ROS-dependent localization of glycolytic enzymes to mitochondria.

Mitochondrial reactive oxygen species (mtROS) regulate cellular signaling pathways, but also cause oxidative stress when de-regulated during aging and pathological conditions such as neurodegenerative diseases. The dynamic redistribution of proteins between cellular compartments is a common mechanism to control their stability and biological activities. By targeting the BirA∗ biotin ligase to the outer mitochondrial membrane in HEK293 cells, we identified proteins whose labeling increased or decreased in response to treatment with menadione, consistent with a dynamic change in their mitochondrial localization in response to increased mtROS production. These proteins represent potential candidates for future studies of mitochondrial oxidative stress signaling. A subset of glycolytic enzymes was found in this screen and confirmed, by mitochondrial fractionation and imaging, to increase localization to mitochondria in response to menadione, despite no change in their overall abundance. Submitochondrial fractionation studies are consistent with import of a pool of these enzymes to the mitochondrial intermembrane space. Localization of glycolytic enzymes to mitochondria was also increased in cells grown under hypoxia or that express a mitochondria-targeted d-amino-acid oxidase (conditions that induce increased mtROS production), and inhibited basally under normal growth conditions by the mitochondrial antioxidant MnTBAP. Finally, primary Alzheimer's disease fibroblasts also had glycolytic enzymes associated with mitochondria that was reduced by antioxidants, consistent with increased mtROS altering their relative distribution between the cytoplasm and mitochondria. We speculate that the increased mitochondrial localization of glycolytic enzymes is an adaptive response to mtROS that alters glucose flux toward the antioxidant pentose phosphate pathway, creates distinct regulatory pools of mitochondrial metabolites or new metabolic circuits, and/or provides cytoprotection or other adaptive responses via moonlighting functions unrelated to their enzymatic activity.