PAX-8 ACTIVATES THE ENHANCER OF THE HUMAN THYROPEROXIDASE GENE

In this study we report on a novel natural target of the paired domain transcription factor PAX 8 in the enhancer element of the human thyro peroxidase gene, one of the most important thyroid differentiation mar kers. It is the primary enzyme involved in thyroid hormone synthesis a nd PAX 8 has been previously identified as an activating factor of the rat thyroperoxidase gene promoter. In vitro, PAX 8 binds a cis elemen t of the human enhancer and its exogenous expression induces the enhan cer activity in co-transfection experiments in Cos-7 cells, When mutat ed at this binding site, the enhancer is no longer activated by PAX 8. Our finding strengthens the PAX 8 role in the maintenance of thyroid differentiation and in particular in the tissue-specific thyroperoxida se gene expression.