The hβc FIΔ mutant generates JAK2- and ERK1/2-independent signals. (A) FDB1 cell populations were cultured without growth factor for 16 hours and then stimulated with mIL-3 or mGM-CSF for 5 minutes. Whole-cell lysates were subjected to Western blot analysis with the indicated antibodies. (B) FDB1 cells were cultured in the absence of growth factor (NF), mIL-3, or mGM-CSF and then fixed, permeabilized, and stained with the indicated primary antibodies (open histograms) or isotype-matched control (gray histograms). (C-D) FDB1 cells cultured in 500 BMU mIL-3 and FDB1 cells expressing FIΔ or V449E cultured in the absence of growth factor were treated for 24 hours with dimethyl sulfoxide (DMSO), (C) JAK2 inhibitor II (J2InhII) or AG490, and (D) U0126 or PD98059 (PD). Viability was measured by 7-amino-actinomycin D staining and flow cytometry. Error bars represent SEM, where n = 3; statistical significance was calculated by the use of a Student t test, *P < .05 **P < .01, ***P < .001.
