Chemical chaperones correct the mutant phenotype of the Delta F508 cystic fibrosis transmembrane conductance regulator protein

Mutations in the cystic fibrosis transmembrane conductance regulator protein (CFTR) often result in a failure of the protein to be properly processed at the level of the endoplasmic reticulum (ER) and subsequently transported to the plasma membrane. The folding defect associated with the most common CFTR mutation (Delta F508) has been shown to be temperature sensitive. Incubation of cells expressing Delta F508 CFTR at lower growth temperatures results in the proper processing of a portion of the mutant CFTR protein. Under these conditions, the mutant protein can move to the plasma membrane where it functions, similar to the wild-type protein, in mediating chloride transport. We set out to identify other methods, which like temperature treatment, would rescue the folding defect associated with the Delta F508 CFTR mutation. Here we show that treatment of cells expressing the Delta F508 mutant with a number of low molecular weight compounds, all known to stabilize proteins in their native conformation, results in the correct processing of the mutant CFTR protein and its deposition at the plasma membrane. Such compounds included the cellular osmolytes glycerol and trimethylamine N-oxide, as well as deuterated water. Treatment of the Delta F508 CFTR-expressing cells with any one of these compounds, which we now refer to as 'chemical chaperones', restored the ability of the mutant cells to exhibit forskolin-dependent chloride transport, similar to that observed for the cells expressing the wild-type CFTR protein. We suggest that the use of 'chemical chaperones' may prove to be effective for the treatment of cystic fibrosis, as well as other genetic diseases whose underlying basis involves defective protein folding and/or a failure in normal protein trafficking events.