FIG. 3.

Inhibition of JNK/AP-1 signaling impairs delNS1 virus-induced IFN-β promoter activation. (A) MDCK cells (10⁶) were transfected with 100 ng of the IFN-β promoter luciferase reporter plasmid p125-Luc (47). After 24 h, the cells were mock infected or infected with influenza PR8 WT or delNS virus at an MOI of 1. Cell extracts were prepared at 4 h postinfection in reporter lysis buffer (Promega) and assayed for luciferase activity. For a comparison, enzyme activity induced by delNS1 virus was arbitrarily set to 100%. Average values determined in three independent experiments are shown. (B) Cells were transfected with p125-Luc together with 4 μg of empty pKRSPA vector (vector) or expression plasmids encoding dominant negative JNK/SAPK (SAPKβ KK>>RR), dominant-negative c-Jun (TAM67) (30), or NS1 protein. Cells were infected with delNS1 virus at an MOI of 1, and 4 h later they were lysed and luciferase activity was determined as described for panel A. Error bars indicate standard deviations.