[Show abstract][Hide abstract] ABSTRACT: To examine whether an ultrashort feedback mechanism of gonadotropin-releasing hormone (GnRH) operates at the level of gene transcription, we studied the effects of GnRH analogs on GnRH promoter activity and GnRH mRNA level in hypothalamic GT1–1 neuronal cells. Treatment of GT1–1 cells with buserelin, a GnRH agonist, or native GnRH for 24 h significantly decreased GnRH promoter activity and its mRNA level, whereas that with GnRH antagonists, antide or [D-Phe2,D-Ala6]-GnRH, showed no effect. The inhibitory effects of buserelin on GnRH gene transcription and GnRH mRNA level were dose-related, and a significant inhibition was observed in cells treated with buserelin at concentrations higher than 0.1 μM. Time-course experiments showed that significant decreases in GnRH promoter-driven luciferase activity and GnRH mRNA level were observed within 12 h and sustained up to 48 h. Moreover, treatment with GnRH agonist for 12 h significantly decreased the transcription rate of the mouse GnRH gene, as revealed by nuclear run-on transcription assay. The promoter analysis with the 5′-deletional constructs demonstrated that cis-acting elements important for GnRH autoregulation by GnRH agonist reside within −854 bp upstream from the transcription start site. These data clearly demonstrate that GnRH can exert autocrine regulation at the level of GnRH gene transcription.
Molecular Brain Research 11/1997; · 2.00 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To precisely analyze the role of ovarian steroids in the regulation of laminin chain gene expression in mouse uterine tissues, the ovariectomized mouse model was used. Ovariectomized mice received a single injection of steroid hormones and total RNA was isolated from whole uterine tissues. Messenger RNA levels of each laminin chain (A, B1, and B2) were determined by competitive RT‐PCR procedures. Estradiol decreased mRNA levels of laminin B1 chain about two‐fold, and B2 chain rather moderately. Estradiol‐induced inhibition of laminin B1 and B2 chain mRNA levels were completely blocked by pretreatment with estrogen receptor antagonist tamoxifen. Estriol, a short acting estrogen which cannot induce hyperplastic responses of rodent uterine tissues, also showed an inhibitory effect on B1 and B2 chain mRNA levels, while estrone, an inactive estrogen, failed to influence either B chain mRNA levels. Effects of steroids on A chain mRNA level were quite different from those on B chains. Laminin A chain mRNA level was slightly increased by estradiol treatment, but negatively affected by progesterone. Progesterone treatment greatly increased both B chain mRNA levels, but slightly decreased A chain mRNA level compared to the control. The effect of progesterone on laminin chain‐specific mRNA levels was further increased by co‐injection of estradiol in a time‐dependent manner. Progesterone‐induced B1 and B2 chain mRNA transcription was inhibited by RU486, a synthetic anti‐progesterone/anti‐glucocorticoid. The present study demonstrates for the first time that steroids are able to regulate laminin gene expression in mouse uterine tissues, indicating that steroid‐regulated laminin gene expression is involved in uterine growth and probably differentiation.
Korean journal of biological sciences 01/1997; 1(1):115-121.