title: Enhanced expression of pulmonary gamma-glutamylcysteine synthetase heavy subunit in rats exposed to cadmium aerosols.
abstract: This investigation sought to determine the effect of cadmium (Cd) aerosol exposure on the pulmonary expression of the heavy subunit (HS) of gamma-glutamylcysteine synthetase (gamma-GCS), the rate-limiting enzyme in de novo synthesis of glutathione (GSH). Using Northern hybridization analysis, we demonstrated that CdO inhalation caused time- and dose-dependent increases in the steady-state levels of gamma-GCS-HS mRNA that were highly correlated with lung Cd burden. Observed increases in gamma-GCS-HS gene expression were maximal 2 h following a single aerosol exposure to Cd and appeared to be triggered by an oxidant stress, characterized by a decline in the reduced to oxidized glutathione ratio. Immunoblotting of proteins in lung extracts from treated and untreated animals produced a single protein band corresponding to a molecular weight of 73 kDa. Elevated levels of gamma-GCS-HS mRNA and gamma-GCS-HS protein in lungs of Cd-exposed animals were also accompanied by higher gamma-GCS enzymatic activity and elevations in glutathione (GSH). Immunohistochemical and in situ hybridization studies were used to identify compartments in the lung where Cd-induced expression of gamma-GCS-HS was localized. The most prominent staining for gamma-GCS-HS protein and gamma-GCS-HS mRNA was observed in the alveolar epithelium of Cd-exposed animals. Quantitative image analysis confirmed a good agreement between relative levels of protein and mRNA transcripts for gamma-GCS-HS. These observations suggest that resistance to Cd toxicity in the lung may reflect the ability of specific lung cells to upregulate gamma-GCS expression and increase de novo GSH synthesis as an adaptive response.
authors.affiliation: Biochemistry Department, University of Vermont College of Medicine, Burlington, Vermont, 05405-0068, USA.
authors.forename: G S
authors.initials: GS
authors.lastname: Shukla
authors.forename: J
authors.initials: J
authors.lastname: Chiu
authors.forename: B A
authors.initials: BA
authors.lastname: Hart
mesh_terms: D000280:Administration, Inhalation; D000336:Aerosols; D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D002104:Cadmium / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000633:toxicity*; D003545:Cysteine / Q000378:metabolism; D004790:Enzyme Induction / Q000187:drug effects; D005721:Glutamate-Cysteine Ligase / Q000096:biosynthesis*; D005978:Glutathione / Q000378:metabolism; D007091:Image Processing, Computer-Assisted; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008168:Lung / Q000187:drug effects / Q000201:enzymology*; D010084:Oxidation-Reduction; D015347:RNA Probes; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D011917:Rats, Inbred Lew; D014018:Tissue Distribution
chemical_list: D000336:Aerosols; D015347:RNA Probes; D012333:RNA, Messenger; D002104:Cadmium; D005721:Glutamate-Cysteine Ligase; D005978:Glutathione; D003545:Cysteine