title: Expression of progesterone receptor A form and its role in the interaction of progesterone with cortisol on cyclooxygenase-2 expression in amnionic fibroblasts.
abstract: BACKGROUND
  Human amnion fibroblasts produce abundant prostaglandins toward the end of gestation, which is believed to be one of the major events leading to parturition. Glucocorticoids have been shown to up-regulate cyclooxygenase-2 (COX-2) expression, the crucial enzyme catalyzing prostaglandin synthesis, in human amnion fibroblasts. Although a major propregnancy hormone, the effect of progesterone and the associated progesterone receptor subtypes in the regulation of both basal and glucocorticoid-induced COX-2 expression in human amnion fibroblasts have not been resolved.
  
  
  RESULTS
  Cultured human amnion fibroblasts prepared from the fetal membranes at term pregnancy without labor mainly expressed the progesterone receptor A form (PRA). Inhibition of endogenous progesterone production with trilostane or knockdown of PRA expression with small interfering RNA significantly enhanced the glucocorticoid receptor (GR)-mediated COX-2 induction by cortisol, whereas overexpression of PRA attenuated the induction by cortisol. Co-immunoprecipitation assay revealed PRA in the GR protein complex. Although exogenous progesterone did not alter COX-2 expression under basal conditions, it attenuated cortisol-induced COX-2 expression at concentrations about 10- to 50-fold higher, which might be achieved by competition with cortisol for GR.
  
  
  CONCLUSIONS
  We demonstrated in this study that endogenous progesterone might counteract the induction of prostaglandin synthesis by cortisol via PRA transdominant repression of GR function, whereas high levels of progesterone might further inhibit the induction by cortisol via competitive binding to GR in human amnion fibroblasts. These inhibitory actions of progesterone and PRA on glucocorticoids and GR may partly explain the inconsistent effects of glucocorticoids on parturition in humans.
authors.affiliation: School of Life Sciences, Fudan University, 220 Handan Road, Shanghai 200433, People's Republic of China.
authors.forename: C M
authors.initials: CM
authors.lastname: Guo
authors.forename: X O
authors.initials: XO
authors.lastname: Zhu
authors.forename: X T
authors.initials: XT
authors.lastname: Ni
authors.forename: Z
authors.initials: Z
authors.lastname: Yang
authors.forename: L
authors.initials: L
authors.lastname: Myatt
authors.forename: K
authors.initials: K
authors.lastname: Sun
mesh_terms: D000328:Adult; D000653:Amniotic Fluid / Q000166:cytology / Q000201:enzymology*; D015153:Blotting, Western; D002478:Cells, Cultured; D051546:Cyclooxygenase 2 / Q000096:biosynthesis* / Q000235:genetics*; D015232:Dinoprostone / Q000096:biosynthesis / Q000235:genetics; D005260:Female; D005333:Fetus / Q000378:metabolism; D005347:Fibroblasts / Q000201:enzymology*; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics; D006801:Humans; D006854:Hydrocortisone / Q000502:physiology*; D047468:Immunoprecipitation; D010957:Plasmids / Q000235:genetics; D011247:Pregnancy; D011374:Progesterone / Q000502:physiology*; D034741:RNA, Small Interfering / Q000235:genetics; D011980:Receptors, Progesterone / Q000096:biosynthesis* / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection
chemical_list: D034741:RNA, Small Interfering; D011980:Receptors, Progesterone; C101118:progesterone receptor A; D011374:Progesterone; D051546:Cyclooxygenase 2; D015232:Dinoprostone; D006854:Hydrocortisone