Figure 2.

Ba/F3 cells stably expressing CYF10 mutants are able to grow in IL‐3 independent manner. (a) Cell growth transducing potential of mutant EGFR is not diminished by abrogation of C‐terminal phosphorylation. Cell proliferation ability of various transformed Ba/F3 cell lines used for panel (a) was assayed by counting cell numbers on 3, 4, 5 and 6 days later (0.2 × 10⁶/ml each cell lines were seeded on day 0 after 2 weeks of IL‐3 withdrawal). The results are indicated as means ± SD of five cell counts. (b) Tyrosine phosphorylation was drastically reduced in CYF10 mutants. Whole‐cell lysates from Ba/F3 cells transformed with L858R, Ex19Del and Ex20Ins EGFR mutant with or without CYF10 mutation were subjected to immunoblotting with antibodies against phosphotyrosine (4G10), EGFR or STAT3. The level of STAT3 expression is shown as a loading control. Based on the molecular weight of EGFR, the lower bands detected by the antiphosphotyrosine antibody in the blot is not likely to be phospho‐EGFR, but an unknown phosphoprotein.