Differential effect of forms A and B of human progesterone receptor on estradiol-dependent transcription

• Published in: The Journal of biological chemistry Vol. 269; no. 37; pp. 23007 - 23012
• Main Authors: Chalbos, D, Galtier, F
• Format: Journal Article
• Language: English
• Published: United States American Society for Biochemistry and Molecular Biology 16.09.1994
• Subjects: 3T3 Cells; Animals; Cathepsin D - genetics; Estradiol - physiology; HeLa Cells; Humans; Mice; Neoplasm Proteins - genetics; Progestins - physiology; Proteins; Receptors, Progesterone - physiology; RNA, Messenger - genetics; RNA, Messenger - metabolism; Transcription, Genetic; Transcriptional Activation; Trefoil Factor-1; Tumor Cells, Cultured; Tumor Suppressor Proteins
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(17)31611-3

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.