Effects of Aromatic Carboxylic Acids on Genistein- and Curcumin- Potentiated G551D-CFTR

The Cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel plays an important role in salt and water transport across epithelia and defective function due to mutations in the CFTR gene cause cystic fibrosis (CF). The glycine-to-aspartate missense mutation at position 551 (G551D) is the third most common CF-associated mutation and G551D-CFTR is characterized by a very low open probability despite of its normal trafficking to the plasma membrane.Numerous small molecules have been shown to increase the activity of G551D-CFTR presumably by binding to the CFTR protein. Among the many G551D-CFTR potentiators, a bioflavonoid found in legumes, genistein is perhaps the most extensively studied. More recently it was reported that a component of the spice turmeric, curcumin strongly activated G551D-CFTR. However, The mechanism through which these compounds increase G551D-CFTR activity is still unclear. On the other hand, we have previously reported that anthracene-9-carboxylate (9-AC) showed an inhibitory effect and an potentiation effect on CFTR channels by binding to two chemically distinct sites for each effect (Ai et al, 2004).In this study, we made a functional probing on genistein-potentiated G551D-CFTR and curcumin-potentiated G551D-CFTR using 9-AC and its positional isomer, anthracene-1-carboxylate (1-AC). In wild type- (WT-) CFTR, 9-AC induced a large voltage-independent enhancement and a voltage-dependent inhibition in the whole-cell (WC) current. 1-AC induced a smaller enhancement and a larger voltage-dependent block in WT-CFTR WC currents in compared with 9-AC. In the other hand, both 9-AC and 1-AC induced only a weak voltage-dependent inhibitions in genistein-potentiated G551D-CFTR WC currents whereas, in curcumin-potentiated G551D-CFTR WC currents, 9-AC and 1-AC induced similar effects to those in WT-CFTR. These suggest that curcumin and genistein potentiated G551D-CFTR via different mechanisms. We speculate that genistein-potentiated and curcumin-potentiated G551D-CFTRs might have different protein conformations.