Le récepteur de l'oestradiol, l'AMP cyclique et la RNA polymérase nucléolaire dans l'utérus de génisseStimulation de la biosynthèse de RNA in vitro

Oestradiol receptor, cyclic 3′,5′-AMP and nucleolar RNA polymerase in calf uteri. Stimulation of RNA biosynthesis in vitro1.1. Two types of enzyme showing RNA polymerase activity have been isolated simultaneously from calf uteri. One of them “nucleolar RNA polymerase” is recovered from the nucleoli which have been obtained by sonication of the isolated nuclei. This enzyme is stimulated by the cytoplasmic receptor 5-S oestradiol. When the endometrium is incubated with [6,7-3H2]oestradiol, 30% of the radioactivity of the nuclei is concentrated in the nucleoli. The RNA polymerase isolated from these nucleoli is also radioactive, and its enzyme activity is greatly enhanced compared with enzyme prepared from tissue which has not been treated with the hormone. A radioactive protein with a sedimentation coefficient of approximately 5 S, can be liberated from the nucleoli, which have been labelled with [6,7-3H2]oestradiol, by treatment with KCl. These results place one of the effects of the hormone in the nucleolus. The receptor 5-S oestradiol could be a factor which stimulates nucleolar RNA polymerase (M. Mousseron-Canetet al., Schering Workshop on Steroid Hormone Receptors, Berlin, 1970; M. Arnaudet al., C. R. Hebd. Séances Acad. Sci., 272 (1971) 635).2.2. The phosphorylation of 5-S oestradiol, the cytoplasmic receptor, by myometrium kinase is a process which is dependent on cyclic 3′,5′-AMP. The stimulation of RNA biosynthesis by isolated nuclei or nucleolar RNA polymerase, due to the 5-S oestradiol receptor, is very clearly increased after phosphorylation, nucleolar RNA polymerase, E2, extracted from tissue which has been incubated with oestradiol and associated with the stimulatory factor 5-S oestradiol has much greater incorporation of 32P than that shown by enzyme extracted from nontreated tissue, E1. The enzymic activity of E2 after phosphorylation is increased considerably, whereas the activity of E1 remains unchanged.3.3. The following hypothesis is proposed: adenyl cyclase is activated by oestradiol through some unknown mechanism and gives rise to cyclic 3′,5′-AMP. The nucleotide causes the phosphorylation of 5-S oestradiol receptor, which then activates the nucleolar RNA polymerase. These results throw some light on the role played by cyclic 3′,5′-AMP the second hormone messenger during the metabolic changes observed in the uterus after the administration of oestrogen (M. Arnaudet al., C. R. Hebd. Séances Acad. Sci., 272 (1971) 635.