title: Phorbol ester treatment of human myometrial cells suppresses expression of oxytocin receptor through a mechanism that does not involve activator protein-1.
abstract: Oxytocin (OT) is a potent uterine agonist. Its receptor (OTR) is a G protein-coupled receptor that is downregulated by prolonged exposure to OT. We hypothesized that activation of PKC mediated this OT-induced decrease in OTR expression. Diminished PKC activity in late pregnancy could underlie the increased expression of uterine OTR preceding labor onset. Using cell cultures of transformed human uterine myocytes, we determined the effects of PKC agonists and antagonists on the expression of OTR. We also explored the effects of overexpression of activator protein-1 (AP-1, a mediator of many PKC- and phorbol ester-induced effects) using adenoviral expression vectors for the AP-1 subunits c-Jun and c-Fos. Stimulation of PKC using the phorbol ester 12-O-tetradecanoylphorbol 13-acetate caused a rapid, significant (P < or = 0.05) increase in c-Jun and c-Fos concentrations but a significant decrease in mRNA for OTR within 6 h followed by a significant decrease in OT binding by 24 h. Adenoviral infection of the cells with expression vectors for c-Jun and c-Fos increased the AP-1 subunits but had no effect on OTR expression. Furthermore, there were no changes in c-Fos or c-Jun levels in human intrauterine tissues around the time of labor onset, as measured by Western analyses. We conclude that phorbol ester treatment decreases OTR expression, likely through a mechanism that does not involve AP-1.
authors.affiliation: Department of Obstetrics and Gynecology, Perinatal Research Centre, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Allison
authors.initials: A
authors.lastname: Ball
authors.forename: Jing Wei
authors.initials: JW
authors.lastname: Wang
authors.forename: Susan
authors.initials: S
authors.lastname: Wong
authors.forename: Barbara
authors.initials: B
authors.lastname: Zielnik
authors.forename: Jana
authors.initials: J
authors.lastname: Mitchell
authors.forename: Nanping
authors.initials: N
authors.lastname: Wang
authors.forename: Michael B
authors.initials: MB
authors.lastname: Stemerman
authors.forename: B F
authors.initials: BF
authors.lastname: Mitchell
mesh_terms: D001798:Blood Proteins / Q000494:pharmacology; D002273:Carcinogens / Q000494:pharmacology*; D002461:Cell Line, Transformed; D005260:Female; D006801:Humans; D009215:Myometrium / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D036801:Parturition / Q000502:physiology; D011247:Pregnancy; D011263:Pregnancy Trimester, Third / Q000502:physiology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics / Q000378:metabolism; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism; D018045:Receptors, Oxytocin / Q000235:genetics*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism*
chemical_list: D001798:Blood Proteins; D002273:Carcinogens; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger; D043562:Receptors, G-Protein-Coupled; D018045:Receptors, Oxytocin; D018808:Transcription Factor AP-1; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate