JAK1 pseudokinase mutations demonstrate transforming capability and result in hyperactivation of the JAK/STAT pathway. (A) Growth curves of Ba/F3 cells expressing JAK1 A634D and JAK1 R629_S632delinsSA cultured in the absence of IL-3 (graph is representative of 3 independent experiments). (B) Immunoblot analysis of Ba/F3 parental cells, Ba/F3 cells expressing JAK1 wild-type, JAK1 A634D, and JAK1 R629_S632delinsSA cultured in the presence of IL-3 and IL-3–independent Ba/F3 cells expressing JAK1 A634D, and JAK1 R629_S632delinsSA. (C) Immunoblot analysis of HEK293 cells expressing JAK1 wild type, JAK1 A634D, and JAK1 R629_S632delinsSA. p-, phosphorylated; WT, wild-type.