A role for protein kinase C-delta in the regulation of ornithine decarboxylase expression by oxidative stress.
The expression of genes that regulate cell growth, such as ornithine decarboxylase (ODC), can be modulated by oxidant tumor promoters. Treatment of murine papilloma PE cells with H2O2 led to a transient induction of ODC enzyme activity, which could be blocked by calphostin, a nonspecific inhibitor of protein kinase C (PKC). Peak activity (11-fold) occurred 5-6 h after treatment, followed by a rapid decline. The increase in ODC activity was associated with an elevation of both ODC mRNA (3-fold) and protein (7-fold). Direct involvement of PKC in the regulation of ODC by oxidants was determined by stable transfection of PE cells with a dominant-negative PKC-delta mutant. PKC-delta activity was completely inhibited in response to H2O2 in cells overexpressing mutant PKC-delta compared with cells transfected with a blank plasmid. Induction of ODC mRNA, protein, and activity was also completely inhibited in cells expressing the PKC-delta mutant after H2O2 treatment. Activation of an ODC promoter-luciferase reporter construct by H2O2 was attenuated in mutant cells compared with control cells, further confirming that ODC is regulated transcriptionally by PKC-delta. However, fold-increases in ODC mRNA and protein were much less than the increase in activity, suggesting that ODC may also undergo posttranscriptional regulation in the presence of oxidants. Taken together, these studies provide new insight into the regulation of ODC by oxidants and suggest that PKC-delta may play a critical role in this regulation.
Otieno
M A
MA
Department of Environmental Health Sciences, School of Hygiene and Public Health, Johns Hopkins University, Baltimore, Maryland 21205, USA.
Kensler
T W
TW
D000818:Animals; D002118:Calcium / Q000378:metabolism; D004790:Enzyme Induction / Q000187:drug effects; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000502:physiology*; D017930:Genes, Reporter / Q000187:drug effects; D006861:Hydrogen Peroxide / Q000633:toxicity; D007527:Isoenzymes / Q000235:genetics / Q000502:physiology*; D051379:Mice; D009955:Ornithine Decarboxylase / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D016877:Oxidants / Q000633:toxicity; D018384:Oxidative Stress / Q000502:physiology*; D010212:Papilloma / Q000201:enzymology / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000187:drug effects; D011493:Protein Kinase C / Q000235:genetics / Q000502:physiology*; D051745:Protein Kinase C-delta; D014158:Transcription, Genetic / Q000187:drug effects / Q000502:physiology; D014162:Transfection; D014407:Tumor Cells, Cultured
D007527:Isoenzymes; D016877:Oxidants; D006861:Hydrogen Peroxide; C497259:Prkcd protein, mouse; D011493:Protein Kinase C; D051745:Protein Kinase C-delta; D009955:Ornithine Decarboxylase; D002118:Calcium