TEL-JAK2 expression results in constitutive phosphorylation of ERK1 and ERK2.

(A) Ba/F3 and Ba/F3-TEL-JAK2 cells were depleted of cytokine and then stimulated in the presence (+) or absence (−) of IL-3. Phosphorylated ERK1 and ERK2 were detected by IB lysates with an antibody specific for phosphorylated ERK1/2 (pERK1/2) (upper panel). Total ERK1/2 was detected upon reprobing with an ERK1/2 antibody (lower panel). (B) U0126 inhibits IL-3 and TEL-JAK2–mediated proliferation. Ba/F3 cells growing in IL-3 (closed squares) and Ba/F3-TEL-JAK2(5-19) cells growing in the presence of IL-3 (closed circles) or in the absence of IL-3 (open circles) were incubated in increasing concentrations of U0126. An XTT assay was then performed.