The anti-progestin RU486 stabilizes the progestin-induced fatty acid synthetase mRNA but does not stimulate its transcription
Chalbos, D.; Galtier, F.; Emiliani, S.; Rochefort, H.
Journal of Biological Chemistry 266(13): 8220-8224
1991
ISSN/ISBN: 0021-9258 PMID: 2022639 Document Number: 316998
The mechanism of action of RU-486 on the progesterone receptor was examined in MCF7 breast cancer cells in vitro, using messenger RNA (mRNA) for the enzyme fatty acid synthetase (FAS) as an indicator. Transcription and half-life of FAS mRNA were assayed by Northern Blot hybridization, with the progestin R5020 as a reference, and the C3 and actin clones as negative controls. Incubating MCF7 breast cancer cells for 5 or 48 hours with RU-486 decreased FAS gene transcription, and inhibited synthesis of its mRNA 50%. Paradoxically, RU-486 lengthened the half-life of FAS mRNA from 6 to 24 hours, as demonstrated by short-term cell labeling with tritiated uridine in the presence of DNA synthesis inhibitors actinomycin D or cordycepin. This treatment did not stabilize mRNA for C3 or actin. The half-size of FAS mRNA was increased from 6 to 26 hours as measured by a pulse-chase experiment. The steady state level of FAS mRNA doubled in a 2-day incubation. The fact that the glucocorticoid dexamethasone did not stabilize FAS mRNA in MDA-MB23 breast cancer cells suggested that the observed stabilization of mRNA in the RU-486 experiments is mediated by the progesterone receptor. This is the 1st demonstration that a steroid hormone antagonist prevents transcription of a regulated gene, but stabilizes its mRNA, suggesting 2 different regulatory steps.