Transcription of the thyroid transcription factor-1 (TTF-1) gene from a newly defined start site: positive regulation by TTF-1 in the thyroid.
Regulation of the thyroid transcription factor-1 (TTF-1) gene expression in the thyroid was investigated. We identified a new transcription start site as nucleotide (nt) -1917, 1700 bp upstream of previously described site, and the region encompassing nt -1242 to -14 as the first intron. Although a probe targeting exon 2 hybridized to both 3.7 and 2.7 kp transcripts, a probe targeting newly identified exon 1 mainly reacted with 3.7 kb transcript, indicating that there exsits a transcript from -1917. Chloramphenicol acetyltransferase (CAT) reporter gene assays demonstrated that 5'-flanking region of the start site exhibited promoter activity in FRTL-5 cells but not in rat liver cells, suggesting that this region confers the thyrocyte-selective expression of the gene. Two consensus TTF-1 binding motifs were detected in this promoter region, and electrophoretic mobility-shift assays showed that oligonucleotide probes, each containing one of these motifs, formed a complex with the recombinant TTF-1 homeodomain. Moreover, recombinant TTF-1 increased the transcriptional activity in FRT cells which do not express TTF-1. These results suggest that transcription from the newly identified start site in the TTF-1 gene is positively regulated by TTF-1 in the thyroid.
Nakazato
M
M
Third Department of Internal Medicine, Yamanashi Medical University, Tamaho, Japan.
Endo
T
T
Saito
T
T
Harii
N
N
Onaya
T
T
D000818:Animals; D002460:Cell Line; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000302:isolation & purification; D004848:Epithelium; D005786:Gene Expression Regulation / Q000187:drug effects; D005796:Genes; D009687:Nuclear Proteins / Q000235:genetics* / Q000502:physiology*; D011401:Promoter Regions, Genetic; D051381:Rats; D013961:Thyroid Gland / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D000074482:Thyroid Nuclear Factor 1; D014157:Transcription Factors / Q000235:genetics* / Q000502:physiology*; D014158:Transcription, Genetic
D018076:DNA, Complementary; C000614416:Nkx2-1 protein, rat; D009687:Nuclear Proteins; D000074482:Thyroid Nuclear Factor 1; D014157:Transcription Factors