title: Evidence for the Existence in Arabidopsis thaliana of the Proteasome Proteolytic Pathway: ACTIVATION IN RESPONSE TO CADMIUM.
abstract: Heavy metals are known to generate reactive oxygen species that lead to the oxidation and fragmentation of proteins, which become toxic when accumulated in the cell. In this study, we investigated the role of the proteasome during cadmium stress in the leaves of Arabidopsis thaliana plants. Using biochemical and proteomics approaches, we present the first evidence of an active proteasome pathway in plants. We identified and characterized the peptidases acting sequentially downstream from the proteasome in animal cells as follows: tripeptidyl-peptidase II, thimet oligopeptidase, and leucine aminopeptidase. We investigated the proteasome proteolytic pathway response in the leaves of 6-week-old A. thaliana plants grown hydroponically for 24, 48, and 144 h in the presence or absence of 50 mum cadmium. The gene expression and proteolytic activity of the proteasome and the different proteases of the pathway were found to be up-regulated in response to cadmium. In an in vitro assay, oxidized bovine serum albumin and lysozyme were more readily degraded in the presence of 20 S proteasome and tripeptidyl-peptidase II than their nonoxidized form, suggesting that oxidized proteins are preferentially degraded by the Arabidopsis 20 S proteasome pathway. These results show that, in response to cadmium, the 20 S proteasome proteolytic pathway is up-regulated at both RNA and activity levels in Arabidopsis leaves and may play a role in degrading oxidized proteins generated by the stress.
authors.affiliation: Laboratoires de Physiologie Cellulaire Végétale, CEA, IRTSV, UMR5168 CNRS/CEA/INRA, Université Joseph Fourier, France.
authors.forename: Cécile
authors.initials: C
authors.lastname: Polge
authors.forename: Michel
authors.initials: M
authors.lastname: Jaquinod
authors.forename: Frances
authors.initials: F
authors.lastname: Holzer
authors.forename: Jacques
authors.initials: J
authors.lastname: Bourguignon
authors.forename: Linda
authors.initials: L
authors.lastname: Walling
authors.forename: Renaud
authors.initials: R
authors.lastname: Brouquisse
mesh_terms: D000626:Aminopeptidases / Q000096:biosynthesis / Q000737:chemistry; D000818:Animals; D017360:Arabidopsis / Q000201:enzymology*; D029681:Arabidopsis Proteins / Q000096:biosynthesis* / Q000737:chemistry; D002104:Cadmium / Q000494:pharmacology*; D002417:Cattle; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases / Q000096:biosynthesis / Q000737:chemistry; D004789:Enzyme Activation / Q000187:drug effects; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects*; D009113:Muramidase / Q000737:chemistry; D018515:Plant Leaves / Q000201:enzymology*; D046988:Proteasome Endopeptidase Complex / Q000096:biosynthesis* / Q000737:chemistry; D012697:Serine Endopeptidases / Q000096:biosynthesis / Q000737:chemistry; D012710:Serum Albumin, Bovine / Q000737:chemistry; D013312:Stress, Physiological / Q000187:drug effects*; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D029681:Arabidopsis Proteins; D002104:Cadmium; D012710:Serum Albumin, Bovine; D009113:Muramidase; D000626:Aminopeptidases; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; C048001:tripeptidyl-peptidase 2; D012697:Serine Endopeptidases; D046988:Proteasome Endopeptidase Complex