| Research Abstract |
To investigate mechanisms of interferon (IFN) resistance, we have established an IFN-resistant cell line Daudi^<res> by long-term exposure of IFN-alpha to Daudi cells. Daudi^<res> cells were I x lO^4 times more resistant to IFN-alpha than parental cells. Expression of IEN receptors, STATI, STAT2, (2'-5') oligoadenylate synthetase, RNase L, and double-stranded RNA-dependent protein kinase was almost equally induced or enhanced by IFN-alpha in both cell lines. Among IFN-inducible genes examined, only ICE expression was deficient in Daudires cells. We then examined the regulatory mechanisms of the ICE promoter, and found that IFN-induced transcriptional activation of ICE was dependent on the binding of IRF-1 to its initiator (Inr) element. IRF-2 also bound to the same sequence and acted, in contrast, as a repressor. mr binding of IRF-1 and IRF-2 was diminished in IFN-treated Daudi^<res> cells due to insufficient induction of both proteins. Moreover, the IRF-l/IRF-2 ratio was significantly lower in Daudires cells than in parental cells. As a result of this imbalance, ICE promoter activation was impaired in this cell line. Forced IRF-l expression was able to activate the ICE promoter in Daudi^<res> cells. Moreover, ICE mRNA induction was also defective in other lFN-resistant cell lines such as HL-60 and K562. Constitutive binding of IRF-2 and the lack of IRF-l binding were observed in the ICE promoter of both cell lines. These results suggest that IRFs and their target genes including ICE are implicated in IEN resistance of some cell types.
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