Steroid-induced early protein synthesis in rat uterus and prostate

An early 'induced protein', after exposure of the rat uterus to estradiol, is detected among the soluble proteins with a double-labelling technique and electrophoretic fractionation. Efforts have been directed to establish the subcellular distribution of the induced protein, since such a protein, observable 1 h after hormone administration, may play an important role in the subsequent amplified responses, especially in terms of RNA synthesis. Moreover such an early discrete induced protein was sought in a comparable system responding to another hormone, namely prostate and seminal vesicles under androgens. The induced protein was not found in uterine nuclei of 21-day-old rats after 1 h of estradiol action in vivo and 1 h of tissue incubation with labelled leucine. This negative result summarizes a search among different nuclear protein fractions using various procedures; nor was induced protein observed in mitochondrial and microsomal pellets. Contrary to these negative findings, slight changes of histone labelling were observed under the experimental conditions used to demonstrate induced protein. In addition histone acetylation was increased after 1 h of estradiol action in vivo and 15 min tissue labelling in vitro with radioactive acetate. Furthermore, an increase in total protein synthesis between 0 and 2 h after estradiol action was observed, the relative increase of incorporation of radioactive leucine into protein of estradiol-treated vs non-stimulated uteri being corrected for variations of the acid-soluble radioactive leucine pool. Attempts to obtain an early and discrete induced protein with androgens in prostate and seminal vesicles of immature or castrated rats after different times of exposure to testosterone, androstanolone and estradiol have been unsuccessful. The contribution of both negative and positive findings in steroid-induced early protein synthesis is discussed in the context of the current knowledge of hormone action.