L. pneumophila activates AP-1 signal through flagellin. (A) Time course of AP-1 activation in Jurkat cells infected with L. pneumophila, evaluated by EMSA. Nuclear extracts from Jurkat cells, infected with Corby or flaA mutant (MOI, 100:1), for the indicated time periods, were mixed with IL-8 AP-1 32P-labeled probe. (B) Sequence specificity of AP-1 binding activity and characterization of AP-1/CREB/ATF proteins that bound to the AP-1 binding site of the IL-8 gene. Competition assays were performed with nuclear extracts from Jurkat cells infected with Corby for 2 h. Where indicated, 100-fold excess amounts of each specific competitor oligonucleotide were added to the reaction mixture with labeled probe AP-1 (lanes 2 to 4). A supershift assay of AP-1 DNA binding complexes in the same nuclear extracts also was performed. Where indicated, appropriate antibodies (Ab) were added to the reaction mixture before the addition of the 32P-labeled probe (lanes 6 to 17 and 19). Arrows indicate specific complexes, while arrowheads indicate the DNA binding complexes supershifted by antibodies. (C) Jurkat cells were infected with Corby or flaA mutant for the indicated time periods. Cell lysates were prepared and subjected to immunoblotting with the indicated antibodies. Data are representative examples of three independent experiments with similar results.