Abstract 5257: Cancer cells have not only sweet tooth but also large mouths: Evidence for uptake of ATP into KRas oncogene-expressing cancer cells by macropinocytosis
Authors: Qian Yanrong , Wang Xuan , Liu Yi , Li Yunsheng , Colvin Robert A. , Chen Xiaozhuo 
Published: May 2015

Abstract
Cancer cells are known to exhibit reprogrammed metabolism and prefer to use glycolygsis for their ATP synthesis even when oxygen is abundant, a phenomenon called the Warburg effect. However, cancer cells are also known for more rapid growth and proliferation, therefore requiring more ATP than normal cells of the same tissues. How cancer cells manage to use low efficiency glycolysis but still meet their higher ATP demands is enigmatic. In our previous study, we found that extracellular ATP induced large intracellular ATP increase and drug resistance to tyrosine kinase inhibitors (TKIs) that function as ATP analogs / competitors in cancer cells. The induced ATP increase was from neither OXPHOS nor glycolysis, and was not dependent on AMPK, the master ATP regulator. Furthermore, the increase did not involve new gene expression or new protein synthesis. Recently, it was reported that cells transformed with an oncogenic form of KRas gene (KRas+) exhibit a phenotype of macropinocytosis, a type of endocytosis. KRas-induced macropinocytosis nonspecifically takes up extracellular proteins. All these led us to hypothesize that the increased intracellular ATP induced by extracellular ATP is, at least in part, not produced intracellularly but is transported into cancer cells. To test this hypothesis, high molecular weight fluorescent dextran was use to determine if KRas+ human non-small cell lung cancer A549 cells exhibit macropinocytosis. Nonhydrolyzable fluorescent ATP analog was used to visualize if the ATP analog can be transported into A549 cells along with dextran. Fluorescence microscopy studies revealed that A549 cells exhibit the phenotype of macropinocytosis, which can be reduced by a macropinocytosis inhibitor EIPA. HMW dextran and the nonhydrolysable fluorescent ATP analog were found co-localized inside A549 cells, demonstrating that they were transported into A549 cells via macropinosomes. It was also found that the ATP increase cannot be explained by purinergic receptor signaling alone. In comparison, KRas- human breast cancer MCF7 cells do not take up HMW dextran, indicating that they do not exhibit macropinocytosis. All these provide strong and visual evidence that ATP can be transported into KRas+ A549 cancer cells by macropinocytosis. Other experiments using radioactive ATP or purinergic receptor inhibitors also strongly support this conclusion. This is the first time that ATP (ATP analog) is shown to be taken into cancer cells. This finding will have major impact on how we view cancer cells in terms of their energy exchange with other cancer or noncancer cells in the tumor and on the Warburg effect. It will also have profound implications on how to more effectively inhibiting KRas+ or KRas- cancer cells by targeting ATP transport and ATP metabolism.
Citation Format: Yanrong Qian, Xuan Wang, Yi Liu, Yunsheng Li, Robert A. Colvin, Xiaozhuo Chen. Cancer cells have not only sweet tooth but also large mouths: Evidence for uptake of ATP into KRas oncogene-expressing cancer cells by macropinocytosis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5257. doi:10.1158/1538-7445.AM2014-5257