The Thyrotropin β-Subunit Gene Is Repressed by Thyroid Hormone in a Novel Thyrotrope Cell Line, Mouse TαT1 Cells**This work was supported by NIH Research Grants R01-HD-20377 and HD-12303 (to P.L.M.) and R01-DK-36843 (to E.C.R.); fellowships from the Spanish Ministry of Education and Science and Fundacion Jaime del Amo, Universidad Complutense de Madrid, Spain (to B.Y.); and a Ford Foundation Fellowship, the President’s Fellowship of the University of California, and NIH National Research Scientist Award Fe

Abstract

TSH is expressed in two populations of thyrotropes in the pituitary: one in the pars distalis and a second in the pars tuberalis. Pars distalis thyrotropes exhibit classical endocrine inhibition of TSH by thyroid hormone, whereas pars tuberalis thyrotropes do not. The majority of our understanding of TSH subunit gene regulation has come from studies conducted in dispersed pituitary, dispersed thyrotropic tumors, or the GH 3 somatolactotrope cell line. However, the dispersed pituitary model is limited because of its inherent heterogeneity, thyrotropic tumors are difficult to grow and maintain, and the GH 3 cells lack endogenous TSH expression. The recent derivation of a clonal thyrotrope cell line, T␣T1, that expresses thyrotrope-specific markers, overcomes these limitations. However, because it was not possible to distinguish whether the tumor from which the T␣T1 cells are derived originated in the pars distalis or the pars tuberalis, it was necessary to define their cellular origin and thereby establish their status as representative thyrotrope cells for future molecular studies. In this study, we demonstrate that the T␣T1 cells express thyroid hormone receptors (␤1 and ␤2) and their heterodimeric partner, retinoid X receptor-␥. Treatment with T 3 causes a dose-and time-dependent decrease in the expression of the TSH ␤-subunit messenger RNA. In contrast to previous reports in rat pituitary cultures, T 3 does not alter TSH ␤-subunit messenger RNA stability in the T␣T1 cells. Based on these data and the presence of thyrotrope-specific isoforms of the transcription factor Pit-1, we conclude that the T␣T1 cells represent differentiated thyrotropes of the pars distalis and will be a useful model system for future analysis of the cis-and trans-acting factors necessary for thyrotrope-specific and thyroid hormone-regulated TSH gene expression. (Endocrinology 139: 4476 -4482, 1998) T SH OCCUPIES a centralized position in the hypothalamo-pituitary-thyroid axis and is responsible for maintaining appropriate thyroid hormone levels in the circulation. It indirectly plays a crucial role in maintaining vital metabolic functions and is a necessary component in clinical treatment regimens for diseases such as thyroid cancer and thyroid dysfunction. It is therefore important to delineate the underlying mechanisms that control expression of TSH in the thyrotrope cells of the anterior pituitary.TSH is a member of the glycoprotein hormone family and consists of two subunits, ␣ and ␤, that are encoded by distinct genes on different chromosomes (1). The ␣-subunit is shared by all members of the glycoprotein hormone family, including LH, FSH, and CG, in addition to TSH. The ␣-subunit gene is, therefore, expressed in three discrete cell types: the thyrotrope and gonadotrope cells of the anterior pituitary and the trophoblast cells of the placenta. In contrast, expression of the ␤-subunit of TSH is restricted to the thyrotrope cells. The cell type specificity exhibited by the ␤-subunit of TSH as well as the ␤-subunits of the ...

Liganded T3 receptor β2 inhibits the positive feedback autoregulation of the gene for GATA2, a transcription factor critical for thyrotropin production

“…Next, we examined the inhibitory effect of liganded TRβ2 in the cells, where the GATA2 gene is endogenously expressed presumably via its positive feedback loop. While TαT1 is known to be a thyrotroph cell line [48], its GATA2 protein expression level is modest [8]; we found that the suppressive effect of T3 on TSHβ and the CGA mRNA was mild (data not shown) and completely lost, respectively. Other candidates are gonadotroph-derived LβT2 [43] and choriocarcinoma-derived JEG3 [52], both of which express the CGA gene [30, 34,35,52].…”

“…Cells were harvested after incubation for an additional 24 hr, and CAT activity was measured as described previously [17]. Mouse thyrotroph-derived TαT1 cells [48] (a kind gift from Dr. Pamela Mellon, University of California, CA, USA) were seeded on Matrigel-coated plates (Becton Dickinson Labware, Bedford, MA, USA). LβT2 cells, a mouse gonadotroph cell line [43], were cultured in DMEM supplemented with 10% FCS.…”

Novel Splicing of Immune System Thyroid Stimulating Hormone β-Subunit—Genetic Regulation and Biological Importance

“…However, it has since been learned that Pit-1 is probably minimally involved, and that GATA-2 may be the primary activator of TRH-driven transcription of the TSHβ gene (43–46). Other studies have shown that thyroid hormone negatively regulates TSHβ by interfering with the binding of transcription factors near the proximal promoter region (47, 48). In the case of immune system TSHβv, no transcription factors have, as yet, been linked to gene activation.…”

Novel aspects of T3 actions on GH and TSH synthesis and secretion: physiological implications

“…These actions are rapidly triggered even in the presence of transcription inhibitors (Yusta et al 1998, Lorenzo et al 2002 by TH interactions with THRs coupled to specific enzymes in the cytosol or to other binding sites located on the plasma membrane and organelles such as mitochondria and endoplasmic reticulum (Moeller et al 2006, Davis et al 2008, 2009, Goulart-Silva et al 2011.…”