Overexpression of TTF-1 and PAX-8 restores thyroglobulin gene promoter activity in ARO and WRO cell lines - Discussion

Background. In anticipation of developing gene therapy against thyroid carcinoma we created an expression vector using the thyroglobulin (Tg) gene promoter. The inhibition of both Tg and thyroid-specific transcription factor (TTF-1 and PAX-8) gene expression, however, has been well documented in thyroid carcinomas. We therefore examined the effects of overexpression of TTF-1 and PAX-8 on Tg gene promoter activity in the human thyroid carcinoma cell lines, ARO (anaplastic) and WRO (follicular). Methods. ARO, WRO, and nonthyroid cells were transfected with an expression vector in which β- galactosidase (β-gal) is driven by the Tg gene promoter (β-gal). Tg, TTF- 1, and PAX-8 gene expression were also examined by reverse transcriptase- polymerase chain reaction (RT-PCR). Results. ARO and WRO exhibited decreased gene expression of Tg, TTF-1, and PAX-8. Transfection with TG-gal alone exhibited minimal β-gal expression, whereas cotransfection with TTF-1 and PAX-8 resulted in markedly increased expression. There was no evidence of β- gal expression with or without TTF-1 and PAX-8 in nonthyroid cells. Conclusions. Weak Tg gene promoter activity in ARO and WRO is associated with decreased expression of transcription factors TTF-1 and PAX-8 but can be restored with their overexpression. This model may serve as a template on which to further develop cell-specific gene therapy against thyroid carcinoma.