Synergistic induction of mouse serum amyloid A3 promoter by the inflammatory mediators IL-1 and IL-6

Serum amyloid A (SAA), one of the major acute-phase proteins, increases sev eral hundredfold in concentration in plasma following acute inflammation, p rimarily as a result of a 200-fold increase in its transcription rate. We h ave previously demonstrated that a 350-bp promoter fragment from the mouse SAAS gene could confer conditioned medium-induced expression in cultured ce lls. The induction is mediated through a 42-bp distal response element (DRE ) consisting of three functional regulatory elements. In this study, we sho w that interleukin-1 (IL-1) is the major cytokine in the conditioned medium responsible for SAA3 induction, and the induction by IL-1 can be effective ly blocked by H-7, a protein kinase C inhibitor. Although IL-6 alone had no effect on SAA3 promoter activity, the addition of IL-6 and IL-1 resulted i n dramatic synergistic activation of the reporter gene. We further show tha t the DRE is both necessary and sufficient to confer synergistic induction by IL-1 and IL-6, Moreover, individual mutation of the three regulatory ele ments within DRE either abolished or drastically reduced the synergistic in duction. Our results indicate that synergistic activation of SAA3 promoter by IL-1 and IL-6 is achieved through integration of signals triggered by th ese two cytokines onto the DRE and that all three functionally distinct reg ulatory elements in the DRE are required to effectively and fully activate SAAS gene transcription.