Activation of AP-1 by okadaic acid in mouse keratinocytes associated with hyperphosphorylation of c-jun.
Okadaic acid (OA), a specific inhibitor of protein phosphatases 1 and 2A, is also a potent mouse skin tumor promoter. The effects of OA on regulation of c-jun/activator protein-1 (AP-1) transcriptional activation were investigated in mouse keratinocytes. AP-1 DNA binding to the jun 12-O-tetradecanoylphorbol-13-acetate-response element (TGACATCA) as determined by gel shift analysis was strongly induced by OA (100 ng/mL) at 6 and 12 h. Preincubation of nuclear extracts with anti-c-jun antibody demonstrated that c-jun was a major component of the DNA-bound AP-1 complex induced by OA in 308 cells. Transfection of a c-jun promoter-reporter construct demonstrated that AP-1 transactivation was induced by OA. The mRNA level of the c-jun proto-oncogene was dramatically increased by 6 and 12 h of OA treatment. Furthermore, a significant induction of c-jun protein was stimulated by 6 and 12 h of OA treatment. Upon further analysis, it was found that OA induced a significant accumulation of Ser 73-phosphorylated c-jun protein in 308 cells. In summary, our data suggest that skin tumor promotion by OA is due at least in part to increased AP-1 DNA binding and transactivation mediated by c-jun hyperphosphorylation.
Peng
J
J
Division of Radiation Oncology, University of Iowa, Iowa City 52242, USA.
Bowden
G T
GT
Domann
F E
FE
D000818:Animals; D002273:Carcinogens / Q000494:pharmacology*; D002460:Cell Line; D004247:DNA / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015603:Keratinocytes / Q000187:drug effects* / Q000378:metabolism; D051379:Mice; D019319:Okadaic Acid / Q000494:pharmacology*; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011485:Protein Binding / Q000187:drug effects; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis; D018808:Transcription Factor AP-1 / Q000378:metabolism*; D015533:Transcriptional Activation / Q000187:drug effects
D002273:Carcinogens; D004791:Enzyme Inhibitors; D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger; D018808:Transcription Factor AP-1; D019319:Okadaic Acid; D004247:DNA