Pax8 has a key role in thyroid cell differentiation.
Transformation of rat thyroid cells with polyoma virus middle T antigen results in loss of the thyroid-differentiated phenotype, measured as the expression of the thyroglobulin (Tg), thyroperoxidase (TPO), and sodium/iodide symporter (NIS) genes. Among the transcription factors involved in the regulation of these genes, TTF-1 and TTF-2 were still detected at nearly wild-type levels, while a specific loss of the paired domain transcription factor Pax8 was observed. In this study, we used the PCPy cell line as a model system to study the role of Pax8 in thyroid differentiation. We demonstrate that the reintroduction of Pax8 in PCPy cells is sufficient to activate expression of the endogenous genes encoding thyroglobulin, thyroperoxidase, and sodium/iodide symporter. Thus, this cell system provides direct evidence for the ability of Pax8 to activate transcription of thyroid-specific genes at their chromosomal locus and strongly suggests a fundamental role of this transcription factor in the maintenance of functional differentiation in thyroid cells. Moreover, we show that Pax8 and TTF-1 cooperate in the activation of the thyroglobulin promoter and that additional thyroid-specific mechanism(s) are involved in such a cooperation. To identify the Pax8 domain able to mediate the specific activation of the thyroglobulin promoter, we transfected in PCPy cells three different Pax8 isoforms. The results of such experiments indicate that for the transcriptional activation of thyroid-specific genes, Pax8 uses an as yet unidentified functional domain.
Pasca di Magliano
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Stazione Zoologica "A. Dohrn," Villa Comunale, 80121 Naples, Italy; and Dipartimento di Biologia e Patologia Cellulare e Molecolare, Università di Napoli, Federico II, via Pansini 5, 80131 Naples, Italy.
Di Lauro
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R
Zannini
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D000818:Animals; D002454:Cell Differentiation / Q000502:physiology*; D002455:Cell Division; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D051858:Forkhead Transcription Factors; D005786:Gene Expression Regulation; D007453:Iodide Peroxidase / Q000235:genetics; D051379:Mice; D009687:Nuclear Proteins / Q000378:metabolism; D000072636:PAX8 Transcription Factor; D051761:Paired Box Transcription Factors; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013954:Thyroglobulin / Q000235:genetics; D013961:Thyroid Gland / Q000166:cytology* / Q000502:physiology; D000074482:Thyroid Nuclear Factor 1; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D014162:Transfection
D004268:DNA-Binding Proteins; C106894:FOXE1 protein, human; D051858:Forkhead Transcription Factors; C000614412:NKX2-1 protein, human; C000614414:Nkx2-1 protein, mouse; C000614416:Nkx2-1 protein, rat; D009687:Nuclear Proteins; D000072636:PAX8 Transcription Factor; D051761:Paired Box Transcription Factors; C499496:Pax8 protein, mouse; C499497:Pax8 protein, rat; D011994:Recombinant Proteins; D012097:Repressor Proteins; D000074482:Thyroid Nuclear Factor 1; D015534:Trans-Activators; D014157:Transcription Factors; D013954:Thyroglobulin; D007453:Iodide Peroxidase