An Sp1 binding site involves the transcription of the fas ligand gene induced by PMA and ionomycin in Jurkat cells

The transcriptional regulation of the Fas ligand (FasL) gene in Jurkat cells was investigated. We demonstrated that an Sp1 binding site, located between -280 and -275 bp relative to the translational start site (+1) of the FasL gene, was important for the transcription of the FasL gene by deletion and mutation analysis in Jurkat cells after phorbol 12-myristate 13-acetate (PMA) and ionomycin treatment. Nuclear extract of Jurkat cells formed complexes with the oligonucleotides bearing the Sp1 site within -280 to -275 of the FasL promoter. Apart from the constitutive complexes, a new complex was observed after PMA and ionomycin stimulation. Plasmid containing the Sp1 site sequence with site-directed mutation reduced the FasL promoter activity in driving the expression of reporter luciferase gene expression in transfected Jurkat cells after PMA and ionomycin stimulation. The binding of activated Jurkat cell nuclear extract to the mutated Sp1 binding site of the FasL promoter was ablated. In addition, the oligomer containing the Sp1 site of the FasL promoter could compete with oligomer with conserved Sp1 binding sequence in nuclear protein binding of activated Jurkat cells. The data presented in this study suggest that the transactivation of the FasL promoter via the Sp1 binding sequence (-280 to -275) involves the PMA- and ionomycin-induced expression of the FasL gene.