Carboxyl region of Mpl is required for the activation of Lyn kinase. (A) Mpl receptor mutations. Truncations are named for the number of residues that remain. (B) BaF3/Mpl, T69, and T111 cells were starved for 12 hours, preincubated with DMSO vehicle or 2 μM PP2, and then stimulated with TPO (15 ng/mL) for 10 minutes. Lysates normalized for total protein concentration were immunoprecipitated with anti-Lyn antibody. A kinase assay was then performed using immune complexes. Data are representative of 3 independent experiments. Immunoprecipitated cell lysates were subject to Western blot analysis using anti-Lyn antibody to ensure amounts of kinase were assayed (bottom). Data are representative of 3 independent experiments. Error bars indicate SD.