Thyroid-specific transcription factors control Hex promoter activity.
The homeobox-containing gene Hex is expressed in several cell types, including thyroid follicular cells, in which it regulates the transcription of tissue- specific genes. In this study the regulation of Hex promoter activity was investigated. Using co- transfection experiments, we demonstrated that the transcriptional activity of the Hex gene promoter in rat thyroid FRTL-5 cells is approximately 10-fold greater than that observed in HeLa and NIH 3T3 cell lines (which do not normally express the Hex gene). To identify the molecular mechanisms underlying these differences, we evaluated the effect of the thyroid- specific transcription factor TTF-1 on the Hex promoter activity. TTF-1 produced 3-4-fold increases in the Hex promoter activity. Gel- retardation assays and mutagenesis experiments revealed the presence of functionally relevant TTF-1 binding sites in the Hex promoter region. These in vitro data may also have functional relevance in vivo, since a positive correlation between TTF-1 and Hex mRNAs was demonstrated in human thyroid tissues by means of RT-PCR analysis. The TTF-1 effect, however, is not sufficient to explain the difference in Hex promoter activity between FRTL-5 and cells that do not express the Hex gene. For this reason, we tested whether Hex protein is able to activate the Hex promoter. Indeed, co-transfection experiments indicate that Hex protein is able to increase the activity of its own promoter in HeLa cells approximately 4-fold. TTF-1 and Hex effects are additive: when transfected together in HeLa cells, the Hex promoter activity is increased 6-7-fold. Thus, the contemporary presence of both TTF-1 and Hex could be sufficient to explain the higher transcriptional activity of the Hex promoter in thyroid cells with respect to cell lines that do not express the Hex gene. These findings demonstrate the existence of direct cross-regulation between thyroid-specific transcription factors.
Puppin
Cinzia
C
Dipartimento di Scienze e Tecnologie Biomediche, Università di Udine, Piazzale Kolbe, 1 33100 Udine, Italy.
D'Elia
Angela V
AV
Pellizzari
Lucia
L
Russo
Diego
D
Arturi
Franco
F
Presta
Ivan
I
Filetti
Sebastiano
S
Bogue
Clifford W
CW
Denson
Lee A
LA
Damante
Giuseppe
G
D016475:3T3 Cells; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002460:Cell Line; D005786:Gene Expression Regulation; D015972:Gene Expression Regulation, Neoplastic; D006367:HeLa Cells; D018398:Homeodomain Proteins / Q000235:genetics*; D006801:Humans; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D051379:Mice; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000502:physiology*; D011401:Promoter Regions, Genetic / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D013961:Thyroid Gland / Q000166:cytology / Q000378:metabolism*; D013964:Thyroid Neoplasms / Q000235:genetics; D000074482:Thyroid Nuclear Factor 1; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*; D014162:Transfection
C078492:HHEX protein, human; C513080:Hhex protein, mouse; C513079:Hhex protein, rat; D018398:Homeodomain Proteins; C000614412:NKX2-1 protein, human; C000614414:Nkx2-1 protein, mouse; D009687:Nuclear Proteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D000074482:Thyroid Nuclear Factor 1; D014157:Transcription Factors; D008156:Luciferases