IV.B.3.b. Studies of overexpression of CFTR in CFT1 cells 
A series of studies were designed to test whether overexpression of CFTR in 
CFT1 cells can lead to abnormalities in growth characteristics of CF airway 
epithelial cells. A clone of CFT1 cells was exposed to a MMLV-based retrovirus 
(LCFSN) containing the normal CFTR cDNA and the neomycin resistance gene 
(37). Following a 1 hour exposure, the cells were allowed to replicate for three days 
in culture, following which they were put under G418 selection. Cells that survived 
G418 selection were then pooled, and plated at clonal density on a 3T3 cell feeder 
layer. Individual clones were expanded, and the amount of CFTR expressed per cell 
quantitated by Western blot analysis. A series of clones expressing high (more than 
T84 cells) versus low (several fold above basal) amounts of CFTR were then 
identified and their growth characteristics compared to an aliquot of CFT1 cells 
exposed the MMLV-based retrovirus containing the truncated IL2R receptor 
(LISN) as a control. As shown in Figure 21, there is clone-to-clone variation in cell 
proliferative capacity, but no systematic relationship between this parameter and the 
level of CFTR expression. These experiments were repeated after activation of the 
expressed CFTR by forskolin, and similar results were obtained. 
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