Mechanism of regulation of thyrotropin-releasing hormone receptor messenger ribonucleic acid in stably transfected rat pituitary cells

• Published in: Endocrinology (Philadelphia) Vol. 130; no. 4; p. 1879
• Main Authors: Fujimoto, J, Narayanan, C S, Benjamin, J E, Heinflink, M, Gershengorn, M C
• Format: Journal Article
• Language: English
• Published: United States 01.04.1992
• Subjects: Animals; Cell Line; Down-Regulation; Mice; Pituitary Gland - chemistry; Rats; Receptors, Neurotransmitter - analysis; Receptors, Neurotransmitter - genetics; Receptors, Thyrotropin-Releasing Hormone; RNA, Messenger - analysis; Thyrotropin-Releasing Hormone - pharmacology; Transcription, Genetic; Transfection
• ISSN: 0013-7227; 1945-7170
• DOI: 10.1210/en.130.4.1879

We showed previously that the level of TRH receptor (TRH-R) mRNA in rat pituitary GH3 cells is down-regulated by TRH. Here, we study the mechanism of regulation of TRH-R mRNA in a line of GH3 cells that are stably transfected with mouse pituitary TRH-R cDNA (GH-mTRHR-1 cells). GH-mTRHR-1 cells were found to have 2.4 times the number of TRH-Rs and to stimulate a 2.5-fold greater increase in inositol phosphates in response to TRH than the parent cell line and to show TRH-induced down-regulation of TRH-R number. GH-mTRHR-1 cells contained 26 +/- 1.6 molecules of mouse TRH-R mRNA/cell and 230 +/- 31 molecules of mRNA for the neomycin resistance gene (NEO) with which it was cotransfected. In GH-mTRHR-1 cells, TRH caused a dose-dependent transient decrease in mouse TRH-R mRNA, with a nadir to 20% of control levels after 6 h. In contrast, TRH did not affect NEO mRNA or glyceraldehyde phosphate dehydrogenase (GAPDH) mRNA, an endogenous gene product. TRH stimulated the rate of transcription of mouse TRH-R DNA by approximately 2-fold, but did not affect total poly(A) RNA synthesis. Most importantly, TRH caused a 4-fold increase in the rate of degradation of mouse TRH-R mRNA, but did not affect degradation of GAPDH mRNA. The half-lives of mouse TRH-R and GAPDH mRNAs were 3 and more than 20 h in control cells and 0.75 and more than 20 h in cells treated with 1 microM TRH for 1.5 h, respectively. These data show that the predominant effect of TRH on mouse TRH-R mRNA in GH-mTRHR-1 cells is to enhance the rate of its degradation. We suggest, therefore, that down-regulation of TRH-R mRNA caused by TRH in the parent GH3 cell line is secondary to increased TRH-R mRNA degradation.