Oxidative stress inhibits the mitochondrial import of preproteins and leads to their degradation.
The mitochondrion depends upon the import of cytosolically synthesized preproteins for most of the proteins that comprise its structural elements and metabolic pathways. Here we have examined the influence of redox conditions on mitochondrial preprotein import and processing by mammalian mitochondria. Paraquat pretreatment of isolated mitochondria inhibited the subsequent import preornithine transcarbamylase (pOTC) in vitro. In intact cells oxidizing conditions led to decreased levels of mature OTC and accumulation of its preprotein. Implicating a mitochondrial import lesion, the fluorescence of pOTC-GFP (a protein in which the presequence of pOTC was fused to green fluorescent protein) transfected cells was decreased by paraquat treatment while cytosolic wild-type GFP remained largely unaffected. The accumulation of preproteins was enhanced by proteasome inhibitors. We observed that precursor proteins that failed to be imported, due to oxidizing conditions or an intrinsically slower import rate, are susceptible to degradation. Inhibition of the proteasome was also found to lead to higher levels of the translocase outer membrane protein 20 (Tom20) and to the perinuclear accumulation of mitochondria. These studies indicate that cellular redox conditions influence mitochondrial import, which, in turn, affects mitochondrial protein levels. A role for the proteasome in this process and in general mitochondrial function was also indicated.
Wright
G
G
Department of Molecular Genetics, Kumamoto University School of Medicine, Honjo 2-2-1, Kumamoto, 860-0811, Japan.
Terada
K
K
Yano
M
M
Sergeev
I
I
Mori
M
M
D000111:Acetylcysteine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D016466:CHO Cells; D019556:COS Cells; D006224:Cricetinae; D003546:Cysteine Endopeptidases; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D019286:Endopeptidase K / Q000494:pharmacology; D049452:Green Fluorescent Proteins; D006367:HeLa Cells; D006540:Herbicides / Q000494:pharmacology; D006801:Humans; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008564:Membrane Potentials / Q000502:physiology; D008930:Mitochondria, Liver / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors; D009954:Ornithine Carbamoyltransferase / Q000235:genetics / Q000378:metabolism*; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D010100:Oxygen / Q000378:metabolism; D010269:Paraquat / Q000494:pharmacology*; D046988:Proteasome Endopeptidase Complex; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport / Q000502:physiology*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014162:Transfection
D015853:Cysteine Proteinase Inhibitors; D006540:Herbicides; D008164:Luminescent Proteins; D009097:Multienzyme Complexes; D011498:Protein Precursors; D011993:Recombinant Fusion Proteins; C067713:lactacystin; D049452:Green Fluorescent Proteins; D009954:Ornithine Carbamoyltransferase; D019286:Endopeptidase K; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D010269:Paraquat; D010100:Oxygen; D000111:Acetylcysteine