title: Inhibition of tumor promoter 12-O-tetradecanoylphorbol-13-acetate-induced synthesis of epidermal ornithine decarboxylase messenger RNA and diacylglycerol-promoted mouse skin tumor formation by retinoic acid.
abstract: Evidence is presented that inhibition of 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced ornithine decarboxylase (ODC; EC 4.1.1.17) by retinoic acid may involve inhibition of protein kinase C-mediated synthesis of ODC mRNA. A single application of 10 nmol of TPA to intact mouse skin led to an increase in the steady state levels of epidermal ODC mRNA; a maximal level of ODC mRNA occurred at about 3.5 h after TPA treatment. TPA-induced increase in ODC mRNA preceded the increase in epidermal ODC activity. Application of 17 nmol of retinoic acid 1 h before application of TPA to mouse skin inhibited the induction of both ODC mRNA and ODC activity. Using the DNA-excess filter hybridization technique, we found that TPA-increased steady state levels of ODC mRNA in primary culture of newborn mouse epidermal cells were the result of enhanced accumulation of newly synthesized ODC mRNA. Furthermore, in a pulse-chase experiment, we could not detect any difference in the half-life of ODC mRNA in epidermal cells after TPA or the vehicle dimethyl sulfoxide treatments; the half-life of ODC mRNA was about 7 h in both cases. Exposure of primary cultures of newborn epidermal cells to retinoic acid, in conjunction with TPA, inhibited the synthesis of ODC mRNA and failed to alter the half-life of ODC mRNA. These results implicate the role of transcription activation in TPA-induced ODC gene expression and indicate that retinoic acid may inhibit TPA-induced ODC gene transcription. We also found that protein kinase C may play a role in the mechanism of inhibition by retinoic acid of ODC gene expression. Supporting evidence is the finding that L-alpha-dioctanoylglycerol, an activator of protein kinase C, is a Stage II mouse skin tumor promoter and the application of retinoic acid 1 h before application of L-alpha-dioctanoylglycerol to mouse skin inhibited the induction of ODC activity and ODC mRNA as well as tumor promotion by L-alpha-dioctanoylglycerol. Taken together, one may conclude that the mechanism of inhibition of TPA-induced ODC by retinoic acid may involve the inhibition of protein kinase C-mediated accumulation of newly synthesized ODC mRNA.
authors.affiliation: Department of Human Oncology, University of Wisconsin Clinical Cancer Center, Madison 53792.
authors.forename: A K
authors.initials: AK
authors.lastname: Verma
mesh_terms: D000818:Animals; D004075:Diglycerides / Q000633:toxicity*; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D005989:Glycerides / Q000633:toxicity*; D051379:Mice; D008807:Mice, Inbred BALB C; D009955:Ornithine Decarboxylase / Q000096:biosynthesis / Q000235:genetics*; D011493:Protein Kinase C / Q000032:analysis; D012333:RNA, Messenger / Q000096:biosynthesis*; D012867:Skin / Q000201:enzymology*; D012878:Skin Neoplasms / Q000139:chemically induced*; D013755:Tetradecanoylphorbol Acetate; D014212:Tretinoin / Q000494:pharmacology*
chemical_list: D004075:Diglycerides; D005989:Glycerides; D012333:RNA, Messenger; D014212:Tretinoin; D011493:Protein Kinase C; D009955:Ornithine Decarboxylase; D013755:Tetradecanoylphorbol Acetate; D004121:Dimethyl Sulfoxide