Elevated Erk signaling in cells expressing p15Ink4b. RAW264.7-Mig0 or RAW264.7-MigDDp15 cells were treated with LPS (1 μg/mL) for the indicated times, lysed, and analyzed by Western blot with Abs against TLR4 (Abgent Technologies); MyD88 and TLR3 (Cell Signaling Technology) and actin (Santa Cruz Biotechnology; A); phospho-Erk1/2(Thr202/Tyr204), Erk1/2, phospho-p38MAPK (Thr180/Tyr182), and p38MAPK (Cell Signaling Technology; B); and phospho-PKCδ (Thr505) and PKCδ (Cell Signaling Technology; C). (D) BM-DCs generated from p15Ink4b^fl/fl-LysMcre BM progenitors infected with Mig- or MigDDp15-expressing retroviruses were treated with LPS (100 ng/mL) for the indicated times and analyzed by Western blot with the specified Abs. (E) RAW264.7-MigDDp15 cells were pretreated with MEK1/2 inhibitor UO126 (5μM) for 30 minutes before treatment with LPS (1 μg/mL) for the indicated times, lysed, and analyzed by Western blot. The representative results shown are from the same membrane that was stripped and reprobed. (F) Luciferase reporter assay for PU.1 was evaluated as described in Figure 6C. RAW264.7-MigDDp15 cells either treated or untreated with UO126 (5μM) and LPS (1 μg/mL) for 24 hours were lysed and analyzed by luminometry. (G) Expression of CD80, CD86, and GAPDH mRNAs in RAW264.7-MigDDp15 cells treated or not with UO126 and LPS as indicated for 6 hours. Data are shown as means ± SD from 2 independent experiments. *P < .05.