Roles of estrogen receptors and protooncogenes in uterine cell proliferation.

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1) Localization of estrogen receptors (ER) in the nucleus of mouse uterine epitheliumLocalization of hormone occupied and unoccupied ER is investigated to clarify if ER translocate within the nucleus after hormone binding, using ultrathin frozen sections combined with the immunogold technique. Adult ovariectomized mice were injected with estradiol (E2) or saline and killed after 1 hr and the uteri were processed for the immunoelectron microscopy. No apparent changes in the structure of chromatin and ER localization were observed ; both unoccuoied and occupied ER were present in the dispersed and slightly condensed chromatin but not in the nucleolus and highly condensed chromatin. These results suggest that ER activate closely locating target genes without a marked intranuclear translocation.2) Hormonal induction of lactofferin (LF) in the uterine cellsTemporal localizaton of estrogen inducible secretory protein, LF was investigated in the uterus of ovariectomized mouse after E2 stimula … More tion. LF immunoreaction was detectable in the secretory pathways, i.e., in the rough surfaced endoplasmic reticulum, the Golgi apparatus and secretory vesicles of epithelial cells. Furthermore, ER were rapidly induced in the in the nucleolus showing a peak at 6-13 hr after E2 injection. These findings suggest that LF is one of early genes which is involved in the synthesis of ribosomes prior to the proliferation, although LF has been thought as a late gene and used as a maker of cytodifferentiation of epithelium.3) Hormonal induction of protooncogenes in the mouse uterusCell type specific and temporal expression of c-fos and c-jun protooncogenes was examined in the mouse uterus after E2 stimulation employing immunohistochemistry and in situ hybridization. The c-fos protein and mRNA were transiently expressed in the epithelial cells 2 hr after E2 injection. In contrast, E2 injection elicited a decrease of c-jun expression after 2-6 hr in the epithelial cells, however, it was increased in the stromal and myometrial muscle cells. In the endothelial cells of blood vessels, both c-fos and c-jun were transiently induced 1-2 hr after E2 stimulation. These results indicate that rapid and transit changes in the concentration of c-fos and c-jun proteins, which form transcription factor AP-1, may trigger the proliferation of uterine epithelium. Less