Ligand-Modulated Regulation of Progesterone Receptor Messenger Ribonucleic Acid and Protein in Human Breast Cancer Cell Lines

Abstract

We gave examined the effects of estrogen and progestin agonist and antagonist ligands on regulation of progesterone receptor (PR) protein and mRNA levels in a variety of human breast cancer cell lines. By Northern blot analysis, using human PR cDNA probes, PR mRNA in T47D and MCF-7 cells appears as five species of approximately 11.4, 5.8, 5.3, 3.5, and 2.8 kilobases. PR mRNA species are not detected in the PR protein-negative breast cancer cell lines MDA-MB-231 and LY2. T47D cells contain high levels of PR mRNA and protein (detected by hormone binding assay or Western blot analysis), and the PR protein and mRNA content of T47D cells are reduced to about 10% of the control level within 48 h of treatment with 10 nM promegestone; 17, 21-dimethyl-10-nor-pregna-4,9-diene-3, 20-dione (R5020) or 16.alpha.-ethyl-21-hydroxy-19-nor-pregn-4-ene-3,20-dione (ORG2058), both potent progestins. In contrast, teratment of T47D cells with the antiprogestin 17.beta.-hdyroxy-11.beta.-[4-dimethylaminophenyl]-17.alpha.-(1-propynyl)-estra-4, 9-dien-3-one) (RU38486) reduces PR protein and mRNA levels only transiently. PR protein and mRNA are virtually undetectable in control MCF-7 cells grown in the absence of estrogens. When estradiol is administered to MCF-7 cells, the PR mRNA and protein levels increase gradually and proportionately (10- or 40-fold, respectively, in 3 days). This estradiol stimulation of PR iIs repressed to basal levels if MCF-7 cells receive a 100-fold excess of the antiestrogen 6-hydroxy-2-(p-hydroxyphenyl)benzo(b)thien-3-yl-p-[2-1-pyrrolidinyl)ethoxy]phenylketone; LY 117018) concomitantly. After estrogen stimulation of PR in MCF-7 cells, treatment with R5020 or RU38486 results in a ca. 50% decrease in PR protein and mRNA content by 2 days. These studies reveal a close correspondence between changes in PR mRNA content and the PR protein content of cells in response to estrogen, antiestrogen, progestin, or antiprogestin exposure, suggesting that the changes in cellular PR protein are accounted for predominantly by changes at the transcriptional (RNA) level.