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Keywords :
Animals; Gene Expression Regulation/*drug effects; Genes/drug effects; Growth Hormone/*genetics; Herpes Simplex/genetics; Pituitary Neoplasms/pathology; Promoter Regions, Genetic/*drug effects; Rats; Recombinant Fusion Proteins/biosynthesis; Thymidine Kinase/genetics; Transcription, Genetic/*drug effects; Triiodothyronine/*pharmacology; Tumor Cells, Cultured/drug effects
Abstract :
[en] Three DNA constructs, the natural human growth hormone gene (hGH-hGH) its 500 bp promoter linked to the chloramphenicol acetyl transferase reporter gene (hGH-CAT), and its structural part linked to the herpes virus thymidine kinase promoter (TK-hGH) were introduced into rat pituitary GC cells by DEAE-dextran transfection. Transient expression was followed as a function of triiodothyronine (T3) concentration. The hGH-CAT expression was specifically inhibited by T3 following a typical dose-response curve while hGH-GH gene expression was not significantly modified. The transient expression of TK-hGH increased as a function of T3 concentration. These results indicate that T3 exerts two opposite effects on hGH gene expression. First, it down-regulates expression by acting on the promoter; second, it up-regulates expression by acting on the structural part of the gene. These action could be due to regulation of transcription and mRNA stabilization, respectively.
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