Cadmium-induced elevations in the gene expression of the regulatory subunit of gamma-glutamylcysteine synthetase in rat lung and alveolar epithelial cells.
The controlled step in de novo glutathione (GSH) synthesis is catalyzed by gamma-glutamylcysteine synthetase (gamma-GCS), a dimeric enzyme consisting of a heavy catalytic subunit (gamma-GCS-HS) and a light regulatory subunit (gamma-GCS-LS). We have previously reported that exposure to cadmium (Cd) induces pulmonary gamma-GCS-HS mRNA and protein, and that these alterations are accompanied by increases in GSH synthesis and its steady-state level. The current study was designed to test the hypothesis that Cd exposure also up-regulates the expression of the regulatory gamma-GCS subunit. By using northern blotting, we have demonstrated that a single Cd aerosol exposure of adult male Lewis rats results in time- and dose-dependent increases in pulmonary levels of gamma-GCS-LS mRNA. Transcripts of gamma-GCS-LS in rat lung are maximally elevated (8-fold) 2 h following Cd inhalation exposure and remain significantly higher than air controls at 24 h. This response is highly correlated with Cd dose, ranging from 0.9 to 5 mg Cd per m(3), and with lung Cd burden. We also observed Cd-induced up-regulation of gamma-GCS-LS mRNA expression in alveolar epithelial cells exposed to Cd in vitro, either acutely or after repeated passaging in Cd-containing medium. The magnitude of the gamma-GCS regulatory subunit induction observed in Cd-treated cells was approximately five times greater than the induction of the catalytic subunit. These modifications in the expression of gamma-GCS subunits may offer protection from Cd toxicity.
Shukla
G S
GS
Biochemistry Department, College of Medicine, University of Vermont, Room C-440, Given Medical Building, 05405-0068, Burlington, VT, USA.
Chiu
J
J
Hart
B A
BA
D019881:Aminoacyltransferases / Q000096:biosynthesis* / Q000235:genetics; D000818:Animals; D015152:Blotting, Northern; D002104:Cadmium / Q000378:metabolism / Q000633:toxicity*; D002478:Cells, Cultured; D004790:Enzyme Induction / Q000187:drug effects; D004847:Epithelial Cells / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D007527:Isoenzymes / Q000096:biosynthesis / Q000235:genetics; D008168:Lung / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D008297:Male; D011650:Pulmonary Alveoli / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D011917:Rats, Inbred Lew; D013054:Spectrophotometry, Atomic; D013268:Stimulation, Chemical
D007527:Isoenzymes; D012333:RNA, Messenger; D002104:Cadmium; D019881:Aminoacyltransferases; C093784:glutathione gamma-glutamylcysteinyltransferase