Stimulation of Ribonucleic Acid Synthesis by Steroid Hormones

Abstract

(Received for publication, March 4, 1965) Earlier reports from this laboratory have described rapid stimulations of ribonucleic acid synthesis in the livers of adrenal- ectomised rats treated with glucocorticoids (1) and in seminal vesicles of castrates after androgen administration (2). In the liver, the effect is limited to nuclear RNA synthesis, and begins between 30 and 45 min after hormone is given. Accumulation of the induced enzyme tyrosine-ar-ketoglutarate transaminase does not begin until 60 min after treatment, and thus the results are kinetically consistent with the conclusion that increased enzyme synthesis (3) is secondary to the hormonal stimulation of RNA synthesis. In the seminal vesicle, a marked elevation in the rate of RNA synthesis can be seen as early as 20 min after testosterone administration. In both organs, RNA synthesis is increased 2- to 3-fold within 2 hours of hormone treatment. These steroid effects on RNA synthesis are thus both rapid and large, and it seems reasonably safe to assume, first, that they play a signifi- cant role in the ultimate physiological shifts that occur as a result of steroid hormone treatment, and second, that RNA syn- thesis is closely linked to the primary site of action of these hormones. In this series, we describe the results of experiments in which we have analyzed the nature of the RNA synthesized in response to hydrocortisone and testosterone. In these experiments, we have used the differential thermal extraction procedure elaborated by Georgiev, Samarina, Lerman, Smirnov, and Severtzov (4), in which extraction with phenol at various temperatures is employed to separate the different types of RNA that are labeled when tissues are exposed to isotopic RNA precursors for a limited time. Extraction of tissue prep- arat.ions with phenol at low temperature yields a fraction con- taining most of the unlabeled tissue RNA as well as the low molecular weight labeled RNA components. In this paper, we will discuss the identification of these low molecular weight components, and the effect of steroid hormone treatment on the labeling of each. The labeled RNAs extracted at low tempera- ture include transfer RNA and a poorly defined heterogeneous fraction. Labeling of transfer RNA can be traced to terminal nucleotide turnover, which is hormone-independent, and to synthesis G% novo, which is stimulated by steroid hormones. * Research supported jointly by the National Institutes of Health, and by the United States Atomic Energy Commission under contract with the Union Carbide Corporation. t Postdoctoral Fellow of the American Cancer Society. $ Public Health Service Postdoctoral Fellow of the National Cancer Institute (Grant 6F2-CA-16, 375-OlAl). Present address, McCollum-Pratt Institute, The Johns Hopkins University, Balti- more, Maryland.