Rap1 mediates Lu/BCAM activation by JAK2V617F. (A) Quantification of Rap1-GTP in BaF3 JAK2 wt (wt) and BaF3 JAK2V617F (V127F) cells, paired t test, **P < .01 compared with wt, (n = 4). (B) Quantification of Rap1-GTP in the presence or absence of JAK2 inhibitors in HEL-Lu cells. The top and bottom panels show the amounts of Rap1-GTP and total Rap1, respectively. The GTP-bound fraction is determined by the Rap1-GTP/Rap1 ratio, with the ratio of the UT column being the reference value. Typical results of 3 experiments. (C) Quantification of Lu phosphorylation in the presence of Rap1 wt or Rap1 dominant-negative mutant S17N. The phosphorylated fraction is determined by the P/WB ratio, with the ratio of the wt column being the reference value. Results are representative of 3 experiments. (D) Cell adhesion to laminin at 2 dyn/cm² of HEL-Lu cells expressing Rap1S17N normalized to values from cells expressing Rap1 wt; paired t test, **P < .01 compared with wt, (n = 3).