Unstable nuclear RNA synthesis following estrogen stimulation

Abstract

The administration of estradiol-17β in vivo stimulates the rate of synthesis into all classes of uterine and liver RNA. The earliest observable effects on macromolecule synthesis involve transcriptional changes in the spectrum of RNA molecules synthesized in target tissues. RNA/DNA hybridization experiments indicate differences in the populations of DNA-like RNA in both the liver and uterus after hormone treatment. No change was observed in lung cells. The results of RNA/DNA hybridization on total cell RNA indicate that the hormone-stimulated RNA species of the liver and uterus are not homologous. Therefore, the estrogen-induced RNA synthesis is partly organ specific. Both normal and hormone-treated tissue contain some RNA molecules which are restricted to the nucleus and do not occur in the cytoplasm. Some RNA molecules restricted to the nucleus in normal liver cells appear in the cytoplasm of hormone-treated liver cells. However, the spectrum of RNA molecules restricted to uterine nuclei before hormone treatment appears much more dramatic. The size pattern of rapidly labeled RNA molecules restricted to the nucleus is similar in normal and hormone-treated uterine cells except in 20–40-S and 4-S regions of sucrose gradients. It is suggested that selective transport of RNA to the cytoplasm may be an important device in the regulation of translation of potential messengers. The organ specificity of hormone action therefore appears to be mediated through three steps: (1) the receptor recognition of the target tissue, (2) transcriptional RNA changes which appear partially organ specific, and (3) selective regulation of nuclear RNA transport to the cytoplasm in tissues with primary response.