Ptpn2 protein levels alter sensitivity to JAK1 inhibition of transformed Ba/F3 cells. (A) IL-3–independent Ba/F3 cells were treated with either JAK inhibitor I (100 nM, white) or DMSO (black). Silencing of Ptpn2 consistently reduced the sensitivity of JAK1-dependent Ba/F3 cells to inhibition of the JAK/Stat pathway. Different JAK1 mutants are shown on the x-axis. The number of the respective untreated cells was set as 100% and the y-axis displays relative cell growth (%). Results shown are the average of 3 determinations. Bars indicate SEM. *P < .05. Black bars indicate shRNA-Ptpn2-A; gray bars, shRNA-control1. The blot shown is representative of 3 independent experiments. (B) Differences in Ptpn2 expression levels affected the sensitivity of JAK1-dependent Ba/F3 cells to JAK inhibition. Reduction of the Ptpn2 protein resulted in a shift of the dose-response curve from 49.3 to 94.8nM. A dose-response curve was obtained by exposure of the cells to increasing concentrations of JAK inhibitor I. Cell numbers were determined 24 hours after inhibitor addition. The y-axis displays cell growth relative to DMSO-treated control cells (%). Each data point is an average of 3 calculations. Error bars represent SEM.