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      Exogenous pyruvate facilitates cancer cell adaptation to hypoxia by serving as an oxygen surrogate

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          Abstract

          Molecular oxygen is the final electron acceptor in cellular metabolism but cancer cells often become adaptive to hypoxia, which promotes resistance to chemotherapy and radiation. The reduction of endogenous glycolytic pyruvate to lactate is known as an adaptive strategy for hypoxic cells. Whether exogenous pyruvate is required for hypoxic cell proliferation by either serving as an electron acceptor or a biosynthetic substrate remains unclear. By using both hypoxic and ρ 0 cells defective in electron transfer chain, we show that exogenous pyruvate is required to sustain proliferation of both cancer and non-cancer cells that cannot utilize oxygen. Particularly, we show that absence of pyruvate led to glycolysis inhibition and AMPK activation along with decreased NAD + levels in ρ 0 cells; and exogenous pyruvate increases lactate yield, elevates NAD +/NADH ratio and suppresses AMPK activation. Knockdown of lactate dehydrogenase significantly inhibits the rescuing effects of exogenous pyruvate. In contrast, none of pyruvate-derived metabolites tested (including acetyl-CoA, α-ketoglutarate, succinate and alanine) can replace pyruvate in supporting ρ 0 cell proliferation. Knockdown of pyruvate carboxylase, pyruvate dehydrogenase and citrate synthase do not impair exogenous pyruvate to rescue ρ 0 cells. Importantly, we show that exogenous pyruvate relieves ATP insufficiency and mTOR inhibition and promotes proliferation of hypoxic cells, and that well-oxygenated cells release pyruvate, providing a potential in vivo source of pyruvate. Taken together, our data support a novel pyruvate cycle model in which oxygenated cells release pyruvate for hypoxic cells as an oxygen surrogate. The pyruvate cycle may be targeted as a new therapy of hypoxic cancers.

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          Most cited references31

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          HIFalpha targeted for VHL-mediated destruction by proline hydroxylation: implications for O2 sensing.

          HIF (hypoxia-inducible factor) is a transcription factor that plays a pivotal role in cellular adaptation to changes in oxygen availability. In the presence of oxygen, HIF is targeted for destruction by an E3 ubiquitin ligase containing the von Hippel-Lindau tumor suppressor protein (pVHL). We found that human pVHL binds to a short HIF-derived peptide when a conserved proline residue at the core of this peptide is hydroxylated. Because proline hydroxylation requires molecular oxygen and Fe(2+), this protein modification may play a key role in mammalian oxygen sensing.
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            Mitochondrial complex III is required for hypoxia-induced ROS production and cellular oxygen sensing.

            Multicellular organisms initiate adaptive responses when oxygen (O(2)) availability decreases, but the underlying mechanism of O(2) sensing remains elusive. We find that functionality of complex III of the mitochondrial electron transport chain (ETC) is required for the hypoxic stabilization of HIF-1 alpha and HIF-2 alpha and that an increase in reactive oxygen species (ROS) links this complex to HIF-alpha stabilization. Using RNAi to suppress expression of the Rieske iron-sulfur protein of complex III, hypoxia-induced HIF-1 alpha stabilization is attenuated, and ROS production, measured using a novel ROS-sensitive FRET probe, is decreased. These results demonstrate that mitochondria function as O(2) sensors and signal hypoxic HIF-1 alpha and HIF-2 alpha stabilization by releasing ROS to the cytosol.
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              A mitochondrial pyruvate carrier required for pyruvate uptake in yeast, Drosophila, and humans.

              Pyruvate constitutes a critical branch point in cellular carbon metabolism. We have identified two proteins, Mpc1 and Mpc2, as essential for mitochondrial pyruvate transport in yeast, Drosophila, and humans. Mpc1 and Mpc2 associate to form an ~150-kilodalton complex in the inner mitochondrial membrane. Yeast and Drosophila mutants lacking MPC1 display impaired pyruvate metabolism, with an accumulation of upstream metabolites and a depletion of tricarboxylic acid cycle intermediates. Loss of yeast Mpc1 results in defective mitochondrial pyruvate uptake, and silencing of MPC1 or MPC2 in mammalian cells impairs pyruvate oxidation. A point mutation in MPC1 provides resistance to a known inhibitor of the mitochondrial pyruvate carrier. Human genetic studies of three families with children suffering from lactic acidosis and hyperpyruvatemia revealed a causal locus that mapped to MPC1, changing single amino acids that are conserved throughout eukaryotes. These data demonstrate that Mpc1 and Mpc2 form an essential part of the mitochondrial pyruvate carrier.
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                Author and article information

                Journal
                Oncotarget
                Oncotarget
                Oncotarget
                ImpactJ
                Oncotarget
                Impact Journals LLC
                1949-2553
                26 July 2016
                21 June 2016
                : 7
                : 30
                : 47494-47510
                Affiliations
                1 Department of Biology, Drexel University College of Arts and Sciences, Philadelphia, Pennsylvania, USA
                2 Department of High Altitude Physiology, the Third Military Medical University, Chongqing, China
                3 Department of Pathology and Laboratory Medicine, Drexel University College of Medicine, Philadelphia, Pennsylvania, USA
                4 Department of Dermatology, Boston University School of Medicine, Boston, Massachusetts, USA
                Author notes
                Correspondence to: Nianli Sang, ns448@ 123456drexel.edu
                Article
                10202
                10.18632/oncotarget.10202
                5216956
                27374086
                4a08ebfb-afff-4d6f-a1de-79367b1cdce6
                Copyright: © 2016 Yin et al.

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 30 March 2016
                : 9 June 2016
                Categories
                Research Paper

                Oncology & Radiotherapy
                atp,hypoxia,metabolism,pyruvate,nad+
                Oncology & Radiotherapy
                atp, hypoxia, metabolism, pyruvate, nad+

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