Identification of Two NF-κB Sites in Mouse CD95 Ligand (Fas Ligand) Promoter: Functional Analysis in T Cell Hybridoma

Abstract

Abstract Fas ligand (FasL) gene expression is critically involved in peripheral T cell tolerance and lymphocyte homeostasis. Previous studies have suggested that nuclear translocation of NF-κB during T cell activation is a critical event for FasL gene activation. In the present study we have identified two NF-κB sites (designated FasL-κB1 and FasL-κB2) on the promoter (∼700 bp) of FasL. The NF-κB sites were identified by electrophoretic mobility shift assay. Transient transfection reporter analyses showed that the FasL promoter activity was comparable between a construct that contains both sites and a shorter construct (433 bp) that contains only the FasL-κB1 site. Furthermore, elimination of FasL-κB1 by site-directed mutagenesis significantly inhibited FasL promoter activity. These observations provide strong evidence that NF-κB directly binds to the FasL-κB1 site and up-regulates FasL gene expression.