ROLE OF THE TRANSCRIPTION FACTOR SOX-2 IN THE EXPRESSION OF THE FGF-4GENE IN EMBRYONAL CARCINOMA-CELLS

It has been shown previously that the FGF-4 gene is regulated by a pow erful downstream enhancer in embryonal carcinoma (EC) cells. This enha ncer contains an essential HMG motif; however, the transcription facto r that binds to the HMG motif in EC cells has not been determined defi nitively. In earlier studies, this HMG motif was shown to bind a heat- stable, redox-insensitive factor expressed by F9 EC cells. Others have proposed that the transcription factor Sox-2 binds to the FGF-4 enhan cer HMG motif. In this study, we demonstrate that the N-terminal half of Sox-2, which contains the DNA binding domain, binds to the FGF-4 en hancer HMG motif and we show that this binding is unaffected by heat a nd oxidation. In addition, we employed two experimental approaches to demonstrate that Sox-2 regulates the transcription of the FGF-4, gene in EC cells. As part of these studies, an expression plasmid that code s for a dominant-negative form of Sox-2 was used in transient expressi on assays. In other experiments, a Sox-2 antisense expression plasmid was used. When co-transfected into F9 EC cells along with an FGF-4 pro moter/reporter gene construct, each expression plasmid caused a signif icant reduction in reporter activity. Our studies also demonstrate tha t Sox-2 affects the expression of the FGF-4 gene in the multipotent EC cell line, P19. Taken together, these studies argue strongly that Sox -2 plays an important role in the expression of the FGF-4 gene in vivo . Mol. Reprod. Dev. 50:377-386, 1998. (C) 1998 Wiley-Liss, Inc.