title: Evidence for Pipecolate Oxidase in Mediating Protection Against Hydrogen Peroxide Stress.
abstract: Pipecolate, an intermediate of the lysine catabolic pathway, is oxidized to Δ1-piperideine-6-carboxylate (P6C) by the flavoenzyme l-pipecolate oxidase (PIPOX). P6C spontaneously hydrolyzes to generate α-aminoadipate semialdehyde, which is then converted into α-aminoadipate acid by α-aminoadipatesemialdehyde dehydrogenase. l-pipecolate was previously reported to protect mammalian cells against oxidative stress. Here, we examined whether PIPOX is involved in the mechanism of pipecolate stress protection. Knockdown of PIPOX by small interference RNA abolished pipecolate protection against hydrogen peroxide-induced cell death in HEK293 cells suggesting a critical role for PIPOX. Subcellular fractionation analysis showed that PIPOX is localized in the mitochondria of HEK293 cells consistent with its role in lysine catabolism. Signaling pathways potentially involved in pipecolate protection were explored by treating cells with small molecule inhibitors. Inhibition of both mTORC1 and mTORC2 kinase complexes or inhibition of Akt kinase alone blocked pipecolate protection suggesting the involvement of these signaling pathways. Phosphorylation of the Akt downstream target, forkhead transcription factor O3 (FoxO3), was also significantly increased in cells treated with pipecolate, further implicating Akt in the protective mechanism and revealing FoxO3 inhibition as a potentially key step. The results presented here demonstrate that pipecolate metabolism can influence cell signaling during oxidative stress to promote cell survival and suggest that the mechanism of pipecolate protection parallels that of proline, which is also metabolized in the mitochondria. J. Cell. Biochem. 118: 1678-1688, 2017. © 2016 Wiley Periodicals, Inc.
authors.affiliation: Department of Biochemistry and Redox Biology Center, University of Nebraska-Lincoln, Lincoln, Nebraska, 68588.|Department of Nutrition and Health Sciences, University of Nebraska-Lincoln, Lincoln, Nebraska, 68583.
authors.forename: Sathish Kumar
authors.initials: SK
authors.lastname: Natarajan
authors.affiliation: Department of Nutrition and Health Sciences, University of Nebraska-Lincoln, Lincoln, Nebraska, 68583.
authors.forename: Ezhumalai
authors.initials: E
authors.lastname: Muthukrishnan
authors.affiliation: Department of Biochemistry and Redox Biology Center, University of Nebraska-Lincoln, Lincoln, Nebraska, 68588.
authors.forename: Oleh
authors.initials: O
authors.lastname: Khalimonchuk
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, Nebraska, 68198.
authors.forename: Justin L
authors.initials: JL
authors.lastname: Mott
authors.affiliation: Department of Biochemistry and Redox Biology Center, University of Nebraska-Lincoln, Lincoln, Nebraska, 68588.
authors.forename: Donald F
authors.initials: DF
authors.lastname: Becker
mesh_terms: D002470:Cell Survival / Q000502:physiology; D000071316:Forkhead Box Protein O3 / Q000235:genetics / Q000378:metabolism; D005954:Glucosephosphate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D009249:NADP / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects; D000587:Oxidoreductases Acting on CH-NH Group Donors / Q000235:genetics / Q000378:metabolism*; D010427:Pentose Phosphate Pathway; D010875:Pipecolic Acids / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D050879:Sarcosine Oxidase / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism
chemical_list: D000071316:Forkhead Box Protein O3; D010875:Pipecolic Acids; D034741:RNA, Small Interfering; D009249:NADP; D006861:Hydrogen Peroxide; D005954:Glucosephosphate Dehydrogenase; D000587:Oxidoreductases Acting on CH-NH Group Donors; C494349:PIPOX protein, human; D050879:Sarcosine Oxidase; C032771:L-pipecolate dehydrogenase; C546842:MTOR protein, human; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; C031345:pipecolic acid
keywords: AMINO ACID METABOLISM; MITOCHONDRIA; OXIDATIVE STRESS; PIPECOLATE; PIPECOLATE OXIDASE