title: Inhibition of tumor promoter-induced transformation by retinoids that transrepress AP-1 without transactivating retinoic acid response element.
abstract: Both retinoic acid (RA) treatment and dominant-negative c-Jun mutant expression effectively inhibit phorbol ester-induced AP-1 activity and induced neoplastic transformation in mouse epidermal JB6 cells. However, both reagents also target non-AP-1 molecules in addition. Because liganded retinoic acid receptors interact with and transactivate RA response elements (RAREs) on DNA, as well as interact with Jun protein to block AP-1 activity, the question arises as to which of these two activities of retinoids is responsible for antitumor-promoting activity. To address this question we generated JB6 promotion-sensitive (P+) cell lines that are stably transfected with a construct containing the collagenase promoter bearing one AP-1-binding site that drives a luciferase reporter gene. The stable collagenase-luciferase-transfected cell lines showed 1.5-3.5-fold enhanced AP-1 activity when treated with 12-0-tetradecanoyl-phorbol-13-acetate (TPA). Up to 90% of TPA-induced AP-1 activity was blocked by retinoids SR11238, SR11302, or trans-RA, but not by retinoid SR11235. Of these retinoids, only RA and SR11235 were able to transactivate RARE-dependent gene expression. Transrepression of TPA-induced AP-1 and transactivation of RARE by RA, SR11238, and SR11302 were concentration dependent at 10(-10) to 10(-6) M retinoid. When tested for activity in inhibiting tumor promoter-induced transformation in JB6 P+ cells, the retinoids specific for AP-1 transrepression were inhibitory, whereas SR11235, which only activated RARE, showed little effect. We thus conclude that the AP-1-blocking activity of retinoids is likely to be responsible for the antitumor-promoting activity. This result, together with the observation that dominant-negative Jun blocks transformation, argues for a requirement of induced AP-1 in the tumor promoter-induced transformation process.
authors.affiliation: Cell Biology Section, National Cancer Institute, Frederick, Maryland 21702-1201, USA.
authors.forename: J J
authors.initials: JJ
authors.lastname: Li
authors.forename: Z
authors.initials: Z
authors.lastname: Dong
authors.forename: M I
authors.initials: MI
authors.lastname: Dawson
authors.forename: N H
authors.initials: NH
authors.lastname: Colburn
mesh_terms: D000818:Animals; D016588:Anticarcinogenic Agents / Q000494:pharmacology*; D001483:Base Sequence; D002273:Carcinogens / Q000633:toxicity; D002471:Cell Transformation, Neoplastic / Q000187:drug effects*; D002478:Cells, Cultured; D015870:Gene Expression; D017930:Genes, Reporter; D008156:Luciferases / Q000096:biosynthesis / Q000235:genetics; D051379:Mice; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D012045:Regulatory Sequences, Nucleic Acid; D012176:Retinoids / Q000494:pharmacology*; D012680:Sensitivity and Specificity; D012867:Skin / Q000187:drug effects / Q000473:pathology; D013755:Tetradecanoylphorbol Acetate / Q000037:antagonists & inhibitors* / Q000633:toxicity; D018808:Transcription Factor AP-1 / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D015533:Transcriptional Activation / Q000187:drug effects*; D014162:Transfection; D014212:Tretinoin / Q000494:pharmacology*
chemical_list: D016588:Anticarcinogenic Agents; D002273:Carcinogens; D012176:Retinoids; D018808:Transcription Factor AP-1; D014212:Tretinoin; D008156:Luciferases; D013755:Tetradecanoylphorbol Acetate