examined using CellTiter 96® Aqueous Kit, scratch, and soft agar clonogenicity assays. Mitochondrial respiration and glycolytic capacity were analyzed using the Seahorse Extracellular Flux Analyzer, and ATP and Lactate Production Kits. Levels of ROS were quantitated using Cellular Reactive Oxygen Species Detection Kit.

Results: Flo-1 cells had low UCP2 protein expression and large spare mitochondrial respiratory capacity, whereas Esc2 cells exhibited high UCP2 protein expression and no spare mitochondrial respiratory capacity. CSC and DCA mediated synergistic increases in lactate levels with decreases in ATP production (Warburg effect) without altering levels of UCP2 or ROS in Flo-1 cells. In contrast, similar treatment did not alter lactate or ATP production, but did synergistically deplete UCP2 and increase ROS levels in Esc2 cells. Whereas CSC and DCA exposure did not alter proliferation, migration, or invasion of Flo-1 cells, these treatments enhanced proliferation, migration, and invasion of Esc2 cells.

Conclusions: Following exposure to CSC and DCA, EAC cells can shift toward glycolysis when spare mitochondrial respiration is present. In contrast, EAC cells with maximal utilization of glycolysis have no ability to increase glycolysis with CSC or DCA exposure. However, in these cells, CSC and DCA down-regulates UCP2 and increases ROS; these metabolic effects coincide with increased malignant phenotype of EAC cells. These differences suggest that low levels of UCP2 may function as a metabolic sensor whereas high levels may serve as a cellular redox trigger effecting ROS. These preliminary insights into mitochondrial function may help guide the development of novel therapeutic strategies for EAC.

Citation Format: Yuan Xu, Kate Brown, Deborah R. Depew, Paul L. Feingold, Mahadev Rao, Jeremy Davis, David S. Schrump, R. Taylor Ripley. Cigarette smoke and bile acids induce metabolic reprogramming mediated by uncoupling protein-2 (UCP2) during esophageal carcinogenesis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1033.