JAK2 V617F-induced TpoR down-modulation is promoted by signaling via TpoR cytosolic Y626 residue. (A) HA-TpoR cell-surface and (B) TpoR total levels were analyzed by flow cytometry and Western blot, respectively, on the indicated cell lines as previously described. (C) Dose-dependence effect of Tpo on the proliferation of the indicated Ba/F3 cell lines. After down-modulation, Ba/F3 TpoR JAK2 V617F cells continue to proliferate both in the presence and absence of Tpo, whereas Ba/F3 TpoR JAK2 cells arrest proliferation in Tpo at concentrations > 1 ng/mL.