title: Regulation by thyrotropin-releasing hormone (TRH) of TRH receptor mRNA degradation in rat pituitary GH3 cells.
abstract: In rat pituitary GH3 cells, thyrotropin-releasing hormone (TRH) down-regulates TRH receptor (TRH-R) mRNA (Fujimoto, J., Straub, R.E., and Gershengorn, M.C. (1991) Mol. Endocrinol. 5, 1527-1532), at least in part, by stimulating its degradation (Fujimoto, J., Narayanan, C.S., Benjamin, J.E., Heinflink, M., and Gershengorn, M.C. (1992) Endocrinology 130, 1879-1884). Here we show that TRH regulates RNase activity in GH3 cells and that specific mRNA sequences are needed for in vivo regulation of TRH-R mRNA by TRH. TRH affected RNase activity in a biphasic manner with rapid stimulation (by 10 min) followed by a decrease to a rate slower than in control lysates within 6 h. This time course paralleled the effects of TRH on degradation of TRH-R mRNA in vivo. The regulated RNase activity was in a polysome-free fraction of the lysates and was not specific for TRH-R RNA. A truncated form of TRH-R RNA that was missing the entire 3'-untranslated region (TRHR-R5) was more stable than full-length TRH-R RNA (TRHR-WT). In contrast to TRHR-WT mRNA, TRHR-R5 mRNA and TRHR-D9 mRNA, which was missing the 143 nucleotides 5' of the poly(A) tail, were not down-regulated by TRH in stably transfected GH3 cells as their rates of degradation were not increased. These data show that TRH regulates RNase activity in GH3 cells, that the 3'-untranslated region bestows decreased stability on TRH-R mRNA and that the 3' end of the mRNA is necessary for regulation by TRH of TRH-R mRNA degradation. We present an hypothesis that explains specific regulation of TRH-R mRNA degradation by TRH in GH3 pituitary cells.
authors.affiliation: Department of Medicine, Cornell University Medical College, New York, New York 10021.
authors.forename: C S
authors.initials: CS
authors.lastname: Narayanan
authors.forename: J
authors.initials: J
authors.lastname: Fujimoto
authors.forename: E
authors.initials: E
authors.lastname: Geras-Raaka
authors.forename: M C
authors.initials: MC
authors.lastname: Gershengorn
mesh_terms: D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D007295:Inositol Phosphates / Q000378:metabolism; D007700:Kinetics; D051379:Mice; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010911:Pituitary Neoplasms; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D017981:Receptors, Neurotransmitter / Q000096:biosynthesis / Q000235:genetics*; D018025:Receptors, Thyrotropin-Releasing Hormone; D013973:Thyrotropin-Releasing Hormone / Q000378:metabolism / Q000494:pharmacology*; D013997:Time Factors; D014158:Transcription, Genetic
chemical_list: D007295:Inositol Phosphates; D012333:RNA, Messenger; D017981:Receptors, Neurotransmitter; D018025:Receptors, Thyrotropin-Releasing Hormone; D013973:Thyrotropin-Releasing Hormone