title: Differential effect of forms A and B of human progesterone receptor on estradiol-dependent transcription.
abstract: In addition to stimulation of the target gene fatty-acid synthetase, the synthetic progestin R5020 strongly inhibited estradiol-induced pS2 and cathepsin D mRNA levels in MCF7 human breast cancer cells as shown by Northern blot analysis. Inhibition was half-maximal with 30 pM R5020, and the antiprogestin RU486 had only a weak effect. Two human progesterone receptor isoforms have been described; isoform A is a truncated form of isoform B and lacks the 164 N-terminal amino acids. We hypothesized that the two isoforms could have a differential capacity to transrepress estrogen-induced responses. Therefore, in MDA-MB231 cells containing no progesterone and estrogen receptors, we transiently transfected progesterone receptor expression vectors coding for form B (hPR1 or hPR0) or form A (hPR2) along with the estrogen receptor expression vector HEO. We show that R5020 inhibited estradiol-induced transcription of the pS2-CAT reporter plasmid only in cells selectively expressing isoform B. The same results were obtained when progesterone receptor isoforms were overexpressed in MCF7, Ishikawa, HeLa, or NIH-3T3 cells. Transrepression was dependent on the promoter context since the extent of inhibition by isoform B was higher when evaluated with pS2 or cathepsin D nonpalindromic estrogen-responsive element-mediated transcription than with the perfect palindromic form of the vitellogenin gene. Isoform A was inefficient regardless of the reporter construct used. Inhibition varied with the isoform ratio, and isoform B had a dominant effect, with > 70% inhibition measured in cells transfected with the same amount of both progesterone receptor isoforms. Progestin repressed only one of the two transcription activation functions of the estrogen receptor, AF-2, which corresponds to the hormone-binding domain. We conclude that differential expression of progesterone receptor isoforms could be responsible for a tissue-specific inhibition of estrogen target genes by progestins.
authors.affiliation: University of Montpellier, France.
authors.forename: D
authors.initials: D
authors.lastname: Chalbos
authors.forename: F
authors.initials: F
authors.lastname: Galtier
mesh_terms: D016475:3T3 Cells; D000818:Animals; D002402:Cathepsin D / Q000235:genetics; D004958:Estradiol / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D009363:Neoplasm Proteins / Q000235:genetics; D011372:Progestins / Q000502:physiology; D011506:Proteins; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011980:Receptors, Progesterone / Q000502:physiology*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D000071163:Trefoil Factor-1; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins
chemical_list: D009363:Neoplasm Proteins; D011372:Progestins; D011506:Proteins; D012333:RNA, Messenger; D011980:Receptors, Progesterone; C051838:TFF1 protein, human; D000071163:Trefoil Factor-1; D025521:Tumor Suppressor Proteins; D004958:Estradiol; D002402:Cathepsin D