Filippone, Maria Grazia (2013) Wnt4 expression in thyroid cells is modulated by the transcription factor Pax8. [Tesi di dottorato]


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Item Type: Tesi di dottorato
Resource language: English
Title: Wnt4 expression in thyroid cells is modulated by the transcription factor Pax8
Filippone, Maria
Date: 2013
Number of Pages: 60
Institution: Università degli Studi di Napoli Federico II
Department: Medicina Molecolare e Biotecnologie Mediche
Scuola di dottorato: Medicina molecolare
Dottorato: Genetica e medicina molecolare
Ciclo di dottorato: 25
Coordinatore del Corso di dottorato:
Date: 2013
Number of Pages: 60
Keywords: Wnt4, transcriptional regulation
Settori scientifico-disciplinari del MIUR: Area 05 - Scienze biologiche > BIO/13 - Biologia applicata
Date Deposited: 12 Apr 2013 11:14
Last Modified: 17 Jun 2014 06:04

Collection description

The transcription factor Pax8 is expressed during thyroid development and is involved in the morphogenesis of the thyroid gland and maintenance of the differentiated phenotype. To date, Pax8 has been shown to regulate all the genes that are considered markers of thyroid differentiation. To identify novel Pax8 target genes we performed a genome-wide expression analysis following Pax8 siRNA. The silencing of Pax8 expression in rat thyroid differentiated FRTL-5 cells and the subsequent analysis of the gene expression profile by microarray identified Wnt4 among the down-regulated genes. As the other members of the Wnt family, Wnt4 has been implicated in several developmental processes including regulation of cell fate and patterning during embryogenesis. Up to now, the only data on Wnt4 in thyroid concern its down-regulation as necessary for the progression of thyroid epithelial tumors. Currently, we believe that it could be involved in thyroid morphogenesis, development and in the maintenance of the epithelial phenotype. We focused our attention on the elucidation of the molecular mechanisms by which Pax8 could regulate Wnt4 expression in thyroid cells. Analysis of the 5’-flanking region of the Wnt4 gene identified a putative Pax8 binding site confirmed by EMSA and ChIP analysis. Moreover, transfection of FRTL-5 cells with different regions corresponding to progressive deletions of the 5’-UTR of Wnt4 showed that all the generated constructs possess a thyroid-specific activity due to the presence of the transcription factor Pax8 and other transcription factors recently demonstrated to be its interactors. The results obtained during this study show that Pax8 is indeed involved in the transcriptional modulation of the Wnt4 promoter. Interestingly, we also revealed that the expression of Wnt4 is TSH dependent in FRTL-5 cells. Taken together, our data indicate that in thyroid cells the transcription factor Pax8 participates to Wnt4 gene expression directly binding to its 5’-flanking region suggesting that Wnt4 is a new target of this master regulatory gene. We propose that in thyroid cells the expression of Wnt4 correlates with the integrity of the epithelial phenotype and is reduced when this integrity is perturbed. Moreover, we would like to suggest that the over-expression of Wnt4 in thyroid cancer cellular models is able to revert the mesenchymal phenotype.


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