Pit-1/GHF-1 binds to TRH-sensitive regions of the rat thyrotropin .beta. gene

Abstract

Three regions within the 5'-flanking region of the TSH beta gene have A-T-rich sequences which have sequence similarity to binding sites for the pituitary-specific POU domain transcription factor Pit-1/GHF-1. These three regions have been termed TSH A (-274 to -258 bp), TSH B (-336 to -326 bp), and TSH C (-402 to -384 bp). TSH A and TSH C are able to confer 2-6-fold TRH stimulation to the heterologous viral thymidine kinase (tk) promoter in transient expression assays in GH3 pituitary cells; TSH C can confer a 3-10-fold increase in basal enhancer activity as well. TSH A, B, and C DNAs all bound Pit-1 from GH3 cell nuclear extracts, based on gel mobility shift analysis in which antibody against Pit-1 prevented the formation of specific DNA-GH3 nuclear protein complexes. TSH A and TSH C also each formed several additional DNA-nuclear protein complexes which were not observed with TSH B. Some of these complexes may contain Pit-1 as their formation was inhibited by the addition of Pit-1 antibody; other complexes, however, were not altered by antibody treatment. All three A-T-rich elements bound in vitro translated Pit-1, with calculated affinities of 360 (A), 125 (B), and 38 (C) nM, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Thyrotropin-Releasing Hormone Gene Expression in the Anterior Pituitary. IV. Evidence for Paracrine and Autocrine Regulation

“…Although TRH and somatostatin appear to inhibit the expression of their genes, the pituitaryspecific transcription factor Pit-1 stimulates the transcription of its own gene (42). Pit-1 is essential for the genesis of three pituitary cell types, somatotrophs, lactotrophs, and thyrotrophs, and also mediates the transcriptional regulation of their genes (42)(43)(44)(45). Positive autocrine regulation of the Pit-1 gene may ensure that sufficient concentrations of this essential transcription factor are available at all times, whereas negative autocrine regulation of genes encoding peptide hormones may provide the necessary fine tuning to control expression levels of these genes (41,42).…”

“…Although the phosphokinase C pathway has been identified as the second messenger system conveying TRH activity, it is not clear which mediators would be involved in the activation of the TRH gene (47). Activation of TSH␤ as well as PRL transcription by TRH are mediated by the pituitaryspecific transcription factor Pit-1 (43)(44)(45). Whether Pit-1-binding sites exist in the promoter region of the TRH gene that could mediate inhibitory rather than stimulatory effects has not been previously investigated (2,48).…”

A Soluble Transcription Factor, Oct-1, Is Also Found in the Insoluble Nuclear Matrix and Possesses Silencing Activity in Its Alanine-Rich Domain

“…Interestingly, however, silencing has not been reported to occur in mouse and rat TSH␤ gene regulation. It was previously shown that upstream regions of the mouse and rat TSH␤ genes that roughly correspond to the hTSH␤ silencer element activated heterologous promoters such as those of Rous sarcoma virus or thymidine kinase (TK) in transient-transfection assays with TtT-97 or pituitary cells (34,48,69), and they therefore were labeled enhancers. Despite the sequence homology between the mouse and rat genes, the localizations of such enhancers did not coincide.…”

“…When tested on the homologous promoter, however, the proximal Ϫ133/Ϫ100 region was shown to be important for basal promoter activity and Pit-1-dependent activation (17,31). The activity of the rat enhancer elements (34,48) in the context of the homologous promoter remains unknown.…”

Expression of the pituitary transcription factor GHF-1/PIT-1 in cell types of the adult porcine adenohypophysis.

“…Effects of growth hormone releasing factor (GRF) on GH expression is likely to be mediated via regulated transcription of GHF-1 (Theill and Karin, 1993), which binds to two DNA elements within the GH promoter region (Bodner and Karin, 1988;Lefevre et al, 1987;West et al, 1987;Ye and Samuels, 1987). In the human TSHP gene promoter, three GHF-1 binding sites have been reported (Steinfelder et al, 1991,199213) that confer TRH-stimulated transcriptional activity as well as basal enhancer activity (Shupnick et al, 1992;Steinfelder et al, 1992a;Mason et al, 1993).…”