Phorbol ester-mediated downregulation of tropoelastin expression is controlled by a posttranscriptional mechanism.
Expression of tropoelastin, the principal precursor of elastic fibers, is tissue-specific and is limited to a brief developmental period. Little is known, however, about the mechanisms that regulate the tissue- and temporal-specific expression of elastogenesis. The tropoelastin promoter contains putative phorbol ester responsive elements, or AP-1 binding sites, but the functional significance of these sequences is unknown. To test if tropoelastin expression is influenced by phorbol esters, we exposed elastogenic fetal bovine chondrocytes to 10(-7) M 12-O-tetradecanoylphorbol 13-acetate (TPA). Tropoelastin mRNA levels decreased greater than 10-fold in response to TPA, and this downregulation was paralleled by a decline in the secretion of tropoelastin protein into the culture medium. As determined by nuclear-runoff assay and transient transfection with a human gene promoter-CAT construct, tropoelastin transcription was unaffected after exposure to TPA. As indicated by actinomycin D experiments, the half-life of tropoelastin mRNA in control cells was about 20 h, but exposure to TPA resulted in an accelerated decay of the tropoelastin transcript (t1/2 = 2.2 h). These data indicate that downregulation of tropoelastin expression was controlled by a posttranscriptional mechanism and that the AP-1 elements in the bovine tropoelastin promoter may not be involved in regulation of production.
Parks
W C
WC
Division of Dermatology, Jewish Hospital, Washington University Medical Center, St. Louis, Missouri 63110.
Kolodziej
M E
ME
Pierce
R A
RA
D000818:Animals; D002356:Cartilage / Q000187:drug effects / Q000502:physiology*; D002417:Cattle; D002478:Cells, Cultured; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics / Q000378:metabolism; D003609:Dactinomycin / Q000494:pharmacology; D005333:Fetus; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D007700:Kinetics; D011401:Promoter Regions, Genetic; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D013997:Time Factors; D014158:Transcription, Genetic / Q000235:genetics; D014162:Transfection; D014333:Tropoelastin / Q000235:genetics*
D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger; D014333:Tropoelastin; D003609:Dactinomycin; D015500:Chloramphenicol O-Acetyltransferase; D013755:Tetradecanoylphorbol Acetate