T cell activation-induced and HIV Tat-enhanced CD95(APO-1/Fas) ligand transcription involves NF-kappa B

CD95(APO-1/Fas) ligand (CD95L) gene expression is critically involved in ac tivation-induced T cell apoptosis. We and other have previously shown that HIV-1 Tat which is essential for efficient HIV gene expression sensitizes C D95-mediated apoptosis and up-regulates CD95L expression in T cells. In the present study we have investigated the regulatory mechanism for CD95L expr ession. Two NF-kappa B binding sites are localized at -537 to -521 and -57 to -47 (relative to the transcription start site) of the human CD95L promot er. We show that both elements bind to NF-kappa B and SP-1 transcription fa ctors and NF-kappa B is involved in transactivation of the CD95L promoter u pon T cell activation. Mutations at each NF-kappa B site by two base pair s ubstitutions resulted in 30-70 % reduction of the promoter activity. The ef fect of Tat on the human CD95L promoter activity was mapped to the same sit es. Mutation of each NF-kappa B site also impaired the effect of Tat on CD9 5L promotor activity. We also show that ectopic expression of Tat protein i n Jurkat T cells greatly increases NF-kappa B binding to its target DNA. Ou r studies provide evidence that Tat-enhanced CD95L expression is regulated at least in part by the NF-kappa B sites of the promoter.