Cadmium-mediated oxidative stress in alveolar epithelial cells induces the expression of gamma-glutamylcysteine synthetase catalytic subunit and glutathione S-transferase alpha and pi isoforms: potential role of activator protein-1.
Exposure of rat alveolar epithelial cells to 10 micromol/L CdCl2 causes time-dependent increases in steady-state mRNA levels of the gamma-glutamylcysteine synthetase catalytic (heavy) subunit (gamma-GCS) and of glutathione S-transferase isoforms (GST-alpha and GST-pi). The expression of gamma-GCS was significantly increased as early as 2 h after addition of cadmium. Maximal induction of gamma-GCS mRNA (approximately 4-fold), at 8 h, was subsequently followed by increases in gamma-GCS activity/protein and glutathione (GSH) levels. Maximal elevations in GST-pi (approximately 2-fold) and GST-alpha (approximately 10-fold) transcripts, at 8 and 24 h, respectively, were also accompanied by enhanced GST activity. Cadmium-induced oxidative stress, assessed by alterations in GSH homeostasis and an accelerated rate of intracellular oxidant production, could constitute early events in the signal transduction pathway mediating these responses. The dimeric transcription factor, activator protein-1 (AP-1), may also play a regulatory role in this process. This association is suggested by transcriptional activation of the immediate-early response genes, c-fos and c-jun, within 15 min after exposure to cadmium and by the enhancement of AP-1 DNA binding activity, involving a c-Jun protein complex, which is maximally induced (approximately 4-fold) by 2 h. These molecular changes likely function together to protect alveolar epithelial cells against cadmium toxicity.
Department of Biochemistry, University of Vermont College of Medicine, Burlington 05405-0068, USA.
G S
GS
Shukla
A
A
Shukla
R J
RJ
Potts
M
M
Osier
B A
BA
Hart
J F
JF
Chiu
D000818:Animals; D015152:Blotting, Northern; D002104:Cadmium / Q000494:pharmacology*; D020134:Catalytic Domain; D002460:Cell Line; D004847:Epithelial Cells / Q000166:cytology / Q000201:enzymology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000502:physiology; D017781:Genes, Immediate-Early / Q000502:physiology; D005721:Glutamate-Cysteine Ligase / Q000235:genetics* / Q000378:metabolism; D051549:Glutathione S-Transferase pi; D005982:Glutathione Transferase / Q000235:genetics* / Q000378:metabolism; D007527:Isoenzymes / Q000235:genetics* / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology*; D011650:Pulmonary Alveoli / Q000166:cytology* / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism; D018808:Transcription Factor AP-1 / Q000378:metabolism*
D007527:Isoenzymes; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; D018808:Transcription Factor AP-1; D002104:Cadmium; D051549:Glutathione S-Transferase pi; D005982:Glutathione Transferase; C496558:Gstp1 protein, rat; C119995:glutathione S-transferase alpha; D005721:Glutamate-Cysteine Ligase