The Delta F508 mutation shortens the biochemical half-life of plasma membrane CFTR in polarized epithelial cells

Although the biosynthetic arrest of the Delta F508 mutant of cystic fibrosi s transmembrane conductance regulator (CFTR) can be partially reversed by p hysical and chemical means, recent evidence suggests that the functional st ability of the mutant protein after reaching the cell surface is compromise d. To understand the molecular basis for this observation, the current stud y directly measured the half-life of DF508 and wild-type CFTR at the cell s urface of transfected LLC-PK1 cells. Plasma membrane CFTR expression over t ime was characterized biochemically and functionally in these polarized epi thelial cells. Surface biotinylation, streptavidin extraction, and quantita tive immunoblot analysis determined the biochemical half-life of plasma mem brane Delta F508 CFTR to be similar to4 h, whereas the plasma membrane half -life of wild-type CFTR exceeded 48 h. This difference in biochemical stabi lity correlated with CFTR-mediated transport function. These findings indic ate that the DF508 mutation decreases the biochemical stability of CFTR at the cell surface. We conclude that the DF508 mutation triggers more rapid i nternalization of CFTR and/or its preferential sorting to a pathway of rapi d degradation.