Abstract LB-312: The regulation of lactate metabolism in the context of EMT of breast cancer cell lines

Lactate is both a metabolite of glycolysis, and a component of several signaling pathways. In recent years, there has been an increased interest in tumor lactate metabolism and signaling, with several studies indicating that lactate is a critical regulator of cancer development. Indeed, tumor lactate levels correlate with increased metastasis, tumor recurrence, and poor overall survival of cancer patients. This recent interest in lactate metabolism has been exclusively studied in the context of neoplastic transformation per se. However, little is known about shifts in lactate metabolism in the context of metastatic transformation that confers increased motility and invasiveness on cancer cells. Epithelial-Mesenchymal transition (EMT) has been proposed as a mechanism involved in the early stage of metastasis. EMT is a physiological process during embryogenesis, but is also activated in some epithelial-derived cancers. EMT reduces cell-cell contacts and incrases the motility and invasiveness of cancer cells. Previously our lab reported that prolonged mammosphere culture induced EMT in two epithelial breast cancer cell lines, MCF-7 and BT-474 cells. This generated the respective mesenchymal types, MCF-7EMT and BT-474EMT. This study has examined whether shifts in lactate metabolism occur during EMT, using these four cell lines. All cells were cultured in a 3-dimensional Matrigel matrix with modified medium that contains glucose, glutamine, pyruvate and lactate at physiological concentrations in order to more accurately mimic the tumor microenvironment than standarad 2-dimensional cell culture conditions. We observed that EMT-induced MCF-7EMT and BT-474EMT exhibit higher glycolytic rates and export more lactate compared to their respective parental epithelial cell lines. Moreover, EMT-induced MCF-7EMT and BT-474EMT cells display altered expression of lactate-related genes. In particular, both the endogenous lactate receptor, GPR81, and the lactate importer, MCT1, are highly expressed in epithelial MCF-7 and BT-474 cells, but are suppressed in post-EMT mesenchymal MCF7EMT and BT474EMT cells. Additionally, the knockdown of GPR81 in epithelial MCF-7 and BT-474 cell lines significantly reduced the expression of MCT1. NMR analysis of cytoplasmic extracts revealed that intracellular lactate levels are significantly higher in the epithelial MCF7 cells vs. the corresponding mesenchymal MCF7EMT cells. The role of GPR81 in cellular lactate balance and cell proliferation was examined by siRNA approach. GPR81 knockdown significantly decreased MCT1 and intracellular lactate, as well as cell proliferation in both epithelial MCF7 and BT474 cells. Interestingly, we found that β-estradiol (E2) treatment of MCF7 cells up-regulates MCT1 expression, whereas Tamoxifen treatment suppresses MCT1 expression. These hormonal effects link the ability of E2 and Tamoxifen to stimulate or inhibit, respectively, cell proliferation through their actions on MCT1-mediated lactate import. Further study will examine whether changes in intracellular lactate levels feedback on either GPR81 and/or MCT1. Citation Format: Denisse G. Tafur, Bruce A. White. The regulation of lactate metabolism in the context of EMT of breast cancer cell lines. [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 LB-312.