JAK2T875N induces constitutive signaling leading to growth factor independence. JAK2T875N induces IL-3-independent growth of EpoR- or TpoR-expressing Ba/F3 cells (B, C) but not parental Ba/F3 cells (A), GMCSFR-expressing Ba/F3 cells (D) or parental 32D cells (E). Three independent experiments, each in triplicate, were realized and the mean plus or minus SD of one representative experiment is shown: MIG empty vector control +IL-3 (♦), MIG empty vector control -IL-3 (▪), MIG JAK2T875N -IL-3 (▴), MIG JAK2WT -IL-3 (×). Controls for functional expression of the different cytokine receptors were obtained by growing Ba/F3 EpoR, Ba/F3 TpoR, and Ba/F3 GMCSFR, respectively, in presence of EPO (squares; G), Tpo (♦; H), GMCSF (×; I) or in absence of cytokine (○). Parental Ba/F3 cells proliferate only in the presence of IL-3 (▴; F). (J) Studies of Jak2, STAT5, ERK1/2, and AKT phosphorylation in the different Ba/F3 clones overexpressing JAK2WT or mutant JAK2T875N.