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 infection, directly induces much higher levels of expression of interleukin-6 (IL-6) mRNA than does the cytokine IL-1beta. Interferon alpha (IFNalpha) by itself does not induce expression of IL-6; nonetheless, IFNalpha pretreatment dramatically enhances IL-6 induction by dsRNA but not by IL-1beta. Mutation of either the activating transcription factor/cyclic AMP response element binding protein (ATF/CREB) or the NF-IL-6 binding element within the IL-6 promoter eliminates most responsiveness of CAT reporter constructs to either dsRNA or to IL-1beta. IFNalpha pretreatment partially restores responsiveness to dsRNA but not to IL-1beta when either the ATF/CREB site or the NF-IL-6 site is mutated, but at least one of these sites must be intact for responsiveness to be restored. Mutation of the kappaB binding site in the IL-6 promoter eliminates responsiveness to either IL-1beta or to dsRNA, and pretreatment with IFNalpha does not restore any responsiveness. Incubation with dsRNA leads to a decrease in protein translation, especially in cells that have been pretreated with IFNalpha. Nonetheless, IFNalpha pretreatment followed by dsRNA leads to very high IL-6 protein levels. These 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 that IFNalpha pretreatment selectively enhances IL-6 induction by dsRNA but not by IL-1beta. 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 pleotropic cytokine.