Stimulus-specific assembly of enhancer complexes on the tumor necrosis factor alpha gene promoter

The human tumor necrosis factor alpha (TNF-alpha) gene is rapidly activated in response to multiple signals of stress and inflammation. We have identi fied transcription factors present in the TNF-alpha enhancer complex in viv o following ionophore stimulation (ATF-2/Jun and NFAT) and virus infection (ATF-2/Jun, NFAT, and Sp1), demonstrating a novel role for NFAT and Sp1 in virus induction of gene expression. We show that virus infection results in calcium flux and calcineurin-dependent NFAT dephosphorylation; however, re latively lower levels of NFAT are present in the nucleus following virus in fection as compared to ionophore stimulation. Strikingly, Sp1 functionally synergizes with NFAT and ATF-2/c-jun in the activation of TNF-alpha gene tr anscription and selectively associates with the TNF-alpha promoter upon vir us infection but not upon ionophore stimulation in vivo. We conclude that t he specificity of TNF-alpha transcriptional activation is achieved through the assembly of stimulus-specific enhancer complexes and through synergisti c interactions among the distinct activators within these enhancer complexe s.