Regulation of endogenous thyrotropin-releasing hormone (TRH) receptor messenger RNA by TRH in GH4C1 cells.
Incubation with TRH causes a decrease (over 2-24 h) in the number of TRH receptors (TRHRs) in GH4C1 rat pituitary cells. Using a homologous cDNA probe prepared from the TRHR cloned from these cells, we demonstrate here that TRH modulates the rate of transcription of TRHR mRNA. Incubation of GH4C1 cells for 4 h with TRH caused an 80% reduction in TRHR mRNA concentration. The TRHR mRNA level remained low for 48 h in the continued presence of TRH. Run-on transcription assays demonstrated that TRH caused a decrease in TRHR mRNA transcription of about 60% at 4 h. The rate of transcription remained low at 12 h. Inhibition of protein synthesis did not prevent the TRH-induced decrease in TRHR mRNA. Activation of protein kinase C with the phorbol ester 12-O-tetradecanoyl-phorbol 13-acetate decreased TRHR mRNA by about 40% in 4 h. Elevation of [Ca2+]i with ionomycin decreased TRHR mRNA by about 25%. The two agents together decreased TRHR mRNA by approximately 70% in 4 h, an effect comparable to that elicited by TRH. We conclude that regulation of endogenous TRHR mRNA by TRH is modulated, at least in part, at the level of transcription by a mechanism that probably involves both activation of protein kinase C and an increase in [Ca2+]i.
Department of Molecular and Cellular Toxicology, Harvard School of Public Health, Boston, Massachusetts.
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Yang
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AH
Tashjian
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D004789:Enzyme Activation / Q000187:drug effects; D015759:Ionomycin / Q000494:pharmacology; D007700:Kinetics; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism; D014176:Protein Biosynthesis; D011493:Protein Kinase C / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D017981:Receptors, Neurotransmitter / Q000235:genetics*; D018025:Receptors, Thyrotropin-Releasing Hormone; D015290:Second Messenger Systems; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*; D014158:Transcription, Genetic / Q000187:drug effects*
D012333:RNA, Messenger; D017981:Receptors, Neurotransmitter; D018025:Receptors, Thyrotropin-Releasing Hormone; D015759:Ionomycin; D013973:Thyrotropin-Releasing Hormone; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium