Cell-type-specific expression of the rat thyroperoxidase promoter indicates common mechanisms for thyroid-specific gene expression.
A 420-bp fragment from the 5' end of the rat thyroperoxidase (TPO) gene was fused to a luciferase reporter and shown to direct cell-type-specific expression when transfected into rat thyroid FRTL-5 cells. Analysis of this DNA fragment revealed four regions of the promoter which interact with DNA-binding proteins present in FRTL-5 cells. Mutation of the DNA sequence within any of these regions reduced TPO promoter activity. The trans-acting factors binding to these sequences were compared with thyroid transcription factor 1 (TTF-1) and TTF-2, previously identified as transcriptional activators of another thyroid-specific gene, the thyroglobulin (Tg) gene. Purified TTF-1 binds to three regions of TPO which are protected by FRTL-5 proteins. Two of the binding sites overlap with recognition sites for other DNA-binding proteins. One TTF-1 site can also bind a protein (UFB) present in the nuclei of both expressing and nonexpressing cells. TTF-1 binding to the proximal region overlaps with that for a novel protein present in FRTL-5 cells which can also recognize the promoter-proximal region of Tg. Using a combination of techniques, the factor binding to the fourth TPO promoter site was shown to be TTF-2. We conclude, therefore, that the FRTL-5-specific expression of two thyroid restricted genes, encoding TPO and Tg, relies on a combination of the same trans-acting factors present in thyroid cells.
Francis-Lang
H
H
European Molecular Biology Laboratory, Heidelberg, Germany.
Price
M
M
Polycarpou-Schwarz
M
M
Di Lauro
R
R
D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D016384:Consensus Sequence; D004252:DNA Mutational Analysis; D003850:Deoxyribonuclease I / Q000378:metabolism; D005786:Gene Expression Regulation / Q000502:physiology*; D007453:Iodide Peroxidase / Q000235:genetics*; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D008745:Methylation; D008969:Molecular Sequence Data; D010544:Peroxidases / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000235:genetics*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D013961:Thyroid Gland / Q000201:enzymology*; D014157:Transcription Factors / Q000502:physiology*
D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D010544:Peroxidases; D007453:Iodide Peroxidase; D008156:Luciferases; D003850:Deoxyribonuclease I