The Y₇₈F mutation leads to increased Tpo-mediated proliferation and signaling. (A) MTT proliferation assays were performed on c-Mpl wild-type–, Y₈F-, Y₇₈F-, and Y₈₊₇₈F-expressing cells. Data points represent the mean of 3 independent experiments using 3 different c-Mpl–expressing clones (**P < .01). Error bars represent SE. (B) Levels of phosphorylated Jak2, STAT5, AKT, and ERK1/2 in response to 50 ng/mL Tpo were determined by Western blot analyses. (C) Tpo-stimulated activation of Jak2, STAT5, AKT, and ERK1/2 in wild-type c-Mpl–expressing cells treated with control or AP2α2 siRNA. Data are representative of 3 independent experiments.