IDENTIFICATION OF 2 NF-KAPPA-B SITES IN MOUSE CD95 LIGAND (FAS LIGAND) PROMOTER - FUNCTIONAL-ANALYSIS IN T-CELL HYBRIDOMA

Fas ligand (FasL) gene expression is critically involved in peripheral T cell tolerance and lymphocyte homeostasis. Previous studies have su ggested that nuclear translocation of NF-kappa B during T cell activat ion is a critical event for FasL gene activation. In the present study we have identified two NF-kappa B sites (designated FasL-kappa B1 and FasL-kappa B2) on the promoter (similar to 700 bp) of FasL. The NF-ka ppa B sites were identified by electrophoretic mobility shift assay,Tr ansient transfection reporter analyses showed that the FasL promoter a ctivity was comparable between a construct that contains both sites an d a shorter construct (433 bp) that contains only the FasL-kappa B1 si te. Furthermore, elimination of FasL-kappa B1 by site-directed mutagen esis significantly inhibited FasL promoter activity. These observation s provide strong evidence that NF-kappa B directly binds to the FasL-k appa B1 site and up-regulates FasL gene expression.