FIG. 6.

Cytokine-independent survival and proliferation of TF-1 myeloid leukemia cells expressing the GFP-Fes CC1 domain point mutant protein. TF-1 cells were infected with recombinant retroviruses carrying GFP as a negative control (open bars), GFP-Fes (gray bars), GFP-Fes L145P protein (hatched bars), or GFP-Fes 2LP (solid bars). Following infection, the cells were placed under G418 selection in the presence of GM-CSF for 10 to 14 days, at which point each of the drug-resistant cell populations exhibited uniform green fluorescence (data not shown). To monitor GM-CSF dependence, cells were washed free of cytokine and replated in the absence (top panel) or presence (bottom panel) of GM-CSF and viable cells were counted following trypan blue staining every 2 days. Two independent experiments yielded comparable results.