Abstract 1119: The oxidation of proline by proline oxidase provides a regulated source of ROS for mitochondria derived cellular signaling

Abstract

Abstract A role for reactive oxygen species (ROS) in intracellular signaling has been generally accepted, but the organellar localization, the enzymatic source and the regulation of ROS generation are not well understood. Recent work by others has focused on mitochondria as a source of ROS and specifically on the reduction of oxygen by electrons from complex III to form superoxide. The accessibility of complex III to the mitochondrial intermembrane space and cytosol provides an attractive hypothesis for mitochondrial ROS as regulators of cellular redox signaling. We now report that the regulated metabolism of proline makes it a special substrate for this process. Proline oxidase (POX) is an inner mitochondrial membrane protein that oxidizes proline to generate superoxide as well as ATP. Work in our laboratory has documented that POX activity is highly regulated during genotoxic and metabolic stress. Inducers of POX include p53, and proline-dependent ROS play a role in mitochondrial apoptosis. PPAR-γ and its ligands also induce POX but depending on the metabolic context, POX initiates autophagy as well as apoptosis. Mechanistic models for ROS generation by POX have come from microorganisms. PutA, the prokaryotic homolog of POX can generate ROS by electrons reducing oxygen directly from its catalytic center. On the other hand, in S. cerevisiae, the POX homolog, Put1, has been shown to directly interact with ubiquinone, thereby contributing electrons derived from proline oxidation into the electron transport chain. In this work, we now report that human POX interacts directly with ubiquinone and that POX activity is markedly increased by the presence of ubiquinone. In addition, by using selective inhibitors of electron transport, we demonstrate that electrons derived from proline can be converted to superoxide by complex III of the electron transport chain. These radicals are directed into both the mitochondrial matrix as well as into the intermembrane space and the cytosol. Thus, POX is not only specifically regulated but also specially located and coupled to the mitochondrial electron transport chain to mediate ROS signaling. These POX- mediated mechanisms provide important insights into its novel apoptotic and metabolic tumor suppressive functions. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1119. doi:1538-7445.AM2012-1119