LPS induces Elk-1–dependent transcription.

(A) Nuclear extracts were prepared from LPS-stimulated THP-1 cells with or without PD98059 (25 μM). Western blot analysis was performed using antibodies against either phosphorylated or nonphosphorylated Elk-1. (B) The pGAL4-LUC (3 μg) and pGAL4–Elk-1TA (3 μg) were cotransfected into THP-1 cells. Transfected cells were preincubated in the presence or absence with PD98059 (25 μM) for 30 minutes prior to incubation with or without LPS for 5 hours. Luciferase activity in cell lysates was determined, and results were expressed as fold induction. Data (mean ± SD) are shown for 3 independent experiments. (C) THP-1 cells were cotransfected with pGAL4–Elk-1TA (4.0 μg) and pGAL4-LUC (1.5 μg) together with either pcDNA3 (4.5 μg) or plasmids expressing a dominant-negative version of Ras, Raf-1, ERK1, ERK2, or MEKK-1. Transfected cells were treated with or without LPS for 5 hours. Luciferase activity in cell lysates was determined, and results were expressed as percentage of the control plasmid (pcDNA3).