Grubraw, a chemogenetic mitochondrial activator, reveals new mechanisms underlying the Warburg effect

Abstract

Upregulation of glycolysis and downregulation of mitochondrial oxidative phosphorylation, termed as the Warburg effect, are characteristic of tumor cells1,2. Restriction of pyruvate flux into the mitochondrial matrix is one of the major mechanisms underlying this phenomenon3. Warburg-type metabolism is beneficial for rapidly proliferating cells, however its function remains unclear. Moreover, it is unknown what the metabolic consequences of activation of mitochondrial respiration in Warburg-type cancer cells are. Here we created a chemogenetic instrument, Grubraw, that generates pyruvate directly in the mitochondrial matrix bypassing restricted pyruvate influx. In cancer cells, Grubraw-driven pyruvate synthesis in the matrix increased mitochondrial membrane potential, oxygen consumption rate, and the amounts of TCA cycle intermediates. In a mouse model of human melanoma xenografts, chemogenetic activation of mitochondria caused a decrease in tumor growth rate. Surprisingly, cancer cells actively exported pyruvate generated by Grubraw in the mitochondria into the extracellular medium. In addition, activation of mitochondria induced downregulation of transcription of the genes that drive cell cycle progression, cell proliferation and DNA replication. Our results demonstrate that cells with Warburg-type metabolism use previously unknown mechanisms of carbon flux control to dispose of excessive mitochondrial pyruvate, and activation of mitochondria in these cells downregulates cellular proliferation.