Abstract
Most tumor cells exhibit a glycolytic phenotype. Thus, inhibition of glycolysis might be of therapeutic value in antitumor treatment. Among the agents that can suppress glycolysis is citrate, a member of the Krebs cycle and an inhibitor of phosphofructokinase. Here, we show that citrate can trigger cell death in multiple cancer cell lines. The lethal effect of citrate was found to be related to the activation of apical caspases-8 and -2, rather than to the inhibition of cellular energy metabolism. Hence, increasing concentrations of citrate induced characteristic manifestations of apoptosis, such as caspase-3 activation, and poly-ADP-ribose polymerase cleavage, as well as the release of cytochrome c. Apoptosis induction did not involve the receptor-mediated pathway, since the processing of caspase-8 was not attenuated in cells deficient in Fas-associated protein with Death Domain. We propose that the activation of apical caspases by citrate could be explained by its kosmotropic properties. Caspase-8 is activated by proximity-induced dimerization, which might be facilitated by citrate through the stabilization of intermolecular interactions between the proteins.
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Acknowledgments
The authors thank Prof. Marie Henriksson and Dr. John Inge Johnsen (Karolinska Institutet, Sweden) for providing cell lines used in the study and Prof. Peter Krammer and Dr. Inna Lavrik (DKFZ, Heidelberg, Germany) for the caspase-8 antibody. We are indebted to Dr. Magnus Olsson for the caspase-2 shRNA construct and Dr. Vitaliy Kaminskyy for his help in conducting experiments and fruitful discussions. The work was supported by grants from the Swedish Research Council, the Swedish and the Stockholm Cancer Societies, the Swedish Childhood Cancer Foundation, the EC FP-6 (Chemores), the Russian Ministry of High Education and Science (11.G34.31.0006), and the EC FP7 (Apo-Sys) programs.
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Kruspig, B., Nilchian, A., Orrenius, S. et al. Citrate kills tumor cells through activation of apical caspases. Cell. Mol. Life Sci. 69, 4229–4237 (2012). https://doi.org/10.1007/s00018-012-1166-3
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DOI: https://doi.org/10.1007/s00018-012-1166-3