Interferon-alpha synergistically enhances induction of interleukin-6 by double stranded RNA in HeLa cells

Double stranded RNA (dsRNA), an intermediate that is common during viral in fection, directly induces much higher levels of expression of interleukin-6 (IL-6) mRNA than does the cytokine IL-1 beta. Interferon alpha (IFN alpha) by itself does not induce expression of IL-6; nonetheless, IFN alpha pretr eatment dramatically enhances IL-6 induction by dsRNA but not by IL-1 beta. Mutation of either the activating transcription factor/cyclic AMP response element binding protein (ATF/CREB) or the NF-IL-6 binding element within t he IL-6 promoter eliminates most responsiveness of CAT reporter constructs to either dsRNA or to IL-1 beta. IFN alpha pretreatment partially restores responsiveness to dsRNA but not to IL-1 beta when either the ATF/CREB site or the NF-IL-6 site is mutated, but at least one of these sites must be int act for responsiveness to be restored. Mutation of the kappa B binding site in the IL-6 promoter eliminates responsiveness to either IL-1 beta or to d sRNA, and pretreatment with IFN alpha does not restore any responsiveness. Incubation with dsRNA leads to a decrease in protein translation, especiall y in cells that have been pretreated with IFN alpha. Nonetheless, IFN alpha pretreatment followed by dsRNA leads to very high IL-6 protein levels. The se studies demonstrate that major differences exist in the induction of IL- 6 at both the mRNA and protein levels by dsRNA compared to cytokines and th at IFN alpha pretreatment selectively enhances IL-6 induction by dsRNA but not by IL-1 beta. The high levels of IL-6 expression that result when cells encounter class I IFN prior to dsRNA suggest a mechanism for a heightened host response to viral infection with heightened production of this pleotro pic cytokine.