TAK1 but not ERK plays key roles in L. pneumophila -induced IL-8 expression. (A) Jurkat cells were pretreated with the indicated concentrations of PD98059 for 1 h prior to L. pneumophila Corby infection and subsequently infected with Corby (MOI, 100:1) for 4 h (A) and 24 h (B). IL-8 mRNA expression on harvested cells was analyzed by RT-PCR (A) and the supernatants were subjected to ELISA to determine IL-8 secretion (B). Data are mean ± SD of three experiments. (C) Jurkat cells were pretreated with or without PD98059 (50 μM) for 1 h prior to L. pneumophila Corby infection and subsequently infected with Corby (MOI, 100:1) for the indicated times. Cell lysates were prepared and subjected to immunoblotting with the indicated antibodies. (D) Jurkat cells were transfected with -133-luc and a dominant negative mutant of TAK1 or empty vector and then infected with Corby for 6 h. The solid bar indicates LUC activity of -133-luc without Corby infection. The activities are expressed relative to that of cells transfected with -133-luc and empty vector without further Corby infection, which was defined as 1. Data are mean ± SD of three experiments. Data in (A) and (C) are representative examples of three independent experiments with similar results.