NF-IL6 AND AP-1 COOPERATIVELY MODULATE THE ACTIVATION OF THE TSG-6 GENE BY TUMOR-NECROSIS-FACTOR-ALPHA AND INTERLEUKIN-1

Tumor necrosis factor alpha (TNF-alpha) and interleukin-1 (IL-1) activ ate transcription of the TSG-6 gene in normal human fibroblasts throug h a promoter region (-165 to -58) that encompasses an AP-1 and a NP-IL 6 site. We show by deletion analysis and substitution mutagenesis that both sites are necessary for activation by TNF-alpha. Activation by I L-1 requires the NF-IL6 site and is enhanced by the AP-1 site. These r esults suggest that the NF-IL6 and AP-1 family transcription factors f unctionally cooperate to mediate TNF-alpha and IL-1 signals. Consisten t with this possibility, IL-1 and TNF-alpha markedly increase the bind ing of Fos and Jun to the AP-1 site, and NF-IL6 activates the native T SG-6 promoter. Activation by NF-IL6 requires an intact NF-IL6 site and is modulated by the ratio of activator to inhibitor NF-IL6 isoforms t hat are translated from different in-frame AUGs. However, the inhibito r isoform can also bind to the AP-1 site and repress AP-1 site-mediate d transcription. The finding that the inhibitor isoform antagonizes ac tivation of the native TSG-6 promoter by IL-1 and TNF-alpha suggests t hat NF-IL6 has a physiologic role in these cytokine responses. Thus, t he functionally distinct NF-IM isoforms cooperate with Fos and Jun to positively and negatively regulate the native TSG-6 promoter by TNF-al pha and IL-1.