Regulation of the human fas promoter by YB-1, Puralpha and AP-1 transcription factors.

Fas (CD95/Apo-1) gene expression is dysregulated in a number of diseased states. Towards understanding the regulation of fas gene expression, we previously identified activator and repressor elements within the human fas promoter. Using a combination of expression screening and reporter gene assays, we have identified transcription factors which bind to these elements and thereby regulate transcription of the fas promoter. These are three single-stranded DNA binding proteins, YB-1, Puralpha and Purbeta and two components of the AP-1 complex, c-Fos and c-Jun. c-Jun is a potent transcriptional activator of fas and stimulated expression levels up to 184-fold in reporter gene assays. Co-expression with c-Fos abrogated c-Jun-mediated activation. YB-1 and Puralpha are transcriptional repressors of fas and decreased basal transcription by 60-fold in reporter gene assays. Purbeta was predominantly an antagonist of YB-1/Puralpha-mediated repression. Overexpression of YB-1 and Puralpha in Jurkat cells was shown to reduce the level of cell surface Fas staining, providing further evidence that these proteins regulate the fas promoter. It has been suggested that YB-1 plays a role in cell proliferation as an activator of growth-associated gene expression. We have shown that YB-1 is a repressor of a cell death-associated gene fas. These results suggest that YB-1 may play an important role in controlling cell survival by co-ordinately regulating the expression of cell growth-associated and death-associated genes.