Erk, Akt and Stat3 are dispensable for hematopoietic transformation induced by Jak2V617F. (A) Left panel: inhibition of Erk1/2 phosphorylation in the BM of Jak2V617F knockin mice by MEK inhibitor U0126. Right panel: BM cells from Jak2V617F knockin mice were plated in the methylcellulose medium in the absence of cytokine with indicated concentrations of U0126. CFU-E colonies were counted after 2 days. (B) Left panel: inhibition of Akt phosphorylation in the BM of Jak2V617F knockin mice by Akt inhibitor wortmannin. Right panel: BM cells from Jak2V617F knockin mice were plated in the methylcellulose medium in the absence of cytokine with indicated concentrations of wortmannin. CFU-E colonies were counted after 2 days. (C) Effect of dominant negative Stat3 (DN-Stat3) on phosphorylation/activation of Stat3 in the BM of Jak2V617F knockin mice and erythroid transformation mediated by Jak2V617F. BM from induced MxCre;V617F/+ mice were transduced with retrovirus expressing either DN-Stat3 or vector. After selection with puromycin (2 μg/mL) for 2 days, BM cells (1 × 105) were plated in methylcellulose medium without any cytokine (Methocult M3234). CFU-E colonies were counted after 2 days. Notably, expression of DN-Stat3 in the BM of Jak2V617F knockin mice almost completely inhibited phosphorylation of Stat3 (left panel); however, erythroid transformation induced by Jak2V617F was only partially inhibited (right panel). Asterisks show significant differences (*P < .05; **P < .005). Data are shown as mean ± SEM.
