Figure 1
CALR mutants specifically activate MPL and lead to cell growth augmentation. (a) 293T cells were transiently transfected with STAT5-LUC and CALR WT, CALRdel52 mutant or CALRins5 mutant in the presence of granulocyte-colony stimulating factor (G-CSF) receptor (CSF3R), erythropoietin receptor (EPOR) or thrombopoietin receptor (MPL). The vertical axis number is the fold induction when compared with that of WT CALR. Only in the presence of MPL, both type of CALR mutants augmented STAT5 activity. *P<0.05 and **P<0.01 vs CALR WT. (b) STAT5 (upper panel) and STAT3 (lower panel) transcriptional activity was assessed by the luciferase assay in 293T cells transiently expressing CALR WT, CALRdel52 mutant or CALRins5 mutant, together with MPL and either STAT5-LUC or STAT3-LUC. Twenty-four hours after transfection, cells were stimulated with several concentrations (0, 1.25, 2.5, 5, 10 and 20 ng/ml) of TPO. STAT5 and STAT3 transcriptional activity is enhanced by TPO stimulation in 293T cells in the presence of WT CALR. In contrast, TPO stimulation shows little effect on STAT5 transcriptional activity in the presence of CALRdel52 or CALRins5. *P<0.05 and **P<0.01 vs cells without TPO stimulation. The average values for relative luciferase activity generated in three independent experiment is shown. Data are presented as means±s.e.m. Tukey’s multiple comparison test with one-way analysis of variance was used.
