FIGURE 2.

A and B, the combination of C18 and C4 reduces the rate of disappearance of ΔF508. Immunoblotting of HEK-293 cells stably transfected with ΔF508, without or with C18 + C4 (10 μm) treatment for 16 h. Cells were treated with cycloheximide (CHX, 25 μg/ml) and harvested at the time points indicated (n = 3). C, quantification of data from Fig. 2A. B, versus 0 h no C18 + C4: *, p < 0.05; **, p < 0.01. Versus 0 h + C18 + C4: ##, p < 0.01. Bars represent the densitometry quantification of immature band B (white) and mature band C (dark bars). D and E, the combination of C18 and C4 rescues NBD1 mutants to the cell surface. Biotinylation of the surface proteins was performed in HEK-293 cells stably transfected with ΔF508, with or without C18 + C4 (10 μm) treatment for 16 h. F, the presence of band C on the surface expression was evaluated 2, 4, and 6 h after stopping the translation of ΔF508, with C18 + C4 treatment (n = 3). Ezrin (Ez), an intracellular protein, was used as a loading control. The absence of ezrin binding to biotin is evidence that the cellular membrane is intact and biotin did not leak into the cell. This is verification that our assay is measuring only proteins in the plasma membrane such as CFTR.