Analysis of CFTR Endocytosis by Cell Surface Biotinylation

Correct localization of cystic fibrosis transmembrane conductance regulator (CFTR) is critical to its function. Although an intracellular role for CFTR is still somewhat controversial (1 ), there is clear agreement on an important role for CFTR in the plasma membrane. However, it is not only important that CFTR be inserted into the plasma membrane, it has to stay there the requisite amount of time. Although many CFTR mutations result in CFTR molecules that reach the plasma membrane (with altered conductance or regulation), the most clinically important mutation, AF508 CFTR, fails to reach the plasma membrane in physiologically relevant quantities. The precise amount of AF508 CFTR that reaches the plasma membrane remains controversial (2 ,3 ). Even so, until the “holy grail” of gene therapy is realized, therapeutic strategies to augment plasma membrane expression of mutant CFTR remain important. Indeed, many laboratories, both academic and commercial, are currently engaged in screening endeavors to identify pharmacological agents capable of improving the folding and traffic of mutant CFTR molecules (especially AF508 CFTR) leading to their insertion into the plasma membrane.