Molecular effects of antiestrogens (tamoxifen and LY117018) on estrogen-dependent glycoprotein (USP-1) synthesized and secreted by rat uterine epithelial cells.

We have previously identified and characterized a 97K secretory glycoprotein (uterine secretory protein-1:USP-1) synthesized and secreted by rat uterine epithelial cells under estrogen stimulation. We now have analyzed the qualitative and quantitative effects of antiestrogens (tamoxifen and LY117018) on the induction of USP-1 biosynthesis when administered alone or combined with 17 beta-estradiol (E2). By radioimmune precipitation assay of [35S]methionine-labeled uterine luminal fluid proteins, it was shown that tamoxifen and LY117018 could weakly induce USP-1 compared with E2. Concomitant administration of either tamoxifen or LY117018 with E2 significantly diminished the effects of E2 on USP-1 induction. Hence, both tamoxifen and LY117018 possess agonistic as well as antagonistic properties affecting the induction of USP-1. These agonistic effects of antiestrogens were also evident from the presence of USP-1 in rat uterine epithelial cells treated with antiestrogens, as revealed by immunohistochemical staining. Sodium dodecylsulfate-polyacrylamide gel analysis of immunoprecipitable [35S]methionine-labeled protein revealed that USP-1 induced by tamoxifen is larger (110K) than that induced by estrogen or LY117018 (97K). Peptide-N-glycosidase treatment of USP-1 induced by E2 or tamoxifen removed asparagine-linked carbohydrate chains and resulted in the appearance of polypeptides with apparent mol wt of 91K and 105K, respectively. Thus, the higher mol wt of tamoxifen-induced USP-1 is not due to changes in asparagine-linked carbohydrates. Since LY117018 could not induce any qualitative change in the USP-1 molecule, tamoxifen may act on uterine epithelial cells through a different molecular mechanism than LY117018.