ESTRADIOL REGULATES ESTROGEN-RECEPTOR MESSENGER-RNA STABILITY

Previous studies suggest that post-transcriptional events play an impo rtant role in estrogen-induced loss of estrogen receptor expression. T he present study shows that treatment of MCF-7 cells with estradiol re sulted in a six-fold decrease in estrogen receptor mRNA half-life from 4h in control cells to 40 min in estradiol treated cells. To determin e the role of protein synthesis in the regulation of estrogen receptor mRNA stability, several translational inhibitors were utilized. Pacta mycin and puromycin, which prevent ribosome association with mRNA, inh ibited the effect of estradiol on receptor mRNA stability, whereas cyc loheximide, which has no effect on ribosome association with mRNA, had no effect on estradiol regulation of estrogen receptor mRNA stability . In control cells, the total cellular content of estrogen receptor mR NA was associated with high molecular weight polyribosomes. Treatment with estradiol resulted in a 70% decrease in estrogen receptor mRNA as sociated with polyribosomes but had no effect on the polyribosome dist ribution of estrogen receptor mRNA. In an in vitro degradation assay, polyribosomes isolated from estradiol-treated cells degraded ER mRNA f aster than polyribosomes isolated from control cells. The nuclease act ivity associated with the polysome fraction appeared to be Mg2+ indepe ndent and inhibited by RNasin. Freeze-thawing and heating at 90 degree s C for 10 min resulted in the loss of nuclease activity. These studie s suggest that an estrogen-regulated nuclease activity associated with ribosomes alters the stability of estrogen receptor mRNA. (C) 1998 El sevier Science Ltd. All rights reserved.