A Sp1 binding site of the tumor necrosis factor α promoter functions as a nitric oxide response element

Abstract

Regulation of gene transcription is an incompletely understood function of nitric oxide (NO). Human leukocytes produce increased amounts of tumor necrosis factor α (TNF-α) in response to NO. This effect is associated with decreases in intracellular cAMP, suggesting that NO might regulate gene transcription through promoter sequences sensitive to cAMP such as cAMP response elements (CRE) and Sp1 binding sites. Here we report that a Sp1 binding site in the TNF-α promoter conveys NO responsiveness. Human U937 cells were differentiated for TNF-α production with phorbol 12-myristate 13- acetate. NO donors and H89, an inhibitor of cAMP-dependent protein kinase increased, while dibutyryl cAMP (Bt2cAMP) decreased TNF-α promoter activity. Deletion or mutation of the proximal Sp1 site, but not the CRE site, abolished the activating effects of NO donors and H89. Further, NO- and H89-mediated increases in TNF-α promoter activity were associated with decreased Sp1 binding. The insertion of Sp1 sites into a minimal cytomegalovirus promoter conferred NO responsiveness, an effect blocked by Bt2cAMP. Mutation of these inserted Sp1 sites prevented this heterologous promoter from responding to NO, H89 and Bt2cAMP. These results identify the Sp1 binding site as a promoter motif that allows NO to control gene transcription.