Differential sensitivity of the cystic fibrosis (CF)-associated mutants G551D and G1349D to potentiators of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel

The genetic disease cystic fibrosis (CF) is caused by loss of function of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel. Two CF mutants, G551D and G1349D, affect equivalent residues in the highly conserved LSGGQ motifs that are essential components of the ATP-binding sites of CFTR. Both mutants severely disrupt CFTR channel gating by decreasing mean burst duration (MBD) and prolonging greatly the interburst interval (IBI). To identify small molecules that rescue the gating defects of G551D- and G1349D-CFTR and understand better how these agents work, we used the patch clamp technique to study the effects on G551D- and G1349D-CFTR of phloxine B, pyrophosphate (PPi), and 2'-deoxy ATP (2'-dATP), three agents that strongly enhance CFTR channel gating. Phloxine B (5 mu M) potentiated robustly G551D-CFTR Cl- channels by altering both MBD and IBI. In contrast, phloxine B (5 mu M) decreased the IBI of G1349D-CFTR, but this effect was insufficient to rescue G1349D-CFTR channel gating. PPi (5mM) potentiated weakly G551D-CFTR and was without effect on the G1349D-CFTR Cl- channel. However, by altering both MBD and IBI, albeit with different efficacies, 2(')-dATP (1mM) potentiated both G551D- and G1349D-CFTR Cl- channels. Using the ATP-driven nucleotide-binding domain dimerization model of CFTR channel gating, we suggest that phloxine B, PPi and 2'-dATP alter channel gating by distinct mechanisms. We conclude that G551D and G1349D-CFTR have distinct pharmacological profiles and speculate that drug therapy for CF is likely to be mutation-specific.