Thyroid or glucocorticoid hormone induces pre-growth-hormone mRNA and its probable nuclear precursor in rat pituitary cells.

Abstract

Thyroid or glucocorticoid hormone increases the synthesis of growth hormone (GH) by clonal lines of rat pituitary tumor cells. To investigate whether these increases arise from increased accumulation of GH-specific RNA sequences in the cytoplasm and nuclei of these cells, 2 existing procedures were adapted so that a 32P-labeled hybrid plasmid containing a complementary DNA sequence could be used to quantitate relative concentrations of the corresponding mRNA. One method (RNA gel blot hybridization) used electrophoresis of RNA, transfer to nitrocellulose paper and hybridization to 32P-labeled plasmid. The other (RNA dot hybridization) used covalent attachment of RNA to activated cellulose paper squares and hybridization to 32P-labeled plasmid. As probe, a hybrid plasmid (pBR322-GH1) was used which was shown by restriction analysis to contain a DNA sequence coding for rat GH. The results were comparable from both techniques and showed that incubation of [rat pituitary tumor] GH3 cells with a thyroid hormone (triiodothyronine), a glucocorticoid hormone (dexamethasone) or both hormones caused an increase of cytoplasmic pre-GH mRNA sequences of .apprx. 4-, 22- and 13-fold, respectively. Results obtained with the RNA gel blot hybridization method showed that hormonal stimulation leads to the induction of a single 1.0-kilobase [kb] species of pre-GH mRNA in the cytoplasm and of 2.7- and 1.0-kb species of GH-specific RNA in the nucleus.