The C-terminal part of the R-domain, but not the PDZ binding motif, of CFTR is involved in interaction with Ca2+-activated Cl- channels

Expression of the cystic fibrosis transmembrane conductance regulator (CFTR ) inhibits Ca2+-activated Cl- channels (CaCC) by an unknown mechanism. This inhibition does not require CFTR activation (activity-independent inhibiti on), but is potentiated when CFTR is activated (activity-dependent inhibiti on). In this study, we evaluated, in endothelial cells, possible structural determinants for this interaction. Bovine pulmonary artery endothelium (CP AE) cells, which do not express CFTR, were transfected transiently with thr ee hybrid CFTR constructs. The functional interaction between CaCC and CFTR was assessed using the patch-clamp technique in the whole-cell configurati on. CaCC was stimulated by application of adenosine 5 ' -triphosphate (ATP) to the bath solution. CFTR currents were evoked by application of a forsko lin/3-isobutyl-1-methylxanthine (IBMX) cocktail. The inhibitory effect of C FTR was conserved when the PDZ (PSD-95/Discs Iarge/ZO-1) binding motif was deleted (CFTR-Delta PDZ). In contrast, both the CFTR activity-independent a nd -dependent inhibition of CaCC were abolished when the C-terminal part of the regulatory (R)-domain of CFTR was deleted (CFTR-Delta R780-830). The a ctivity-dependent inhibition of CaCC, but not the activity-independent inhi bition, could be rescued by introducing the multiple drug resistance (MDR)- 1 mini-linker in place of the deletion (CFTR-DeltaR-linker). It is conclude d that the C-terminal part of the R-domain is an important determinant for CFTR-CaCC interaction.