Estrogen-induced modification of uterine RNA polymerase activity depends on localization of the estrogen receptor

Abstract

The aim of this study was to examine the effects of estradiol (E2) on activity of RNA polymerase I and RNA polymerase II in uterine nuclei of ovariectomized (OVX) female rats. The obtained results show that estrogen-receptor (E-R) complexes in 30 min induced an increase of polymerase II activity. A second increase of polymerase II activity was observed after 3 h-incubation of nuclei with the E-R complex formed in the cytosol fraction. However, activity of polymerase I was increased 2 h after the start of incubation, with highest activity detected at 3 h in nuclei incubated with E-R complexes. On the contrary, no stimulatory effect on either polymerase I or polymerase II activity was observed in nuclei incubated with E2 alone. These results indicate that E2 stimulates the cytosolic estrogen receptor (ER), which in turn causes uterotrophic responses in OVX rats. In addition, they suggest that in order to provoke uterotrophic responses E-R complexes formed in the cytosol need to be retained in the nucleus for a longer period of time.